BEAKER POTTERY FROM ROSS ISLAND, KILLARNEY CO.KERRY, IRELAND

R.A.Ixer
Email: R.Ixer@btinternet.com
Synopsis.

Eight beakers and one food vessel were petrographically analysed and described. Pot 16 (sherd 651), the food vessel, is petrographically different from the other sherds. It is tempered with deliberately crushed, non-ophitic, unaltered basalt. Basalts form only a very small part of the local bedrock succession, if present at all, and hence this pot may not have been made locally.
All the beakers are tempered with crushed local bedrocks, namely silicified, fossiliferous limestone, vein calcite and chert. Metasandstone/metasiltstone found as unconsolidated pebbles may have come from the drift or beach sand. Although different pots have different amounts of these four lithic components, when seen together they form a continuum.
No sulphide ore was found in the sherds. Malachite-stained limestone, botryoidal haematite, limonite-cemented sandstones/ angular sand grains comprise very minor components of the temper and have been recovered from the excavation site.
The petrography suggests that the beakers were locally made using local crushed rocks but not to a single formula by people associated with the copper mining.

Sampling and Preparation

One thin section was prepared from each of the eleven sherds and crumbs taken from eight beakers and one food vessel. In addition, polished blocks were made of pots 10, 11 and 12 (sherds 1286 and 1293), 16 and 23 (sherd 536). The firing colour and any variation for each off-cut were determined for each sherd/crumb using the Geological Society of America's Rock-Color Chart. An initial investigation of this section using a land lens determined the size and shape of the largest temper.
Routine transmitted and reflected light petrography, the latter using X40 oil immersion lenses, was employed to determine the identity of the clay and temper components, plus the degree of tempering, the presence or absence of bone, grog and organic matter and the size, shape and size range of the temper were also determined. No attempt was made to deduce firing temperatures.
Representative material of the local limestones and cherts were collected from outcrop and thin-sectioned. In addition thin and polished sections were made of loose material taken from the occupation site and from lakeside beach sands from a small bay immediately east of the copper mine.

Local Geology as Source Rocks for the Temper.

The regional geology of the Killarney area is simple and comprises swathes of approximately east-west trending Devonian siliciclastics, Carboniferous Limestones and a further siliciclastic sequence - the Millstone Grit (Pracht , 1997).
The bedrocks closest to the Ross Island Mine and occupation sites are a series of Carboniferous Limestones including recrystallized, partially silicified and dolomitized, mineralized limestones, unmineralized silicified limestones and limestones with chert bands.
The nearest Millstone Grit is approximately five kilometres to the northwest of Ross Island whilst the nearest Devonian rocks are the purple sandstones and siltstones of the Ballinskelligs Sandstone Formation about two kilometres west across Lough Leane.
The area was heavily glaciated and there are thick fill sequences around the town of Killarney and much of this fill comprises Devonian rocks as the ice moved down from the Devonian high ground onto the low ground covering the Carboniferous. These erratics include large numbers of red and green Devonian sandstones, up to cubic metres in size. These are scattered close to the northern shore of the lake including some that are very close to the Bronze Age work camp area. There are only minor outcrops of igneous rocks but these include rhyolites and volcaniclastics in the Devonian and small dolerite dykes, although their precise localities are not given (Pracht, 1997).
It seems likely therefore that, with the exception of pot 16, all of the pots were tempered with rocks that were locally available as bedrock for example limestones and cherts occur within 100 metres of the find sites - or from the drift (limonitic sandstones/siltstones). These sandstones/siltstones have a low-grade metamorphic fabric that suggests they are Devonian sandstones rather than Upper Carboniferous Millstone Grit. Pot 16, the food vessel, is tempered with non-ophitic basalt. This does not match with the Devonian volcanics of the region but might match the minor Carboniferous dolerite. Equally, however, the temper might be Tertiary in age from the north of Ireland. As the distribution of Tertiary basic rocks in the glacial fill of the Killarney area is not known, the possibility that this pot was locally made and tempered by an erratic cannot be discounted. However, on balance, it is believed that this is an exotic pot of non-local manufacture.

Fabric Interpretation.

