J. W. Powell—Types of Orographie Structure. 417 
9, Monoclinal Ridges only.—Sometimes we find that an anti- 
clinal upheaval has been eroded in intaglio, so that there is no 
great central mountain mass, but the axis of upheaval is the 
site of a valley or low plain, but the monoclinal ridges on the 
anks remain. 
8. Inclined Pluteaus.—Where the anticlinal upheaval has a 
great amplitude, as compared with the vertical uplift, the beds 
incline but slightly. Under such conditions inclined plateaus 
or mesas are found instead of monoclinal ridges, usually having 
steep escarpments facing the axis of the flexure. 
Ill. Uinta Structure. 
In the Uinta Mountains we have a great range carved from 
an anticlinal upheaval, the axis of which has an easterly and 
westerly trend, and is more than one hundred and fifty miles 
in length. It terminates abruptly against the Wasatch Moun- 
tains on the west and is cut off by the short, abrupt anticlinal 
of Junction Mountain on the east, the latter having its axis In 
anorth and south direction. There are several important facts 
observed in the study of this great flexure. Its axis has been 
lifted above the level of the sea about thirty thousand feet. and 
fl 
great displacement is partly by faulting, partly by flexing, and 
either flank is a zone rt ivetss displasement where the strata 
are faulted, flexed, twisted and contorted in many ways. 
_ The character of these displacements in the Uinta Mountains 
8 illustrated in Plates, 1, 2 and 3 of the Atlas, and in a subse- 
qent chapter the subject will be more fully discussed. — 
€ simplest topographic forms, produced by such displace- 
ments under conditions of erosion in general outline, are pla- 
With gently rounded summits and abrupt shoulders on 
€ flanks; but such general outline is often modified by the 
