538 



JOHN L. RICH 



first mile of its course the channel is very distinct, flat bottomed and 

 from ICO to 150 feet in width. Farther down it is less distinct owing 

 to the entrance of tributary valleys whose streams have modified the 

 old channel bottom. 



Contrary to what would be expected, the channel does not begin 

 at the divide. Here the notch is V-shaped in cross-section, and at the 

 bottom scarcely wider than the highway. Rock is visible in the walls, 

 but there is a considerable drift filling. About two hundred feet 



Fig. 6. — Spencer Summit channel. A typical lateral channel. The ice-tongue 

 moved southward through the deep, steep-walled valley in which Spencer Summit is 

 situated. Scale 1/62,500. 



east of the divide the channel begins suddenly. It is very swampy 

 and attains almost its full width at the very beginning. 



A probable explanation of the absence of the channel at the divide 

 is that a small ice-lobe from the main Cayuga valley tongue pu.shed 

 partly through the notch, and from its terminus discharged the 

 stream which formed the channel. This is a condition almost exactly 

 similar to that found by Tarr at Floral Pass, along the eastern border 

 of Hayden Glacier, Alaska. 



