DAVIS: THE PLATEAU PROVINCE OF UTAH AND ARIZONA. 27 
* Hurricane ledge” from the fault line. A more remote date seemed to 
me proved by the great recession of the Shinarump and Triassic cliffs in 
the higher (Uinkaret) block east of the fault than in the lower (Shiv- 
wits) block west of it: I was indeed led on my first excursion to believe 
here as elsewhere that the faulting had taken place long before the 
occurrence of the uplift by which the canyon cycle was introduced, so 
that the obliteration of the initial relief due to faulting and the general 
baselevelling of the plateau area had been accomplished before the ero- 
sion of the canyon was begun. According to this view, the Hurricane 
ledge as a topographic feature is not the direct result of faulting, but 
the result of renewed erosion on a faulted, baselevelled, and uplifted 
mass. 
The work of last summer showed, in effect, that both these supposi- 
tions are in a measure correct; for the Hurricane fault has suffered 
repeated displacements, a long interval having elapsed between its ear- 
liest and latest movements. The relief produced by the earliest displace- 
ment was demonstrably obliterated over a large area before the later 
displacements occurred: while the relief produced by the latest displace- 
ment is still in certain places but little affected by erosion. 
The remote date of the earliest displacement is proved by the great 
amount of erosion that has taken place after it. This is shown first by 
the retreat of the escarpments in the uplifted (Uinkaret) block several 
-miles in excess of their retreat in the other (Shivwits) block, and 
second by the continuity of a level lava flow resting on an even surface of 
erosion that crosses the fault line. The first line of evidence was pre- 
sented in my previous essay (b, p. 142-148) ; the second may be intro- 
duced here. ; 
Tue Section NEAR Coat Sprine. — A ride of some ten miles west- 
southwest of Mt. Trumbull carries one to a point near Coal spring, about 
eighteen miles north of the canyon, where the western escarpment of 
the Uinkaret plateau is capped with a lava bed, whose essential features 
are shown in the front block of Figure 8. The escarpment at this point 
is of moderate slope, quite different from its usual bold form ; and in- 
stead of consisting of a cliff of upper Aubrey above a talus-slope of lower 
Aubrey, as is the case for most of its length further north, the escarp- 
ment here shows abundant outcrops of gray and reddish Permian clays, 
one thousand feet or more in thickness. 
These Permian beds evidently belong in the western or Shivwits 
block, where they follow normally above the yellowish super-Aubrey beds 
which to-day constitute so much of the surface of that block below the 
