The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the northeastern seaboard of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. It also extends northwards into

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...

and

Svalbard Svalbard ( , ), also known as Spitsbergen, or Spitzbergen, is a Norwegian archipelago in the Arctic Ocean. North of mainland Europe, it is about midway between the northern coast of Norway and the North Pole. The islands of the group range ...

. These areas were a part of the ancient

continent A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...

of Euramerica/Laurussia. In Britain it is a

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geology, geological science associated with the study of stratum, strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are ...

unit (a sequence of

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

) to which stratigraphers accord

supergroup Supergroup or super group may refer to: * Supergroup (music), a music group formed by artists who are already notable or respected in their fields * Supergroup (physics), a generalization of groups, used in the study of supersymmetry * Supergroup ...

status and which is of considerable importance to early

paleontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

. For convenience the short version of the term, ORS is often used in literature on the subject. The term was coined to distinguish the sequence from the younger

New Red Sandstone The New Red Sandstone, chiefly in British geology, is composed of beds of red sandstone and associated rocks laid down throughout the Permian (300 million years ago) to the end of the Triassic (about 200 million years ago), that under ...

which also occurs widely throughout Britain.

Sedimentology

The Old Red Sandstone describes a suite of

sedimentary Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...

rocks deposited in a variety of environments during the

but extending back into the late

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

and on into the earliest part of the

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

. The body of

rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...

, or

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

, is dominated by

alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

s and conglomerates at its base, and progresses to a combination of

dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

s and

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

sediments. The familiar red colour of these rocks arises from the presence of

iron oxide Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...

but not all the Old Red Sandstone is red or sandstone — the sequence also includes conglomerates,

mudstones Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' ...

siltstones Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

and thin

limestones Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms when th ...

and colours can range from grey and green through to red and purple. These deposits are closely associated with the erosion of the Caledonian Mountain chain which was thrown up by the collision of the former continents of

Avalonia Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent underlie south-west Great Britain, southern Ireland, and the eastern coast of North America. It is the source of many of the older rocks of Wester ...

Baltica Baltica is a paleocontinent that formed in the Paleoproterozoic and now constitutes northwestern Eurasia, or Europe north of the Trans-European Suture Zone and west of the Ural Mountains. The thick core of Baltica, the East European Craton, is mo ...

and

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although ...

to form the

Old Red Sandstone Continent Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

- an event known as the

Caledonian Orogeny The Caledonian orogeny was a mountain-building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occ ...

. Many fossils are found within the rocks, including early fishes, arthropods and plants. As is typical with terrestrial

red beds Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain ...

, the vast majority of the rock is unfossiliferous; however there are isolated, localized beds within the rock that do contain fossils. Rocks of this age were also laid down in

South West England South West England, or the South West of England, is one of nine official regions of England. It consists of the counties of Bristol, Cornwall (including the Isles of Scilly), Dorset, Devon, Gloucestershire, Somerset and Wiltshire. Cities and ...

(hence the name 'Devonian'; from

Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon is ...

) though these are of true marine origin and are not included within the Old Red Sandstone.

Stratigraphy

Since the Old Red Sandstone consists predominantly of rocks of

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

origin, it does not generally contain marine

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s which would otherwise prove useful in correlating one occurrence of the rock with another, both between and within individual

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subsidence ...

s. Accordingly, local

stage Stage or stages may refer to: Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly British theatre newspaper * Sta ...

names were devised and these remain in use to some extent today though there is an increasing use of international stage names. Thus in the Anglo-Welsh Basin, there are frequent references to the Downtonian, Dittonian, Breconian and Farlovian stages in the literature. The existence of a number of distinct sedimentary basins throughout Britain has been established.

