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Sierra Club Bulletin 



its channel to a depth exceeding three feet since it first began to 

 flow at the close of the glacial epoch, although acting under 

 every advantage of concentration and quick descent. The high- 

 est flood-mark the young river has yet recorded upon the clean 

 glacial tablets of its banks is only seven or eight feet above the 

 present level, at ordinary stages. Nevertheless, the aggregate 

 annual quantity that formerly passed down these canon valleys 

 was undoubtedly far greater than passes at the present time, be- 

 cause on the gradual recession of the glaciers at the close of the 

 period, the supply would necessarily be more constant, from 

 their melting all through the seasons. The evidence, however, is 

 incontestable, which shows that the highest floods of Sierra riv- 

 ers in the upper and middle regions of the range never much 

 exceeded those of the present time. 



Five immense glaciers from five to fifteen hundred feet in 

 depth poured their icy floods into Yosemite, uniting to form one 

 huge trunk, moved down through the valley with irresistible and 

 never-ceasing energy, crushing and breaking up its strongest 

 rocks, and scattering them in moraines far and near. Many, 

 while admitting the possibility of ice having been the great 

 agent in the production of Yosemite valleys, conjecture that 

 earthquake fissures, or cracks from cooling or upheaval of the 

 earth's crust, were required to enable the glaciers to make a be- 

 ginning and to guide them in the work. We have already shown 

 ("Studies in the Sierra," in Overland for May*) that cleavage 

 planes and joints exist in a latent or developed condition in all 

 the granite of the region, and that these exert immense influ- 

 ence on its glacial erodibility. During five years' observation in 

 the Sierra, I have failed to discover a single fissure of any kind, 

 although extensive areas of clean-swept glacial pavements af- 

 ford ample opportunity for their detection, did they exist. Deep 

 slots, with regular walls, appearing as if sawed, or mortised, 

 frequently occur. These are formed by the disintegration of soft 

 seams a few inches or feet in thickness, contained between walls 

 of stronger granite. Such is the character of the so-called fissure 

 said to exist in a hard portion of the south wall of Yosemite, op- 

 posite the Three Brothers, so frequently quoted in speculations 

 upon the valley's origin. 



* Reprinted in Sierra Club Bulletin, Vol. IX, No. 4, January, 1915. 



