300 The American Geologist. November. 1894 
close of the episode which ended 14,000 years ago. Whilst, 
however, the date of the decadence of the Ice age in this region 
is told, the falls do not necessarily record its termination in 
other and distant regions. 
1 '). Recurrent Drainage of the Great Lakes into the Mis- 
sissippi Hirer by way of Chicago. Long ago, Dr. E. Andrews 
described the deserted beaches south of Chicago, and found 
that the highest reaches an elevation of 45 feet above the 
lake. For many miles around the head of the lake, the de- 
serted shores are found far inland. There are other raised 
beaches near the lake. The different sets form an apparent 
succession, but in reality there is confusion between the old 
water-margins and the very recent beaches. The low plain at 
the head of the lake rises so gradually that at the divide be- 
tween it and the Mississippi drainage southwest of Chicago it 
is only eight feet above the lake, with a rocky floor a foot or 
two lower (canal survey). In proceeding northward along 
the margin of the Michigan basin, beaches are found emerg- 
ing from beneath the waters. From the measured deformation 
of the various sets of deserted shores, the depth to which 
the tilted beaches are depressed beneath the lake can be 
calculated.* These record the shrinking of the lake from the 
highest level south of Chicago to others even hundreds of feet 
beneath. 
The Ridgeway beach extends from the Erie basin across 
southern Michigan, by way of Saginaw bay and the Grand 
river valley, and southeast of lake Michigan it descends and 
is lost in the sand dunes of that region ; but, with the meas- 
ured rate of deformation, it is computed to pass about 40 feet 
beneath the surface of the water. The Forest beach, the last 
strand of Warren water, is about 100 feet lower. The still 
lower Algonquin beach (the great shore line of the dismem- 
bered upper lakes) occurs well defined about the northern 
half of the lake (Andrews and Taylor); but if produced to 
the southern end of the basin, it would be submerged between 
250 and 300 feet. There are other lower and less important 
deserted shores; but all these represent the subsiding of the 
lakes during the time of discharge of the waters of lake Huron 
*"High Level Shores in the region of the Great Lakes and their De- 
formation," before cited. 
