The Story of a Piece of Coal | Page 9

form of cones, such as the fir, larch, cedar, and others. The
order is one which is familiar to all, not only on account of the cones
they bear, and their sheddings, which in the autumn strew the ground
with a soft carpet of long needle-like leaves, but also because of the
gum-like secretion of resin which is contained in their tissues. Only a
few species have been found in the coal-beds, and these, on
examination under the microscope, have been discovered to be closely
related to the araucarian division of pines, rather than to any of our
common firs. The living species of this tree is a native of Norfolk
Island, in the Pacific, and here it attains a height of 200 feet, with a
girth of 30 feet. From the peculiar arrangement of the ducts in the
elongated cellular tissue of the tree, as seen under the microscope, the
fossil conifers, which exhibit this structure, have been placed in the
same division.
The familiar fossil known to geologists as Sternbergia has now been
shown to be the cast of the central pith of these conifers, amongst
which may be mentioned _cordaites, araucarites_, and _dadoxylon._.
The central cores had become replaced with inorganic matter after the
pith had shrunk and left the space empty. This shrinkage of the pith is a
process which takes place in many plants even when living, and
instances will at once occur, in which the stems of various species of
shrubs when broken open exhibit the remains of the shrunken pith, in
the shape of thin discs across the interval cavity.
We might reasonably expect that where we find the remains of fossil

coniferous trees, we should also meet with the cones or fruit which they
bear. And such is the case. In some coal-districts fossil fruits, named
cardiocarpum and _trigonocarpum_, have been found in great
quantities, and these have now been decided by botanists to be the
fruits of certain conifers, allied, not to those which bear hard cones, but
to those which bear solitary fleshy fruits. Sir Charles Lyell referred
them to a Chinese genus of the yew tribe called salisburia. Dawson
states that they are very similar to both taxus and _salisburia._. They
are abundant in some coal-measures, and are contained, not only in the
coal itself, but also in the sandstones and shales. The under-clays
appear to be devoid of them, and this is, of course, exactly what might
have been expected, since the seeds would remain upon the soil until
covered up by vegetable matter, but would never form part of the clay
soil itself.
In connection with the varieties which have been distinguished in the
families of the conifers, calamites, and sigillariae, Sir William Dawson
makes the following observations: "I believe that there was a
considerably wide range of organisation in cordaitinae as well as in
calamites and _sigillariae_, and that it will eventually be found that
there were three lines of connection between the higher cryptogams
(flowerless) and the phaenogams (flowering), one leading from the
lycopodes by the _sigillariae_, another leading by the _cordaites_, and
the third leading from the equisetums by the calamites. Still further
back the characters, afterwards separated in the club-mosses,
mare's-tails, and ferns, were united in the _rhizocarps_, or, as some
prefer to call them, the heterosporous filicinae."
In concluding this chapter dealing with the various kinds of plants
which have been discovered as contributing to the formation of
coal-measures, it would be as well to say a word or two concerning the
climate which must have been necessary to permit of the growth of
such an abundance of vegetation. It is at once admitted by all botanists
that a moist, humid, and warm atmosphere was necessary to account for
the existence of such an abundance of ferns. The gorgeous waving
tree-ferns which were doubtless an important feature of the landscape,
would have required a moist heat such as does not now exist in this

country, although not necessarily a tropical heat. The magnificent giant
lycopodiums cast into the shade all our living members of that class,
the largest of which perhaps are those that flourish in New Zealand. In
New Zealand, too, are found many species of ferns, both those which
are arborescent and those which are of more humble stature. Add to
these the numerous conifers which are there found, and we shall find
that a forest in that country may represent to a certain extent the
appearance presented by a forest of carboniferous vegetation. The ferns,
lycopods, and pines, however, which appear there, it is but fair to add,
are mixed with other types allied to more recent forms of vegetation.
There are many reasons for believing that the amount of carbonic acid
gas then existing in the atmosphere was larger than