Prior to slates from North Wales being widely available later in the nineteenth century, poorer quality roofing material was obtained locally by working the flaggier sandstones within the Old Red Sandstone, notably the mica-rich strata of the basal Tilestones Formation. Referred to informally as the ‘Long Quarry' (the origin of the ‘Long Quarry Formation', an earlier name for this rock unit), the workings along the narrow linear outcrop can still be seen across Mynydd Bach Trecastell and Mynydd Myddfai and further west along the strike of this unit.