CORRASION BY GRAVITY STREAMS. 299 



and which possess almost vertical slopes; furthermore 

 whose side streams cascade or fall into the main stream, 

 the valley profiles being such as to show marked under- 

 cutting at points facing the direction followed by the 

 strongest portion of the stream, but nevertheless possess- 

 ing a floor occupied by a winding stream, then we simply 

 continue the visible profiles downwards after the manner of 

 those known to be produced by streams, and the meadow 

 now concealing the lower rock profiles may be confidently 

 expected to represent the readjustment of channel slope 

 over an old rock basin floor, shallow or deep, which origin- 

 ated in the action of a strong glacier. The meadow with 

 meandering stream occupying the "tread" of a valley 

 "step" may not hide so deep a rock basin as that formed 

 in a valley constriction. The reason for this has been given 

 earlier. 



This meadow stage it is towards which all the Fiord and 

 Alpine Lake basins are progressing, but the stronger the 

 old ice floods have been, the longer will be the period of 

 channel readjustment before water and ice can recommence 

 their general work of corrasion. 



(b) Yosemite Valley. — This canon is about seven miles 

 in length, and is bordered by very steep walls, about 3,000 

 feet in height. The lower end of the valley proper is the 

 narrower portion and is enclosed by the steepest walls, 

 that of El Oapitan being almost vertical and more than 

 3,000 feet above the valley. The floor is a gigantic meadow 

 occupying the whole length of the valley, and varying from 

 a half to three-quarters of a mile in width. Upstream from 

 El Oapitan the walls are almost continuous, forming a 

 spurless valley; a very slight distance below El Oapitan, 

 however, the meadow floor disappears, the gorge becomes 

 rather V-shaped, and under Inspiration Point the cliffs 

 have shrunken to 1,500 or 1,700 feet in height, besides 



