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Show 264 GEOLOGY OF THE HIGH 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 filled 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 plateau, 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, inviting 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 the work which has been performed 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 southeastern walls of the plateau, for such inclination as it possesses is in those directions. The grander wall, which overlooks the great gorge, is not perceptibly 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 |