«Prepared by Dyfed Archaeological Trust For: Cambrian Mines Trust DYFED ARCHAEOLOGICAL TRUST RHIF YR ADRODDIAD / REPORT NO. 2013/77 RHIF Y DIGWYLLIAD ...»
Pleistocene/Quaternary: Cwm Ddu and Cwm Tinwen are important features interpreted as nivation cirques. They are exceptional in occurring at much lower altitudes than predicted for true glacial cirques in the area and are believed to have originated through nivation processes during the Devensian. In Cwm Tinwen a large ridge of debris is thought to have formed from the accumulation of frost-shattered material below a large snowpatch. In contrast, the more open, cirque-like basin of Cwm Ddu is floored by terraced superficial deposits. While it has been proposed that this debris accumulated as solifluction deposits beneath an inert mass of neve, recent examination suggests that this explanation is not entirely satisfactory; possibly glacial processes may have been responsible for some of the deposits. The interpretation of the landforms and sediments in Cwm Ddu and Cwm Tinwen, with their bearing on whether these sites acted as major ice sources during the Devensian, is crucial to the understanding of Late Pleistocene events and processes in the area. The contrasting and exceptional features exhibited by the two sites, and their still controversial origin, makes them important localities for Pleistocene studies.
The bog at the head of the River Elan (Cors Lwyd) is an important palynological site recording detailed evidence for vegetation and environmental changes in central Wales during the Devensian Late-glacial and Holocene. It is the only site so far studied in central Wales with a pollen record extending back to the Devensian Late-glacial. The extensive and detailed nature of the pollen stratigraphic record, together with the location of the site, make the bog an essential site for studies of regional variations in vegetation history in Wales.
Fluvial Geomorphology: The upper Elan is a particularly good example of an upland meandering stream in a low relief floodplain. It shows several contrasting planform types in a relatively confined area. The dominant channel change characteristics are lateral growth, loop expansion and relative stabilisation against a confining northern valley wall and southern terraces. Confined cut banks in the section are being actively eroded and provide the main sources of sediment. Sedimentation occurs locally as point bars and medial bars. The upper Elan is representative of an upland valley meandering channel. It is particularly important for the detailed studies that have been carried out and the contrast it provides with lowland meandering sections altered by human interference.
Mineralogy (Cwm Ystwyth Mine): The extensive workings of this longestablished mine display a uniquely interesting association between structure and mineralisation. Two early lodes show lateral zoning and are cut and downthrown by a third, later lode which shows vertical zoning. Minerals found include galena, sphalerite, pyrite, chalcopyrite, quartz and calcite. The importance of this site lies in its structure and in the chronology of its mineralisation, rather than in the occurrence of rare mineral species.
Llandovery (Caban Coch Quarry): This locality shows the type section of the Caban Coch Conglomerate, a distinctive deposit formed as a proximal submarine fan in early Silurian times. The conglomeratic unit is around 100 metres in thickness, with shales in its middle part, and it shows sole marks proving derivation from the south-east. This is an important site for studies of the Llandovery basin and sedimentary environments.
The site includes Nant Irfon National Nature Reserve (141.5 ha), declared in 1962, 1972 and 1983 and owned and managed by the Countryside Council for Wales. A further 12 ha at Bwlchgwallter in the Ystwyth Forest are managed by the Council as a Forest Nature Reserve by agreement with the Forestry Commission. The site also includes the Llanerch-yrfa nature reserve (14 ha) managed by the Brecknock Wildlife Trust on a lease from the owners.
Edited version taken from CCW website.
