Volume One - Into the Victorian Age - Rhondda coal = Cardiff gold . . .

The book, Steam Boilers, Engines and Turbines [179] by S. F. Walker published in 1908 provides further explanation of the gases:

"The Gases found in Collieries: There is another source of fuel that at present is both a nuisance and a danger, but which in time to come will probably be employed as a source of power, viz. the gas which is found in the coal measures, and which has been produced by the distillation of the organic substances contained in the plants from which the coal was formed, during the ages since the plants were buried.

The gas consists almost entirely of that known as marsh gas, having the chemical formula CH4. It is largely imprisoned in the pores of the coal itself, it is thought in the liquid, and possibly even in the solid form and under very great pressure, with the result that it comes away freely as the coal is worked and the pressure to which it is subject is reduced. One great reservoir of this form of natural gas is found in the coal fields of South Wales in the faults in the strata.

It was explained, in dealing with the production of coal, that the coal seams or coal measures had been subject to great disturbing influences from upheavals of the strata, from the same causes that produce earthquakes and the eruptions of volcanos. The result has been that the strata has been broken and that the edges of the coal seams have been presented to the edges of other rocks, a very fine capillary space being present between them, and in this space the gas from the coal seam is apparently stored.

On several of the colliery pit banks in South Wales may be seen jets of gas burning day and night, something on the lines of the flares that butchers favour on their stalls on Saturday nights, the gas issuing from the end of a pipe. These flames are produced by the gas carried by means of these pipes from the faults mentioned above, and it is merely a step from burning them wastefully, to storing them and using them for power. In one colliery in South Wales they have been used for some time, after scrubbing, for illuminating purposes."