i66 Transactions of the Canadian Institute. [Vol. VII. 



back from the lake shore. Provisionally this bed, from its position, not 

 from any identification of underlying beds, may be correlated with the 

 middle till sheet, the lower of the two sheets exposed at Scarboro'. 



Except in the Scarboro' section, the edge of the third till sheet is 

 found at a varying distance back from the lake shore. At Trenton it is 

 about three miles from the Bay of Quinte ; in Northumberland county 

 it is about six miles north of the lake. Its extent northwest of Toronto 

 has not been traced. The upper till in these localities is thus provision- 

 ally correlated with the upper till in the Scarboro' section and in the 

 vicinity of Toronto. In no place, so far as the writer is aware, is it 

 known to rest upon the middle till sheet, but always upon stratified 

 sands, gravels, or clays. In Northumberland and Durham, and else- 

 where, the upper till sheet is overlain by a series of stratified sands and 

 gravels. 



In the districts around Lake Scugog and around Lake Simcoe, and 

 for some distance on either side of these areas, till sheets, overlying 

 sands and gravels also occur. From their relative position and other 

 relations, there is reason to think that the upper one of these is the 

 equivalent of the third till sheet on the Lake Ontario side of the ridge. 



The middle till sheet rests unconformably upon the beds of the first 

 interglacial epoch ; the amount of erosion which preceded its deposition 

 cannot at present be determined because the necessary data are not all 

 collected. Obviously the amount of erosion to be attributed to the ice 

 sheet is also, at present, indeterminate. A maximum limit of less than 

 five miles may be assigned in one case for part of the underlying 

 deposits, because of the fragments of Utica shale in the middle till. It 

 may be possible to define the upward limit later when the precise 

 relations of the stratified beds are worked out. 



In the Scarboro' section this till sheet fills an old erosion valley in 

 the underlying stratified deposits. Hinde ( '77, 402), who first described 

 the depression, regarded it as a result of glacial erosion, but recent 

 investigators, because of its form, location transverse to the direction of 

 the ice movement, and the absence of any evidence of violent erosion, 

 consider it an old river valley. Similar but smaller depressions, some 

 of which even Hinde regarded as stream channels, are found elsewhere 

 in the Scarboro' section, and more rarely in sections to the east. At 

 the eastern end of the Scarboro' section, where the ice ascended across 

 the beds, the stratified beds, which underlie the till sheet, are very much 

 contorted and plicated. Westward from this there is little or no 



