. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. DAVIS: THE GRAND CANYON OF THE COLORADO. 165 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
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. DAVIS: THE GRAND CANYON OF THE COLORADO. 165 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; atid 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 (Button, 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 can
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