164 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
during the last chapter of the great denudation must have been over 
a considerable distance, for each line of cliffs should have been, before 
the faults were made, worn back further on the west of a flexure than 
on the east; while now, in consequence of the faults, the reverse 
relation has been brought about. The total recession since faulting 
has therefore probably been decidedly greater than the distance by 
which the cliffs on the east of a fault-line now stand north of their 
fellows on the west ; and thus an even greater antiquity for the faults 
is suggested than has been thus far suspected. 
The Bends of the Grand Canyon. — There are three peculiar features 
in the course of the Grand canyon: one is the southward bend around 
the Kaibab, the second is a northward bend toward the mouth of 
Kanab creek, and the third is a southward bend around the Shivwits 
plateau. Jefferson has suggested that the first and third of these bends 
may be consequent on the form of the surface given by the flexures; 
but according to the analysis of events here presented, the drainage 
consequent on the flexures ran to the east and northeast, and the west- 
ward course of the Colorado was not assumed until after the flexed 
plateaus had been greatly denuded, and until the denuded surface had 
been raised on the east by the block faulting. Something later than 
the initial slopes of the flexed surface should therefore be found to 
guide the river, if an antecedent or initially consequent origin is not 
accepted for it. It has seemed to me that certain details in the flexing 
of the Kaibab and Coconino plateaus may here be appealed to. 
The eastern lobe of the Coconino is a striking feature as seen from 
the lower plateau on the south (Figure 13) and from the valley of the 
Little Colorado on the east. The surface of the district at the time of 
flexure was presumably covered by some of the mesozoic formations. 
Just before the time of faulting, the Trias may have been pushed back 
to some such outline as would reveal the Permian in the valleys on the 
south and west of the Kaibab, and perhaps even some of the Aubrey 
was laid bare on the highest part of the Kaibab. Up to this time, the 
drainage hereabouts was eastward down the slopes of the Kaibab and 
Echo flexures, but many longitudinal subsequent streams must have 
been developed along the weak lower Triassic and Permian strata west 
of and underlying the Triassic escarpment: that was then retreating 
eastward towards its present position on the axis of the Echo flexure. 
Now as the drainage of the interior basins of the northeast was turned 
southwestward by the upheavals associated with the faulting— long 
after the close of the Eocene — the most available point for its escape 
