For, after that first assertion, we read of continued acts of “separation” by an Almighty _fiat_. Thus light is separated from darkness; waters from waters; water from earth. And by a like analogy we may suppose that the “firmament” or atmosphere, the lower part of which we breathe, was also eliminated in its component gases from the primitive shapeless bulk of matter. If we take forty-five miles as the average height of this atmosphere above the surface of our globe, it is proportionately, like the thin rind upon an apple, or the bloom upon a peach; and may very well have come forth without any violence done to nature, or any waste of her resources, from the womb of the earth. OXYGEN is a gas universally diffused, for without a large supply of it human beings and all the mammals, birds, and reptiles, would die. But oxygen is not a more _simple_ element than CARBON or SILICON; and silicon is almost as universal, for it enters largely into the composition of all known rocks, excepting coal, limestone, and rock-salt. Then, beside silicon and carbon, there is BORON, and many others, all of which will combine permanently with the principal gases, and which we may, therefore, fairly suppose did so in the beginning. The oxygen which we breathe enters into composition with almost all known substances. It constitutes about one-fifth of the atmosphere, perhaps eight-ninths of the water, and helps chemically to compound all forms of earth and rock, and all the metals save five. Now this proclaims at once a _kindred_ element, and does not look like a substance made independent of all the others at the first. Even _potash_ and _soda_, which were long called “fixed alkalis,” having resisted all attempts to decompose them, yielded at last to a galvanic process, and were found to be compound; oxygen, in both cases, having united itself intimately with a metallic base.