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 * This article describes the geology of the ceremonial county of Shropshire, England which includes the modern administrative county together with the district of Telford and Wrekin.

The geology of Shropshire largely consists of sedimentary rocks of Palaeozoic and Mesozoic age, surrounding restricted areas of Precambrian metasedimentary and metavolcanic rocks. The exploitation of the Coal Measures and other Carboniferous age strata in the Ironbridge area made it one of the birthplaces of the Industrial Revolution.

Precambrian
The oldest rocks preserved at the surface within Shropshire are the late Precambrian schists and meta-volcanics found along the Church Stretton and Pontesford-Linley faults.(ref p48, Toghill) The poorly exposed green/brown Rushton Schist occurs around the hamlet of Rushton, west of the Wrekin. The metamorphism of these metasediments is dated to 670 million years ago (Ma), though the date of deposition of the original shales and sandstones is not known. They likely reflect the basement under the wider Midland region. At Little Hill (formerly Primrose Hill), southwest of the Wrekin is a rock known as the Primrose Hill Gneiss, similar to rocks found in the Malvern Hills which are dated between 700 and 600 Ma. The Rushton Schist and the assorted rocks of the Primrose Hill Metamorphic Complex are each assigned to the Cryogenian period.

The lavas and tuffs of the Ediacaran age Uriconian Group overlie the Primrose Hill rocks. These rocks extend northeast beneath Wrockwardine and southwest to Harnage and appear again to form the hills of the Lawley, Caer Caradoc, Helmeth Hill and Ragleth Hill, east of Church Stretton, with a further outcrop at Wart Hill, west of Cheney Longville. There are outcrops at Pontesford Hill and to the west of Linley and also to the southeast of the Stiperstones, each along the line of the Pontesford-Linley Fault.

The remaining Precambrian rocks are those of the Longmyndian Supergroup, a roughly 6500m thick sequence of Ediacaran sedimentary rocks. The Longmyndian sequence is divided into a lower Stretton Group and an upper Wentnor Group. The former comprises between 2700 - 4000m thickness of metasediments incorporating some tuffs. The latter consists of volcaniclastic sandstones and other sedimentary units of 1800 - 3600m thickness. Whether the relationship between the two units is an unconformity is still debated.

Haughmond Hill is formed from purple to ?? mudstones with sandstones assigned to the Portway Formation. This sequence is overlain by the Bayston-Oakwood Formation which comprises sandstones, mudstones, siltstones and conglomerates.

Cambrian
There are only a few limited localities in Shropshire where Cambrian rocks occur.

The Wrekin Quartzite lies unconformably on Uriconian volcanics and is itself conformably overlain at the Ercall by the sandstones of the Lower Comley Sandstone Formation. The presence of the mineral glauconite gives these latter rocks a green-brown colour. Lower Comley shales and sandstones also occur in a small and largely fault-bound area at Lilleshall alongside mudstones and siltstones of the Dolgellau Formation. Sandstones and mudstones of the Upper Comley Sandstone Formation unconformably overlie the Lower Comley strata. The fossiliferous Lower Comley Limestones were the first in Britain to yield Lower Cambrian fossils; the site at Comley Quarry is managed as a geological reserve in respect of its importance to the history of geological science. formerly Upper Comley Group (unconformity) formerly Lower Comley sandstone & limestones Wrekin Quartzite (unconformity)

Ordovician
Shineton Shale Fmtn SHSH Tremadoc series (Trem was Cambrian) Acton Scott Fmtn ASGP Actonian Harnage Shale Fmtn HASH Caradoc Series Chatwall Flags & Sandstone CHCH Caradoc series Cheney Longville Fmtn CHLF Longvillian-Marshbrookian

Silurian
Worldwide, the Silurian period is divided into four epochs; Llandovery, Wenlock, Ludlow and Pridoli, the second and third of which derive their name from Shropshire localities, reflecting the work of nineteenth century geologists in this area in understanding the rock sequences laid down during this period of geological time.

