626 IMPROVEMENTS IN NORTH AMERICAN HYDROGRAPHY. 
more complete, and it is certain that there are numerous points 
within our territory where the courses of great rivers, or the 
discharge of considerable lakes, might be completely diverted, 
or at least partially directed into different channels. 
The surface of Lake Erie is 565 feet above that of the Hud- 
son at Albany, and it is so near the level of the great plain 
lying east of it, that it was found practicable to supply the 
western section of the canal, which unites it with the Hudson, 
with water from the lake, or rather from the Niagara which 
flows out of it. The greatest depth of water yet sounded in 
Lake Erie is but two hundred and seventy feet, the mean depth 
one hundred and twenty. Open canals parallel with the Nia- 
gara, or directly towards the Genesee, might be executed upon a 
scale which would exercise an important influence on the drain- 
age of the lake, if there were any adequate motive for such an 
undertaking. Still easier would it be to enlarge the outlet for 
the waters of Lake Superior at the Saut St. Mary—where the 
river which drains the lake descends twenty-two feet in a single 
mile—and thus to produce incalculable effects, both upon that 
lake and upon the great chain of inland waters which com- 
municate with it. 
The summit level between the surface of Lake Michigan at 
its mean height and that of the River Des Plaines, a tributary 
of the Illinois, at a point some ten miles west of Chicago, is 
but ten and a half feet above the lake. The lake once dis- 
charged a part or the whole of its waters into the valley of the 
Des Plaines. <A slight upheaval, at an unknown period, eleva- 
ted the bed of the Des Plaines, and the prairie between it and 
the lake, to their present level, and the outflow of the lake was 
turned into a new direction. The bed of the Des Plaines is 
higher than the surface of the lake, and in recent times the 
Des Plaines, when at flood, has sent more or less of its waters 
across the ridge into the bed of the South Branch of Chicago 
River, and so into Lake Michigan. 
A navigable channel has now been cut, admitting a constant 
flow of water from the lake, by the valley of the Des Plaines, 
