
Parr VL] FAULTS. —. - 525 
The amount of displacement is represented as the same in both in- 
stances, so that the level of the beds is raised between the two 
faults above the uniform horizon which it retains beyond them. 
: The effect of the inclination of faults is to give the appearance 
of lateral displacement. In Fig. 254, for example, where the hade of 
one fault is considerable, the two severed ends (c and d) of the black 
bed appear to have been pulled asunder. ‘The horizontal distance 
to which they are removed does not depend upon the amount of 
vertical displacement, but upon the angle of hade. A small fault 
with a great hade will shift strata laterally much more than a large 
fault with a small hade. It is obvious that the angle of hade must. 
seriously affect the value of a coal-field. If the black bed in the 
same figure be supposed to be a coal-seam, it could be worked from 
either side up to ¢ and d, but there would be a space of barren 
ground between these two points, where the seam never could be 
found. ‘The lower the angle of hade the greater the breadth of 
such barren ground. Hence the more nearly vertical the lines of 
fault, the better for coal-fields. 

Fic, 254.—SrctTion oF INCLINED AND VERTICAL FAULTS. 
In the vast majority of cases faults hade in the direction of 
downthrow, in other words, they slope away from the side which has 
risen. The explanation of this structure is doubtless to be found in 
the fact that the portion of the terrestrial crust towards which a 
fault hades presents a less area of base to pressure from below, and 
has thus a smaller support than the mass with the broad base on 
the opposite side. The mere inspection of a fault in any natural or 
artificial section suffices, in most cases, to show which is the upthrow 
side. In mining operations the knowledge of this rule is invaluable, 
for it decides whether a coal-seam, dislocated by a fault, is to be 
sought for by going up or down. In Fig. 254, a miner working from 
the left, and meeting with the fault at ¢, would know from its hading 
towards him that he must ascend to find the coal. On the other 
hand, were he to work from the right, and catch the fault at d, he 
would see that it would be necessary to descend. According to this 
rule, a normal fault never brings one part of a bed below another part, 
so as to be capable of being pierced twice by the same vertical shaft. 
Exceptional cases, however, or “reversed faults,’ where the hade is 
reversed, do occasionally appear, especially in regions where the 
rocks have been excessively plicated, and where one half of a fold 
has been pushed over another (Figs. 253 and 255, section 4). 
