FAULTS. 
89 
course of the same fault it is sometimes founds to produce in 
different places very unequal changes of level, the amount 
of shift being in one place 300, and in another 70O feet, 
which arises from the union of two or more faults. In oth¬ 
er words, the disjointed strata have in certain districts been 
subjected to renewed movements, which they have not suf¬ 
fered elsewhere. 
We may occasionally see exact counterparts of these slips, 
on a small scale, in pits of loose sand and gravel, many of 
which have doubtless been caused by the drying and shrink¬ 
ing of argillaceous and other beds, slight subsidences having 
taken place from failure of support. Sometimes, however, 
even these small slips may have been produced during earth¬ 
quakes ; for land has been moved, and its level, relatively to 
the sea, considerably altered, within the period when much 
of the alluvial sand and gravel now covering the surface of 
continents was deposited. 
I have already stated that a geologist must be on his 
guard, in a region of disturbed strata, against inferring re¬ 
peated alternations of rocks, when, in fact, the same strata, 
once continuous, have been bent round so as to recur in the 
same section, and with the same dip. A similar mistake 
has often been occasioned by a series of faults. 
If, for example, the dark line A H (Fig. 76) represent the 
surface of a country on which the strata c frequently 
Fig. 76. 
Apparent alternations of strata caused by vertical faults. 
crop out, an observer who is proceeding from H to A might 
at first imagine that at every step he was approaching new 
strata, whereas the repetition of the same beds has been 
caused by vertical faults, or downthrows. Thus, suppose 
the original mass. A, B, C, D, to have been a set of uniform¬ 
ly inclined strata, and that the different masses under E F, 
F Gr, and G D sank down successively, so as to leave vacant 
