to the
man with the microscope.

The fossil remains of the plants that flourished when coal was forming
are gigantic, compared with plants of the same families now living. We
must conclude that the climate was tropical, the air very heavy with
moisture, and charged much more heavily than it is now with carbonic
acid gas.

These conditions produced, in rapid succession, forests of tree ferns
and horsetails and giant club mosses. These are the three types of
plants out of which the coal was made. They were all rich in resin,
which makes the coal burn readily. The ferns had stems as large as tree
trunks. Some have been found that are eighteen inches in diameter. We
know they are ferns, because the leaves are found with their fruits
attached to them in the manner of present-day ferns. The stems show the
well known scar by which fern leaves are joined. And the wood of these
fossil fern stems is tubular in structure, just as the wood of living
ferns is to-day.

Among the ferns which dominated these old marsh forests grew one kind,
the scaly leaves of which covered the stems and bore their fruits on the
branching tips. These giants, some of them with trunks four feet in
diameter, belong to the same group of plants as our creeping club
mosses, but in the ancient days they stood up among the other ferns as
trees forty or fifty feet high.

The giant scouring rushes, or horsetails, had the same general
characteristics as the little reed-like plants we know by those names
to-day.

The highest plants of the coal period were leafy trees with nut-like
fruits, that resemble the yew trees of the present. These gigantic trees
were the first conifers upon the earth. They foreshadowed the pines and
the other cone-bearing evergreens. Their leaves were broad and their
fruits nut-like. The Japanese ginkgo, or maidenhair fern tree, is an
old-fashioned conifer somewhat like those first examples of this family.
Trunks sixty to seventy feet long, crowned with broad leaves and a spike
of fruit, have been found lying in the upper layers of the coal-seams,
and in sandstone strata that lie between the strata of coal. Peculiar
circular discs, which the microscope reveals along the sides of the wood
fibres of these fossil trees, prove the wood structure to be like that
of modern conifers.

Generation after generation of forests lived and died in the vast
spreading swamps of this era. The land sank, and freshets came here and
there, drowning ou