Very little scientific work has been done on either of these matters, though a study on metal degradation has just begun at Nottingham Trent University. The following sections summarise what is known at present. Context Evidence suggests that the integrity of horizontal contexts is not always disrupted by ploughing. A valuable horizontal context often remains even when the vertical context is gone. However, some experimental work suggests that in some circumstances artefacts can be displaced by ploughing, by distances of several metres.
Mean values taken at a later date show a more or less consistent pattern of increase with time.
Downslope movement may also influence the degree of lateral displacement. Clark and Schofield suggest that the level of material displacement in ploughsoil is likely to be highly specific to certain areas, soil types, land uses and agricultural regimes. It may be, they report, that 'in an arid environment with light soils, artefact movement may be less than in a temperate climate where heavier soils predominate'. Clark and Schofield have also shown that the extent of lateral displacement, even when subject to the same cultivation regime, varies according to the shape and weight of the items. They recognise 'a bias towards irregular shaped and perhaps larger artefact classes' in those that tend to suffer maximum displacement.