Production after 1938 was on a reduced scale, and the quarry closed in the winter of 1946/47, mainly due to a lack of workers.

[4] Transportation was an issue, as the nearest turnpike road had been built in 1771 from Wem in Shropshire to Bronygarth, where there was a limestone quarry and kilns.

It was opposed by the owner of Chirk Castle, Colonel Biddulph, who wanted it to be a public carrier, and so the bill was withdrawn.

The turnpike trustees then produced their own bill, which included a clause to allow the Cambrian Slate Company to construct a tramway beside their road.

The House of Commons Select Committee rejected the clause, as "they had never before been asked to unite railroads and turnpike roads together and did not consider it their duty to do so now for the first time."

Underground mining of the slate began when chambers were excavated close to the main tunnel near Townsend's quarry.

The quarry flooded, and a valve controlled the flow of water through the concrete plug, which then drove a turbine to power the dressing mill.

[7] In March 1896, the Cambrian quarry announced in a journal that they would be replacing the horses which were used to pull wagons on the internal railway system with locomotives.

It was a 20 hp (15 kW) bow-frame model, weighing 2.5 tons, and fitted with a Dorman twin-cylinder petrol engine.

[13] Apart from the closure in the 1870s, the quarries were worked consistently, employing up to 90 men, and producing around 2000 tons of finished product per year.

[16] This was a particular blow to Alan Taylor, the company chairman, who had been propping up the quarry with his own money for some years, in order to ensure there was work for the residents of Glyn Ceiriog.

[17] A closing auction took place on 14 July 1948, and during the winding up procedure the accountants found that Taylor had invested some £10,000 of his own money to keep the quarry solvent.

A routine inspection in 1975 by the Forestry Commission, who owned the site, found that a landslide had partially blocked the main tunnel, resulting in further flooding.

[19] The Ceiriog Valley is some 17 miles (27 km) long, and is composed of many types of rock, including china stone, coal deposits, granite, limestone, silica, slate, and volcanic ash.

Much of the slate also included deposits of iron disulphide, a shiny yellow mineral which weathered rapidly, as well as cephalopods and other marine fossils from the Palaeozoic era.

This is in contrast to the quarry at Ty Draw, on the southern side of the valley, where the harder Ordovician slate has prevented much vegetation from growing.