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Pentrwyn Bronze Age Metalworking Site,
Great Orme
The
Pentrwyn site (immediate foreground) in the mid 1850's before the construction
of the Marine Drive.
Summary
In 1997 David Chapman identified
archaeological remains eroding out off a cliff on the Pentrwyn headland, Great
Orme. These remains consisted of an apparent
burnt layer and a ‘v’-shaped feature, both exposed in section. Charcoal, shell and bone fragments were
observed within these deposits, as were small fragments of copper slags. The potential of this site was raised by the
near location of the prehistoric copper mines in the Pyllau valley on the Great
Orme. The remains were brought to the
attention of the Cadw: Welsh Historic Monuments who subsequently funded a
partial excavation of the site. The
excavation of the upper layers produced over one hundred fragments of copper
slag, the highest proportion of which were
associated with a small feature which has been dated to the fifteenth
century BC, contemporary with the earlier periods of activity at the Pyllau
valley site and making the Pentrwyn site the earliest known metal working site
in Great Britain.
Re-deposited slags were also found in higher layers which appear
to be the remains of medieval (cal AD 1220) activity, which consisting of a pit
containing burnt stones and food debris and an associated hearth.
Please
read on for the interim report of the excavation and the historical background
of this fascinating sites. You can skip to each section via the headings
below:
Archaeological
Background
Smelting
Evidence
Excavation
Finds
XRF
Trace Element Data
Conclusions
Discussion
of the results
Acknowledgements
Bibliography
Archaeological Background
The earliest archaeological evidence
for human activity on the Great Orme comes from the Upper Palaeolithic period
(Sieveking 1960) when a number of natural caves were occupied. Some of these caves continued to be used
into the Neolithic and Bronze Age periods (Lewis 1993, 12). Lloches yr Afr rock shelter is within 200m
of the Pentrwyn site, and which when excavated in the 1970’s produced evidence
for archaeological remains from the Mesolithic period through to the Neolithic
and possibly the early Iron Age (Davies 1989, 93).
The
most notable, surviving monument on the Great Orme, is the chambered tomb of
Llety’r Filiast, an Irish type Portal
Dolmen (Lynch 1969, 140) , probably dating from the late Neolithic
period. At least four cairns, one other
possible megalithic tomb and one probable long barrow, now destroyed, are
reported on the Great Orme (Lewis 1993, 13).
At the foot of the Great Orme where the present town of Llandudno is
located, there was reported an ‘oval-shaped mound’ (Roberts 1909) called ‘Y
Gorseddau’ or ‘high places/throne’.
When the mound was levelled in the nineteenth century ‘several earthern
urns containing what was believed to be cremated human remains’ were
uncovered. The land-ward side of the
Orme is dominated by the promontory fort Pen y Dinas. Precipitous cliffs and earth and stone ramparts defended at least
sixty five round huts. The only dating
evidence for this site was a single sherd of Samian ware recovered in the
nineteenth century, although its origins may be much earlier (Muckle 1993,
1). Both isolated and groups of round
huts some with associated filed banks,
indicate prehistoric or Romano-British occupation.
Evidence for Medieval activity is
represented by a number of rectangular huts and extensive areas of associated
ridge and furrow systems, some of which probably relate to the three Medieval
townships of Gogarth, Cyngreawdr and Yr Wyddfid. A small group of rectangular structures, with associated
enclosures and cultivation ridges,
probably from the medieval period, are located on the plateau at the top
of the cliffs above the Pentrwyn site.
The church of St Tudno’s on the
headland, structurally dates to the twelfth century, but it is thought that its
original foundation dates to the period contemporary with St Tudno
himself, in the sixth century (Bibby
1979, xi). At the south-western foot of
the Orme are the remains of the late thirteenth century, ecclesiastical grange
of Gogarth.
A number of finds from the Bronze Age
period have been found on the Great Orme, the most notable was discovered in
1898, when two boys uncovered a group of objects consisting of two gold, finely
engraved, penannular ear-rings (not a pair), a damaged bronze palstave and a
socketed bronze implement, probably an awl for leatherworking ‘amongst the debris at the back of a large
loose rock’ near Pigeon’s Cave (Savory 1954, 51). All the objects are thought to be of the Late Bronze Age, while
the ear-rings have been identified as Irish in style. No accompanying burial was found with the hoard. This cave is located to the west of Pentrwyn
(300m from the site), below the Marine Drive.
