186 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



been already suggested, to a depth of one thousand or one thousand five 

 hundred feet (probably revealing the lower Aubrey group, but not cut- 

 ting through it) befoi'e the introduction of the canyon cycle, and a broad 

 floor, an esplanade, must have been opened through it, indifferent to 

 structure, at the level of the denuded plateaus on the east and west. 

 Since then there has been time for the deep cutting and rapid widening 

 of the new canyon to destroy all traces of this floor and bring about the 

 correlation of form and structure that to-day so fully characterizes this 

 section of the canyon. 



Hints for a Visit to the Canyon. — A few words as to the descent 

 into the canyon from the Coconino rim opposite the Kaibab, with special 

 reference to a sight of the " wedge," may not be out of place. The best 

 geological map of this district is that made by Walcott (e, Plate LX.). 

 The Grand View trail, descending from Cameron and Berry's, gives a 

 convenient approach to the apex of the " wedge." Horses for riding and 

 donkeys for carrying a small pack of blankets and provisions can be 

 hired at the hotel ; but if the visitor goes on foot, an early morning 

 start should be made, before sunrise, if possible, as the temperature in 

 the canyon is very high over the noon hours during clear summer 

 weather. It would be certainly a great advantage to plan a visit at the 

 time of full moon, so as to be able to use the night hours for at least 

 part of the climb out of the canyon. The Coppermine spur may be 

 easily reached in the morning before the greatest heat sets in, and noon 

 may be passed at its end on the Red-wall platform, studying the 

 " wedge," as exposed in the northern wall, and examining the canyon 

 to the east and west. A light shelter of canvas to keep the sun off 

 would be a great comfort in this work, as shade is scanty and the glare 

 from the bare rocks is fatiguing while one is attentively studying details 

 of structure and form. A field-glass greatly aids and extends observation 

 in all parts of the canyon, for distances are large. A camp for the night 

 may be made in the side canyon next west of the Coppermine spur, 

 where a small stream is found just above the level of the basal Tonto 

 sandstone ; but the descent to this spot will be more enjoyed if it is left 

 till late in the day, as the trail down a gulch in the Red-wall cliff is 

 directly exposed to the afternoon sun. A second day can be well spent 

 in descending to the river and in examining the palaeozoic floor ; or in pass- 

 ing around the Tonto platform at the base of the Coppermine spur so as 

 to enter the next ravine on the east, where the " wedge " seemed to be 

 exposed on the south side of the canyon. When viewed from above, the 

 various slopes and platforms seem very smooth, as if one could walk over 



