all land animals. But a large proportion of it must have at one time
been in the atmosphere. The atmosphere would then, of course, be
incapable of supporting life in land animals. It is important,
however, to observe that such an atmosphere would not be inconsistent
with a luxuriant land vegetation; for experiment has proved that
plants will flourish in air containing ONE-TWELFTH of this gas, or
166 times more than the present charge of our atmosphere. The
results which we observe are perfectly consistent with, and may be
said to presuppose an atmosphere highly charged with this gas, from
about the close of the primary non-fossiliferous rocks to the
termination of the carboniferous series, for there we see vast
deposits (coal) containing carbon as a large ingredient, while at the
same time the leaves of the Stone Book present no record of the
contemporaneous existence of land animals.

The hypothesis of the connexion of the first limestone beds with the
commencement of organic life upon our planet is supported by the
fact, that in these beds we find the first remains of the bodies of
animated creatures. My hypothesis may indeed be unsound; but,
whether or not, it is clear, taking organic remains as upon the whole
a faithful chronicle, that the deposition of these limestone beds was
coeval with the existence of the earliest, or all but the earliest,
living creatures upon earth.

And what were those creatures? It might well be with a kind of awe
that the uninstructed inquirer would wait for an answer to this
question. But nature is simpler than man's wit would make her, and
behold, the interrogation only brings before us the unpretending
forms of various zoophytes and polypes, together with a few single
and double-valved shell-fish (mollusks), all of them creatures of the