Figure 1: The Great Orme headland and the location of sites mentioned in the text.
The
first recorded exploitation of the copper ores from the Great Orme appears in
1692, when a 21 year lease was given to Sir Thomas Mostyn (Williams 1979,
7). Little is then recorded until 1748, when Lewis Morris, the map maker,
describes the mines as ‘quite sizeable
and drowned out’. However, by the
end of the Eighteenth Century two mines in the Pyllau valley area were being
exploited: the ‘Old’ and ‘New’ mines and later in the nineteenth century they
were joined by the ‘Ty Gwyn Mine’ located in Happy Valley. At the height of production, between
1830-1850, the mine employed up to three hundred men (Smith 1988, 11),
producing over a quarter of a million pounds worth of ore. The abolition of import duties on copper
combined with the large copper deposits discovered in Australia and increasing
problems of flooding within the mines as they extended below sea level, ushered
in the end of copper mining on the Great Orme, with the ‘New Mine’ closing in
1864 and the ‘Old Mine’ and ‘Ty Gwyn Mine’ in 1881 (Dutton et al 248).
Evidence for Nineteenth century stone
quarrying is also visible on the
south-eastern side of the Great Orme, producing stone for the construction of
the hotels of the nearby resort and also for export. At Pigeon’s Cave stone was quarried for the construction of the
Conwy Cob and Telford’s Suspension Bridge (1826) and Stevenson’s Tubular Bridge (1848) (Ormesday Project, GOES). Small, Nineteenth century trials are also
located around the whole of the Great Orme.
Previous Archaeological Work
Mining
Indications of early mining activity on
the Great Orme first emerged in 1831 when miners in the ‘Old Mine’ broke into
underground workings, the type and
character of which were unfamiliar to them.
These workings contained a ‘broken stag horn’ and ‘two bronze items’
(Smith 1988, 10). Again in 1849, a
large chamber was discovered, with its roof and sides covered in stalactites
and containing stone hammerstones and bone tolls (Stanley 1850, 68). These ‘Old Men’s Workings’ as they became
known, were attributed to the Romans.
This date, for the early mines, was reiterated by Oliver Davies, a Roman
mining expert, in the 1930’s. He
examined the spoil tips around the mines in the Pyllau valley identifying stone
hammers, pestles and ‘sawn’ bone in the
tips (Dutton et al, 250), but felt
that such artefacts could be from post-Roman as well as Roman periods. He also excavated trial trenches through an
occupation site at the foot of the Great Orme near Gogarth. Here he found occupation debris and some
hammer stones, but no ore or slags.
Sherds of Romano-British pottery date this site to the late 2nd
century AD.
The Roman date for the ‘Old Men’s
Workings’ remained unquestioned until the 1970’s when underground explorations
of the ‘older’ workings by
Duncan James, beneath Bryniau Poethion provided the first date in Britain for
Bronze Age mining 2940+/-80 BP (HAR-4845) 1410-920cal BC (Lewis 1998, 45). Since then further investigations in the
Pyllau valley area to the south of Bryniau Poethion by the Great Orme Mines
Ltd, Gwynedd Archaeological Trust and the Great More Exploration Society have
identified an extensive area (5,000 sq m) of bedrock and surface workings
(Dutton et al, 252) and over 6km of
prehistoric underground passages, covering an area of almost 24,000m square and
occurring to a depth of 65m below surface (Lewis 1998, 51).
A total of thirteen radiocarbon dates
have been obtained from both above and below workings. These span a calibrated range of 1880-600
BC, covering the Early to Late Bronze Age (Lewis 1998, 49), with a notable
grouping around 1300-1400 BC (Lewis 1998, 49).
Excavations at the Pyllau valley site
have produced thousands of artefacts from prehistoric mining assemblages:
Bone
tools
The neutral to alkaline conditions at the
mine site and within the spoil tips help to preserve bone material, much of
which is discoloured blue/green by impregnation of the copper carbonates solutions present in the ground water,
or blackened by manganese solutions in the ground water (Dutton et al 1994, 269). A marked proportion
of these bone fragments exhibit wear and fracturing consistent with use as
primitive scrapers, chisels and gouges to remove the rotted dolomitized host
rock around the ore bearing material.
