DAVIS: THE GRAND CANYON OF THE COLORADO. 128 
the Triassic escarpment should by this time have given the bordering 
cliffs — Vermilion on the west, and Echo on the east —a relatively 
stable profile, such as they usually have elsewhere; but as a matter of 
fact, it is precisely in the notch of the escarpment that the cliffs are 
most unstable and that landslides are most numerous, The cliffs have 
not retreated here far enough to allow the weak underlying strata — 
especially the blue clays of the lower Trias— to be concealed beneath 
a graded slope ; it is because the cliffs are sapped by the rapid removal 
ir 
(an 
Pe 
FicureE 5. 
Landslides of Vermilion cliffs. The Triassic cliffs rise to the rim of the Paria plateau. 
Monoclinal slides lie on the Shinarump bench, one of whose promontories is seen in the 
centre and another on the right, half smothered in tumultuous slides that descend to 
the plain of Marble platform in the foreground. Drawn from rough sketch. 
of the clays that the landslides result. Yet twenty miles northwest of 
the river, in Honse-rock valley between the Kaibab and Paria plateaus, 
a graded basal slope is well established beneath the cliffs and no slides 
occur. The same is true along the foot of the Echo cliffs, twenty miles 
south of Lee’s Ferry; the weak blue clays are there concealed under 
a well-graded monoclinal valley floor, and slides are wanting. It is only 
as the river is approached that the clays are laid bare, and that, with 
