The existence of a slate industry in Wales is attested since the Roman period, when slate was used to roof the fort at Segontium, now Caernarfon. The slate industry grew slowly until the early 18th century, then rapidly during the Industrial Revolution in Wales until the late 19th century, at which time the most important slate producing areas were in northwest Wales. These sites included the Penrhyn Quarry near Bethesda, the Dinorwic Quarry near Llanberis, the Nantlle Valley quarries, and Blaenau Ffestiniog, where the slate was mined rather than quarried. Penrhyn and Dinorwig were the two largest slate quarries in the world, and the Oakeley mine at Blaenau Ffestiniog was the largest slate mine in the world.Jones p. 72 Slate is mainly used for roofing, but is also produced as thicker slab for a variety of uses including flooring, worktops, headstones as well as high quality surfaces for games such as shove ha'penny, snooker and billiards.Lindsay p. 133
Up to the end of the 18th century, slate was extracted on a small scale by groups of quarrymen who paid a royalty to the landlord, carted slate to the ports, and then shipped it to England, Ireland and sometimes France. Towards the close of the century, the landowners began to operate the quarries themselves, on a larger scale. After the government abolished slate duty in 1831, rapid expansion was propelled by the building of narrow gauge railways to transport the slates to the ports.
The slate industry dominated the economy of north-west Wales during the second half of the 19th century, but was on a much smaller scale elsewhere. In 1898, a work force of 17,000 men produced half a million tons of slate. A bitter industrial dispute at the Penrhyn Quarry between 1900 and 1903 marked the beginning of its decline, and the First World War saw a great reduction in the number of men employed in the industry. The Great Depression and Second World War led to the closure of many smaller quarries, and competition from other roofing materials, particularly tiles, resulted in the closure of most of the larger quarries in the 1960s and 1970s. Slate production continues on a much reduced scale.
On 28 July 2021, the slate landscape of northwest Wales was awarded the status of a UNESCO World Heritage Site,The Slate Landscape of Northwest Wales; https://whc.unesco.org/en/list/1633/ whilst as early as 2018 Welsh slate was designated by the International Union of Geological Sciences as a Global Heritage Stone Resource.
Beginnings
The slate deposits of Wales belong to three geological series: Cambrian, Ordovician and Silurian. The Cambrian deposits run south-west from Conwy to near Criccieth; these deposits were quarried in the Penrhyn and Dinorwig quarries and in the Nantlle Valley. There are smaller outcrops elsewhere, for example on Anglesey. The Ordovician deposits run south-west from Betws-y-Coed to Porthmadog; these were the deposits mined at Blaenau Ffestiniog. There is another band of Ordovician slate further south, running from Llangynnog to Aberdyfi, quarried mainly in the Corris area, with a few outcrops in south-west Wales, notably Pembrokeshire. The Silurian deposits are mainly further east in the Dee valley and around Machynlleth.Richards 1995 pp. 10–11
The virtues of slate as a building and roofing material have been recognised since the Roman period. The Roman fort at Segontium, Caernarfon, was originally roofed with tiles, but the later levels contain numerous slates, used for both roofing and flooring. The nearest deposits are about five miles (8 km) away in the Cilgwyn area, indicating that the slates were not used merely because they were available on-site.Lindsay p. 18. Slate flagstones were also used at the smaller fort of Caer Llugwy between Capel Curig and the Conwy Valley. During the mediaeval period, there was small-scale quarrying of slate in several areas. The Cilgwyn quarry in the Nantlle Valley dates from the 12th century, and is thought to be the oldest in Wales.Lindsay p. 314 The first record of slate quarrying in the neighbourhood of the later Penrhyn Quarry was in 1413, when a rent-roll of Gwilym ap Griffith records that several of his tenants were paid 10 pence each for working 5,000 slates.Lindsay p. 27 Aberllefenni Slate Quarry may have started operating as a slate mine as early as the 14th century. The earliest confirmed date of operating dates from the early 16th century when the local house Plas Aberllefenni was roofed in slates from this quarry.Richards 1995 p. 13
Transport problems meant that the slate was usually used fairly close to the quarries. There was some transport by sea. A poem by the 15th century poet Guto'r Glyn asks the Dean of Bangor to send him a shipload of slates from Aberogwen, near Bangor, to Rhuddlan to roof a house at Henllan, near Denbigh.Lindsay p. 14 The wreck of a wooden ship carrying finished slates was discovered in the Menai Strait and is thought to date from the 16th century. By the second half of the 16th century, there was a small export trade of slates to Ireland from ports such as Beaumaris and Caernarfon.Lindsay p. 24 Slate exports from the Penrhyn estate are recorded from 1713 when 14 shipments totalling 415,000 slates were sent to Dublin. The slates were carried to the ports by pack-horses, and later by carts. This was sometimes done by women, the only female involvement in what was otherwise an exclusively male industry.For example the pack-horses carrying Penrhyn slate were usually tended by girls; see Richards 1999 p. 19
