Stonehenge on Salisbury Plain is one of the most impressive British prehistoric(c.3000–1500 BC) monuments. It is dominated by large upright sarsen stones, some of which are joined by lintels. While these stones are of relatively local derivation, some of the stone settings, termed bluestones, are composed of igneous and minor sedimentary rocks which are foreign to the solid geology of Salisbury Plain and must have been transported to their present location. Following the proposal of an origin in south-west Wales, debate has focused on hypotheses of natural transport by glacial processes, or transport by human agency. This paper reports the results of a programme of sampling and chemical analysis of Stonehenge bluestones and proposed source outcrops in Wales.Analysis by X-ray-fluorescence of fifteen monolith samples and twenty-two excavated fragments from Stonehenge indicate that the dolerites originated at three sources in a small area in the eastern Preseli Hills, and that the rhyolite monoliths derive from four sources including northern Preseli and other (unidentified) locations in Pembrokeshire, perhaps on the north Pembrokeshire coast. Rhyolite fragments derive from four outcrops (including only one of the monolith sources) over a distance of at least 10 km within Preseli. The Altar Stone and a sandstone fragment (excavated at Stonehenge) are from two sources within the Palaeozoic of south-west Wales. This variety of source suggests that the monoliths were taken from a glacially-mixed deposit, not carefully selected from anin situsource. We then consider whether prehistoric man collected the bluestones from such a deposit in south Wales or whether glacial action could have transported bluestone boulders onto Salisbury Plain. Glacial erratics deposited in south Dyfed (dolerites chemically identical to Stonehenge dolerite monoliths), near Cardiff, on Flatholm and near Bristol indicate glacial action at least as far as the Avon area. There is an apparent absence of erratics east of here, with the possible exception of the Boles Barrow boulder, which may predate the Stonehenge bluestones by as much as 1000 years, and which derived from the same Preseli source as two of the Stonehenge monoliths. However, 18th-century geological accounts describe intensive agricultural clearance of glacial boulders, including igneous rocks, on Salisbury Plain, and contemporary practice was of burial of such boulders in pits. Such erratics could have been transported as ‘free boulders’ from ‘nunataks’ on the top of an extensive, perhaps Anglian or earlier, glacier some 400,000 years ago or more, leaving no trace of fine glacial material in present river gravels. Erratics may be deposited at the margins of ice-sheets in small groups at irregular intervals and with gaps of several kilometres between individual boulders.‘Bluestone’ fragments are frequently reported on and near Salisbury Plain in archaeological literature, and include a wide range of rock types from monuments of widely differing types and dates, and pieces not directly associated with archaeological structures. Examination of prehistoric stone monuments in south Wales shows no preference for bluestones in this area. The monoliths at Stonehenge include some structurally poor rock types, now completely eroded above ground. We conclude that the builders of the bluestone structures at Stonehenge utilized a heterogeneous deposit of glacial boulders readily available on Salisbury Plain. Remaining erratics are now seen as small fragments sometimes incorporated in a variety of archaeological sites, while others were destroyed and removed in the 18th century. The bluestones were transported to Salisbury Plain from varied sources in south Wales by a glacier rather than human activity.

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Obsidian provenancing studies comprise one of the most productive and successful research programmes of archaeological science. Obsidian characterization has been successful because workable obsidian is homogeneous on a small scale, analysable by a large number of methods, and is restricted to a small number of mainly readily distinguishable geological sources. Analytical, dating, source, and trade studies within the western Mediterranean, central and eastern Europe, the Aegean, and Anatolia and the Near East during the last 30 years or so are reviewed. Research has shown that distributions are mainly separate in the four regions examined, and that obsidian was traded up to 900km in the prehistoric period. Publications on obsidian in the areas under review reached a peak of frequency in the later 1970s and 1980s, but have now decreased in number. This may reflect changing fashions in archaeometric studies, and a current lack of routine application of the provenancing methods developed.

