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Wednesday, 23 October 2013

Castell Grogwynion … Fort of the white … Ceramics?

The Early Mines Research Group supported by Sarahjayne Clements, CBA bursary holder, RCAHMW, and Keith Haylock, PHD Researcher, Geography Department, University of Aberystwyth, excavating Castell Grogwynion Hillfort.
A small excavation was undertaken at the Iron Age hillfort Castell Grogwynion last week in an attempt to identify a potential Iron Age metal working site located on the northern terrace of the fort. Early mines are fairly elusive archaeologically and searching for them has been the focus of over twenty years’ research by the Early Mines Research Group. Evidence of Iron Age metal working is particularly rare in Ceredigion, despite the importance raw materials evidently held for Iron Age material culture.

Aerial Photograph of the Iron Age hillfort, Castell Grogwynion.

The excavation at Castell Grogwynion was the conclusion of a series of surveys conducted on three north Ceredigion hillforts, Castell Grogwynion, Darren Camp and Pen Dinas, for a research project by Keith Haylock at the Institute for Geography and Earth Sciences (IGES), Aberystwth University, in collaboration with The Royal Commission, and with permission from Cadw.

Using a special portable X-ray Fluorescence (pXRF) ‘gun’ Keith can find out what metals are present in the soils of the hillfort, with the aim of finding high concentrations of prehistoric metal working evidence. This equipment has revolutionised non-destructive archaeological identification of early mine areas, through the detection of metal slag and smelting activities.
Keith Haylock, operating pXRF survey.
The results of the Geophysical Survey taken in 2012. Areas of interest are highlighted with red, 1 = the area excavated.
Out of the three hillforts surveyed only Castell Grogwynion, in English “The fort of the white pebbles”, demonstrated high lead readings, which were focused on the terrace. Geophysical survey in 2012 by ArchaeoPhysica LTD further confirmed this concentration.

To test the nature and date of the lead concentration, Dr Simon Timberlake and the Early Mines Research Group, carried out a limited excavation on the terrace at Castell Grogwynion in early October.

The Early Mines Research Group excavating.
Some of the seventeenth or eighteenth-century pottery recovered at Castell Grogwynion.

Rather than an Iron Age smelting site, far more recent evidence of seventeenth or eighteenth-century lazy-bed cultivation was discovered with lead-glazed pottery and other domestic rubbish tipped into the soil. These findings confirmed that a nearby platform and cultivation terraces within the hillfort, first identified by Louise Barker during the new Royal Commission survey, were indeed the remains of a post-medieval upland cottage settlement.

Post Excavation Analysis.
Post medieval cottage settlements are fairly common in the Welsh landscape, however the structural evidence is rarely accompanied by any artifactual remains. Although Iron Age finds were limited to a single sling shot, it was exciting to discover the sheer quantity of pottery uncovered through the excavation, surprising in such a remote location. Further scanning the pottery with the XRF gun revealed the cause of the initial high metallic reading: the glazing of the pottery contained an unusually high lead content.  The leaching of the lead glaze into the soil was hypothesised to have been the most likely cause of the high metallic readings. The discovery of this pottery demonstrated the importance of XRF for archaeological survey ― it can detect vital and less structural remains including spoil heaps and rubbish dumps, where the most significant artifactual data is often recovered.

All in all it was great to be part of this excavation and watch the story of the Iron Age hillfort unfold and exciting to be part of such important research into the varied uses of new and powerful forms of archaeological remote sensing.
Kimberly Briscoe and Sarahjayne CBA Community Bursary Holders, RCAHMW, Castell Grogwynion.
By Kimberly Briscoe, Community Archaeology Placement Holder.

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