REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 rl21 



Form and character of the channels. The character of the 

 channels depends on several conditions, of which three may be 

 noted, namely: 1) the nature of the rock, 2) the relation of the 

 ice front to the topography, and 3) the relation in altitude of the 

 stream to the receiving land surface or water body. These three 

 elements will be discussed in order. 



1 The higher channels in each of these groups are mainly in the 

 Helderberg and Corniferous limestones, while the lower channels 

 are in the Salina shales. The highest scourways of the Eagle 

 hill and Cranson hill groups are in Hamilton shale. This differ- 

 ence in the rock causes great difference in the form and size of 

 the channels. Those in the limestone are often shallow, or only 

 broad scourways. If deep, they usually have steep or even verti- 

 cal walls, with cascades and cataracts if the underlying shale is 

 reached. Those in the shales are relatively deep, but the walls 

 are more sloping and smoother. The rapid weathering of the 

 shale has cut back the walls and partially filled the channel 

 bottoms, so as to give them a Y shape, which they did not have 

 originally. The limestone channels, on the other hand, are prac- 

 tically as the rivers left them, being stretches of bare rock, greatly 

 dissolved along the joints and fissures. This solution of the lime- 

 stone has often given to the scourways the appearance of a field 

 of boulders (pi. 22-24). 



2 A peculiar and interesting feature of these channels is the 

 absence in many cases of the north bank. Those on steep slopes 

 are sometimes only shelves or terraces cut in'to the escarpment. 

 In such cases the north wall is in the air, as it was constituted by 

 the ice which has disappeared. For a long time, centuries at 

 least, and possibly for thousands of years, the waning ice sheet of 

 the Ontario basin pressed against the escarpment or steep slope 

 which formed the southern side of the basin. The waters which 

 were held in the valleys and were escaping eastward from one 

 lake to another w^ere often compelled to squeeze through between 

 the rock wall ^on one side and the ice wall on the other. The 

 north ends of the high ridges are in consequence of this relation- 

 ship cut into a series of steps or shelves. In the case of the West 



