Vol. 6] Beid: The Oeomorphogeny of the Sierra Nevada. 109 



roof of the batholith; or, (2), the remnants of an older surface 

 of peneplanation ; or, (3), merely monadnoeks rising from the 

 ancient plain. The first possibility is of particular interest be- 

 cause Professor Lawson concludes that the level summits of the 

 High Sierra in the Kern River region are due to the form of the 

 under surface of the roof of the Sierra batholith. In the Carson 

 region the crystalline and metamorphic rocks are about equally 

 resistant to attacks of erosional agencies, so that plateaus above 

 base level could not be formed by the removal of a softer rock 

 above a harder. Hence the facts here are in dissonance with the 

 hypothesis of structural control. There are factors that favor 

 such interpretation, however. These are (1) the approximately 

 level upper surface of the granite batholith, and (2) the nearness 

 of the surface to the flat-topped summits. Here the fact enters 

 that Genoa Peak is flat-topped and composed of schist. Were 

 the hypothesis of structural control compatible with the facts, 

 outside the Genoa schist area, the form of this peak and its as- 

 sociates might be explained on the basis of structural control 

 within the mass of the metamorphic rocks. But in the light of the 

 facts of erosion elsewhere noted, this test fails. Hence the idea 

 of structural control upon the formation of flat-topped summits 

 must be abandoned. 



The second possibility, that these summits represent an older 

 cycle of erosion than that producing the high plateau, is one dif- 

 ficult to handle with the few facts obtainable. The hypsometric 

 test of like elevations is obviously impossible on account of the 

 excessive faulting. The only remaining criteria of value are 

 (1) similar hypsometric range between plateau and summits; 

 and (2) the form of the summits themselves. If these fail to 

 establish the hypothesis of an erosional surface, the summits 

 must be regarded as mere monadnoeks rising above the plateau. 

 If we compare the elevation of the summits above their plateau 

 remnants, we have the following. Slide Mountain rises about 

 600 feet above the plateau. However, faulting, combined with 

 tilting of the block, makes this figure here uncertain. A second 

 summit occurs about three miles west of Slide Mountain that has 

 about the same elevation, and tends to confirm the figure above. 

 Marlett Peak rises between 500 and 600 feet above its plateau 



