190 



Sierra Club Bulletin 



upheaval, it is merely a remnant of the common mass of the range, 

 which, from relative conditions of structure and position, has suf- 

 fered a little less degradation than the portions circumjacent to it. 



Regarded as measures of mountain-building forces, the results of 

 erosion are negative rather than positive, expressing more directly 

 what has not been done than what has been done. The difference be- 

 tween the peaks and the passes is not that the former are elevations, 

 the latter depressions ; both are depressions, differing only in degree. 

 The abasement of the peaks having been effected at a slower rate, 

 they were, of course, left behind as elevations. 



The transition from the spiky, angular summit mountains to those 

 of the flanks with their smoothly undulated outlines is exceedingly 

 well marked; weak towers, pinnacles, and crumbling, jagged crests 

 at once disappear,* leaving only hard, knotty domes and ridge- 

 waves as geological illustrations, on the grandest scale, of the sur- 

 vival of the strongest. 



Figure 7 illustrates, by a section, the general cause of the angu- 

 larity of summit mountains, and curvedness of those of the flanks; 



the former having been J<?'Z£;fj-flowed, the latter i?z;er-flowed. As we 

 descend from the alpine summits on the smooth pathways of the an- 

 cient ice-currents, noting where they have successively denuded the 

 various rocks — first the slates, then the slaty-structured granites, 

 then the curved granites — we detect a constant growth of specializa- 

 tion and ascent into higher forms. Angular masses, cut by cleavage 

 planes begin to be comprehended in flowing curves. These masses, 

 in turn, become more highly organized, giving rise by the most grad- 

 ual approaches to that magnificent dome scenery for which the 

 Sierra is unrivaled. In the more strongly specialized granite regions, 



* For exceptions to this general law, real or apparent, see Study No. I. 



Fig. 7 



