
FAULTS 157 
has the effect of producing a lateral displacement or heave— 
the amount of which is determined by the hade and the 
throw. For example, the truncated end of the coal-seam a 
(Fig. 33) is removed laterally by F* from its disconnected 
continuation a? by the distance a—z} but it is obvious that 
this distance would be increased if the amount of downthrow 
were augmented. Again, with the more gently inclined fault 
(F?), the lateral displacement or eave is considerably 
mmereased. In the case of the vertical fault (F) there is, of 
course, no heave or lateral displacement. The inclination 
of faults, therefore, is of great importance in a coal-field, for 
the further the hade deviates from the vertical the wider will 
be the extent of “barren ground” between the two ends of 
a dislocated coal-seam. 
The faults shown in the diagrams are straight lines, but 
in reality faults are not always or even often so smooth as 
they are here represented to be. Although the walls of a fault 
may be in close apposition, they are often separated either 
continuously or at irregular intervals by masses of jumbled 
and shattered rock-débris, known as fault-rock or fault- 
breccia (Plate XX XIX.). In many cases, also, cavities occur 
along a line of dislocation, and these are often filled or parti- 
ally filled with crystallised minerals, as will be shown more 
particularly when we come to consider the phenomena of 
lodes or metalliferous veins. The walls of a fault and the 
stones in a fault-breccia are frequently slickensided, and 
afford other evidence of friction and crushing—the rocks 
along one or both sides being sometimes comminuted or 
pulverised for some inches or even for many feet back from the 
dislocation. Phenomena of this kind occur chiefly in con- 
nection with the more powerful faults—those, namely, which 
have produced the greatest amount of vertical displacement. 
In the neighbourhood of such large faults the rocks are not 
only broken and jumbled, particularly on the downthrow side, 
but on the same side strata are frequently turned up more or 
less abruptly against the dislocation. On the high side of the 
fault there is usually less disturbance and distortion, although 
the rocks tend to be bent over as if they had been dragged 
downwards in the direction of displacement. The annexed 
sections (Figs. 35, 36) will suffice to illustrate these appearances. 
