The Slate Industry of North and Mid Wales

Dyffryn Nantlle and Dorothea Slate Quarry

A view of part of Dyffryn Nantlle with Craig Cwm Silyn in the distance.

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.

Image produced from the Ordnance Survey Get-a-map service.
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.

A view of Dorothea quarry pre 1940 looking east.  The wires and towers are for the aerial ropeways or "Blondins".

Approximately the same view today.

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. 

Remains of a steam engine, once used to haul slate out of the Dorothea quarry pit.

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 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.

By the 1840's production at Dorothea had built up to about 5,000 tonnes per annum and had reached over 17,000 tonnes by the 1870's.  The future looked good for Dorothea but serious flooding problems then befell the quarry.  In 1884 several men were drowned when the pit was engulfed.  In 1895 the Afon Llyfni which flowed through the valley was realigned and deepened to flow to the south of the slate workings.  This cured the flooding problems to some extent but as the workings deepened, the need to continually pump out water became a constant drain on the quarry's profits.  In 1904 the decision was taken to install a Cornish Beam Engine on site to replace the waterwheels.  The following page contains more details of the beam engine and engine house.

This tramway tunnel passes under one of the pyramids and once lead onto the Nantlle Railway.

As the quarries of the valley continued to grow it led to the removal of the village of Talysarn which was relocated to the west.  Some of the old village buildings remained in use by the quarries and their ruins can still be seen today.  This was followed in 1927 by the relocation of the main road to the south of the valley.  The route of the old road can still be followed.

To lift the slate out of the pit, wire inclines were installed in the 1840's.  There were ultimately eight of these and they were complimented after 1900 by aerial ropeways or Blondins.  At first steam powered, the Blondins were electrically worked from 1959.  They remained in use until 1965 when a road was built to the bottom of the pit.  The last of the wire inclines went out of use in 1957.   Other powered inclines were used at the quarry to lift the waste rock up to the elevated rubbish tips.

Aerial ropeways or "Blondins" were used to raise the slate from the pits. These five disused examples were photographed at Penyrorsedd quarry in 1992.  Today only one is left standing.

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.

Dorothea quarry pool in the foreground with the Cilgwyn quarry tips behind.

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.  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.  A visit to Dyffryn Nantlle is highly recommended before development changes the character of this unique area for ever.
The Cornish beam engine at Dorothea Quarry

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