Working for the Irish Archaeology Field School!

Rock and Role of the Geoarchaeologist

Dr Stephen Mandal of the Irish Archaeology Field School, describes the role of the geologist in archaeological research at the Blackfriary, a C13th Dominican Friary site in Trim, Co. Meath, Ireland.

As a geoarchaeologist one of my main research interests is in the use of stone in the archaeological record as a source for making tools and other material objects, and as a building material. The Black friary was made from rock and understanding the building materials used – where they were sourced, how they were used, and why they were chosen – is an important part of the story of the friary.

The main building stone used in the friary was limestone, which is not surprising given it is the underlying bedrock of the area. Individual beds were laid down over 300 million years ago, during the Carboniferous Period, at a time when time Ireland was submerged under a shallow tropical sea. Each horizontal layer (bed) is roughly 10-30cm thick and much later folding and faulting of this bedrock has given vertical joints and fractures. This combination of depositional layering and post-depositional fracturing provided the medieval architects and builders with perfect, locally abundant, blocks to build the friary and the other medieval structures in the town, such as the castle and the yellow steeple.

The curtain wall of Trim castle; the wall was built on top of the limestone bedrock, from which the stone was sourced for the building of the castle.

During the first season of excavations at the Blackfriary in 2010, it was discovered that limestone was not the only building material used. There were at least three other types of stone used; slate as roof tiles, red / yellow sandstone in decorative architectural pieces and an unusual and highly distinctive limestone used in the cloister columns and arches. It is the latter that is the focus of this post.

The main building stones of the Blackfriary: 1. Limestone; 2. Sandstone; 3. Slate; 4. Purbeck

When the friary was systematically dismantled in the 1700s to reuse the stone to service a building boom in the town, the builders clearly encountered, but appear to have not valued, the decorative stone of the cloister arcade. Beautifully ground and polished architectural fragments of an obviously different limestone was either ignored or in places used to provide a flat surface for the carting away of the ‘useful’ limestone building blocks.

Visiting the site early in that first season, Kevin O’Brien (architectural heritage expert with the Office of Public Works, Ireland) suggested that these architectural fragments were made from an imported stone, Purbeck Limestone, from quarries in Dorset on the south coast of England.

My role in this rock story was to verify this identification, and the purpose of this blog post is to describe that process. Whilst this stone is visually distinctive – it is a variety of colours from green to red and comprises 90-95% small shelly fossils in a very fine grained matrix, consistent with Purbeck Limestone – to confirm a source requires a more detailed examination. This required the taking of samples to make thin slivers of the rock to view under a microscope.

To take a sample of an architectural fragment clearly requires damaging it, and to do this requires permission from the National Museum of Ireland. A representative sample of small broken pieces of the material were chosen and a ‘Licence to Alter’ was applied for. The application included details of the methodology to be used to take the sample and examine it, the research objective, and a justification for the damage caused. The license was issued (Licence no. 5811), and the samples were taken to the Geological Laboratories in Trinity College Dublin for preparation. A diamond tipped saw was used to take a small portion from each of the samples and these were fixed to a glass slide and ground down to a specified exact thickness of 30 µm, producing what geologists call ‘thin-sections’.
One of the nice by-products of the process was that the unused portions of the samples were left with highly polished surfaces, allowing us to envisage how magnificent the stone would have looked when the friary was built.

The thin-sections were viewed under a special type of microscope – a polarising light microscope; one of the most important tools of a petrologist (a type of geologist who specialises in the identification, interpretation and origin of stone). This microscope differs from a standard microscope in that the light source is below the thin-section, so the petrologist views the sliver of rock with the light shining through it, and the viewing plate rotates. Importantly, the microscope allows the user to polarise the light waves; an invaluable aid in identifying the minerals that make up the rock, as different minerals behave in different ways when they are rotated through polarised and crossed polarised light.

Example: Polarized Light Microscope, showing the different parts

Under the microscope, it was immediately apparent that the shell types, their alteration, and the fine crystalline matrix in which they sit are all consistent with this being Purbeck Limestone. I am working with Dr Patrick Wyse Jackson of the School of Geology, Trinity College Dublin to record the thin-sections and compare with Purbeck source materials. The results of this work will be published in due course, but what is now clear is that the use of important Purbeck Limestone provides an interesting piece of evidence as to how wealthy this friary was (or more accurately, its patrons were).

Image of Purbeck limestone in thin section, showing the abundance of shelly fossils – the width of the image is 3cm.

