Report - - Cwmorthin Slate mine Jan/April 2019 | Mines and Quarries | 28DaysLater.co.uk

Report - Cwmorthin Slate mine Jan/April 2019


Under a mountain
28DL Full Member
Having visited Cwmorthin at the weekend I finally have some decent enough pictures to post a report. I have now visited 3 times, the first being with the guys from Aditnow (Highly recommend a trip with these guys, very knowledgeable and without that trip I would have probably got lost on subsequent visits.) The second in Jan was with @Mr Sam and last weekend with a mate from work.

I'm not going to write a full historical account as it is so extensive so I will so a summary and provide links.

Quarrying was started around 1810 by the Casson family who owned Diphys Casson quarry on the other side of Blaenau Ffestiniog. Diphys was much more successful than Cwmorthin which they abandoned around 1830. The ownership of the quarry was tossed around between a few different partnerships/companies until 1860 when it was connected to Ffestiniog railway and the mass extraction could begin.

In 1861 the Cwm-Orthin Slate company was formed with £100k of capital - a wharf was leased at Porthmadoc and the Cwmorthin tramway was built down to the ffestiniog at Tanygrisiau by the way of 2 inclines.
Early progress was good, in 1862 350 tons of slate was produced which raised to 12,500 tons in 1876. Shortly after this a court was brought against the company for not reporting a death - required by the metalliferous mines act. They argued that they were not bound by act as it was an underground quarry and not a mine, the court didn't agree and the company went into liquidation in 1876.

There was then a despute with the neighbouring Oakeley quarry over 'tresspass chambers' on Cwmorthins land. In 1884 there was a big collapse in the Cwmorthin workings which went all the way to the surface, draining the lake above it and leaving huge holes which remain to this day. This caused production to halve from 11,600t in 1884 to 6,900t in 1896. After the fall they were forced to work down under the lake level (floor 1) adding the expensive of pumping equipment and development work.

There was then some issues about companies causing collapses in the others mine. In 1900 Oakeley brought Cwmorthin quarry and some of the chambers were to flooded to try and stabilise them. Floating bridges were installed to keep access to the rest of the mine. During the first world war Cwmorthin was ignored by Oakeley management until the early 20s. They had tried working the upper floors but years of pillar robbing and illegal mining had left it in a right state so they had to go down. In 1932 the process began draining the quarry of water through a borehole - this has was widened enough to take a tramway even though it's about 2 foot higher than the Cwmorthin floor. From this point slate was taken out via Oakeley and Cwmorthin surface working was stopped.

During WW2 only the pumps were left running. Up until the 1960s the equipment was all in situ and working order until a contractor came and removed it. Small scale work was continued into the late 90s but was never really successful.

If you want to read this by someone has better writing skills than a 6 year old I recommend Graham Isherwoods book 'Cwmorthin Slate Quarry'

Other links:

Adit Now
Go Below - These do adventure trips into the mine - You will see some of their rigging in my photos.

It was pissing it down on Saturday so I didn't take any exterior photos. It was surprisingly dry inside apart from when I climbed up a waterfall.

Heres a map I will try to give you the chamber numbers if I can.

A rather dodgy area behind the Back Vein Incline (BVI)

Former bridge just of the incline on Floor C Chamber 1 East

Inside the same chamber but on Floor D

A truck wedged in the incline. Off to the right is one of the bridges above.

Looking up the incline

Electrical switch at the bottom of the incline. Marked a 'loom' and 'pump space' on the map.

Now heading the chamber to the right on the map - Floor E Chamber 1 East

Here we have the crane which hauled slate up from Floor G. It was installed by Oakeley Quarry in 1937.

There's a train of wagons in this room as well.

Heading back east now past the incline there is another train parked up. E1East

Sam in E2E

Level Ffrench. Right comes from Chamber E11E left goes to Oakeley DE floor.

Follow it far enough you will come across the Chamber 34 incline with its impressive winding gear. Built 1934.

Heading down the incline and going along a few chambers takes you to a really dodgy catwalk in Chamber G36

Back up the incline and onto the Floor DE compressor chamber, marked CC on the map. There is a collection of artifacts and a guest book to sign.

There is also this lovely old switch

The next chamber has a drill in it, this was rescued from somewhere else in the mine.

We then made our way along DE floor which connects to floor E on the old vein via some dodgy pipe bridge. We crawled up the old vein incline which is about 2ft high in places and covered in loose rock, it hasn't been used for slate since 1899. My hard hat fell off and rolled to the bottom, so if anyone can save it I'd be very grateful!

The top of the incline is very dodgy, recently new telegraph poles have been put in to stabilise it.

The winding drum at the top of the OVI

Well that's it for the tour. All I have left are photos of bridges from throughout the mine.

I nearly fell down the slab in front of the camera on the last two pictures but my mate grabbed me. Looked like a mere leg breaker rather than death though :thumb


Fear is the little death
Regular User
Didnt fancy doing any of the ziplines then.


Under a mountain
28DL Full Member
Didnt fancy doing any of the ziplines then.

I nearly fell down the rock face in chamber E10 East. That's enough excitement for me for one day.

I did take my harness/cowstails to have a go on some of the bridges but I chickened out.


Fear is the little death
Regular User
Well, you could always do the GoBelow trip but its more fun when you dont have to deal with all the H&S crap with them.


28DL Full Member
28DL Full Member
Amazing pictures, some of the machinery is so we preserved and looks like you could start it right back up.
Quite a scary explore I'm sure but well worth it to record this place.