Age: 443-428 million years (Silurian, Llandovery)
Classification: Sedimentary
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Overview
Silurian rocks in Herefordshire and Worcestershire are used as markers for this period of earth history throughout the world. They mark a time when the world’s great oceans were in the process of closing, leading to the formation of marine sandstones, mudstones and limestones. The rocks are also famous for their diversity and richness of fossils, and this has led to accurate sub-divisions of the period being devised: the Llandovery (443-428Ma), Wenlock (428-423Ma), Ludlow (423-419Ma) and the Pridoli (419-416Ma). All four of these time frames are represented the two counties.
The Wyche Formation forms the upper part of the Llandovery Series May Hill Sandstone Group and crops out in the Malverns area. The Yartleton Formation is an equivalent unit in terms of age and characteristics but crops out in the May Hill area of southern Herefordshire. Another equivalent unit is the Haugh Wood Formation of the Woolhope Domebut has not been used as aggregate.
Lithology
Wyche Formation
Consisting of buff, grey mudstones, siltstones, sandstones and occasional limestones, the Wyche Formation was deposited in a shallow sea above storm wave base. Multiple storm events had a great effect on the sediment, creating the rapid changes in lithology and varied sedimentary structures. The oldest bentonites (volcanic ash) in the two counties are also found in these rocks. Aside from Gullet Quarry, the Formation is very poorly exposed along its outcrop, with small stream sections providing the best sites, although many of these are now overgrown. Around West Malvern, a lost quarry formerly exposed the Formation, where it could be seen to be resting directly on the Malverns Complex.
A conglomerate lies at the base of the Wyche Formation that appears to rest directly on the Pre-Cambrian. This unit is the famous Miss Phillips Conglomerate; another important exposure that reveals the relationship of the Malverns Complex with the surrounding rock.
Yartleton Formation.
The Yartleton Formation crops out on May Hill Common and conformably overlies the Huntley Hill Formation. It comprises flaggy, fine-grained sandstones and siltstones with subordinate mudstones and its upper beds may display calcareous siltstones and crystalline limestones. The unit is locally very fossiliferous, preserving examples of several species of brachiopod and solitary corals.
Sites
Gullet Top Quarry, Herefordshire (Wyche Formation)
New House Farm, Herefordshire (Yartleton Formation)
