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Title: The Romance of Modern Geology - Describing in simple but exact language the making of the earth with some account of prehistoric animal life
Author: Grew, E. S.
Language: English
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Transcriber Note
Emphasis denoted as _Italics_ and =Bold=. Whole and fractional parts
of numbers as 123-4/5.
THE ROMANCE OF
MODERN GEOLOGY
[Illustration: Megalosaurus
Total length about 25 feet.
(Remains found in England, France, South Africa, and India.)]
THE ROMANCE OF
MODERN GEOLOGY
DESCRIBING IN SIMPLE BUT EXACT
LANGUAGE THE MAKING OF THE
EARTH WITH SOME ACCOUNT OF
PREHISTORIC ANIMAL LIFE
BY
E. S. GREW, M.A.
EDITOR OF "KNOWLEDGE"
AUTHOR OF "THE FAR EAST" _&C._, _&C._
WITH TWENTY-FIVE ILLUSTRATIONS
LONDON
SEELEY AND CO. LIMITED
38 GREAT RUSSELL STREET
1909
_UNIFORM WITH THIS VOLUME_
THE LIBRARY OF ROMANCE
_Extra Crown 8vo. With many illustrations. 5s. each_
"=Splendid volumes."=--_the Outlook._
"=This series has now won a considerable and well deserved
reputation.="--_The Guardian._
"=Each volume treats its allotted theme with accuracy, but at
the same time with a charm that will commend itself to readers
of all ages. The root idea is excellent, and it is excellently
carried out, with full illustrations and very prettily designed
covers.="--_The Daily Telegraph._
By Prof. G. F. SCOTT ELLIOT, M.A., B.Sc.
THE ROMANCE OF SAVAGE LIFE
THE ROMANCE OF PLANT LIFE
THE ROMANCE OF EARLY BRITISH LIFE
By EDWARD GILLIAT, M.A.
THE ROMANCE OF MODERN SIEGES
By JOHN LEA, M.A.
THE ROMANCE OF BIRD LIFE
By JOHN LEA, M.A., & H. COUPIN, D.Sc.
THE ROMANCE OF ANIMAL ARTS AND CRAFTS
By SIDNEY WRIGHT
THE ROMANCE OF THE WORLD'S FISHERIES
By the Rev. J. C. LAMBERT, M.A., D.D.
THE ROMANCE OF MISSIONARY HEROISM
By G. FIRTH SCOTT
THE ROMANCE OF POLAR EXPLORATION
By ARCHIBALD WILLIAMS, B.A. (Oxon.), F.R.G.S.
THE ROMANCE OF EARLY EXPLORATION
THE ROMANCE OF MODERN EXPLORATION
THE ROMANCE OF MODERN MECHANISM
THE ROMANCE OF MODERN INVENTION
THE ROMANCE OF MODERN ENGINEERING
THE ROMANCE OF MODERN LOCOMOTION
THE ROMANCE OF MODERN MINING
By CHARLES R. GIBSON, A.I.E.E.
THE ROMANCE OF MODERN PHOTOGRAPHY
THE ROMANCE OF MODERN ELECTRICITY
By EDMUND SELOUS
THE ROMANCE OF THE ANIMAL WORLD
THE ROMANCE OF INSECT LIFE
By AGNES GIBERNE
THE ROMANCE OF THE MIGHTY DEEP
By E. S. GREW, M.A.
THE ROMANCE OF MODERN GEOLOGY
SEELEY & CO., LIMITED
Grateful acknowledgment is due to Mr. Henry R. Knipe for his kind
permission to reproduce some of the illustrations of extinct animals
contained in his scholarly work entitled, _From Nebula to Man_ (J. M.
Dent and Co.).
CONTENTS
PAGE
CHAPTER I
THE BUILDING OF THE EARTH 17
CHAPTER II
THE EARTH'S SHAPE 29
CHAPTER III
EFFECTS OF WEATHER ON THE EARTH'S HISTORY 39
CHAPTER IV
RECORDS LEFT BY RIVERS 50
CHAPTER V
RECORDS LEFT BY THE SEA 59
CHAPTER VI
COLD AND ICE ON THE EARTH 67
CHAPTER VII
THE FIRE-HARDENED ROCKS 78
CHAPTER VIII
THE EARTH AT ITS BEGINNING 90
CHAPTER IX
THE CHILDHOOD OF THE EARTH 98
CHAPTER X
THE EARTH AS THE ABODE OF LIFE 108
CHAPTER XI
LIFE IN OTHER WORLDS 118
CHAPTER XII
THE HARDENING OF ROCKS 128
CHAPTER XIII
EARTHQUAKES IN GEOLOGY 137
CHAPTER XIV
SOME FAMOUS EARTHQUAKES 148
CHAPTER XV
THE CAUSES OF EARTHQUAKES 165
CHAPTER XVI
VOLCANOES AND MOUNTAIN FORMATION 179
CHAPTER XVII
FAMILIES OF ROCKS AND THEIR DESCENDANTS 197
CHAPTER XVIII
HOW THE COAL BEDS WERE LAID DOWN 212
CHAPTER XIX
THE AGE OF REPTILES 226
CHAPTER XX
THE AGE OF REPTILES (_continued_) 235
CHAPTER XXI
THE CHALK PERIOD 245
CHAPTER XXII
THE AGE OF MAMMALS 256
CHAPTER XXIII
THE ICE AGE 269
CHAPTER XXIV
THE KINGDOM OF MAN 284
INDEX 293
LIST OF ILLUSTRATIONS
PAGE
MEGALOSAURUS _Frontispiece_
MAP SHOWING DISTRICTS OF WORLD-SHAKING EARTHQUAKES 15
ONE OF THE COLOSSAL NATURAL BRIDGES OF UTAH 40
THE GARDEN OF THE GODS, COLORADO 44
A CURIOUS ROCK GREATLY REVERED BY THE NATIVES 46
THE GRAND CAÑON OF ARIZONA 52
CLEOPATRA TERRACE, YELLOWSTONE PARK, U.S.A. 56
A PETRIFIED TREE 58
THE CRATER OF AN EXTINCT VOLCANO 104
THE PINNACLED CASTLE-LIKE PEAKS OF THE RAMSHORN
MOUNTAINS OF WYOMING 130
A GEYSER IN ACTION 140
A CURIOUS ERUPTION OF MOUNT ASAMA, JAPAN 154
A HOUSE DESTROYED BY AN EARTHQUAKE 158
THE RUINS OF THE MAGNIFICENT CITY HALL OF SAN FRANCISCO 160
THE TRACK OF AN EARTH WAVE 166
A GEYSER AT REST IN YELLOWSTONE PARK, U.S.A. 170
THE NEW SPINE OF MONT PELÉE 184
THE DEAD CITY OF ST. PIERRE, MARTINIQUE 186
A YORKSHIRE POT-HOLE: SHOWING THE EFFECTS WHICH CAN
BE PRODUCED IN LIMESTONE BY UNDERGROUND WATER 196
PLESIOSAURS 238
DIPLODOCI CARNEGIEI 240
ARCHÆOPTERYX AND COMPSOGNATHUS 242
EVOLUTION OF THE HEAD, PROBOSCIS, NOSTRILS, AND TUSKS
OF THE ELEPHANT 260
TWO ARSINOITHERIUMS AT BAY BEFORE A PACK OF HYÆNODONS 266
DIPROTODON 278
[Illustration: The Number of world-shaking earthquakes from 1899 to
1908 which have originated in districts marked A, B, C, &c., are
shown by figures. (See pp. 171 and 172.)]
ERRATA
[Transcriber Note: Corrections have been applied!]
Page 19, line 9. For "Sir Thomas Holdich," read "Sir Thomas
Holditch."
Page 25, line 17. Read, "they are always, as it were, imperceptibly
quivering; and they are always liable, if the strain on them
should be increased in the slightest degree, to give way, or to
resettle the weight on their shoulders in some way."
Page 29, line 11. For "a greasy spot," read "a greasy shot."
Page 35, line 5. For "evidence," read "existence."
THE ROMANCE OF
MODERN GEOLOGY
CHAPTER I
THE BUILDING OF THE EARTH
Everybody who has ever been to the coast of these islands has become
aware that changes in the outline of the land are continually taking
place. In some parts of the east coast of England, such as that
which lies between Harwich and Walton-on-the-Naze, the sea appears
to be slowly encroaching on the land, so that places which were
grazing-fields twenty or thirty years ago are now covered by the
sea at high tide, and at low tide are mere sandy wastes threaded
by rivulets of sea-water. On the south coast of the Isle of Wight,
between Sandown and the Culver Cliff, which is the most easterly
point, the same loss of land is going on in another way. Some years
ago a fort stood rather near the edge of the cliff, and it would
have been possible to climb round the seaward wall of the fort. It
is not possible now, for the outer sea-wall of the fort has long ago
slipped into the sea; so have some of the inner fortifications: and
it has been necessary to dismantle the whole of this fort lest every
part of even the inner landward wall should follow the outer parts
and slip with the solid ground down the cliff. It is easy to see
what is happening here. The wind and the waves are undermining and
honeycombing the cliff. They are weakening its base and its body, and
so the upper crust on which the fort was built, and into which its
foundations were dug, is slipping away. If we imagine for a moment
that nothing was done to save the fort or protect the cliff, but that
all was left to nature to deal with, it would not be hard to picture
what would happen. The cliff would gradually be eaten away: its
gravel and clay would be drawn into the sea, and the Isle of Wight
would become a little smaller. The same thing is going on at a good
many places along the coast of the British Isles, as well as on the
coast of Florida and in the Gulf of California in America.
The little islet of Heligoland in the North Sea, which once belonged
to Great Britain, but was some years ago handed over to Germany, is
so fiercely attacked by the sea in this way, that it almost has to
be armour-plated in order to preserve its integrity. It is fenced
in stone in order to protect it. What is happening on the coasts of
islands like England and Heligoland is happening all over the world.
It has always happened. If it had not happened in past ages there
would be no British Isles at all, because once England and Scotland
and Ireland were joined to Europe, and it would have been possible to
walk across the North Sea from Harwich to the Hook of Holland. The
North Sea was once dry land. But the sea encroached on it from the
north, and the Atlantic Ocean battered a way through on the south,
till the English Channel was bored through into the shallow waters of
the newly-formed North Sea, and the lands that had once been part of
Europe became these "sceptred isles set in the silver sea."
This is not all the story. What the sea takes away it gives again.
Sir Thomas Holditch is our authority for saying that on some parts of
the Pacific coast of America you may at some points see on the one
hand dry land which by the shells found on it shows that the sea once
flowed over it; while side by side with this raised land you may sail
a boat over forests now sunk beneath the sea. The loss of bits and
corners of England is serious--so serious that a Royal Commission on
Sea Erosion, as the process is called, was appointed to inquire into
the extent of the loss and the means by which it might be remedied.
But in some parts of our coast the land is not losing, but gaining.
If the sea takes away sand and gravel, chalk and shale and clay from
the cliffs, these materials are not lost. Something is done with
them. They must at some points, where the tides and currents of the
sea deposit them, make the sea more shallow. Perhaps the sea lays
them down as beds or sand-banks. Perhaps it carries them round the
coast to some other point and there drops them. Can you not see that
in this way the sea which at one point is dragging down the coast
may at other points be building it up, or may be even constructing
breakwaters made out of these stolen materials?
The sea is not the only carrier which is thus laying down beds of
material. The rivers are doing the same thing. Every shower of
rain washes some dirt--by which we mean sand or gravel or loam or
chalk--from the land into the nearest rivulet. The rivulet hurries
with it down to the neighbouring river, and the river carries it down
to the sea. If the river is going very fast it carries most of its
dirt along with it, and we generally find the river muddy after rain.
But when the river slackens its pace, as it usually does when it
nears the sea and meets the sea's tides, then it lets the dirt fall;
and thus at the river's mouth we find mud-banks or sand-banks. If a
river is left long enough to its own devices, these sand-banks will
so increase in bulk that the mouth of the river will become shallower
and shallower and will spread. It silts up, and when a river is
needed for the navigation of ships large sums of money have to be
spent, as in the Scheldt or at the mouth of the Thames, in dredging
this mud so as to keep the channels clear.
There are many striking examples of this land-building by rivers;
and the deltas of rivers, so called from their resemblance to the
Greek letter Δ, form in some instances great areas. The
Mississippi, the Nile, and the Ganges, for example, are surrounded by
great tracts of land at their mouths, which are formed entirely from
matter brought down by the rivers and deposited at lower levels than
those at which the rivers originated. The Mississippi, which drains
a river basin of 1,147,000 square miles, has an annual discharge
of sediment of no less than 7,459,267,200 cubic feet. The Italian
River Po, draining an area of 30,000 square miles, discharges
1,510,137,000 cubic feet of sediment annually. This is equivalent
to a lowering of its whole drainage area by 1/729th of a foot per
annum, so that in a thousand years the whole area over which it flows
has been lowered by the river by more than a foot. The Thames alone
carries down 5,000,000 tons of material each year. All this must be
redeposited somewhere. Where the redeposition takes place we find new
land forming, new beds, new _strata_, in which in ages to come the
future tenants of the globe may find relics of the people and animals
living to-day.
Thus there are several evident ways in which the coast-line of a
country might be altered, either in the direction of enlarging its
boundaries by additions to it made by the sea or by rivers; or in
the direction of losing parts of its territory by wear and tear. But
there are other changes going on which are not so easy to perceive,
and which are not so easy to account for. The thing hardest to
explain is why what is now dry land should have risen out of the sea,
as certainly it did. The white cliffs of Dover are made of chalk, and
chalk is made of innumerable shells of tiny animals which once lived
in the sea and which at their death sank to the sea's bottom. They
steadily accumulated there for ages in a grey ooze, and in course of
time this grey ooze rose above the waves. It dried and became land.
But chalk is not found in cliffs by the sea only. It is found far
inland. It is found, for example, in the North Downs, which run from
Guildford to Reigate and from Reigate to Limpsfield and Westerham--a
great ridge of chalk, at some points 600 to 800 feet high. That
ridge must at one time have been at the sea bottom. And if we were
to examine the whole of England and sink borings in it, we should at
one point or another come to some remains of rocks, or some "strata,"
as they are called, which are of such make and material that we can
only believe them to have been laid down at the sea bottom. The
only conclusion we can come to, therefore, is that by some means or
other, and at some time or other, the islands of England were slowly
lifted above the sea, and that at some other time the sea was slowly
lifted above them. What is true of England is true of nearly all the
regions of the world that have been closely examined by geologists.
Everywhere there is the evidence of different stages of existence in
the land's history--stages when it was covered by the sea; stages
when it was dry land again; perhaps stages when it was covered by
lakes, by vast forests; stages when it may have been covered by ice;
stages when it was desert. Some of these stages show far vaster
upheavals than others, and the changes wrought were of far greater
extent. Everybody has heard that the great Saharan desert was perhaps
once the bed of an ocean. That is an assertion to which, perhaps, we
may be a little chary of committing ourselves; but there is excellent
reason for believing that once some of the great African lakes were
connected with the sea; and we are quite certain that once Africa was
an island. So that in the case of that vast continent we know that it
must have seen periods of great depression and elevation; ages when
it was much lower than it is now, and ages when it was higher.
We will not at this moment stop to give further examples. We will
only try to see whether there is any explanation which would make
it possible to understand why there should be these slow upheavals
and subsidences of the earth's surface. The chief and most important
reason is that the earth is not so solid as it looks, and not so
solid as it feels. It would be easier to realise this if, instead of
living in a part of the earth like Great Britain, where there are
very few earthquakes, we lived in Japan, or Central America, or in
the archipelago of islands which runs from Java to Borneo and further
south. In these places, where never a year passes but that the earth
can be felt to quiver beneath one's feet, and where earthquakes
which wreck houses are at least as common as eclipses of the moon,
it is easier to believe that the earth is a rather shaky body; or,
as scientific men would call it, a rather unstable body. But if,
like those scientific men who take up the study of earthquakes, or
"seismology," we equipped ourselves with instruments to measure or
record earthquakes, we should perceive even in England that the earth
is nearly always quivering. Something is always snapping or giving
way in its interior, and producing trembling fits that sometimes can
be felt hundreds of miles away, and sometimes can be felt all over
the earth. There are on the average at least twenty earthquakes a
year which make the whole of this round globe tremble.
It would seem, therefore, that either these shocks or breakages
in the earth's crust, or the earth's interior, must be very great
indeed, or else that the earth must be composed of rather shaky
materials. Well, perhaps both these suppositions are true. We spoke
just now of the instruments which seismologists use to record
earthquakes. They are known as "seismometers," and a great many of
them are used in Japan and on the Californian or Pacific coast of
America. Now it is perhaps scarcely necessary to say here (when we
recollect how many cyclones and anticyclones England receives from
the Atlantic) that a storm or rainy weather is usually heralded or
accompanied by a fall in the barometer, or a depression. Now when
there is a depression in the barometer that means that the weight of
air above the barometer is less than it was before, though it is not
so great a difference that human beings could tell it, unless it were
accompanied by other signs. But the earth can tell it, and the mere
fall of the barometer, owing to changes of the air, will make the
earth tremble or quiver slightly, as if it were a jelly. We cannot
perceive it; but the delicate seismometers can; and when a storm is
coming to Japan or to California from the Pacific, the instruments
show that the earth feels the passage of it. The comparison of the
earth to a jelly--a very stiff jelly--is on the whole a useful one.
If a very tall jelly is allowed to stand for some time, or if
the table on which it stands is shaken a good deal, then, as we
know, rifts will sometimes appear in the jelly. The reason for
these breakdowns in the jelly's composition is that owing to the
distribution of its weight it is always in what we call a state of
strain; and it is sometimes not strong enough to support this strain,
and, almost without apparent cause, will sometimes give way. Much
more solid bodies than jelly act in the same way. The great bridge
near Quebec which collapsed in 1907 was to all appearance quite sound
and strong; but there were strains in the iron girders, and without
warning these strains suddenly produced rifts in the iron and steel
framework and it broke down. Similarly the towers of churches and
cathedrals, which are built on arches, will give away quite suddenly
after standing to all appearance quite firm for hundreds of years.
There is an architect's maxim which runs, "The arch never sleeps."
That means that the arches on which the great weight of a church
or cathedral tower rests are always in a state of strain; they are
always, as it were, imperceptibly quivering; and they are always
liable, if the strain on them should be increased in the slightest
degree, to give way, or to resettle the weight on their shoulders in
some way.
The whole of the great globe which we call the earth is in this
state of strain; and it is always liable to rifts within itself and
to readjustments of the weights of its own parts. It is not so easy
to understand how a great globe spinning through space can be in a
state of strain, or can attempt to readjust the weight of its parts,
as in the instances we have just given of the quivering jelly or the
solid cathedral tower. Perhaps another illustration may help us. We
will presume that nearly everybody is acquainted with the modern
rubber-cored golf ball. The modern golf ball, as those who are
aware who either intentionally or unintentionally have cut through
its outer cover, consists first of a small hard core. Round this is
wound very tightly some two hundred yards of elastic. The tighter
this is wound the better, or at any rate the more "bouncing" will
be the resulting ball of india-rubber elastic. But consider what is
the usual condition of this rubber-wound ball. Like our jelly it is
always in a state of stretch or strain. Even when covered with the
outer shell which completes the golf ball, the whole ball is still,
we might say, in a state of strain or tension. That is one of the
reasons why it bounces, and why it flies better than the old solid
ball off the face of a golf club. But if you were to keep a golf ball
for a hundred years these strains in its interior would alter and
adjust themselves. One result would certainly be that the golf ball
might lose its elasticity. Another result would be that its shape
would slightly alter.
Now a golf ball, however carefully it is made, is not always evenly
made. It weighs a little more on one side than another; and the best
golf balls, those which fly truest and farthest, are those which are
most evenly made: so that we might say of them that the centre of
their weight was exactly the same as the centre of the ball. If it
is not, then the strains in the ball are always pulling it a little
more out of shape; and the ball, as golfers say, flies badly. Now
the earth is like a badly made golf ball. The centre of its weight,
or, as we call it, the centre of gravity, is not quite at the centre
of the earth. Moreover, owing to the enormous pressures which exist
right through the earth, and which are by no means the same at every
place inside the earth, but are, in fact, continually changing,
owing to hundreds of causes, the whole of the earth's interior is in
a state of unequal strain. What is the consequence that you would
expect? Is it not that the earth should always be making efforts to
adjust its weight, and, as it were, to distribute it evenly? It has
been doing this for millions of years. It has not yet finished.
Lastly, the cover of a golf ball is comparatively a stiff and
unyielding substance which does not betray on its surface, if it is
allowed to lie at rest, the tensions and strains of the rubber core
inside. But the crust of the earth, which we have compared to the
golf ball's cover, is not unyielding or rigid. It is practically
a part of the case of the earth; and it does show and reflect the
strains and tensions of the movements and rifts of the core. So that
as in the course of ages the straining core changes, and gives way,
alters itself and adjusts itself--so the crust of the earth alters
with it. Some of these changes are sudden and violent. Some of them
take place very slowly, occupying thousands or hundreds of thousands
of years in the gradual process of change; and then perhaps for ages
the earth's crust will be slowly sinking in one place and slowly
rising in another. Thus, what was once a depression in the earth's
surface may be now an elevation; what was once below the level of
the sea may be now a continent of land; and what was once land may
now have sunk beneath the incoming sea. Thus, what was sandstone
rock of the earth's surface may become covered with forest, and the
forest may sink below the sea, only to be pushed up again and become
dry land a million years later. Each of these changes will leave
its mark, each will be accompanied by deposits. The deposits may be
vegetable matter, trees and mosses, and the growth of swamps, such
as coal was first made of; or they may be the ocean sludge, which at
last became chalk or limestone.
CHAPTER II
THE EARTH'S SHAPE
We have compared the earth to a golf ball, and as it spins through
space, impelled by a force millions of times greater than the
strongest driver ever imparted to the best-made "Haskell," its flight
and general appearance are not unlike those of the rubber-cored
ball. The earth, for one thing, is not smooth; it has roughnesses
and corrugations all over its surface, similar to those of a golf
ball, though much less regular, and it spins as it flies. But let us
now consider the differences. Suppose the golf ball had a spot of
water clinging to it as water clings to a greasy shot. Where would
the water lie? The first answer that occurs to one is that the water
would be shaken off the ball in the course of its flight; and that
is, indeed, very likely. But suppose the water were very sticky, or
were very much attracted by the golf ball (which is another way of
stating the same supposition), where would it lie then? To that we
can only say that there does not seem any very evident reason why
it should lie on one part of the flying golf ball more than on any
other--if the golf ball were perfectly round.
That is, on the whole, a reasonable answer. But apply the same
reasoning to the question of where the waters of the earth in the
shape of oceans ought to lie as they cling to the spinning globe.
They cling to the globe, not because they are sticky, but because
of the attraction which we say is due to gravity--the force which
makes everything in nature attract every other thing, and which makes
everything tend to fall to the earth (and to stay there). They do
so because the earth, being so very heavy and bulky in comparison
with anything in its neighbourhood, has such an enormous pull. How
great that pull is may be dimly gathered from the reflection that
though the earth is spinning at the rate of a thousand miles an hour,
nothing is ever shaken off. The oceans are not shaken off. They
cling. But why is it that they are not equally distributed all over
the face of the earth? If a map of the earth be examined, or still
better a globe with the oceans and continents correctly drawn on it,
it will be found that there is a great mass of land all lying grouped
together on one side of the earth, and a great basin of waters on
the other. Let the reader imagine himself a thousand miles above the
earth, looking down at a point in it about midway between Madeira and
the Bermudas. What would he see? He would see the Atlantic Ocean, but
all around it would be grouped great masses of land--Europe, Africa,
North America, Asia--and if it were his first sight of the earth and
he knew nothing of its geography, he would be likely to suppose that
the earth was nearly all land, with one comparatively small stretch
of unfrozen ocean. But now let the reader move round the earth to a
point exactly opposite that at which he took his first observations
and look down again. He will now see the Australian continent and the
land which covers the South Pole, but except for the pointed tail of
South America, and perhaps a glimpse of the blunter point of South
Africa, he will be looking down on a globe which seems to be largely
covered with water.
Why should this be? It must be due to the shape of the earth. The
fact is, the earth would make a very bad golf ball. It is by no
means of that perfection of symmetry which they say enables a golf
ball to fly well and to run true on the putting greens. The earth
is, in fact, not perfect as a sphere, either within or without.
Its centre is not in the same place as the centre of its weight,
and it is not round in shape. Everybody has heard that the earth
is slightly flattened at the poles; but its irregularity goes much
further than that. If we could strip it of its oceans, which fill up
a good many of its imperfections, we should find its shape not that
of a neat, round golf ball at all. The earth's actual shape without
its oceans, its "geoid," as it is called, is that of a pear. The
stalk of the pear is in the southern part of Australia, and contains
Australasia and the Antarctic continent. This is surrounded on all
sides but one (towards South America) by a sort of belt of depression
in which the waters lie. That is the waist of the pear. This again
is surrounded on all sides but one (towards the east of Japan) by
a belt of elevation. That is the protuberant part of the pear, and
here the great continental land areas rise. Finally, we find the
nose of the pear in the central Atlantic, between the Madeiras and
the Bermudas. Of course, the resemblance to a pear is not a very
marked one. Our observer a thousand miles above the earth would not
be able to perceive it, nor would the astronomers in the moon, if any
astronomers existed there. But the earth is pear-shaped to a small
extent nevertheless, and in the case of such an enormous mass a very
slight deviation from rotundity will produce very great effects.
Most of us have played at such ball games as bowls or billiards;
and I have assumed that everybody knows something about golf. What
happens in a game at bowls to the bowl which is not evenly weighted
all through? It will not run straight. It has a bias. What happens
to a billiard ball which is not perfectly round, or has lost its
symmetry through age? It wobbles. And what happens to a badly made
golf ball? That performs all sorts of exasperating antics. It ducks,
it soars, it curls, it takes a slice. It also wobbles. Now that is
exactly what the spinning, unevenly shaped globe which we call the
earth has been doing for millions of years. It has been wobbling;
and as we showed in the last chapter, it has always been trying to
right itself. Thus the two poles have not always been in the same
position; the oceans have not always been where they are. The waters
have sometimes crawled up the land towards the poles and sometimes
receded. Regions that have sometimes been frozen and cold have
become warmer, and have covered themselves now with oceans, and now
with forests, and now with deserts. There is no corner of the whole
world which has not undergone changes of climate. These changes
are very slow. There is no reason for supposing, in spite of the
laments we sometimes hear about the loss of old-fashioned winters
and old-fashioned summers, that the climate of England, for example,
has changed in the least since Cæsar's legions landed on its shores.
The Roman settlers in Britain doubtless experienced sloppy winters
and wet summers now and again, just as we do; and King Arthur's
knights, no doubt, had their saddening experiences of November
fogs. Yet slowly and surely changes of climate do take place, and
nothing except the winds influence them more than does the presence
of a neighbouring sea or ocean. Most of us reckon the warmth of a
locality's climate by the distance it is from the pole. That is,
however, a very rough and ready method. Vladivostok is roughly the
same distance from the North Pole as Venice; but there is a good deal
of difference in the temperature of the two places. In Manchuria when
the Russians and Japanese were entrenched before Mukden men died of
cold and were frozen at their posts at a time when other people in
Mentone and Monte Carlo, at the same distance from the Arctic Circle,
were complaining of the heat. So that we see that it must not be
assumed that a place like England (where for two thousand years we
occasionally have had winters that would kill trees like eucalyptus
or fig trees, and where oranges could never ripen in the open air)
was always equally cold. It may have been, in fact we know it must
have been, warm enough once to encourage and support what resembled
a tropical vegetation. It must also have been at one time as cold as
Siberia in the winter.
Therefore we should expect to find, if we digged down in the
earth, or in any portion of the earth which had undergone these
changes, some traces of them. For example, if at one time the sea
covered England for thousands or hundreds of thousands of years,
depositing the remains of millions of animals on the sea's bottom
during that period, we should expect to find some traces of these
remains--perhaps in the form of chalk, seeing that the bones and
shells of fishes dwelling in the sea contain a good deal of lime.
Or again, if a forest covered England and grew and decayed there,
not merely for a period like that which has elapsed since the Romans
first set foot in Britain, but for a hundred times as long, we should
expect to find some sort of vegetable deposit, hardened most probably
by other layers above it. Do we? Well, coal is a vegetable deposit.
If there was a time when ice covered the land we should expect to
find traces of that; if a time when the land was desert; or when it
was a lake--each and every one of these periods ought to leave some
remains, some epitaph of itself. So they do.
Let us for a moment consider with Sir Archibald Geikie[1] the
subsoil beneath cities that have been inhabited for many centuries.
In London, for example, when excavations are made for drainage,
building, and other purposes, there are sometimes found, many
feet below the level of the present streets, mosaic pavements and
foundations, together with earthern vessels, bronze implements,
ornaments, coins, and other relics of Roman time. Now if we knew
nothing from actual authentic history of the existence of such a
people as the Romans these discoveries deep beneath the surface
of modern London would prove that long before the present streets
were built the site of the city was occupied by a civilised race
which employed bronze and iron for the useful purposes of life,
had a metal coinage, and showed not a little artistic skill in its
pottery, glass, and sculpture. But down beneath the rubbish wherein
the Roman remains are embedded lie gravels and sands from which
rudely fashioned human implements of flint, arrow-heads, hammers,
and the like have been obtained. From that we learn that before the
Romans came an earlier race had been there which employed weapons and
instruments of roughly chipped flint.
[Footnote 1: Sir Archibald Geikie's _Introduction to Geology_.]
We have no doubt that this was the order of the successive peoples
occupying the site of London. It is obvious. Why is it? We see that
there are, broadly, three layers or deposits. The upper layer is that
which encloses the foundations and rubbish of our own era and times.
Next below is that which encloses the relics of Roman occupation. At
the bottom lies that which encloses the scanty traces of the early
flint-folk. The uppermost deposit is necessarily the newest, for it
could not be laid down until after the accumulation of those below
it; and those below it must be progressively older, as they are
traced deeper from the surface. By the mere fact that the layers lie
one above the other we are furnished with a simple clue which enables
us to determine the order of their formation. We may know nothing
whatever as to how old they are, measured by years or centuries. But
we can be absolutely certain that the bottom layer came first, and
the top layer came last. This kind of observation will enable us to
find proofs everywhere that the surface of the land has not always
been what it is to-day. In some districts, for example, when the dark
layer of soil in which vegetables grow is turned up, there may be
found beneath it sand and gravel full of smooth, well-rounded stones.
Such materials are to be seen in course of formation where water
keeps them moving to and fro, as on the beds of rivers, the margins
of lakes, or the shallow shores of the sea. Wherever smooth-rolled
pebbles occur they point to the influence of moving water, so that
we conclude, even though the site is now dry, that water once moved
above it. Again, below the soil in other regions lie layers of
oysters and other sea shells.
Pits, quarries, and mines that cut down still deeper into the earth
and lay it bare bring before our eyes most impressive testimony
regarding the ancient changes of the land. Suppose, by way of further
illustration, that underneath a bed of sand full of oyster shells
there lies a dark brown band of peat. This substance, composed of
mosses and other water-loving plants, is formed in boggy places by
the growth of marshy vegetation. Below the peat there might occur
a layer of soft white marl full of lake shells, such as may be
observed on the bottom of many lakes at the present time. These
three layers--oyster beds, peat, and marl--would be like a family
pedigree showing the history of the place. The bottom layer of white
marl would show that there was once a lake. The next layer of peat
would show that by the growth of marshy vegetation the lake became
choked up and was gradually changed into a swamp and then a morass.
The other layer of oyster shells would show that the ground was
afterwards submerged by the sea. The present condition of the ground
would show that the sea at last retired, and the place passed into
dry land as it is to-day.
By such a method of examination we may frame for ourselves pictures
of the earth's surface long before history began, or before man
roamed the earth. It is for this reason that geology has been
called the science that investigates the history of the earth. The
records in which this history is chronicled are the soils and rocks
underneath our feet. It is the task of the geologist so to arrange
and interpret these records as to show through what successive
changes the globe has passed, and how the dry land came to wear the
aspect which it presents at the present time.
To do this efficiently the geologist has to learn many things. He has
to observe very closely the changes which are going on about him on
the world's surface. Only in so far as he makes himself acquainted
with these sudden changes can he hope to follow intelligently and
successfully the story of earlier phases in the earth's progress. Nor
is it sufficient to observe, however closely, inanimate things. If
he did not know the peculiarities of fresh-water shells, how would
he be able to say the shells in the marl deposit were fresh-water
animals (and that therefore a lake once lay there) and not sea
shells. If the labour of the geologist were concerned merely with
the former changes of the earth's surface--how sea and land have
changed places, how rivers have altered their courses, how valleys
have been dug out, and how mountains have been carved, how plains
have been spread out, and how all these things have been written on
the framework of the earth--he would still feel one very great want,
the want of living interest. But that also his science gives him,
for in these past eras living things dwelt and moved and had their
being. And it is one of the most entrancing pursuits of the geologist
to trace their lives, their descent and ascent, and the relics of
themselves that they left.
CHAPTER III
EFFECTS OF WEATHER ON THE EARTH'S HISTORY
The same causes that produced the layers of peat or sand, or
limestone, or clay, which we find by examination of the earth's
surface, are acting to-day. Coal is forming now; and so is limestone;
and so is sandstone; so even is granite. But these layers or strata
form very slowly, so that since man has kept historical records
the thickness of new strata laid down could be measured in inches.
Consequently we are only able to see the beginnings of the processes.
After the materials were laid down by water or the shifting winds, or
by the decay of other materials already in position, they underwent
various changes. For example, many layers, instead of consisting of
loose materials such as gravel, sand, or mud, are now hard stone.
Sometimes this consolidation has been the result of pressure. As
bed was piled over bed those at the bottom would be more and more
compressed by the increasing weight of those laid down upon them;
the water would be squeezed out; the particles would stick closer
together. Mud, for example, might thus turn into clay; and clay,
pressed harder and harder, might be converted into mudstone or
shale. But there is another agency at work. We have all seen mortar
hardening and binding bricks together; or cement hardening into
concrete. Similarly sedimentary deposits are bound together by
cements, of which there are many which exist naturally. For example,
silica is a natural cement; and so is carbonate of lime; and so is
peroxide of iron. All these will bind other particles together. But
how do they arrive at the layers of particles? By the same action
which lays down the particles themselves. They are rubbed off the
places where they exist by the wind or by water. Perhaps they were
laid down among the deposited particles of mud or sand. Perhaps they
were brought to them by streams or rivers or lakes, and sank with
the water into them. In a red sandstone, for example, the quartz
grains of the rock may be often observed to be coated with earthy
iron peroxide, which serves to bind them together into a rather hard
stone. On the other hand, the process is often being reversed. The
weather frequently conspires by frost and wind and rain to remove
the binding cement, and thereby to allow the stone to return to its
original condition of loose sediment.
[Illustration: One of the Colossal Natural Bridges of Utah
This is an instance in which water has hollowed out the lower strata,
leaving a harder upper stratum partially intact.]
For millions of years the winds have blown over the surface of the
earth, the rain has fallen on it, the sun heated it by day, the
frost cracked it. Consider the winds that have circled the earth.
All movements of the air are due in the first place to the sun which
heats the atmosphere and causes it to expand. The sun's rays passing
through the air do not heat it at once, or directly, but heat the
land and the sea, which absorb some of the rays and reflect others
and so warm the air in contact with them. But, as will readily be
understood, the land and the sea do not absorb and reflect the heat
rays in the same way or to the same extent; nor do the sun's rays
fall equally or constantly on all portions of the earth's surface.
So that from various causes one part of the earth is always being
warmed in a different way from other parts, and the air above the
earth is being warmed in an immeasurable number of different ways.
Even if the earth's surface were all water or all land, we should
expect therefore that there would be movements of the air due to
unequal heating. If, however, the earth's surface were quite even
and uniform, we should expect that there would be a certain evenness
and uniformity about the movements of the air. These movements
would be due partly to the regular heating and regular cooling of
the surface, and partly due to the fact that the earth is spinning
round taking the air with it--but not taking it quite evenly. The
air does not fit tightly on to the earth. It is rather like a loose,
baggy envelope with a tendency to slip as the earth moves round.
Furthermore, a point situated on the Equator has much farther to
travel in twenty-four hours as the earth spins round than a point
situated in the Arctic Circle, where a tape measure placed along one
of the parallels of latitude (let us say the eighty-sixth parallel,
where Nansen turned back in his search for the Pole) would show the
earth's girth there to be, not twenty-four thousand miles, but only
so many hundreds. This also would make a difference in the way the
air would be whirled round the earth; but we could take this point
into consideration, and should be able, if, as we have said, our
earth were quite uniform, to say always and at all times of the year
in what direction the prevailing wind should blow.
Even with all the earth's irregularities we do know a good deal
with certainty about the earth's prevailing winds: the trades; the
anti-trades; the south-west monsoon, which sets in so regularly in
India that year by year its advent hardly varies by more than a day;
and, in the descending scale of regularity, the east winds that
usually sweep England in March, and the prevailing south-westerly
to westerly winds which bend most of the young trees of the country
a little to the north-east. Besides these regularly or irregularly
defined winds, there are certain paths along the earth's surface
where the winds always move like a trout stream with eddies in it.
These eddies of the air we call cyclones, and they are continually
travelling in one direction. No doubt they arise from the air in one
place becoming hotter or moister than in the surrounding regions.
As the air grows hotter it becomes lighter and ascends, while the
heavier air round it pours in. These eddies always travel eastwards
and incline in the northern hemisphere towards the north. They
usually originate somewhere on the North American continent, and move
across the Atlantic about the pace of a slow railway train, winds
whirling round them all the time at a much greater pace. Usually
the centres of these eddies bear northward past the north coast of
Scotland to the north-west of Norway. Sometimes, however, they take
a more southerly course, keeping to the south of the British Isles
and passing over Central Europe on to Siberia, where they appear to
die away.
Such are the cyclones which are in the main part responsible for
British weather; and the winds that accompany them vary a great
deal in strength. They depend on the size of the eddy. If the eddy
is a very big one (and sometimes the eddies are thousands of miles
across) the winds will not be so strong as in the smaller ones. It
is, therefore, the smaller ones which cause the violent storms.
In the tropical regions whirling eddies of a rather different
character occur. To quote Mr. J. H. N. Stephenson: "Instead of being
measured by some hundreds or even thousands of miles, they are
usually only some hundreds of yards across; and as we found that
the smaller the cyclone the more violent the wind, we shall not be
surprised that the wind in these is more violent than anything we
ever experience in this part of the world. They are called by many
different names; in the West Indies they are known as _hurricanes_,
in the south-east of Asia as _typhoons_, and in North America as
_tornadoes_. These hurricanes or tornadoes travel much faster than
the larger cyclones, and the winds blowing into them are so violent
that everything--trees, houses, bridges--are swept before them, and
so strong is the in-draught of air in the centre that strong walls
are sucked in just as a piece of paper is in front of a grate when
the fire begins to blaze up; and even heavy metal objects are carried
_upwards_. Fortunately these tornadoes do not travel continuously
along the ground but bump along it, so to speak, sometimes passing
harmlessly overhead, then striking the earth again and causing more
havoc. Where they pass over the surface of the sea the water is
sometimes sucked in just in the same way, causing what is known as a
_waterspout_. These may do even more damage than a tornado on land,
for the water is sometimes carried bodily on to the land, sweeping
everything away in a deluge. This happened many years ago in the
delta of the Ganges, when thousands of people perished."
Now let us see how these winds might leave traces in the geological
record. When soil is exposed to the sun its surface becomes dust, and
the wind carries it off. Even where turf protects the surface, bare
places may always be found whence this covering has been removed.
Rabbits and moles bring up the earth to the surface; the earthworms
sometimes bring as much as ten tons of earth to the surface of a
single acre of turf in the course of a year. The earthworms bring up
only the finest particles of mould; and these, of course, are the
very particles readily converted into dust and borne away by the
wind if they are not washed away by rain. In tropical countries the
white ant conveys a prodigious amount of fine earth up into the open
air, building walls sometimes sixty feet high. Although, therefore,
the layer of vegetable soil which covers the land appears to be a
permanent protection, it does not really prevent a large amount
of material from being removed even from grassy ground. The wind
carries this fine dust far and wide over the land, and over the sea
as well. After the eruption of the island of Krakatoa in 1883, the
dust which was the product of that mighty explosion was carried round
the world, and even in England we saw the dust particles furnishing
extraordinary colours in sunset skies.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
The Garden of the Gods, Colorado
These peaks exhibit the gradual wearing away of hard rocks by the
action of rain and wind.]
In dry countries, especially in the large tracts of Central Asia
and of Africa, the air is often so thick with a fine yellow dust
that the sun's light struggles through it as through a London fog.
