A scatter of tin ingots was found in 1991/2 near West Mary's Rocks by divers. The location indicates loss from a ship or perhaps a wreck site. Detailed investigation has not been possible owing to sediment accumulation over the site since its initial discovery. The ingots are very rare and although it has not been possible to date the finds, the range of shapes and weights suggest they were made before 1000 BC, but the method of working suggests that they may be as early as the Bronze Age.
Although the ingots were found in association with some timber, this is believed to be evidence of a submarine forest rather than of a shipwreck. The site itself is thought to represent a vessel involved in the export of tin, an industry known in south-western England from an early period.
Crudely cast tin ingots were found by chance in the Erme estuary during visual and metal-detector surveys of the area during 1991/2 Over forty tin ingots have so far been recorded and recovered.
Three large pieces of wood, thought to be hull fragments, were found embedded in the seabed close to the ingots. These were radiocarbon dated and found to be of quaternary date. It is likely that the wood is associated with a submerged forest known to exist around the coast.
Designation Order: (No 3), No 2895, 1993
Made: 24th November 1993
Laid before Parliament: 25th November 1993
Coming into force: 26th November 1993
Protected area: 100 metres within 50 18.15 N 03 57.41 W
No part of the restricted area lies above the high-water mark of ordinary spring tides.
The almost pure tin ingots were discovered by members of the South-West Maritime Archaeology Group on the landward side of West Mary's Rocks in 1991/2 at a depth of about 10 metres. The site is centred on a gently sloping area of shingle with broken rock on the sheltered north side of a 3 metre high reef adjacent to the site, which almost breaks the surface at low water. Much of the shingle is covered in sand while the reef and larger rock fragments are covered in kelp and other weed.
Initially, seven ingots were recovered but following visual and metal-detector surveys of the area, over 40 tin ingots have so far been recorded and recovered. The ingots were made from a mould in earth or sand with one side being flat: This method of ingot manufacture dates back to the Bronze Age. The ingots are of various sizes ranging from 41cm long, 21cm wide, 6.5cm deep weighing 13 kilos to a smaller 7.8cm, weighing less than a quarter of a kilo.
The ingots are difficult to date without any associated evidence: They could be as early as the Bronze Age or as late as the medieval period, but parallels from other sites, notably in France, suggest a probable late Roman date. In July 2002, the ingots were donated to the Royal Albert Memorial Museum, Exeter. From the number, concentration, and location of the ingots, it appears fairly clear that they were being carried in a vessel and that any associated shipwreck was involved in the export of tin mined from the local area, the same area also being known for the import of wines, with associated amphora finds.
Three large timbers found embedded in the seabed close to the ingots were radiocarbon-dated at 6305+/- 50 BP and 6270 +/- BP and are thought to be evidence of a submerged forest since they predate the tin industry.