Geology.
In the chemical and mineral sections of this volume we have heard something concerning the formation of the globe and its composition, its clays, rocks, etc. With these internal arrangements Chemistry and Mineralogy have dealt. Geology tells us about the external surface of the earth, its stones and rocks, and how they were formed, and generally something about the conformation of the crust of the earth, and its history.
When we speak of “crust” of the earth, we do not simply mean the exterior layer of gravel, clay, or stone. The crust is a thick one, and our crust extends just so far as we can cut into it. The surface of the sea can scarcely be termed a crust, but we must penetrate that ever-moving liquid boundary, and touch upon (and examine) what lies down below far beyond the “full fathom five” of the lead line. In this study we must not forget our Book of Nature, which is always open and inviting us to read. We shall see how things are produced, and how our physical surroundings will continue to be produced until the age of miracles returns, and Providence sees fit to interfere with the otherwise immutable laws which He in His wisdom has laid down for the universe.
It will be of no use to go back into space and imagine the world a red-hot fragment of matter, whirling through the heaven around the sun which, as a larger aggregation of burning atoms, kept it, as it now keeps it, in its place. The earth was a globe of liquid fire, or in gaseous state, and the atoms gradually cooled on the surface; the fire is still under our feet. The outer part would by degrees lose all its heat, while the interior remained hot; the planet must then have been surrounded by a steamy atmosphere, and enveloped in vapours condensed from the air through which no light of the sun could by any appreciable degree penetrate.
We can give an example of this, and it will be seen how the surface of the earth gradually became formed from the vaporous condition. If any one will take the pains to evaporate any saline solution in a capsule till it is about to crystallise, and observe attentively the pellicle of salt as it forms on the surface; first a partial film will show itself in a few places, floating about and joining with others, then when nearly the whole surface is coated, it will break up in some places and sink into the liquid beneath, another pellicle will form and join with the remains of the first, and as this thickens it will push up ridges and inequalities of the surface from openings and fissures in which little jets of steam and fluid will escape; these little ridges are chains of mountains, the little jets of steam those volcanic eruptions which were at that period so frequent, the surface of the capsule is the surface of the earth, and the five minutes which the observer has contemplated it, a million years.
The next effect of the cooling of the earth would be the gradual condensation of the vapour of water with which it was surrounded; this falling upon the earth formed seas and oceans, leaving only the higher portions exposed above its level. The clearing up of the dense dark clouds for the first time let in upon the earth’s surface the glorious and vivifying rays of the sun, and this great effect possibly accords with the earliest record in the Bible of the acts of creation: “And God said, let there be light, and there was light.”
This clearing up of the vapours and the subsequent rain no doubt gave rise to terribly grand electrical phenomena—thunderings and lightnings. By degrees the waters got their own way, and then many changes took place, land and water fighting, as it were, for the mastery, as they are fighting to this day.
But perhaps some reader may not think that the land and water of our earth are thus engaged. A very few minutes’ reflection will suffice to confirm our assertion. Look at the lofty crags in the Alps, for instance; what has shattered those peaks, and sent the masses toppling down in stone avalanches to the lower slopes, and then into the valleys?—Water. Water has been in the crevices, and was frozen there; in freezing it expanded and loosened the crags, which, forced asunder, gave an opening to more snow and ice, and so this powerful leverage, aided by the wind and storm, is disintegrating our mountains.
