Post-medieval kelp pit on the western coast of Tinkler's Hill, St Martin's


Heritage Category: Scheduled Monument

List Entry Number: 1013810

Date first listed: 17-Jan-1996


Ordnance survey map of Post-medieval kelp pit on the western coast of Tinkler's Hill, St Martin's
© Crown Copyright and database right 2018. All rights reserved. Ordnance Survey Licence number 100024900.
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This copy shows the entry on 19-Dec-2018 at 16:22:56.


The building or site itself may lie within the boundary of more than one authority.

District: Isles of Scilly (Unitary Authority)

Parish: St. Martin's

National Grid Reference: SV 91591 16500


Legacy Record - This information may be included in the List Entry Details.

Reasons for Designation

The Isles of Scilly, the westernmost of the granite masses of south west England, contain a remarkable abundance and variety of archaeological remains from over 4000 years of human activity. The remote physical setting of the islands, over 40km beyond the mainland in the approaches to the English Channel, has lent a distinctive character to those remains, producing many unusual features important for our broader understanding of the social development of early communities. Throughout the human occupation there has been a gradual submergence of the islands' land area, providing a stimulus to change in the environment and its exploitation. This process has produced evidence for responses to such change against an independent time-scale, promoting integrated studies of archaeological, environmental and linguistic aspects of the islands' settlement. The islands' archaeological remains demonstrate clearly the gradually expanding size and range of contacts of their communities. By the post- medieval period (from AD 1540), the islands occupied a nationally strategic location, resulting in an important concentration of defensive works reflecting the development of fortification methods and technology from the mid 16th to the 20th centuries. An important and unusual range of post- medieval monuments also reflects the islands' position as a formidable hazard for the nation's shipping in the western approaches. The exceptional preservation of the archaeological remains on the islands has long been recognised , producing an unusually full and detailed body of documentation, including several recent surveys. Kelp pits are small slab-lined hollows in which seaweed was burnt to produce soda-ash rich in sodium carbonate: this was required chiefly for the manufacture of glass, as well as soap and alum. The term `kelp' is the common name for the seaweed burnt, and also for the ash product of the burning. Kelp pits are generally 1m-1.5m in diameter and 0.4m-0.7m deep, and are lined with flat slabs which sometimes show reddening due to the intense heat to which they were subjected. Occasionally the slab lining projects slightly above the surrounding ground level and traces of an outer stone ring may be present. The process involved seaweed being gathered from the coastline, dried, then burnt in the kelp pits, which were located near the shoreline. Once cooled, the solidified ash was removed from the pit and stored ready for shipment to regional ports. Kelp burning was carried out on a domestic scale, the sale of the ash to merchants supplementing the island families' incomes. Soda production by this method was introduced to south west England from France in the early 1680s. Initially centred at Falmouth, Cornwall, the production moved in 1684 to the Isles of Scilly where the national distribution of its recorded remains is confined. From about 1720, kelp burning spread north along the western coast of Britain to Wales and particularly to western Scotland. Kelp burning on Scilly became uneconomic in the early 19th century due to competition from cheaper imported soda-ash, while the establishment of the method to convert salt to soda on an industrial scale effectively ended the practice. The last kelp burning on the Isles of Scilly was recorded in 1835. Only about a dozen kelp pits on the islands are known to survive from over 100 recorded at the height of kelp burning. Together with traces of small quays near surviving kelp pits and the remains of the dwelling of the Nance family, who brought kelp burning to the islands, kelp pits form the major field evidence for this former distinctive contribution to the nation's economy.

This kelp pit below Tinkler's Hill has survived well, with no evident disturbance. Its location illustrates well the often isolated coastal setting of kelp pits, situated close to the richest supplies of seaweed.


Legacy Record - This information may be included in the List Entry Details.


The monument includes a post-medieval kelp burning pit situated on the coastal margin at the foot of the western slope of Tinkler's Hill, on western St Martin's in the Isles of Scilly. The kelp pit is visible as a rounded hollow, shaped as an inverted bowl, measuring 1.5m east-west by 1.4m north-south and up to 0.5m deep. The hollow is neatly lined by granite slabs ranging from 0.25m to 0.45m across. The kelp pit is situated 3.5m from the edge of the 3m-4m high coastal cliff below Tinkler's Hill. Here it overlooks the boulder shores facing Tean Sound, typical of the sites favoured for gathering seaweed.

MAP EXTRACT The site of the monument is shown on the attached map extract. It includes a 2 metre boundary around the archaeological features, considered to be essential for the monument's support and preservation.


The contents of this record have been generated from a legacy data system.

Legacy System number: 15423

Legacy System: RSM


Books and journals
Over, L, The Kelp Industry in Scilly, (1987)
Thorpe, C/CAU, AM 107 for Scilly SMR entry PRN 7189, (1988)
Title: 1:2500 Ordnance Survey Map; SV 9116 Source Date: 1980 Author: Publisher: Surveyor:
Title: 6": 1 mile Ordnance Survey Map; SV 91 NW Source Date: 1963 Author: Publisher: Surveyor:

End of official listing