The Namurian is a stage in the regional stratigraphy

Stratigraphy

Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....

 of northwest Europe with an age between roughly 326 and 313 Ma (million years ago). It is a subdivision of the Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 system or period and the regional Silesian series

Series (stratigraphy)

Series are subdivisions of rock layers made based on the age of the rock and corresponding to the dating system unit called an epoch, both being formally defined international conventions of the geological timescale. A series is therefore a sequence of rock depositions defining a...

. The Namurian is named for the Belgian city and province of Namur

Namur (province)

Namur is a province of Wallonia, one of the three regions of Belgium. It borders on the Walloon provinces of Hainaut, Walloon Brabant, Liège and Luxembourg in Belgium, and on France. Its capital is the city of Namur...

 where strata of this age occur (part of the Belgian Coal Measures). The Millstone Grit Group in the lithostratigraphy

Lithostratigraphy

Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology...

 of northern 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...

 and parts of Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

 is also of Namurian age.

The Namurian age lasted from 326 to 313 million years ago. It is preceded by the Visean

Viséan

The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from 345.3 ± 2.1 to 328.3 ± 1.6 Ma...

 stage/age (which corresponds to the upper Carboniferous Limestone

Carboniferous limestone

Carboniferous Limestone is a term used to describe a variety of different types of limestone occurring widely across Great Britain and Ireland which were deposited during the Dinantian epoch of the Carboniferous period. They were formed between 363 and 325 million years ago...

 of Great Britain) and succeeded by the Westphalian

Westphalian (stage)

The Westphalian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 313 and 304 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Westphalian is named for the region of Westphalia in western Germany where strata...

 stage/age (which corresponds to the lower and middle Coal Measures

Coal Measures

The Coal Measures is a lithostratigraphical term for the coal-bearing part of the Upper Carboniferous System. It represents the remains of fluvio-deltaic sediment, and consists mainly of clastic rocks interstratified with the beds of coal...

 of Great Britain). In the official geologic timescale of the ICS

International Commission on Stratigraphy

The International Commission on Stratigraphy , sometimes referred to by the unofficial "International Stratigraphic Commission" is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigraphy, geological, and geochronological matters on a global...

, the Namurian straddles the boundary between the Mississippian epoch (359-318 Ma) and the Pennsylvanian

Pennsylvanian

The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...

 epoch (318-299 Ma).

The upper part of the (regionally defined) Namurian stage corresponds to the (internationally used) Bashkirian

Bashkirian

The Bashkirian is in the ICS geologic timescale the lowest stage or oldest age of the Pennsylvanian, the youngest subsystem of the Carboniferous...

 stage whilst the lower part is assigned to the preceding Serpukhovian

Serpukhovian

The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from 328.3 Ma tot 318.1 Ma...

 stage. Frequent references appear in scientific literature to a Namurian epoch or Namurian series

Series (stratigraphy)

Series are subdivisions of rock layers made based on the age of the rock and corresponding to the dating system unit called an epoch, both being formally defined international conventions of the geological timescale. A series is therefore a sequence of rock depositions defining a...

reflecting the stage's earlier status.