SAINT LAWRENCE OUTLET 239 



movement, upper end if one considers the form of the channel valley, 

 it is found that the valley gradually becomes narrower and shallower. 

 The most northern, the Bateau channel, at its east end turns abruptly 

 to the south to join the middle channel. Following the middle channel 

 eastward, it is again found to narrow and become shallow rapidly ; to 

 reach the main river it again turns to the right of its axial direction. 

 The third or American channel narrows and shallows eastward as do 

 the others. Between Wells island and the mainland its course is some- 

 what sinuous. 



The western ends of each of the channels are submerged rock valleys 

 of the first type here described. The islands between the channels mark 

 unsubmerged portions of the valley sides. Each of these valleys and 

 the ridges between them may be traced southwest for a considerable 

 distance under the waters of lake Ontario (plate 9). The upper ends of 

 each of the channels are located on the Archean belt. Each channel 

 ends in a well defined valley between Archean ridges, parti}' submerged, 

 it is true, but the ridges stand above water-level as the largest islands of 

 the Thousand Island group. A study of the topographic features of the 

 Thousand Island group shows that it is the characteristic semi-sub- 

 merged Laurentian topography that is found in literally hundreds of 

 other places throughout the Laurentian peneplain. We find the same 

 succession of longitudinal valleys between ridges of Archean rocks, the 

 axes of the ridges being parallel to the strike of the rocks, and the same 

 series of shallower connecting straits across sags in the ridges. A refer- 

 ence to the map will show that an almost exactly similar system of longi- 

 tudinal and cross-channels would be formed were the regions to the north 

 of the present river submerged. 



That each of the valleys with limestone sides become narrower east- 

 ward is due in part to the shape of the valley and in part to the fact that 

 the highest point of the partly submerged Frontenac axis lies to the east 

 of the eastern ends of the valleys. 



From the foregoing descriptions and by reference to the accompanying 

 maps, it will be seen that the outlet course of the Saint Lawrence river is 

 not a well defined channel, but rather is a complicated series of channels. 

 In fact, it is a series of partly submerged longitudinal basins, with cross- 

 connections between the basins, the complex forming what is erroneously 

 termed the channel of the Saint Lawrence. In reality the river has no 

 channel of its own west of the Frontenac axis. East of the axis, in the 

 lower parts of its course, it has cut a modern channel in drift deposits. 

 The immaturity of parts of the channel east of the axis is shown also 

 by the braided character of the stream. It is probable that east of the 

 axis the course of the river is in part also of a compound character. 



