
a i. 
GEOLOGICAL SURVEYING 295 
it can hardly be missed. In Fig. 114, which is a ground-plan 
of an unconformity and overlap, the latter structure is not 
shown in the area traversed by the section line A—B. Here 
no appearance of overlap is apparent, but as the outcrops are 
followed towards the area C D, the bed 4 gradually overlaps 
the bed a, while the former is overlapped by the sandstone c 
which come to rest directly, and with a strong unconformity, 
on the highly inclined strata S S. The section C D shows 
the overlap and unconformity—é overlapping a, and being in 
turn overlapped by c. 


FIG, 114.—GROUND-PLAN OF UNCONFORMITY AND OVERLAP. 
S S=Silurian strata; x x. unconformity ; a, 6, c,=younger series of strata showing 
overlap ; 1.sSection along the line A—B; 2. Section along the line C—D. 
Normal Faults.—Faults are not infrequently observed in 
natural sections, but these, as a rule, are small downthrows of 
little importance. The larger dislocations of a faulted region 
may now and again be encountered in railway cuttings and 
other excavations, but they are rarely observed in natural 
rock exposures. One reason for this is obvious enough: 
highly shattered rocks are usually associated with great 
faults, so that when these are exposed by denudation the 
shattered materials readily fall asunder and the actual fracture 
becomes concealed. Or the shattered rocks on one or both 
sides of the fault being easily broken up and removed by 
epigene action, a hollow may be washed out along the line 
of dislocation, and form eventually a receptacle for alluvium 
and other products of surface erosion. Many faults fail to 
show at the surface of regions which, like our own, have long 
been exposed to denudation, simply owing to the fact that any 
inequalities of surface which may originally have been caused 

