RIVER SYSTEMS AND GENERAL SURFACE SLOPES. 



421 



The following tabulation gives the altitude of the water surface of 

 the Wisconsin at prominent points from the source to the mouth: 



The average velocity of the river below Portage is remarkably uni- 

 form and is just about two miles per hour.' The daily discharge of 

 of the river at Portage in times of extreme low water is about 

 259,000,000 cubic feet.^ The average fall of the water surface 

 of the river below Portage is li feet per mile. General Warrren, 

 from whose report^ this statement is taken, very truly says that this 

 rapid fall, were it not for the great amount of sand in the river-bed, 

 would make the stream a series of pools and rock rapids; so that, 

 whilst making a great obstruction, the sand really gives the river 

 what navigability it possesses. 



In subsequent pages are given a number of geological sections 

 across the valley of the Wisconsin below Portage. The profiles of 

 these sections are reduced from the profiles given in the atlas of Gen. 

 Warren's report, and the geology has been added from my own ob- 

 servations. 



Black river rises in townships 31 and 32, on the high drift-covered 

 divide near the Fourth Principal Meridian, at elevations of over 800 

 feet above Lake Michigan, runs first west into range 2, and then takes 



■ Mai C. R. Sutter, in Chief of Engineer's Report, 1867, p. 353. ' The same 

 ■' '■ Report on the Transportation Route along the Wisconsin and Fox River, by Gen. 

 G. K. Warren, U. S. Engineers, Washington, 1876. 



