

296 STRUCTURAL AND FIELD GEOLOGY 
by such dislocations have long ago been planed away, and the 
ground has become more or less swathed in soils, subsoils, and 
superficial accumulations of every kind. Although denudation 
tends in this way to reduce a land-surface generally, neverthe- 
less it is obvious that hard rocks will not be so readily 
reduced as soft rocks. Thus any marked or sudden change 
in the form of the ground will be due in most cases to an 
abrupt change in the petrographical character or the geological 
structure of the rocks. In most cases the low grounds will 
be composed of weakly arranged or of relatively soft rocks, 
while the higher ground will indicate the presence of harder 
rocks, or stronger structures better fitted to withstand the 
destructive action of epigene agents. As one frequent result 
of great faults is to bring relatively soft and hard rocks 
together, we may expect to find that such faults, although 
not actually seen in section, have yet influenced the form 
assumed by the ground under the influence of denudation— 
the hard rocks will tend to project above the level of the 
relatively soft or less durable rocks. 
Abrupt changes in the form of the ground may be due, however, to other 
structures than faults—the more important of which are the following :— 
(z) An abrupt change of level may be caused by the outcrop of a 
relatively durable stratum occurring in a series of less durable strata. In 
the annexed diagram (Fig. 115) we have the structure known as escarp- 

Fic. 115.—ESCARPMENT AND DIP-SLOPE. 
b, dolerite; s, sandstones and shales. 
ment and dip-slope—one of the commonest forms of land-surface, 
especially in regions of moderately inclined strata. Now and again the 
dip of the strata, instead of being towards the high ground as in 
escarpment-structure, may be in the opposite direction. This occurs 
when a thick series of relatively hard rocks are overlaid by softer strata. 
The former, as in other cases, tend to form a line of heights, but the 
descent from these to the low grounds is usually less abrupt than in the 
case of escarpments (see Fig. 116). In both cases the lines of elevation 
caused by such outcrops may be either very sinuous or approximately 
