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.

[13] The wreck of a wooden ship carrying finished slates was discovered in the Menai Strait and is thought to date from the 16th century.

[23] 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 railway was graded so that loaded slate waggons could be run by gravity downhill all the way from Blaenau Ffestiniog to the port.

This helped expansion at the Blaenau Ffestiniog quarries,[33] 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.

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.

[38] 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.

The slate mill evolved between 1840 and 1860, powered by a single line shaft running along the building and bringing together operations such as sawing, planing and dressing.

[41] The splitting of the blocks to produce roofing slates proved resistant to mechanisation, and continued to be done with a mallet and chisel.

An extra source of income from the 1860s was the production of "slab", thicker pieces of slate which were planed and used for many purposes, for example flooring, tombstones and billiard tables.

Alun Richards comments on the importance of the slate industry: It dominated the economy of the north-west of Wales, where, by the middle of the 19thC.

In 1870, De Winton built and equipped an entire workshop for the Dinorwig Quarry, with machinery powered by overhead shafting that in its turn was driven by the largest water-wheel in the United Kingdom, over 50 feet in diameter.

Part of the payment was determined by the number of slates the gang produced, but this could vary greatly according to the nature of the rock in the section allocated to them.

[53] Because of this arrangement, the men tended to see themselves as independent contractors rather than employees on a wage, and trade unions were slow to develop.

[54] One of the founders of the union, Morgan Richards, described in 1876 the conditions when he started work in the quarries forty years before: I well remember the time when I was myself a child of bondage; when my father and neighbours, as well as myself, had to rise early, to walk five miles (8 km) before six in the morning, and the same distance home after six in the evening; to work hard from six to six; to dine on cold coffee, or a cup of buttermilk, and a slice of bread and butter; and to support (as some of them had to do) a family of perhaps five, eight or ten children on wages averaging from 12s to 16s a week.

The owners and top managers at most of the quarries were English-speaking, Anglican and Tory, while the quarrymen were Welsh-speaking and mainly Nonconformist and Liberal.

This culminated in the suspension of 57 members of the union committee and 17 other men in September 1896, leading to a strike which lasted eleven months.

[65] The loss of production at Penrhyn led to a temporary shortage of slates and kept prices high, but part of the shortfall was made up by imports.

[69]The First World War hit the slate industry badly, particularly in Blaenau Ffestiniog where exports to Germany had been an important source of income.

[72] The quarries and mines made increasing use of mechanisation from the start of the 20th century, with electricity replacing steam and water as a power source.

[75] For many years, the quarry owners had denied that slate dust was the cause of the high levels of silicosis suffered by quarrymen.

From 1909, they had been responsible for all accidents and illnesses caused by the work, but had managed to persuade successive governments that slate dust was harmless.

The museum has a working water wheel, and a restored incline formerly used to carry slate waggons uphill and downhill.

[92] The Braichgoch slate mines at Corris have been converted into a tourist attraction named "King Arthur's Labyrinth" where visitors are taken underground by boat along a subterranean river and walk through the caverns to see audiovisual presentations of the Arthurian legends.

[94] In July 2021, after development of a bid for over 10 years,[95] the slate landscape of Northwest Wales was inscribed as a World Heritage Site by UNESCO.

The caban, the cabin where the quarrymen gathered for their lunch break, was often the scene of wide-ranging discussions, which were often formally minuted.

A surviving set of minutes from a caban at the Llechwedd mine at Blaenau Ffestiniog for 1908–1910 records discussions on Church Disestablishment, tariff reform and other political topics.

Burn calculates that there are around fifty men judged worthy of an entry in the Dictionary of Welsh Biography who started their working lives as slate quarrymen, compared to only four owners, though obviously there was also a distinct disparity in the numbers of the two groups.

Several novels by Kate Roberts, the daughter of a quarryman, give a picture of the area around Rhosgadfan, where the slate industry was on a smaller scale and many of the quarrymen were also smallholders.

Her novel Traed mewn cyffion (1936), translated as Feet in chains (2002), gives a vivid picture of the struggles of a quarrying family in the period between 1880 and 1914.