In Britain, and in the Old World generally, the
Coal-measures are composed partly of genuine terrestrial
deposits--such as the coal--and partly of sediments accumulated
in the fresh or brackish waters of vast lagoons, estuaries, and
marshes. The fossils of the Coal-measures in these regions are
therefore necessarily the remains either of terrestrial plants
and animals, or of such forms of life as inhabit fresh or brackish
waters, the occurrence of strata with marine fossils being quite
a local and occasional phenomenon. In various parts of North
America, on the other hand, the Coal-measures, in addition to
sandstones, shales, coal-seams, and bands of clay-ironstone,
commonly include beds of limestone, charged with marine remains,
and indicating marine conditions. The subjoined section (fig. 107)
gives, in a generalised form, the succession of the Carboniferous
strata in such a British area as the north of England, where
the series is developed in a typical form.
As regards the _life_ of the Carboniferous period, we naturally
find, as has been previously noticed, great differences in different
parts of the entire series, corresponding to the different mode of
origin of the beds. Speaking generally, the Lower Carboniferous
(or the Sub-Carboniferous) is characterised by the remains of
marine animals; whilst the Upper Carboniferous (or Coal-measures)
is characterised by the remains of plants and terrestrial animals.
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