38 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
the level of the upper Aubrey limestones, a gentle sloping surface, 
C B, over Permian and lower Triassic strata, in which the Shinarump 
cliff must have been nearly extinguished, is inferred to have extended 
from the river plain northward to the base of the faded Vermilion cliffs. 
To-day, the plateau in the neighborhood of Fredonia and Pipe spring 
is a thousand feet lower than it is at the rim of the canyon. It is true 
that some of this difference of level may be attributed to an inequality 
in the uplift by which the canyon cycle was initiated; but the great 
altitude of the High plateaus further north does not encourage the sup- 
position of less uplift there than in the south. It seems more probable 
that the lower surface by Fredonia and Pipe spring is due to the ex- 
tensive erosion, during the early stages of the canyon cycle thus far 
elapsed, of a large body of weak strata, whose persistence to the close 
of the plateau cycle was due to their lying below the level at which 
streams could then attack them, and whose early removal in the cur- 
rent cycle is due to their being raised high above the level of active 
stream work. It should be remembered in this connection that good 
warrant for the abundant erosion of Permian clays during the canyon 
cycle has been found in the study of the Hurricane fault in the Trum- 
bull district. Accompanying the removal of the weak strata in the 
Pipe spring district, there must have been a resurrection of the nearly 
extinguished Shinarump cliffs, Sh, and a refreshment of the subdued 
Vermilion cliffs, T. These bold forms, presenting to-day every indi- 
cation of rapid retreat, are therefore to be associated with the Grand 
canyon as the work of very modern erosion on pre-existent forms of 
much weaker relief. How general this change may be I cannot say, 
but it may well include all the Shinarump escarpments in whose under 
slope the Permian clays are laid bare in sharp-cut ravines as in Plate 
3 B, and all the ragged Triassic escarpments along which landslides 
have occurred as stated in my earlier essay (b, p. 121) in consequence 
of the recent removal of the weak lower Triassic clays: views of such 
escarpment are given in Plates 2 B, 6 A, and 7 A. 
ReviveD Erosion oF THE PINK Cuirrs.— The Pink cliffs of the 
Paunsagunt platean did not fulfil the expectation that had been 
awakened by Powell’s and Dutton’s descriptions of them, probably 
because the southwestern border of the plateau that we saw is less pre- 
cipitous than that on the southeast (Dutton, a, p. 254). In the thirty 
miles or more of the escarpment that we followed, it is only inter- 
mittently bare and pink ; much of the front has a graded slope, green 
with forest trees. Cliffs of bare and precipitous rock occupy only about 
