Bushdown Mine in southwest England was operational in the late 18th to early 19th Centuries for the extraction of tin. Natural concentrations of five soil gas components were investigated across the probable position of an adit. The gas variations detected are attributed to the presence of the adit and the near-surface enhanced fracturing thought to be associated with it. A tracer gas was released underground near the collapsed end of another adit at shallow depth. A programme of monitoring at a series of locations on the surface indicated the emergence of the gas a few hours after its release. The increase of tracer gas at the surface and the time lapse between gas release and measurement of the maximum increase is attributed to increased permeabilities along preferential gas migration pathways leading from the adit.