Beyond Stonehenge: Carn Menyn Quarry and the Origin and Date of Bluestone Extraction in the Preseli Hills of South-West Wales
Total Page：16
File Type：pdf, Size：1020Kb
Beyond Stonehenge: Carn Menyn Quarry and the origin and date of bluestone extraction in the Preseli Hills of south-west Wales Timothy Darvill1 & Geoff Wainwright2 Recent investigations at Stonehenge have been accompanied by new research on the origin o f the famous ‘bluestones’, a mixed assemblage o f rhyolites and dolerites that stand among the much taller sarsens. Some o f the rhyolite debitage has been traced to a quarry site at Craig Rhosyfelin near the Pembrokeshire coast; but fieldwork on the upland outcrops o f Carn Menyn has also provided evidence for dolerite extraction in the later third millennium BC, and for the production o f pillar-like blocks that resemble the Stonehenge bluestones in shape and size. Quarrying at Carn Menyn began much earlier, however, during the seventh millennium BC, suggesting that Mesolithic communities were the first to exploit the geology o f this remote upland location. Keywords: Britain, Preseli Hills, Stonehenge, Mesolithic, Neolithic, megalithic, bluestone, dolerite, meta-mudstone, prehistoric quarrying Introduction For nearly a century it has been known that the 80 or so pillars of dolerite, rhyolite and tuff, collectively known as ‘bluestones’, that were incorporated into the structure of Stonehenge, Wiltshire, originated over 220km away to the north-west in the Preseli Hills of south west Wales (Thomas 1923). However, despite the publication of numerous excavations and surveys within and around Stonehenge (RCHME 1979; Richards 1990; Cleal et al. 1995; Darvill & Wainwright 2009; Parker Pearson 2012), it is only relatively recently that systematic archaeological fieldwork has been undertaken in west Wales to investigate the bluestone sources and their original context (Darvill & Wainwright 2002; Darvill et al. 1 Department o f Archaeology and Anthropology, Faculty o f Science and Technology, Bournemouth University, Fern Barrow, Poole BH 12 5BB, U K (Email: [email protected]) 2 March Pres, Ponfaen, Fishguard SA65 9TT, U K (Email: [email protected]) © Antiquity Publications Ltd. ANTIQUITY 88 (2014): 1099-1114 http://antiquity.ac.uk/ant/088/ant0881099.htm 1099 Beyond Stonehenge 2012b with earlier references; Nash et al. 2012; Parker Pearson 2012: 261-91; Cummings & Richards 2014). Careful geological detective work has established that outcrops at Craig Rhosyfelin, Pembrokeshire, match the main types of rhyolite found as waste debris at Stonehenge (Ixer & Bevins 201 la & b), and archaeological investigations around the outcrops are now ongoing (Parker Pearson 2012: 261—91). Attention has also been given to the dolerites at Stonehenge that have long been sourced to a series of exposed outcrops, locally known as earns, at the eastern end of the Preseli Ridge (Thomas 1923; Thorpe et al. 1991). A recent re-analysis of published geochemical data suggests at least three main kinds of dolerite are represented at Stonehenge, with Carn Goedog on the northern side of the ridge providing the closest match for just over half of the samples examined. Other outcrops, possibly including Cerrig Marchogion to the south-west and Carn Gyfrwy/Carn Menyn to the south-east, collectively contributed the remainder (Bevins etal. 2014; see below for further discussion). In July 2012 the authors excavated a trench on the southern flanks of Carn Menyn, Mynachlog Ddu, to investigate evidence of stone quarrying and a dolerite-working area. The investigation revealed a well-preserved stratigraphic sequence spanning the period from before 3000 BC through to 1000 BC that provides secure evidence for pre-Neolithic stone quarrying in the region and absolute dates for the extraction of dolerite pillars from a source outcrop high in the Preseli Hills. Following a brief overview of the background surveys, this report describes the stratigraphic sequence revealed at the Carn Menyn Quarry and assesses its wider implications. Landscape surveys Between 2002 and 2011 the Strumble-Preseli Ancient Communities and Environment Study (SPACES) undertook extensive walk-over surveys combined with geophysical surveys, aerial photography and limited excavation within a study area of 450km2 extending from Mynydd Dinas in the west to Crymych in the east (Figure 1). The overarching aim was to provide an archaeological context for the source of the Stonehenge bluestones. More than 500 sites and monuments of archaeological interest were recorded, many of them for the first time. Two key findings rapidly became clear. First was that throughout the study area prehistoric communities had a close relationship with local stone, variously selecting and manipulating blocks for the construction of monuments including portal dolmens, chambered tombs, circles, standing stones, and sometimes just lifting slabs out of the ground as ‘propped rocks’. Second, within the eastern part of the study area our fieldwork supports a suggestion by Richard Bradley (2000: 92—96) that the arrangement of various bluestone lithologies used in the later stages of Stonehenge broadly replicates in