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Sunday, 30 April 2017

Foel Drygarn Prehistoric "Quarries"

 Bing image of Foeldrygarn, showing the main Bronze Age and Iron Age settlement and fortification features, and the rock outcrops / quarries in the lower (southern) part of the image

 The crags at the western end of the series of rock outcrops

The same view in winter.  This gives an impression of Preseli as it might have appeared over 10,000 years or so of intense periglacial activity after the melting of the Devensian Irish Sea Glacier.  There might have been a small glacier in the cwm beneath the summit of Foelcwmcerwyn during Zone III / Younger Dryas times.  Around 10,000 years ago Ice Age conditions finally gave way to much warmer interglacial or post-glacial conditions much more favourable for human settlement.

If you are into Neolithic / Bronze Age quarries, and want to see a real one for a change (instead of the fantasy quarries at Rhosyfelin, Carn Meini and Carn Goedog), go to have a look at Foeldrygarn, at the eastern end of the Mynydd Preseli upland ridge.   Here we can see some real evidence of extensive "quarrying"or stone gathering activities.  It's interesting that the quarries are not mentioned on the otherwise excellent Coflein description of the site written by Toby Driver.   This is reproduced below.

First, the site geology.  It's very complex indeed, with at least three different igneous rock types in close proximity.  Probably it was once a volcano or maybe the core of a volcanic complex, but not all of the rocks are "deep" rocks intruded and cooled far beneath the earth's surface-- some of them appear to be volcanic ashes and lavas laid down from surface eruptions.  There were probably many phases or eruptions, some of them very violent or explosive, revealing and then burying materials of different ages.  I wouldn't like to be a geologist trying to work it all out.  Maybe Rob or somebody else can enlighten us -- since there is not much that I can find in the literature.  Actually rock lithology is not that important here -- no particular rock type seems to have been preferred over any other by the quarrymen.  For the record, I think there are dolerites (none of them spotted, as far as I can see), rhyolites, lavas and ashes all exposed within a very small area.

This is the description from the Geology of Britain viewer:

Unnamed Igneous Intrusion, Ordovician - Microgabbro. Igneous Bedrock formed approximately 444 to 488 million years ago in the Ordovician Period. Local environment previously dominated by intrusions of silica-poor magma.

Setting: intrusions of silica-poor magma. These rocks were formed from silica-poor magma intruded into the Earth's crust. It cooled to form intrusions ranging from large, coarse-crystalline, often gabbroic, plutons at depth to smaller, fine to medium crystalline, often basaltic dykes and sills.

Fishguard Volcanic Group - Tuff And Lava. Igneous Bedrock formed approximately 464 to 467 million years ago in the Ordovician Period. Local environment previously dominated by explosive eruptions of magma.

Setting: explosive eruptions of magma. These rocks were formed from viscous and highly gaseous magma. It rose to the surface, where sudden pressure relief caused explosive volcanic eruptions, producing fragmentary pyroclastic material or ash.

The key man-made features here are the three massive Bronze Age burial cairns that give the hill summit its name, and the embanked enclosures and hut sites of the Iron Age hilltop village.  There are several features that have made this site attractive: (1) it's an isolated hill with panoramic views in all directions -- valuable from a strategic or defensive point of view; (2) there is a broad summit plateau which is not by any means flat but which was not so steeply sloping as to discourage settlement; (3) there is an abundant stone supply from the summit crags and the accumulated scree on the southern and south-western flanks of the summit.  I suspect that this latter factor was of vast importance -- especially for the tribal groups who decided to build those three massive burial cairns.

Yesterday I led a group of walkers around the eastern part of Mynydd Preseli -- very cold and windy.....!  Here are some of my photos:

Foel Drygarn from the south, showing the outcropping igneous rocks in the crags to the left of the summit. If you zoom in you can see the clear "quarrying platform" beneath the crags from which hundreds of tonnes of stone have been taken --almost all of it from accumulated scree banks of frost-shattered material.

 A close-up of some of the crags.  Between the grassy banks and the rock face there is a back-slope in places, indicative of stone removal on a substantial scale. I need more time to examine the micro-morphology of the site.......

On the left, the edge of one of the cairns, with a dolerite rock collection site immediately adjacent.  They did not need to go far for their rocks........

Some of the walkers scrambling over one of the cairns.  Look at the stone sizes -- there is no stone here which is heavier than c 40 kg, ie capable of being carried by two men with a stretcher......

 Close-up of the flank of one of the cairns.  The great majority of these stones can be carried by one man, woman or older child without too much difficulty.  Nonetheless, there are many thousands of stones in the three cairns, indicative of substantial community commitment and effort.

 So -- the lessons arising from all of this?  Yes, Bronze Age people did "quarry" or collect stone on a substantial scale in this area, but the guiding principle always was economy of effort, and the easy availability of stone in convenient-sized blocks on the hill summit of Foel Frygarn may well be the explanation for (a) the choice of the hill as a burial site, and (b) the extraordinary size of the cairns themselves.

I see no signs here that there was any preference for a particular rock type over any other, or that there was any physical breaking away of lumps of stone from the exposed rock faces.  I think that no tools were used.  All of the stones have been taken from pre-existing banks of scree or slope deposits, made of accumulated masses of frost-shattered material.  By and large, the edges of the stones in the cairns themselves are sub-angular rather than angular.  If the stones had been taken from "the living rock" by quarrymen with tools, the edges of the stones would certainly be very sharp.

