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Geophysical Survey

Date 2010

Event ID 633328

Category Recording

Type Geophysical Survey

Permalink http://canmore.org.uk/event/633328

NM 2868 2451 A geophysical survey was commissioned by the NTS as part of a management project on Iona. The work aimed to use non-invasive techniques to aid in the identification of any sub-surface archaeological features in three fields to the N, E and S of Iona Abbey. In particular it intended to provide more information about the system of field drains in the area, including a broken field drain to the S of the abbey, which had caused severe water-logging.

Gradiometer and resistance surveys were undertaken over c3ha with selective transects also covered using GPR. The gradiometer and resistance surveys produced good results, although the presence of igneous intrusions and magnetic sands and gravels across the site complicated the interpretation of data from the gradiometer survey. The resistance survey produced a more coherent series of results. Both the gradiometer and resistance surveys detected the vallum bank and ditch running to the N and E of the Abbey complex. A further probable ditched feature was visible in both surveys, running to the S of and along a similar alignment

to the vallum. The resistance survey identified an apparent return at the eastern end of this feature, where it turns to run SSW–NNE. This feature coincides with an earthwork recorded by RCAHMS.

The resistance survey also detected a possible enclosure associated with the Bishop’s House. A series of ditches and enclosures were visible in the resistance data from the southernmost field surveyed. For example, a possible rectangular ditched enclosure was recorded immediately SW of St Mary’s Chapel. Some of these features, particularly those along the W edge of the field, correlated with anomalies identified during the gradiometer survey.

Archive: ORCA Geophysics

Funder: The National Trust for Scotland

Amanda Brend – ORCA Geophysics

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