The aerial survey of vertical cut bogs may allow the assessment of an important and diminishing archaeological resource for the first time.
Irish peat bogs have long been recognised as important repositories of not only important artefactual information but many thousands of archaeological sites including settlements, ritual sites and hoard sites, trackways, platforms and post-rows dating from the Neolithic to the Medieval period. The traditional method of indentifying archaeological sites in peatland has been to walk the along the drains cut into the horizontally milled bogs by Bord na Móna the Irish semi-state peat development company. These regularly spaced drains provide a readymade section through the bog that allow sites at various depths above the water table to be identified (see Figs 1 and 2). Sites at the bog surface are also identified during survey. This survey work has been possible because Bord na Móna has been supportive of archaeological survey and investigation on its lands.
However, there are bogs on private lands where this type of survey has not been possible. Although these bogs are also exploited for their turf (see Fig. 3) there are no requirements for planning consent or environmental impact assessment and they have generally not been subject to archaeological assessment. Another difficulty in assessing the private bogs is the lack of regularly spaced drains. The only available sections are in the vertical cuttings that are usually on the external sides of the bogs. As a result very few archaeological sites have been identified in areas of privately owned peatland. There have been artefactual finds reported from these private peatlands over the years and it is just as likely that important archaeological sites are present in private bogs as in the Bord na Móna bogs. In order to remedy the situation a method of identifying archaeology in privately held areas of peatland is required.
Aerial survey has been used to identify archaeological sites across the landscape with great success, but this remote sensing technique has generally not been applied to peatlands. It was assumed that the same soil and cropmarks and the play of light and shade across earthworks would not occur in peatland. However examination of recent aerial coverage provided by Google Earth and Google Maps has indicated a range of linear features extending across areas of both milled and vertical cut peatland. These features tend to cross the narrow necks of bogs between areas of dryland. In some cases they parallel the routes of modern roads. In one case at Corradrehid/Monghagh Co. Roscommon a linear feature extends directly from a dryland road across the bog. At Cullahill/Dromard, Co. Tipperary a linear feature has been identified by the Archaeological Survey as a trackway and published and at Edera, Co. Longford linear features appear to represent trackways identified during ground survey. Eight examples are presented below of features visible in both milled and vertical cut bogs.
Features in milled bogs
These bogs have had the upper surfaces removed by milling and have a characteristic pattern of regularly spaced drains.
Fig. 1. Google Maps image of Edera, Co. Longford. Coordinates 53°33'48.80"N 7°50'2.80"W
At Edera, Co. Longford a number of linear features can be seen running into the narrow end of a bog from the dryland at north-east heading into the interior in a south-western direction (Fig. 1). The northern example appears to correspond with trackway LFDR001 recorded in the recent archaeological survey (Fig. 2). The middle example may correspond with LFDR002. The southern example may indicate a trackway not identified in the current survey.
Fig. 2. Survey of trackways identified in Edera Bog, Co. Longford, based on Rohan 2009, Fig. 14.
Fig. 3. Google Maps image of Cullahill/Dromard More bog, Co. Tipperary. Coordinates 52°52'3.35"N 7°44'33.55"W.
At Cullahill/Dromard More, Co. Tipperary a linear feature crosses the narrow end of the bog from the dryland at north to an area of cut bog at south where it may have been dug out (Fig. 3). This feature has been identified in the Archaeological Survey of County Tipperary Vol I as a Togher or trackway (No. 1166; RMP TS024-011).
Fig. 4. Google Maps image of Newpark Townland, Co. Longford. Coordinates 53.627667,-7.912193.
At Newpark, Co. Longford a linear feature extends from the dryland at west across the narrow neck of the bog to the eastern side where it disappears (Fig. 4).
Fig. 5. Google Maps image of Derrycooley, Co. Offaly. Coordinates 53°16'31.61"N 7°41'4.01"W.
At Derrycooley, Co. Offaly a liner feature extends from the dryland at south across the bog to an area of higher ground within the bog (Fig. 5).
Features in non-milled bogs.
The non-milled bogs retain the original bog surfaces that appear in aerial photos as greyish flat areas. They are characterised as having vertical cut areas penetrating to the interiors from the exterior sides.
Fig. 6. Google Maps image of Corradrehid and Monghagh townlands, Co. Roscommon. Coordinates 53°44'57.13"N 8° 0'59.31"W.
At Corradrehid/Monghagh, Co. Roscommon a roadway extends from the dryland on the west and runs north-east across the length of an area of uncut bog almost to the eastern end where it peters out (Fig. 6). Note areas of cut bog extending into the interior of the bog and the lack of drains running across the bog.
Fig. 7. Google Maps image of Erra townland, Co. Roscommon. Coordinates 53°43'21.67"N 7°58'35.73"W.
At Erra, Co. Roscommon a linear feature extends from the dryland at south-west, an island of land next to the river Shannon, into an area of uncut bog running roughly parallel to the line of a modern road (Fig. 7).
Fig. 8. Google Maps image of Timone, Co. Tipperary. Coordinates 52°55'8.37"N 7°44'4.81"W.
At Timone, Co. Tiperary a liner feature crosses an area of uncut bog from north-west to south-east, between two areas of old cut bog, running in the same general direction as the modern road network (Fig. 8).
Fig. 9. Google Maps image of Magheraveen/Cloonfore, Co. Longford. Coordinates 53°39'34.79"N 7°56'12.96"W.
At Magheraveen/Cloonfore, Co. Longford, Co. Roscommon a linear features extends across the centre of a bog from an area of cutaway in the north-east towards the south-west where it appears to be visible on the dryland (Fig. 9). This appears to be a dug feature. It is not a mapped townland boundary but could represent an ancient boundary.
The aerial images presented here indicate that aerial survey has the potential to be useful for indentifying features in both milled and and vertical cut bogs. To definitively establish whether these linear features are archaeological will require assessment in the field. Other techniques such as LIDAR survey may also prove to be effective at identifying linear features. If aerial survey is able to identify archaeology in bogs it will allow the assessment of an important and diminishing archaeological resource for the first time.
Excavations and Survey in the Bord na Móna Peatlands
Research and Training in the Bord na Móna Peatlands
Rohan, N. 2009. Peatland Survey 2007 & 2008: Blackwater, Derryfadda, Coolnagun, Mountdillon Group of Bogs. Archaeological development Services Report for Department of the Environment, Heritage and Local Government and Bord na Mona.
Cite this post as:
Mount, C. The aerial survey of archaeology in peatland. The Charles Mount Blog, August 18, 2011. http://charles-mount.ie/wp/?p=367