On
the other hand, the animal remains of the beds accompanying the
coal are typically the remains of air-breathing, terrestrial,
amphibious, or aerial animals, together with those which inhabit
fresh or brackish waters. Marine fossils may be found in the
Coal-measures, but they are invariably confined to special horizons
in the strata, and they indicate temporary depressions of the
land beneath the sea. Whilst the distinction here mentioned is
one which cannot fail to strike the observer, it is convenient
to consider the animal life of the Carboniferous as a whole: and
it is simply necessary, in so doing, to remember that the marine
fossils are in general derived from the inferior portion of the
system; whilst the air-breathing, fresh-water, and brackish-water
forms are almost exclusively derived from the superior portion
of the same.
[Illustration: Fig. 114.--Transparent slice of Carboniferous
Limestone, from Spergen Hill, Indiana, U.S., showing numerous
shells of _Endothyra_ (_Rotalia_), _Baiteyi_ slightly enlarged.
(Original.)]
[Illustration: Fig. 115.--_Fusulina cylindrica_, Carboniferous
Limestone, Russia.]
The Carboniferous _Protozoans_ consist mainly of _Foraminifera_
and _Sponges_. The latter are still very insufficiently known,
but the former are very abundant, and belong to very varied types.
Thin slices of the limestones of the period, when examined by the
microscope, very commonly exhibit the shells of _Foraminifera_
in greater or less plenty.
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