Orcadian Basin

The

Orcadian Basin The Orcadian Basin is a sedimentary basin of Devonian age that formed mainly as a result of extensional tectonics in northeastern Scotland after the end of the Caledonian orogeny. During part of its history, the basin was filled by a lake now know ...

extends over a wide area of North East Scotland and the neighbouring seas. It encompasses the

Moray Firth The Moray Firth (; Scottish Gaelic: ''An Cuan Moireach'', ''Linne Mhoireibh'' or ''Caolas Mhoireibh'') is a roughly triangular inlet (or firth) of the North Sea, north and east of Inverness, which is in the Highland council area of north of Scotl ...

and adjoining land areas, Caithness, Orkney and parts of

Shetland Shetland, also called the Shetland Islands and formerly Zetland, is a subarctic archipelago in Scotland lying between Orkney, the Faroe Islands and Norway. It is the northernmost region of the United Kingdom. The islands lie about to the no ...

. South of the Moray Firth, two distinct sub-basins are recognised at

Turriff Turriff () is a town and civil parish in Aberdeenshire in Scotland. It lies on the River Deveron, about above sea level, and has a population of 5,708. In everyday speech it is often referred to by its Scots name ''Turra'', which is derived f ...

and at Rhynie. The sequence is more than thick in parts of Shetland. The main basin is considered to be an intramontane basin resulting from crustal rifting associated with post-Caledonian

extension Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (predicate logic), the set of tuples of values that satisfy the predicate * E ...

, possibly accompanied by strike-slip faulting along the

Great Glen Fault The Great Glen Fault is a strike-slip fault that runs through the Great Glen in Scotland. The fault is mostly inactive today, but occasional moderate tremors have been recorded over the past 150 years. Location Aligned northeast to southwest, t ...

system.

Argyll

There are a scatter of exposures of the Old Red Sandstone around

Oban Oban ( ; ' in Scottish Gaelic meaning ''The Little Bay'') is a resort town within the Argyll and Bute council area of Scotland. Despite its small size, it is the largest town between Helensburgh and Fort William. During the tourist season, th ...

and the Isle of Kerrera on the

West Highland The Highlands ( sco, the Hielands; gd, a’ Ghàidhealtachd , 'the place of the Gaels') is a historical region of Scotland. Culturally, the Highlands and the Lowlands diverged from the Late Middle Ages into the modern period, when Lowland Sco ...

coast, this unit is sometimes referred to as the Kerrera Sandstone Formation. The unit is up to 128m thick in its type area and consists of green and red sandstones and conglomerates, typically containing large ( across) elliptical well rounded clasts, accompanied by siltstones, mudstones and limestones. On Kerrera a conglomerate of

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomi ...

boulders rests unconformably on

Dalradian The Dalradian Supergroup (informally and traditionally the Dalradian) is a stratigraphic unit (a sequence of rock strata) in the lithostratigraphy of the Grampian Highlands of Scotland and in the north and west of Ireland. The diverse assembla ...

black, pyritic

slate Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. ...

s (

Easdale Easdale ( gd, Eilean Èisdeal) is one of the Slate Islands, in the Firth of Lorn, Scotland. Once the centre of the Scottish slate industry, there has been some recent island regeneration by the owners. This is the smallest of the Inner Hebrides' i ...

Slate) of the Easdale Subgroup. On Oban there is merely an erosional contact incorporating debris of the slate in a basal conglomerate. The ORS around Oban are considered latest

( Pridoli) to earliest Devonian in age. They are interpreted as

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...

s which filled a depositional basin from the east and northeast. Small

outliers In statistics, an outlier is a data point that differs significantly from other observations. An outlier may be due to a variability in the measurement, an indication of novel data, or it may be the result of experimental error; the latter are ...

occur near

Taynuilt Taynuilt (; , meaning 'the house by the stream') is a large village in Argyll and Bute, Scotland located at the western entrance to the narrow Pass of Brander. Location The village is situated on the River Nant about a kilometre before the rive ...

and either side of

Loch Avich Loch of Avich is a large freshwater loch that lies approximately west of Loch Awe in Argyll and Bute in Scotland. It is the second biggest loch in the Etive basin after Loch Awe. It trends east-northeast, west-southwest and is narrowly triangul ...

