Natural England - Herefordshire

Herefordshire

The solid geology of the greater part of Herefordshire is of Devonian age and belongs to the Old Red Sandstone, which, through weathering, gives rise to the characteristic colour of the local soil.

Comprising mudstones and sandstones the Old Red Sandstone was laid down by large rivers that crossed a broad, flat tropical plain. The Old Red Sandstone is not the oldest sequence of rocks present in the County. This accolade belongs to a small outcrop of mudstones, sandstones and volcanic rocks of late Pre-Cambrian and Cambrian age that occur close to the Welsh border in the north-west of Herefordshire around Brampton Bryan. Mudstones and siltstones of Silurian age also outcrop in this corner of the County and form the steep-sided, shallow-domed hills of the Clun Forest area.

Limestones and mudstones of Silurian age also outcrop in the Woolhope area, at the centre of a dome-like structure that pokes up through the surrounding, and much younger rocks of the Old Red Sandstone. In the far east of the County, rocks of this age also occur on the western flanks of the prominent Malvern Hills which demarcate the border with neighbouring Worcestershire.

Throughout the County, Quaternary sediments deposited by ice sheets and meltwaters over the past 500,000 years mantle the land surface. The influence of these glacial tills, sands and gravels on the landscape is evident in many areas of Herefordshire.

Precambrian

Rocks of probable Pre-Cambrian age (approximately 600 million years old) outcrop at three localities in Herefordshire. On the western border, Stanner Rock, a craggy hill near Kington, which is made of a number of igneous rocks (including dolerite and gabbro). At nearby Brampton Bryan Park, some ancient mudstones, sandstones and conglomerates outcrop and which represent an extension of similar age rocks that form the Long Mynd plateau to the north in Shropshire. On the other side of the County, the Malverns, which mark the border between Herefordshire and Worcestershire, are composed of metamorphosed Pre-Cambrian rocks (gneisses and schists) and rocks of volcanic origin.

Cambrian

Small outcrops of rocks of Cambrian age (545 - 495 million years ago) occur in the County. These comprise quartzites, sandstones and shales that are exposed at the southern end of the Malvern Hills. These rocks yield occasional fossil brachiopods indicating that they were deposited in a shallow sea. At Pedwardine on the other side of the County, deep water marine muds, now preserved as shales, outcrop over a small area. These shales yield the fossils of marine planktonic animals known as graptolites, now extinct, graptolites were small floating colonial animals which were widespread in the Palaeozoic oceans.

Silurian

The succeeding Silurian Period (443 - 417 million years ago) is represented by rocks in the north-west part of the County, between Presteign and Ludlow [Ludlow is in Shropshire so may be a little confusing); and isolated outcrops along the western flanks of the Malvern Hills and in the Woolhope area. The Silurian of the Welsh Borders has traditionally been split into three units on the basis of the type of rocks and the fossils they contain.

The lowest unit, the Llandovery Series, in Herefordshire comprises sandstones, mudstones and thin limestones. The sediments making up these rocks were originally deposited within a shallow shelf sea with much deeper water lying to the west and north-west. The marine and semi-tropical environment in which they were laid down is demonstrated by the occurrence of fossil brachiopods, crinoids (sea 'lillies') and corals.

The middle unit comprises limestones and shales of the Wenlock Series containing abundant fossil brachiopods, corals and trilobites again indicating deposition in a shallow shelf sea. The Wenlock Limestone is well known for the small fossil coral reefs (known sometimes as ‘ballstone’ reefs) that are preserved in the sequence of limestone rocks.

The upper unit, the Ludlow Series, can be split into rocks that were deposited in the shallow shelf sea and those that were deposited in the much deeper ocean basins to the west. The effective division between these two areas lies in the Presteign-Ludlow area in north-west Herefordshire. Here, shelf limestones and mudstones, rich with the fossil remains of corals, brachiopods and trilobites dominate, while just over the border with Wales, deep water shales and mudstones of the same age occur. The Woolhope and Ledbury area, were at this time, closer to land and here shelf sea limestones and muds predominate.

Devonian

The predominant underlying geology of Herefordshire comprises mudstones and sandstones belonging to the Devonian Period (417-354 million years ago) and which form part of the Old Red Sandstone sequence. The lower part of this thick sequence of rocks is present in Herefordshire and has, over the years, been split into a number of divisions.

The basal red and green shales and mudstones form the solid geology around Hereford and Ledbury and give rise to an undulating lowland that is crossed by the rivers Lugg, Wye and Frome. These rocks were deposited on a wide coastal plain over which large rivers meandered and conditions varied between estuarine and freshwater. Fossils from these easily eroded sediments include large water-going scorpion-like animals known as eurypterids, armoured fish and estuarine brachiopods.

