Town Geology 5

Town Geology 5

Now let us do the same, and say--If this strange dream be true, and

the lowlands of the North were once under an icy sea, ought we not to

find sea-shells in their sands and clays? Not abundantly, of course.

We can understand that the sea-animals would be too rapidly covered

up in mud, and too much disturbed by icebergs and boulders, to be

very abundant. But still, some should surely be found here and

there.

 

Doubtless; and if my northern-town readers will search the boulder-

clay pits near them, they will most probably find a few shells, if

not in the clay itself, yet in sand-beds mixed with them, and

probably underlying them. And this is a notable fact, that the more

species of shells they find, the more they will find--if they work

out their names from any good book of conchology--of a northern type;

of shells which notoriously, at this day, inhabit the colder seas.

 

It is impossible for me here to enter at length on a subject on which

a whole literature has been already written. Those who wish to study

it may find all that they need know, and more, in Lyell's "Student's

Elements of Geology," and in chapter xii. of his "Antiquity of Man."

They will find that if the evidence of scientific conchologists be

worth anything, the period can be pointed out in the strata, though

not of course in time, at which these seas began to grow colder, and

southern and Mediterranean shells to disappear, their places being

taken by shells of a temperate, and at last of an Arctic climate;

which last have since retreated either toward their native North, or

into cold water at great depths. From Essex across to Wales, from

Wales to the aestuary of the Clyde, this fact has been verified again

and again. And in the search for these shells, a fresh fact, and a

most startling one, was discovered. They are to be found not only in

the clay of the lowlands, but at considerable heights up the hills,

showing that, at some time or other, these hills have been submerged

beneath the sea.

 

Let me give one example, which any tourist into Wales may see for

himself. Moel Tryfaen is a mountain over Carnarvon. Now perched on

the side of that mountain, fourteen hundred feet above the present

sea-level, is an ancient sea-beach, five-and-thirty feet thick, lying

on great ice-scratched boulders, which again lie on the mountain

slates. It was discovered by the late Mr. Trimmer, now, alas! lost

to Geology. Out of that beach fifty-seven different species of

shells have been taken; eleven of them are now exclusively Arctic,

and not found in our seas; four of them are still common to the

Arctic seas and to our own; and almost all the rest are northern

shells.

 

Fourteen hundred feet above the present sea: and that, it must be

understood, is not the greatest height at which such shells may be

found hereafter. For, according to Professor Ramsay, drift of the

same kind as that on Moel Tryfaen is found at a height of two

thousand three hundred feet.

 

Now I ask my readers to use their common sense over this astounding

fact--which, after all, is only one among hundreds; to let (as Mr.

Matthew Arnold would well say) their "thought play freely" about it;

and consider for themselves what those shells must mean. I say not

may, but must, unless we are to believe in a "Deus quidam deceptor,"

in a God who puts shells upon mountain-sides only to befool honest

human beings, and gives men intellects which are worthless for even

the simplest work. Those shells must mean that that mountain, and

therefore the mountains round it, must have been once fourteen

hundred feet at least lower than they are now. That the sea in which

they were sunk was far colder than now. That icebergs brought and

dropped boulders round their flanks. That upon those boulders a sea-

beach formed, and that dead shells were beaten into it from a sea-

bottom close by. That, and no less, Moel Tryfaen must mean.

 

But it must mean, also, a length of time which has been well called

"appalling." A length of time sufficient to let the mountain sink

into the sea. Then length of time enough to enable those Arctic

shells to crawl down from the northward, settle, and propagate

themselves generation after generation; then length of time enough to

uplift their dead remains, and the beach, and the boulders, and all

Snowdonia, fourteen hundred feet into the air. And if anyone should

object that the last upheaval may have been effected suddenly by a

few tremendous earthquakes, we must answer--We have no proof of it.

Earthquakes upheave lands now only by slight and intermittent upward

pulses; nay, some lands we know to rise without any earthquake

pulses, but by simple, slow, upward swelling of a few feet in a

century; and we have no reason, and therefore no right, to suppose

that Snowdonia was upheaved by any means or at any rate which we do

not witness now; and therefore we are bound to allow, not only that

there was a past "age of ice," but that that age was one of

altogether enormous duration.

