Geology of Upper Illinois. 139 
from the Des Plaines, nearly opposite the mouth of Portage lake, 
to the Fox river at Elgin, (thirty-five miles south of the State 
line,) where the surface of the stream is one hundred and fifteen 
feet above Lake Michigan, it was found, that the intervening 
ridge had an elevation of fifty or sixty feet, the cutting down of 
which would be too expensive to justify the expedient. The 
commissioners were accordingly led to adopt the magnificent plan 
of making Michigan the feeder to the canal. The first level 
thereby becomes thirty-four miles in length, with an average 
depth of cutting of eighteen feet, which is principally in solid 
rock. The depth of six feet of water has been decided on, in 
order to secure to the canal a constant depth of four feet during 
the fluctuations of tide in the lake, occasioned by high winds. 
A declivity is given to the bottom of the canal, of one tenth of 
a foot per mile. There are two locks situated at the end of this 
level, having a lift of eighteen feet. Above the first of these, for 
‘the distance of three quarters of a mile, the canal has a width of 
one hundred and twenty feet. The estimated expense of this 
level is $5,871,324. 
The middle division of the work extends thirty-seven miles 
from the head of the first lock. It has six locks, with an aggre- 
gate lockage of fifty-seven feet in the first four miles, for the 
whole of which distance the route is over little better than solid 
rock, and is consequently very expensive. Another difficult por- 
tion ok this division commences about two miles below the cross- 
ing of the Du Page, and extends nearly to Dresden, below the 
mouth of the Kankakee. The bluffs here are from one hundred 
to one hundred and fifty feet high, and approach so near the river 
as to be washed by it, which renders it necessary to construct the 
towing path wholly or in part, in the river, for a distance of more 
than two miles; consequently, an expensive protection will be 
demanded to defend the work from the ice-floods of the Kankakee. 
The western division has sixty-eight feet lockage, and is twen- 
ty-nine miles in length, exclusive of four miles of the Fox river 
feeder. F yom the first lock, below Ottawa, to the termination of 
the canal at La Salle, (on section fifteen,) the route lies through 
much wet ground, being along the bottoms of the Illinois, just 
under its northern bluff. As these lands are overflowed during 
the spring-freshets, the level of the canal requires to be con- 
siderably raised, and to be guarded by strong embankments. 