. The deposits are especially obvious on

Kerrera Kerrera (; gd, Cearara or ''Cearrara'') is an island in the Scottish Inner Hebrides, close to the town of Oban. In 2016 it had a population of 45, divided into two communities in the north and south of the island. Geology The oldest bedrock ...

where they form the bedrock across half of the island. These are conformably overlain by

peperite A peperite is a type of volcaniclastic rock consisting of sedimentary rock that contains fragments of younger igneous material and is formed when magma comes into contact with wet sediments. The term was originally used to describe rocks from th ...

and the

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic and

andesitic Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

Lorne plateau lavas The Lorne plateau lavas are basaltic lava flows extruded in the late Silurian, 424 to 415 million years ago, which are found today in the Oban - Kerrera area of Scotland. Peperite occurs where they flowed into Old Red Sandstone The Old Red S ...

. The ORS on Kerrera and isolated localities around Oban are known for their fossils, particularly fish. Gardenstown Old Red Sandstone - geograph

Midland Valley of Scotland

The Midland Valley

graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...

defined by the

Highland Boundary Fault The Highland Boundary Fault is a major fault zone that traverses Scotland from Arran and Helensburgh on the west coast to Stonehaven in the east. It separates two different geological terranes which give rise to two distinct physiographic terr ...

in the north and the

Southern Uplands Fault The Southern Uplands Fault (or occasionally Southern Upland Fault) is a fault in Scotland that runs from Girvan (or more specifically from the Rhins of Galloway) to Dunbar on the East coast. It marks the southern boundary of the Scottish Midland ...

in the south harbours not only a considerable amount of Old Red Sandstone sedimentary rocks but also igneous rocks of this age associated with extensive

volcanism Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called ...

. There is a continuous outcrop along the Highland Boundary Fault from

Stonehaven Stonehaven ( , ) is a town in Scotland. It lies on Scotland's northeast coast and had a population of 11,602 at the 2011 Census. After the demise of the town of Kincardine, which was gradually abandoned after the destruction of its royal cast ...

on the

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...

coast to

Helensburgh Helensburgh (; gd, Baile Eilidh) is an affluent coastal town on the north side of the Firth of Clyde in Scotland, situated at the mouth of the Gareloch. Historically in Dunbartonshire, it became part of Argyll and Bute following local governm ...

and beyond to Arran. A more disconnected series of outcrops occur along the line of the Southern Uplands Fault from

Edinburgh Edinburgh ( ; gd, Dùn Èideann ) is the capital city of Scotland and one of its 32 Council areas of Scotland, council areas. Historically part of the county of Midlothian (interchangeably Edinburghshire before 1921), it is located in Lothian ...

Girvan Girvan ( gd, Inbhir Gharbhain, "mouth of the River Girvan") is a burgh and harbour town in Carrick, South Ayrshire, Scotland. Girvan is situated on the east coast of the Firth of Clyde, with a population of about 6,450. It lies south of Ayr, ...

. Old Red Sandstone often occurs in conjunction with conglomerate formations, one such noteworthy

cliff In geography and geology, a cliff is an area of rock which has a general angle defined by the vertical, or nearly vertical. Cliffs are formed by the processes of weathering and erosion, with the effect of gravity. Cliffs are common on co ...

side exposure being the Fowlsheugh Nature Reserve,

Kincardineshire Kincardineshire, also known as the Mearns (from the Scottish Gaelic meaning "the Stewartry"), is a historic county, registration county and lieutenancy area on the coast of northeast Scotland. It is bounded by Aberdeenshire on the north and w ...

Scottish borders

A series of outcrops occur from

East Lothian East Lothian (; sco, East Lowden; gd, Lodainn an Ear) is one of the 32 council areas of Scotland, as well as a historic county, registration county and lieutenancy area. The county was called Haddingtonshire until 1921. In 1975, the histo ...

southwards through

Berwickshire Berwickshire ( gd, Siorrachd Bhearaig) is a historic county, registration county and lieutenancy area in south-eastern Scotland, on the English border. Berwickshire County Council existed from 1890 until 1975, when the area became part of th ...