 

But meanwhile some of you, I presume, will be ready to cry--Stop! It

may be our own weakness; but you are really going on too fast and too

far for our small imaginations. Have you not played with us, as well

as argued with us, till you have inveigled us step by step into a

conclusion which we cannot and will not believe? That all this land

should have been sunk beneath an icy sea? That Britain should have

been as Greenland is now? We can't believe it, and we won't.

 

If you say so, like stout common-sense Britons, who have a wholesome

dread of being taken in with fine words and wild speculations, I

assure you I shall not laugh at you even in private. On the

contrary, I shall say--what I am sure every scientific man will say--

So much the better. That is the sort of audience which we want, if

we are teaching natural science. We do not want haste, enthusiasm,

gobe-moucherie, as the French call it, which is agape to snap up any

new and vast fancy, just because it is new and vast. We want our

readers to be slow, suspicious, conservative, ready to "gib," as we

say of a horse, and refuse the collar up a steep place, saying--I

must stop and think. I don't like the look of the path ahead of me.

It seems an ugly place to get up. I don't know this road, and I

shall not hurry over it. I must go back a few steps, and make sure.

I must see whether it is the right road; whether there are not other

roads, a dozen of them perhaps, which would do as well and better

than this.

 

This is the temper which finds out truth, slowly, but once and for

all; and I shall be glad, not sorry, to see it in my readers.

 

And I am bound to say that it has been by that temper that this

theory has been worked out, and the existence of this past age of

ice, or glacial epoch, has been discovered, through many mistakes,

many corrections, and many changes of opinion about details, for

nearly forty years of hard work, by many men, in many lands.

 

As a very humble student of this subject, I may say that I have been

looking these facts in the face earnestly enough for more than twenty

years, and that I am about as certain that they can only be explained

by ice, as I am that my having got home by rail can only be explained

by steam.

 

But I think I know what startles you. It is the being asked to

believe in such an enormous change in climate, and in the height of

the land above the sea. Well--it is very astonishing, appalling--all

but incredible, if we had not the facts to prove it. But of the

facts there can be no doubt. There can be no doubt that the climate

of this northern hemisphere has changed enormously more than once.

There can be no doubt that the distribution of land and water, the

shape and size of its continents and seas, have changed again and

again. There can be no doubt that, for instance, long before the age

of ice, the whole North of Europe was much warmer than it is now.

 

Take Greenland, for instance. Disco Island lies in Baffin's Bay, off

the west coast of Greenland, in latitude 70 degrees, far within the

Arctic circle. Now there certain strata of rock, older than the ice,

have not been destroyed by the grinding of the ice-cap; and they are

full of fossil plants. But of what kind of plants? Of the same

families as now grow in the warmer parts of the United States. Even

a tulip-tree has been found among them. Now how is this to be

explained?

 

Either we must say that the climate of Greenland was then so much

warmer than now, that it had summers probably as hot as those of New

York; or we must say that these leaves and stems were floated thither

from the United States. But if we say the latter, we must allow a

change in the shape of the land which is enormous. For nothing now

can float northward from the United States into Baffin's Bay. The

polar current sets OUT of Baffin's Bay southward, bringing icebergs

down, not leaves up, through Davis's Straits. And in any case we

must allow that the hills of Disco Island were then the bottom of a

sea: or how would the leaves have been deposited in them at all?

 

So much for the change of climate and land which can be proved to

have gone on in Greenland. It has become colder. Why should it not

some day become warmer again?

 

Now for England. It can be proved, as far as common sense can prove

anything, that England was, before the age of ice, much warmer than

it is now, and grew gradually cooler and cooler, just as, while the

age of ice was dying out, it grew warmer again.

 

Now what proof is there of that?

