The geological ramble outlined for the BGS Wales office in Cardiff included a description of the Gorsedd stone circle, in front of Amgueddfa Cymru – National Museum Wales, erected to celebrate the Eisteddfod held in Cardiff in 1909.

The outer ring of stones is made from ‘Radyr Stone’. Radyr Stone is a ‘freestone’, meaning it can be cut in any direction without breaking, and it is a local speciality produced from a number of quarries in Cardiff. These include sites on the west side of the Taff, north-west of Llandaff Bridge, Plymouth Woods near St Fagans, and at Cadoxton near Barry.

This short walk is to one such quarry at Radyr Woods Community Nature Area and the adjoining Hermit Woods Local Nature Reserve, where Radyr Stone can be examined in situ. This is an area of ancient, semi-natural woodland on the southern edge of the village of Radyr at the northern edge of Cardiff. The quarry is at the south of Hermit Woods.

Geology

‘Radyr Stone’ is a local name given to the Triassic-aged breccia and conglomerates of the . At the time of its deposition, sedimentation was influenced by the Triassic topography of hills and cliffs, which would have accumulated scree at their bases. The climate was hot and arid but occasional heavy storms produced flash flooding that created wadis and transported mainly Carboniferous-aged sandstone and limestone pebbles and cobbles (‘clasts’). The clasts were deposited in large alluvial fans, which are visible in the bases of the thick beds in the quarry.

The clasts are contained within a red matrix with a calcareous (calcium carbonate) cement. The sediments become finer grained upwards, illustrating the decreasing speed of flow of the storm-influenced rivers. The repeating pattern of decreasing grain size indicates multiple storm events.    

Quarry and examples of use

Radyr Stone was quarried from a number of locations across Cardiff from the 1850s to the 1920s. Radyr Quarry main period of extraction was from around the 1850s up to until 1908, although it did supply stone for Insole Court in Llandaff during the First World War. The quarry position close to the railway line meant that the stone could be easily transported; for example, the stone was taken to build Penarth Dock as well as a number of local bridges along the Taff Vale Railway.

To the south of Hermit Woods is another area of parkland called Hailey Park. Here you can see an example of Radyr Stone used in the five-arched Taff Vale Railway Bridge, which crosses the River Taff. It was designed by Isambard Kingdom Brunel and is now a Cadw Grade II listed structure. The early parts of the bridge were built in locally sourced Radyr Stone, quarried on the west side of the railway just opposite the park.

Radyr Stone is also commonly used as a decorative stone in the buildings of the city and its surrounding area, where it is often seen capping or as courses in walls and buildings:

• the cottages of Junction Terrace, near the entrance to Radyr Woods, are a good example of buildings constructed in part from Radyr Stone
• on the north side of Station Road, close to the Radyr railway station, walls are capped by Radyr Stone
• Ty-Mynydd Lodge, on Heol Isaf and once home to Roald Dahl, has quoins of Radyr Stone
• another example is the lychgate at Llandaff Cathedral, which is also constructed of Radyr Stone

Your challenge (should you choose to accept it) it is to spot Radyr Stone in use elsewhere in the city. My example, close to home, is along the tops of the walls at our chapel in Old St Mellons, in the east of the city of Cardiff. 

Getting to the quarry

The Radyr Quarry can be accessed by walking south through Radyr Woods and via rough paths into the adjacent Hermitage Woods.

There is a railway station very close by at Radyr. The suburb is also well serviced by buses from the city centre. If arriving by car, there is parking at the Radyr railway station and some on-street parking close to the entrance to Radyr Woods.  

Safety

If you are going to visit the quarry, please don’t get too close to the faces and take care for dumped rubbish underfoot. The main face is loose and there is a footpath along the top. The quarry faces are in nature reserves so no hammering or collecting.

About the author

Rhian Kendall

51���� Chief Geologist, Wales

51���� Cardiff

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Many of the pretty villages and towns of south Somerset contain attractive buildings constructed from a distinctive, warm honey-coloured building stone known as Hamstone.

This stone has a long history of use, with examples found at sites dating back as far as the Roman and Norman periods. During the Medieval period, Hamstone was transported from where it was extracted at Ham Hill, near Yeovil in Somerset, via horse and cart and then boat along the River Perrett to Taunton. From there it was transported for use in churches across Devon, Dorset and west Somerset. The Victorians transported the stone even further afield via railway networks. Hamstone is still in demand today for new buildings and extensions as well as for restoration work, especially in conservation areas where the stone has been traditionally used.

Hamstone was extracted from quarries on Ham Hill, from which the stone takes its name. The rock unit was formerly known as the (now part of the ), which is a sedimentary rock formed approximately 174 to 183 million years ago in the Jurassic Period (Upper Lias, Toarcian). The sediments were deposited in a shallow-marine environment and the rock is generally composed of coral and shell fragments, which accumulated in beds and reefs in the shallow, carbonate sea that covered this area at the time.

