While existing equiseta rarely exceed three feet in height, and the
stems are generally under half an inch in diameter, their kindred,
entombed in the coal beds, seem to have been generally fourteen or
fifteen feet high, with stems from six inches to a foot in thickness.
Arborescent plants of this family, like the arborescent ferns, now
grow only in tropical countries, and their being found in the coal
beds in all latitudes is consequently held as an additional proof,
that at this era a warm climate was extended much farther to the
north than at present. It is to be remarked that plants of this kind
(forming two genera, the most abundant of which is the calamites) are
only represented on the present surface by plants of the same FAMILY:
the SPECIES which flourished at this era gradually lessen in number
as we advance upwards in the series of rocks, and disappear before we
arrive at the tertiary formation.

The club-moss family (lycopodiaceae) are other plants of the present
surface, usually seen in a lowly and creeping form in temperate
latitudes, but presenting species which rise to a greater magnitude
within the tropics. Many specimens of this family are found in the
coal beds; it is thought they have contributed more to the substance
of the coal than any other family. But, like the ferns and
equisetaceae, they rise to a prodigious magnitude. The lepidodendra
(so the fossil genus is called) have probably been from sixty-five to
eighty feet in height, having at their base a diameter of about three
feet, while their leaves measured twenty inches in length. In the
forests of the coal era, the lepidodendra would enjoy the rank of
firs in our forests, affording shade to the only less stately ferns
and calamites. The internal structure of the stem, and the character
of the seed-vessels, shew them to have been a link between single-
lobed and double-lobed plants, a fact worthy of note, as it favours