Prehistoric Gold Markers and Environmental Change: a Two-Age System for Standing Stones in Western Ireland

Prehistoric Gold Markers and Environmental Change: A Two-Age System for Standing Stones in Western Ireland

K.R. Moore* Department of Earth and Ocean Science, National University of Ireland Galway, Galway, Ireland

The Murrisk Peninsula in southwest County Mayo is a major target for gold exploration in Ireland. The most productive areas include the Cregganbaun Shear Zone and Cregganbaun Quartzite Belt on Croagh Patrick, both geologically related to Iapetus closure, and gold is concentrated in alluvial deposits of river systems draining these areas. A comparison of gold occurrences with the location of prehistoric stone monuments reveals that simple standing-stone monuments, though isolated from other monument types, correlate with alluvial gold. South of the Murrisk Peninsula in Connemara, isolated standing stones are associated with a wide range of mineral resources and with other monuments. Dating of the stones relative to blanket-bog expansion and coastal landform changes indicates that standing stones were raised as markers of gold placer deposits before a climatic deterioration at 1200 B.C. Late Bronze Age monuments with a ceremonial purpose are more complex and include stone alignments. © 2006 Wiley Periodicals, Inc.

INTRODUCTION The predominance of wedge tombs in the west of Ireland is attributed to builders who settled initially in the copper-rich lands of west Munster (McNally, 1984), the metal-ore deposits of which may have been exploited for commerce. Metalworking was introduced to Ireland around 2500 B.C., and the earliest metal artifacts were tools or weapons made of pure copper and discs or lunulae (neck ornaments) of gold (Kelly, 2002). The advantages of copper and gold as raw materials were (a) the ease of extraction from the environment because of their concentration in alluvial deposits, and (b) the ease of working because of the softness of the metal. An Irish source for the 47 kg of Bronze Age goldwork housed in the National Museum of Ireland in Dublin is difficult to trace chemically because of remelting and mixing of gold (Chapman et al., 1998). Large slabs or pillars of stone were erected from the later part of the Neolithic (~4500–2000 B.C.), through the Bronze Age (2000 B.C.–post-500 B.C.) and continu- ing into the Iron Age in western Ireland (McNally, 1984; Flanagan, 1992; Cooney, 1996; Corlett, 1997). The purpose of these stones, often situated in very isolated

*E-mail: [email protected].

Figure 1. Topographic map showing important upland areas, drainage patterns, and location of prehistoric monuments in the Murrisk Peninsula, southwest County Mayo, western Ireland. Evidence of domestic activity (dots) are pre-bog field enclosures, cooking pits called fulachta fiadh, stone enclosures, and shell middens (Corlett, 1997). Burial sites (squares) are court tombs, wedge tombs, and cists (Corlett, 1997). Domestic activity and burial sites are indicative of human settlement in a NNE–SSW trend across the peninsula. Standing stones (open circles) are (1) single standing stone surrounded by an oval arrangement of small stones, (2) low standing stones, (3) standing stone pairs or triplets; (?) reported locations of standing stones that have been removed by field clearance. Disregarding the standing stones that no longer exist, the distribution of the standing stones is in two general groups: a western group to the west and northwest of the Mweelrea Mountains and Sheefry Hills and an eastern group to the north and east of Croagh Patrick.

locations (McNally, 1984), is uncertain, but they may have been ceremonial, boundary or route markers, or scratching posts for cattle. The latter has been ruled out because of the occurrence of standing stones in rocky terrain unsuitable for cattle (Lohan, 1999), but standing stones as markers of an ancient pagan trackway to the east of Croagh Patrick may have influenced the route of Christian pilgrimage (Mulveen, 1999). Many stone rows and circles are noted to have either a proces- sional relation to a burial site or an astronomical alignment (Burl, 1990; Kelly, 2002), but isolated standing stones in western Ireland have no significant alignments that can prove a ceremonial connection. In the Murrisk Peninsula, southwest County Mayo (Figure 1), archaeological sites indicative of domestic activity include shell middens, cooking mounds (fulachta fiadh), pre-bog stone enclosures, and field walls (Corlett, 1997). Burial sites include court tombs, wedge tombs, and cists. Court tombs are early Neolithic burial monu-

