Two major facies are represented: one predominantly carbonate and the other with a higher proportion of non-carbonate clastics. The lower two-thirds of the former consists mainly of small and large reef bodies and reef detrital beds which can not easily be correlated regionally. The clastic sequence on the other hand offers an opportunity of regional faunal correlation in spite of detailed changes in facies.

The dolomitic siltstones of the Ghost River formation lie below undoubted Devonian over much of the region and are of uncertain age. In the clastic sequence they are overlain in turn by dark, coarse-grained dolomites of the lower, and the black argillaceous limestones of the upper Flume formation; black calcareous and non-calcareous shales of the Perdrix formation; interbedded shales and limestones with some small algal and coral reefs of the Mount Hawk formation; silty and sandy dolomites, limestones, and mudstones of the Alexo formation; massive crystalline limestones and dolomites of the Morro member and thin-bedded dolomites, dolomitic breccias and cherty limestones of the Costigan member of the Palliser formation.

Seven rhynchonellid zones are recognized in this sequence, each with a characteristic fauna. Several are distinguishable in well cores from the plains to the east and most of them may be traced in the northern outcrop regions of the Mackenzie River basin. Of the zone fossils, two species and one subspecies are new and, with one additional rhynchonellid species, are described in the appendix.