In northwest Somerset Island quartz sandstones of the Aston formation and dolostones of the overlying Hunting formation rest unconformably on metamorphic basement rocks. Except for stromatolites and trace fossils the formations are unfossiliferous, and their age has been interpreted as Proterozoic by previous authors.The Aston sandstones pass conformably upward into the Hunting dolostones, which are conformably overlain by Ordovician strata. A similar succession with Middle Cambrian trilobites at the base occurs on Boothia Peninsula. It is therefore suggested that the Aston and Hunting formations comprise a Palaeozoic succession continuous with the fossiliferous Ordovician rocks. This hypothesis does not appear to be incompatible with regional interpretations of Proterozoic–Palaeozoic relationships.The sedimentary structures and petrology of the Aston sandstones suggest that they were derived from the basement rocks and deposited in a shallow marine environment. Sedimentary structures and stromatolites in the Hunting dolostones show that they were laid down in coastal lagoons and tidal flats.