CHAPTER II.PRELIMINARIES.

“Of old hast thou laid the foundation of the earth.”David.

“Of old hast thou laid the foundation of the earth.”

David.

As yet we have only beentalkingabout 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 bothhowandwhatto 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 graniteAwill be observed forming the supposed boundary between the superlying strata and the fireBbelow 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 lowerlevels, 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 “consequenceof 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 anonion, 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 inferencesof 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 seeMore than the heedless impress that belongsTo lonely nature’scasualwork; they bearA semblance strange to Power intelligent,And of Design not wholly worn away.And I ownSome shadowy intimations haunt me here,That in these shows a chronicle survivesOf purposes akin to those of man,Measuring through all degrees, until the scaleOf time and conscious nature disappear,Lost in unsearchable eternity.”—Wordsworth.

“Among these rocks and stones, methinks I see

More than the heedless impress that belongs

To lonely nature’scasualwork; they bear

A semblance strange to Power intelligent,

And of Design not wholly worn away.

And I own

Some shadowy intimations haunt me here,

That in these shows a chronicle survives

Of purposes akin to those of man,

Measuring through all degrees, until the scale

Of time and conscious nature disappear,

Lost in unsearchable eternity.”—Wordsworth.

We will now proceed to the diagram to which we have made allusion, and which represents an ideal section of the earth’s crust as the various formations are there found arranged. (Diagram II.)

DIAGRAM II.

Here, in the words of another writer, we would add for the reader’s guidance, that “the unstratified or igneous rocks occur in no regular succession, but appear amidst the stratified without order or arrangement; heaving them out of their original horizontal positions, breaking up through them in volcanic masses, and sometimes overrunning them after the manner of liquid lava. From these circumstances they are, in general, better known by their mineral composition than by their order of occurrence. Still it may be convenient to divide them into three great classes;granite,trappean, andvolcanic—granitebeing the basis of all known rocks, and occurring along with the primary and transition strata; thetrappean, of a darker and less crystalline structure than the granite, and occurring along with the secondary and tertiary rocks; and thevolcanic, still less crystalline and compact, and of comparatively recent origin, or still in process of formation.” This the student will observe by another reference to the previous diagram; but, in looking at the one now before him, we must also add for his further guidance,—for we are presuming that we address those who need initiation into the rudiments of thisscience, and the circumstance that we never met with a preliminary treatise that quite satisfied us, or helped such intelligent youth as were prying into the apparently cabalistic mysteries of the earth’s structural divisions, is one strong inducement to the present undertaking;—we must add, that “it must not be supposed, however, that all the stratified rocks always occur in any one portion of the earth’s crust in full and complete succession as represented” in Diagram II. “All that is meant is, that such would be their order if every group and formation were present. But whatever number of groups may be present, they never happen out of their regular order of succession; that is, clay-slate never occurs above coal, nor coal above chalk. Thus in London, tertiary strata occupy the surface; in Durham, magnesian limestone; in Fife, the coal measures; and in Perthshire, the old red sandstone and clay-slate; so that it would be fruitless to dig for chalk in Durham, for magnesian limestone in Fife, or for coal in Perthshire. It would not be absurd, however, to dig for coal in Durham, because that mineral underlies the magnesian limestone; or for old red sandstone in Fife, because that formationmight be naturally expected to occur under the coal strata of that country, in the regular order of succession.”[8]

Still, after reading all this, we can easily imagine, not so much an air of incredulity taking possession of the countenance of our courteous reader as a feeling somewhat like this, with which we have often come into contact in those geological classes of young persons which it has been our pleasure to conduct: “Well, all that’s very plain in the book; I see granite lies at the bottom, and pushes itself up to the top very often; and I see in the diagrams that coal and chalk are not found in the same place, and that different localities have their different formations, and the various formations have their different fossils, but I confess that I cannot realize it. I know the earth is round like an orange, a little flattened at the poles—what is called an oblate spheroid; but all this surpasses my power of comprehension; can’t you make it plainer?” Well, let us try; on page27is a diagram, representing no ideal, but an actual boring into the earth. London is situated on the tertiary formation, in what is calledgeologically the basin of the London clay, that is almost on the very top of the crust, or external covering that lies on the vast mass of molten and other matter beneath. Here is first a drawing and then a section that may represent this basin:—

DIAGRAM III.

DIAGRAM IV.

The water which falls on the chalk hills flows into them, or into the porous beds adjoining, and would rise upwards to its level but for the superincumbent pressure of the bed of clayabove it,cccc. Under these circumstances, in order to procure water, Artesian[9]wells are sunk through the bed of clay, perhaps also through the chalk, but at any rate till the depressed stratum of chalk is reached; and this gives exit to the subterranean water, which at once rises through the iron tubes inserted in the boring to the surface. By these borings through the clay, water is obtained where it would be impossible to sink a well, or where the expense would prohibit the attempt. To explain this matter, here is a diagram (No. V.) which represents the Artesian well at the Model Prison at Pentonville, London, the strata upon which London is built, and which we can apply to the diagram on page21, that the theory of the earth’s crust may be the more thoroughly understood before we proceed.