The earliest Silurian rocks locally are the Pentamerus and Purple Shales formations, both being assigned to the Llandovery epoch. Their outcrop to the southeast of the Church Stretton Fault Zone extends from Wistanstow northeast to Buildwas. Overlying these to the southeast is the mudstone-dominated Coalbrookdale Formation which was traditionally known as the Wenlock Shale. It extends through the Sheinwoodian and Homerian ages which together constitute the Wenlock epoch. The Much Wenlock Limestone Formation (formerly simply the Wenlock Limestone) forms the long northwest-facing escarpment of Wenlock Edge. Immediately to its southeast is the discontinuous strike valley known as Hope Dale which is formed within the siltstones and mudstones of the Lower Ludlow Shales. Nowadays these Gorstian age strata are given 'group' status. A broken secondary scarp is formed by the overlying Aymestrey Limestone Formation (formerly the Aymestrey Group), also of Gorstian age. At the base of its dip-slope are the outcrops of the Pridoli age Downton Castle Sandstone and Temeside Mudstone formations. At the base of the former is the Ludlow Bone Bed, representing the base of the Old Red Sandstone sequence of the Anglo-Welsh Basin. Southeast again runs the parallel Corve Dale which is developed in the Raglan Mudstone Formation, also of Pridoli age. The southeastern edge of Corve Dale is provided by the outcrop of the overlying St Maughans Formation, the base of which is marked by the thick and regionally extensive calcrete known as the Bishop's Frome Limestone Formation which marks the transition from the Silurian to the Devonian. This unit was traditionally referred to as the Psammosteus Limestone. Small fault-defined inliers of parts of this sequence occur in the Neen Sollars and Caynham areas of the south of the county.

Northwest of the Church Stretton Fault Zone, the Pentamerus and Purple Shales wrap around the southern and western margins of the block of Precambrian rocks of the Long Mynd and the district extending west to the Vale of Montgomery. They are overlain by the sandstones, siltstones and mudstones variously of the Sheinwoodian age Bromsleymill Shale Formation and then by the Aston Mudstone, Oakeley Mynd and Bailey Hill formations of Homerian through Gorstian to Ludfordian age. The succeeding Knucklas Castle, Cefn Einion and Clun Forest formations form the core of the Clun Forest range on the county's western border with Wales. These sequences are further overlain by the Temeside Mudstone and the overlying Raglan Mudstone around Vennington between Westbury and Long Mountain.

Clun Forest Formation CLF (Sil) Cefn Einion Formation CEF Ludford Knucklas Castle Formation KCA Ludford Irfon Formation IRF (Sil) Bailey Hill Fmtn BAI Gorst-Ludford Aston Mudstone Fmtn AST Homer-Gorst Bromsleymill Shale Fmtn BSF Sheinwood

Raglan Mudstone Fmtn RG Pridoli Temeside Mudstone Fmtn TSH Pridoli Downton Castle Sandstone Fmtn DCS Pridoli (with Ludlow Bone Bed at base) Upper Ludlow Shales Gp ULYS Ludfordian Aymestrey Limestone Fmtn AL Gorstian (formerly Aymestrey Group) Lower Ludlow Shales Gp LLUS Gorstian Much Wenlock Limestone Fmtn WEL Homer (formerly Wenlock Limestone) Coalbrookdale Fmtn CBRD (Sheinwood-Homer) (?formerly Wenlock Shales) Purple Shales Fmtn PUS Telych (?formerly Hughley Shales) Pentamerus Sandstone Fmtn PEB Llandovery epoch (formerly Pentamerus Beds)

Devonian
Stratigraphically above the Bishop's Frome Limestone is the thick sequence of mudstones, with occasional sandstones, known as the St Maughans Formation, the lowermost part of the Devonian succession in Shropshire, assigned to the Early Devonian epoch. The outcrop occupies much of the country between Ludlow and Bridgnorth and extends to the county boundary south of Cleobury Mortimer. The Emsian age Clee Sandstone Formation overlies the St Maughans rocks around Cleobury Mortimer. In a tract of country to the south of Stottesdon, the Clee Sandstone is itself overlain by the yellow and sometimes pebbly Farlow Sandstone Formation. Together with the Pridoli strata, these Devonian rocks constitute the Old Red Sandstone of Shropshire.

Carboniferous
The earliest Carboniferous rocks, the Village Farm and Jackie Parr Limestone formations, are seen in the Lilleshall inlier where they unconformably overlie the Old Red Sandstone sequence. These are in turn overlain unconformably by the Lydebrook Sandstone and Sylvan Limestone formations. Within the latter is the Little Wenlock Basalt.

Parts of several small coalfields are found within Shropshire - the Coalbrookdale, Clee Hills, Wyre Forest, Leebotwood and Shrewsbury coalfields, together with the southernmost extension of the Denbighshire Coalfield around Oswestry.

