Geology
The Wye Valley AONB contains some excellent geology, and includes several
Sites of Special Scientific Interest (SSSIs) noted for their geological features.
These include Great Doward and the Upper Wye. The conservation of geological
features forms part of the Wye Valley AONB Management Plan.
The varied landscapes of the Wye Valley AONB can be explained by underlying rocks and structures, and how ice and then the river and tributary streams have acted upon them through time.
Geological zones
The Woolhope Dome, to the north, is a ‘dome' of layers of rock (now largely worn away, but the general shape remains) largely made up of Silurian limestones, shales and sandstones. These are the oldest rocks in the AONB. The dome has had its top worn away to expose a succession of different rocks. At the centre are the oldest rocks, the Llandoverian sandstones of Haugh Wood and Broadmoor Common. Surrounding this are steep, concentric scarps formed by the Woolhope, Much Wenlock and Aymestrey limestones. Gentler shale valleys intervene where the softer rocks, such as the Elton Beds and the Coalbrookdale Shale, have been worn away more quickly.
The Herefordshire lowlands are largely made up of red mudstones and sandstones (hence a redder soil). These rocks are softer than the limestones elsewhere, so the river created more meanders on its way to the Severn. This led to a wider area of floodplain and a gentler and more rolling landscape. The Old Red Sandstone and fluvio-glacial deposits forms soils of high agricultural quality on the floodplain of the Wye between Goodrich and Mordiford. The fertility of the land has given rise to a distinctive settlement and farming pattern.
Around Symonds Yat, limestones and red sandstones meet. This leads to a landscape of hills and plains, as well as substantial meanders in the river. The areas of limestone cut through by the river have formed impressive river cliffs, favoured by rock climbers. Both the Devonian and Carboniferous systems are represented in this area. The area provides excellent exposures of most of the formations with many now designated as regionally important.
The Lower Wye Gorge landscape was formed by the river acting on a series of layers of rock that dip towards the Forest of Dean. The properties of these rocks have lead to the river acting on them differently - leading to differences in the landscape. This is why we see variance from steep cliffs in the limestones, to more gentle scarp slopes and plateaux further away from the river itself. Old Red Sandstone forms the outer rim of the Forest of Dean plateau. The river has incised into the margins of this plateau to form a gorge with substantial river cliffs such as those at Pen Mael and the Seven Sisters. The steepest parts of the Wye gorge are cut through the Carboniferous Limestone. Here the combined action of the river, natural joints in the rocks and quarrying have exposed many vertical faces.
Underground
Geological interest extends underground. There are many rock shelters and solution caves in the area. These include King Arthur's Cave, Little Doward Caves, Symonds Yat East caves and Symonds Yat West caves (all in the area of Symonds Yat in Herefordshire). At St Arvans, near Chepstow, the underground watercourses have carved out long cave systems, which exit at Otter Hole at the base of Piercefield Cliffs - the only cave system in England or Wales which has to be reached through a tidal sump, making it a mecca for experienced cavers.
The gorge is an important district for palaeontologists and some of these caves and rock shelters have yielded evidence of how prehistoric human populations lived in the Wye Valley as nomadic hunters and traders.
Geology Trails
The Wye Valley AONB is supporting the Herefordshire and Worcestershire Earth Heritage Trust in developing a series of geological and landscape trails for areas which include Goodrich, Symonds Yat, Woolhope Dome, and the Wye Gorge. Visit their website for details.
Geology Links:
- Gloucestershire Geoconservation Trust
- Herefordshire and Worcestershire Earth Heritage Trust
- English Nature (for details re SSSIs)
