
166 STRUCTURAL AND FIELD GEOLOGY 
it cuts out a much larger part of the outcrop. The faults 
represented in B and B! have downthrows in the opposite 
direction to those shown in A and Al’, but otherwise they 
resemble the latter in behaving partly as dip-faults and 
partly as strike-faults. It will be observed, however, that 
the downthrows are in an opposite direction. In B, for 
example, a coal-seam is represented, as before, dipping due 
north, and intersected by a north-west and south-east disloca- 
tion hading towards south-west. The fault produces the 
effect of a dip-fault by shifting the outcrop, but since it 
crosses the strike obliquely it causes a duplication of the out- 
crop between a and 6. The fault shown in B! approximates 
much more closely to the strike, with the necessary result that 
a longer stretch of outcrop is repeated. These diagrams 
should be compared with the models shown in Figs. 37, 
40, and 41. From a study of the latter it becomes evident 
that the effects produced by the fault in A’ more closely 
resemble those caused by the strike-fault C (Fig. 40), than 
those that result from the normal dip-fault C (Fig. 37). 
Again, the most notable feature in the diagram B! is the 
duplication of the outcrop—the fault having, for some con- 
siderable distance, the effect upon the outcrop of a strike- 
fault with downthrow against the dip (Fig. 41). 
Groups of Faults.—Although faults often occur singly, 
‘more particularly when their throw is small—yet they 
frequently form associated 
groups or systems. Great 
dislocations, for example, 
which often extend for long 
distances, are rarely un- 
accompanied by parallel 
Fic. 44.—COMPLEX FAULT. faults having downthrows 
in the same or opposite 
directions. Sometimes these parallel dislocations are so 
numerous and occur so closely together that it is often hard 
to say which is the main or principal fault. When the down- 
throw of all or most of them is in the same direction, the 
result is practically the same as if there had been only one 
dislocation with a large downthrow (see Fig. 44). Successive 
parallel strike-faults having their downthrows in one direc- 



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