Studies in the Sierra 



6s 



find their debris in the same condition as in Yosemite, and not 

 more abundant. Indeed, in some portions of valleys as deep and 

 sheer as Yosemite there is absolutely no talus, and that there 

 never has been any is proved by both walls and bottom being 

 solid and ice-polished. Many examples illustrative of this truth 

 may be seen in the great Tuolumne and Kings River valleys. 



Where the granite of Yosemite walls is intersected with feld- 

 spathic veins, as in the lowest of the Three Brothers and rocks 

 near Cathedral Spires, large masses are loosened, from time to 

 time, by the action of the atmosphere, and hurled to the bottom 

 with such violence as to shake the whole valley ; but the aggre- 

 gate quantity which has been thus weathered off, so far from 

 being sufficient to fill any great abyss, forms but a small part of 

 the debris slopes actually found on the surface, all the larger 

 angular taluses having been formed simultaneously by severe 

 earthquake shocks that occurred three or four hundred years 

 ago, as shown by their forms and the trees growing upon them. 

 The attentive observer will perceive that wherever a large talus 

 occurs, the wall immediately above it presents a scarred and 

 shattered surface whose area is always proportional to the size 

 of the talus, but where there is no talus the wall is invariably 

 moutonee or striated, showing that it is young and has suffered 

 little change since it came to light at the close of the glacial pe- 

 riod. On the 23rd of March, 1872, I was so fortunate as to wit- 

 ness the sudden formation of one of these interesting taluses by 

 the precipitation of the Yosemite Eagle Rock by the first heavy 

 shock of the Inyo earthquake, whereby their local character and 

 simultaneity of formation was fully accounted for. This new 

 earthquake gave rise to the formation of many new taluses 

 throughout the adjacent valleys, corresponding in every partic- 

 ular with the older and larger ones whose history we have been 

 considering. 



As to the important question. What part may water have 

 played in the formation of Sierra valleys? we observe that, as 

 far as Yosemite is concerned, the five large streams which flow 

 through it are universally engaged in the work of filling it up. 

 The granite of the region under consideration is but slightly 

 susceptible of water denudation. Throughout the greater por- 

 tion of the main upper Merced Valley the river has not eroded 



