28o 



Sierra Club Bulletin. 



the cirques unite to form glacial troughs, and these 

 troughs are separated, at a somewhat lower level, by 

 ridges constituting subordinate features of the range. 

 Some of the ridges between cirques and between troughs 

 are equally steep on both sides of their crest-lines, but 

 many — a large minority — are notably steeper on one side 

 than on the other, and this asymmetry of cross-profile is 

 definitely related to the cardinal points. Ridges trending 

 east and west are steeper on the north side than on the 

 south, those trending north and south are steeper on the 

 east side, and those trending northwest and southeast 

 are steeper on the northeast side. In general, the gentler 

 slope has the grade of a steep roof, and it is often clothed 

 by rock fragments approximately in situ. Ordinarily 

 it is too steep for the horse, but is readily scaled by the 

 mountaineer. As a rule, the steeper slope either is con- 

 stituted by, or else includes, an abrupt cHff which at most 

 points cannot be climbed. Figure i of Plate XLI shows a 

 group of high ridges in which the steeper faces are turned 

 to the north, and Figure 2 a group in which they are 

 turned to the northeast. 



These slopes are not controlled by rock structure. 

 The principal rock is granite, and this granite is in large 

 part structureless. Where it is traversed by joint systems 

 the details of sculpture are greatly influenced by the 

 joints, but the trend and slope of the greater features 

 are independent of the joints. 



A little reflection shows that the distribution of steep 

 slopes is correlated with the alimentation of Pleistocene 

 glaciers. The southward slopes of the east-west ridges, 

 because turned toward the sun, lost more snow by melting 

 and evaporation than did the northward slopes, and a ^ 



