“Of old hast thou laid the foundation of the earth.”
David.
As yet we have only been talking about the crust of the earth; we shall now return and enter upon its actual examination. It will not be necessary for us personally to descend into the abysmous caverns that lie beneath our feet, nor, with hammer in hand, to go forth and explore the district of country in which we may happen to dwell: we may do all this by and by, when we know both how and what to observe. Meanwhile, with such teachers as Buckland, Sedgwick, Murchison, Pye Smith, Hugh Miller, De la Beche, Lyell, Owen and others, we may for some while to come be only tarry-at-home travellers; for in a true sense, in this department of knowledge, “other men have laboured, and we enter into their labours.” Let us now look at the crust of the earth, as it may be represented in two imaginary sections. Suppose we could make a vertical section of the earth’s crust, and cut straight down some eighty miles till we reached the central mass of incandescence that we believe lies beneath this crust, or Erdrinde (earth-rind), as the Germans call it, and then bring out this section to daylight, it would present something very much like the following appearance.
DIAGRAM I.
Here the granite A will be observed forming the supposed boundary between the superlying strata and the fire B below to which we have just referred, and thus will be seen the origin of all plutonic rocks. Here too will be seen how the granite is not confined to the lower levels, but rises, as mentioned in the first chapter, far above all the other strata, and forms some of the highest peaks on the face of the globe.[[6]] Here, too, will be seen how the granite is frequently traversed by veins of trap-dykes, those black-looking branches, which rise often above the whole mass of metamorphic and stratified rocks, often occasioning great difficulties in mining operations. Here, too, the student will see how, supposing the theory of a central globe of heat to be founded in fact, the volcanoes that are now active, C, form, as the volcanoes that are extinct, D, once did, the safety valves of this mighty mass of incandescence, B; and in the same way may be seen how certain strata may be above the granite, or above any other formation, though they do not overlie them, and how the lowest strata, being formed first, is said to be older than any superlying strata, notwithstanding any accidental arrangement produced by upheaval or depression. For, in “consequence of the great commotions which the crust of the globe has undergone, many points of its surface have been elevated to great heights in the form of mountains; and hence it is that fossils are sometimes found at the summit of the highest mountains, though the rocks containing them were originally formed at the bottom of the sea. But, even when folded or partly broken, their relative age may still be determined by an examination of the ends of their upturned strata, where they appear or crop out in succession, at the surface or on the slopes of mountains.”[[7]]
But to make this view of the subject clearer, let us imagine that some Titanic power was granted us to push down these towering masses of granite to their original situation, below the metamorphic and stratified rocks, by which means we should at the same time restore these curved and broken strata to their originally horizontal position; and let us suppose that we were now again to descend to the foundations of the earth for the purpose of making another vertical section; then the crust of the earth would present to us an arrangement something like the leaves of a book, or the coats of an onion, arranged in successive and uninterrupted layers, or in concentric and unbroken circles. Such a diagram must of course be imaginary, and unless it is taken into connexion with the previous remarks, it is more likely to bewilder than to assist the beginner. Let it again be urged upon the reader, that such a chart as we are about to lay before him is only intended to give him an idea of the succession of these formations and systems, and that the details found in it are anticipatory of many future references to it on the student’s part. Let it not be supposed that this is a mere barren research into dry facts that have no connexion with our truest welfare; for if, as Lord Bacon somewhere finely observes, all study is to be valued “not so mush as an exercise of the intellect, but as a true discipline of humanity,” then what study is calculated to be more useful than Geology, in enlarging and purifying the powers of the mind, by teaching us how harmonious, and orderly, and economic are the works of God; in removing all narrow notions of the extent and age of this solid globe, which from the beginning had its origin in the almighty will of God; in checking the presumptuous or the chilling inferences of a sceptical philosophy, by everywhere pointing out the design, skill, and adaptations of an ever-present and most beneficent Creator; and in chastening those overweening ideas of ourselves which both ignorance and knowledge may create and foster, by saying to us, in the language of God himself, as we stand amazed in the presence of huge pre-Adamite vestiges of creation, “Where wast thou,” vain man, “when I laid the foundations of the earth? Declare if thou hast understanding.” (Job xxxviii. 4.)
“Among these rocks and stones, methinks I see
More than the heedless impress that belongs
To lonely nature’s casual work; they bear