IMPROVEMENTS IN NORTH AMERICAN HYDROGRAPHY. 601 



slight upheaval, at an unknown period, elevated the bed of the 

 Dos 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 tlie lake, and in recent tunes 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, 

 into the Ilhnois. The mean discharge by this channel does not 

 much exceed 23,000 cubic feet per minute, but it would be quite 

 practicable to enlarge its cross-section indefinitely, and the flow 

 through it might be so regulated as to keep the Illinois and the 

 Mississippi at flood at all seasons of the year. The increase in 

 the volume of these rivers would augment their velocity and 

 their transporting power, and, consequently, the erosion of their 

 banks and the deposit of slime in the Gulf of Mexico, while the 

 opening of a communication between the lake and the aflluents 

 of the Mississippi, unobstructed except by locks, and the intro- 

 duction of a large body of colder water into the latter would very 

 probably produce a considerable effect on the animal hfe that 

 peoples them. The diversion of water from the common basin 

 of the great lakes through a new channel, in a direction opposite 

 to their present discharge, would not be absolutely without influ- 

 ence on the St. Lawrence, though probably this effect might be 

 too small to be readily perceptible.* 



* From Reports of the Canal Commissioners of the State of Illinois, and 

 especially from a very interesting private letter from William Gooding, Esq.» 

 an eminent engineer, (which I regret I have not space to print in full), I leara 

 that the length of the present canal, from the lake to the River Illinois, is 101 

 miles, with a total descent of a trifle more than 145 feet, and that it is pro- 

 posed to enlarge this channel to the width of one hmidred and sixty feet, with 

 a minimum depth of seven, and to create a slack-water navigation in the Illi- 

 nois by the construction of five dams, one of which is already completed. 

 The descent from the outlet of the canal at La Salle on the Illinois to the 

 Mississippi is twenty-eight feet, the distance being 230 miles. The canal thus 

 enlarged would cost about $16,000,000, and it would establish a navigation 

 for vessels of 1,300 to 1,500 tons burden between Lake Michigan and the Mis- 

 sissippi, and consequently, by means of the great lakes and the Welland Ca- 

 nal, between the St. Lawrence and the Gulf of Mexico. 

 26 



