1913] COOPER—ISLE ROYALE 117 
plants, are abundant in the crevices (fig. 16). Very different is the 
shore just southwest of McCargoe’s Cove (Sec. 23, T. 66 N., 
R. 35 W.). The material here is a sandstone, and the cliff is being 
rapidly eroded by the waves. Lichens are absent, and the soil 
and forest growth at the top are being undermined. Several 
recently overturned trees were seen. On the whole, wave erosion 
at the present lake level has not yet notably modified the configura- 
tion of the coast, so that shore recession need not be reckoned with 
as an important influence upon the vegetation. 
Fic. 16.—Inward-facing cliff of one of the small islands bounding Rock Harbor 
on the southeast: resistant volcanic rock produces stable cliffs; because of sheltered 
lecation the limit of forest extension is near the water’s edge, but the trees are con- 
fined to ledges and crevices. 
II. The rock shore succession 
With regard to the comparative areas which have been vegetated 
through the instrumentality of the various successions, bo 
hydrarch and xerarch, the rock shore succession is by far the most 
important of all. A conservative estimate would indicate that at 
least nine-tenths of the forest of Isle Royale has developed along 
the line of this succession. At the same time it is a comparatively 
simple one, and will not require extended treatment. 
The fundamental fact in the process, throughout the history 
