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 drainage. 



