|Everett, P A, Gillespie, M R and Tracey, E A. 2015. Provenance of building stones in four 'galley castles' in Argyll. British Geological Survey Internal Report, OR/15/053.|
This report describes the outcomes of a project to assess the character and provenance of decorative stones in four ‘galley castles’ in Argyll: Castle Sween, Dunstaffnage Castle, Skipness Castle and Kilchurn Castle (Figure 1). A single sample of decorative stone from a fifth castle, Kisimul Castle on Barra, is included in the assessment.
The term ‘decorative stone’ is used here to refer to any stone that would have been selected to stand out visually or to perform a particular function in the castle masonry; in this context it includes visually distinctive stone that typically was used to form window and door surrounds, quoins and corbels, and stone that breaks naturally into tabular blocks and typically was used to form lintels and sills.
The term ‘galley castle’ refers to any castle that could be reached by a substantial water-borne vessel (galley) at the time it was constructed. In Scotland, nearly all the structures that have been identified as galley castles are on the west coast, but a few are on inland lochs drained by navigable rivers. The availability of water-borne transport would have provided opportunities to import some of the building materials used in a galley castle from outwith the area in which the castle is sited. The provenance of building stones used in such castles — in particular the decorative stones which are more likely to have been imported than the walling stone — may shed light on the trade and transport routes used by the castle builders, and may help to reveal the locations of historical quarry sites.
The principal objective of the project is to describe the geological character of the decorative stones used in the four galley castles in Argyll mentioned above, and from this establish:
- whether each stone can be tied back to a geological or geographical source (e.g. an area of outcrop or a quarry);
- whether the same stones occur in different castles;
- whether geographical and/or temporal patterns of stone distribution can be discerned from the outcomes of (i) and (ii).
The four Argyll castles were visited in the course of a three-day site visit on the 28th, 29th and 30th of July 2015 by Martin Gillespie and Paul Everett (BGS Building Stones team). Building stones in the accessible parts of each castle were examined carefully by eye and using a hand lens (x10 magnification). Each site is a Scheduled Monument, so it was not possible to collect stone samples for detailed analysis from in situ stonework. However, three small pieces of stone that had become detached from the stonework through natural means (weathering) and were lying on the ground were collected from Dunstaffnage Castle (one piece from the castle and one from the adjacent chapel) and Castle Sween, and a thin section (a slice of the stone cut thin enough to be transparent so it can be examined by microscope) was prepared from each of these.
A sample of decorative stone from Kisimul Castle was provided to BGS by Historic Scotland and is included in this assessment, though BGS staff have not visited the castle; a thin section was prepared from this sample. Four historical quarries in Argyll were also visited during the site visit, and a thin section of the stone from each quarry was prepared. Full descriptions of all the samples and thin sections are presented in Appendix 1.
A brief description of the geology and geological history in the area of interest is presented in the Geological context section of this report to provide context for later sections. All of the decorative stones encountered are either metamorphic rock or sandstone, and a brief introduction to some of the possible sources of these stones is included in the Geological context section. Information for each castle — layout and chronological development, building stones and building stone provenance — is provided in Castle Sween, Skipness Castle, Kilchurn Castle, Dunstaffnage Castle, and Kisimul Castle. The key conclusions are presented in the Summary and conclusions.
The project was commissioned by Historic Scotland (HS), and was conducted by the Building Stones team of the British Geological Survey (BGS) under the terms of the Memorandum of Agreement (2011–2016) between HS and Natural Environment Research Council (as represented by BGS).