Difference between revisions of "Stonehenge quarries"
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Revision as of 09:26, 15 June 2019
Carn Goedog and Craig-Rhos-y-felin are outcrops of igneous rock found in the Preseli Hills in Pembrokeshire, west Wales.
Excavations and geological work carried out since 2011 have definitively identified the two sites as quarry sources for the bluestone megaliths that form the inner stone circle at Stonehenge.
In research published in the journal Antiquity in 2015 and 2019, the teams leading the excavations were able to identify recesses in the rock face where stones had been quarried, as well as evidence of the Neolithic masons' campfires at the sites. The Stonehenge bluestones have been geologically linked with the mountains of west Wales since the 1920s, but these new findings are the first to provide exact matches for the rock, as well as precise locations for where it was quarried.
The monument at Stonehenge is composed of two distinct types of stone: the larger sarsen standing stones and lintels, which are of a silicified sandstone known to be local to the area around Stonehenge, and an inner circle of standing igneous 'bluestones', so called for their distinct blue-gray coloring; the bluestones are not of local origin, being linked with the Preseli mountains in Wales, around 140 miles away.
How the bluestones came to be used at Stonehenge has long been a matter of contention. Some theories held that the stones had been carried south-east by the Irish Sea Glacier, deposited as erratics on Salisbury Plain. Research published in 1923 by the geologist Herbert Henry Thomas, however, linked the bluestones to the hills of west Wales, reinforcing the theory that they were quarried and transported to Stonehenge, either overland or by sea routes.
Thomas identified the tor at Carn Meini as a possible site for the stones' extraction, and excavation work has largely focused on that location over the years. Renewed research since 2011, however, led by Richard Bevans, keeper of geology at the National Museum of Wales, shifted attention to Carn Goedog and Craig-Rhos-y-felin. Rob Ixer, of University College London, who also took part in the new excavations, said: "Almost everything we believed 10 years ago about the bluestones has been shown to be partially or completely incorrect."
The megalithic bluestone quarry at Craig Rhos-y-felin was discovered in 2011, with excavations carried out over five field seasons between 2011 and 2015.
The outcrop of rock forms natural pillars at the site, its vertical sections roughly corresponding to the dimensions of the megaliths used at Stonehenge. Several recesses where stone has likely been extracted are apparent, with smoother surfaces adjacent to the more weathered rock face surrounding. Evidence of extraction methods for the megaliths exist in the form of indentations carved at the joints of the pillar sections, where wedges were likely to have been inserted into the natural fissures. Director of the project and professor of British later prehistory at University College London, Prof. Mike Parker Pearson noted: “The nice thing about these particular outcrops is that the rock has formed 480m years ago as pillars. So prehistoric people don’t have to go in there and bash away … All they have to do is get wedges into the cracks. You wet the wedge, it swells and the stone pops off the rock,” Parker Pearson explained. “It’s the Ikea of Neolithic monument building.”
An artificially mounted upright stone adjacent to the quarry face shows evidence of crushing on top, and it is speculated that the stone was used as a pivot as the megaliths were lowered away from the rock face. A large horizontal slab may have been used as a loading bay, before hauling the quarried stones off site. Carbon dating of hazelnut shells from a hearth set against the north end of the outcrop gave dates in the range of 3500–3120 BC for Neolithic activity at the site.
The stone at Craig-Rhos-y-felin is classified as a 'rhyolite with fabric', and has been linked with at least one of the standing bluestones at Stonehenge, as well as providing an exact match for bluestone chips excavated at some of the 'Aubrey Holes' at the monument. The Aubrey Holes are a series of pits surrounding the current monument at Stonehenge, and were likely the location of an earlier stone circle at the site.
