Town Geology 6

Town Geology 6

Both near Warwick, and near Elgin in Scotland, in Central India, and

in South Africa, fossil remains are found of a family of lizards

utterly unlike anything now living save one, and that one is crawling

about, plentifully I believe--of all places in the world--in New

Zealand. How it got there; how so strange a type of creature should

have died out over the rest of the world, and yet have lasted on in

that remote island for long ages, ever since the days of the New Red

sandstone, is one of those questions--quite awful questions I

consider them--with which I will not puzzle my readers. I only

mention it to show them what serious questions the scientific man has

to face, and to answer, if he can. Only the next time they go to the

Zoological Gardens in London, let them go to the reptile-house, and

ask the very clever and courteous attendant to show them the

Sphenodons, or Hatterias, as he will probably call them--and then

look, I hope with kindly interest, at the oldest Conservatives they

ever saw, or are like to see; gentlemen of most ancient pedigree, who

have remained all but unchanged, while the whole surface of the globe

has changed around them more than once or twice.

 

And now, of course, my readers will expect to hear something of the

deposits of rock-salt, for which Cheshire and its red rocks are

famous. I have never seen them, and can only say that the salt does

not, it is said by geologists, lie in the sandstone, but at the

bottom of the red marl which caps the sandstone. It was formed most

probably by the gradual drying up of lagoons, such as are depositing

salt, it is said now, both in the Gulf of Tadjara, on the Abyssinian

frontier opposite Aden, and in the Runn of Cutch, near the Delta of

the Indus. If this be so, then these New Red sandstones may be the

remains of a whole Sahara--a sheet of sandy and all but lifeless

deserts, reaching from the west of England into Germany, and rising

slowly out of the sea; to sink, as we shall find, beneath the sea

again.

 

And now, as to the vast period of time--the four or five worlds, as I

called it--which elapsed between the laying down of the New Red

sandstones and the laying down of the boulder-clays.

 

I think this fact--for fact it is--may be better proved by taking

readers an imaginary railway journey to London from any spot in the

manufacturing districts of central England--begging them, meanwhile,

to keep their eyes open on the way.

 

And here I must say that I wish folks in general would keep their

eyes a little more open when they travel by rail. When I see young

people rolling along in a luxurious carriage, their eyes and their

brains absorbed probably in a trashy shilling novel, and never lifted

up to look out of the window, unconscious of all that they are

passing--of the reverend antiquities, the admirable agriculture, the

rich and peaceful scenery, the like of which no country upon earth

can show; unconscious, too, of how much they might learn of botany

and zoology, by simply watching the flowers along the railway banks

and the sections in the cuttings: then it grieves me to see what

little use people make of the eyes and of the understanding which God

has given them. They complain of a dull journey: but it is not the

journey which is dull; it is they who are dull. Eyes have they, and

see not; ears have they, and hear not; mere dolls in smart clothes,

too many of them, like the idols of the heathen.

 

But my readers, I trust, are of a better mind. So the next time they

find themselves running up southward to London--or the reverse way--

let them keep their eyes open, and verify, with the help of a

geological map, the sketch which is given in the following pages.

 

Of the "Black Countries"--the actual coal districts I shall speak

hereafter. They are in England either shores or islands yet

undestroyed, which stand out of the great sea of New Red sandstone,

and often carry along their edges layers of far younger rocks, called

now Permian, from the ancient kingdom of Permia, in Russia, where

they cover a vast area. With them I will not confuse the reader just

now, but will only ask him to keep his eye on the rolling plain of

New Red sands and marls past, say, Birmingham and Warwick. After

those places, these sands and marls dip to the south-east, and other

rocks and soils appear above them, one after another, dipping

likewise towards the south-east--that is, toward London.

 

First appear thin layers of a very hard blue limestone, full of

shells, and parted by layers of blue mud. That rock runs in a broad

belt across England, from Whitby in Yorkshire, to Lyme in

Dorsetshire, and is known as Lias. Famous it is, as some readers may

know, for holding the bones of extinct monsters--Ichthyosaurs and

Plesiosaurs, such as the unlearned may behold in the lake at the

Crystal Palace. On this rock lie the rich cheese pastures, and the

best tracts of the famous "hunting shires" of England.

