The Ludlow Group are

geologic formations A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

deposited during the

Ludlow epoch In the geological timescale, the Ludlow Epoch (from 427.4 ± 0.5 million years ago to 423.0 ± 2.3 million years ago) occurred during the Silurian Period, after the end of the Homerian Age. It is named for the town of Ludlow in Shropshire, Engl ...

of the

Silurian period The Silurian ( ) is a geologic period and system spanning 23.5 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 third and shortest period of t ...

in the

British Isles The British Isles are an archipelago in the Atlantic Ocean, North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner Hebrides, Inner and Outer Hebr ...

, in areas of

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

Ireland Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

, and

Wales Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...

Formations

This group contains the following formations in descending order: # Tilestones Formation, Downton Castle Sandstone formation (90 ft./27.7 m), # Ledbury Formation

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

s 270 ft./83 m), # Upper Ludlow sub-group formation (140 ft./43 m), # Aymestry Limestone Formation (up to 40 ft./12.3 m), # Lower Ludlow sub-group formation (350 to 780 ft./108 m-240 m).

Geology

The Ludlow group is essentially shaly in character, except towards the top, where the beds become more

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

y and pass gradually into the Old Red Sandstone. The Aymestry

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

, which is irregular in thickness, is sometimes absent, and where the underlying Wenlock limestones are absent the shales of the Ludlow group graduate, downwards into the Wenlock shales. In

the group is typically developed between namesake

Ludlow Ludlow ( ) is a market town and civil parish in Shropshire (district), Shropshire, England. It is located south of Shrewsbury and north of Hereford, on the A49 road (Great Britain), A49 road which bypasses the town. The town is near the conf ...

and

Aymestrey Aymestrey ( ) is a village and civil parish in north-western Herefordshire, England. The population of this civil parish, including the hamlet of Yatton, Aymestrey, Yatton, at the United Kingdom Census 2011, 2011 Census was 351. Location It ...

, and it occurs also in the detached Silurian areas between

Dudley Dudley ( , ) is a market town in the West Midlands, England, southeast of Wolverhampton and northwest of Birmingham. Historically part of Worcestershire, the town is the administrative centre of the Metropolitan Borough of Dudley. In the ...

and the mouth of the

Severn The River Severn (, ), at long, is the longest river in Great Britain. It is also the river with the most voluminous flow of water by far in all of England and Wales, with an average flow rate of at Apperley, Gloucestershire. It rises in t ...

. In the

Lake District The Lake District, also known as ''the Lakes'' or ''Lakeland'', is a mountainous region and National parks of the United Kingdom, national park in Cumbria, North West England. It is famous for its landscape, including its lakes, coast, and mou ...

the Silurian Coldwell beds, forming the upper part of the Coniston Flags, are the equivalents of the Lower Ludlow. They are succeeded by the Coniston Grits (4,000 ft./1,230 m), the Bannisdale Slates (5200 ft./1,600 m) and the Kirkby Moor Flags (2,000 ft./615 m). In the Silurian areas of southern

, the Ludlow rocks are represented in the

Kirkcudbright Kirkcudbright ( ; ) is a town at the mouth of the River Dee, Galloway, River Dee in Dumfries and Galloway, Scotland, southwest of Castle Douglas and Dalbeattie. A former royal burgh, it is the traditional county town of Kirkcudbrightshire. His ...

Shore and

Riccarton Riccarton may refer to: New Zealand * Riccarton, New Zealand, a suburb of Christchurch ** Riccarton (New Zealand electorate), the electorate named after it ** The location of Riccarton Race Course * a locality on the Taieri Plains in Otago Scot ...

districts by the Raeberry Castle Beds and Balmae Grits (500–750 ft.). In the northern belt within Lanarkshire and the

Pentland Hills The Pentland Hills are a range of hills southwest of Edinburgh, Scotland. The range is around in length, and runs southwest from Edinburgh towards Biggar and the upper Clydesdale. Etymology The hills take their name from the hamlet of Pe ...

, the Lower Ludlow portion consists of mudstones, flaggy shales, and greywackes; and the upper Downton Castle Sandstone part is made up principally of thick red and yellow sandstones and conglomerates with green mudstones. The Ludlow Group formations of Ireland include the Salrock beds of

County Galway County Galway ( ; ) is a Counties of Ireland, county in Republic of Ireland, Ireland. It is in the Northern and Western Region, taking up the south of the Provinces of Ireland, province of Connacht. The county population was 276,451 at the 20 ...

, and the Croagmarhin beds of

Dingle Peninsula The Dingle Peninsula (; anglicised as Corkaguiny or Corcaguiny, the name of the corresponding barony) is the northernmost of the major peninsulas in County Kerry. It ends beyond the town of Dingle at Dunmore Head, the westernmost point of m ...

County Kerry County Kerry () is a Counties of Ireland, county on the southwest coast of Republic of Ireland, Ireland, within the Provinces of Ireland, province of Munster and the Southern Region, Ireland, Southern Region. It is bordered by two other countie ...

Lower Ludlow sub-group

The Lower Ludlow rocks are mainly grey, greenish and brown

mudstone 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.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

s and sandy and

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

shales. They contain an abundance of

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 preserve ...

s. The Lower Ludlow series has been zoned by means of ''

Monograptus ''Monograptus'' is a genus of graptolites in the order Graptoloidea. This particular genus is the last stage of the graptoloid evolution before its extinction in the early Devonian. A characteristic of the genus includes one uniserial stipes ...

