Glacial Lake Nicolet.—Upham. 107 
period of French possession of the Mississippi valley. Still 
later it was long the chief avenue of travel, commerce, and 
military expeditions from the eastern United States, until rail- 
roads supplied other lines of communication between the great 
lakes of the St. Lawrence and the upper Mississippi. 
Besides my desire to see this old portage ground on ac- 
count of its history, another motive for its examination was 
to observe any evidence of its having been a channel of out- 
flow from a glacial lake, which would be expected because 
the Fox river descends thence northeastward, in the direction 
of the recession of the ice-sheet. Such channels are found 
leading across the lowest points of the watersheds from all 
the glacial lakes before mentioned, as of the Western Super- 
ior or Duluth lake, crossing the divide between the Bois Brule 
and St. Croix rivers, and of lake Chicago, passing from the 
Chicago river to the Des Plaines and Illinois rivers. In the 
distance of nearly 400 miles between these old outlets to the 
Mississippi from the basins of the upper Laurentian lakes, 
the short and low crossing from the Fox to the Wisconsin at 
Portage seems the most probable place for an outlet from 
lake Chicago when it appears to have been temporarily lowered, 
as made known by the observations of Andrews and Leverett, 
beneath the Chicago outlet after the formation of its first beach 
and before its second and third beaches were formed. 
Around the south end of lake Michigan the altitudes of 
these beaches are respectively about 50 to 60 feet, 30 to 40 
feet, and 15 to 25 feet, above the present lake, which at its av- 
erage stage is 581 feet above the sea. A peaty deposit occurs 
at some places under the gravel and sand of the second beach, 
and thence continues down the slope of the old lake bed, show- 
ing that its water rose over a former land surface to that shore 
line after it had stood for some time below the outlet near 
Chicago, with which these beaches are connected, marking 
stages of the downward erosion of that outlet. From the 
vicinity of Chicago to the St. Croix outlet of the glacial lake 
Duluth, the lowest sag on the watershed is at Portage, where, 
a- I think, the outflow of lake Chicago passed during a short 
interval between the stages shown by its first and second 
beaches. 
