INACCESSIBLE VALLEYS 



and decomposition of rocks. Small cracks thus produced 

 receive water which freezes at night, and the crack is 

 widened by the irresistible force of the ice wedge. It is 

 by this agency that the final touches have been given to 

 the Yosemite scenery, after all the softer and more decom- 

 posable portions of the rock had been removed by the 

 ordinary modes of weathering. The huge domes and 

 spires, and the subquadrangular mass of El Capitan, must 

 be looked upon as intensel}' hard and compact cores of 

 rock that remain after all the more friable masses that 

 inclosed them have been removed. They show us the 

 natural forms into which granite weathers, due perhaps to 

 the mode in which it has originally cooled from the 

 molten or plastic state. In the case of the dome the 

 mass consists of concentric layers, probably of different 

 densities, which peel off successively like the coats of a 

 gigantic onion. On some of the domes we can see one of 

 these coats partially removed, and the same thing was 

 observed by myself in the dome- shaped mountains as well 

 as in the smaller subglobular masses of granite in the Rio 

 Negro. 



The fact ihat the process of denudation, continued 

 perhaps throughout the greater part of the tertiary period, 

 has now eaten away all the more friable and soluble 

 portions of the rocks which once occupied the site of the 

 valley, leaving only those compact central masses which 

 are hardly affected by ordinary atmospheric action, will 

 account for what seemed such a great difficulty to Pro- 

 fessor Whitney — the small amount of rock debris under 

 the great precipices or in the valley generally. For the 

 last few thousand years, probably, the amount of rock- 

 flills has been comparatively small, so that it barely equals 

 the rate at which atmospheric agencies, aided by vegeta- 

 tion, break up and decompose the fallen masses, which 

 then, in the form of the coarse granitic sand that con- 

 stitutes the surface soil in all the drier portions of the 

 valley, is gradually carried by wind, rain, and melting 

 snow into the river, and ultimately into the great bay of 

 San Francisco. That some considerable amount of decay 

 is still going on in these giant ^liffs is evident, not only 



