Vol. 6] Bcid: The Geomorphogeny of the Sierra Nevada. 105 



other unaffected by the change. No residuals of the metamorphie 

 strata project up above the general level. Minor irregularities 

 do exist, and usually the small schist areas are a few feet above 

 the granodiorite. The reason is not hard to find. Were neither 

 rock jointed and therefore open to atmospheric agencies except 

 through pore spaces, the granodiorite would be disintegrated and 

 eroded much the faster. On the other hand, were the two rocks 

 equally resistant to decomposition and disintegration, the schist 

 would disappear more rapidly, due to its condition of excessive 

 jointing and fracturing. The actual result of these two sets of 

 conditions is a mean. The rocks are about equal in their ability 

 to withstand disintegrating forces. As a further result, the 

 granodiorite on the old level surfaces presents its usual features 

 of deep sandy soil covered with boulders of rotten rock, while 

 the schist has a rough appearance, and is covered with small, 

 sharp, angular fragments, the larger of which commonly have 

 centers of fresh material. The larger schist areas that form 

 part of the old erosional plain show some soil, the top of which 

 is covered by a layer of angular schist fragments of small and 

 remarkably uniform size. This latter condition is a natural re- 

 sult of the breaking down of the schists on a level or nearly 

 level surface, where the disintegration proceeds faster than the 

 erosion by running water. The difference between this and the 

 appearance of the small schist residuals is significant. Here the 

 support of granite material is carried away, with resultant 

 coarse disintegration of the metamorphie rock. This allows all 

 fine sandy material to be removed as fast as formed to the slightly 

 lower surrounding granodiorite, and leaves the sharp jagged 

 edges of joint fragments uncovered. A further result of the 

 different mode of weathering between the plutonic and the 

 schistose rocks is found in the appearance of the slopes due to 

 faulting. The granodiorite tends to maintain its sharply cut 

 outlines, even though quite deeply disintegrated. The schist, 

 on the contrary, because of its intense fracturing, usually pre- 

 sents more rounded slopes and smoother lines. The maximum 

 effect of this variation in resistance to atmospheric forces is thus 

 one that but slightly modifies some of the lesser physiographic 

 forms. 



