IVA GTLIA CHAE, WEAVLIEIBIES (OM WITLI, NUS SIRS SVM EVEN 743 
moraine in southern Wisconsin, southward to the mouth of the 
Kishwaukee, a few miles below Rockford, Illinois, where it turns 
to the southwest and follows a new valley to the Mississippi. 
The preglacial course of the river is plainly traceable southward 
from the mouth of the Kishwaukee across eastern Ogle county to 
the vicinity of Rochelle, the drift being insufficient to fill the old 
valley to the level of the bluffs. From Ogle county southward 
across Lee and Bureau counties to the bend of the Illinois River 
at Hennepin, borings have shown the presence of a deep channel. 
Several have gone to depths below that of the rock surface a few 
miles to the west. Only one of these borings, the artesian well 
at Princeton, Illinois, has reached the rock floor. This shows a 
drift filling of 440 feet, and probably strikes the deepest part of 
the old valley, the rock floor being as low as at any point yet 
found in the course of the whole channel. There can scarcely 
be a doubt that the preglacial course of Rock River was south- 
ward along this line to the Illinois, and thence to the Mississippi, 
though we have as yet no borings, except the one at Princeton, 
which test its deepest portion at any point between the Wisconsin 
line and bend of the Illinois. 
The courses of the preglacial tributaries of the Rock-Illinois 
are known only in a few instances, owing to the great amount of 
drift which conceals them. The Pecatonica Valley which enters 
from the west, just below the Wisconsin line, is mainly in a pre- 
glacial course and so are its main tributaries, Yellow Creek and 
Sugar River. The Kishwaukee is largely in a new valley and 
enters the Rock River Valley through a gorge at its mouth. 
The upper portion of the IJlinois, including its headwater streams 
—the Fox, the Des Plaines and the Kankakee —are all in post- 
glacial valleys. They cross a somewhat elevated limestone dis- 
trict which, like the Niagara escarpment to the north, seems to 
have formed the preglacial watershed between the Rock-Illinois 
drainage basin and the basin now occupied by Lake Michigan. 
They thus bring to the present Illinois the drainage of a large 
district which formerly discharged into the Lake Michigan basin. 
* Changes of drainage in the Rock River basin in Illinois, by FRANK LEVERETT, 
Proc. A. A. A.S., Madison Meeting, Vol. XLII., 1893, p. 179. 