. Hutton's famous unconformity at Siccar Point occurs within this basin - see History of study below.

Anglo-Welsh Basin

This relatively large basin extends across much of South Wales from southern

Pembrokeshire Pembrokeshire ( ; cy, Sir Benfro ) is a Local government in Wales#Principal areas, county in the South West Wales, south-west of Wales. It is bordered by Carmarthenshire to the east, Ceredigion to the northeast, and the rest by sea. The count ...

in the west through

Carmarthenshire Carmarthenshire ( cy, Sir Gaerfyrddin; or informally ') is a county in the south-west of Wales. The three largest towns are Llanelli, Carmarthen and Ammanford. Carmarthen is the county town and administrative centre. The county is known as ...

into

Powys Powys (; ) is a Local government in Wales#Principal areas, county and Preserved counties of Wales, preserved county in Wales. It is named after the Kingdom of Powys which was a Welsh succession of states, successor state, petty kingdom and princi ...

and

Monmouthshire Monmouthshire ( cy, Sir Fynwy) is a county in the south-east of Wales. The name derives from the historic county of the same name; the modern county covers the eastern three-fifths of the historic county. The largest town is Abergavenny, with ...

and through the southern

Welsh Marches The Welsh Marches ( cy, Y Mers) is an imprecisely defined area along the border between England and Wales in the United Kingdom. The precise meaning of the term has varied at different periods. The English term Welsh March (in Medieval Latin ...

, notably into

Herefordshire Herefordshire () is a county in the West Midlands of England, governed by Herefordshire Council. It is bordered by Shropshire to the north, Worcestershire to the east, Gloucestershire to the south-east, and the Welsh counties of Monmouthshire ...

Worcestershire Worcestershire ( , ; written abbreviation: Worcs) is a county in the West Midlands of England. The area that is now Worcestershire was absorbed into the unified Kingdom of England in 927, at which time it was constituted as a county (see His ...

and

Gloucestershire Gloucestershire ( abbreviated Glos) is a county in South West England. The county comprises part of the Cotswold Hills, part of the flat fertile valley of the River Severn and the entire Forest of Dean. The county town is the city of Gl ...

. Outliers in

Somerset ( en, All The People of Somerset) , locator_map = , coordinates = , region = South West England , established_date = Ancient , established_by = , preceded_by = , origin = , lord_lieutenant_office =Lord Lieutenant of Somerset , lord_ ...

and north

complete the extent of this basin. With the exception of south Pembrokeshire, all parts of the basin are represented by a range of lithologies assigned to the Lower Devonian and to the Upper Devonian, the contact between the two being unconformable and representing the complete omission of any Middle Devonian sequence. The lowermost formations are of upper Silurian age, these being the Downton Castle Sandstone Formation and the overlying Raglan Mudstone Formation except in Pembrokeshire where a more complex series of formations is recognised. In the east of the basin, the top of the Raglan Mudstone is marked by a well-developed

calcrete Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions, ...

, the Bishop's Frome Limestone. The lowermost Devonian formation is the St Maughans Formation, itself overlain by the Brownstones Formation though with an intervening Senni Formation over much of the area. The Upper Devonian sequence is rather thinner and comprises a series of formations which are more laterally restricted. In the Brecon Beacons, the Plateau Beds Formation is unconformably overlain by the Grey Grits Formation though further east these divisions are replaced by the Quartz Conglomerate Group which is itself subdivided into a variety of different formations. Yensaby castle 1

Pembrokeshire

The sequence in Pembrokeshire differs from that of the main part of the basin and falls into two parts. In North Pembrokeshire to the north of the Ritec Fault, both the middle and upper ORS are missing with only the lower ORS present; this is divided into an earlier Milford Haven Group comprising in ascending order, the Red Cliff, Sandy Haven and Gelliswick Bay formations and a later

