XXVI FISHES OF ILLINOIS 



descends rapidly, 25 feet in a mile, to the sandy plain outside the 

 moraine. There it soon enters the Inlet swamps lying about 775 

 feet above tide. These swamps are 10 miles long and 2 to 5 miles 

 wide. Through them the stream has no definite channel but seems 

 to be entirely lost. They are mostly covered with a dense prairie 

 grass among whose roots a thin sheet of water is concealed in the 

 wet seasons of the year. Towards the center the water is deeper and 

 patches of cattails and rushes abound. From the western edge of 

 this area, two to three miles southeast of Lee Center, the surplus 

 waters of the swamps are gathered into a stream with a well-defined 

 channel. This leads westward for 15 miles to another wet area, 

 the Winnebago swamps, making a descent of about 3 feet per mile. 

 These swamps are very similar to the Inlet swamps but much larger. 

 Hills of sand rise in chains and clusters from the midst of them. 

 These hills were originally heaped up by the winds from the sands 

 of the old lake-bed. Some of them are 40-50 feet high and are 

 covered with a scattering and stunted growth of trees. The inter- 

 vening swamps are fringed with bands of thick-growing swamp 

 grass on a miry, mucky soil. Within these are inner fringes of 

 dense cane-like rushes and cattails growing so thick and tall that it 

 is almost impossible to penetrate them. Then come stretches of 

 clear water with hard sand bottoms. In the next 25 miles, to the 

 crossing of the Bureau-Henry county line, the stream has a poorly 

 defined channel, meandering about through a series of marshes 

 among sand-hills but making a descent of 60 feet. In the remaining 

 35 to 40 miles to its mouth, the stream falls about 40 feet and main- 

 tains a well-defined channel. In the lower 18 to 20 miles, below 

 Geneseo, it has excavated a valley fully 20 feet in average depth 

 and nearly half a mile in width. In this section of its course its 

 uplands are far less sandy. 



Along the whole course of Green River, there are no bold bluffs 

 except at Lee Center, where some low outcrops of Galena limestone 

 are quarried. 



The Northwestern Area 



The waters of extreme northwestern Illinois differ sufficiently in 

 condition and surroundings from those of the smaller tributaries of 

 the Mississippi farther south to warrant their separate discussion in 

 this report. The .surface drained by them is the southernmost part 

 of a tract known to geologists as the Wisconsin driftless area, a 

 region not covered by ice during the glacial period, and conse- 

 quently wholly destitute of glacial drift. Because of its prolonged 



