The Lyonesse Project: a study of the coastal and marine environment of the Isles of Scilly (OASIS ID cornwall2-58903)

Dan Charman, Charlie Johns, Kevin Camidge, Peter Marshall, Steve F Mills, Jacqui Mulville, Helen M Roberts, 2014

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https://doi.org/10.5284/1025045
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Dan Charman, Charlie Johns, Kevin Camidge, Peter Marshall, Steve F Mills, Jacqui Mulville, Helen M Roberts (2014) The Lyonesse Project: a study of the coastal and marine environment of the Isles of Scilly (OASIS ID cornwall2-58903) [data-set]. York: Archaeology Data Service [distributor] https://doi.org/10.5284/1025045

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Overview

Underwater survey as part of the Lyonesse Project

Six main types of work were involved in the Lyonesse Project: an audit of recorded and reported coastal and subtidal 'peat' exposures, auger and GPS surveys of the intertidal 'peat' sites; geophysical survey and diver inspection of the subtidal 'peats', sampling and palaeoenvironmental analysis of selected intertidal and subtidal sites; a programme of radiocarbon and optically stimulated luminescence (OSL) dating; and outreach to inform the public, disseminate results and encourage volunteer participation.

Two very successful fieldwork campaigns were carried out in 2009 and 2010. Samples for palaeoenvironmental analysis and scientific dating were recovered from seven intertidal sites, Porth Coose (St Agnes), Par Beach (St Martin's), Porth Hellick, Porth Mellon and Old Town Bay (St Mary's), Crab's Ledge and Bathinghouse Porth (Tresco) and two subtidal sites, St Mary's Road and Great English Island Neck, north of Nornour in the Eastern Isles. In addition, samples for OSL dating were taken from the Lower Moors on St Mary's.

A notable aspect of Scilly's historic environment is the presence of stone walls and other remains below high water, the result of low-lying land being submerged by the gradual rise in sea-level. The timing and nature of changing land areas and the separation of the individual islands has, in the past, been the subject of much conjecture and debate. Seventy-eight new radiocarbon dates and 15 new OSL ages were obtained for the Project and the new data provide a much more secure basis than previously existed for reconstructing the evolution of the islands during the Holocene.

The results corroborate existing evidence that in c 7000 cal BC Scilly was a single large island with a rapid rise in sea-level separating St Agnes, Annet and the Western Rocks from the main land mass by c 4000 cal BC. By c 2500 cal BC there was a major change with tidal flooding between the northern islands, although Tresco, Bryher and Samson remained joined. The late third and early second millennium BC saw the most rapid loss of land at any time in the history of Scilly, so that by c 1500 cal BC the pattern of islands was approaching that of today, but with the dramatic difference of a vast intertidal area of saltmarsh in what is now the islands' inner lagoon. However, much of this would have remained useful land, especially for grazing animal stock. After this point in time the rate of change slowed down significantly and it was not until there was an open channel north of St Mary's that the saltmarsh began to erode rapidly. The age depth model from the Crab's Ledge radiocarbon dates suggest this is likely to have occurred around cal AD 969±294. Scenarios for future sea-level rise suggest a major change in the character of Scilly with the loss of very large intertidal areas.

Beach survey as part of the Lyonesse Project

The Project's pollen data represent almost the entire last 13,500 years of vegetation history on Scilly providing a unique insight into the development of the landscape through the Holocene; set against the backdrop of changing sea levels. Overall, the islands' vegetation reflects the widespread climate changes in north-west Europe since the end of the last ice age. Woodland colonisation in the early Holocene was rapid and the island must have been largely forested during the Mesolithic (c 8500-4000 cal BC), with open ground created gradually by a combination of fire and flooding from rising sea levels. There was greater diversity in vegetation cover during the Neolithic (c 4000-2500 cal BC) but the islands have been largely open and probably well-used for grazing and cultivation from at least c 900 cal BC. The most significant vegetation changes since then are the introduction of exotic species for hedges, tree cover and crops from the mid nineteenth century.

Conventionally it has been considered that Scilly was not permanently settled until the Early Bronze Age although there is now increasing evidence for Mesolithic and Neolithic occupation. The Early Bronze Age (c 2000-1500 cal BC) is marked by a flourishing of burial and ceremonial monuments such as entrance graves, cairns and standing stones, resulting in one of the densest concentrations of megalithic monuments in Western Europe. The Later Bronze Age (c 1500-800 cal BC) and Iron Age (c 800 cal BC-cal AD 43) are characterised chiefly by settlements of substantial, stone-built roundhouses which replaced the less tangible domestic evidence of earlier periods. It is suggested that many of these sites which have a coastal location today were originally positioned so that they had a share of the valuable intertidal saltmarsh areas and also access to arable inland ground for crop husbandry, rather than for maritime reasons, and that the relict prehistoric upland and intertidal field systems of the islands enclosed pastures for summer grazing rather than arable cultivation.

From the Roman period (cal AD 43-410) long distance trade brought Scilly into the wider world; the shrine to a marine deity at Nornour, with its collection of Roman coins, brooches and other artefacts is one of the most iconic archaeological sites in the islands. During the early medieval period (cal AD 410-1066) a number of small insular hermitages were established by followers of the Early Christian church and from the twelfth century administration was divided between the monks of Tavistock Abbey who ruled over Tresco and the northern islands, and the secular lords who governed St Mary's and St Agnes from Ennor Castle. During the mid sixteenth century the islands became strategically important in the defence of England, being successively fortified over almost 350 years. The sea, the coast and the intertidal zone continued to shape the post-medieval island economy and this is reflected in the historic environment record. As well as kelp pits, gigsheds and smugglers' caches, there are ruined quays and slipways, a seventeenth century day mark, four lighthouses and an eighteenth century isolation hospital.

The results of the project will be presented in a monograph publication, funded by English Heritage, in autumn 2014.