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Dorothea Quarry, Pyramids, Inclines, Mill & Winding Houses, etc

A Scheduled Monument in Llanllyfni, Gwynedd

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Latitude: 53.0544 / 53°3'15"N

Longitude: -4.2397 / 4°14'22"W

OS Eastings: 249987

OS Northings: 353135

OS Grid: SH499531

Mapcode National: GBR 5K.CNKN

Mapcode Global: WH43T.VH99

Entry Name: Dorothea Quarry, Pyramids, Inclines, Mill & Winding Houses, etc

Scheduled Date: 25 May 2022

Source: Cadw

Source ID: 3322

Cadw Legacy ID: CN199

Schedule Class: Industrial

Category: Engine house

Period: Post Medieval/Modern

County: Gwynedd

Community: Llanllyfni

Traditional County: Caernarfonshire


The relict remains of Dorothea Quarry survive to the S and E of the flooded quarry workings that today form a large lake c.0.5km E of the village of Talysarn, Caernarfon. The lake gives the false impression that Dorothea was centred around a single pit working but by the 1880s Dorothea exploited 5 pits in Dyffryn Nantlle.

During the late 19th and early 20th Centuries Dorothea was the principal quarry in the area, producing, at its peak in the 1870s, 13,000 tons of roofing slates per annum and employing around 500 men. The monumental relict remains and the massive slate tips associated with these operations continue to dominate the landscape today.

The first slate quarrying on an industrial scale began at Dorothea in 1829 when a quarry adventurer, William Turner, and his son-in-law John Morgan opened what was then known as Cloddfa Turner. In 1849 a consortium of local quarrymen, entrepreneurs and farmers formed the Dorothea Quarry Co and took over the

workings. The name ‘Dorothea’ came from the wife of Richard Garnons who owned the Pant Du estate on which the quarry was sited. This was unusual since virtually all the large scale operations were under English management at that time. In 1860 the company became known as ‘John Williams and Co’ and the Williams family

retained control until voluntary liquidation in March 1970.

By the 1880s the pit workings had been sunk to over 100m. It is this depth which marks Dorothea from other quarries and which forced important innovations, particularly in lifting material from the quarry floor up to the processing area and then up again to the extensive slate waste tips that over shadow the quarry. The handworked turntrees of the early working were followed by horse-powered whims in the 1830s and, when tramways were introduced, water-powered inclines led down to the pit floor. A complex system of aqueducts, leats and waterwheels (8 in total) utilised a single water source to power both mills and uphaulage systems.

In 1841 the first of a series of steam-powered chain inclines (later cable inclines) was installed and these remained the principal means of extraction until they were phased out in the 1950s. These were supplemented by steam-Blondin cableways in 1900. The last Blondin operated until 1965 when a road was blasted to the lowest floor then being worked, and road transport took over. Prior to the introduction of

road haulage an extensive internal tramway system had been developed utilising both 2’ and 3’6” gauge rails. In the processing area the tramway provided connections between the uphaulage systems and the longitudinal mill as well as an onward connection to the Nantlle Railway. At the summit of the massive slate waste tips a further tramway system facilitated waste management.

The relict remains today comprise a number of impressive monumental structures arranged around the lake. The flooded quarries do not form part of the scheduling. At the southern edge of the lake a well-built masonry water wheel pit – evidence of the water-powered incline system – survives below the processing area. Above this the main processing area is arranged around the integrated mill / dressing shed

which survives as a roofless ruin some 80m in length by 25m transversely. Although the structure is over grown it is well-preserved – machine bases are evident and the gable ends survive to full height. To the E of the mill many structures have been cleared in the later 20th century but this area remains one of significant archaeological potential – the bases of buildings and occasional railway sleepers are evident. To the W of the mill a number of ruinous ancillary buildings survive including offices, workshops, smithies and stables. The route of the internal tramway system is legible as a well-made path through the slate waste tips to the S. This path leads to the SE processing area that survives as illustrated on the Ordnance

Survey map of 1916. Here, scattered slate splitting shelters are evidence of ad-hoc secondary working. Dorothea quarry is dominated by two massive masonry bastions, thought to be a unique feature of this quarry. These structures are actually well built revetments built against the extensive slate tips but are known locally as pyramids. Their positions at the E and SW edge of the main lake were the principal locations for uphaulage during the 19th century, firstly utilising water-powered inclined planes and latterly using steam-powered engines. The engines drove chain-, and later cable-inclines to enable quarry wagons to be pulled from the deep quarry pits and returned to the working faces effectively.

