

178 STRUCTURAL AND FIELD GEOLOGY 
defined as a detached area of rock, surrounded on all sides 
by rocks which are geologically older than itself. Such being 
the case, outliers very often appear capping hills and ridges. 
They occur amongst all kinds of rocks, no matter how these 
may be arranged—whether they be horizontal, inclined, or 
highly flexed and folded. Examples are met with almost 
everywhere throughout these islands. They often appear 
scattered along the front of prominent escarpments, of which 
they are really the outposts, as may be seen in Fig. 54, which 

Fic. 54.—ESCARPMENT, E, AND OUTLIER, O. 
represents diagrammatically the outliers and escarpments of 
the Jurassic and Cretaceous strata of Central England. These 
outliers are obviously detached portions of the more durable 
strata, of which the escarpments are composed, and have been 
left behind, so to speak, during the slow retreat of the latter 
under the influence of denudation. Sometimes outliers owe 
their preservation not so much to the durability of their rocks, 
as to their relatively strong geological structure. Hence, not 
infrequently, outliers occur in synclinally arranged strata 
(Fig. 55, O). The rocks of which an outlier is composed may 
all belong to one and the same series, or the upper portion 
may rest discordantly upon the lower—showing that they 
belong to very different geological horizons (Fig. 55, O2). 
Although outliers usually occur on high-lying ground as 
the direct result of denudation, yet they occasionally owe their 
existence to faults, and in such cases they may appear either 
on heights or in depressions. Trough-faults, for example, 
necessarily bring down younger beds against older formations, 
and thus detached portions of strata are preserved—the rocks 
with which they were formerly connected having been entirely 
removed from the immediate neighbourhood. 
An Inlier is the converse of an outlier, and consists of 
rocks which are surrounded on all sides by rocks which are 
geologically younger. The rocks of an inlier may belong to 