Of the 43 standing bluestones at Stonehenge, 27 are of spotted dolerite, a blue-gray igneous rock speckled with ovate patches of pale-colored secondary minerals. In 2013, scientists from Aberystwyth University, University College London and National Museum of Wales used laser mass spectrometry to analyze the chemical composition of the rock and the microbiology present when it was formed. The team were able to match at least five of the spotted dolerite standing stones at Stonehenge to the Carn Goedog quarry.
Archaeological excavations were carried out at Carn Goedog between 2014 and 2016. As at Craig-Rhos-y-felin, the outcrop was formed into natural pillars by the volcanic activity that created it around 480 million years ago.(14) Recesses in the face of the outcrop reveal where stone has been extracted, with no evidence on site of the removed sections. The relatively fresh faces of the rock that remains in place adjacent to where stone has been removed is in marked contrast to the rougher and more weathered surfaces of the undisturbed stone. “One recess is large enough for four or five 4m-long × 0.7m × 0.5m pillars to have been removed from this part of the outcrop,” observed the Antiquity article that first published the findings in February 2019.
Stone tools were also found at Carn Goedog, made of a mudstone and sandstone softer than the local dolerite. It is suggested that the softer stone may have been used so that any cracking during extraction would occur to the stone tools first, rather than the stone being quarried. Carved widening holes at the edge of the extraction points again indicate where wedges are likely to have been inserted into the natural fissures in the rock. Organic materials in the form of wedges, ropes, and wooden planks were all likely to have been used, however no evidence has survived of these in the acidic Preseli soil.
As at Craig-Rhos-y-felin, a stone platform next to the rock face was likely used to lower extracted megaliths onto, before they were slid away. Charcoal hearths found at the level of this platform date the masons' activity at the site in the range of 2890-2630 BC. Unlike Craig-Rhos-y-felin, there is no evidence of continued quarrying work at Carn Goedog after the Neolithic period; an artificially created stone ditch filled with debris effectively blocks the removal of larger stones, and it is theorized that this was created in order to decommission the quarry sometime around 2880 BC.
In separate research published in the journal Nature in 2018, it was revealed that the remains of 10 of 25 analyzed individuals buried at Stonehenge could be linked with west Wales. A team led by archaeologists from the University of Oxford tested cremated bone fragments found at Stonehenge using strontium isotopic analysis, concluding that the individuals studied did not spend their lives on the Wessex chalk on which the monument is found, and that their most plausible origin lies near the Preseli Hills.
The cremated remains were found in the Aubrey Holes at Stonehenge, a circle of 56 Late Neolithic pits that surround the standing stones at the site's outer bank, and which are associated with the earliest dates of the monument's construction. While these findings cannot prove that the bone fragments analyzed belong to the people who built the monument, the earliest bones have been dated to about 3000 BC, "tantalisingly close to the date we believe the bluestones arrived", John Pouncett, a lead author of the study, said.
Strontium analysis can reveal the region that an individual lived in the last ten years of their life, as isotope levels will vary based on the underlying geology on which consumed plant and animal food sources grew or grazed. The research was also able to surmise likely areas where the individuals died, based on analysis of the woods used in their cremation. Several of the individuals analyzed showed results consistent with living and dying in west Wales; the fact that their remains were subsequently transported to and interred at Stonehenge suggests that the individuals were of special significance to the earliest stages of the monument.
The confirmation of the quarry sites at Carn Goedog and Craig-Rhos-y-felin have reinforced the theory that the stones were transported across land to Salisbury Plain. These outcrops are further north than previously speculated locations that assumed the stones were taken south before being transported by boat from Milford Haven. This would likely prove impossible for stone quarried at Carn Goedog and Craig-Rhos-y-felin, which would have to be dragged up the steep northern edge of Mynydd Preseli before being carried down the southern slopes to the valley of the Afon Cleddau to Milford Haven. The more likely method would be across land, along a route similar to the modern A40 road.
