130 STRUCTURAL AND FIELD GEOLOGY 
weathering. Rain-water insinuates itself between the bedding- 
planes, and the strata are thus exposed not only to its 
chemical and mechanical action, but to the more powerful 
action of frost. The latter tends to force the beds apart— 

FIG. 12a.—TERMINAL CURVATURE IN STEEPLY INCLINED STRATA. 
movement taking place chiefly in the line of least resistance, 
which, of course, is downhill. In this way the edges of the 
beds are gradually turned over, so as to present an apparent 
dip which may be exactly opposite to the true inclination of 
the strata. In high-lying districts this inverting process is 

Fic. 124.—TERMINAL CURVATURE IN HORIZONTAL AND INCLINED STRATA. 
often aided by the movement of massive heaps of snow, and 
by the downward creeping of water-saturated sheets of earthy 
rock-débris, which tend to drag forward the edges of the beds 
in the direction of movement. 
Outcrop is the term applied to the edges of the strata 
which appear at the surface. An outcrop may be exposed 
or visible, or it may be covered and concealed under younger 
accumulations (see Figs. 13, 14). As a rule, the direction of 
the outcrop is influenced partly by the inclination of the 
strata and partly by the form of the ground. When the 
beds are quite horizontal, every change in the configuration 

