Studies in the Sierra 



229 



hibit none of these planes, and appear to be as entirely homo- 

 geneous in structure as leaden balls. Thus, let Fig. i represent 

 a horizontal section of the range; A, B, C, D, cones and co- 

 noides where none of the cleavage planes appear. The question 

 here arises, are these domed portions cleavageless, or do they 

 possess the same cleavage as the surrounding rock, in an un- 

 developed or latent condition? Careful observation proves the 

 latter proposition to be the true one, for on the warm and moist 

 surfaces of some of the older domes we detect the appearance 

 of incipient planes running parallel with the others, and in gen- 

 eral wherever any rock apparently homogeneous in structure 

 is acted upon by the spray of a water-fall, its cleavage planes 

 will appear. We may conclude, therefore, that however 

 numerous the areas may be which seem solid and equal in 

 structure, they are still traversed in definite directions by in- 

 visible cutting planes, which render them separable when the 

 conditions required for their development have been supplied. 



Fig. 2. 



Fig. 2 represents the side of a dome at the head of Yosemite 

 Fall, with parallelopipedal blocks developed along its base. 



