26. In consequence of the displacement of the waters, the grounds which produced these masses of vegetation were many times submerged, covered again with terrestrial sediment, during which those which had become dry appeared in their turn with a similar vegetation; thus there were many successive generations of vegetables destroyed and renewed again. The animals being aquatic suffered nothing from these changes.
These remains accumulated during a long series of years, and formed beds of great thickness. Under the actions of heat, of humidity, of pressure, exercised by subsequent terrestrial deposits, and, without doubt, also various chemical agents, such as gas, acids, and salts, products of a combination of primitive elements, these vegetable substances were submitted to a fermentation converting them into coal. The coal-mines are, then, the direct result of the decomposition of a mass of vegetables accumulated during the transition period. That is why they are found in almost every country. *
* Turf is produced in the same manner by the decomposition of vegetable matter in marshy grounds; but with this difference, being much more recent and formed under different conditions, it has not had time to carbonize.