Author James Boyd suggests that the earliest predecessor to the Penrhyn Quarry Railway was the 1 mile (1.6 km) long 2 ft 1⁄2 in (622 mm) gauge Llandegai Tramway, built in 1798.

[7] It included two balanced gravity inclines one from the floor of the Cegin valley near Llandegai to the hills above Bangor, the other dropping from there to the mill.

The quarry suffered a strike in 1874, which slowed down plans to replace the railroad, but in July 1875 the decision was made to build a new railway and introduce steam.

Contractor Richard Parry and civil engineer Robert Algeo were in charge of building a completely new railway that took a more circuitous route to the quarry but avoided the need for any inclines.

[5] There was a significant demand for building materials after the First World War, as Britain recovered from the conflict and many new houses were built to replace slums.

Shortly after the war, the quarry began producing Fullersite - ground slate waste - which was shipped in large quantities along the railway.

These had been built for war use by the United States Army Transport Corp, and were refurbished before being sold to the railway, but were not successful, and after three years of intermittent use they were put aside.

[5] Immediately after the Second World War, there was a short boom in demand for Welsh slate, to meet reconstruction needs throughout the United Kingdom.

However this proved to be a short-lived period of success, and cheap foreign imports of slate and new man-made roofing materials quickly began to eat into the market for the higher-quality and more expensive Penrhyn product.

A steady decline in traffic through the 1950s and growth in the use of roads for transporting slates direct from the quarry to market meant the end of the railway was inevitable.

The main line's primary purpose was to carry finished slates and Fullersite (powdered slate)[10][11] to Port Penrhyn where they were loaded onto ships or, from February 1852 when the Chester and Holyhead Railway opened its Port Penrhyn Branch,[12][13] onto standard gauge trains.

[20] An example of the second type of passenger vehicle – an Incline Carriage – has survived in the Penrhyn Castle Railway Museum.

[25] 16 of these were built in two batches between 1878 and 1908, each bore a single letter in the series A to P. The service was withdrawn on 9 February 1951,[26] rendering the carriages redundant.

Contradicting this to a degree is the Moseley Railway Trust which has carriage "O", which came into their hands after a long tour of various preservation sites, starting with Bressingham Steam and Gardens.

The section of restored railway was approximately one-fifth mile (0.3 km) in length and ran between Coed y Parc bridge (Felin Fawr) (grid ref.

In July 2017, all railway operations ceased at short notice and the rolling stock was removed from the site.

[4] The track remained in place in August 2017, though the lines leading to the loco shed and crossing the footpath, which were removed in September 2017.