174 CrEOLOGY OF THE COMSTOGK LODE. 



tions on the contacts between the plates, and the cross-section of the coun- 

 try will show two logarithmic curves with a common tangent at the origin 

 in Fig. 8. Each curve can of course be reduced to the form 



Case involving different rocks. — If thc tlssurc wcrc ou a coutact betwceu two 

 different rt)cks, tlie one might be divided into thinner plates than the other, 

 and they might have different coefficients of friction. If the coefficient 

 being the same the thickness of the plates varied, the origin would remain 

 unchanged, but the curves would be different. The curvature depends on 

 the throw of the fault and on the number of partings, and it can readily be 

 shown that the natural unit of the curves formed will be proportional to 

 the thickness of the sheets of rock. The two curves will therefore not 

 have a common tangent. Conversely it is evident that the relative thick- 

 ness of the sheets is calculable from the observed curvature, but the abso- 

 lute thickness of the one or the other is a matter of observation. If the 

 coefficients of friction are unequal, the inequality will manifest itself only 

 at the contact, for the fundamental equation of condition 



/{K+i—K+i) K+i 



is independent of /so long as /is constant. The curves, however, will not 

 be continuous with one another. There is reason to suppose that, at least 

 between similar rocks, the difference of the coefficients of friction is very 

 small. 



Faulting accompanied by formation of parallel fractures. If a fault takcS plaCC OU a 



fissure in otherwise solid rock, and if lateral pressure accompanies the dislo- 

 cation, a great amount of energy will be brought to bear at the fissure. 

 If, as before, the foot wall is supposed to rise, the hanging wall as a whole 

 may be regarded as a fixed mass either from its cohesion with the surround- 

 ing country, or from the indefinite amount of inertia which it opposes to move- 

 ment. As has been shown earlier in this chapter, friction is a force which 

 produces motion as well as destroys it, and Professor Reuleaux is doubt- 

 less correct in asserting that motion always results from friction, although 



