The aerial survey of archaeology in peatland

The aerial survey of vertical cut bogs may allow the assessment of an important and diminishing archaeological resource for the first time.

Introduction

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.

Conclusion

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.

Further reading.

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

A day of archaeology in the peatlands of Ireland I & II

View across Killaderry Bog, Co. Galway

 

For those who missed it here are my two contributions to the Day of Archaeology 2011 combined as a single post. You can see the originals here and here  and the homepage here. There are more than 400 posts from 400 archaeologists which present a snapshot of archaeology in the

About me
As an archaeologist my work ranges widely from advising developers how to avoid impacts on archaeology and built heritage, to the preparation of the cultural heritage sections of environmental impact assessments, to the commissioning of field-based investigations such as geophysical survey and the traditional archaeological excavation. Part of my professional work involves overseeing the archaeological programme of Bord na Móna, where I act as Project Archaeologist. Bord na Móna is the commercial Semi-state body with responsibility for the development of the Irish national peat resource. Bord na Móna owns and manages more than 80,000 ha of land spread across Ireland. Most of this is peatland which has preserved a wealth of organic archaeological and palaeoenvironmental material. Once thought to be areas of wilderness we now know that the bogs were used by people for thousands of years.

Up with the lark
Today I will be travelling to Killaderry and Castlegar bogs in Co. Galway to have a final look at the results of this year’s fieldwork.  There’s no need to set an alarm as our toddler has the household awake at 5.30am and part of the morning has already been spent watching Jungle Junction!

The project
The archaeological survey of the peatlands in the ownership of Bord na Móna has been a huge two decade long task, that has indentified thousands of archaeological sites that are not only near the bog surface but also buried quite deeply. The Bord na Móna method of working is to harvest a few centimetres of peat each year from the top of the bog. This slowly reduces the height of the bog and as the archaeological features come close to the surface they are either excavated or a decision is made to preserve them in situ. To find out more about the project

The excavation work is being carried out by Archaeological Development Services (ADS) who have been carrying out the programme since 1998, under the direction of Operations Manager Jane Whitaker. To date ADS has carried out more than 250 excavations and surveyed more than 45,000 ha of bog lands. For more on ADS peatland click here. I’m going to be meeting Jane on site and she is going to show me around the Killaderry and Castlegar excavations.

This year the investigations are focussing on the wooden trackways in Gowla, Killaderry and Castlegar bogs and ADS were joined earlier in the month by a group from the University of Florida at Gainesville lead by Prof. Florin Curta. Killaderry and Castlegar bogs are situated just to the west of the River Suck, a tributary of the River Shannon, and in the past would have presented a barrier to anyone trying to cross the river (see Google Map above).

It’s time to hit the road!

Getting to the site
It’s a two hour drive from my base in Kildare to Killaderry, part of the trip is on the new Motorways built during the Celtic Tiger period but once you cross the Shannon these roads run out and you are back on the old single carriageways and narrow bridges that characterise the country.

The excavations
I Arrived at Killaderry, Co. Galway just after 11am and Jane Whitaker of ADS showed me around. These are raised bogs, which means they developed from ancient lakes. The natural vegetation has been removed by milling so they give the impression of solidified dark brown lakes. The only visible features are the long and deep drains extending into the distance that break up the bog into long narrow fields. The figures of archaeologists in reflective yellow safety gear can be seen beside shallow excavation cuttings filling out recording sheets. The trackways are spread around the bog and it takes a long time to walk out to them and then from site to site. This year 13 sites were excavated in Killaderry Bog and 3 in Castlegar. Dan Young from Reading University is busily taking samples from around the trackways for environmental analysis. When it rains this can be a bleak place as there’s no cover. In a hot summer there’s no shade from the sun. The peat dries out and can become airborne and tractors and harvesters create mini-dust-storms as they pass.

A section of a trackway prepared for environmental sampling at Killaderry Bog. Co. Galway.
The trackways have a wide date range from the Bronze Age right through to the fifteenth century AD. The longer trackways tend to cross the bogs at their narrowest points linking areas of dryland. In a number of cases trackways follow the routes that were established at earlier periods. There are other alignments of trackway that are being investigated this season that will soon be dated and will provide more detail. At this stage the evidence indicates that this routeway through Killaderry bog was in use for at least two thousand years and is probably the preserved wetland part of an ancient road network that existed in this area. Investigation of the nearby River Suck also has the potential to identify ancient fording points and possibly the remains of bridges. There have been interesting finds, a Late Bronze Age wooden shovel, a rough-out for a handled bowl and a spoon that resembles a chisel. Now that the season’s fieldwork has come to an end the next part of work, the post-ex phase, begins.

Thanks for organising the Day of Archaeology go to: Lorna Richardson, Matt Law, Jessica Ogden, Tom Goskar and Stu Eve for their inpsiration and hard work!