Cosheston Group The Cosheston Group is an early Devonian lithostratigraphy, lithostratigraphic group (stratigraphy), group (a sequence of rock strata) in west Wales. The name is derived from the village of Cosheston in south Pembrokeshire. The Group comprises (i ...

with, again in ascending order, its constituent Llanstadwell, Burton Cliff, Mill Bay, Lawrenny Cliff and New Shipping formations. These respectively equate with the Temeside, Raglan Mudstone and St Maughans formations of the central and eastern part of the basin. *''- middle and upper ORS missing -'' *

** New Shipping Formation ** Lawrenny Cliff Formation ** Mill Bay Formation ** Burton Cliff Formation ** Llanstadwell Formation * Milford Haven Group ** Gelliswick Bay Formation ** Sandy Haven Formation (inc. Townsend Tuff Beds) **

Albion Sands Formation Albion is an alternative name for Great Britain. The oldest attestation of the toponym comes from the Greek language. It is sometimes used poetically and generally to refer to the island, but is less common than 'Britain' today. The name for Scot ...

/ Lindsway Bay Formation ** Red Cliff Formation In south Pembrokeshire to the south of the Ritec Fault, the lower ORS is represented by, in ascending order, the Freshwater East, Moors Cliff and Freshwater West formations. These are

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

overlain by the Ridgeway Conglomerate Formation. The middle ORS is missing whilst the Upper ORS is represented by the Gupton and West Angle formations. * Skrinkle Sandstone Group **

West Angle Formation West or Occident is one of the four cardinal directions or points of the compass. It is the opposite direction from east and is the direction in which the Sun sets on the Earth. Etymology The word "west" is a Germanic word passed into some ...

** Gupton Formation * ''- part of middle ORS missing -'' * Ridgeway Conglomerate Formation * ''- part of middle ORS missing -'' * Milford Haven Group ** Freshwater West Formation (inc. Rat Island Mudstone Member and Conigar Pit Sandstone Member) **

Moor Cliffs Formation Moor or Moors may refer to: Nature and ecology * Moorland, a habitat characterized by low-growing vegetation and acidic soils. Ethnic and religious groups * Moors, Muslim inhabitants of the Maghreb, Iberian Peninsula, Sicily, and Malta during ...

(inc. Chapel point calcretes member and Townsend Tuff Bed) **

Freshwater East Formation Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

The Freshwater East Formation, and corresponding Red Cliff Formation of north Pembrokeshire, are both late Silurian in age.

Anglesey

A small and separate basin exists here where both

and

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

deposits are recorded. Both the middle and upper ORS are missing but the lower ORS is represented, in ascending order, by the Bodafon, Traeth Bach, Porth y Mor and Traeth Lligwy formations.

Calcrete Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions, ...

s are also recorded representing carbonate-rich soils developed between periods of sediment deposition. The present day outcrop occupies a narrow zone from

Dulas Bay Dulas Bay (Welsh: ''Bae Dulas'') is a small bay on the north east coast of Anglesey (''Ynys Môn''), north Wales, forming the boundary between Llaneilian and Moelfre communities. The bay is bordered by three beaches. Overview The north-western ...

on Anglesey's northeast coast, southwards to the town of

Llangefni Llangefni (meaning "church on the River Cefni", ) is the county town of Anglesey in Wales and contains the principal offices of the Isle of Anglesey County Council. United Kingdom Census 2011 recorded Llangefni's population as 5,116 people, maki ...

