Natural England - Leicestershire (including City of Leicester and Rutland)

Leicestershire (including City of Leicester and Rutland)

The landscape character of Leicestershire and Rutland is strongly influenced by landform, which in turn directly reflects the geology of the area.

The rolling hills of eastern Leicestershire and Rutland are underlain by Jurassic rocks, with limestones forming the hills and softer mudstones underlying the valleys

Leicestershire and Rutland is generally of moderate elevation, lying mainly between 60m and 180m above sea level, with the broad floodplain of the River Soar roughly dividing area east-west.

The rocks of Leicestershire and Rutland are gently tilted to the east with the consequence that the oldest rocks occur in the west and the youngest in the east. Immediately to the north-west of Leicester, the oldest rocks found in the area, the Precambrian rocks of Charnwood Forest, form an isolated and distinctive area of high relief to the west of the River Soar. Tilting, folding and erosion of these ancient volcanic sediments have created distinctive outcrops that contribute much to the area’s characteristic landscape. In the far north-west of Leicestershire, Carboniferous rocks outcrop, including the Upper Carboniferous Coal Measures. The working of coal seams in north-west Leicestershire, particularly through open-cast mining techniques, has strongly influenced the local landscape in areas such as Measham and Heather.

The geology of much of the western half of Leicestershire is dominated by the red mudstones of the Triassic aged Mercia Mudstone Group. The outcrop of these rocks gives rise to a moderately undulating landscape characterised by mixed pasture and arable agricultural use that has developed on the neutral clay soils. To the east of the River Soar, in East Leicestershire and Rutland, Jurassic rocks predominate, the erosion of which has given rise to a ridge and valley landscape, where clays floor the valleys and harder limestones and ironstones form the tops of hills and valley sides.

The landscape of the area has also been significantly influenced by the tremendous climatic changes and physical forces that have dominated the last two million years of geological time. During this period, known as the Ice Age, large quantities of sediment were deposited over the land surface by the waxing and waning of glaciers and ice sheets.

Precambrian

The oldest rocks in Leicestershire and Rutland belong to the Charnian System (approximately 600 million years old), a series of volcanic ashes, grits and slates, into which other molten rocks (igneous) were intruded at a later date (Ordovician - 495-443 million years ago). These rocks emerge from the surrounding plain as a group of isolated hills and peaks to form the unique character of Charnwood Forest and represent some of the oldest that outcrop in England and Wales. Many millions of years ago these rocks would have formed a mountain range, the lower slopes of which are still buried under the Mercia Mudstones of Triassic age. The exposures at Charnwood are famed in geological circles for the fossils of soft-bodied jellyfish-like and worm-like creatures that they contain; these representing some of the oldest multicellular organisms so far known to science. Since their initial discovery at Charnwood communities of similar fossils have been described from localities as far afield as Russia, Newfoundland and Australia.

Carboniferous

To the west of Charnwood lies the Leicestershire coalfield, where rocks of Carboniferous age (345-290 million years old) are present. The Carboniferous Limestone, which is the youngest part of the Carboniferous rock succession in England, is not well represented in Leicestershire, unlike Derbyshire to the north. This is probably due to the fact that the Precambrian rocks of Charnwood formed a series of islands in the shallow tropical Carboniferous sea and effectively reduced the extent of area over which the limestone was deposited. The overlying sandstones and shales of the Millstone Grit just outcrop in the very north-east of Leicestershire, while the overlying Upper Carboniferous Coal Measures occupy a considerable area round Ashby-de-la-Zouch. The Coal Measures consist of mudstones, sandstones and coal seams; the coals representing the fossilised remains of swamp vegetation which grew as luxuriant forests on extensive deltas which extended into the shallow sea.

Triassic

At the beginning of the Permian Period (290-248 million years ago) all of the main continental landmasses came together to form one 'supercontinent' known as Pangaea. Although no Permian aged rocks occur in Leicestershire, rocks from the succeeding Triassic Period (248-205 million years old) when continental conditions still prevailed do occur. These are represented by red mudstones and sandstones of the Mercia Mudstone Group which form and underlie much of the undulating western half of the Leicestershire. These rocks were deposited under arid, desert conditions the mudstones probably being wind-blown dust that settled in shallow salt-lakes and sun-baked mudflats.

Jurassic

Rocks of Jurassic age (205-142 million tears old) dominate and make up much of the eastern half of Leicestershire and all of Rutland. Thick clay formations alternate with thinner layers of limestones and ironstones, with the harder bands of limestone tending to stand out as small ridges. These rocks belong to the oldest part of the Jurassic succession, termed The Lias, and were deposited as layers of mud and sand in warm, tropical shallow seas which covered much of central England at this time. Where exposed the clays and limestones of the Lias yield many fossils including ammonites, bullet-like belemnites (the internal shell of extinct squid-like animals) and bivalves. The highest parts of east Leicestershire, including the Belvoir Scarp and the Laughton Hills and the higher ground between Caldecott and Uppingham in the Oakham area, are formed by the Marlstone Rock (Middle Lias) which has formed a resistant capping above the clays . This bed of iron-rich, sandy limestone formed from sand deposited in a shallow current-swept coastal area, the iron may have originated from tropical soils on nearby Jurassic islands.

