Four Mile Dam Formation
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The Four Mile Dam Formation, also called the Four Mile Dam Limestone, is a geologic formation in Michigan. It preserves fossils dating back to the middle Devonian period.
Gravel Point Formation
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The Gravel Point Formation is a geologic formation in western Michigan. It preserves fossils dating back to the middle Devonian period and correlates with the Long Lake Limestone and Alpena Limestone.
Fossiliferous limestone from the Gravel Point Formation
Image: Gyracanthus NT small
Image: Tentaculitid Devonian