36 



ing the retreating phase, until the ice front had receded to 

 the northeast end of lake Erie. By the time it had reached 

 this position, however, the relatively deep basin of lake 

 Ontario became the controlling factor in the ice movements 

 of this region. This was the position of the ice front a 

 short time before the moraines to be visited were made. 

 The ice field was then confluent and continuous over the 

 whole region between the lake Ontario basin on the south 

 and the Trent valley, the lake Simcoe basin and the basin 

 of Georgian bay on the north. At this time the ice front 

 rested against the face of the Niagara escarpment from 

 Hamilton northward to Georgian bay, and the ice lay as 

 an unbroken sheet over the whole region to the east. It 

 was already growing thin, however, over the ridge north 

 of Toronto, and with further steps of retreat the ice soon 

 parted and the ridge began to emerge. 



. The first parting of the ice lobes in the manner described 

 probably occurred during the time of lake Arkona, but was 

 temporary, for the pronounced readvance of the ice to the 

 Crystal beach (Alden, Port Huron) moraine carried the 

 ice front back again to the base of the escarpment, and the 

 moraines which had just been made were overridden and 

 destroyed. This episode of glacial history is not estab- 

 lished on evidence seen in the localities visited on this ex- 

 cursion, but is fully supported by facts recorded in other 

 parts of Ontario and in Michigan and New York. Then, 

 when the ice front retreated again, the ridge was once more 

 uncovered and the moraines now seen on the heights 20 

 miles north of Toronto began to be formed. This was 

 probably during the times of lakes Wayne and Warren, but 

 later phases farther east were probably correlatives of lake 

 Lundy. 



The two moraines were formed on the top of the emerged 

 ridge, first at the west end near the base of the Niagara 

 escarpment, and later at places farther east. As the flanks 

 of the ridge were gradually uncovered, lake waters stood 

 high upon them, but these waters were only narrow arms 

 that reached northward from the main lake in the basin 

 of lake Erie and made no perceptible record by wave action. 

 At this stage of retreat the ice did not enter the western 

 part of the lake Ontario basin over the ridge north of To- 

 ronto, but came in at the northeastern end chiefly in the 

 gap between Trenton, Ontario, and Oswego, New York. 



