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University of California. 



[Vol. 3. 



the heaving action of frost. This veneer of loose blocks is so 

 thick that the waters from summer rains and from melting snows 

 do not gather in riin ways, and so establish lines of stream cut- 

 ting, but flow in a diffused fashion between and beneath the 

 blocks. Even this diffused flow is quite limited, for there is no 

 notable escape of the water at the lower limits of the upland 

 slopes nor at the brink of the cirques which interrupt these 

 slopes. This would seem to indicate that the water which falls 

 upon these surfaces disappears almost immediately into the intri- 

 cate and abundant system of jointages which traverse the 

 underlying rocks, and so makes its way to lower levels. The 

 water from the melting snow would, of course, meet with the 

 same fate. It is only when we get to the bottom of the canons 

 and cirques that the granite is tight enough to hold water 

 upon its surface. It would thus appear that these upland sur- 

 faces are as free from the attack of running water as are the 

 dryest deserts. This fact explains the remarkable smoothness of 

 their profiles, assures us of their great longevity when once 

 established, and so enables us to understand their survival of the 

 long and vigorous sculpture of other parts of the basin, which 

 were originally not so high. 



Having now tentatively adopted the hypothesis of differential 

 degradation as an explanation of the configuration of the Summit 

 Upland surface, a serious question arises as to where we shall 

 stop in its application. Why may not the Sub-summit Plateau 

 represent also a surface determined by the original configuration 

 of the surface of the granite batholith? There is no denying this 

 possibility; but one gets the impression that it is an old valley 

 floor, and it does not present the inequalities of slope and altitude 

 which characterize the Summit Upland. The remnant of the pla- 

 teau, which lies to southwest of Mt. Vandever at an altitude of 

 11,200 feet, and which has been correlated with the Sub-summit 

 Plateau, abuts upon the nearly vertical plane of contact between 

 the Mineral King belt of sedimentaries and the granite. This 

 relationship of the plateau surface to the contact between granite 

 and sedimentaries, proves it to be an erosional feature, evolved 

 independently of that structure, and if the writer's correlation of 

 this plateau remnant with the Sub-summit Plateau of the Upper 