156 GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, VOL. 21, NO. 2 DOI: 10.1002/GEA A TWO-AGE SYSTEM FOR STANDING STONES IN WESTERN IRELAND ments (McNally, 1984), and wedge-tomb construction was replaced around 2200 B.C. (Kelly, 2002) with simple burial pits or Bronze Age cists. Burial sites and domestic sites (Corlett, 1997) are located exclusively in the western half of the peninsula. The remaining monuments include a stone row, a possible stone circle, a standing stone complex, and isolated standing stones. The latter are observed in various arrangements: (a) A single standing stone surrounded by an oval arrangement of small stones, (b) low standing stones, and (c) standing stones in pairs or triplets. Prehistoric and Christian carvings are reported on one standing stone near Croagh Patrick (Mulveen, 1999) and a wedge tomb (Corlett, 1997), respectively. The distribution of monuments shows that sites of human inhabitation have a NNE–SSW arrangement across the peninsula while standing stone distribution is apparently independent of evidence for inhabitation. There are two general groups of standing stones (Figure 1). The western group consists of standing stones to the west and northwest of the Mweelrea Mountains and Sheefry Hills. The eastern group is to the east and north of Croagh Patrick. The former position of two additional standing stones is indicated (by a question mark) near the coast to the west of Croagh Patrick. Standing stones are often located close to main rivers, such as the Carrownisky River, and their tributaries. The apparent distribution of the megalithic monuments recorded does not appear to have been affected by archaeological survey or preser- vation bias for the following reasons: 1. Sites of inhabitation are recorded in the lower lands that would have been most suitable for cultivation; but monuments are also recorded in highland areas less accessible to scrutiny. 2. The area was sparsely populated for most of its history from the Iron Age to present, such that human interference is likely to have been minimal. 3. Accumulation of peat has not overwhelmed the monuments. There is a general coincidence between the distribution of prehistoric rock art and local copper resources in Ireland (Kelly, 2002), and prehistoric monuments within the Murrisk Peninsula may also be related to the occurrence of gold deposits (Kelly, personal communication, 2003). The prominent position of Croagh Patrick in the local landscape of this area has led to the hypothesis that all prehistoric monuments are related to the magnificently conical mountain as the center of a ceremonial system (Corlett, 1997). In this article, the distribution of gold occurrence and prehistoric monuments in the Murrisk Peninsula is reviewed and the correlation between the location of standing stones and alluvial gold is statistically tested. The purpose of standing stones as markers of important metal deposits or as purely ceremonial monuments is further examined by consideration of the arrangement of standing stones in relation to evidence for environmental change, and the significance of gold to a society dependent on the environment is discussed.

GEOLOGICAL SETTING AND GOLD DISTRIBUTION IN COUNTY MAYO The Murrisk Peninsula is a major target for gold exploration in Ireland. The most productive areas, the Cregganbaun Shear Zone and Cregganbaun Quartzite Belt in

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Figure 2. Map summarizing major structural lineaments, gold exploration licenses, and targets and sites where gold has been located, both in situ (open circles) and as alluvial deposits (squares) in the Murrisk Peninsula (After McArdle et al., 1987; Aherne et al., 1992; Thompson et al., 1992). The western boundary of the licensing blocks generally follows the Carrownisky River, rich in alluvial gold. Alluvial gold is also reported from up to 18 streams surrounding Croagh Patrick. Prospects (1–4) that have been targeted by exploration companies as significant resources are located in the Cregganbaun Shear Zone and the Cregganbaun Quartzite of Croagh Patrick.

County Mayo (Figure 2), are part of a Palaeozoic continental collision zone. The Clew Bay Fault Zone is the southwest extension of the Scottish Highland Boundary Fault with higher grade continental rocks to the north and lower grade arc-related rocks to the south (Ryan et al., 1980), including early Ordovician turbidites and tuffs of the Sheefry Formation. Accretion of ophiolite remnants onto the margin of the South Mayo Trough (Thompson et al., 1992) is significant for the later formation of listvenite pods, a combination of altered mafic rock with the general assemblage carbonate mica pyrite and fracture-filling vein quartz and calcite. Ordovician rocks are unconformably overlain by a Silurian sequence to the north, and the Croagh Patrick Succession consists of conglomerate, pelite, quartzite, and sandstone. The principal sinistral deformation events in south Mayo are late Silurian to early Devonian in age and are related to the final closure of the Iapetus Ocean (Dewey, 1963; Dewey and Strachan, 2003). Resulting lineaments include shear structures, such as the Cregganbaun Shear Zone (Thompson et al., 1992) and Croagh Patrick folds that face and verge to the south (Aherne et al., 1992). The subvertical Cregganbaun Shear

