Geology
The island is composed largely of ridges, running roughly southwest-to-northeast. The main ridge, Greenstone Ridge, is over 1,000 feet (300 m) in many places. Greenstone belts are exposed, with rounded stones of chlorastrolite or greenstone near and in the Lake.
According to the National Park Service, the North sides of the ridges tend to be steeper than the south sides. Coastal areas were once submerged beneath prehistoric lake waters, and contain many tumbled boulders and other large rocks.
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