 

This. Underneath London--as, I dare say, many of you know--there

lies four or five hundred feet of clay. But not ice-clay. Anything

but that, as you will see. It belongs to a formation late

(geologically speaking), but somewhat older than those Disco Island

beds.

 

And what sort of fossils do we find in it?

 

In the first place, the shells, which are abundant, are tropical--

Nautili, Cones, and such like. And more, fruits and seeds are found

in it, especially at the Isle of Sheppey. And what are they? Fruits

of Nipa palms, a form only found now at river-mouths in Eastern India

and the Indian islands; Anona-seeds; gourd-seeds; Acacia fruits--all

tropical again; and Proteaceous plants too--of an Australian type.

Surely your common sense would hint to you, that this London clay

must be mud laid down off the mouth of a tropical river. But your

common sense would be all but certain of that, when you found, as you

would find, the teeth and bones of crocodiles and turtles, who come

to land, remember, to lay their eggs; the bones, too, of large

mammals, allied to the tapir of India and South America, and the

water-hog of the Cape. If all this does not mean that there was once

a tropic climate and a tropic river running into some sea or other

where London now stands, I must give up common sense and reason as

deceitful and useless faculties; and believe nothing, not even the

evidence of my own senses.

 

And now, have I, or have I not, fulfilled the promise which I made--

rashly, I dare say some of you thought--in my first paper? Have I,

or have I not, made you prove to yourself, by your own common sense,

that the lowlands of Britain were underneath the sea in the days in

which these pebbles and boulders were laid down over your plains?

Nay, have we not proved more? Have we not found that that old sea

was an icy sea? Have we not wandered on, step by step, into a whole

true fairyland of wonders? to a time when all England, Scotland, and

Ireland were as Greenland is now? when mud streams have rushed down

from under glaciers on to a cold sea-bottom, when "ice, mast high,

came floating by, as green as emerald?" when Snowdon was sunk for at

least fourteen hundred feet of its height? when (as I could prove to

you, had I time) the peaks of the highest Cumberland and Scotch

mountains alone stood out, as islets in a frozen sea?

 

We want to get an answer to one strange question, and we have found a

group of questions stranger still, and got them answered too. But so

it is always in science. We know not what we shall discover. But

this, at least, we know, that it will be far more wonderful than we

had dreamed. The scientific explorer is always like Saul of old, who

set out simply to find his father's asses, and found them--and a

kingdom besides.

 

I should have liked to have told you more about this bygone age of

ice. I should have liked to say something to you on the curious

question--which is still an open one--whether there were not two ages

of ice; whether the climate here did not, after perhaps thousands of

years of Arctic cold, soften somewhat for a while--a few thousand

years, perhaps--and then harden again into a second age of ice,

somewhat less severe, probably, than the first. I should have liked

to have hinted at the probable causes of this change--indeed, of the

age of ice altogether--whether it was caused by a change in the

distribution of land and water, or by change in the height and size

of these islands, which made them large enough, and high enough, to

carry a sheet of eternal snow inland; or whether, finally, the age of

ice was caused by an actual change in the position of the whole

planet with regard to its orbit round the sun--shifting at once the

poles and the tropics; a deep question that latter, on which

astronomers, whose business it is, are still at work, and on which,

ere young folk are old, they will have discovered, I expect, some

startling facts. On that last question, I, being no astronomer,

cannot speak. But I should have liked to have said somewhat on

matters on which I have knowledge enough, at least, to teach you how

much there is to be learnt. I should have liked to tell the student

of sea-animals--how the ice-age helps to explain, and is again

explained by, the remarkable discoveries which Dr. Carpenter and Mr.

