Interpreting our site: the structure of the mound

Author: Rachel

Last week I talked about the structure of the mound. I explained how we were able to confirm that the site is a man-made mound not a natural one. I also explained how we have begun to understand the structure of the mound as being made of multiple layers of soil and turf. This week I want to talk about the stone structure that surrounds the mound.

At the end of week one we were trowelling back across the larger half of the trench when a row of stones began to appear.

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Stones beginning to emerge in Trench 1. Image: Rachel

 

As we continued to methodologically trowel over the area it became clear that these were not random stones but a specific structural part of the mound

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It begins to become clear we have some kind of structure! Image: Rachel

 

What we exposed in our trench was what appears to be a ring of stones that surround the edge of the mound. The majority of these stones are slate with a smaller proportion of quartz (in some areas there appears to almost be bands of quartz – something we would like to explore more in the future). Some of the rocks are relatively angular and others are more rounded like beach pebbles – they range in size up to about 30cm in length. Before our excavation the geophysical survey had picked up indications for some kind of stone layer surrounding the mound but the results suggested this was deeper underground so we had been unsure whether what we were picking up was archaeology or geology. What we can now tell is that the ground penetrating radar survey was identifying the ring of stones that surrounds the mound.

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A curve of stones running from the lower left part of the trench around to the upper right part of the trench. further away from the camera, the other side of the rocks is the mound material. Image: Rachel

 

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In this photograph you can see the large curve of rocks running around the edge of the mound material. Image: Rachel

 

Careful observers of the photographs above might have noticed that as well as the small rubbly material surrounding the mound there are also two much larger blocks of rock. One in particular, on the lower slope of the mound is particularly huge. These are blocks of slate. The local geology on the hill has layers of glacial sand and gravels overlaying the bedrock. As a result we do not thing these blocks are outcropping bedrock rather we think they are large blocks of bedrock from elsewhere that have been quarried and deliberately placed around the edge of the mound.

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A very large slate block is visible in the left of the photo. Image: Rachel

 

Avid blog readers might recall that we’ve blogged before about ring cairns and kerbed cairns (check out part two of our history of round mounds blog). Ring cairns are rubbly rings of rocks that can surround a mound or can be left open in the middle (looking a bit like a doughnut of rocks). Kerbed mounds and cairns are mounds which are usually surrounded by a ring of larger blocks of rock that often act to contain and support the mound within. We feel confident that our rubbly material around the mound is evidence of a ring cairn, and it may well be that the larger blocks of rock within this could be more properly described as a form of kerbing.

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The downside of the ring cairn is that every rock needs drawing on the site plan! Original Drawing by: Eloise, Eleanor, Charlotte, Kathleen and Rachel; Digitisation by Mareike.

 

So where does this leave us? We know we have a man-made mound constructed of layers of earth and turf. We know it is surrounded by rubbly material around the edge including some much bigger blocks of slate that we suspect have been quarried and brought to the site. We also know that it was into this rubbly ring-cairn material that a Bronze Age community chose to insert a small cist containing an inverted Collared Urn. What we cannot tell you yet is the chronological relationship between the mound and the ring-cairn material – i.e we don’t know which came first. We began to explore this in two small areas on the site this summer but time was short and our results are not yet conclusive. Working out the chronological sequence of events at a site is one of the most important aspects of excavation. At the moment Chris and I both have slightly different preferred theories about the construction sequence for the mound and ring-cairn. What we both agree on though is that only more excavation will be able to help us know for sure!

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Interpreting our site: the basics, the mound

Author: Rachel

Over the past few weeks the blog has focused on explaining how we recorded the site during the excavation in July. As I mentioned last week we are busy preparing the report for the site at present. Over the next few blogs I want to talk a bit about what we actually found and how are trying to understand it. I also want to highlight some of the things we couldn’t work out (we only had two weeks!) that we’d like the chance to try and explore in the future.

So – what is our site? It is definitely a mound! And it is definitely a mound made by people rather than a natural mound that formed through geological processes! This week I am just going to focus on trying to understand the nature of the mound.

