The prehistoric quarries at Foel Drygarn

Above is a drone image (courtesy Iain P) of one of the most famous prehistoric sites in Wales-- Foel Drygarn (the bare hill with three cairns) at the eastern end of Mynydd Preseli.  There are four different components to the site:  

1.  the three prominent hill summit cairns, believed to be Bronze Age burial mounds;

2.  the defensive embankments and walls associated with a defended settlement, assumed to be Iron Age;

3.  the multiple pits, hollows or little platforms believed to mark the sites of around 270 huts;

4.  the rampart of crags running across the southern part of the fortified site.

Iain has made available some fabulous drone footage of the site,  here:

https://vimeo.com/222373142

                         

In the abundant literature on the site the crags are hardly ever mentioned, except maybe for a passing mention of their scenic beauty, or maybe a reference to the fact that they are "natural features used to enhance the defensive capabilities of the site".  The Coflein record is typical:

http://map.coflein.gov.uk/index.php?action=do_details&cache_name=&numlink=94948#tabs-4

I'm rather intrigued by all of this, in these days of prehistoric quarrying mania, since nobody seems to have asked the question "Where did all the stone needed for these constructions (the cairns and the embankments) actually come from?"  A lot of stone was needed, as I have pointed out in two 2017 posts:

https://brian-mountainman.blogspot.com/2017/04/foeldrygarn-prehistoric-quarries.html.  

https://brian-mountainman.blogspot.com/2017/04/foel-drygarn-annotated-image.html

Let's look at stone quantities.   Each of the burial cairns has a diameter of c 20m and a height of c 4 m.  Reduce to a box of dimensions 15 m x 15 m x 3 m.  The volume of stone contained in each one is  675 sq m, giving a solid rock weight of 1822 tonnes.  Allow for "open work" air spaces occupying 20% of each mound, and the weight of stone contained in each mound becomes c 1458 tonnes.  Using a figure of 2.7 tonnes per cubic metre, the total weight of stone in the three mounds is therefore approx 4,374 tonnes.

Add to that the weight of stone contained within the defensive mounds.  The total length of the defensive embankments is between 950 m and 1000 m.  The embankments vary quite substantially in their cross-sections, but let's take an intelligent guess at a base 5 m wide and a height of 3 m.  Reduce to a box of dimensions 1000 m x 2 m x 2 m.  That gives a solid rock volume of 4,000 sq m and a weight of 10,800 tonnes.  Reduce by 10% to allow for incorporation of earth and rubble -- and we arrive at a total of 9,720 tonnes for the embankments.

So our grand total for stone required in the construction of this site is around 14,094 tonnes.  That's  a lot of stone.  Where did it come from?  It's pretty obvious -- from the on-site quarries on the hilltop.  Nobody with any sense would want to carry stone uphill  from the surrounding lower moorlands anyway, and economy of effort must have been just as important in prehistoric times as it is today.

So what is the physical evidence of prehistoric quarrying on the site? There is actually a great deal, and I have been up there today to have a look.

At the outset, it needs to be said that a lot of the stone collecting on this site has been opportunistic in the sense that it has involved gathering up stones from pits hollows, rock outcrops and surface litter here, there and everywhere.  Some of the stone from the levelling of hut platforms or pits has clearly gone into the stone embankments. A section of the outer embankment to the NW of the three cairns has been made of stone picked up from broken outcrops of volcanic ash in the immediate vicinity.  Immediately adjacent to the three cairns, and only about 20m away from them, we find a series of low cliffs of dolerite (unspotted) which are abraded and well weathered, but which have clearly not had fresh rock pillars, boulders or slabs extracted from them -- but the accumulated scree which once existed on their southern and eastern flanks has virtually all been taken away. One can see the extraction pits quite clearly, and in several locations one can see that all manageable (small) fragments have been removed, leaving behind all of the larger (greater than 100 kg) blocks and slabs. There has been selective extraction of handy materials on a substantial scale.

To the west of the main entrance into the fortified area we find the most spectacular crags on this isolated mountain summit. They are made of several different rock types, including dolerite, volcanic ash, and rhyolite.  The group of volcanic ash rags closest to the entrance point have clear signs of rubble and stone extraction on a high terrace, whereas the more spectacular crags to the west, which must originally have had thick accumulations of rockfall debris and scree on a lower terrace, much of which has been removed.  The extraction pits are clearly visible, separated by ridges of grassed-over rubble c1m high.  the trackway along which this extracted debris was carried is still used as the footpath to thus day, running eastwards towards the place where the southern entrance of the fort was located.

From a close examination of the crags and the extraction pits beneath the vertical or steeply-sloping rock walls, it's clear that no stone was physically levered away from the living rock. The stone gatherers were not interested in big pillars or monoliths -- all they wanted was the broken rock debris.  So maybe we should not call this a quarry at all -- maybe just a stone collection site, used on a substantial scale.  But maybe, since there are clearly still traces in the landscape of all this extractive activity, with 14,000 tonnes of stone shifted, the word "quarry" is right after all..........? 

The surface of one of the burial mounds.  The great bulk of these stones, extracted from scree slopes, can be shifted by one man.

A remnant of vertical stonework, on the outside of the inner ridge, showing that the ridges were at one time formidable defensive barriers.

Dolerite rock face in the SE part of the settlement site, with virtually all of the rockfall debris removed for incorporation into the burial mounds.

At the foot of one of the eastern dolerite cliffs these huge boulders have been left behind, while all of the smaller material has been taken away.

The westernmost crags, shaped by periglacial and glacial processes.  Beneath these crags we find the most dramatic evidence of stone removal on a substantial scale.

Interconnected extraction pits on the lower terrace, beneath the western crags.

In some areas a litter of frost-shattered scree still survives; but most of this material has been removed for incorporation into the defensive embankments.

The inner defensive ridge at the western extremity of the defended settlement site.  there is a slight ditch on the inside, from which stone has been extracted.  The outer face is here almost 5m high.

So what does this site tell us about prehistoric quarrying in the Preseli hills?  Well, our ancestors knew all about minimising effort.  They used stone -- of manageable sizes -- as close to the source as possible.  They had no particular preference for one type of stone over another; here they have used at least three different local rock types without any sign that one was revered more than the others.  There does not seem to be any spotted dolerite here, imported from the nearby spotted dolerite outcrops of Carn Gyfrwy, Carn Ddafad-las  and Carn Meini.  Even in the Bronze Age and the Iron Age, when metal tools were available, there seem to have been no attempts here to extract slabs of rock from cliff faces.

And most important of all, although some of the stone extraction here must have occurred almost 5,000 years ago, the traces of the work in the landscape is still apparent.  There are no natural explanations for the features described above.  In contrast, what do we see at Rhosyfelin and Carn Goedog that can be attributed to quarrying or stone removal?  Nothing at all.