Cropmarks of an Iron Age
settlement in Barley ©
Buried remains
The way we see things depends on whether or not the archaeological remains survive above ground or
have been levelled. Standing archaeological remains are commonly in the form of earth banks, ditches or
low walls, often collectively referred to as earthworks.
Earthwork photography is best carried out when the sun is low in the sky, either in the winter or late
evening in the summer so that the archaeology is picked out in contrasting and complimentary areas
of highlight and shadow. Even substantial earthworks can be almost invisible if photographed in flat light,
but in the right conditions very slight height differences can be startlingly clear from the air.
'Cropmarks can be found at all stages of the growth cycle, from germination to harvest.'
When it comes to buried or levelled remains there are many more factors - such as the time of day, the recent weather patterns, soil type, underlying geology, the agricultural regime and more - that determine whether or not the archaeology can be seen and recorded, usually as a cropmark or soilmark. Cropmarks
are essentially patterns of differential growth in vegetation that correspond to and are caused by variations
in the subsoil. So, for instance, fissures in the underlying bedrock or a man-made trench or pit will often fill with soils and matter that have greater moisture retention and more nutrients than the surrounding, undisturbed subsoil.
Looking for clues in the Wolds ©
In drought conditions these moisture-retentive soils hold a reserve of available water that allows the plants growing above to thrive, growing fuller and taller for longer. The rest of the crop suffers stress due to lack of moisture and plants can be weaker, shorter and tend to ripen quicker. Other archaeological deposits, such as compacted surfaces or stone wall foundations, have the reverse effect, causing poor, stunted growth as the plants above struggle to survive.
Many crops will develop good marks when conditions are right, but some of the best - from an archaeologist's point of view - are cereals, sugar beet and peas. Cropmarks can be found at all stages of the growth cycle, from germination to harvest; they are sometimes seen as height differences (rather like seeing an earthwork), sometimes as colour differences - either subtle or vivid. Soilmarks are a little more straightforward. With soilmarks the observer is looking directly at the archaeological deposits brought to the surface by the plough, where they show as colour differences against the non-archaeological plough soil.
