Studies in the Sierra 



427 



throughout the middle granitic region in considerable numbers : 

 some with their protecting boulders still poised in place, others 

 naked, their boulders having rolled off on account of the stool 

 having been eroded until too small for them to balance upon. It 

 is because of this simple action that all very old, deeply weath- 

 ered ridges and slopes are boulderless, Nature having thus 

 leisurely rolled them off, giving each a whirling impulse as it 

 fell from its pedestal once in hundreds or thousands of years. 



Moutonneed rock forms 

 shaped like Figure 3 are 

 abundant in the middle 

 granitic region. They fre- 

 quently wear a single pine, 

 jauntily wind-slanted, like 

 a feather in a cap, and a 

 single large boulder, poised 

 by the receding ice - sheet, 

 that often produces an im- 





'1 'f*' 









Ikii'illl! 



pression of having been 



thus placed artificially, exciting the curiosity of the most apa- 

 thetic mountaineer. Their occurrence always shows that the 

 surfaces they are resting upon are not yet deeply eroded. 



Ice - planed veins of quartz and feldspar are frequently 

 weathered into relief by the superior resistance they offer to 

 erosion, but they seldom attain a greater height than three or 

 four inches ere they become weather-cracked and lose their 

 glacial poHsh, thus becoming useless as means of gauging de- 

 nudation. Ice-burnished feldspar crystals are brought into re- 

 lief in the same manner to the height of about an inch, and are 

 available to this extent in determining denudation over large 

 areas in the upper portion of the middle region. 



This brief survey of the various forces incessantly or occa- 

 sionally at work wasting the Sierra surface would at first 

 lead us to suppose that the sum total of the denudation must be 

 enormous ; but, on the contrary, so indestructible are the Sierra 

 rocks, and so brief has been the period through which they 

 have been exposed to these agents, that the general result is 

 found to be comparatively insignificant. The unaltered pol- 

 ished areas constituting so considerable a portion of the upper 



