Archaeologia Islandica - 01.01.2002, Blaðsíða 32

Timothy J. Horsley & Stephen J. Dockrill
Skálholt reduce this thermoremanent
input, allowing more subtle archaeologi-
cal anomalies to be detected.
An important discovery from this
project concerns the data collection
method for magnetometer surveys. Many
of the surveys revealed an enhanced
effect of 'bunching' produced when data
is collected in the 'zig-zag' fashion, possi-
bly exaggerated by the strong geological
anomalies. The only solution is to under-
take carry out gradiometer surveys in the
'parallel' fashion. Unfortunately this will
increase the time taken to survey each
grid, but will produce clearer results.
It has been demonstrated that the
most information of archaeological value
was produced by the small-scale noise
caused by individual rocks associated
with structural remains. Being small
anomalies, these are best identified at a
higher resolution of surveying than might
ordinarily be undertaken. Consequently
it is advised that a high resolution of data
collection, i.e. 0.5m x 0.25m, is
employed for most effective and inform-
ative results.
Magnetic susceptibility
Throughout this assessment it was possi-
ble to collect only a limited number of
soil samples for measurement of magnet-
ic susceptibility at Bradford.
The preliminary results imply that,
despite very high natural background
values (generally in the range 100 to 250
SI xl0"8m3kg‘’), archaeological sedi-
ments associated with buming produce
strong enhancements, with values above
400 SI xl0"8m3kg‘', and even as high as
1800 SI xl0"8mJkg"'(midden material
from Neðri Ás). However, it is not
known how effective this method would
be for reconnaissance surveying, as in
many areas aeolian deposits overlay the
archaeology and the natural mixing
processes in the soil might not be
extreme enough to bring enhanced mate-
rial to the surface. Instead, this technique
might prove valuable by aiding the inter-
pretation of deposits during excavation
by distinguishing between samples with
natural and anthropogenic enhancement.
Detection of archaeological remains
As a preliminary evaluation, it was nec-
essary to target archaeological remains
known from other sources to allow a
proper and confident assessment of these
techniques to be made. Surveys at a num-
ber of sites, and over different remains
make it possible to talk generically about
certain feature-types.
Many sites presented visible earth-
works constructed of turf. As discussed
earlier in this paper, a lack of good build-
ing stone has meant that many structures
and field boundaries are constructed of
turf. Where geophysical surveys included
such remains, they were shown to appear
as low resistance anomalies. This might
be surprising since such extant remains
could be expected to be better drained
and therefore possess a higher resistance.
These results therefore seem to indicate
that the turf is water retentive, and it
might be possible to use this characteris-
tic for the future prospection of now-
buried turf remains.
Buried stone walls have been detect-
ed in earth resistance and magnetometer
surveys, despite the intense geological
30