enormous quantities of carbonic acid
gas are exhaled in the vicinity of the extinct craters of the Rhine (in
the neighborhood of the Laacher-see, for example, and the Eifel), and
also in the mineral springs of Nassau and other countries, where there
are no immediate traces of volcanic action. It would be easy to
calculate in how short a period the solid carbon, thus emitted from the
interior of the earth in an invisible form, would amount to a quantity
as great as could be obtained from the trees of a large forest, and how
many thousand years would be required to supply the materials of a dense
seam of pure coal from the same source. Geologists who favor the
doctrine of the former existence of an atmosphere highly charged with
carbonic acid, at the period of the ancient coal-plants, have not
sufficiently reflected on the continual disengagement of carbon, which
is taking place in a gaseous form from springs, as also in a free state
from the ground and from volcanic craters into the air. We know that
all plants are now engaged in secreting carbon, and many thousands of
large trees are annually floated down by great rivers, and buried in
their alluvial deposits; but before we can assume that the quantity of
carbon which becomes permanently locked up in the earth by such agency
will bring about an essential change in the chemical composition of the
atmosphere, we must be sure that the trees annually buried contain more
carbon than is given out from the interior of the earth in the same
lapse of time. Every large area covered by a dense mass of peat, bears
ample testimony to the fact, that several million tons of carbon have
been taken from the air, by the powers of vegetable life, and stored up
in the earth's crust, a large quantity of oxygen having been at the same
time set free; but we cannot infer from these circumstances, that the
constitution of the atmosphere has been materially deranged, until we
have data for estimating the rate at which dead animal and vegetable
substances are daily putrefying,--organic remains and various calcareous
rocks decomposing, and volcanic regions emitting fresh volumes of
carbonic acid gas. That the ancient carboniferous period was one of vast
duration all geologists are agreed; instead, therefore, of supposing an
excess of carbonic acid in the air at that epoch, for the support of a
peculiar flora, we may imagine Time to have multiplied the quantity of
carbon given out annually by minera