i86 



Sierra Club Bulletin 



outline thus determined is maintained by the glaciers in eroding 

 their way backward into the mountain masses against which they 

 head; and where these curved basins have been continued quite 



mountain chain, and C D E F G H, etc., the wombs of glaciers dead 

 or active, then the residual masses 123 will be the so-called moun- 

 tains. 



It may well excite surprise that snow collected in these fountain- 

 wombs should pass so rapidly through the neve condition, and begin 

 to erode at the very head; that this, however, was the case is shown 

 by unmistakable traces of that erosion upon the sides and heads as 

 well as bottoms of wombs now empty. The change of climate which 

 broke up the glacial winter would obviously favor the earlier trans- 

 formation of snow into eroding ice, and thus produce the present 

 conditions as necessary consequences. 



The geological effects of shadows in prolonging the existence and 

 in guiding and intensifying the action of portions of glaciers are 

 manifested in moraines, lake-basins, and the difference in form and 

 sculpture between the north and south sides of mountains and val- 

 leys. Thus, the attentive observer will perceive that the architecture 

 of deep valleys trending in a northerly and southerly direction, as 

 Yosemite, abounds in small towers, crests, and shallow flutings on 

 the shadowy south side, while the sun-beaten portions of the north 

 walls are comparatively plain. The finer sculpture of the south 

 walls is directly owing to the action of small shadow- glacier ets — 

 which lingered long after the disappearance of the main glaciers that 

 filled the valleys from wall to wall. 



Every mountaineer and Indian knows that high mountains are 

 more easily ascended on the south than on the north side. Thus, the 

 Hoffmann spur may be ascended almost anywhere from the south 

 on horseback, while it breaks off in sheer precipices on the north. 

 There is not a mountain peak in the range which does not bear wit- 



through the axis of the chain or 



H spur, separate mountains have 



^ been produced, the degree of 



H whose individuality depends 



^ upon the extent and variation 



^ of this erosion. Thus, let A B 



(Fig. 4) represent a section of 



Fig. 4 



a portion of the summit of a 



