52 NEW YORK STATE MUSEUM 



rows perceptibly southward, till at the whirlpool its width is less 

 than the average width of the Niagara gorge. What the depth of 

 the gorge is has not been determined, though from the depth of 

 the whirlpool, we may assume that its floor is 200 feet or more be- 

 low the level of Lake Ontario. At, and to the north of the escarp- 

 ment it probably equals in depth Lake Ontario, opposite to it. The 

 channel is undoubtedly much more irregular than is shown on the 

 map, the sides being probably much diversified by lateral gullies. 

 The great width of the channel at St Davids may perhaps be due 

 in some small degree to widening by glacial erosion; for we know 

 that the channel was occupied by ice, from the glacial scratches 

 which are preserved on its walls, where these are exposed in the 

 present ravine of Bowman's creek near the whirlpool. The influence 

 of this buried channel on the direction and width of the Niagara 

 gorge will be discussed later. 



Valley of Georgian bay. Georgian bay is in many respects the 

 analogue of Lake Ontario. Like the latter, it also occupies a valley 

 lying between the Niagara escarpment and the crystalline old-land 

 on the northeast. As has previously been shown, the Niagara es- 

 carpment extends northward from Hamilton into the Indian penin- 

 sula between Georgian bay and Lake Huron, and, after passing the 

 Cove island channel, it reappears in the northwestern face of Grand 

 Manitoulin island. At Cabot's head, on the Indian peninsula, the 

 escarpment rises to 324 feet above the surface of the water, while 

 just of¥ the promontory soundings show a depth of 510 feet, thus 

 making the total hight of the escarpment at this point 834 feet. In 

 some places the summit of the escarpment rises to an elevation of 

 1700 feet above tide, or more than iioo feet above Georgian bay 

 (Spencer). The depth of the transverse channel connecting Georgian 

 bay and Lake Huron has been found to be 306 feet, which is more 

 than 200 feet less than the depth of the channel of Georgian bay. 

 It is possible however that the soundings do not show the absolute 

 depth of the rock bottom in the channel; for there may be a filling 

 of drift which raised the bottom of the channel above that of the 

 bav. 



