Ixvi FISHES OF ILLINOIS 



Lake county in another swampy intermorainic area at an elevation 

 of 660 ft., and in its length of 12 miles makes a descent of SO ft. 

 Although the upper courses of this stream and of the main river 

 can not be definitely traced farther up-stream than mentioned 

 above, they seem to drain indirectly a series of marshes lying be- 

 tween moraines extending north and south within those directly 

 bordering Lake Michigan and bounded on the west by the Des 

 Plaines watershed. About one mile from its mouth Chicago River 

 is joined by the South Branch. This river connects with the Des 

 Plaines near Summit and, as stated in the description of the latter 

 river, it has afforded a line of discharge for the upper Des Plaines 

 from the time of the withdrawal of the lake down to historic times. 

 The size and depth of its channel are such as to seem to demand the 

 work of a stream as large as the Des Plaines. Even in quite recent 

 years this river at high-water has been known to overflow into the 

 South Chicago channel and thus to discharge some of its water into 

 Lake Michigan. With the exception of a few miles at the head- 

 waters of North Fork, the entire drainage system lies within the 

 limits of old Lake Chicago. The southward course of the stream 

 .outside of the lake bottom is occasioned by till ridges of the Lake 

 Border morainic system, the one on the east -preventing direct dis- 

 charge into Lake Michigan. Within the limits of Lake Chicago 

 the stream follows the slope of the old lake bottom. 



Calumet River has its headwaters in the Valparaiso morainic 

 system south of Michigan City, Indiana. Its numerous tributaries 

 also rise in this system, and they and the main stream, on descending 

 "from this ridge, flow in the lowland formerly covered by Lake Chi- 

 cago. Here their courses are controlled to some extent by the 

 lines of sand-dunes formed along the benches of the old lake, and, 

 -to a slight extent, by till ridges. The streams have almost no fall, 

 and the section through which they flow is filled with swamps and 

 lakes. The course of the river is meandering, and at times it is 

 almost impossible to determine the direction of the flow of water, 

 as in the swampy region near Blue Island. Lake Calumet, near 

 Pullman, Illinois, is the largest of the many tributary lakes. The 

 mouth of the stream is at South Chicago, Illinois, at an altitude of 

 580 ft. 