The dust settles on everything, and after many centuries a deposit,
which may be hundreds of feet deep, is thus accumulated on the
surface of the land. Some of the ancient cities of the old world,
Nineveh and Babylon for example, after being long abandoned by man,
have gradually been buried under the fine soil which the wind blew
over them. Even in England the Roman town of Silchester, not far
from Reading, after falling into decay when its inhabitants left it,
has been buried under the accumulations of two thousand years, and
its walls and floors now lie underground and have to be carefully
unearthed in order to lay them bare. But we need not seek these
exceptional cases in order to perceive what the wind is doing with
sand and the fine dust of the earth's uppermost layers. At many
places round the coast are sand-dunes. On sandy shores, exposed
to the winds that blow off the sea, the sand is dried and carried
away from the beach, gathering into long mounds or ridges which run
parallel to the coast-line. These ridges are often fifty or sixty
feet, sometimes even more than 250 feet high, with deep troughs and
irregular hollows between them, and they sometimes form a strip
several miles broad bordering the sea. These sand-hills creep
farther inland, till their progress is stopped by the fields or woods
they encounter, or till, by seeds finding a root, vegetation springs
up on them and they harden and consolidate under the influence of
their own vegetation and move inland no farther. But in many parts of
Western Europe and Eastern America the dunes are marching inland at
the rate of twenty feet a year. Off the coast of Friesland and North
Germany the danger has grown so threatening that scientific attention
has been given to the problem; and the German scientific men have
employed ingenious devices of planting wind-stakes--something like
the wooden breakwaters that are to be found along every seaside
beach, but arranged at different angles,--of forcing the sand-dune
to heap itself up so as to form an obstruction to further arrivals;
or of sowing those plants in the sand that will bind its particles
together, in order to preserve the land from further invasion.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
A Curious Rock greatly revered by the Natives
This is the Dance Rock of the Walpi Indians of Arizona. Its curious
shape is the result of weathering.]
What goes on along the coast finds a parallel in the interior of
continents where, as in Arizona, in America, or by the desert of
Gobi, in Asia, or in the Karroo of South Africa, or in Central
Australia and Africa, there is great dryness of climate and a
continual disintegration of the surface rocks. Sometimes the dust or
sand remains and gradually consolidates or hardens. More often it is
only a temporary visitor. Wind and rain are continually removing it,
sometimes in vast quantities, into the sea; and in the course of time
the most astounding changes are wrought in the surface and appearance
of the land. The softer rocks are worn down; the harder ones are left
sticking out. Gradually the surface is carved out into heights and
hollows. The harder rocks become the hills and ridges; the softer
rocks are worn into valleys and plains. If there were no water left
on the earth's surface a great deal of this process would still go
on. In some respects it might become more violent, for owing to the
absence of moisture the winds of the earth would always be laden with
fine particles; and every one who has seen a "sand-blast" at work, or
even the modified sand-blast which is sometimes used for cleaning the
stonework of some of our cities, will appreciate what a tornado laden
with sand grains might do in the way of destroying the surface of any
rock on which it was playing. But, as a matter of fact, the action of
water in carving the surface of the earth is the most important of
all the factors we have at present to consider.
As rain falls from the clouds it absorbs the gases of the air,
including oxygen and carbonic acid. Now both these are what we call
corroding agents. If water is allowed to fall on a steel knife the
knife rusts; but it has been shown by Dr. Gerald Moody, during the
last few years, that if there were no acid gas present, the rusting
would not take place. Oxygen and carbonic acid will rust other things
beside metal; they will rust stone. Moreover, when the rain reaches
the earth it absorbs any other acids of the soil which rotting
vegetation may afford, and reinforced by these it goes on to attack
the stones over which it flows. When it rolls along as a brook or a
river it is no doubt attacking in this way the rocks and stones of
its channel, though this action is not very strikingly shown. But
sometimes the rusting or dissolving action of water is very evident.
When it issues from a peat bog, for example, and is consequently
highly charged with acid, it will make a very great impression on any
limestones it may encounter; for as any schoolboy knows who has ever
put a piece of chalk in vinegar, or in any of the stronger acids of
the school laboratory, all the limestones are peculiarly susceptible
to this form of chemical attack. Peat-water eats into limestone
rapidly, while the limestone above the stream escapes, though it is
a little (and much more slowly) dissolved by rain. Hence arise some
curious features in the scenery of limestone districts. The walls of
limestone above the water are not eaten away so fast as their base
over which the water flows. Consequently they are undermined and are
sometimes cut into tunnels and caverns and caves.
The rivers carry away the dissolved material. The carbonate of lime
is taken to the sea; and this substance, of which sea shells, for
example, are principally formed, is constantly supplied to the sea
by the rivers that transport it from the land. The rivers of Western
Europe have been known to convey one part of dissolved mineral matter
in every 5000 parts of water, and of this mineral matter one half is
carbonate of lime. The Rhine alone bears enough carbonate of lime
to the sea every year to make 332,000,000,000 oyster shells of the
usual size. The Thames conveys 180,000 tons of sulphate of lime past
London every year. It has been computed that more than 8,000,000 tons
of dissolved mineral matter are removed from the rocks of England
and Wales in one year. That is equivalent to a general lowering of
the surface of the country, by chemical solution alone, at the rate
of one foot in 13,000 years. That is not much, it may seem; but in a
million years, which is not a long period in geological time, half
the present towns of England would be sunk under water by this cause
alone.
CHAPTER IV
RECORDS LEFT BY RIVERS
When we come to examine more closely the work which rivers do in
removing mineral substances from the land by washing particles
of them from the surface, we find that the records they leave in
geological history must be plainly marked. Every stream, large or
small, is always busy carrying mud, sand, or gravel. Rivers are the
"navvies" of geology. When they are swollen by rain they sweep large
stones away with them. If we look at the bed of a mountain torrent
we shall often see huge blocks of stone that have fallen from the
cliffs on either side blocking the pathway of the stream. To all
appearance the stream is quite powerless to remove these blocks,
and has to circumnavigate them. But visit such a torrent when the
snows are melting, or heavy rain has fallen, and you will hear the
stones knocking against each other or on the rocky bottom as they are
driven downwards by the flood. It is not easy to estimate the driving
power of water. M. Gustave le Bon has furnished an illustration of
its power which is very curious. In the south of France a stream
is led downwards from the mountains to drive the turbine of some
machinery at a manufactory. It comes down several thousand feet. In
the manufactory there is a vent-hole, out of which the water can be
allowed to shoot. The vent-hole is about an inch in diameter; and the
water rushes out with such swiftness and force that the water-jet
becomes as rigid as steel. It is impossible to cut through this
water-jet; and if any one were to try to do so with a sword, the
sword might break but it could never pierce or pass through those
swiftly moving particles of water. A more commonplace illustration is
the use that is sometimes made of water-jets to break up the surfaces
of rock in quarries; nor must it be forgotten that horse-power of
great value and extent for electric lighting and other purposes is
always being drawn from waterfalls. Thus as a mechanical force merely
the river can be immensely powerful; and must leave marks of its
power on the rocks.
The aspect of its force with which we are, however, most concerned is
that which is directed to lowering gradually the surface of the land.
In the last chapter we showed how much mineral might be dissolved
in the waters of rivers. If we are to include also the amount of
mud, sand, and other things classed altogether as silt which a river
carries down, the figures become much more imposing. Sir Archibald
Geikie says that, taking the Mississippi as a typical river (it is
as good an example as would be found, because in its great length
it passes through many different kinds of land, soil, and climate),
we may assume that the average amount of sediment carried down by a
river is one part of sediment to every 1500 parts of water.
If now, says he, we assume that all over the world this is the amount
carried down, we can see how seriously the level of the land is
lowered by rivers. The Mississippi carries from the land it drains
every year the 1/6000th part of a foot of rock. If we take the
general height of the land of the whole globe to be 2100 feet, and
suppose it to be continuously wasted at this rate, then the whole
dry land would be carried into the sea in 12,600,000 years. Or if
we assume the average height of the continent of Europe to be 940
feet, and to be lowered by its rivers at the same rate, then the last
vestige of Europe would have disappeared in 8,640,000 years. Such
figures are of course not exact; and it must always be remembered
that the rivers are merely robbing Peter to pay Paul, and whatever
they take away are always putting somewhere else, but we may learn
from the foregoing considerations that the lowering of the land is
much more rapid than is sometimes supposed. Another thing about the
excavating work of rivers has to be remembered. The torrents carry
sand, shingle, and rock with them, and these very materials act as
agents of destruction on the beds of the water-courses. If we want
to polish brass or steel we mix emery powder (or something finer or
coarser) with the polishing liquid. The torrent or river uses sand
or shingle as its polishing powder. It then wears out the rock over
which it travels, and sometimes carves it into holes or caverns,
gorges or ravines. Sometimes the process is varied, as when a stream
finds its way over a hard rock which overlies a softer rock. If the
arrangement is like that of a series of steps (there may be only one
or two steps) it is possible for the river as it foams in a waterfall
over the hard step at the top to eat its way into the lower softer
step. The lower softer step will gradually disappear, and then the
waterfall, still eating its way in, will begin to undermine the hard
top step, and when that has gone on long enough the hard top step
will fall down and the waterfall will have to begin a little farther
up the stream. In this way a waterfall, gorge, or ravine can be
constructed by a river.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
The Grand Cañon of Arizona
The Colorado River at this point is nearly 200 feet wide. The man
is seated about 1200 feet above the river's level. This whole cañon
up to the top of the mountains in the distance has been worn away
by prehistoric current; and the river has gradually cut its bed
deeper.]
The Falls of Niagara are an illustration of this method. The river
flows from Lake Erie through a level country for a few miles, then
begins to go faster as the path becomes steeper, and finally plunges
over a hard limestone precipice. Beneath the hard limestone (the top
step) are softer beds of shale and sandstone. As the water eats into
them and removes them, large portions of the face of the limestone
precipice on the top fall into the stream below. Thus gradually the
Falls of Niagara are eating their way back to Lake Erie, and have
been doing so for hundreds of thousands of years. In the process of
doing so the Niagara River has cut out below the Falls a gorge which
is not less than seven miles long, from two hundred to four hundred
yards wide, and from two hundred to three hundred feet deep. There
is no reason to doubt that the Niagara gorge has been entirely cut
out in this way, and that at first the river fell over cliffs seven
miles farther down its course at Queenstown. The amount of rock thus
tunnelled would make a rampart about twelve feet high and six feet
thick going round the world at the Equator. Still more gigantic are
the gorges or caverns of the Colorado and its tributaries in Western
America. The Grand Cañon of the Colorado is three hundred miles long,
and in some places more than six thousand feet deep. The country
traversed by it is a network of deep ravines, at the bottom of which
flow the streams that have dug themselves down from the top of the
Colorado tableland.
Now suppose that the river has dug itself in as far as it can go.
There must be a limit, and the limit is reached when the slope of
the bed has been made so slight that the current can only go on
languidly. In that case it cannot sweep along stones, or shingle,
or even coarse gravel; and then the river so far from deepening
its channel begins to raise it by allowing more of the transported
sediment to settle down. If a fast stream meets a slower one
deposition of material will take place; and the same thing will
occur when the rivers meet a lake or a sea. Whatever checks the
swiftness of a current weakens its carrying power and causes it to
drop some of its sediment to the bottom. Therefore accumulations of
sediment occur at the foot of torrent slopes along the lower and
more level ground. These deposits we call alluvium, and sometimes
when the mountain torrent ends abruptly in the plain they may stand
up in cones of silt. They are sometimes called _alluvium cones_ or
_fans_. Quitting the steep descents, and reinforced by tributaries on
either side, the stream ceases to be a torrent and becomes a river.
It goes fast enough at first to carry still coarse gravel; but the
big angular blocks of rock have been dropped, and the stones it now
leaves in its bed are smaller, and become rounded and smoothed as it
goes farther and farther across the plain. At many places it deposits
gravel or sand, more especially at the inner side of the curves which
the stream makes as it winds down the valley. When the stream runs
low in summer, strips of bare sand and shingle are seen at each of
these bends; and the stones are always well smoothed and lie on the
whole regularly. Those that are oblong are so placed that the greater
length of the stone points across the stream; those that are flat
usually slope upstream. These facts, though apparently insignificant,
are really of importance, because they point to us a method by which
geology can determine, after a river has disappeared, the slope of
the bed and the direction of the curves which once it had. If we
examine the steep banks or cliffs by the side of a river the layers
of gravel or shingle in the strata may be found to lie not flat on
one another but in sloping planes. That at once will furnish a clue
to the direction of the river. Another thing of great importance
are the terraces which a river forms by the side of itself. When it
overflows in floods it deposits mud on either side, and when after
the flood it subsides the mud is left. If the reader will imagine
the river in the course of ages sinking lower into its bed he will
see that successive eras of flood-levels will leave their mark in a
series of steps, or _river terraces_ as they are called, on either
side of the channel.
But besides the stones and gravel and mud carried down by a river, we
must also consider the fate of the remains of plants and animals that
are swept along by it, especially in flood-time. In any ordinary
flood trees and shrubs, and the smaller animals like mice and moles
and rabbits, are drowned by the flood. In greater floods birds and
even large animals are drowned, and their remains are buried in
the sediment. If they are quite covered over they may perhaps be
preserved, and their bones may last for an indefinite period. If,
further, the mud deposit hardens, these remains may be preserved so
well and so long that they become the fossil records of creatures
which lived before man emerged to dwell in the world and to become
the arbiter of many of its destinies.
What we have said of rivers is true also of lakes. Rivers pour
into lakes, bringing with them, especially in flood-time, enormous
freights of gravel, sand, and mud, and mingled with them the remains
of vegetation and of animal life. Hundreds of thousands of tons may
be swept down by one storm. To the Lake of Lucerne, for example, the
River Reuss, which comes down from the St. Gothard, brings seven
million cubic feet of sediment every year with it. Since the time of
the Romans the Rhone has so filled up part of the Lake of Geneva that
the Roman harbour, Port Valais, is now nearly two miles from the edge
of the lake. The ground between it and the Lake first became marsh.
It is now farm land. And though these accumulations are most marked
where the rivers drain into the lake, there are deposits always
taking place from the hills all round the lake. Thus lake bottoms
become most interesting and valuable receptacles of the life that has
for ages lived by or near their shores. These deposits are in many
ways peculiar. The snails that live in lake waters are distinct from
the land snails of the adjoining shores. Their dead shells gather at
the bottom of some lakes in such numbers as to form there a deposit
of white crumbling _marl_, sometimes many yards in thickness. On the
sites of lakes that have been gradually filled up, or artificially
drained, this marl shows at once where the lake borders were, and,
roughly, the period of the lake. In some lakes also are found
concretions of iron-oxide, which are formed by the chemical action
of the water on some of the rocks by the lake-side; and in several
Swedish lakes this ironstone forms so fast that the lakes are
regularly dredged for it.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
Cleopatra Terrace, with its Mirror-like Pools, Yellowstone Park,
U.S.A.
These beautiful basins are formed of incrustations of volcanic
limestone. They are of all colours: pink, orange-yellow, green,
and blue. The water in them is of a brilliant blue, caused by the
growth of water plants (algæ), which live in water with as high a
temperature as 150 F.]
Thus among the rocks which form the dry lands of the globe there
occur masses of limestone, sand, marl, and other materials which we
know were deposited in lakes, because they contain types of plants
and animals like those found in the lakes of our own time. From this
kind of evidence we can mark out the places of great lakes that have
long ago vanished from the face of Europe and North America.
There are also the so-called Salt Lakes to consider. These are
generally the lakes that have no outlet and into which a small
amount of water now flows, but never enough to cause the lake now to
overflow, whatever it may have done in past times. The water that
now runs in escapes merely by evaporation. But just as the bottom of
a kettle in which hard water is constantly boiled gradually becomes
furred, so a lake bottom into which water is continually pouring,
bringing dissolved in it all sorts of mineral salts, becomes coated
with sediment. The mineral salts are not evaporated, consequently
the lakes become gradually more mineral--or, for convenience, let us
say, become salter. Among the mineral salts common salt and gypsum
are most important; but some bitter lakes contain sodium carbonate
or magnesium chloride. The Dead Sea and the Great Salt Lake of Utah
show by the deposits round them how they have changed their shape
and depth. In the upper terraces of the Great Salt Lake, 1000 feet
above the present level of the water, fresh-water shells occur,
showing that the basin was at first fresh. The valley bottoms around
salt lakes are now crusted with gypsum, salt, or other deposits,
and their waters are without sign of life. Such conditions help us
to understand how great deposits of salt or gypsum were once laid
down in England, Poland, and Germany, and in many other places where
now the climate would not permit of the necessary evaporation and
condensation of the water.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
A Petrified Tree
This magnificent fossil is in the Petrified Forest of Arizona; and it
affords one of the most striking examples known of the solidification
and petrifaction of material by the infiltration of mineral salts.
The trunk is now not merely encrusted with stone: it is permeated by
silica, and is, in fact, itself a stone as hard as flint.]
CHAPTER V
RECORDS LEFT BY THE SEA
We have already spoken of the story which the sea writes in the
annals of geology. It is a story with two plots. In the first place,
the sea is always wearing away the land. In the second place, it is
arranging on its own bed the materials which it takes from the land,
either directly or indirectly. As a sequel to both stories, the
materials all neatly ranged, packed, and folded are revealed when the
sea subsides from them, or when, in process of one of those great
geological changes, the origin of which we have already attempted
to account for, the sea bottom is raised to become the land of a
continent. The first part of the sea's belligerent story is written
so plainly for all eyes to see that one scarcely need dwell on it.
Every strip of coast around these islands bears witness to it.
Off Shetland masses of rock twelve or thirteen tons in weight have
been cut out from the cliff seventy feet above the smooth-water
level. The sea's battering-rams are the masses of shingle, gravel,
and loose blocks of stone which it carries with it; but it has
subtler methods in the corrosive action of its salts, for just as it
rusts or wears away iron, so its salts and acids must eat their way
into many rocks.
But, after all, the coast-line of the world is a small fraction of
the whole land surface of the globe; and a smaller fraction of the
sea's own wide area. On that area are flung all the records and
treasures which the sea has wrested from the land. The rivers, as
we have already several times repeated, are the chief carriers of
deposits to the sea. By their deltas they may be known. The deltas of
the Ganges and Brahmaputra cover an area as large as that of England
and Wales. The delta has been bored through to a depth of nearly five
hundred feet, and has been found to consist of numerous alternations
of fine clays, marls, and sands or sandstones, with occasional layers
of gravel. In all this accumulation of sediment there are no traces
of marine animals; but land plants and the plants and animals of the
river and of the surrounding land have been discovered in quantity.
The sea most often destroys land; but it sometimes deposits beaches;
and, we might almost say, silts up the land. At Romney Marsh, for
example, a tract of eighty square miles which was marsh in Julius
Cæsar's time is now dry land, and has become so partly by the natural
increase of shingle thrown up by the waves. The coarsest shingle
usually accumulates towards the upper part of the beach, and the rest
arranges itself generally according to size and weight, that which is
finest being nearest to low-water mark.
It is often long before the stuff brought down by the rivers settles
on the floor of the ocean. The finer particles may be carried out to
sea for three hundred miles or more before they settle. Within this
three-hundred-mile zone the land-derived materials are distributed
over the floor in orderly succession. Nearer the land we shall find
coarse gravel and sand. Beyond there will be tracts of finer sand
and silt, with patches of gravel here and there. Still farther off
will come fine blue and green muds, which are made of the tiny
particles of such materials as form the ordinary rocks of the land.
But when we are once past this zone of land material we come upon
deposits which are the ocean's own freehold--materials which it does
not derive from the continents, but which may be called oceanic in
origin. First there are vast sheets of exceedingly fine red and brown
clay. Whence comes it? It is by far the most common deposit in all
the deeper parts of the ocean. It may either be the dust of volcanic
fragments washed away from volcanic islands, or (which is much more
likely) it may be supplied by eruptions under the sea. For it must
be remembered that the sea floor is two to five miles nearer the hot
rocks that are in the interior of the earth than the land surface is,
and that consequently the water coming into contact with them may
cause explosions arising from the action of steam. This is a question
we shall have to consider later, and for the present we must ask the
reader to accept the fact--and read on.
There is one very curious thing about this red clay, and it is that
the accumulations of it appear to be built up very slowly. Where it
occurs farthest from land great numbers of sharks' teeth with ear
bones and other bones of whales have been dredged up from it. Some
of these relics are quite fresh; others are coated with a crust of
brown peroxide of manganese. Some are covered with this material and
hidden in it. One haul of an ocean dredge will bring up the bones in
all these states, so that they must be lying side by side. The bones
are probably those of many generations of animals, and it must take a
long time to cover them with the manganese deposit. But the clay is
deposited even more slowly than the manganese, so that it must fall
very slowly indeed.
But besides these things the bottom of the sea receives deposits of
the remains of all kinds of shells, corals, and all sorts of marine
creatures, great and small. As the countless myriads of the animals
of the sea die, the shells with which they are covered, or the bones
which form their framework, fall continually to the bottom of the
oceanic gulfs in which they dwell. Then the ocean floor is covered
with the remains of tiny animals incomparably more numerous than the
stars of the sky; and this grey slimy ooze of organic matter hardens
by pressure into sedimentary rock. In the course of ages, when the
slow decline of the water lays it bare, it may become part of the
land on which men dwell. But it is always forming, has always been
forming, since life first appeared on the earth. It is on this ocean
floor that man to-day lays his telegraph cables. Mr. Rudyard Kipling,
in his verses "The Deep Sea Cables," has drawn a vivid picture of the
bed of the deep ocean:--
The wrecks dissolve above us: their dust drops down from afar--
Down to the dark, to the utter dark where the blind white
sea-snakes are.
There is no sound, no echo of sound, in the deserts of the deep,
On the great grey level plains of ooze, where the shell-burred
cables creep.
It is in these silent depths that for uncounted and innumerable
years the crust of the earth has been forming and has been growing
outwards, while it has been slowly hardening inwards above the fires
of its unplumbed interior.
It has been calculated that in a square mile of the ocean down to
a depth of one hundred fathoms there exist more than sixteen tons
of carbonate of lime in the form of the bones or shells of living
animals. A continual fine "snow-storm" of dead chalky animals is
therefore falling on to the bottom. Here and there, especially among
volcanic islands, portions of the sea-bed have been raised up into
land and masses of modern limestone. Though these rocks are full of
the same kinds of shells as are still living in the neighbouring sea,
they have been cemented into hard rock. This cementing is due to
the water which has penetrated and permeated the stone, dissolving
chalky matter from the outside shells, and depositing it once more
lower down and farther in, like a fine mortar, so as to bind the mass
together.
Every one has heard of coral reefs. They are one of the best and most
familiar examples of the way in which great masses of solid rock
can be built up by the dead bodies of animals. In the warmer seas
of the earth, and notably in the track of the great ocean currents,
various kinds of coral polyps, as they are called, take root on the
edges and summits of submerged rocks and peaks, as well as on the
shelving shores of islands. The coral polyp is a jelly-like creature,
but it has a hard chalky skeleton inside its transparent body. It is
a great colonist, with no liking for a solitary life, but with, on
the contrary, a great fancy for its neighbours; in fact, the polyps
grow and thrive in clumps, and the clumps unite to form communities,
and the communities increase to colonies and nations, till they unite
to form what is called a reef. The coral polyps are rather exigent
in the choice of their residential neighbourhoods. They cannot live
at a greater depth than fifteen or twenty fathoms, and in defiance
of the inclinations which rule human beings, they have the strongest
distaste for sun and air; in fact, they die when exposed to it.
Now when the polyp dies its skeleton remains behind it, and millions
upon millions of these coral skeletons make a layer of coral. These
layers of coral gradually lift the generations of polyps upwards to
the surface of the water. But as we have seen, the living polyps
die when they get so far, and consequently the reef then spreads
outwards. On the outer edges of the reef the coral polyps flourish in
the most vigorous way. There they are as completely provided for as
in a County Council Utopia. The breakers bring them the food on which
they live; the water and the climate suit them exactly. The only blot
on their lives are the occasional storms which break off fragments of
the coral foundation on which they live. But even this, while it is
disastrous to the individual polyp, is for the good of the community,
because these blocks as they roll down form a new foundation on
which new generations of polyps can grow and feed. Moreover, it is
better for the polyp to take the risks of these evictions than to
vegetate _inside_ the reef, for there in the calmer water he will
not have enough to eat, and will dwindle and die. Thus the tendency
of all reefs must be to grow seawards, and to increase in breadth.
Perhaps their breadth may tell us roughly how old they are. But there
is another possibility to be taken into consideration, which is that
while the polyps are building the sea bottom or island foundation may
be slowly sinking. In that case it is quite likely that the coral
builders might just keep pace with the subsiding foundations of
their home, and build up a great thickness of coral rock during the
countless years of change.
Sir Archibald Geikie has called attention to the swiftness with
which the structure of the coral polyp's skeleton is effaced from
the foundation and a compact mass of rock put in its place. The
sea-water's chemical and dissolving action, and the vast amount of
mud and sand produced by the breakers are chiefly responsible for
this. As the rock is being formed it is always being cemented. On
the portion of a reef laid dry at low water, the coral rock looks in
many places as solid and old as some of the ancient white limestones
and marbles of the land. In pools where a current of water keeps the
grains of coral sand in motion, each grain may be seen to be rounded.
This is because on each particle of coral the dissolved carbonate of
lime in the water is always being deposited (like the sediment in the
bottom of a kettle). A mass of these rounded or egg-like grains all
gathered together in a lump is called _oolite_, from the Greek word
"oon" (Latin "ovum"), an egg. In many limestones, now forming parts
of agricultural land, this _oolitic_ structure is strikingly shown,
and there can be no doubt that in such cases it was produced just as
now coral reefs are being formed before our eyes. In the coral tracts
of the Pacific Ocean there are nearly three hundred coral islands,
besides extensive reefs round volcanic islands. Others occur in the
Indian Ocean. Coral reefs abound in the West Indian seas, where in
many of the islands they have been upraised into dry land--in Cuba
to a height of 1100 feet above the sea-level. The Great Barrier Reef
that fronts the north-eastern coast of Australia is 1250 miles long
and from ten to ninety miles broad.
It will thus be seen that, apart from any other consideration, the
animals of past ages leave permanent records of their existence
merely by the accumulation of their dead bodies. Nevertheless, alike
on land and on sea, the proportions of organic remains thus sealed
and preserved is only a small part of the total population of plants
and animals living at any given time.
CHAPTER VI
COLD AND ICE ON THE EARTH
The astronomers who look at the planet Mars tell us that at the
Northern and Southern Poles there are great areas of snow, very much
greater than the arctic regions of the earth, for the south polar
area alone occupies 11,330,000 square miles. But the geological
records of the earth show that our own arctic regions once extended
very much farther than they do at present, a fact which need not in
any way surprise us, for as we have already remarked, snow and ice
are very largely a matter of the nearness of the sea to the land.
We may put the same thing in another way by saying that winter
cold and summer heat depend largely on the distribution of sea and
land. Thus Venice, which is not very much farther from the North
Pole than Vladivostok, has an altogether different climate, and
inhabitants of the Shetland Isles have a very different kind of
climatic experience from those who delve by the frozen Yukon. There
is another consideration which is sometimes overlooked. We do not
think of the earth as a very warm body. But at its very coldest
part, where the thermometer goes down to seventy or ninety degrees
below freezing, it is several hundreds of degrees warmer than the
space outside the earth. Midway between the earth and the moon the
temperature must be 430° F. below freezing; so that if we take the
surface of the earth as a whole we may say that it is between four
hundred and five hundred degrees warmer than the space by which it is
surrounded. Every one knows what is happening when he warms his hands
at a fire. The fire being hotter than its surroundings is giving out
heat towards them, and the hands catch some of this radiated heat.
Similarly the earth is radiating heat, and the atmosphere round the
earth catches some of it. So also do the seas. While therefore it
is certain that the heat of the sun warms the earth and the air and
the sea, and so gives rise to currents of air and perhaps of water,
so also is it likely that the heat of the earth causes warm air to
rise, and so plays its part in forming the winds, the currents of
air, and the currents of water. When the earth was warmer than it is
now it had more and greater effects in this direction. It caused more
evaporation of the water, more clouds, and therefore more rain, and
in winter more snow.
Suppose, then, a period when there was very much more snow in winter
than now. As the snow accumulated layer on layer the lower part would
become squeezed into a mass half ice, half snow; and it is quite
likely that the heat of the summer sun (especially if, as we have
supposed, the atmosphere was much cloudier then than now) would be
unable to dissolve it. Thus the snow age would gradually merge into
an ice age, and we can imagine a period when a great deal of Europe
was covered with snow or ice as Greenland is to-day. What records
would it leave behind? Now, on slopes the sheet of snow would tend to
slip just as it slips from sloping house-roofs. In doing so it would
push before it any loose material which lay in front of it; and trees
or bushes, stone or soil, would be gradually pushed downhill. If the
slopes were steep enough the snow-sheets would occasionally break
off and sweep down as avalanches. Sometimes these great masses are
many thousands of square yards in area and fifty feet thick, and in
the late winter and early spring often do immense damage, carrying
away houses, trees, and great masses of rocks in their progress. They
leave their imprint not only in ground swept bare, but in huge mounds
of debris piled up in the valleys below.
But when the snow has taken the form of a glacier its record is left
in more unmistakable characters. Imagine a great mass of snow and
ice descending between the clefts of mountains to lower levels. As
it slips slowly down its valley, like a very slow river--slower than
a river of thickest mud or pitch or lava would be--earth, sand, mud,
gravel, boulders, and masses of rock sometimes are washed down on its
surface from the slopes on either side. Avalanches will occasionally
bring other contributions. Nearly all this rubbish accumulates on
the edges of the glacier nearest the slopes, and it is slowly borne
to the journey's end on the glacier's shoulders. Some of it falls
into rents or crevasses in the ice, and may be imprisoned there and
carried down as an inside passenger, or it may reach the rocky floor
over which the ice is sliding. Its progress then resembles that of
the Irish gentleman who was travelling in a Sedan chair out of which
the seat and the bottom had fallen, and who said that if 'twere not
for the fashion of the thing he'd as lief walk. The rubbish borne
onward on the surface of the glacier is known as _moraine-stuff_,
and the mounds of it at the edge of the glacier are called _lateral
moraines_. Where two glaciers unite like two rivers, their moraines,
right-hand and left-hand, will join, and in the new glacier a new
moraine will appear running down the middle, and so called a _medial
moraine_. Where a glacier has many tributaries bearing a good deal
of moraine-stuff, its surface may be like a bare plain so covered
with stones that the ice beneath can hardly be discerned except here
and there. At the end of the glacier where the ice melts, the heaps
of stones, ever adding to their numbers, are deposited in heaps, to
which are given the name of the _terminal moraine_.
With such tokens of their existence as this, glaciers, as will
readily be understood, leave visiting-cards in history that cannot
easily be mistaken. Even existing glaciers tell strange stories.
Nowadays glaciers are carefully measured and examined both in
Switzerland and in Canada. During the last decade of the nineteenth
century and the first decade of the twentieth the Swiss glaciers
were found to show signs of receding farther up their valleys. The
same thing has been observed about some of the Canadian glaciers.
There are several plausible reasons for this. Professor Schaeberle
says that the earth is growing cooler, and that in the temperate
regions the winter rainfall (which would turn to falls of snow
in the mountains) is less than it has been. It is certain that a
shortage of winter rain over a number of years in succession would
account for the shrinkage of the glaciers, but it is not by any
means certain that a number of dry winters will not be followed by
wet ones, in which case the glaciers would increase again. Some of
the glaciers show that during their existence they have shrunk and
lengthened alternately like gutta-percha in a variable climate. How
do we know that they have shrunk and lengthened? The _moraines_ of
which we have spoken give us the testimony. As a glacier shrinks
either in length or in breadth and depth it leaves the blocks of
rock at its edges stranded on the sides of the valley. Such perched
blocks or _erratics_ are the best of glacier marks, and their great
size, some of them as large as a cheap villa residence, is such that
no current of water could have brought them there. They are often
poised on the tops of crags, on the very edges of precipices, or on
steep slopes, where they could never have been left by any flood,
even had the flood been able to move them. The only thing that could
have carried them must have been a vehicle that moved very, very
slowly and deposited them very, very gently--in fact, glacier ice.
We can see blocks like this on the glaciers now, and others stranded
at the sides. In the Swiss valleys the scattered ice-borne boulders
may be seen by hundreds far above the glaciers and far beyond the
places where the glaciers end. We _know_ they must have been left
by glaciers, and by inference we surmise that when we find a valley
filled with them, then, though the valley may have no glacier now,
it must have once been occupied by one.
These erratic blocks, now found all over Europe, tell us a good deal
about the ice on which they were transported. The blocks that fall
on the edges of the glacier remain on the side where they descend.
Hence, if there is any notable difference in the composition of the
rocks on either side of the valley, the existence of this difference
will be preserved in the _moraines_. If, therefore, in a country
where the glaciers have disappeared we can trace the scattered
blocks up to their sources among the mountains, we can say what was
the track followed by the prehistoric glaciers. In Europe there are
several examples of the uses of this detective evidence. Thus the
peculiar blocks of the Valais mountains can be traced right on to
Lyons; and this shows us that the glacier from which the River Rhone
sprang extended once right across the east of France to Lyons, and
probably farther. It was therefore once at least 170 miles longer.
Similarly, blocks which are exactly like the characteristic rocks
peculiar to Southern Scandinavia are found in Northern Germany,
Belgium, and East Anglia; and we therefore believe that a great sheet
of ice once filled up the Baltic and the German Ocean, carrying with
it immense numbers of northern "erratics." In our own country, in
fact, glacier boulders are found in nearly every county, and show
that once the greater part of the country was buried under ice.
But, as we have said, it is not only on its shoulders, but in its
interior and beneath its base that a glacier rolls and pushes its
rubbish along. It is not all stones. Clay and earth mingle with
it, often enclosing the stones; and the debris left by extinct
glaciers of ages ago is sometimes called the boulder-clay. This is
the deposit, earthy and stony, that the glacier leaves on the floor
of the valley as it shrinks--unless the river which usually springs
from the end of glaciers sweeps it away. Most of the stones thus left
are smoothed or polished and covered with scratches or ruts, such
as would be made by rubbing against other hard pointed fragments of
stone. This is to be explained by the fact that these stones as they
were carried on by the glacier were rubbed on the floor of rock over
which the glacier was slipping. If their journey was long enough,
they stood a chance of being rubbed away altogether and of finishing
their existence as sand or mud. What the valley did to the glacier's
stones, the stones did to the valley. They scratched it and scored
it. Every promontory of rock which stood in the path of the ice had
its angles and corners ground away. The polish and the directions of
the scratches are especially remarkable, because, whether the marks
are mere lines or deep-worn ruts, they are all on smooth surfaces,
and they all run one way. That way is the direction in which the
glacier moved. How high a degree of polish or how deep the markings
may be depends a good deal on the kind of rock over which the glacier
moved. Tough, close-grained rocks, such as hard limestone, are
sometimes polished to look like marble. But there is a great deal of
difference between the smoothing effected by a river or a torrent and
that which is produced by a glacier, because the river tosses the
rocks and stones in all directions, polishes them on every side, and
leaves no distinctive parallel scratches or grooves on them. That can
only be done by glaciers which hold the rocks, the rubbers and the
rubbed, pressed firmly together and grind them continually in the
same way.
These scratchings or striations of rocks, the smoothed and grooved
surfaces, and the deposited boulder-clay and boulders enable us to
trace the march of great ice-sheets over regions of the earth which
are now of totally different aspect. From this kind of evidence
we have been able to find that the whole of Northern Europe was
once buried under a great expanse of snow and ice. The sheet was,
as we should expect, thickest in the north and west, and thinned
away southward and eastward. Over Scandinavia it was between 6000
and 7000 feet in thickness--as we can tell from the scratches on
the sides of the high mountains. Similar marks 3000 feet above the
sea-level in the Scottish Highlands lead us to believe that over
Scotland the glaciers were 5000 feet thick, and even as far south as
the Hartz Mountains in Germany it could not have been far short of
1500 feet in thickness. Imagine this great mass of ice ever slowly
moving and ever creeping solemnly down to the sea. By the markings
it left we can trace where the greater glaciers slid grandly along.
In Scandinavia it swept westwards to the Atlantic and eastwards to
the Gulf of Bothnia, then frozen as solid as the Pole. Southward the
ice ground its way across Denmark to the Low Countries and North
Germany. The Baltic was choked with ice, and so was the North Sea
as far south as London. Ice in that day flowed in glaciers from the
British Isles, eastwards from Scotland into the hollow of the North
Sea, and westwards down all the clefts of the mountains, burying the
western isles and breaking off in icebergs that drifted far into the
Atlantic. Sir Archibald Geikie says that the western margin of the
ice-fields from the south-west of Ireland to the North Cape of Norway
must have presented a vast wall of ice 1200 to 1500 miles long and
hundreds of feet high--like that great barrier which the Antarctic
explorers tell us frown on the waters that lap the boundaries of
the south polar land. Northern Europe must have been like North
Greenland of to-day. The rock scratches tell us (since even the
southern coast of Ireland is intensely ice-worn) that the edge of
ice must have extended some distance beyond Cape Clear, rising out
of the sea with a precipitous front that faced to the south. Thence
the ice-cliff swung eastwards, passing probably along the line of the
British Channel and keeping to the north of the valley of the Thames.
Its southern margin ran across what is now Holland and skirted the
high grounds of Westphalia, Hanover, and the Hartz Mountains--which
probably barred its further progress southward. "There is evidence
that the ice swept round into the lowlands of Saxony up to the chain
of the Erz, Riesen, and Sudenten Mountains, whence its southern limit
turned eastward across Silesia, Poland, and Galicia, and then swung
round to the north, passing across Russia by way of Kieff and Nijni
Novgorod to the Arctic Ocean."
In North America there are similar traces of the great ice-sheet,
one of the branches of which streamed southward into the basin of
the Mississippi, the second moving westward from Hudson Bay to the
Rockies, and southward to Iowa, and the third setting out from the
great mountain ranges of British Columbia. Right across North America
to-day for thousands of miles stretch accumulations and mounds of
rock which were pushed forward by the ice, and were dropped by the
glaciers when they reached "farthest south." These accumulations are
called, from their origin, the great "terminal moraines" of the North
American Ice Age.
It must not be thought that these great ice-sheets of both
hemispheres remained constant in extent and thickness. There were
periods of retreat and advance, of progress and shrinking, and the
shrinkings of these took place on a large scale, and perhaps lasted
for hundreds or thousands of years; so that mixed with the strata
of boulder-clay, which are the characteristic strata of the glacial
periods, are other strata of sand, ordinary clay, and even peat.
Remains of plants and animals are found in these strata, showing
that sometimes the glaciers retreated so far and for so long that
vegetation sprang up and animals lived on the ground that they had
covered--in the intervals when the cold of centuries was replaced by
other centuries of mild and equable climate.
At last, after many of these swallow-like retreats and advances,
the warmer climate at length came to stay, and the ice retreated
farther and farther to the north. It still remained among the
mountains, so that we might describe the glaciers of the Alps
and of the Canadian Rockies as the last relics existing to-day of
the great Ice Age of the past. The retreat to the Arctic Circle
left many other relics behind it, the great lakes, for example,
like Winnipeg and Manitoba, and the Great Salt Lake of Utah. All
were once mightier sheets, because during the Ice Age their waters
were held back. Other smaller lakes formed by the dumping-heaps or
terminal moraines of the glaciers still exist, and are especially
noticeable in Finland. During the later stages of the Ice Age the
level of the land was lower than it is now in Western Europe. When
the ground began to rise--in slow upheavals with long pauses for
rest--it left its impress in raised beaches, which can be seen on
both sides of Scotland and on the Norwegian coast. The climate grew
gradually milder, the animals and the plants followed in the train of
the retreating ice, and even the traces of man's existence began to
appear. The change was not sudden; it was so gradual that the Ice Age
slipped as imperceptibly as its own glaciers into the age in which
Man's activities in Europe began.
