FAULTS. 41 



seams. It is naturally an important matter to know whether 

 to search for the lost portion of a seam above or below the line 

 where it is lost. Normal faults are of more frequent occur- 

 rence than reversed faults. A rule to find the lost portion of 

 a faulted seam, when the fault is a normal one, is to follow 

 the larger angle made by the intersection of the seam with the 

 fault. Thus in Fig. 15. if the fault is first met with in the 

 roof look for the lost portion under foot on the other side of 

 the fault; or if the fault is first met with in the floor, search 

 for the lost portion overhead. With, vertical faults (Fig. 17), 

 this rule is indefinite. tTnfortunately one cannot tell by merely 

 observing a fault at the point where it is struck, whether it is 

 a normal or reversed fault. If the latter, then this rule does 

 not hold good. 



Sometimes a seam and adjoining beds are bent up on one 

 side of a fault and down on the other (Fig. 18), in which case 

 they wedge out, instead of being cut off straight. Miners take 

 this as an indication of what direction to go, in order to find 

 the lost portion of a seam, and follow the bent end near the 

 fault; but if the fault has taken place in a fractured fold, as in 

 Figs. 20, 21, and 22, even though normal, or if it is a reversed 

 fault (Fig. 19), this indication may lead one astray. The 

 safest rule is to note the relative positions of the 

 rocks faulted when they are sufficiently distinctive in 

 character. (Fig. 17). Here, again, one must be 

 cautious, for beds may be locally thickened or thinned 

 out so that they are not recognised; or may be con- 

 founded with other, but somewhat similar, beds. If the sedi- 

 mentary rocks contain an eruptive among them, it cannot be 

 relied on too much, on account of its liability to irregularities. 

 A series of parallel faults may cause the seam to out- 

 crop at the surface several times, which may at first lead people 

 to think each outcrop is a separate seam. 



To distinguish between a true reversed fault and a fold 

 fault; fold faults are only found in regions of folding accom- 

 panied by other phenomena, such as harmonic second class 

 folds, cleavage, etc., and they always have the same strike as 

 the undisturbed folds. Fold faults are more frequent than 

 reversed faults, which are only local in character, and have 

 no relation to folds of the strata. With fold faults the plane 

 of dislocation is generally steeper, and always dip in the same 

 direction as the strata, which is not necessary with true faults. 

 A fault plane may be occupied by broken country or clay, 

 or a dyke rock. In either case the coal near a fault is gene- 

 rally inferior to that further from it, being broken and dirty, 

 or if near a dyke coked or cindered. A fault does not have 

 the same displacement all along its course: its greatest dis- 



