Report - - Dorothea Slate Quarry - Nantlle Valley - October 2014 | Mines and Quarries | 28DaysLater.co.uk

Report - Dorothea Slate Quarry - Nantlle Valley - October 2014

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Dorothea Slate Quarry – Nantlle Valley



(The history has been more or less copied/plagiarised from a couple of websites on the slate quarries of the Nantlle Valley, they make an interesting read and far better than Wikipedia ;)).

Across the North West corner of Wales lies a long belt of Cambrian slate formed about 500 million years ago. This stretches from the Nant Ffrancon valley in the East to the Nantlle valley in the West. Along this belt were situated some of the largest and most productive slate quarries in the world. In the east the slate was won by open quarries using the gallery method, while at the west end, the slate beds were found beneath the floor of the valley. It was the depth of the slate beneath the valley floor which influenced the quarrying techniques of Nantlle.

The only way to obtain the rock was by digging down and creating large pits. These can be found in many locations in the Nantlle valley. Some of the difficulties of pit working included the need to pump out any water entering the workings and the need to haul out waste as well as good rock. Both of these imperatives increased costs, added to which was the Nantlle area's greater distance from the markets. Nantlle slate was always at a disadvantage compared to the more easily won rock at Penrhyn and Dinorwic further east and was always the first to suffer from any downturn or recession.


(There are two of these large structures, known as pyramids, at Dorothea, they served as bases for the chain inclines and allowed the waste rock to be tipped behind).

Other difficulties were faced by the Nantlle industry. There were a large number of very small quarries, a situation brought about by numerous landowners. These small quarries had little capital to invest and no way to expand. Although there were amalgamations and takeovers which created large units like Dorothea, the tradition of the small quarry survived and can be seen today in the long line of small workings along the south side of the valley. Another major problem was disposal of waste rock. After the time and trouble of bringing it up to surface level, it then had to be hauled up again onto the raised waste tips, so typical of the valley. This of course meant that any winnable slate under the waste tips was destined to remain there. If history had been different and the whole valley had been operated as a single undertaking, then the prospects for Nantlle slate could have been transformed.

The oldest quarry in the Nantlle district was Cilgwyn quarry, this is situated to the north of Dorothea on the hillside and is now a landfill site. It is thought to have been first worked in the fourteenth century and it is believed that some of Edward the 1st's Welsh castles were roofed with Cilgwyn slate.

Dorothea itself opened in 1820 and remained in production until 1970. The land the quarry stands on was owned by a Richard Garnons (1774 -1841) but the main driving force for quarrying in the valley was a Lancastrian - William Turner (1776 -1857). The original name for the quarry was Cloddfa Turner but it was renamed Dorothea after Gamona's wife. The workings grew out of a series of smaller workings with names such as Hen Dwll, Twll Bach, Twll y Weirglodd, Twll Coch and Twll Fire. Over the years these pits were deepened and amalgamated into the large flooded pit seen today. Turner gave up his interest in the quarry in 1848 and following a brief period of closure it was acquired by a family called Williams.
John Hughes Williams was from Llangernyw near Denbigh. He married into the Rev John Jones of Talysarn's family & bought shares in the Company set up by Jones & local Nantlle quarrymen (though half the money was raised outside the area). Williams gradually bought out most of the others by the 1860s, and his family continued in charge thereafter.

In 1828 the Nantlle Railway opened giving the quarries of the valley a route to the sea. The horse powered railway was of 3' 6" (105cm) gauge and ran originally to Caernarfon. From 1872 the tramway ran only as far as Talysarn where connection was made with the national rail network. The Nantlle Railway continued in use, as a part of British Railways, until 1963 and remained horse worked until a couple of years before closure. The final two horses in use were "Prince" and "Corwen". After the horses were retired a tractor was used for the diminishing amount of traffic. Over its lifetime the route of the railway was moved many times as the quarries expanded. Much of its route is traceable today as far as the easterly terminus at Penyrorsedd Quarry. Dorothea Quarry used the Nantlle Railway to dispatch slate from 1829 until 1959.

There was an extensive rail network on site at ground level and on the waste tips. The track gauge of the internal quarry railways was 2' (60cm) as opposed to the "main line" gauge of the Nantlle Railway of 3' 6" (105cm). There are records of 5 steam and 4 petrol driven locos being used at various times and horses were also used. Use of the 2' gauge quarry rail network had ceased by 1968.

