KASKASKIA RIVBE DRAINAGE BASIN. 525 



about 40 miles, but drains a much narrower strip than that of West Fork. 

 Below the junction of the East and West forks the stream has a length by 

 direct course of about 25 miles. 



This watershed has a perceptible southward descent, the altitude at the 

 headwaters being 700 to 750 feet at tide and at the mouth only 400 feet. 

 The mouth of the creek is but 380 feet. The three streams have each formed 

 channels 50 to 75 feet or more in depth and nearly one-fourth mile in average 

 width in their passage through southern Montgomery County. A similar 

 depth is maintained as far down as the jrmction of the East and West forks 

 near Greenville. Below this point the valley is more shallow and the 

 stream soon enters the Kaskaskia Basin, where its valley is but little lower 

 than the basin plain. 



East Shoal Creek is bordered closely on the east throughout its entire 

 length by a system of drift knolls and ridges which, as previously described, 

 attain great prominence in eastern Montgomery County. Shoal Creek 

 passes through a break in this system of ridges just below the junction of 

 the East and West forks, beyond which its course is largely independent of 

 drift ridges. Middle Shoal Creek winds about among prominent drift knolls 

 near Hillsboro, and West Shoal Creek is deflected eastward by a ridge of 

 drift at its junction with Middle Shoal Creek. With these exceptions the 

 streams are not markedly deflected by drift aggregations. They pursue, 

 as a rule, nearly direct southward courses, following the slope of their 

 watershed. 



Their courses appear to be mainly independent of preglacial drainage 

 lines. East Shoal Creek touches the line of a deep preglacial valley near 

 Greenville, but above that point it has opened a new course, in places 

 trenching into the rock. Even the lower course seems to be largely inde- 

 pendent of any preglacial line of drainage. 



SILVER CREEK. 



Silver Creek has its source in southeastern Macoupin County and 

 flows nearly due south its entire length of fully 50 miles, crossing the 

 eastern part of Madison and St. Clair counties. Its watershed is scarcely 

 10 miles in average width, and has an area of about 500 square miles. At 

 the source of the stream the altitude is fully 650 feet, but the watershed 

 descends within 10 miles to about 550 feet, and in the next 15 miles to 



