Twenty-two graptolite zones are recognized in the Ordovician and Silurian graptolitic shales of northern Yukon, and their geographical distribution, faunal assemblages, and correlation with Europe and Arctic Islands are commented upon. All the stages and subseries in the Ordovician and Silurian of Britain are recognized. A new formational name, Road River, is proposed for the Siluro-Ordovician graptolitic shales and carbonates of the region. At its type locality, the formation is underlain conformably by Cambrian(?) shales and argillites and overlain disconformably by Devonian Fort Creek shale. The formation is Tremadocian to Ludlovian in age and the Siluro-Ordovician boundary is located on a faunal break.