As far as I can see, no big blocks (the sort of things used in megalithic stone settings or cromlechs) have been taken from here.

As I have said before, maybe the term "collecting"or "gathering" should be used in preference to the term "quarrying".......


My description of the site:

Foel Drygarn (158336 )

This prominent hill mass towards the eastern end of the Preseli upland ridge stands in glorious isolation, and the summit can only be reached via a stiff climb from the nearly "Golden Road" footpath.  The name means "the bare hill with three cairns" -- and the three massive Bronze Age burial mounds on the summit are the most spectacular features of this age in Pembrokeshire.  They lie within the confines of an Iron Age hillfort which contained both an animal enclosure and a substantial settlement site.  Scores of hut circles can still be made out in the turf.  The defensive ramparts are prominent.  A gorgeous location, with spectacular views in all directions.  Maybe we shouldn't classify this as a "Preseli tor" but on balance I have included it in this list because there are indeed spectacular crags here towards the western end of the summit.  The rocks are rhyolites rather than spotted dolerites, and as with the other high tors the dominant process which has shaped the crags in recent millennia is frost shattering and the downslope movement of detached blocks under the influence of gravity.  The jury is still out on whether the summit of Foel Drygarn was affected by glacier ice during the last glaciation.


Coflein Site Description

Frequently photographed and one of the most dramatically sited and visually striking Iron Age hillforts in Wales, Foel Trigarn occupies the easternmost ridge on Mynydd Preseli, its characteristic silhouette dominating much of the east Pembrokeshire skyline. Three main enclosures can be traced, defined by stone walls or stone-revetted banks, with traces of a ditch around the inner rampart. The earliest was probably that on the very summit, an oval fort set against natural cliffs on its southern side, enclosing 1.2 hectares and with main gates on the east, west and south sides. Attached to this first enclosure, and probably representing later periods of expansion, are a second enclosure on the north and east side which mirrors the outer ramparts of the first, and a third outer annex to the east. The most striking characteristic of Foel Trigarn is its pock-marked interior, the sites of at least 227 levelled house platforms where Iron Age houses once stood. There are also fainter traces of a further 42 uncertain platforms bringing the total closer to 270 house sites. It is highly unlikely that all these house sites were occupied at the same time. The entire hillfort was probably occupied and expanded over many centuries, rather than being used by a single leader or group of people. We are effectively seeing the remains of a complex and long-lasting prehistoric village, with all its phases of occupation on show. Early excavations in 1899 by S Baring Gould unearthed Iron Age and Roman pottery and artefacts which included spindle-whorls, fine glass beads and a jet ring from some of the house platforms. Sling stones were also found in ‘…great numbers…some in piles..’ (Baring Gould et. al., 1900, 210). A new survey by the Royal Commission and researchers from Portsmouth Polytechnic (in 1988) provided the first detailed plan.

On the summit stand three massive stone cairns after which the hill is named. These are interpreted as Bronze Age burial cairns, massive communal monuments covering the bones, or ashes, of one or several special individuals. Similar examples of pre-existing cairns surviving within later stone forts can be seen at Carn Goch in Carmarthenshire, Pen Dinas, Aberystwyth in Ceredigion and at Tre’r Ceiri on the Llyn Peninsula, Gwynedd. As these cairns were never plundered for their stone, despite being surrounded by hundreds of houses, we must conclude that the occupants venerated their distant ancestors, while at the same time deriving power and social status from the acquisition of such a prominent, and sacred, hilltop.

The size and complexity of Foel Trigarn, one of the largest north Pembrokeshire hillforts along with Carn-ingli, Garn Fawr and St David’s Head, suggests a role and function distinct from the numerous smaller hillforts like Castell Henllys. It is likely that this was a significant centre of population in its time, its design and construction initiated and overseen by a powerful regional leader. If, as one interpretation of the place mentioned by Ptolemy indicates, the Octapitai tribe occupied St David’s Head, perhaps a similar group whose name was never recorded by the Romans sited their ‘tribal capital’ here, commanding the Iron Age lands hereabouts.

Sources: Baring-Gould and others in Archaeological Cambrensis 5th series 17 (1900), 189-211

T. Driver, RCAHMW, 21 September 2009


 This is probably how the heavier stones were carried for a maximum distance of c 60m


Dave Maynard said...

The image of the south of Foel Drygarn, showing the 'quarrying platform'. Doesn't this contradict what you were saying in the rest of the discussion? If they were simply picking up loose scree, would thay have created a platfrom?

I'd always viewed this as a southern rampart. I'm also not sure that scree would have developed to any great extent on these slopes, but then maybe it does. Sounds like a full engineering study is needed to work out the volume of rock in the ramparts and cairns, whether rock faces have seen quarrying and what the surface beneath a scree slope would look like, if the scree were removed.


BRIAN JOHN said...

If I was collecting lots of stones from a scree slope, I sure as eggs would want to make a little platform for myself, rather than trying to carry stones laterally across an unstable scree face. But yes, this is an interesting site -- I want to go back and examine it in more detail. Too much of a hurry the other day, when I was acting as native guide for a group of visitors........