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Page:Popular Science Monthly Volume 4.djvu/718

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THE POPULAR SCIENCE MONTHLY.

these minerals and metals came down in just the form and order that we have indicated, or that they were regularly deposited, and left the orderly traces that perhaps our hasty sketch would seem to imply. There were unquestionably constant and profound commotions in the atmosphere, and the commingling of the most diverse elements. There were doubtless repeated meltings and chemical recombinations at the surface, and the rending and comminuting of the newly-formed crust by internal forces. The history of the earth's irregularities and disorders forms the greater part of geology. But what we do claim as certain is, that all the constituents of the outer shell of our globe existed at one time as elemental gases above a sea of matter that was held in condensation by superincumbent pressure; that, as the earth gradually cooled, these gases condensed somewhat in the order, inversely of their volatility, and directly of their nearness to the outer bounds of the atmosphere, and fell to the surface like rain and snow from water-clouds; that they formed chemical combinations at the instant of their condensation, or subsequently according to the power of their affinities or the elements that were present; and that, excepting the more recent displacements by mechanical forces, they now lie in the earth as they fell from the heavens.

The silica and silicates, which form the base, and by far the greater part of the earth's crust, became oxides of their several elements because oxygen was the superabundant gas in its composition. There have been worlds made up apparently without oxygen; for the meteorites, which must be regarded as sample specimens from some stranger world, however they may have been dispatched to us, are mostly composed of pure crystalline and malleable iron, which could have cooled into that condition only where there was no oxygen nor carbonic gases. If chlorine had been our superabundant gas, the silicon would perhaps quite as readily have united with it, and formed as stable a compound as with oxygen. But the product, instead of being the hardest of rocks, would have been a liquid very much resembling water, a little heavier, and nearly as volatile, as the common ethers. In this case there could have been no dry land, and no living beings that we can conceive of. Eternal clouds and storms would have covered the face of a surging boundless ocean.

Hitherto, in our accounts of terrestrial phenomena, water has played no part. It is probable that it was early formed, and in the condition of vapor or steam diffused through the upper air. In this state it bears the highest degree of heat that we can produce, without decomposition. Hydrogen is the lightest of all the gases, and unquestionably took its place on the outer limits of the atmosphere. There it was brought into contact with oxygen by the commotion of the elements, and converted into steam as fast as its lowering temperature allowed of the combination. As we might expect from the respective positions of the gases, all the hydrogen which fell to the