Variations in the colour or growth of a crop or other vegetation, shown on an aerial photograph, may reveal the buried walls, ditches and pits of an archaeological site. In particular, buried pits and ditches may retain moisture better than the surrounding subsoil, and during a dry spell plant growth is often enhanced over such features. Crop marks of this kind are best seen during a dry summer, and in drier areas.
The Macmillan dictionary of archaeology, Ruth D. Whitehouse, 1983Copied