Cite this post as:

Mount, C. A day of archaeology in the peatlands of Ireland I & II. The Charles Mount Blog, August 14, 2011. http://charles-mount.ie/wp/?p=322

Irish Peatland Archaeology in 2011: the Bord na Móna Archaeological Programme

Bronze Age trackway under excavation in Killaderry bog, Co. Galway July 2011

Part of my professional work involves providing archaeological advice to Bord na Móna, where I act as Project Archaeologist. Bord na Móna is the commercial Semi-state body with responsibility for the development of the Irish national peat resource. Bord na Móna owns and manages more than 80,000 ha of lands, the majority of which are peatlands, that contain a wealth of preserved archaeological and palaeoenvironmental material. The archaeological survey of the peatlands in the ownership of Bord na Móna has been a huge task, carried out under the auspices of the Archaeological Survey of Ireland and funded by the Department of the Environment, Heritage and Local Government. It has been continuing for two decades and has indentified thousands of archaeological sites that are not only near the bog surface but also quite deeply buried.

The Bord na Móna method of working is to harvest a few centimetres of peat each year from the top of the bogs that are in operation. This slowly reduces the height of the bog and as the work goes on, like an archaeological excavation that stretches across the landscape, the archaeological features close to the top are either excavated or a decision is made to preserve them in situ. Bord na Móna workers attend annual training seminars provided by the National Museum of Ireland and the National Monuments Service and are well aware of the types of features and finds that might be uncovered. The excavation of the archaeological features and the post-excavation and palaeoenvironmental work is funded by Bord na Móna, under a set of principles agreed with Government and is the subject of an annual excavation programme. Today the Bord na Móna archaeological programme is the largest ongoing archaeological excavation project in Ireland.

The Bord na Móna excavation project is let as a single Peatland Archaeological Services contract covering three years of operations. Archaeological Development Services (ADS) have been carrying out the programme since 1998, under the Direction of Operations Manager Jane Whitaker, and to date have carried out more than 250 excavations and surveyed more than 45,000 ha of bog lands.

The current programme, covering the years 2010-13, is focusing on the bogs of Littleton, Derryvella, and Longford Pass, Co. Tipperary; Cloonshanagh, Mountdillon and Edera, Co. Roscommon; and Castlegar, Killaderry and Gowla, Co. Galway. In 2011, investigations of the wooden trackways in Gowla, Killaderry and Castlegar bogs are taking place and ADS are joined by a group of students from the University of Florida at Gainesville lead by Prof. Florin Curta.

Google Earth image indicating the location of Gowla, Killaderry and Castlegar bogs. The River Suck, highlighted with a blue line, crosses the image from north to south.

Gowla, Killaderry and Castlegar bogs are situated just to the west of the River Suck, a tributary of the River Shannon, and in the past would have presented a barrier to anyone trying to cross the river over a substantial stretch between Ballyforan and Clooncoran. The trackways have a wide date range from the Bronze Age right through to the fifteenth century AD. The longer trackways tend to cross the bogs at their narrowest points linking areas of dryland. In a number of cases trackways follow the routes that were established at earlier periods. For example trackway 5 in Killaderry bog, which dates to the period 660-770 AD, probably allowed travel from the area of Ahascragh, Co. Galway to Ballyforan, Co. Roscommon by crossing Killaderry bog at its narrowest point between Killaderry and Cloonshee. The interesting thing is that Killaderry 5 runs parallel to Killaderry 3 which dates from 910-820 BC. An earlier trackway, Killaderry 13, dated to 1380-1210 BC, also runs in a parallel direction a little to the east. There are other alignments of trackway that are being investigated this season that will soon be dated and will provide more detail. At this stage the evidence indicates that this routeway through Killaderry bog was in use for at least two thousand years and is probably the preserved wetland part of an ancient road network that existed in this area. Investigation of the nearby River Suck has the potential to identify ancient fording points and possibly the remains of bridges associated with this ancient routeway.

In nearby Castlegar bog trackway 1 links the lands around the Late Medieval Carmelite Monastery at Eglish, Co. Galway, founded in 1376, to an island of land in Dalysgrove townland next to the River Suck. This trackway dates to the historic period 1410-40 AD and indicates that the construction of wooden trackways continued almost to the post-Medeival period.

The bogs not only contain archaeological features but preserve a wealth of stratified environmental data. This is an integrated archaeological and palaeoenvironmental project with the environmental sampling and analysis work carried out by QUEST and ArchaeoScape. QUEST Quaternary Scientific, is part of the School of Human and Environmental Sciences in the University of Reading under the Direction of Dr. Nicholas Branch. The palaeoenvironmental investigations involve taking samples for pollen, plant macrofossils, insects and peat humification. Dr. Branch’s work focuses on the relationships between human activities, vegetation history and climate change. ArchaeoScape is part of Royal Holloway Geography Department, University of London, and is an environmental archaeological (‘palaeoenvironmental’ and ‘palaeoeconomic’) interpretation facility.

The excavation programme wil be continuing in 2012 and will be followed by post-excavation and palaeoenvironmental analysis and eventual publication of results.

Cite this post as:

Mount, C. Irish Peatland Archaeology in 2011: the Bord na Móna Archaeological Programme. The Charles Mount Blog, July 14, 2011. http://charles-mount.ie/wp/?p=238