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

A Scheduled Monument in St. Martin's, Isles of Scilly

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Latitude: 49.9688 / 49°58'7"N

Longitude: -6.3025 / 6°18'8"W

OS Eastings: 91590.846377

OS Northings: 16499.657849

OS Grid: SV915164

Mapcode National: GBR BXTR.XMH

Mapcode Global: VGYBY.P1ZR

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

Scheduled Date: 17 January 1996

Source: Historic England

Source ID: 1013810

English Heritage Legacy ID: 15423

County: Isles of Scilly

Civil Parish: St. Martin's

Traditional County: Cornwall

Lieutenancy Area (Ceremonial County): Cornwall

Church of England Parish: Isles of Scilly

Church of England Diocese: Truro


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.

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.

Source: Historic England

Reasons for Scheduling

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'
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
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.

Source: Historic England


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

Title: 6": 1 mile Ordnance Survey Map; SV 91 NW
Source Date: 1963

Source: Historic England

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