Natural England - Staffordshire (including City of Stoke-on-Trent)

Staffordshire (including City of Stoke-on-Trent)

The geology of Staffordshire is strongly reflected by the landforms and landscape of the County, particularly in the north. Essentially the geology comprises a swathe of Permian and Triassic sandstones and mudstones, which occupy much of the central and southern part of Staffordshire and older Carboniferous rocks which outcrop in the Potteries area of Stoke and form the south-west corner of the Peak District.

Goyts Moss

The western Peak District is underlain by Upper Carboniferous sediments. Goyt's Moss, pictured, cuts through important rocks in the Pennine Coalfield.

Carboniferous Limestone occupies the far north-east of the County and gives rise to the limestone plateau of the White Peak. This area demonstrates landforms typical of the weathering and solution of limestone such as sink holes and steep-sided valleys such as Manifold Valley and Dovedale along the eastern boundary of the County. The Carboniferous Limestone gives way to the coarse sandstones and shales of the Millstone Grit, the outcrop of which around the Potteries forms a series of escarpments and valleys. Folding and faulting of the rock and erosion by watercourses has produced a varied and dramatic landscape, including the well known and prominent natural gritstone crags of The Roaches and Ramshaw Rocks. The high altitude and heavy rainfall have created acidic soils dominated by moorland vegetation.

The industrialised and densely settled conurbation of the Potteries in the north-west of Staffordshire and Stoke-on-Trent owes its existence to the outcrop of the Upper Carboniferous Coal Measures in this area. Although covered by much younger Quaternary glacial deposits, the underlying Carboniferous coals, clays and ironstones have been heavily exploited to form the basis of the once thriving coal and pottery industries. The Coal Measures also outcrop in the south-east of Staffordshire, where the northern end of the South Staffordshire Coalfield (much of which is in the West Midlands) intrudes into the County.

In south and east Staffordshire the landscape becomes more undulating and is dominated by arable farming on the fertile floodplain soils of the upper Trent River and the weathered Triassic mudstones and sandstones that form the solid geology of the area. The higher plateau surface of Cannock Chase forms a markedly different landscape to the surrounding countryside, the Chase marking the outcrop of the Triassic Chester Pebble Beds. These beds, which were deposited by a huge braided river that ran across the Triassic desert plain, give rise to very free-draining thin soils which are of poor agricultural value and support heathland vegetation and coniferous woodland plantations. At some locations such as Kinver Edge, harder sandstone layers in the Triassic succession, the remnants of former desert sand dunes, form more prominent crags and cliffs.

In the east, the presence of Quaternary sediments deposited by Ice Sheets and meltwaters over the past 500,000 years becomes more prominent. The influence of glacial till, sands and gravels on the landscape is evident in the complex undulating ground and the ponds and meres, such as Aqualate Mere, which represent hollows and depressions in the till.

Cambrian

The oldest rocks in the County, the Stockingford Shales, are of Cambrian age (570-510 million years ago) and occur as small outcrops located within younger Triassic rocks at Dosthill, near Tamworth. These marine muds contain fossil brachiopods and trilobites which can be matched with very similar fossils that occur in Cambrian aged rocks in Newfoundland. Molten rock (igneous) was intruded into these shales at a later date (Ordovician 495-443 million years ago) and now forms the so-called Dosthill "Granite" which has been quarried for roadstone.

Carboniferous

Carboniferous rocks (354-290 million years old) outcrop in the northern half of Staffordshire where they have been folded into a shallow basin and form the economically important North Staffordshire Coalfield. The oldest part of the Carboniferous succession belongs to the Carboniferous Limestone Series and consists of thick-bedded limestones, rich in fossil corals and brachiopods, showing that they were deposited in a warm shallow sea. These rocks form the distinctive gently sloping hills and deep valleys of the south-western edge of the White Limestone area of the Peak District National Park and Cauldon Low. Fissures in the limestone have locally been mineralised by copper, lead, haematite and barytes, which were once worked at places such as Ecton Hill. The thicker limestones give way to marine shales, with thin limestones and sandstones (the Pendleside Series) which contain distinctive fossil brachiopods, corals and trilobites. These rocks outcrop around the central part of the basin and the northern margins of the coalfield before giving way to the massive sandstones of the Upper Carboniferous Millstone Grit Series (approximately 300 million years old).

The hard "grit" sandstones of the Millstone Grit outcrop as a series of escarpments (e.g. Leek Moors) over a wide area of North Staffordshire, between the northern coalfields and the limestone area of Peak District National Park. The sandstones were deposited in a coastal environment where large river deltas were building out into the shallow marine waters. Continuing deposition over the millennia led to the further building out of the deltas and the formation of an extensive low-lying, swampy land area in which the succeeding Coal Measures were deposited. The periodic flooding and building of the deltas along the coastline resulted in the deposition of a series of layers of coals (representing the compressed remains of the luxuriant swamp vegetation) interspersed with layers of shale, clay, sandstone and mudstone. The Lower and Middle Coal Measures contain the once economically important coal seams, together with fireclay and ironstone. The overlying Upper Coal Measures are mainly barren of workable coal seams and are largely composed of red marls, mudstones, siltstones and sandstones, the clays originally forming the basis for the World famous pottery manufacturing industry.

