the fusion, and the heat is increased till the whole mass becomes
liquid. The object is to separate the earthy matter, which, from being
specifically lighter, rises to the surface of the liquid mass in the
form of slag, and is drawn off. After two or three charges, the
furnace becomes quite filled, and an aperture is then opened in it,
through which the red-hot liquid flows into an adjoining pit filled
with water. It is by this means granulated, and is now termed 'coarse
metal,' or 'regulus;' and is, in fact, an admixture of the sulphurets
of iron and copper, containing about 30 per cent. of the latter.

But it is to the earthy impurities here given off that we especially
wish to direct attention. This slag, as it is termed, when drawn from
the furnace, is run into oblong sand-moulds, from which, when cold, it
is taken outside to the 'slag-bank,' as it is called--'slag-mountain,'
we prefer saying; and an ugly mountain it is!--where it is broken into
small pieces, examined to see whether it still contains metal, and if
not, is left to accumulate. It consists essentially of silicon,
oxygen, iron; or, to speak more correctly, it is a silicate of the
protoxide of iron. It is, in fact, a true _igneous rock_. Portions of
quartz and silica still remaining unfused, are often contained in the
masses, which give to them, when broken, a true porphyritic
appearance, while, from the great preponderance of the protoxide of
iron, it is invariably black.

So hard, solid, and indurated do these slags, in process of time,
become, that a very tall chimney, the most conspicuous object in the
works, is built on the top of a slag-bank. And this beautiful
commodity is not without its use in the arts. Part of it is
occasionally cast into iron moulds, shaped like old Gothic arches,
only uglier; and the casts are applied in great quantity as
coping-stones to the walls and fences in the regions of the
copper-works. Although not a very tasteful, it is yet a very useful,
and, at the same time, a very characteristic application. We may add
here, that the aggregate produce of the substance of the different
Swansea works may be estimated at about 260,000 tons a year. Our
readers may judge for themselves of the ultimate change this is
calculated to bring about in the Carboniferous System, and of the
learned controversies that are likely to arise among future geologists
with respect to the character and constitution of these carefully
disintegrated