• "The Skelgill Formation in the western Lake District consists mainly of black shales ranging in age from the P. persculptus Biozone (uppermost Ordovician) to the S. sedgwickii Biozone (upper middle Silurian). In its lowest part, however, it preserves both shelly and graptolite faunas. Kneller et al. (1994, p. 231) assigned the pale limestones, commonly with nodules, at the base of the formation to the Spengill Member. Deposition in an anoxic, relatively deep basin has been suggested for the formation, probably to the west of active fault scarps." Addition discussion mentions "slightly calcareous, shelly mudstones" just above Ordovician/Silurian boundary. Stratigraphic section lists "Black, pyritic shale with abundant graptolites" for bed A, "Grey, laminated shale with occasional graptolite and brachiopod-rich intervals" for beds B-F, and "Skelgill Shale with graptolites and rare brachiopods" for beds G-H.