ABSTRACT

The well entrenched Ordovician series of Britain, though not entirely suitable for use in the graptolitic facies in Canada, are retained, but it is suggested that the use of the Lancefieldian, Bendigonian, Castlemainian, and Yapeenian subseries of Australia would provide a valuable qualification when discussing the Tremadocian and Arenigian units in North America.

Thick successions of graptolitic shale exist only in the Cordilleran and Franklinian geosynclines; many of these units are the lateral equivalents of carbonates, evaporites, and clastics of the craton. The bases of some of the shale units can be shown to be markedly diachronous. A section on Peel River, Yukon Territory exposes the most complete succession of graptolitic shale in the world and yields graptolite faunas of Tremadocian to Siegenian age.

An intra-Ordovician unconformity (probably of Caradocian age) exists in southern British Columbia and probably in southern Northwest Territories and the Arctic Islands. The disappearance of the Graptoloidea is coincident with an Early Devonian unconformity that is present in some parts of northern Yukon Territory. It is preferable to interpret the dearth of graptolite faunas of Wenlockian age in the Cordillera as a feature of the Pacific Faunal Province rather than to a regional unconformity.