Tool marks consistent with this have been identified in the prehistoric
workings, especially in areas of shale or mudstones. Animal long bone predominate, typically tibia, ulna and rib. Although, some may relate to food use, the
butchery marks on some samples seem to indicate tool manufacture rather than
marrow extraction (Lewis 1998, 49).
Stone
tools
Over two thousand stone hammers/mauls have so far been
identified. Typically ovoid in shape,
and between 20kg to 29kg in weight, most are pebbles of igneous types common to
local beaches. Wear patterns on the
surfaces suggest a crushing or pound action taking place, and generally there
is a low degree of modification for hafting (Lewis 1998, 49). Approximately 10% of stone tools found have
‘hollowed crushing surfaces’ (Dutton et al 1994, 272) with ‘mortar’ and
‘pestle’ types present in surface or near surface contexts, suggesting on site
primary crushing.
Spoil
Due to the different techniques used to
extract the ore in the prehistoric and modern periods, it has been possible to
develop criteria for identifying waste types.
In general perceived prehistoric waste comprise predominately uniformly
sub-angular rotted dolomite with associated bone and stone tools. More recent waste generally comprises harder
crystalline dolomite and limestones, of more angular and less sorted spoil.
Processing sites
In recent years work has been carried
out to identify secondary processing sites on the Great Orme associated with
the Bronze Age mining activity (Jones 1994 & Wager 1996). The crushing of the material removed from
the mine, and the concentration of the ore to separate the ore from the gangue
(host rock) would have been an important stage in the preparation of the ore
for smelting. Mortar and pestle type
stones found at the mine site suggest that some crushing was taking place
there, but it has been hypothesised, that water separation or concentration may
have taken place at the number of well sites on the Great Orme. As a result, these possible ‘washing’ sites
have been the subject of a number of recent studies (Jones 1994 & Wager
1996). One of these at Ffynnon
Galchog/Porth y Helig was identified as
a ‘Roman’ washing site by a series of newspaper article written in 1909
(Roberts 1909). Such a statement
follows a local, as yet unproven, tradition that the Romans mined copper on the
Great Orme. However, as the site is
attributed to such a tradition it infers that the site had not been used as a
washing site in living or recent memory.
The article goes on to describe how ‘tons of copper slime’ located
around the well were transported to the smelters ‘many years ago’ (Roberts
1909), probably sometime before 1850.
Excavation by the Great Orme Exploration Society and Gwynedd
Archaeological Trust in 1990 of two small trenches through the spoil tips which
are still visible, confirmed that they consisted of well-sorted and graded
deposits of dolomitic silts, sands and gravels similar to the dolomitic waste
found at the mines (Lewis 1990, 10).
Copper-stained bone artefacts, including three shaped tools and a number
of hammerstone fragments were also recovered.
Both the artefacts and the mineralogy resembled those from the
prehistoric assemblages at the mining site and the crushed nature of the
material suggests processing taking place (Jones 1994, 69). A single radiocarbon date was obtained from
bone collagen within the tip, producing a date of 1200 +/- 60 BP (BM – 2753) or
720 – 740 AD and 680 – 960 AD Cal. (Lewis 1993, 56). This surprising date, remains unsatisfactorily explained, but may
indicate that early Medieval mining activity, using techniques and tools almost
identical to prehistoric ones, were taking place, or that this single sample
may have been contaminated.
Smelting evidence
During
the past ten years further work by archaeologists have identified over twenty
sites in Wales alone which have produced evidence for possible prehistoric
phases of workings, seven of which have
been radiocarbon dated to the Bronze Age (Pickin 1990, 69). As of writing no definite smelting residues
or sites have been identified from known early British mining sites. This is the case on the Great Orme, where in
the past prehistoric mining has generally been seen as a large-scale activity,
which would have soon depleting the fuel sources on the Orme, resulting in the
ore being transported to more accessible fuel resources.
In 1997, the University of Wales Bangor
undertook a geochemical survey of the Great Orme, with the aim of locating
mining, processing or smelting sites.
