THE TOPOGKAPHY AXD HYDROGRAPHY OF ILLINOIS Ixxi 



of the stream lying at about 600 ft. above tide. Nine miles 

 from its source Chicago River is joined by a branch from the 

 east. This latter stream rises in Lake county in another swampy 

 intermorainic area at an elevation of 660 ft., and in its length 

 of 12 miles makes a descent of 50 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 between moraines 

 extending north and south within those directly bordering Lake 

 Michigan and bounded on the west by the Des Plaines water- 

 shed. 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 headwaters 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 discharge 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 mo- 

 rainic 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 Chicago. 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 about 580 ft. 



