Shorelines of the Glacial Great Lakes in Cook County, Minnesota

Abstract

Lateral tracing of shoreline features of the Glacial Great Lakes provides a better basis for recognition and correlation of ancient water planes than heretofore available in Cook County, Minnesota. In addition to the shore features of Lake Duluth, Lake Algonquin, and Lake Nipissing, previously identified in this area, five lower Algonquin shorelines, resembling those of Georgian Bay in Lake Huron, are distinguished and provisionally assigned local names. Possibilities appear good that a relation can be established between the lowest of these, the Deronda, and the Minong beaches of Isle Royale, thus ultimately providing a possible means of relating lower Algonquin levels in the Superior and Huron basins. The degree of tilt displayed by various shorelines in Cook County is consistently lower than previously stated. The uplift in Cook County may have been more uniform than in other parts of the Superior basin indicating differential warping in the Earth's crust during the postglacial recoil rather than uniform tilting as a rigid plate over a wide area.