the great sandstone masses of the summit were unaltered and 
from them have been excavated the gorges. Along the dike- 
filled fissures there has been some faulting, but there is 
no reason to believe that the displacement is great in amount. 
Toward the flanks of the mountain there are a few sheets, the 
outermost of which is far within the line of maximum flexure. 
Their escarpments instead of facing upward like the revet- 
ting sheets of Mount Ellsworth, face downward; their buried 
and unknown edges are the edges toward the mountain. Their 
thinning toward the periphery of the arch is conspicuous to 
the eye in many instances, as is also the thinning of the 
dikes . 
" Another peculiarity of dike form, one which has since 
been noted in a number of localities, was first detected in 
Mount Holmes. It consists in a definite upper limit. The 
dike so marked is often as even upon its upper surface as 
an artificial stone wall. The upper surface may be level or 
may incline toward one end of the dike, but in either case 
it is sure to be found parallel to the bedding of the strata 
which inclose the dime. this fact led to the suspicion, after- 
ward confirmed by more direct evidence, that the flat top 
of the dike was molded by an unbroken stratum of rock bridging 
across the fissure which the lava filled (Figure 20). The 
converse phenomenon can be observed in the ridge which joins 
Mounts Ellsworth and Holmes. A great dike there forms the 
crest of the ridge for half a mile, its base being buried in 