Exposures of both the Marlstone and the overlying clays and limestones of the Upper Lias are rare, apart from within stream sections and quarries. The clays of the Upper Lias cover much of the western side of Rutland and have been worked for bricks at Luffenham and Seaton

There is a distinct change from the Lias to the overlying and varied sequence of limestones and clays of Middle Jurassic age (the Inferior Oolite and Great Oolite) which outcrop in the east and north-east of Rutland. The lowest unit of the Inferior Oolite is the iron-rich Northampton Sand which has yielded iron ore at Manton and Cottesmore. The overlying Lincolnshire Limestone forms the undulating, higher ground between Stamford and Clipsham. These limestones were deposited in a very shallow sea and at times under estuarine conditions as evidenced by the presence of fine muds in the succession which often contain many fossil shells such as small oysters and other bivalves. The Lincolnshire Limestone has been extensively quarried for building stone, including the production of roofing slates. The succeeding clays and sandy limestones of the Great Oolite Group outcrop north of Stamford in the Essendine and Stretton area and at Ketton to the south-west of Stamford. Collectively these rocks, which belong to the Rutland Formation, Blisworth Limestone and the Blisworth Clay, were deposited near to the shore of a shallow tropical sea. Some beds are very fossiliferous, notably the White Limestone, and yield the fossils of extinct bivalves, sea-urchins, brachiopods and occasionally ammonites.

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.

Within Leicestershire evidence for the mix of glacial and warmer conditions is provided by deposits of clay, sand and gravel scattered throughout Leicestershire and Rutland. The most extensive deposit is till (or boulder clay) which occurs throughout much of the area, mantling the underlying rocks, and which was formed in and beneath glaciers and ice-sheets. Along the valley of the Soar, and to a lesser extent along the Welland, Wreake and Trent, there are deposits of sands and gravel deposited by the more extensive river systems that would have been present following the melting of the last ice sheet some 12,000 years ago. These deposits have been commercially worked for aggregate in many locations and the working of these has in places had a significant effect on present day landscape character.

Geological Highlights:

  • The geology of the Charnwood Forest comprises some of the most interesting and important rocks in England and Wales. The majority of the rocks are of volcanic origin and were deposited on the flanks of volcanic islands similar to those of modern day Hawaii. Although there are still ongoing debates about the exact age of the Charnwood volcanic sediments it is apparent that they are very old, somewhere in the region of 600-580 million years, and are therefore of Precambrian or early Cambrian age. In 1957 the first fossils were found and described from the rocks exposed at Charnwood, particularly those present in Bradgate Park. These fascinating fossils include a number of forms such as simple fronds or multifronded balls, discs which are usually ovoid and contain variable numbers of concentric rings, worm burrows, and other forms which do not fit into these groups. These impressions of soft-bodied organisms have been interpreted as jellyfish and types of crustacean-like creatures and provide a glimpse of an ancient seabed community and important evidence for documenting the evolution of early animal life.

  • During the middle Ordovician Period (495-443 million years ago), igneous rocks were intruded into the Precambrian and Cambrian rocks which now occur in the Charnwood area. These igneous rocks probably represent an uprising of molten rock that occurred at the edge of a tectonic plate (a massive, irregularly shaped slab of solid, but slowly-moving rock that forms part of the Earth's crust) as it sank beneath the margin of another plate. A similar situation exists in several parts of the World today, notably along the western seaboard of North America. The distinctive red Mountsorrel granite, which is exposed through quarrying at Buddon Hill, represents part of this complex of igneous rocks.

  • An exposure of the Lower Jurassic Marlstone Rock and succeeding Transition Bed at Tilton have been taken as the standard for this part of the Jurassic (approximately 180 million years old) in the East Midlands. The Marlstone Rock Bed consists of a workable ironstone overlying a hard lime-rich sandstone and basal pebble bed, while the Transition Bed is considered to represent the weathered upper portion of this sequence. A rich assemblage of fossils has been found here, including gastropods, brachiopods and a species of ammonite named after the location and the village and which is known as Tiltoniceras acutum.

  • The geology of Leicestershire is reflected visually in the landscape in traditional building materials. Many of Leicestershire’s building are of brick, but in eastern Leicestershire and Rutland warm brown Jurassic ironstone is a common material. In the extreme east of Leicestershire and in Rutland the Lincolnshire limestone is reached and this is reflected in the building stone. Charnwood Forest is also a major area of quarrying for building stone with the Mountsorrel granite and Swithland slates (Precambrian) being used.

  • Opencast working of the iron-rich Marlstone Rock was carried on around Eastwell and Eaton and near to Harston, Sproxton and Buckminster until the early 1970s, but these workings have now largely been restored to agricultural use.

  • The large Castle Cement quarry at Ketton provides one of the largest and most extensive continuous exposures in the Middle Jurassic rocks of the area. The Lincolnshire Limestone is very well exposed and shows the development of small-scale cycles of deposition reflecting repeated changes between marine and estuarine conditions. A section within the quarry has been designated as the reference or type-section of the Rutland Formation of the Middle Jurassic (Bathonian) and the full Rutland Formation succession is excellently displayed here.

  • The fragmentary remains of a very large marine reptile known as a pliosaur were discovered during building works at Barnstone Hall, Rutland. The limited material suggests that the reptile was a Rhomaleosaurus which was possibly in the order of 7.5 to 8 metres in length. Pliosaurs are very closely related to the long-necked plesiosaurs, but have much larger heads, shorter necks and bigger and more robust teeth. They were the largest carnivores that lived in the Jurassic seas.

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.