APPENDIX 3: CITATION FOR MWYNGLODDFA CWMYSTWYTH SSSI FROM
COUNTRYSIDE COUNCIL FOR WALES WEBSITE
SITE OF SPECIAL SCIENTIFIC INTEREST CITATION
MWYNGLODDFA CWMYSTWYTHDate of Notification: 2000 National Grid Reference: SN 803746 O.S. Maps: 1:50,000 Sheet number: 135 1:10,000 Sheet number: SN 87 SW Site Area: 14.1 ha
Mwyngloddfa Cwmystwyth is of special interest for its mineralogy and for the plant communities that have developed on the metal-rich spoil tips, associated rock outcrops and ruined buildings. These habitats support a great variety of lichens, including a number of rare species which are typically only found associated with heavy-metal-rich sites. The underground mine workings are important for hibernating bats. The site is situated on the north bank of the Afon Ystwyth 1.5 km upstream of the village of Cwmystwyth, at an altitude of 300 m, and incorporates gently sloping ground on either side of the mountain road to Rhayader. The former mine workings extend into steep crags to the north and into the slopes to the east and to the south of the Afon Ystwyth; these areas lie within the adjacent Elenydd Site of Special Scientific Interest. Cwmystwyth contains the most extensive area of metal mine workings in Ceredigion. Mining began in Bronze Age times but production of metals peaked in the early years of the 20th Century. The workings were officially abandoned in 1923, at which time reported mineral returns amounted to approximately 51,000 tons of lead (galena) and zinc (sphalerite) ore and over 33,000 ounces of silver, although this is almost certainly a gross underestimate of total ore extraction.
Geological The geological interest at this site lies both in the spoil tips and in the underground workings, and is contiguous with an area of national mineralogical importance located at Graig Fawr and Copper Hill, in the adjacent Elenydd SSSI.
Both the early (A1) and late (A2) phases of mineralization are well displayed at the site. A1 mineralization is represented by various quartz-sphalerite-galenachalcopyrite-dolomite breccias, whilst A2 mineralization, which provided most of the ores mined, is represented by a sphalerite-galena-quartz-calcite-pyrite assemblage. Additional geological interest is provided by the intersection of the south-dipping Kingside and Comet lodes by the younger north-dipping Mitchell’s Lode and also by an apparent lateral and vertical mineral zonation exhibited by the Comet and Mitchell’s lodes, respectively.
Biological Many of the spoil tips are largely unvegetated but, in places, there is a sparse sward of common bent Agrostis capillaris and sheep’s-fescue Festuca ovina. The lichen flora of these spoil tips is well developed. It includes species such as Acarospora sinopica, Baeomyces placophyllus, Sarcosagium campestre, Vezdaea leprosa, the scarce Coppinsia minutissima, Leptogium intermedium, Polyblastia gelatinosa and Stereocaulon condensatum and the rare Gyalidea subscutellaris, Vezdaea cobria and V. rheocarpa, which are all characteristic of soils or rocks with a high metal content. The rare metal-tolerant moss Ditrichum
plumbicola occurs in one of the damper areas. The lichen Placynthiella hyporhoda occurs here at its only known British location. Further characteristic lichen species can be found on the walls of the ruined mine buildings, including Psilolechia leprosa and the scarce Massalongia carnosa.
Additional botanical interest is provided by the rocky stream banks within the site, which support a small population of the scarce forked spleenwort Asplenium septentrionale.
The complex system of underground mine workings at Cwmystwyth is the best known location in Ceredigion for hibernating bats. Long-term monitoring of these workings has shown that Daubenton’s Myotis daubentonii, Natterer’s M. nattereri, Brown long-eared Plecotus auritus and Whiskered/Brandts M. mystacinus/M.
brandtii bats are regularly present during the winter months.
Edited version taken from CCW website.
Paratowyd yr adroddiad hwn gan / This report has been prepared by James Meek Swydd / Position: Head of DAT Archaeological Services Llofnod / Signature.........
Mae’r adroddiad hwn wedi ei gael yn gywir a derbyn sêl bendith This report has been checked and approved by
KENNETH MURPHYar ran Ymddiriedolaeth Archaeolegol Dyfed Cyf.
on behalf of Dyfed Archaeological Trust Ltd.
Swydd / Position: TRUST DIRECTOR
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