Wyville Thompson have just made, in the deep-sea dredgings in the

North Atlantic. I should have liked to tell the botanist somewhat of

the pro-glacial flora--the plants which lived here before the ice,

and lasted, some of them at least, through all those ages of fearful

cold, and linger still on the summits of Snowdon, and the highest

peaks of Cumberland and Scotland. I should have liked to have told

the lovers of zoology about the animals which lived before the ice--

of the mammoth, or woolly elephant; the woolly rhinoceros, the cave

lion and bear, the reindeer, the musk oxen, the lemmings and the

marmots which inhabited Britain till the ice drove them out

southward, even into the South of France; and how as the ice

retreated, and the climate became tolerable once more, some of them--

the mammoth and rhinoceros, the bison, the lion, and many another

mighty beast reoccupied our lowlands, at a time when the

hippopotamus, at least in summer, ranged freely from Africa and Spain

across what was then dry land between France and England, and fed by

the side of animals which have long since retreated to Norway and to

Canada. I should have liked to tell the archaeologist of the human

beings--probably from their weapons and their habits--of the same

race as the present Laplanders, who passed northward as the ice went

back, following the wild reindeer herds from the South of France into

our islands, which were no islands then, to be in their turn driven

northward by stronger races from the east and south. But space

presses, and I fear that I have written too much already.

 

At least, I have turned over for you a few grand and strange pages in

the book of nature, and taught you, I hope, a key by which to

decipher their hieroglyphics. At least, I have, I trust, taught you

to look, as I do, with something of interest, even of awe, upon the

pebbles in the street.

 

 

 

III. THE STONES IN THE WALL

 

 

 

This is a large subject. For in the different towns of these

islands, the walls are built of stones of almost every age, from the

earliest to the latest; and the town-geologist may find a quite

different problem to solve in the nearest wall, on moving from one

town to another twenty miles off. All I can do, therefore, is to

take one set of towns, in the walls of which one sort of stones is

commonly found, and talk of them; taking care, of course, to choose a

stone which is widely distributed. And such, I think, we can find in

the so-called New Red sandstone, which, with its attendant marls,

covers a vast tract--and that a rich and busy one--of England. From

Hartlepool and the mouth of the Tees, down through Yorkshire and

Nottinghamshire; over the manufacturing districts of central England;

down the valley of the Severn; past Bristol and the Somersetshire

flats to Torquay in South Devon; up north-westward through Shropshire

and Cheshire; past Liverpool and northward through Lancashire;

reappearing again, north of the Lake mountains, about Carlisle and

the Scotch side of the Solway Frith, stretches the New Red sandstone

plain, from under which everywhere the coal-bearing rocks rise as

from a sea. It contains, in many places, excellent quarries of

building-stone; the most famous of which, perhaps, are the well-known

Runcorn quarries, near Liverpool, from which the old Romans brought

the material for the walls and temples of ancient Chester, and from

which the stone for the restoration of Chester Cathedral is being

taken at this day. In some quarters, especially in the north-west of

England, its soil is poor, because it is masked by that very boulder-

clay of which I spoke in my last paper. But its rich red marls,

wherever they come to the surface, are one of God's most precious

gifts to this favoured land. On them, one finds oneself at once in a

garden; amid the noblest of timber, wheat, roots, grass which is

green through the driest summers, and, in the western counties,

cider-orchards laden with red and golden fruit. I know, throughout

northern Europe, no such charming scenery, for quiet beauty and solid

wealth, as that of the New Red marls; and if I wished to show a

foreigner what England was, I should take him along them, from

Yorkshire to South Devon, and say--There. Is not that a country

worth living for,--and worth dying for if need be?

 

Another reason which I have for dealing with the New Red sandstone is

this--that (as I said just now) over great tracts of England,

especially about the manufacturing districts, the town-geologist will

find it covered immediately by the boulder clay.

 

The townsman, finding this, would have a fair right to suppose that

the clay was laid down immediately, or at least soon after, the

sandstones or marls on which it lies; that as soon as the one had

settled at the bottom of some old sea, the other settled on the top

of it, in the same sea.

 

A fair and reasonable guess, which would in many cases, indeed in

most, be quite true. But in this case it would be a mistake. The

sandstone and marls are immensely older than the boulder-clay. They

are, humanly speaking, some four or five worlds older.

 

What do I mean? This--that between the time when the one, and the

time when the other, was made, the British Islands, and probably the

whole continent of Europe, have changed four or five times; in shape;

in height above the sea, or depth below it; in climate; in the kinds

of plants and animals which have dwelt on them, or on their sea-

bottoms. And surely it is not too strong a metaphor, to call such

changes a change from an old world to a new one.

