MOUNTAINS olT 
(Figs. 190 and 191). The plateau pedestal of the Ap- 
palachians averages between two and three thousand 
feet above sea-level, that of the western mountains 
over a mile. Really then, the main feature in the 
mountain fold is the broad plateau, and the mountains, 
COAST SIERRA 
RANGE NEVADA ROCKY MTS. 
15,000 FT. 
410,000 FT. L aon n = - - - - if --------------------fH-- > ------ - ------ > 
6,000 FT. |} --ge~=--—= éK[p pp G222l=TF EEE 
WN 
SEA LEVEL .zz 
Fic. 190. 
Diagrammatic section of the Cordilleras to show the importance of the plateau 
element. (Vertical greatly exaggerated.) 
though attracting more attention, are inconsiderable 
sections of the uplift. Both are formed at the same 
time, but the rocks over the greater part of the area 
which is upfolded, remain nearly horizontal, though 
15,000 FT. 
10,000 FT. }---—------ Ding = = 5 - - - - 
5,000 FT. 
SEA reve. ZA PLE WIIIIII000#7” ti HH 
Fie. 191. 
A section of a part of Fig. 190, showing on a larger scale the relative importance 
of the plateau and the mountain uplifts. (Vertical greatly exaggerated.) 
locally, along certain narrow lines, they are broken by 
faults or raised and depressed by folds, some large and 
some small. 
Permanence of Mountains. — These great lines of disturbance, 
the broad uplifted parts, seem to be permanent lines of weakness, 
along which the rocks fold again and again. In eastern United 
States there have been at least four or five periods of mountain 