Table 90 lists the relative proportions of the lithics present in the Ross Island pots, whilst figure 259 shows a classification scheme based on shared characteristics between these lithic components. It is recognised that this scheme is one of a number of possible classification schemes.
Table 90 shows that the main lithics, for all the sherds except sherd 16, including rock clasts and individual mineral grains are quartz grains carbonate dust, chert carbonate dust dolomite rhombs, polycrystalline, strained quartz (metamorphic quartz), limestones and vein calcite and metasediments including sandstones, siltstones and shales.
Comparisons between these lithics and the local, bedrock, silicified limestones and cherts; with local beach sands and with fine pebbles (<0.5cm) from the drift showed that all the lithics could be obtained from very local sources, mainly from outcrop, subcrop or, in the case of the metasediments, from the local drift/surface sediments. In addition, the trace amounts of microcline and plagioclase feldspar that are also present could be locally derived as seen by their presence in the local beach sands and their concentration in sherds that carry a high metasediment component. Hence the lithic component of the sherds is consistent with their being of a local manufacture, perhaps in the immediate vicinity of the work camp.
It is more difficult, however, to show any link between the pottery and any metal-working activity. No ore, roasted ore, slag or metal have been recognised within any sherd. A few sherds carry rare, malachite-stained limonite, botryoidal haematite/manganese oxides or angular quartz grains enclosed in limonite. Although all three are present in the Central Excavation Area their metallurgical significance, if any, remains unclear indeed they may be part of the natural 'bedrock'.
The green copper staining seen on some of the sherds and on some of the lithic clasts within them is not a primary feature but is associated with the enclosing sediments. On a number of sherds (especially pot 23) sediment adhering to the surface contains abundant fine-grained chalcopyrite and charcoal. Much of this chalcopyrite has oxidised to malachite, locally staining the surface of the pot green.
Figure 259 shows a classification scheme based on shared lithic characteristics. It clearly shows that the division of the sherds into Beaker ware and Food Vessel ware (Pot 16) is fundamental. The lithic component of the food vessel is very different from all of the other sherds. Its main component, a non-ophitic phenocrystic basalt, is unlikely to be of local origin, suggesting either the use of a glacial erratic, if of local manufacture, or that the pot was made elsewhere.
Within the Beaker pots, the shape and size range of the lithics suggests that the majority of them were tempered by adding crushed rock. Crushed chert was added to pot 2; crushed limestone/vein calcite to pots 4 and 11; crushed limestone/calcite and chert to pot 23 and crushed sandstone/metasandstone to pot 12. Pots 5, 6 and 10 have few rock fragments and may only be tempered by local sand or may be untempered.

Catalogue.

Pot 2. Sherd 92E081: 1247-24. Undecorated body sherd.

Macroscopically the sherd has a 2mm wide dusky-red core (10R 2/2 on the GSA rock-color chart) within a moderate reddish-brown, inner and outer margin (10R 4/6) The sherd shows many tabular to angular voids (a "corky texture") which are up to 2mm in length. These are not due to the burning out of organic matter but are sparite crystals that have been lost. A coiled fabric is present. The pot is lightly gritted or, assuming that the voids were originally filled with clasts, then the pot is densely gritted. The clay is clean and dark enclosing a restricted range of angular temper which in decreasing order of abundance include fine-grained chert > single quartz crystals many showing strained extinction carbonate dust inclusions > polycrystalline quartz (quartzite) and rare opaque phases, single laths of muscovite and zircon plus a little black ?organic matter and brown isotropic ??bone. A few rounded areas within the clay matrix have a darker firing colour. If these are grog, then their rarity suggests that they were not intentionally added. The voids show a large size range and are similar in shape and size to the chert temper and to calcite crystals; there are many small 'dolomite rhombs'. Together their shape and size suggest that crushed rock was added to quartz-bearing, clean clay.

Pot 4. Sherd 92E081: 3561-1. Body sherd.

The top one millimetre of the sherd is a moderate reddish-orange (10R 6/6) above a pale brown body (5YR 5/2). There are many flattened gas bubbles and sand-sized, angular to subrounded grit and fine-grained mica are visible to the eye. The pot is quite densely gritted and in order of decreasing abundance the temper comprises crinoidal, silicified, fine-grained limestone > angular, single quartz grains, >polycrystalline quartz showing strained extinction carbonate dust inclusions plus rarer quartz-sericite (?altered metasiltstone), fine-grained chert and single plagioclase laths. The coarse, angular temper is restricted to limestone/calcite clasts. The alignment of the flattened gas bubbles and orientation of the white mica flakes gives a feint fabric to the pot. Small areas of darker fired clay have temper that is in a different orientation from the body of the pot but, if this is grog, there is little of it and it is unlikely to have been added intentionally. Some of the voids appear to be partially infilled with fine-grained carbonate, which may be post depositional in origin. The lithics suggest that crushed limestone/calcite was added to a local, quartz-bearing clay.

