Avon Group

Age:  359 to 345 million years  (Lower Carboniferous)


At the beginning of the Carboniferous the arid terrestrial environment of the Devonian gave way to shallow marine conditions. South Herefordshire became part of a shallow tropical sea that stretched from Belgium westwards into Pembrokeshire. The initial flooding of the region produced the Avon Group (Lower Limestone Shale) and Black Rock Limestone.


The Avon Group is locally known as the Lower Limestone Shale Group and the dominant lithologies of interbedded fissile mudstone and limestone reflects deposition in a shallow sea.

These rocks are found in the Great Doward and Wye Gorge area and as far north as Howle Hill. A very exciting discovery of a shrimp-like fossil was made during the geodiversity audit of Herefordshire in this area. This is similar to the Malacostraca Pseudotealliocaris etheridgei, though larger, and may be a new species. This is only the fifth location in Britain at which these fossils have been found and these specimens are remarkably well preserved and fairly abundant at the location.

Further research is continuing to find out more about this nationally important site.


Beech Cottage Quarry, Herefordshire

Seven Sisters Cliffs Quarries, Herefordshire

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