CHAPTER VII
THE FIRE-HARDENED ROCKS
So far we have been considering the deposits laid down, for the most
part, in a leisurely and orderly manner, by the action of air and
water; by floods, rivers, lakes, the sea, or by the slow movements
of ice. If these, however, had been the only agents by which the
earth's strata were accumulated, then it is clear that for the most
part these deposits and these strata would lie evenly, one on top of
the other, like the lines of print on this page. But as a matter of
observation the earth's strata do not lie like that. If we were to
tear this page out and crumple it up in a ball, first having torn it
in half and shredded a few irregular pieces out of it, we should get
a truer picture of the way in which many of the earth's strata are
contorted, crumpled, and displaced. They have not been so distorted
by the action of the sea, violent as are some of the sea's assaults
on the land; nor would the heat of the sun at its greatest ever
produce such effects. They must have taken place from some causes
which arise in the earth itself. These causes can be summed up in one
word--fire. Some of the strata of which we have spoken, and which
are called sedimentary strata, although they were composed of soft
materials to begin with, have become very hard since, in some cases
owing to the enormous pressure of the accumulated deposits above
them, in other cases because of chemical action. In a few cases
they have become hardened not so much by losing their water, as by
direct heat. But the hardest of them is not so hard as another class
of rocks with which we are all acquainted--rocks like granite, or
quartz, or basalt. And it will be evident to any one who thinks about
the subject for a moment that no amount of pressure would make a
rock as hard as a diamond. Now how have these rocks been made? The
answer is that they have been made in some interior furnace of heat
deep down in the earth. Sometimes they have boiled up, and we can
trace them bursting their way through the sedimentary strata above
them. We do not know very much about the furnaces or cauldrons whence
they have come; in fact, we know very little about the depths of
the earth. The deepest mine-shaft known is near Lake Superior, and
is only 5000 feet in depth. In Silesia a bore-hole has been made by
the Austrian Government of a mile and a quarter in depth. It would
be by no means an easy task to sink a great boring. The Hon. Charles
Parsons has described some of the difficulties.
The shaft would have to be sunk in a neighbourhood where it would not
be likely to encounter water on its way down, because otherwise there
would be the necessity of pumping operations. In order to be of value
for purposes of observation, the shaft would be of the size usual
in ordinary mines and coal-pits. It would be sunk in stages each of
about half a mile in depth, and at each stage there would be placed
the hauling and other machinery for dealing with the next stage
below. This machinery, in order to economise space and limit the heat
of the workings, would be electrical. Even so there would have to be
special arrangements for cooling; and the depth of each stage in the
boring would be restricted to half a mile in order to avoid great
cost in the hauling arrangements, great weight of rope, and the great
cost of keeping the machinery and workings cool. At each second or
third mile down there would be air-locks to prevent the air-pressure
from becoming excessive, owing to the weight of the superincumbent
air. For when we got between two and three miles down below the
surface of the earth the atmospheric pressure there would be double
what it is at the earth's surface, or, therefore, about thirty pounds
to the square inch. It would not be easy to work under greater
air-pressure than that, firstly because of the strain on the workmen,
and secondly because of the rise of temperature which this increased
air-pressure would cause. Therefore special chambers would have to
be constructed to relieve the pressure, as well as special pumps to
provide ventilation, and other machinery to carry the superfluous
heat to the surface. This last-named machinery would be of the nature
of brine-filled pipes, in which a freezing mixture would always be
kept circulating. (The arrangements suggested by Mr. Parsons for
keeping the underground workings cool are rather too complicated
for description here; but no doubt the means he suggests would be
effective, and it would be possible, though with great difficulty, to
keep the workings cool.)
When the borings extended to a depth of some miles it would be
necessary to freeze the bottom of the shaft. This is a thing which
is sometimes now done when a shaft is being sunk through quicksands
that may be encountered on its way down. Round the circle of the
main shaft a number of small bore-holes are driven, and into them
is poured very cold brine, which freezes the material through which
the shaft is to be driven. In the case of the great boring we are
considering this would have to be done not only at the bottom of the
shaft but also for some time on the newly pierced shaft sides, until
the surrounding rock has been cooled for some distance from the face.
What would such a shaft cost? How long would it take to build? What
would the temperature be that it encountered on the way down? The
following is the estimate offered by Mr. Parsons:--
Cost Time in Temperature
£ Years of Rock
For 2 miles depth from the surface 500,000 10 122° F.
" 4 " " " 1,100,000 25 152°
" 6 " " " 1,800,000 40 182°
" 8 " " " 2,700,000 55 212°
" 10 " " " 3,700,000 70 242°
" 12 " " " 5,000,000 85 272°
But this estimate does not include the cost of cooling the shaft or
of providing it with air-locks. Mr. Parsons in delineating the scheme
remarked on the vast amount of information with which such a boring
would furnish engineers, miners, and geologists; but the point that
we wish to make is that even with this enormous expenditure of time,
industry, and money we should be as far as ever from knowing anything
about the core of the earth. We should have only gone about a third
of the way through what geologists call the earth's crust.
Here, again, we are in a condition of difficulty. How thick is the
earth's crust? and what is there beneath it? Well, as we are still
such a long way from exploring it we can only give a rather doubtful
answer; and we must therefore try to show not only what is thought
about the earth's interior but why we think it. From Mr. Charles
Parsons' table it will be seen that he calculates that as the boring
went deeper it would find a higher and higher temperature among the
rocks. At two miles down it would be hotter than the hottest summer's
day at the earth's surface; at eight miles down water would boil
by itself; at twelve miles down, unless the cooling arrangements
were extremely good, the workmen would die like flies. How does
Mr. Parsons know that there would be these temperatures, seeing
that the deepest boring hitherto made is only a mile? He bases his
calculations on what we know already of the ascending temperature at
deepening levels.
For ten years Professor Agassiz took observations concerning a very
deep mine in the United States called the Calumet and Hecla Mine.
He and Professor Chamberlin, after examining all the observations
very carefully, came to the conclusion that in going down from the
earth's surface the temperature rose at a rate of about 1° of heat
(Fahrenheit) for every 125 feet.
At the North Garden Gully Mine, Bendigo, Australia, and at the New
Chum Mine a temperature of 99° F. was reached at 3000 feet, and 107°
at 3645 feet. The rate of increase of temperature was reckoned to be
1° of heat (Fahrenheit) for every 80 feet.
This rate of 1° for 80 feet was also found at a South German mine,
Maldon, as well as at a Ballarat mine, and at a mine near Port
Jackson.
In a French mine more than 3000 feet deep, at the collieries of
Ronchamp, the rate of increase was as high as 1° in 50 feet.
In the North Staffordshire mines Mr. Atkinson, H.M. Inspector of
Mines, found the increase to be on the average 1° in 65 feet; whereas
in the South Staffordshire Hamstead Colliery Mr. F. G. Meachem found
that the increase was 1° F. for every 110 feet. The same rate was
obtained at the Baggeridge Wood Colliery, South Staffordshire.
In South Wales, in the neighbourhood of Rhondda and Aberdare, the
rate is 1° for 95 feet; at Dowlais, in the Merthyr coalfield, it
was 1° in 93 feet; at the Niddrie Collieries, near Edinburgh, the
increase is at the rate of 1° in 99 feet.
It will thus be seen that all over the world there is an increase of
temperature at a rate which, on the average, is about 1° for every
100 feet. There are 5280 feet in a mile; therefore, if this rate of
increasing temperature were maintained, at a depth of 100 miles the
temperature would be perhaps 5000° F.; a temperature at which steel
would melt and boil away into vapour. At a depth of 200 miles the
heat would be greater than that of the surface of the sun.[2]
[Footnote 2: According to the calculations made by the late Mr. W.
E. Wilson, F.R.S., in Ireland, 5773° Centigrade above the lowest
temperature which is possible in space, or about 10,500° F.]
Now at temperatures like that everything we know on the surface of
the earth would melt. Something else would happen to it besides that.
Those of our readers who have ever seen experiments at the Royal
Institution in London by Sir James Dewar or Sir William Crookes will
know that if metals are made hot enough they will not only melt but
will boil away into vapour as water boils into steam. And perhaps
we need tell no one that air, if it be subjected to a low enough
temperature, can be made a solid like ice. In fact, everything in
nature, whether we generally know it as a solid (like iron), or a
liquid (like water), or a gas (like air), can be made to assume
either of the two other forms. Thus the solid iron can be turned into
a liquid or a gas, and the liquid water can be turned into a gas
by boiling, or into ice by freezing. The gaseous air can be turned
into a liquid by lowering its temperature to some 300° F. or more
below the point at which water turns into ice; while if we lower the
temperature to about 390° F. below freezing, it will turn into a
solid. At a temperature of about 490° F. below freezing everything
in nature, whether gaseous or liquid, would become a solid, and
that temperature, which is the lowest that can possibly exist, is
called Absolute Zero. But just as every gas becomes a solid at that
temperature, so there are temperatures at which every solid becomes a
gas. Gold, for instance, begins to be a liquid at about 1900° F., and
if we heat it to 2000° it will become a gas.
Therefore it will be seen that if we were to suppose that the earth
grew steadily hotter all the way down to its centre, we should
comparatively soon come to a point when everything would be trying
to turn into a gas. But there is one other thing to be thought of.
Imagine what the pressure of the weight of the rocks themselves must
be. At a depth of a mile pressure from above arising from the weight
of the overlying rock is about 6000 lb. to the square inch. At three
miles the weight has increased to 18,000 lb., at four miles to about
24,000 lb., and at five miles to about 30,000 lb. to the square inch.
Now the average strength required to crush rocks has been shown to
be about 25,000 lb. to the square inch for granite, for limestones
about 16,000 lb. to the square inch, and for the sandstones about
6000 lb. to the square inch. At a depth of five miles, therefore, the
weight above must be equal if not greater than the resisting power
of the rock. What will happen lower than that? An experiment shown
some years ago by Sir William Roberts Austen at the Royal Institution
gives us some idea of what might happen. He subjected iron to very
great hydraulic pressure, and he arranged the experiment in such a
way that the spectators could see an image of what was happening
projected by a beam of light on to a kind of magic-lantern screen.
The iron began to move like slowly melting pitch, or very thick
gum. In fact, at depths of about six, seven, or eight miles, it is
supposed by many geologists that if the lower rocks had room to move
they would have a tendency to flow.[3]
[Footnote 3: _Geology: Earth History_, p. 127. Chamberlin and
Salisbury.]
Suppose, however, they cannot flow, that there is no room for them to
flow, and that the pressure is not merely thirteen or fifteen tons to
the square inch, as it would be at depths between five and six miles,
but a hundred times that amount, as it might be between five and six
hundred miles down. What would happen then? We can only imagine what
does happen by stating what does not happen. It used to be supposed
as late as half a century ago that the earth consisted of a crust of
hard rocks perhaps thirty to fifty miles in thickness, and that below
this crust the whole earth was a mass of red-hot or white-hot molten
stuff with flaming gases mixed with it. If that were the case it
would explain a good deal of what we see around us. It would explain
the volcanoes, for instance, which belch out fire and lava and ashes
and molten rock, and sometimes great fragments of rock. Perhaps some
of our readers may remember the great eruption of Mount Pelée, which
took place in Martinique some years ago. At one stage of the eruption
a great obelisk of rock a thousand feet high was pushed upwards out
of the crater, and eventually sank back again. It came out of the
depths of the earth. It was like a vent-peg plugging some boiling
mass below. Similarly we might suppose that all volcanoes were
vent-holes for the tremendous commotion of boiling fiery rocks below
the earth's surface. The only thing we can urge is that they do not
seem big enough for the purpose, if the earth were indeed all molten
except for a thin crust--thirty miles thick. For that would leave a
molten ocean more than 7900 miles across any way it was measured:
7900 miles deep, 7900 miles broad, 7900 miles long, if we take the
diameter of the earth to be 8000 miles. We all know what great tides
the Moon and Sun by their attraction raise in the earth's outer ocean
of water. Think what tides they would raise in this inner ocean of
molten rock and metal. The earth's crust would not be able to hold
such tides in. The molten stuff would be always breaking through the
flimsy thirty miles of outer solid rock as if it were egg-shell.
Twice a day there would be outbreaks of lava vast enough to submerge
continents.
No, that will not do. We will not confuse our readers by telling them
all the theories that have been formed, but will only state what
the late Lord Kelvin believed, and most of the present generation
of geologists believe. It is that the heat of the earth's crust
continues to increase only for a certain distance of the way down,
and that owing to pressure the earth is solid (though very hot
except towards the surface) for two thousand miles down. There
remains a thickness of another four thousand miles on either side
of the earth's centre to be considered. That might be molten, but
the pressure would be so great that it would behave as if it were a
solid. We know the earth cannot be solid all through because it does
not weigh enough. The earth cannot, of course, be weighed in any
scales, but there are methods of weighing it nevertheless. One of
two methods is by seeing how strongly it attracts bodies to itself.
But these things belong rather to the romance of astronomy than to
that of geology. We need only trouble ourselves at present about the
results.
One word more about the deep interior of the earth. Dr. J. J. See,
an American astronomer, has found how heavy and how hard the earth
is, taken as a whole. He finds that if it were built from surface
to surface of hardened steel it would be just about as heavy and
as hard--or as rigid. The steel would be like that used for the
armour-plate of battleships. Dr. See is not prepared, however, to
discard the idea that the earth has a large fluid interior. If it
were fluid, yet it would be subjected to such enormous pressure by
its own weight, that if there were a moderately thick earth-crust,
its tidal surgings would be so "cabin'd, cribbed, confined," that
they would be comparatively ineffectual. We must not run away with
the idea (against which Dr. See specially warns us), that there is
any free circulation of currents within the fluid interior. The
rigidity produced by pressure (or weight) is too great for that.
Indeed, this pressure is so great that, as another scientific
authority, Professor Arrhenius, has pointed out, the matter at
the core of the earth might even be gaseous; and yet would be so
compressed by pressure that it would possess a rigidity equal to the
hardest steel. The earth may be partly solid, partly liquid, partly
gaseous, but for all practical purposes Professor See would have us
regard it as a solid sphere having an average hardness and weight
and "rigidity" greater than that of ordinary steel.
We are still some way off an explanation of how the many igneous
rocks which were and are being "boiled up" in some inner molten
cauldron came to the surface; but the better to understand that we
must ask our readers to carry their imagination back to the very
beginning of the world when it was "without form and void."
CHAPTER VIII
THE EARTH AT ITS BEGINNING
If we look up at the sky with the eye of knowledge we can read in the
celestial objects with which it is strewn something of the history
of our earth. We can only read it dimly even with the aid of the
greatest telescopes, and it is quite possible that in some respects
we may read it wrongly. Let us, however, consider what the eye and
the telescope will reveal to us. The eye will see the Sun--a great
ball, into which the earth might sink without greatly altering the
Sun's appearance, and surrounded with flaming gases hotter than the
hottest furnace man has ever been able to contrive. In that heat
every solid thing on the earth would melt and be turned into vapour.
The eye will also perceive the Moon--another ball, much smaller than
the earth, surrounded by no gases at all, having as far as can be
seen no water; and being so cold during its long nights that all
gases and liquids of which we know would be frozen solid there.
The eye can also see a myriad of stars of varying brightness, but
for the most part only thus distinguishable. If the telescope be
now called in to aid, the eye will, however, be able to discern
differences and distinctions in the stars. It will see that some
are balls like the Earth, the Sun, and the Moon. If these balls are
studied attentively we shall discover that one of them, Jupiter, is
a great deal hotter than the earth, though a great deal cooler than
the Sun; and that another of them, Mars, is a great deal colder than
the earth, but a great deal warmer than the Moon. Perhaps we might
now begin to surmise that the Sun coming first, Jupiter next, the
Earth next, Mars next, and the Moon last, were all like stages in the
history of one of these balls; and that, for example, any one ball
began by being as hot as the Sun, and ended, after passing through
stages like Jupiter, the Earth, and Mars, in being as cold and
lifeless as the Moon.
But if one had a very good telescope, and could examine those more
distant specks of light which we call stars, we perhaps could spy a
little earlier into the history of these great balls. For example,
among the blazing lights of the heavens--the stars which we know to
be suns--there are others which are not balls at all. There are the
Pleiades, for instance, of whom the Prophet Amos wrote, "Seek Him
that maketh the seven stars and Orion" (Amos v. 8). The seven stars
(in the Authorised Version rendered Pleiades),[4] when seen through a
great telescope, are caught in a mesh or a veil of something that may
be starry matter, but of the exact nature of which we are uncertain.
In other parts of the sky there are great masses of this starry
mist; and to these bright patches astronomers have given the name
of "nebulæ." The most wonderful of them all is the great nebula in
Orion;[5] and one of the most beautiful is the great spiral nebula of
Andromeda. These objects are not only wonderful and beautiful; they
also give us a hint as to what might have been the earliest state
of our earth, and of the Sun itself in those almost inconceivably
distant ages before order took the place of chaos.
[Footnote 4: It has been cogently suggested that by the "seven stars"
the biblical writer meant the constellation of the Great Bear; but
Mr. E. W. Maunder, F.R.A.S., of Greenwich Observatory, is of opinion
that the Pleiades were signified.]
[Footnote 5: "God maketh Arcturus, Orion, and Pleiades, and the
chambers of the south" (Job IX. 9).]
Let us ask the reader to imagine what would take place if the earth
were to come into collision with another planet. Some of our readers,
at any rate, will know that the Sun and all its planets--the earth
among them--is moving swiftly to some unknown destination among
the stars.[6] Suppose that some great planet, not of the Solar
System, barred our path. We should not be taken wholly unawares, for
astronomers would know of the approach of the star and our earth
to one another months, and perhaps years, beforehand. That would
be because the light of the Sun falling on it would be reflected,
just as the reflection of the Sun's rays light up the Moon for our
eyes. If the strange planet were a very large body, like the sun
for bigness, it would become visible far beyond the confines of
the Solar System. It might first be taken for a new star such as
sometimes blazes up in the sky and then sinks into darkness again.
But its steadiness would make it an object of suspicion. There would
be another brief period in which it might be taken for a comet; but
comets have a light quite different from that of reflected sunlight.
So that anxious expectation would be dissipated, and the world would
begin to recognise the monster for what it really was. If its size
were the same as that of the Sun, then it would first become visible
to us when 15,000,000,000 miles distant,[7] or let us say 1600 times
farther away from us than we are from the Sun. We and it would
approach slowly at first. It would be nearly ten years before the
distance had been reduced to 6,000,000,000 of miles, and the intruder
had begun to be visible to the naked eye. In fourteen years it would
have reached the outer edge of the Solar System, and would be the
brightest star in the heavens. In another year it would be twice as
bright as Venus at her brightest, and would be coming nearer with
appalling swiftness. In less than two months it would be as near the
Sun as we are. In a week more it would have plunged into the Sun at
the rate of 400 miles a second, and in the awful heat born in that
collision, Sun and earth and planets would be molten, and the Solar
System overwhelmed
In unremorseful folds of rolling fire.
[Footnote 6: It is usually supposed that this movement, amounting to
perhaps ten miles a second, is in the direction of the constellation
of Vega.]
[Footnote 7: See an article by Mr. Ellard Gore in _Knowledge_,
November, 1905. The object would not be visible at this distance
except through large telescopes.]
Suppose that this catastrophe were to take place. Would that be the
end of all things? No. Out of the fiery mist many millions of miles
across--like one of those great nebulæ which the telescopes reveal
to us--order would be evolved. Two things would at once begin to
happen, since in the Universe nothing stands still. The fiery mist
would be giving out heat all about it, sending out heat-waves as a
fire or a red-hot poker will do. The red-hot poker cools; so, too,
would the fiery nebula. Then the nebula would begin to condense; not
quite in the same way that a cloud of steam does, for it would be
whirling all the time, and its fiery particles would be all trying
to fall inwards, just as anything dropped from our hands tends to
fall towards the centre of the earth. As this whirling mass of gas
condensed some great masses of it would become detached, and would
begin to enjoy separate existences of their own.
Let us imagine, for the sake of argument, that a mass of gas vast
enough, when it condensed, to form the earth itself became detached
from the parent nebula. Suppose we follow its history. At first it
may have been a globe hardly distinguishable from a whirling flame.
In brightness it was like the Sun, and like the Sun, it was covered
with elemental gases. It was, in fact, in its earliest days a sphere
of gas continually giving out heat, and continually cooling, till
from a sphere like the Sun it became a ball like Jupiter. It had
an intermediate stage when its gases were condensing into liquids,
as steam condenses into water; for though the nebula as a whole
was hot it was always travelling through cold space. Gradually the
earth became partly liquid and partly gas. For millions of years it
continued to revolve as a ball of liquid--still cooling--still being
pressed very hard at its central parts by the weight of all the gases
and liquids round it, till at last the first crust of solid matter
began to form on the liquid surface. This crust continued to thicken,
but it was subject to many appalling catastrophes and breakages.
We have already used the occurrence of the tides of the earth as an
instance of the Sun's attraction. The Sun (and the Moon) attract the
waters of the earth, pulling them up towards themselves. So would
they also attract the molten materials of which the early earth was
composed. The liquid mass would be continually surging like a tide
against its wall of solid crust, and the liquid would now and again
burst through. There must have been a time when the thin solid crust
covering the molten interior became, owing to the solidification
and contraction of the crust, much too small to contain the liquid
material. The lava would then break through, and would form huge
craters, not unlike some of those which we see on the Moon. We can
faintly imagine these terrible outbreaks in which the molten tide
rose not thirty or forty feet but many miles high!
Later, after some relief had been given by these outbreaks and the
crust thickened, the interior regions of the earth by cooling shrank
away from the solid shell, which was now too large. This solid shell
being insufficiently supported sometimes caved in, and other great
outflows of lava resulted. These lava floods dissolved the original
solid shell whenever they came in contact with it. The earth probably
once had gigantic craters like those which we can see in their
extinct form on the Moon; but they were destroyed by these outflows
of lava of which we have spoken.
Then, still cooling, the earth's crust grew thicker and thicker. The
great outflows and eruptions of molten elements from underneath grew
fewer, and more liquid elements cooled into solids, and more gases
condensed into liquids. There was another thing happening of which,
as conscientious recorders of the history of the earth's geology, we
must take note; and it is that in those early days meteorites were
falling on the earth in vastly greater numbers than they do to-day.
Meteorites are masses of cooled rock flying through space which still
occasionally fall on the earth, and specimens of them are still to be
found, many of them preserved in museums, such as the Natural History
Museum in Cromwell Road, London. But the earth in its path has
swept most of them up, as the housemaid's dusting-pan collects the
fragments of dust. When the earth was young there were incomparably
more fragments to collect, and they fell on the earth like rain.
Meanwhile the cooling water vapour became the oceans; clouds and
rain and cool winds and eventually snow and ice became possible; and
the hardening lavas, or fire-born rocks, became subject to their
influences, till above them were raised the stratified rocks, of
which we have spoken in our earlier chapters, and the lineage and
descent of which is part of the study of geology. On the earth most
of the traces of its earlier history have been removed, but there
are some signs of them perceptible to the comprehending eye. The
earth is probably seamed with great cracks that do not now reach to
the surface, but which are indicated by the presence of chains of
volcanoes. The volcanoes of the great chains of the Andes lie along a
straight crack reaching from Southern Peru to Terra del Fuego, 2500
miles in length. The volcanoes of the Aleutian Islands lie along a
curved track equally long. Other shorter lines of volcanoes are very
numerous, and since countless others existed in former times, the
cracks in the earth's crust must be exceedingly numerous. There is
one crack which comes to the surface in various places in Eastern
Asia and Western Africa, and stretching from the Dead Sea to Lake
Nyassa, reaches the enormous length of 3500 miles.
From this brief sketch of the formation of the earth, its progress
and processes, and from the hints which the volcanoes and earthquakes
of to-day afford us, we may obtain some idea of the underworld that
lies far beneath our feet. Not much, however, for we are ignorant of
the actual conditions which exist towards the centre of the earth.
But there seems a strong case for supposing that there is an outer
solid crust of earth and an inner molten core of very great heat.
CHAPTER IX
THE CHILDHOOD OF THE EARTH
Let us now sum up the various stages in the early growth of the
earth, as most geologists believe them to have occurred.
The first stage was that when the earth, shining like a star, existed
as a fluid globe surrounded by heavy vapours of great thickness,
which contained the future waters of the globe.
Then began the second era of the earth's existence, when it was a hot
solid globe--solid at any rate at the surface, and with a temperature
of about 2500° F. The globe's atmosphere still contained all the
waters of the earth. It contained all the carbonic acid gas which now
exists in the limestones and in coal and other minerals containing
carbon. It contained also all the oxygen since shut up in the rocks
and in vegetation and in animal substances. Such an atmosphere was
probably at least two hundred times as great as the atmosphere which
now surrounds the earth.
Then followed an epoch when great volcanic action set in. We have
partially described it already. Just a thin solid crust was all that
covered the molten interior of the globe. It was too thin always
to contain the boiling liquid, and Titanic explosions, followed by
enormous overflows of lava, continually broke up the crust. The
pressure was relieved by these explosions, and gradually the earth
would settle down again to its process of consolidation. Another
explosion would follow; again a great flow of lava; and again the
effects of the catastrophe would subside. After each explosion and
outflow the earth's crust would grow a little thicker. All this time,
and for long succeeding ages, the earth was attracting to itself,
as a magnet attracts iron filings, all the small bodies which it
encountered on its path round the Sun. These little rocks or masses
of matter, some great and some small, would each add something to the
size of the earth, and, by the shock of collision with it, something
to the earth's heat--just as a bullet flattening itself against a
target melts in the heat of collision. Just also as the bits of
matter which we call "shooting-stars" are set on fire by friction as
they rush into the earth's atmosphere. These meteorites, as they are
called when they are comparatively small bodies, or "planetismals,"
as they are called when they are large, still exist. But the earth,
in the millions on millions of years which it has been coursing round
the Sun, has swept up all the large ones that are likely to fall into
it, and there remain only the small ones which occasionally cross its
path. These are called "Leonids" or "Lyrids" or "Perseids," and these
meteor showers occur at nearly the same time every year when the
earth runs through a swarm of them on its pathway round the Sun. But
they are very small. Some of them are no bigger than a slate pencil.
Few are as big as brickbats, and nearly all are burnt up by the
air-friction before they reach the earth's surface. Larger ones still
fall on the earth, however, and it is calculated that many hundreds
reach us in fragments every year. But when the earth was young many
thousands fell every day.
To this era, or immediately before it, belongs the birth of the Moon.
It is a subject of interest to geologists, because it is admitted
that the materials of which the Moon is constituted are similar
to those of the earth; and it is believed that its history up to
a certain point was very like that of the earth. It had its great
volcanic era such as we have described; but its development closed
shortly afterwards. We are considering, however, at this moment
its origin. It was once part of the earth. All of us have read of
those little animals, of which one form is the amœba and another
form the white corpuscles of the blood. If we watch them under the
microscope we may see one of them slowly lengthen out, then break in
two, and each part go swimming away by itself, a perfect animal. It
was Sir G. H. Darwin, F.R.S., who proved mathematically in 1879 that
the origin of the Moon was such that we may properly compare it to
the splitting up of the little animals just described. The date of
this event cannot be fixed even approximately--beyond saying that
as astronomical events go it must have been rather recent, though
not less than fifty million years ago. The Moon is therefore one of
the younger members of the Solar System. But no other catastrophe,
either before or since, has occurred on the earth to compare with
its prodigious birth. Five thousand million cubic miles of material
left the earth's surface never again to return to it. Whether it all
left at once or whether the action was prolonged we do not know, but
we may try in vain to imagine the awful uproar and fearful volcanic
phenomena exhibited when a planet was cleft in twain and a new moon
was born into the Solar System.
Then, life still being absent from the earth, the _Oceanic Era_
began. The waters condensed into an ocean over the earth, or else
collected in some great oceanic depression. Lands presently emerged
from it. It was a hot ocean, steaming no doubt, for its temperature
was perhaps about 500° F. Some one may ask--Why, then, did it not
steam away into clouds? The answer is that the atmosphere was still
very heavy in that past era, probably still exerting a pressure
as much as fifty times as great as to-day. The pressure of the
atmosphere at the earth's surface to-day is usually about fifteen
pounds to the square inch. In such circumstances water boils rapidly
away at the temperature of 212° F. But if the water be taken up to
the top of Mont Blanc, where the air pressure is less than that at
the sea-level (or if, which amounts to the same thing, we reduce the
pressure on the water's surface by placing it under the receiver
of an air-pump and partially exhaust the air), it will boil at a
lower temperature than this. If, on the other hand, we increase
the pressure on the surface of the water by any means, such, for
example, as by placing it in a chamber of compressed air, the water
can be heated to a higher temperature without boiling away. In the
bygone era of which we are speaking the pressure of the atmosphere
on the water's surface was 700 lb. or 800 lb. to the square inch;
and therefore it could be heated up to a high temperature without
evaporating rapidly.
Another thing began to happen in those days. All bodies in space
attract one another; the Sun attracts its planets; the planets
attract the Sun and their satellites; and the satellites in their
turn attract the planets. Ages before the earth had a moon these
forces were at work. But the attractions of solid bodies for one
another do not bring about any very perceptible alterations in their
shapes; though if the bodies are spinning they effect slow changes in
their speed of rotation. It is different when the bodies are liquid,
or if they have liquid surfaces. Then the attractions of a sun or
a moon on a planet begin to draw up the waters of the planet and
produce tides. The attraction of the earth would produce tides on
the Moon if an ocean existed there; and, it is suspected, do produce
something resembling tides on the present surface of the Sun.[8] As
soon, therefore, as oceans appeared on the earth the waters began
to ebb and flow in tides. (Another consequence of this constant ebb
and flow was that the friction of these movements began to diminish
the speed of the earth's rotation--just as a string that was placed
round the circumference of a spinning-top would, if constantly
pulled backwards and forwards, gradually help to slow down the top.)
Then oceanic waves and currents would begin to eat a way into the
land that was on their borders, or which was emerging from their
depths. Rivers would begin to arise, and they would carry on the
work of erosion. Other causes tending to break up the rocks would
be the gases in the air--the excessive quantities of carbonic acid
and oxygen would be active chemical agents in this work. Before the
close of this era the limestones and iron carbonates began to form;
sediments arose in the lifeless oceans, and thus began the first
formation of those sedimentary rocks and strata which have been dealt
with in the earlier chapters.
[Footnote 8: A paper read by Mr. E. W. Maunder before the Royal
Astronomical Society in 1907 gave reasons for believing that the
earth has perceptible effects on the movements of sun-spots.]
After the lifeless era began the age when the lowest forms of life
came into existence. The initial stage was perhaps the _Era of the
First Plants_, Algæ, and later still aquatic fungi or bacteria.
This began when the general temperature of the ocean may have been
as high as 150° F. (some water plants can now live in waters up to
and above 180° F.). Limestones began to form from the secretions of
plants, and deposits of silica from silica secretions. Also where
the conditions were favourable there were large sedimentary deposits
and accumulations. In the second part of this æon the earth, still
continuing to cool, and going down in temperature to 115°, gave
opportunity to animal life. At the end of this era the general
temperature of the earth and its oceans was as low as 90° F. The
first animal life had begun to appear; its activity greatly increased
under what were favourable conditions for it. This increase of animal
life had its effect on the earth's crust. We have already spoken of
the formation of limestones from the bodies of sea animals. This was
going on in those ages millions of years ago before any of the higher
forms of life had appeared on the earth, and though it was not going
on so rapidly, still it must be remembered that at some point of
the world's history the oceans were of greater extent than now, and
consequently the deposits of lime and the accumulations of sediment
were more widespread. The sedimentary rocks grew faster and faster,
especially on the floors of the oceans.
It will be understood by those who have read the foregoing two
chapters closely that the "igneous" or fire-born rocks must lie
underneath the sedimentary ones. But that is only true in general
terms, for a double reason. In the first place, owing to the
inestimable forces which for millions of years were still continually
effective below the earth's crust, the igneous rocks over and over
again were able to burst their way through the slow-forming sediment
of other rocks laid down above them. In the second place, the igneous
rocks, owing to their composition and superior hardness, were much
less worn by wind and weather than the less compact "sedimentary
rocks," and these remained, showing themselves at the surface as
coast-lines of oceans and in mountain ranges, after the sandstones
and shales and limestones had disappeared.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
The Crater of an Extinct Volcano
This is the entrance to the long extinct volcano of Red Mountain,
Arizona.]
The memorials of volcanic action remain, we had almost said
permanently, among the decay of other rocks, though, of course, even
hard volcanic or igneous rocks will be worn down in time. In many
cases volcanoes themselves are left, though they may have been for
ages extinct. In some volcanic regions where no great central cones
have existed the vast floods of lava that were poured forth extend
to-day as vast black plains of naked rock, mottled with shifting
sand-hills, or as undulating tablelands carved by running water
into valleys and ravines, between which the successive sheets of
lava are exposed in terraced hills. Beyond the limits over which
the lava sheets have spread there are often great veins or parapets
or sunken walls of lava to which are given the names of igneous or
volcanic "dykes." Dykes vary from less than a foot to one hundred
feet in breadth, and often run in nearly straight courses sometimes
for many miles. They consist usually of very hard rock like basalt,
"andesite," or "diabase."
They were fissures in the earth's surface, and, after the manner we
have described, the molten rock welled forth through these fissures,
and spread out sheet after sheet, till like a rising lake it has not
only overflowed the lower grounds but even buried all the minor hills.
Lava eruptions of this kind have taken place in recent years in
Iceland. On a small scale they can be seen to take place in the
island of Hawaii, where the outflows of lava reproduce for us,
like models in miniature, the great outbreaks of the past. On the
largest possible scale similar effects may be seen on the great lava
plains of the Moon, where the giant craters that we can see through
telescopes are not the mouths of extinct volcanoes, but the banked-up
edges and shores of lava outflows.
On a much smaller scale than this, but still on a gigantic scale,
the same thing took place in Western North America, where there are
vast tracts of land which are best to be explained by supposing that
there were once great outbreaks and overflows. The area which has
there been flooded with lava has been estimated to be larger than
that of France and Great Britain put together, and the depth of the
total mass erupted reaches in some places as much as 3700 feet.
Some rivers have cut gorges in this plain of lava, laying bare its
component rocks to a depth of 700 feet or more. Along the walls of
these ravines we see that the lava is arranged in parallel beds or
sheets often not more than ten or twenty feet thick, each of which,
of course, represents a separate outpouring of molten rock.
These are comparatively modern lava plains, although, of course, the
outpourings in North America occurred ages before historic time,
or, indeed, before there are any traces of man's existence on the
earth. Such lava outflows can only occasionally be examined--as
in the instance just quoted when rivers have cut deep into them.
Consequently we have to speculate on the connection between the
dykes and fissures and the lava flood itself. But in various parts
of the world lava plains of much older date have been so eaten into
and worn by the action of the elements that not only the successive
sheets of lava are exposed but the rock floor over which they poured.
Exposed also are the abundant dykes which served as the channels
by which the lava rose to the surface. In Western Europe important
examples of this structure occur from the north of Iceland through
the inner Hebrides and the Faroe Islands to Iceland. This volcanic
belt presents a succession of lava sheets, which even yet, in spite
of enormous waste, are in some places more than 3000 feet thick.
These sheets are nearly flat and rise in terraces over one another
into green grassy hills or into the dark fronts of lofty sea-washed
precipices. Where sheets have been stripped off or worn down by wind
and weather thousands of volcanic dykes are exposed. These dykes are,
as it were, the roots of which the lava sheets were the branches; and
even where the whole of the material that gushed up to the surface
has been worn away the dykes remain as evidence of the vigour and
energy of the volcanic forces.
CHAPTER X
THE EARTH AS THE ABODE OF LIFE
In the last chapter we spoke of the formation of the atmosphere of
the earth and of the growth of the oceans. We must now consider the
formation of these more closely, and we must distinguish between the
great vaporous clouds which rolled about the earth in its molten
state and the settled atmosphere which formed about it when it grew
cooler.
After the earth had begun to solidify it was at first covered with
a collection of porous fragments of rock covering the earth like a
shell and containing the elements of water. Such materials in general
appearance would be not unlike the pumice stone which is expelled
from volcanoes to-day. Those who have never had the fortune to see
volcanic eruptions for themselves usually imagine that the volcano
throws out nothing but fire and smoke. As a matter of fact it throws
out vast quantities of vapour, of which, according to Sir Archibald
Geikie, 999 parts in 1000 are steam. At the great eruption of Mount
Pelée the cloud of steam continually arising from the volcano for
months in succession was several cubic miles in measurement.
Consequently it will be seen that the porous volcanic rocks with
which the young earth was covered contained all the materials for
water-manufacture within themselves. As the water began to form,
squeezed out of the porous rocks as we can squeeze it out of a sponge
(or as we might steam it out if we put the moist sponge in an oven),
it gathered itself into reservoirs underground. As it increased in
bulk it rose nearer to the surface; because, of course, owing to
the heat of the inner portions of the earth it could never succeed
in sinking below a certain depth. Doubtless it first appeared at
the bottom of the pits which had been sunk by volcanoes or volcanic
action. There must have been innumerable depressions in the earth's
surface as widespread and deeper than those which we can perceive
on the rugged surface of the Moon. We may gain an idea on a very
minute scale of what the first pits of water were like from the
examples (formed, however, at a much later period and probably in a
different way) of the crater lakes that are left to-day. Some curious
examples of "crater lakes" are to be found in the Eifel district
of Germany, an ancient volcanic region which lies in the triangle
formed by the junction of the Rhine and the Moselle at Coblenz. One
of the pleasing peculiarities of this district is that, owing to
the volcanic nature of the soil, the neighbourhood is seldom dusty,
even in August or September, after the dry continental summer. It is
well worth visiting for its castles as well as for its crater lakes
and other volcanic relics, and it is the scene of R. L. Stevenson's
romance _Prince Otto_. The chief crater lakes are between Daun and
Manderscheid. There are, of course, many other and larger crater
lakes in existence, but we select these because they are so easily
accessible.
The flow of the lakes into one another followed. Innumerable lakelets
developed into rivers or chains of lakes on the surface of the young
planet, continually becoming larger bodies of water, till they
developed into the vast irregular oceans of to-day. This evolution is
of great importance from a geological point of view, because it leads
the way to the origin of the ocean basins and the great platforms of
land which we call continents. It is easy to see that because of the
weight of water in the depressions the earth under the waters tended
to become more and more depressed, so that the water areas tended
to grow larger and deeper. The wash of earths from the land tended
to build its borders out into the water basins, but the deepening
and spreading of the water basins is believed to have been the most
marked feature of the earth's early growth. All this time the earth
was growing in diameter and circumference.[9] When this growth ceased
other causes and effects came into play, and the proportions of sea
and land became better balanced.
[Footnote 9: For reasons which are a little too complex to be
considered here. We can only indicate the general line of reasoning
by saying that the central heat as it moved outwards from the rocks
nearer the surface expanded them.]
There is nothing in our human knowledge to tell us with certainty
when or how life first appeared on the earth. We have already spoken
of animal and vegetable remains that for ages are preserved in the
rocks. But clearly no such remains could ever be found in the
volcanic or molten rocks of the earliest stages of the earth's life.
Think for a moment of what the simplest forms of life are. A great
deal has been heard of microbes and bacteria during recent years,
and we may therefore assume that every one has some knowledge of the
structure of these simplest living things. They may be compared to
tiny bladders of jelly--so small that the microscope is necessary
in order to see them, and sometimes so much smaller than this that
the best microscopes cannot distinguish them. Such forms of life are
called "unicellular organisms," because they consist of a single
cell, which contains the jelly-like substance called protoplasm, and
a smaller body, smaller even than these tiny cells themselves, which
is called the nucleus.
These are the simplest forms of life. But all the higher forms of
life, and we may say, roughly speaking, any form of life that the
unaided eye can see, is made up not of one cell but of many cells.
A human being, for example, is made up of uncounted millions of
cells; and millions of cells go to the formation of a worm, a fish,
a gnat, or indeed to the formation of the simplest well-known animal
that the ordinary person could name. Similarly millions of cells go
to the formation of a leaf or a twig. These higher forms of life
are called "multicellular organisms," because they have many cells,
and most often many different kinds of cells. For instance, in the
body of a man there are different kinds of cells to form the skin,
or the lining of the mouth, or the substance of the eyes, or the
red or white corpuscles of the blood, or the grey matter of the
brain, or the roots of the hair--to name only a few. Thus we see how
complicated the structure of animals has become since life first
made its appearance on the earth. The cells joined themselves to
form tissues; and the tissues joined themselves to form organs; and
these things had to happen before anything like a complete animal of
the higher type, or even a complete vegetable, made its appearance.
Suppose by some great cataclysm, not so great as that which we have
imagined in an earlier chapter, but still world-wide in its effects,
the whole world should once again be swept by a great outbreak of
lava and molten rocks, which of all the living things would leave
traces of its existence? Perhaps a few of the animals with great
bones, or the great trees, might leave an impress of themselves
in the depths of the overwhelming rocks, just as we can stamp the
impress of the skin of our finger-tips on hot sealing-wax; but it is
fairly evident that all the soft-tissued animals and vegetables would
disappear entirely and leave not a trace behind--certainly no trace
that anybody could recognise many millions of years afterwards. It is
still more certain that the simplest forms of life, "the unicellular
organisms," would leave no trace at all. We know that side by side
with the complicated organisms that we can see the simplest organisms
exist now; and must have existed at the beginning of life. Yet when
we examine the records of living things in the rocks which were
formed in the youth of the world, and go back right to the earliest
of these forms of life that have ever been discovered, we find that
such specimens are all of the rather higher (if not of the highest
forms of life). From that we infer that life must have existed many
ages before the period of such remains, though, as we should have
expected, all examples of the earlier forms have disappeared.