 

Originally posted on 11/04/2017 www.iafs.ie

Centuries in sod – excavating the Black Friary, Trim, Co. Meath

In its sixth season of excavation, the archaeological research project at the Black Friary, Trim, Co. Meath, Ireland, has thus far uncovered, through archaeological excavation, the outline remains of the 13th century AD Dominican church and cloister, with the west, north and east ranges including the chapter house, and burials within these. Non-invasive survey is ongoing and through LiDAR and geophysics, the kitchen gardens have been identified, along with numerous other walls, boundaries, ditch features and additional potential burial cuts.

In 2015, Season 6 excavations are seeking to further understand the phases of construction and destruction of the church (the site was eventually sold off and used as a quarry in the 18th century). To do this we have been extending an existing investigation area centred on the south aisles of the church. This has required hand de-sodding of an area that in grass.

The Black Friary site was designated a National Monument in 1972; the modern expansion of the town in this period rendered the site an island surrounded by houses, effectively isolating it from the archaeological and historical fabric of the town. As it was well out of general sight, it fell from collective minds and the grassed over remains became a place that was used for unwanted household appliances at best, and at worst, a dumping place for construction waste including topsoil and rubbish that has been used to fill in and even out the medieval ditch and bank features of the site. The research project and student training dig is working with the Blackfriary Community Heritage and Archaeological Project to increase awareness of the site, change attitudes to it, and in turn, hopefully, result in respect and protection of the site.

De-sodding involves the manual cutting and lifting (with spades and shovels) of grass sod to expose the underlying soil, which can then be hand excavated (with mattocks and trowels). Any items found are collected and placed in trays with information on the area of the site, and the required archaeological recording information. In the sod, we find the modern remnants of the site’s most recent past; these are recorded as in a non-secure context – interpreted as a jumble of items from decades of disturbance. While not strictly archaeological, the items recovered do give us insight into the recent past and events on the site. This short photo essay charts the evidence from the last century of activity on the site, from bed springs to poly-filler, from bathroom tiles to butchered animal bone, from jam jars to early 20th century currency. And underneath it all, a prize – (our fourth ever!) fragment of medieval decorated line-impressed floor tile. While much of this will be discarded as refuse, the items are all kept in record, in photos and notes, to inform later interpretation of the underlying, yet to be discovered archaeological remains.

For more on our project, see www.iafs.ie and on our dig diary.

 

 

 

 

 

 

 

 

Expert Guidance from the National Museum of Ireland Conservation Department

The Blackfriary Community Archaeology Project in Trim, Co. Meath Ireland, now in its fifth year, focuses research led archaeological excavation at the site of the 13th century Dominican Black Friary in Trim, Co. Meath. Founded in 1263 by Geoffrey de Geneville Lord of Meath, the friary was a significant site for centuries until the Dissolution of the monasteries in the mid 16th century. It was finally razed to the ground in the 18th century when sold off as a quarry. During the past five years university students, under the direction of the Irish Archaeology Field School, have been excavating the buried remains of this friary, and rediscovering its secrets.

The 18th century activity on the site had a devastating impact on the majestic architecture of the friary; the quarry men dug ‘robber trenches’ to access the wall foundations and remove as much of stone work as they could from the buildings. The stained glass windows were also removed and the lead harvested for recycling. The glass was discarded and, as we have found, beaten out of its lead matrix leaving behind only fragments of the stained glass windows that would have adorned the east window of the church, and possibly elsewhere in the friary precinct.

 

Stained glass window within its lead matrix

Stained glass window within its lead matrix

This year, working westward from the ecclesiastical buildings towards the garden range, students have uncovered three surviving fragments of stained glass window, with the glass still in its lead matrix.

This is an unprecedented find for the site, and due to the extreme fragility of the glass, we immediately sought advice from Head of Conservation at the National Museum of Ireland, Rolly Read. Rolly advised that the window fragments should be block lifted and came to the site himself to undertake the block lift. Block lifting is a technique used by conservation professionals to recover delicate or sensitive archaeological objects.

 

Site director Finola O'Carroll and supervisor Laura Corrway excavate the plinths

Site director Finola O’Carroll and supervisor Laura Corrway excavate the plinths

The block lifting took place over two days; to facilitate this we excavated a small regular area around the window fragments, creating a pedestal for each piece. This work required precision excavation to ensure that the window fragments remained supported by the soil matrix in which they had survived, while allowing scope to undercut each pedestal when they had been prepared for block lifting. When Rolly was satisfied that we had excavated to a sufficient depth around each piece, he got to work. With the assistance of a number of our staff and students, and an audience of most of the rest of the crew, he started by packing each pedestal with moistened acid-free conservation grade tissue paper, to support the delicate leadwork. Each piece was then wrapped in film to consolidate and protect it from the final stabilising stage. Once sufficiently wrapped and stable, Rolly used a quick drying mesh bandage to ‘cast’ each piece. This required precise and quick execution to ensure each piece was fully wrapped before this material started to set. The setting or curing process took about 20 minutes. When set this mesh formed a solid case around the piece, encasing it in the surrounding soil matrix. The final undercutting was carried out using trowels. Each piece was deftly flipped over into a tray, and further stabilised with film wrap, ready for transport. Each piece will now be fully excavated in lab conditions by conservators, allowing them to carry out consolidation and conservation work as they uncover the window fragments.

