*silurian*

a. [ From L. Silures, a people who anciently inhabited a part of England and Wales. ] (Geol.) Of or pertaining to the country of the ancient Silures; -- a term applied to the earliest of the Paleozoic eras, and also to the strata of the era, because most plainly developed in that country. [ 1913 Webster ]

☞ The Silurian formation, so named by Murchison, is divided into the Upper Silurian and Lower Silurian. The lower part of the Lower Silurian, with some underlying beds, is now separated under the name Cambrian, first given by Sedwick. Recently the term Ordovician has been proposed for the Lower Silurian, leawing the original word to apply only to the Upper Silurian. [ 1913 Webster ]