DAVIS : THE GRAND CANYON OF THE COLORADO. 



16; 



was, as has been stated, near the centre of greatest local upheaval (the 

 Kaibab) where the revelation of weak underlying strata had reduced the 

 level of the Trias by sapping, and had thus produced an amphitheatre, 

 open on the southwest. At the same time, the subsequents under the 

 Triassic escarpment were gathered into a single stream to form the 

 Little Colorado, discharging northward ; but this result may have been 

 in part the effect of spontaneous interaction among the streams them- 

 selves, after their habit in such cases, and only in part the effect of 

 upheaval at the time of faulting. Once reaching the Kaibab amphi- 

 theatre, the new-born river followed southward along the subsequent 

 Permian valley which must have been opened along the east Kaibab 

 flexure, until the slopes of the northeast-dipping flexure that limits the 



Figure 13. 



The eastern lobe of the Coconino plateau, as seen from near Lockett's tank. The fore- 

 ground shows a ravine in the upper Aubrey limestone, once filled with lava, and now 

 partly re-excavated. The "tank " is a waterfall pool. Drawn from rough sketch. 



Coconino plateau were encountered. The river then turned northwest- 

 ward along a trough of weak and low-lying Permian strata that occu- 

 pied a depression between the two uplifts ; and it is notable that 

 the small but sharp flexure which bounded this trough on the south 

 may now be traced through the spurs of Carboniferous strata on the 

 southern canyon wall (Dutton, c, p. 185). The flexure comes from the 

 southeast, where it forms the northern border of the eastern lobe of 

 the Coconino plateau ; it trends northwest, as if to join the now-faulted 

 flexure at the western base of the Kaibab. We had a good view of it 

 from the southern rim and from the bottom of a side canyon. Thus 

 interpreted, it appears that a part of the true Kaibab uplift lies south 

 of the canyon, where it slopes into what is locally known as " the 



