and would premise that there is no fact better established in all the range of physical science than that of Priestley's, heretofore mentioned, that plants grow at the expense of the atmosphere. I further call to mind the indubitable fact that all coal, whether bituminous or anthracite, is of vegetable origin; that all the great deposits of these carbonaceous materials, occurring in Europe, Asia, Africa, America, and in the islands of the sea, for hundreds of miles in extent, and of unknown thickness, are vegetable matters once formed under the influence of the sunlight, and existing as luxuriant forest-growths—forests that in succession were entombed in the bowels of the earth. There was then most assuredly a time when all this carbon existed as carbonic-acid gas in the air, giving rise to an atmosphere in which, as we know, animal life could not exist. But the sun had charge of the matter, and as centuries rolled by he was extracting that poisonous gas from the atmosphere, effecting its decomposition, as he did for Priestley, bringing forth from it vital air, oxygen gas, and getting things ready for the appearance and continuance of animal life.
I therefore regard, in a philosophical point of view, the period of the deposit of the coal as the great event in the earth's history. Those who are familiar with the details of these things will recognize it as the epoch which parts off a blank solitude on one side, broken by the rude beginnings of low animal life, from that later period, on the other, which is adorned by all the beautiful contrivances of animated Nature, and crowned by the presence of man. The laws of Nature have ever from the beginning been such as they are now. We are fully able to trace the clear relationship between the condition of living things on the surface of the earth and the constitution of the atmosphere; and what chemistry says ought to have taken place in successive centuries, geology tells us actually occurred. Understanding the changing condition of things as respects the air, we could predict the corresponding changes in animated Nature, and the evidence that we are right is engraved on the rocks and stamped on the ocean.
So, therefore, we see that that relation which now exists between animals and plants, and the atmosphere, is an affair that has sprung out of a prior order of things—that there was a time when the constitution of the air was utterly unfit for the support of animal life; that a purification took place through the action of the rays of the sun; and the deposit of coal marks out the great epoch when life of a high order, among air-breathing animals, became a possibility. And is it not interesting to remark how gradually, from a totally different order of things, have sprung those great laws which determine not only the fixity of the constitution of the air, but also the duration of species and individuals; that automatic, self-acting machine in which animal and vegetable life are the opposing forces.
In thus sketching out the course of events as we now know them to have taken place in those ancient times, and in explaining how one
