Connagill, Strath Halladale, Sutherland Trial Pit and Bore Hole
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Connagill, Strath Halladale, Sutherland Trial Pit and Bore Hole Excavations Archaeological Monitoring Catherine Dagg For ASH 21, Gordon Street Glasgow G1 3PL Connagill, Strath Halladale, Sutherland: Trial Pit and Bore Hole Excavations Archaeological Monitoring Site Name Connagill, Strath Halladale, Sutherland Location NC 90595 59816 Site Type Multi-period settlement and field system Project Preliminary site works: trial pits and bore hole excavations Work required Archaeological monitoring Client ASH, 21 Gordon Street, Glasgow G1 3PL 1.0 Executive Summary Archaeological monitoring of the mechanical excavation of 27 trial pits and 12 boreholes, aimed at ascertaining the nature and depth of underlying glacial deposits and geological strata, noted no archaeological deposits or features, but noted the nature, depth and extent of improved soils associated with prehistoric cultivation. 2.0 Aims A new electricity substation is proposed at Connagill, Strath Halladale, adjacent to Tower 33 on the Dounreay – Beauly 275Kv overhead transmission line. A programme of excavation of test pits and boreholes was required in advance of the finalising of the plan and location of the substation and submission for planning consent. These excavations are located along the proposed access road and across the substation construction area, and consist of: Trial pits measuring approximately 2.5-3m by 0.6-0.7m Boreholes measuring approximately 0.30m by 0.30m to a maximum of 0.50m by 0.5m 3.0Archaeological Work 3.1 Marking of archaeological exclusion zones In advance of any plant being brought on site or any ground breaking work, the archaeologist identified and marked out exclusion zones around all visible archaeological features, using high visibility tape, and explained the system to the site crew. Sites were sketched and location recorded using GPS as a precaution, and to both compare with previous survey results and inform the Environmental Statement on the proposed substation site. A gazetteer of minor archaeological features is given in Appendix 1. 3.2 Protection of Features Plant was directed to avoid all marked archaeological features, to approach the site through the extant gap in the head dyke and to cast spoil away from adjacent archaeological features. Where avoiding crossing of linear features was impractical, a route was agreed and speed kept to the minimum to reduce the dislodging of stones. 3.3 Ground-Breaking Work All ground breaking work for each of the test pits was monitored by the archaeologist until a depth was reached which was considered to be natural deposit. After this stage, excavation work was allowed to continue unmonitored. Hand digging of boreholes was not directly monitored, but each location was checked and recorded. The trial pits were excavated by mechanical digger at locations decided by the drilling contractor, although after advice from the archaeologist on avoidance of archaeological features. Boreholes were partially excavated by hand using spade and shovel to a depth where the drill could be inserted. 4.0 Site Description The area of the proposed sub station is a level terrace south of the Connagill Burn. A narrow, intermediate terrace occupies a slightly lower level to the north and west, after which the ground falls steeply to the burn and to the strath of the Halladale River. To the east the ground rises sharply with exposed rock faces. Vegetation cover varies from good grassland on the west slope falling to the Halladale River and covering the north and west part of the main terrace, to almost vegetation-free stony ground on the intermediate terrace to the north, and wet, mossy peat to the south and east. Rushes have colonised much of the terrace. The site is crossed by a modern access track, which forks at the centre of the terrace, the north track giving access to a water treatment plant on the hill, and the south track added recently to give access to the Dounreay-Beauly OHL, which passes to the east of the terrace. There are also modern, mechanically excavated drainage ditches, draining westwards. Low mossy mounds scattered across the southern part of the terrace were probed and proved to have no stone content; these are probable peat stack bases The archaeological site, Connagill farmstead, is located on the steep west-facing slope to the west of the sub station site. One long house and attached enclosure survive, but two further buildings recorded on the 1st edition OS map have now been completely removed and at their location is a substantial quarry scoop. It is assumed that the stone of the buildings was removed during construction of retaining walls at the edge of the public road and that the quarry was opened at the same time. A further scoop into the hillside appears to be the robbed remains of a corn kiln. These features all lie to the north of the present access track, on the relatively steep but stepped slope from the road to the terrace. 