Problems, Middle Mississippi River Region, Pleistocene Time 231 
cupied the present course of the Illinois River. Apparently the 
present trough of the Mississippi, above the Illinois, was used 
by a relatively unimportant tributary. This appears to be the 
only major difference in the drainage of the region that devel- 
oped during the entire Pleistocene. 
GRANDIAN Epocu 
During the Nebraskan age it seems reasonably certain that 
an ice sheet invaded Scott County in Illinois in the vicinity 
of Winchester (Fig. 18.) This is perhaps the only completely 
demonstrated fact regarding Nebraskan glaciation in this vicin- 
ity and, at that, Winchester is many miles north of the Middle 
Mississippi River Region. There are many important questions 
regarding the results of the Nebraskan ice sheet. Is the drift in 
the quarries above Alton of Nebraskan age? Is any or all of the 
pre-Illinoian drift in St. Louis of Nebraskan age? Did the Nebras- 
kan ice border actually extend beyond the better known and 
much later Illinoian ice border? These questions have been raised 
y geologists at one time or another. The answer for the present 
must be that there is no positive evidence upon which any of 
them can be answered, and the final answer to these questions 
must rest upon more detailed knowledge. 
OTTUMWAN EpocnH 
-\n ice lobe from the Kewatin center entered Lincoln County 
from the north (Fig. 14). It spread eastward across the present 
course of the Mississippi River into Calhoun County near Batch- 
town, Illinois. This must have dammed the stream, if there was 
one, that flowed in the course which the Mississippi now oc- 
cupies north of this point. A part of the ice sheet extended 
southward across St. Charles County and reached the south 
bank of the Missouri River in the general vicinity of Vigus, St. 
Louis County. The Missouri River was thereby dammed above 
this point. The ice front of this Kansan lobe was probably 
parallel to the present course of the Missouri River to the west- 
ward, but some distance north of it. There were some pools 
of quiet water adjacent to the ice front in which a considerable 