 

Rolly Read, Head of Conservation at the National Museum of Ireland, wraps the glass as the IAFS crew look on

Rolly Read, Head of Conservation at the National Museum of Ireland, wraps the glass as the IAFS crew look on

Rolly Read, Head of Conservation at the National Museum of Ireland, 'casts' the stained glass

Rolly Read, Head of Conservation at the National Museum of Ireland, ‘casts’ the stained glass

 

There are few surviving examples of medieval windows from archaeological contexts in Ireland so we are absolutely thrilled to have uncovered these pieces, and to have had expert guidance and assistance from the Museum to ensure that they may be consolidated in the best possible conditions!

 

 

 

The glass is ready to be lifted and taken to the museum for conservation

The glass is ready to be lifted and taken to the museum for conservation

 

Public Archaeology – a community view

This all singing, all dancing contribution was undertaken by local film makers Delphine Coudray, and Roy Murray includes archaeologists, university students, local children and Paddy Rispin, from the Trim Living History group.

Dodging torrential rain showers, in between excavation cuttings, this is archaeological interpretation, community style: Blackfriary Community DoA 2013

DoA video

The Archaeology:

The Blackfriary Community Archaeology Project is collaboration between the Irish Archaeology Field School (IAFS), Meath Local Authorities and the community of Trim, Co. Meath, Ireland. The focus of the project is the Blackfriary, a 13th Dominican Friary, founded by the Anglo-Norman Geoffrey de Geneville, Lord of Meath in 1267. The friary was quarried out in the 18th century and the remains of are mostly buried. The site, listed as a National Monument in the 1970’s, is situated in a large field and is surrounded by housing. As the town developed, around it, the field fell into disuse and eventual dereliction. The Project is challenged with investigating the archaeological remains of the site, much now underground, and working with the local community to create a space where community and visitors alike can explore heritage and use the site in a mutually beneficial and sustainable way. The Irish Archaeology Field School carries out a summer excavation project at the site annually; this incorporates a practical field programme for archaeology, anthropology and forensic students into the archaeological research project.

The Community:

Our summer excavation season depends very much on the good relationship the School has with the community; Trim has an active community that are creative, resourceful and proud of their heritage. The School asked members of the community to help out with a contribution for the Day of Archaeology, something that the community themselves would be interested in… Although not perhaps a typical day for archaeologists, the imagination, enthusiasm and fun of this contribution is very typical of the School’s experience of working in this wonderful community. Enjoy!

 

An Intern’s Experience/My First Excavation

Its the third season for the field school and community archaeology project at Blackfriary, Trim, Co. Meath.  Blackfriary is a 13th century friary, the buildings were sold off for stone the 18th however sub-surface foundations and other features still survive and archaeological excavation is ongoing to discover extent of these.

 

Photo  1   Exposed masonry on site

Today, the 29th of June, ends the fifth week of season three at Blackfriary. The season has been flying in and we have already seen a number of students come and go. We are nearly half way through the season with only six weeks left on site for 2012.

The excavation at Blackfriary is also part of a community archaeology project; the field school works alongside the local council and community groups to provide a programme of events to engage the local community with the project, from understanding the archaeology of the site to integrating the Blackfriary as part of the Trim townscape.

As an intern with the IAFS the first thing I have learned is that no day on site is ever the same! This is due to the coming together of different groups of people from schools groups to students, and from local visitors to tourists (as well as the unpredictable Irish summer weather).

On a daily basis the field school teaches students the skills and techniques for excavating features along with skills such as planning and drawing that help to record finds and features and assisting in the archiving of the site. Another key learning outcome for non-Irish students is how to make the perfect pot of tea!

Photo 2  Students practicing excavation and recording skills

The second thing I have learned as an intern at the Blackfriary is to be prepared for a lot of bones (and it’s a good thing that I’m not squeamish)!

On site, to date, there have been nine burials found, and countless amounts of disarticulated human bone. We had a resident bio-archaeologist on site for the month of June, Professor Rachel Scott of Arizona State University.

 

Photo 3 Contemplating an infant  burial

She gave a module on  bio-archaeology and osteoarchaeology, teaching students the techniques to excavate, record and process human remains. Following this module, one of our students, Anna from Macalester College, was able to give a presentation to a groups of forty plus high school students visiting from the USA, presenting and explaining the bones found on site.