At Clee Hill, The Oreton Limestone is succeeded by the Cornbrook Sandstone above which is a sandstone at the base of the Lower Coal Measures. This is overlain by mudstones within which are several coal seams. The sequence is intruded by a dolerite sill known locally as 'dhustone'. At Brown Clee, Pennine Coal Measures lying directly on the late Devonian Clee sandstone, form the upper parts of Abdon Burf and Clee Burf though the summits themselves are formed by an igneous intrusion of dolerite/dhustone.

Salop Fmtn SAL Asturian(C) - Cisuralian (P) Alveley Member ALY Astur (C) Halesown Fmtn HA Asturian local unconformity Etruria Fmtn ETR Westphalian Pennine Middle Coal Measures Formation PMCM Duckmant-Bolsov (C) Pennine Lower Coal Measures Formation PLCM Langsett (C) Sylvan Limestone Formation Little Wenlock Basalt Member LWKB Brigant Lydebrook Sandstone Formation LYS Holker-Asb (C) Jackie Parr Limestone Formation Village Farm Formation

Permian
Within Britain, the rocks of the Permian and Triassic periods are often lumped together as the Permo-Triassic and typified as they are by desert sandstones, also labelled the New Red Sandstone. In Shropshire they extend across the North Shropshire Plain, itself a southerly continuation of the Cheshire Plain where similar rocks are to be found. Much of this flat area is covered by more recent deposits but sandstone hills are prominent at Ruyton, Nesscliffe, Myddle, Grinshill and Hawkstone. Rocks from these periods also underlie the plains in the east of the county. The names of the various sequences have undergone a number of changes

The Enville member of the Salop Formation (formerly the Enville Beds) comprises a sequence of Carboniferous/Permian sandstones, conglomerates and breccias up to 110m thick which occur in the east. To the west are sporadic outcrops of the Alberbury Breccia (a.k.a. Cardeston Stone). These are both unconformably overlain by the Bridgnorth Sandstone, formerly thought to be Triassic in age, best exposed in the cliffs of the town which has lent them its name. These are aeolian 'millet seed' sandstones which originated as desert dunes.

During the Early Triassic epoch, a river system flowed from the south bringing sand and gravel (rounded quartz pebbles) which formed what were once known as the Bunter Pebble Beds, later the Kidderminster Conglomerate and to the north, the Chester Pebble Beds but which are now known (along with a host of other locally named rocks) as the Chester Formation.

They are overlain by the Helsby Sandstone Formation, a name which encompasses the Grinshill and Ryton sandstones.

Salop Fmtn SAL Asturian(C) - Cisuralian (P)

Triassic
The North Shropshire Plain is largely underlain by rocks of the New Red Sandstone, largely of Triassic age. However much of the area is covered by recent superficial deposits, not least glacial till and glacio-fluvial deposits which obscure the bedrock over wide areas.

range of hills between Lee Brockhurst and Hodnet. Helsby Sst overlain by Tarporley Siltstone Clive and Grinshill - Helsby sst Myddle south past Harmer Hill - Helsby sst Nesscliffe to Brownhill

Penarth Group https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=PNG (Rhae) Blue Anchor Formation https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=BAN (Nor/Rhae) Branscombe Mudstone Formation https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=BCMU (Nor/Rhae) Wilkesley Halite Member https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=WHT (Carn) Sidmouth Mudstone Formation https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=SIM (Olenek/Carn) Northwich Halite Member https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=NWHF (Anis) Bollin Mudstone Member https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=BOM (Anis) Tarporley Siltstone Formation (Olenek/Anis) Helsby Sandstone Formation https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=HEY (Anis) Wilmslow Sandstone Formation https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=WLSF (Olenek) Chester Formation https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=CHES (Olenek) Kinnerton Sandstone Formation https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=KNSF (Early Triassic Epoch)

Jurassic
Dyrham Formation https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=DYS (Pliensbach) Triassic/Jurassic Lias Group https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=LI (Rhae/Aalen)

Igneous rocks
Neoproterozoic age intrusions at the Wrekin and Haughmond Hill. Also in the Shropshire hills. A sill of microgabbro (dolerite) was intruded into the Pennine Coal Measures rocks at Kinlet during the Bolsovian stage of the Carboniferous. It forms a part of the Clee Hill swarm. A NW-SE aligned dyke of Palaeogene age cuts the sandstone at Clive.

