Caradoc Series
Encyclopedia
In geology, Caradoc Series is the name introduced by Roderick Murchison
in 1839 for the sandstone series of Caer Caradoc in Shropshire
, England
. It is the fifth of the six subdivisions (in ascending order) of the Ordovician
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
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 indifferently by geologists when referring to the uppermost substage of the Ordovician
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
s, Harnage shale
s and Hoar Edge grit
s and limestone
. 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) -
Rocks of Caradoc age are well developed in southern Scotland; in the Girvan
district they have been described as the Ardmillan series with the Drtimmock 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
.
In Ireland the Caradoc or Bala series is represented by the limestones of Portraine near Dublin and of the Chair of Kildare; by the Ballymoney series of Wexford
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
, also in Lambay Island
.
Roderick Murchison
Sir Roderick Impey Murchison, 1st Baronet KCB DCL FRS FRSE FLS PRGS PBA MRIA was a Scottish geologist who first described and investigated the Silurian system.-Early life and work:...
in 1839 for the sandstone series of Caer Caradoc in Shropshire
Shropshire
Shropshire is a county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. It borders Wales to the west...
, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. It is the fifth of the six subdivisions (in ascending order) of the Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
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
Charles Lapworth was an English geologist.-Biography:He was born at Faringdon in Berkshire and educated as a teacher at the Culham Diocesan Training College near Abingdon, Oxfordshire. He moved to the Scottish border region, where he investigated the previously little-known fossil fauna of the area...
the several members of the series have been precisely defined by means of graptolitic
Graptolite
Graptolithina is a class in the animal phylum Hemichordata, the members of which are known as Graptolites. Graptolites are fossil colonial animals known chiefly from the Upper Cambrian through the Lower Carboniferous...
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 indifferently by geologists when referring to the uppermost substage of the Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
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
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
s, Harnage shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
s and Hoar Edge grit
Grit
Grit may refer to:* GRIT , also known as Arhgap32 or PX-RICS* Grit , a U.S. periodical founded as a newspaper in 1882* Grit , by Celtic fusion musician Martyn Bennett* Grit , by Norwegian rock band Madrugada...
s and limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
. 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 conglomerateConglomerate (geology)A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
; Yarlside rhyoliteRhyoliteThis page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
; 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
Girvan is a burgh in Carrick, South Ayrshire, Scotland, with a population of about 8000 people. Originally a fishing port, it is now also a seaside resort with beaches and cliffs. Girvan dates back to 1668 when is became a municipal burgh incorporated by by charter...
district they have been described as the Ardmillan series with the Drtimmock 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
Peeblesshire
Peeblesshire , the County of Peebles or Tweeddale was a county of Scotland. Its main town was Peebles, and it bordered Midlothian to the north, Selkirkshire to the east, Dumfriesshire to the south, and Lanarkshire to the west.After the local government reorganisation of 1975 the use of the name...
, Ayrshire
Ayrshire
Ayrshire is a registration county, and former administrative county in south-west Scotland, United Kingdom, located on the shores of the Firth of Clyde. Its principal towns include Ayr, Kilmarnock and Irvine. The town of Troon on the coast has hosted the British Open Golf Championship twice in the...
and Dumfriesshire
Dumfriesshire
Dumfriesshire or the County of Dumfries is a registration county of Scotland. The lieutenancy area of Dumfries has similar boundaries.Until 1975 it was a county. Its county town was Dumfries...
.
In Ireland the Caradoc or Bala series is represented by the limestones of Portraine near Dublin and of the Chair of Kildare; by the Ballymoney series of Wexford
Wexford
Wexford is the county town of County Wexford, Ireland. It is situated near the southeastern corner of Ireland, close to Rosslare Europort. The town is connected to Dublin via the M11/N11 National Primary Route, and the national rail network...
and Carnalea shales of County Down
County Down
-Cities:*Belfast *Newry -Large towns:*Dundonald*Newtownards*Bangor-Medium towns:...
. 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
County Tyrone
Historically Tyrone stretched as far north as Lough Foyle, and comprised part of modern day County Londonderry east of the River Foyle. The majority of County Londonderry was carved out of Tyrone between 1610-1620 when that land went to the Guilds of London to set up profit making schemes based on...
, Meath
County Meath
County Meath is a county in Ireland. It is part of the Mid-East Region and is also located in the province of Leinster. It is named after the ancient Kingdom of Mide . Meath County Council is the local authority for the county...
and Louth
County Louth
County Louth is a county of Ireland. It is part of the Border Region and is also located in the province of Leinster. It is named after the town of Louth. Louth County Council is the local authority for the county...
, also in Lambay Island
Lambay Island
Lambay lies off the coast of Fingal / north County Dublin, Ireland in the Irish Sea. It is located north of Ireland's Eye at and is the easternmost point of the Republic of Ireland...
.