NHER 62661 (Monument record) - Middle to Late Saxon salt industry and post-medieval features

February-March 2017. Trial Trenching and Borehole Survey.
Evaluation of two proposed development areas (Lynnsport 4 and 5).
The trenches excavated to the north of Greenpark Avenue revealed evidence associated with salt production at two separate locations. At the first, in the westernmost part of the site (now designated Saltern 1), the features exposed included a truncated, clay-lined pit that was probably a filtration unit associated with brine production and the equally truncated remains of a brine-boiling hearth. Layers of burnt hearth waste and probable filtration unit waste were also identified. Similar deposits were identified in a trench in the eastern half of this site along with a pit containing burnt material that was probably waste from a brine-boiling hearth (Saltern 2).
The central trench of the three excavated to the south of Greenpark Avenue revealed another deposit that was believed to represent salt filtration waste, indicating the presence of a third area associated with salt production (now designated Saltern 3).
Although these various features and deposits produced a large amount of fired clay that would have been associated with salt production, no artefacts were recovered that could suggest a possible date for this activity.
The small number of later features included two narrow ring-gullies that were interpreted as the drainage channels associated with post-medieval hayricks; the only finds recovered being fragments of clay tobacco pipe. Other post-medieval features included a row of pits identified to the east of the ring-gullies that were interpreted as orchard tree pits, two of which also produced fragments of clay tobacco pipe.
Two ditches of obviously modern date were also exposed in one of the trenches excavated to the south of Greenpark Avenue.
As part of this evaluation a series of boreholes were drilled, the results of which were combined with those from an earlier geotechnical survey to establish a detailed deposit model for the site. The earliest deposit encountered was the Kimmeridge Clay bedrock, which was overlain by a dense brown sand and gravel, above which was a dark brown peat deposit (the latter radiocarbon dated to the Iron Age during recent work in the vicinity). This organic layer was overlain by a firm bluish grey silty clay likely to represent a marine tidal flat deposit. The layers of material associated with the saltern sites lay above this marine clay and were in turn sealed by a light brown silty clay believed to represent an alluvial deposit lain down in a low energy, more brackish or freshwater environment - almost certainly during the medieval period. The overlying subsoil and topsoil deposits are thought to have formed during the post-medieval period, after this land was drained.
See report (S1) for further details.
P. Watkins (HES), 16 April 2018.

April-May 2017. Excavation.
Three separate areas were excavated in the area to the north of Greenpark Avenue, which targeted Saltern 1 and Saltern 2 (Areas A and C respectively) and the two probable hayrick gullies (Area B).
A range of additional features associated with salt production were exposed at the two probable saltern sites. Significantly, evidence recovered during this phase of work allows the salt industry at this site to be reasonably firmly dated to the Saxon period with calibrated radiocarbon dates of 684-878 AD, 720-945 AD, 772-968 AD and 777-985 AD obtained for material recovered from various deposits associated with the two salterns (all 95% probability; SUERC-75156, SUERC-75157, SUERC-75161 and SUERC-75162). These Middle to Late Saxon dates are consistent with the small number of artefacts recovered from saltern contexts, which include several sherds of Late Saxon pottery and a glass bead of probable Saxon date. There is also a notable absence of later, medieval material.
The remains associated with Saltern 1 are thought to represent two distinct phases of activity and included clay-lined features and hearth rake-out pits (one of which was probable associated with the hearth excavated during the evaluation). The clay-lined features are thought to represent the remains of filtration units that were used to generate brine. The most complete example comprised a sub-circular, flat-based filtration pit with a channel connecting it to a much deeper, circular water tank with a concave base. Elsewhere it appears that only the deeper tank element had survived. A silty sand deposit overlying these features almost certain represents waste from silt filtration. Several substantial circular clay-lined tanks associated with the second phase of activity were probably tanks used to store the brine generated by filtration units and were located close to the brine-boiling hearths.
At Saltern 2 there was also evidence for two phases of salt-making activity. Here the features associated with salt-production included several clay-lined probable filtration units. Although no hearths survived the pit containing probable hearth rake-out identified at this location during the evaluation demonstrates that at least one had originally lain nearby.
A total of 364 fragments of fired clay were recovered from saltern contexts during the two phases of work, including ten pieces could be identified as either fragments of brick-like objects or pieces of hearth lining. Unlike the briquetage associated with earlier salt industries no pan fragments were present suggesting that metal pans had almost certainly been used.
Several sediment samples were processed and examined for ostracods, the most notable result being the identification of cypideis torosa within one of the filtration units associated with Saltern 1 and presumed be represent a population actually living within the tanks. Its presence indicates water that was of moderate to high salinity but not concentrated enough to be a proper brine. It is therefore likely that this liquid would have been subsequently evaporated to brine within another tank prior to being boiled.
As during the preceding work there was little evidence for activity on the site after the Late Saxon period, with all of the small number of later features likely to be of post-medieval or modern date. Excavation Area B fully exposed the two probable hayrick gullies, which were both c.10m in diameter. The relatively recent date of the features was confirmed by the recovery of a clay tobacco pipe bowl and a post-medieval roof tile. The western ring-gully also appeared to truncated a group of three parallel elongated pits which also produced post-medieval finds (including pottery of 19th-century date). Several post-medieval features were also identified in excavation Area A, including a pit containing a horse burial and a line of four post-holes that probably represented the remains of a fence. Both the pit and one of the post-holes also produced pottery of 19th-century date.
A topographic survey of the whole proposed development carried out during this phase of work identified four discrete areas of higher ground, three of which correspond with the known saltern sites. The forth, at the northern edge of the site, almost certainly indicates the location of a fourth, as yet uninvestigated saltern mound (designated Saltern 4).
See assessment report (S1) for further details. The results of this work are also summarised in (S2).
P. Watkins (HES), 16 April 2018. Amended A. Cattermole (King's Lynn UAD), 18 July 2019.