Lost Worlds in Slate - Exporing Oakeley Slate Quarry

The mighty Oakeley and Cwmorthin slate quarries just outside the slate quarrying town of Blaenau Ffestiniog (North Wales), perhaps need no further introduction, except to say that it was here that the world class roofing slate was extracted from deep under the Allt Fawr. An increasingly expanding and complex operation from Victorian times up until the early 1970' s, it eventually exploited a series of slate veins lying on a slant one below the other, comprising the north vein at the top of the formation, and below that, the back vein, then the old vein and deeper still the new vein. (some smaller veins where also worked) Oakeley eventually connected into Cwmorthin on a number of levels, and a couple of these connections are still accessible, although the boundary area itself is generally in an unstable condition due to a combination of over-extraction and geological factors.

The aim of this visit was to explore along some levels leading deeper into Oakeley from the Cwmorthin side and see what we could find.

Since this visit took place, it must be said that exploration further into Oakeley has been discouraged – thus for the foreseeable future, at least, much of this area is out of bounds, and this account is thus a record, of sorts, describing a forsaken and slowly disintegrating place.

The way into Oakeley took us through Cwmorthin's old vein workings, via floor A, thence down to floor C by way of the rather unstable chamber 8E with it's substantial stone staircase. Down still further, via an inclined shaft, which once contained a stairway, and was, in its day, an important access route for workers making their way into Oakeley from the Cwmorthin direction, finally brought us out into the modestly sized compressor chamber (33) on floor DE, which is well known and need no further mention here.

At this point we decided to take a detour to look at the trial tunnel out of the neighbouring chamber (32), on level DE, which was of interest as it offers an insight into how quarry operations where conducted.

This long level was driven to intercept the new vein, but reaches a dead end. The new vein was never proved in this part of the quarry. A lot of effort went into making this trial. Perhaps the nature of the rock where the tunnel terminates was sufficient to indicate that nothing would be gained by proceeding any further. Perhaps economic factors dictated that exploratory work be abandoned.  What is clear, however, is that such trials - and there are many scattered throughout the workings serve to emphasize the trail and error nature of underground quarrying in Victorian and early 20th century times - a fact that is often overlooked and which is essential for a true understanding of the site.

An alternative way of entering “Oakeley proper” or the eastern workings is by descending a slate slab in chamber 31 from floor DE into the lonely world of floor F, which, to me at least, has a palpable feeling of the remote about it.  ( This is probably less risky than crossing the boundary collapse in chamber 29 which has become increasingly unstable in recent years). Down here, as on floor DE, levels go through the hanging wall to intercept the old vein. Most are in various stages of collapse!

Continuing along Floor F in this area leads one to very fractured ground which, judging from the various plans available, may be traversable with great care, ultimately taking one to the base of a hidden little incline tucked away in the workings, and a way back up to the main level on floor DE.

Cwmorthin Dam

A short way into Oakeley on floor F, we encountered a dam at the end of a little detour off the main level. I have been informed that it blocks a chamber, but I know little else about it as it rarely attracts visitors and photographs of it are rare: - thus my determination to have it documented. All I know is that not long ago there was a fair bit of water backed up behind it apparently coming from a feeder somewhere in the workings behind. It has recently been drained.

I have no idea of the extent of the chamber it seals, - very much off plan here.

The similar dams on floor A and B off Cwmorthin's back vein incline far to the west have been well documented. Interestingly they were installed by Oakeley in the 1930's and have a very similar appearance. They were used to capture water finding its way down though the shattered upper Cwmorthin workings.

Along level F, drops into chambers and the openings of roofing shafts can be seen plunging to floor G, below which the quarry is flooded. After a short discussion, we decided to clamber down into one of these remote floor G chambers by way of a short roofing shaft following a stream of water over loose stones. The way on down this chamber, (shown below) entailed a scramble down tipped material, or possibly and, more worryingly, detached bits of former ceiling: - It didn't help matters examining the roof of the small chamber itself, which looked impressively awful!


It was both intriguing and shocking: - Rough edged slabs and large flakes in the roof, were suspended seemingly at a steeper angle than usual, looking for all the world as if the strata had been hit by a minor earthquake.

Among these was a very noticeable slab, which called to mind a slate window-sill, but for the fact it was precariously pointing in a downward direction!
The floor was covered with what looked like bits and pieces of former ceiling in assorted shapes and sizes: - but nothing that big, if I remember rightly.

