My dear readers, let me, before touching on the special subject of
this paper, say a few words on that of the whole series.
It is geology: that is, the science which explains to us the RIND of
the earth; of what it is made; how it has been made. It tells us
nothing of the mass of the earth. That is, properly speaking, an
astronomical question. If I may be allowed to liken this earth to a
fruit, then astronomy will tell us--when it knows--how the fruit
grew, and what is inside the fruit. Geology can only tell us at most
how its rind, its outer covering, grew, and of what it is composed; a
very small part, doubtless, of all that is to be known about this
planet.
But as it happens, the mere rind of this earth-fruit which has,
countless ages since, dropped, as it were, from the Bosom of God, the
Eternal Fount of Life--the mere rind of this earth-fruit, I say, is
so beautiful and so complex, that it is well worth our awful and
reverent study. It has been well said, indeed, that the history of
it, which we call geology, would be a magnificent epic poem, were
there only any human interest in it; did it deal with creatures more
like ourselves than stones, and bones, and the dead relics of plants
and beasts. Whether there be no human interest in geology; whether
man did not exist on the earth during ages which have seen enormous
geological changes, is becoming more and more an open question.
But meanwhile all must agree that there is matter enough for
interest--nay, room enough for the free use of the imagination, in a
science which tells of the growth and decay of whole mountain-ranges,
continents, oceans, whole tribes and worlds of plants and animals.
And yet it is not so much for the vastness and grandeur of those
scenes of the distant past, to which the science of geology
introduces us, that I value it as a study, and wish earnestly to
awaken you to its beauty and importance. It is because it is the
science from which you will learn most easily a sound scientific
habit of thought. I say most easily; and for these reasons. The
most important facts of geology do not require, to discover them, any
knowledge of mathematics or of chemical analysis; they may be studied
in every bank, every grot, every quarry, every railway-cutting, by
anyone who has eyes and common sense, and who chooses to copy the
late illustrious Hugh Miller, who made himself a great geologist out
of a poor stonemason. Next, its most important theories are not, or
need not be, wrapped up in obscure Latin and Greek terms. They may
be expressed in the simplest English, because they are discovered by
simple common sense. And thus geology is (or ought to be), in
popular parlance, the people's science--the science by studying
which, the man ignorant of Latin, Greek, mathematics, scientific
chemistry, can yet become--as far as his brain enables him--a truly
scientific man.
But how shall we learn science by mere common sense?
First. Always try to explain the unknown by the known. If you meet
something which you have not seen before, then think of the thing
most like it which you have seen before; and try if that which you
know explains the one will not explain the other also. Sometimes it
will; sometimes it will not. But if it will, no one has a right to
ask you to try any other explanation.
Suppose, for instance, that you found a dead bird on the top of a
cathedral tower, and were asked how you thought it had got there.
You would say, "Of course, it died up here." But if a friend said,
"Not so; it dropped from a balloon, or from the clouds;" and told you
the prettiest tale of how the bird came to so strange an end, you
would answer, "No, no; I must reason from what I know. I know that
birds haunt the cathedral tower; I know that birds die; and
therefore, let your story be as pretty as it may, my common sense
bids me take the simplest explanation, and say--it died here." In
saying that, you would be talking scientifically. You would have
made a fair and sufficient induction (as it is called) from the facts
about birds' habits and birds' deaths which you know.
But suppose that when you took the bird up you found that it was
neither a jackdaw, nor a sparrow nor a swallow, as you expected, but
a humming-bird. Then you would be adrift again. The fact of it
being a humming-bird would be a new fact which you had not taken into
account, and for which your old explanation was not sufficient; and
you would have to try a new induction--to use your common sense
afresh--saying, "I have not to explain merely how a dead bird got
here, but how a dead humming-bird."