Dorothea's closure came about due to the national decline in the industry, the slate industry had reached a peak in the 1890's but from then on it was a story of contraction. Dorothea was no exception as tonnages declined and manning was cut - a cycle of decline set in. Other large quarries in Dyffryn Nantlle also closed - Pen y Bryn in 1950 and Cilgwyn (now a landfill site) in 1956. Today the only significant quarry still in production in the valley is Penyrorsedd, now owned by the Welsh Slate group, and busily exploiting a newly found seam of green rock.


At the beginning of the 20th Century, Dorothea quarry was urgently in need of a long term solution to the ongoing problem of keeping the workings, by then over 500 feet deep, free of water. It was decided to purchase a Cornish beam engine. An old but reliable technology. The engine was built by Holman Brothers and was the last but two ever built. It is also believed to be the newest Cornish beam engine still in existence. The engine was able to pump 10 gallons of water per second from a depth of over 500 feet. The engine started work in 1906 and served until 1951 when it was replaced by a 60hp electric pump. Apart from a brief period in 1956 the engine has been disused ever since.


Following closure of the quarry in 1969, the site has been owned by several companies, each with its own priorities and plans - none of which have included the engine. This has made the restoration and maintenance of this important artefact extremely difficult. In fact, grants have been made available towards its restoration but have subsequently been withdrawn because of the problems of access. The engine house is a Grade 1 listed structure which is the same as Caernarfon Castle. Despite this, and despite the valiant efforts of the engine's custodian, it continues in a state of limbo. What should be one of North Wales finest examples of industrial heritage is now a forgotten link to a golden age.


The main beam is a steel casting and weighs over 23 tons and the engine pumped water from a shaft 155 yards deep.

Today, Dorothea is a popular although unofficial diving centre and sadly there have been quite a number of divers who have lost their lives there. The main problems I have been reliably informed is the depth of the water is nearly 100 meters deep and the temperature as low as 1 degree Celsius. Recreational divers usually dive on a mixture of gas and air and it is usually only safe to dive to a depth of 50 meters on this; requiring decompression stops on the way back to the surface. The interesting stuff lies below 50 meters and attract divers down where they then get into trouble.

There have been numerous changes of ownership of Dorothea over the years, each successive owner promising investment and regeneration only to be replaced by yet another optimist with yet more plans.

My Visit

I actually paid 3 brief visits here as it was fairly close to where we were based, the first visit was with the mini TLR’s as I have wetted their appetites for dark holes and derelict buildings over the years, we were not disappointed. The second was a quick stroll on a sunny morning as the day before we missed the flooded quarry as we got distracted with the buildings and the Nantlle Railway. Last of all it was a full team wander in the rain as Mrs TLR was getting fed up having just to sit in the cottage knitting!

Not knowing what we’d find me and the kids were impressed with what we stumbled across first, the remains of the old hall.





We continued looking around the many derelict building and tunnels through the pyramid structures looking for an opening to take us deep inside the hills.





We then struck it lucky, dark heavy skies were threatening to empty themselves, so this looked a pleasant retreat.


I had no idea what it was or where it lead, I found out afterwards it was part of the Nantle Railway which looked as if it ran into one of the huge water filled pits.




The tunnel finishes at either a collapse or has been back filled after a couple of hundred meters, there was this checky little passage running off it which was very tempting and could see it had a 90 degree bend after about 6 meter which led to who knows?


A good reason to head back, the main reason for not having a proper look was my fellow explorers that day, I’d have a lot of explaining to do to Mrs TLR if the shit had hit the fan and not know what or where the tunnel went we called it a day and took the obligatory group photo.


We hid in the entrance for a fair bit as the heavens had opened by the time we got there, after plucking up courage we rushed of for a couple of hot chocolates and a well earned beer.

The whole valley in Nantlle is riddled with quarries and mines, after a week in the area I feel I have only scraped the surface and the potential of some hidden gems are out there. We found 3 or 4 shafts on the hillsides as well as many small quarries, the derelict buildings are like a rash across the hills.

Somewhere I’ll be back to no doubt, and having spent much time in the Llanberis Slate Quarries over the years; I think these are far more interesting and definitely well off the beaten track in the main.


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