1913] COOPER—ISLE ROYALE 139 
miles of rocky coast absolutely unbroken by beaches of any kind. 
Wave erosion at the present lake level has not yet produced an 
irregular coast line, in the reentrants of which they might develop, 
nor has it furnished abundance of sand, gravel, and shingle for 
their building. The general steepness of the shores is another 
unfavorable feature. Such as are present occur in the bays and 
coves, most of which are due not to wave erosion but to the original 
configuration of the rocks. The fragments eroded from the bold 
cliffs and headlands near by are swept into these reentrants and 
come to rest there in the comparatively quiet water. Most of 
the beaches are of limited extent, but at the head of Siskowit Bay 
there are two magnificent stretches, separated by Senter Point, 
which have a total length of 2km. The materials range from 
fine sand to coarse shingle, the larger sizes being by far the com- 
moner. Back from many of the present beaches extend similar 
accumulations which were made when the water level stood higher 
than now, and formations identical in character occur at various 
levels upon the ridges. 
6) Vegetation—From their nature, beaches occupy situations 
that are more or less protected from the full force of waves and ice, 
and usually from wind also by reason of neighboring headlands. 
As compared with the rock shores they thus provide favorable 
opportunity for invasion by plants. The limit of possible forest 
extension, as in the case of the rock shores, varies with the effective 
reach of waves and ice, but is never high. Below this limit 
materials are frequently moved about by the waves, and all vegeta- 
tion except annuals is manifestly impossible. Even lichens must 
be destroyed by the movement and friction. Above the limit of the 
waves, where the fragments are not disturbed, conditions are 
particularly favorable for invasion. If the material is fine a soil is 
already present, if coarse there is opportunity for the accumulation 
of soil in the interstices of the shingle. In the latter case water 
drains off too rapidly, but as the openings become filled, this fault 
is gradually corrected. 
Because of the favorable conditions enumerated above, the 
climax forest in most cases has already advanced to its limit of 
possible extension. Very often a bank of solid humus, formed 
