Dig Report 5

Interim Dig Report No. 5

Test Pit Trench 12 (TR12)

Plate 01:  Parch mark viewed eastward

Author: David .W. Savage BA Honours Humanities with History (Open University) MA Archaeology (University of Bristol) Certificate Humanities (Open University)

Interim report no.5 is to collate Test Pit 12 (TR12) east Glebe Field information

Contents                                                                                        page

1. Summary and Research Questions                                 3

2. Trench                                                                                         5

3. Stratification                                                                           15

4. Conclusion                                                                               16

5. Future objectives                                                                  16

6. Acknowledgements                                                             17

List of plates 

Number                                                                                             page

01Oblique ground view of parch mark                                            1

02 Drone vertical image                                                                    3

03 Base of context 05                                                                        6

04 Context 05 Potsherds                                                                   8

05 Context 04Compacted fill of land drain                                      9

06Context 04 Potsherds                                                                   10

07 Context 03 plan view image                                                        11

08Context 03 Potsherds                                                                   12

09 Context 02 Plan view image                                                        13

10.Context 02 Potsherds                                                                   14

11. Context 01 Artefacts                                                                    15

List of figures

Number                                                                                             page

1.      01 Resistivity survey                                                             4

2.      02 TR12 position upon Resistivity survey                          5

1.      03 Sketch Plan and levels of test pit                                    7

04  Land drain section and approx. dimension                       17

Summary and Research Questions

During the 2022 dig season very hot and dry conditions exposed linear parch marks on the east Glebe Field site, see Figure 01 and Plate02 below.

Plate02: Diagonal ‘parch marks’ leading to Siston Brooke on west side of image. 

The parch marks appear to be land drain channels, but construction and the period they were made could only be understood by excavating a test pit.  It was found they may date from the medieval period due to being local limestone build similar to the other structures in the Glebe Field but also as numerous medieval potsherds were found in and around the drain structure that was less than 160 to 200mm below ground level. For test pit TR12 position see Figure 2 below.

 Figure 01 Resistivity survey, note diagonal linear anomalies.

Questions

1. Why are the land drains there, especially on sloping ground?

2. What period do they belong? And do they relate to other features in the Glebe Field.

The Test Pit (TR12)

Figure 02: Test pit TR 12 position upon the resistivity survey. 

TR12’s position was chosen as the parch mark at this point cuts diagonally across the grids centreline and would be most easily located at a later date if necessary. 

Plate:03 Deepest extent of excavation Context 05 is S.E. and N.W. corners. Note capping stone removed west of direction arrow

Figure03: Sketch plan of 1mt x 1mt TR12 test pit

Context 05 is the areas to the north and south of the drain channel and is the deepest extent of the excavation either side of the land drain cutting diagonally across the test pit as can be seen in Fig. 03 and Plate 03 above. The North West corner was Datum 4 (D4) minus 1.840mts.  and is 70.962mts. ‘above sea level’. (Note: D4 adjacent to the brook running through the centre of the Glebe Field is 72.802 mts. ‘above sea level’). The ground conditions were very hard, the natural layer was at D4 minus 1.840 mts. and is heavy clay with mica and fine gravel; the colour is a light grey to green. Immediately above this is darker and heavy grey/ green clay material with tiny shell, ceramic and possibly iron oxide particles in it.

Plate04: Potsherds found within Context 05 mostly on the south edge of the drainage channel.

Nine potsherds were found in this context, see plate 04 above, one in particular was poorly fired and breaking up, the others were soft to hard material and slightly abraded but some having sharp edges. One piece, top right of Plate 04, had an incised pattern upon its outer surface.

Context 04 is within the confines of the drain channel, see figure 03 above. The channel was full with a fine sandy soil, mid grey/brown in colour that had been drawn through the dry stone construction; and apart from 1 larger piece it seems possible the potsherds found in the channel, were carried in over time by water movement along with the soil, or simply fell through gaps into the channel when possibly scattered there. See plate 05 and06 below. 

Plate 05: Compacted fill of land drain channel.

Plate06: Potsherds found within drain channel, Context 04.

