\XX FISHES OF ILLINOIS 



City. It has a length of about 40 miles, with an alt'tude of 

 750 feet at its source and of 300 feet at its mouth. In the upper 

 7 miles it falls 300 feet and the banks are steep and abrupt; 

 but below, the river valle3 r expands into a swampy region 3 to 

 4 miles in width. These swamps connect with those of the 

 Cache River, and often the headwaters of the latter stream find 

 their way to the Big Bay and down it to the Ohio. At other 

 times, high water in the Ohio produces a flow through Big Bay, 

 the swamps, and down the Cache. Much is now being done, 

 through tiling and ditching, to separate complete^ the basins 

 of the two streams and to make each course distinct. In the 

 lower 8 miles of its course the banks again hug the river closely, 

 and rise on either side to a height of 250 to 300 feet. 



The Lake Michigan Drainage 



In the northeastern part of the state there is a narrow belt 

 of 7 and from ten to twenty miles in width bordering Lake 

 Michigan and sending its waters into that lake through many 

 small, short streams, only two of which are of sufficient size to 

 received especial mention, namely, the Chicago and the Calumet 

 rivers. Much of this area, including the present site of Chicago, 

 was formerly part of a great glacial lake known to geologists as 

 Lake Chicago, which existed at the same time as the "Chicago 

 Outlet" (see page xxxiv) . It discharged its waters southward 

 through this outlet instead of northward as at the present time. 

 This tract of land now lies as a relatively level plain, diversified 

 with old lake-beaches and low glacial moraines. It is very 

 poorly drained and is filled with swamps and lakes. 



The small short streams are mostly to be found in Lake 

 county, where they drain a strip from two to four miles in width 

 directly bordering the lake. They rise in the morainic ridge 

 which here extends north and south along the shore at an 

 altitude of about 700 ft., and from its crest they make very 

 rapid and direct descents to the lake. 



Chicago River rises in northern Cook county and flows 

 south and east for a distance of 29 miles, emptying into Lake 

 Michigan about a mile and a half north of the Illinois Central 

 station in Chicago, and draining an area of 226 square miles. 

 It rises in a swampy area at an elevation of 630 ft. above tide 

 and makes a descent of 20 ft. in the first two and a half miles of 

 its course. Below this, however, it has almost no fall, the mouth 



