.

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, an