Studies in the Sierra 



range in the section under spe- 

 cial consideration are capped 

 with slates; so are several 

 peaks of outlying spurs, as 

 those of the Merced and Hoff- 

 mann, and all the base is 

 slate - covered. The circum- 

 stances connected with their 

 occurrence in these localities 

 and absence in others, furnish 

 proof little short of demon- 

 stration that they once cov- 

 ered all the range, and, from 

 their known thickness in the 

 places where they occur, we 

 may approximate to the quan- 

 tity removed where they are 

 less abundant or wanting. 

 Moreover, we have seen in 

 Study No. Ill that the physi- 

 cal structure of granite is such 

 that we may know whether or 

 not its forms are broken. The 

 opposite sides of valley walls 

 exhibiting similar fragmen- 

 tary sections often demon- 

 strate that the valleys were 

 formed by the removal of an 

 amount of rock equal in 

 depth to that of the valleys. 



Fig. 10 is an ideal section 

 across the range from base to 

 summit. That slates covered 

 the whole granitic region be- 

 tween B and D is shown by 

 the fact that slates cap the 

 summits of spurs in the de- 

 nuded gap where they are suf- 

 ficiently high, as at C. Also, 



