DAVIS : THE GRAND CANYON OF THE COLORADO. I/O 



palaeozoic 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 palaeozoic 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 caiion 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 Archaean schists 

 and granites are seen beneath nonconforming members of the Grand 

 canon 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 evenly capped 

 by the Tonto as they are in the Kaibab section. The palaeozoic 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 

 palaeozoic 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 pi-ofiles 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 to a 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 