History of study

In 1787

James Hutton James Hutton (; 3 June O.S.172614 June 1726 New Style. – 26 March 1797) was a Scottish geologist, agriculturalist, chemical manufacturer, naturalist and physician. Often referred to as the father of modern geology, he played a key role i ...

noted what is now known as

Hutton's Unconformity Hutton's Unconformity is a name given to various notable geological sites in Scotland identified by the 18th-century Scottish geologist James Hutton as places where the junction between two types of rock formations can be seen. This geological ph ...

at Inchbonny,

Jedburgh Jedburgh (; gd, Deadard; sco, Jeddart or ) is a town and former royal burgh in the Scottish Borders and the traditional county town of the historic county of Roxburghshire, the name of which was randomly chosen for Operation Jedburgh in su ...

, and in early 1788 he set off with

John Playfair John Playfair FRSE, FRS (10 March 1748 – 20 July 1819) was a Church of Scotland minister, remembered as a scientist and mathematician, and a professor of natural philosophy at the University of Edinburgh. He is best known for his book ''Illu ...

to the

coast and found more examples of this sequence in the valleys of the Tower and Pease Burns near

Cockburnspath Cockburnspath ( ; sco, Co’path) is a village in the Scottish Borders area of Scotland. It lies near the North Sea coast between Berwick-upon-Tweed and Edinburgh. It is at the eastern extremity of the Southern Upland Way a long-distance footpa ...

. They then took a boat trip from Dunglass Burn east along the coast with the geologist Sir James Hall of

Dunglass Dunglass is a hamlet in East Lothian, Scotland, lying east of the Lammermuir Hills on the North Sea coast, within the parish of Oldhamstocks. It has a 15th-century collegiate church, now in the care of Historic Scotland. Dunglass is the birthpla ...

and at

Siccar Point Siccar Point is a rocky promontory in the county of Berwickshire on the east coast of Scotland. It is famous in the history of geology for Hutton's Unconformity found in 1788, which James Hutton regarded as conclusive proof of his uniformitar ...

found what Hutton called "a beautiful picture of this junction washed bare by the sea", where 345-million-year-old Old Red Sandstone overlies 425-million-year-old

greywacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...

. In the early 19th century, the paleontology of the formation was studied intensively by

Hugh Miller Hugh Miller (10 October 1802 – 23/24 December 1856) was a self-taught Scottish geologist and writer, folklorist and an evangelical Christian. Life and work Miller was born in Cromarty, the first of three children of Harriet Wright ('' ...

Henry Thomas De la Beche Sir Henry Thomas De la Beche Knight Commander of the Order of the Bath, KCB, Fellow of the Royal Society, FRS (10 February 179613 April 1855) was an English geologist and palaeontologist, the first director of the Geological Survey of Great Bri ...

Roderick Murchison Sir Roderick Impey Murchison, 1st Baronet, (19 February 1792 – 22 October 1871) was a Scotland, Scottish geologist who served as director-general of the British Geological Survey from 1855 until his death in 1871. He is noted for investigat ...

, and

Adam Sedgwick Adam Sedgwick (; 22 March 1785 – 27 January 1873) was a British geologist and Anglican priest, one of the founders of modern geology. He proposed the Cambrian and Devonian period of the geological timescale. Based on work which he did on W ...

—Sedgwick's interpretation was the one that placed it in the

: he coined the name of that period. The term 'Old Red Sandstone' was originally used in 1821 by Scottish naturalist and

mineralogist Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...

Robert Jameson Robert Jameson Robert Jameson FRS FRSE (11 July 1774 – 19 April 1854) was a Scottish naturalist and mineralogist. As Regius Professor of Natural History at the University of Edinburgh for fifty years, developing his predecessor John ...

to refer to the red rocks which underlay the 'Mountain Limestone' i.e. the Carboniferous Limestone. They were thought at that time to be the British version of Germany's

Rotliegendes The Rotliegend, Rotliegend Group or Rotliegendes (german: the underlying red) is a lithostratigraphic unit (a sequence of rock strata) of latest Carboniferous to Guadalupian (middle Permian) age that is found in the subsurface of large areas in wes ...

, which is in fact of

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

age. Many of the

science Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence for ...

stratigraphy Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sedimentary and layered volcanic rocks. Stratigrap ...

