St Maughans Sandstone
Lying stratigraphically above the Bishops Frome Limestone is the Early Devonian St Maughans Formation. This unit underlies the Bromyard Plateau of northeastern Herefordshire, the tops of the ‘cornstone’ hills to the north-west of Hereford, the area to the west of the Golden Valley (and extending up onto the flanks of the Black Mountains), and a roughly east–west trending swathe of land to the south of Hereford. The formation comprises a mix of red-brown, green or purple mudstones, sandstones, conglomerates and calcretes, which are superficially similar to the lithologies of the underlying Raglan Mudstone Formation.
The sandstone bands, meanwhile, have been quarried for rubble, flagstone and, where thick enough, for dimension stone. Though not often occurring in continuous bands, the sandstones of the St Maughans Formation are more abundant and thicker than those of the Raglan Mudstone. These sandstones (and perhaps some of the sandstone bands within the Raglan Mudstone) are the principal sources of Herefordshire stone roofing ‘slate’. A small number of quarries still actively work the St Maughans Formation sandstones for building and roofing stone in the Golden Valley area.
Both the colour and grain size of those beds suitable for building stone are highly variable. In general, the coarser beds tend towards a pale grey colour and these are the beds most often used for the main quoinstones and buttresses of churches and other large buildings. There are also essentially medium-grained, cream-coloured sandstones which often show stripes of purple-red. The finer-grained sandstones and siltstones are often well laminated but tend to be very soft and easily eroded. Although usually a more uniformly darker red or purple colour, they may occasionally be greenish-grey. Within any one building, therefore, it is not at all unusual to find the full range of stone types, sometimes doubtless indicating different ages of construction, but not necessarily a common source. [Summarised from the Strategic Stone Study Building Stone Atlas of Herefordshire, English Heritage 2012]