130 
constitute a very important element in the fluctuations of the 
main stream, and its contributions of detritus are extensive. 
The basin of the Kankakee, occupying 5,146 square miles, 
lies in a single belt of latitude, extending 216 miles in an east 
and west direction. About 700 square miles of the lower part 
of the basin have a slope sufficient to afford a rapid run-off,and 
of the remainder fully one half is swamp and marsh, the other 
half being flat or slightly rolling, but capable of cultivation. 
The drift, except in the lower portion, is of considerable depth, 
and in much of the marshy region extensive deposits of sand 
are found. The lower stream is also bordered by extensive 
sand deposits, and these afford a storage basin for the waters 
derived from the adjacent slopes. Cooley (’89) estimates the 
mean of the extreme flood-discharges of the Kankakee at its 
junction with the Des Plaines at 31,200 cubic feet per second, 
and the mean of the extreme low-water discharges at 500 cubic 
feet per second. Flood water at the mouth of the Kankakee 
has been known to reach sixteen feet above low-water level. 
Aside from the uniformity in latitude, the physical features of 
the Kankakee basin, under present conditions, favor a gradual 
run-off, with floods which rise slowly to a moderate height and 
continue for a considerable period. Owing to the storage facil- 
ities of the basin the stream maintains a relatively large flow 
even in periods of prolonged drouth. The Kankakee is thus an 
important factor in moderating the extremes of high and low 
water in the Illinois. Its contributions of silt are but slight. 
The northern part of the basin of the Fox River is similar to 
that of the Des Plaines, and acts as a storage reservoir; but the 
southern part, which is of greater extent, has steep slopes, and 
the rapidity of the run-off is thereby heightened. Leverett (’96) 
states that its flood waters reach a level of fifteen feet above the 
. normal,and that the discharge, presumably at low water, is 526 
cubic feet per second. Cooley (91) gives the discharge of the 
Fox in the flood of February, 1887, as 13,680 cubic feet per sec- 
ond. The conditions of its basin are such as to aggravate the 
fluctuations and to increase the amount of silt in the I[]linois, 
