Recession of Cliffs 
41 
though occasionally they may approach this condition on one ’ 
side or the other, and more rarely on both sides at once, de¬ 
pending on the geological formations of the locality. Owing 
to the immense height of the walls of such canyons as those 
on the Colorado, the cliffs frequently appear perpendicular 
The “ Hole in the Wall,” near Ft. Defiance, Arizona. 
This kind of sandstone has the peculiarity of weathering in this way, 
sometimes producing larger arches, alcoves, etc. 
Photograph by Ben Wittick. 
when they are far from it, just as a mountain peak often seems 
to tower over one’s head when in reality it may be a consid¬ 
erable distance off. In the nature of the formation and devel¬ 
opment of canyons, they could not long retain continuous 
vertical walls. What Powell calls the “recession of cliffs” 
comes into play. The erosive and corrasive power of water 
