Lawson] 



The Upper Kern Basin. 



303 



northwest and southeast. The horizontal and vertical jointages 

 are the most regular and persistent, but there arc many parts of 

 the region where the joint planes have all attitudes except verti- 

 cal and horizontal. In such cases they intersect without apparent 

 system and are often distinctly curved; and the intensity of this 

 jointing is, also, characteristically much more marked in the 

 upper part of cliff faces than in the lower. Some interesting 

 divergencies of joint planes were observed in the case of sharp 

 crests between opposing cirques, in which the jointage in each 

 cirque was parallel to the slope of its walls. In general no 

 definite and persistent system of jointage can be said to charac- 

 terize the region, the directions of all but the horizontal jointage 

 varying greatly, and even that is only called horizontal by cour- 

 tesy, for it is not uncommonly inclined at as much as 10° or 

 more to the horizon. But there appears to be a more or less 

 definite relationship between the intensity or frequency of joint- 

 age, particularly horizontal, oblique and curved jointage, and 

 proximity to the high surfaces of the region, and a similarly 

 close relation between the oblique or curved jointage and the 

 form of the surface. If this general proposition be true, and it 

 certainly has an observational basis, then the jointage would 

 appear to have been developed in part, at least, pari passu with 

 progress of erosion, and to be, in a sense, dependent upon it. 

 If this be the case, then jointage in these granites cannot be a 

 structural feature altogether antecedent to the geomorphic evolu- 

 tion and so controlling the latter. They cannot, therefore, be 

 supposed to be due to compressive stresses in the rocks according 

 to the current doctrines on the subject, but rather to tensile or 

 expansive stresses arising from the relief of load as affected by 

 erosion. The stresses in mountain masses due to simple gravity, 

 as discriminated from tangential compression, which is of course 

 itself a phase of gravitation, are very great and become com- 

 plexly distributed as the region undergoes dissection. The 

 balance of stress is destroyed in proportion as the surface is 

 uneven and asymetric, and an elastic tension is developed near 

 the surface, which is relieved from time to time by the rifting of 

 joint fissures. This hypothesis, explanatory of jointage of 

 granites in the High Sierra, may not be of universal applica- 