Using a portable XRF field analyser (TN Spectrace 9000) soil samples
from a 200m grid were taken, revealing major anomalies of copper (Cu). Some of theses anomalies were identified
with the known mining areas, while others were located at the suspected
secondary processing sites at Ffynnon Galchog and Ffynnon Rhufeinig. In addition, a area of possible smelting
activity was identified around the summit of the Orme (Jenkins et al 1997, 29). During the fieldwork for this project and
prior to the excavation, three samples were taken from the exposed section of
the Pentrwyn site. At ground level, on
the top of the terrace, a reading of 138 mg/g of Cu was recorded, a reading of
490 mg/g of Cu was recorded from a burnt
layer just beneath the top soil (probably context 021) and a notably high
reading of 1,260 mg/g of Cu was recorded from the ‘v’ - shaped feature
originally identified in section (Jenkins pers
comm.). All these reading are above
natural levels, the final reading is
particularly high.
Site Location
The
site is located on the headland known as Pentrwyn, at the foot of overhanging
limestone cliffs. It is all that
remains of a once much larger natural terrace (c. 8 - 9m wider than present), that was truncated during the
construction, between 1875 – 1878 (Wynne Jones 1975, 45), of the Marine Drive,
which not only removed all the soil cover but also blasted away the underlying
bedrock, as confirmed by the number of drill holes still visible in the exposed
cliff between the road and the terrace.
This road replaced a rough, and in places very dangerous, path known as Cust’s Path (the path and
original terrace can be seen in the immediate foreground of the front cover
illustration).
There are no known areas of dolomitized
limestone in the immediate vicinity and no notable deposits of copper
mineralisation. There is a small trial
(probably nineteenth century) below the site, to the west, at Pigeon’s Cave,
but it does not appear to have been productive. This cave forms part of a natural quay (it was indeed used as
such in the nineteenth century to shipped quarried stone from adjacent cliffs
(Jones 1994, 58). It is, also, one of
very few coastal landing places on the eastern side of the Great Orme, accessible
at high and low water and sheltered from the prevailing winds from the
south-west and most other wind directions.
Recent work on sea-level changes in the area, suggest that the present
coastline on the eastern side of the Great Orme, has been much the same since
the Neolithic period (Bannerman pers.
comm.). The location of the site, on the end of a headland, near to one of
the few marine access points on the eastern side of the Orme, therefore, may
indicate the importance of the sea as a transport route to the prehistoric
metalworkers on the Orme.
The
site itself is protected from the prevailing winds and close-up to the cliff
also from easterly winds and rain due to the overhang directly above. This overhang would also prevent debris from
the plateau above from falling directly onto the site.
The
possible prehistoric copper ore ‘washing’ site at Ffynnon Galchog lies c. 500m to the west, on the plateau
above the site. The extent of the spoil
heaps associated with this site do not appear to extend to the area directly
above the site, so contamination from the ‘washing’ area seems very
unlikely. The absence of graded mining
spoil on the Pentrwyn site (typical debris associated with ‘washing’
techniques) also seems to confirm this.
Excavation
Initially, a survey of the site and the
immediate area around, was undertaken.
The eroding section was then cleaned, photographed and drawn. The dark layer (005), at the top of the ‘v’
- shaped feature (see figure 2) that had originally lead to the discovery of
the site, was identified as a possible buried ground surface, with evidence for
leaching and deposition occurring below.
The ‘v’-shaped feature was sealed by a brownish pink silty clay (002),
above which copper working debris was identified eroding out of a thin deposit
(021) located immediately below the topsoil (001).
Figure 2: The main east facing section.
The topsoil was removed manually from
an area measuring 2.2m by 1.8m, which constituted about 70% of the surviving
terrace. Samples from all contexts
were wet sieved on site in order to check for the presence of small fragments
of metal working debris. Samples for
post-excavation analysis were also collected.
This area was excavated down to a
brownish pink silty clay (052), consistent with context 002 recorded in
section. Bone and shell fragments were still present in the upper part of
this silty clay, as were fragments of slag.
This clay was interpreted as disturbed or possibly re-deposited natural, due to its mixed nature. It sealed the ‘v’-shaped feature and the
possible buried ground surface (005)
(this feature remains unexcavated).
Directly overlying the clay, several
pockets of a grey silty layer were found across the area excavated. They appeared to be at the same
stratigraphic position, although, were separated by outcropping bedrock in
places, and differential drainage over the site resulted in a number of
different context numbers being allocated to it. This grey layer contained
fragments of bone and ore (malachite in dolomitised limestone), as well as slags.
