marsh gas

Many varieties of coal give off a gas known as marsh-gas or fire-damp.

Franklin's study of marsh gas and effect of oil on water, 390.

A similar relation holds good between marsh gas and olefiant gas (ethylene).

But here is another gas, about which I may have to say something directly, called marsh gas (the gas of coal-mines).

Here goes: marsh gas, or methane as it is sometimes called, is the first of the group of hydrocarbons known as paraffins.