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, England ...

of the

Silurian period 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 ...

in the

British Isles The British Isles are a group of islands in the 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 and Outer Hebrides, the Northern Isles, ...

, in areas of

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

, and

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

Formations

This group contains the following formations in descending order: # Tilestones Formation,

Downton Castle Sandstone The Downton Castle Sandstone is a geologic formation in England. It preserves fossils dating back to the Silurian period. As its name would suggest the formation predominantly consists of sandstone with minor siltstone and mudstone. The oldest kn ...

formation (90 ft./27.7 m), #

Ledbury Formation The Ledbury Formation is a geologic formation in Herefordshire, England. The shale formation preserves fossils dating back to the Silurian period. See also * List of fossiliferous stratigraphic units in England See also *Lists of fossi ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

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 defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...

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

limestone 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 whe ...

, 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 in Shropshire, England. The town is significant in the history of the Welsh Marches and in relation to Wales. It is located south of Shrewsbury and north of Hereford, on the A49 road which bypasses the town. The t ...

and Aymestrey, and it occurs also in the detached Silurian areas between

Dudley Dudley is a large market town and administrative centre in the county of West Midlands, England, southeast of Wolverhampton and northwest of Birmingham. Historically an exclave of Worcestershire, the town is the administrative centre of the ...

and the mouth of the

Severn , name_etymology = , image = SevernFromCastleCB.JPG , image_size = 288 , image_caption = The river seen from Shrewsbury Castle , map = RiverSevernMap.jpg , map_size = 288 , map_c ...

. In the

Lake District The Lake District, also known as the Lakes or Lakeland, is a mountainous region in North West England. A popular holiday destination, it is famous for its lakes, forests, and mountains (or ''fells''), and its associations with William Wordswor ...

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 ( ; sco, Kirkcoubrie; gd, Cille Chùithbeirt) is a town, parish and a Royal Burgh from 1455 in Kirkcudbrightshire, of which it is traditionally the county town, within Dumfries and Galloway, Scotland. The town lies southwest of C ...

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 Scotlan ...

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 name is first recorded for the farm of Pentlan ...

, 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 "Righteousness and Justice" , anthem = () , image_map = Island of Ireland location map Galway.svg , map_caption = Location in Ireland , area_footnotes = , area_total_km2 = ...

, and the Croagmarhin beds of

Dingle Peninsula The Dingle Peninsula ( ga, Corca Dhuibhne; anglicised as Corkaguiny, 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 o ...

County Kerry County Kerry ( gle, Contae Chiarraí) is a county in Ireland. It is located in the South-West Region and forms part of the province of Munster. It is named after the Ciarraige who lived in part of the present county. The population of the co ...

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 (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

s and sandy and

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

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 preserved ...

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 the L ...

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 ( ; cy, Sir Ddinbych; ) is a county in the north-east of Wales. Its borders differ from the historic county of the same name. This part of Wales contains the country's oldest known evidence of habitation – Pontnewydd (Bontnewy ...

and

Merionethshire , HQ= Dolgellau , Government= Merionethshire County Council (1889-1974) , Origin= , Status= , Start= 1284 , End= , Code= MER , CodeName= ...

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 ''Cyathaspis'' is the type genus of the heterostracan order Cyathaspidiformes. Fossils are found in late Silurian strata in the Cunningham Creek Formation, New Brunswick, Canada and Europe, especially in the Downton Castle Sandstone of Great ...

'', the earliest British

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

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 in f ...

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 ...

, a noted fossil locality.

Trilobites Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

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

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan 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 end, w ...

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

pelecypod Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biva ...

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

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

s and

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

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 (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...

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 ''Pterygotus'' is a genus of giant predatory eurypterid, a group of extinct aquatic arthropods. Fossils of ''Pterygotus'' have been discovered in deposits ranging in age from Middle Silurian to Late Devonian, and have been referred to several di ...

'' and

mollusca Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

. This layer, known as the "Ludlow Bone bed," has been traced over a very large area. The Tilestones,

, and

shales are occasionally grouped together under the term Downtonian. They are in reality passage beds between the Silurian and

Old Red Sandstone The Old Red Sandstone 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 northeastern seaboard of North America. It also exte ...

, 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 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 ...

. 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 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typical ...

, phyllocarids,

eurypterids Eurypterids, often informally called sea scorpions, are a group of extinct 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 group is l ...

; 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 of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

s);

s (

Phyllocarida Phyllocarida is a subclass of crustaceans, comprising the extant order Leptostraca and the extinct orders Hymenostraca and Archaeostraca. See also *''Ceratiocaris'' *''Cinerocaris'' *''Vladicaris ''Vladicaris'' is an arthropod known from the ...

, ''Platyschisma helicites'');

bivalvia Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of w ...

; 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