30 2 A. P. COLEMAN 



Heights where 150 feet of cool climate beds overlie 36 feet of 

 warm climate beds, making 186 feet in all. However as the 36 

 feet of unio sands and clays commence 5 feet below the level 

 of Ontario and its water filled the well sunk there before the 

 bowlder clay was reached, it is certain that the Scarboro' section 

 contains more than 186 feet of interglacial beds, but how much 

 more cannot be told. It is probable also that the upper sands 

 once reached higher than at present, since their surface evi- 

 dently underwent great erosion before the overlying bowlder 

 clay covered them. 



DRAINING OF THE SCARBORO' LAKE 



At its highest point the great interglacial lake must have 

 stood more than 150 feet above Ontario, since the upper beds of 

 the cold climate deposits reach 152 feet. Then came a fall in the 

 level, whether sudden or slow is uncertain, though a slow drain- 

 age seems more probable. The cause of the original rise of the 

 water was probably the elevation of the lower part of the Lau- 

 rentian river valley, near the Thousand Islands. If so we may 

 suppose that the rise of the northeastern portion of the conti- 

 nent was slow, as it is at present ; and it may not have gone on 

 at a uniform rate, for there seems to have been a halt at 60 feet 

 above the present lake. If the rise was slow the sinking of the 

 barrier at the Thousand Islands at the close of interglacial 

 times was probably equally deliberate. Ultimately the water 

 fell below the present level of Ontario, as shown by the erosion 

 of interglacial valleys in the strata of the Toronto Formation ; 

 but whether the lake was completely drained so as to restore 

 the open valley with its great river or was only partially drained 

 is uncertain. 



With the lowering of the lake the channels of the rivers 

 must have been rearranged, for the old bay was now largely 

 filled with clay and sand ; and in the Scarboro' section there is 

 evidence of the cutting of three valleys through the stratified 

 sand and peaty clay. The one to the east, where the River 

 Rouge and Highland Creek now flow, was cut down below the 



