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 the 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 Flexures. — 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 Flexures. — The "Waterpocket and the Escalante flexures 

 lie northeast of the field of onr excursion, but as they are the only dis- 

 turbances which have been regarded as pre-Tertiary, it is important to 

 make some 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 ; c, p. 215 ; 

 Gilbert, c, p. 10). The San Rafael swell, still further northeast (Dutton, 

 c, Atlas, sheet 11), is described as of Miocene date, probably because of 



