DAVIS : THE GRAND CANYON OF THE COLORADO. 181 



ing far up and down the canyon, and fully deserving the name, esplanade, 

 given by Dutton ; but the Tonto platform is wanting ; the cliff's from 

 the top of the Red-wall descend with their steepness little diminished 

 nearly to the river, enclosing the narrow inner canyon or chasm ; while 

 the Aubrey walls of the upper or outer canyon are five miles or more 

 apart. It is significant that the floor of the esplanade everywhere lies 

 on the same stratum, namely, a calcareous sandstone ; the upper mem- 

 ber of the Red-wall group. 1 



Two Theories of the Esplanade. — Dutton explained the esplanade 

 as a mature valley, eroded during a pause in the uplift by which the 

 broadly denuded plateaus gained their present altitude. During this 

 pause, " the river sought and quickly found a new base-level at the bot- 

 tom of the great esplanade of the Grand canon. . . . The cliffs . . . 

 receded away from the river, gradually developing the broad avenue of 

 the outer chasm. . . . Again the country was hoisted, this time more 

 than before. . . . Swiftly the inner gorge was scoured out, and the 

 chasm assumed its present condition. At present the uplifting force is 

 inactive . . . and the river has nearly but not quite reached another 

 base-level" (c, p. 121). 



It had been suggested to me before our trip to the canyon that it 

 was not necessary to assume a pause of this kind in the later uplift of 

 the plateaus in order to account for the esplanade, for its relation to 

 the resistant Red-wall group was such as to indicate its dependence on 

 structure rather than on a former baselevel. Several reasons for adopt- 

 ing this view presented themselves. 



Comparison of the Kaibab and the Kanab Sections. — In the first 

 place, if the form of the canyon in the Uinkaret, Kanab, and Kaibab 



1 In Gilbert's section of the canyon at the mouth of Kanab creek, a heavy 

 cross-bedded sandstone of the lower Aubrey is placed at the floor of the espla- 

 nade, and no such sandstone is shown in the wall of the outer canyon above 

 the esplanade (a, p. 70, Figure 38) ; while the section of the Shivwits canyon 

 sets the floor of the esplanade on the Red-wall group, and places the cross-bedded 

 sandstone of the Aubrey as a cliff in the wall of the outer canyon. Gilbert explains 

 tli is variation by the statement that the order of the hard and soft beds in the 

 lower Aubrey is not constant (a, p. 177) ; but Dutton says : "The cliff formed out 

 of the upper and lower Aubrey series is very remarkable for the constancy of its 

 profile throughout the entire extent of the great chasm." As far as my own ob- 

 servations went, they agreed with the latter view. It is possible that the cross- 

 bedded sandstone which Gilbert placed on the floor of the esplanade at the entrance 

 of the canyon of Kanab creek into the Grand canyon was really the calcareous 

 sandstones which as a rule forms the upper member of the Red-wall group, capping 

 its great cliff. 



