Selected text from The Archaeology Coursebook-Pt3
[These posts are excepts from The Archaeology Coursebook by Jim Grant, Sam Gorin and Neil Fleming. This is an introductory text book which should prove useful in writing about archeologocal methods for stargate fic.]
(Note: Excerpts from the complete text)
Excavation-Part Three:Trenches, Test Pits, and Area Excavation
How to dig?
The excavation methodology debate centres on the fact that all sites have two key elements. A vertical sequence of layers containing structures and finds, and the horizontal layout of an occupation area or individual structure. It is difficult for a method to explore both equally well but to record both elements is vital.
Unless the archaeologist can establish the correct succession of levels an excavation will have limited, if any, value. Similarly the inability to produce the plan (layout) of a building or a cemetery leaves the researcher well short of the required results. Archaeologists have therefore developed a series of methods appropriate to different types of site.
Trenches and test pits
The term ‘trench’ has been applied to any linear excavation and sometimes to any hole cut into the ground by archaeologists, whatever its surface shape. A stricter definition is a rectangular shaped excavation of variable width and length.
Test pits or ‘sondages’ are essentially square trenches, usually 1 metre square. Trenches and test pits are used either to evaluate the stratig¬raphy of a site before a decision is made on whether or not to excavate or as part of an excavation sampling strategy.
By digging down either to bedrock or the top of the archaeological deposits the vertical profile of part of the site can be examined. This provides information about depth of deposits and complexity of contexts. It can also provide an opportunity for sampling environmental remains.
Figure 2.8 A section cut across a feature to reveal its profile in section. The depth and shape of the feature can be determined as well as its fill and any stratigraphy.
Sometimes mechanical diggers are used to dig part or all of the trench in which case the trench width is determined by the dimensions of the digger’s bucket.
Those of you who have watched the TV programme ‘Time Team’ will be familiar with the use of trial trenches to investigate possible features identified by reconnaissance methods. This is also done on many sites after ‘top-stripping’ of topsoil [...].
In very large sites trenches are used to investigate linear archaeological features such as defensive earthworks by being placed at 90° to the alignment of the feature. The trenches cut by Alcock through the defences of South Cadbury hill fort in Somerset provide a classic example.
By strategically placing a series of 2-metre wide trenches around the hill he was able to study and report on the developmental sequence of the site’s fortifications. This had the added bonus of disturbing a small proportion of the site in return for a large volume of evidence. Most of the site was left undamaged for future archaeologists.
Other linear features such as roads and boundaries can be cross-sectioned in this way. Offa’s Dyke, an early medieval feature running from north to south Wales, has been the focus of a long-term study by Manchester University and over 100 trenches have been put across it to check and confirm details of its construction.
Sometimes test pitting is the main method used. The site is gridded with 1 metre squares and sampling used to select a number of locations to dig. This produces a series of vertical profiles across the site which gives some idea of the horizontal plan.
On very shallow sites with little stratigraphy, shovel pit testing [...] is sometimes used for this. Cutting lots of test pits or trial trenches into a site is quick, cheap and provides valuable information about stratigraphy. For this reason they are the most common type of excavation in the UK. However, they are relatively poor as a means to understand how a site fitted together.
Area Excavation
This is the most common form of excavation of whole sites as can be seen in most reports or archaeological magazines. ‘Area’ or ‘open-stripping’ occurs where the extent of the features to be uncovered determines the size of the excavation.
This does not mean that whole sites are always laid bare. This can be an outcome but more frequently other factors limit the total recovery of evidence or perhaps development only threatens part of the site and the rest is left ‘in situ’. On some research digs such as those run by universities digging may take place over several seasons. Different parts of the site are dug and recorded each year. [...]
Finally there may be research considerations. Only a sample of the site may be needed to answer the director’s questions. Financial con¬straints may limit the amount of digging. Although destructive, area excavation has become the key approved method for several reasons.
• Complete structures can be studied.
• Complex relationships between features can be clarified.
• It provides excellent recording possibilities.
• A total understanding of horizontal relation¬ships is possible.
Figure 2.9 An area excavation of the Anglo-Saxon site at West Heslerton showing that extensive features are preserved just below the surface of the ground. Attempting to interpret these features without excavation could be very misleading
Figure 2.10 The training dig [...] on this Romano-British site has adopted an area approach. Once topstripped the individual features such as the ditch in the foreground are sectioned or excavated. Barrow runways ensure spoil is quickly and safely removed and protect the surface.
