of coal with the remains of a new forest, and.
above this again a layer of materials left by a second freshet, and so
on through a number of alternate strata. It is evident from these facts
that there have been a succession of forests, one above another, but
that in the intervals of their growth great floods have poured over the
marshes, bringing with them all kinds of loose materials, such as sand,
pebbles, clay, mud, lime, etc., which, as the freshets subsided, settled
down over the coal, filling not only the spaces between such trees as
remained standing, but even the hollow trunks of the trees themselves.

Let us give a glance now at the animals which inhabited the waters of
this period. In the Radiates we shall not find great changes; the three
classes are continued, though with new representatives, and the Polyp
Corals are increasing, while the Acalephian Corals, the Kugosa and
Tabulata, are diminishing. The Crinoids were still the most prominent
representatives of the class of Echinoderms, though some resembling the
Ophiurans and Echinoids (Sea-Urchins) began to make their appearance.
The adjoining wood-cut represents a characteristic Crinoid of the
Carboniferous age.

[Illustration]

Among the Mollusks, Brachiopods are still prominent, one new genus among
them, the Productus, being very remarkable on account of the manner in
which one valve rises above the other. The wood-cut below represents such
a shell, looked at from the side of the flat valve, showing the straight
cut of the line of juncture between the valves and the rising curve of
the opposite one, which looks like a hooked beak when seen in profile.

[Illustration]

Other species of Bivalves were also introduced, approaching more
nearly our Clams and Oysters, or, as they are called in scientific
nomenclature, the Lamellibranchiates. They differ from the Brachiopods
chiefly in the higher character of their breathing-apparatus; for they
have free gills, instead of the net-work of vessels on the lining skin
which serves as the organ of respiration in the Brachiopods. We shall
always find, that, in proportion as the functions are distinct, and, as
it were, individualized by having special organs appropriated to them,
animals rise in the scale of structure. The next class of Mollusks, the
Gasteropods, or Univalves, with spiral shells, were numerous, but,
from their brittle character, are seldom found in a good state of
preservation.

The Chambered She