# Wenlock Group

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{{Short description|Middle series of strata in the Silurian (Upper Silurian) of Great Britain}}
{{Update-EB|date=March 2020}}
The '''Wenlock Group''' (Wenlockian), in [geology](/source/geology), is the middle series of [strata](/source/stratum) in the [Silurian](/source/Silurian) (Upper Silurian) of [Great Britain](/source/Great_Britain). This group in the typical area in the [Welsh](/source/Wales) border counties contains the following formations: [Much Wenlock Limestone Formation](/source/Much_Wenlock_Limestone_Formation), 90–300&nbsp;ft.; [Wenlock Shale](/source/Wenlock_Shale), up to 1900&nbsp;ft.; Woolhope or Barr Limestone and shale, 150&nbsp;ft.<ref name="EB1911">{{EB1911|inline=y|wstitle=Wenlock Group|volume=28|page=519|first=John Allen|last=Howe}}</ref>

== Stratigraphy ==
=== Woolhope Beds ===
The Woolhope Beds consist mainly of [shale](/source/shale)s which are generally calcareous and pass frequently into irregular nodular and lenticular limestone. In the [Malvern Hills](/source/Malvern_Hills) there is much shale at the base, and in places the limestone may be absent. These beds are best developed in [Herefordshire](/source/Herefordshire); they appear also at May Hill in [Gloucestershire](/source/Gloucestershire) and in [Radnorshire](/source/Radnorshire). Common [fossil](/source/fossil)s are ''[Phacops](/source/Phacops) caudatus'', ''[Encrinurus](/source/Encrinurus) tuberculatus'', ''[Orthis](/source/Orthis) calligramma'', ''[Atrypa](/source/Atrypa) reticularis'', and ''[Orthoceras](/source/Orthoceras) annulatum''.<ref name="EB1911"/>

=== Wenlock Shales ===

The Wenlock Shales are pale or dark-grey shales which extend through [Coalbrookdale](/source/Coalbrookdale) in [Shropshire](/source/Shropshire), through Radnorshire into [Carmarthenshire](/source/Carmarthenshire). They appear again southward in the Silurian patches in Gloucestershire, Herefordshire and [Monmouthshire](/source/Monmouthshire). They thicken from the south northward. The fossils are on the whole closely similar to those in the limestones above with the natural difference that [coral](/source/coral)s are comparatively rare in the shales, while [graptolite](/source/graptolite)s are abundant. Six graptolite zones were recognized by [Gertrude Elles](/source/Gertrude_Elles) in this formation.<ref name="EB1911"/>

=== Wenlock Limestone ===
The Wenlock Limestone occurs either as a series of thin limestones within shales or as thick massive beds; it is sometimes hard and crystalline and sometimes soft, earthy or [concretion](/source/concretion)ary. It is typically developed at [Wenlock Edge](/source/Wenlock_Edge), where it forms a striking feature for some 20&nbsp;mi. It appears very well exposed in a sharp [anticline](/source/anticline) at [Dudley](/source/Dudley), whence it is sometimes called the Dudley Limestone; it occurs also at [Aymestrey](/source/Aymestrey), [Ludlow](/source/Ludlow), [Woolhope](/source/Woolhope), May Hill, [Usk](/source/Usk) and Malvern.<ref name="EB1911"/>

