156 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
Kaibab flexure, as has already been indicated. If so, there should have 
been a time in the denudation of the uplifted strata when their laterai 
slopes were deeply gashed by consequent streams; and when subse- 
quent longitudinal branches of these streams were developed in auticli- 
nal valleys, opened north and south from the head of each consequent 
stream on the weak Permian and lower Triassic beds that were discov- 
ered along the axis of the uplift. The longitudinal valleys would be 
then enclosed by the retreating escarpments of the Triassic sandstones 
on the east and west; the Jura mountains of to-day offer many exam- 
ples of this kind. In the early stages of this development there would 
be many separate anticlinal valleys along 
the axis of the uplift, each drained by 
its own outflowing consequent stream ; 
but as time went on, the branches of the 
deeper-cut consequents would capture 
the anticlinal drainage area of the shal- 
lower-cut consequents, and as the axis of 
the uplift descends to the north, these 
captures would generally be made in a 
southward direction; thus the drainage 
areas of the successful consequents would 
become unsymmetrical ; each one would 
receive a longer anticlinal branch from 
the south than from the north. As 
between east and west flowing conse- 
quents, the former would generally be 
more successful than the latter, because 
Figure 12. the eastern slope of the Kaibab de- 
Diagram of self-adjusted drainage on .,4ndg to a much lower level than the 
the Kaibab. i : 
western ; the difference of altitude of cor- 
responding strata in the Kanab plateau and the Marble platform being 
nearly two thousand feet (Dutton, ec, Plate II.). If the rule regarding 
the earlier date of flexures than of faults prevailed here as well as else- 
where, the eastern descent from the Kaibab during the pre-faulting period 
would have been three thousand feet or more in excess of the western 
descent ; and all the anticlinal valleys would thus come to discharge 
eastward from near their northern ends, as in Figure 12. 
The more important of the longitudinal streams thus established on 
the Kaibab might have worn down their channels into the resistant 
Aubrey strata before the Triassic sandstones had retreated so far on the 
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