r, under the
influence of the sun-rays, plants decompose carbonic acid, appropriating
its carbon, and, for the most part, setting the oxygen free. The
quantity of carbon which can thus be condensed for the use of a plant,
and, indeed, every such decomposing action by light, is directly
proportionate to the quantity of light consumed, as experiments which I
have personally made have proved. For the production of so great a
weight of combustible matter a very long period of time was necessarily
required, that the sun might supply the necessary luminous influence.

Age after age the sunbeams continued their work, changing the mechanical
relations and composition of the atmosphere, the constitution of the
sea, and the appearance of the surface of the earth. There was a
prodigious growth of ferns, lepidodendra, equisetaceae, coniferae. The
percentage of oxygen in the air continually increased, that of carbonic
acid continually declined; the pressure of the air correspondingly
diminished, partly because of the replacement of a heavy gas by a
lighter one, and partly because of the general decline of temperature
slowly taking place, which diminished the absolute volume of vapour.
[Sidenote: and also on the sea.] The sea, in its deepest abysses, was
likewise affected by the sunlight; not directly, but in an indirect way;
for, as the removal of carbonic acid from the atmosphere went on,
portions of that gas were perpetually surrendered by the ocean in order
to maintain a diffusion-equilibrium between its dissolved gas and the
free gas of the air. And now no longer could be held in transparent
solution by the water those great quantities of carbonate of lime which
had once been concealed in it, the deposit of a given weight of coal in
the earth being inevitably followed by the deposit of an equivalent
weight of carbonate of lime in the sea. This might have taken place as
an amorphous precipitate; but the probabilities were that it would
occur, as in fact it did, under forms of organization in the great
limestone strata coeval with and posterior to the coal. The air and the
ocean were thus suffering an invisible change through the disturbing
agency of the sun, and the surface of the solid earth was likewise
undergoing a more manifest, and, it may be said, more glorious
alteration. Plants, in wild luxuriance, were developing themselves in
the hot and dank climate, and the possibility was now approaching for
the appearance of animal