When area excavation became fashionable there was criticism from those traditionalists who had used trenches. The sides of trenches have the advantage of revealing the vertical sequence of deposits (stratigraphy*) and there was concern that this essential record might be lost. The depth of deposits can vary and the issue is of great significance where the stratification is deeper and more complicated. This problem can be addressed by leaving baulks (undug strips of ground) at strategic points or, increasingly, by carefully recording the horizontal picture of a site layer by layer and feeding the data into a computer. This can be interrogated to produce sections along any chosen line. The problem is that without baulks no check is left in place if the director wishes to refer back, so the recording systems must be of the highest quality.
Figure 2.11 Recording a section across an excavated ditch. This approach to features is typical of area excavations. The planning frame against the vertical section helps the recorder to produce an accurate profile on gridded paper. The context labels on the face of the section ensure that slight changes in the fill which might be very difficult to see or photograph are recorded.
Note: I'm not sure when Area excavations started to be done, but I did find reference elsewhere to 'an example of new excavation techniques being applied' as being some large area excavations done in the 60's and 70's. I have only found the one mention so far, but it would seem that this would be common practise under some circumstances by the 80's.
More on this Trenches, Test Pits, and Area Excavation later.
*From Wikipedia:
Stratification is a paramount and base concept in archaeology, especially in the course of excavation. It is largely based on the Law of Superposition. When archaeological finds are below the surface of the ground (as is most commonly the case), the identification of the context of each find is vital in enabling the archaeologist to draw conclusions about the site and about the nature and date of its occupation. It is the archaeologist's role to attempt to discover what contexts exist and how they came to be created. Archaeological stratification or sequence is the dynamic superimposition of single units of stratigraphy, or contexts.
Contexts are single events or actions that leave discreet, detectable traces in the archaeological sequence or stratigraphy. They can be deposits (such as the back-fill of a ditch), structures (such as walls), or "zero thickness surfaciques," better known as "cuts." Cuts represent actions that remove other solid contexts such as fills, deposits, and walls. An example would be a ditch "cut" through earlier deposits. Stratigraphic relationships are the relationships created between contexts in time, representing the chronological order they were created. One example would be a ditch and the back-fill of said ditch. The temporal relationship of "the fill" context to the ditch "cut" context is such that "the fill" occurred later in the sequence; you have to dig a ditch before you can back-fill it. A relationship that is later in the sequence is sometimes referred to as "higher" in the sequence, and a relationship that is earlier, "lower," though this does not refer necessarily to the physical location of the context. It is more useful to think of "higher" as it relates to the context's position in a Harris matrix, a two-dimensional representation of a site's formation in space and time.
More on stratification in my next post.
(Note: Excerpts from the complete text)
Excavation-Part Three:Trenches, Test Pits, and Area Excavation
How to dig?
The excavation methodology debate centres on the fact that all sites have two key elements. A vertical sequence of layers containing structures and finds, and the horizontal layout of an occupation area or individual structure. It is difficult for a method to explore both equally well but to record both elements is vital.
Unless the archaeologist can establish the correct succession of levels an excavation will have limited, if any, value. Similarly the inability to produce the plan (layout) of a building or a cemetery leaves the researcher well short of the required results. Archaeologists have therefore developed a series of methods appropriate to different types of site.
Trenches and test pits
The term ‘trench’ has been applied to any linear excavation and sometimes to any hole cut into the ground by archaeologists, whatever its surface shape. A stricter definition is a rectangular shaped excavation of variable width and length.
Test pits or ‘sondages’ are essentially square trenches, usually 1 metre square. Trenches and test pits are used either to evaluate the stratig¬raphy of a site before a decision is made on whether or not to excavate or as part of an excavation sampling strategy.
By digging down either to bedrock or the top of the archaeological deposits the vertical profile of part of the site can be examined. This provides information about depth of deposits and complexity of contexts. It can also provide an opportunity for sampling environmental remains.
Figure 2.8 A section cut across a feature to reveal its profile in section. The depth and shape of the feature can be determined as well as its fill and any stratigraphy.
Sometimes mechanical diggers are used to dig part or all of the trench in which case the trench width is determined by the dimensions of the digger’s bucket.
Those of you who have watched the TV programme ‘Time Team’ will be familiar with the use of trial trenches to investigate possible features identified by reconnaissance methods. This is also done on many sites after ‘top-stripping’ of topsoil [...].
In very large sites trenches are used to investigate linear archaeological features such as defensive earthworks by being placed at 90° to the alignment of the feature. The trenches cut by Alcock through the defences of South Cadbury hill fort in Somerset provide a classic example.
By strategically placing a series of 2-metre wide trenches around the hill he was able to study and report on the developmental sequence of the site’s fortifications. This had the added bonus of disturbing a small proportion of the site in return for a large volume of evidence. Most of the site was left undamaged for future archaeologists.