Permian and Triassic

The Permian (248-290 million years ago) and Triassic (248-205 million years old) Periods in Staffordshire are represented by red mudstones and sandstones that underlie much of the central and southern part of the County. These rocks were deposited under arid, desert conditions. Permian aged sandstones, which outcrop in the far south-west of the Staffordshire at Kinver and in the north-west around Broughton represent the remnants of a vast area of sand dunes that extended across much of what is now southern England and the Midlands. The Lower Triassic sandstones of the Sherwood Sandstone Group occupy the central part of the County in the Cannock Chase area, the south-west (Stourbridge) and around the margin of the North Staffordshire Coalfield (The Potteries). The Sherwood Sandstone Group consists largely of red, yellow, and brown sandstones that often show colour mottling. Pebbles are scattered through much of the sequence in central England and include the well known Chester Pebble Beds which come to the surface at Cannock Chase. The smoothness and roundness of the pebbles within the Chester Pebble beds indicates that they were transported by a large and powerful braided-river system, probably on the margin of an arid, desert mountain system. The sandstones and pebble beds are free-draining and give rise to acidic soils that typically support heathland vegetation.

The mudstones of the overlying Triassic Mercia Mudstone Group probably represent wind-blown dust that settled in shallow salt-lakes and sun-baked mudflats on the extensive alluvial plain. These rocks occur throughout much of central Staffordshire and the upper part of the River Trent catchment, where they give rise to neutral clay-rich soils supporting woodland and some areas of pasture.

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 Staffordshire. The most extensive deposit is till (or boulder clay), which is formed in and beneath glaciers and ice-sheets. Much of Staffordshire has been covered at least twice by the melting and refreezing of ice sheets over the past 1.5 million years. During the Anglian Glaciation (approximately 400,000 years ago) ice from the North Sea area reached east Staffordshire as evidenced by the presence of rocks of Cretaceous and Jurassic age in the till in this area. During the last glacial advance some 20,000 years ago, ice invaded from the Irish Sea area and deposited till, sands and gravels in North Staffordshire and South Staffordshire. Till with large amounts of gravel and boulders derived from the Lake District and southern Scotland formed at the edge of the ice sheet and now occur around the marginal hills of the Potteries area. During this last glaciation some areas of high ground stuck out above the general ice mass and caves provided natural shelter for animals including bears and hyenas. Deposits of glacial till, sands and gravels in north-west Staffordshire have given rise to an undulating and locally complex landscape which includes a number of ponds and lakes, known locally as meres. These areas of open water have developed in natural depressions in the glacial drift left by the ice sheets which covered the area. Aqualate Mere, west of Stafford, is the largest of the meres and now supports a range of important wetland habitats.

Geological Highlights:

  • The rocks present in the North and South Staffordshire coalfields have been important economic drivers for over two centuries, their exploitation having significantly contributed to the industrial development of the area. The Carboniferous rocks of the North Staffordshire Coalfield have been of particular importance. Here, over 50 horizons have been worked for either coal, clay or ironstone in a 2,000 metres thick Coal Measures (Upper Carboniferous) sequence. The North Staffordshire Coalfield comprises four mining areas: Goldsitch Moss, Shaffalong, Cheadle, and the Potteries, with the last of these being the largest covering an area of about 260 square kilometres. The mining industry in North Staffordshire goes back far into the thirteenth century, but gradually expanded due to demand from the pottery and iron industry and the later establishment of canals and railways. The coal industry went from private small owners to big group owners, nationalisation in 1947, oversupply in the 1960s, competition from cheap subsided imported coal in the 1980s and 1990s and finally the end of the industry with the closure of the last deep mine (Silverdale) in 1998.

  • A similar story can be told for the South Staffordshire Coalfield. The exposed coalfield is elliptical in shape, extending from the Linley Hills in the south to Rugeley in the north. The only part of the exposed coalfield that lies within Staffordshire is a small area around the Himley Wood/Gornal area. Coal seams lie close to the surface in the southernmost part of Cannock Chase. These were the first to be extracted and early records indicate that small scale mining occurred around Beaudesert from 1298 onwards. As these early workable deposits of coal started to become exhausted in the mid-19th century, deeper and more productive mines were sunk to the north of Watling Street in the second half of the 19th century and first quarter of the 20th century. The depression of the 1930s saw many pit closures and declining output. The nationalisation years saw progressive massive pit closures and now the only productive operation in the coalfield within Staffordshire is the Bleak House opencast coal site.

  • The Potteries have also been, as the name indicates, the centre of pottery manufacture for many years. The clay for the manufacture of bricks, ceramics and pots comes from the soft mudstone horizons of the Upper Carboniferous Etruria Formation (Upper Coal Measures). This once thriving industry, which also drove the coal industry, has now all but ceased, with locally derived clays now only furnishing coarse ware and the saggars in which pottery is baked.