DIAGRAM V.

In the same manner Artesian wells have been sunk in other places, as at Hampstead Water Works, 450 feet deep; Combe & Delafield’s, 500 feet deep; and the Trafalgar-square Water Works, 510 feet deep.[10]Now, the reader has only to take this last diagram, and in imagination to apply it to the one on page21, in order to see that so far as actual boring and investigation go, the geological theory of the earth’s crust is correct; only again let it be observed that this order is never inverted, although it frequently happens that some one or more of the strata may be absent.

Hitherto we have spoken of the earth’s crust without reference to that wondrous succession and development of living beings which once had their joy of life, and whose fossil remains, found in the different strata, waken such kindling emotions of the power of Deity, and enlarge indefinitely our conceptions of the boundless resources of His Mind. This will open before us a new chapter in the history of our planet, already the theatre of such vast revolutions, and which, under the influence of Divine truth, is yet to undergo one greater and nobler than any of these. We have as yet only glanced at the surface page of the wondrous book, now happilyopened for us by geologists, to whose names we have already made reference; and as the mind rests with intense pleasure on the discoveries of Champollion, Belzoni, Lane, Layard, Botta, and others who have deciphered the hieroglyphics, in which were written the wars and the chronicles of ancient nations, whose names and deeds are becoming, by books and lectures, and above all by our noble national Museum, familiar even to our children, and a source of help and solace to the hard-toiling artisan; so with profounder interest, as carried back into remoter ages of antiquity, so remote that they seem to lie beyond the power of a human arithmetic to calculate, do we humbly endeavour to decipher the hieroglyphics,[11]not of Egypt or of Nineveh, but of the vast creation of God, written in characters that require, not only learning and science to understand, but modesty, patience, and triumphant perseverance. He who with thesepre-requisites combines reverence for God and His revelation, will always find in Geology material both for manly exercise of thought, and also for reverent adoration of Him who is Himself unsearchable, and whose ways are past finding out.

“We not to explore the secrets, askOf His eternal empire, but the moreTo magnify His works, the more we know.”—Milton.

“We not to explore the secrets, ask

Of His eternal empire, but the more

To magnify His works, the more we know.”—Milton.

Most happily for Christendom, our noblest men of science are not ashamed of the “reproach of Christ;” and we know not how to conclude this chapter in a strain more accordant with our own thoughts than by quoting the words of an eminent living naturalist:—“I can echo with fullest truth the experience of Bishop Heber; ‘In every ride I have taken, and in every wilderness in which my tent has been pitched, I have found enough to keep my mind from sinking into the languor and the apathy which have been regarded as natural to a tropical climate.’ Nay, I may truly say, I foundno tendencyto apathy or ennui. Every excursion presented something to admire; every day had its novelty; the morning was always pregnant with eager expectation; the eveninginvariably brought subjects of interest fresh and new; and the days were only too short for enjoyment. They were not days of stirring adventure, of dangerous conflicts with man or with beast, or of hair-breadth escapes in flood and field; their delights were calm and peaceful, I trust not unholy, nor unbecoming the character of a Christian, who has his heart in heaven, and who traces, even in earth’s loveliest scenes, the mark of the spoiler. The sentiments expressed by my friend[12]and fellow-labourer are those which I would ever associate with the study of science. ‘If the sight of nature,’ observes Mr. Hill, ‘were merely the looking at a painted pageantry, or at a spectacle filling the carnal mind with wonder and delight, the spirit would be overpowered and worked into weariness; but it is admiration at the wisdom, and reverence for the beneficence of Almighty power. He who dwelleth in the light which no man can approach unto, whom no man hath seen, nor can see,’ is yet visible in His perfections throughthe works of His hand, and His designs are made manifest in the purpose of His creatures. Wherever our lot is cast, into whatever scenes our wayward impulses lead us, the mind-illumined eye gazes on divine things, and the spirit-stirred heart feels its pulses bounding with emotions from the touch of an ever-present Deity. The habit that sees in every object the wisdom and the goodness as well as the power of God, I may speak of, as Coleridge speaks of the poetical spirit, ‘it has been to me an exceeding great reward; it has soothed my afflictions; it has multiplied and refined my enjoyments; it has endeared my solitude; and it has given me the habit of wishing to discover the good and the beautiful in all that meets and surrounds me.’

“‘Great are thy works, Jehovah, infiniteThy power! what thought can measure thee, or tongueRelate thee?’”[13]

“‘Great are thy works, Jehovah, infinite

Thy power! what thought can measure thee, or tongue

Relate thee?’”[13]

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