MOUNTAINS 307 
are the Appalachians, but are really a great plateau 
of durable sandstone and conglomerate rock, cut into 
rugged peaks with intervening deep valleys. Although 
somewhat disturbed, the rocks remain in a_ nearly 
horizontal position, and denudation has cut into these 
strata with less result than upon softer rocks on either 
side. Hence the Catskills stand above the surrounding 
country, just as folded or true mountains do. Their 
Fie. 180. 
Green River Butte, Wyoming, a hill or peak of circumdcnudation. 
counterpart is found in the Cumberland Mountains of 
Tennessee, as well as in many other parts of the world. 
While mountain peaks and ridges, grouped together, 
make a range, groups of ranges may combine into 
systems (Fig. 181). Thus in our western country, there 
are many ranges formed into the Rocky Mountain 
system, and in each range are numerous ridges and 
peaks. Several systems, with their enclosed plateaus 
