Soil marks are traces of archaeological features, which are visible in ploughed or harrowed fields, usually where there are restricted periods before the crops grow.
Depending on the area in the aspect of geology the soil marks can show up as brown against white background or vice versa with even darker against lighter tones.
This allows archaeologists to understand the concept of the artefacts found in the region of the soil mark and can see whether or not fire was used.
Archaeology that involves plough-damaged field systems, burial mounds, Roman villas or former sites usually produce soil marks.
An example was given that this might be a dried-up river channel (known as a palaeochannel), which may subsequently reveal rich waterlogged archaeological deposits in its lower layers, or an area of slightly higher ground above winter flood level on an alluvial floodplain, which may be very hard to detect from the ground but which has attracted settlement for thousands of years.