[mass noun] Methane, especially as generated by decaying matter in marshes.
- ‘Methane is often called marsh gas because it forms in swamps and marshes from the underwater decomposition of plant and animal material.’
- ‘The cow came loose from the bog with a fearful sucking noise and an overwhelming smell of marsh gas.’
- ‘Occasionally a hiss of marsh gas would sound, like a snake's venomous warning.’
- ‘In 1914, marsh gas explosions occurred in the Lumb Lane district of Bradford.’
- ‘The smell of sulfurous marsh gas drifted over the stockade to mix with the smell of disease and spoiling food.’