The origin of coal, that combustible which is distributed over the earth in all latitudes, from the frozen regions of Greenland to Zambesi in the tropics, utilized by the Chinese from the remotest antiquity for the baking of pottery and porcelain, employed by the Greeks for working iron, and now the indispensable element of the largest as well of the smallest industries, is far from being sufficiently clear.  The most varied hypotheses have been offered to explain its formation.  To cite them all would not be an easy thing to do, and so we shall recall but three:  (1) It has been considered as the result of eruptions of bitumen coming from the depths, and covering and penetrating masses of leaves, branches, bark, wood, roots, etc., of trees that had accumulated in shallow water, and whose most delicate relief and finest impressions have been preserved by this species of tar solidified by cooling. (2) It has also been considered as the result of the more or less complete decomposition of plants under the influence of heat and dampness, which has led them to pass successively through the following principal stages:  peat, lignite, bituminous coal, anthracite. (3) Finally, while admitting that the decomposition of plants can cause organic matter to assume these different states, other scientists think that it is not necessary for such matter to have been peat and lignite in order to become coal, and that at the carboniferous epoch plants were capable of passing directly to the state of coal if the conditions were favorable; and, in the same way, in the secondary and tertiary epochs the alteration of vegetable tissues generally led to lignite, while now they give rise to peat.  In other words, the nature of the combustible formed at every great epoch depended upon general climatic conditions and local chemical action.  Anthracite and bituminous coal would have belonged especially to primary times, lignites to secondary and tertiary times, and peat to our own epoch, without the peat ever being able to become lignites or the latter coal.

As for the accumulation of large masses of the combustible in certain regions and its entire absence in others belonging to the same formation, that is attributed, now to the presence of immense forests growing upon a low, damp soil, exposed to alternate rising and sinking, and whose debris kept on accumulating during the periods of upheaval, under the influence of a powerful vegetation, and now to the transportation of plants of all sorts, that had been uprooted in the riparian forests by torrents and rivers, to lakes of wide extent or to estuaries.  Not being able to enter in this place into the details of the various hypotheses, or to thoroughly discuss them, we shall be content to make known a few facts that have been recently observed, and that will throw a little light upon certain still obscure points regarding the formation of coal.