THE TOPOGRAPHY AND HYDROGRAPHY OF ILLINOIS IxV 



into the Ohio near Bay City. It has a length of about 40 miles, 

 with an altitude 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 valley 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 completely 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 land 

 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 receive 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 xxxi). It dis- 

 charged its waters southward through this outlet instead of north- 

 ward 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 w4dth 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 26 miles, emptying into Lake Michigan about 

 a mile and a half north of the Illinois Central station in Chicago. 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 of the stream 

 lying at about 600 ft. above tide. Five miles from its source Chi- 

 cago River is joined by the North Branch. This stream rises in 



(e) 



