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BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



direct line. Through very nearly all this distance, the floor is covered 

 by the basal (Tonto) sandstones of the palaeozoic series. When the 

 actual contact is seen, it is found to be ragged, but in the twenty-mile 

 stretch that I saw, the vertical inequalities of the floor were trifling in 

 comparison to its horizontal extent. A few miles west of the Grand 

 view trail into the canyon, a broad flat mound of the crystallines rose 

 high enough in the northern wall of the canyon to interrupt the whole 



Figure 15. 



The canyon in the crystallines, looking down the river (northwest) from Coppermine spur, 

 Grand View trail. The crystalline floor is generally covered by the Tonto sandstone; 

 but a low crystalline monadnock rises through the Tonto in the distance. Drawn from 

 a sketch. 



thickness of the Tonto sandstones (Figure 15), but this was the only 

 significant unevenness of the surface between the Tonto and the schists 

 visible in that direction. A short distance east of the apex of the 

 " wedge," the more resistant members of the older series are not so well 

 planed down as are the crystallines just west of the same point, and the 

 Tonto sandstone is there greatly reduced in thickness or altogether 

 wanting fur large fractions of a mile. But these inequalities in the 



