Field Trip: Black Mountain (western, Mynydd Du) - traverse north of Swansea, from Brynamman to Llangadog

Leader: Dr. Geraint Owen, Swansea University

Entry Fee

Members: Free

Visitors: £3.00

Date and Time



Brynammom, Ammanford, Wales

Field Trip Description

The Black Mountain (Mynydd Du) is the western part of the Brecon Beacons. It lies within the Fforest Fawr Geopark and the Brecon Beacons National Park and is traversed by the Beacons Way. The geology comprises gently southward-dipping Palaeozoic strata on the north side (“North Crop”) of the South Wales Coalfield, ranging in age from late Silurian to late Carboniferous. As befits its location within the National Park, the area is scenically attractive, with extensive views to the south over the industrialised South Wales Coalfield and to the north into rural mid Wales. Although outside the area of coal-bearing rocks, the area contains an important legacy of extractive industries and associated infrastructure.

This field meeting will comprise a traverse of the Black Mountain from Brynamman in the south towards Llangadog in the north. The major units of the succession will be examined from youngest to oldest, including the “Farewell Rock” at the base of the South Wales Coal Measures, the Bishopston Mudstone Formation (“Shale Group”) and Twrch Sandstone (“Basal Grit”) of the Marros Group (“Millstone Grit”), the Carboniferous Limestone, Old Red Sandstone, and marine Silurian rocks. The traverse provides excellent examples of sedimentary features indicative of changing palaeoenvironments, contrasting fossil assemblages, structural features of tectonic origin, and evidence of a variety of extractive industries, as well as a close relationship between geology and landscape.

Several sites will be visited, all close to parking places, although the ground conditions may be rough and wet underfoot in places. Bring warm, waterproof clothing and sturdy, waterproof footwear. Please bring a packed lunch. Safety helmets are advisable at one site.

Useful reading

  • British Geological Survey, 2013. Fforest Fawr: exploring the landscape of a Global Geopark (1:50,000 scale geological map). British Geological Survey, Keyworth.
  • George, G.T., 2008. The geology of South Wales: a field guide. [email protected]
  • Harlow, D., 2014. The land of the Beacons Way: scenery and geology across the Brecon Beacons National Park. Geologists’ Association South Wales Group, Cardiff.
  • Howells, M.F., 2007. British Regional Geology: Wales. British Geological Survey, Keyworth.

Geraint Owen, 2015 ([email protected])

A coach has been booked with the following stops:

7.55 am Keynsham Football Club 8.05 am Bath Newbridge Park & Ride 8.10 am Bath Queens Square 8.30 am Box Pharmacy 10.45 am Arrival at Brynammom 3.30 pm Anticipated return

The cost for a seat on the coach is £25.

Location Map

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Important Notice: Bath Geological Society Insurance

Each person attending a field meeting does so on the understanding that he/she attends at his/her own risk. The Bath Geological Society has Public Liability Insurance Cover for field and indoor meetings, but Personal Accident Cover and Personal Liability Cover remain the responsibility and personal choice of the participant.

There may be an element of appropriate cover included in house insurance or in travel insurance: although Bath Geological Society activities are not particularly dangerous members are advised to check whether exclusions apply to activities in which they plan to participate in case they wish to arrange further cover. An annual travel insurance may be the best solution for any member who regularly attends field events: this again is a matter of choice.

Please note however that all members participating in overseas events will be required to have travel insurance for the duration of the event: this is so that participants are covered for Medical, Repatriation and Personal Liability expenses. The Personal Accident element remains the personal choice of the member and again members are advised to check exclusions so that they can make an informed decision about the cover they want.