DAVIS: THE GRAND CANYON OF THE COLORADO. 139 
but no such conclusion seems compulsory in a case where only two 
formations are involved, and where tie upper of the two is the weaker. 
It therefore seems legitimate to say that a peneplain, so far as one was 
developed at the close of the first cycle, lay in the Permian formation at 
some unknown height above the present plateau surface in the Kanab 
district ; and that the Carboniferous platform as now exposed in the 
Kanab plateau is a stripped and somewhat dissected plain, with refer- 
ence to whose northern margin the Permian plain of to-day is graded : 
the stripping and moderate dissection of the Carboniferous and the new 
grading of the Permian being the work of the canyon cycle. The Uin- 
karet and the Shivwits plateau seem to be susceptible of similar inter- 
pretation. The Marble platform also is probably to be regarded, like 
the Kanab and other western blocks, as a stripped structural surface. 
It must have been covered by baselevelled Permian and lower Triassic 
strata at the close of the plateau cycle, but these have been now for the 
most part stripped down to the upper Aubrey. In brief, the evidence 
for two cycles of erosion in the evolution of the existing topography of 
the Grand canyon district is not to be found so much in the general 
evenness of the great Carboniferous platform, beneath which the narrow 
canyon is cut, as in the great recession of the Triassic and other cliffs 
compared with the small width of the rapidly widening canyon, and in 
the minor phenomenon therewith correlated. 
Dates of Displacements. 
THe EasTeRN FLEexures. — Flexures appear to preponderate in the 
eastern part of the Grand canyon district, while faults are the chief 
form of displacements in the western part, as shown in Figure 10. It 
will be shown that there is much probability that the flexures are older 
than the faults as a whole, and that the displacements of both classes 
seem to deserve an earlier date than has been assigned to them in 
Dutton’s reports. 
The Earliest Flecures. — The Waterpocket and the Escalante flexures 
lie northeast of the field of our excursion, but as they are the only dis- 
turbances which have been regarded as pre-Tertiary, it is important to 
make s@me mention of them here. They involve Cretaceous strata, 
whose eroded edges are unconformably buried by the Eocene of the High 
plateaus on the northwest (Dutton, a, p. 43, pp. 280, 288, 294; ¢, p. 215; 
Gilbert, c, p. 10). The San Rafael swell, still further northeast (Dutton, 
ce, Atlas, sheet 11), is described as of Miocene date, probably because of 
