This drawing shows the flat marshlands of Foulness Island . The draughtsman has indicated the sands by stippling and detailed the channels leading  from the North Sea. The most striking feature is the sea wall,  shown as a  grey angular line  extending along the coast and the channels.    A signal staff is marked at Wakering Stairs, while the word  'Flag', indicating a trigonometric station,  is marked at Aspins Head.