ich occur above the
Devonian or Old Red Sandstone and below the Permian or Triassic
systems, belonging to the Carboniferous period. The name was first
applied by W.D. Conybeare in 1821 to the coal-bearing strata of England
and Wales, including the related grits and limestones immediately
beneath them. The term is a relic of that early period in the history
of stratigraphy when each group of strata was supposed to be
distinguished by some peculiar lithological character. In this case the
carbonaceous beds--coal-seams--naturally appealed most strongly to the
imagination, and the name is a good one, notwithstanding the fact that
coal-seams occupy but a small fraction of the total thickness of the
Carboniferous system; and although subsequent investigations have
demonstrated the existence of coal in other geological formations, in
none of these does it play so prominent a part. The stratified rocks of
this system include marine limestones, shales and sandstones;
estuarine, lagoonal and fresh-water shales, sandstones and marls with
beds of coal, oil-bearing rocks, gypsum and salt.

In many parts of the world there is no sharp line of demarcation between
the Devonian and the Carboniferous rocks; neither can the fossil faunas
and floras be clearly separated at any well-defined line; this is true
in Britain, Belgium, Russia, Westphalia and parts of North America.
Again, at the summit of the Carboniferous series, both the rocks and
their fossil contents merge gradually into those of the succeeding
Permian system, as in Russia, Bohemia, the Saar region and Texas. This
has led certain geologists to classify the Devonian, Carboniferous and
Permian into one grand system; E. Renevier in 1874 proposed to include
these three into a single "Carbonique" system, later he retained only
the two latter groups. There seems to be sufficient reason, however, to
maintain each of these groups as a separate system and limit the term
Carboniferous (_carboniferien_) in the manner indicated above. At the
same time it must be remembered that there is in India, South Africa,
the Urals, in Australasia and parts of North America an important series
of rocks, with a "Permo-Carboniferous" fauna, which constitutes a
passage formation between the Carboniferous, _sensu stricto_, and
Jurassic rocks.

[Illustration: Distribution of Carboniferous Rocks]

_Stratigraphy._--No assemblage of stratified rocks has received such
careful and detailed examination