The Landscape of Worcestershire strongly reflects its geological makeup. The broad floodplain of the Severn and the Vale of Evesham are floored by easily eroded mudstones and sandstones of Triassic and Jurassic age.
The Triassic rocks were laid down on a broad desert plain across which large, braided rivers made their way. The sandstones found in the Triassic have been quarried and used as a traditional building stone in much of the area, but particularly around Bromsgrove and Kidderminster. To the east, the Triassic mudstones are overlain by Jurassic clays and thin limestones, deposited in a shallow sea. These rocks give rise to the lower lying land adjacent to the escarpment formed by the harder Middle Jurassic limestones of the Cotswolds. Bredon Hill, to the south-east of Evesham represents an outlying fragment of the Cotswolds and comprises the same Lower Jurassic sands and clays and Middle Jurassic limestones.
In the north-west of Worcestershire, sandstones and shales of the Devonian Old Red Sandstone outcrop in the Teme Valley and together with underlying limestones and shales of Silurian age form the main mass of the Abberley Hills. To the north of this area, west of Kidderminster, red marls form the upper part of the Carboniferous Coal Measures occur. These form part of the Wyre Forest Coalifield.
The oldest rocks in the County are the much altered Precambrian igneous and volcanic rocks that form the prominent Malvern Hills, to the east of Worcester. These relatively hard rocks have probably formed an area of upstanding relief above desert and river plains for many millions of years.
Throughout the County, Quaternary sediments deposited by Ice Sheets and meltwaters over the past 500,000 years cover the land surface.
The dramatic north-south aligned Malvern Hills, which rise out of the surrounding lush landscape of the Severn Vale, are largely formed from ancient Precambrian rocks, dating back some 680 million years. The main ridge comprises granites, diorites and volcanic rocks which have been altered over time through heat and pressure. These lie in the core of a complex folded structure which formed during a mountain building period at the end of the Carboniferous (the Variscan Orogeny) when compressive forces thrust the rocks upwards and westwards. Overlying strata were subsequently eroded, leaving old rocks exposed and their hardness and resistance accounts for the prominent ridge today.
A small outcrop of Cambrian age (545 - 495 million years ago) rocks occur at the southern end of the Malverns. These comprise quartzites, sandstones and shales which yield fossil brachiopods indicating that they were deposited in a shallow sea.
The succeeding Silurian Period (443 - 417 million years ago) is represented by rocks in the Abberley Hills area, and represent a northern extension of the Malverns Hills axis. The Silurian rocks of the West Midlands and the Welsh Borders have traditionally been split into three units on the basis of the type of rocks and the fossils they contain. In the Abberley area, rocks of the Upper Silurian, the Ludlow Group occur. These limestones and shales were deposited in a shallow shelf sea and where exposed yield fossil brachiopods and trilobites.
Devonian (417-354 million years ago) rocks belonging the Old Red Sandstone occur in the north-west of the County, forming part of the much larger outcrop that underlies much of Herefordshire and south Shropshire. This thick sequence of rocks has been split into a number of divisions. The basal part, the Downton Series, occur in the Teme Valley, east of Tenbury Wells, and comprises red and green shales, mudstones and sandstone. 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. Only small areas of the succeeding Ditton Series are present on the higher land above the Teme Valley and just to the west of Stourport. This part of the sequence comprises alternating beds of siltstone and sandstone with nodular limestones. These harder beds tend to give rise to higher ground and were laid down on coastal deltas under a hot climate.
The succeeding Carboniferous Period (354-290 million years old) is represented by rocks that form part of the Forest of Wyre Coalfield and form the solid geology to the west of Kidderminster, between Bewdley and Mamble. These rocks were deposited on a low-lying area of river deltas on which lush tropical vegetation grew. 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. Most of the sequence in the Wyre Forest comprises red beds, with the Highley Brooch being the main worked coal seam.
A series of breccias, that represent the onset of continental conditions that continued through into the succeeding Permian and Triassic Periods, occur in the Clent Hills area. These comprise large amounts of rock fragments set in a red sandy matrix. Much of the material comprises rock of Precambrian age and it is suggested that this was eroded from a mountainous or hilly area where rocks of this age outcropped, but which no longer exist.
During the Permian (290-248 million years ago) and Triassic (248-205 million years ago), what is now Britain formed part of a large supercontinent, known as Pangea (All Earth), located close to the equator. Dry arid, desert-like conditions predominated and were responsible for oxidation of iron compounds within the rocks whilst earth movements at the end of the Carboniferous resulted in uplift of the land and the formation of mountainous areas in the Midlands and other parts of Britain. Erosion of these over millions of years formed thick sequences of sediments over the plains and basins adjacent to the mountains. These deposits are now represented by the red sandstones, breccias and mudstones that underlie the Severn Vale running through central Worcestershire. The bulk of the succession belongs to the Triassic Sherwood Sandstone Group and the overlying Mercia Mudstone Group. The Sherwood Sandstone Group comprises red sandstones with horizons of pebbles deposited by desert flash floods. These form the solid geology to the area around Kidderminster. The Severn Vale is largely floored in the overlying Mercia Mudstone Group, which comprise red and green mudstones, sandstones and thin horizons of gypsum and rock salt. These sediments probably represent wind-blown dust that settled in shallow salt-lakes and sun-baked mudflats on the extensive flood plain. The arid conditions under which these rocks were deposited are indicated by the occurrence of numerous layers of salt, which formed through the evaporation of mineral-rich water under the intense desert sun.
A large part of eastern Worcestershire is underlain by rocks of Jurassic age (205-142 million years old) which were deposited as layers of mud and sand in warm, tropical shallow seas which covered much of central England at this time. The oldest part of the Jurassic succession is termed the Lias and comprises clays, limestones and sands. The clays of the Lias tend to form lower-lying ground and give rise to heavy clay soils. The Lias floors the valley of the River Avon and the undulating plain running northwards up to Inkberrow and the Vale of Evesham. When exposed the Lias yields many fossils of marine creatures such as ammonites, bullet-like belemnites (the internal shell of extinct squid-like animals) and bivalves.
Apart from Bredon Hill, to the north-east of Tewkesbury, there is no exposure of the higher parts of the Jurassic sequence in Worcestershire. At Bredon, clays and silts of the Middle Lias form the bulk of the main hill mass, overlain by the iron-rich sandy limestone of the Marlstone Rock. The top of Bredon Hill is formed by the shallow-water sands and limestones of the Middle Jurassic Inferior Oolite.
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 Worcestershire. 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 and Welsh Ice Sheets to the west, and advanced along the present-day route of the Severn. 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. The late glacial Severn, Salwarpe and Teme shed much of their loads of glacial outwash gravels in this area of confluences. The light, well drained soils close to these major watercourses provided the locus for the growth of the City of Worcester.
Following the melting of the last ice sheet, some 13,000 years ago, the main Rivers have deposited large amounts of alluvium, sands and gravels over their floodplains. Much of this area now forms valuable and fertile agricultural land.
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.