When fresh, Hamstone is a light golden-coloured stone, which can be readily sawn or split and dressed, making it useful as blocks, ashlar and door and window dressings. Weathering causes the stone to darken to richer-coloured tones, a process that also picks out the weaker, less well-cemented layers and cross-bedding in what is mainly a well-cemented, medium- to coarse-grained, shelly limestone with thin beds and inclusions of claystone.

Disused quarries that once produced Hamstone can be seen at Ham Hill Country Park, where there is a suggested geological trail to follow. The trail starts and finishes at the Ham Hill Centre where geological trail guides can be picked up.

Many of the local villages have buildings which use Hamstone and South Petherton is a great place to see examples as the town is largely built of the stone. Another fine example is the Elizabethan Montacute House, which was commissioned in 1588 and is mainly constructed of Hamstone.

Ham Hill is an area of high ground on the southern edge of the Somerset Levels, with good views across this large area of mainly flat coastal plains and wetlands. For the most part, the Somerset Levels are only about 6 m above sea level and have a documented history of efforts to manage the water levels going back to the 13th century.

Ham Hill is well worth a visit to explore its geology as it is a Site of Special Scientific Interest (SSSI) and a Local Geological Site (LGS), scheduled for its geology. The hill also includes a Scheduled Ancient Monument, an Iron Age hill fort, a Roman site, and is a local nature reserve and country park.

Ham Hill is accessible by car with parking at the visitor centre.  South West Coaches operate a bus service that stops in the centre of Stoke Sub Hamdon, from where you need to walk up the steep Ham Hill Road.

Caution: stay away from the base and top edges of the quarry faces and from the edges as they are loose and overhanging in places and could fall. It is illegal to hammer the rocks or collect fossils from this site as Ham Hill is a SSSI.

Further reading

[online]. (Nottingham, UK: 51����.)

[online] (BGS online image portal). (Nottingham, UK: 51����.)

Somerset Council. [online].

Wilson, V, Welch, F B A, Robbie, J A Green, G W, Anderson, F W, Buchan, S, and Melville, R V. 1958. . (London, UK: HMSO.)

About the author

Rhian Kendall

51���� Chief Geologist, Wales

51���� Cardiff

Find out more

For the most part, the cliffs at Penarth Head in South Wales comprise beds of striking red and green calcareous mudstone with bright bands of white and pink gypsum. They were deposited in the Triassic Period (251-201 million years ago) when this part of Wales was arid desert on the northern margin of a sea. The rocks, which are part of the Mercia Mudstone Group, are mostly lacustrine in origin (deposited in lakes). Gypsum is the hydrated form of calcium sulphate and is precipitated as a sediment when shallow lagoons that contain dissolved calcium sulphate in their waters partially evaporate in hot climates. Gypsum is often used as the ornamental stone known as alabaster.

Towards the top of the cliff, above the red and green layers (Blue Anchor Formation), the grey-coloured rocks record a change from a terrestrial (on the land) lacustrine environment to marine conditions. These rocks are known as the Penarth Group and comprise beds of mudstone and limestone. Interesting amongst the formations that make up the Penarth Group is the Westbury Formation, which contains a ‘bone bed’ in which fragments of fish bone and tiny black shiny teeth can be found. Look out for these of these in the pebbles on the beach as well as slabs of fossilised ripples that have fallen from these beds onto the beach below.

Care needs to be taken when examining the cliffs at Penarth Head as rocks do fall from time to time, especially after wet weather. Maintain a safe distance at all times.

Most of the pebbles on the beach are formed of Lower Jurassic aged limestones and mudstones, which are best seen further south of Penarth Head where the Lias Group makes up more of the cliffs. Amongst these pebbles are many fossils: two very distinctive ones found here and along the coast of the Vale of Glamorgan are Gryphaea and Plagiostoma.

The Penarth alabaster has been exploited at least as far back as the 17th century and examples of its use can be found across South Wales and beyond. If you read the article about the geology around our 51���� office in Cardiff, you may remember the pink staircase in the main entrance to our building, which is tiled with alabaster from Penarth.

Other notable places to visit in Cardiff where this stone can be seen in use include a doorway inside the clock tower and the spectacular smoking room at Cardiff Castle (remodelled by William Burgess and the third Marquess of Bute). At Insole Court in the Llandaff part of the city, it is put to use in number of ways, including a stone balustrade, window arches, columns and fireplaces. Another interesting example is St Margaret’s Church in the Roath suburb of the city, where it is expensively used in the walls of the nave, chancel, sedilia and pulpit. The church also includes the mausoleum of the marquesses of Bute.

Getting to Penarth

• Buses run from Cardiff City Centre to Penarth (92, 93 and 94).
• Take a train from Cardiff Central then walk to the sea front.
• There is car parking on the sea front at Penarth and also at the Cardiff Bay Barrage.

Further reading

Statham, M. 2017. Penarth Alabaster. Welsh Stone Forum. ISBN 9781526206770.

