xlvi FISHES OF ILLINOIS 



20 feet of slope, and was apparently occupied by a shallow lake until 

 a st ream had been given time to open a channel from the Illinois back 

 several miles into the plain. There are sandy deposits along the 

 southern border of the plain which tend to confirm this view. In 

 the lower 25 miles the stream corrades rapidly, making a descent of 

 about 150 feet and cutting its valley mainly in rock. The channel 

 is very narrow, steep, and rocky, especially near the mouth of the 

 river, where the walls rise abruptly 150 feet from the water's edge. 



A few miles from the mouth, at a bend in the river, a deep canon 

 extends off to the east through Deer Park Glen. It is about one 

 fourth of a mile long, with perpendicular walls, and is in the form 

 of an elongated S. It terminates abruptly in a cirque, open at 

 the top and about 150 feet in diameter at the bottom, with a fine 

 spring of soft water bubbling up at its base. In the wet season 

 there is a waterfall of 25 feet which enters it through a narrow 

 chasm at the head. The walls of the cirque are about 175 feet high. 



The stream is not of much value as a water-power on account of 

 the unsteadiness of its flow. It has no marshy gathering ground, 

 and the formations in its basin are mainly compact till which yields 

 but little water in seasons of drought. 



MACKINAW RIVER 



Mackinaw River rises in eastern McLean county. It flows west- 

 ward through the northern part of this county and across the south- 

 ern end of Woodford, then turning southwest into Tazewell county. 

 From the center of this county it bends again to the west, following 

 this direction for about 15 miles,when it turns north and east, empty- 

 ing into the Illinois a little below Pekin. It is about 120 miles long, 

 and drains an area of about 1,200 square miles (Leverett). 



The upper part of the river lies inside the main ridges of the 

 Bloomington morainic system, and drains a plain which lies 300 to 

 350 feel above the Illinois. This section of the Mackinaw is about 

 40 miles in length, most of its course being along the southern border 

 of the basin. In the first mile it descends 40 feet, but below this its 

 fall averages about 3 feet to the mile. 



In its middle course the stream crosses the Bloomington and 

 Shelbyville morainic systems and the narrow plain separating them. 

 The width of the valley increases from about one fourth of a mile in 

 the inner part of the Bloomington belt to about one half of a mile at 

 the outer pari .ami to nearly a mile in its passage across the Shelbyville 

 moraine. Its fall is still rapid, about. 3 feet per mile. There are lew 

 tributaries, only a small area being drained. 