Pot 5. Sherd 92E081: 1334. Body sherd.

The sherd has a one millimetre dark red-brown (10R 3 /4) outer rim above a dark black (N3) body and a thin, <1mm wide, red-brown, inner rim. It is quite densely gritted with white, angular to subrounded grit up to one millimetre in diameter. There is a poor fabric. The temper is heterolithic and, in order of decreasing abundance, comprises single and polycrystalline quartz showing strained extinction carbonate dust inclusions, > fine-grained sandstone-siltstone > chert, plus very rare, fine-grained quartz-plagioclase and single grains of muscovite, plagioclase and zircon and rare ??bone. Rounded areas within the clay with a different firing colour and containing temper showing a different orientation to the main body of the pot suggest grog. There is an absence of large, angular rock clasts suggesting that crushed rock was not added to the clay.

Pot 6. Sherd 92E081: 576. Decorated body sherd.

Macroscopically the sherd shows a 2mm wide light brown (5YR 6/4) outer rim above a black core (N3) and a thin, brown-black inner rim. It is lightly gritted with up to 2mm diameter siltstone/sandstone and black or colourless grits. It has a distinct fabric. The temper is heterolithic; in decreasing order it comprises single quartz grains plus lesser amounts of polycrystalline quartz (including vein quartz and schistose quartz), much of the quartz shows strained extinction carbonate dust inclusions > quartz-white mica plagioclase metasiltstone/fine sandstone > fine-grained chert plus rare, single flecks of muscovite and single grains of plagioclase, alkali feldspar (including microcline), opaque phases and high grade metamorphic minerals? and mudstones. If grog is present it only occurs in minor amounts and so was not intentionally added. The pot has a very similar fabric and petrography to Pots 5 and10. The lithics are small in diameter and rock clasts are few and rounded suggesting that crushed rock was not added to a local clay.

Pot 10. Sherd 92E081: 147-1. Decorated body sherd.

The crumbs have a uniform body colour that is moderate reddish-orange (10R 6/6). The pot is lightly gritted with one millimetre angular voids (after chert fragments?) and siltstone clasts up to 3mm in length. There is a definite fabric. The temper is heterolithic and shows size-variations between lithologies, rare, large clasts are composed of rounded to subangular sandstone/siltstone or polycrystalline quartz whereas all other lithics are smaller. In decreasing order of abundance, the temper comprises single quartz grains many with strained extinction and carbonate dust inclusions > polycrystalline quartz clasts > fine-grained chert some with a radiating fabric opaque phases and quartz veinlets > quartz-mica (but feldspar-free) metasiltstone/fine sandstone, plus rare plagioclase, opaque and organic inclusions. Rare, rounded areas with a different firing colour from the main clay may be grog or mudstone clasts. If it is grog it was unintentionally added. The clay carries very small grains of haematite, Ti02 minerals and limonite pseudomorphs after framboidal pyrite. Small opaque clasts include rare, botryoidal haematite, graphite flakes, limonite/cuprite replacing sulphides and ? delafossite. Many clasts are cemented or stained with banded limonite/manganese oxides. Charcoal is present on the surface of the pot but also within void spaces in the sherd; fine-grained pyrite and chalcopyrite altering to limonite and malachite are also present on the surface. Angular rock fragments are missing from this sherd suggesting that crushed rock was not added to a dirty, local clay.

Pot 11. Sherd 92E081: 802. Undecorated body sherd.