We opened one trench this year. This trench covered around a quarter of the mound area. In the image below you can see the largest red rectangle covers the area that we have geophysics results from, the smaller blue box show the mound we were investigating and the smallest pink box shows the location of our trench.

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LiDAR image of the site. Red rectangle marks the geophysics survey area. Blue square surround the mound we are beginning to explore. The Pink square marks the location of our 2017 trench

 

We left a 50cm wide strip of earth running just-off centre through the middle of our trench. We call this bit of archaeology we leave in-tact – the baulk. Baulks are handy because they allows us to see a slice through the layers we are excavating.

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In this photo you can see the baulk running down the middle of our trench and people working in the other part of the trench on the other side of it. Image: Rachel

 

It is this baulk running down the middle that helped us to understand how the mound was constructed. In particular we took a strip about 80cm next to the baulk and focused some of our excavating efforts on digging deeper in this area to try and understand whether the mound was built or natural, how deep it might be and what it was formed of.

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The trench at the end of the dig with the deeper area running parallel to the baulk on the right hand-side. Image: Rachel

 

Mareike did a great job stitching together all our photos of the section in this area so that we can present you with a lovely image of what the whole of the trench looks like. Looking at this slice through the earth we can see a number of layers of different colours – these are the contexts the blog focused on last week!

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Composite image of the baulk section. Photos: Chris, Image: Mareike

 

In the image below we’ve marked up the image to help you see what we see. The top two layers (labelled (1001) and (1002)) are the soil and the sub-soil. (1003) is a light orangey-brown in colour and this layer does not extend beyond the edges of the mound, it is the upper-most surviving layer of the mound. Below (1003) the colour becomes darker to give a darker orangey-brown – this is another layer of the mound (1005). Below (1003) only visible in the left of the photograph is a darker layer, a dark greyish-brown in colour, this is the lowest layer we exposed during our excavation.

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Layer of the mound. (1001) is the topsoil, (1002) is the subsoil, (1003) is the upper-most layer of the mound exposed, (1015) is the middle layer of the mound exposed, (1021) is the lowest layer of the mound exposed (only visible on the left side of the image). Photos: Chris, Image: Mareike and Rachel.

 

How do we know these are man made layers? There are a good number of finds that came from these layers including a type of flint scraper that dates to the Early Bronze Age. This evidence combines with what we can tell you about the soil – you should be able to spot three discrete dark greyish oblongs between the (1003) and (1015) in the photo below. We think these are buried turfs that show up in the section and tell us that people were piling up earth and turf to make the mound. We can also see evidence of tracks that run from the top of the surface of the mound in a downward direction – we interpret these as evidence the top of this surface was once exposed as the old ground surface, we think they are tracks left by creatures like worms and by the roots of plants.

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Turfs in the mound – the three grey oblongs visible in the middle f the photo between the ligher orangey-brown layer (1003) and the orangey-brown layer below (1015). Photo: Chris

 

We only excavated about a quarter of the mound in 2017 – in the future we would like to consider whether the mound has the same construction across the whole site or whether it varies? We also want to know if there might be even more layers of mound below the ones that we exposed this year. We are also interested in whether there is a layer of turfs in the mound construction across the whole site? This should help us to understand the construction process of the mound more clearly. We are also looking forward to getting the results of the geoarchaeology research that might help us understand how the mound layers formed in more details and hopefully confirm that these are clods of earth and turf that we can see between (1003) and (1015).

Recording our site: contexts

Author: Rachel

Over the past few weeks I’ve been explaining how we record the site using techniques such as drawings and photography. This week we are going to tackle context recording.

An archaeological context is the name we give to refer to an individual event that we can excavate on site. Contexts are preserved past events on the site, this could be a layer that built up over a number of years, a pit that someone dug and filled with rubbish, a wall that a community built or a burial that was placed in the ground. If each of these kinds of practice leaves a trace within the archaeological record then we term it a context.

