dwards to differ
generally from all living zoophytes; so that conclusions as to a warmer
climate drawn from such remote analogies must be received with caution.
Hitherto, few, if any, contemporaneous vegetable remains have been
noticed; but such as are mentioned agree more nearly with the plants of
the carboniferous era than any other, and would therefore imply a warm
and humid atmosphere entirely free from intense cold throughout the
year.

This absence or great scarcity of plants as well as of freshwater shells
and other indications of neighboring land, coupled with the wide extent
of marine strata of this age in Europe and North America, are facts
which imply such a state of physical geography (so far at least as
regards the northern hemisphere) as would, according to the principles
before explained, give rise to such a moist and equable climate. (See p.
109, and fig. 5, p. 111.)

_Carboniferous group._--This group comes next in the order of
succession; and one of its principal members, the mountain limestone,
was evidently a marine formation, as is shown by the shells and corals
which it contains. That the ocean of that period was of considerable
extent in our latitudes, we may infer from the continuity of these
calcareous strata over large areas in Europe, Canada, and the United
States. The same group has also been traced in North America, towards
the borders of the arctic sea.[196]

There are also several regions in Scotland, and in the central and
northern parts of England, as well as in the United States, where marine
carboniferous limestones alternate with strata containing coal, in such
a manner as to imply the drifting down of plants by rivers into the sea,
and the alternate occupation of the same space by fresh and salt water.

Since the time of the earlier writers, no strata have been more
extensively investigated, both in Europe and North America, than those
of the ancient carboniferous group, and the progress of science has led
to a general belief that a large portion of the purest coal has been
formed, not, as was once imagined, by vegetable matter floated from a
distance, but by plants which grew on the spot, and somewhat in the
manner of peat on the spaces now covered by the beds of coal. The former
existence of land in some of these spaces has been proved, as already
stated, by the occurrence of numerous upright fossil trees, with their
roots terminating downwards in seams of coal; and still more