At the Hartley showing, a 50 centimetre thick phosphorite bed occurs in an overturned sequence at the base of the Jurassic Fernie Group. The phosphorite is pelletal, dark grey to black, recessive and weakly calcareous. It contained 21.5 per cent phosphate (P2O5) (Open File 1987-16). Stratigraphically underlying the phosphorite is a black dolomitic siltstone of the Triassic Sulphur Mountain Formation (Spray River Group).