524 THE ILLINOIS GLACIAL LOBE. 



Upon entering the older drift the valley continues small for a few miles, 

 but is perceptibly increased in size below the point of entrance of Robinson 

 Creek. This stream appears to follow the lower course of a drainage line 

 whose former headwater portion has been concealed by the Shelby ville drift 

 sheet. Its valley has a breadth of nearly a half mile, and this breadth 

 characterizes the portion of the Kaskaskia immediately below its mouth. 

 Upon entering Fayette County the river soon opens into a broad preglacial 

 valley whose course farther north has been concealed. The valley has a 

 width of about 3 miles near Vandalia, but increases to greater width farther 

 south. Masked as it is by the drift, it presents the appearance of a broad 

 shallow basin rather than a river valley. This basin-like valley continues 

 nearly to the mouth of the stream, where the width contracts abruptly to 

 about a mile upon entering the Eocarboniferous limestone which there 

 borders the Mississippi Valley. 



This stream recedes but one noteworthy eastern tributary — Crooked 

 Creek — and two western tributaries — Shoal Creek and Silver Creek. 

 Crooked Creek 1 is relative^ unimportant, as it drains only a narrow strip, 

 35 or 40 miles in length, leading from north-central Marion County south- 

 westward past Salem and Centralia and entering the Kaskaskia a few miles 

 below Carlyle. Coal shafts at Salem, Odin, and Sandoval show the pres- 

 ence of a preglacial valley on the north border of this watershed, with bed 

 100 feet or more below the present surface, but the present stream flows 

 through a region of comparatively thin drift. 



SHOAL CREEK. 



Shoal Creek has a drainage area of about 1,000 square miles, or one- 

 sixth the entire watershed of the Kaskaskia River. Its watershed embraces 

 the greater part of Montgomery and Bond counties and the western part of 

 Clinton County. The stream enters the Kaskaskia in the southwest part of 

 Clinton County, about 20 miles below Carlyle. In the headwater portions 

 there are three streams, known as West, Middle, and East Shoal creeks. 

 West and Middle Shoal creeks are each about 20 to 25 miles in length and 

 unite near Walshville in southwestern Montgomery County. The united 

 stream below that point is known as West Fork to its junction with East 

 Shoal Creek, 20 miles farther south. East Shoal Creek has a length of 



'This stream should not be confuseil with one of the same name that enters the Illinois Eiver. 



