THE INTERGLACIAL GORGE PROBLEM 



147 



inlet would drain over the divide at Spencer Summit, and the 

 drainage of a small lake in Ten Mile Creek valley would natu- 

 rally have to pass over the divides, not along the axis of the 

 valley where these channels are located. For this reason, any 

 gorges which would be formed as overflow channels ought to 

 show on the divides, where a careful search has revealed none. 



. Fig. 5. — Looking down stream. Postglacial gorge of Map No. II on the right. 

 Gorge D on the left. 



Could the gorges have been formed interglacially? After 

 glaciation, streams naturally begin to flow along the lowest 

 courses. If the drift deposit is great enough to obscure much of 

 the preglacial topography, the streams may take very different 

 courses from those occupied preglacially; but if the amount of 

 drift-filling is slight, they will naturally follow preglacial drain- 

 age lines. There may be partial abandonment of old drainage 

 lines, as in the Genessee River/ or the stream may follow 



' An enumeration of the cases of reversions of drainage which have been 

 described by various writers would be too large an undertaking for the scope of this 



