CHAPTER XIV 



CLEAVAGE, JOINTS, MINERAL VEINS, UNCONFORMITY 



Cleavage, Fissility, and Schistosity. — Cleavage is " a capacity 

 present in some rocks to break in certain directions more easily 

 than in others," while fissility is a " structure in some rocks, by virtue 





1mN$ 



Fig. 113. — Fissile quartzite, California. (U. S. G. S.) 



of which they are already separated into parallel laminae in a state 

 of nature. The term fissility thus complements cleavage, and the 

 two are included under cleavage as ordinarily defined " (Van Hise). 

 Schistosity, or foliation, is either cleavage or fissility, or both, 



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