Saying a context represents a past event can sound a little confusing. When we think of an event we might think of a party at a specific time and place – an event in our diary as it were. Events on archaeological sites can have short time spans like this, for example a grave that was dug and filled in a few hours, or they can have longer time frames such as a layer that built up gradually over many years.

Different sites and archaeologists sometimes define slightly different types of context. On our site we excavated and recorded four main types of context. The first type are layers (sometimes referred to as deposits) these are (usually) soil layers that have formed. The second type are cuts – cuts form when someone in the past has dug into the ground – imagine someone digging a ditch or a pit, or a hole to place a post in. The shape left in the surrounding soil once they had finished removing the earth they are digging out is what we refer to as a cut. The third type is a fill – a fill is the material that literally fills back up a cut. The fill could be material dumped in the hole by humans or material that accumulates in the hole over time. The fourth type of context we identified on our site were structures – in our case we have our cist as an example of a structure, but on sites from other periods there might be walls, roads or even drains.

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This shows a cross section through a cut feature. The numbers in brackets label the contexts. (1003) is a layer, [1012] is a cut (represented here by the black line between the lighter and darker browns) and (1011) is a fill. Drawing: Holly and Maddie. Digitised by Mareike.

When we identify contexts on site we try to dig them one-by-one, digging the context we think formed most recently first and the older ones last. This helps us to try and understand the sequence of events at the site.

Each context that we find on site receives a detailed description so that once we have dug it up there is a paper (and later digital) record of what was there as well as all the photographs, drawings, samples and finds. We give each context a number which we can refer to it by and then we go about recording the location it was found in, the size of the context and what it was. In the case of layers and fills we record the type of soil that makes it up, the compaction of that soil, its colour and the inclusions within it that aren’t soil (for example rocks and charcoal). For cuts and structures we record their shape and dimensions. We then try and work out how the context we are recording relates stratigraphically to the others around – this basically means working out what came before it and what came after it! We also write a discussion and interpretation of what we have found where we try to work out what it was and how it relates the rest of the site

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Front page of a context Sheet

 

This week I’ve been writing summaries of the contextual data from the dig for the report on the excavation we are preparing for Manx National Heritage. We found 8 different layers during the excavation, 4 different types of fill, 4 different cuts and 3 types of structure.

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Processing the context data back in the office. Image: Rachel

Heritage Open Days 2017: Round Mounds event

Author: Rachel

Manx National Heritage are running two weekends of Heritage Open Days this year. One from Friday 29th September to Sunday 1st October and the second from Friday 6th October to Sunday 8th October. These events are free and offer you the chance to access some of the more unusual or less publically accessible historic sites across the island in the company of experts who can tell you all about them.

Heritage Open Day

There are numerous events scheduled for this year from walking tours of the World War II civilian internment camps in Douglas to twilight tours of Castle Rushen with MNH Director Edmund Southworth. There is a chance to tour Government House and the Parliamentary buildings for those with an interest in politics and architecture. There is also a Douglas Pub Walk which will reveal the history of some of Douglas’ pubs! Details of all the events are available via the MNH website, by clicking here.

Followers of the Round Mounds project might particularly enjoy the tour of Balladoole on Friday 29th and Saturday 30th September with MNH curator Allison Fox. Balladoole is home to a chapel, a Viking boat burial, spectacular views, and an Iron Age site! More significantly for the project it is also home to some Bronze Age burials that Michelle will be examining the bones from later this month.

We also think that the tour of Knock-e-Dhooney in Andreas will be really fascinating. This tour is run by Dave Martin who has provided invaluable help and support to the Round Mounds project. Knock-e-Dhooney is home to a keeil and an impressive Viking ship burial and Dave is a great tour guide!

Michelle and I will also be participating in the Heritage Open Days on Sunday 8th October. We will be running a family event hunting for the round mounds in Archallagan plantation. Keen blog readers might remember that we carried out geophysics outside of the plantation and have blogged before about the 1860s maps and LiDAR images of the area. We will be showing participants the geophysics results from our work and then setting them off with an 1860s map into the plantation to hunt for the traces of the remaining mounds in between the trees. Our event has limited places and requires booking to take part. To book your place please follow this link.

