
STRUCTURE AND SURFACE FEATURES 409 
forming more or less regular ranges. In other places, again, owing to 
the presence of confused and complicated structures, the heights may 
exhibit little or no trace of alinement, although it is obvious that in this 
case, as in the other, the position of the mountains has been determined 
by the nature of the rocks and their arrangement. 
Plains and plateaus do not necessarily consist either of 
horizontal or of highly contorted rocks. Between these two 
extremes of rock-structure there are many gradations. The 
degree of crustal deformation varies indefinitely. There are 
wide regions throughout which the rocks show only long, 
gentle undulations—the inclination of the strata from the 
horizontal not exceeding a few degrees. The Midlands of 
England, for example, are composed of rocks which have 
a general dip at a low angle towards the east. Throughout 
the Central Lowlands of Scotland, from the base of the 
Grampians to the foot of the Southern Uplands, steep dips 
are exceptional. And the same may be said of many other 
parts of the world. Away from regions of mountain-uplift, 
indeed, there are vast continental tracts throughout which 
the strata show little disturbance—the beds rising and falling 
in more or less gentle undulations. Sometimes the undula- 
tions succeed each other somewhat rapidly; in other places 
the crust has been bent up in one broad, depressed arch, 
measuring many miles across. In highly denuded countries 
the tops of the anticlinal arches—the crests of the undulations 
—have invariably been removed, and the truncated ends of 
the beds exposed. In other words the shape or form of 
the ground does not coincide with the undulations of the 
strata, but is the result of erosion. 
The most characteristic type of hill or mountain carved 
out of rocks which have a gentle dip or inclination is the 
Escarpment, the conditions for the formation of which are 
referred to in Chapter XIX. This is the type of hill most 
commonly met with in Central England. A glance at any 
geological map of the country will show that all the prominent 
hills and high grounds are developed along the outcrops of 
the Jurassic limestones and the Chalk, and thus have a 
general northerly or north-easterly trend. Proceeding from 
the foot of the Malvern Hills towards the east, we first 
traverse low-lying plains of sandstone and argillaceous strata, 
until on the other side of the Severn we reach the Cotswolds, 

