MARINE MOLLUSCS Introduction Chronology of the Samples
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APPENDIX G: MARINE MOLLUSCS by Greg Campbell Introduction This section presents the analysis and conclusions based on the 28,980 identifiable items of marine invertebrate organism recovered from 49 samples of the 22 deposits recognized as containing this type of remains. Of the identifiable items, 3400 were quantified by their dimensions, producing a dataset of approximately 10,000 measurements. While not all the assemblage was weighed, quantification by weight to the nearest gram was undertaken for 16.5 kg of these remains and of associated material, producing a dataset of approximately 320 weights. Chronology of the samples Of those deposits with samples containing shell, the earliest is from the Iron Age layer 644 in the south part of Trench 41, from the La Tène final period (c.120–c.50 BC). Shell-bearing samples from the early Roman Empire (c.50 BC–AD 260) came from two successive shell- rich layers (643 followed by 646) in the south corner of the building formed by walls F726 and F731 in the south part of Trench 41. Shell-bearing samples from the Gallic Empire (AD 260–AD 600) came from the base fill 523 of feature F600 pre-dating the gate structure in Trench 38, and from the very large shallow pit F1081 in the plot of land to the rear of post- built structure F1000 in the central part of Trench 41. Samples were taken from the pit’s initial fill 700 (rich in sea urchins), later fill 685, and final fill 681 (Sample 682 from its north part, and Sample 678 from its southern part and probably later, as the pit seems to have been filled in from the north side). The sole shell-bearing sample from the early medieval came from layer 708, the final activity within the complex of walls of possible ecclesiastical structures in the north part of Trench 41. This layer has been radiocarbon dated to 666– 775 AD (95% probability, calibrated). Most shell-bearing samples came from the high medieval period (AD 1000–1500). Within the south-east part of Trench 41, deposit 634 was one of two shell-rich spreads which lay in the patches of rubble E of the postulated oval building defined by wall F623, and was limited to the south-west by curb F725. Shell-bearing layers 557 and 558 lay in the patches of rubble south-west of the curb and south of the oval building. Further to the south, on the flat area defined by earlier (Roman) rubble spread 552 and wall F726, were the two successive deposits 586 and 560 separated by a rubble layer 578 associated with the walls F676, F677, F629. In the same area lay the extensive spread of cockles and mussels 569 (referred to by this author as ‘the East midden’). These were all relatively early in the high medieval period, as was the earlier part of a long sequence of shell-rich deposits (beginning with layer 581, followed by 585, then 561 and ending with 543) in the extreme southern part of Trench 41 in the area between medieval structures and the remains of the rampart. This sequence formed what this author called ‘the South midden’. To the south of Trench 41, in Trench 6 in Parcelle 20, shell-bearing high medieval samples were taken from layer 219 within Building 4, from layer 217 within the succeeding Building 6, and from external layer 204. Also in Parcelle 20, a shell-bearing sample was taken from late medieval deposit 451 in Trench 34. Research aims During the first seasons of excavation, several deposits from a range of periods were observed to be rich in marine shell. In 1998 four shell-rich medieval deposits were sampled (contexts 204, 217, 219, 451), and analysis showed that shells were preserved well enough at the site for identifications and measurements to be useful. From these results a number of questions emerged for later years in the excavation programme. The aims were • to study the changes through time in the broad strategies used to collect shellfish (such as parts of the sea exploited), and to study the changes through time in the role of shellfish (such as changes in culinary preferences or the overall contribution of shellfish to the diet); • to study changes through time in the tactics used by collectors during specific episodes of collecting shellfish (the methods of extraction, the selection criteria for the various types of shellfish, or the tidal zone exploited for a particular type); • to determine whether the shell-rich deposits are tips or middens. At Le Yaudet shells are preserved only in shell-rich deposits. Typical deposits containing normal or average types and quantities of rubbish have lost their shell content through leaching. So the typical types and quantities of shellfish being used at various periods must be inferred from the rich deposits rather than observed directly. A deposit is rich in shell for one of two reasons. It is either a discrete tip (containing shell discarded as a mass from a single distinct event in the past, such as a feast), or it is a midden (containing shell discarded at the same place from a large number of successive events in the past). Discrete tips contain data directly relevant to tactics and indirectly to strategy. Middens contain data directly relevant to broad strategy, but must be dissected into something approximating individual discard events to investigate tactics. Sampling methods During the excavation programme large samples of the usual size (30 litres where available) were taken from the bulk of almost any deposit clearly containing shell. Such bulk samples were taken to recover data regarding past strategies by collecting a broad enough range of marine remains to include those that are quite rare. The aim was the recovery of about 2400 items in each large sample, so that the actual proportion of any particular shell type in the deposit would lie within 2 percentage points either side of the value estimated for that proportion by the sample, in 19 of every 20 samples (Veen and Fieller 1982, 296). During the 2000 excavations extensive and thick shell layers were exposed and bulk sampled, and these were more finely sampled in 2001. A column 10 cm square in plan was excavated from the late medieval shell accumulation at the south baulk of Trench 41 (contexts 581, 565, 561, 543), with each 5 cm increment of depth collected as a sample. A distinct lens of shell within 581 but pre-dating the column was also collected. A similar incremental column 10 cm square in plan was excavated in late medieval shell accumulation 569 in the east baulk, where the deposit had been protected from contamination by the stone footing 618 and rubble layer 552. The late medieval shell spread 634 was sampled by excavating 15 cm squares 50 cm apart along a N-S line at its widest point. It had been hoped that sampling would include at least one 15 x 15 x 5 cm incremental unit from all shell-rich deposits revealed in the 2001 and 2002 seasons. Similar small samples similar in weight to a typical incremental sample (3.0 kg) were taken from several bulk samples where it was clear the deposit had not been incrementally sampled. These small samples were taken to study the nature of the deposits by recovering data on • non-shell material: the amounts of soil, artefacts and stones being incorporated will vary during the accumulation of a midden, and therefore will vary with depth within the deposit. As middens are exposed for longer than discrete tips, the amount of non- shell material in an incremental sample will be relatively high in a midden and low in a tip, except for the upper surface where such incorporation will be similar; • shell richness: this varying in the incorporation of non-shell material also means that the proportion of shells to non-shell material will vary during the accumulation of a midden, and therefore will vary with depth within the deposit. As middens are exposed for longer than discrete tips, the proportion of shell to non-shell material in an incremental sample will be relatively low in a midden and high in a tip, except for the upper surface where such incorporation will be similar; • shell fragmentation: Shells exposed to the elements will have been eroded by leaching and been broken up by forces such as frost action, roots, and trampling. As shells in a midden are exposed for longer during its accumulation, they should be recognizably fragmented throughout its depth. For a particular kind of shell within a particular incremental sample, the ratio of weight of shell in the 10–6 mm size range to the weight in the >10mm range will be relatively large. In contrast, a discrete tip will have been exposed only on its upper surface, so fragmentation (as measured by the same weight ratio) will be relatively low, and highest at the surface. These small samples were also taken to recover data regarding tactics of collection by statistical analysis of measurements taken from each kind of shell. Meat yield is proportional to shell size, so it will be possible to trace changes through time in the residents’ trade-off between palatability and meat yield within a type of shellfish, and between types of shellfish. Differences in shell form revealed by these shell measurements can be related to differences in habitat, and therefore to position in the tidal range. Such samples should be large enough to contain statistically usable amounts of marine remains, while being small enough to relate to individual collection events.