Science, Geology and Physics 



the gorge, especially eroding the western wall because of the 1901 

 movement in a southwesterly direction, and filled the channel ' c coc 

 with till and modified drift, to the height of 300 feet. (3) The 

 return of temperate conditions melted the ice and restored 

 Niagara River, but it had not sufficient volume to overflow the 

 barrier of till. Hence, it turned its direction to the northeast, 

 following a slight depression in the plateau to the edge of the 

 escarpment at Lewiston. After the stream had cut its way back 

 to what remained of the original channel, the whirlpool was set 

 in motion. 



Erosion of the Lower Gorge. 



There must have been some erosion in pre-glacial times along 

 the lower part of this section, as is evidenced by the tributary 

 canyons at the Devil's Hole and Smeaton Creek. What it 

 amounted to in the main stream, no one can tell. The top of the 

 cliff at Lewiston is about 575 feet, and the fall 325 feet. It 

 would not have been well defined at first, because of the greater 

 altitude of Lake Ontario and the character of the rock. The 

 fall being over the Niagara limestone and shale directly into the 

 level of the lake, would present a cataract 100 feet high, and 

 could not act energetically upon the Clinton limestone beneath. 

 Hence this becomes an upper fall, receding more rapidly than a 

 second one, which would make its appearance as soon as the 

 lake disappeared. For similar reasons this would wear away 

 only the Clinton limestone and shale of 30 feet thickness. Thus 

 there would be two cataracts, separated by a considerable inter- 

 val. There remains the Medina sandstones and shales, which 

 would have their own cataract, and so Niagara commenced 

 the excavation of the lower gorge by a triple division of its 

 energy. . . . 



Two very important conclusions follow : First, the upper falls, 

 receding more rapidly at first and more slowly afterwards, must 

 have reached the island at Wintergreen flat before the lower 

 cataracts caught up with it. Second, the falls being worn out 



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