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Zone (Figure 2) cuts across the north of the Sheefry Hills (Figure 1); mylonitic fab- rics, foliation, and dislocation occur mostly within the tuffaceous horizons of the Sheefry Formation (Thompson et al., 1992). Flexure in the Cregganbaun Shear Zone is continuous with the Maum Valley Fault Zone (Figure 2), a contemporaneous dex- tral shear zone that extends south into the Dalradian of Connemara (Reynolds, 1987; Harris and Harris, 1995). The late Caledonian Corvock Granite and associated lamprophyres intrude the Ordovician and Silurian rocks in the north–central South Mayo Trough. Fluids associated with emplacement of calc-alkaline lamprophyres migrated into the Cregganbaun Shear Zone and Cregganbaun Quartzite of the folded Croagh Patrick Succession and formed quartz-carbonate veins containing native gold and sul- fides (Aherne et al., 1992; Thompson et al., 1992). Gold localities have been identified by both drilling and sediment panning (Figure 2); alluvial gold was also recovered in variable amounts from up to 18 streams (localities unpublished) around Croagh Patrick by Tara Prospecting Ltd (McArdle et al., 1987). There are four areas of significant in situ mineralization identified by exploration companies: 1. Quartz veins from the Lecanvey Prospect 1 km west of the summit of Croagh Patrick had an average grade of approximately 10 g/t Au (Aherne et al., 1992). 2. An isoclinally folded, sheared, pyritized, and quartz-veined tuff band within the Kinnadoohy Prospect assayed 280 g/t Au (Thompson et al., 1992). 3. Stockworks and contorted quartz veins cross-cutting tuff and listvenite in the Srahoosky Prospect contained up to 24 g/t Au (Thompson et al., 1992). 4. The sheared lamprophyre-bearing complex with visible quartz pods up to 6.5 m wide of the Cushinyen Prospect had sample grades up to almost 20 g/t Au (Thompson et al., 1992). The effectiveness of soil geochemistry as an initial exploration tool (Thompson et al., 1992) is indicative of the extent of chemical weathering of the gold-bearing rocks. Erosion of rocks and soil, and the occurrence of quartz-bearing veins within streams (Aherne et al., 1992), explain the prevalence of gold located in alluvial sediments, for example, along the Carrownisky River (Figure 2).

STANDING STONES IN THE MURRISK PENINSULA Topographic drainage divides within the Murrisk Peninsula include the Mweelrea Mountains, Sheefry Hills, and Croagh Patrick (Figure 1), where in situ gold is located (Figure 2). Figure 3 relates gold deposits in the Cregganbaun Shear Zone and Cregganbaun Quartzite to standing stones of the western and eastern groups, respectively, by river patterns. The apparent correlation of the western group of standing stones with gold deposits is better than the eastern group, although the map disre- gards alluvial deposits around Croagh Patrick. To quantify the strength of the relationship between the location of standing stones and alluvial gold, the null hypothesis (Ho) that there is no difference between (a) standing stone distribution with respect to alluvial gold, and (b) a random distribution with respect to alluvial gold, is tested. The distance from the standing stones to the nearest potential alluvial gold

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Figure 3. Map relating in situ gold and alluvial gold through a network of streams and rivers to standing stone locations in the Murrisk Peninsula. The western group of standing stones correlates strongly with gold transport directions while the eastern group has general correlation. Standing stones on the south shore of Clew Bay include more complex stone monuments (alignment and Killadangan) that are likely to have ceremonial significance.

deposit—a river from which gold was extracted by exploration companies or which drains from a weathering gold-bearing outcrop —was measured to the nearest five meters (Table I) using the Ordnance Survey Discovery Series map sheets 30, 31, 37, and 38. The nearest distance between locations in a series of random populations and alluvial gold was likewise measured: The random sample populations shown in Table I are a systematic rectangular grid sample, a systematic circular grid sample, and a random sample. A two-sample unequal variance (heteroscedastic) t-test was used to compare the standing stone sample population (Table I) to each of the random sample populations (Table I) to show reproducibility of the results. The percentage prob-

ability that they are the same (i.e., Ho is correct) is given as a percentage. The statistical analysis, therefore, shows that, for all random sample populations, there is more than a 99% certainty that the distribution of standing stones with respect to alluvial gold deposits is not random. The early exploitation of gold is, unsatisfactorily, inferred from the distribution of gold artifacts because of the lack of field evidence for gold mining (Weisgerber and Pernicka, 1993). The reason there is little trace in the archaeological record is that early methods of gold extraction from the environment would have been by sediment