Where did this life come from? Lord Kelvin once rashly committed
himself to the notion that life might have been brought to the earth
on one of those flying pieces of rock, which we have already spoken
of, which are named meteorites, or on a fragment of some other
planetary body that had been cast out into space. The speculation is
not so wildly improbable as it has sometimes been considered to be,
because recent researches have shown that it is not impossible for
life to survive at the very low temperatures which a meteorite would
experience on its way through space, and also that the time which a
small body would occupy in travelling, let us say from Mars to the
earth, would not be too great for the prolonged existence of some
germ of life on the meteorite. On the other hand, there is nothing
in known meteorites to suggest that they came from worlds where
conditions exist suitable for life as we know it; and, moreover, even
if we shut our eyes to these improbabilities, we are no nearer to
a solution of the problem of where and how life began. To say that
it was brought to earth on a meteorite is merely to throw back the
problem another stage, for we have still to ask how life began on the
meteorite and on the planet from which it came. The indirect evidence
regarding the probable beginning of the era of life on the earth is
also extremely difficult to examine, and we can only say that the
best geological authority leans to the idea that the conditions
when life would have been possible on the earth were finished long
before the earth had finished growing, and that these conditions may
have existed when the earth was about the size of Mars. Consequently
the first beginnings of life may have existed at depths hundreds
of miles below the earth's surface of to-day. The life was then,
however, only of the very simplest kind; it was probably vegetable
life. Probably also the first life appeared in the ocean, though it
is not altogether unlikely that it may have begun, and have gone on
developing, in fresh water--in those great pits which were first
formed by volcanoes and which afterwards became lakes and then seas.
For our purpose, however, it will be sufficient to say that life
began in the great bodies of water which were accumulating on the
globe, and which owing to the washing down by rain and rivers and
stream and wave action of land materials were becoming "saltier," or
more highly charged with mineral salts of various kinds. The early
forms of life were of the nature of jelly-fish, or simple organisms
which were permeated by the fluid in which they dwelt. The sea was
then warmer than it is now, and there are reasons for believing that
it was something above 100° F., perhaps higher--perhaps rather hotter
than we should now care to bathe in. It was also at the beginning
an ocean which was much less salt and had much less lime in it than
now. Its water was a good deal "softer." It was, however, becoming
much more hard, more like the Dead Sea, which, as everybody knows,
is a body of water so charged with mineral salts and accumulations
that a bather cannot sink in it, and will emerge from his bath
encrusted with salty deposits. As the early ocean became more and
more saturated (with lime and carbonates, etc.), the more vigorous of
the living forms in the water began to resist the change in various
ways. They tried to meet it, or to alter themselves so as not to be
incommoded by it.
This is a very familiar occurrence in natural life and evolution.
Perhaps the commonest example of it that we can select is the
formation of corns on the human feet and hands. A corn, properly
considered, is the defence raised by the skin against unusual or
discommoding pressure or friction. When a boot is too tight, or
when a plough handle or a cricket bat or a golf club is continually
clasped tightly, a "callosity" or horn-like defence is formed. In
some cases a blister is antecedent to the corn; and we may regard
this not only as showing the need for the hardening of the skin, but
as being a stage preliminary to it. There are many other instances.
Hair is formed as a protection to the body, and owing to nature's
economies is not usually formed when clothing takes its place or
heat renders it unnecessary. If the heat is too great, or the light
beating on the unprotected skin is too strong, then another form
of protection takes the place of hair. Why is it that races living
near the Equator wear "the burnished livery of the burning sun,"
and show black or brown pigmentation of the skin? It is because
this pigmentation arrests the penetration of the rays of the sun
more effectively than a garment. Lately Dr. Sambon has pointed
out that the white linen clothes which Europeans generally wear
in the tropics, though they look cool, are not sufficient screens
against the rays of light and heat, and has suggested that white
men's clothes, to be properly protective against the sun, ought to
be woven of threads of two colours, so that the garments should be
white outside and black inside. Apply these principles to animals in
sea-water, who were distressingly affected by conditions to which
they had never been subjected. What would happen? The weaker would
probably be killed by the change in the conditions, just as some
fresh-water fishes and animalculæ would be killed now if plunged into
sea-water. The stronger would, however, become acclimatised, and
would in the course of successive generations struggle to adapt their
bodies to the new conditions.
Thus the living organisms in the earth's early sea contrived to cut
themselves off from being bathed with the novel carbonaceous water.
They cut themselves off from it in the course of generations by
closing themselves off from it with skin or membrane. Many of them
stirred up their cells to secrete lime and exude it so as to form for
themselves a more or less impervious covering or shell. Finally, as
they grew to like the mineral water less, they continually made fresh
experiments to avoid it, and the more enterprising and adventurous
got out of the ocean altogether, and migrated to the air or the land,
perhaps by way of the shore sands and muds. This period, when the
ocean seems to have passed its best stage for supporting all forms of
life, appears to have been that which is geologically known as the
Cambrian. After this period there was a wealth of ferns, of animals
able to leave hard traces of themselves in the fossil records. Before
this period there was no physiological need for either skin or shell.
But once the skin and shell had been developed, primarily as a
defence against the sea-water, their great advantages for purposes of
the struggle for life among all forms of animals soon made themselves
felt, and so they were retained.
CHAPTER XI
LIFE IN OTHER WORLDS
If life was not brought to the earth from another planet, then life
was created, or originated, on the earth. Some of the conditions
which attended its birth have been considered, and they amount to
this: that the temperature of the earth, the elements of the earth,
the conditions of the earth's surface, oceans, and atmosphere were
exactly those which favoured the origination, the continuance, and
the development of living things. The earth, among all the heavenly
bodies which we can examine at all closely, is probably the only one
on which life, as we know it, would have much chance of survival.
The Sun as an abode of life we may at once put out of the question.
Taking the planets in order of distance from the Sun: of Mercury we
know very little, but astronomers like Schiaparelli and Lowell have
pronounced it to be an airless, dead planet with a surface cracked in
cooling untold ages ago. Venus is believed to be much like the earth,
not differing greatly in size, and probably having an atmosphere of
considerable extent;[10] but its appearance is so bright, viewed
from the earth, that it has been surmised that what we see is not
the planet itself but its atmosphere always charged with clouds or
possibly snow. Of Mars as an abode of life, and of the Moon, which
is the body nearest to us, we shall speak more fully in the present
chapter. Coming to the outer major planets, the giant Jupiter--with
a bulk more than a thousand times as great as the earth--has a
constitution by no means so solid. For many reasons the belief seems
justified that Jupiter must be a still hot, and almost gaseous body,
without a solid crust. If Jupiter's comparatively small weight for
its size and its wonderful and varying system of cloud coverings
are evidence of an early stage of development and a high internal
temperature, still more is this the case with Saturn. In bulk it is
not far inferior to Jupiter; but it is so much lighter than water
that if some of its fragments fell into one of the earth's oceans
they would float there. Its outer coverings or envelopes must consist
of heated gases in active circulation. Of Uranus and Neptune, still
farther off, we know very little, and the progress of knowledge
concerning them is very slow; but it is more probable that they are
in the early stage of development attributed to Jupiter and Saturn
than in the solid stage of planets like the earth. So that we may
fairly dismiss the probability of the existence of life as we know it
on any of them--and neglect incidentally, therefore, any possibility
that life could have been carried in a meteorite from them to us.
Whether there are other forms of "life" than any we know is a
question hardly needing discussion.
[Footnote 10: W. W. Bryant, _A History of Astronomy_ (Methuen),
1907.]
There remains the question of the probability of life on the Moon or
on Mars; and the question of possible life on the Moon is specially
worth consideration, because the earth's satellite was once part of
the earth's mass. We may first repeat briefly the explanation which
Sir G. H. Darwin has given of the Moon's separation from the earth.
If a flexible hoop or ring is spun very rapidly it will be seen to
flatten itself at top and bottom (or, as we might say, at its poles)
and broaden itself out at its middle or equator. The semi-liquid
earth once rotated so rapidly that its swelling equatorial belt was
almost at the point of separation from the parent body. Before this
occurred, however, the tension was so great that one large portion
of the protuberance, where it was weakest, broke away, and began
to move around the earth at a considerable distance from it. There
are several estimates of the bulk of the earth thus shot off; but
we may assume that about one-fiftieth of the earth escaped thus. It
must have consisted of a considerable portion of the earth's solid
crust, and a much larger quantity of the molten rocks of the earth's
interior.
The Moon is much lighter than the earth. The earth taken as a whole
weighs about five and a half times as much as water. If we consider
its surface alone, this weighs rather more than two and a half times
the weight of water--from which it can be seen that the interior of
the earth is very much denser than the earth's surface crust.[11]
The Moon weighs rather less than three and a half times its bulk
in water. This shows clearly that the Moon is composed of material
scraped off from the outer surface of the earth, rather than of
matter obtained from a considerable depth. At the same time the layer
of material removed had an appreciable thickness. The volume of the
Moon is equivalent to a solid body whose surface is equal to the
area of all the earth's oceans, and whose depth would be thirty-six
miles. It seems probable, therefore, that at the time when the Moon
was torn off, or shot off, from the earth, the parent body had a
solid crust averaging at least thirty-six miles in thickness, while
beneath this crust the temperature was so high that the materials
underneath were molten or liquid, and in other places were only kept
solid by the enormous pressure of the material above them. When
the Moon separated from the earth three-quarters of this crust was
carried away. It has sometimes been supposed that the remainder was
torn into two parts, one of which formed the great land area of the
Eastern Hemisphere and the other the great land area of which North
and South America are the relics in the Western Hemisphere. These two
great areas, at that time, floated on the semi-liquid surface like
two large ice-floes. But they were, of course, a good deal heavier
than ice, and the molten stuff on which they floated was a good deal
heavier than water. Later on this liquid stuff cooled and hardened.
But its bottom was still a good deal lower than the surface of the
great areas of land which had "floated" on it; and therefore it
formed great depressions all about and surrounding them. Thus the
depressions were there ready formed, into which the waters of the
earth, beginning as rain and ending as rivers or lakes, could flow as
into reservoirs. On the whole scientific men incline to believe that,
according to a popular tradition, the Moon may have been torn from
the earth where the Pacific Ocean now lies, and may have left that
hollow behind it when it went.
[Footnote 11: The figures are: earth's specific gravity = 5·6. The
specific gravity of the surface material ranges from, in general,
between 2·2 and 3·2, with an average of 2·7. The specific gravity of
the Moon is 3·4.]
Many people, scientific men and astronomers among them, have imagined
the possibilities of life on the Moon. In his clever romance, _The
First Man on the Moon_, Mr. H. G. Wells has gathered together all
the more reasoned speculations on the subject. They all turn on one
point--Is there an atmosphere on the Moon which would support life?
There are gases of some kind on the Moon. There must be gases, for
example, shut up in the moon's rocks; there may be gases in the
Moon's interior. Mr. Wells imagined that there was a good deal of gas
inside the Moon; indeed, he went so far as to suppose that the Moon
was partly hollow. If it were we should perhaps be able to accept
that as an explanation of the fact that the Moon is, bulk for bulk,
considerably lighter than the earth, and is, in short, rather lighter
than we should expect it to be. If the Moon were hollow there might
be an atmosphere and water inside it, and a race of beings might
live there--in the underworld of the Moon. The "Selenites," as Mr.
Wells called them, would probably be not in the least like human
beings, though they might be immeasurably more intelligent, because,
seeing that the earth cooled at a later period than the moon, life
might have begun earlier on the Moon, and would have had, perhaps,
many hundreds of thousands of years in which to develop. Mr. Wells
therefore imagined the "Selenites" to resemble in some respects a
race of very large insects with enormous brains. However, we need
pursue these romantic speculations no further, but must turn to
inquire not whether life might exist in the interior of the Moon
(which we can never see), but what would be the kind of life that
could exist on the part of the Moon that we can see.
In the first place, we believe that the atmosphere there would be
very, very thin; as thin as the atmosphere which is left in the
bell-receiver of an ordinary air-pump when the experimenter has done
the best he can to exhaust it of air altogether.[12] In the second
place, the atmosphere would not be one of oxygen and nitrogen as
that of the earth is, but of some heavy gas like carbon-dioxide
(which will not support animal life). The question is whether it
would support vegetable life. Several astronomers (no less eminent
a one than W. H. Pickering, of Harvard University, among them)
have supposed that it might, and they have imagined great jungles
of vegetation springing up on the surface of the Moon under the
influence of the Sun's rays--jungles which are stricken down again
when they are four days old under the oncoming of night. For the
Moon's day is equal to several of ours, and when night comes there
the temperature sinks to a level colder far than that of the earth's
Arctic regions; so cold, in fact, that even gases would be turned
to liquid and then frozen solid. It is by no means certain that the
gases we have mentioned would support vegetable life, but assuming
that they would, we should then expect the vegetation to spring up
with extraordinary rapidity--because it would be so little hampered
by its own weight--when the vertical rays of the Sun were beating
down on the Moon. When that was the case the temperature there would
be from 500° (F.) to 600° (F.) higher than during the night.
[Footnote 12: The exhaustion produced by an ordinary air-pump is
never a complete vacuum. Exhaustion which leaves only 1/2000th of the
original air is unusually efficient.]
Perhaps we may here explain some of the reasons why vegetation would
be little hampered by its own weight on the Moon. It is similar to
the reasons why light gases escape from the Moon. The mass of the
Moon--that is to say, the amount of matter it contains--is 1/80th
that of the earth. Therefore since the weight of a body means the
measure of the force by which gravity attracts it (to the earth or
to the Moon), bodies on the Moon's surface are much lighter than
they are here. The ratio is almost exactly one-sixth; consequently a
man weighing 180 lbs. on the earth if transplanted to the Moon would
find that he only weighed 30 lbs. there, and could carry two men at
once on his back for twenty miles much more easily than he could walk
that distance without a load here. He could throw a stone six times
as far as on the earth, and jump six times as high. Indeed, jumping
over a moderate-sized house would be a gymnastic feat scarcely worth
mentioning on the Moon.
After consideration of all these facts; and despite the belief of
some distinguished astronomers that changes are sometimes perceptible
on the Moon's surface; and that hoar frost can be perceived there;
and perhaps volcanic eruptions--the general conclusion arrived
at by astronomical authority is that organic life does not exist
either on the Moon or in it; and we may conclude this outline of
the speculations concerning it by quoting the American astronomer,
Professor N. S. Shaler: "It is naturally painful to conclude that the
Moon is and always has been deprived of those features of existence
which we deem the nobler; that it has never known the stir of air
or water or the higher life of beings who inherit the profit of
experience, and thereby climb the way that has led upward to man.
That these large gifts have been denied to the nearest companion of
the earth has its lesson for the naturalist. How vast are the effects
arising from the interrelation of actions.... If the gases could
have been retained in the Moon (by its attractive force) there is no
reason why it should not have had the history of a miniature earth.
As it is, from the beginning it appears to have been determined
that the Sun should not warm it in the same way as the earth; that
rain should not fall on it, nor the stirrings of life and energy be
visible on it. There is no imaginable accident that can alter its
state. Just as it is, our Moon is likely to see the Sun go out."
This chapter may be ended by a brief application of some of these
considerations to the case of the planet Mars. Next to the Moon Mars
is our nearest neighbour, and the erection of great telescopes in
America, one of them at Flagstaff Observatory, Arizona, where the air
is extraordinarily clear and telescopic vision unusually penetrating,
has stimulated the observation of the planet to a very great degree
during recent years. Mars has an atmosphere not nearly so dense as
that of the earth, but still dense enough in all probability to
support some form of organic life. It may, for example, support
vegetation. In some other respects Mars resembles the earth. It has
arctic circles; it has clouds, though whether these are of vapour or
of dust is not quite certain; and it has a less variable temperature
by far than that of the Moon. There are, at any rate, some of the
conditions to support and perhaps to encourage life; and if we could
be certain that the atmosphere in Mars more nearly resembles that of
the earth, and that its temperature was such as to be sometimes above
that of our Arctic regions, then it would be difficult to deny that
life, and probably intelligent beings, existed there. One very able
and intelligent astronomer is convinced that life and intelligent
beings do exist there. This is Professor Lowell, of Flagstaff
Observatory, who has devoted a number of years and a great deal
of money to the careful observation of the planet. He has brought
forward many cogent arguments to show that Mars might be inhabited,
and that great telescopes can discover signs on it, and may discover
further signs, which are a reason for supposing it to be so. It is
not, however, within the range of this book to examine these reasons
in detail; and we need only say that in the first decade of the
twentieth century most astronomers, despite the close examination
of Mars and its markings, which had been conducted for more than a
generation, were still not convinced that life as we know it could
exist there.
CHAPTER XII
THE HARDENING OF ROCKS
After the time when the great overflows of lava took place, spreading
over continents and sometimes seas, there was an era when the
explosions and outbursts began to diminish in violence, and the
world slowly settled down to conditions something like those which
we see in our own day. The seas were forming; there was rainfall and
summer and winter on the earth. The rains and the winds, the summer
heats and winter snows were more violent than now, and the volcanic
activity of which we have spoken was much more fierce than anything
of which mankind has any recollection. In the British Isles the
rainfall in a year averages something in the neighbourhood of thirty
inches. In some regions of the earth it is as much as four times
that amount, and deluges of fifteen inches have fallen in a day. But
in the era of which we have spoken deluging rains that were to be
measured in feet rather than inches fell incessantly. The air was
saturated with moisture, and it no sooner descended on the warm earth
than it steamed back to the clouds again. For reasons not unlike
these, nor unconnected with them, the great currents of air fed by
the constant transference of vapour from the earth to the skies, and
the condensation of the vapour to rain, falling again on the earth,
were greatly magnified. Thus the rocks of the earth, some of them
only cooling and not yet hardened, were subjected to "weathering"
of a kind of which it is hard to form any sufficient idea. The key
to all geology is that what is going on now on the earth is similar
to what always has been happening, (differing in degree rather than
in kind), and that consequently the rocks of millions of years ago
were washed by rivers down to the lower levels and were deposited
as sediment in streams, in lakes, and in the sea. Thus the age of
the "sedimentary rocks" began while the earth was still too warm to
preserve any vestiges of life.
Earthquakes much more violent than now and volcanic outbursts often
upset the steady order of things, but the earth was settling down.
During this settling-down process rocks, as we have seen, were being
formed by deposits; but they were very liable still to be invaded by
bursts of volcanic activity from the inner cauldron of the earth,
and they were very apt to be twisted out of their regular shape by
great earth movements. They were also liable to be baked by the
neighbourhood of the restless, unconfined molten rocks, nearer then
to the surface than now. Geologists call the great period of time
when all the rocks continually flowed out on to the surface of the
earth, and were, in fact, all molten before they solidified, the
Archæan Era (from a Greek word signifying the beginning). Next in
order to these rocks are those which were laid down in the agitated
times when the earth was still warm, and when the climate of the
earth might be described as a continual thunderstorm. In this period
earthquakes still had a great deal to do with the formation of the
rocks, but then, as now, the sea and lakes and oceans laid them down.
Geologists call this the Proterozoic Era. There are great masses
of these Proterozoic rocks in North America. In Arizona the three
periods of rock formation are sometimes visible together, and may,
indeed, be perceived in some of our photographs; the Archæan all
jumbled together being the lowest; Proterozoic lying crumpled or
tilted over them, and the later rocks resting more regularly on these
strata. In America, however, these separate ages of the Proterozoic
rocks can be identified, and each age is represented by rocks
thousands of feet in thickness. Three separate ages of rocks are
found in this great era in North America. It is not very important to
remember their names, which are merely those of the localities where
these great deposits are most marked, but it is important not to
forget that each of these depositions of rocks represents a period in
the earth's history older than the lifetime of a river or a lake and
as old as the lifetime of a continent. The lowest of these divisions
consists of rocks that are much altered by the heat of the rocks
below. The topmost division is hardly altered at all. In Scotland we
have similar rocks. The Torridonian sandstones, 8000 to 10,000 feet
thick, are believed to belong to this era. In France also, in Spain,
Germany, Finland, Sweden, India, and Brazil, the Proterozoic rocks
are found. In the lowermost of them are no signs that living things
ever existed, but in the upper ones f life begin to appear. We may
see in them to-day the first fossils. A fossil means literally a
thing dug up, and was a term applied at first to all kinds of mineral
substances taken out of the earth. We use the word now exclusively
for the remains of plants and animals embedded in any kind of rock.
In later chapters of this volume a good deal will have to be said
about fossils, and of the way in which they tell us the kind of life
that existed when they were first sunk in the rocks where now they
are found, and how also they give us information about the climate
and the distribution of land and sea, of lake and of river, in those
eras far "in the backward and the dark abyss of time."
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
The Pinnacled Castle-like Peaks of the Ramshorn Mountains Of Wyoming
The successive strata of sandstone are clearly evident in the
peaks.]
For the present, however, we may concern ourselves with the condition
of the earth and its rocks in Proterozoic times, observing merely
that the remains of animals which we find there are of an order
(Crustacea) which shows that life had progressed a good deal from
its earliest beginnings in the age when the rocks containing these
crustacea were laid down. After these rocks had been deposited
they were subjected to many influences of which we have only dim
conceptions. In a previous chapter we have compared the layers of
the undermost and harder rocks of the earth to the lines on a page
of this book as they would appear if the pages were crumpled up into
a ball. Sometimes the beds of solid rock have been so distorted that
they look like waves of the sea; sometimes they have been completely
overturned; hardly ever have they been suffered to lie down flat.
More than that has happened to them. Their very nature has been
changed. This was done partly by heat, partly by pressure, partly by
shock.
Let us consider the heat first. When a mass of erupted molten rock
forces its way through the earth's crust, it produces effects which
are quite easily recognised on the rocks it penetrates. Limestone
becomes hard and crystalline. Rocks with silica in them become glassy
and like quartz or other hard rocks which are sometimes polished
to make ornaments. Clayey strata become baked into hard brick-like
rocks. The changes are not altogether due to the heat. The eruption
of rocks is accompanied by steam at high pressure and with all sorts
of acids in the steam, so that chemical changes are also produced.
It has been supposed by Sir William Crookes that diamonds, which are
crystals of carbon, were produced by carbon being melted at some
enormous heat under great pressure. Given the requisite conditions
of heat and pressure, the parts of rocks which by their chemical
composition are susceptible to crystallisation will form into
enormous crystals--not unlike the intrusive rocks themselves. They
can, however, be readily distinguished from the shapes which the
intrusive rocks (like basalt) assume. The basalt rocks which form,
for example, the Giant's Causeway in Ireland were volcanic lavas.
Sometimes the lavas were masses which had solidified underground and
had been thrust up by pressure from below or have been exposed by the
weathering of the rocks above. Sometimes they have been lava poured
out on the surface. The black compact kinds most often are seen in
forms like columns. If these veins of volcanic rock have been thrust
up through a bed of coal, the coal is changed or "metamorphosed"
where the basalt has pierced it. Sometimes it becomes hard coal like
anthracite; sometimes it is changed into graphite--the black rock of
which pencils are frequently made.
Limestone pierced by basalt becomes marble. When sandstone is
discovered in contact with ancient volcanic rock it is found to have
lost its reddish colour, and to have become white, grey, green, or
black. It separates into crystals; it becomes glassy and hard. All
these instances are those of rocks which we can perceive to have been
altered by coming into contact with great heat. But there is another
kind of change of a very much more widespread character which can
be perceived among the most ancient of those rocks which we know
must have been first quietly laid down as sediments. It is sometimes
spoken of as "general metamorphism."
This widespreading change may extend over great regions and vast
extents of country. The most striking series of such rocks was first
described by Sir W. E. Logan, Director of the Canadian Geological
Survey; and he estimated the thickness of them at 30,000 feet. They
lie beneath all the unaltered rocks, and are (in North America)
the rocks which were the base or foundation of the North American
continent before the later sedimentary rocks were laid down on them.
They are called the Laurentian rocks, because they were first found
in the neighbourhood of the St. Lawrence River; but they exist in
many places besides Canada and North America; and the foundations
of Scandinavia and of the Hebrides are of the same texture and
material. Now this change or metamorphism does not appear to be the
same as that produced by the intrusion of hot eruptive rocks. Let us
take a simple instance. We have seen that limestone is changed by
heat into marble. Sometimes its fossils are preserved; sometimes they
completely disappear. Sometimes it is threaded by veins of harder
and more crystalline rocks. But in the case of the white marble of
Carrara, which was once a bed of coral, the change seems to have
taken place less violently, less suddenly, more gradually. The change
was due, therefore, not to violent heat suddenly applied, but to the
penetrating action of water, probably aided by sustained heat, and
certainly aided by pressure. When a rock is subjected to sufficient
pressure its very structure will alter; its original constituents
may be torn out of it, pressed out of it, filtered out of it, and
afterwards rearranged.
Once more let us call attention to the astounding effects which great
pressures can have. If pressure enough be applied iron can be made to
flow like treacle; and the pressure of two or three miles of strata
is enough to crumple or shear or tear any rock however hard. Now we
have shown that in the earth's long history some regions are always
being denuded of materials in order that these materials may be laid
down as sediments elsewhere. These movements may be compared to those
of a pair of scales, in which we are continually taking weight from
the scale pan that is weighted in order to put it into the scale that
is empty. The scale that is weighted is the land from which material
is being removed by the rains and the rivers; the scale that is
empty is the sea, in which the eroded material is laid down to form
beds and strata. These two scales are never quite balanced. But
suppose a time comes when we have taken all the material we can from
the weighted scale, so as to make the hitherto unweighted one the
heavier--what will happen? The newly weighted scale will inevitably
fall, and we shall have to begin to reverse our system of taking
from, and adding to, the scales. Similarly there will always come
a time when there will be a flow of the earth-mass from the areas
which have been receiving great loads of sediments, towards the areas
which have been robbed to supply them. Think for a moment how the
weight of a mountain set up in a plain might act if we can imagine
some giant force piling up the mountain higher and higher. The mere
weight of the mountain would tend to make it settle, and begin to
press outwards all round its base. If you find a difficulty in seeing
how this could be, imagine the mountain to be made of pitch. In such
a case we can quite easily realise how it would spread. Similarly
mountains, or even great plains and plateaux, of sediment built up
for millions of years in the oceans, would tend to spread; and they
would _spread towards the land which in the first place had supplied
them with materials_. At first, of course, the stiffness or rigidity
of the land would resist this spreading. But the masses thus built up
would become so great and so heavy in the course of millions of years
that no stiffness of the land could resist their spread. They would
begin to roll or slide towards the land; the heavier parts must
always roll towards the lighter. The action would be as resistless as
the slow moving onward motion of those masses of ice called glaciers;
or as the movement of the great ice plains in Greenland; or of those
ice plains which in Antarctic regions are always spreading towards
the sea.
There are two views of it. There is the outward pressure of the
regions where the sediments of rock are being laid down. There is the
inward pressure towards the regions which have lost soil. Sometimes
these two actions may conspire. A region where great denudation is
taking place may send its waste material towards the sea, where
it is deposited near the coast and not far from the highlands or
mountains or plateaux which founded the soil. The shallows near the
shore become a belt which is being loaded; the big mountains near by
are a belt which is unloading; and thus there are two strains set up
together. It is not hard to see the enormous crumpling effect which
this would produce on the lower strata one or two miles beneath the
surface of the sea and three or four miles below the topmost crests
of the mountains. These are circumstances which may not be common;
but the reader will find a quite sufficient explanation of some of
the crumpling, and many of the changes in composition and appearance
of the deep-sunk rocks, if he remembers the great pressure over them,
and the fact that the high regions may be supposed always to have a
tendency to slip towards the lowlands.
CHAPTER XIII
EARTHQUAKES IN GEOLOGY
It is more than likely that earthquakes in the geological past were
very much more violent, widespread, and frequent than they are
now; and they may have had a more potent effect in overturning the
rocks of the earth. Even now their effects and the circumstances
which accompany them are tremendous and terrifying. When the
great earthquake comes, says Major Edward Dutton in his book on
_Earthquakes_, it comes quickly and is quickly gone. Its duration
is generally a matter of seconds rather than of minutes, though
instances have been known in which it lasted from three to four
minutes. Perhaps forty-five seconds would be a fair average. The
first sensation is a confused murmuring sound of a strange and
even weird character. Almost simultaneously loose objects begin
to tremble and clatter. Sometimes almost in an instant, sometimes
more gradually, but always quickly, the sound becomes a roar, the
clattering becomes a crashing. The rapid quiver grows into a rude
violent shaking of increasing amplitude. Everything beneath seems
beaten with rapid blows of measureless power; loose objects begin to
fly about; those that are lightly hung break from their fastenings.
The shaking increases in violence. The floor begins to heave and rock
like a boat on the waves. Plaster ceilings fall, the walls crack, the
chimneys go crashing down, everything moves, heaves, tosses. Huge
waves seem to rush under the foundations as if driven by a gale. The
swing now becomes longer and still more powerful. The walls crack
open. A sudden lurch throws out the front wall into the street, or
tears off or shakes down in rubble the whole corner of the building.
Then comes a longer swaying motion, not unlike a ship at sea, but
more rapid; not alone from side to side, but forward and backward
as well, and both motions combined with a wriggle which it seems
impossible for anything to withstand. It is this compound, figure-8
motion which is so destructive, rending asunder the strongest
structures as if they were built of clay. It is the culmination of
the quake. It settles into a more regular and less violent swing;
then suddenly abates and ceases.
Out in the open country the signs and portents are of a different
character. The first intimation is a strange sound. Some have likened
it to the sighing of pine trees in the wind, or to falling rain;
others to the distant roar of the surf; others to the far-off rumble
of the railway train. It grows louder. The earth begins to quiver,
then to shake rudely. Soon the ground begins to heave. Then it is
actually seen to be traversed by visible waves--something like waves
at sea, but of less height and moving much more swiftly. The sound
becomes a roar. It is difficult to stand, and at length becomes
impossible to do so. People fling themselves to the ground to avoid
being dashed against it. The trees are seen to sway violently,
sometimes so much that they touch the ground with their branches....
As the waves rush past the ground opens in cracks and closes again.
As the cracks close the squeezed-out air blows out sand and gravel,
and sometimes sand and water are spurted high in air. The roar
becomes appalling. Through its din are heard loud, deep, solemn booms
that seem like the voice of some higher Power speaking out of the
depths of the universe. Suddenly the storm subsides, the earth comes
speedily to rest, and all is over.
And yet, says Major Dutton, this description suggests but a single
instance, or a few instances, of what earthquakes are like. In
some the full vigour of the shock comes with explosive suddenness.
People find themselves suddenly thrown to the earth, the ground
swept from under their feet. Sometimes the rolling waves of earth
are absent, and the movement is a rude quiver, rapidly vibrating in
every direction--twisting, contorting, wrenching the ground as if
in a determined effort to shake it into dust. Sometimes the most
pronounced motion is up and down, as if the earth beneath were being
hammered with giant strokes. Sometimes the growth, the climax, the
dying out of the earthquake movement are repeated before the first
shocks have ceased, or a few minutes afterwards, or even with an
interval of several hours. The last-named case is, however, uncommon,
though after the first shocks of a great earthquake there are minor
shocks and tremblings for days, weeks, or months afterwards. Some
of these are of considerable force, though they do not inflict the
devastation of the principal earthquake. The greatest earthquakes
are not always those which wreak the largest amount of destruction.
Evidently an earthquake, the centre of which is situated near a great
city, is more appalling in its effects than one which takes place in
some desert place like the steppes of Siberia. Recent earthquakes
in Italy and near San Francisco were regarded as great earthquakes
because they took place in thickly populated neighbourhoods. In
cities, writes Professor W. H. Hobbs, to the rumbling of the
earthquake is quickly added the crash of falling masonry, and to this
succeeds an uncanny grey darkness as the air becomes filled with the
dust from broken bricks, mortar, and plaster.... In places the ground
opens and swallows the objects which lie upon it. Ponds are sucked
down and disappear, and great fountains of water gush out and flood
the country. During the New Madrid earthquakes of 1811 and 1812 water
was shot upwards in vertical sheets and carried to the tops of the
highest trees. Near Lake Baikal, during the earthquake on January
26th, 1862, the surface of the steppe, over two hundred square miles,
was suddenly dropped; fountains opened at many parts within the
sunken area, and water shot up to heights of twenty feet. The water
gushed also in great volume from the open wells, and where these were
tightly covered by wooden caps, their lids were shot up into the air
like corks from champagne bottles. On the night of September 5th,
1896, during heavy earthquake shocks in Iceland, a new warm spring
suddenly opened to the accompaniment of loud roaring and whistling,
and threw water, steam, and fragments of rock to a height estimated
at six hundred feet. The force of the new geyser was, however,
soon spent, and ten days later it ceased to flow. Nearly all the
Icelandic geysers suffered changes during this earthquake, and the
famous _Strokkur_, which had been born during the earthquake of 1789,
suddenly ceased its eruption and came to an end.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
A Geyser in Action
In geysers the suggestion that the fountains of steam and hot water
originate by the contact of water with hot rock is irresistible.]
In steep-walled mountain valleys earthquakes nearly always cause
landslips, and these may completely block the course of a river. The
lake formed in this manner during the great earthquake of January
25th, 1348, in Carinthia destroyed no fewer than seventeen villages,
and to-day, nearly six centuries afterwards, the area is a great
marsh. After the earthquake near Lake Baikal in Siberia, of which
we have spoken and in which the ground sank, the sunken area was
soon after invaded by the waters of the lake. Sometimes when the
earthquake takes place near the mouth of a great river, the channels
of the streams are changed. After the Californian earthquake of
1857 the current of the River Kern was turned upstream; and the San
Gabriel River left its bed to follow a new course offered to it
by an earthquake fissure. After the Japanese earthquake of 1891 a
former lake was cut in half by one of the earthquake displacements,
and one half of the lake was left high and dry. Near Flagstaff,
Arizona, there is an old earthquake crack along which the waters of
several rivers which intersect it all disappear down the crevice.
The most remarkable revelation of the process of lake draining
during earthquake shocks was furnished, however, according to
Professor Hobbs, by the former Lake Eulalie near New Madrid. After
the shocks of 1812 the lake completely disappeared. On the lake
bottom thus exposed there was revealed a series of fissures down the
funnel-shaped openings which the waters had disappeared.
It will be seen from many of the foregoing instances that whatever
are the principal causes of earthquakes, they must have played a
great part in the shaping of events in the geological past; and
the only limitation which we can place in the importance of the
part they played will depend on whether we regard the earthquake
as having been caused by a movement of the underlying strata, or
whether we believe that the same cause which produces earthquakes
may produce alterations in the lie of the strata themselves. In the
next chapter we shall describe some of the effects produced on land
by earthquakes. But impressive as some of these effects are, it is
by no means certain that the greatest earthquakes take place on land
at all. They may take place at sea, deep underneath the ocean. Our
opportunities for observing such quakes, however, are much smaller
than are afforded by land earthquakes. The instruments which have
been devised for observing earth tremors will measure the smallest
of such disturbances, and will record earthquakes the centres of
which are thousands of miles away. These delicate instruments often
record distant earthquakes, the exact locality of which is never
determined. No doubt, some of these distant tremors originate in the
ocean bed; but the seaquake can only be localised when the water is
put into a state of vibration sufficiently energetic to rock the ship
and its loose objects and thus affect the senses. Vast waves are
sometimes rolled in on the shores of continents, and are undoubtedly
caused by some great disturbance beneath the ocean.
Such waves have been known through a long period of history in the
Eastern Mediterranean, where they have ravaged the shores of Syria
and Asia Minor; and it is sometimes supposed that the great deluge on
which the Ark of Noah floated was accompanied by a mighty sea-wave,
rolled in upon the lands of Chaldea from the Persian Gulf. Off the
Pacific coast of South America these waves arise most often and most
mightily. They have been especially formidable in the angle where
the coast of Peru meets that of Chili, and the harbours of Pisco,
Arica, Tacna, Iquique, and Pisagua have been repeatedly subjected
to these destructive invasions. Usually they are foreshadowed by a
violent earthquake, and the inhabitants, taking warning, fly to the
hills. The sea-wave does not, however, always follow the earthquake,
but it appears often enough to arouse serious fear that it may come
whenever the ground is strongly shaken. The first sign of the coming
disaster is the withdrawal of the sea from the shore, leaving bare
the bed of the harbour. A few minutes later the sea returns in a
high, irresistible wave, which overflows the adjoining lands. Again
it withdraws and again returns, and these oscillations may last for
many hours, slowly diminishing in the amount of rise and fall till
they die out.
The most memorable seaquake of the Chilian coast was that of August
13th, 1868, when the coast of South America was shaken from Ecuador
to Valdivia. In the town of Arica most of the buildings were thrown
down. A few minutes later the sea began to retire slowly from the
shore, so that ships anchored in seven fathoms of water were left
high and dry. Then the sea returned like a great wall of water, which
caught up the ships in the roadstead and swept them inland like chips
of wood. Among them was the United States war vessel _Wateree_,
which was carried inland nearly half a mile and was left, little
injured, on dry land when again the wave receded. The wave of this
catastrophe was felt far away from Chili. It was perceived on the
coasts of Australasia, Japan, Kamchatka, Alaska, and California. In
the harbour of Hakodate, in Japan, a series of waves was registered
on the tide-gauge. The ordinary tide in that port is only about two
and a half to three feet. On this occasion the water rose and fell
a height of ten feet in twenty minutes. It had taken the first wave
twenty-five hours to travel the distance of 7600 miles from South
America. On May 9th, 1877, another seaquake almost as great as this
was felt in many of the same places. This was on the occasion of the
Iquique earthquake. At Arica the stranded hulk of the _Wateree_,
which had remained high and dry for nine years, was picked up and
swept farther inland. Like its predecessor, the wave was felt all
over the Pacific. At Samoa the height of the waves varied from six
to twelve feet; in New Zealand from three to twenty feet; in Japan
from five to ten feet.
When a wave reaches shallow water it piles itself up to a height, as
any one knows who has watched the waves coming in on the sea-shore,
so that the height of a wave measured on the tide-gauge of a seaport
is a good deal greater than that of the height of the wave when it
is far out on the ocean. In fact, the mid-ocean height of the wave
is likely to be inches while the in-shore wave is measured in feet.
An illustration of this can be seen on the coast of Cornwall, where
sometimes, on quite a calm day the sea that looks so still breaks
on the shore in big rollers. We cannot tell exactly how high an
earthquake wave may be in mid-ocean, but we know it cannot usually be
very great, though it travels at great speeds--sometimes as much as
five miles a minute, or three hundred miles an hour.
Thus we should not expect that ships far out at sea would often
notice seaquakes unless the quake took place very near them. There
are, however, some instances. Captain Gales, of the ship _Florence
Nightingale_, reported that on January 25th, 1859, while near St.
Paul's Rocks, not far from the Equator, "we felt a strong shock of
an earthquake. It began with a rumbling sound like distant thunder
and lasted about forty seconds. I was quite well acquainted with
earthquakes, as I had experienced a good many on the west coast of
America, but never had I felt so severe a one. Glass and dishes
rattled so vigorously that I was surprised to find them uninjured.
A good many objects fell down, and it was as if the ship were
grounding on a reef." Another report from a locality not far from
this speaks of a strange submarine noise not unlike distant thunder,
or still more like the distant firing of heavy guns. At the same time
there was a vibration of the ship as though the anchor had been let
go.
The foregoing are representative of the large majority of the reports
of seaquakes. The ship quivers, vibrates; loose objects clatter and
tumble. There is a strange thunderous noise in the sea. The first
impression is as if the ship were grinding upon the bottom, and
there is an instinctive rush of the crew to the deck to see if the
ship is not on a reef. In some instances there are some forcible
disturbances. M. Vulet d'Aourst speaks of a seaquake so severe that
"the Admiral feared the complete destruction of the corvette." Heavy
objects, including cannon and their carriages, were thrown upon the
deck. The ship itself seemed to be hurled upwards.
One of the explanations offered of a phenomenon such as the last
described is that the vessel has been near a submarine volcanic
eruption of great power. The places where some or most of the
seaquakes have been observed have been charted, and certain districts
of the ocean have been found to produce more of these disturbances
than others. Among the first to be thus determined were two, located
in the Atlantic Ocean, very near the Equator and nearly midway
between Cape Palmas on the southeastern coast of Liberia and Cape
St. Roque, Brazil. One of them is the St. Paul's Rocks district,
of which mention has already been made. Another district from which
seaquakes have been reported with exceptional frequency is the North
Atlantic in the neighbourhood of the Azores. Between these islands
and the coast of Portugal it may be remembered that the great quake
originated which, on November 1st, 1775, destroyed Lisbon. The West
Indian Deep, that profound basin of the Atlantic lying north of the
Lesser Antilles and east of the Bahamas, where the Atlantic has its
greatest depths and where its bottom has its greatest inequalities,
is another district from which an unusual number of seaquakes have
been reported. The usual explanation of their origin is that in these
neighbourhoods, owing to the great pressure of water above them,
there are continual slips and fractures of the sea bottom, like
landslips on land, and that into the great cavities thus produced the
water rushes, and thus sets up disturbances which show themselves
on the surface like waves, very much in the same way that the water
rushing through the escape of a bath produces small disturbances on
the surface of the water in the bath. To satisfy the requirements of
such a wave as rolled in upon the South American coast at Arica in
1868 would require the sudden drop of many hundred square miles of
sea bottom--perhaps of several thousand square miles.
