834 A. Winchell on the Prairies of the Mississippi Valley. 
gorge—setting back through the chain of the lakes, would cause 
a rise in lake Michigan, above its present level, of 25 feet, This 
small elevation of Jake Michigan would probably open an outlet 
toward the Illinois river, But it is highly probable that the 
escarpment at Queenston, by extending further north, attained, 
in consequen 
much higher level, of which we have equally the indisputable 
records. We need but refer to the well known proofs of aque- 
ous erosion along the shores of the lakes, extending from their 
present levels to the altitude of 200 and 300 feet. Mark them 
in the escarpments of the south shore of lake Erie; in the lake 
ridges of Ohio and Michigan;* in the caverns and arches and 
purgatories of Mackinac island*—especially in the side of 
“Sugar .” whose base is now inland and elevated 150 feet 
above the surface of the water. Whatever may have been the 
barrier which dammed the waters to these heights, the evidences 
of their former presence are incontestable. But the moment we 
grant this ancient level to the waters, they inevitably escape from 
us toward the south, through the valleys of the Illinois and Mis- 
sissippi rivers.* Turning our attention in this direction we find 
corro 
large volume of water. At Lamont, this valley is distinct, with 
its bounding bluffs and its “ pot holes” worn in the solid rock 
of the ancient river bed. But with the waters of lake Michigan 
standing one or two hundred feet above their present level, how 
much of the region south and west of Chicago must have been 
submerged? ‘The ancient lake must have reached its arms into 
Towa, northern Indiana and southwestern Michigan. These, the 
- writer is convinced, were the relative levels of the land and water 
_ * We are aware that Col. Whittlesey has attributed the higher ridges to a sub- 
marine origin, and that Sir Charles Lyell has advanced the same opinion in refer- 
_ence to the ridges of lake Ontario. In regard to the latter, it will be remembe 
that lake Ontario is 330 feet lower than lake Erie, and may easily be surrounded 
found to enclose lacustrine shells. To say the least, even if we do not insist upon 
r custri igin of the higher ridges, the lower ones, which blend with the ter 
establish a former altitude of the lakes which is quite 5 
* Foster and Whitney, Rep. L. Sup, ii, pp. 164-6; Winchell, Mich. Geol. Rep» 
the earlier portion of the gorge of the Niagara was undergoing excavation 
a large portion of the waters of the lakes was being drained through the val- 
ley of the Illinois river, the force and of erosion must have been materially di- 
nished below the present standard by the diminution of the volume of water. 