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Table I. Statistical analysis of the distribution of standing stones with respect to alluvial gold deposits. Standing Stones Systematic Grid Sample Systematic Circular Sample Random Sample

1000 9255 1670 3930 1100 5700 1665 3570 1450 6300 2620 3925 750 5100 2380 3450 80 10150 3930 1430 900 4048 1310 2855 100 2855 2380 0665 50 400 2385 3810 400 1500 2140 6905 350 7450 2145 5952 250 150 950 5119 500 2145 1430 0 1075 400 3810 3930 500 2350 3335 3810 3940 3220 6430 833 1750 150 4525 2620 2030 350 6665 2740 2400 400 4900 240 2750 6650 5715 235 1620 6995 8335 1190 t-test result (%)a 0.14 0.00 0.33 Note. The distances from points within a population to the nearest potential alluvial gold deposit—either a river from which gold has been extracted by exploration companies or a river draining an area where an outcrop of gold is known to be weathering—are given in meters. aThe t-test result gives the percentage probability that there is no difference between the standing-stone population and each of the random populations with respect to alluvial gold. panning in rivers or on beaches. Rivers deposit comparatively heavy sediments where there is any sudden drop in the velocity of a current, for example, where there are changes in gradient, meanders, spreading, or obstruction. Irregularities, or riffles, in the bedform of the river caused by the relative hardness of interbedded units are excellent traps for placer deposits (Evans, 1993). The Carrownisky River runs rap- idly over steeply dipping interbedded Silurian pelites and psammites, and Ordovician mudrocks and sandstones that form riffles at higher gradients and in straight sections, and it deposits large gravel banks on wide meanders at lower velocities. Of the western group, there are two standing stones located by tributaries to the river, known to contain gold deposits, and one standing stone midway along its length (Figure 3). The abundance of alluvial gold deposits (Figure 2) along the Carrownisky River indicates that it has been a dominant transport path for weathered rock detritus for a con- siderable period of time. Standing stones of the western group are also located near lakes and rivers parallel to the western shoreline of the Peninsula. Beaches here have optimum conditions for coastal placer deposit formation; a long, unsheltered beach with a strong tide (Evans, 1993). Alluvial gold is reported from around Croagh Patrick (McArdle et al., 1987), but the eastern group of standing stones also has an

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Figure 4. Map of Connemara, located to the south of the Murrisk Peninsula, summarizing the distribution of standing stones and Earth resources. Standing stones are generally distributed in two groups. The coastal group is associated with many stone monuments, indicating extensive human settlement, and varied mineral deposits. The inland group is isolated and correlates with highlands of Bennabeola quartzite, a potential gold source, or copper deposits more than with evidence of human inhabitation. (After Gibbons and Higgins, 1988; Long and McConnell, 1995; McArdle et al., 1997; Cole, 1998.) Cu copper; Asb asbestos; W tungsten; M Connemara Marble; MVF Maum Valley Fault.

extreme easterly cluster that may be generally related to an along-strike continua- tion of either the northerly Cregganbaun Quartzite or the southerly Cregganbaun Shear Zone (Figure 3). Alternatively, the most easterly standing stones may be related to local deposits of serpentinite that were also exploited during the Neolithic or may have served as route markers predating the Pilgrim’s Way (Tóchar Phádraic), an ancient pilgrimage route to Croagh Patrick (Mulveen, 1999).

STANDING STONES IN CONNEMARA To test the veracity of the relationship between standing stones and resources, the distribution of prehistoric monuments in Connemara to the south of Killary Harbour was investigated. There are two general groupings of prehistoric monuments (Figure 4), both of which include standing stones. The first group is a high concentration of monuments around coastal areas, including the low-land of river valleys (Gibbons and Higgins, 1988), and the second group is an inland collection of six disparate sites (Figure 4). Overall, there is a lack of reported prehistoric monuments in inland Connemara. This may be a sampling bias because artifacts are less commonly found

