The Friends of Cwmorthin Slate Quarry

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Map of the Cwmorthin Workings

A coloured composite plan of Cwmorthin is available for download below as a PDF file:

Map of Cwmorthin Slate Mine
cwmorthin_plan.pdf (577kb)

Having been drawn from numerous original mine plans, it should be considered as a general guide rather than very specific on detail. Most of the adits on the plan are no longer open - the two that are are the Back Vein's "1 North", more commonly referred to as Lake Level, and the Old Vein's "2 South", more commonly referred to as the Smoke Flue.

Floors going upwards from Lake Level are numbered sequentially, Floor 1 being Lake Level, going up to ultimately to floor 8. Floors going downwards from Lake Level are lettered, Floor A being the first one down, then B, C, D, and finally E. There is an F floor and a G floor in Oakeley, but floors deeper than these are all under water now (they actually go down as far as S floor!). Almost all workings above Lake Level (Floor 1) are inaccessible now.

Cwmorthin mainly worked two slate veins - the Back Vein and the Old Vein. These can almost be considered separate mines, just interconnected in several places. Several smaller veins were also worked on a very limited scale (such as the Stripy Vein, which sits between the Back Vein and the Old Vein).

The areas in Blue on the map show the Old Vein workings. Most Old Vein workings from Lake Level down to E floor are accessible by one means or another but most of this ground is fractured and in generally poor condition. The areas in Orange show the Back Vein Workings from Lake Level and below. There are also upper floors in the back vein right up to floor 8 - but they are omitted from the map for clarity and like the upper Old Vein floors, are largely inaccessible now. Almost all of the lower Back Vein workings are accessible and are in a good condition, with the exception of some localised damage from Pillar Robbing.

The areas in Green represent the only small areas of the neighbouring Oakeley Mine to which access is permitted. Please do not stray beyond the map into deeper parts of Oakeley as there is no access agreement or permission in place for us to do so.

Cwmorthin Technical Guide

A separate map covering all the many pitches, zip-lines and traverses, complete with accompanying notes is available for download here:

Cwmorthin Slate Mine Technical Guide
technical_guide.pdf (1mb)

This is the map to refer to if you are keen to use the extensive rope systems but obviously their use requires the correct caving equipment and training.

Cwmorthin and Related Documents

A small selection of surviving records are in our possession, relating to Cwmorthin itself and the local slate industry in general. They have been scanned to very high quality and some are available to download below. Please be aware that they are large files. We'll add more when time allows.

  • Letter Jan 19th 1889: This letter, written on genuine Cwmorthin Slate Quarries Limited headed paper, is from the company liquidator just before the New Welsh Slate Company took over the mine.
  • Letter Jan 16th 1889: A similar letter requesting supplies from Manchester on behalf of the company liquidator.
  • Oakeley Note July 10th 1888: A curious small note on Oakeley Upper Quarries headed paper listing the Smiths employed at several of the major Ffestiniog quarries.
  • Cwmorthin Slate Company Logo: A modern digitised copy of the original company logo, as found on headed paper documents of the period.
  • Festiniog Railway: Three separate purchase orders from the FR to Bells Asbestos Ltd in Manchester, dated 1888, for brass lubricators and other items. See Part1, Part2 and Part3.
  • Bettws-y-Coed Advert 1900: A rare advert placed in the Stone Trades Journal. This small quarry, long closed, was very unusual in that they could enamel their slates and had all the requisite plant onsite to do so.
  • Graig Ddu Slate Quarries Nov 11th 1888: A postcard ordering something in a hurry from Chester.
  • Graig Ddu Slate Quarries Jan 25th 1889: A purchase order for Asbestos products. Another purchase order dated 1889 appears to be a repeat order for 1000 copying sheets.
  • Port Penrhyn Oct 10th 1889: A letter requesting advice on Asbestos rope products from Bells in Manchester.
  • Llay Hall Colliery 8th Feb 1899: A purchase order for 12" x 12" Asbestos sheets,1/8" thick.