DAVIS: THE GRAND CANYON OF THE COLORADO. 175 
palzozoic floor are of small value compared to the strong relief that 
must have been developed in the mature stage of erosion on the tilted 
Grand canyon series and their underlying schists. The ancient floor 
was certainly a topographically old surface, in a far advanced stage of its 
erosion cycle. 
The extension of the paleozoic floor further west may be briefly 
sketched. Powell noted “ patches of granite, like hills thrust up into 
the limestone ” in his passage through the Kanab section of the canyon 
(a, p. 92). Dutton describes the floor in detail, emphasizing its small 
relief, and Holmes made an admirable drawing of the southern wall 
in the Kaibab section of the canyon (c, pp. 178-181, 207, 209, Plate 
XXXV.). Newberry wrote, when describing the section in the Shivwits 
plateau : “ The erosion of the cafion has beautifully displayed the ancient 
surface of the granite, and shows it to have been extremely irregular ; 
hills several hundred feet high, many of which have precipitous sides, and 
deserve the name of pinnacles, have been exhumed from the sediments 
in which they were enveloped. The sandstones and shales are seen to 
have been deposited quietly around them ; their strata, nearly horizontal, 
abutting against their sides” (p. 58). Gilbert says that “all along the 
southwestern border of the plateau region in Arizona, the Archean schists 
and granites are seen beneath nonconforming members of the Grand 
eafion rock system; usually the Tonto sandstone” (a, p. 186), and 
his diagrams represent the contact of the two systems by a straight 
line. My lamented classmate, Marvine, records similar observations 
(p. 199). A photograph of a point in the western part of the Grand 
canyon, near Peach spring, Ariz. (View No. 173, taken by W. H. 
Jackson and Co., Denver, Colo.), shows the crystallines as eveniy capped 
by the Tonto as they are in the Kaibab section. The paleozoic floor is 
thus traced for over a hundred miles from the Kaibab section, and in 
spite of its inequalities, it is nearly everywhere capped by the lower 
paleozoic strata. It was certainly a surface of moderate or small 
relief. 
The slope by which the crystallines descend to the river under the 
stratified rocks has different profiles east and west of the apex of 
the “ wedge.” Under the Unkar, the slope is uniformly steep from top 
to bottom. Under the Tonto, a bench of crystallines stands forth for 
several hundred feet, and then bends by a strong curve toa slope as 
steep as that beneath the Unkar (Figures 14 and 15). The persistence 
of this feature in the view down the river from a point over the edge of 
the “ wedge” is remarkable, and strongly suggests that the crystallines 