This paper examines the limitations arising from sample mineralogy when a portable X‐ray fluorescence instrument is applied to the direct in situ analysis of silicate rocks. Estimates were made of the size of the excited volume from which the X‐ray fluorescence signal originates by calculating the critical penetration depth for selected X‐ray lines. Measurements were made of the variations in detected intensities over the area of the P‐XRF analyser window and showed that, using radioisotope sources incorporated in the instrument used in this study (Spectrace TN9000), excitation intensities were six to ten times greater at the centre compared to the edge of the analyser window. These data indicated that the region of the sample at the centre of the window will make an enhanced contribution to detected spectra. Replicate measurements on slabs of rock selected to represent fine‐to coarse‐grain size textures indicated the magnitude of the sampling precision that can be achieved in the direct analysis of silicate rocks. Typical values were better than 5% relative standard deviation of the mean from an average of five determinations on fine‐ to medium‐grained rocks and better than 10 % relative standard deviation in a single determination on these samples.

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Magnetic susceptibility provides a rapid, cheap and non‐destructive method of in situ characterization of archaeological artefacts containing magnetic minerals, and can be used as an aid to geological provenancing. Three hundred and sixty‐three Roman granite columns were measured by this method and results show clear groupings and similarities with potential granite sources in Italy, Turkey and Egypt. Magnetic susceptibility measurements must be made on representative, unweathered surfaces of rocks and artefacts, and corrected for object size and surface relief according to manufacturers’recommendations. In addition, corrections for column curvature have been derived for use with measurements made on columns.

Provenancing and archaeological information on Roman granite columns in the Mediterranean area has been collated from a range of published papers by the author and others, together with new analyses for Rome, to produce an integrated dataset comprising 1176 columns. This dataset allows an overview of Roman granite trade in seven regions across the Mediterranean area. Examination of the data indicates that columns made from Troad (Turkish) granite are the most numerous observed overall (compatible with Lazzarini's earlier (2004) observation that this is the most widely distributed type), followed by Aswan, then Elba and Giglio, and Kozak Dag (Marmor Misium). In the city of Rome, Mons Claudianus columns predominate. In geographically peripheral parts of the Roman world (Spain, Israel), granite columns are mainly from local sources, and are generally of smaller sizes than those seen in Rome and Tuscany. Analytical data can be used to suggest multiple extraction sites within some quarries, and have the potential for identification of specific intra-quarry provenance. Dating evidence for primary use of columns from the quarries considered is relatively sparse, but suggests early (first century BC) exploitation of Spanish and Elba granites, while column production at Aswan and Troad persisted into the fourth century followed by reuse within later antiquity, in the fifth and seventh centuries AD.introduction Granite columns are key components of many notable and impressive Roman buildings, and tracing the quarry sources of the granite raw material offers opportunities for understanding this aspect of the Roman stone trade. There is now a large body of evidence concerning Roman granite quarries and the distributions of their products, evidence stemming from continuing projects both in Italy (in particular from Lazzarini, e.g. 2004 and see references therein), and the UK (e.g. Peacock et al. 1994;Peacock and Maxfield 1997). The UK work incorporated non-destructive scientific provenancing studies carried out largely at the Open University and reported in a series of regional papers (e.g. Williams-Thorpe et al. 2000;Williams-Thorpe and Potts 2002).The provenancing evidence and publications include geochemical, magnetic and mineralogical data on columns and quarries, together with measurements of column sizes. In 73 addition, some information on the dates of column use (and, therefore, of quarry exploitation) is available. By examining this evidence all together, we can take a Mediterranean-wide view of the Roman granite trade and address the following questions: 1. Which quarry sources were numerically dominant in the Roman Mediterranean? 2. How do source distributions vary geographically, for example from west to east, and comparing central and peripheral parts of the Roman Mediterranean? 3. How big are the columns, and is there a relationship between column size and quarry source or region of use? 4. How much analytical variation is there within individual quarry sources, and can the data throw light on how individual ...