FAULTS 173 

be one of subsidence, it is preferable to consider all normal faults as 
downthrows rather than upthrows. Nevertheless, our knowledge of the 
nature of crustal movements is not so complete that we can deny the 
possibility, or even the probability, that normal faults may now and 
again have come into existence during movements of upheaval. 

Fic. 51.—MONOCLINAL FLEXURE PASSING INTO A NORMAL STRIKE-FAULT, 
VIEWED IN OPPOSITE DIRECTIONS. 
(After Chamberlin and Salisbury.) 
Reversed faults do not often occur in regions where the rocks show 
little trace of disturbance. This seems to be due to the simple fact 
that they are the result of lateral pressure or compression, so that they 
are best developed and of most common occurrence amongst highly 
folded and distorted rocks. Now and again, however, where monoclinal 
flexures have obviously resulted from horizontal movements, the flexures 
have yielded and given place to reversed faults (see Fig. 52). In 

FIG. 52.—REVERSED FAULT REPLACING MONOCLINAL FLEXURE. 
other cases gently inclined strata, when subjected to lateral pressure, 
have, instead of first folding, at once yielded to the strain by snapping 
obliquely—and one portion of the severed mass has been pushed bodily 


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