DAVIS: THE GRAND CANYON OF THE COLORADO. 179 
adjoining salients will be spurs with rounded front. But where the 
upland is of so small an area that it cannot gather streams, then 
the head of the axial line of a re-entrant has no more importance as a 
stream way than the lines that join it from either side; as a result the 
retreat of the walls will be of about uniform value for a considerable 
length of front, and the head of the re-entrant will here assume a con- 
cave or cirque-like pattern. At the same time, the widening of the re- 
entrant will narrow the adjacent spurs to mere skeletons of their original 
size and sharpen their salients into cusps. 
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Figure 16. 
Notches and cusps in cliff patterns. Diagram of two cliff-makers; the lower one showing 
acute notches between rounded spurs; the upper showing rounded cirques between acute 
cusps. Slightly modified from Bodfish’s map of part of the canyon wall in the Kaibab. 
(Dutton, c, Plate XLII.) 
If this analysis be correct, rounded spurs and sharp re-entrant notches 
should prevail in the cliffs near the base of the canyon walls, because 
streams will generally descend into such re-entrants from the higher 
slopes ; unless, indeed, time enough has elapsed for the strata overlying 
a low-level cliff to have been swept away, and the area of its platform 
reduced by the widening of adjoining side-canyons, so as to imitate 
conditions that would prevail only at higher levels in an early stage of 
erosion. On the other hand, cirque-like re-entrants should prevail in 
the high-level cliffs that rim the sides of the great spurs of the canyon 
