Studies in the Sierra 



227 



them, and make them separable from one another while yet 

 forming undisturbed parts of the mountain. The force which 

 binds these blocks together is not everywhere equal ; therefore, 

 when they are subjected to the strain of glaciers, they are torn 

 apart in an irregular and indeterminate manner, giving rise to 

 endless variety of rock forms. 



The granite in some portions of the range is crumbling like 

 meal by the decomposition of its feldspar throughout the mass, 

 but the greater portion has suffered scarcely any disintegra- 

 tion since the close of the glacial period. These harder areas 

 display three series of cleavage or separating planes, two 

 nearly vertical, the other horizontal, which, when fully de- 

 veloped, divide the rock into nearly regular parallelopipeds. 

 The effects of this separable structure upon the glacial erodi- 

 bility of rocks will be at once appreciated. In order that we 

 may know how mountain chains are taken apart, it is important 

 that we first learn how they are put together ; and now that we 

 have ascertained the fact that the Sierra, instead of being a 

 huge wrinkle of the earth's crust without any determinate 

 structure, is built up of regularly formed stones like a work of 

 art, we have made a great advance in our mountain studies ; 

 we may now understand the Scripture: "He hath builded the 

 mountains," as not merely a figurative but a Hteral expression. 



In order that we may obtain some adequate estimate of the 

 geological value of this cleavage factor in the production of 

 cations, rock forms, and separate mountains, with their varied 

 sculpture, we must endeavor to find out its range, variations, 

 and what forces are favorable to its development ; what are the 

 effects of its suppression in one place, and development in an- 

 other; what are the effects of the unequal development of the 

 several series. In the prosecution of these inquiries, we soon 

 discover that the middle region of the west flank is most favor- 

 able for our purposes, because the lower is covered to a great 

 extent with soil, and the upper, consisting of sharp peaks, is so 

 shattered, or rather has all the various planes so fully devel- 

 oped, we are unable to study them in their simple, uncombined 

 conditions. But the middle region, while it has all its cleavage 

 phenomena on the largest scale both of magnitude and speciali- 

 zation, is also simple and less obscured by forests and surface 



