The use of Gabbroic clay from the Parish of St.
Keverne on the Lizard Peninsula by Prehistoric
people.
Much has been written over the years about the
uniqueness of the geology of the Lizard Peninsula but
it is only comparatively recently in the
archaeological record that this uniqueness has been
applied to the lives of the people in Cornwall in
prehistory.
The question of the source of the clay from which
most of the pottery found on the archaeological sites
in Cornwall and a number in Devon and Wiltshire was
first hypothesized by Dr. H. Thomas of the Royal
Geological Museum in 1932, when he thinned sectioned
sherds from Henbury in East Devon. He suggested that
the clay used for the pottery from the site could
have derived from the Dartmoor granite masses.
It was not, however, until Dr. D. Peacock of
Southampton University when he examined numerous
sherds from Cornwall in the late 1960's, came to
the conclusion that they were all made from the same
source of clay. A type which was found at St. Keverne
on the Lizard Peninsula.
Map of the Lizard Peninsula showing location of
Gabbroic clay
This clay covers an area of approximately 7 square
miles and lies mostly at a varying depth of eight to
eighteen inches below modern plough surface. The main
composition of these clays are Felspars, olivines and
augites. It is the white Felspars in the fired fabric
of the pottery which gives the sherds the highly
diagnostic feature, when it is retrieved from
archaeological sites or in the course of field
walking.
Experiments with the various methods of firing from
the bonfires of prehistory at 900º C to modern
kiln firing at 1,400º C have shown that it is in
the lower temperatures of the bonfires that the
Felspar crystals do not melt out, and so can be seen
in pieces of pot as old as 4,000 years. Whilst in the
higher temperatures the Felspars are melted and
absorbed into the fabric. Most of the pottery in
archaeological sites in Cornwall has been found to be
of gabrroic clay. For example at the hill fort of
Carn Brea at Redruth it was found that a very high
percentage of the 550 pieces of pot recorded were of
gabbroic fabric.
The great debate since Dr. Peacock's work has
been; was the raw clay exported out from St. Keverne
or were the pots made in the immediate vicinity of
the clay? With the hope of resolving this question a
group of members of the Cornwall Archaeological
Society spent time in the late 1970's and early
1980's walking ploughed fields hoping to find a
mass of wasters, i.e. broken pottery, which would
have indicated a firing site. Though gabbroic sherds
were found on many of the fields walked, there was
never enough to indicate pottery processing.
Why did early people in Cornwall find this clay so
eminently suitable for this use? Might it have been
the accessibility of such a vast amount of clay or
maybe it was the Felspar forming a grog which helped
in the successful firing of pots in low temperatures?
Experiments in firing, using the raw clay with only
the largest pieces of grits removed, have fired
successfully in a bonfire. Washing and sieving of the
clay produced a material suitable to be turned on a
wheel. Or maybe it was trade, "I'll exchange
two pots for a goat or a sack of corn". Who
knows?
However, there cannot be any debate for whatever
reason, great quantities of the clay were used for
the production of their pots by those living from
3,000 B.C. to 400 A.D. in the area that was one day
to become the Parish of St. Keverne.
Examples of Gabbroic Pottery from Prehistoric
sites in Cornwall
A. BOWL - CARN BREA - Neolithic 3,500
B.C.
B. URN - KYNANCE - Bronze Age 2,500 B.C.
C. BOWL - THREEMILESTONE - Iron Age 500
B.C.
For further reading:
Cornwall Archaeological Journals
D. Peacock No 6 40 - 44
D. Peacock No 8 47 - 65
R. Mercer No 20 1 - 205
H. Quinnel No 26 1 - 7
G. Smith No 26 13 - 67
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