Taken together, the dating evidence for the extraction of the stones at Carn Goedog and Craig-Rhos-y-felin falls in the vicinity of the second half of the fourth millennium BC, c. 3350–3000 BC—a few hundred years prior to the erection of the first stone circle at Stonehenge. This has raised the question as to what the stones were used for in the intervening period, and one of the possibilities is that they formed part of an earlier monument in west Wales, before being dismantled and moved to Salisbury Plain. The team that worked on the excavations are now looking closely at possibilities among some of the extant Neolithic sites around Preseli. A partial stone circle at Waun Mawn, identified in the 1920s, and as yet unexcavated, lies just 3km west of Carn Goedog and Craig Rhos-y-felin.
- Mike Parker Pearson, Richard Bevins, Rob Ixer, Joshua Pollard, Colin Richards, Kate Welham, Ben Chan, Kevan Edinborough, Derek Hamilton, Richard Macphail, Duncan Schlee, Jean-Luc Schwenninger, Ellen Simmons and Martin Smith, "Craig Rhos-y-felin: a Welsh bluestone megalith quarry for Stonehenge", Antiquity 89, no. 348 (December 2015), 1331–1352. https://doi.org/10.15184/aqy.2015.177
- Mike Parker Pearson, Josh Pollard, Colin Richards, Kate Welham, Chris Casswell, Charles French, Duncan Schlee, Dave Shaw, Ellen Simmons, Adam Stanford, Richard Bevins and Rob Ixer, "Megalith quarries for Stonehenge's bluestones", Antiquity 93, no. 367 (February 2019), 45–62. https://doi.org/10.15184/aqy.2018.111
- Parker Pearson et al., "Craig Rhos-y-felin", 1332.
- Parker Pearson et al., "Megalith quarries", 46.
- Steven Morris, "Archaeologists looking for Stonehenge origins 'are digging in wrong place'", The Guardian, November 20, 2013. https://www.theguardian.com/culture/2013/nov/20/archaeologists-stonehenge-origins-wrong-place/.
- Parker Pearson et al., "Craig Rhos-y-felin", 1335.
- Parker Pearson et al., "Craig Rhos-y-felin", 1335.
- Dalya Alberge, "Stonehenge may have been first erected in Wales, evidence suggests", The Guardian, December 7, 2015. https://www.theguardian.com/uk-news/2015/dec/07/stonehenge-first-erected-in-wales-secondhand-monument/.
- Parker Pearson et al., "Craig Rhos-y-felin", 1341.
- Parker Pearson et al., "Megalith quarries", 58.
- Parker Pearson et al., "Craig Rhos-y-felin", 1333.
- Neil Prior, "Another piece in Stonehenge rock source puzzle", BBC News, November 19, 2013, https://www.bbc.com/news/uk-wales-25004282/.
- Parker Pearson et al., "Megalith quarries", 58.
- Parker Pearson et al., "Megalith quarries", 57-58.
- Christophe Snoeck, John Pouncett, Philippe Claeys, Steven Goderis, Nadine Mattielli, Mike Parker Pearson, Christie Willis, Antoine Zazzo, Julia A. Lee-Thorp, and Rick J. Schulting, "Strontium isotope analysis on cremated human remains from Stonehenge support links with west Wales", Nature, August 2, 2018, https://doi.org/10.1038/s41598-018-28969-8.
- Parker Pearson et al., "Megalith quarries", 59.
- Maev Kennedy, "Bones found at Stonehenge belonged to people from Wales", The Guardian, August 2, 2018. https://www.theguardian.com/science/2018/aug/02/revealed-stonehenge-buried-welsh/.
- Christophe Snoeck et al., "Strontium isotope analysis", 5.
- Parker Pearson et al., "Craig Rhos-y-felin", 1347-1348.
- Esther Addley, "Mega lift? Stonehenge pillars were carried 230km over land – research", The Guardian, February 19, 2019. https://www.theguardian.com/uk-news/2019/feb/19/stonehenge-pillars-were-carried-230km-over-land-research/.
- Parker Pearson et al., "Megalith quarries", 59-61.