By. J. W. Spencer — Subsidence versus Glacial Dams. 269 



would have been 600 or 700 feet beneath the surface of the water. 

 The drainage must have been under the ice, and have amounted 

 to a discharge equal to that of the modern Detroit Eiver, as the 

 drainage of Lake Superior, Lake Michigan, and Lake Huron basins 

 would have been thus borne seaward, descending 300 feet to the 

 level of the Iroquois water. Under such conditions, the question 

 may be asked, how could the lake surface be retained long enough 

 at any level to carve out the deeply-graven water-lines and terrace- 

 plains of the Algonquin Beach, in place of the discharging waters 

 melting away the icy barriers, which were supposed to have been 

 the means of retaining the lake 300 feet above the level of the 

 Iroquois waters ? 



We now rise to the shores which bounded the Warren water. 

 These have been explored from Lake Michigan to New York, and 

 to north-east of Toronto, upon the Ontario peninsula. Upon the 

 glacial dam theory, this sheet of water would need a barrier to the 

 north as well as to the east. The drainage of the lake, at all stages 

 from the Eidgeway Beach downward, was to the north-east, and 

 beneath a greater mass of ice than in the case of the Algonquin or 

 the Iroquois water. But above the Eidgeway Beach, ^ at the 

 Maumee level, ^ there were outlets across Ohio and Illinois, if it were 

 a lake. The difficulties are increasing. 



The shore markings occurring near Kalamazoo, at about 900 

 feet above tide, represent a sheet of water having at least five 

 outlets across Ohio and Illinois. 



Again, the sea-cliffs of the Ontario peninsula, at from 1200 to 

 1425 feet and more, and the beaches now found up to 1689 feet, 

 would demand great dams to the south as well as to the north. But 

 such dams could scarcely have existed, with open waters carving 

 out sea-cliffs and terraces on the high peninsula of Ontario, and 

 also leaving records, 200 miles to the south. It should be noted 

 that gravel deposits of the so-called knme and bsnr structures occur 

 at all high levels, but of these I do not take cognizance. 



The drainage of this high country, such as the Genesee valley, 

 with terraces up to 1900 feet or more, and of the "terminal 

 moraine " up to 2680 feet, was toward the north without obstruction. 



Ascending now to Potter County, we find the gravel ridge at 

 2660 feet, on the very edge of the highest knob of the "terminal 

 moraine." This high point could not have stood out of the ice as 

 a Greenland Niinatak, with a lake around it, for it is at the margin 

 of the drift, and glaciers do not deposit their tei-minal detritus within 

 the ice, but at their very margins. It seems impossible to conceive 

 a glacial mass retaining a lake about this flattened knob, even if the 

 country were submerged to almost sea-level. 



There are other similar deposits on adjacent summits. Again, 

 had a glacier existed on the top, or on the southern side of this 

 " moraine " ridge, its melting ice must have carried great quantities 

 of drift into the valleys to the south, which neither Mr. Lewis nor 



^ " High Level Shores in the Eegion of the Great Lakes and their Deformation," 

 by J. W. Spencer, Amer. Journ. Sci. vol. sli. 1891. - Ibid. 