CHAPTER XIV
SOME FAMOUS EARTHQUAKES
Of all earthquakes perhaps the best known and remembered is that of
Lisbon on November 1st, 1755, and volumes have been written about it.
The first shocks of this earthquake came without other warning than a
deep sound resembling thunder, which appeared to proceed from beneath
the ground, and it was immediately followed by a quaking which threw
down the entire city of Lisbon. In six minutes sixty thousand persons
perished. The day was almost immediately turned into night, owing
to the thickness of the dust from the ruined city. A few minutes
afterwards fire sprang up among the ruins. The new Lisbon quay, which
had been built entirely of marble, suddenly sank down into the bay
with an immense crowd of people, who thronged to it for safety, and
it is said that none of the bodies of the drowned were ever seen
again. Following hard on the first shocks the sea retired from the
land, carrying boats and other craft with it, only to return in a
great wave, which completed the destruction in and about the city.
This great sea wave, the mightiest that has ever been described in
connection with an earthquake, is said to have washed not only the
coasts of Portugal and Spain, but to have extended with destructive
violence to other countries. At Kinsale, in Ireland, it was strong
enough to whirl vessels about in the harbour and to pour into the
market-place, and it was of great violence also at the island of
Madeira. Portions of the sea-coast between Cape-da-Roca and Cape
Carvociro fell away into the sea, and the damage was very great along
the coast between Cape St. Vincent and the mouth of the Guadiana. The
great Sierra da Estrella, on the west of the Tagus valley, was split
and rent in a most remarkable manner, and threw down avalanches of
rock into the valley.
The great earthquake which shook Calabria and North-Eastern Sicily
in the year 1783 stands out in rather striking contrast with other
disturbances of history, because it was carefully studied by a
great number of skilled observers. Among them were Vivenzio, the
court physician of the King of Naples, who has supplied us with a
narrative of the events; Grimaldi, the Minister of War, who at the
King's command visited the region and has left accurate measurements
of the greater and lesser fissures associated with the earthquake;
Pignaturo, a physician, who kept a record of the long-continuing
shocks, together with an estimate of their intensities; the French
geologist Dolomieu; and Sir William Hamilton, who was the British
Ambassador at Naples. The Academy of Naples sent a special commission
to the scene of the earthquake's destruction, and prepared a bulky
report of great scientific value. Calabria is a country which has
many times been racked with earthquakes; the disturbances being
almost as conspicuous for number as in Japan. The areas shaken have
not usually been great in extent, but as regards the geological
changes and the loss to life by which they have been accompanied,
they rank among the greatest in history.
The shocks of 1783, which cost thirty thousand lives, came without
warning on February 5th, and in two minutes threw down the structures
in hundreds of cities and villages scattered through Calabria
and North-Eastern Sicily. The great central granite formation of
Calabria, which was but slightly disturbed by the first shock, was
more heavily shaken by those which followed; and it was noted by the
early writers on this earthquake that the mountains had been a little
raised in comparison with the neighbouring plains at their bases.
The fact of the elevation of mountains by earthquakes or some other
underground disturbance has been elsewhere noted. On November 19th,
1822, a great earthquake shook the Chilian coast for a distance of
twelve hundred miles north and south. The greatest energy was shown
about one hundred miles north of Valparaiso, where the coast was
found to have risen suddenly from three to five feet for a distance
which has never been accurately ascertained, but which is known
to have exceeded thirty-five miles. In 1835 and in 1837 similar
elevations of the coast were caused by earthquakes at Concepcion,
about three hundred miles south of Valparaiso, and at Valdivia,
about two hundred miles south of Concepcion. Charles Darwin, in the
_Voyage of the "Beagle,"_ says: "I have convincing proofs that this
part of the continent of South America has been elevated near the
coast at least from four to five hundred feet, and in some parts from
one thousand to thirteen hundred feet, since the epoch of living
shells." Darwin finds his evidence in the raised beaches near the
coast on which these shells abound. That this uplift has been going
on by small and sudden movements, from a foot to ten feet at each
shock, for more than two centuries is attested by good evidence.
The coast in many places is proven to be from twenty to thirty feet
higher to-day than it was in the middle of the seventeenth century.
Sir Charles Lyell, in his _Principles of Geology_, gives a most
interesting account of the sudden upheaval of a portion of a mountain
range, with the accompaniment of a great earthquake, near Wellington,
in New Zealand, in January, 1855. Both the North and South Islands of
that colony have been affected by upliftings during the nineteenth
century, and these movements have been attended by powerful and
far-reaching earthquakes. The changes wrought by these movements on
the shores and farther inland as well have been remarkable during the
last hundred years.
Another example of the same kind of activity is seen in the
occasional rise of islands from the sea; but to this we shall refer
again, and for the present we may return to the Calabrian earthquake,
which presented many curious and many characteristic features.
During the earthquake the surface of the country heaved in great
undulations, which were productive of a feeling of sea-sickness, and
which, according to some observers, made the clouds appear to stand
still, as they will sometimes seem to do from the deck of a tossing
ship. The fissures which appeared in the ground were numbered by
thousands, and sometimes the displacements of the earth amounted to
as much as ten feet. Houses were lifted high up; in other places the
land or the sea-floor sank several feet. Many of the fissures opened,
spurted out sand or water, and then closed again; and some of the
Calabrian plains after the earthquake were found to be dotted with
circular hollows, on the average about the size of carriage wheels,
which were like wells, but were sometimes filled with sand instead
of water. These were afterwards found to be =V=-shaped. In addition
to these hundreds of small cone-shaped hollows or wells there were
other water basins more deserving the name of ponds or lakes. One of
these in the neighbourhood of Seminara, to which the name of Lago di
Tolfilo was given, was about a third of a mile in length, and was so
copiously fed by the springs ranged in a fissure in its bottom that
all attempts to drain it proved useless. Near Sitizam a valley was
completely choked up by the landslip from opposite sides, and behind
this new dam a lake was formed which was about two miles in length
and one mile in breadth. Vivenzio states that fifty lakes arose
at the time of the earthquake, and the Government surveyors, who
included ponds, counted no fewer than 215. The first effect of the
more violent shocks was generally to dry up the rivers. Immediately
afterwards many of their beds were so blocked up over them that the
rivers overflowed. From the rock of Scylla opposite to Charybdis, in
the Straits of Messina, large sections of cliff were broken off,
in one instance for a whole mile's length of coast. The sea and the
neighbourhood was greatly disturbed; and soon after the fall of the
cliffs of Scylla the sea rose to a height of twenty feet, and the
wave rolling over the coast-line drowned 1500 people.
Japan is perhaps as unstable an area as anywhere exists on the
earth, and the records of its earthquakes are more complete than in
any other country. The number of destructive earthquakes recorded
there in the last fifteen hundred years is 223. Since the beginning
of the seventeenth century the records are fairly perfect, and it
is found that since then a destructive earthquake has occurred
somewhere in the Japanese islands nearly every two and a half years.
For the lighter shocks systematic observation has become necessary,
and the Japanese, with that development of the scientific spirit
which is so remarkable an accompaniment of their progress during the
last generation, have organised an Earthquake Recording Service--a
Seismological Bureau--at which such conspicuous meteorologists as Mr.
John Milne and Dr. Knott have worked, and which has produced great
seismologists among the Japanese themselves. As many of our readers
are aware, the earth is hardly ever still; it trembles continually
like a boiling kettle, though not for the same reasons; and the
delicate instruments for measuring earthquakes, which are called
seismometers, show continual earth tremors or earth shivers. Since
1888 the earthquakes of all intensities recorded in Japan give a
yearly average of 1447 shocks, or a daily average of four. Until the
great earthquake of 1891, the greatest shocks within the memory of
living men were those of 1854-5.
The earthquake of October 28th, 1891, shook an area of 243,000
square miles, or more than three-fifths of the entire area of Japan,
though the greatest damage was done on the Mino-Owari Plain, a
broad expanse of country occupied by rice fields and surrounded by
mountains. Without the least warning the blow came, and in the first
shock 20,000 buildings fell, 7000 people were killed and 17,000 were
injured. Innumerable fissures great and small appeared all over the
plain, and the houses in the thickly packed villages fell like packs
of cards. The plain is one of Japan's great gardens, and supported
almost 1000 people to the square mile. Villages were thereabout
continuous, and a narrow lane of unusual destruction could be traced
through them for twenty miles. After the first shock there were
numerous smaller ones, and during the next five months no fewer than
256 shocks were recorded in all. Among the more remarkable effects
of the earthquake was the actual shifting of the country. Along a
crack many miles in length the plain after the earthquake was some
feet lower on one side than on the other. Reservoirs and swamps were
formed, as well as sand pits and mud craters. The most conspicuous
effect, however, from a geological standpoint was the shifting and
distortion of the strata.
[Illustration:
_Photo, G. C. Niven_
The Curious Eruption of Mount Asama, Japan
Mount Asama is nearly 8000 feet high, and the crater is nearly a
mile across, and has a depth of about 1000 feet. Steam is being
continually discharged. The above display was photographed from about
8 miles distance. The discharge was about 1-1/2 miles high, and shot
up to that height in some ninety seconds. The evident inference
is either that water is being forced out of the rocks by volcanic
action, or that the eruptions are of the nature of steam explosions
caused by water which comes in contact with molten rock.]
A few years later, on the 26th and 27th August, 1896, occurred
the remarkable Icelandic earthquake, which affected a triangular
plateau, bordered by high mountains, including Mount Hecla and other
well-known volcanoes, in the south-western portion of the island.
During the shocks the earth's surface was thrown into waves, so that
neither man nor cattle could stand. Persons who were lying on the
ground near a cliff were by the shock thrown bodily over the edge. A
high hill in the plain is described as shaken "like a dog coming out
of the water," and a thick mantle of loose soil which had covered it
was afterwards found distributed in heaps about its base. The surface
of the plain was scarred by open fissures or by rock walls which had
been caused by the earth's rising on one side of a fissure. One of
the fissures was nine miles and another seven miles in length. The
mountains round the plains were riven by clefts, and many landslips
occurred. As we have mentioned elsewhere, a new geyser was formed,
throwing up water to an enormous height, but soon spending its early
force; and many geysers and springs were violently disturbed.
An earthquake of a very different kind occurred the next year in the
province of Assam, India (June 12th, 1897). Unlike the Icelandic
earthquake, almost the whole damage was here the result of the first
shock. Everything was destroyed within the first fifteen seconds of
the earthquake, and the heavy shocks had all passed before two and
a half minutes had elapsed. In this brief space of time an area of
1,750,000 square miles had been shaken and 150,000 square miles laid
in ruins. A member of the Geological Survey of India, who was in
the town of Shillong, says that a rumbling sound like near thunder
preceded the shocks by a second or so and increased in loudness,
so that when masonry began to fall the noise and rattle of the
falling stones were hardly to be perceived. Unable to stand on his
feet, this observer sat down on the ground, and not only felt but
saw the ground thrown into violent waves as if "composed of soft
jelly." These waves seemed to run along the ground. When the shocks
had passed all the masonry houses in Shillong had been levelled to
the ground, and over each hung a cloud of pink plaster particles
and dust. Some of the shocks seem to have occurred with a kind of
twist, and stone monuments were given the appearance of corkscrews.
There were left many fissures and depressions in the ground, and
the rivers and lakes and streams were greatly affected. Thirty new
lakes were formed; along the great Brahmaputra River rolled a great
wave ten feet high. One great rent in the geological strata at the
earth's surface was twelve miles long. Important changes of level
of great blocks of country were clearly shown by the alterations in
the aspect of the landscape. Ranges of hills which before had not
been visible from certain points now came into view for the first
time, while others had disappeared. Though the most destructive shock
was that felt during the first few seconds, there were others which
followed, lasting for nearly a week afterwards. This earthquake is of
special interest, because it was the first one which was registered
on the earthquake instruments set up in Europe. Since that date
these instruments have been set up all over the world, and, as we
say elsewhere, a great earthquake is now usually recorded on the
seismometers and seismographic instruments set up in observatories
stationed thousands of miles away.
All of our readers will recollect the Jamaica earthquake which
occurred comparatively recently. Port Kingston, in Jamaica, has had
its share of earthquake disasters. In the year 1692 Port Royal, the
then chief city, was destroyed, and in rebuilding it the Jamaicans
moved it across the harbour, because the old town site was largely
submerged beneath the sea. It was a recurrence of the settlement
of the ground which in part produced the earthquake of January
14th, 1907. There were slight shocks preceding the earthquake, and
subterranean rumblings. The chief damage was done before thirty-five
seconds had gone by, and of course the catastrophe was greater
because the shocks were felt in the neighbourhood of a city.
Considered by itself the earthquake was not of the order of "great"
earthquakes, but many of the effects were most curious. A statue of
Queen Victoria on a pedestal was partly turned round; a series of
steep terraces was formed by the side of the harbour; a small spring
was converted into a stream eight feet wide; and, as we all know,
very great destruction was inflicted on life and property. Soundings
which have since then been made in the harbour show that its depth
has greatly increased in some parts, in one instance by not less
than twenty-seven feet. The greatest depression occurred near Port
Royal (the old city), where a hundred yards or more of the ground was
submerged by water varying from eight to twenty-five feet in depth.
Proceeding northwards from the Antilles to North America, we come
to other famous areas of earthquake disturbance. In 1811 and 1812
there were earthquakes along the lower lands of the great Mississippi
River, which were felt throughout the whole of the eastern portion
of the United States and as far west as exploration had gone. At
New Madrid, which appears to have been near the centre of the
disturbance, "subterranean thunder" appears to have been heard
frequently for many years preceding the earthquake, though it had
ceased for nearly a year. About two o'clock in the morning of
December 16th, 1811, there came a severe shock accompanied by a noise
which was like near thunder, and a few minutes afterwards the air was
filled with sulphurous vapour. People thought that the end of the
world had come. Light shocks were felt till sunrise; and then one
more violent than the first occurred. But this was not the end. For
three months the shocks went on, and in that time no fewer than 1874
shocks were recorded, eight of them great ones. The shock of January
23rd, though as violent as any that preceded it, was surpassed by
the so-called "hard shock," which came at about four o'clock in the
afternoon of February 7th. It was accompanied by a discharge of
sulphurous vapour in the atmosphere, and an unusual darkness which
added greatly to the terror of the people.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
A House destroyed by an Earthquake
This was Senator Stanford's house at Palo Alto, about 25 miles from
San Francisco, which is situated on a fault or ancient fracture of
the earth's surface.]
The Mississippi seemed to recede from its banks, and its waters
gathered up like mountains, leaving boats high up on the sands. "The
waters then moved inwards with a front wall fifteen to twenty feet
in height, tearing the boats from their moorings and carrying them
closely packed up a creek for a quarter of a mile. The river fell
as rapidly as it had risen, and receded from its banks with such
violence that it took with it a grove of cotton-woods which hedged
its borders. These trees were broken off with such regularity that
it was hard to persuade people who had not witnessed the catastrophe
that it had not been brought about by human agency." During all the
greater shocks the earth's surface was reported to have been raised
in great crumplings, the crests of which opened into fissures. Some
of these were six hundred to seven hundred feet long and twenty
to thirty feet wide, and water and sand and even coal[13] were
spouted out of them to a height of forty feet. Many craters and
holes in the ground were formed, surrounded by rings of sand; and
traces of them remain to this day, a century-old monument of the
destruction wrought. Notable changes in the level of the country were
effected; new lakes and new islands came into existence; some lakes
disappeared; some of the lakes then formed remain to this day. On
the eastern bank of the Mississippi a lake a hundred miles long, six
miles wide, and ten to fifty feet in depth was formed; and another
lake, known now as Reelfoot Lake, which came then into existence,
is twenty miles long, seven miles broad--larger than Windermere,
and deeper. The fishermen's boats to-day float over the top of
eighteenth-century cypress trees. In addition to sections of country
which were depressed and submerged, an area of some twenty miles in
diameter was elevated into a low dune twenty to twenty-five feet
above the level of the plain of the Mississippi. Many years after the
great shocks, smaller ones were felt; and even now scarcely a year
passes without slight tremors in this region, and small fissures are
still formed in the ground.
[Footnote 13: Or "lignite," a form of hard pitch.]
It must be repeated that the great earthquakes are not those of
which most is heard. The earthquake of San Francisco which did such
widespread damage because it took place in the neighbourhood of a
thickly populated city was, after all, less in magnitude than the
Sonora earthquake of 1887, which took place in a great expanse of
desert country in which few people lived and few towns had been
built. But this earthquake was felt all over the countries of Mexico
and the State of Arizona; and a range of mountains, the Sierra Teras,
was uplifted between faults which opened upon either side. Millions
of cubic feet of rock were thrown down from the slopes of the
mountains into the deep cañons and water-courses, and cliffs of hard
rock were shattered and split as though by a charge of giant powder.
The Yakutat Bay earthquake in Alaska changed the whole face of the
country over thousands of square miles during September, 1899; and
along the shore of the bay the shore showed that in some cases it had
been lifted from five to thirty and in some cases even fifty feet.
New reefs and islands were formed; and a study of the country and the
coast-line seems to show that from time to time this neighbourhood,
like the beaches south of Valparaiso, is being lifted by some agency,
perhaps the gradual elevation of a continent, perhaps by continuous
earthquake action.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
The Ruins of the Magnificent City Hall of San Francisco
The great earthquake of 1906 caused this destruction. Some of the
distortive effects of an earthquake movement can be perceived.]
But if the San Francisco earthquake of April 18th, 1906, was not of
itself a very great earthquake, it brought about an enormous amount
of damage. The heavy shocks came without warning at about five
o'clock in the morning of April 18th. They lasted about a minute, and
then went off into lighter quakes, which were felt till evening, and
for many days after, gradually growing smaller and smaller. The loss
of life, though great, was but a tenth of what it would have been had
the worst shocks come at a later hour when men were at their places
of business and the children in school. As it was, the greatest loss
was due to the fire which was started by the earthquake, and which
was soon beyond control, because the water-main had been snapped by
the earth movement. The cause of the earthquake has been generally
assigned to the slipping of the strata of California. Athwart the
whole state runs a straight furrow, like an ancient earthquake crack
of primeval times, which is about four hundred miles long, and the
rocks about which are still liable to slip. As we have said, however,
the Californian earthquake, though accompanied by great destruction
of property, and by the characteristic accompaniments of fissures in
the ground, and slight elevations and depressions of the country over
a line sixty miles long, was not a very profound earthquake.
Rather a curious coincidence may be here noted. We have spoken of
submarine earthquakes and volcanoes and of islands which are raised
by something akin to volcanic action or earthquake action underneath
the sea.
Some weeks after the Californian earthquake the officers and crew
of the U.S. Fish Commission steamer _Albatross_, while on their way
to investigate, with Professor Charles H. Gilbert, the fisheries of
Japan, passed the group of islands known as the Bogoslofs, and to
their astonishment perceived that a third island had been added to
the other two. Professor Gilbert, in a letter concerning the first
sight of the island, on May 28th, wrote: "When I saw the Bogoslofs
in 1890 there were really two small islands about 1-1/2 miles apart,
one of them steaming and the other cooled off. This has been the
condition for a number of years, so the hot one had received the name
of Fire Island, the cold one, Castle Island. When they came in sight
yesterday, we were astonished to find that Fire Island was no longer
smoking, and that a very large third island had arisen half-way
between the other two. It was made of jagged, rugged lava, and was
giving off clouds of steam and smoke from any number of little
craters scattered all over it. Around these craters the rocks were
all crusted with yellow sulphur. The new cone, occupying much of the
space between the two older ones, was somewhat higher than either,
but was certainly far from 900 feet high--300 feet would be an
extreme figure. There was no evidence of a central crater. The steam
and fumes were given off most abundantly from cracks and fumaroles
on the slopes. About these were heavy incrustations of sulphur. We
saw no indications of boiling water, nor did we believe that landing
would be impossible."
All three of these Bogoslof islands, which are about 120 miles
south of the Pribyloff Islands, belonging to Russia in the Behring
Sea, have risen above the waters hot and steaming in the last 150
years. The oldest Bogoslof, now called Castle Island, rose from the
sea in 1796; and Kotzebue describes the first glimpse of it, as
seen by a trader, named Krinkof, who had been forced to seek refuge
from a storm on a neighbouring island. The birth of the volcanic
islet was accompanied by an earthquake which shook the island
where the trader had taken refuge, and by an outburst of fire with
thunderous explosions. The island was said to emit fire for months
afterwards, and for eight years afterwards the water round it was
warm and its ashes unbearably hot. The eruption of 1883, in which
the second Bogoslof, called Fire Island, was born, had no witnesses;
but in September of that year great volumes of steam and smoke,
accompanied by showers of ashes, were thrown out from the summit
and through fissures in the sides and base, the bright reflections
from the heated interior being visible at night. At the time of this
eruption a severe earthquake was felt in the sea off Cape Mendocino,
apparently in the line of the Californian furrow or rift.
The islands were visited in 1884 by the officers of the U.S. revenue
cutter _Corwin_, and Lieutenant J. C. Cantwell and Surgeon H. W.
Yemans made the ascent of New Bogoslof. Lieutenant Cantwell thus
describes his experience in the _Cruise of the Corwin_:--
"The sides of New Bogoslof rise with a gentle slope to the crater.
The ascent at first appears easy, but a thin layer of ashes, formed
into a crust by the action of rain and moisture, is not strong enough
to sustain a man's weight. At every step my feet crushed through the
outer covering and I sank at first ankle deep, and later on knee
deep, into a soft, almost impalpable dust, which arose in clouds and
nearly suffocated me. As the summit was reached the heat of the ashes
became unbearable.... On all sides of the cone there are openings
through which steam escaped with more or less energy."
Seven years after that Drs. Merriam and Mendenhall, of the Behring
Sea Seal Commission, found the newer island still smoking, steaming,
and occasionally roaring like a giant steam escape. The older island
had quite cooled, and had become a sheer cliff or hill of cold ashes,
and was, and is, the home of countless sea birds, as well as of a
small herd of sea lions. Captain Cook, in the eighteenth century, had
passed by the neighbourhood of this island. This was eighteen years,
however, before it was born, and he named a pillar of ash or rock
which he found there Ship Rock. Ship Rock fell in ruins five years
after the birth of Fire Island.
Since that time the new island has again sunk beneath the waves.
But it will probably rise again, or another island somewhere in its
neighbourhood will take its place, for a great new submarine ridge of
volcanic rocks is forming in this neighbourhood and has been forming
for many hundreds of years. The Pribyloff Islands are known to be
volcanic from the materials of which they are composed, and sprang up
above the waves in the same way.
CHAPTER XV
THE CAUSES OF EARTHQUAKES
Now that we have before us some of the examples of the changes which
historic earthquakes have brought about in the face of the country,
it is easy to see what an important effect they must have exerted
in geological history. But there are still weighty questions to be
answered about earthquakes. We have seen that an earthquake can
contort, upset, and twist the surface strata of the earth as easily
as we can crumple a sheet of cardboard. We have yet to find whether
the crumpling of the strata is always _produced_ by earthquakes, or
whether an earthquake is the culminating symptom that some agency
is at work crumpling the strata. Let us try to imagine an example
on a small scale. Suppose we take the top of a pill-box, and,
holding it in the crook between our thumb and forefinger, compress
it very tightly on all sides. What will happen? The lid of the
pill-box, being subjected to stress or strain on all sides, will
presently buckle and crack. We shall have produced an earthquake on
a small scale, and there will be an earthquake fracture--perhaps an
earthquake fissure. If the whole pill-box had been used for the
purpose of our experiment, and had been packed to the brim with
ointment or thick liquid, and if it had been squeezed in a vice
instead of in our hands, then perhaps we should have provoked still
more striking symptoms of an earthquake. The ointment might have
broken out through the lid. Perhaps even tiny jagged holes or craters
would have been formed in the lid. Thus we see how strain may produce
earthquakes. Take some more examples. Suppose a cork is very tightly
fixed in a wine bottle, and in order to get it out we employ a very
powerful lever corkscrew. The neck of the bottle, under the effect
of the too powerful pressure put on the inside surface of the glass,
will crack or break. Similarly if we screw down a microscope too
hard on a slip of glass the glass will often crack suddenly. Both
these instances recently occurred within the writer's experience,
and few readers can have escaped noticing one or other of them. The
breakage in these instances is always caused because a strain is set
up somewhere in the glass--there is more pressure at one point than
another, and the glass, unable to resist this unequal pressure, gives
way.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
The Track of an Earth Wave
Showing portion of a street in San Francisco after the terrible
earthquake of 1906. The resemblance of the break in the ground to the
appearance of a stationary wave should be noted.]
What happens when it gives way? To answer this question we had better
carry our minds to the example of the pill-box lid. If the top of
the box were of very brittle material, like pottery or glass, then
after the breakage we know that most likely one of the broken pieces
would be a little higher than the other--would perhaps overlap it.
That is what we often see when examining the geological earth strata.
One stratum, instead of lying evenly with another where a crack
has occurred, rests a little above it or below it. This inequality
or unevenness geologists call a fault. Now we can easily see that
whenever, and by whatever causes, a fault is produced, there is
probably at the same time an earthquake. The fault cannot be produced
without a great and shaking disturbance. Mr. John Milne, the most
distinguished of British authorities on earthquakes, says that all
large earthquakes originate from the formation or extension of these
"faults" or great cracks in the strata.
The occurrences of these "faults" are most frequent when the process
of mountain building has been going on over the earth. In other
words, if we imagine a period in which some great continental area
of the world's surface was slowly rising above the oceans, then at
that time we should expect that there would have been great "faults"
occurring in the strata, and great earthquakes following them. To
quote his words: "If therefore we wish to know when earthquakes
were greatest and most frequent, we must turn to those periods in
geological history when mountain ranges were built, when volcanic
activity was pronounced, and when great 'faults' were made. The first
of these periods would be coincident with the creation of the Ural
Mountains, the Grampians, and other mountain ranges. This took place
in the earliest geologic times. Another period of mountain formation
was when the Himalayas and the Alps were slowly but intermittently
brought into existence. In both these periods volcanic activity was
pronounced, and beds of coal were formed. When the crust of the earth
was crumbling, mountains grew spasmodically--(they sprang up, as it
were, from out of the giant forces which we have described earlier
in this book)--'faults' gave rise to earthquakes, volcanic forces
found their vents, and conditions existed which gave rise to the
accumulation of materials to form coal."
But, the reader will naturally inquire, if "faults" gave rise to
earthquakes, and faults are the result of pressure, what produces the
pressure? And what produces the mountains? Before we answer that we
must again have recourse to examples taken from common experience.
A sheet of glass or of marble we usually regard as a thing that may
break but does not bend. But all of us have seen glass strips, if
they are long enough, bend under their own weight; and there are
even marble mantelpieces which, if examined, show that the slab of
marble has _bent_. Thus we can readily imagine that sometimes the
strata of the earth will bend by reason of the weight put upon them.
If that weight is not put on them quite evenly the strata will be
still more likely to bend; it will go from bending to buckling,
and from buckling to breaking. As soon as it breaks there will be
a "fault" formed. Those who recollect what we have said about the
enormous weight of the rocks one above the other will not have to
search far for the cause of weight sufficient to bend or buckle the
rock strata of the earth. And those who have followed carefully all
that has been written about the shifting of materials from the land
to the sea by the processes of denudation and erosion set up by rain
and wind and carried out by streams and rivers, will easily discover
where and how the shifting of great weights of the earth's surface
goes on. Little by little great weights are taken from one place
on the earth's surface to another, as we might shift the weights
in balanced scale-pans grain by grain, till at last the heavier
scale-pan goes down quickly, or it may be with a crash, and the
"fault" occurs, while the earthquake follows.
There remains another question, however, to be answered, and it is,
How were the mountains formed? Mountains are very closely connected
with earthquakes, for nearly all the regions of the earth where
the great disturbances take place are in the neighbourhood of
great mountain ranges; and many, indeed most, of the students of
earthquakes believe this to be the case, because the great weight of
the mountains, especially when near the deep sea, induces pressure
on the rocks, and consequently slipping and "faults." But the causes
of mountain formation are very difficult to show with certainty.
One such explanation, that of the continual shifting of portions
by weight of the earth, we have already given. There is another
one which may perhaps supply an additional cause. It is that just
as "faults" produce earthquakes, perhaps in some cases earthquakes
produce "faults." In the illustration we gave of the bottle-neck
being broken by continual pressure, or the slide of a microscope
suddenly breaking with a crash, because the increasing pressure of
a screw was greater than it could bear, we have considered cases
where the pressure was _slowly_ applied. But a tap with a hammer or
any sudden shock would also produce a breakage--and "faults," and
an earthquake on a small scale--and it is possible that some of the
convulsions of nature and some of their permanent effects are caused
by sudden and violent causes.
One such cause might be the violent and sudden formation of steam by
the contact of water with rock at a very high temperature. Everybody
knows what happens to the kitchen boiler after a severe frost. The
frost clogs the pipes with ice, so that the kitchen boiler becomes
dry because no water is reaching it; but it continues to grow hotter
and hotter till the iron plates or iron lining become red-hot. Then
the frost perhaps gives way and a small amount of water finds its
way into the red-hot boiler. The water is converted instantly into
steam; and, as a result, the boiler, if it is a weak one, is blown
out into the kitchen, causing grave personal inconvenience to the
cook. If the boiler is a strong one, it may merely crack. Now, apply
these considerations to the instance of the earth, its oceans, its
thin crust, and its hot rocks situated at a depth of not more than
thirty miles, and perhaps at a good deal less depth than that. What
would happen if the ocean leaked through into the strata of red-hot
or molten rocks? There would be enormous quantities of steam formed;
and if, owing to the vast pressure of strata and water above, these
quantities of steam did not instantly produce violent explosions,
yet underneath there would be imprisoned, peak, forces of tremendous
power which would only await a favourable opportunity in order to
manifest themselves. The hot steam until this favourable opportunity
arose would be absorbed by the rocks, just as hot steel can be shown
to absorb gases.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
A Geyser at Rest in Yellowstone Park, U.S.A.
The encrusted deposits of mineral salts should be observed.]
We are thus face to face with the following situation, as it is
expressed by Dr. T. J. J. See, the American physicist:--The internal
temperature of the earth is extremely high with heated rocks quite
near the surface, while the crust is fractured and leaky everywhere,
and especially where the depth of the sea is greatest. The sea
covers three-fourths of the earth's surface, and earthquakes are
found to be most violent where the sea is deepest, and volcanoes
most numerous on the adjacent shores. Can we then suppose that both
earthquakes and volcanoes depend on the explosive power of steam
which has developed in the heated rocks of the earth's crust? We
have said that earthquakes and volcanoes are most common in regions
where high mountains are near deep oceans--as on the westward of
South and Central America, the Aleutian Islands, the Kurile Islands,
Japan, Sumatra, Java, and other islands of the East Indies bordering
on the deep waters of the Indian Ocean, New Zealand, and the Lesser
Antilles in the West Indies, Iceland, Italy, and Greece. These are
also the regions where, owing to the existence of high mountains, the
weight, the pressure, the tear and stress on the underlying strata
are greatest, and where consequently there is the greater chance of
strata slipping or bending or giving way. Mr. John Milne divides the
world into eleven such great "world-earthquake" districts; and he
has endeavoured to show that all the great convulsions of the earth
have their origin in one or other of these areas--where usually a
great mountain range slopes steeply down to the sea. There are eleven
such world-earthquake districts. There is the Alaskan region, where
on the shore Mount Elias rises to a height of 18,000 feet and where
the water is 7000 feet deep sixty miles from the shore--altogether
a drop of 25,000 feet from the top of the mountain to the bed of
the ocean in 200 miles. This drop, without going into measurements,
may be taken as typical of the rest, which are classified as the
Cordillerean region, the Antillean region (in the earthquake district
of which Mount Pelée at Martinique and the Soufrière in St. Vincent
are situated); the Andean district; the Japan district; the Javan
district; the Mauritius district; the Antarctic district; three
submarine districts of sunken ridges in the North-Eastern Atlantic,
the North-Western Atlantic, and the Northern Atlantic; and one great
land district, distant from the sea, which lumps together all the
mountains of the Alps, the Balkans, the Caucasus, and the Himalayas.
In thirteen years, from the time in which earthquake investigation
has become a science, 750 great earthquakes originated in these
districts. On the average, about sixty great earthquakes occur
every year, or a little more than one a week. In addition to these
world-shaking effects there are about 30,000 small earthquakes every
year, England's annual contribution to this number being about half a
dozen.
What is the meaning of a "great earthquake," and how do we define
"small" earthquakes? A small earthquake is one such as we have
described as taking place in the valley of the Mississippi, and
which, even though it may produce considerable disturbance in its
neighbourhood, is not perceptible at any great distance away. A great
earthquake is one which sends its vibrations thousands of miles. A
very large earthquake, originating in any part of the world, _may
be recorded in any other part of the globe_. Although only a few
people in Great Britain have been privileged to feel a home-made
earth tremor, every one of us is very many times a year moved by
earthquakes. We do not perceive them because the back-and-forth
motion of the ground is performed too slowly, while if there is
a movement of the ground the undulations are so very flat that
they cannot be perceived. But at several places in England and at
earthquake observatories (seismological stations) all over the
world, from Japan to Australia and from South Africa to Greenland,
instruments are set up which are sensitive enough to record these
tremors, though not always to locate them. Sometimes when Professor
Behar in Germany, or Mr. Milne from his observatory in the Isle of
Wight, telegraphs to the newspapers that signs of a great earthquake
have appeared on their instruments, the world hears no more of these
disturbances. They have occurred we are certain, but the place where
the great cataclysm which has thus shaken the whole round world took
place has been fortunately remote from inhabited portions of the
earth, and has very likely been beneath the waters of some ocean.
Earthquake waves start out from the great area where the cataclysm
took place, and begin to disturb the earth in all directions,
just as if we were to put a row of marbles on a table and were to
strike the end marble of the row. The marble farthest from it would
presently receive the shock as it travelled along the row of marbles.
Any one of our readers who has ever seen a train of luggage wagons
being shunted is familiar with the way in which the shock of a
sudden pull or push on the part of the engine travels all down the
line of wagons, and we may think of the shock of an earthquake as
travelling along and through the earth in the same way. Observation,
however, shows that these waves are propagated farthest in one
particular direction. For example, the chief movement following
the San Francisco earthquake, which originated from fault lines
running parallel to the coast of California, was much more marked in
countries lying to the east or west of California than in countries
lying towards the south. England and Japan obtained large records of
the disturbance, while in Argentina the records were extremely small.
In the case of the Jamaica earthquake, where the lines of origin ran
east and west, the phenomenon was reversed. Toronto received a large
quantity of motion, and England a very little. Another peculiarity of
this phase of earthquake motion is that it may be propagated in one
direction round the world to a greater distance than in an opposite
direction. The suggestion is that the initial impulse was delivered
in the direction towards which motion was propagated farthest. That
which happens corresponds to what we see if we dip the blade of
a spade in water and suddenly push the blade in some particular
direction. The water waves thus created travel farthest in the
direction of the impulse.
Another curious phenomenon connected with the large waves of certain
earthquakes is that they may be very marked for one thousand miles
round their origin, and may be perceived on the exactly opposite
side of the earth (though, of course, much reduced in size), but
cannot be recorded on the earthquake instruments of the regions in
between. For example, an earthquake originating near New Zealand may
be recorded in that country, but not in India, Egypt, West Asia, or
east of Europe, though in Britain it may make itself evident on the
seismometer's record. The phenomenon may be compared to a water wave
running down an expanding estuary. At the mouth of such an estuary it
may have become so flat that it is no longer recognisable. Should it,
however, run up a second estuary, we can imagine concentration taking
place, so that near the top of the second estuary it would eventually
become recordable on instruments. In these antipodean survivors we
see the final efforts of a dying earthquake. It is only occasionally
that the precursors and the followers of these large waves have
sufficient energy to reach their antipodes. They die _en route_.
From the earliest times philosophers have held that the causes of
earthquakes were associated with the contact between fire and water.
Plato, Aristotle, Strabo, and Pliny all held that water and air
penetrate into the earth through hollows, fissures, and crevices,
thus developing in the heated interior great vapour, a part of
which is expelled from volcanoes. Aristotle correctly associated
seismic sea waves with earthquakes, and even Homer assigned these
great disturbances of the sea to Poseidon's trident, which was also
the means employed for raising up islands from the sea bottom. The
withdrawal of the water from the shore after an earthquake and its
return as a great wave were familiar to Aristotle, and are implied in
his description of the sinking of Helike in 373 B.C.
Before leaving the subject of earthquakes we may quote some passages
from Mr. John Milne on the influence which these great disasters have
exercised on the emotions. Immediately after the Kingston earthquake
we read of the dazed and almost insane condition of the people. Many
were affected with an outburst of religious ecstasy, thinking the
last day had come. The negro population camped on the racecourse
and spent their time in singing hymns. Somewhat similar scenes took
place in Chili; men and women ran hither and thither, mad with terror
and devoid of reason. Amid shrieks and sobs and the wailing of a
multitude an "Ora pro nobis" or a "Pater noster" might now and then
be heard. In early civilisations underground thunderings have so far
excited the imagination that subterranean monsters or personages
have been conjured into existence, and these in many instances have
played a part in primitive religions. At the time of an earthquake in
Japan the children are told that the shaking is due to the movement
of a fish which is buried beneath their country, and in Japan we
find references to this fish in the pictorial art, pottery and
carving, literature, and everyday conversation, all of which would
be unintelligible if we did not know the story of the earthquake
fish. In other countries the subterranean creature will be a pig, a
tortoise, an elephant, or some other animal.
The most interesting myths, however, relate to underground
personages. The forty-five Grecian Titans, who were of gigantic
stature and of proportionate strength, were confined in the bowels
of the earth. According to the poets, the flames of Etna proceeded
from the breath of Enceladus, and when he turned his weary body the
whole island of Sicily was shaken to its foundations. Neptune was
not only a god of the oceans, rivers, and fountains, but with a blow
of his trident he could create earthquakes at pleasure. The worship
of Neptune was established in almost every part of the Grecian
world. The Livians, in particular, venerated him, and looked upon
him as the first and greatest of the gods. The Palici were born in
the bowels of the earth, and were worshipped with great ceremonies
by the Sicilians. In a superstitious age the altars of the Palici
were stained with the blood of human sacrifices. In Roman mythology
two very familiar deities are Pluto and Vulcan. These and a host of
other deities, the outcome of imagination, excited by displays of
seismic and volcanic activity, we meet with every day in picture
galleries, in museums, in literature, and in our daily papers.
Earthquakes have led to the abolition of oppressive taxation, the
abolition of masquerades, the closing of theatres, and even to the
alteration in fashions. A New England paper, of 1727, tells us that
"a considerable town in this province has been so far awakened by the
awful providence in the earthquake that the women have generally laid
aside their hooped petticoats."
In the next chapter we shall consider more particularly the terrible
effects of earthquakes on geological history.
CHAPTER XVI
VOLCANOES AND MOUNTAIN FORMATION
The great prominence which we have given in the preceding pages
to earthquakes is owing to the growing belief in the influence of
earthquakes on the appearance and structure of those portions of the
world's crust which are known to us. There are two views which we
can take of earthquakes. One is to regard the larger number of them
as being caused by slipping movements of the earth's crust. Looking
at things in this way we should say that whenever there was a sudden
break in the earth's strata, such as might occur (in accordance with
an illustration given in a previous chapter) if all the level strata
were broken up like a crumpled page of type--then that an earthquake
would result. So that whenever we saw what geologists call a "fault"
in strata we should know that an earthquake had occurred there. And
why did it occur? Well, if we had a massive column of steel or of
granite five miles high, the steel or granite at the bottom of the
column would have to sustain such an enormous weight of material
above it that it would begin to spread. If we had a pyramid of the
same materials five miles high, the tendency to spread would not be
so great, but still it would be there. Consequently, wherever there
are high mountains there is a tendency of the earth strata beneath
them to spread, perhaps slowly, but inevitably; and if there is any
weakness in the structure of the rocks near the base of the mountain,
then these will give way with a crash. A great "fault" will be
produced, and with it an earthquake.
People living on the earth will only see the results of the
earthquake on the ground just immediately below their feet; and there
these results are often very destructive to life and property; yet if
they were all that happened, we should expect them to be covered up
in time, and the "geological record" of an earthquake would not be a
very important or even discernible thing a million years after it had
happened. But are these things, which the eye of man can perceive,
the only things that are happening during an earthquake? Is nothing
happening underneath the earth which will leave its mark thousands of
years after man has left the spot where the earthquake took place?
