(Hie rocks which constitute Mount Holmes are the same as 
those about its base. The Yermilion Cliff and Gray Cliff 
Sandstones alone appear in the crests . The underlying 
Shinarump shales are cut by the erosion at a few points only, 
and those are near the base. For this reason the Yermilion 
Sandstone is not undermined abooit the base, and the circle of 
revetcrags which surrounds Mount Ellsworth finds no counterpart. 
There are, indeed, a few revetments of Gray Cliff sandstone, 
but they are scattered and for the most part inconspicuous. 
In the general view of Mount Holmes (Figure 16), one of 
the main dikes crowns the 'nearest spur, and another the spur 
leading to the right. At the left are minor dikes, and high 
up is a trap sheet notched on its lower edge. At the left base 
of the mountain lies the lesser arch. 
Figure 23 gives a section exhibited by one of the northward 
canons. It shows one of the faults of the upper part of the arch 
and illustrates the thinning of the sheets as they descend. )j 
(Report on the Geology of the Henry Mountains, by G. K. Gilbert. 
1877. Pages 27-30. 
