In geology, Caradoc Series is the name introduced by Roderick Murchison in 1839 for the sandstone series of

Caer Caradoc Caer Caradoc ( cy, Caer Caradog, the fort of Caradog) is a hill in the English county of Shropshire. It overlooks the town of Church Stretton and the village of All Stretton and offers panoramic views to the north towards the Wrekin, east to ...

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 ...

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 ...

. It is the fifth of the six subdivisions (in ascending order) of the

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

System, comprising all those rocks deposited worldwide during the Caradocian Age (458 to 448 million years ago). The limits of Murchison's Caradoc series have since been somewhat modified, and through the labours of

Charles Lapworth Charles Lapworth FRS FGS (20 September 1842 – 13 March 1920) was a headteacher and an English geologist who pioneered faunal analysis using index fossils and identified the Ordovician period. Biography Charles Lapworth was born at Faring ...

the several members of the series have been precisely defined by means of graptolitic zones. These zones are identical with those found in the rocks of the same age in North Wales, the Bala Series, and the terms Bala or Caradoc series are used interchangeably by geologists when referring to the uppermost substage of the

System. The Ordovician rocks of the Caradoc district have been subdivided into the following beds, in descending order: the Trinucleus shales, Acton Scott beds, Longville flags, Chatwell and Soudley

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s, Harnage shales and Hoar Edge

grits Grits are a type of porridge made from boiled cornmeal. Hominy grits are a type of grits made from hominy – corn that has been treated with an alkali in a process called nixtamalization, with the pericarp (ovary wall) removed. Grits are of ...

and

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 ...

. In the Corndon district in the same county the Caradoc series is represented by the Marrington group of ashes and shales and the Spy Wood group beneath them; these two groups of strata are sometimes spoken of as the Chirbury series. In the Breidden district are the barren Criggeon shales with ashes and flows of andesite. In the Lake district the Coniston limestone series represents the Upper Caradocian, the lower portion being taken up by part of the great Borrowdale volcanic series of rocks. The Coniston limestone series contains the following subdivisions Ashgill group (Ashgill shales and Staurocephalus limestone) - *Kiesley limestone. *Sleddale group (Applethwaite beds) Upper Coniston limestone conglomerate; Yarlside rhyolite; stye end beds=Lower Coniston limestone. *Roman Fell group (Corona beds). *The Dufton shales and Drygill shales are equivalents of the Sleddale group. Rocks of Caradoc age are well developed in southern Scotland; in the

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 Ay ...

district they have been described as the Ardmillan series with the Drummock group and Barren Flagstone group in the upper portion, and the Whitehouse, Ardwell and Balclatchie groups in the lower part. Similarly, two divisions, known as the Upper and Lower Hartfell series, are recognized in the southern and central area, in Peeblesshire, Ayrshire and

Dumfriesshire Dumfriesshire or the County of Dumfries or Shire of Dumfries (''Siorrachd Dhùn Phris'' in Gaelic) is a historic county and registration county in southern Scotland. The Dumfries lieutenancy area covers a similar area to the historic county. I ...

. In Ireland the Caradoc or Bala series is represented by the limestones of

Portraine Portrane or Portraine (Irish: ''Port Reachrann'') is a small seaside settlement, three kilometres from,the small town of Donabate in Fingal, Ireland. It lies in the Barony of Nethercross, in the historic County Dublin. Portrane has a long ...

near Dublin and of the Chair of Kildare; by the Ballymoney series of

Wexford Wexford () is the county town of County Wexford, Ireland. Wexford lies on the south side of Wexford Harbour, the estuary of the River Slaney near the southeastern corner of the island of Ireland. The town is linked to Dublin by the M11/N11 ...

and Carnalea shales of County Down. In the Lough Mask district beds of this age are found, as in Wales, interstratified with volcanic lavas and tuffs. Other localities are known in counties Tyrone, Meath and

Louth Louth may refer to: Australia *Hundred of Louth, a cadastral unit in South Australia * Louth, New South Wales, a town * Louth Bay, a bay in South Australia **Louth Bay, South Australia, a town and locality Canada * Louth, Ontario Ireland * Cou ...

, also in Lambay Island.

Early descriptions of the Bala series

The Bala Series was described as a group of dark slates and

s with

beds A bed is an item of furniture that is used as a place to sleep, rest, and relax. Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many be ...

which occurs in the neighborhood of Bala, Gwynedd, in north

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

. It was first described by Adam Sedgwick, who considered it to be the upper part of his Cambrian System. The Bala limestone is from 20 to thick, and is recognizable over most of North Wales. The series in the type area consists of the Hirnant limestone, a thin inconstant bed, which is separated by . of slates from the Bala limestone, below this are more slates and volcanic rocks. The latter are represented by large contemporaneous deposits of tuff and felsitic lava which in the Snowdon District are several thousand feet thick. In South Wales the Bala Series contains the following beds in descending order: the Trinucleus seticornis beds (Slade beds, Redhill shales and Sholeshook limestone), the Robeston Wathen beds, and the Dicranograplus shales. The typical

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 ...

are, in the upper part, ''Dicellograptus anceps'' and ''D. complanatus''; in the lower part, ''Pleurograptus linearis'' and ''Dicranograptus clingani''.

References

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Bibliography

*Nat. Hist., 5th series, vol. vi., 1880; Geol. Mag., 1889; C. Lapworth and W. W. Watts, Proc. Geol. Assoc., xiii., 1894; J. E. Marr, Geol. Meg., 1892; J. B. Marr and T. Roberts, Q. J. G. S., 1885; B. N. *Peach and J. Home, Silurian Rocks of Great Britain, vol. I., 1899 Geologic formations of the United Kingdom Stratigraphy of the United Kingdom