's early debates were about the Old Red Sandstone. In older

geological Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...

works predating theories of

plate tectonics Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

, the United States'

Catskill Delta The Devonian Catskill Formation or the Catskill Clastic wedge is a unit of mostly terrestrial sedimentary rock found in Pennsylvania and New York. Minor marine layers exist in this thick rock unit (up to ). It is equivalent to the Hampshire Form ...

formation is sometimes referred to as part of the Old Red Sandstone. In the modern day it is recognized that the two are not stratigraphically continuous but are very similar due to being formed at approximately the same time by the same processes.

Use as a building stone

The Old Red Sandstone has been widely used as a building stone across those regions where it outcrops. Notable examples of its use can be found in the area surrounding

Stirling Stirling (; sco, Stirlin; gd, Sruighlea ) is a city in central Scotland, northeast of Glasgow and north-west of Edinburgh. The market town, surrounded by rich farmland, grew up connecting the royal citadel, the medieval old town with its me ...

Perth Perth is the capital and largest city of the Australian state of Western Australia. It is the fourth most populous city in Australia and Oceania, with a population of 2.1 million (80% of the state) living in Greater Perth in 2020. Perth is ...

and

Tayside Tayside ( gd, Taobh Tatha) was one of the nine regions used for local government in Scotland from 15 May 1975 to 31 March 1996. The region was named for the River Tay. It was created by the Local Government (Scotland) Act 1973, following recom ...

. The inhabitants of

Caithness Caithness ( gd, Gallaibh ; sco, Caitnes; non, Katanes) is a historic county, registration county and lieutenancy area of Scotland. Caithness has a land boundary with the historic county of Sutherland to the west and is otherwise bounded by ...

at the northeastern tip of Scotland also used the stone to a considerable extent. Old Red Sandstone has also frequently been used in buildings in

and the former

Brecknockshire , image_flag= , HQ= Brecon , Government= Brecknockshire County Council (1889-1974) , Origin= Brycheiniog , Status= , Start= 1535 , End= ...

(now south

) of south Wales.

Notable buildings

;Canada *

New York Life Insurance Building, Montreal Montreal's New York Life Insurance Building (also known as the Quebec Bank Building) is an office building at Place d'Armes in what is now known as Old Montreal, erected in 1887-1889. At the time of its completion, it was the tallest commercial b ...

;England *

Goodrich Castle Goodrich Castle is a Norman medieval castle ruin north of the village of Goodrich in Herefordshire, England, controlling a key location between Monmouth and Ross-on-Wye. It was praised by William Wordsworth as the "noblest ruin in Herefordshir ...

Ross-on-Wye Ross-on-Wye (Welsh: ''Rhosan ar Wy'') is a market town in England, near the border with Wales. It had a population of 10,582 according to the 2011 census, estimated at 11,309 in 2019. It lies in south-eastern Herefordshire, on the River Wye and ...

market hall,

Shrewsbury Castle Shrewsbury Castle is a red sandstone castle in Shrewsbury, Shropshire, England. It stands on a hill in the neck of the meander of the River Severn on which the town originally developed. The castle, directly above Shrewsbury railway station, is a ...

Shropshire Shropshire (; alternatively Salop; abbreviated in print only as Shrops; demonym Salopian ) is a landlocked historic county in the West Midlands region of England. It is bordered by Wales to the west and the English counties of Cheshire to th ...

Hereford Cathedral Hereford Cathedral is the cathedral church of the Anglican Diocese of Hereford in Hereford, England. A place of worship has existed on the site of the present building since the 8th century or earlier. The present building was begun in 1079. S ...

;Scotland *

Arbroath Abbey Arbroath Abbey, in the Scottish town of Arbroath, was founded in 1178 by King William the Lion for a group of Tironensian Benedictine monks from Kelso Abbey. It was consecrated in 1197 with a dedication to the deceased Saint Thomas Becket, who ...

