
of the beds be supposed to be east and west, then a horizontal plane 
cutting the dislocated strata will show the portion on the west 
or upthrow side of the fault lying to the north of that-on the east 
or downthrow side. The effect of denudation has usually been 
practically to produce such a plane, and thus to exhibit an ap- 
parently lateral shift. This surface displacement has been termed 
the heave of a fault. Its dependence upon the angle of dip of the — 
strata may be seen by a comparison of Sections A and B in Fig. 257. 
W 
ee 
' 
“ 
Dana 
i] 
‘ 
w 
ana 

Fic. 257.—SrcTIoNs TO SHOW THE VARIATION OF HorIzonNTAL DISPLACEMENT OR 
HEAVE OF FAULTS, ACCORDING TO THE ANGLE OF INCLINATION OF STRATA. 
In the former, the bed a 6, which may be supposed to be one of those 
in Fig.256, dipping north, at 20°, once prolonged above the present 
surface (marked by the horizontal line), is represented as having 
dropped from w 6 to ¢ d. ‘The heave amounts to the horizontal 
distance between c¢ and 6b, the throw being the vertical distance 
between b and d. But if the angle should rise to 50°, as in B, 
though the amount of throw or vertical displacement is there one- 
fourth greater, the heave or horizontal shift diminishes to less than a 
half of what itisin A. This diminution will continue with ever 
increase of inclination in the strata till among vertical beds there 
can be no heave at all. 
Strike-faults, where they exactly coincide with the strike, may 
va 


Fie. 258.—Srrike-F avr. 
A, Plan; B, Section across the plan in the line of the arrows. 
remove the outcrop of some strata by never allowing them to 
reach the surface. Jig. 258 shows a plan (A) and section (B) of 
one of these faults f f, having a downthrow towards the direction 
of dip. In crossing the strike we pass successively over the edges 
Vp Je 
, —t 
o Se 
528 GEOTECTONIC (STRUCTURAL) GEOLOGY. [Boox IV. 
