Recording The Layers Upon And Under The Land: Wanderings #44/52a - A Year In The Country
There have been a number of books published on the subject and having something of a weakspot for cultural artifacts from around 1973, Flights Into Yesterday by Leo Deuel caught my eye. Apparently tiny differences in ground conditions caused by buried features can be emphasised by a number of factors and then viewed from the air: Slight differences in ground levels will cast shadows when the sun is low and these can be seen best from an aeroplane. These are referred to as shadow marks. Buried ditches will hold more water and buried walls will hold less water than undisturbed ground, this phenomenon, amongst others, causes crops to grow better or worse, taller or shorter, over each kind of ground and therefore define buried features which are apparent as tonal or colour differences. Such effects are called cropmarks.