d.

The sulphurous impurities which are always present in the coal, and which
are, to a certain extent, retained in coke made at the gas-works,
themselves have a value, which in these utilitarian days is not long
likely to escape the attention of capitalists. In coal, bands of bright
shining iron pyrites are constantly seen, even in the homely scuttle, and
when coal is washed, as it is in some places, the removal of the pyrites
increases the value of the coal, whilst it has a value of its own.

The conversion of the sulphur which escapes from our chimneys into
sulphuretted hydrogen, and then into sulphuric acid, or oil of vitriol,
has already been referred to, and we can only hope that in these days
when every available source of wealth is being looked up, and when there
threatens to remain nothing which shall in the future be known as
"waste," that the atmosphere will be spared being longer the receptacle
for the unowned and execrated brimstone of millions of fires and
furnaces.

CHAPTER VII.

THE COAL SUPPLIES OF THE WORLD.

As compared with some of the American coal-fields, those of Britain are
but small, both in extent and thickness. They can be regarded as falling
naturally into three principal areas.

The northern coal-field, including those of Fife, Stirling, and Ayr
in Scotland; Cumberland, Newcastle, and Durham in England; Tyrone
in Ireland.

The middle coal-field, all geologically in union, including those of
Yorkshire, Derbyshire, Shropshire, Staffordshire, Flint, and
Denbigh.

The southern coal-field, including South Wales, Forest of Dean,
Bristol, Dover, with an offshoot at Leinster, &c., and Millstreet,
Cork.

Thus it will be seen that while England and Scotland are, in comparison
with their extent of surface, bountifully supplied with coal-areas, in
the sister island of Ireland coal-producing areas are almost absent. The
isolated beds in Cork and Tipperary, in Tyrone and Antrim, are but the
remnants left of what were formerly beds of coal extending the whole
breadth and length of Ireland. Such beds as there remain undoubtedly
belong to the base of the coal-measures, and observations all go to show
that the surface suffered such extreme denudation subsequent to the
growth of the coal-forests, that the wealth which once lay there, has
been swept away from the surface which formerly boasted of it.

On the continent of Europe the coal-fields, though not occu