PRELIMINARIES.
“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.
[Illustration:
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
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.)
[Illustration:
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_, and _volcanic_—_granite_
being the basis of all known rocks, and occurring along with the primary
and transition strata; the _trappean_, of a darker and less crystalline
structure than the granite, and occurring along with the secondary and
tertiary rocks; and the _volcanic_, 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 this science, 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 formation might 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 page 27 is a diagram,
representing no ideal, but an actual boring into the earth. London is
situated on the tertiary formation, in what is called geologically 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:—
[Illustration:
DIAGRAM III.
]
[Illustration:
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 clay above 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 page 21, that the theory
of the earth’s crust may be the more thoroughly understood before we
proceed.
[Illustration:
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 page 21, 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 happily opened 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 these pre-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, 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 found _no tendency_ to apathy or ennui. Every excursion
presented something to admire; every day had its novelty; the morning
was always pregnant with eager expectation; the evening invariably
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 through the 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, infinite
Thy power! what thought can measure thee, or tongue
Relate thee?’”[13]