8o THE POPULAR SCIENCE MONTHLY 



The present-day frequency with which great joint-blocks of granite 

 give way in weathering, or from earthquake shocks, and fall to talus 

 still suggest the subsidence hypothesis of Whitney. 



A compromise, composite theory may now be advanced. Considera- 

 tion of all the evidences of the structure and sculpture of the Yosemite 

 region will justify the premise that during the upheaval of the molten 

 granitic magma, domes swelled in rounded masses to much their 

 present form, cooling in concentric layers, which were later exfoliated 

 by aqueous and glacial denudation and aerial forces. Between these 

 domes, the trough of the stone wave, faulted and cross-fractured along 

 cleavage planes, formed the original floor of the Yosemite Valley. 

 Subsequently, the tilting of the Sierra range caused the carving of the 

 usual form of V-shaped valleys. Then, during the Quaternary period, 

 down plowed the glaciers scooping out the bed-rock, sapping and 

 scoring the walls of the valley, and leaving their moraines as mementoes 

 to remind mankind of their ancient estate and power. But these 

 moraines are either so wasted or considerable that much doubt is still 

 entertained as to their extent. If erosive forces carved out the mile- 

 deep Yosemite, the question of the transportation of the detritus is 

 still to be raised. The comparatively lightly-covered bed of the Merced 

 Biver below the valley does not indicate the accumulation of any 

 immense amount of detritus. Only by extremely fine comminution of 

 boulders to silt could this immense mass be almost completely carried 

 away. There is every evidence that a glacier reached the floor of the 

 Yosemite Valley, but the extent of its quarrying is still unknown. 

 Whether by direct grooving, or by undermining the overhanging escarp- 

 ments, it unmistakably transformed the canyon's V into a broad, 



Lros-s he.c~ti'o-n. o-f >0 Semite. Vo-lleu 



l&etwee-n^ Ylorth. ZT)ome ancl Qj-lacicr roiTi"ir 

 Scatc- h 500 -feet to th*. '"<* • i— ^ & w x 



I !^ 1 * ' ;\ ; 



T)ome *» _ , ■ , Cifnon of- 



Nercccl Rtv<l— 

 (z-leutiqr 



