Meirionydd Slate Mines

Introduction
A number of Ffestiniog workings are still operating, most slate now being removed by quarrying with overlying overburden being bulldozed away. With working quarries it is better to request a visit rather than making a clandestine trip. Fforwm Plas Tan-y-Bwlch is probably the best source of current information about the workings and whether they are currently working. From a sporting point of view, several are of interest including Croesor, Rhosydd, Cwmorthin and Wrysgan.

There are also several large mines near Corris which generally specialised in slab rather than roofing slate.

Warning: Slate mines are particularly dangerous. Apart from the roofs being unstable (Croesor being the prime example), slopes consisting of great lumps of slate debris present a particluar hazard.

Abercorris (Corris)
Grid Reference: SH 754 089

Underground workings. One adit at top of incline open, leading to chambering and shaft to lower level.

Abercwmeiddau (Corris)
Grid Reference: SH 746 089

Number of large bore machined tunnels.

Aberllefenni (Corris)
Grid Reference: SH 768 103

Large underground quarry still working for slab. 6 or 7 underground chambers about 600' high. Workings extend through hill emerging at pit with abandoned crane.

Braich Goch (Corris)
Grid Reference: SH 748 078

Large underground quarry. Area landscaped. Three adits open. No 6 adit below road over 3000' long with chambers leads to inclines, one down into water, another up into Vane's Level - the upper adit.

Bryneglwys (Abergynolwyn)
Grid Reference: SH 695 054

Large underground workings. Underground workings enterable.

Conglog
Grid Reference: SH 670 467

Small mine situated between Cwmorthin and Rhosydd. 2 adits leading to chambering

Croesor
Grid Reference: SH 657 457

Medium sized wholly underground workings on seven levels, bottom three flooded. Worked late 19C until 1930. 1300’ adit leads to workings and incline. Linked underground to Rhosydd Mine to the east. Underground traverse between the mines is dangerous and quite involved and requires the passing of various ‘hurdles’ including Tyrolean traverse, rotten bridges, flooded chambers using dinghies, abseils, prussiks and ‘a cheval’ traverse of bendy metal rail and rotten beam liberally supplied with protruding nails. Access to the main workings is via an eyehole on the left near the top of the incline.

Further details regarding this through trip can be found here: Croesor Rhosydd Through Trip.

Cwmorthin
Grid Reference: SH 681 459

Extensive underground quarry linked to and worked with Oakely Quarry on the other side of the mountain. The working are complex with slate being won on several levels and in several veins. The main adit is at lake level. There were a number of higher adit, but some have been lost by untopping work. At least one adit at level 2 is open and leads to dangerous and collapsed chambers. The lake adit leads to two inclines leading downwards to an extensive series of working. A number of trips are possible, the two most interesting being the round trip via the two inclines and the cunning through trip to the huge chambers of Oakely.

Cwt y Bugail
Grid Reference: SH 734 468 Partly underground quarry, some chambering of which is accessible.

Diffwys Casson
Grid Reference: SH 712 463

First large quarry to work in Ffestiniog. Modern untopping work has confused the site. Much underground work during the end of the 19th century. Some adits are accessible. Some untopping work and a collapse reveal underground chambers.

Llanfair
Grid Reference: SH 580 288

Moderate sized underground near Harlech. Show mine open to public.

Llechwedd
Grid Reference: SH 700 470

Well known underground quarry operated both as a show mine and a working quarry.

Maenofferen
Grid Reference: SH 714 465

Underground quarry. Working.

Manod
Grid Reference: SH 732 455

Underground quarry. Used for art storage during WW2 and by DDE until 1980. Following 1980 serious untopping work commenced.

Moelwyn
Grid Reference: SH 661 442

At altitude of 1700' above the Stwlan reservoir on Moelwyn Mawr. Number of adits with dangerous internal shafts (fatalities during mid 1990's). Adits currently gated.

Nyth y Gigfran
Grid Reference: SH 689 462

Small working. Two adits and tunnel through to Oakeley open.

Oakeley
Grid Reference: SH 695 470

Working quarry with two show mine trips at Gloddfa Ganol (now closed). Amalgamation of Holland, Gloddfa Ganol and Welsh Slate workings. Also linked underground to Cwm Orthin.

Ratgoed (Corris)
Grid Reference: SH 787 119

Mainly underground working. A number of adits. Site is in coniferous forest. Remains of incline and winding house. Several buildings. Lower adit has been visited. A 800' long adit leads to the base of 3 to 4 large, square bore shafts about 40' high. These are presumed to enter the chambered workings. Purpose of the shafts presumed to be for dumping waste for removal, unless there was some mechanism for lowereing slate produce in a controlled manner.

Rhosydd
Grid Reference: SH 664 461

Started 1840, closed 1930. Largest underground quarry outside of Ffestiniog. Workings in 170 chambers on 14 levels, those below 9 now flooded. Long adit leads to chambering which apart for a couple of trial chambers are confined to one vein. An incline leads from the end of the adit to the surface at the West Twll where slate extraction originally commenced. During 1900, the eastern part of the workings collapsed underneath the area of the East Twll and the chambers are loose. The working to the west which are entered from the West Twll are safer and lead to the link passage with Croesor Mine. There are another couple of adits and shafts. The collapsed East Twll has quite a few deep looking crevices amongst the confusion.

Further details regarding the through trip from Croesor Mine can be found here: Croesor Rhosydd Through Trip.

Rhiwbach
Grid Reference: SH 740 462

Worked 1812 to 1880s. Underground workings on a number of levels enterable and begin at a large pit. A long drainage tunnel from the workings emerge at SH 745 475.

Wrysgan
Grid Reference: SH 676 458

Small mine with impressive incline and short tunnel above Llyn Tanygrisiau. Workings entered through five adits, but are unstable. Bolts and traverse lines have recently been installed providing interesting short round trips.