50 GEOLOGY OF OHIO. 
Fourth. The final retirement of the glaciers over the Canadian high- 
lands; the gradual subsidence of the water in the lake basin until it 
reached its present level, and occupied only the deeper portions, forming 
our modern chain of lakes. In this descent, the shore line was marked 
at different intervals with terraces and beaches. 
In Southern Ohio, the succession of events was somewhat different, in- 
as much as the Forest bed, an old soil, with stumps, logs, and leaves, there 
rests on the Bowlder clay, and is covered locally by an upper stratum of 
Till, which is the product of glacier or iceberg action. No evidence of 
this has been found in the lake basin, where there is no forest bed— 
unless it be represented by the drifted vegetable matter which is some- 
times found in the Erie clay, but which is not covered by a second 
bowlder clay. So far as yet observed, the facts seem to indicate that the 
basin of Lake Erie was filled with water or ice during all the time that 
the alternations of temperature recorded in Southern Ohio we:e taking 
place. 
Professor Winchell is represented, by Professor Geikie (Great Ice Age, 
page 462), as claiming the existence of a forest bed, overlain by a second 
Bowlder clay, in north-western Ohio, but this is probably due to a mis- 
understanding of Professor Winchell’s language, when he had reference 
to the north-western States. No forest bed has been seen or heard of by 
the writer in north-western Ohio, and nothing of the kind is reported by 
My. G. K. Gilbert, or Mr. J. H. Klippart, in their papers on the Drift of 
the Maumee Valley, nor by Professor Winchell, in his reports on the 
counties surveyed by him. : 
Prof. Winchell, in his ‘‘ Drift Deposits of the North-west,” attributes 
the excavation of the basins of the great lakes to the great continental 
glacier cutting locally deep into beds of soft rock. His language is as 
follows: ‘Southward, prolongations of the ice sheet follow the north- 
south outcropping edges of argillaceous formations. Lake Michigan les 
in one of these troughs; Lake Huron les in another. Lakes Erie and 
Ontario are only shallow basins dug out of soft rocks by ice that passed 
south-westwardly. The shale bed that gave rise to Lake Ontario als 
determined the location of Georgian Bay and Green Bay. The basin of 
Lake Erie is much shallower toward the west end than toward the east, 
and it finally runs out altogether by reason of the westward attenuation 
and finally entire disappearance of the Salina formation in which it is 
largely excavated. The ice was then thrust up on to harder rocks that 
form the basis of north-western Ohio and north-eastern Indiana. Lake 
Michigan was terminated southwardly by the eastern trend of the rocky 
outcrops at an angle that the ice could not follow.” 
