The Ffestiniog Railway was constructed between 1833 and 1836 to transport slate from the quarries around the inland town of Blaenau Ffestiniog to the coastal town of Porthmadog where it was loaded onto ships.

https://www.festipedia.org.uk/wiki/The_Fairlie_Duplex_Engine
The Fairlie Duplex Engine is a folk song that was written by Hughie Jones and was performed by The Spinners in the 1980s. It was also released on a VHS cassette tape. It describes the unusual features of the Ffestiniog Railway's Double Fairlie locomotives and the trials of Little Wonder against the England Engines.