The continuity of Ordovician strata in any area of occurrence can be demonstrated through the recognition of regionally distinct, tectonically delineated stratigraphic units. The recognition of these units in their areas of occurrence provides a remarkably similar and in some places almost identical picture of Ordovician successions. It is concluded that these stratigraphic units may be correlated between various regions in the manner envisaged by d'Orbigny for stages. The terminology for inter-regional classification is proposed and is shown in relation to the alternate terms of the British succession. In this scheme some modification of graptolite ranges is required, notably that of the Nemagraptus gracilis fauna.