Air-breathers of the American Coal.
Changes of Condition of Land and Sea indicated by the Carboniferous Strata of
Nova Scotia.
PRINCIPAL SUBDIVISIONS OF THE CARBONIFEROUS GROUP.
The next group which we meet with in the descending order is the Carboniferous,
commonly called "The Coal," because it contains many beds of that mineral, in a
more or less pure state, interstratified with sandstones, shales, and
limestones. The coal itself, even in Great Britain and Belgium, where it is most
abundant, constitutes but an insignificant portion of the whole mass. In South
Wales, for example, the thickness of the coal-bearing strata has been estimated
at between 11,000 and 12,000 feet, while the various coal seams, about 80 in
number, do not, according to Professor Phillips, exceed in the aggregate 120
feet.
The Carboniferous formation assumes various characters in different parts even
of the British Islands. It usually comprises two very distinct members: first,
the sedimentary beds, usually called the Coal-measures, of mixed fresh-water,
terrestrial, and marine origin, often including seams of coal; secondly, that
named in England the Mountain or Carboniferous Limestone, of purely marine
origin, and made up chiefly of corals, shells, and encrinites, and resting on
shales called the shales of the Mountain Limestone.
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