And now, if your imaginative friend chimed in triumphantly with: "Do
you not see that I was right after all? Do you not see that it fell
from the clouds? that it was swept away hither, all the way from
South America, by some south-westerly storm, and wearied out at last,
dropped here to find rest, as in a sacred-place?" what would you
answer? "My friend, that is a beautiful imagination; but I must
treat it only as such, as long as I can explain the mystery more
simply by facts which I do know. I do not know that humming-birds
can be blown across the Atlantic alive. I do know they are actually
brought across the Atlantic dead; are stuck in ladies' hats. I know
that ladies visit the cathedral; and odd as the accident is, I prefer
to believe, till I get a better explanation, that the humming-bird
has simply dropped out of a lady's hat." There, again, you would be
speaking common sense; and using, too, sound inductive method; trying
to explain what you do not know from what you do know already.
Now, I ask of you to employ the same common sense when you read and
think of Geology.
It is very necessary to do so. For in past times men have tried to
explain the making of the world around them, its oceans, rivers,
mountains, and continents, by I know not what of fancied cataclysms
and convulsions of nature; explaining the unknown by the still more
unknown, till some of their geological theories were no more
rational, because no more founded on known facts, than that of the
New Zealand Maories, who hold that some god, when fishing, fished up
their islands out of the bottom of the ocean. But a sounder and
wiser school of geologists now reigns; the father of whom, in England
at least, is the venerable Sir Charles Lyell. He was almost the
first of Englishmen who taught us to see--what common sense tells us-
-that the laws which we see at work around us now have been most
probably at work since the creation of the world; and that whatever
changes may seem to have taken place in past ages, and in ancient
rocks, should be explained, if possible, by the changes which are
taking place now in the most recent deposits--in the soil of the
field.
And in the last forty years--since that great and sound idea has
become rooted in the minds of students, and especially of English
students, geology has thriven and developed, perhaps more than any
other science; and has led men on to discoveries far more really
astonishing and awful than all fancied convulsions and cataclysms.
I have planned this series of papers, therefore, on Sir Charles
Lyell's method. I have begun by trying to teach a little about the
part of the earth's crust which lies nearest us, which we see most
often; namely, the soil; intending, if my readers do me the honour to
read the papers which follow, to lead them downward, as it were, into
the earth; deeper and deeper in each paper, to rocks and minerals
which are probably less known to them than the soil in the fields.
Thus you will find I shall lead you, or try to lead you on,
throughout the series, from the known to the unknown, and show you
how to explain the latter by the former. Sir Charles Lyell has, I
see, in the new edition of his "Student's Elements of Geology," begun
his book with the uppermost, that is, newest, strata, or layers; and
has gone regularly downwards in the course of the book to the lowest
or earliest strata; and I shall follow his plan.
I must ask you meanwhile to remember one law or rule, which seems to
me founded on common sense; namely, that the uppermost strata are
really almost always the newest; that when two or more layers,
whether of rock or earth--or indeed two stones in the street, or two
sheets on a bed, or two books on a table--any two or more lifeless
things, in fact, lie one on the other, then the lower one was most
probably put there first, and the upper one laid down on the lower.
Does that seem to you a truism? Do I seem almost impertinent in
asking you to remember it? So much the better. I shall be saved
unnecessary trouble hereafter.
But some one may say, and will have a right to say, "Stop--the lower
thing may have been thrust under the upper one." Quite true: and
therefore I said only that the lower one was most probably put there
first. And I said "most probably," because it is most probable that
in nature we should find things done by the method which costs least
force, just as you do them. I will warrant that when you want to
hide a thing, you lay something down on it ten times for once that
you thrust it under something else. You may say, "What? When I want
to hide a paper, say, under the sofa-cover, do I not thrust it
under?"
No, you lift up the cover, and slip the paper in, and let the cover
fall on it again. And so, even in that case, the paper has got into
its place first.
Now why is this? Simply because in laying one thing on another you
only move weight. In thrusting one thing under another, you have not
only to move weight, but to overcome friction. That is why you do
it, though you are hardly aware of it: simply because so you employ
less force, and take less trouble.
