ARO4: The Late Neolithic pitchstone artefacts from Barnhouse, Orkney – an unusual assemblage from an unusual site By Torben Bjarke Ballin Lithic Research/Honorary Research Fellow, University of Bradford Archaeology Reports Online, 52 Elderpark Workspace, 100 Elderpark Street, Glasgow, G51 3TR 0141 445 8800 | [email protected] | www.archaeologyreportsonline.com ARO4: The Late Neolithic pitchstone artefacts from Barnhouse, Orkney – an unusual assemblage from an unusual site Published by GUARD Archaeology Ltd, www.archaeologyreportsonline.com Editor Beverley Ballin Smith Design and desktop publishing Gillian McSwan Produced by GUARD Archaeology Ltd 2013 ISBN: 978-0-9575435-3-9 ISSN: 2052-4064 Requests for permission to reproduce material from an ARO report should be sent to the Editor of ARO, as well as to the author, illustrator, photographer or other copyright holder. Copyright in any of the ARO Reports series rests with GUARD Archaeology Ltd and the individual authors. The maps are reproduced by permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationery Office. All rights reserved. GUARD Archaeology Licence number 100050699. The consent does not extend to copying for general distribution, advertising or promotional purposes, the creation of new collective works or resale. ARO4: The Late Neolithic pitchstone artefacts from Barnhouse, Orkney – an unusual assemblage from an unusual site. Introduction • examine and catalogue all archaeological pitchstone in Scottish museums; In the late 1980s, Colin Richards, University of Manchester, excavated an extensive Late • produce a computer database of these Neolithic settlement at Barnhouse on Orkney finds; (Richards 2005) (Figure 1). The excavation • re-interpret the distribution of archaeo- revealed a number of house structures of Skara logical pitchstone across northern Britain. Brae type (Clarke & Maguire 1989; Foster 2006), and in and around these houses a large lithic In total, 5,542 pieces of worked pitchstone assemblage of 1,585 pieces was recovered were examined and characterised during the (Middleton 2005). This assemblage consisted project, deriving from approximately 350 sites. mainly of flint, but a surprisingly numerous sub- In addition, 14,707 pieces were included in the assemblage of pitchstone artefacts (23 pieces) database of none-examined artefacts, deriving was also retrieved. from c. 125 sites. Approximately 13,300 of the latter were retrieved in connection with Glasgow University’s Archaeological Research Division’s work on Arran in 1999. The results of the examination of the museum collections (supplemented by finds still with the excavating units) have been summarised, revealing an interesting distribution. Prior to this work, it was the author’s subjective impression that Neolithic Scotland may have been sub-divided into a number of main zones or potential territorial units (I-IV), based on the average number of pitchstone artefacts in pitchstone-bearing assemblages. This impression is supported by the figures from the SAPP (Table 1; Figure 2; see zonation in Figure 4 below). With the future inclusion of further assemblages, these figures may change but the four numerically based groups are likely to remain. In Table 1, the regions are sequenced according to their distance from Arran, the probable source Figure 1: Location map. of all archaeological pitchstone. The approximate area and location of each zone (see below, Figure Present consensus is that all, or almost all, 4). archaeological pitchstone derives from sources on the Isle of Arran in the Firth of Clyde (Williams Zones Numbers Thorpe and Thorpe 1984), from where it was Arran 230 distributed across northern Britain by means IIW 14 of a wide-ranging exchange network. However, IISW 33 Williams Thorpe and Thorpe’s pioneering III 3 research into this topic was carried out at a time IV 2 when relatively little archaeological pitchstone Orkney 14 had been retrieved. Since then much worked pitchstone has been recovered. This has altered Table 1: Average number of pitchstone artefacts per pitchstone-bearing assemblage per region. the distribution patterns considerably, and as a consequence, a project was undertaken to look into archaeological pitchstone and its distribution (Ballin 2009b; 2011c). The aims of the Scottish Archaeological Pitchstone Project (SAPP) were to: 3 © Archaeology Reports Online, 2013. All rights reserved. ARO4: The Late Neolithic pitchstone artefacts from Barnhouse, Orkney – an unusual assemblage from an unusual site. The pitchstone types are defined in the raw material section (below); the definitions of the main lithic categories are as follows: Chips: All flakes and indeterminate pieces the greatest dimension (GD) of which is £ 10mm. Flakes: All lithic