microcosm the actual arrangement of stone types across the landscape of the Preseli Hills and surrounding areas. Thus, the dolerites of the Bluestone Horseshoe in the centre of Stonehenge derived from the central Preseli Ridge, while the various rhyolites and tuffs present in the Outer Bluestone Circle originated at outcrops within a wider catchment (Darvill 2006: 136-39). Geological investigations in the early 1990s by a team from the Open University used petrological and chemical analysis to show that two or three types of dolerite were represented amongst the pillar-stones and debris sampled from Stonehenge, and that these derived from © Antiquity Publications Ltd. 1100 Timothy Darvill & Geoff Wainwright A tla n tic N o rth Sea O cean Research SPACES C h3p s tu d y a re a 200 Land over 244m ASL Figure 1. Location o f the SPACES study area, Pembrokeshire, U K (drawing by Vanessa Constant). a number of source outcrops in the landscape of the eastern Preselis including Carn Menyn, Carn Goedog and Carn Breseb (Thorpe et al. 1991). A recendy published re-analysis of the original data, supplemented by a sample from Stone 34 recovered during our 2008 excavations at Stonehenge (Darvill & Wainwright 2009: 17) and additional samples from outcrops in the eastern Preselis, provides further resolution (Bevins et al. 2014). Based on concentrations of four selected elements (MgO, Ni, Cr and Fe2 0 3 ) this work confirmed and characterised three distinct types of dolerite amongst the Stonehenge samples (designated Groups 1—3). Bivariate analysis of the same elements in samples from the eastern Preselis (Bevins et al. 2014: figs. 13—16 with sample source areas listed on the keys but selectively quoted in tab. 3 and in the text) suggests that, with appropriate margins of uncertainty to © Antiquity Publications Ltd. 1101 Beyond Stonehenge accommodate sample variability, Group 1 correlates with samples from Carn Goedog on the northern side of the ridge (see Bevins et al. 2014: fig. 1); Group 2 with samples from Carn Bica, Carn Arthur, Carn Sian, Craig Talfynyndd and Cerrig Machogion/Mynydd-bach to the south-west; and Group 3 with samples from the adjacent outcrops of Carn Gyfrwy, Carn Menyn, Carn Breseb and Carn Gwr to the south-east. A Principle Components Analysis shows much the same picture, although the clusters are far from discrete. What becomes very clear is that the chemical composition of dolerites in the Preselis varies considerably from place to place. Uneven sampling during the original fieldwork means that some outcrops are very poorly represented. This is especially problematic in the case of Carn Menyn, which, although widely considered to be a major source, is represented by just one sample (CM1) that cannot possibly reflect the variability expected across the outcrop. Clearly, further informed sampling is needed, and Bevin et alls recent publication can be taken as an alternative rather than a revised interpretation of the Open University’s datasets (Bevins et al. 2014: 181, 192). Moreover, as only around 55 per cent of the 21 Stonehenge samples in the study (including unattributed debris as well as identified extant pillar-stones) can be attributed to a source at Carn Goedog (Bevins et al. 2014: 189), any claim that this was the main source for the Stonehenge bluestones must be treated with extreme caution. Notwithstanding the implications of these recent debates, Carn Menyn remains a probable source for some of the dolerite pillar-stones used at Stonehenge. Archaeologically, our surveys show that Carn Menyn was the focus of a great deal of activity in the later Neolithic and early Bronze Age. Burial cairns have been recorded at either end, standing stones on the outcrops, a walled enclosure around the highest point, and natural springheads elaborated through the creation of pools and the occasional application of rock art on the southern side. The surveys found that on the southern flanks of Carn Menyn there was a scatter of broken or abandoned dolerite pillar-stones of the same size and proportion as the stones present in the two visible structures at Stonehenge today (see Figure 2), as well as occasional hammer stones. Shallow hollows suggestive of quarry pits were also recognised and, on the basis of surface evidence, seemed to be for the extraction of a fine, light-grey coloured meta-mudstone (Darvill et al. 2008). Surface evidence including a broken pillar-stone, intercutting quarry pits and indications of dolerite extraction on a terrace on the southern slopes of Carn Menyn at an altitude of 310m asl was especially noteworthy (NGR: SN 143324). Samples of spotted dolerite taken from this area were submitted for analysis and described by Ixer and Bevins (2011a: 13) as petrologically indistinguishable from Stone 35a and very close to Stones SH34 and SH61 at Stonehenge. Accordingly, in July 2012 a single trench covering an area of 30m2 was excavated across the terrace in order to further examine the features visible on the surface (Figure 3). The re-analysis of geochemical data discussed above, published after the fieldwork described here was completed, goes some way to support the initial petrological work.