5.0 Summary of findings of trial pit monitoring. A total of 27 trial pits were excavated over four days. One day was lost due to access issues, so the original goal of 42 trial pits was not reached, but the pits were distributed across the whole site. Only five pits were not located on the main terrace: pits C01, C02 and C04 were located on the slope to the west of the terrace and C03 and C06 were located to the north, on an intermediate terrace (C03) and on ground sloping gently to the Connagill Burn. The only feature of archaeological interest was the depth of soil, indicative of improvement for cultivation or grazing. Of the 27 pits, 14 contained no soil, six contained a thin mineral soil layer less than 100mm, and 7 contained soil deeper than 100mm. These 7, pits C01, C02, C05, C14, C19, C20 and C27, were located either on the west and north of the terrace, adjacent to field clearance mounds and banks, or on the grassy west slope adjacent to Connagil farmstead remains. The soil was richest, a black loam, at the base of slope near the road, but deepest at the west edge of the terrace, at pit C19 with a depth of 250mm. Much of the soil was poor, sandy and gritty with noticeable quartz inclusions. In two pits, substantial soil deposits were overlain by peat: pit C02 with 150mm of peat covering 120mm of soil, and C27, with 80mm of peat overlying 120mm of soil. Pit C02 is located on the intermediate terrace between the main terrace and the west slope, while pit C27 is located SW of centre of the main terrace and some distance from field clearance piles. The other five pits with soil depths measuring 100mm or more had no peat cover, but five pits with soils measuring up to 100mm in depth , pits C03, C11, C16, C17 and C21, had a cover of peat measuring up to 260mm. The fourteen pits containing no soil contained peat measuring between 150mm and 600mm in depth, lying directly on the gravel subsoil. Fig.2 Soil depths and peat cover 6.0 Conclusions Results of monitoring of test pitting suggest that while the broad terrace which is the proposed location of the substation does not contain any archaeological remains of habitation dating to either the prehistoric or to more recent settlement which terminated with the clearances, the more favoured and drained area of the terrace was improved for cultivation or grazing. This area covers the north edge of the terrace, approximately 300m E-W and 150m N-S where soils have built up to a maximum depth of 200mm. Subsequent to this phase of land use, some of the margins of this area was covered with peat, to a maximum depth of 240mm, while the central part has persisted as grassland to the present day. Habitation during the prehistoric period is represented by two hut circles, both located to the west of the terrace, on well-drained locations overlooking the strath. Later habitation, in the form of the post- mediaeval farmstead of Connagill, also occupied the western slope and the construction of a head dyke cutting off the terrace from the farmstead suggests that in the post-mediaeval period, this area was no more than hill grazing for the farmstead. 7.0 Recommendations Siting of the electricity substation on this terrace will remove all archaeological features identified on the upper terrace above Connagill, but should not impact on the township features or on the two hut circles to the west. Further archaeological investigation may be advisable to clarify the nature and function of the minor features and to retrieve dateable and environmental samples. Catherine Dagg 12.2.13 Appendix 1. Gazetteer of archaeological features Field Clearance mounds. The following eight mounds had the appearance of typical bronze-iron age field clearance piles. Mostly circular, although some were more linear, and covered in moss with few stones visible, these are mostly distributed at the north edge of, and on the north west part of, the main terrace. NC 90693 59814 NC 90616 59811 NC 90614 59798 NC 90617 59796 NC 90634 59811 NC 90638 59817 NC 90634 59823 NC 90672 59822 Other possible features Small ring of stones at NC 90608 59790 A setting of medium-sized stones, forming a ring of approximately 1.5m in diameter Area of rubble NC 90589 59790 A scatter of medium-sized stones covering an area approximately 2m by 1m Small ring of stones on slope NC 90535 59818 A setting of medium-sized stones forming a ring of approximately 1.5m in diameter Linear feature, rubble bank 90544 59814 to 90544 59789 Low, moss covered rubble bank spread to 500mm but to a height of no more than 300mm Linear feature, rubble bank 90534 59774 to 90525 59765 Low, moss covered rubble bank spread to 500mm but to a height of no more than 300mm Possible hut circle at 90504 59846 Located immediately to the east of the north east corner of the farmstead enclosure, on the west edge of a narrow intermediate terrace between the main terrace and the slope west to the and described as a small road, are circular banks of what appears to be a hut circle of similar dimensions to the one located by CFA (CFA5) An entranceway to the south is extended by further banks.