the upper reaches; the middle valley is largely underlain by Old Red Sandstone; and the lower Wye is primarily a product of Carboniferous limestone, although here as elsewhere there are substantial tracts of glacial and alluvial deposits masking the underlying geology.
The detail is, of course, much more complicated. At the head of the valley the broad Plynlimon massif is formed by an inlier of older Ordovician rocks within the Silurian outcrop that otherwise underlies the upper valley – including the great moorland plateau of Elenydd, which is often described as the ‘green desert’ of Wales. The vast emptiness of Elenydd, with its thick blanket of postglacial peat above the Silurian strata, rises above the Wye to the west, relieved only by the scattered conglomerate outcrops that form the highest summits, such as Drygarn Fawr with its spectacular summit cairns. This is Wales at its most elemental; a heavily dissected and eerily quiet grass, bilberry and heather moor.
The heather-clad slopes of Esgair Dderw, looking to Cerrig Gwalch and Moelfryn (Walk 28)
Some way downstream a tributary, the Ithon, hosts a remarkable landscape feature known as the Builth Inlier. The rugged topography here, with its low rocky hills, is a result of the intrusion of volcanic lavas and pyroclastic rocks into the surrounding mudstones. There are several locations between Llanelwedd and Llandegley where the rocks are exposed, sometimes with excellent fossils, and most remarkably of all it is still possible to identify an ancient shoreline with fossilised cliffs, sea stacks and beach deposits.
To the south of Builth Wells lies the area in which Silurian geology was first understood. Successive rock formations were deposited in a marine environment and are now exposed at classic locations including the lower crags of Aberedw Rocks, where olive-grey calcareous siltstones form a line of cliffs; the higher crags, with flaggy siltstones and fine sandstones full of shelly marine deposits; and the River Edw south of Aberedw, where there is an interesting exposure with signs of folding, tectonic distortion and even the ripples and scours of Silurian lake-bed activity.
As the river approaches Hay-on-Wye it takes on the characteristics of a mature lowland river, meandering across a broad, damp valley below the northern scarp of the Black Mountains. The floodplain betrays plenty of evidence of the shifting course of the river, with abandoned river channels and several oxbow lakes, especially to the west of Glasbury. The effects of glaciation are plainly visible between Hay-on-Wye and Clyro, where the river has cut a narrow channel through an impressive moraine where glacial deposits are heaped up to a height of 50m (165ft).
This impression of maturity follows the Wye on its journey through Herefordshire as a tree-lined river centred in a broad floodplain flanked by low, rolling hills. There are far-reaching views across quintessential English farmland, with the underlying Old Red Sandstone giving a characteristic rich red colour to the soils. Rock exposures are rare, but occasionally the meandering river has carved out low cliffs – for example at Brobury Scar and at Bridstow near Ross-on-Wye. Below Hereford the meanders become more pronounced, isolating the low-lying King’s Caple and Foy peninsulas.
Looking across the Wye Valley to Banc-y-Celyn from the northern scarp of Aberedw Rocks (Walk 20)
To the west of the river the land gradually rises to the brownstone scarp, with astonishing views westward to the Black Mountains from the summit of Aconbury Hill and extensive woodlands on ancient sites such as Athelstan’s Wood. To the east the uplifted older rocks of the Woolhope Dome form an area of complex geology and spectacular landscape, with hidden valleys and narrow parallel ridges. An intricate blend of orchards, pastures and semi-natural woodland typifies the area, with the nature reserves of Common Hill and Lea and Paget’s Wood providing particular highlights.
South of Ross-on-Wye the river continues sluggishly at first between lush river meadows before suddenly entering a narrow, twisting gorge between high river cliffs. The rim of the plateau above the gorge consists in several places of puddingstone – a hard quartz conglomerate (previously much in demand for millstones) – which outcrops on Coppet Hill near Goodrich and, spectacularly, at the Buckstone and Near Hearkening Rock, where the breakaway boulder known as the Suck Stone – the largest detached boulder in Britain – lies where it fell just below the ridge.
From Monmouth to the river’s mouth south of Chepstow the Wye is confined in a narrow valley below steep wooded slopes punctuated by limestone cliffs. On either side of the river is an extensive plateau – around Trellech to the west and the Forest of Dean to the east – with woodlands and heathland. The extent to which the river has cut down through the plateau is shown by the abandoned meanders at Newland (where the misfit valley is now more than 100m/330ft above the level of the Wye) and St Briavels.
The massive bulk of the detached boulder known as the Suck Stone (Walk 6)
Plants and wildlife
In very broad terms, the Wye Valley can be divided into three ecological zones: the valley grasslands, with riverside meadows and enclosed fields; the steeper slopes on the valley sides, with hanging woods and encroaching bracken; and the moorlands above, with gorse, bilberry and occasional heather among rough grasses.
The great moorland plateau of Elenydd is characteristic of the uplands flanking the upper Wye. Aptly characterised as a vast, pale sheepwalk, it consists mostly of rank grasses with a little heather, and cotton grass and purple moor grass in the wetter areas. The mountain grazings traditionally supported the ‘hafod and hendre’ system of transhumance where the hafod – or shepherd’s cottage – was only inhabited in summer.
In and around the river itself there is a gradual transition from mosses, lichens and liverworts higher up (especially in the gorge above Rhayader) to extensive beds of ranunculus (water-crowfoot) in the more mature, lowland river, with particularly luxuriant beds around Boughrood and near Monmouth, while below Builth Wells wild chives dominate the banks for several miles.
In Herefordshire the Wye and Lugg have yellow water lily, water aven and great pond sedge, but the greatest interest lies in the few remaining Lammas Meadows, managed under a medieval system where stock were excluded until after the hay cut in July. Most were enclosed by 1900, but Lugg meadows and Hampton Bishop meadows still survive.
The woodlands of the Wye Valley are world-renowned, from the oak, alder and willow along the infant river to the amazing hanging woods of the lower gorge. The Woolhope Dome and Wye Gorge retain wild service trees and small-leaved and large-leaved limes – species that dominated the woods here five millennia ago – and at Coppet Hill two precious fragments of medieval woodland have survived. The gorge woodlands are of exceptional ecological interest, with limes and rare whitebeams and a ground plantlife that includes herb paris, yellow archangel and dog’s mercury.
Clockwise (from top-left): The distinctive marsh cinquefoil at Cors y Llyn (Walk 23); Ragged robin at Cors y Llyn (Walk 23); Bee orchid at White Rocks Nature Reserve (Walk 7); Heath spotted-orchid at Cors y Llyn (Walk 23)
Wildflowers come into their own below Builth Wells, with meadow saxifrage and cowslips common, while bluebells, anemones and ramsons colour the woodland floors in spring and 27 species of orchid grace the lower Wye, with bird’s nest and butterfly orchids in the gorge woodlands and pyramid and bee orchids thinly but widely distributed. Semi-natural grassland still clings on in the lower valley and is best seen on the Seven Sisters rocks above Monmouth, which host a remarkable assemblage of rare plants such as bloody crane’s-bill and lesser calamint.
Heathland
