
532 GEOTECTONIC (STRUCTURAL) GEOLOGY. [Boox IV. 
¥ 



steps to some distance below. Excellent examples of these step- — 
faults (Fig, 263) are to be seen in the coal-fields on both sides of ~ 
the upper part of the estuary of the Forth. Instead, however, of — 
* BONNYTOUN HILL, 
EINLITHCOW 
LOCH. 

Fie, 263.—Srrer-FavuutTs, LINLITHGOWSHIRE. 
having the same downthrow, parallel faults frequently show a move- 
ment in opposite directions. If the mass of rock between them has 
subsided relatively to the surrounding ground, they are trough- 
faults (Fig. 264). They enclose wedge-shaped masses, of which the 
apices, formed by the junction of two faults, point downwards. It 
will be observed that the hade of these faults is in each case towards 
the downthrow side, and that the wedge-shaped masses with broad 
bottoms have risen, while those with narrow bottoms and broad tops 
have sunk. 
WDA IMV PN wo} | 
> , Whit AD Boyde och Dy Re ; 
———\" p : DN ype HRY, \y by 2 Pogh) Sy Wrz \U%, (oct 


ar rm few! an 








Fic. 264.—Trovucu-Fav.ts. 
Detection and tracing of Faults.—As a rule, faults give rise 
to little or no feature at the surface, so that their existence would 
commonly not be suspected. They comparatively rarely appear in 
visible sections, but are apt rather to conceal themselves under — 
surface accumulations just at those points in aravine or other 
natural section where we might hope to catch them. Yet they 
undoubtedly constitute one of the most important features in the 
geological structure of a district or country, and should consequently 
be traced with the greatest care. In the majority of cases, in 
countries like much of central and northern Europe, where the 
ground is covered with superficial deposits, the position of faults 
cannot be seen, but must be inferred. Experience will teach the 
student that the mere visible section of a fault on some cliff or shore 
does not necessarily afford such clear evidence of its nature and 
effects as may be obtained from other parts of the region where it 
does not show itself at the surface at all. In fact, he might be 
deceived by a single section with a fault exposed in it, and might be 
