Olive-blue-grey calcareous siltstones, silty mudstones and mudstones. From a building-stone perspective a classification for the Silurian strata based on rock type is most appropriate, not least because the best building stone yielded by this ‘series’ – the Aymestry Limestone – is diachronous and, in the north-west part of Herefordshire, tends to be variable in its limestone content, grading into the Lower Ludlow Shales Group (below) and Upper Ludlow Shales Group (above) to such an extent that both the precise age and source of the ‘limestone’ blocks observed in buildings are often difficult to determine.
Although the Ludlow Shales comprise two distinct geological units (the Lower and Upper Ludlow Shales groups) separated by the Aymestry Limestone (Formation), they are herein treated together from the point of view of their use as a building stone. The ‘Shales’ are thinly bedded, blue-grey siltstones and mudstones, with some interbedded limestones. When weathered, they become a more olive-buff colour and tend to be more fissile in character.
Though not widely used as a building stone in this area, the Shales may have been extracted during the quarrying of the Wenlock Limestone (stratigraphically below the Lower Ludlow Shales Group) and/or the Aymestry Limestone. The ‘Upper Ludlow Shales’ appear to have provided a more useful building stone, owing to the fact that this group is more flaggy in character and has fewer calcareous beds occuring in the sequence. The ‘Ludlow Shales’ and Aymestry Limestone can be seen in buildings located close to their outcrops both north and east of Ledbury. [Summarised from the Strategic Stone Study Atlas of Herefordshire, English Heritage 2012]