me Mihi a= gt cae ae 
1913] COOPER—ISLE ROYALE 215 
24, T. 64 N., R. 37 W.), head of Siskowit Bay (Sec. 33, T. 64 N., 
R. 37 W.). 
II. Physiographic development of the habitat 
The history of the present deltas began with the initiation of 
stream activity as the island emerged from the lake. The amount 
of erosion accomplished by the streams of Isle Royale has been 
very slight. The sources of the materials transported by them 
have been principally two: the products of wave erosion left high 
and dry as the lake level sank, and weathered rock material, 
including some decomposed by organic agencies. Deposits were 
made at the mouths of the streams at all stages during the emergence 
of the island. As the lake surface sank these were transported 
to successively lower levels, and more materials were added. Of 
course some of the earlier deposits may have been so situated 
as to have escaped removal, but no such remnants have been 
reported. It is therefore probable that the present deltas include 
most of the materials that made up the earlier ones, brought down 
from level to level as the streams were repeatedly rejuvenated by 
successive sinkings of the lake surface. 
Delta building seems to have practically ceased, at least tempo- 
rarily, for three reasons: (1) th ilable | terial lated 
during the successive stages has all been brought down and 
deposited; (2) the complete forest covering of the uplands prac- 
tically inhibits further weathering and erosion, except what may 
be accomplished by the slow organic processes; (3) (applicable only 
to northeastward-flowing streams, which, however, are in the 
majority) tilting has taken place in the Lake Superior region since 
the formation of the Nipissing beach (Apams 4). At Isle Royale 
the elevation of this beach is about 18 m., and it rises northward 
to 27m. at Nipigon. This has decreased the gradient of north- 
eastward-flowing streams and thus has tended to reduce their 
erosive and transporting power. 
The result of these processes has been the formation of flat 
delta plains of gravel, sand, and silt at the heads of many of the 
harbors, with streams, practically currentless, meandering over 
them. Cut-and-fill and scour-and-fill are going on to some extent 
