Cropmark

Cropmarks or Crop marks are a means through which sub-surface archaeological, natural and recent features may be visible from the air or a vantage point on higher ground or a temporary platform. Along with parch marks,soil marks and frost marks can reveal buried archaeological sites not visible from the ground.

Description

Crop marks appear due to the principle of differential growth. One of the factors controlling the growth of vegetation is the condition of the soil. A buried stone wall for example will affect crop growth above it, as its presence channels water away from its area and occupies the space of the more fertile soil. Conversely, a buried ditch, with a fill containing more organic matter than the natural earth, provides much more conducive conditions and water will naturally collect there, nourishing the plants growing above.

The differences in conditions will cause some plants to grow more strongly and therefore taller, and others less strongly and therefore shorter. Some species will also react through differential ripening of their fruits or their overall colour.