98 
Tur GEOLOGICAL AND HyprograpHic FEATURES OF THE 
Iutinors River Basin. 
These subjects have received elaborate treatment, in con- 
nection with the problem of the disposal of the sewage of the 
city of Chicago, by Cooley (’89 and’91); and by Leverett (’96) 
in a report to the U. 8. Geological Survey upon the “Water 
Resources of Illinois.” The following discussion of those 
physical features which are more or less directly related to the 
heme of this paper has been, to a considerable extent, com- 
piled from these papers, with such supplementary data as 
could be gleaned from the reports of the U. 8S. Engineers and 
from the observations and records made by the biological 
station staff at Havana and at other points along the river. 
In many respects the Illinois River may be regarded as a 
typical stream of the prairie region of the North-Central 
States; and its basin, in the glaciation of its surface, the level 
character of the land, the fertility of the soil, the: absence of 
extensive forest areas, the amount of rainfall, the general 
climatic conditions, and its central position, might well be 
called a typical one for the central region of the Mississippi 
Valley. On the other hand, in several very important respects 
the river presents features and combinations of features that 
are exceptional and even unique. Foremost among such 
features is the very large amount of sewage received, an 
amount largely increased by the opening of the Drainage 
Canal in December, 1899, by which almost the entire sewage 
of a metropolis of about two million inhabitants enters the 
river. This, together with the large amount of organic refuse 
from the distilleries and cattle-yards along the course of the 
river, adds immensely to the fertility of its waters, especially 
when the river islow. Again, the present river is a babe in a 
giant’s bed. The channel and the bottom-lands of the present 
stream lie in the bed of an ancient outlet of Lake Michigan 
whose flood-plain constitutes the fertile “second bottom.” In 
this channel of its predecessor the Illinois River is now rapidly 
building up its flood-plain, the low gradient of the former oc- 
