Dove-gray-weathering, black to dark- gray, fine-grained poorly fossiliferous limestone. Distinguished from the Middlebury Limestone with difficulty, especially in the area west of the Sudbury slice. Part of the Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts). Rocks of the Laurentian Margin. Also part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).