artefacts with one identifiable ventral (positive or convex) surface, GD > 10mm and L < 2W (L = length; W = width). Figure 2: Average number of pitchstone artefacts per Indeterminate pieces: Lithic artefacts which can- pitchstone-bearing assemblage per zone. not be unequivocally identified as either flakes or cores. Generally the problem of Referring to Table 1 and Figure 2, it is obvious that identification is due to irregular breaks, the Barnhouse finds represent a deviation from frost-shattering or fire-crazing. ‘Chunks’ an otherwise logical distribution pattern. Forming is a popular term for larger indeterminate part of Distribution Group IV (‘peripheral’ sites), pieces. approximately two pitchstone artefacts should have been expected from an Orcadian pitchstone- Blades and microblades: Flakes where L ³ 2W. In bearing assemblage - not 23 pieces! The aims of the case of blades W > 8mm, in the case this paper are therefore to give a more detailed of microblades W £ 8mm. characterisation of this unusual group of lithic Cores: Artefacts with only dorsal (negative or con- artefacts by allowing comparison with published cave) surfaces – if three or more flakes pitchstone assemblages from southern Scotland, have been detached, the piece is a core, such as Auchategan, Blackpark Plantation and if fewer than three flakes have been de- the Biggar sites (Ballin 2006; Ballin et al. 2008; tached, the piece is a split or flaked peb- Ballin & Ward 2008), and to place the Barnhouse ble. pitchstone in its Scottish Neolithic context by Tools: Artefacts with secondary retouch (modif drawing on the latest information gained via cation). the SAPP and recent research into the Scottish Neolithic. Raw material The Assemblage In order to characterise the Barnhouse pitchstone precisely, it is necessary to briefly summarise what From the excavations at Barnhouse, 23 pitchstone pitchstone is, and to define its main components. artefacts were recovered. (see Table 2). Pitchstone is a volcanic glass, which is found as two main forms. One is obsidian (< 1% H O), Type 1 Type 2 Total 2 whereas the other is pitchstone (typically 3-10% Debitage H O). Most pitchstone has > 5% H O, and most Chips 2 2 2 2 Flakes 5 7 12 obsidian < 0.5%. Volcanic glass is known from Blades 2 2 igneous complexes throughout the world, but in Crested flakes 1 1 Britain it is only found in western Scotland and Total debitage 10 7 17 Northern Ireland (the British Tertiary Volcanic Province; Emeleus and Bell 2005). All volcanic Cores glass found in Britain is in the form of pitchstone, Levallois-like cores 1 1 and it is generally accepted that only pitchstone Other discoidal cores 1 1 from the island of Arran, immediately west of Bipolar cores 1 1 Glasgow (Figure 1), had the properties required Cores total 3 3 to become widely used as a toolstone. Tools As explained in Ballin and Faithfull (2009), Blade-scrapers 1 1 pitchstone may be described in terms of a number Flakes with edge-retouch 2 2 of components, such as: Total tools 2 1 3 • Glassy matrix. TOTAL 15 8 23 Table 2: General artefact list. © Archaeology Reports Online, 2013. All rights reserved. 4 ARO4: The Late Neolithic pitchstone artefacts from Barnhouse, Orkney – an unusual assemblage from an unusual site. • Phenocrysts: larger isolated or clustered crystals formed at depth during slow cool- ing. • Spherulites: finely crystalline, usually radi- ating intergrowths of quartz and feldspar indicating devitrification of the glass phase. • Crystallites (in older literature occasion- ally termed microlites): very small skeletal or dendritic crystals, often Fe-Mg silicates, in glass; banding in pitchstones is often marked by variation in crystallite density. • Other alteration products. Tyrrell (1928) distinguishes between four main types of pitchstone, and they are defined, primarily, by their presence/absence of phenocrysts and spherulites, phenocryst composition, and style of devitrification. The four pitchstone types are: the Coriegills Type (east Arran), the Glenshurig Type (north-east Arran), the Glen Cloy Type (north-east Arran), and the Tormore Type (west Arran). Usually, specialised Plate 1: Debitage in pitchstone Type 1. analysis would be necessary to distinguish Type 2 (Plate 2) between some of these pitchstone forms, but it is relatively easy to visually distinguish between Almost black with a green hue. pitchstone of Corriegills Type, which is aphyric, or A small number of relatively large inclusions (up non-porphyritic (i.e. it has no phenocrysts), and to 3 mm), which may be phenocrysts or larger the other three types, which are all porphyritic spherulites (porphyritic?). (i.e. they are characterised by one or the other form of phenocrysts). The Glen Cloy Type is Many elongated, parallel