JARIEGILA CHASE, WATILILIBNGS OLE IIE MIS SUSSIVLIN, 753 
greater volume than the present river. This stream effected a 
great amount of erosion, but its duration was too brief to enable 
it to cut down its bed in the new portion of the valley, to a uni- 
form slope. Mr. Cooley has well expressed the influence of the 
strata in his discussion of the old lake outlet: 
“The ancient stream carved its grade according to the resisting 
material, steep in the Niagara limestone to Lake Joliet, steep in the 
Cincinnati limestone at the mouth of the Kankakee, light through the 
friable Coal Measures, to the resisting strata at Marseilles, and steep in 
the St. Peter’s sandstone from above Ottawa to Utica, where the water- 
lime group checked the lakeward extension of the alluvial valley. ... . 
“Below Utica a wide valley in the Coal Measures, narrowing toward 
the mouth in the resisting rock of the older formations, extends for 
230 miles to the Mississippi, with a present fall of about 28 feet (31 
feet). The sand and gravel of the ancient stream bed lie deep below 
the silts and ooze, the spoils of the land through which the compara- 
tively insignificant modern stream struggles to maintain a channel 
and build up its bed and inadequate grades to present requirements. 
A wide expanse is there of shallow lakes, bayous, marshes and fens, 
reed growing lowlands, and low bottoms, which in a true alluvial 
stream adjusted to its work should be at ordinary extreme high water, 
but which are but little more than half way there” (Report to Chicago 
Drainage Commission, p. 2). 
Mr. Cooley’s words introduce us to a consideration of the 
cause for the low rate of fall below Peru. If we divide this por- 
tion of the valley into small sections, we find interesting con- 
trasts. There is, between Peru and Peoria, a distance of sixty 
miles, an average fall of one inch per mile. This is distributed 
as follows: 
Peru to Hennepin, - 13.6 miles. Rate of fall, 1.5 inches per mile. 
Hennepin to Henry, 13.5 miles. Rate of fall, 1.07 inches per mile. 
Henry to Chillicothe, 13.3 miles. Rate of fall, .55 inch per mile. 
Chillicothe to Peoria, 18.3 miles. Rate of fall, .26 inch per mile. 
From Peoria to Beardstown, a distance of seventy-four miles, 
the average fall is 1.67 inches and from Beardstown to the mouth, 
a distance of eighty-six miles, it averages a little more than two 
inches per mile (2.09). Even this, the most rapid rate shown 
in the lower Illinois is remarkably small, compared with that of 