Other linear features such as roads and boundaries can be cross-sectioned in this way. Offa’s Dyke, an early medieval feature running from north to south Wales, has been the focus of a long-term study by Manchester University and over 100 trenches have been put across it to check and confirm details of its construction.
Sometimes test pitting is the main method used. The site is gridded with 1 metre squares and sampling used to select a number of locations to dig. This produces a series of vertical profiles across the site which gives some idea of the horizontal plan.
On very shallow sites with little stratigraphy, shovel pit testing [...] is sometimes used for this. Cutting lots of test pits or trial trenches into a site is quick, cheap and provides valuable information about stratigraphy. For this reason they are the most common type of excavation in the UK. However, they are relatively poor as a means to understand how a site fitted together.
Area Excavation
This is the most common form of excavation of whole sites as can be seen in most reports or archaeological magazines. ‘Area’ or ‘open-stripping’ occurs where the extent of the features to be uncovered determines the size of the excavation.
This does not mean that whole sites are always laid bare. This can be an outcome but more frequently other factors limit the total recovery of evidence or perhaps development only threatens part of the site and the rest is left ‘in situ’. On some research digs such as those run by universities digging may take place over several seasons. Different parts of the site are dug and recorded each year. [...]
Finally there may be research considerations. Only a sample of the site may be needed to answer the director’s questions. Financial con¬straints may limit the amount of digging. Although destructive, area excavation has become the key approved method for several reasons.
• Complete structures can be studied.
• Complex relationships between features can be clarified.
• It provides excellent recording possibilities.
• A total understanding of horizontal relation¬ships is possible.
Figure 2.9 An area excavation of the Anglo-Saxon site at West Heslerton showing that extensive features are preserved just below the surface of the ground. Attempting to interpret these features without excavation could be very misleading
Figure 2.10 The training dig [...] on this Romano-British site has adopted an area approach. Once topstripped the individual features such as the ditch in the foreground are sectioned or excavated. Barrow runways ensure spoil is quickly and safely removed and protect the surface.
When area excavation became fashionable there was criticism from those traditionalists who had used trenches. The sides of trenches have the advantage of revealing the vertical sequence of deposits (stratigraphy*) and there was concern that this essential record might be lost. The depth of deposits can vary and the issue is of great significance where the stratification is deeper and more complicated. This problem can be addressed by leaving baulks (undug strips of ground) at strategic points or, increasingly, by carefully recording the horizontal picture of a site layer by layer and feeding the data into a computer. This can be interrogated to produce sections along any chosen line. The problem is that without baulks no check is left in place if the director wishes to refer back, so the recording systems must be of the highest quality.
Figure 2.11 Recording a section across an excavated ditch. This approach to features is typical of area excavations. The planning frame against the vertical section helps the recorder to produce an accurate profile on gridded paper. The context labels on the face of the section ensure that slight changes in the fill which might be very difficult to see or photograph are recorded.
Note: I'm not sure when Area excavations started to be done, but I did find reference elsewhere to 'an example of new excavation techniques being applied' as being some large area excavations done in the 60's and 70's. I have only found the one mention so far, but it would seem that this would be common practise under some circumstances by the 80's.
More on this Trenches, Test Pits, and Area Excavation later.
*From Wikipedia:
Stratification is a paramount and base concept in archaeology, especially in the course of excavation. It is largely based on the Law of Superposition. When archaeological finds are below the surface of the ground (as is most commonly the case), the identification of the context of each find is vital in enabling the archaeologist to draw conclusions about the site and about the nature and date of its occupation. It is the archaeologist's role to attempt to discover what contexts exist and how they came to be created. Archaeological stratification or sequence is the dynamic superimposition of single units of stratigraphy, or contexts.
Contexts are single events or actions that leave discreet, detectable traces in the archaeological sequence or stratigraphy. They can be deposits (such as the back-fill of a ditch), structures (such as walls), or "zero thickness surfaciques," better known as "cuts." Cuts represent actions that remove other solid contexts such as fills, deposits, and walls. An example would be a ditch "cut" through earlier deposits. Stratigraphic relationships are the relationships created between contexts in time, representing the chronological order they were created. One example would be a ditch and the back-fill of said ditch. The temporal relationship of "the fill" context to the ditch "cut" context is such that "the fill" occurred later in the sequence; you have to dig a ditch before you can back-fill it. A relationship that is later in the sequence is sometimes referred to as "higher" in the sequence, and a relationship that is earlier, "lower," though this does not refer necessarily to the physical location of the context. It is more useful to think of "higher" as it relates to the context's position in a Harris matrix, a two-dimensional representation of a site's formation in space and time.
More on stratification in my next post.