XXVI FISHES OF ILLINOIS 



part of its course the stream maintains a width of 500 feet, 

 but its valley varies in width from 1,000 feet to fully 1 mile 

 (Leverett). It forms long undulating curves, except at Grand 

 Detour, where it doubles upon itself in short, abrupt bends. 

 The face of the country along the river is rough, broken, and 

 timbered. The prairie extends to the water's edge in only a few 

 places. The bluffs approaching closely to the river are bold, 

 rocky, and precipitous, rising abruptly at times to a height of 

 125 feet. The little streams on either side have cut deep ravines 

 in the banks, often exposing the several formations of the Ordo- 

 vician. The result is certainly very picturesque and somewhat 

 awe-inspiring. Below Dixon the bluffs gradually recede and grow 

 lower until, at Sterling, Rock River begins to flow through a 

 sandy plain known as the Green River basin, a plain which 

 lies 25-40 feet above the stream. Here the course of the river 

 is entirely independent of preglacial lines, and its current is 

 broad and swift. The bluffs of the Mississippi strike Rock 

 River at Milan and for several miles above this point they rise 

 on either side abruptly, in some places towering 150 feet above 

 the water. They then break away and the river flows in an 

 alluvial plain of good farming land. This plain is about 5 miles 

 wide. Near the mouth of Rock River there are several small 

 islands which divert the river into three channels. Two of these 

 branches meet again near Milan, flowing into the Mississippi 

 two and a half miles distant, while the southern stream, known 

 as Kickapoo slough, pursues a winding course southward and 

 westward, opening into the Mississippi a few miles south of the 

 mouth of Rock River. 



The upper Rock River is a clear, quiet-flowing stream with 

 sandy bottom. Lower in its course the bed becomes more often 

 rocky and the current quickens. Naturally, the water, unless 

 roiled by freshets, keeps its bright, clear character until well 

 down near the mouth. Its tributaries, however, at times pour 

 in a flood of stained and muddy water, making the lower portion 

 a turbid stream, while, of late, sewage and other contamination 

 have done much to impair the original brilliancy of the water. 

 Yet, as Illinois rivers go, it must even now be considered a 

 clear stream, while the bold bluffs and out-cropping rocks along 

 its banks make it one of the most picturesque rivers in the state. 



The principal branches of Rock River are Pecatonica, 

 Kishwaukee, and Green rivers. 