162 GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, VOL. 21, NO. 2 DOI: 10.1002/GEA A TWO-AGE SYSTEM FOR STANDING STONES IN WESTERN IRELAND in remote areas, obscured by bog, or a construction bias because rock types may have been less suitable for raising obvious large stone structures than elsewhere in Ireland (Moore, 2004). However, a low population density for the area would also be likely, given the boggy Knock and Lochan Terrain in south Connemara (Gibbons and Higgins, 1988) and the network of rivers and lakes that may have discouraged Mesolithic nomadic people in north Connemara. Later populations may have built up around areas already favored by Mesolithic migrants. The coastal area would have been eminently suitable for settlement because of good fish resources and a diversity of geological resources. Green Connemara marble was traded as far as County Limerick during the Neolithic period (Gibbons and Higgins, 1988). The abundance and variety of mineral and edible resources, as well as monuments, complicates the identification of standing stones as markers for routes associated with human movement, resource location, or ceremonial proces- sion. The correlation between Earth resources and standing stones along the coast cannot be proven because of the coincidence of standing stones with a high concentration of signs of inhabitation. However, interesting standing-stone patterns in relation to potential geological resources (Figure 4) are clusters near deposits of asbestos (Long and McConnell, 1995), marble (Long and McConnell, 1995), and copper (Cole, 1998), and downstream from a gold locality (McArdle et al., 1987), as well as standing stones on opposing banks of larger rivers. Of the inland group of standing stones, the two most northerly sites are associated with minor prehistoric field enclosures (Gibbons and Higgins, 1988), indicating there is some associated human inhabitation. All of the sites are located along major rivers or within sight of lakes and two are also in close proximity to the Maum Valley Fault (Figure 4), a single, well-defined fault in Connemara, as opposed to the splayed fault zone in the Murrisk Peninsula to the north. Gold in Dalradian rocks upstream from the standing stones is attributed to movement and base-metal mineralization along the Maum Valley Fault (McArdle et al., 1987). However, abundant gold and copper deposits in Connemara, possibly representing an ancient placer deposit, correlate with three major outcrops of the Dalradian Bennabeola Quartzite Formation, rather than the Maum Valley Fault. The outcrops are distributed in the highlands of the Twelve Pins and the Maumturk Mountains and in a band stretching from the north of Loch Corrib to the south of Derryclare Lough (the Glan mineralized belt). Transport of detritus from eroded quartzite could account for gold deposits in four of the standing stone locations. The greatest abundance of alluvial gold localities is located near the south shore of the western end of Lough Corrib (McArdle et al., 1987), where there are no standing stones. This is an area isolated by lakes and rivers that may have been unsuitable for exploitation, particularly given that the lakes and rivers were significantly larger in the past (Dunne and Feehan, 2003). Two sites have no reported gold occurrences associated with them, but these are located in areas where copper deposits occur (O’Raghallaigh et al., 1997; Cole, 1998). Overall, coastal standing stones have a close relationship both with areas of human settlement and with mineral resources while the inland standing stones are isolated from the majority of human settlement in Connemara but have a loose spatial relationship with metal-bearing outcrops. Where gold is not present, another deposit

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known to have been of value to early societies, such as serpentine, asbestos, talc, marble, and, most commonly, copper, occurs. The function of standing stones is less apparent in Connemara because of resource variability and the coincidence of domestic and ritual monuments with standing stones. To further test the hypothesis that standing stones mark the positions of resources, alternative case studies must be found where there is separation of standing stones from other monuments.