The sherd has a uniform, light brown body colour (5YR 5/6) and is lightly gritted with mudstone, banded calcite and quartz clasts up to 3mm in diameter. Voids are present within the fabric. The temper is heterolithic. It comprises, in decreasing order of abundance, angular calcite, some showing replacement along its cleavage by limonite, plus rounded silicified, fossiliferous, fine-grained limestone pyrite > single and polycrystalline quartz carbonate dust inclusions > rounded chert quartz veinlets opaques > limonite-and sericite-cemented metasiltstone and fine sandstone plus rare phyllite and large, rounded, mudstone clasts. Opaque phases include magnetite altering to haematite, haematite, Ti02 minerals, chromite and zircon as part of the clay component and very rare graphite flakes and limonite pseudomorphing sulphides. Fine-grained chalcopyrite altering to limonite is present within the sediments adhering to the sherd surface. No grog was recognised. The fabric of the lithics suggest crushed calcite/limestone added to dirty, local clay.

Pot 12. Sherd 92E081: 1286. Undecorated rim sherd.

The sherd has a uniform body colour, a moderate reddish-brown (10R 4/6). It is heavily gritted with coarse-grained sandstone and carbonate plus black coloured grit up to 2mm in diameter. Void spaces are present. The temper is heterolithic and, in a relative order of abundance, comprises coarse-grained quartz-muscovite Kspar (microcline) chert metasandstone that has been extensively replaced by limonite-stained sericite to give quartz-sericite or sericite clasts > angular, fine-grained limestone and vein calcite > strained single quartz crystals carbonate dust inclusions dolomite rhombs > unaltered microcline >fine-grained chert plus rare single muscovite and plagioclase laths and opaque phases. Sandstone and carbonate lithics are coarser than the rest of the temper, much of which has the same grain size as the individual components of the sandstone. Rare yellow-green ?phyllosilicate/??bone is present with low birefringence. Very fine-grained Ti02 minerals, haematite, ilmenohaematite and rare zircon are part of the clay component. Magnetite altering to haematite, mixed haematite-Ti02 and quartz-schistose haematite belong to the temper. Many void spaces are partially infilled by banded limonite/manganese oxides. Small amounts of limonite replacing chalcopyrite coat the surface of the sherd or are found within void spaces close to the edge of the sherd. No grog was recognised. The shape and size of the lithics suggest that crushed limestone/calcite and perhaps sandstone were added to a local clay.

Pot 12. Sherd 92E081: 1293. Highly burnished rim sherd.

The three crumbs have a uniform reddish-brown (10/R 4/6) colour and are densely gritted with rounded to subrounded, up to one millimetre, white carbonate and sericitic sandstone grit. There is a feint fabric. The temper is heterolithic, in order of decreasing abundance it comprises coarse-grained quartz-muscovite plagioclase Kspar chert metasandstone which shows much alteration to limonite-stained sericite > strained quartz carbonate dust, plus some serrated (metamorphic) quartz > coarse, sparitic limestone and single calcite crystals > unaltered microcline > fine-grained chert quartz veinlets plus very rare muscovite flakes, altered plagioclase, large perthite crystals and fine-grained mudstone clasts. Small Ti02 minerals, haematite and zircon belong to the clay component. Small amounts of quartz-haematite schist is present as temper. Chalcopyrite altering to limonite and belonging to the enclosing sediments coats the crumbs and is associated with green staining. No grog was recognised. The fabric suggests that crushed sandstone and limestone/calcite were added to local clays.

Pot 16. Sherd 92E081: 651. Undecorated body sherd. Food Vessel.

The sherd has a light brown (5YR 5/1) outer rim and a greyish black (N2) inner body therefore it is not totally oxidised. It is lightly gritted in a very dark matrix with angular to subrounded porphyritic basalt up to 2mm in diameter. The temper is essentially monolithic comprising non-ophitic ?Tertiary basalt with minor quantitites of strained quartz (not carrying carbonate dust), plus spherulitic chert/?rhyolite opaques. A few grains of magnetite surrounding a haematite core are present No grog was recognised. The fabric suggests that crushed basalt was added to a clean clay.

Pot 23. Sherd 92E081: 529. Undecorated body sherd.

The sherd has an even pale reddish-brown, body colour (10R 5/4) and is lightly gritted with rounded to subangular heterolithic clasts including white limestone/chert, rounded sandstone and red mudstone up to 3mm in size. Void spaces are present. The temper, in decreasing order of abundance, comprises very angular, radiating, Rockfield Formation, fine-grained chert carbonate dust rare dolomite rhombs > recrystallized, limonite-stained limestone > single quartz crystals showing strained extinction, plus rare muscovite laths, epidote and long opaque grains. Rare, black organic laths are present. Grog, recognised as spherical areas with a darker firing colour and displaying a fabric that is at an angle to the main fabric of the pot, is in sufficient amounts to suggest that it was intentionally added. Chert and carbonate clasts are angular and their shape suggests they were intentionally added as crushed rock to a local clay.