Check out our Archallagan blog here.

Recording our site: finds

Author: Rachel

This week I want to tell you a little bit about how we recorded finds on our site. We recorded all the 1100 finds from the site. Our finds are placed in bags with lots of detail about the finds written on the bag.

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Finds bag and finds laid out for photographing. Image: Rachel

 

The bag has CG17 on the top line – this is the code we use to designate the excavation – CG for Cronk Guckley and 17 for 2017. This is joined by the trench number – this year we opened just one trench (though we did divide it into two halves – 1a and 1b). On the line below we write the context number that the find came from – contexts are the number we give to the different archaeological events that we can identify on the site, generally speaking these are layers of soil though they also include structures such as the cist and the rubbly cairn material. The context number goes in round brackets. Next to the context number we put the finds number inside a triangle. Underneath we usually note the find date and we give a description of what is in the bag – this could be a basic one like ‘flint’ or ‘burnt bone’ or if we are able to give more detail such as ‘burnt flint scraper’ we will.

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Even more flint!

 

Finds that come from the topsoil and the subsoil are less informative than those from the ‘proper’ prehistoric layers below. The topsoil and subsoil layers contained a range of archaeological finds including glass and modern pottery as well as prehistoric flint, charcoal, burnt bone and even a loom weight. The finds in these layers have been mixed together over time by ploughing (we can see plough scars on the site which go into the surface of the mound). As a result of this mixing we can learn less from these finds and so we do not give every individual find its own find number but rather group all the flint under one number and sherds of modern pottery under a second. This means that for these finds we do not record the precise location on the site grid that the finds came from. The exception to this is burnt bone and prehistoric pottery sherds which we do record detailed locations for as these represent disturbed burials and we might be able to try and identify a general area they came from using spatial analysis back in the office after the dig.

For all the finds from within the ‘proper’ prehistoric layers we record a location on the site grid for every single find – this slows down our digging a bit (and kept Mareike busy!) but it means we can think about whether different types of finds have come from different areas and whether this might represent different kinds of activity.

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Processing finds on a rainy day. Image: Mareike

 

When the finds come off site they go through some basic processing. All of our students had a go at finds processing. This involves each find being entered into a database that records the finds number, the context number, the material the finds is made of, what it is, and how many of them there are. This data is then matched with the location data from the total station so we know where the finds came from. The contents of each bag is then photographed so that we have a big database of basic photos. Some finds, such as flint are gently cleaned before photographing. Others such as the burnt bone are left for Michelle, our osteologist, to clean.

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Sorting out some of the flint. Image: Mareike

Recording our excavation: samples

Author: Rachel

This week I want to talk a bit about the samples we took during our dig. We took two main types of samples during the dig this year. The first type were bulk soil samples. These are collected as buckets full of soil. We usually collect three buckets from every different context and feature we find on the site. These buckets are labelled with tags that detail where they have come from and what is inside them. Then they are sealed up with plastic lids to stop anything getting in or out! These samples will soon be floated. Flotation is an archaeological technique that allows us to effectively dissolve and wash away the soil to find out what other things are within the soil. Some things float out of the sample (hence the name!) and other things sink. Flotation can be a really good way to get at small finds (on the Iron Age digs on the Isle of Man at Ballanorris and Ballacagen we found lots of tiny beads using flotation), especially the tiny things that might be missed during digging. It is also a very effective way to get at environmental data such as seeds and charcoal which float when released from the soil. We are also able to collect the heavy elements that are within the soil which do not float, or dissolve, such as different types of rocks, any tiny stone tools (called micro-liths) and even fragments of bone.

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Flotation at Ballanorris Iron Age site.

