DAVIS: THE GKAND CANYON OF THE COLORADO. 129 



astonishingly bare of fossils ; we saw only an occasional Productus in 

 the limestones of the Kaibab. 



The migrating divide between the two platforms near Pipe spring 

 seems to indicate a recent aud active revival of a contest that should, 

 in a single cycle of erosion, have been settled long ago, but that might, 

 on the other hand, be still in progress in the present youthful stage of a 

 second cycle following the late maturity or the fine old age of the first. 

 It is as if the news of the uplift that enabled the Colorado to incise its 

 canyon beneath the plateaus had but lately reached the Pipe spring 

 district. We may, therefore, suppose that a stable divide between the 

 western branches of Kanab creek and the eastern headwaters of the 

 westward drainage once existed somewhere to the east of the present 

 unstable divide. If the stable divide were reconstituted in the position 

 indicated for it by the remnants of the west-sloping graded platform, 

 the east-sloping platform would necessarily stand above the level that it 

 occupies to-day. This would demand the reconstitution of a graded 

 Permian platform several hundred feet above the level of the Kanab 

 plateau southeast of Pipe spring, a position that is entirely consistent 

 with certain expectations as to the altitude of the ancient lowland of 

 denudation produced in this neighborhood by the long-continued denu- 

 dation of the first cycle of erosion, as will be shown further on. A 

 reason fur the present advantage of the eastern drainage may be found 

 in some slight tilting associated with the uplift by which the second 

 cycle was introduced ; or it may be found in the lower stand of the 

 resistant upper Aubrey strata in the nearly level structures of the 

 Kanab plateau than of the same strata on the somewhat upturned west- 

 ern side of the Uiukaret plateau ; but no decision can be announced 

 without much more field work. The evidence furnished by this exam- 

 ple of a migrating divide as to the date of the Sevier-Toroweap fault 

 will be considered in connection with the fault lines. 



The Cedar Midge Divide under Echo Cliffs. — A second example of a 

 migrating divide occurs in the monoclinal belt of the weak blue lower 

 Trias clays already described as running along the base of Echo cliffs. 

 The belt is followed by a wagon-road from Tuba to Lee's Ferry, first 

 slowly ascending the graded floor of a south-discharging monoclinal 

 valley, then slowly descending the graded floor of a north-discharging 

 valley ; the divide between the two valleys being known as Cedar 

 ridge. The divide is, however, not a ridge in any proper sense. The 

 southern valley undercuts the head of the northern one, and the two 

 are separated by an abrupt southward slope, exposing the blue clays 



