GENERAL PHYSICAL FEATURES. 135 



Lakes and rivers.] 



opposite sides of the water divide, have the same level, and probably con- 

 stitute one connected body of water, although they have no visible over- 

 land connection. A short, low portage trail unites them, and constitutes 

 the international boundary line. 



The St. Louis and lake Superior dminaye system includes 8,552 square 

 miles, not counting any portion of lake Superior itself. Taken altogether 

 this is the most elevated and most hilly portion of the state. Its waters 

 descend, with frequent cascades, from over 2200 feet above the sea to 602 

 feet, the level of lake Superior, the most rapid fall being within five or ten 

 miles of that lake, and sometimes within two. The upland is a high rock- 

 plateau marked by three mountain ranges, a large part of the northern- 

 most, or Giant's range, however, being tributary to the Rainy river system. 

 The waters of this system have at present no visible over-land communi- 

 cation with those of the Mississippi ; but in glacial times, when the volumes 

 of all the streams and lakes were many times greater than now, and lake 

 Superior stood five hundred feet above its present level, or 1100 feet 

 above the ocean, it had a continuous water-channel through the Moose 

 and Kettle rivers to the St. Croix and thus to the Mississippi.* It appears, 

 therefore, that anciently the whole drainage of the interior of North 

 America may have been carried to the ocean through its main water-way, 

 the Mississippi. 



The Des Moines river runs along the northeast side of the Coteau des 

 Prairies from which it receives numerous small tributaries, and carries off 

 the surface waters from an area of prairie, in Minnesota, equal to about 

 1940 square miles. As this water finally reaches the Mississippi, it might 

 perhaps with propriety be embraced in the drainage system of that river. 



The Rock river system, which is tributary to the Missouri river through 

 the Big Sioux, includes about 1702 square miles, and embraces Nobles, Rock 

 and Pipestone counties in the southwestern corner of the state. This sys- 

 tem is confined to the southwesterly slopes of the Coteau des Prairies, and 

 the surface is smooth and treeless. 



The Cedar river system, which is also connected with the Mississippi 

 through the state of Iowa, is the smallest of the seven drainage areas of the 



*See the American Journal of Science and Arts (S), If. 15, for an account of another ancient outlet of lake Superior 

 into lake Michigan. Lake Michigan was tributary to the Mississippi through the Illinois, and lake Erie to the Missis- 

 sippi through the W abash river in Indiana. 



