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this same declivity. The immediate result of such action 

 was that the mouth of the Bridal Veil stream was cut off 

 by the glacier, the upper portion of its channel being finally 

 hung up more than 800 feet above the floor of the main 

 channel. During the recession an enormous " step" was 

 formed near the present Hanging Valley of the Yosemite 

 Creek. This "step" must have been at least 2,000 feet in 

 height. It is evident that as the declivity was cut back so 

 rapidly owing to the great steepness of the declivity (in 

 other words, to the great thickness of the structures lying 

 above the local base-level immediately down stream) the 

 glacial energy had no time in which to excavate deep basins 

 beloW the associated base level, but merely formed a huge 

 tread with relatively shallow basins upon it. Inasmuch 

 again as the immense volume of the structures so removed 

 in the formation of the "step" and "tread" increased the 

 cross section of the Yosemite, so at this later stage the ice 

 which formerly had flowed round the summit < >f El Capitan 

 and had made a roche moutonnee of it, now had its surface 

 lowered considerably, the glacier not exceeding a depth of 

 2,000 feet above the present floor of the Yosemite. 



This rapid and peculiar change of vertical position set 

 up sapping by lateral -ihcial action, the lateral however 

 being subordinate to the vertical action. This gives to the 

 Yosemite the appearance of roches moutonnees on the up- 

 lands. On the other hand, it is the still later sapping which 

 gives the peculiar and rough appearance to the upper 

 portions of the walls where observers would naturally have 

 looked for signs of abrasion. On passing Glacier Point the 

 great Yosemite "step" and "tread" became duplicated, 

 one following the course of the Tenaya, the other following 

 that of the Merced. Glacier Point was not reached by the 

 ice stream so soon as the huge "steps" of the Tenaya and 

 Merced had been carried some little distance upstream of 



