Abandoned lake beaches in the northern part of the Great Lakes region have been known to geologists for nearly ninety years. They record a series of episodes that intervened between the Algonquin and the Nipissing stages, which have been well worked out elsewhere. Study of later Algonquin strandlines on Isle Royale in 1930 led the writer to doubt the interpretation hitherto given these beaches. Researches were carried on in areas closer to the region of earlier studies. Those on Penetang (short for Penetanguishene) peninsula (Fig. 1, for location) were of especial value in interpreting the geologic history, and furnished the material for this paper.
Field work was done in August, 1935, with the aid of a grant from the Penrose Bequest of the Geological Society of America, for which the writer is grateful. The work of Mr. James Calver, of Ann Arbor, in assisting with the tedious instrumental work, . . .