Geology of XJ^per 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 (eet. 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 of 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 himdred 

 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 av holly 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. From 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. 