I initially thought that the chamber may have been tipped into in the past, but on reflection I realised this couldn't have been the case, as it appeared only to be accessible via the roofing shaft, thus was not somewhere likely to have been used to dump waste slate. At this point I vividly imagined the “window-sill slab” harbouring a future ambition to join all its friends on the floor, not a very nice idea when you’re stood almost directly under it!!

Oddly this slab looked different from the others: - smoother, more regular almost, with a “sawn off” edge, hence my reference to a slate window sill, and appeared to hang in a different direction to the rest. (I can't account for this, maybe I remembered it incorrectly, although the photo seems to show this as well. I can't really explain it).

In passing, I might mention that amongst the fresh looking debris ,were what looked like chossy pale cream coloured flakes of a geological something that resembled stale white chocolate, or maybe, seriously compressed off-white icing sugar. - something that might contribute to overall instability – A type of volcanic tuff perhaps? ( indeed a band of this material lies between the new and old veins – formed by volcanic ash settling on top of the mud stones which would later become slate. The quarrymen refered to it as “chert” due to its brittle nature and like quartz it was often the cause of instability. Geologically, it's not a chert - I think one could refer to it rather as an sedimentary igneous deposit).

A year later, I collected some samples of this rock from the chamber. (More seemed to have come down.) They are solid chunks of white flinty material often with a silver shiny coating.

Cwmorthin floor G roof
Detail of chamber roof - somewhere on floor G

Cwmorthin floor G
The photograph above shows the rough chamber on floor G, as far as it is now possible to go, looking towards a level through the wall. Have no idea where this leads, or if it's still passable.
Below the explorers, the floor drops away to level H, now flooded. I was told that recently this area was drained, as the pumps were operating in the opencast, making some of level H accessible at least for a short time.

We finally gained floor DE by an assisted climb in a small chamber further along F floor, which involved a rather untidy scramble, two short metal ladders - situated at a rather inconvenient distance from each other, SRT kit, and lots of loose slate chippings, which insisted on finding their way into both my wellies!

At the top of this pitch was a long tunnel which we travelled to finally reach it's junction with the main Oakeley DE level Here we passed across the base of a number of chambers.

Cwmorthin Caban

For example In chamber 18 we found a compact little caban, where a quarryman could take a well earned break. This chamber had a rather lovely acoustic and it would have been nice to have investigated it further.

Cwmorthin Caban

Moving on, chamber 16 contains a substantial staircase from floor DE to C. According to some sources, this was installed as part of a Victorian underground tour, although in the deeper, now flooded reaches of Oakeley, such well constructed staircases and man- ways were common place. At the top of the stairway, levels on C and 1 veer off to some forgotten end, but along the way there are some impressively large chambers in the new vein. With time running out, and a couple of chambers on the boundary still to investigate, we turned back, our own little tour into Oakeley completed, East of the stairway, DE, also proceeds still onwards into the dark, eventually to be cut off from further exploration by collapses brought about by recent quarrying in the opencast pit.

Having retraced our route, back towards Cwmorthin, we made a short detour up to Oakeley floor 1 to look at a the Oakeley/Cwmorthin boundary area - a strange, remote and un-nerving place with an seemingly odd arrangement of chambers, some in better condition than others.

Below - Chamber 30, on the disputed boundary, has collapsed in a spectacular manner, possibly through a number of levels. This photo shows what is thought to be the only way in. This could well be the most dangerous chamber in the whole complex. It may have collapsed due to pillar robbing and/or mineral impurities in the rock : - Further exploration here is not recommended!

Cwmorthin Chamber 30

I will conclude with some more photographs of our Oakeley discoveries: -

Cwmorthin floor G
Above shows some fragments of newspapers and magazines which we found laid out at the side of a level on either floor DE or F. Subsequent investigation by Peter Hamilton turned up the following: -
That the fragment pictured above is a copy of TGWU publication called "The Record" - "A journal devoted to all transport and general workers", volume X No. 117. This particular issue dates from June 1931. This was almost certainly brought in while the mine was working.

Oakeley floor DE
One of the timbered levels leading off floor DE Oakeley (new vein) each has run in due to a band of poor rock. It is thought a sizeable area of Oakleley old vein may lie beyond, probably itself in an advanced state of collapse These have apparently not been traversable within the memory of the exploring community.

The road back : - Massive pit props help support the hanging wall, rather like those in a metal mine.
All the timbered cross cuts between the new and old vein have collapsed due to a zone of unstable rock which may also have been subjected to natural earth movements, and, or destabilising effects brought about by the sheer scale of Oakeley's quarrying operations.

Author Siriol Richards, photographs Peter Hamilton
(CCC & members of UCET et al)

Siriol Richards