The middle part of the Old Red Sandstone comprises beds of red and greenish-grey silts and locally calcareous mudstone, which give rise to the rich red soils of much of the area around Bromyard and the hilly south-west drained by the River Monmow. The alternating beds of siltstone and sandstone contain nodular limestones formerly known as 'cornstones'. These harder beds of limestone form a cap to hills (eg Merry Hill, Credenhill and Nupton Hill at Wormsley) and the plateau surface of north-west Herefordshire.

These nodular limestones were laid down on coastal deltas under a hot climate and contain the remains of freshwater armoured fish. The sandstones often yield the remains of some of the earliest known land plants, which must have grown close to water across the delta. The highest part of the Old Sandstone sequence crops out in the Black Mountains in the south-west corner of the County and comprises brown sandstones and greenish mudstones deposited under similar conditions to the rest of the succession.

Quaternary

Over the last two million years the climate of Britain has varied tremendously with periods of temperate climate interrupted by repeated advances and retreats of glaciers and ice sheets. Collectively these periods have become known as the Ice Age (we are still in one of the temperate phases) and the actions of the ice sheets have been instrumental in forming the landscape we see today.

Various deposits of Quaternary age occur throughout Herefordshire. The most extensive deposit is till (or boulder clay), which is formed in and beneath glaciers and ice-sheets. There is little evidence for glacial activity prior to last main advance some 20,000 years ago (known as the Devensian Glacial). At this time glaciers spread out from the main Irish Sea Ice Sheet to the west, and advanced along the present-day route of the River Lugg and the Wye. Ice from the Wye Glacier probably spread out in a massive lobe over the Herefordshire lowlands to the east. Boulders recognisable as from Stanner Rock and Hanter Hill were carried by this ice to just south of Bromyard. When the glaciers melted and retreated they left behind large deposits of till, sands and gravels over the land surface, particularly along the main river courses.

Caves in the Carboniferous Limestone at Symond's Yat in south Herefordshire have produced evidence of human activity spanning over 25,000 years. In these caves have been found stone and bone tools and the bones of species of giant deer, hyena, woolly rhinoceros and mammoth.

Geological highlights:

  • In Herefordshire, in the early 1990's a unique fossil deposit was found within nodules in mudstones of Silurian age. It was discovered that, when cracked open, some of the nodules contained small fossils. On close inspection it was found that these fossils preserved not only the commonly found hard parts of invertebrate animals, but the soft parts as well. The fossils are approximately 425 million years old and represent small marine invertebrates that lived for the most part on the sea floor, although some burrowed into the mud, and others swam or floated. The Herefordshire specimens are especially informative as, almost uniquely for soft-bodied fossils, they are not flattened impressions but three-dimensional, uncrushed and almost undamaged, which preserve the shape of the original animals with astonishing accuracy. The Herefordshire fauna contains something like 30 different species, including burrowing worms, although most of the fossils have yet to be investigated in any detail. Rare 'soft-body' fossil sites such as the Herefordshire one represent vital windows onto the past, and allow palaeontologists to fill in many missing details about the creatures that inhabited Earth many millions of years ago.

  • The spectacular gorge of the River Wye in the south-east of Herefordshire provides excellent, if somewhat inaccessible, exposures of Carboniferous Limestone and Old Red Sandstone. It is perhaps, though, the structure of the gorge that is of greatest geological interest. Two theories have been suggested for the development of the Wye Gorge. The generally accepted origin for the deeply entrenched meanders of the gorge is that, as the course of the Wye shows virtually no adjustment to the underlying geology or relief present today, the river developed on a land surface of more recent rocks than are currently visible, which were removed by erosion, and the drainage pattern has therefore been superimposed on the underlying rocks. A more recent and alternative theory is that the dramatic downcutting of the river was caused by huge volumes of water issuing from a lake that formed from meltwater at the end of the last glacial.

  • The rocks of north-west Herefordshire have played an important role in the development of modern geology. In 1831, the British geologist Sir Roderick Murchison undertook a series of investigations of the rocks underlying the Old Red Sandstone that outcrop along the Welsh borders. Through extensive fieldwork and description of the rock types and fossils, Murchison was able to group these previously undifferentiated rocks into a series of units very different from those of the other rocks of England. The results of his research was the establishment of the Silurian (named after the old British Silures tribe that inhabited the area) as a new division of geological time. His work was described in a massive two volume work called The Silurian System (1839) and the Silurian Period is now today firmly established as a distinctive period of time around the World.

Local sites

The following localities represent, in part, the geology of this county. Each locality has a grid reference, a brief description of how to get there and a short summary of the geology you are likely to find. All the localities listed are openly accessible.

Related articles