230 



Sierra Club Bulletin 



The development of the brick structure is probably due to spray 

 blown back from the brow of the fall in storms. It is to the 

 development of these brick-making planes by long-continued 

 atmospheric action, that the picturesque ruins so frequently 

 met with on lofty summits are due. Where only one of the 

 cutting vertical series has been developed in a granitic region 

 otherwise strong in its physical structure, and a sufficient 

 amount of glacial force exerted in a favorable direction has 

 been concentrated upon it, its rocks have been broken up in 

 flakes and slabs, and those majestic mural precipices produced 

 which constitute so sublime a part of the Yosemitic scenery of 

 the Sierra. Fig. 3 represents a granite tower on the crest of 

 Mount Hofifmann, composed of jointed blocks. 



Another series of cutting planes which pass diagonally 

 tiirough those we have been considering, give rise to pyramidal 

 and roof-shaped forms. This diagonal cleavage is found in its 

 fullest development in the metamorphic slate of the summit, 

 producing the sharp-pointed peaks for which the summit region 

 is noted. To it is also due the huge gables which are found in 

 Yosemite and Tuolumne canons, such as the Three Broth- 

 ers, and the pointed rock adjoining the Royal Arches. Fig. 4 

 represents the highest of the Three Brothers, Yosemite Valley. 



Fig. 3. 



Fig. 4. 



