370 Pyof. J. F. JBlaJie — Recent Papers on Faults. 



The writer remarks that some former "suggestions" of his "are 

 not generally satisfactory," and he probably saj's the same of the 

 present by this time ; indeed at the end of the paper he has found 

 the beginning unsatisfactory. 



We now start with the paper of June, and we read that " we have 

 already seen that a direct fault must have a higher hade (to horizon) 

 than 45°." "What is really stated is quoted above, viz. " the hade of 

 the fault-surface will be 45°," and faults with higher hades are only 

 possible when the angle of repose is > 45°. What the erroneous 

 equations show is that it requires the stronger force to make the 

 higher hade, which is manifestly contrary to experience. He now 

 says " any fault with lower hade than 45° must be a reversed fault," 

 which is also contrary to experience. 



We next get to a new condition for faulting which, I suppose, 

 should be equally true for direct faults, namely, that the shearing 

 force must be greater than the friction, only in this case both hori- 

 zontal and vertical components are used. As before, I should say, 

 that this was self-evidently always the case, if by shearing force we 

 mean a force sufficient to produce shearing, but this is not the case 

 here. All that is done is to solve the following elementary problem. 

 Given a crack and the coefficient of friction, what is the ratio between 

 the forces for equilibrium ? That this has nothing to do with the 

 greater forces required for shearing if there is no crack, is seen from 

 the results, namely, that less horizontal force will make a reversed 

 fault (as distinguished from distortion) in clay than in solid rock, 

 which is obviously false. 



Fortunately the author at the close of this part sees that he is 

 wrong ; for he adds, " There can be no doubt that some of the most 

 important faults are not produced by such a disposition of forces as 

 we have contemplated." 



Finally we have Part IV. on Cleavage. Here at least we have a 

 definite idea expressed, and the mathematics, if not probative, are at 

 least illustrative. The idea is that cleavage is brought about by the 

 slipping of one slice over another with something like the motion of 

 sand in an hour-glass. This is very like the old explanation of 

 trough faults, only there are to be a great number of them. The 

 author, however, says there can be no faulting, but he means 

 reversed faulting, and seems to have forgotten his May paper. It 

 is obvious that, if the middle of the anticlinal sinks fastest, the 

 faulting will be direct, and hence, according to the author, will be 

 more nearly vertical and perfectly possible. This is the only argu- 

 ment, and therefore the whole idea falls through. To start with 

 two oblique lines, and to show that the intervening ones will 

 gradually change over, — to imagine forces and write down the 

 mathematical relations between them and get no further — these are 

 not arguments, and cannot therefore be answered. Daubree has 

 indeed shown experimentally that cleavage may be produced by 

 pressure which forces the mass uptoards, unless the strain be re- 

 lieved by faulting ; if this is not strong enough to do it, d fortiori 

 sinking down again would not be. 



