The name Silurian, like Cambrian and Ordovician, refers to Wales. The term was proposed byMurchison in 1835 for a great system of strata older than the Devonian, and was taken from the Silures, another ancient tribe of Britons which inhabited part of Wales. Murchison gave great extension to his Silurian system, including in it most of Sedgwick's Cambrian, but, as already pointed out, the present tendency is to divide this vast succession of rocks into three systems of equivalent rank. It is unfortunate, and even unjust, that Murchison's term should not have been retained for the more important and widely developed lower division, now called the Ordovician, rather than for the upper division.

As in the Ordovician and Devonian, the New York classification, given in tabular form below in comparison with that of Wales, is the standard of reference for the American Silurian: -

Silurian System

N.B. Until very lately a basal series, the Oswegan, with the Oneida conglomerate and Medina sandstone, has been regarded as the lowest member of the Silurian, but this is now referred to the Ordovician. (See p. 565).