May it not be that the earthquake is the outcome of some mighty
force deep down in the earth; and may not this force cause both the
earthquake and the geological "fault" which remains as the witness
of its occurrence? If this be the case then the earthquake may be of
enormous importance in geology.
We regard an earthquake, as we see it, as a destructive force.
That is because it destroys the works of man. But earthquakes are
doing constructive work as well; or, at any rate, they are usually
present when constructive work is being done. Destructive forces,
such as erosion, are wearing down the structure of the globe, while
earthquakes are the only known forces that are building it up. It
is true that when an earthquake occurs rocks often fall, loose
sediment is shaken down, and other settlements occur, but the real
constructive work consists in upheavals, little by little, as it may
be, of beaches, islands, coasts, plateaux, and perhaps larger areas.
These elevations are actually witnessed in certain earthquakes.
Many islands in the sea have been raised from time to time within
even living memory.
The south-western part of the island of Crete has been elevated
within the historical period.
The region about Pozzuoli and the Bay of Naples has suffered both
elevation and depression. There is the famous instance cited by
Sir Charles Lyell nearly eighty years ago of the Temple of Jupiter
Serapis. This temple had many columns; and they are now situated
on dry land. The pillars are forty-two feet in height, and for
twelve feet upwards they are of smooth undisfigured marble. Then for
another twelve feet they are pitted with the holes made by a marine
shell-fish called _Lithodomus_, the stone-dweller. What are we to
judge from this? The temple was first built on dry land. Then the
land sank taking the temple with it, and the columns were submerged
in sea sediment to a depth of some thirty feet above their pedestals.
The lower portions of these pedestals were preserved intact, but
the marine shell-fish found a home in the upper part of the marble
columns, and pierced them with the channels and grooves. After this
had gone on for a number of years the elevation of the land lifted
the temple and its columns clean out of the sea again, and the marine
shell-fish could no longer live in the columns. But the traces of
their habitation remain.
The elevation of this coast was actually witnessed at the time of the
eruption of Monte Nuovo in 1538. Moreover, the raising of the land
was perceived on a larger scale round the whole of the Bay of Naples
during the eruption of Vesuvius in April, 1706. Professor Lorenzo
found the elevation of the land at Pozzuoli to be six inches, and at
Portici one foot.[14] The foundations of both Etna and Vesuvius were
ages ago laid in the sea.
[Footnote 14: The coast about Pozzuoli is now sinking again.]
In almost every part of the world there are raised beaches, such as
we have already mentioned in the neighbourhood of Valparaiso, on the
Chilian coast. The idea has been put forward by Dr. T. J. See that
the same cause which produces earthquakes produces these elevations
of the land and produces also volcanoes. There are many circumstances
which favour this idea. Let us consider what is happening at the
bed of the sea. Some years ago, when certain officers of the United
States Navy were making ocean surveys, it was found that if hollow
balls of thick glass were sunk to great depths in the ocean, they
came up more and more completely filled with water in proportion as
the depth increased, though no breakage or cracking of the glass had
occurred, and no holes in it could be discovered even by the best
microscopes. In other words, it became evident that the water had
been slowly but bodily forced through the thick walls of the glass
(under a pressure of less than 15,000 lb. to the square inch) in less
than an hour's time. Evidently, then, even such a substance as glass
will be penetrated by water if the pressure is great enough.
To make a practical application of these principles, what shall
we now say with respect to the ocean bottoms? In deep places the
pressure of the sea-water on them is very great, sufficient to force
water through glass. Obviously most of these bottoms will leak, and
leak at a rapid rate under the enormous pressure operating in the
greatest depths of the sea. The bed of the ocean will not leak with
equal rapidity in all places; but almost universal leakage will
certainly develop, and the water will be driven back into the earth
at various rates. Where the rock is volcanic and badly fractured,
or sandy, the leakage will be most rapid; and where the bed is made
of clay or unbroken granite the leakage will be much more gradual.
It will also depend on the depth of the sea, and will be greatest
where the ocean is deepest, and quite insignificant in shallow
water. A rapid rate of leakage would mean that large quantities of
water quickly come in contact with the heated rock, and develop
correspondingly great steam pressure in the crust which underlies
that part of the ocean. One case in which we may suppose a rapid
leakage to be taking place is in the case of volcanoes near the
sea. In the case of lava pouring from a volcano, it is observed that
the molten rock emits vast quantities of vapour, of which, according
to Sir Archibald Geikie, 999 parts in 1000 are steam. The enormous
volume of these has been brought home to us in recent years by the
behaviour of the volcano Mount Pelée, from which for several years
after the great eruption which devastated Port au Prince the vapours
rose in clouds that were to be measured in cubic miles. Similar
observations about the quantities of vapour ejected by volcanoes have
been made in Japan.
While speaking of Mount Pelée we may recall another phenomenon
connected with it, which also appears to bear out the supposition
that in the volcano's activity the action of steam takes a very
large share. After its first outburst Mount Pelée continued to pour
out lava and great quantities of vapour, as if like some gigantic
cauldron it were being fed with fresh supplies of water; and there
in the early March of the following year a most amazing thing took
place, under the very eyes of a celebrated investigator of volcanoes,
now dead, Professor Angelo Heilprin, who was remaining on the island.
A great obelisk of andesite (a stone not unlike basalt) was forced
up from the crater. It rose rapidly, as much as five feet a day; and
it reached altogether a height of 840 feet above the crater's lip.
It was calculated to be about 300 feet in diameter at its base. It
continued to push itself up for some months, sometimes sinking a
little, sometimes rising like a colossal piston above a steam boiler.
Its greatest height was 1100 feet above the height of Mount Pelée,
and therefore at a height of 5143 feet above the sea-level.
[Illustration: The New Spine of Mont Pelée, showing Fissures and
Vertical Grooves
Photographed on March 15th, 1903. The spine was then 82 feet lower
than it became ten days later.]
[Illustration: The New Spine of Mont Pelée, viewed from the Basin of
the Lac des Palmistes
The apex, 1174 feet above the rim directly in front; the remains of
Morne la Croix on the edge of the crater at the right.]
A violent eruption would reduce its mass and its steeple-like
pinnacle; but after its losses it generally pushed up again.
Professor Heilprin at last got near enough to observe it, and the
obelisk was found to be not of pumice stone, as had at first been
suspected, but of the hard rock we have mentioned. It had, in fact,
been comparable to a Titanic cork of rock which had closed up some
vent far down in the crust of the earth, and which had at last been
lifted by the steam pressure beneath it. It finally sank back into
the crater, but it was replaced by a dome of rock which underwent
similar changes in height, though on a smaller scale, to those of
the obelisk. The dome of rock was, however, on a more massive scale
even than the obelisk, and at one period of its career a spine, 100
feet in height, like a smaller obelisk, was pushed up through its
middle. This dome was examined by the explorers, the Abbé Yvon and M.
Beaufroy, who found that the dome was a great mass of andesite, while
about it were fragments of the rock of which the obelisk had been
composed. They wrote at the time:--
"It is an error to suppose that there exists in the bottom of Mount
Pelée a hole from which lava and gases have come out. At present
there is a tremendous cork of andesite, which is called the 'Dome,'
and which must have as its dimensions a diameter half a mile across
at its base and a height of about 1200 feet. On all sides of the dome
there are fumaroles (small cone-like craters), some of which throw
out a reddish smoke, others of which discharge white smoke, and
others are still surrounded with a carpet of sulphur several yards in
depth."
After the great eruption of Mount Pelée in 1902 it was found by
measurement that a considerable portion of the adjacent sea bottom
had sunk down many fathoms. It is impossible to believe that this
sinking had been caused by the mere shaking of the earthquakes
accompanying that eruption. We must, therefore, suppose that after
the dreadful explosions which destroyed St. Pierre and devastated
Martinique a subsidence near the roots of the mountain (which is just
by the sea) took place. What we should judge to have happened is that
by some means an explosion took place below the sea bottom; that
parts of the molten rock, moved by the forces of the explosion, were
moved towards the mountain (Mount Pelée), which thereupon broke into
eruption, acting as an outlet for the imprisoned rocks. When these
molten rocks were thus removed a great cavity was formed in the bed
of the sea, which accordingly caved in.
A similar explanation would account for the raising of the Chilian
coast-line after the great earthquakes of 1835, of which we have
already spoken. The coast and, indeed, the whole country back to
the Andes was slightly raised. This could only be explained by the
pushing in or forcing in of a corresponding bulk of lava under the
land; and this lava could come from nowhere except from under the
bed of the great trough in the adjacent sea. After an explosion
(which is caused by the sea penetrating through to the molten rocks)
the trough, where the "accident" first took place, would naturally
deepen.
[Illustration:
_Stereo Copyright, Underwood & U._ _London and New York_
The Dead City of St. Pierre, Martinique
The town of St. Pierre was perhaps the most beautiful in the West
Indies. The volcano of Mont Pelée, which is seen in the background,
and which is five miles away, suddenly belched out deadly gases,
dust, steam, and boiling mud, which overwhelmed the town and
completely destroyed it. The houses were reduced to ruins, and the
people were killed by the wave of hot gases sweeping down from the
volcano.]
Moreover, if we suppose that after a time the water again penetrates,
and again comes into contact with rocks that have again become heated
up, there will be another explosion, and yet others. Each of these
explosions will push along the ejected streams of lava, step by step,
till they reach the land, and even till they reach the mountains
bordering the sea. The forces thus arising would cause upheavals,
even if they did not cause earthquakes. Such forces might bend
strata, contort the rocks, and cause "faults."
But why, the reader may ask, do you suppose that all these explosions
of lava are directed to the land? We do not suppose that they are.
The lava may be forced away from the land. Then if that occurs a
ridge may be upheaved, or possibly a submarine volcano.
"At the Hawaii Islands on 25th February, 1877," writes Sir Archibald
Geikie, "masses of pumice during a submarine volcanic explosion were
ejected to the surface, one of which struck the bottom of the boat
with considerable violence and then floated. At the same time, when
we reflect to what a considerable extent the bottom of the great
ocean basin is dotted over with volcanic cones, rising often solitary
from profound depths, we can understand how large a proportion of
the actual eruptions may take place under the sea. The foundations
of these volcanic islands doubtless consist of submarine lavas and
fragmentary materials, which in each case continue to accumulate to
a height of two or three miles, till the pile reaches the surface
of the water and appears above it. The immense abundance and wide
diffusion of volcanic ash, pumice, etc., over the bottom of the
Pacific and Atlantic oceans, even at distances remote from land, as
has been made known by the voyage of the _Challenger_, may indicate
the prevalence and persistence of submarine volcanic action."
It is fairly clear, therefore, that the sea bottom is leaky, and that
volcanoes which are a consequence of it are scattered freely over
the deep ocean floor. In some places, of course, very few eruptions
occur, either because the underlying rocks are less leaky or the sea
is too shallow for pressure.
We have pictured the water of the oceans thus sinking down into the
hot rocks. It will not always cause an explosion at once. The steam
may not immediately become free, but will become absorbed in the
hot rocks till the lava grows so fully saturated by the hot vapour
that it swells and requires more space. When the tension becomes
great enough the crust begins to shake and the paroxysm continues
till the steam-saturated lava moves along the nearest break or
"fault" or vent. When the underlying molten rock has thus obtained
more space the agitation ceases till the tension again becomes too
powerful for the crust to withstand, when another readjustment takes
place. A familiar illustration of this process is seen in the lid
of a tea-kettle when the steam pressure accumulates till it sets
the lid quivering. As the steam escapes at the sides the agitation
slowly dies down and the lid then remains quiet till the accumulating
pressure again requires relief, when the shaking is renewed. Thus the
process is periodic, and the period depends on the rapidity with
which the steam is developed. In the case of earthquakes, as already
remarked, the steam is not free, but absorbed in the molten rock,
and when the agitation begins this gives a similar quivering motion
to the block of the earth's crust overlying it, and ceases only when
readjustment occurs--usually by the neighbouring "fault" slipping in
some way so as to give more space to the swelling lava beneath. Of
course, many of the cracks caused by this swelling are never seen;
and the molten lava seldom reaches the surface except when through
volcano vents or cracks in mountains that are near the sea-shore; but
such outbreaks are probably more common in the deep sea.
To see how effective the pressure arising from the depths of the
ocean may be in driving water into the crust of the earth, we may
observe that the tendency to penetrate is everywhere proportional to
the depth of the sea. Now everybody knows that if a cistern be placed
at the top of a house and connected with a fountain in the garden the
fountain ought to throw a jet as high as the cistern because water,
as the saying goes, always rises to its own level. As a matter of
practice the water does not rise so high because of the resistance of
the air. But for theoretical purposes we may consider the proportion
true, and we might similarly say that the pressure in a sea one
mile deep would thus throw a stream a mile high; in a sea two miles
deep, two miles high; and so on. Now some of the ocean depths exceed
five miles, the greatest, near Guam, being 5269 fathoms, almost
exactly six miles. Is it therefore any wonder that the deeps east
of Japan, near the Aleutian Island, west of South America, near
Guam, between Samoa and New Zealand, give rise to enormous leakage of
the sea bottom, and consequently many world-shaking earthquakes? A
comparatively feeble pressure of water, such as hydraulic engineers
use in mining, rapidly cuts away hills and washes out all their gold;
in the same way the waters of Niagara, falling through only 160 feet,
slowly wear away the solid rock over which they pour. What, then, may
be expected of a constant water pressure which will throw a jet five
miles high? Such is the pressure all over the bed of the Tuscarora
Deep, and it continues from year to year, century to century. It is
this pressure which forces the water so rapidly into the earth, and
gives rise to all the great earthquakes and sea-waves with which
Japan is afflicted. No stone on earth, however thick its layers,
could withstand such a pressure; nay, under it the water would go
through the hardest metals, and sink down deeper and deeper into the
bowels of the earth. Thus subterranean steam would arise beneath the
crust and accumulate till relief was afforded by a shaking of the
earth.
Thus we see how immensely important the same causes that give rise
to earthquakes may be in moulding the outlines and contours of the
rocks and the "everlasting hills." In the present state of geological
knowledge we cannot say that these steam explosions are the sole
causes of mountain building, but it is evident that they must play
a great part in them. The action of the submarine explosions may
be compared to a man digging out a trench. As he digs along the
trench, the earth that he excavates he throws on to either side of
the trench, so that a ridge appears on each side of the excavation.
The result is the same in the case of the continuous lava explosions
in deep seas, especially in those deep seas like the waters off the
west coast of South America, where a great range of mountains runs
parallel to an ocean that is of great depth only a short distance
from the land. A trough or trench is cut downwards by successive
explosions and expulsions of lava. As the trough is arched downwards
like a broad letter =U=, the steam pressure from beneath cannot
easily force it upwards. What will therefore happen? Imagine what
would happen in a steam saucepan or kettle if the vapour could
not get out at the top or lid. It would tend to blow out at the
sides. Or if you think of a slab of dough rising under the effect
of yeast. Suppose the baker presses a flat board on the top of the
rising dough, and presses down on it so that it cannot force its way
upwards. It will then naturally spread out to the sides. Similarly
the rising yeasty lava under the curved ocean bed has to force its
way sideways under the crust. It forces its way partly towards the
land--where the mountains run along the coast as in the case of the
Andes--or farther out underneath the ocean. Generally the movement
of the lava will be towards the mountains till the trough gets broad
and deep and the mountains very far away, and so high that their
weight offers unexpectedly great resistance to the underground stream
of lava. Then the release will at length become easier towards the
ocean by the forcing up of ridges or volcanoes along the other margin
of the trough. Ridges with peaks in them will usually result, and
this is the beginning of a new range of mountains in the sea, which
are destined to rise slowly from it parallel to the great range
of mountains on the shore. There may thus be two parallel ridges,
perhaps hundreds of miles apart, with a valley between them. This
valley may be drained in the course of ages, or filled in by the
processes of erosion which we have described in the earliest chapters
of this volume.
It will be of interest to quote at this point what Pliny nearly two
thousand years ago said in his _Natural History_ (Book II) on islands
which have been uplifted from the Mediterranean, evidently as the
result of volcanic causes:--
"Land is sometimes formed in a different manner, rising suddenly out
of the sea, as if nature was compensating the earth for its losses,
restoring in one place what she had swallowed up in another. Delos
and Rhodes, islands which have now been long famous, are recorded
to have risen up in this way. More lately there have been some
smaller islands formed: Anapha, which is beyond Melos; Nea, between
Lemnos and the Hellespont; Halone, between Lebedos and Teos; Thera
and Therasia, among the Cyclades, in the fourth year of the 135th
Olympiad. And among the same islands, 130 years afterwards, Hiera,
also called Automate, made its appearance; also Thia, at the distance
of two stadia from the former, 110 years afterwards, in our own
times, when M. Junius Silanus and L. Balbus were consuls, on the 8th
of the Ides of July.
"Opposite to us, and near to Italy, among the Æolian Isles, an island
emerged from the sea; and likewise one near Crete, 2500 paces in
extent, and with warm springs in it; another made its appearance in
the third year of the 163rd Olympiad, in the Tuscan Gulf, burning
with a violent explosion. There is a tradition, too, that a great
number of fishes were floating about the spot, and that those who
employed them for food immediately expired. It is said that the
Pithecusan Isles rose up in the same way in the Bay of Campania, and
that shortly afterwards the mountain Epopos, from which flame had
suddenly burst forth, was reduced to the level of the neighbouring
plain. In the same island it is said that a town was sunk in the sea;
that, in consequence of another shock, a lake burst out, and that,
by a third, Prochytas was formed into an island, the neighbouring
mountains being rolled away from it."
There are, no doubt, other causes which warp and bend strata. We have
compared the earth to the core of a tightly wound golf ball--always
in a state of strain. The strain at great depths below the surface
might amount to several tons to the square inch, and it can easily
be understood that breaks might occur in consequence, especially if
some slight additional shock set the rocks into vibration. In the
deep copper mines of the northern peninsula of Michigan the behaviour
of the whole earth, with respect to earthquakes and stresses due
to other causes, is well illustrated on a small scale. At certain
times during each day blasts are set off in the solid rock at
various places in each mine. Each battery of blasts is a miniature
earthquake. In that particular spot, the earthquake centre, the rock
is fractured within a space limited by a radius of a few feet. Within
a large space, limited by a radius of a few hundred feet, elastic
vibrations are set up in the solid rock which are sufficiently
violent to be perceptible to the touch and to the hearing. Within
this larger space no fracture of the rock occurs. Feebler vibrations
doubtless extend out for miles from the point of fracture, just as
vibrations extend over the whole earth from an earthquake centre.
Now it also happens that in the lower levels of these deep mines,
at a mile below the surface of the earth, the solid rock is slowly
yielding, in a non-elastic manner, under the influence of the great
weight above it, so that the larger openings are gradually closing
up. This is so clearly recognised and progresses so rapidly that
it is proposed as routine practice, at the deep levels in these
mines, to take out the ore at the distant end of each drift first.
The miners will then work back slowly toward the shaft from which
the drift is entered, while the spaces in which they have recently
laboured gradually close up behind them. The gradual collapse known
to be in progress occurs apparently by imperceptible flow and by
minor fracturing, but not, as a rule, by catastrophes which close up
any opening suddenly. In this respect it is an epitome of what is
taking place every year in the failing earth as it yields under such
stresses.
There may be local tremors due to causes which are less immense and
world-wide. One such cause might be the collapse of cavities in the
earth. We are well acquainted with some such caves near the surface
of the earth. These caves, especially in limestone, are commonly
caused by the action of springs. Even pure water will dissolve a
minute quantity of the substance of many rocks, and rain water is far
from being chemically pure water. It takes oxygen and carbonic acid
out of the air as it falls, and it abstracts acids out of the soil
through which it sinks. The presence of this acid gives the water a
greatly increased power of attacking carbonate of lime. Now limestone
is a rock almost entirely composed of carbonate of lime. It occurs
in most parts of the world, covering sometimes tracts of hundreds
or thousands of square miles, and often rising into groups of hills
and ranges of mountains. The abundance of this rock offers ample
opportunity for the display of the dissolving action of subterranean
water. The water trickles down the vertical fissures along the planes
below the limestone beds. As it flows on it dissolves and removes the
stone till in the course of centuries these passages are gradually
enlarged into clefts, tunnels, and caverns. The ground becomes
honeycombed with dark subterranean chambers, and running streams fall
into these chambers and continue their course underground.
In England there are famous "pot-hole" caverns in Yorkshire and the
west of England. The Peak Cavern in Derbyshire is believed to be
1200 feet long, and in some places 120 feet high. The caverns of
Adelsberg near Trieste have been explored to a distance of several
miles. The River Poik has broken into one part of the labyrinth of
chambers through which it rushes before emerging again to the light.
"Narrow tunnels," says Sir Archibald Geikie, "expand into spacious
halls, beyond which egress is again afforded by low passages into
other lofty recesses. The most stupendous chamber measures 669 feet
in length, 630 feet in breadth, and 111 feet in height. From the roof
hang white stalactites which uniting with the floor form pillars
showing endless varieties of form and size." Still more gigantic is
the system of subterranean passages in the Mammoth Cave of Kentucky,
the accessible parts of which are believed to have a combined length
of about 150 miles. The caverns of Luray, in Virginia, are scarcely
less wonderful; and in their case American ingenuity has hit on the
idea of sucking the pure, dustless air out of these caverns in order
to ventilate a sanatorium. Indeed, a book might easily be written
on the wonders of the limestone caverns of the world, but our only
purpose in mentioning them in this chapter is to indicate how the
rocks of the earth may be made unstable, so that a slight shock may
precipitate a catastrophe in them--a kind of subterranean landslip
which in its turn may give rise to some of the symptoms of earth
tremors.
[Illustration: A Yorkshire Pot-Hole: showing the Effects which can be
Produced in Limestone by Underground Water
The immense depth may be better realised by comparing the pot-hole
with the Nelson Monument, which is 162 feet in height.]
CHAPTER XVII
FAMILIES OF ROCKS AND THEIR DESCENDANTS
Thus far, in accordance with the principles of the great geologists
from Sir Charles Lyell onwards, we have tried to disclose the
history of the earth's crust by observing the processes which are
going on to-day under our eyes. That is not, however, the only way
in which history has to be written. The documents on which history
rests are often lamentably incomplete. The records have great
gaps in them, and very often the gaps have to be filled by that
exercise of the imagination which Bishop Creighton once described
as the rearrangement of facts. We shall later in this book show
how naturalists can reconstruct the skeleton and even the general
appearance of an animal which for ages has not been seen alive on
the earth, from a consideration of fragments of the bony structure.
Similarly the archæologists who inquire into the history of forgotten
peoples can picture to us their lives and habits and manners from a
consideration of the fragmentary weapons and pottery and architecture
which they left in their buried cities; and similarly the geologist,
knowing, or partly knowing, how the forces of nature are at work
to-day, can attempt to describe the conditions under which rocks were
laid down before man ever trod them.
In speaking or writing of the earliest stages of the world's history
we have to adopt what seems to be the most likely history, modestly
qualifying what we say by adding that these speculations are only
the fruits of an inquiry that man has pushed beyond the ascertained
facts. But we are on firmer footing when we come to deal with that
portion of the globe which we can examine. The crust of the earth
has been found to consist of successive layers of rock which, though
far from constant in their occurrence, and though often broken and
crumpled by subsequent disturbances, have been recognised over a
large portion of the globe. They are the earth's own chronicle of its
history. Had these rocks of the Geological Record remained in their
original positions we should have known little of them, because only
the most recent would have been visible. Owing, however, to the way
in which the earth's crust has been twisted and cracked and broken,
portions of the bottom layers have been pushed up to the surface,
and the lower rocks have been inclined so that we can examine their
upturned edges. Instead, therefore, of being restricted to examining
a few hundred feet of earth crust we can examine many thousand
feet. The total thickness of the rocks of Europe which contain
fossil remains has been estimated at 75,000 feet, or fourteen miles.
This vast depth of rock has been laid open to our observation by
disturbances, twists, contortions, upsettings of the crust.
We shall not press on the reader in a volume of this kind any
detailed classification of the strata, but he will like to know the
names of the five great periods into which geologic time is divided.
The first period was the Archæan, embracing the periods of the
earliest rocks wherein few or no traces of life occur.
The second period was the Palæozoic (ancient life) or Primary, which
includes the long succession of ages during which the earliest types
of life existed.
The third period was the Mesozoic (middle life), comprising a series
of ages when more advanced types of life flourished.
The fourth period was the Cainozoic (recent life) or Tertiary period,
when such types of life as we know and see now appeared. This period,
however, does not include man.
The fifth period is the Quaternary or Post-Tertiary and Recent, and
includes the time since man appeared on the earth.
These divisions were not of the same length. The Palæozoic ages were
probably far, far longer than those of any other division, while
the Quaternary period is shorter than any of those which preceded
it. Each of these main divisions is divided further into systems or
shorter periods (just as the dynasties of ancient Egypt could be
subdivided into reigns). Though the broad outlines of the sequence
of the living things which existed in those periods has been the
same all over the world, many local differences may be traced in the
nature and grouping of the sedimentary materials in which the remains
of the living things of these epochs have been preserved.
To find the oldest rocks, we must seek those which lie at the bottom
or underneath all the others. Judged by this test, the oldest
rocks in Great Britain are certain hard rocks (like gneiss, or the
material of which volcanic veins are composed) which crop out in the
north-west of Scotland, and which form the outer Hebrides. They are
also known in Anglesea, and in the extreme west of Wales, at St.
David's. Similar strata form the Malvern Hills of Worcestershire,
the Longmynd Hills, Caer Caradoc and the Wrekin Hills of Shropshire,
and the hilly district of Charnwood Forest in Leicestershire. For a
long time the Cambrian rocks of Wales, so called from North Wales's
ancient name of Cambria, were believed to be the oldest on the face
of the earth. Up to the year 1830 even these rocks had no name or
recognition, for geologists believed that it was impossible to
classify them. But in 1831 Professor Adam Sedgwick, of Cambridge,
began the diligent study of the rocks in North Wales, and after five
years' work he was able to announce in 1836 that he had determined
the general order of succession in that district of a certain ancient
group of slaty, gritty, and flaggy strata. However, eighteen years
later, in 1854, Sir William Logan, who was then engaged in mapping
the rocks of Canada, found along the River St. Lawrence an enormous
thickness (30,000 feet or more) of gneiss, quartzite, schist,[15]
limestone, etc., these rocks underlying--and being, therefore, older
than--the Cambrian strata, which are also well developed in that
country. To these "bottom" rocks Logan gave the name of Laurentian.
For some time afterwards the same name was also applied to the
somewhat similar rocks which were found to underlie the Cambrian
formation in Britain, but it was felt safer to give the English
rocks a more general name. They are therefore now usually called
Pre-Cambrian, which simply means older than the Cambrian strata, or
Archæan.
[Footnote 15: Hard rocks are sometimes composed of different
minerals, which are arranged in a way that reminds us of a bed
of fallen leaves, and are called "foliated," from the Latin word
_folium_, a leaf. Gneiss is a good example of a foliated rock. It is
composed of the three minerals, quartz, felspar, and mica, arranged
in this foliated manner. Mica schist, talc schist, and other rocks
have a similar structure, and are sometimes briefly called "schists."]
In Canada the total thickness of the Laurentian, Pre-Cambrian,
or Archæan rocks is now estimated at 50,000 feet. In Britain it
is nothing like so great as this (though still considerable);
but the thickness of these extremely old and altered rocks is a
very difficult matter to determine, for all signs of the original
stratification in them have often been destroyed, and the rocks have
been so bent and folded that it is possible the same beds may have
been measured more than once in the same section.
It will be understood from some of the foregoing sentences that the
task of dating or classifying these early rocks is one which is far
from simple, and which has given rise to many different opinions. We
may here give another example. "During the years between 1831 and
while Sedgwick was occupied in studying the rocks of North Wales,"
writes Mr. W. Jerome Harrison, "another geologist, Mr. (afterwards
Sir) Roderick Murchison, was engaged in the examination of the
strata which occupy the south-east of Wales and the adjoining border
counties of England. To these rocks Murchison gave, in 1835, the
name of Silurian, from the ancient British tribe of the Silures, who
inhabited that part of the country when the Romans invaded Britain."
Later in last century, in order to distinguish more clearly the
periods of the rocks which began or ended in these areas, the name
of another ancient British tribe was called into requisition--the
Ordovics; and thus for certain strata which were neither Silurian nor
Cambrian Professor Lapworth proposed the name Ordovician.
Let us, however, now leave these geological controversies,
enthralling as they are to those who have taken part in them, to
consider briefly what was the aspect of the earth during the ages
when these rocks were being laid down. The earliest rocks do not
generally contain fossils, though there is no doubt that life existed
during the later part of the time when they were laid down. The
few fossils that have been preserved are those of crustacea (the
species from which shrimps, for example, are derived), and there are
certain tracks of two kinds of burrowing worms. It is noticeable
that crustacea, the oldest definite fossils yet found, belong to a
family which is well up in the animal kingdom, and therefore we know
that lower forms of life must have been long in existence. Since we
can only draw conclusions of the climate of a period from its fossil
remains, and as these fossil remains are so scarce, we cannot say
really anything of value about the world's climate in the earliest
eras.
When we come to the Cambrian, however, we are on firmer ground. In
the Cambrian rocks there is, for the first time, a fair preservation
in fossil form of the life of the period. Even here the record is far
from complete, but it is an immeasurable advance on the records of
previous periods. The most striking thing about this comparatively
plentiful appearance of life is that while the animal kingdom is
fairly well represented the plant remains are hardly to be recognised
at all. Yet there must have been plants if only to feed the animals,
and we have very good reasons for believing that the surface of the
land was clothed with some form of vegetation. Not a few of the
Cambrian animals were fixed to the bottom of the sea, and therefore
there must have been enough matter of some organic kind floating
in the water to bring them their daily food. Possibly many of the
plants were of the minute kind which forms scum on rivers and ponds,
and so would not readily leave fossil impressions. Turning to the
record of animal life, it appears that nearly every division of
the animal kingdom, except such as had backbones, had some kind of
a representative in Cambrian times. Crustaceans, molluscs, worms,
corals, jelly fish, sponges, quite a large variety of sea-animals,
suddenly make their appearance, and although no traces of land
animals have yet been found, we have reason to believe that some land
animals may have existed. Our reason is that in the next era but one
(Silurian) scorpions and insects appear, and these are such highly
developed forms of land-life that they probably had some primitive
ancestors in the Cambrian. No real fish have been found in the
Cambrian rocks, but they appeared in the next era (Ordovician). It
is the trilobite which is the characteristic animal of the Cambrian
times. They were crustaceans; they had eyes; and they gave the
promise of development; but there is no reason for believing that
they were as high in the order of creation as the commonest lobster
of the sea-shore. Nothing remains to us of them except their bony
structure, but we believe that they could both swim and walk on the
sea-bottom; that some were swift of movement, and that they acquired
the habit of moulting their shell. They may have been sociable
animals, for the shells of trilobites are sometimes found together
in large numbers, occasionally closely packed, "spoon fashion," and
though these may be moulted shells, we are warranted in supposing
that the early trilobites lived in colonies, hunted for food, and
made war like their descendants millions of years after. What were
the actual conditions of life in this world of Cambrian days we
do not know positively. The first beginnings of life, the simple
one-celled plants, may have first dwelt in the deep ocean. The land
was barren, its lakes unfitted to support life. On the other hand, it
is equally likely that the first beginnings of life may have been the
simple plants growing in inland waters and gradually spreading down
to the sea. We do not know, but it is most probable that life began
in some great body of water, where plants and insignificant animals
grew together, perhaps fought together, and certainly in this
environment became more and more fitted for the business of living.
In Mr. Henry R. Knipe's scholarly and well-informed volume, _Nebula
to Man_ (J. M. Dent & Co.), to which we are indebted not only
for several of our illustrations but for many extremely valuable
suggestions, the struggle for existence in the early ocean is well
summed up:--
Thus through the brine life manifold proceeds,
Impelled to higher states by growing needs;
And all these early life-types in the seas
Will branch in time to many species;
And some amid conditions too severe,
Must, after stress and struggle, disappear.
And when a species falls from Life's domain
It never gains a place on Earth again.
We may speculate with some approach to certainty on the general
appearance of the earth in those days. There was far more water
on the surface of the globe; the land surfaces were small and
infrequent. The seas may have been shallower than those which we
know, but they were far greater in extent. There must have been far
more rain and a very much greater number of violent storms arising
from the constant condensation of the waters by the rays of the sun.
The sun was probably seen far less often in those days, and there
are some geologists who believe the earth to have been perpetually
covered with cloud, as the planet Venus is now.
Europe as a continent did not exist. A few islands showed their heads
above the waves where Germany and Switzerland, Eastern France and
Spain now stand. Scotland's rocky islets were probably visible, on
the extreme west, though these islands were destined to sink again
below the waves. Thence the ocean stretched without a break, as at
present, to Canada. A great part of Canada's bleak lands was above
the waters; but the United States, except for a few great islands,
were submerged. In the southern hemisphere South America, split into
numerous long reefs and islands, gave promise of the continent to
be; and there were great stretches of land over Brazil, extending
to the west where the great chains of mountains now rise. Asia was
largely covered with shallow waters, and the whole extent of the
northern plains of Africa was sea. So far as we are able to judge
the distinctions of climates were less marked then than now, and
the conditions seem to have been much more uniform over all the
northern hemisphere. This equality of climate lasted into the next or
Ordovician period.
The Ordovician period glides insensibly into the Cambrian. There was
no distinct break in the succession of life. The species seem to have
slowly extended and developed from one of these great periods into
another. But the life of the Ordovician era, which has been preserved
for us, is much more abundant. Land was beginning to emerge from
the sea in greater bulk; life was springing up on the land and was
emerging from the sea, perhaps to take up its habitation there. The
first insect life appears in the Ordovician. It is not an imposing
relic except when seen through the eye of imagination. It is just an
obscure wing of an insect which was found impressed on some shales
found in the upper Ordovician rocks of Sweden, and all we can say of
it is that it belonged to the same class of insects as lady-birds.
The existence of this insect shows that there must have been land
vegetation and an atmosphere which was suited to active air-breathing
things. The other appearance of great interest in the Ordovician
rocks is that of the first fish. They were found in Colorado, but
they are very much shattered and tell us very little about the
animals they represent. These fish were covered with plates, and were
evidently thus defended against attack, so that we may surmise the
existence of some other animal that preyed on fishes. Whether these
fishes were themselves ferocious we cannot, however, say. But that
which was the chief characteristic of the Ordovician era was the
climax of the trilobite. More than half of all the known trilobites
were present in Ordovician times. Only a few of these came over from
the Cambrian, while the others make their first appearance in this
period. In the next period (Silurian) their numbers fell to one half,
and in later periods declined still further, till they disappeared
altogether at the close of the Palæozoic era. Some of these curious
animals appear to have been able to move very quickly; others would
roll themselves up like hedgehogs to defend themselves against
attack; and some of the larger ones were from eighteen inches to
two feet in length. Next to these in interest were the cephalopod
types, marine animals, that may have resembled the swimming nautilus
of to-day in some of their developments. They attained to enormous
sizes, some of the shells being twelve to fifteen feet in length and
a foot in greatest diameter. From this maximum they ranged down to
forms smaller than a pipe-stem. Their habits are to be gathered only
from their structure and from the habits of their relations in the
present seas. Perhaps they floated, shell uppermost, or crawled upon
the bottom and preyed on a variety of the weaker forms of life. There
appear to have been fewer worms, perhaps because the muddy and chalky
sea bottoms of the Ordovician period were less congenial to them than
the Cambrian sands.
The changes in the structure of the earth's crust which brought
the Ordovician period to an end marked also the beginning of the
Silurian period. These changes affected sometimes small areas
and were very intense; sometimes they affected larger areas more
slightly. It must not be assumed, however, that these changes were
necessarily sudden or violent. In examining the rocks now, we see
merely the effects, and of these effects it is the more remarkable
alone which have survived the march of ages. There was more water on
the earth's surface then than now; and side by side with continuous
storms of tropical violence, it is extremely likely that volcanoes
and earthquake movements were more frequent and more considerable
in their effects. The tide of movement by material things may have
been faster; and certain it is that the land was now lifting itself
up above the shallow seas. Mountains were being built along the
coast-lines; behind the coast-lines the continents were shouldering
their way upwards in large land areas. North America began to show
in this period the first signs of becoming a continent; Europe's
countries, or some of them, assumed a distinct existence. With the
advent of mountains came streams and rivers; and the streams, fed
by the abundant rainfalls, rushed down to the seas in torrents that
performed the work of erosion with a rapidity perhaps unequalled by
even the greatest rivers of our present-day knowledge--though at
first the land areas were not large enough to give rise to streams
as long as great rivers like the Amazon or Mississippi. We cannot
say exactly what the areas and localities of the water and the land
were; but it is safe to assume that at the beginning of the Silurian
period beds of sediment brought down by the rivers and the rain
were accumulating about the borders of the land, and as far out as
the waves and currents were able to convey the earth materials. The
climate was still equable and was much the same over great areas of
the world's surface, for the forests of warm temperate latitude are,
in part, the same as those in Arctic regions. Certain parts of the
land appear to have been desert.
Life began to change a great deal in Silurian times. The extensive
withdrawal of the sea from great stretches of submerged surface
reduced the area of shallow water available for the forms of life
that had so richly peopled it during the Ordovician period. Then
there came an age during which the sea invaded some of the regions
of the earth's crust, and again withdrew, leaving behind it great
stretches of water which gradually grew more intensely salt. All
these things had naturally a great effect on the development of the
plants and animals of Silurian times. We cannot in a brief summary
of this kind do more than indicate some of the more conspicuous
features. Corals began to spread through the clearer seas: and reef
building on a great scale took place, generally some distance from
the shores of the land. Other life in great abundance and variety
gathered upon or about these reefs, and they became rich depositories
of the animals of their day. The Crinoids, which, though animals,
are sometimes called the lilies of the sea, developed strongly;
sea urchins appeared, and forms akin to barnacles. The ancestors
of the pearl oyster and the mussel date from Silurian times; and
so do the first Ammonites, those creatures known to the youngest
collectors of fossils, and deriving their names from the Canaanitish
god Ammon, which had a ram's head. Sea scorpions, sand fleas, king
crabs, sea squirts, and worms and fishes of various kinds haunted
the Silurian seas. The Silurian fish were most of them armed for
defence, some with plates of bone; some of them had their tails
stiffly joined to their backbones; some had skin like a prickly
pear; some were not unlike the modern shark. The plants have left
us many records--liverworts, ferns, and club-like mosses. The
growing vegetation gave a new impulse to insect life--plant-lice
and cockchafers and the scorpions we have named: and the vastness
of their numbers is shown by the fact that they have outlasted the
changes and vicissitudes of a myriad generations.
We may conclude this chapter by saying what we imagine of the general
appearance of our own islands to have been. At the close of the
Silurian period Britain was probably an archipelago, ranging over
ten degrees of latitude, like many of the island groups now found
in the great Pacific Ocean; the old gneissic hills of the western
coast of Scotland, culminating in the granite range of Ben Nevis,
and stretching to the Southern Grampians, forming the nucleus of
one island group; the South Highlands of Scotland, ranging from
the Lammermuir Hills, another; the Pennine chain and the Malvern
Hills, the third and most easterly group; the Shropshire and Welsh
mountains, a fourth; and Devon and Cornwall stretching far to the
south and west. Every spot of the island lying now at a lower
elevation than 800 feet above the sea was under water at the close of
the Silurian period, except in those instances where depression by
subsidence has since occurred.
CHAPTER XVIII
HOW THE COAL BEDS WERE LAID DOWN
In following the history of the rocks, we shall have presently to
speak of that period which embraces the strata which contain coal.
The geologists who lived in the early part of last century--William
Smith and others--noticed that beneath the coal-bearing strata
there lay a considerable thickness of red sandy beds containing the
remains of fresh-water fishes, shells, and plants, while above the
coaly strata they found another thick mass of red sandstone. To the
lower and older red rocks they consequently gave the name of Old Red
Sandstone, and to the upper and newer ones the name of the New Red
Sandstone. The Old Red Sandstone formation, therefore, lies between
the Silurian rocks below and the rocks of the coal period above. But
in Devonshire we find a considerable thickness of shales, slates, and
limestones containing _marine_ fossils, and these also lie between
these two formations, and must therefore be somewhere about the
same period, or geological age, as the Old Red Sandstone. The name
"Devonian" has therefore been given to these shales, slates, and
limestones, which were evidently being deposited in an open sea at
or about the same time at which the Old Red Sandstone strata were
being laid down on the floors of inland fresh-water lakes.