 

Photo 4  Excavation in progress – Rachel and the infant burial

 

Photo  5   A presentation on bones to students

The site is located in the centre of a housing estate which many people walk past or use to walk their dogs on a daily basis. This means there is a lot of interaction with residents of the local community and a common part of a days dig can be showing locals around the site and explaining to them both what is being excavated and being found.

 

Photo  6   Giving visiting high school a tour of the site

A further mix of interactions is with tourists who visit the site through Cultural Tourism Ireland. Through CTI members of the public with an interest in heritage and archaeology come on site and experience the process of excavation for themselves.

Throughout the dig the coming together of this large and diverse group of international budding archaeologists, Irish students, local community members, site visits from school children and those with a keen and common interest in the heritage of Ireland adds to (and in my opinion enriches) the experience of being on site.

 

Photo  7   Blackfriary crew in action

Caroline Henry, Heritage Intern with the Irish Archaeology Field School: reporting for Day of Archaeology 2012

 

Burials & the Last Day on Site

Who are we?

Irish Archaeology Field School is a research project and teaching dig based in the Boyne Valley in Co. Meath, Ireland. We have three sites, one at Blackfriary in Trim, a C13th Dominican abbey, one in Rossnaree, near Slane, a multi-period site, and one at Bective Abbey, a C12th Cistercian Abbey. Blackfriary is a community archaeology initiative with support from the Department of Arts, Heritage & Local Government, the local authority, and the American Institute of Archaeology Site Preservation Fund. The sites at Rossnaree and Bective are being excavated by our research partners, with funding from the Royal Irish Academy.

Blackfriary: A day in the life:

Blackfriary Abbey in Trim, Co. Meath is the site of the abbey has lain abandoned for decades and been surrounded by the expanding town. The abbey walls have largely been robbed out and the site is mostly under grass.

The current season’s research programme was designed explore the interface between the church and the cloister, which is situated immediately to the north of the church. The first month of excavation revealed lots of loose stone, evidence of the deliberate destruction of the abbey walls (the stone was likely reused elsewhere) and it is only in the last few weeks that we are finally accessing the base of the walls with foundations and stone work in situ. We are only using hand tools to excavate so there is a lot of mattocking and shovelling involved, to move a lot of material:

Plate 1: Melissa Clarke wields a mattock

While the cloister wall was found reasonably quickly, the north wall of the church was heavily robbed out, and we are also reaching levels that contain f burials, both disturbed and undisturbed.

Following the dissolution of the monasteries in C16th, the abbey was no longer officially a religious centre. However people still considered the site as sacred and such sites were often used as graveyards in the centuries following. The abbey graveyard, lies to the south west of the church. There are also burials within the church. As yet we have found no conclusive diagnostic material to date them – we may have to wait for radio-carbon dates. What we do know is that we have 3 distinct burials, but we at least 6 individuals are represented by the skeletal remains recovered so far.

When a burial is uncovered, we first try to find a grave cut – that is the evidence that might remain of the grave that was dug for the burial. We then photograph it, to add to the record. The photo board notes the site registration number, the number assigned to this burial, area of the site in which it occurs, the date, and the initials of the photographer:

Plate 2: Malika Hays photographs Burial 3 prior to excavation

Burial 3 is that of a young child or infant; the remains are in reasonable condition however the bones are fragile and are particularly difficult to recover. The tools of an archaeologist include a standard trowel, and a leaf trowel for intricate or delicate work but is this instance we improvise with some wooden skewers; these are useful for precision and because the point is softer.

Plate 3: Malika excavating: using a wooden skewer for precision

Excavation of material this delicate is slow work: the soil must be cleaned off each fragment of bone and stored for sieving, and each bone fragment lifted and placed in a specific box for that burial. Given the age of the individual when he or she died, the bones are small and delicate, only partially fused in some instances. Some bones are so small they may not be identifiable during excavation and may only be recovered from the sieved material. We had barely made any progress on the excavation of this burial by the end of the day so the burial has been carefully packed with bubble wrap and covered to protect it and keep it from drying out overnight.

Rossnaree – today was a day of logistics:

The dig at Rossnaree finished up today. The site is in a rapeseed field and with the harvesters on the way, the heat was on to backfill the excavations, to ensure that all the recording of the archaeological features is complete and that every detail has been noted.

Behind the scenes though is the inevitable demobilisation of the site. At Rossnaree, there was a small crew of 8-10 people for most of the four week excavation. The contents of their site cabin fitting into the back of our small van:

Plate 4: Mattocks and sieves – tools of the trade

After loading up all the equipment, finds, samples, registers, plans and notebooks, all that’s left to do is close the gate behind us…. until next year!

Plate 5: The laneway to Rossnaree archaeological site, located in the Boyne Valley – Knowth passage tomb is just out of view behind the trees on the right.

References