264 GEOLOGY OF THE niGn PLATEAUS. 



US and notched deeply here and there by great recesses of peculiar form 

 and appearance. These alcoves are half a mile or more in width, and set 

 back into the plateau mass a mile or two. They are Hlled with coarse 

 broken rubble or talus, over which it is extremely difficult to make progress, 

 but still practicable. These alcoves are the work of ancient glaciers, and 

 extending from the opening of each of them is a pile projecting out towards 

 or even into the lake basin and forming a terminal moraine. Near the 

 lower end of the lake is a moraine a projecting a mile and a half from the 

 jilateau, and consisting of soil, rubble, and bowlders piled in a confused 

 mass to the height of nearly 200 feet and having a width of nearly a mile. 

 It almost divides the lake into two. The summit of the moraine holds 

 many pools of water embowered in aspens and bushes of many kinds, invit- 

 ing to lovers of the picturesque, but disappointing to him who accepts the 

 invitation. This is the largest moraine in the vicinity, though absolutely 

 it is not a very extensive one. It is instructive chiefly because it indicates 

 how small a part glaciation has played in the sculpture of this country. 

 There is never any difficulty in distinguishing tlie work which has been per- 

 formed here by ice from that which has been accomplished by the more 

 usual processes of degradation. The effects of glaciation are distinct and 

 peculiar, and cannot easily be confounded by a skilled observer with the 

 results of any other action. Doubtful cases do not seem to occur ; at least 

 I cannot recall any which conveyed doubt to my own mind. The ice which 

 formed the ancient glaciers of course accumulated upon the summit of the 

 plateau. That summit is about 12 miles in length and 2 to 3 miles in width. 

 It is very nearly level and is not deeply scored by ravines in the central 

 parts, but only upon the edges of the walls which bound the table on nearly 

 all sides. The ice may have accumulated to a considerable thickness upon 

 this summit, so broad and so nearly level, before attaining sufficient mass to 

 flow readily. Most of the effects were exerted upon the eastern and south- 

 eastern walls of the plateau, for such inclination as it possesses is in those 

 directions. The grander wall, which overlooks the great gorge, is not per- 

 ceptibly affected by glacial action, and it is not probable that the ice flowed 

 over it to any considerable extent. 



In the glacial gorges the rocks are very accessible for study. They form 