In the west of England the Old Red Sandstone stretches from Hereford
and Monmouth into the neighbouring Welsh counties of Brecknock
and Glamorgan. It is here at its greatest thickness of nearly two
miles. The lower part consists of red and yellow sandstones, marls,
and shales, with a certain kind of limestone concrete. The red
colour is due to iron, and wherever this is abundant fossils are
scarce, though remains of fishes have been found in it. Scotland
is the classic ground of the Old Red Sandstone, for it was here
that Hugh Miller, when a working mason at Cromarty, first collected
its wonderful fossil fishes. Hugh Miller's discovery is one of the
romances of geological annals. "Let any one picture to himself,"
wrote the late Mr. Bristow, "the surprise he would feel should he, on
taking his first lesson in geology, and on first breaking a stone--a
pebble, for instance, exhibiting every external sign of a water-worn
surface--find, to appropriate Archdeacon Paley's illustration, a
watch, or any other delicate piece of mechanism, in its centre.
Now this, many years ago, is exactly the kind of surprise that
Hugh Miller experienced in the sandstone quarry opened in a lofty
wall of cliff overhanging the northern shore of the Moray Frith.
He had picked up a nodular mass of blue Lias limestone, which he
laid open by a stroke of the hammer, when, behold! an exquisitely
shaped Ammonite was displayed before him. It is no surprising that
henceforth the half mason, half sailor, and poet, became a geologist.
He sought for information, and found it; he found that the rocks
among which he laboured swarmed with the relics of a former age. He
pursued his investigations, and found, while working in this zone
of strata all around the coast, that a certain class of fossils
abounded; but that in a higher zone these familiar forms disappeared,
and others made their appearance.
"He read and learned that in other lands--lands of more recent
formation--strange forms of animal life had been discovered; forms
which in their turn had disappeared, to be succeeded by others, more
in accordance with beings now living. He came to know that he was
surrounded, in his native mountains, by the sedimentary deposits of
other ages; he became alive to the fact that these grand mountain
ranges had been built up grain by grain in the bed of the ocean, and
the mountains had been subsequently raised to their present level
by the upheaval of one part of its bed, or by the subsidence of
another...." _The Old Red Sandstone_, a book which was the result of
Hugh Miller's researches, is a geological classic.
There are three other regions in England and Scotland where the Old
Red Sandstone is conspicuous, and all of them were probably old
fresh-water lakes of great extent in which sands accumulated. Sir
Archibald Geikie has named them the Welsh Lake, Lake Cheviot, Lake
Caledonia, Lake Arcadie, Lake Lorne. There are similar sandy deposits
in Russia, in North America, near the Catskill Mountains, and in many
parts of Canada; and there is little doubt that in all these places
there were great lakes which gradually became the depositories of
rivers and developed a life of their own.
The most remarkable fossils of these deposits were the fishes. The
fishes began to appear in the later Silurian: they are strikingly
abundant in Devonian times. The most remarkable of them are fishes
which are only just like fishes after having been developed out of,
or perhaps descending from, some other form of life. These fishes are
now called the _Ostracoderm_ group, and they bear strange resemblance
to some of the trilobites and the king crabs of previous eras. The
_Pteraspis_ is one of the earliest of these strange creatures, and
its "fins," very much developed, were used as oars. Perhaps the most
curious of all these strange creatures were the _Pterichthyds_ or
winged fish; though it is not at all likely that the appendages we
call wings were used for aerial flight. These fishes were all small;
their forms were clumsy and their powers of moving about small. They
had poor mouths and eyes, and they probably ploughed the soft bottoms
of the sluggish waters, above which little besides their peculiarly
placed eyes and the backs of their plated bucklers were habitually
exposed. Another strange class of fish-like creatures was represented
by a little creature which was found in Scotland and is sometimes
supposed to be the ancestor of the lamprey.
Besides the fresh-water fishes there were some which dwelt in the
sea; but in the Devonian era the fresh-water fishes were far more
numerous. We cannot mention them all. The fish called _Coccosteus_
and its allies had great bony plates of considerable thickness on
its head and shoulders (some fine examples are to be seen at the
Natural History Museum, Cromwell Road, London), but its tail and
middle body were left unprotected. The sharks of to-day had their
representatives among the Devonian fishes. Sharks have throughout
geological time nearly always been sea-dwellers, though they still
occasionally live in fresh water, as in Lake Baikal in Siberia and
Lake Nicaragua. It seems clear, however, that in the Devonian period
they lived in the open sea. But their remains are found in the Old
Red Sandstone, and therefore it is likely that they lived in fresh
and brackish waters also. In the same strata as these remarkable
fishes there are found some large and peculiar crustaceans, something
like our modern king crabs, but reaching the enormous length of six
feet. There have also been mussels found and a few water plants, but
not many.
In the Devonian relics the land vegetation has for the first time
been fairly well preserved. The huge club mosses made good their
tenure on the land; and along the flats and low-lying lands by the
rivers there were dense brakes of reedy calamites and masses of true
ferns. The club mosses and the calamites diminished from their giant
size eventually, but the ferns went on increasing, and ancestral
types of the pines and the yews began to appear. The vegetation of
Devonian times was sombre; there could have been no flowers, and the
insects were not of the kind that speed from bloom to bloom. Insects
there were, gigantic dragon-flies and insects akin to the many flies
that haunt the water; but the myriad buzz of insect life as we know
it in field and forest was not yet heard. It is rather an interesting
fact that unmistakable evidence has been collected of the existence
in Devonian times of those smallest of living things, the bacteria.
Of the general distribution of the land we cannot speak with great
certainty. The violent disturbances of Silurian times seem to have
ceased, but movements of the land did not cease. Great parts of
England were rising from the water, and stretching out above the
waves to Belgium and Northern France. There was no German Ocean and
no St. George's Channel at the end of the period; and Scotland,
also rising above the waves, was accumulating deposits of volcanic
ash and lava. While, however, the British Isles and great parts of
Belgium, Denmark, Scandinavia, and Western Russia, and smaller areas
in mid-France, mid-Germany, and the Balkans were rising the rest of
Europe was submerged beneath the waters. In the United States there
were similar risings and sinkings of the land, but, on the whole, the
course of geological history seems to have been more peaceful across
the Atlantic. In Europe, as in America, there do not seem to have
been notable changes at the end of the Devonian, though there was
some alteration in level in Russia, Bohemia, and Great Britain. The
rolling waste of waters south of the Bristol Channel began to deepen.
The continental area in which the Old Red Sandstone lakes lay (a kind
of far Western Europe without a Russia) began now to sink in its
turn. All of the British Isles, except a very thin slice just cut
across the Midlands from North Wales to Norfolk, was sunk beneath
the sea. The lakes disappeared, and above their deposits, as above
the rest of England and nearly all Europe except Scandinavia and
patches of Spain, Italy, and the Balkans, a deep ocean rolled, and
for many thousands of years deposited a grey ooze of limestone. This
limestone is called the Carboniferous or Mountain Limestone. But as
time went on this old sea floor began to be slowly raised, and in
the shallower waters a great quantity of coarse sand and stones and
conglomerate--the Millstone Grit, as it is called--was deposited.
Limestone denotes clear seas; but the borders of clear seas are often
the sites of accumulation of land rocks, and the clear waters of the
early Carboniferous sea which stretched from Ireland to the north of
Europe were bordered by shores along which mud and shale, gravel and
sand were deposited.
The end of this period was marked in Europe by great disturbances
of the earth's crust--though perhaps these disturbances, as we have
shown in a previous chapter, were not sudden or violent, but were
slow upheavals, lasting hundreds of thousands of years. It was at
this time that a great system of mountains, sometimes referred to
as the Palæozoic Alps, began to rise. This system of mountains
crossed the central part of Europe from the Western Islands to the
Sudetes Mountains in the east. Their remnants are seen in the Vosges
Mountains, the Hartz Mountains, and the Black Forest at the present
time; and the development of the Ural Mountains was contemporaneous
with them. During this time a mild climate spread all over Europe,
and as far north as Spitzbergen the waters were warm enough to
support coral reefs and plants which we associate with the seas of
genial latitudes. In time the Carboniferous sea became quite filled
up; and its floor was raised up to or a little above the waters. Then
in great swamps, marshes, and low lands, the burgeoning vegetable
life of the northern hemisphere entered on its long-deferred reign.
It was then that the coal which we burn in our grates to-day was laid
down. Let us consider the circumstances in which coal is to be found.
The coal formations, as we know them, are found in the same state,
and evidently laid down in the same era, from the Equator up to
Melville Island in the Arctic regions, where in our day it is always
freezing. They stretch from Nova Zembla to the middle of China; and
they are much the same in New Zealand and New South Wales. Therefore
the first conclusion we draw was that nearly all over the globe the
climate was the same--hot, close, moist, muggy. Whatever the climate
was the growth of vegetation was tremendous.
We shall have presently to say a little more about the vegetation;
but for the present we need only say that it was very different
from the vegetation with which most of us are familiar. Imagine a
hot, damp atmosphere, a kind of perpetual warm fog through which
the rays of the sun struggled with difficulty, and where rain fell
on most days of the year--a perpetual steaming hothouse. There
was little variety in the appearance of the vast forest swamps.
It certainly possessed, wrote Louis Figuier, the advantage of
size and rapid growth; but how poor it was in species--how uniform
in appearance! No flowers yet adorned the foliage or varied the
tints of the forests. Eternal verdure clothed the branches of the
Ferns, the Lycopods (club mosses), and Equiseta, which composed to
a great extent the vegetation of the age. The forests presented an
innumerable collection of individuals, but very few species, and all
belonging to the lower types of vegetation. No fruit appeared fit for
nourishment; none would seem to have been on the branches. Suffice
it to say that few land animals seem to have existed yet; while the
vegetable kingdom occupied the land, which at a later period was more
thickly inhabited by air-breathing animals. A few winged insects gave
animation to the air while exhibiting their variegated colours; and
many mollusca (such as land-snails) lived at the same time.
Ultimately all this richness of vegetation became by decay, by
compression, by submergence, perhaps by being buried under earthquake
movements and volcanic outbreaks, converted into coal; and we
may now ask how long did this process take. A vigorous growth of
vegetation has been estimated to yield annually about one ton of
dried vegetable matter per acre, or 640 tons to the square mile. If
this annual growth of vegetable matter were all preserved for 1000
years, and compressed till it was as dense and heavy as coal, it
would form a layer about seven inches thick. But a large portion of
the vegetable matter even in peat bogs escapes as gas in the making
of coal. Four-fifths of it escapes in this way. If this be true the
seven-inch layer would be reduced to less than one and a half inches,
and a layer a foot in thickness would require between 8000 and 9000
years. The aggregate thickness of coal is frequently as much as 100
feet (when all the thicknesses of the seams are added together), and
sometimes as much as 250 feet. At the foregoing rate of accumulation
periods ranging from 1,000,000 to 2,500,000 years would be needed
for the accumulation of such thicknesses of coal. It must be borne
in mind that much depends on the rate of growth of Carboniferous
vegetation, which may have been, and probably was, much more rapid
than any we know outside tropical forests. On the other hand, we
have been speaking of the aggregate thickness of the coal beds only.
The greater part of the coal-bearing strata consists of shale and
sandstone with layers or seams of coal like streaky bacon. Of the
shale and sandstone there are thousands of feet, even where the
sediments are fine and their accumulations therefore probably slow.
For, as we have said, this was a period of great change, in which
the forests were always sinking and rising again, being submerged by
lakes, being covered by the sea, and again emerging as islands, to be
overrun by vegetation.
As sinks some sylvan scene in all its pride
Changed to lagoons of overflowing tide,
Assiduous labours Land to win again
Her leafy breadths, invaded by the main.
Down bring the rivers to the flooded shore
Cargoes of shale and silt that slow restore
The sunken glebes, till they again can hold
Thick ferny brakes, and forests as of old.
(H. R. Knipe.)
It would hardly seem unreasonable to suppose that these depositions,
and the changes that brought them about, might have occupied as
much time as the formation of the coal beds. This would double the
figures, and make this period last something between two million and
five million years.
In the coal as we know it are the remains of great forest trees;
gigantic tree-ferns for the most part, and of many small plants
forming a close thick sod, partially buried in whole countries of
marsh land.
Every one knows those marsh plants, which bear the vulgar name of
"mare's-tail." These humble plants were represented during the coal
period by trees from twenty to thirty feet high and four to six
inches in diameter. Their trunks have been preserved to us: they bear
the name of _Calamites_.
The _Lycopods_ of our age are humble plants, scarcely a yard in
height, and most commonly creepers; but those of the ancient world
were trees of eighty or ninety feet in height. Their leaves were
sometimes twenty inches long, and their trunks a yard in diameter.
Such are the dimensions of some specimens which have been found.
Another Lycopod of this period attained dimensions still more
colossal. The _Sigillarias_ sometimes exceeded 100 feet in height.
Herbaceous Ferns were also exceedingly abundant and grew beneath
the shade of these gigantic trees. It was the combination of these
lofty trees with the undergrowth of smaller vegetation which formed
the forests of the Carboniferous period. "What could be more
surprising," exclaims Figuier, "than the aspect of this exuberant
vegetation, these immense trees, these elegant arborescent ferns
with airy foliage, fine cut, like delicate lace. Nothing at the
present day can convey to us an idea of the prodigious and immense
extent of never-changing verdure which clothed the earth, from pole
to pole, under the high temperature which everywhere prevailed over
the whole terrestrial globe. In the depths of these inextricable
forests parasitic plants were suspended from the trunks of the great
trees, in tufts or garlands, like the wild vines of our tropical
forests. They were nearly all pretty, fern-like plants, they attached
themselves to the stems of the great trees, like the orchids of our
times." The margin of the waters would also be covered with various
plants with light and whorled leaves, belonging, perhaps, to the
Dicotyledons. Before leaving the subject of the plants of the coal
measures, we should perhaps mention as one of the most interesting
discoveries of the present generation that whereas the links between
the fern-like trees of those days and the cycads, or early group of
seed-bearing plants, were for long missing, they have been found by
the researches of Professor F. W. Oliver, F.R.S., who has identified
in the _Lyginodendron_ a seed-bearing fern from the coal measures.
We must now turn to the less interesting but not less important topic
of the animal life of the Carboniferous period. At the beginning of
the period when only a small portion of the British Isles was above
the waters, and an ocean rolled from Ireland to China, the life of
which the most important relics were left was that of the sea. In
the early Carboniferous seas the rhizopods, some small as dust, laid
down with their tiny shells the foundations of mountains yet to be;
the "sea lilies" were at the height of their pride, occupying vast
areas in the flowing tide; forms like the present-day nautilus began
to appear, and the "lamp-shells" attained their greatest size. The
trilobites, hitherto the most conspicuous and noticeable animals of
the earth's childhood, were beginning to die out, vanquished in the
struggle for life by more adaptable forms, and the big sea scorpions
were waning fast. The king crabs and the water fleas still throve,
and the fishes, though most of them not very large, were growing
larger, some of them taking the appearance of the dog-fish, some of
the ray, some of the shark; and, what is more important than the
fact of size, the fishes were growing speedier and more capable of
attacking weaker creatures.
In the course of these ages the sea invaded the land; and shores
where land-snails and millipedes and centipedes, beetles and
scorpions, spiders and cockroaches had found a home became entirely
changed, not only in their appearance and character, but in the
type which subsisted on them. It is possible (for something of the
kind has been noticed in our own days in the West Indies, where
a sea-crab species is showing signs of becoming a land animal)
that some of the forms of water animals became used to living in
shallower and shallower water as the generations went on till they
became partly land and partly water animals--amphibians, as they
are called. Thus small newt-like beings, moving clumsily through
the swamps, made their appearance, and others with stronger limbs
pushed onwards through the forest. Others in form resembling snakes
crept through the mud and lived among the swamps by the side of the
sea. Not much is known of the food and life-habits of any of these
amphibians. From their teeth we may perhaps judge that they lived on
fish, crustaceans, insects, and on one another, and their predatory
life sometimes led them to climb trees in search of food. What,
however, is most important about the amphibian is that they were the
pioneers of the march of those creatures which had backbones--the
vertebrates--from the sea to the land.
CHAPTER XIX
THE AGE OF REPTILES
We have already said that in the many hundreds of thousands of
years which went by during Carboniferous times the sea sometimes
advanced and sometimes receded, and nothing shows this better than
the great thickness of the deposits in which the coal lies in
seams. In America, as in Europe, Asia, Africa, Australia, and New
Zealand, South and Central America, the Carboniferous system is
found. In Arkansas, in North America, the coal measures attain the
remarkable thickness of 18,000 feet; in the Wasatch Mountains the
Carboniferous strata have been estimated to be 13,000 feet thick,
and in silver-bearing Nevada 10,000 feet. The formations of the
Western European coal measures, like those of Eastern North America,
consist principally of shales and clays, with smaller amounts of
sandstone and limestone. They attain great thickness, and, including
5500 feet of the Millstone Grit, are 13,500 feet thick in Lancashire
and several thousand feet thick in many parts of Great Britain and
Ireland. The extraordinary thicknesses show that near our islands
must have been a very extensive and lofty area of land. In Germany
the same strata, thickly seamed with coal, are 10,000 feet thick.
There must also have been considerable volcanic or earthquake
action as we know, because in Germany, near the Hartz Mountains and
elsewhere, there are many igneous rocks thrust into the strata,
and also because in Belgium and in France the coal strata are very
much twisted and contorted. The same or similar beds are found in
Siberia, in Japan, and in China, where the coal beds are said to be
thicker than anywhere else in the world. The Carboniferous system
is also found in Africa, in the north, south-east, and south of the
continent; and in Australia and New Zealand Carboniferous strata to
the thickness of 10,000 feet are indicated.
At the close of this period the changes ever taking place transformed
the conditions of life in a way the reverse of that which we have
hitherto been examining. So far each age has shown an increase
of life on the age preceding it. But when the great outburst of
carboniferous activity began to wane it was followed by a lessening
of the wave of life. As we said in the last chapter, there lie on the
top of the coal-bearing strata beds to which the older geologists
gave the name of New Red Sandstone. But in 1841 the New Red Sandstone
was divided into two distinct geological formations. To the lower
and older part Murchison gave in 1841 the name of Permian (from
_Perm_ or _Permia_, an ancient kingdom in Russia, where red sandy
rocks of this age form nearly all the surface), but in Germany it
is more frequently called the Dyas (from Lat. _duo_, two), because
in that country it is composed of _two_ well-marked divisions--red
sandstones below and magnesian limestones above. Thus there are two
types of this Permian formation: the Permian type proper--a mixed
series of red sandstones, marls, shales, and limestones, with some
thin beds of coal, as found in Russia; and the Dyassic type, as seen
in Germany.
We do not know what brought about the change: though we do know
that during it there was great volcanic activity over Europe and
that the waning forests of vegetation and the steaming swamps gave
place to desert plains. Vegetation sank lower and lower. The forests
disappeared or dwelt only in clusters. The soft sappy trees gave
place to hardy pines which clung to the plains and the mountains, and
other sterner types began to appear, allied to the spruces, yews,
and ginkgo. The ginkgo tree is one of the oldest of the tree type
which now has a living representative. Any reader interested enough
in the matter to walk along Royal Hospital Road, Chelsea, will find a
ginkgo tree just outside the Old Physic Garden; and of course a good
many other examples are preserved in botanic gardens. The cycads,
offshoots of the ferns, through the strange group of trees known as
the cycado-filices, spread through the woods.
The trilobites, to turn to animal life, all but disappeared,
though one elegant example remained; the corals were changing; and
the lamp-shells were dropping out. There were a few new species
of fishes, but none of any great strength or capacity, and all
preserving still the tail which is part of the backbone. There was an
all-round impoverishment of life--so great, indeed, that the early
geologists used to believe that a complete destruction of all life
followed this, the closing stage of the Palæozoic era, and that a
re-creation followed. They would have been confirmed in this belief
had they but known that intense cold and glaciation were setting
in where the tropics were situated and that the dryness of vast
deserts was sweeping away life elsewhere. But we now know that life
was not entirely lost; that many species survived, and that others,
altering to suit altering conditions, became stronger in the process.
Nevertheless, life was greatly impoverished. A census made a few
years ago gave the known animal species of the Carboniferous period
as 10,000, while those of the Permian period were only 300, or three
per cent. Possibly the percentage was larger than that, but still it
was small.
But if the Permian was poor in life it was very interesting. The
amphibians had been growing in strength during the later stages of
the Carboniferous age, and may possibly have been more numerous then
than at any other time, for the vast swamps were very favourable for
them. They diminished in the Permian, though the Permian amphibians
showed some advances, and began to assume a likeness to reptiles.
Perhaps the reptiles may have first appeared in the Carboniferous,
but they declared themselves in the Permian age. Two great branches
of reptiles seem already to have defined themselves; perhaps they
had never formed a common group as reptiles, but had separated while
still amphibians. The one bore resemblance to, and were perhaps the
forerunners of, the great hosts of lizards, crocodiles, dinosaurs,
ichthyosaurs, and flying saurians, which are the most pronounced
of the reptiles, and of which we shall have a great deal to say
presently. The other group were perhaps the ancestors of the turtles
and plesiosaurs which appeared later, and possibly led the way to
the mammals. This rapid and diverse spreading out of the reptiles
in a period when life as a whole was at a low ebb is not a little
remarkable. These creatures seem to show the arrival of a more
pronounced form of _air-breathing_ animal; and that may have been the
consequence of the presence of more oxygen in the earth's atmosphere.
Of the Permian amphibians, one of the most interesting was like the
Sphenodon, which still creeps about the northern islands of New
Zealand. The most striking of the reptiles was the _Naosaurus_, a
beast-like creature with a high back of spines webbed together like a
solid porcupine. It was from three to ten feet in length.
All these changes were brought about by the general withdrawal of
the sea, both in the North American continent and in Europe. In both
continents there are beds which accumulated fresh water; in both beds
which were laid down in salt lakes or inland seas; and in both beds
which were laid down on the floor of seas washing the continents.
Great areas seem to have been sometimes dry and sometimes submerged;
other and greater areas, bordered by ice and sometimes swept by icy
blasts, or subject to burning sun in summer, were deserts such as
we are aware of now in Asia or North Africa or mid-Australia, but
much larger in extent than any of these. It was in conditions such
as these that the ancient or Palæozoic rocks came to an end and the
Mesozoic or Middle Period began.
The Middle period of strata and of the life which those strata have
preserved has usually been separated from the older rocks because,
owing to the great period of arid desert conditions, the character of
life changed a great deal; but fuller knowledge shows that the links
were still there, and that ceaseless adaptation of animals to their
surroundings was ceaselessly going on. We need not follow closely
all the changes and relationships, and only much greater knowledge
than geologists yet possess will enable them to trace all the
alterations of the land and sea. But we may trace the alterations in
the appearance of the continents in broad outline. Nearly the whole
extent of the British Isles was now above the sea, and was enjoying a
climate perhaps as cold as present-day Iceland. To the south and east
of Scotland was a great shallow inland lake, while north of Great
Britain a huge plain stretched across Europe. To the south of the
lake was a belt of land, and farther south still the sea had invaded
Italy and reached to Southern Germany, and in this sea was being
laid down the limestone which in later eras was to be elevated into
the mountains of the Apennines, the Alps, and the Pyrenees. North
Africa was under water, but farther south the uplifted lands were
joining hands with India. Sea swept part of Asia, but North America
was larger and broader than it is now, her western coast stretching
farther out into the ocean.
In this period, which is called the Triassic (the name given to it
by the German geologist Bronn because of the three distinct beds
he found in it, though the middle of these, a shelly limestone,
does not exist in Great Britain), there was a wide development of
large reptiles and amphibians. We cannot enumerate them all, for
not one chapter nor one volume would suffice to deal adequately
with the reptiles of the Trias formations and of the Jurassic rocks
which followed them, and of the Permian which preceded them. But
we may speak of some of them. One of the most striking was the
_Pareiasaurus_, which has been found in the Jurassic sandstones and
limestones of South Africa, of Russia, of India and Scotland, and of
middle England. The skeleton of the Pareiasaurus looks like that of a
gigantic pug dog eight feet long; but it was a comparatively harmless
animal, the teeth of which show that it largely fed on vegetable food.
In Sir E. Ray Lankester's lectures on "Extinct Animals" he described
the finding of a great many of these fossil reptiles by Professor
Amalitzky on the banks of the River Dwina, near Archangel. There is a
cliff of Permian strata on the banks of the Dwina, and in this cliff
there is a peculiar pocket or accumulation of sandy matter with large
hard nodules embedded in it. These nodules are removed and broken up
for mending the roads. The pocket seems to be in a fissure and of
Triassic age, later, that is to say, than the Permian rocks on either
side of it. However that may be, the nodules are usually removed
for road-mending, and four or five years ago Professor Amalitzky on
visiting the spot was astounded and delighted to find that when
broken each nodule was seen to contain the skeleton or skull of
a great reptile. The Russian geologist determined to make a most
thorough investigation of this wonderful deposit, and for years spent
several thousand pounds in having the nodules dug out by the peasants
after the year's farming work was over, and in removing them to the
University of Warsaw, where with the finest instruments and greatest
care the nodules are opened, and each bone removed in fragments is
put together from its more or less broken parts, and firmly cemented
and set up in its natural position as a complete skeleton.
These Pareiasaurs reconstructed by Professor Amalitzky were about as
big as well-grown cattle, but not so high on the legs. Living at the
same time, and its skeleton now found near them, was an enormous and
truly terrible flesh-eating animal, with a skull two feet long and
enormous tiger-like teeth. This creature was named Inostransevia.
No doubt the vegetarian herds of Pareiasaurus, whose small peg-like
teeth indicate their harmlessness, were preyed on by the terrible
Inostransevia, as were their brethren in South Africa devoured by
other carnivorous reptiles of that remote Triassic age. So we see the
co-existence of blood-sucker and victim--of the destructive oppressor
and the helpless oppressed--forced on our attention in these two
localities, Russia and South Africa, in days long before man was.
Other land forms were grotesque and curious in shape, the Chelonians
for example, big birds and crocodiles rolled into one, and clothed
in lizard-like skin--queer pear-shaped brutes with huge hind limbs,
short fore limbs, narrow chests, and pigmy skulls.
Both branches of the reptilian horde, those representing the saurians
and those which were the forerunners of the mammals, sent delegations
to the sea before the close of the Triassic period. The Ichthyosaurs
represented the more pronounced reptilian line; the Plesiosaurs were
the representatives of the coming mammals. It is not difficult to
find good reason for this movement to the sea. Besides the inevitable
tendency of every masterful race to invade all accessible realms,
the renewed extension of the sea that set in during the Triassic
period and became pronounced before its close, especially invited
this, for the shallow waters creeping out upon the land with their
now prolific life set tempting morsels before the voracious reptiles,
on the one hand, while on the other, the reduction of the land area
and the restriction of their feeding-grounds, intensified by the
multiplication of the reptiles themselves, forced a resort to the
sea. One of the reptiles of this period, the _Lariosaurus_, shows by
its development how the change affected the reptiles. In the earlier
stages of the Trias it resembled a rather swollen alligator with four
limbs symmetrically situated and used for crawling. In the later
forms of these reptiles the limbs were modified with paddles, and all
power to move about on land was lost.
CHAPTER XX
THE AGE OF REPTILES
(_Continued._)
The Triassic period in its later stages was very like the earlier
period of the era which followed it, and the reptiles which were
characteristic of the close of the first were continued in some cases
with only slight differentiation in the second. The Plesiosaurs and
Ichthyosaurs are associated with the Trias, and we may therefore
describe them now. Though some of these large aquatic creatures must
have measured thirty feet from snout to tail, they do not equal in
size the great aquatic mammals of to-day--the whales. In life the
Plesiosaur had a body like the hull of a submarine with four great
paddles attached--the fore and the hind legs. It had a long neck like
a gigantic swan, and an elongated head provided with powerful jaws
armed with numerous pointed teeth. It probably could swim under water
as well as on the surface, and when floating could snap small lizards
from the land. The paddles have a definite structure like legs, with
five toes, wrist or ankle, forearm or foreleg, and upper arm or
thigh. A great number of these Plesiosaurs have been found in the
Lias formation of the south of England; and slabs containing whole
skeletons have frequently been obtained. They and two similarly
embedded and flattened skeletons of different kinds of Ichthyosaurs
may be seen in quantity on the wall of the gallery of fossil reptiles
in the Natural History Museum at South Kensington.
The Ichthyosaurs were much more fish-like or whale-like in form than
the Plesiosaurs. "They were, indeed," says Sir E. Ray Lankester,
"singularly like the porpoises and grampuses among living whales
and stand in the same relation to land-living reptiles that the
porpoises do to land-living mammals. Their fish-like appearance and
fins are not primitive characters and do not indicate any closer
blood relationship to fishes than that possessed by other reptiles.
They are the offspring of four-legged terrestrial reptiles which
have become specially modified and adapted to submarine life." Like
many whales, they had a fin on the back devoid of bony support.
The Ichthyosaur had a ring of bony plates supporting the eyeball
(as birds also have), and these are often preserved in the fossil
specimens.
At the end of the Triassic period some strata were laid down which
have been called "Beds of passage." We have seen that the Triassic
strata were probably deposited, altogether or in part, in extensive
salt lakes or inland seas. At the close of the Triassic period the
waters of the ocean were admitted to these areas by the sinking of
the land at some point or other of their margins. With the sea-water
came many living things--fishes, shells, etc.--and the very scanty
life of the Triassic lake was replaced by an abundance of marine
life. These beds were called the Rhætic beds because they were first
found in the old Roman province of Rhætia, which occupied an Alpine
district between Bavaria and Lombardy. Here they were thickest,
3000 feet of limestones and shales; but they have since been found
either thicker or thinner everywhere in England, and in the United
States, as well as in other parts of Europe wherever we can find the
Lias lying on the Trias. They are especially interesting, because
they contain the teeth of the earliest known traces of the highest
division of the animal kingdom--the mammals. These early mammals
belonged to the lowest of all the mammalian tribes--the Marsupials,
or pouched animals, now so common in Australia. The little banded
ant-eater of South America, which lives upon insects and is about
the size of a rat, is probably something like the first mammal, the
_Microlestes_, in habit and appearance.
Let us now return, however, to the reptiles of the Jurassic period.
It is so called from the Jura Mountains which occupy the north-west
of Switzerland, separating that country from France. They are
composed of a thick series of clays, shales, and limestones, to
which, in 1829, the name Jurassic was given by the French geologist
Brogniart. It was soon found, however, that the lower rocks of this
period were very different from the upper. The lower rocks were very
shaly and clayey with thinnish layers of limestone. These were called
Lias. The name Lias is derived from "layers"--pronounced broadly by
the Somerset quarrymen as "lyers"--a very suitable name for the lower
beds of the Lias especially, since the alternation of thin beds of
limestone and of shale gives to the rock a banded or ribbon-like
appearance, which may well cause the workmen to describe it as
occurring in "lyers."
To the upper Jurassic beds, which contained much more limestone and
also occasional beds of sandstone, the name of Oolite was given. The
Oolitic strata have a special interest for English geologists, for
it was in them that William Smith, the west of England surveyor,
first made out (about the year 1790) the _order of succession_ of
the strata, and by this was led to his great discovery that "strata
could be identified by their organic remains," that is by their
fossils. He noticed that some of the limestone beds of the strata
we are about to describe consisted of small rounded grains, which
made them resemble the roe of a fish--indeed, they were called
"roestone" by the workmen. Hence Smith--when seeking a name for
this set of strata--bethought himself of the term "Oolite," which
means "egg-stone" (Gr. _oon_, an egg, and _lithos_, a stone). Where
the grains are very large the limestone is called "pea-grit" or
_pisolite_ (Lat. _pisum_, a pea). Some beds which contain numerous
and irregularly shaped fragments of shells, corals, etc., are called
_rag-stones_.
[Illustration: Plesiosaurs
Different species ranged from ten to forty feet in length.]
The Jurassic strata of Great Britain were sediments laid down in
warm seas surrounding an archipelago of which Dartmoor, Wales, and
Cumberland formed some of the islands. The whole of Western Europe
was sinking and had sunk; and the waters of the open ocean were
admitted into and mingled with the salt mineral waters of the great
Triassic lakes. The change was at first very like what would happen
at the present day if the coast of Palestine were depressed, so
that the waters of the Mediterranean flowed into the Dead Sea. The
few fish of the salt lakes were killed; and as the land continued
to sink, the sea at last flowed all over Central and West England,
bringing with it an abundance of marine life. But the reptiles were
far from being finished with; and the progress of the small mammals
was extremely slow.
First, as to the reptiles. The whale-shaped Ichthyosaurs continued to
develop in the seas, and grew larger and larger till some of which
we have found traces reached a length of forty feet. The long-necked
Plesiosaurs also advanced from strength to strength, and some types
grew larger. But by this time new breeds were developing, with
shorter necks and larger heads (and consequently larger brain-power),
which had a better chance of surviving in the struggle for existence
than the unwieldy and slow-witted reptiles which preceded them.
The Ichthyosaurs became more and more fish-like, and some of them
developed the habit of breeding at sea instead of having to return
to the land to deposit their eggs, as do the sea-going turtles and
crocodiles. Descended from quite a different stock, the Plesiosaurs
adapted themselves to sea life in their own fashion. Instead of
adopting the flowing lines of a fish, the body took on a form more
like that of a turtle, while the lengthened neck gave rise to the
description applied to him since that they had the "body of a turtle
strung on a snake." At their longest their necks had as many as
seventy-six bones, or vertebræ, which is more than any other animal
living or extinct ever possessed. A smaller order of crocodiles
appeared and flourished for a time; and the ancestors of the sea
turtles, which were to enjoy so long a reign, began to make their
first appearance.
Among the land animals the Dinosaurs[16] (or the "fearful" saurians)
attained remarkable size and diversity, and their dominant species
were easily lords of the reptile horde. They developed not only as
flesh-eating monsters, but also in vegetable-eating species. Of the
flesh-eaters the _Ceratosaurus_ was the most terrific. It was only
seventeen feet long, but when standing on its powerful hind legs it
could have looked in at most first-floor windows, and it used its
cruel fore limbs for seizing and holding prey. Imagine a kangaroo
with the teeth of a crocodile, the size of an elephant, and the
ferocity of a tiger and you will have a fair idea of what you would
have met in a _Ceratosaurus_.
[Footnote 16: From Gr. "_deinos_," fearful.]
The vegetarian Dinosaurs first became known in this system, but
their development was so extraordinary that they soon outranked
the flesh-eaters both in size and diversity. Among these the
_Brontosaurus_ attained the extraordinary length of sixty feet,
and possibly more. It walked on its four legs, and is one of the
largest known of all land animals. This enormous creature in spite
of all its size and bulk was yet rather weak than strong. Its
general organisation was unwieldy; the head was very small, and
the brain hardly bigger than a walnut. The task of providing food
for such a body must have been a severe tax on so small a head.
The inconvenience of its bulkiness was perhaps reduced by living
in and about water; but from the excellent preservation of some of
the skeletons it has been thought that its life was often ended by
sinking in some quicksand or shoal, from which its own massiveness
forbade that the _Brontosaurus_ should extricate itself.
[Illustration:
Ornitholestes Diplodoci Carnegiei
From skeletons found in Jurassic strata in Wyoming, U.S.A.
(These reptiles attained a length of about 80 feet.)]
Not greatly removed in habit or appearance from the _Brontosaurus_
was the _Diplodocus_, a magnificent specimen of which has been set
up in Pittsburg, and a fine replica, owing to the generosity of Mr.
Andrew Carnegie, in the Natural History Museum. The _Diplodocus_,
a harmless placid beast, was over eighty feet from the tip of his
snout to the end of his enormous tail. It has been calculated that
impulses travel along the nerves to the brain at the rate of about
twelve yards a second. The rate may have been less in the case of
the sluggish _Diplodocus_, but in any case it would evidently take
at least two seconds for a nerve impulse to travel the length of
this reptile; so that if any enemy attacked him at the end of his
tail it would be two seconds before the _Diplodocus_ would realise
the fact, and perhaps four seconds before he could begin to turn
round to defend himself. Even larger than these was the tremendous
_Brachiosaurus_, who weighed as much as a steam-engine and whose
thigh-bone was nearly eight feet high. These were the largest
reptiles ever known, and may be taken as reaching the point when
bulk becomes a burden, and as signalising an approach to the limit
of evolution in the line of size. Less bulky than these were the
_Stegosaurs_, which were also four-footed. They were curiously
armoured, and formed a group of very remarkable creatures found in
England and Western America. While they were less gigantic than
some of those we have just described, they found compensation
in protective plates, spines, and similar modes of defence. A
_Stegosaurus_ found in Wyoming was probably the most hideous to look
upon; but like his relatives he had an extraordinarily small head
and brain, and was a sluggish creature depending on his ugliness and
armour for protection. Very likely this small size of the brain of
great extinct reptiles had to do with the fact of their ceasing to
exist. Animals with bigger and ever-increasing brains outdid them in
the struggle for existence.
It has already been noted that the crowding of the land may have
led some reptiles to take to the sea. The same influence may have
led others to take to the air and thereby escape the monsters of
the swamps, jungles, and forests. Whatever the cause, the most
striking and wonderful feature of this period was the development
of flying reptiles. They had just been seen in the Trias. In the
Jurassic they appeared fully developed. They doubtless sprang from
some agile hollow-boned saurian, more or less akin to the slender
leaping Dinosaurs. Between the ponderous Brontosaurs and the airy
Pterodactyls was the most striking of contrasts. At first these
bird-like reptiles were small, but later their wings had a spread
of as much as twenty feet, veritable flying dragons. They were not
adorned with feathers, but like bats had leathery membranes stretched
from the fore limbs to the body and to the hind limbs. Their heads
were bird-like, and their jaws at first were set with teeth. They had
true powers of flight, as is shown by the discovery of their remains
in places where they must have been far out at sea when they sank
and were buried. Later Pterodactyls had no teeth, and were, perhaps,
milder in habits.
[Illustration: Archæopteryx (the earliest known fossil bird), and
Compsognathus (a small Dinosaur)]
It seems natural to pass from the fossil reptiles to the birds. But
as a matter of fact the birds are not very closely related to the
Pterodactyls, and seem to have been descended from some other very
special form of reptiles, so peculiar as to be considered a distinct
class. It may actually have been descended from those reptiles among
the Dinosaurs which walked on their hind legs and had only three toes
to the foot. The first bird found belongs to Jurassic times; and its
skeleton, found in some slate remains at Solenhofen in Bavaria, is
now to be seen in the Natural History Museum. There is another one
in Berlin. This bird, called the _Archæopteryx_, was of the size of
a large pigeon, had a short head apparently without a beak, and its
jaws were armed with teeth. Whereas living birds have the fingers
of their "hands" tied together in their wings, this bird has three
distinct fingers at the corner of its wings, each armed with a claw.
Its legs were like those of living birds, and it had four toes. Its
tail was unlike that of any living bird, and like that of a lizard.
Whereas the bony part of the tail of living birds is very short and
bears the tail feathers set across it fanwise, the _Archæopteryx_ had
a long bony tail made up of many bones, and the feathers were set in
a series one behind the other till the tail looked like the leaf of
a date palm in shape. Strange as this little creature appears it was
a genuine bird, for it had these feathers well developed, as the two
fossil specimens showed. There are two sets of feathers forming the
wings, and the thighs were also covered with feathers.
CHAPTER XXI
THE CHALK PERIOD
Once again the European continent and with it Great Britain began
to sink. Great Britain at the beginning of the era which followed
the Jurassic system, was joined to France, but south of this barrier
was a great fresh-water lake, into which rivers and streams poured
from the north and the east. Great forests grew on its borders,
forests still crowded with ferns and cycads as in previous ages,
but affording scope for pine trees to grow as well. On its borders
flourished the giant _Iguanodon_, a great lizard-like animal which
could raise itself on its hind legs and lift a fifteen-foot body
so as to feed on the branches of the trees. The _Iguanodon_ is a
specially interesting fossil reptile, because it was one of the
first to be discovered. The first bones and teeth of the Iguanodon
were found seventy years ago by a celebrated and most delightful
explorer of the earth's crust, Dr. Gideon Mantell, in the strata
known as the Wealden, in Sussex, just below the chalk. Dr. Mantell
was only a country practitioner, and when he first produced before
the Geological Society his _Iguanodon_ remains, and suggested
that they were those of a reptile, some doubt was thrown on this
conclusion, because geologists believed from the appearance of the
teeth that the animal must be of some other animal family. But
Dr. Mantell found that a little lizard living in South America had
teeth like those he had discovered in his reptile remains, and he
persisted in his view. Many years later a wonderful find was made
near Brussels in a coal mine near Bernissart, the skeletons of no
fewer than twenty-two huge _Iguanodons_ were found complete and
embedded in a fairly soft clay-like rock. The authorities of the
Government Museum took charge of the place and most carefully removed
the skeletons to Brussels, where the complete skeletons of seven
were with enormous difficulty and care removed bit by bit from the
rock and set up as entire skeletons in the Brussels Museum, where
they may be seen. A replica of one of them is at South Kensington.
