sandstone; 'but at the end of the ridge the strata are seen 
to he continuous beneath it (Figure 21). 
'That a fissure' several feet or several scores of feet 
in width should end thus abruptly, demands explanation, and 
the phenomena immediately concerned offer none. Nevertheless 
it is easy to make an assumption which if true renders both 
cases clear. If we assume that the fissure instead of ending 
at the crosshead is merely offset, and resumes its course be- 
yond, and that the dike contained in it has two bodies con- 
nected by a thin sheet (Figure 22), we shall have no diffi- 
culty in conceiving the erosion which will produce either of 
the natural appearances described. 
"The rocks which constitute Mount Holmes are the same as 
those about its base. The Vermilion Cliff and Gray Cliff 
Sandstones alone appear in the crests. The underlying Shina- 
rump shales are cut by the erosion at a few points only, and 
those are near the base. For this reason the Vermilion Sand- 
stone is not undermined about the base, and the circle of 
revet -crags which surrounds Mount Ellsworth finds no counter- 
part. There are, indeed, a few revetments of Gray Cliff 
sandstone, but they are scattered and for the most part in- 
cons picuous . 
"In the general view of Mount Holmes (Figure 16), one of 
the main dikes crowns the nearest spur, and another the suer 
leading to the right. 
at the left are minor dikes, and high 
