THE ANCIENT OUTLET OF LAKE MICHIGAN. 223 



by the cleaning out of the clogged valleys. A pretty contrast 

 for our geographical lessons ! 



It is noticeable that the abandoned channels of the glacial lakes 

 are now generally utilized as natural paths of communication. 

 The Indians easily passed from the head of the Minnesota to the 

 Red River of the North ; and indeed at times of high water they 

 paddled their canoes over the flat divide. The Chicago outlet of 

 Lake Michigan was naturally chosen for the path of the Illinois 

 and Michigan Canal, and now two railroads follow the same well- 

 graded course. More important still is the broad channel into 

 which the Mohawk flows from the Adirondacks, and which we 

 therefore call the Mohawk Valley. This well-opened passage de- 

 termined the location of the Erie Canal ; and that, taken with the 

 drowning of the Hudson River, by which navigable tidewater is 

 carried up to Albany, has undoubtedly been the determining 

 cause in the development of New York city as our greatest 

 seaport. 



As a good number of these abandoned channels have been de- 

 scribed, and as it is very probable that others will be found, it 

 seems to me worth while to recognize them as constituting a 

 special group of river-made forms of brief and peculiar history, 

 deserving recognition and representation in our study of physi- 

 ography. In this connection a particular interest attaches to the 

 former outlet of Lake Michigan, because it is the only one of the 

 old outlets that is now mapped with any approach to accuracy. 

 Twelve sheets prepared by the United States Geological Survey 

 namely, the Chicago, Riverside, Calumet, Desplaines, Joliet, 

 Wilmington, Morris, Ottawa, Marseilles, Lasalle, Hennepin, and 

 Lacon sheets already represent a length of over a hundred miles 

 of the former lake outlet, and give an efliective illustration of its 

 peculiar features. 



Before speaking of the old channel, I must turn from that 

 theme to give the maps a fuller introduction, for they seem as 

 yet to be very little known to our teachers and scholars. They 

 are constructed to serve as the topographical basis for the geo- 

 logical map which our national survey is charged to prepare. 

 No suitable map existing. Major Powell, director of the survey, 

 organized a topographical corps in 1882, under the charge of Mr. 

 Henry Gannett, to whom the mapping of the country was in- 

 trusted. The progress of the work has manifestly been embar- 

 rassed by the expense of the survey over so vast a country, by 

 the need of comparatively rapid progress, and by the difficulty of 

 securing experienced topographers ; but all considerations of dis- 

 tribution, scale, cost, and time have been duly discussed, and as a 

 result we have already several hundred map sheets of areas dis- 

 tributed over many States, on which the topographic features of 