 

Mind. I do not say that these changes were sudden or violent. It is

far more probable that they are only part and parcel of that vast but

slow change which is going on everywhere over our whole globe. I

think that will appear probable in the course of this paper. But

that these changes have taken place, is my main thesis. The fact I

assert; and I am bound to try and prove it. And in trying to do so,

I shall no longer treat my readers, as I did in the first two papers,

like children. I shall take for granted that they now understand

something of the method by which geological problems are worked out;

and can trust it, and me; and shall state boldly the conclusions of

geologists, only giving proof where proof is specially needed.

 

Now you must understand that in England there are two great divisions

of these New Red sandstones, "Trias," as geologists call them. An

upper, called in Germany Keuper, which consists, atop, of the rich

red marl, below them, of sandstones, and of those vast deposits of

rock-salt, which have been long worked, and worked to such good

purpose, that a vast subsidence of land has just taken place near

Nantwich in Cheshire; and serious fears are entertained lest the town

itself may subside, to fill up the caverns below, from whence the

salt has been quarried. Underneath these beds again are those which

carry the building-stone of Runcorn. Now these beds altogether, in

Cheshire, at least, are about 3,400 feet thick; and were not laid

down in a year, or in a century either.

 

Below them lies a thousand feet of sandstones, known in Germany by

the name of "Bunter," from its mottled and spotted appearance. What

lies under them again, does not concern us just now.

 

I said that the geologists called these beds the Trias; that is, the

triple group. But as yet we have heard of only two parts of it.

Where is the third?

 

Not here, but in Germany. There, between the Keuper above and the

Bunter below, lies a great series of limestone beds, which, from the

abundance of fossils which they contain, go by the name of

Muschelkalk. A long epoch must therefore have intervened between the

laying down of the Bunter and of the Keuper. And we have a trace of

that long epoch, even in England. The Keuper lies, certainly,

immediately on the Bunter; but not always "conformably" on it. That

is, the beds are not exactly parallel. The Bunter had been slightly

tilted, and slightly waterworn, before the Keuper was laid on it.

 

It is reasonable, therefore, to suppose, that the Bunter in England

was dry land, and therefore safe from fresh deposit, through ages

during which it was deep enough beneath the sea in Germany, to have

the Muschelkalk laid down on it. Here again, then, as everywhere, we

have evidence of time--time, not only beyond all counting, but beyond

all imagining.

 

And now, perhaps, the reader will ask--If I am to believe that all

new land is made out of old land, and that all rocks and soils are

derived from the wear and tear of still older rocks, off what land

came this enormous heap of sands more than 5,000 feet thick in

places, stretching across England and into Germany?

 

It is difficult to answer. The shape and distribution of land in

those days were so different from what they are now, that the rocks

which furnished a great deal of our sandstone may be now, for aught I

know, a mile beneath the sea.

 

But over the land which still stands out of the sea near us there has

been wear and tear enough to account for any quantity of sand

deposit. As a single instance--It is a provable and proven fact--as

you may see from Mr. Ramsay's survey of North Wales--that over a

large tract to the south of Snowdon, between Port Madoc and Barmouth,

there has been ground off and carried away a mass of solid rock

20,000 feet thick; thick enough, in fact, if it were there still, to

make a range of mountains as high as the Andes. It is a provable and

proven fact that vast tracts of the centre of poor old Ireland were

once covered with coal-measures, which have been scraped off in

likewise, deprived of inestimable mineral wealth. The destruction of

rocks--"denudation" as it is called--in the district round Malvern,

is, I am told, provably enormous. Indeed, it is so over all Wales,

North England, and West and North Scotland. So there is enough of

rubbish to be accounted for to make our New Red sands. The round

pebbles in it being, I believe, pieces of Old Red sandstone, may have

come from the great Old Red sandstone region of South East Wales and

Herefordshire. Some of the rubbish, too,