DAVIS: THE GRAND 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 and 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 for 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 Uinkaret 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 Ridge 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 