Structure
Almost all of the geological structures within the county are aligned broadly northeast-southwest following the Caledonoid trend established during the Caledonian Orogeny.The Church Stretton Fault Zone is a major one whilst the Wem Fault Zone and Hodnet Fault faults partly define the southeastern extent of Cheshire Basin, the Shropshire portion of which is sometimes referred to as the North Shropshire Basin. The Jurassic outcrop is preserved within the shallow Prees Syncline, the axis of which parallels the Wem fault to its northwest. The Carboniferous outcrops in the Clee hills are preserved along the axes of the Brown Clee and Titterstone Clee synclines which lie to either side of the Ludlow Anticline.

Glacial legacy
Shropshire was doubtless affected by glacial ice during the Anglian glaciation but evidence for that does not remain. The county was subjected to incursions by glacial ice both of Welsh origin and of Irish Sea origin during the more recent Devensian ice age, a combination of the two ice-masses reaching their maximum extent over the county around 18,000 years ago when thicknesses over the plain were perhaps up to 400m. At this point Irish Sea Ice having advanced south across the Cheshire Plain reached as far as Wenlock Edge and the Wolverhampton area. Ice tongues from the Welsh Icesheet reached down the Teme, Clun and Onny valleys to the south of Long Mynd and Stiperstones though the higher ground remained ice-free. The Severn and Rea valleys were also occupied by Welsh ice moving either side of Long Mountain. The so-called Ellesmere and Welsh readvances occurred around 16,000 years ago but began retreating 1000 years later. All ice had gone by 11,000 years ago. A northwest-southeast aligned boundary between the two ice-masses is recognised between Ellesmere and Oswestry, its position changing over time. Southeast Shropshire remained unaffected by glaciers though as with other areas rising above the ice surface, the landscape was affected by intense periglaciation.

Till is up to 100m thick in parts of north Shropshire. Erratics within the till can be traced back to granite outcrops in southern Scotland and the Lake District as well as sources which are closer. Freeze-thaw cycles operated on the exposed quartzites of Stiperstones leading to the development of rock tors and of patterned ground i.e. stone stripes and polygons. Dolerite screes on Titterstone Clee also date from such processes at that time.

Glacial meltwater flowing beneath, beside or down-valley of the glaciers cut several gorges, the most significant of which is the Severn Gorge at Ironbridge. Its formation was traditionally ascribed to the overflowing of a hypothetical proglacial lake termed Lake Lapworth deemed to have covered much of northern Shropshire and adjacent parts of Staffordshire. The currently accepted explanation involves the proven existence of a major subglacial trench (now infilled by later sediments) beneath the ice sheet west of Shrewsbury and leading towards the gorge. Large quantities of water under considerable pressure were able to then move uphill and over the pre-existing watershed east of Buildwas, powerfully eroding it in the process and giving rise to the modern gorge feature, possibly during multiple glacial phases. The deeply incised Marrington Dingle conveys the Camlad north from Churchstoke and originates as the outflow from a glacial lake in the Churchstoke/Snead area. The Plowden gorge permits the Onny to flow east around the southern end of the Long Mynd and was also initiated by meltwater.

Sediment-filled valleys are recorded from the Telford area, one of which, the Lightmoor Channel, runs southeast from Madeley on a line sub-parallel to that of the Severn gorge. Another, the Oakengates Channel, approximates the line of the A442 immediately northeast of the town centre whilst a third, the Shifnal Channel, runs beneath the course of the Wesley Brook south from Shifnal.

During deglaciation, ice masses often wasted away in situ to leave kettle holes, some of which remain today as part of the county's population of meres; there is a notable assemblage in the Ellesmere area. One kettle hole unearthed during gravel extraction at Condover in 1986 yielded numerous bones of a woolly mammoth.

Landslips
There are numerous landslips recorded within the Ironbridge gorge and further downstream around Apley Forge and along parts of the Borley Brook, near Highley. Also within Clun Forest.

Alluvium
River silt, sands and gravels (termed alluvium) occupy the floodplains of the major Shropshire rivers with especially widespread floodplains around the confluence of the Vyrnwy with the Severn on the county's western margins and downstream of Shrewsbury. Multiple terraces are developed within the valley of the Severn and that of the Worfe which joins it north of Bridgnorth.

Such is the interest in the geology of Shropshire that the British Geological Survey devote six (of nearly 50 in total) of their 'Classical Areas' 1:25,000 scale geological map sheets to coverage of parts of the county.