Shadow marks are a form of archaeological feature visible from the air. Unlike cropmarks, frost marks and soil marks they require upstanding features to work and are therefore more commonly seen in the context of extant sites rather than previously undiscovered buried ones.
They are caused by the differences in height on the ground produced by archaeological remains. In the case of ancient, eroded earthworks these differences are often small and they are most apparent when viewed from the air, when the sun is low in the sky. This causes long shadows to be cast by the higher features, which are illuminated from one side by the sun, with dark shadows marking hollows and depressions.
Shadow marks are best viewed obliquely rather than from directly above in order to emphasise the effect of the shadows.
Famous quotes containing the words shadow and/or marks:
“...A shadow now occasionally crossed my simple, sanguine, and life enjoying mind, a notion that I was never really going to accomplish those powerful literary works which would blow a noble trumpet to social generosity and noblesse oblige before the world. What? should I find myself always planning and never achieving ... a richly complicated and yet firmly unified novel?”
—Sarah N. Cleghorn (1876–1959)
“The clock runs down
timeless and still.
The days and nights turn hours to years
and water in a gutter marks the circle of another world
hating, resentful, and afraid
stagnant, and green, and full of slimy things.”
—Margaret Abigail Walker (b. 1915)