
GEOLOGICAL SURVEYING 297 

straight—according as the strata are gently or steeply inclined. If an 
escarpment be due to the outcrop of such a rock as limestone it will 
usually extend for some considerable distance. If, on the other hand, it 
has been determined by the presence of a sill or a thick conglomerate, 
its lateral extension will probably be limited. 
(4) A sudden change in the form of the ground may indicate an 
unconformity (see Fig. 113), where a series of “soft” rocks (B) repose 
on the truncated ends of much older and more indurated strata (A). 
In a case of this kind the line of high ground will usually be more or 
less sinuous and irregular, for it simply represents a former coast-line, 

Fic. 116.—INCLINED “SoFT” ROCKS OVERLYING *‘ HARD” ROCKS. 
the younger rocks ever and anon extending into what were old bays 
and inlets. Evidence of so well-marked an unconformity as this could 
hardly escape an observer; but in nature the proofs of unconformity 
are not always so conspicuous. 
The observer who encounters a sudden or abrupt change 
from low to high ground, and has satisfied himself that the 
form Ot the surface cannot be explained either by~ the 
occurrence of interbedded hard rocks, of intrusive rock, or 
of an unconformity, will be justified in suspecting the presence 
of a fault. If a fault be present, then the line separating 
low and high ground will be somewhat straight or very 
gently sinuous, while seepage of water and more or less 
numerous springs will probably occur, and so indicate the 
position of the actual line of fracture. When the presence 
of a fault is thus suspected, the field-geologist will carefully 
search for the more direct evidence, some account of which 
is) been given in’ Chapter XI.. The fault itself, if it be 
one of considerable displacement, will probably not appear 
in section, but he may find that the strata seen in the low 
ground become more or less abruptly turned up at high angles 
of inclination as he approaches the base of the hilly ground, 
until, at last, they may stand on end. Should such be the 
case, the strata so disturbed will probably be abundantly 

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