Big Pit and the Blorenge – 30th March 2008
This wasn’t a trip of two sites; it was a trip of three. When you stand in the
Big Pit car park and look out over the topography of the landscape it’s
hard not to be taken aback by the view. Mother Nature has started to take
back control of the spoil tips and rekindle them with life again so that they
can be discovered by future geologists. In 2000 Blaenafon was
designated a World Heritage site.
Eighteen of us met in the car park and were given a very in-depth
handout by our leader for the day, Dr Tom Sharpe from the National
Museum of Wales, Cardiff. Tom explained how the day would unfold and
explained the mining rules. Even though the pit is not a working one, the
rules still apply. We couldn’t take anything electrical or battery-operated
down the pit that could cause a spark; so no pictures (sorry).
We all headed towards the pit entrance with Tom leading the way. We were
ushered into what I can only describe as an old Victorian waiting room
where we waited for the mining staff to kit us up with our safety gear: hard
hat, lamp and gas mask. At this point my heart started racing due to the
fact that there was no sign of any modern technology. Everything that you
could see looked like it had just stepped out of a black and white World
War One movie. It was also at this point that I saw the cage ( yes, I said
cage) and not a lift come up ready to take us 300m down to the bottom.
We were introduced to our mine guide, who was there to give us the
history of the mine rather than the geological details. As the cage
descended one of our team asked the guide whether the water running
down the sides of the shaft was due to the amount of rainfall we had been
having or was due to a natural stream. The Mine guide replied, “No, that’s
due to the broken toilet." This set the humour for the next 50 minutes
underground, which made it just that bit more entertaining.
Locality 1, Pit Bottom
The shaft is located within the Blaenafon trough just east of the fault and
is 293.8m above sea level. It descends 89m from above the Elled seam to
the level of the black vein. The guide then warned us about the rats. He
explained that we were not meant to feed them and that they only fed on
the people that the guides leave down there if they can’t keep up!
Locality 2, Old Side Manhole between air doors
The Blaenafon fault cuts through here but little can be seen of it.
However, in the next section the upthrown side of the fault has been
displaced some 76m and contains lower strata such as Old Coal and Garw.
In the manhole you can see thin seams of ironstone as well as a large
septarian ironstone nodule near the roof. The guide made us turn off our
head lamps here just to demonstrate how dark it would have been for the
children who used to operate the doors – this darkness was an
experience I would prefer not to have again. We stopped at seven other
locations in the tunnels. All exposures were of shale and Old, Lower and
Middle Coal; Garw, Carboniferous shale, grey shale and small seams of
limestone. At locality 6 we saw some traces of Stigmaria in the shale roof.
After lunch we met on the Blorenge at the Foxhunter car park, which has
some exposed white sandstone known locally as the Garw Rock. On a
clear day, you can see the Brecon Beacons, southern end of the Black
Mountains, the limestone edge of the Mynydd Llangatwg, the Pennant
Sandstone plateau above Big Pit, Blorenge, and the Severn Estuary. From
the summit the path descends to underlying Bishopston Mudstone. The
path crosses an escarpment of conglomerate where jasper and some
large impressions of plant fossils are found. As you continue along the
path you can clearly see the change in vegetation. This marks the
quarried outcrop of the Castell Coch Limestone formation.
From the edgeof the hill there is a fine view down to Abergavenny at the confluence of
the Afon Gavenny and River Usk. The rich agricultural land to the east of
Abergavenny is underlain by the Lower Old Red Sandstone. Tom gave us
a lot more locality information with a comprehensive handout.
This was a great fieldtrip and I have a new-found interest in mining and a
whole new respect for miners. The Blorenge has some fantastic geology
to see and some very unusual plant fossils, but you have to look very
closely to find them. The views take your breath away.
Terry and Tracy Fitzgerald
Reference: Howells M. F 2007 British Regional Geological WalesNottingham: British
Geological Survey, X + 230pp