
‘Part Vi] FAULTS. _ 523 
the fissures being merely enlarged joints. It is common to meet 
with traces of friction along the walls of fissures, even when no proof 
of actual vertical displacement can be gleaned. The rock is then 
often more or less shattered on either side, and the contiguous faces 
present rubbed and polished or “slickensided ” surfaces. Mineral 
deposits may also commonly be observed encrusting the cheeks of a — 
fissure, or filling up, together with broken fragments of rock, the 
space between the two walls. The structure of mineral veins in 
fissures is described in Part IX. 
In a large proportion of cases, however, there has been not only 

Fig. 250.—Section oF SHARPLY-DEFINED FAULT WITHOUT CoNTORTION OF THE Rocks. 
fracture but displacement. The rents have become faults as well 
as fissures. Faults on a small scale are sometimes sharply-defined 
lines, as if the rocks had been sliced through and fitted together 
again after being shifted. In such cases, however, the harder 
portions of the dislocated rocks will usually be found slickensided. 
More frequently some disturbance has occurred on one or both sides 
of the fault (Fig. 251). Sometimes in a series of strata the beds on 





Fia. 251.—Sxrction or A FAvLtT, SHOWING DisTURBANCE oF ROCKS. 
the side which has been pushed up are bent down against the fault, 
while those on the opposite side are bent up (Fig. 252). Most com- 
monly the rocks on both sides are considerably broken, jumbled, 
and crumpled, so that the line of fracture is marked by a belt or 
