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Strandlines and related features representing former high glacial-lake levels possibly related to the Glenwood and Calumet phases of glacial Lake Chicago were identified from Oceana County north to Benzie County in the northwestern lower peninsula of Michigan. Lacustrine features occur as far as 25 km inland from the Lake Michigan shore at altitudes above the rebounded water planes of glacial Lake Algonquin and the Nipissing Great Lakes identified by earlier investigators.

In order to determine if the water planes identified in this study and those of previous investigators represent the Glenwood and/or Calumet phases, water-plane altitudes are compared with a height/distance curve for the highest level of the Lake Algonquin water plane constructed by J. W. Goldthwait. The Goldthwait curve north of his zero isobase indicates the nature of glacial isostasy for the northern Lake Michigan basin following the development of the Glenwood and Calumet phases. The rebounded water planes of both the Glenwood and Calumet phases should follow exponential curves similar to that of Lake Algonquin but at higher altitudes.

The water-plane data were projected onto a vertical plane oriented perpendicular to Goldthwait’s Lake Algonquin isobases in the northern part of the Lake Michigan basin and parallel to the axis of Lake Michigan in the southern part of the basin. From Ludington north to Frankfort, Michigan, the array of water-plane altitudes is diffuse but has an upper boundary that corresponds to a theoretical Glenwood II water plane. Only two sites occur at elevations high enough to be attributed to a Glenwood I water plane. Lacustrine features that occur at lower altitudes within the array, but above the Algonquin level, are within range of a theoretical Calumet water plane.

Correlation of water-plane data with either the Glenwood or Calumet phase will probably remain unclear until ages are determined for many of the features.

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