10 STUDIES, SCIENTIFIC AND SOCIAL chap. 



the only difficulty in this place being the great vertical 

 displacement of such a small area, he adds : 



By the adoption of the subsidence theory for the formation of the 

 Yosemite we are able to get over one difficulty which appears 

 insurmountable with any other. This is, the very small amount of 

 debris at the base of the cliffs, and even, at a few points, its entire 

 absence. We see that fragments of rock are loosened by rain, frost 

 and other natural causes, along the walls, and probably not a winter 

 elapses that some great mass of detritus does not come thundering 

 down from above, adding no inconsiderable amount to the talus. 

 Several of these great rock-avalanches have taken place since the 

 valley was inhabited. One, which fell near Cathedral Rock, is said 

 to have shaken the valley like an earthquake. This abrasion of the 

 edges of the Valley has unr^uestionably been going on during a vast 

 period of time ; what has become of the detrital material ? Some 

 masses of granite now lying in the valley are as large as houses. 

 Such masses as these could never have been removed from the 

 valley by currents of water. ... It appears to us that there is no 

 way of disposing of the vast mass of detritus, which must have 

 fallen from the walls of the Yosemite since the formation of the 

 valley, except by assuming that it has gone down to fill the abyss 

 which was opened by the subsidence which our theory supposes to 

 have taken place. 



This extraordinary theory, put forth by an experienced 

 geologist in 1874, will probably not be accepted now; but 

 it serves to show that the Yosemite has always been con- 

 sidered a remarkable and exceptional valley which could 

 only have been produced by some equally exceptional 

 causes. A visit to the valley a few years since satisfied 

 the present writer that the modern and now generally 

 accepted theory of valley- formation is quite sufficient to 

 account for the Yosemite, though its features have been 

 rendered almost unique by the peculiar character of the 

 rocks out of which it has been hollowed, combined with 

 the meteorological and physical conditions of the locality, 

 both now and during the latter part of the tertiary epoch. 

 After having described the Australian valleys referred to 

 at the commencement of this chapter, an attempt will be 

 made to show that both are true valleys of denudation. 



The Cox mid Grose Valleys. 



In some respects the valleys carved out of the great 

 sandstone plateau of New South Wales are even more 