  • Within the Triassic Mercia Mudstone Group of south Staffordshire, Rock salt or halite occurs as salt-rich marl and thin beds of salt are recorded from boreholes around Stafford. Rock salt is a soluble material which naturally dissolves into brine when it comes into contact with circulating ground water. Natural solution results in a zone of permeable broken rock formed where the mineral has been dissolved, causing collapse and leading to surface subsidence. Brine was discovered at Stafford Common, just north of Stafford town, about 1881 in a boring for water put down by Stafford Corporation. The first boring for brine started about 1887 and rapidly increased to 80,000 tons of salt per year in 1914. By the early 1960’s, British Soda Ltd, were producing 95,000 tonnes of salt per year. However, after 1964, subsidence from brine pumping, which had been reported since 1948, became a more serious problem. Following court action regarding damage to property caused by subsidence, British Soda Ltd was ordered to cease production in August 1970.

  • The Carboniferous Limestone at Ecton, about 12 km east of Leek, contains valuable copper and lead deposits which have been worked from the 16th Century, being abandoned late in the 19th Century. The mineral deposits are concentrated within a series of pipe-like deposits that formed when mineralising fluids penetrated the rocks some 270-235 million years ago during the Permian Period. Mineralisation consists of an upper, lead rich zone, and a lower, copper rich zone. The zoning reflects processes that took place during the precipitation of minerals from the mineralising fluid. Large areas of the mines are now flooded and inaccessible, but the remnants of individual mine workings and spoil dumps can still be seen at Ecton Hill.

  • Pebble beds form conspicuous horizons within the Triassic Sherwood Sandstone Group. The main pebble bed, as exposed at Cannock Chase, was originally known as the Bunter Pebble Bed (now known as the Chester Pebble Beds), the name stemming from the German word bunter, meaning 'brightly-coloured', as the constituent pebbles occur in a wide range of colours, mainly reds, browns and yellows. The pebble beds are comprised of a coarse conglomerate of pebbles, averaging around 2-10cm in diameter, loosely cemented in a reddish-coloured sand, which is also present in the intervening sandstones. The massive water-course responsible for transporting the pebbles and associated sediment has been named the Budleighensis River, after Budleigh Salterton in Devon, where its existence was first established. The pebbles have the same mineral content as rocks present in northern France, which indicates that the main flow of the river was from the south.

  • The Chester Pebble Beds are a natural source of gravel and sand, both of which are used throughout the construction industry, primarily as the basis of concrete and cement, also as hardcore for road surfaces. The pebble beds beneath Cannock Chase represent the largest deposit of such strata in the whole of western Europe, and this has resulted in the exploitation of large areas by quarrying.

  • The Bridgnorth Sandstone of the Lower Permian is seen in superb three-dimensional exposures along Kinver Edge, near Stourbridge. The sandstone displays many features that are characteristic of the deposits having been formed by the migration of sand dunes across the Permian desert landscape. The arrangement of the individual sandstone layers indicates that the winds forming the dunes blew mainly from the east. Another characteristic, and much later feature at Kinver, are the rock houses that have been carved out of the soft sandstone. These cave houses, such as those found at Nanny's rock and Vale’s Rock, were used as homes by many of the families involved in the Iron industry around Kinver in the 1750's onwards and up until the 1960's.

  • The main reference site for the last glacial period of the Quaternary (the Devensian Glacial) in the United Kingdom is at Four Ashes Pit in south Staffordshire. The sediments exposed through quarrying here consist of a sequence of sands and gravels, overlain by till (all lying on top of Triassic Sandstone). Analysis of fossil beetle remains from organic deposits within and below the gravels, together with characteristic sediment structures within the till, provide a picture of a change from temperate conditions, similar to those of today, to arctic conditions some 20,000 years ago when the glacial was at its maximum.

  • Caves within the Carboniferous Limestone outcrops in north-east Staffordshire have yielded important fossil mammal remains from the last Ice Age (the Devensian Glacial). Bones of arctic lemming, Norway lemming, various voles, bears, lion, spotted hyaena, horse, woolly rhino, reindeer have been recovered from Elderbush Cavern, near Ecton. Nearby Thor’s Fissure and Ossoms Cave are important in that they have provided evidence in the form of artefacts and worked bones for occupation, some 11,000 years ago, by human hunters.

  • Throughout Staffordshire, the immense power of the ice sheets of the last Ice Age can be appreciated by the presence of rocks and boulders that do not outcrop within the County. These so-called erratics have been transported by glacial action (estimated at up to 500m/year for the main ice sheet) to their present locations. One such example is a large boulder of granite set upon a pedestal of Triassic pebbles beside the Chase Road, near Brockton on Cannock Chase. There are no granite outcrops anywhere in the Midlands and the boulder has been matched to an igneous rock outcrop at Cniffel in Dumfries and Galloway, approximately 280km away in the Southern Uplands of Scotland.

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.

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