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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 lateral 

 slopes were deeply gashed by consequent streams ; and when subse- 

 quent longitudinal branches of these streams were developed in anticli- 

 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 captui'e 

 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 

 the eastern slope of the Kaibab de- 

 scends to a much lower level than the 

 western ; the difference of altitude of cor- 

 responding strata in the Kanab plateau and the Marble platform being 

 nearly two thousand feet (Dutton, c, 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 



Figure 12. 



Diagram of self-adjusted drainage on 

 the K;iibab. 



