Coal is found overlying
the carboniferous limestone of the Cantabrian chain, the seams being from
5 feet to 8 feet thick. In the Satero valley, near Sotillo, is a single
seam measuring from 60 feet to 100 feet thick. Coal of Neocomian age
appears at Montalban.

When we look outside the continent of Europe, we may well be astonished
at the bountiful manner in which nature has laid out beds of coal upon
these ancient surfaces of our globe.

Professor Rogers estimated that, in the United States of America, the
coal-fields occupy an area of no less than 196,850 square miles.

Here, again, it is extremely probable that the coal-fields which remain,
in spite of their gigantic existing areas, are but the remnants of one
tremendous area of deposit, bounded only on the east by the Atlantic, and
on the west by a line running from the great lakes to the frontiers of
Mexico. The whole area has been subjected to forces which have produced
foldings and flexures in the Carboniferous strata after deposition. These
undulations are greatest near the Alleghanies, and between these
mountains and the Atlantic, whilst the flexures gradually dying out
westward, cause the strata there to remain fairly horizontal. In the
troughs of the foldings thus formed the coal-measures rest, those
portions which had been thrown up as anticlines having suffered loss by
denudation. Where the foldings are greatest there the coal has been
naturally most altered; bituminous and caking-coals are characteristic of
the broad flat areas west of the mountains, whilst, where the contortions
are greatest, the coal becomes a pure anthracite.

It must not be thought that in this huge area the coal is all uniformly
good. It varies greatly in quality, and in some districts it occurs in
such thin seams as to be worthless, except as fuel for consumption by the
actual coal-getters. There are, too, areas of many square miles in
extent, where there are now no coals at all, the formation having been
denuded right down to the palaeozoic back-bone of the country.

Amongst the actual coal-fields, that of Pennsylvania stands
pre-eminent. The anthracite here is in inexhaustible quantity, its output
exceeding that of the ordinary bituminous coal. The great field of which
this is a portion, extends in an unbroken length for 875 miles N.E. and
S.W., and includes the basins of Ohio, Maryland, Virginia, Kentucky, and
Tennessee. The workable seams of anthracite about Pottsville measur