The E bastion, the Chain Inline Pyramid, has clear evidence of phasing but the masonry structure appears today much as it did in 1889. The pyramid is 15m in height and is an irregular plan c.20x20m. The structure comprises a rubble core faced with sawn blocks of slate and would have been mortared and pointed in lime.

Little evidence of the pointing survives and numerous buttresses have been added to the irregular faces of the bastion during the first half of the 20th century, especially on the southern face where there is evidence of both historic and more recent collapse. To the NE of the bastion is a much overgrown uphaulage incline orientated NW-SE connecting the processing area with the E tips.

A well-made tunnel runs NNE-SSW through the E bastion and the adjacent incline for c.40m, built to connect the tramway system from the southern processing area with the Nantlle Railway to the N. No rails survive but occasional sleepers survive in situ. The tramway system passes a small complex of buildings - some of which represent reused remnants of Old Talysarn Village - before turning sharply to the E where it connects with the Nantlle Railway (CN420) via a short but dramatic cutting through the slate waste. This cutting is a section of the original 1828 route of the Nantlle Railway which was later realigned to the NE as Dorothea Quarry expanded.

The cutting is supported by two unique flying arches that protect the track bed from the encroaching tips. At the summit of the E Chain Incline Pyramid stands the remains of the winder house and engine house along with a number of other relict structures. Further E is a large area of archaeological potential, where slate waste obscures numerous buildings associated with Dorothea and the adjacent Cloddfa’r Lon Slate Quarry (CN302).

Whilst many of these structures are not readily identifiable they appear to broadly correspond with the changing landscape of quarry buildings as illustrated on the Ordnance Survey historic maps of 1899, 1900 and 1916.

At the SW edge of the lake the Cable Incline Pyramid was built soon after 1900 to gain access to the increasingly deep excavations. This massive masonry bastion is constructed from large rubble blocks and stands at over 20m in height. It is orientated NNE-SSW and is c.15m in width by almost 40m transversely. It is a more regular shape than the E bastion and appears to be stable despite large cracks on the NNE elevation and substantial masonry revetments supporting the adjacent slate waste below the E elevation. At the foot of the Cable Incline Pyramid are two distinct groups of buildings, both of which pre-date the construction of the adjacent bastion. The western group of structures comprises a much overgrown chain incline headframe and engine house.

The eastern complex is an additional chain incline winding house that survives as a roofless structure with walls up to 3m in height, generally to the eaves and an extant stone staircase to the first floor winding mechanism. Historic map evidence illustrates the way in which the internal tramway system connected the uphaulage, processing and tipping areas. The Ordnance Survey 3rd edition map of 1916 illustrates that the Dorothea Quarry Beam Engine (CN165) also relied on this system to feed the coal hopper. Whilst only occasional sleepers survive in situ the functional relationships between each of the elements are highly legible.

At the summit of the SW Cable Incline Pyramid are a winder-house and weighhouse. A tramway formation extends for more than 300m to the S and forms the crest of the principal slate waste ‘fingertip’. These fingertip runs survive as illustrated on the 1916 Ordnance Survey 3rd edition map and remain a significant and impressive landform. Historic map evidence illustrates that the southern tips also retains significant archaeological potential with successive phases of quarrying, processing and tipping having part buried or obscured earlier evidence. Numerous gwaliau survive as evidence of secondary working on these tips.

Dorothea Slate Quarry was the principal quarry in the Nantlle Valley and its relict remains continue to dominate the area today. The well preserved monuments are of national importance as evidence of the many technical innovations developed by the quarry and as a group the elements remain highly legible and coherent illustrating the process of slate quarrying, processing, waste management and transportation.

Source: Cadw

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