
FAULTS 159 
meem@edsto as the “heave” of a fault. It is the degree of 
inclination or “hade,” and the amount of downthrow that 
determine the extent of lateral displacement, or “heave.” A 
dip-fault, if vertical, produces no heave; but whether vertical 
or inclined, it never fails to cause an apparent horizontal 
shift of the outcrops—either forward or backward—according 
to the direction of downthrow. This apparent advance or 
retreat of faulted outcrops is greatest when the angle of dip 
is low, diminishes in proportion as the dip augments, and 
ceases altogether when the beds are vertical. The shifting, 
however, is not the result of any horizontal movement along the 
line of dislocation, but is simply the effect produced by denu- 
dation, as a glance at the models in Fig. 37 will show. Let 
A represent a block of strata dipping in one determinate 
direction. A dislocation, we shall suppose, takes place along 
the interrupted line f # In B we have the same model 
showing the vertical displacement effected. A line dropped 
from the truncated end of the bed a@ to its disconnected con- 
tinuation a? is a perpendicular—in other words, the fault is 
a vertical displacement. Now let us suppose that the surface 
is cut even by denudation along the line s s. The portion 
above this line we remove, and we have in C a ground-plan 
of the new surface thus produced. It now becomes evident 
that the horizontal shift is only apparent, and is simply the 
result of the removal of strata from the high or “upcast” 
side of the fault. 
When dip-faults traverse anticlinal and synclinal folds, 
they necessarily cause similar apparent horizontal shifting of 
outcrops. But as the outcrops are shifted by one and the 
same fault in different directions, it is obvious that this effect 
cannot be the result of horizontal movements. This is made 
clear by the models in Figs. 38, 39. In Fig. 38, A represents 
a block of strata arranged in the form of a syncline which 
is eventually fractured along the line f f and displaced as 
shown in B. When the strata on the high side of the fault 
have been removed by denudation, and the whole area has 
been reduced to the same level s s, the outcrops will exhibit 
the appearance shown in C. It is evident, therefore, that a 
fault traversing a syncline has the effect of causing a mutual 
approach of the outcrops on the high side, and a correspond- 
