THE TOPOGRAPHY AND HYDROGRAPHY OF ILLINOIS lvii 



erally 14 to 10 feet above the ordinary stage of water, with 

 sometimes a second bottom a few feet higher. During the wet 

 seasons the river often covers the first bottom to a depth of 

 several feet. The hills on each side of the river are from 60 to 

 70 feet in height. On entering Faj-ette county, the river opens 

 into a broad preglacial valley whose course farther north is buried 

 under drift. The valley has a width of about 3 miles near 

 Vandalia, but reaches a greater width farther south. It is so 

 masked by drift that it presents the appearance of a broad 

 shallow basin rather than a river valley. It continues nearly to 

 the mouth of the river, where the width contracts abruptly to 

 about a mile upon entering the subcarboniferous limestone 

 which there borders the Mississippi Valley. The bottom-lands 

 are subject to annual overflow, and are still covered with a 

 heavy growth of timber. 



The stream is subject to great variations in volume as the 

 compact clay subsoil promotes a rapid run-off and furnishes 

 but little water in seasons of drought; consequently, in summer 

 and fall, the river dwindles to a very small size. At times it 

 may be crossed dry-shod at Vandalia, where it is 60 to 70 feet 

 wide. A rise of 20 feet in its lower course is not rare in flood 

 time, and its flood-plain has been built nearly to that height 

 above the stream-bed. 



The two principal tributaries of the Kaskaskia are from the 

 west — Shoal creek and Silver creek. . 



SHOAL CREEK 



Shoal creek drains an area of 947 square miles, or one 

 sixth of the entire basin of the Kaskaskia River (Leverett) . This 

 area includes most of Montgomery and Bond counties and west- 

 ern Clinton county. Shoal creek is made up of three branches 

 known as West, Middle, and East Shoal creeks. West and 

 Middle creeks unite to form the West fork, by the union of 

 which with East creek, twenty miles below, the main stream is 

 formed. From the rise of its branches to its mouth in the Kas- 

 kaskia this stream has a total length of 79 miles. The watershed 

 has a distinct southward slope, the altitude at the headwaters 

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



The three branches have each formed a channel 50 to 75 feet 

 or more in depth and nearly one fourth of a mile in average 

 width in their passage through southern Montgomery county, 

 and a similar depth is maintained as far down as the junction of 



