Clay in the Dolgellau area

North West Wales is not known for it’s clay. The area is dominated by slate and igneous rock and as a result Dolgellau is a town (a very grey town) built almost exclusively of granite walls and slate roofs. I could find no evidence of potteries nearby although it has a rich history of mining and other industries. Granite from quarries on the Lleyn peninsula supplied stone to pave the streets in English cities to the east such as Manchester and Liverpool.

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Dolgellau

Dolgellau nestles inside the  Snowdonia National Park so it’s no surprise that tourism is the major industry in the area. Much of the surroundings is rural countryside and sheep farming is another important industry. Interestingly, gold was discovered here in the 1850s and as a result the area was hit by a mini gold rush. Two of the most famous gold mines are Gwynfynydd near Ganllwyd and the Clogau St David’s mine in Bontddu. Clogau was originally opened as a copper and lead mine but gold veins were soon discovered and at one point the mine employed over 500 workers and the total output from the mine so far has been recorded at 4 tonnes. All rings for the royal weddings since the Queen Mother’s marriage to King George VI have been made from Clogau gold.

Earlier, during the 18th century the area had a thriving wool trade and coarse wool from sheep in the surrounding hills was exported to New Zealand via the Mawddach Estuary. Leather tanning was another big industry in the town and the large tannery business closed as late as the 1980s.

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Superficial deposits in Dolgellau

The map above was taken from the Geology of Britain Viewer on the British Geological Survey website. The faded yellow on either side of the town, along the river Wnion indicates alluvium deposits of clay, silt and sand left by flowing floodwater in a river valley (producing fertile soil). In the bottom left peat has formed which suggests the environment nearby below the slopes of Cader Idris was dominated by swamps and bogs. The town itself sits on an alluvial fan deposit of sand and gravel (in orange) which formed up to 3 million years ago.

My first effort to find clay took me to the banks of the Mawddach Estuary, down one of the tributaries. In the riverbank here I found a small amount of greyish clay but mixed in with it was lots of sand, brown soil and vegetation. The texture was crumbly and it didn’t have much plasticity, so I decided to look elsewhere.

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Mawddach River from top of Moel Faner hill fort
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River feeding in to the Mawddach at Arthog where I found clay
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Clay with lots of vegetation

After consulting Natural Resources Wales I decided to look a little further afield. I finally came across what I’d been looking for. Just over 10 miles away from Dolgellau in the direction of Trawsfynydd just off the straight line of the Roman road, lies the village of Bronaber with it’s collection of holiday chalets. Turning right here we followed a road into the hills and drove parallel to the Afon Gain until coming to a landslide at a turn in the river. It was clear from a distance that this bank was oozing with blue-grey clay. This clay turned out to be much more plastic than what I found previously. Although it had no vegetation in it, it turned out to be full of small pebbles which I sieved out later while processing it.

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Sun setting on the Afon Gain

Clay is formed when igneous rocks (such as granite and basalt) break down over millions of years. It’s made up of three main ingredients: alumina, silica and water. 

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Clay in the bank of the Afon Gain

Around a mile away from this site at Pen y Stryd there are the remains of two Roman tile kilns which would have been in use between the 1st and 4th centuries AD. Nearby is a waste heap into which the broken tiles and bricks went. It’s believed these kilns once supplied tiles to the Roman fort of Tomen y Mur above Trawsfynydd.

The cross on the map below indicates where the clay by the Afon Gain was found (grid reference: SH743321). The yellow colour running along the river indicates a superficial deposit of alluvium. Alluvium is composed of silty clay which can also contain sand, peat and gravel. Further downstream the circle indicates the site where Roman tile kilns were found. These also sit upon a deposit of clay silt, sand and gravel which is indicated by the purple colour.

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Superficial geology only

The map below shows the same area from above but with only the bedrock visible. The grey green seam that the clay site sits on is Maentwrog mudstone: sedimentary rock of sandtone and siltstone. The nearby purple seams represent Igneous rock formed in silica rich magma and the blue lines are part of the Clogau formation of mudstone and sedimentary bedrock formed on the ocean floor 502-508 million years go.

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Bedrock only
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Dot on the end of the arrow shows where I found clay on the banks of the Afon Gain
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Clay straight from the bag and ready to be processed.
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