EVIDENCE FOR ENVIRONMENTAL CHANGE IN THE MURRISK PENINSULA Sediment and landform changes are important considerations when relating the distribution of standing stones and gold deposits using present-day drainage patterns and the distribution of alluvial deposits. Published literature regarding archaeological context and oral tradition, as well as place-names, provide supporting evidence for environmental change visible in landforms and soil types in the Murrisk Peninsula. For example, a gold dress-fastener dated to the late Bronze Age (900–700 B.C.) was found at Castlekelly, County Galway, in river gravel beneath a bog (Cahill, 2002). In the Murrisk Peninsula, the Srahwee (Yellow River Land) wedge tomb near the Cregganbaun Shear Zone is located next to a peat lake within which the remains of a fossilized forest can be seen, and through which the place-name indicates a Yellow River once ran. In both cases, peat has accumulated where there was previously a river. Three isolated standing stones at Killadangan on the south shore of Clew Bay are located in a salt marsh, surrounded by salt-water pools that expose the underlying mineral soil into which they were inserted. The marine incursion into the area is recorded in a folklore tale in which the pagan king of Killadangan and his worthless servant Thulera died fighting the encroaching tide (Berry, 1988, p. 97). The salt marsh that has developed since the raising of the isolated standing stones has been attributed to erosion of drumlins and silting up of Clew Bay to the north of the Murrisk Peninsula (Corlett, 1998). A paleo-coastline is in evidence along the western coastline of the Peninsula, where a row of lakes coincides with the westerly limit of alluvial gold deposits and standing-stone locations (Figure 3): Marine regression probably occurred here because of longshore deposition of terrigenous river detritus. Dating of marine regression on the west coast, marsh formation on the north coast, and peat encroachment onto woodland areas with rivers in the interior of the peninsula is subjective, as no radiocarbon dates have been ascertained for south Mayo (Corlett, 1997). Individual radiocarbon dates for the initiation of growth of blanket peat in northern parts of County Mayo range from 4340 65 yr B.P. (Håkansson, 1974) to 3210 45 yr B.P. (O’Connell, 1990a), and, in Connemara to the south, peat initiation was locally retarded until 1700 yr B.P. through land-use management (Molloy and O’Connell, 1993). In general, however, pollen analysis shows that there was a massive expansion of blanket peat shortly after 2000 B.C. in County Mayo and between 2000–1000 B.C. in Connemara and that pine pollen was in sharp decline just after 1200 B.C. (O’Connell, 1990b; Mitchell and Ryan, 2001), the boundary between the early and late Bronze Age. There is some debate about whether the causes of blanket-bog growth are climatic or anthropogenic. Rainfall in excess

164 GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, VOL. 21, NO. 2 DOI: 10.1002/GEA A TWO-AGE SYSTEM FOR STANDING STONES IN WESTERN IRELAND of 1250 mm per annum, or more than 225 rain days every year, is considered neces- sary for the development of ombrotrophic lowland or oceanic blanket bog (Moloney et al., 1995, p. 165), and even partial destruction of pre-peat forest by humans increases waterlogging and initiates blanket-bog development, particularly where woodland is already under climatic stress (Moore, 1993). The evidence of marsh formation on the north coast because of deposition in Clew Bay and beach formation on the west coast indicate accelerated erosion rates of drumlins and highlands, respectively. Increased weathering rates of exposed rocks and tills would have accompanied a wet phase that encouraged blanket-bog growth. Evidence for a widespread climatic deterioration has been observed in other sedimentary records and includes major peri- ods of flooding identified by analysis of 346 Holocene alluvial sediments with radiocarbon dates between 3940 and 1940 yr B.P. that correspond well to climatic deteriorations inferred from mire wet shifts (Macklin and Lewin, 2003). Phase shifts to wetter and/or cooler climates, identified by bog-surface wetness reconstruction from quantified analyses of plant macrofossil remains of three radiocarbon-dated raised bog-peat profiles from western Ireland to northern England, were observed in two cases at 4400–4000 yr B.P. and in all three cases at 3200 yr B.P. (Barber et al., 2003). While anthropogenic factors play a part locally in expansion of blanket bog, the coincidence of evidence from disparate bogs and alluvial sediments indicates that climatic changes had a strong regional effect on landforms at the end of the Neolithic and the end of the early Bronze Age. The variability in the date of the initiation of blanket-bog expansion in western Ireland is most likely a result of the interplay between climatic and anthropogenic factors. It is possible, as postulated by Corlett (1997), that variable blanket-bog expansion in the Murrisk Peninsula is purely a function of intensive human activity at different times across the peninsula. However, Figure 1 shows that human activity was most concentrated across the west of the peninsula. The setting of the isolated standing stones into the mineral soil beneath the marsh on the north coast and within the paleo-coastline on the west coast indicate the isolated standing stones were raised before climate change, either at the end of the Neolithic or the end of the early Bronze Age. Corlett (1997) related abandonment of court-tomb sites midway along the Carrownisky River to local early Neolithic blanket-bog expansion, but a maximum (local) age for the expansion of the blanket bog can tentatively be obtained in the vicinity of Srahwee, where the wedge tomb is accompanied by woodland dated to approximately 4500 yr B.P. (Hackett, 2004). Thus, blanket-bog growth may have been initiated early in the Neolithic, but it did not overwhelm the woodland at Srahwee until the end of the Neolithic or the early Bronze Age. This is com- parable to the case of Céide fields in north County Mayo where peat encroached diachronously over the Neolithic landscape of farmland, ritual monuments, and settlement sites, following their abandonment (Molloy and O’Connell, 1995; Caulfield et al., 1998). The fact that peat growth followed, rather than caused, abandonment of agricultural activity at both Céide fields to the north and in the Connemara National Park to the south (Molloy and O’Connell, 1993; O’Connell, 1994), supports the hypothesis that climate change promoted peat growth more strongly than anthropogenic factors in the Murrisk Peninsula. If the accelerated expansion of blanket bog, indicated

