Following on from a walkover survey undertaken in 2006, which confirmed the locations of a number of known sites within the development area and identified a number of additional previously-unrecorded sites, staff from Headland Archaeology Ltd conducted an archaeological evaluation on the site of a proposed housing development at Tighnabruaich, Argyll. WoSAS, the archaeological advisor to Argyll and Bute Council, recommended that this pre-determination archaeological evaluation should be undertaken due to the identified presence of archaeological material within the area. A total of thirty-one trenches were excavated by machine under archaeological supervision, while hand-dug trenches were excavated at the site of a cup-marked boulder and a possible platform and clearance cairn. These works identified material relating to activity on the site in a number of periods, from possible flintworking in the vicinity of a cup-marked rock to a post-medieval field system.
The cup-marked boulder is located deep within a gorse thicket, at the edge of a level platform overlooking a burn to the south-west. Inspection by RCAHMS in 1987 reported the presence of five cup-marks in total. Although originally reported by RCAHMS as an 'outcrop', the Headland report indicates that it is in fact a free-sitting boulder, low with rounded sides and a level top. Although presently very moss covered, at least two cup-marks were visible on this surface.
A trench measuring 2 x 1 m was excavated immediately adjacent to the boulder, on the level platform. Turf and topsoil were removed by hand, and three flint flakes were recovered from the topsoil close to the boulder. An irregular spread of charcoal-rich sediment was located adjacent to the boulder, beneath the topsoil and overlying natural deposits. No excavation of this material was attempted, as preservation in situ was judged to be the most appropriate approach to delicate archaeological deposits associated with the boulder at this early stage in the planning process.
Two recessed platforms were reported within the development area in 1994. When the site was visited by Headland in 2006 a single low rectangular platform was located in the vicinity of the coordinates previously given for the platform locations. At the time of the walkover a number of low mounds were located in the vicinity of this platform, and it was thought possible that they could represent clearance cairns.
A trench measuring 2 x 1 m was hand-dug across the rectangular platform, which revealed it to be formed by a natural outcrop of bedrock. The topsoil was thin (0.1 m) and showed no indication of any human activity associated with the platform. A section across one of the low mounds near to the bedrock platform revealed it to consist mainly of redeposited natural till, containing several large boulders. These deposits were found to be overlying a recent ground surface and soil profile, suggesting that this feature may be formed from dumped spoil related to the construction of a powerline corridor immediately to the north.
Part of a curvilinear feature was located in one of the machine-dug evaluation trenches. The feature was approximately 0.50 m wide and 0.20 m deep, with a V-shaped profile. Extension of the evaluation trench around this feature revealed that it probably forms a small oval enclosure 8m long by 5 m wide. A second curvilinear feature, wider and shallower than the first, appeared to form a smaller enclosure within the circuit it. South-west of the enclosure was a single circular posthole.
Trial trenching towards the south-eastern boundary of the development area identified a dump of stones within a deposit of sandy colluvium. These whinstone boulders ranged in size from 0.1 m to 0.5 m and greater in diameter, though there was no obvious structure, order, or sorting to the dump. Following the initial location of the stones, the evaluation trench was extended in order to trace its extent, which appeared to be limited to an area 6.5 m by 4 m. The stone dump was investigated by sondage and was found to have a depth of 0.8 m, and overlay a leached buried soil horizon. No dating evidence was found within the dump of stone, or within the colluvium burying it, though the type and sizes of boulders bear some similarity to piles of quarried stone lying at the former site of a farmstead identified within the development area, and it is possible that this dump is related to the demolition and quarrying around the farmstead, and the construction of the nearby road. Alternatively, the stones could be related to field clearance in the post-medieval period.
A topographic survey was also carried out on prior to the archaeological evaluation. This survey was checked against ground conditions during the evaluation, and appears to have recorded all of the visible field banks within accessible parts of the development area. Machine-dug sections were excavated across the remaining section of the head-dyke and across another upstanding field banks. The head-dyke was formed from natural sediments upcast from an associated ditch on the north side of the feature and overlay a buried soil horizon. The bank had a height of 0.5 m above the buried soil horizon, and a width of 2 m. The ditch appears to have filled in naturally with silts and plant material. A similar construction method was noted in the field banks elsewhere in the development area.