e recognised by the great size and concentric woody rings
of their prostrate, rarely erect trunks, and by the presence
of disc-bearing fibres in their wood, as demonstrated by the
microscope; and the principal genera which have been recognised
are _Dadoxylon, Paloeoxylon, Araucarioxylon_, and _Pinites_.
Their fruit is not known with absolute certainty, unless it be
represented, as often conjectured, by _Trigonocarpon_ (fig. 113).
The fruits known under this name are nut-like, often of considerable
size, and commonly three- or six-angled. They probably originally
possessed a fleshy envelope; and if truly referable to the
_Conifers_, they would indicate that these ancient evergreens
produced berries instead of cones, and thus resembled the modern
Yews rather than Pines. It seems, further, that the great group
of the _Cycads_, which are nearly allied to the _Conifers_, and
which attained such a striking prominence in the Secondary period,
probably commenced its existence during the Coal period; but
these anticipatory forms are comparatively few in number, and
for the most part of somewhat dubious affinities.

CHAPTER XIII.

THE CARBONIFEROUS PERIOD--Continued.

ANIMAL LIFE OF THE CARBONIFEROUS.

We have seen that there exists a great difference as to the mode
of origin of the Carboniferous sediments, some being purely marine,
whilst others are terrestrial; and others, again, have been formed
in inland swamps and morasses, or in brackish-water lagoons,
creeks, or estuaries. A corresponding difference exists necessarily
in the animal remains of these deposits, and in many regions
this difference is extremely well marked and striking. The great
marine limestones which characterise the lower portion of the
Carboniferous series in Britain, Europe, and the eastern portion
of America, and the calcareous beds which are found high up in
the Carboniferous in the western States of America, may, and
do, often contain the remains of drifted plants; but they are
essentially characterised by marine fossils; and, moreover, they
can be demonstrated by the microscope to be almost wholly composed
of the remains of animals which formerly inhabited the ocean. 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 th