. An ecological survey of Isle Royale, Lake Superior. Animal ecology; Botany; Zoology; Plant ecology. 34 MICHIGAN SURVEY, 1908. IVakes became isolated from the Mississippi drainage. The lake level was lowered, and it was perhaps at this level that the beach lines were formed on the north side of Ijake Superjor, which are now 400-500 feet above the present lake level (Taylor, '97, p. 126). Similar evidences of ancient beaches have been recognized by Lane ('98, pp. 188-191) upon Isle Royale, but he is inclined to place the level of this Glacial Lake Algonquin at about 485 feet. It is probable th
. An ecological survey of Isle Royale, Lake Superior. Animal ecology; Botany; Zoology; Plant ecology. 34 MICHIGAN SURVEY, 1908. IVakes became isolated from the Mississippi drainage. The lake level was lowered, and it was perhaps at this level that the beach lines were formed on the north side of Ijake Superjor, which are now 400-500 feet above the present lake level (Taylor, '97, p. 126). Similar evidences of ancient beaches have been recognized by Lane ('98, pp. 188-191) upon Isle Royale, but he is inclined to place the level of this Glacial Lake Algonquin at about 485 feet. It is probable that more field work will be necessary before adequate correlations of these beaches can be made. Some general idea of the extent of the island at this stage may be gained by reference to the 460 foot contour on the accompanying map>. Fig. 52.—Showing the Algonquin stage of the Great Lakes, dispersal of the land bioto. A water barrier to northward Fig. 53. At this time, Fig. 52, the ice sheets had retreated far enough to the northeast that the climate of the Superior basin must have been so greaitly ameliorated that animal life could have lived in its water. This inference seems probable because fossil shells have been found in the beach lines of the same lake farther to the south by Lane and Walker (Lane '00, pp. 248-252), and at Port Huron, Michigan by the writer in company with Dr. J. W. Goldthwait and Dr. A. G. Euthven (Goldthwait, '07, p. 118). Here were found an abundance of Gonio'basis livesceiis, occa- sional valves of Sphaerium striatimtm Lam. and Unionid fragments, a fauna like that of the present beaches. It is therefore not improbable that this fauna invaded the Great Lakes drainage from the Mississippi during the early stages of the great glacial lakes, when they still over- flowed into the Mississippi Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance
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