Until the late 18th century, slate was extracted from many small pits by small partnerships of local men, who did not own the capital to expand further. The quarrymen usually had to pay a rent or royalty to the landlord, though the quarrymen at Cilgwyn did not. A letter from the agent of the Penrhyn estate, John Paynter, in 1738 complains that competition from Cilgwyn was affecting the sales of Penrhyn slates. The Cilgwyn slates could be extracted more cheaply and sold at a higher price.Lindsay pp. 29–30 Penrhyn introduced larger sizes of slate between 1730 and 1740, and gave these sizes the names which became standard. These ranged from "Duchesses", the largest at by , through "Countesses", "Ladies" and "Doubles" to the smallest "Singles".Lindsay pp, 36–7
Growth (1760–1830)
Methusalem Jones, previously a quarryman at Cilgwyn, began to work the Diffwys quarry at Blaenau Ffestiniog in the 1760s, which became the first large quarry in the area.Lewis p. 6 The large landowners were initially content to issue "take notes", allowing individuals to quarry slates on their lands for a yearly rent of a few shillings and a royalty on the slates produced.Richards 1995 pp. 16–17 The first landowner to take over the working of slates on his land was the owner of the Penrhyn estate, Richard Pennant, later Baron Penrhyn. In 1782, the men working quarries on the estate were bought out or ejected, and Pennant appointed James Greenfield as agent. The same year, Lord Penrhyn opened a new quarry at Caebraichycafn near Bethesda, which as Penrhyn Quarry would become the largest slate quarry in the world.Lindsay p. 45 By 1792, this quarry was employing 500 men and producing 15,000 tons of slate per year.Richards pp. 21–22 At Dinorwig, a single large partnership took over in 1787, and in 1809 the landowner, Thomas Assheton Smith of Vaynol, took the management of the quarry into his own hands. The Cilgwyn quarries were taken over by a company in 1800, and the scattered workings at all three locations were amalgamated into a single quarry.Lewis p.5 The first steam engine to be used in the slate industry was a pump installed at the Hafodlas quarry in the Nantlle Valley in 1807, but most quarries relied on hydropower to drive machinery.Williams p. 16
Wales was by now producing more than half the United Kingdom's output of slate, 26,000 tons out of a total UK production of 45,000 tons in 1793.Williams p. 5 In July 1794, the government imposed a 20% tax on all slate carried coastwise, which put the Welsh producers at a disadvantage compared to inland producers who could use the canal network to distribute their product.Lindsay pp. 91–2 There was no tax on slates sent overseas, and exports to the United States gradually increased.Lindsay p. 99 The Penrhyn Quarry continued to grow, and in 1799 Greenfield introduced the system of "galleries", huge terraces from 9 metres to 21 metres in depth.Williams p. 10 In 1798, Lord Penrhyn constructed the horse-drawn Llandegai Tramway to transport slates from Penrhyn Quarry, and in 1801 this was replaced by the narrow gauge Penrhyn Quarry Railway, one of the earliest railway lines. The slates were transported to the sea at Port Penrhyn which had been constructed in the 1790s.Lindsay pp. 49–50 The Padarn Railway was opened in 1824 as a tramway for the Dinorwig Quarry, and converted to a railway in 1843. It ran from Gilfach Ddu near Llanberis to Port Dinorwic at Y Felinheli. The Nantlle Railway was built in 1828 and was operated using horse-power to carry slate from several slate quarries in the Nantlle Valley to the harbour at Caernarfon.Richards 1999 p. 15
Peak production (1831–1878)
Expansion at Blaenau Ffestiniog
In 1831 slate duty was abolished, and this helped to produce a rapid expansion in the industry, particularly since the duty on tiles was not abolished until 1833.Lindsey p. 117 The Ffestiniog Railway line was constructed between 1833 and 1836 to transport slate from Blaenau Ffestiniog to the coastal town of Porthmadog, where it was loaded onto ships. The railway was graded so that loaded slate waggons could be run by gravity downhill all the way from Blaenau Ffestiniog to the port. The empty waggons were hauled back up by horses, which travelled down in 'dandy' waggons. This helped expansion at the Blaenau Ffestiniog quarries,Strictly speaking, most of the slate produced in the Blaenau Ffestiniog area was mined from underground workings rather than quarried. These workings are frequently called "quarries" in the industry, and many began as surface workings. which had previously had to cart the slate to Maentwrog to be loaded onto small boats and taken down the River Dwyryd to the estuary, where it was transferred to larger vessels.Hughes p. 23 There was further expansion at Blaenau when John Whitehead Greaves, who had been running the Votty quarry since 1833, took a lease on the land between this quarry and the main Ffestiniog to Betws-y-Coed road. After years of digging he struck the famous Old Vein in 1846 in what became the Llechwedd quarry.Burn p. 5 A fire which destroyed a large part of Hamburg in 1842 led to a demand for slate for rebuilding, and Germany became an important market, particularly for Ffestiniog slate.Hughes p. 31
Mechanization and increased production
In 1843, the Padarn Railway became the first quarry railway to use steam locomotives, and the transport of slate by train rather than by ship was made easier when the London and North Western Railway built branches to connect Port Penrhyn and Port Dinorwic to the main line in 1852. The Corris Railway opened as the horse-worked Corris, Machynlleth & River Dovey Tramroad in 1859, connecting the slate quarries around Corris and Aberllefenni with wharves on the estuary of the River Dyfi.Holmes p. 13 The Ffestiniog Railway converted to steam in 1863, and the Talyllyn Railway was opened in 1866 to serve the Bryn Eglwys quarry above the village of Abergynolwyn. Bryn Eglwys grew to be one of the largest quarries in mid Wales, employing 300 men and producing 30% of the total output of the Corris district.Holmes pp. 9, 11 The Cardigan Railway was opened in 1873, partly to carry slate traffic, and enabled the Glogue quarry in Pembrokeshire to grow to employ 80 men.Richards 1995 p. 95