The climax forest of Isle Royale . s. At several points it reaches an altitude of more than 150 the lake level. Between the ridges are narrow valleys,corresponding with the less resistant peripheral portions of theflows and the sedimentary layers that are interbedded with contain many lakes, and where submerged at the ends of theisland form narrow fiord-like harbors and channels. The drainageis well adjusted to structure, the streams flowing along the strike I9I3] COOPER—ISLE ROYALE of the less resistant beds, entering the lake at the ends of thevalleys, or occasionally thro
The climax forest of Isle Royale . s. At several points it reaches an altitude of more than 150 the lake level. Between the ridges are narrow valleys,corresponding with the less resistant peripheral portions of theflows and the sedimentary layers that are interbedded with contain many lakes, and where submerged at the ends of theisland form narrow fiord-like harbors and channels. The drainageis well adjusted to structure, the streams flowing along the strike I9I3] COOPER—ISLE ROYALE of the less resistant beds, entering the lake at the ends of thevalleys, or occasionally through narrow cross valleys, most ofwhich are due to faults. The quaternary history of Isle Royale is briefly as follows: Atthe beginning of the glacial period the topography, producedduring a long period of subaerial erosion, was essentially as ice completely covered the island, moving southwestwardnearly with the strike of the beds, but wrought only shght modi-fications in the topography. Rock basins were excavated in the. Fig. I.—Southeast across Scovill Point and the outer islands from the slope of theGreenstone Range: Tobins Harbor in the foreground; Rock Harbor beyond; LakeSuperior in the distance. valleys and many surfaces were smoothed and striated. Rochesmoutonnees are common. Of the httle drift that was left behindmost was dropped upon the southwest end, and practically allhas been rehandled by the waters of the successive postglacial the retreat of the ice, Isle Royale was left entirely sub-merged beneath, the waters of Lake Duluth. The remaininghistory records a gradual emergence corresponding with therepeated changes of the water level as the lake found successivelylower outlets. That this emergence was frequently interruptedis shown by the beaches, sea cliffs, and wave-cut terraces thatoccur at various altitudes, corresponding with similar ones along the 6 BOTANICAL GAZETTE [januaey mainland coast. These indicate periods when the water level wa
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, booksubjectfo