And so do clays and sands and stones. They are laid down on each
other, and not thrust under each other, because thus less force is
expended in getting them into place.
There are exceptions. There are cases in which nature does try to
thrust one rock under another. But to do that she requires a force
so enormous, compared with what is employed in laying one rock on
another, that (so to speak) she continually fails; and instead of
producing a volcanic eruption, produces only an earthquake. Of that
I may speak hereafter, and may tell you, in good time, how to
distinguish rocks which have been thrust in from beneath, from rocks
which have been laid down from above, as every rock between London
and Birmingham or Exeter has been laid down. That I only assert now.
But I do not wish you to take it on trust from me. I wish to prove
it to you as I go on, or to do what is far better for you: to put
you in the way of proving it for yourself, by using your common
sense.
At the risk of seeming prolix, I must say a few more words on this
matter. I have special reasons for it. Until I can get you to "let
your thoughts play freely" round this question of the superposition
of soils and rocks, there will be no use in my going on with these
papers.
Suppose then (to argue from the known to the unknown) that you were
watching men cleaning out a pond. Atop, perhaps, they would come to
a layer of soft mud, and under that to a layer of sand. Would not
common sense tell you that the sand was there first, and that the
water had laid down the mud on the top of it? Then, perhaps, they
might come to a layer of dead leaves. Would not common sense tell
you that the leaves were there before the sand above them? Then,
perhaps, to a layer of mud again. Would not common sense tell you
that the mud was there before the leaves? And so on down to the
bottom of the pond, where, lastly, I think common sense would tell
you that the bottom of the pond was there already, before all the
layers which were laid down on it. Is not that simple common sense?
Then apply that reasoning to the soils and rocks in any spot on
earth. If you made a deep boring, and found, as you would in many
parts of this kingdom, that the boring, after passing through the
soil of the field, entered clays or loose sands, you would say the
clays were there before the soil. If it then went down into
sandstone, you would say--would you not?--that sandstone must have
been here before the clay; and however thick--even thousands of feet-
-it might be, that would make no difference to your judgment. If
next the boring came into quite different rocks; into a different
sort of sandstone and shales, and among them beds of coal, would you
not say--These coal-beds must have been here before the sandstones?
And if you found in those coal-beds dead leaves and stems of plants,
would you not say--Those plants must have been laid down here before
the layers above them, just as the dead leaves in the pond were?
If you then came to a layer of limestone, would you not say the same?
And if you found that limestone full of shells and corals, dead, but
many of them quite perfect, some of the corals plainly in the very
place in which they grew, would you not say--These creatures must
have lived down here before the coal was laid on top of them? And
if, lastly, below the limestone you came to a bottom rock quite
different again, would you not say--The bottom rock must have been
here before the rocks on the top of it?
And if that bottom rock rose up a few miles off, two thousand feet,
or any other height, into hills, what would you say then? Would you
say: "Oh, but the rock is not bottom rock; is not under the
limestone here, but higher than it. So perhaps in this part it has
made a shift, and the highlands are younger than the lowlands; for
see, they rise so much higher?" Would not that be as wise as to say
that the bottom of the pond was not there before the pond mud,
because the banks round the pond rose higher than the mud?
Now for the soil of the field.
If we can understand a little about it, what it is made of, and how
it got there, we shall perhaps be on the right road toward
understanding what all England--and, indeed, the crust of this whole
planet--is made of; and how its rocks and soils got there.
But we shall best understand how the soil in the field was made, by
reasoning, as I have said, from the known to the unknown. What do I
mean? This: On the uplands are fields in which the soil is already
made. You do not know how? Then look for a field in which the soil
is still being made. There are plenty in every lowland. Learn how
it is being made there; apply the knowledge which you learn from them
to the upland fields which are already made.
