Hachures, those short radiating lines used by cartographers to suggest relief and surface irregularity, can indicate anything from an earthwork to a natural mound. When someone finally went to look in 1983, half a century after the map was drawn, the feature turned out to be an overgrown hollow, most likely the remains of a sand or gravel pit. Not ancient, not mysterious, just a working extraction site that had quietly returned to vegetation and been absorbed into the bog around it.