Angus Angus may refer to: Media * ''Angus'' (film), a 1995 film * ''Angus Og'' (comics), in the ''Daily Record'' Places Australia * Angus, New South Wales Canada * Angus, Ontario, a community in Essa, Ontario * East Angus, Quebec Scotland * An ...

Muchalls Castle Muchalls Castle stands overlooking the North Sea in the countryside of Kincardine and Mearns, Aberdeenshire, Scotland. The lower course is a well-preserved Romanesque, double-groined 13th-century tower house structure, built by the Frasers of ...

Aberdeenshire Aberdeenshire ( sco, Aiberdeenshire; gd, Siorrachd Obar Dheathain) is one of the 32 Subdivisions of Scotland#council areas of Scotland, council areas of Scotland. It takes its name from the County of Aberdeen which has substantially differe ...

St Magnus Cathedral St Magnus Cathedral dominates the skyline of Kirkwall, the main town of Orkney, a group of islands off the north coast of mainland Scotland. It is the most northerly cathedral in the United Kingdom, a fine example of Romanesque architecture built ...

Orkney Orkney (; sco, Orkney; on, Orkneyjar; nrn, Orknøjar), also known as the Orkney Islands, is an archipelago in the Northern Isles of Scotland, situated off the north coast of the island of Great Britain. Orkney is 10 miles (16 km) north ...

Stonehaven Tolbooth The Stonehaven Tolbooth is a late 16th-century stone building originally used as a courthouse and a prison in the town of Stonehaven, Aberdeenshire, Scotland. Constructed of local Old Red Sandstone, the prison probably attained its greatest not ...

;Wales *

Raglan Castle Raglan Castle ( cy, Castell Rhaglan) is a late medieval castle located just north of the village of Raglan in the county of Monmouthshire in south east Wales. The modern castle dates from between the 15th and early 17th centuries, when the succ ...

Tintern Abbey Tintern Abbey ( cy, Abaty Tyndyrn ) was founded on 9 May 1131 by Walter de Clare, Lord of Chepstow. It is situated adjacent to the village of Tintern in Monmouthshire, on the Welsh bank of the River Wye, which at this location forms the bor ...

http://www.museumwales.ac.uk/media/4/9/5/2/Newsletter_5.pdf *

Brecon Cathedral Brecon Cathedral ( cy, Eglwys Gadeiriol Aberhonddu), in the town of Brecon, Powys, is the cathedral of the Diocese of Swansea and Brecon in the Church in Wales and seat of the Bishop of Swansea and Brecon. Previously the church of Brecon Priory ...

References

External links

{{commons category, Old Red Sandstone
Cawdor Castle — built from Old Red Sandstone
Geologic groups of Europe Geologic groups of North America Geologic formations of Canada Geologic formations of Greenland Geologic formations of Ireland Geologic formations of Norway Geologic formations of the United Kingdom Geologic formations of the United States Carboniferous paleontological sites Carboniferous System of Europe Devonian System of Europe Silurian System of North America Devonian System of North America Carboniferous System of North America Silurian paleontological sites Devonian Canada Devonian England Devonian Ireland Devonian Greenland Devonian Norway Devonian Scotland Devonian United Kingdom Devonian United States Silurian Canada Silurian England Silurian Ireland Silurian Greenland Silurian Norway Silurian Scotland Silurian United Kingdom Silurian United States Carboniferous England Carboniferous Norway Carboniferous Scotland Carboniferous United Kingdom Sandstone formations Conglomerate formations Limestone formations Mudstone formations Shale formations Siltstone formations Geologic formations with imbedded sand dunes Aeolian deposits Fluvial deposits Lacustrine deposits Fossiliferous stratigraphic units of Europe Fossiliferous stratigraphic units of North America Paleontology in Canada Paleontology in England Paleontology in Ireland Paleontology in Greenland Paleontology in Norway Paleontology in the United Kingdom Paleontology in the United States