If you wish to form some intelligible conception of the state and condition of the earth, you need simply go to a foundry, and watch the cooling of a cannon-ball heated to redness; as it cools you see the surface becoming gradually covered with pellicles, or flakes of oxide of iron, whilst a touch will speedily convince you that the heat beneath the surface continues still unabated; and it is only after a certain time, when the process of cooling has extended to the inner part, that you may take up the ball without burning your fingers. Now proceed a little further; take up a mass of cinder, or scoria, that has cooled, and break it to pieces—you will find that the inside shows streaks and veins of different materials, and presents many cavities or holes, called by foundrymen “honeycomb.” Reflect now that these cavities were formed in the cinder while yet in the red-hot state, either by air or by gases. Think that at the bottom of these cavities there once was floating a small drop of melted matter. Now bring your imagination into play, and let that cinder represent the earth; the cavities subterranean caverns of many hundred square miles, and the melted drop an immense lake of liquid fire, burning, boiling, heaving to the top, enlarging the cavern, melting away parts of the crust nearest to it, or swelling it up until it cracks, and forms crevices and fissures for the escape of smoke, flames, and fused matter. Here you have, also, at once, an intelligible theory of earthquakes and volcanic eruptions.