 

Lying on it, as we go south-eastward, appear alternate beds of sandy

limestone, with vast depths of clay between them. These "oolites,"

or freestones, furnish the famous Bath stone, the Oxford stone, and

the Barnack stone of Northamptonshire, of which some of the finest

cathedrals are built--a stone only surpassed, I believe, by the Caen

stone, which comes from beds of the same age in Normandy. These

freestones and clays abound in fossils, but of kinds, be it

remembered, which differ more and more from those of the lias

beneath, as the beds are higher in the series, and therefore nearer.

There, too, are found principally the bones of that extraordinary

flying lizard, the Pterodactyle, which had wings formed out of its

fore-legs, on somewhat the same plan as those of a bat, but with one

exception. In the bat, as any one may see, four fingers of the hand

are lengthened to carry the wing, while the first alone is left free,

as a thumb: but in the Pterodactyle, the outer or "little" finger

alone is lengthened, and the other four fingers left free--one of

those strange instances in nature of the same effect being produced

in widely different plants and animals, and yet by slightly different

means, on which a whole chapter of natural philosophy--say, rather,

natural theology--will have to be written some day.

 

But now consider what this Lias, and the Oolites and clays upon it

mean. They mean that the New Red sandstone, after it had been dry

land, or all but dry land (as is proved by the footprints of animals

and the deposits of salt), was sunk again beneath the sea. Each

deposit of limestone signifies a long period of time, during which

that sea was pure enough to allow reefs of coral to grow, and shells

to propagate, at the bottom. Each great band of clay signifies a

long period, during which fine mud was brought down from some wasting

land in the neighbourhood. And that land was not far distant is

proved by the bones of the Pterodactyle, of Crocodiles, and of

Marsupials; by the fact that the shells are of shallow-water or shore

species; by the presence, mixed with them, of fragments of wood,

impressions of plants, and even wing-shells of beetles; and lastly,

if further proof was needed, by the fact that in the "dirt-bed" of

the Isle of Portland and the neighbouring shores, stumps of trees

allied to the modern sago-palms are found as they grew in the soil,

which, with them, has been covered up in layers of freshwater shale

and limestone. A tropic forest has plainly sunk beneath a lagoon;

and that lagoon, again, beneath the sea.

 

And how long did this period of slow sinking go on? Who can tell?

The thickness of the Lias and Oolites together cannot be less than a

thousand feet. Considering, then, the length of time required to lay

down a thousand feet of strata, and considering the vast difference

between the animals found in them, and the few found in the New Red

sandstone, we have a right to call them another world, and that one

which must have lasted for ages.

 

After we pass Oxford, or the Vale of Aylesbury, we enter yet another

world. We come to a bed of sand, under which the freestones and

their adjoining clays dip to the south-east. This is called commonly

the lower Greensand, though it is not green, but rich iron-red. Then

succeeds a band of stiff blue clay, called the Gault, and then

another bed of sand, the upper Greensand, which is more worthy of the

name, for it does carry, in most places, a band of green or

"glauconite" sand. But it and the upper layers of the lower

Greensand also, are worth our attention; for we are all probably

eating them from time to time in the form of bran.

 

It had been long remarked that certain parts of these beds carried

admirable wheatland; it had been remarked, too, that the finest hop-

lands--those of Farnham, for instance, and Tunbridge--lay upon them:

but that the fertile band was very narrow; that, as in the Surrey

Moors, vast sheets of the lower Greensand were not worth cultivation.

What caused the striking difference?

 

My beloved friend and teacher, the late Dr. Henslow, when Professor

of Botany at Cambridge, had brought to him by a farmer (so the story

ran) a few fossils. He saw, being somewhat of a geologist and

chemist, that they were not, as fossils usually are, carbonate of

lime, but phosphate of lime--bone-earth. He said at once, as by an

inspiration, "You have found a treasure--not a gold-mine, indeed, but

a food-mine. This is bone-earth, which we are at our wits' end to

get for our grain and pulse; which we are importing, as expensive

bones, all the way from Buenos Ayres. Only find enough of them, and

you will increase immensely the food supply of England, and perhaps

make her independent of foreign phosphates in case of war."