If there is, as there usually is, a river-meadow, or still better, an
aestuary, near your town, you have every advantage for seeing soil
made. Thousands of square feet of fresh-made soil spread between
your town and the sea; thousands more are in process of being made.
You will see now why I have begun with the soil in the field; because
it is the uppermost, and therefore latest, of all the layers; and
also for this reason, that, if Sir Charles Lyell's theory be true--as
it is--then the soils and rocks below the soil of the field may have
been made in the very same way in which the soil of the field is
made. If so, it is well worth our while to examine it.
You all know from whence the soil comes which has filled up, in the
course of ages, the great aestuaries below London, Stirling, Chester,
or Cambridge.
It is river mud and sand. The river, helped by tributary brooks
right and left, has brought down from the inland that enormous mass.
You know that. You know that every flood and freshet brings a fresh
load, either of fine mud or of fine sand, or possibly some of it
peaty matter out of distant hills. Here is one indisputable fact
from which to start. Let us look for another.
How does the mud get into the river? The rain carries it thither.
If you wish to learn the first elements of geology by direct
experiment, do this: The next rainy day--the harder it rains the
better--instead of sitting at home over the fire, and reading a book
about geology, put on a macintosh and thick boots, and get away, I
care not whither, provided you can find there running water. If you
have not time to get away to a hilly country, then go to the nearest
bit of turnpike road, or the nearest sloping field, and see in little
how whole continents are made, and unmade again. Watch the rain
raking and sifting with its million delicate fingers, separating the
finer particles from the coarser, dropping the latter as soon as it
can, and carrying the former downward with it toward the sea. Follow
the nearest roadside drain where it runs into a pond, and see how it
drops the pebbles the moment it enters the pond, and then the sand in
a fan-shaped heap at the nearest end; but carries the fine mud on,
and holds it suspended, to be gradually deposited at the bottom in
the still water; and say to yourself: Perhaps the sands which cover
so many inland tracts were dropped by water, very near the shore of a
lake or sea, and by rapid currents. Perhaps, again, the brick clays,
which are often mingled with these sands, were dropped, like the mud
in the pond, in deeper water farther from the shore, and certainly in
stilt water. But more. Suppose once more, then, that looking and
watching a pond being cleared out, under the lowest layer of mud, you
found--as you would find in any of those magnificent reservoirs so
common in the Lancashire hills--a layer of vegetable soil, with grass
and brushwood rooted in it. What would you say but: The pond has
not been always full. It has at some time or other been dry enough
to let a whole copse grow up inside it?
And if you found--as you will actually find along some English
shores--under the sand hills, perhaps a bed of earth with shells and
bones; under that a bed of peat; under that one of blue silt; under
that a buried forest, with the trees upright and rooted; under that
another layer of blue silt full of roots and vegetable fibre; perhaps
under that again another old land surface with trees again growing in
it; and under all the main bottom clay of the district--what would
common sense tell you? I leave you to discover for yourselves. It
certainly would not tell you that those trees were thrust in there by
a violent convulsion, or that all those layers were deposited there
in a few days, or even a few years; and you might safely indulge in
speculations about the antiquity of the aestuary, and the changes
which it has undergone, with which I will not frighten you at
present.
It will be fair reasoning to argue thus. You may not be always right
in your conclusion, but still you will be trying fairly to explain
the unknown by the known.
But have Rain and Rivers alone made the soil?
How very much they have done toward making it you will be able to
judge for yourselves, if you will read the sixth chapter of Sir
Charles Lyell's new "Elements of Geology," or the first hundred pages
of that admirable book, De la Beche's "Geological Observer;" and
last, but not least, a very clever little book called "Rain and
Rivers," by Colonel George Greenwood.
But though rain, like rivers, is a carrier of soil, it is more. It
is a maker of soil, likewise; and by it mainly the soil of an upland
field is made, whether it be carried down to the sea or not.
If you will look into any quarry you will see that however compact
the rock may be a few feet below the surface, it becomes, in almost
every case, rotten and broken up as it nears the upper soil, till you
often cannot tell where the rock ends and the soil begins.
