LIS RGILA CHAIIL, WAULILIENGS (QU WIENS NIMS SIS SIUM. 741 
sheet in giving this basin its low altitude. The slope of pregla- 
cial valley floors will throw light upon differential crust move- 
ments which have affected the basin. Unfortunately we have as 
yet very few data from Wisconsin, a district which should furnish 
many important data when the reports of its borings are collected 
and its preglacial drainage lines worked out. 
COURSES OF THE MAIN PREGLACIAL DRAINAGE LINES. 
Concerning the course of the Mississippi above the mouth of 
the Minnesota River very little is known. It is probable, how- 
ever, that its drainage area was about as great as that of the 
present stream. From the mouth of the Minnesota southward 
to the mouth of the Wapsipinnicon River below Clinton, Iowa, a 
distance of about 300 miles, the present stream follows the line 
of the preglacial, the only deviations from that line being slight 
encroachments on the bluffs of the old valley, as at Fulton, IIli- 
nois, where a rocky point belonging to the old west bluff has 
been cut off by the present stream. Below the mouth of the 
Wapsipinnicon, the present stream for a distance of forty miles 
(to Muscatine, Iowa) is ina new course. The bordering dis- 
tricts are heavily covered with drift and it is not an easy matter 
to determine the course of the old valley. I expressed the opin- 
ion, some three years ago, that the course was southeastward 
through the Green River basin to a bend of the Illinois River 
near Hennepin.* This opinion was based upon the existence of 
a low tract of country connecting the Mississippi with the Illinois 
along the north border of the Coal Measure formations. It has 
since been discovered by Professor J. A. Udden that a similar 
tract of country more completely concealed by the drift follows 
the northern border of the Coal Measure area westward and south- 
westward from the mouth of the Wapsipinnicon through Scott 
and Muscatine counties, Iowa, to the old valley below Musca- 
tine. Which of these courses was taken by the preglacial upper 
Mississippi is being made a matter of special investigation by 
Professor Udden, and we look for an early publication of the 
results of his investigations. He informs me that the lowest 
*Proc. A. A. A. S., Rochester Meeting, Vol. XLI., 1892, p. 176. 
