\Ni*ag"a*ra pe"ri*od\ (Geol.)
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}.