'' species of

Graptolites Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian (Miaolingian, Wuliuan) through th ...

by E. M. R. Wood. The zonal forms in order from older/lower to younger/upper are: ''Monograptus vulgaris''; ''Monograptus nilssoni''; ''Monograptus scanicus''; ''Monograptus tumescens''; and ''Monograptus leintwardinensis''. In

Denbighshire Denbighshire ( ; ) is a county in the north-east of Wales. It borders the Irish Sea to the north, Flintshire to the east, Wrexham to the southeast, Powys to the south, and Gwynedd and Conwy to the west. Rhyl is the largest town, and Ruthi ...

and

Merionethshire Merionethshire, or Merioneth ( or '), was Historic counties of Wales, one of the thirteen counties of Wales that existed from 1536 until their abolishment in 1974. It was located in the North West Wales, north-west of Wales. Name 'Merioneth' is a ...

the upper portion of the Denbighshire Grits belongs to this horizon. Those from lower to upper are: the Nantglyn Flags; the Upper Grit beds; the ''Monograptus leintwardinensis'' beds; and the Dinas Bran beds. ;Lower Ludlow fossils '' Cyathaspis ludensis'', the earliest British

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

fossil, was found in these rocks at

Leintwardine Leintwardine ( ) is a small to mid-size village and civil parish in north Herefordshire, England, close to the border with Shropshire. History Roman A popular misconception is that the Romans called the village ''Branogenium''. Branogenium i ...

Herefordshire Herefordshire ( ) is a Ceremonial counties of England, ceremonial county in the West Midlands (region), West Midlands of England, bordered by Shropshire to the north, Worcestershire to the east, Gloucestershire to the south-east, and the Welsh ...

, a noted fossil locality.

Trilobites Trilobites (; meaning "three-lobed entities") are extinct marine arthropods that form the class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, ...

are numerous (''Phacops caudatus'', ''Lichas anglicus'', ''Homolonotus delphinocephalus'', ''Calymene Blumenbachii'');

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s (''Leptaena rhomboidalis'', ''Rhynchonella Wilsoni'', ''Atrypa reticularis''),

pelecypod Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

s (''Cardiola interrupts'', ''Ctenodonta sulcata'') and

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

s and

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s (many species of Orthoceras and also Gomphoceras, Trochoceras) are well represented. Other fossils are ''Ceratiocaris'', ''Pterygotus'', ''Protaster'', ''Palaeocoma'' and ''Palaeodiscus''.

Upper Ludlow sub-group

The Upper Ludlow sub-group rocks are mainly soft mudstones and shales with some harder sandy beds capable of being worked as building-stones. These sandy beds are often found covered with ripple-marks and

annelid The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to vario ...

tracks. One of the uppermost sandy layers is known as the " Fucoid bed " from the abundance of the seaweed-like impressions it bears. At the top of this sub-group a brown layer occurs, from a quarter of an inch to 4 in. (63 mm to 100 mm) in thickness, full of the fragmentary remains of fish associated with those of '' Pterygotus'' and

mollusca Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

. This layer, known as the "Ludlow Bone bed," has been traced over a very large area. The Tilestones, Downton Castle Sandstone, and Ledbury Formation shales are occasionally grouped together under the term Downtonian. They are in reality passage beds between the Silurian and

Old Red Sandstone Old Red Sandstone, abbreviated ORS, is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the eastern seaboard of North America. It ...

, and were originally placed in the latter system by Sir

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

. They are mostly grey, yellow or red micaceous, shaly sandstones. ;Upper Ludlow fossils The common Upper Ludlow fossils include: plants (Actinophyllum, Chondrites),

ostracods Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant) have been identified,Brandão, S.N.; Antonietto, L.S; Nery, D.G.; Santos, S.G.; Karano ...

, phyllocarids,

eurypterids Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 million years ago. The ...

; trilobites (less common than in the older Ludlow sub-groups); numerous brachiopods ('' Lingula cornea'', ''Lingula minima'', ''

Chonetes ''Chonetes'' is an extinct genus of brachiopods. It ranged from the Late Ordovician to the Middle Jurassic. Species The following species of ''Chonetes'' have been described: * ''C. (Paeckelmannia)'' * ''C. baragwanathi'' * ''C. billingsi' ...

striatella''); crustaceans (

ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...

s);

s (

Phyllocarida Phyllocarida is a subclass of crustaceans, comprising the extant order Leptostraca and the extinct orders Hymenostraca and Archaeostraca. This clade of marine crustaceans diversified extensively during the Ordovician. See also *'' Ceratiocari ...

, ''Platyschisma helicites'');

bivalvia Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

; and cephalopods (''Orthoceras bullatum''); and fish (Cephalaspis, Cyathaspis, Auchenaspis).

References

*{{EB1911 , wstitle=Ludlow Group , volume=17 , page=113 Geologic formations of the United Kingdom Geological groups of the United Kingdom Geologic groups of Europe Ludlow epoch Geologic formations of England Geologic formations of Ireland Geology of Scotland Geology of Wales Silurian United Kingdom Silurian England Silurian Ireland Silurian Scotland Silurian Wales Silurian System of Europe