158 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
crown ; thus the evidence from drainage confirms that derived from 
structure and erosion. 
Tue ORIGIN OF THE CoLORADO IN THE Granp Canyon District. — In 
view of the various origins other than antecedent that may be ascribed 
to the branches of the Colorado in the Grand canyon district, it does 
not seem legitimate to adduce these streams in support of the antecedent 
origin of the trunk river. That question must be settled by itself, and 
it is by no means free from difficulty. The antecedent origin of Green 
river in its passage through the Uinta mountains has been seriously im- 
pugned by Emmons (1877), who maintains that it is a superposed river 
(a, pp. 194, 205; 6). The antecedent origin of certain parts of the 
Colorado in the Grand canyon district has later been questioned by 
Jefferson (1897), who points out the southward bends of the river 
around the Kaibab and Shivwits plateaus, and suggests that these 
deflections may be consequent on local uplifts instead of regardless of 
them. ‘To these doubts must be added a whole series of considerations 
which had no place in the discussions of Powell and Dutton regarding 
the spontaneous rearrangement of watercourses during the dissection 
of aregion which has suffered repeated movements and heavy denuda- 
tion. It is true that, as the Colorado runs for the most part on nearly 
horizontal strata and in a general way transverse to the displacements 
that its basin has suffered, it cannot be classed with subsequent rivers, 
for they always follow the strike of a weak stratum in a series of tilted 
rocks. But the studies of Hayes and Campbell on the migration of 
certain divides in a region of nearly horizontal strata that has repeatedly 
suffered slight tilting during the development of its rivers deserve se- 
rious consideration in the plateau province, where they have as yét found 
no exponent. Until this new aspect of the problem shall have been dis- 
cussed by some one who has a wide acquaintance with the region, it 
does not seem safe to regard even the trenchant Colorado in its course 
through the Grand canyon as a purely antecedent river. 
In the mean time I cannot resist the temptation of speculating some- 
what freely as to the possible development of the great river across the 
Grand canyon district, especially in view of what has been said in 
previous sections as to the successive movements that the region has 
suffered, and in view of the many ways in which drainage lines may be 
modified during and after such movements. Certain considerations that 
I wish to bring forward in this connection concern not only the Grand 
canyon district, but also the adjacent district of the High plateaus and 
the province of the Basin ranges (or the Great basin) which have not 
