Big Pit and the Blorenge 30Th March 2008

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