Waters, R A, and Lawrence, D J D. 1987. . Third Edition. Memoirs of the British Geolological Survey Sheet 263 (England and Wales). (Nottingham, UK: 51����.)

About the author

Rhian Kendall

51���� Chief Geologist, Wales

51���� Cardiff

Find out more

The BGS office in Wales is based in Cardiff University’s Main Building on Park Place in the city’s rather grand Civic Centre. It’s an interesting part of the city with a history linked to shipping of south Wales coal and steel. The land now occupied by the Civic Centre was once part of the private grounds of the Bute family. The second Marquis of Bute built his first dock at Cardiff in the mid 19th century which catalysed the rapid growth of Cardiff as an important port town at that time. 

The geology of Cardiff is not very visible from our city centre location but there are still interesting geological stories to be unearthed just a stone’s throw from the office. Starting at the front entrance (on the west side) of Main Building, is the grand frontage, faced in Portland Stone, just like all the other buildings in the Civic Centre. This stone is often used for public buildings and it’s a whitish grey limestone of Jurassic age quarried on the Isle of Portland in Dorset. The sediments which make up this rock were deposited in shallow tropical seas, and with a close look, you will see it’s made up of tiny round ooliths and fragments of shell, often more obviously seen where the stone is worn by weather or passage of feet. This finery is only skin deep and in less prominent places the Pennant sandstone blocks can be seen (more on this later). Through the door and down the green marble steps is the Viriamu Jones Gallery.

Viriamu Jones was the first principal of the University and his statue carved of white marble from Serevezza in Italy sits on a plinth of orange veined Arabescato marble. One of the highlights is the lovely staircase in the gallery which is tiled with striking pinkish alabaster. These are a local specialty being quarried just down the road in Penarth. The alabaster is probably better termed gypsum and is a product of evaporating lakes during the Triassic when Wales was part of a hot desert. I take great pleasure in using this staircase as I remember being told as a little girl by a very intimidating retired schoolteacher friend of my Grampa that only the lecturers  were permitted to use them when she was a student so I in contrast should take every opportunity do so. And so I do, even if it means a detour! 

Out through the west door, and cross Museum Avenue lies Alexandra Gardens, a favourite of student lunch breaks (and BGS staff) on a sunny day. There are many interesting and moving memorials and statues to explore here. The biggest is the Welsh National Memorial . Built in Portland Stone echoing the surrounding buildings, it takes the form of a circle of Corinthian columns surrounding a sunken court and fountain. Another interesting one, from a stone point of view, is the memorial to the Falklands conflict as it was shipped from the Falklands. 
 
Exiting the gardens in the south east corner, Cardiff’s City Hall is on the right and the Amgueddfa Cymru – National Museum Wales on the left. In front of the museum, is another of Cardiff’s special building stones. They form a stone circle (which is not an ancient stone circle) but actually a ring of Gorsedd Stones. Stone circles such as these were erected here to commemorate the National Eisteddfod which was been held in Cardiff a number of times. This set (one of many in Cardiff and across Wales) was placed here in 1909. Eisteddfodau are a big deal here in Wales and are festivals held to celebrate the arts and Welsh Culture. These stones are Triassic aged breccias and conglomerates of the marginal facies of the Mercia Mudstone Group, known locally as “Radyr Stone”. On some of the standing stones you can still see the plug and feather drill marks of the quarrymen.  Radyr Stone can be seen in many places as it tends to be used as red copings on walls and stringers breaking up faces of buildings. 

 
The beautiful steps in front of the museum are made of Cornish granite of Bodmin Moor type, look for the porphyritic granite feldspar phenocrysts. 

Across the main road (Park Place) is Park House, built in 1874 by William Burges for the 3rd Marquis of Butes land agent.  Burges worked for the 3^rd Marquis of Bute on many projects including the spectacular interiors of Castell Coch and Cardiff Castle, deigned in his gothic revival style. Park House is mainly constructed in Pennant Sandstone Formation sandstone with Bath Stone dressings and pinkish Scottish granites are used in the porch and veranda. The finer grained being from Craigton Quarry in Aberdeen and the coarser variety is from Peterhead. The majority of the building is constructed of Pennant Sandstone, it greenish grey blocks are very commonly used throughout south Wales.  

Heading north, back towards the university, is the museum car park on the left, there are many lovely trees here including a Ginkgo biloba, who relatives are as fossils dating back to the early Jurassic and monkey puzzle (Araucaria) which date back to the Triassic. The earlier parts of Main Building, including where we have our offices, date to the 1920 but this southern corner wasn’t constructed until the 1960s. Along this face of the building are grey slate panel which have rusty patches of weathered pyrite nodules. It is thought that these might be Dolemaen slates. 

Continuing around the southern edge of the building ends up back to the west entrance at the start. I hope you’ve enjoyed this behind the scenes tour!

Further information 

John W Perkins. 1984. The Building Stones of Cardiff. University Collage Cardiff Press.  

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About the author

Rhian Kendall

51���� Chief Geologist, Wales

51���� Cardiff

Find out more