as the Carboniferous system;
consequently our knowledge of the stratigraphical sequence in isolated
local areas, where the coals have been exploited, is very full.

In Europe, the system is very completely developed in the British
Isles, where was made the first successful attempt at a classification
of its various members, although at a somewhat earlier date Omalius
d'Halloy had recognized a _terrain bituminifere_ or coal-bearing
series in the Belgian region.

The area within which the Carboniferous rocks of Britain occur is
sufficiently extensive to contain more than one type of the system,
and thus to cast much light on the varied geographical conditions
under which these rocks were accumulated. In prosecuting the study of
this part of British geology it is soon discovered, and it is
essential to bear in mind, that, during the Carboniferous period, the
land whence the chief supplies of sediment were derived rose mainly to
the north and north-west, as it seems to have done from very early
geological time. While therefore the centre and south of England lay
under clear water of moderate depth, the north of the country and the
south of Scotland were covered by shallow water, which was continually
receiving sand and mud from the adjacent northern land. Hence vertical
sections of the Carboniferous formations of Britain differ greatly
according to the districts in which they are taken.

The Coal-Measures and Millstone Grit are usually grouped together in
the _Upper Carboniferous_, the Carboniferous Limestone series
constituting the _Lower Carboniferous_.

In addition to the above broad subdivisions, Murchison and Sedgwick,
when working upon the rocks of Devonshire and Cornwall, recognized,
with the assistance of W. Lonsdale, another phase of sedimentation.
This comprised dark shales, with grits and thin limestones and thin,
impure coals, locally called "culm" (q.v.). These geologists
appropriated the term "culm" for the whole of this facies in the west
of England, and subsequently traced the same type on the European
continent, where it is widely developed in the western centre.

Besides the considerable exposed area of Carboniferous rocks in Great
Britain, there is as much or more that is covered by younger
formations; this is true particularly of the eastern side of England
and the south-eastern counties, where the coal-measures have already
b