Now this change has been produced by rain. First, mechanically, by
rain in the shape of ice. The winter rain gets into the ground, and
does by the rock what it has done by the stones of many an old
building. It sinks into the porous stone, freezes there, expands in
freezing, and splits and peels the stone with a force which is slowly
but surely crumbling the whole of Northern Europe and America to
powder.
Do you doubt me? I say nothing but what you can judge of yourselves.
The next time you go up any mountain, look at the loose broken stones
with which the top is coated, just underneath the turf. What has
broken them up but frost? Look again, as stronger proof, at the
talus of broken stones--screes, as they call them in Scotland;
rattles, as we call them in Devon--which lie along the base of many
mountain cliffs. What has brought them down but frost? If you ask
the country folk they will tell you whether I am right or not. If
you go thither, not in the summer, but just after the winter's frost,
you will see for yourselves, by the fresh frost-crop of newly-broken
bits, that I am right. Possibly you may find me to be even more
right than is desirable, by having a few angular stones, from the
size of your head to that of your body, hurled at you by the frost-
giants up above. If you go to the Alps at certain seasons, and hear
the thunder of the falling rocks, and see their long lines--moraines,
as they are called--sliding slowly down upon the surface of the
glacier, then you will be ready to believe the geologist who tells
you that frost, and probably frost alone, has hewn out such a peak as
the Matterhorn from some vast table-land; and is hewing it down
still, winter after winter, till some day, where the snow Alps now
stand, there shall be rolling uplands of rich cultivable soil.
So much for the mechanical action of rain, in the shape of ice. Now
a few words on its chemical action.
Rain water is seldom pure. It carries in it carbonic acid; and that
acid, beating in shower after shower against the face of a cliff--
especially if it be a limestone cliff--weathers the rock chemically;
changing (in case of limestone) the insoluble carbonate of lime into
a soluble bicarbonate, and carrying that away in water, which,
however clear, is still hard. Hard water is usually water which has
invisible lime in it; there are from ten to fifteen grains and more
of lime in every gallon of limestone water. I leave you to calculate
the enormous weight of lime which must be so carried down to the sea
every year by a single limestone or chalk brook. You can calculate
it, if you like, by ascertaining the weight of lime in each gallon,
and the average quantity of water which comes down the stream in a
day; and when your sum is done, you will be astonished to find it one
not of many pounds, but probably of many tons, of solid lime, which
you never suspected or missed from the hills around. Again, by the
time the rain has sunk through the soil, it is still less pure. It
carries with it not only carbonic acid, but acids produced by
decaying vegetables--by the roots of the grasses and trees which grow
above; and they dissolve the cement of the rock by chemical action,
especially if the cement be lime or iron. You may see this for
yourselves, again and again. You may see how the root of a tree,
penetrating the earth, discolours the soil with which it is in
contact. You may see how the whole rock, just below the soil, has
often changed in colour from the compact rock below, if the soil be
covered with a dense layer of peat or growing vegetables.
But there is another force at work, and quite as powerful as rain and
rivers, making the soil of alluvial flats. Perhaps it has helped,
likewise, to make the soil of all the lowlands in these isles--and
that is, the waves of the sea.
If you ever go to Parkgate, in Cheshire, try if you cannot learn
there a little geology.
Walk beyond the town. You find the shore protected for a long way by
a sea-wall, lest it should be eaten away by the waves. What the
force of those waves can be, even on that sheltered coast, you may
judge--at least you could have judged this time last year--by the
masses of masonry torn from their iron clampings during the gale of
three winters since. Look steadily at those rolled blocks, those
twisted stanchions, if they are there still; and then ask yourselves-
-it will be fair reasoning from the known to the unknown--What effect
must such wave-power as that have had beating and breaking for
thousands of years along the western coasts of England, Scotland,
Ireland? It must have eaten up thousands of acres--whole shires, may
be, ere now. Its teeth are strong enough, and it knows neither rest
nor pity, the cruel hungry sea. Give it but time enough, and what
would it not eat up? It would eat up, in the course of ages, all the
dry land of this planet, were it not baffled by another counteracting
force, of which I shall speak hereafter.
