J. W. Powell—Types of Orographic Structure. 419 
which are the channels of intermittent or permanent streams, 
and these ridges are very irregular and often interrupted. 
Where the downthrow is by simple flexure, a complete series is 
formed. Where it is partly by flexing and partly by faulting, 
some of the monoclinal ridges disappear. Where the faulting 
ison the side of the zone of maximum flexure nearest to the 
axis, the ridges of the upper beds appear; but where the fault- 
Ing is on the side of the zone of maximum flexure farthest 
from the axis, the ridges of the lower beds appear; and where 
the displacement is chiefly or entirely by faulting, there are no 
monoclinal ridges. 
IV.— Kaibab Structure. 
West and its Tributaries. published in 1875; and in fig. 3 
reproduce a section and bird's eye view of the plateaus north 
of the Grand Cafion, which was used in that volume. An ex- 
amination of this will fully reveal the characteristics of what I 
have called the Kaibab structure. The grand topographic 
tures which result from this structure are plateaus with 
broken edges where they are bounded by faults, flexed edges 
where they are bounded by monoclinal flexures, and with 
“carpments where they are bounded by cafions or lines of cliffs. 
CONCOMITANT FoRMs. 
L. Cliffs of Displacement.—When a plateau is bounded on one 
Thave discussed these cliffs and slopes of displacement some- 
What at length in the volume already quoted several times, 
: ‘nticlinal upheavals the central mass may be 
Kait leaving but monoclinal ridges, in like manner In 
a bab structure the principal plateau mass ™ma : 
disc. leaving only the monoelinal or This I have also 
5 in the volume already quoted. 
Pee Projecting Ridges.—It is Aik perhaps never, the = 
at the strata of one of these plateaus are left by the gene 
