| Railroad Name: | Merionethshire Railway |
| Gauge: | Mixed and |
| Hq City: | London |
| Locale: | Gwynedd, Wales |
| Length: | 8ch41ch |
| Short Title: | Merionethshire Railway Act 1871 |
| Type: | Act |
| Parliament: | Parliament of the United Kingdom |
| Long Title: | An Act for making a Railway from Festiniog in the county of Merioneth to the railway of the Cambrian Railways Company, in the parish of Llandecwyn in the same county; and for other purposes. |
| Year: | 1871 |
| Citation: | 34 & 35 Vict. c. lxxii |
| Royal Assent: | 29 June 1871 |
| Original Text: | https://www.legislation.gov.uk/ukla/Vict/34-35/72/pdfs/ukla_18710072_en.pdf |
| Collapsed: | yes |
| Short Title: | Merionethshire Railway (Extension of Time) Act 1876 |
| Type: | Act |
| Parliament: | Parliament of the United Kingdom |
| Long Title: | An Act to extend the time for the completion of the Merionethshire Railway. |
| Year: | 1876 |
| Citation: | 39 & 40 Vict. c. lxxvii |
| Royal Assent: | 27 June 1876 |
| Collapsed: | yes |
| Short Title: | Merionethshire Railway (Extension of Time) Act 1879 |
| Type: | Act |
| Parliament: | Parliament of the United Kingdom |
| Long Title: | An Act to further extend the time for the completion of the Merionethshire Railway. |
| Year: | 1879 |
| Citation: | 42 & 43 Vict. c. liii |
| Royal Assent: | 3 July 1879 |
| Original Text: | https://www.legislation.gov.uk/ukla/Vict/42-43/53/pdfs/ukla_18790053_en.pdf |
| Collapsed: | yes |
The Merionethshire Railway (MR) was a proposed and dual gauge railway in south Caernarfonshire (now part of Gwynedd) North Wales, United Kingdom. It was incorporated by an act of Parliament (34 & 35 Vict. c. lxxii) on 29 June 1871. Powers to build the line lapsed in 1885 and were abandoned on 12 July 1887. Work to build the line never started, though parliamentary extensions of time to do so were obtained in 1876 (39 & 40 Vict. c. lxxvii), 1879,[1] and 1882.
The line was to start at an end-on junction with the Festiniog and Blaenau Railway (F&BR) at Llan Ffestiniog and head southwest to make a triangular junction with the Cambrian Railways just north of, though the clearest published map of the route shows a triangular junction at both ends of the line.
The junction with the F&BR meant the MR would use the same gauge, which was formally, though the Act cited "2-foot gauge". While the bill was before Parliament, the Bala and Festiniog Railway (a proxy for the GWR) obtained an Act authorising it to build from to Blaenau Ffestiniog where it aimed to tap the town's prolific slate output. This proposed line was to meet the narrow gauge F&BR at Llan Ffestiniog, so the MR's Act was updated to allow mixed gauge by laying a third rail.
By proposing the line its backers sought to threaten the Festiniog Railway into reducing charges and raising service levels.
The Bala and Festiniog Railway (B&FR) reached Llan Ffestiniog in 1882 and converted the F&BR to standard gauge in 1883. This long, mountainous route of the B&FR posed little threat to the FR. Most of the slate traffic it did carry was taken to the FR at Blaenau Ffestiniog.
The northern end of the MR's planned route would have followed the course of the Bala and Festiniog line from south to near . It then ran westerly, descending along the south side of the valley of the Afon Dwyryd running parallel to the course of the FR on the northern side of the valley. It would have ended at interchange facilities with the Cambrian near Talsarnau directly competing with the FR's facilities at .