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 con- centrated in alluvial deposits of river systems draining these areas. A comparison of gold occur- rences 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]. Geoarchaeology: An International Journal, Vol. 21, No. 2, 155–170 (2006) © 2006 Wiley Periodicals, Inc. Published online in Wiley Interscience (www.interscience.wiley.com). DOI:10.1002/gea.20095 MOORE 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 DOI: 10.1002/GEA GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, VOL. 21, NO. 2 157 MOORE 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 Ϯ mica Ϯ 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 158 GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, VOL.

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