in the south of France and in India masses of coal are
known up to 200 ft. in thickness. These very thick seams are, however,
rarely constant in character for any great distance, being found
commonly to degenerate into carbonaceous shales, or to split up into
thinner beds by the intercalation of shale bands or partings. One of the
most striking examples of this is afforded by the thick or ten-yard seam
of South Staffordshire, which is from 30 to 45 ft. thick in one
connected mass in the neighbourhood of Dudley, but splits up into eight
seams, which, with the intermediate shales and sandstones, are of a
total thickness of 400 ft. in the northern part of the coalfield in
Cannock Chase. Seams of a medium thickness of 3 to 7 ft. are usually the
most regular and continuous in character. Cannel coals are generally
variable in quality, being liable to change into shales or black-band
ironstones within very short horizontal limits. In some instances the
coal seams may be changed as a whole, as for instance in South Wales,
where the coking coals of the eastern side of the basin pass through the
state of dry steam coal in the centre, and become anthracite in the
western side. (H. B.)

Geographical distribution of coalfields.

The most important European coalfields are in Great Britain, Belgium and
Germany. In Great Britain there is the South Welsh field, extending
westward from the march of Monmouthshire to Kidwelly, and northward to
Merthyr Tydfil. A midland group of coalfields extends from south
Lancashire to the West Riding of Yorkshire, the two greatest industrial
districts in the country, southward to Warwickshire and Staffordshire,
and from Nottinghamshire on the east to Flintshire on the west. In the
north of England are the rich field of Northumberland and Durham, and a
lesser field on the coast of Cumberland (Whitehaven, &c.). Smaller
isolated fields are those of the Forest of Dean (Gloucestershire) and
the field on either side of the Avon above Bristol. Coal has also been
found in Kent, in the neighbourhood of Dover. In Scotland coal is worked
at various points (principally in the west) in the Clyde-Forth lowlands.
In Belgium the chief coal-basins are those of Hainaut and Liege. Coal
has also been found in an extension northward from this field towards
Antwerp, while westward the same field extends into north-eastern
France. Coal is widely distributed in Germany. The principal field is
that of the lower Rhine