MINOR TRIBUTARIES OF THE MISSISSIPPI. 479 



due to peculiarities of drift topography, there being in the district through 

 which Edwards River flows a tendency to slight ridging in a general east- 

 west direction, with broad, shallow depressions separating the ridges. 

 Edwards River follows one of these depressions, while Pope Creek, which 

 flows parallel with it on the south, follows a neighboring depression. A 

 depression north of Edwards River differs from that of the two valleys just 

 mentioned in separating its waters, a portion flowing directly west to the 

 Mississippi through Copper Creek and a portion east and north into Rock 

 River through Mill Creek. None of these streams, so far as the writer is 

 aware, reach the bottom of the drift, yet it can not be assumed that they 

 follow preglacial lines, for well sections indicate that the ridges and depres- 

 sions are largely independent of the altitude of the underlying rock surface. 



HENDERSON KIVER. 



Henderson River, which drains much of northern Henderson, northern 

 Warren, and part of Knox counties, Illinois, though having a length of 

 scarcely 50 miles, furnishes a discharge through its numerous branches 

 for an area of fully 500 square miles. The courses of the main branches 

 seem to have no dependence either upon the underlying rock surface or 

 upon drift topography. They traverse a very smooth district having 

 gradual westward descent. The courses of the several streams are proba- 

 bly the result of slight advantages in the inclination of the slopes, at 

 present difficult to discern. These streams have now in several instances 

 cut down into the rock, and their courses seem to be independent of pre- 

 glacial lines. 



FLINT RIVER. 



The first western tributary of the Mississippi to claim attention is 

 Flint River, a small stream entering the Mississippi immediately north of 

 Burlington, Iowa. Its source is in the marginal ridge of the Illinoian drift 

 near New London, Iowa. The stream flows thence southeastward to the 

 Mississippi across a gradually descending plain. It appears to disregard 

 the courses of preglacial drainage lines, for in its upper course drift 

 deposits extend in places to a depth of 250 feet, while in its lower course it 

 has carved a channel through the rock ledges, whose cherty layers give to 

 the stream its name. 



