ILLINOIS RIVER DRAINAGE BASIN. 503 



Lake Chicago, and also from the ice lobes north and east of the Kankakee, 

 is plainly shown in the great size of this valley, as lias been pointed out 

 on preceding- pages. 



DES PLAINES RIVER. 



The Des Plaines River drains a narrow strip extending north to south 

 a distance of 90 miles, from Kenosha Comity, Wisconsin, to the head of the 

 Illinois in eastern Grundy County, Illinois. The greatest width of the 

 watershed is scarcely 25 miles. The area, as above noted, is 1,392 square 

 miles. Aside from the Des Plaines River there are only four noteworthy 

 tributaries — Dupage River, Jackson Creek, Hickory Creek, and Salt Creek. 



The portion of the Des Plaines watershed north from the Chicago Out- 

 let falls within the low area bordering Lake Michigan inside the Valparaiso 

 morainic system. It still discharges into the lake at flood stages through 

 a portion of the old outlet known as "Mud Lake" and South Chicago 

 River. It is thought by Cooley and by others familiar with the ground, 

 including the present writer, that the entire discharge may, until within a 

 few hundred years, have been into the lake instead of down the Chicago 

 Outlet. The divide between Mud Lake and Chicago River is a flat silt- 

 covered tract situated near Kedzie avenue, in Chicago. The south branch 

 of Chicago River has a channel with a capacity proportioned to such a stream 

 as the Des Plaines, and the bed of Mud Lake bears evidence of being the 

 line of discharge from the Des Plaines to the Chicago River. Furthermore, 

 the portion of the Des Plaines Valley below Summit (where Mud Lake leads 

 off from the Des Plaines) carries only a poorly defined channel a foot or 

 two in depth. Cooley remarks: "Had the Des Plaines gone southward 

 ever since the abandonment of the ancient outlet, it would ere this have 

 grooved itself in the rock, built up its banks, and reduced the prism of Lake 

 Joliet to present requirements." 1 The cause for the deflection into the old 

 lake outlet is supposed to be a silting up of the Mud Lake channel. This 

 matter, however, has not been carefully investigated by the writer. Cooley 

 remarks concerning this diversion: 



There are many ways in which the long flat divide at Kedzie avenue could have 

 • been built up, and we believe there is a tradition that the beaver was concerned in 

 the matter. In any event, the work once initiated, natural silting would carry it on 

 until the waters were turned out across the old pass. 2 



1 See report of Illinois State Board of Health, 1889, pp. 54, 55, 69-75. 

 »Op. cit., p. 71. 