Pot 23. Sherd 92E081: 536. Undecorated body sherd.

The sherd consists of an outer 4mm, moderately reddish-orange (10R 6/6) rim and 3mm, black (N2), inner portion and thin, brown-red, inner rim. It is fairly lightly gritted with up to 1mm diameter, white chert and black clasts and brown grog and rare clasts up to 4mm long. The temper comprises, in decreasing order of abundance, rounded to very angular chert > single strained quartz crystals carbonate dust > single calcite crystals, and metasandstone and opaques. Fine-grained, pale TiO2 minerals, haematite, rare mixed haematite-TiO2 aggregates and zircon belong to the clay component of the pot. Limonite-stained metasiltstone, malachite-stained carbonate and spongy haematite and quartz-haematite schist are part of the temper. Void spaces are partially infilled by banded manganese oxide/limonite. Fine-grained charcoal and chalcopyrite altering to limonite coat the surface of the pot and belong to the enclosing sediments. There is much rounded to angular grog that has the same temper as the main pot but is more densely gritted; the temper lies in a different orientation to the main fabric. One 80 x 5 micron sized, yellow metal inclusion (a turning) which was identified optically as brass not copper is present in a void space and is believed to be adventitious. It should be noted that brass contamination was not seen in any other pot. The fabric of the pot suggests that crushed chert limestone/calcite and grog were intentionally added to a local clay.

Beach Sand -sand size fraction.

The sample was taken from a small bay immediately east of the Bronze Age copper mine. The sand is well-sorted and comprises subangular to rounded grains. In order of decreasing abundance the grains comprise single quartz and chert plus minor amounts of metasediments and trace amounts of feldspar. Most quartz grains show strained extinction and some carry fine-grained, carbonate dust inclusions. Chert, carbonate dust inclusions dolomite rhombs/rhombic void spaces/limonite, is also common. Minor amounts of pyritic metashale, fine metasiltstone and meta-arkosic sandstone are present as are rare, single grains of unaltered microcline, plagioclase feldspar and micritic limestone.

Beach Sand- larger than sand-size fraction.

Small, <0.5cm diameter, pebbles were separated from the beach sand. They mainly comprise chert or polygonal, metamorphic quartz together with lesser amounts of metasandstone, phyllite and limestone.Fine to medium-grained chert carbonate dust rhombic shaped void spaces/limonite is the most common rock-type and much of it is limonitically stained. Polygonal grains of serrated quartz showing strained extinction are abundant. Lesser amounts of arkosic, micaceous, limonite-stained metasandstone - metasiltstones are present, as are flattened phyllites (metashales) some of which are pyritic. Partially silicified, micritic limestones are rare, as are limonite clasts enclosing angular quartz. Both the limestone and the cherts are from the Rockfield formation.

Pracht, M. 1997 A geological description to accompany the bedrock geology 1:100,000 scale map series, Sheet 21, Kerry and Cork. Geological Survey of Ireland.

Table 1. Summary table giving the relative proportions of the lithic components from the Ross Island Pots. 2 4 5 6 10 11 12 12 16 23 23 Quartz carbonate dust Mi Ma Ma Ma Ma Ma Ma Ma Mi Mi Ma Polycrystalline Quartz Mi Ma Ma Ma Ma Ma Ma Ma Mi Tr - Chert Ma Mi Mi Mi Ma Mi Mi Mi - Ma Ma Limestone & Calcite - Ma - - - Ma Mi Mi - Ma Mi Metasiltstone/Sandstone - Mi Ma Ma Mi Mi Ma Ma - Tr Tr Basalt - - - - - - - - Ma - - Grog Tr Mi Mi Tr Tr - - - - Mi Mi Muscovite Tr Tr Tr Tr Tr Tr Plagioclase Tr Tr Tr Tr Tr Tr Microcline Kspar Tr Mi Mi Zircon Tr Tr Ma - Major constituent Mi - Minor constituent Tr - Trace element