1913] COOPER—ISLE ROYALE 5 
of the less resistant beds, entering the lake at the ends of the 
valleys, or occasionally through narrow cross valleys, most of 
which are due to faults. 
The quaternary history of Isle Royale is briefly as follows: At 
the beginning of the glacial period the topography, produced 
during a long period of subaerial erosion, was essentially as now. 
The ice completely covered the island, moving southwestward 
nearly with the strike of the beds, but wrought only slight modi- 
fications in the topography. Rock basins were excavated in the 
.—Southeast across Scovill Point and the outer islands from the slope of the 
Fic. 1 
Greenstone Range: Tobin’s Harbor in the foreground; Rock Harbor beyond; Lake 
Superior in the distance. 
valleys and many surfaces were smoothed and striated. Roches 
moutonnées are common. Of the little drift that was left behind 
most was dropped upon the southwest end, and practically all 
has been rehandled by the waters of the successive postglacial lakes. 
Upon the retreat of the ice, Isle Royale was left entirely sub- 
merged beneath the waters of Lake Duluth. The remaining 
history records a gradual emergence corresponding with the 
repeated changes of the water level as the lake found successively 
lower outlets. That this emergence was frequently interrupted 
is shown by the beaches, sea clifis, and wave-cut terraces that 
occur at various altitudes, corresponding with similar ones along the 
