The Pennant Measures is the traditional name for a sequence of

sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

rocks of the

South Wales Coalfield The South Wales Coalfield () extends across Pembrokeshire, Carmarthenshire, Swansea, Neath Port Talbot, Bridgend, Rhondda Cynon Taf, Merthyr Tydfil, Caerphilly, Blaenau Gwent and Torfaen. It is rich in coal deposits, especially in the South Wales ...

. They were also referred to as the Upper Coal Measures and assigned to the Westphalian 'C' and Westphalian 'D' stages of the

Carboniferous Period The Carboniferous ( ) is a geologic period and system of the Paleozoic era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the Permian Period, Ma. It is the fifth and penultimate perio ...

. The Pennant Measures were divided into the Lower Pennant Measures and the Upper Pennant Measures, differing from the underlying Middle and Lower Coal Measures in being principally of sandstone

units Unit may refer to: General measurement * Unit of measurement, a definite magnitude of a physical quantity, defined and adopted by convention or by law **International System of Units (SI), modern form of the metric system **English units, histo ...

– known collectively as the Pennant Sandstone – with

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.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

being the subsidiary rock type. Numerous

coal seam Coal mining is the process of extracting coal from the ground or from a mine. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extrac ...

s occur within the Pennant Measures though they are less common than in the underlying Coal Measures.British Geological Survey 1:50,000 map sheet 231 'Merthyr Tydfil' & accompanying memoir. However recent reclassification of the sequence has resulted in the definition by the

British Geological Survey The British Geological Survey (BGS) is a partly publicly funded body which aims to advance Earth science, geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. ...

of the Pennant Sandstone Formation as a sub-unit of the newly established Warwickshire Group. The formation is recognised to be of Bolsovian to 'Westphalian D' age. It overlies the uppermost strata of the newly defined South Wales Coal Measures Group and underlies the rocks of the succeeding Grovesend Formation. The Pennant

Sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

Formation is now formally subdivided (in ascending order) into the Llynfi, Rhondda, Brithdir, Hughes and Swansea members, each of which units formerly had 'bed' status. Being relatively resistant to erosion, the Pennant Sandstones form the plateau surface of the Coalfield into which the coalfield valleys have been deeply incised by water and ice. They reach their greatest height (though not their highest stratigraphic level) at the flat summit of Craig y Llyn where they are represented by the Hughes Member. The sandstone were quarried both in South Wales and the Bristol area for use in paving and roofing is also known as Pennant Stone.

References

{{Reflist Sandstone formations Coal in Wales Geology of Wales Carboniferous Wales Carboniferous System of Europe Geologic formations of the United Kingdom Stratigraphy of the United Kingdom