The greatest concentration of slag was
found in a small, charcoal-rich feature (021) first seen in the section.
It was a sub-circular patch of dark material, cutting the grey silty
clay layer. It was about 200mm in
diameter and 30mm deep and was removed in its entirety. Directly beneath this was a small,
conical-shaped hole (030) (40mm in diameter and 1200mm in depth) which cut the
grey silty clay and was filled by a charcoal rich, dark silt (029). Two small fragments of slag were recovered
from this context, along with nine small (ca.
5mm) fragments of a fine grained, weakly cemented, sediment matrix with one
surface coated with a thin grey/dark
grey curved vitreous skin, with small blebs penetrating the matrix below. These fragments are thought to relate to a
smelting process, perhaps representing the remains of a crucible fragment or
slag spill (Jenkins pers comm.). Further analysis of these fragments is being
undertaken by Dr Chris Salter, Oxford University. Charcoal fragments from this context have produced a radiocarbon
date of 3310+/- 80 BP or cal BC 1580
(Beta-127076).
Two further charcoal concentrations
were found on the terrace (though not visible in the main section). The earliest (023) was a thin layer of burnt
debris, which overlaid the grey silty layer.
It contained charcoal fragments, slag, burnt stone and some unburnt
animal bones (032), and became more mixed at the edges. This was cut by a shallow bowl-shaped
feature (031), 150mm deep and 550mm in diameter, which also cut the grey silty
layer. The lower fill of this feature
(036) consisted of almost 100% charcoal, dropping to 70% charcoal in
places. This was covered by a layer of
ash suggesting in situ burning. A charcoal sample from 036 produced a date
of 840+/-60BP or cal AD 1220 (Beta-127077).
The hearth was cut by a pit (025). This pit also cut the grey silty and on its
north-eastern side, it also cut a small, roughly triangular depression (042),
which overlaid the grey silty clay and was filled by a firm yellowish brown
silty clay (044). It was not fully
excavated, with the northern side continuing into the section at the northern
limit of the excavation; while on the western side it slightly undercut the
base of the cliff. The excavated portion
was sub-circular in shape and approximately 1m in diameter. It contained two fills: the lowest of which (035) was a dark grey
clayey silt, containing fragments of burnt stone and animal bone (including one
tooth) and marine shells, mostly limpets (Patella
vulgata). This fill sloped from north to south within
the pit and was seen to underlay a mid brownish grey silty clay (026 &
038). Again this fill contained
fragments of burnt stones (pebbles), sea and land snails and bone fragments,
both burnt and unburnt. A whetstone was
recovered from the top fill (026) of the pit.
It shows signs of polishing, and also, there is evidence that it has
been used to hammer or crush material.
The pit was approximately 0.4m deep, sloping (east to west) at the bottom
with the fills of the pit probably consisting of the mixed disturbed grey silty
clay and debris.
Few examples of slag material were
recovered during excavation, due to the small nature of the artefacts
(<5mm). However, on site wet sieving
did produce nearly one hundred fragments of slag. Most slags were found around the small feature of Bronze Age date
(029) and the lower contexts, with few slags recovered from the southern and
western sides of the area.
Fragments of burnt stones, shells (both
land and sea) and bones were found in the topsoil, as was a fragment of a dark
shale bracelet. No slag fragments were
recovered from the topsoil.
Finds
Slags
Close to a hundred small pieces of
copper-rich debris were recovered from the site. These consisted of crushed malachite and dolomite and small
fragments of copper metal within a slag matrix. These finds suggest that
several different processes were being carried out in the vicinity. Copper ores do not occur naturally on this
part of the Orme and must therefore have been brought to the site; and copper
metal can only be produced in a furnace at high temperatures (Chapman pers. comm.). The slags are currently being analysed by Oxford University,
where initial analysis has identified them as slags derived from the smelting
of sulphide ores and not the expected carbonate ores (Salter pers. comm.).
The small, crushed nature of the slag
material recovered may be the direct result of a crushing process used to
retrieve prills of copper from the slag matrix after the initial smelting. Once
separated from the slag the prills could then be melted into larger quantities
of copper metal. Identical crushed
slags have recently been produced during experimental smelting of Great Orme
ore using a bowl furnace by Chapman and Roberts (Chapman pers comm.).
