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between 12:00 Friday 15th December and 12:00 Monday 18th December


A' Chlach Thuill

Dun (Period Unassigned), Vitrified Stone (Period Unassigned)

Site Name A' Chlach Thuill

Classification Dun (Period Unassigned), Vitrified Stone (Period Unassigned)

Alternative Name(s) The Split Rock, Clachtoll

Canmore ID 140944

Site Number NC02NW 25

NGR NC 03813 26716

Datum OSGB36 - NGR


Ordnance Survey licence number AC0000807262. All rights reserved.
Canmore Disclaimer. © Copyright and database right 2023.

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Administrative Areas

  • Council Highland
  • Parish Assynt
  • Former Region Highland
  • Former District Sutherland
  • Former County Sutherland

Archaeology Notes

NC02NW 25 038 267

NC 038 267 Short length of vitrified walling on the landward side of the Split Rock.

M Bangor-Jones 1998


Field Visit (1 April 2009 - 30 April 2009)

Vitrified walling of possible Dun (NC 13813 26716)

The split rock of Clachtoll is a well known feature of the Assynt coast probably created by the slippage of a massive section of cliff down the inclined bedding plane of the Torridonian sandstone where it now forms a massive stack. The landward side of the split is a high knoll with almost vertical rock faces falling 20m down to the sea to N, S and W. To the E a much lower rock face descends 3m down to a small level area before climbing up the bedding plane to the top of a further rock face which also drops down 3m to where the headland widens out considerably. Approaching from the wider section of headland the knoll presents an impressive sight with its ground surface above two rock faces and vertical cliffs on both sides. At the N edge of the high knoll is a small section of vitrified walling and the whole surface of the knoll is made up of charcoal rich dark soil. The top of the knoll, as well as the vitrified walling was surveyed at 1:100.

The vitrified walling (A1) survives only along a 1.5m long section of the N corner of the knoll. At A1.1 it is approximately 1m high and 1m long before dropping down sharply to A1.2 where it is about .5m high. A1.2 appears to be a corner turning south after which the face peters out and only a small fragment of core survives at A1.3. The surviving sections of vitrified walling consist of small, often rounded stones (up to 20cms across) some of which are Torridonian sandstone like the bedrock of the headland and some Lewisian Gneiss, which outcrops nearby. Beach pebbles in the area are of both rock types. Close to the walling at B there is a Gneiss pebble and at C on the S side of the knoll three Gneiss pebbles are embedded in an eroding area of very dark, reddish-brown soil with flecks of charcoal. The top of the split rock is high above the sea and over 100m from the nearest accumulations of shingle, so it is unlikely that these pebbles made their way there naturally. The soil of the headland as a whole is light coloured and consists mainly of sand, whereas all visible soil on top of the knoll is much darker. It seems plausible that a small Dun,, which could have encompassed an internal area of up to 7m x 10m, was created on top of the knoll by vitrifying a large number of predominantly small beech pebbles. These would have been much easier to carry up the two 3m high rock faces to the top of the knoll than the larger stones needed for a dry stone structure.

Gordon Sleight

Historic Assynt

Note (2 February 2015 - 8 September 2016)

A small fragment of vitrified walling has been noted on the landward side of the stack known as the Split Rock of Clachtoll, which forms part of the headland on the S side of the mouth of the Bay of Clachtoll. The stack falls sheer to the sea some 20m below on three sides, but the summit is more accessible on the E, where the bedding plane of the bedrock slopes up from a lower rockface. Traces of any defences are scant, but at the N corner of the summit area a short fragment of wall standing up to 1m high can be seen, and there are also several loose stones on the SSE. The irregular and uneven summit of the stack measures about 14m from ENE to WSW by 7m transversely (77 sq m), though to what extent this was ever enclosed by the wall is not known.

Information from An Atlas of Hillforts of Great Britain and Ireland – 08 September 2016. Atlas of Hillforts SC2776

Archaeological Evaluation (1 September 2017 - 2 September 2017)

NC 03786 26731 (NC02NW 25) An evaluation was undertaken, 1–2 September 2017, as part of the wider Clachtoll Broch Project. The work consisted of a 3 x 1m test pit on the promontory side of Split Rock, Clachtoll.

The test pit uncovered a series of charcoal/organic rich deposits abutting the side of a wall consisting of a foundation course and single surviving upper course of linear/sub-angular sandstone blocks. Two sherds of

decorated Iron Age pottery were found, similar in style to sherds recovered from Clachtoll Broch, suggesting the wall could be Iron Age in date and contemporaneous with the use of the broch.

Archive: NRHE (intended)

Funder: Historic Assynt

Alex Wood, Graeme Cavers and Gordon Sleight – AOC Archaeology Group and Historic Assynt

(Source: DES, Volume 18)


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