Ellsworth arch, but the vertical displacement is less. In 
the formation of the greater Holmes arch the amount of up- 
lift was 3,000 feet; for the lesser arch, 1,500 feet. 
"There is no evidence in the forms of the arches which 
i 
proves one to be older than the other. Studying the curves 
in the field, I could not discover that either arch assorted 
itself more strongly than the other in their common ground. 
They seem to meet upon equal terms. Still it is probable, 
a priori, that they were formed successively and not simul- 
taneously. The coincidence in time of two eruptions of lava 
from neighboring vents is no more unlikely ' than the coincidence 
of the two irruptions, and the same principle of least resis- 
tance which causes individual laqcolitlc arches to assume 
spheroidal forms, would have given to the compound arch of two 
laccolites, coincident in time, a simple instead of a compound 
form. 
"Assuming that the arches were successive in origin, I shall 
in another and more appropriabe chapter discuss the problem 
of their chronological order in the light of their somewhat 
peculiar drainage system. 
"The lesser arch betrays no dikes nor sheets . The Vermilion 
Cliff sandstone covers it to the top. The greater Is crowned 
by a few grand dikes which govern its topography. Prom the 
center a long dike runs to the south# a short one to the north, 
two to the east, and one to the west. The course of each is 
a mountain spur, and between them are amphitheaters and gorges, 
clinging to the dikes are bodies of altered sandstone, but 
