ants growing in its shade, mixed
with a little earthy matter, the layers of coarse coal. The condition of
the durable outer bark of erect trees, concurs with the chemical theory
of coal, in showing the especial suitableness of this kind of tissue for
the production of the purer compact coals."--(Dawson, "Structures in
Coal.")

There is yet one other family of plants which must be mentioned, and
which forms a very important portion of the constituent _flora_ of the
coal period. This is the great family of the _coniferae_, which although
differing in many respects from the highly organised dicotyledons of the
present day, yet resembled them in some respects, especially in the
formation of an annual ring of woody growth.

The conifers are those trees which, as the name would imply, bear their
fruit in the 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 f