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by alluvial sediments, macrofossils, and pollen, coincides with a climatic deterioration (Kelly, 2002) at 1200 B.C., which would have caused increased erosion of drumlins and highlands, then the isolated standing stones predating climate change must at least be older than 1200 B.C. and may be older than late Neolithic or early Bronze Age landform changes.

A TWO-AGE SYSTEM FOR STANDING STONES Twelve hundred B.C. also marks a movement to cremation rather than burial, construction of stone circles, and an alignment of monuments with respect to the sun and moon (Kelly, 2002); in other words, a shift to religious practice using astronomical alignments as a reference frame. The changes in ritual behavior may be attributed to the wide-ranging contacts of Irish prehistoric society with Britain and with northwestern Continental Europe, indicated by comparison of novel types of (Bishopsland Phase) goldwork and the morphology of weapons across Europe (Waddell, 2000, p. 190). However, the shift in religious practice coincident with environmental change is fortuitous with respect to constructing a relative-age sequence for standing stone monuments in the Murrisk Peninsula. The isolated standing stones appear to predate the major geomorphological changes in the Murrisk Peninsula, and are, therefore, older than 1200 B.C., but there is a lack of convincing evidence to determine whether they predate any blanket-bog growth at the end of the Neolithic period. More complex arrangements of standing stones are observed on the south shore of Clew Bay: a stone alignment in the northwest of the Murrisk Peninsula and a standing stone complex at Killadangan (Figure 1). The complex at Killadangan is particularly revealing as it includes isolated standing stones and a stone alignment within an embankment (additional archaeological features at the site are described in detail by Corlett, 1998). Corlett (1998) asserts that, because of the spatial association of the isolated standing stones with the stone row at Killadangan, and the increase in height of the stone row towards Croagh Patrick, all the standing stones (both the western and eastern groups) of the Murrisk Peninsula have ceremonial significance and are of one overall generation (late Bronze Age). It is interesting to note that the stone row at Killadangan is parallel to the stone alignment in the northwest of the Murrisk Peninsula, which is not aligned towards Croagh Patrick, sug- gesting that Croagh Patrick may not have been the central focus of the ceremonial landscape. The relative position of the stone row with respect to the rest of the stones in the complex is highly significant, however. The stone row is situated on an elevated platform protected from the sea by earthen banks of clay built on top of the salt marsh and ditches cut into the salt marsh for drainage; the neighboring isolated standing stones are situated on the lower salt marsh, are set into the mineral soil underlying the marsh, and are not protected from flooding. Consequently, it appears that the location of the stone row was chosen with a changed environment in mind. The ceremonial purpose of the stone row, as indicated by its alignment towards a sacred mountain, is in contrast to the purpose of the isolated standing stones as markers of resources, as indicated by their distribution with respect to alluvial gold. Thus, it appears that there are two generations of standing-stone monuments: an

166 GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, VOL. 21, NO. 2 DOI: 10.1002/GEA A TWO-AGE SYSTEM FOR STANDING STONES IN WESTERN IRELAND early simple form that predates environmental change and acts as markers and a later form of complex standing-stone monuments with ceremonial significance that postdates the majority of environmental change and is, therefore, late Bronze Age. The two-age system of standing stones in the Murrisk Peninsula reconciles the views of archaeologists who have previously assigned standing stones to either the Neolithic (Cooney, 1996) or the late Bronze Age (Corlett, 1997, 1998).