 

His advice was acted on; for the British farmer is by no means the

stupid personage which townsfolk are too apt to fancy him. This bed

of phosphates was found everywhere in the Greensand, underlying the

Chalk. It may be traced from Dorsetshire through England to

Cambridge, and thence, I believe, into Yorkshire. It may be traced

again, I believe, all round the Weald of Kent and Sussex, from Hythe

to Farnham--where it is peculiarly rich--and so to Eastbourne and

Beachey Head; and it furnishes, in Cambridgeshire, the greater part

of those so-called "coprolites," which are used perpetually now for

manure, being ground up, and then treated with sulphuric acid, till

they become a "soluble super-phosphate of lime."

 

So much for the useless "hobby," as some fancy it, of poking over old

bones and stones, and learning a little of the composition of this

earth on which God has placed us.

 

How to explain the presence of this vast mass of animal matter, in

one or two thin bands right across England, I know not. That the

fossils have been rolled on a sea-beach is plain to those who look at

them. But what caused so vast a destruction of animal life along

that beach, must remain one of the buried secrets of the past.

 

And now we are fast nearing another world, which is far younger than

that coprolite bed, and has been formed under circumstances the most

opposite to it. We are nearing, by whatever rail we approach London,

the escarpment of the chalk downs.

 

All readers, surely, know the white chalk, the special feature and

the special pride of the south of England. All know its softly-

rounded downs, its vast beech woods, its short and sweet turf, its

snowy cliffs, which have given--so some say--to the whole island the

name of Albion--the white land. But all do not, perhaps, know that

till we get to the chalk no single plant or animal has been found

which is exactly like any plant or animal now known to be living.

The plants and animals grow, on the whole, more and more like our

living forms as we rise in the series of beds. But only above the

chalk (as far as we yet know) do we begin to find species identical

with those living now.

 

This in itself would prove a vast lapse of time. We shall have a

further proof of that vast lapse when we examine the chalk itself.

It is composed--of this there is now no doubt--almost entirely of the

shells of minute animalcules; and animalcules (I use an unscientific

word for the sake of unscientific readers) like these, and in some

cases identical with them, are now forming a similar deposit of mud,

at vast depths, over the greater part of the Atlantic sea-floor.

This fact has been put out of doubt by recent deep-sea dredgings. A

whole literature has been written on it of late. Any reader who

wishes to know it, need only ask the first geologist he meets; and if

he has the wholesome instinct of wonder in him, fill his imagination

with true wonders, more grand and strange than he is like to find in

any fairy tale. All I have to do with the matter here is, to say

that, arguing from the known to the unknown, from the Atlantic deep-

sea ooze which we do know about, to the chalk which we do not know

about, the whole of the chalk must have been laid down at the bottom

of a deep and still ocean, far out of the reach of winds, tides, and

even currents, as a great part of the Atlantic sea-floor is at this

day.

 

Prodigious! says the reader. And so it is. Prodigious to think that

that shallow Greensand shore, strewed with dead animals, should sink

to the bottom of an ocean, perhaps a mile, perhaps some four miles

deep. Prodigious the time during which it must have lain as a still

ocean-floor. For so minute are the living atomies which form the

ooze, that an inch, I should say, is as much as we can allow for

their yearly deposit; and the chalk is at least a thousand feet

thick. It may have taken, therefore, twelve thousand years to form

the chalk alone. A rough guess, of course, but one as likely to be

two or three times too little as two or three times too big. Such,

or somewhat such, is the fact. It had long been suspected, and more

than suspected; and the late discoveries of Dr. Carpenter and Mr.

Wyville Thompson have surely placed it beyond doubt.

 

Thus, surely, if we call the Oolitic beds one new world above the New

Red sandstone, we must call the chalk a second new world in like

wise.

 

I will not trouble the reader here with the reasons why geologists

connect the chalk with the greensands below it, by regular

gradations, in spite of the enormous downward leap, from sea-shore to

deep ocean, which the beds seem (but only seem) to have taken. The

change--like all changes in geology--was probably gradual. Not by

spasmodic leaps and starts, but slowly and stately, as befits a God

of order, of patience, and of strength, have these great deeds been

done.

 

But we have not yet done with new worlds or new prodigies on our way

to London, as any Londoner may ascertain for himself, if he will run

out a few miles by rail, and look in any cutting or pit, where the

surface of the chalk, and the beds which lie on it, are exposed.

 

On the chalk lie--especially in the Blackheath and Woolwich district-

-sands and clays. And what do they tell us?

 

Of another new world, in which the chalk has been lifted up again, to

form gradually, doubtless, and at different points in succession, the

shore of a sea.

