common character by which they may be distinguished from the more modern
coals; containing less water, less oxygen, and more carbon, and usually
exhibiting the property of coking, which is rare in coals of later date.
Though there is great diversity in the Carboniferous coals, and it would
be absurd to express their composition by a single formula, it may be
said that, over the whole world, these coals have characteristics, as
a group, by which they can be recognized, the result of the slow
decomposition of the tissue of plants which lived in the Carboniferous
age, and which have, by a broad and general change, approximated to
a certain phase in the spontaneous distillation of plant-tissue. An
experienced geologist will not fail to refer to their proper horizon
a group of coals of Carboniferous age any more than those of the
Cretaceous or Tertiary.

_Anthracite_--In the ages anterior to the Carboniferous, the quantity
of land vegetation was apparently not sufficient to form thick and
extensive beds of peat; but the remains of plant-tissue are contained
in all the older formations, though there only as anthracite or
graphite--the last two groups of residual products. Of these we have
examples in the beds of graphite in the Laurentian rocks of Canada,
and of anthracite of the lower Silurian strata of Upper Church and
Kilnaleck, Ireland.

From these facts it is apparent that the carbon series is graded
geologically, that is, by the lapse of time during which plant-tissue
has been subjected to this natural and spontaneous distillation. But we
have better evidence than this of the derivation of one from another
of the groups of residual products which have been enumerated. In many
localities, the coals and lignites of different ages have been exposed
to local influences--such as the outbursts of trap-rock, or the