SIGNIFICANCE OF GOLD TO NEOLITHIC–BRONZE AGE SOCIETY Many Celtic myths and religious beliefs associated with the supernatural or “otherworld” focused on water, both surface and groundwater (Ó Dochartaigh, 2000). A huge hoard of gold objects at Mooghaun North in County Clare found on an old lake shore near a late Bronze-Age hill fort was interpreted as a significant sacrifice by ritual abandonment (Cahill, 2002). Hence, Celtic religion used parts of their natural aqueous environment as sacred sites, and votive treasures of gold were often cast into water bodies as sacrifices to the deities. Prehistoric people extracted gold from the environment by panning in rivers and may, therefore, have viewed gold as a sacred commodity or gift from the otherworld. This is consistent with other ancient religions: the Aztecs and Incas considered gold to be a direct product of the gods, and, in the warmer Egyptian climate with a heavenly otherworld, gold was understood as the materialization of the sun—the sun god, Horus was worshipped as the god of gold (Betz, 1993). Votive offerings are more common in the late Bronze Age after a deterioration of climatic conditions, an expansion of blanket bog over previously arable land, and the development of stone circles or rows as ceremonial or religious sites, perhaps to appease angry gods who made the environment less hospitable. The circumstantial evidence points to a religious significance of gold to Neolithic and Bronze Age people, and the raising of standing stones would surely not have been seen as excessive effort to mark localities where it was found. Gold was worked into ornaments and decoration, as it was too soft to be useful for tools, implying its use as a symbol of wealth and status, and a pilgrimage to Croagh Patrick may have been a symbol of status. Croagh Patrick is an impressive conical mountain that, understandably, would be viewed as magical and otherworldly. The location of this mountain in an area known for gold production would only serve to invest it with further magical properties, particularly given that many standing stones are within sight of the mountain. The erection of standing stones as markers of resources is consistent with their location such that they can be seen from great distances (Gibbons and Higgins, 1988). The interpretation of standing stones as ceremonial because of their arrangement around Croagh Patrick alone (Corlett, 1997) is flawed because they are infrequently oriented with respect to the mountain, but, as markers of gold deposits, they may have been invested with religious significance. As a gold-producing province, the Murrisk Peninsula must have been an affluent district. However, there is a lack of Bronze Age votive deposits in the Mayo study area compared to elsewhere in Ireland just when gold use was developing and expand- ing across Europe (Eluère, 1993). There are several explanations that may account for this disparity: (a) Late Bronze Age blanket-bog expansion (Corlett, 1997) may

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have simply concealed any votive offerings; (b) gold may have been removed from the locale by a brisk trade with the many visitors to the area, indicated by the long history of the Pilgrim’s Way, or Tóchar Phádraic (Mulveen, 1999); or (c) early blanket- bog expansion may have covered gold-bearing river gravels. If standing stones mark both flowing rivers and Neolithic–early Bronze Age river gravel beneath blanket bog, then the latter could be a target for future gold exploration.

CONCLUSIONS Burial sites and domestic sites were combined as evidence of human inhabitation in western Ireland and have distributions independent of standing-stone sites in the Murrisk Peninsula of County Mayo. Isolated standing stones correlate strongly with the locations of alluvial gold deposits from weathering of mineral veins and pods in the Cregganbaun Shear Zone and the Cregganbaun Quartzite of Croagh Patrick; there is greater than a 99% certainty that standing stone and alluvial gold locations are related. Standing stones in Connemara correlate with a wider variety of resources, including gold, copper, serpentine, marble, and asbestos, as well as with other monuments, and cannot, therefore, be proven to act as markers. The coincidence of standing stones, alluvial placer deposits of gold, and votive treasures is significant. If water was seen as an interface between the natural and supernatural worlds and springs were revered as gifts from the gods, then it is likely that gold extracted from water was imbued with religious significance. A religious interpretation of the isolated standing stones in their own right is rejected as they have no known astronomical alignment, those in the Murrisk Peninsula are not oriented with respect to Croagh Patrick, and those in County Galway have no association with Croagh Patrick. It is suggested that a climatic deterioration correlates with a shift in the style of standing-stone monuments from isolated markers of metal extraction sites in the early Bronze Age or Neolithic to ceremonial alignments and other, more complex forms in the late Bronze Age. This coincides with an increase in the occurrence of gold votive offerings and a transition from elaborate to simple burial sites. The climatic deterioration resulted in increased weathering rates, caus- ing sedimentation in Clew Bay and on the west coast of the Murrisk Peninsula, and the expansion of blanket bog, such as at Céide Fields to the north in County Mayo.

The author wishes to thank E. Kelly for consultation and G. Gazzilli for drafting assistance, funded by the Leonardo da Vinci Programme. A. Bettis, P. Coxon, and an anonymous reviewer are thanked for very helpful and constructive comments that significantly enhanced the manuscript.

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Received April 23, 2004 Accepted for publication December 21, 2005

170 GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, VOL. 21, NO. 2 DOI: 10.1002/GEA