486 THE ILLINOIS GLACIAL LOBE. 



Kite River, which now flows northwestward into Rock River at Ore- 

 gon, Illinois, occupies a preglacial western tributary of the old Rock River 

 which may be traced southeastward into the old valley at a point south of 

 Rochelle. The head of the preglacial stream appears to have been in the 

 hills back of the town of Oregon. The present Rock River therefore cuts off 

 only the headwater portion of this preglacial valley. 



The preglacial drainage of southern Ogle, northern Lee, and eastern 

 Whiteside counties appears to have been directly toward the preglacial 

 Rock River in southern Lee and northern Bureau counties. The present 

 Rock River intersects several of these streams midway of their course and 

 diverts them westward into the Mississippi. The lower courses of these 

 preglacial streams are now concealed beneath the sand deposits of the 

 Green River Basin. Probably western Whiteside and neighboring portions 

 of Henry and Rock Island counties, now tributary to Rock River, were 

 tributary to a preglacial stream which connected directly with the Mississippi, 

 if they did not themselves discharge directly into the stream. 



PRESENT COURSE OF ROCK RIVER. 



At the mouth of the Kishwaukee River, 7 miles south of Rockford, 

 Rock River turns directly away from the broad preglacial valley and for 

 50 miles takes its course southwestward through a much narrower valley 

 (see PI. XII). The narrow valley extends to western Lee County, a few 

 miles below the city of Dixon. From this point to the Mississippi, a dis- 

 tance of about 80 miles, the river flows in the broad lowland known as the 

 Green River Basin. A few miles above its mouth, however, the basin is 

 interrupted by island-like strips of upland, around which the stream takes 

 its course, as shown in PL XVIII. Its main channel is south of the islands, 

 the other channels being occupied only by sloughs and sandy plains. 



A somewhat detailed study of the narrow portion of the valley has 

 been made with a view to determining the amount of rock excavation accom- 

 plished. This study has brought to light an interesting series of changes in 

 drainage, some of which have already been mentioned. This narrow 

 portion is naturally divided into the following sections, taken in order, 

 beginning at the point of deflection from the preglacial valley and passing 



