116 BOTANICAL GAZETTE [FEBRUARY 
into those exposed to the lake winds and waves, and those protected 
from them. In classifying according to kind of rock, the physical, 
not the chemical, characteristics are the important ones. The 
rocks of Isle Royale are partly volcanics, which are resistant, and 
subordinately sedimentaries (sandstones and conglomerates), which 
are much less so. On the southeast coast of the island the shores, 
where of volcanic rock, have smooth sloping surfaces, and where 
composed of sandstone or conglomerate are often much broken and 
Fic. 15.—Outer shore of Long Island, southeast of Siskowit Bay: sandstone beds 
dipping southeast; a glacial bowlder of granite in the foreground; notable disintegra- 
tion of the sedimentary rock is exhibited; the forest extends low down because the 
force of the waves is broken by irregularities of the shore (cf. fig. 27, where the degree 
of exposure is the same 
very irregular (compare figs. 24 and 15). Striking differences in 
rate of erosion were noted on the northwest coast. Near Blake 
Point the great “Greenstone” layer, which forms the backbone of 
Isle Royale, is at the shore, and forms smooth cliffs which rise 
direct from the water to a height of 20m. or more. The stable 
character of these clifis is shown by the thick coating of lichens 
which covers them, the belt of brilliant orange Placodium being 
especially conspicuous. ‘Trees of large size, as well as many smaller 