The fossils include corals in great variety (''[Halysites](/source/Halysites) catenularis'', ''[Favosites](/source/Favosites) aspera'', ''[Heliolites](/source/Heliolites) interstinctus''), [crinoid](/source/crinoid)s (''[Crotalocrinus](/source/Crotalocrinus)'', ''[Marsupiocrinus](/source/Marsupiocrinus)'', ''[Periechocrinus](/source/Periechocrinus)''), often very beautiful specimens, and [trilobite](/source/trilobite)s (''[Calymene](/source/Calymene) blumenbachii'', the Dudley locust, ''[Phacops](/source/Phacops) caudatus'' and ''[Illaenus](/source/Illaenus) ([Bumastus](/source/Bumastus)) barriensis''). [Brachiopod](/source/Brachiopod)s are abundant (''[Atrypa](/source/Atrypa) reticularis'', ''[Spirifer](/source/Spirifer) plicatilis'', ''[Rhynchonella](/source/Rhynchonella) cuneata'', ''[Orthis](/source/Orthis)'', ''[Leptaena](/source/Leptaena)'', ''[Pentamerus](/source/Pentamerus)''). [Lamellibranch](/source/Lamellibranch)s include the genera ''[Avicula](/source/Avicula)'', ''[Cardiola](/source/Cardiola)'' and ''[Grammysia](/source/Grammysia)'' whilst ''[Murchisonia](/source/Murchisonia)'', ''[Bellerophon](/source/Bellerophon)'' and ''[Omphalotrochus](/source/Omphalotrochus)'' are common gastropod genera. Common [cephalopod](/source/cephalopod) genera include ''[Orthoceras](/source/Orthoceras)'', ''[Phragmoceras](/source/Phragmoceras)'' and ''[Trochoceras](/source/Trochoceras)''.<ref name="EB1911"/>

== Silurian fauna ==
The greater part of the known Silurian fauna of Britain comes from Wenlock rocks; J. Davidson and G. Maw obtained no fewer than 25,000 specimens of [brachiopod](/source/brachiopod)s from seven tons of the shale. Not only are there many different genera and species but individually certain forms are very numerous. The three principal zonal [graptolites](/source/graptolites) are, from above downwards: ''[Monograptus](/source/Monograptus) testis'', ''[Cyrtograptus](/source/Cyrtograptus) linnarssoni'', and ''[Cyrtogra](/source/Cyrtogra) murchisoni''.<ref name="EB1911"/>

== Other areas ==
When traced northward into [Denbighshire](/source/Denbighshire) and [Merionethshire](/source/Merionethshire), the Wenlock-age rocks change their character and become more slaty or [arenaceous](/source/arenite). They are represented in this area by the [Moel Ferna Slates](/source/Moel_Ferna_Slates), the [Pen-y-glog Grit](/source/Pen-y-glog_Grit), and [Pen-y-glog Slates](/source/Pen-y-glog_Slates). All of those layers belong to the lower part of the [Denbighshire Grits](/source/Denbighshire_Grits), a great series of slates and grits {{convert|3000|ft|m}} thick.<ref name="EB1911"/>

Similar deposits of similar age occur on this horizon still farther north. In the [Lake District](/source/Lake_District), the Wenlock rocks are represented by the [Brathay Flags](/source/Brathay_Flags), the lower part of the [Coniston Flags](/source/Coniston_Flags) series. In southern [Scotland](/source/Scotland), their place is taken by the variable [Riccarton Beds](/source/Riccarton_Beds) of [Kirkcudbright](/source/Kirkcudbright) shore, [Dumfriesshire](/source/Dumfriesshire), [Riccarton](/source/Riccarton%2C_Ayrshire), and the [Cheviots](/source/Cheviots). In [Lanarkshire](/source/Lanarkshire), they are represented by sandstone in the form of [greywacke](/source/greywacke)s and by shales. In the [Pentland Hills](/source/Pentland_Hills), one finds mudstones, shales, and grits. In the [Girvan](/source/Girvan) area are the Blair and Straiton Beds.<ref name="EB1911"/>

In [Ireland](/source/Ireland), there is more rock of Wenlock age. In the [Dingle Peninsula](/source/Dingle_Peninsula) one finds the [Ferriters Cove Beds](/source/Ferriters_Cove_Beds), a thick series of shales, slates, and sandstones with [lava](/source/lava)s and [tuff](/source/tuff)s. In [County Tipperary](/source/County_Tipperary) and [County Mayo](/source/County_Mayo) are the [Mweelrea Beds](/source/Mweelrea_Beds) and others.<ref name="EB1911"/>

== Economic geology ==
[Lime](/source/Lime_(material)) and flagstones are the most important economic products of the British Wenlock rocks.<ref name="EB1911"/>

== References ==
{{Reflist}}

Category:Lithostratigraphy of England
Category:Geological groups of the United Kingdom
Category:Lagerstätten

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Adapted from the Wikipedia article [Wenlock Group](https://en.wikipedia.org/wiki/Wenlock_Group) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Wenlock_Group?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.