Lithics
Only
three stone artefacts were recovered from known contexts: a piece of shale
bracelet from the surface of a brownish grey silty clay (020) overlying the
pit; a flint flake from the topsoil
(001) and a whetstone from the pit (025).
Whetstone
The
whetstone was retrieved from the upper fill (026) of the pit 025. The stone surface is uniform “light olive
grey” (Munsell: 5Y6/1) in colour, and its well defined orthogonal shape is
determined by a major and two minor planar joint surfaces. It has a uniform
fine grained texture (grain size 0.1-0.2mm) with quartz, felspar and biotite
visible, together with occasional blebs of pyrite: it would appear to be fine grained silicic/intermediate igneous
rock such as a microgranite.
The whetstone showed several distinct
wear patterns, suggesting different uses.
Whilst the larger flat surfaces and the side edges show evidence of polish,
suggesting use as a whetstone, short edges and corners show evidence of
abrasion by percussion, suggesting use as a hammerstone. The corners show
damage consistent with having been used to crush some material, while larger
missing flakes from the corners suggest a far more vigorous battering or
hammering action. In places these
crushing and battering marks had been partly worn flat by it’s re-use as a
whetstone. Therefore, the stone appears to have been a multi-purpose tool, used
as a sharpening implement tool and also a crushing implement.
It is possible that the whetstone was
used to crush up the ores found on site.
However, microscopic inspection of the abraded surfaces of the whetstone
revealed no evidence of its use in ore or slag crushing – for example in
embedded fragments of chalcopyrite or of malachite (Jenkins pers. comm.). Any fragments of ore or slags, though, may have already
corroded. It is, therefore, unclear if
this stone was involved in any prehistoric metalworking on the site and was
re-deposited in the Medieval/post-medieval pit or is indeed a
Medieval/post-medieval artefact.
Shale
bracelet fragment
A fragment of a shale bangle/bracelet
was recovered from the surface of the grey silty clay 020 at the southern end
of the site. It appears to have delaminated along natural bedding plains, so
that it now appears as half sectioned.
It is made from a very dark grey carboniferous shale, examples of which
are found locally at Bangor and on Anglesey.
The identification of micro-fossils in the shale could locate its origin
more precisely. It has a number of cut
marks on the outer surface. By
extrapolating the curvature of the bracelet it is possible to reconstruct its
original dimensions. It’s external
diameter would have been approximately 850mm and it’s internal diameter
approximately 660mm. Jet ornaments are
known from the Beaker period in Gwynedd, but shale ornaments from any period
are rare. A shale ring from the
Romano-British period has been found in
Caernarfon (White, 1985), and a number of Late Bronze Age examples are known
from Flag Fen (Pryor, 1991, 117 & 96).
Flint
Flakes
A weathered flint flake was recovered
from the topsoil (001) at the southern end of the site. It still retained part of the original nodule surface, suggesting that was not,
originally a beach pebble and may well be imported.
A weathered flint flake, with possible
micro chipping, was also recovered from slump material that had eroded out of
the main site section, prior to excavation.
XRF
Trace element data
During the excavation, Dr David Jenkins
of the University of Wales, Bangor, took twenty seven samples from the main
contexts on the site for XRF trace element analysis. These samples showed a range of values for copper (Cu) from
around the crustal average (55mg/g) to 1%.
Two samples, from 021 and 029 had levels that indicated ‘major’
contamination (10,400mg/g &
9,750mg/g), which could only realistically arise if metal working
was taken place on site, as the solid geology is devoid of any indications of
local mineralisation. Other values (200-100mg/u) could
indicate either minor direct contamination through metal working or,
post-depositional distribution of Cu through leaching from other contexts. Such readings were identified in most
contexts apart from the topsoil and the in
situ burnt area. Contamination
levels were also recorded in the re-deposited, brownish pink clay layer which
overlay the unexcavated ‘v’-shaped feature.
The original geochemical survey of 1997, also recorded a notably high
level of copper contamination in the top (old ground surface?) of this
‘v’-shaped feature. Both may be the
result of the minerals leaching down
through the contexts.
Of the other elements for which the XRF
produced data, none of the chalcophilic elements which might be associated
directly with copper (Cu) show any significant correlation with high readings
of copper. This might suggest that
either the purer hydroxy-carbonate (malachite) ore was being processed or that
a pure metal was being worked (Jenkins pers.
comm.).