As you go on beyond the sea-wall, you find what it is eating up. The
whole low cliff is going visibly. But whither is it going? To form
new soil in the aestuary. Now you will not wonder how old harbours
so often become silted up. The sea has washed the land into them.
But more, the sea-currents do not allow the sands of the aestuary to
escape freely out to sea. They pile it up in shifting sand-banks
about the mouth of the aestuary. The prevailing sea-winds, from
whatever quarter, catch up the sand, and roll it up into sand-hills.
Those sand-hills are again eaten down by the sea, and mixed with the
mud of the tide-flats, and so is formed a mingled soil, partly of
clayey mud, partly of sand; such a soil as stretches over the greater
part of all our lowlands.
Now, why should not that soil, whether in England or in Scotland,
have been made by the same means as that of every aestuary.
You find over great tracts of East Scotland, Lancashire, Norfolk,
etc., pure loose sand just beneath the surface, which looks as if it
was blown sand from a beach. Is it not reasonable to suppose that it
is? You find rising out of many lowlands, crags which look exactly
like old sea-cliffs eaten by the waves, from the base of which the
waters have gone back. Why should not those crags be old sea-cliffs?
Why should we not, following our rule of explaining the unknown by
the known, assume that such they are till someone gives us a sound
proof that they are not; and say--These great plains of England and
Scotland were probably once covered by a shallow sea, and their soils
made as the soil of any tide-flat is being made now?
But you may say, and most reasonably "The tide-flats are just at the
sea-level. The whole of the lowland is many feet above the sea; it
must therefore have been raised out of the sea, according to your
theory: and what proofs have you of that?"
Well, that is a question both grand and deep, on which I shall not
enter yet; but meanwhile, to satisfy you that I wish to play fair
with you, I ask you to believe nothing but what you can prove for
yourselves. Let me ask you this: suppose that you had proof
positive that I had fallen into the river in the morning; would not
your meeting me in the evening be also proof positive that somehow or
other I had in the course of the day got out of the river? I think
you will accept that logic as sound.
Now if I can give you proof positive, proof which you can see with
your own eyes, and handle with your own hands, and alas! often feel
but too keenly with your own feet, that the whole of the lowlands
were once beneath the sea; then will it not be certain that, somehow
or other, they must have been raised out of the sea again?
And that I propose to do in my next paper, when I speak of the
pebbles in the street.
Meanwhile I wish you to face fairly the truly grand idea, which all I
have said tends to prove true--that all the soil we see is made by
the destruction of older soils, whether soft as clay, or hard as
rock; that rain, rivers, and seas are perpetually melting and
grinding up old land, to compose new land out of it; and that it must
have been doing so, as long as rain, rivers, and seas have existed.
"But how did the first land of all get made?" I can only reply: A
natural question: but we can only answer that, by working from the
known to the unknown. While we are finding out how these later lands
were made and unmade, we may stumble on some hints as to how the
first primeval continents rose out of the bosom of the sea.
And thus I end this paper. I trust it has not been intolerably dull.
But I wanted at starting to show my readers something of the right
way of finding out truth on this and perhaps on all subjects; to make
some simple appeals to your common sense; and to get you to accept
some plain rules founded on common sense, which will be of infinite
use to both you and me in my future papers.
I hope, meanwhile, that you will agree with me, that there is plenty
of geological matter to be seen and thought over in the neighbourhood
of any town.
Be sure, that wherever there is a river, even a drain; and a stone
quarry, or even a roadside bank; much more where there is a sea, or a
tidal aestuary, there is geology enough to be learnt, to explain the
greater part of the making of all the continents on the globe.