DAVIS: THE GRAND CANYON OF THE COLORADO. 163 
manner the Colorado found its way across the Grand canyon district to 
the broken-down mountains of the Basin range province, and thence 
southwestward to the sea. The river would thus seem to have been for 
the most part consequent on the form and slope of the surface at the 
time of faulting, yet it may have been antecedent to various subordi- 
nate movements of the crust here and there; and there is a possibility 
that it may have been in some greater or less degree developed after the 
faulting by the retrogressive erosion of west-flowing streams that had 
been encouraged by a favorable tilting of their courses. McGee has 
suggested the latter process to explain certain streams in “ Papagueria ” 
(Arizona and Sonora), whose growth is thought to have been thus 
accclerated during a time corresponding to what is here called the 
canyon cycle (c, p. 352), and this process certainly deserves deliberate 
consideration. 
It should be pointed out that a consequent origin for the Colorado is 
indicated by the following passage in Powell’s report on the Uinta 
mountains: ‘At last the movements which began at the commence- 
ment of Tertiary time succeeded in bringing the whole [Plateau] area 
not only above the level of the sea, but above the general level of the 
Basin province itself ; so that while the Basin province was drained into 
the Plateau province in earlier Tertiary time, in late Tertiary time the 
drainage was reversed, and the streams of the Plateau province found 
their way to the sea by passing through the Basin province. .. . It is 
the opinion of Mr. Howell, and I believe also that of Captain Dutton, 
that this drainage was in some cases reversed along the very channels 
occupied by the ancient streams which ran from the Basin province into 
the Plateau lakes” (4, p. 35). There is in this quotation much more 
suggestion of a consequent origin of the Colorado than is elsewhere to 
be found in the reports of the observers whose names have been so 
often cited here : nevertheless, the published reports give no indication 
of the manner in which the denudation of the upflexed area on the 
southwest may have prepared the way for the production of a south- 
westward slope when the district was afterwards broken and heaved by 
faulting. 
If there be any truth in the suggestion that the Colorado did not 
eross the Grand canyon district until after the faulting of the plateau 
blocks, then it was in the cycle of erosion thus initiated (the post-fault- 
ing cycle) that the great denudation was essentially completed, leaving 
little more than the stripping of weak strata and the canyon-cutting for 
the canyon cycle. The retreat of the escarpments on the faulted blocks 
