Cymdeithas Daeareg Gogledd Cymru
North Wales Geology Association

Brymbo Steelworks Field Meeting
Cyfarfod y Maes, Gwaith Dur Brymbo

It is not often that we attempt a field meeting in December, but this one would not wait for better weather in the Spring! The site of the former Brymbo Steelworks is undergoing remediation, involving open-cast mining for coal across the disturbed ground of the works site, which saw production for 200 years from Wilkinson opening the first blast furnace, which is still in-situ and a listed structure. It is expected that the site will close by February 2005.

Brymbo Opencast Mine, 12/04 Brymbo Opencast Mine, 12/04
Views of the site, including the open cut and remains of the road tunnel.
Photographs by Jonathan Wilkins

The weather was misty and dull, so pictures are not of the highest quality, but the basic geology of the site can be appreciated, together with the structure of the made ground. The face shovel is standing on outcrop of mudstones, in front of a low face of brownish-yellow sandstone which dips at about 10 degrees towards the East. The pale material seen to the right of the machine is broken concrete, the remains of the public road tunnel beneath part of the works. This was constructed by cut and cover methods, and has been buried by burnt, red shale (left) and foundry slag (right). Stratigraphy can be detected in the made ground depending upon the source of material, and dips indicate the direction from which it was brought in. In the far right (south of the cut) red shale can be seen resting upon glacial till, indicating the base of this huge man-made sedimentary pile. The open cut extends for about 30m below the machine, to the outcrop of the lowest coal seam which is being extracted. The ground is extensively fractured as a consequence of the nearby Brymbo Fault and the long history of mining by shaft and adit. Approximately 85,000 tons of coal has been won so far, and inspection shows that it is not of high quality. Some is sold to the cement works at Padeswood, the remainder to Ironbridge Power Station. On completion, the site will be occupied by housing, light industry and amenity spaces. Quite a change!

Fossil tree, Brymbo Opencast Mine, 12/04
In-situ Lycopod stem, hammer length 35cms.
Photograph by Jonathan Wilkins

Fossil collecting was mandatory, of course. Only one area was fruitful, although the mudstones were very rich in the impressions of plant debris, as would be expected in this organic-rich, freshwater environment. The sandstones contained concretionary nodules which yielded several exceptionally-preserved lycopod fronds with spore cones up to 15cm long (photo soon, I hope). The other major find was a series of complete tree-trunks in situ, only one as a complete cast, unfortunately. The best was almost 3m in height, and showed a fault parallel to the bedding of the sandstones which enclosed it. Valiant attempts at removal were somewhat thwarted by its being very fractured, but a number of disc-shaped sections were collected for subsequent display. Other stems were present only as casts with carbonaceous films representing their bark. Note that the trees of the day were actually giant horestails and ferns, and not like our modern oaks and ashes!

Our thanks for this opportunity go to Parkhill Estates Ltd., the site developers and especially to Colin Davies for his patient and enthusiastic leadership while we were on site.


Yr Arddu Field Meeting
Cyfarfod y Maes, Yr Arddu

Once again, Will The Meetings had organised superb weather, even to the extent of ensuring a cooler morning so that we did not overheat during the climb.

Llyn yr Arddu Nodular Tuff Outcrop
Lunch break by the Lake - & - Colin poses by some rocks for scale.
Photographs by John Newsome

The outcrops proved to be controversial, as ever, and thoroughly diverting. Discussion centred upon the origin of nodules in the tuffs, the definition of tuff-flow surfaces, and the relations of dolerite intrusions (Is it a sill? Is it a dyke? Is it BOTH a sill and a dyke?).


South Wales Weekend
Penwythnos De Cymru

Nant Helen Open-cast mine visit

Seen here on Saturday afternoon, in company with the members of the South Wales Local Group of the Geologists' Association. The Nant Helen open-cast mine is near the head of the Swansea valley, and is associated with the reclamation of a number of pits which formerly worked by adits from the valley sides. 3 million tons of anthracite are to be produced from seams with delightful names like Stwrin, Soap and Nine-feet. It was a most strange experience to walk on the outcrop of the Soap seam where it had been cleaned ready for coaling.

Our thanks got to Peter Ham of Celtic Energy for permission to visit and for providing a most welcome cup of tea.

By the way, my briefing notes tell me that the machine behind the group is a Komatsu PC3000 diesel-hydraulic face shovel, with a bucket capacity of 14 cubic metres. Not the biggest machine on site, but that one was parked in the shade at the pit bottom.

Trias - Penarth Lias - Lavernock Point

Sunday was spent by the sea between Penarth and Sully. The walk from Penarth to Lavernock point was very instructive, with wonderful, colour-coded outcrops of Triassic and Jurassic marls, sandstones and limestones. The effect - wholly deleterious - of coastal defences on these exposures of SSSI was amply demonstrated.

At Lavernock point the outcrop is of Jurassic limestones - and just look at that wonderful paving that has been provided so thoughtfully to enable wheelchair access to the beach.

Notable geologist wearing his field-slippers Sully saw us arguing over the Carboniferous/Triassic unconformity and discovering dinosaur footprints. The highlight was Steve Howe (National Museum of Wales) demonstrating the gait of quadrupedal versus bipedal dinosaurs. Eventually it started to get dark and we had to go home.

A special thank you to everyone who helped to make our visit so rewarding.