Geological Survey Professional Paper 754-A Glacial and Postglacial Geologic History of Isle Royale National Park, Michigan

A brief summary of the direction of ice movement will be helpful to an understanding of discussions that follow; supporting details are presented in appropriate sections.

Glacial striations indicate that the last ice movement on the east half of the island was toward the southwest, parallel to the bedrock ridge and valley topography (pl. 1). On the west half, striations and drumlins indicate that the direction of movement was westward, crossing the linear landforms at an angle. The westerly direction is roughly perpendicular to a series of ice-margin deposits that crosses the island near its west end. This westerly swing appears to be associated with the ice margin that built these deposits. Southwesterly striations in the Huginnin Cove area presumably reflect the direction of the main Valders advance down the Lake Superior basin prior to retreat to the position of the ice-margin deposits. A few westerly striations in the Tobin Harbor area (at the east end of the Island) may have been caused by local aberrations in ice movement related to topography or even possibly by boulders pushed shoreward by lake ice (McLellan, 1971); no age relation between these striations and abundant ones in the same area with "normal" (southwest) direction was established.