A common mineral embracing many varieties varying in color and in composition. It occurs in monoclinic crystals; also massive, general…
Its definition shares important concepts with this word: subdivision, american, upper, silurian, system.
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Niagara period
A subdivision or the American Upper Silurian system, embracing the Medina, Clinton, and Niagara epoch. The rocks of the Niagara epoch, mostly limestones, are extensively distributed, and at Niagara Falls consist of about eighty feet of shale supporting a greater thickness of limestone, which is gradually undermined by the removal of the shale. See Chart of Geology.
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