 

As well as flotation we have taken geoarchaeology samples that have been handed over to Dr Lisa-Marie Shillito at Newcastle. Lisa-Marie is a geoarchaeologist. We took one sample, referred to as a column sample, where we effectively removed a vertical slice from the site. We use a drain pipe to do this, we cut off one side and then, once all the recording of the site was completed, we prepared a narrow area and dug into the walls of the trench to remove the sample. The sample is then clingfilmed and wrapped tightly within the drainpipe and labelled with all the relevant detail about where the sample has come from and what is within it. This sample is then characterised by Lisa-Marie who will write detailed soil descriptions and then send the sample off to be made into thin-sections ready for micromorphology. Micromorphology can reveal all sorts of information about the site – human activity can be identified and we can learn new things about how the soils have formed and been deposited (and re-deposited). From the same area as the column sample we take a smaller bag of loose earth from each type of soil. This bag provides soil suitable for magnetic and loss-on-ignition analysis that can also be used to interpret human activity at the site.

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Preparing to take the column sample. You can see we’ve selected the area. Image: Chris

 

Column sample 2
Preparing the sample. With the drain pipe in place and correctly labelled, we’ve dug behind the sample to remove it. Image: Chris.

Recording our excavation: drawings

Author: Rachel and Mareike

With drawings from: Chris, Eleanor, Eloise, Charlotte, Cathleen, Holly, Maddie, and Rachel

It might seem a bit old fashioned in the world of digital photographs, RTI, and 3D modelling but archaeologists still do a lot of drawing. We do two main types of drawings: plans and sections. Plans are drawings done from above: a bird’s-eye-view. Sections are drawings of the archaeological layers we dig through. Plans help us to understand the layout and extent of a site. Sections are particularly helpful when it comes to understanding the history of the site and working out how different events in the past have produced different layers in the site. Sections help us to work out how these relate to each other in time (i.e. what came first and what came after). All our drawings are to scale (either 1:20 or 1:10) and follow standard drawing conventions in archaeology. These are not artistic drawings aimed at giving an impression of the site but accurate drawings to capture data and represent the nature of the site.

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Drawing of a section of the site by Eloise and Eleanor. This drawing joins with others on either side. You can see all the individual rocks that have been drawn, the edges of the trench and the hachures (black triangles with tails) which indicate the shape of the slope of the site.

 

Drawings are not just representations though, they actively help us understand it. When you are carefully drawing the site (literally stone-by-stone) you are able to consider what it is you are looking at, how it was constructed or formed, and what it might be. Often more importantly, you have the power (and the pencil) to decide how the site will be represented – what you decide to emphasise and where you place boundaries between different features can go on to effect the overall interpretation of the site.

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Section drawing by Chris. This shows the different layers on the site and how they relate to each other. The light nature of these drawings is because they are completed on a type of tracing paper (so they can be layered) using a particularly light type if pencil.

 

Some drawings on site are completed using tapes strung between known-points on the site with measurements taken in relation to these known points (this is known as an off-set plan). Alternately when we are drawing complicated parts of the site with lots of details we use planning frames. These are meter square wooden or metal frames with internal divisions (usually at 20cm intervals) that help us to accurately (and hopefully quickly) draw the different features we can see. Drawings done with planning frames are also (crucially) related into the overall site grid. Some of our drawings might be of single parts of the site such as a pit or the cist (commonly referred to as single-context plans), these drawings all contain information on the spatial location of the feature and can be related to the overall site grid and layered together with other drawings to show the whole site effectively. We do all our drawings on a type of weather-proof paper called perma-trace so that we can layer them together. All the drawings also contain ‘spot heights’ these are points we have recorded the location and height of using the total station. Changes in the spot heights, together with the ‘hachures’ (black triangles with tails coming off them) can be used to interpret the varying shape of the ground.

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Off-set planning  underway on site. Image: Mareike

 

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Grid planning underway on site. Image: Mareike

 

Since we travelled back to the UK Mareike has been working hard digitising our plans from the site. We completed 25 drawings whilst on site so this has been a big task. The digitised drawings are excellent and will be used in up-coming blogs, in lectures and presentations and in the report about the excavation we are writing for MNH.

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Digitised section drawing. Drawn by Chris. Digitised by Mareike

 

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Overall Site plan. Drawn by Eloise, Eleanor, Cathleen and Charlotte. Digitised by Mareike