A property of soil and sediment, measured as a ratio of intensity of magnetization of the material to the strength of an applied magnetic field. Topsoil often has a somewhat enhanced 'magnetic susceptibility' due to magnetic minerals in the material, especially compared with the subsoil. The filling of a ditch or a pit has greater susceptibility than the surrounding area because of higher humus content and perhaps the presence of burnt occupation material. On the basis that contrast between feature and surroundings locates the features, walls, and other stone settings can also be located since they have less susceptibility than the area around them, i.e. they exhibit a reverse anomaly.