214 G. r. WRIGHT AGE OF DON mVER GLACIAL DEPOSITS 



and the center of Lake Ontario, extending in the vicinity of Toronto into 

 a region which was occupied by some species of plants and animals which 

 now exist only at a considerable distance to the south. At that time the 

 lower Don beds were deposited. 



2. Later the Labrador Glacier pushed outward as the Keewatin Glacier 

 receded, moving, as is shown by the glacial scratches and transportation 

 of boulders nearly east and west in the basins of lakes Ontario and Erie, 

 and pushing on as far as the Mississippi Eiver at Keokuk, Iowa, there 

 indeed crossing the river for a short distance. During this advance over 

 the deserted Keewatin deposits in the vicinity of Toronto the Scarboro 

 beds, overlying the Don beds, were deposited and some of the fossil plants 

 and animals native to the lower beds incorporated into the lower portions 

 of the upper beds. In the early part of this movement the Eome outlet 

 to the Ontario basin was still free from ice and probably at a lower level 

 than now. This was subsequently either filled with ice or gradually ele- 

 vated so as to account for the rise of the water and the accumulation of 

 the Scarboro beds. 



3. On the retreat of the Labrador ice the basin of the upper lakes 

 was uncovered, bringing Lake Warren into existence, while the western 

 boundar}^ of the ice obstructed the drainage to the east. At a later stage 

 this boundary retreated farther east and north, so as to uncover the Rome 

 outlet into the Mohawk Valley, giving rise to Lake Iroquois and allowing 

 for the erosion of the shelf 200 feet above Lake Ontario, now- covered by 

 Iroquois sands north of Toronto and Scarboro. The elevation of this 

 Iroquois beach at Toronto corresponds closely to that of the col at Eome. 



4. At a later stage the ice retreated so as to open the outlet into the 

 Saint Lawrence. 



5. Following this there was the rapid differential rise of land toward 

 the northeast, which elevated the Iroquois beaches toward the north and 

 northeast. 



Thus we have brought into order all the complicated facts involved in 

 this most puzzling problem, including those which demonstrate the late 

 date of the shorelines of Lake Warren south of Lake Erie in Ohio. Any 

 supposed sequence of events which fails to account for the late date of 

 these shorelines must Involve some error which vitiates the theory. While 

 we have no data from which to draw even approximate conclusions con- 

 cerning the date of the beginning of the Glacial period, there is nothing 

 which would appear to contradict the opinion of the geologists both of 

 England and Sweden that while the departure of the glacial ice-sheets 

 was very rapid, taking place only a few thousand years ago, the advance 

 was very gradual, occupying an immense period and accompanied by 

 numerous temporary mtermissions. 



