22. At the commencement of the transition period the solid granite crust had thickened only a little, and offered but a feeble resistance to the effervescence of the burning substance which it covered and repressed. Numerous rents were made, by means of which the interior land was thrown out. The soil presented considerable inequalities of surface.
Waters not very deep covered nearly all the surface of the globe, with the exception of elevated lands formed of rocks frequently submerged at their base.
The air gradually became purged from the heavier gaseous substances, which, while condensing by the cooling process, were precipitated to the surface of the ground, then drawn into and dissolved by the waters.
At this epoch it is necessary to understand “cooling process” in a relative sense; that is to say, in connection with the primitive state; for the temperature must have still been burning.
The thick aqueous vapor which was raised on all sides from the immense liquid surface fell in abundant and warm rains, obscuring the air. Soon, however, the rays of the sun began to shine through this foggy atmosphere.
One of the last substances of which the air has been purged, because it is naturally in a gaseous state, is carbonic-acid gas, which then formed one of its constituent parts.
23. At this epoch beds of earthly sediment began to form, deposited by waters charged with lime and other matters peculiar to organic life.
Then appeared the first living beings of the vegetable and animal kingdom. At first few in number, one finds more and more frequent traces of such as one penetrates more and more deeply into the beds of this formation. It is to be remarked, that everywhere life is manifested as soon as conditions are propitious to vitality, and that each species is born as soon as the proper conditions of its existence are produced.
24. The first organized existences which appeared upon the Earth were vegetables of the least complicated organization, designated in botany under the names of cryptogams, acotyledonous plants and monocotyledonous plants, such as lichens, mushrooms, mosses, ferns, and herbaceous plants. One does not now see trees with woody trunks, but only those of the palm species, whose sponge-like trunks are analogous to the stems of herbs.
The animals of this period, which have succeeded to the first vegetation, are exclusively marine. These were at first polyps, radiates, zoophytes, animals whose rudimentary and simple organizations approach most nearly to vegetable forms. Later came fishes and shellfish, the species of which do not exist now.
25. Under the empire of heat and humidity and in consequence of the excess of carbonic acid dispersed into the air – a gas improper for the respiration of terrestrial animals but necessary to the plants – the exposed terrains were quickly covered with a pungent vegetation while at the same time aquatic plants multiplied on the surface of marshes. Plants, which in our day are simple herbs a few inches high, attained a prodigious height and magnitude; there were then forests of tree-like ferns from eight to ten yards in height, and of proportionate magnitude; plants called wolfs foot, and a kind of moss of the same size, equisetum arvense, * four or five yards high, which we hardly see now. At the end of this period pines or fir-trees began to appear.
* A marsh-plant commonly called horsetail.
26. In consequence of the displacement of the waters, the grounds which produced these masses of vegetation were many times submerged, covered again with terrestrial sediment, during which those which had become dry appeared in their turn with a similar vegetation; thus there were many successive generations of vegetables destroyed and renewed again. The animals being aquatic suffered nothing from these changes.
These remains accumulated during a long series of years, and formed beds of great thickness. Under the actions of heat, of humidity, of pressure, exercised by subsequent terrestrial deposits, and, without doubt, also various chemical agents, such as gas, acids, and salts, products of a combination of primitive elements, these vegetable substances were submitted to a fermentation converting them into coal. The coal-mines are, then, the direct result of the decomposition of a mass of vegetables accumulated during the transition period. That is why they are found in almost every country. *
* Turf is produced in the same manner by the decomposition of vegetable matter in marshy grounds; but with this difference, being much more recent and formed under different conditions, it has not had time to carbonize.
27. The fossil remains of the luxuriant vegetation of this epoch are being discovered today under the ice of the polar regions, as well as in the torrid zone: therefore it is necessary to conclude, that, since vegetation was uniform, the temperature also must have been equally so. The poles were then not covered with ice as now: then the Earth drew its heat from itself, from the central fire which equally heated all the solid bed, then too thin to offer to it successful resistance. This heat was much greater than that conveyed by the solar rays, enfeebled as they were by the density of the atmosphere. Later on, when the central heat could exert only a feeble influence upon the surface, that of the sun preponderate; and the Polar Regions, receiving only oblique rays giving very little heat, became covered with ice. One understands that at the epoch of which we speak, and for a long time after, ice was unknown upon the Earth.
This period has been a very long one, judging from the number and thickness of the coal-beds. *
* In the Bay of Fundy (Nova Scotia), M. Lyell found upon a coal-bed four hundred yards in thickness, sixty-eight different levels, presenting evident traces of many forest soils, the trunks of the trees of which were still garnished with their roots (L. Figuier). Supposing that it takes one thousand years to form each of these levels; it must have taken sixty-eight thousand years to form this coal-bed alone.