Rev. 0. Fisher — On Faulting, Jointing, and Cleavage. 207 



Fig 



(6). Suppose three faults all 

 hading inwards towards the 

 enclosed space X. 



By putting down trial lines 

 we see that, 



A will be thrown b -\- c ; 



B „ ,, a -\- c ; 



O ,, ,,. a -\- b ; 



X ,, ,, a -\-b-^ c. 



The relative throws of , B, 

 and C, will be the differences 

 of their total throws ; so that 

 the relative throw of 



A and B will be 5 — a, 



B „ G „ c — b. 



If it should then happen that the throws of the three faults were 

 all equal, we should find A, B, and G, each of them thrown through 

 2a, and therefore left with their beds on the same level ; while X 

 would be thrown through a space 3a with respect to the subjacent 

 hidden mass Y, and would have a relative throw a with respect to 

 ul, B, and C. In this case X would terminate downwards in a 

 point, and the appearance would be that of a pointed pyramidal 

 mass, forced down like a wedge in the midst of A, B, and C, with- 

 out these latter seeming to be disturbed. 



As for the areas P, Q, R, the total downthrow of each would be 

 a, so that A, B, C would be thrown through a with respect to F, 

 Q,Ii. 



A vertical fault must be regarded as hading towards the down- 

 throw side, and be included among the faults cut by a trial line on 

 that side ; which may be supposed to happen to it at an infinite depth. 



To obtain the throw of the beds at any specified depth we must 

 omit the throws of the faults cut by the trial line before reaching 

 that depth. 



§ II. — Beversed Faults. 



(7.) Propositions analogous to the above vrill hold for reversed 

 faults if for "throw" we substitute "lift," and remember that, by 

 every fault which hades under them, a thickness of beds equal to 

 the "lift" of the fault is reduplicated instead of missed. Thus, in 

 the case analogous to (6), 



A will be lifted through b -\- e. 



B „ „ a -\- e. 



C „ „ a -\- h. 



X ,, „ a -^ b + c. 



A trial line put down in X will encounter an additional thickness 

 of beds equal to a -{- b c, a of which will be reduplicated after 

 passing through the fault a a, b after passing b b, and c after passing 

 c c. If a b and c are all equal, A, B, C will be left at a uniform 