Conclusions
The excavation has revealed two
principal phases of use: the earliest is interpreted as a Bronze Age smelting
site, and the later phase as Medieval domestic activity.
The only remaining in situ feature from the early phase is the small feature
(021&030) located on the very edge of the eroding section, which contained
the highest concentration of slag material.
It has been suggested (Chapman pers.
comm.) that the contents of this feature may be the contents of a cleaned
crucible, the fragments of possible crucible or furnace surface also found
within this context may confirm this interpretation. The grey silty clay layer, that contained slag fragments, may
have be a contemporary layer, however, it has been disturbed by Medieval
(possibly post-medieval) activity, notably by the cutting of the pit (025) and
hearth (031), resulting in residual slags (and perhaps the fragment of shale
bracelet) being re-deposited.
The food debris found associated with
the Medieval features suggests that the terrace was used as a domestic site utilising edible shell fish from the
beach below, and perhaps taking advantage of the slightly overhanging cliff for
shelter. The remains of the hearth are
more consistent with cooking than with the high temperature furnaces needed for
smelting. The whetstone found within the pit may be a re-deposited find, but
unfortunately, examination of the crushed surfaces on the stone have failed to
identify any slag or ore remains, so its connection with the prehistoric
smelting site remains unproven. It would appear unlikely that copper smelting
was taking place at the site during the Medieval phase.
If Medieval activity was indeed taking
advantage of the cliff overhang directly above the site, disturbance it may have been restricted to
the area immediately up against the cliff.
Other level areas survive to the east and north of the excavated site
which hold great potential for our understanding of the present site and its
context.
This site represents the earliest
evidence for copper smelting yet discovered in Great Britain and adds yet
another dimension to the developing picture of one of the most complete Bronze
Age copper production centres in the country.
Discussion
of results
As stated earlier the preliminary
analysis of the slags indicates that primary sulphide ores were being processed
on the site. This along with the
radiocarbon date (cal 1580BC) has interesting implications for the development
of metallurgy on the Great Orme. In the past it has generally been accepted
that the colourful carbonate (secondary) ores were the first to be exploited,
before exhaustion of these ores led to the exploitation of the sulphide
(primary) ores. Also, on the Great Orme
the process of dolomitisation which occurred during the transformation of
primary ores to secondary carbonate ores, softened the host rock, allowing for
the relatively easy extraction of the carbonate ores. Present evidence suggests that fire-setting was used only occasionally
throughout the prehistoric period, and notably where harder rock was
located. Therefore, this technique,
along with the introduction of metal tools, would have allowed for the
exploitation of the primary sulphide ores generally found within harder host rock. Evidence, from the Pyllau valley mines, suggests that certain
abandoned areas of workings were subsequently reworked to extract the residual
primary ores. In one area, evidence of
fire-setting produced a date of 1428-975 BC (CAR-1280), while adjacent (worked)
areas were dated between 1885-1465 BC (CAR-1184) (Dutton et al, 284). Dutton states
that this does not necessarily imply that available carbonate ores had been
exhausted (certain carbonate bearing workings have been dated to 1410-920 (HAR-4845)),
rather that the exploitation of sulphide ores was developed in parallel to the
carbonate ores (Dutton et al, 384).
The dated smelting activity at Pentrwyn
indicates that the exploitation of sulphide ores was taking place earlier than
previously thought on the Great Orme, during the earlier period of mining
activity in the Pyllau valley. It is
known that in eastern Europe sulphide ores were being smelted as early as
3200-3000 cal BC (Budd et al 1994,
100), so the technology to do this may have existed from the beginnings of the
mining on the Great Orme, but it was easier to extract and process the
carbonate ores first.
Acknowledgements
The excavation was carried out by Gwynedd Archaeological Trust,
under the supervision of David Hopewell. The excavators would like to thank
the following for their co-operation and assistance:
Mostyn Estates; Mr Tom Gravett (Great Orme Country Park); Mr David
Chapman; Dr David Jenkins (University of Wales Bangor);
Dr Astrid Caseldine; Ms Kate Barrow (University of Wales Lampeter);
Dr Peter Northover and Dr Chris Salter (University of Oxford).
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