Cores drilled from a quarry north of Montreal show a distinct lithostratigraphic unit occurring below the Upper Cambrian Cairnside Formation. The unit was previously considered as the Covey Hill Formation of the Lower Potsdam Group. This paper describes the regional geological setting, lithology, and depositional environment of this unit. Evidence for considering the unit as part of the Rivière Aux Outardes Member (Clark, 1966) is presented. Correlations with other stratigraphic units in southern Quebec are discussed along with evidence for a possible Cambrian carbonate platform in the region. Two scenarios of possible regional depositional episodes are also hypothesized.

This paper documents some aspects of the lithostratigraphic and sedimentological attributes of the Upper Cambrian Cairnside Formation, as observed in drill core and in surface exposures in a quarry near Covey Hill, southern Quebec. The paper begins with a review of previous research and stratigraphic terminology, then describes the lithology and depositional environment of the uppermost beds of the underlying Covey Hill Formation. The two units of the Cairnside Formation are then described and correlations with other localities are discussed. The final section briefly describes the Cairnside Formation depositional environment.