 

But what proof is there of this?

 

The surface of the chalk is not flat and smooth, as it must have been

when at the bottom of the sea. It is eaten out into holes and

furrows, plainly by the gnawing of the waves; and on it lie, in many

places, large rolled flints out of chalk which has been destroyed,

beds of shore-shingle, beds of oysters lying as they grew, fresh or

brackish water-shells standing as they lived, bits of lignite (fossil

wood half turned to coal), and (as in Katesgrove pits at Reading)

leaves of trees. Proof enough, one would say, that the chalk had

been raised till part of it at least became dry land, and carried

vegetation.

 

And yet we have not done. There is another world to tell of yet.

 

For these beds (known as the Woolwich and Reading beds) dip under

that vast bed of London clay, four hundred and more feet thick, which

(as I said in my last chapter) was certainly laid down by the estuary

of some great tropic river, among palm-trees and Anonas, crocodiles

and turtles.

 

Is the reader's power of belief exhausted?

 

If not: there are to be seen, capping almost every high land round

London, the remains of a fifth world. Some of my readers may have

been to Ascot races, or to Aldershot camp, and may recollect the

table-land of the sandy moors, perfectly flat atop, dreary enough to

those to whom they are not (as they have long been to me) a home and

a work-field. Those sands are several hundred feet thick. They lie

on the London clay. And they represent--the reader must take

geologists' word for it--a series of beds in some places thousands of

feet thick, in the Isle of Wight, in the Paris basin, in the volcanic

country of the Auvergne, in Switzerland, in Italy; a period during

which the land must at first have swarmed with forms of tropic life,

and then grown--but very gradually--more temperate, and then colder

and colder still; till at last set in that age of ice, which spread

the boulder pebbles over all rocks and soils indiscriminately, from

the Lake mountains to within a few miles of London.

 

For everywhere about those Ascot moors, the top of the sands has been

ploughed by shore-ice in winter, as they lay a-wash in the shallow

sea; and over them, in many places, is spread a thin sheet of ice

gravel, more ancient, the best geologists think, than the boulder and

the boulder-clay.

 

If any of my readers ask how long the period was during which those

sands of Ascot Heath and Aldershot have been laid down, I cannot

tell. But this we can tell. It was long enough to see such changes

in land and sea, that maps representing Europe during the greater

part of that period (as far as we can guess at it) look no more like

Europe than like America or the South Sea Islands. And this we can

tell besides: that that period was long enough for the Swiss Alps to

be lifted up at least 10,000 feet of their present height. And that

was a work which--though God could, if He willed it, have done it in

a single day--we have proof positive was not done in less than ages,

beside which the mortal life of man is as the life of the gnat which

dances in the sun.

 

And all this, and more--as may be proved from the geology of foreign

countries--happened between the date of the boulder-clay, and that of

the New Red sandstone on which it rests.

 

 

 

IV. THE COAL IN THE FIRE

 

 

 

My dear town-dwelling readers, let me tell you now something of a

geological product well known, happily, to all dwellers in towns, and

of late years, thanks to railroad extension, to most dwellers in

country districts: I mean coal.

 

Coal, as of course you know, is commonly said to be composed of

vegetable matter, of the leaves and stems of ancient plants and

trees--a startling statement, and one which I do not wish you to take

entirely on trust. I shall therefore spend a few pages in showing

you how this fact--for fact it is--was discovered. It is a very good

example of reasoning from the known to the unknown. You will have a

right to say at first starting, "Coal is utterly different in look

from leaves and stems. The only property which they seem to have in

common is that they can both burn." True. But difference of mere

look may be only owing to a transformation, or series of

transformations. There are plenty in nature quite as great, and

greater. What can be more different in look, for instance, than a

green field of wheat and a basket of loaves at the baker's? And yet

there is, I trust, no doubt whatsoever that the bread has been once

green wheat, and that the green wheat has been transformed into

bread--making due allowance, of course, for the bone-dust, or gypsum,

or alum with which the worthy baker may have found it profitable to

adulterate his bread, in order to improve the digestion of Her

Majesty's subjects.

 

But you may say, "Yes, but we can see the wheat growing, flowering,

ripening, reaped, ground, kneaded, baked. We see, in the case of

bread, the processes of the transformation going on: but in the case

of coal we do not see the wood and leaves being actually transformed into coal, or anything like it."