DAVIS: THE GRAND CANYON OF THE COLORADO. 167 
rising mountains, for there are some well-attested examples of such a 
process, in which its successive steps are more or less fully traced ; but 
rather that this theory makes a single stride from the beginning to the 
end of a long and complicated series of movements and erosions, over- 
looking all the opportunities for drainage modifications on the way. 
The simplicity of the theory is certainly attractive in comparison with 
the rather tedious length of the considerations that are involved in the 
attempt to analyze the processes of spontaneous river adjustments ; but 
it should now be generally recognized that nothing less than a deliberate 
analysis of all movements (of which the uplift of the present plateaus is 
the last) and erosions (of which the cutting of the,Grand canyon is the 
least) will suffice to discover the actual origin of the Colorado. The 
preceding paragraphs are offered as the beginnings of such an analysis. 
The Erosion of the Grand Canyon, 
Tue Canyon Cycie. — The general uplift that introduced the canyon 
cycle in the Grand canyon district seems to have been accompanied by 
a strong renewal of movement on the faults that divide the Basin range 
province from the plateaus. The northward increase in the heave of 
the bounding faults between the Basin range province and the plateaus 
suggests that the uplift of the High plateaus at this time was greater 
than that of the Grand canyon district. Duttom says: ‘ Until near 
the close of the Pliocene the High plateaus were not only the theatre of 
an extended vulcanism, but those portions which never were sheeted 
over by lavas were low-lying areas, where alluvial strata tended to 
accumulate. They remained, in fact, base levels of erosion during the 
greater part of Tertiary time” (a, p. 23). It is possible that some 
movement was renewed on other than the bounding fault-lines at the 
time of the general uplift, but it has been pointed out above that there 
is good reason for thinking such movement to have been insignificant on 
the fault line near Pipe spring. Still, in the south Toroweap valley 
(Dutton, ¢, p. 94), in the Great Basin (Gilbert, d, p. 341), and in the 
High plateaus (Dutton, a, pp. 250, 277), there are various indica- 
tions of faulting at a much later date than the beginning of the canyon 
cycle. 
Comparison of Glen and Marble Canyons. —Chief among the fore- 
going considerations that point to the division of the Tertiary history 
of the Grand canyon district into at least two cycles of erosion is the 
similar resistance to weathering manifested by the Triassic and the 