The potsherds are soft to sub hard with a small amount of abrasion. The largest piece is hand made, light tan to grey with mild abrasion with a straight combed pattern; brown marks on its surface are probably caused by roots. 

Context03 is a purposefully placed layer of stone designed to gather and guide water to the drainage channel, see plate08 below to view before removal. Over time soil, clay and fines are brought down into the cavities and inevitably the drainage channel fills and ceases to function as such.  The subsoil material is dark brown – grey colour and was very dry and hard when dug.

Plate 07: Context 03, after partial removal of rubble overlay to drainage channel.

There were nearly 30 potsherds in amongst the stones and soil. All are medieval and generally speaking can be considered courseware, some are hand made, while some may be wheel finished; all are hard with no glaze with one rim section potsherd, see plate08 below.

Plate 08: Potsherds found in context 03

Context 2 was the subsoil layer removed to expose the placed rubble upon the drainage channel.  Similar to context 03 the subsoil material is dark brown to grey colour and was very dry and difficult to dig.

Plate 09: Context 02 placed rubble and stones to gather water to the drainage channel. 

The potsherds found in context 02 were quite distinct from the deeper contexts; this layer has some green glazed ware and courseware. Some have combing and are hard to very hard fabric. This may indicate a later phase of work or changes to the structure.

 Plate 10: Potsherds from Context 02.

Plate11: Context 01 Artifacts, typical of the Glebe Field dig so far.

The date range of the artefacts in this context is 18^th to early 20^th century. Some of the ceramic sherds show signs of secondary firing with bubbling to the glaze and delamination. The clay pipe, top left of Plate 10 above is possibly mid to late  18^th Century. Small lumps of coal are also regularly found in this layer elsewhere within the Glebe Field.  

Stratigraphy

For Stratigraphy changes see Contexts above. Stratigraphy layers align with Contexts except Context 04, which is purely a context confined to the drain channel. 

Conclusion

This test pit was very successful in determining the cause of the parch mark.  The structure was clearly designed and built to drain and guide water to the brook that runs ‘north to south’ through the Glebe Field.  The structure is crudely but effectively built and is close to the surface; see Figure 04 sketch below. But exactly to perform what task is not totally clear. It could be for a few possible reasons.

As the field is sloping the ground would not become waterlogged for any long period of time in the areas of the drains. So the water was possibly diverted to stop it drenching the lower part of the Glebe Field or simply to divert as much water as possible to the brook for any number of purposes, such as domestic, small scale industrial, fish weirs or watermills. The Glebe Field is on a Rhaetic /Heavy Clay boundary and springs can and do appear and disappear. It could be springs were causing problems, as they do some times today, and they needed to be diverted.

The land drain build echo’s other structure found in the west Glebe Field, for example, the curving drain in TR 11, the dry stonewalls in TR07 and the drystone lined pit in TR13. The finds are mostly medieval potsherd with possibly Saxo Norman courseware being the most prolific. Slightly unusually, very little bone and no metal objects were found compared to other test pits and trenches in the medieval contexts. However, it should be noted for a one square metre test pit nearly fifty potsherds were found and is a high number by any measure. It could be the potsherds were spread along the drain to aid the free draining nature of the backfill. Some of which, over time, have found their way into the main cavity of the land drain channel.

A great deal of effort went into making the drains, eleven in total.  This can only mean keeping the lower south areas of the Glebe manageably dry was very important or more water was needed westward and down stream.

Figure04:  Sketch of land drain structure. 

Future objectives

The main question, what are the linear parch marks has been answered however, it would be worthwhile uncovering at least one or two further small sections of the land drain to check for consistency. But more work is needed to understand the usefulness of their effect to the users and occupiers of the Glebe Field. 

6. Acknowledgements

- Alex Christofides     alexchristofides@hotmail.com

 Drone imagery and digital 3D modelling

- Community Archaeology on the Mendip Plateau (CAMP)

Contact: Pip Osbourne  https://www.camp-plateau.co.uk/home

Services: Pottery typology, artifact dating

- Mary Lennox, David Lambie and Mary Knight for Geophysical Surveying, digging the test pit and providing images   

- Shared Past

Contact: Mark Haworth https://sharedpast.org/

Services: Community group organisation and technical advice.