At the Herbert Inlet occurrence, two masses of Pennsylvanian to Permian limestone (Buttle Lake Group), each up to 250 metres wide, outcrop on the east side of Herbert Inlet, 83 kilometres west of Port Alberni. Both limestone masses are underlain by volcanic breccia, tuff and argillite and overlain unconformably by basalts of the Upper Triassic Vancouver Group, Karmutsen Formation.

The limestone correlates with the Azure Lake Formation of the Buttle Lake uplift and the Mount Mark Formation of the Cowichan uplift, both units of the new Buttle Lake Group. See Cream 1,3 (092F 220) for a description of the revised stratigraphy nomenclature.

The southernmost body strikes 040 degrees for 1000 metres and dips 40 degrees southeast. About 750 metres to the north a second limestone lens trends northward for 1250 metres.