The fore feet of the _Iguanodon_ had five fingers, but the hind foot
was very much like that of a bird, and had only three toes, and the
bones of the pelvis or hip girdle were extraordinarily like those of
a bird. When Professor Huxley examined the first fragments of the
_Iguanodon's_ remains he was inclined to believe them to be those of
a gigantic bird; and it is generally believed now that it is from
this extraordinary reptile stock that the birds were derived.
But the great lake with all its varied stores was doomed to sink
lower and lower, till the great sea overwhelmed England. Another
ocean joining it to the east overwhelmed Germany; and the whole of
Europe, south of a line drawn through Scotland, Christiania, and
Moscow, became sunk under salt water. There were patches standing up
here and there--Ireland, Brittany, Cornwall, Spain or a good part of
it, Switzerland, part of Italy (and also part of what is now the
Western Mediterranean), and most of Turkey and Hungary. But elsewhere
marine animals succeeded the reptiles, and the foundations of all the
chalk hills and cliffs of modern Europe were laid.
Of what were they made? We may borrow a capital suggestion from
Mr. Jerome Harrison, of Birmingham University. "Take," he says,
"a piece of chalk and brush it vigorously with a tooth-brush in a
glass of water until the liquid looks quite milky. Allow the greater
part of the sediment to subside, and then pour away the water and
wash the material which has sunk to the bottom of the glass by
pouring water on it two or three times. Put the whitish powder which
finally remains under a microscope; and examine it with, say, the
quarter-inch power, which will magnify about 300 diameters. The
greater part of the white powder will then be seen to be composed of
the minute shells of creatures called Foraminifera--little specks of
jelly-like matter which secrete for themselves a shell or covering
from the carbonate of lime dissolved in the sea-water in which they
live.
"Countless millions of foraminifera inhabit the waters of the North
Atlantic (and of other deep seas) at the present day; and of these at
least one species--_Globigerina bulloides_--cannot be distinguished
from one of the commonest species found in the White Chalk. When
these tiny animals die their soft parts soon decay and disappear, and
their skeletons (or shells) fall on the sea floor, where they form
a whitish mud or 'ooze.' The time required for the accumulation of
so thick a deposit composed of the remains of organised beings--the
White Chalk is in Norfolk quite 1200 feet thick--must have been very
great. If we allow that the tiny shells of the foraminifera may
have accumulated at the rate of two feet in thickness in a century,
then it would have required 50,000 years to form the chalk of the
south-east of England, whose thickness we have estimated at 1000
feet."
Every one who has been on a chalk cliff or hill has found, and
perhaps thrown, chalk flints. Flints are made of mineral called
silica, and very often these flints, or nodules of silica, surround
some organism like a sponge or a shell. During the formation of the
chalk the sea floor appears to have been covered at intervals by a
growth of sponges, which were composed of siliceous matter, and their
death and decay produced most of the flint. Sometimes flint is found
in bands, in which case it may have been deposited by siliceous water
trickling through fissures or cracks in the chalk.
In the sea which thus existed the Plesiosaurs and Ichthyosaurs still
pursued the even tenor of their way, growing larger and larger.
They were of many shapes, and probably of many habits. Some were
certainly fish-eaters, and with their enormous jaws must have been
most undesirable neighbours. Probably, however, they had plenty of
diversity in their lives, and may have had many a bitter struggle
with equally ferocious sea animals of other types. The scaly
saurians, for example, were beginning to come on; and began in
this era to assume the size and appearance that have occasionally
since been attributed to sea serpents. These reptiles, known as
_Dolichosaurs_, were long-necked, lizard-like reptiles in the
beginning of their career, and grew longer and longer in succeeding
generations, till at last their descendants were so long and snaky
that geologists have called the later specimens "serpents." These sea
serpents were from fifteen to forty-five feet in length, and their
remains have been found in the valley of the Meuse. They do not seem
to have had a very long career, for they do not appear after the
Chalk Age, and no direct descendants are known; but while they lived
they ranged from North and South America to Europe and New Zealand.
The first true sea turtles appeared and lived and extended their
families in great variety. They had broad flat forms, their shells
only just covering their ribs like a short Eton jacket; but they were
very large. The greatest of them, _Archelon_, had a skull larger than
that of a horse, and must have measured fully twelve feet across the
shell.
We may consider the birds at the same time as the sea animals or sea
reptiles, since they, perhaps, were relations. Moreover, while the
birds of Jurassic times were land birds, those of the Chalk period
were aquatic. These birds belonged to two widely different classes,
one consisting of large birds which did not fly, the other of small
birds with great strength of wing and great powers of flight. Of the
first kind was the _Hesperornis_. This was a large flightless bird,
specially adapted to diving. Its wings hardly existed, for they had
only one bone left; and that implies the passage of a very long
flight of time, during which the wings once in existence had become
more and more useless, till they had dwindled to a mere nothing.
But the _Hesperornis_ had enormously strong legs, which were used
as paddles, and their efficiency was increased by the bones of the
foot being so joined to the leg as to turn edgewise in the water
when brought forward. Any one who has ever paddled a Canadian canoe
will appreciate the advantage of this. But this was not all, for
the legs were so joined to the body-frame as to stand out nearly
at right angles (like a pair of oars), instead of standing under
the body as walking legs do. Apparently walking as well as flying
had been abandoned, and this bird had become a diver and swimmer
merely. The head, neck, and body were long, and admirably shaped for
plunging through the water. Favoured by the powerful hind limbs,
the _Hesperornis_ must have been very swift both on and under the
water, and a formidable enemy to the fishes on which it preferred to
feed. Its jaws were armed with teeth set in a groove, and, like the
jaws of snakes, were separable so as to admit large prey. As these
strange birds were sometimes six feet long, they must have been able
to account for fish and reptiles of considerable size. They probably
lived nearly altogether on and in the water.
The second type of bird, _Ichthyornis_, were small birds, scarcely
larger than pigeons and a little like terns in appearance. They
were splendid fliers, and were armed with teeth set in sockets.
Their legs and feet were small and slender, but their wings very
strongly developed. They frequented the same seas and places as the
_Hesperornis_, and yet the two were farther apart in structure than
any two types of birds now living. Compared with the _Archæopteryx_,
both these types of birds show progress in the shortening of the
long, curiously feathered tail and the loss of the fingers and claws;
but both retained the teeth of primitive birds. We may perhaps be
allowed to depart from the strict adherence to geologic chronology
by tracing here, instead of in the next chapter, the subsequent
history of the early birds. In the strata of the next era remains of
various birds were found. One of great interest, on account of its
enormous size, was the _Pharorachus_ of America. It was rather like,
in type, a living bird known as the Cariama or Screamer. But if the
extinct bird (of which the skull only has been found) had the general
proportions and habits of the Cariama it must have been a terrible
monster, standing some twelve feet high, and far exceeding the most
powerful eagles and vultures in strength and the size of its beak and
claws. Great extinct wingless birds are found in the quite recent
"alluvial" deposits in New Zealand and Madagascar.
Something more than half a century ago a piece of bone was sent to
Sir Richard Owen by a visitor to New Zealand who had just arrived
there, and who had found it in his garden. Professor Owen, on
examination, was able to say, from the general make and structure of
the bone, that it was the bone of a bird. It was about seven or eight
inches long. On examining the ridges and various marks on the bones,
Owen was able to say that it was identical with the middle of the
thigh-bone of an ostrich. He ventured then to publish that this bone
was a proof that there existed formerly in New Zealand a huge land
bird like the ostrich, only bigger. After a few years more bones were
sent to Owen from New Zealand, which entirely confirmed what he said;
and in the course of a few years he was able to put together from
the bones sent a skeleton with enormous legs and neck--the skeleton
of the ostrich-like bird the _Moa_ of New Zealand. Since that time a
great number of these birds have been found buried in the morasses
and swamps of that country. The _Moa_ is allied to the ostriches of
Africa, the emus and cassowaries of Australia, and the rheas of South
America.
The _Moa_ of Madagascar was smaller, and is known as the _Æpyornis_.
But it lays the largest egg known, a tremendous thing as big as
a Rugby football. It was this very large egg which inflamed the
imagination of ancient navigators, and led to the vast exaggeration
in describing the so-called "Roc," which Sindbad met with in the
_Arabian Nights_. In concluding these brief notes on extinct birds
we must also mention the present-day "kiwi" in New Zealand, which
resembles in some respects the _Apteryx_, or most ancient of birds.
Let us now return to the land reptiles of the Chalk period. These are
chiefly found in America, which was not submerged, as the greater
part of Europe was, beneath the ocean. The incursion of the sea
was more limited in the western hemisphere, and the land area was
large enough to allow the continued progress of the land reptiles,
though even here the sea reptiles seem to have done best. The great
Dinosaurs still kept in the forefront, but they were not quite so
pre-eminent as heretofore. The flesh-eating forms were less abundant,
though among them an enormous kangaroo-like reptile, fifteen feet
long, made its appearance. The _Dryptosaurus_ must have been speedy,
very powerful, and its habits must have made it appear like an ogre
in seven-league boots to its smaller inoffensive neighbours. The
Spoonbill Dinosaurs (_Hadrosaurus_) were very curious creatures, who
also faintly resembled a kangaroo, but had enormous lower parts and
crocodile-like tails.
But the most singular development appeared in the Ceratops family
of the vegetarian reptiles, particularly in the genus called
_Triceratops_. These were very large quadrupeds with enormous skulls
which stretched back over the neck and shoulders in an enormous
cape or hood of bone. Added to this was a sharp parrot-like beak, a
stout horn on the nose, a pair of large pointed horns on the top of
the head, and a row of projections round the edge of the cape. The
_Triceratops_ wanted all the protection it could get, for it had no
intelligence worth mentioning. Professor Marsh remarks that they had
the largest heads and the smallest brains of the reptile race.
The heavy armour of the head of the _Triceratops_ must have been
developed for purposes of attack and defence, but we do not know
whether it was for fighting their own species or for protection
against the carnivorous reptiles. "So long," says Professor F.
A. Lucas, "as _Triceratops_ faced an adversary he must have been
practically invulnerable, but, as he was the largest animal of his
time, it is probable that his combats were mainly with those of his
own kind, and the subject of dispute some fair female upon whom rival
suitors had cast covetous eyes. What a sight it would have been to
have seen two of these big brutes in mortal combat, as they charged
upon each other with all the impetus to be derived from ten tons
of infuriate flesh! We may picture to ourselves horn clashing upon
horn, or glancing from each bony shield until some skilful stroke or
unlucky slip placed one combatant at the mercy of his adversary....
"A pair of Triceratops's horns in the National Museum (at Washington)
bears witness to such encounters, for one is broken midway between
tip and base; and that it was broken during life is evident from the
fact that the stump is healed and rounded over, while the size of the
horns shows that their owner reached a ripe old age."
In connection with the concluding part of the last sentence it
should be mentioned that reptiles, like fishes, but unlike birds
and mammals, continue to grow throughout their entire span of
life, so that unusually large bodily size is, at all events as a
rule, an indication of advanced age. As regards general appearance
_Triceratops_ may, perhaps, be best described as a reptilian
rhinoceros, with the proviso that the tail was much larger and
thicker than in that group of animals, and passed insensibly into the
body, as in reptiles generally, while the number and arrangement of
the horns were different.
The _Pterosaurs_, or flying reptiles, made, as we have said
elsewhere, a great advance. Williston regards them as having come
to excel all other flying vertebrate animals. Some attained a
wing-spread of twenty feet, and they could fly far and fast. They
were all short-tailed; some of them probably could scarcely walk,
and the larger of them had no teeth. Their bills resembled those
of modern birds, and they have been styled the kingfishers of the
Cretaceous seas. Terrific to look upon, they were probably not very
deadly animals except to small fishes. The lizards did not make much
progress; but the snakes made their first appearance, though they
remained small; and the mammals showed little progress from the forms
which were found in the previous era of the Jurassic.
At the close of the geological period whose natural physiognomy
we have thus traced, Europe was still far from displaying the
configuration which it now presents. A map of the period would
represent the great basin of Paris (with the exception of a zone
of Chalk), the whole of Switzerland, the greater part of Spain and
Italy, the whole of Belgium, Holland, Prussia, Hungary, Wallachia,
and Northern Russia as one vast sheet of water. A band of Jurassic
rocks still connected France and England at Cherbourg--which
disappeared at a later period, and caused the separation of the
British Islands from what is now France.
CHAPTER XXII
THE AGE OF MAMMALS
The Geological Record is not perfect. There are breaks in it such
as have not and may never be filled up; and it is because of these
breaks that some of the divisions are made in geologic time. At
present the earth's crust has only been scratched for fossils.
Great parts of Asia and of Africa and of South America remain to be
explored, and they may in some future generation fill the gaps of
our knowledge and render superfluous some of the divisions which
geologists now place in the eras of the rocks and of the fossils. But
so far as we know at present there were real breaks in the history
of the continents, perhaps not swift or sudden, but wholly changing
the appearance and the life, vegetable and animal, of half a world,
perhaps the whole world at a time. Many geologists believe that the
secret of these changes lies in the core of the earth; and that, to
use our old simile of the golf ball, when the tension and pressures
inside the earth grow too much for its strength something gives
way, and the whole world begins to change, the continents sinking
under the oceans and new lands arising. We shall not again consider
this idea in all its bearings, or ask whether there is any simpler
explanation to be found in the never-ceasing explosive tremors of the
crust; but we shall only say that the last of these great changes
set in at the end of the Chalk age. After that era we arrive at the
period among the rocks which, with all its subdivisions, Eocene,
Miocene, Pliocene, Quaternary, is classed as Cainozoic or Modern.
Let us sum up the changes broadly. The Tertiary period, which now
begins, has been called the Age of Lakes: but this merely means
that there were great lake deposits, and it is true to say that as
contrasted with a period of great waters, the Tertiary is to be
considered as the period of land. That does not mean that there
were in all the hundreds of thousands of years which it embraces no
advances and retreats of the sea, no submergings and uprisings of the
land. There certainly were. But the land was dominant, and it is the
land animals and the land vegetation that are the most important and
progress most. After the earth movements which occurred at the end
of the Mesozoic or Secondary period there appears to have followed a
period of quiet. There was a considerable area of land standing high
above the waters; and there began one of the minor but considerable
encroachments of the sea in North America. It is probable that the
Pacific and the Atlantic joined between North and South America. At
the end of this first period the sea withdrew again, and what is
called the Miocene period began with a lowering of the temperature of
the waters of the Atlantic; and lastly followed the great extension
of the land towards the north, the great withdrawal of the sea of
Pliocene times, and the growing cold which led to the glacial era of
the Pleistocene period. In Europe and in Asia we may note that the
great areas which are now covered by the Alps and the Himalayas were
at the beginning of the Tertiary period still under water and only
a few signs (in the form of islands) of these mighty ranges were
beginning to appear.
Pre-eminently the age which comprises all these periods is the Age
of Mammals. But one of the changes which European geologists first
noticed was the surprising change which took place in the marine
fossils. The animals of the sea which were familiar during the
Chalk period nearly all disappeared and were replaced by new ones.
The great saurian reptiles, from the monsters of the land to the
mososaurus serpents of the sea, disappeared, and most other reptiles
showed profound changes, showing a revolution in the animals of the
land corresponding to that of the sea. Lastly, in this first period,
the Eocene, mammals suddenly appear in force and occupy the first
place among the animals. The vegetation did not change so much as
might have been expected.
Whence came the mammals? That, again, is one of the questions which
time alone can completely answer. But the opinion of most geologists
is that they arose and developed in Asia first of all, and then
spread to other continents. The rise of the mammals, which, unlike
the reptiles, bring forth their young relatively mature and nourish
and protect them, was contributing to the downfall of the reptiles,
though it cannot be considered an actual cause. The mammals' young
had a better chance of living and surviving than had the eggs of
reptiles. Moreover, the mammals began with superior agility and
higher brain-power. It is not surprising, therefore, that the
invasion of the mammals resulted in the clumsy, affectionless,
small-brained reptiles being driven either into extinction, or into
the sedges and rushes, the swamps and lagoons, the coverts of the
jungles, the crevices of the rocks, and the various by-ways which the
mammals cared least to frequent, and that they have been kept there
to this day.
At first the mammals were not very different in habit or type from
one another. Small animals, which, like the shrews, moles, and
hedgehogs lived on insects were among the earliest. There were others
whose toes were turning to hoofs in order to fit them for fleetness;
and there were some curious creatures called _Coryphodons_, which
were like the modern tapir, though they were tusked like boars. The
_Coryphodon_ was a slow beast, with toes like those of an elephant,
though it was much smaller.
In America appeared a small animal not much bigger than a
fox-terrier, which was the ancestor of the horse, and of which we
shall have more to say. The birds increased, and forms like those
of the heron mingled in the swamps with other goose-like birds that
kept in their serrated bills some traces of the teeth of their early
ancestors. Others, like kingfishers, flitted over the streams; and
the emu, ostrich, and moa, as well as the albatross, find their
earliest representatives in the Eocene times.
It is impossible for us to follow, or even to enumerate, all the
varied ancestral lines which sprang up, some of them already
vigorous, in the early Tertiary times, and which developed so
mightily in the successive ages. We can only trace the careers of
a few such as are better and more popularly known, while admitting
that there are many others equally interesting from a scientific or
from any other point of view. From a geologist's point of view the
most important, perhaps, of all the mammal developments was that of
the elephant. The first mammal which geologists discovered that was
like the elephant was the Mastodon, the American variety of which
is called _Tetrabelodon_. But this Mastodon had no proper trunk as
has the elephant. Instead of that he had a very long upper lip which
apparently rested on his projecting upper tusks. Mr. Kipling once
suggested that the elephant's trunk was originally formed by an
accident--an unfortunate young elephant before the days of trunks
having stopped to drink at a pool, and his nose being seized by a
crocodile, who pulled and pulled till the nose lengthened out a
trunk. There certainly was some reason for the elephant's trunk,
which has developed, we do not quite know how, from a long nose. But
a great deal has been found out about the early development of the
elephant by Dr. Andrews of the British Museum.
[Illustration: Evolution of the Head, Proboscis, Nostrils, and Tusks
of the Elephant
The drawings are to the same scale; the nostrils indicated by the
letter N, the upper lips by L, and the tusks by T.
1. Mœritherium of Eocene Libya, with a flexible upper lip and
the small incisor tusks.
2. Palæomastodon of Eocene Libya, with a short proboscis and
powerful upper and lower tusks.
3. Mammoth (Elephas Columbi) from the State of Indiana, with
gigantic upper tusks or ivories, and long proboscis with
nostrils at the tip.
]
Dr. Andrews was travelling in Egypt some years ago, and joined a
party of officers of the great survey of Egypt in a visit to the
Great Western Desert, the rainless, sandy waste west of the Nile, not
very far from what is now called the Fayoum, and where in Roman days
was the great Lake Mœris, now dried up to a mere brine pool, in the
salt water of which the fresh-water fishes of the Nile still live.
The surveying party intended to determine the geological age of these
sands, which stretch for hundreds of miles, often rising into cliffs
which are cut sharp by the wind and show horizontal stratification.
The geologists determined that the sands of this region were of
Eocene and Miocene Age, and from them Dr. Andrews brought home
some very interesting bones. These included the remains of a more
primitive Mastodon than any as yet known, and of an animal which he
called Meritherium, which is a connecting link between elephants
and other mammals. The collection included also remains of great
flesh-eating beasts, and of sea cows, of tortoises, and of a snake
sixty feet long!
However, in regard to the history of elephants, the upshot of Dr.
Andrews' most important discoveries is that we find living here in
the Upper Eocene period (which is older than the age in which the
_Tetrabelodon Mastodon_ was found) an elephant ancestor of the kind
to which Dr. Andrews gave the name of _Palæomastodon_ or "ancient
mastodon." We thus arrive at an ancestral elephant-like creature
which serves to join the elephant stock on to more ordinary mammals.
This beast was not so very big, perhaps about the same size as an
ordinary cart-horse.
Dr. Andrews' further triumph was the additional discovery of the
rather smaller animal which he called the _Meritherium_, and which
was undoubtedly an elephant of sorts, though at first sight it has no
resemblance to one, and probably had no trunk at all. It certainly
had no big tusks; but its teeth make us certain that it belonged
to the elephant family. "Here, then," says Sir E. Ray Lankester,
"we have arrived at a form which undoubtedly was closely related
to the ancestors of all the elephants, if not actually itself that
ancestor, and in it we see the origin of the elephants peculiar
structure. From this comparatively normal pig-like _Meritherium_, the
wonderful elephant, with his upright face, his dependent trunk, and
his huge spreading tusks has been gradually, step by step, produced.
And we have seen some, at least, of the intermediate steps--the
lengthening of the jaws and the increase in the size of the teeth in
the _Palæomastodon_--carried still further on by the _Tetrabelodon_,
and then followed by a shrinkage of the lower jaw and final evolution
of the middle part of the face and upper jaw into the drooping,
wonderful, prehensile trunk."
The long-chinned elephant requires, however, a few moments'
consideration from an altogether different point of view. This
species appears to have had the widest geographical distribution of
any member of the family, of which it may be regarded as the great
colonising or emigrant representative. First developed in North
Africa, where its remains occur in the early Miocene strata of Mogara
and Tunisia, this species ranged right across Europe to the confines
of North-Western India, having probably reached Italy from Africa
by means of a land-bridge by way of Sicily, and thence travelling
through Greece into Asia. On the latter continent it appears to have
given rise to the modern elephants, as remains of the former are
unknown in any other part of the world.
If this be true, it follows that elephants of the modern type
subsequently migrated into Europe and thence to Africa, while in the
other direction they wandered by way of Behring Strait to America.
Hence we are led to the remarkable conclusion that while the first
elephants appeared in Africa, the modern African elephant is of
Asiatic parentage, and a comparatively recent immigrant into the
land of its forefathers. Next to man and the carnivora, elephants
appear to have been the greatest travellers the world has ever
produced, for, starting from their North African birthplace, they
reached by the Behring Strait route nearly to the extremity of South
America, while to the north they penetrated the Arctic circle, and
to the south, on their return journey, reached the coast in the
neighbourhood of Cape Town.
Another great traveller was the horse. The first undoubted
horse-like animal was _Eohippus_, a little creature about eleven
inches in height at the shoulder, and in general rather more like
the flesh-eaters than the horses of the present day. The back was
arched, the head and neck were short, and the limbs of moderate
length, showing no remarkable adaptation for speed. This genus had
a remarkable range, having apparently originated in England (then
a part of Western Europe), and migrated by way of Europe and Asia,
and what is now Behring Strait, to America, where it got as far east
as New Mexico. This migration of _Eohippus_ shifted the scene of
evolution to the western hemisphere, for while examples of it are
continually and continuously found there in succeeding strata it only
appears occasionally in Europe, as if the remains there had been
those of mere emigrants.
Later on the horse developed in America, growing larger till it was
first as big as a collie-dog, with signs of being more adapted for
speed. It then had four toes on its foot. It continued, though very
gradually, to grow larger, and even more gradually its unnecessary
toes grew fewer and fewer till at last they disappeared.
At length appeared the horse which had only one toe. This type,
that of the modern horse, first becomes known in the Upper Pliocene
beds of Europe, and represents the culmination of the race. The
completeness of the record of the evolution of the horse tells us
something of the enormous numbers of ancestral forms which must
have existed in the more than two million years that have elapsed
since the first diminutive horse appeared in North America. While
not strongly given to migration, in the course of time these
animals wandered over the entire world, with the exception of such
inaccessible places as Australia and the Oceanic Islands.... It
would seem that the original stock was of Eurasian derivation, though
the great theatre of the evolutionary drama was soon transferred
to North America, the Eurasian, African, and South American horses
which appear from time to time being in all probability of North
American origin. The ultimate fate of the horses in both North and
South America was extinction, all wild horses of our own time,
including the asses and zebras, being confined to Asia and Africa.
The apparently wild bands of the American western plains, and those
which roam over the pampas of South America, are the descendants of
domestic horses that have escaped from human bondage, largely from
the early Spanish explorers.
The rhinoceroses of to-day, the one-horned Indian variety and the
two-horned African rhinoceros, were preceded by a whole regiment of
rhinoceroses in the Tertiary period. One such was dug out in Fleet
Street during the excavation for the _Daily Chronicle_ office.
This rhinoceros had a hairy coat like the Mammoth which lived much
later, and in Siberia is found sometimes side by side with the later
quadruped. Many of the extinct rhinoceroses had two horns like the
African square-mouthed rhinoceros, which is sometimes misleadingly
called the white rhinoceros. One great extinct beast, the
_Elasmotherium_, allied to them, had a great horn carried on a huge
boss in the middle of its head instead of on the nose, while another
still huger animal called the _Titanotherium_ and found in North
America had a pair of horns perched on either side of its nose. As
large as the rhinoceros but having a very different arrangement of
the bones of its ankles and wrists and very different teeth and horns
are the extraordinary creatures known as _Dinoceras_, whole skeletons
of which have been disinterred from the Eocene strata of Wyoming
in the United States by Professor Marsh. These creatures had three
pairs of horns on the top of the head and a pair of great tusks as
well. Nearly all these animals, though they were more brainy than the
reptiles, had much smaller brains in proportion to their size than
the bulk of the animals which now roam the earth, from which we may
surmise that though a small brain suffices to guide a great animal
machine in established ways, yet in order to learn new things in its
lifetime an animal must have a big brain.
The last great mammal we must mention in this series is the
_Arsinoitherium_, which was found only a few years ago by Dr.
Andrews in Egypt, in the same strata whence he obtained the fossil
ancestors of the elephant. It was so called because it was found
near the palace of Arsinoë, the name of the Egyptian queen of Greek
race. But _Arsinoitherium_ was far from being a graceful ladylike
creature, and, resembling in general appearance a rhinoceros, had two
enormous bones, which grew out of its nose on either side of it. The
bones were hollow and were probably covered with skin in life; and
_Arsinoitherium_ had a wonderful and wonderfully even set of teeth.
To conclude, we must add a representative mammal of this period, the
_Sivatherium_, found in India, and the _Samotherium_, found in the
Isle of Samos, which were like giraffes, and the beginning of the
sloth-like animals, whose appearance we must, however, deal with in
another chapter.
[Illustration: Two Arsinoitheriums (Prehistoric Rhinoceros) at Bay
before a Pack of Hyænodons
The Arsinoitherium stood 5 feet 9 inches at the withers, and measured
9 feet 9 inches from snout to rump. The hyænodons (hyæna toothed)
were no relation of the modern hyæna. They had bodies like the
Tasmanian wolf, and were wonderfully adapted to capture both land and
water living prey.
(Drawn under the direction of Prof. Osborn.)]
The whales whose remains are found in the Pliocene rocks differ
little from those now living; but the observations geologists have
been able to make upon these gigantic remains of the ancient world
are too few to allow of any very precise conclusion. It is certain,
however, that the fossil differs from the existing whale in certain
characteristics perceptible in the bones of the skull. The discovery
of an enormous fragment of a fossil whale, made at Paris in 1779,
in the cellar of a wine merchant in the Rue Dauphine, created a
great sensation. Science pronounced, without much hesitation, on the
true origin of these remains; but the public had some difficulty in
comprehending the existence of a whale in the Rue Dauphine. It was in
digging some holes in his cellars that the wine merchant made this
interesting discovery. His workmen found, under the pick, an enormous
piece of bone buried in a yellow clay. Its complete extraction
caused him a great deal of labour, and presented many difficulties.
Little interested in making further discoveries, our wine merchant
contented himself with raising, with the help of a chisel, a portion
of the monstrous bone. The piece thus detached weighed 227 lbs. It
was exhibited in the wine-shop, where large numbers of the curious
went to see it. Lamanon, a naturalist of that day, who examined it,
conjectured that the bone belonged to the head of a whale. As to the
bone itself, it was purchased for the Teyler Museum, at Haarlem.
Lastly, we must not omit to mention that in the Old World the first
true apes, _Oreopithecus_ and _Dryopithecus_, appeared. The first
of these united some of the characteristics of apes and monkeys;
the second, about the same size, was more closely related to the
chimpanzee and gorilla.
CHAPTER XXIII
THE ICE AGE
For some reason or reasons concerning which there has been a great
deal of speculation but not a large amount of agreement, the closing
stages of the last geologic era which precedes our own and which
links the great past to the present, were distinguished by great cold
and by widespread fields of ice. Ice-sheets spread over six or eight
million square miles of the earth's surface where not long before
mild climates had prevailed. Were it not for this great Ice Age and
for its far-reaching effects on the conditions under which Man has
developed, this period, which is sometimes called the Pleistocene,
(from Greek words meaning the "most recent"), would be more properly
joined to the era which we have just been discussing, the two
periods constituting a single period of great land elevation and of
ocean-shrinking. This period, however, is now thought to be much more
important than it was formerly, and perhaps longer in duration.
More than half the ice-covered land lay in North America and more
than half the rest in Europe. The glaciation, therefore, was probably
confined to certain parts of the world and did not stretch all over
the planet. But the whole world felt its effects; even in tropical
regions ice and glaciers occurred on mountains where they did not
exist before and do not exist now, and on mountains which now have
glaciers the ice descended to levels 5000 feet below the point where
it now stops. The southern hemisphere was affected as well as the
northern, but to a much less degree. In Patagonia and New Zealand
glaciers crept down from the mountains and spread out on the plains.
Glaciers formed on the mountainous tracts of Tasmania and Australia
where none exist now. Most of the higher mountains of the southern
hemisphere bore glaciers. The Antarctic regions were presumably
buried beneath ice and snow as they are at present, but of that we
are not certain.
In Asia ice-fields far greater than those existing to-day affected
the higher mountains, and from the Lebanon to the Caucasus and from
the Himalayas to Siberia and China traces of glaciers are found where
they are not to be seen now. Yet on the plateaux and lowlands of
Asia ice-sheets were far less extensive than in Europe and in North
America.
In Europe there were large glaciers in the southern mountains and
extensive ice-sheets on the southern plains. Radiating from the
Scandinavian highlands a succession of great ice-sheets crept forth
on the lowlands of Russia, Germany, Denmark, Holland, and Belgium,
and crossing the shallow basin of the North Sea touched the shores
of Great Britain, where they were met by ice radiating from the
mountains of these isles.
From the Alps gigantic glaciers descended to the lowlands in all
directions. Then the Rhine glacier moved out far beyond the mountains
and joined with the glaciers of Savoy and Dauphiny on the plains of
France, while from the Southern Alps glaciers invaded the fertile
plains of Italy.
Glaciers of similar size and extent descended into the valleys of
the Rhine and Danube. The Pyrenees, some of the higher mountains of
the Spanish plateau, the higher mountains of France, the Apennines,
the Carpathians, the Balkans, the Urals, all had their ice-sheets.
Iceland and the Faroe Islands were buried under ice, and even Corsica
had snowfields and glaciers, some of which were not small.
Nearly one half of North America was buried in ice. Strangely enough,
it was not the whole northern half, but the north-eastern half that
was specially ice-invaded, and, more strangely still, not so much
the mountainous portions, though these were affected, as the plains.
Alaska was largely free from ice except on or about the mountains:
and there was less ice on the western plains than in the valley of
the Mississippi. Much the greater part of the four million square
miles of ice-field lay on the plains of Canada and in the upper
Mississippi valley. The Missouri and Ohio rivers like two great arms
embraced the borders of the ice-fields to which they owe their origin.
We do not propose to examine the several theories which have been
proposed to account for this extraordinary cold, for none is
completely acceptable or accepted, but we may just mention them. Dr.
Croll a century ago suggested that the cold may have been due to
the alterations in the shape of the earth's orbit, alterations which
astronomers tell us take place regularly, though very slowly and at
intervals of millions of years. If so, this glacial period was only
the last of many glacial periods; the traces of the earlier ones
having, however, been for the most part obliterated and destroyed.
Sir Charles Lyell has urged that geographical changes (elevations
and subsidences) would of themselves be sufficient to bring about
a glacial period, which (he says) would be the result of a great
continent being formed round the North Pole while oceanic conditions
prevailed at the Equator. Another theory is that the heat given out
by the sun is not always equal, being sometimes more (when even polar
countries enjoy a warm climate) and sometimes less (when only the
equatorial regions are habitable). The objection to this theory is,
of course, that we have no proof that our sun is of greatly variable
heat. Whatever may have been the cause of the glacial period, we know
as a proved fact that a long time ago (as measured by years, although
the event itself is among the latest of the many changes recorded
in the geological history of the earth) the climate of the British
Isles was so intensely cold that the greater part of this country was
covered with ice and snow, and we know also that this intense cold
was sufficient to change in many respects the habits and appearance
of the animals and vegetation of the earth. How much this was the
case can be gathered from the fact that in the period which preceded
it animals which now live in the tropics roamed in the Arctic circle,
and figs and magnolias grew in Greenland.
The last word we shall have to say on the climatic conditions of
this period is that the Ice Age had its sub-periods and divisions
like all other epochs and in them the ice sometimes retreated, and
consequently in parts of the earth where there had been snow and ice,
and where there were to be ice and snow again, the wintry conditions
retreated (for centuries, perhaps, at a time), and the valleys and
plains basked during these intervals in sun and rain and warmth.
These epochs are called "inter-glacial epochs."
The life of the regions not much affected by the rigours of snow and
ice is gradually being ascertained by geologists now. One of its most
marked features was the retreat of the northern and Asiatic animals
before the advancing ice towards the warmer tropics and Equator;
these animals journeyed back northward again whenever the retreating
ice would let them. The great _Proboscideans_, the Mastodon and the
Mammoth were members of this group, and so were the bear, the bison,
the musk ox. With these mingled towards the south several types
(which were gradually becoming extinct in North America) such as the
horse, tapir, llama, and the sabre-tooth cat. A second prominent
feature was a southern group in the western hemisphere, consisting of
gigantic sloths, armadillos, and water-hogs; and now for the first
time the interest of animal life shifts to South America.
"There are many instances," says Sir Edward Ray Lankester in his
book on _Extinct Animals_, "in which small living animals were
represented in the past by gigantic forms very close in structure
to the little living beasts, but of much greater size. Hence it is
concluded that these particular living animals are the reduced and
dwindled representatives of a race of primeval monsters. There is
some truth in this, as may be seen from the history of the living
sloths and armadillos of South America, as compared with the extinct
gigantic sloths and armadillos dug up in that country. But it is a
great mistake to conclude from this that it is a law of nature that
recent animals are all small and insignificant as compared with
their representatives in the past. That is simply not true. Recent
horses are bigger than extinct ones; recent elephants are much bigger
than their earlier elephantine ancestors. There never has been
any creature of any kind--mammal, reptile, bird, or fish--in any
geological period we know of, so big as some of the existing whales,
the Sperm Whale, the great Rorqual, and the whalebone whales.
"It is true that there were enormous reptiles in the past, far larger
than any living crocodiles, standing fourteen feet at the loins, and
measuring eighty feet from the tip of the snout to the end of the
tail; but their bodies did not weigh much more than a big African
elephant, and were small compared with whales. So let us be under no
illusions as to extinct monsters, and proceed to look at those of
South America with simple courage and confidence in our own day."
The peculiar productions of South America in the way of animals
appear to be the members of the group of mammals called _Edentata_
found nowhere else. When, however, South America, which once was an
island, joined on to North America, numbers of animals, mastodons,
horses, tigers, and tapirs, emigrated from north to south, and
perhaps proved too much for the aboriginal or native beasts. At any
rate, all the big South American mammals died out, and now there
are left only the small tree sloths, the small armadillos, and the
strange-looking ant-eaters. But in quite late geological deposits
of South America we find the bones of gigantic armadillos and of
gigantic ground sloths, which lasted on till the time when man
appeared on the scene.
The _Glyptodon_, of which there were several different kinds, was an
enormous armadillo as big as an ox. Like their small, puny, modern
descendants, they carried on their backs a hard case of bones,
something like the shell of a tortoise. The modern armadillo's shell,
however, is jointed so that the little animal can roll itself up into
a ball, and in this direction, therefore, the armadillo, though it
has decreased so much in size, has advanced in adaptability.
The _Megatherium_ was nearly as big as an elephant, and its skeleton,
though so much larger, is very similar to those of the small sloths
of present-day South America. Its teeth also are very much like
theirs. But whereas the living sloths climb trees, as they have
learnt to do, the _Megatherium's_ method was more primitive though
quite as effective. It stood on the ground and pulled the trees down
in order to eat the young branches. The _Mylodon_, which lived at
the same time, was not so big, and its habits were similar. It had
a number of little bony pieces scattered in its skin in the region
of the back, like the pieces forming the bony case of the ancient
armadillos; but the pieces in this case were not closely fitted
together.
It was supposed that the _Mylodon_, like all the peculiar gigantic
animals of South America, had become extinct as long ago as the
Mammoth (of which we shall say more presently) or of the woolly
rhinoceros which used to haunt Fleet Street. All these extinct South
American animals were distinguished by peculiarly shaped teeth, and
had no teeth at all in front. They are called, therefore, _Edentata_,
and their representatives to-day are much smaller.
But some years ago Dr. Nordenskjold, a Scandinavian traveller, while
exploring in Patagonia, found a vast cavern called the _Ultima
Speranza_ cave, on the western coast. From this cavern the settlers
who lived close by had removed an enormous piece of skin covered with
greenish-brown hair, and studded on its inner side with little knobs
of bone. The skin was dry but sound. When it was placed in water it
gave out a smell which, though unpleasant, was very interesting, for
it showed that the animal which had worn it could not have been dead
thousands or even many hundreds of years. It was, in fact, evidently
a piece of the skin of a _Mylodon_, which had survived in this region
until modern times.
Further explorations were made in the cavern by Dr. Moreno, of La
Plata, and other naturalists, and an immense quantity of bones was
obtained, and more portions of the skin of _Mylodon_ with the hair
on. The cavern had been inhabited probably several centuries ago by
Indians, for human bones and weapons were obtained.
The remains of as many as twenty _Mylodons_ have been obtained from
the cavern, and many of the bones are cut or broken in a way which
leads us to suspect that the human inhabitants of the cave cut up the
dead _Mylodons_ for food, and split their bones to obtain the marrow!
Some of the _Mylodon_ bones, skulls, jaw-bones, leg-bones, etc., are
smeared with blood and have pieces of cartilage and tendon attached.
There are other evidences which go to show that the Indians may have
kept the _Mylodons_ alive in the cave and fed them with hay brought
from the outside. Anybody who would care to see the last of the great
extinct animals can inspect some of these remains at the museum in
Cromwell Road, London.
Besides the relics of the _Mylodon_ and of Man the cavern has yielded
bones and teeth, and many horny hoofs belonging to a kind of extinct
horses; and this constitutes one of the puzzling things about this
cave treasure. The cave is in a part of the country very difficult
to reach, and though Sir Thomas Holdich and Mr. Hesketh Prichard
made efforts to reach it again and explore it systematically and
scientifically, there is a great deal about it that seems likely to
remain unexplained.
The bones that were found are not buried in lime or any preserving
stone; but lie in sand where one would expect them to have perished
long ago if they had been of any great age. Yet side by side with
them are the bones of a long-extinct horse; and there is no tradition
among the Indians to-day of any huge beast corresponding to the
_Mylodon_. Sir E. Ray Lankester has pointed out that the whole of
South America has been submerged and has risen (and is rising still)
for many centuries. Possibly the rocks and high lands where the
_Mylodon_ cavern occurs formed an island during the submergence,
where a number of early animals took refuge and survived until the
re-elevation of the land--and so lived on in the present condition of
the land surface until fifty or a hundred years ago. The great land
tortoises (like the Galapagan[17] tortoise) have similarly survived
on a few equatorial islands. Possibly, though it does not seem very
likely, the _Mylodon_ is still living in similar caverns in this
region, as yet unvisited by man.
[Footnote 17: Of the Galapagos Islands.]
In Australia, the land of the marsupials or mammals with pouches,
the bones of many gigantic creatures belonging to that tribe of
animal have been found. Giant kangaroos, twice as tall as the biggest
living kangaroo, wombats and voles as big as a rhinoceros, have been
discovered. One of these is the _Diprotodon_, which Sir Richard Owen
reconstructed much in the same way that he reconstructed the _Moa_,
and of which Dr. Stirling has since found complete specimens in a
morass in South Australia.
[Illustration: Diprotodon
Equal in size to a large rhinoceros. (Remains found in Australia.)]
Last of all of the great extinct mammals which we shall mention
is the Mammoth, which has a peculiar interest because, like the
_Mylodon_, it certainly survived until man was on the earth, as there
are many more evidences to prove.
In one of the caves of France inhabited by prehistoric men and
thickly strewn with the chipped flints which they used as tools and
weapons, as well as with the bones of extinct animals which they
ate, a piece of Mammoth's tusk has been found on which is rudely but
cleverly carved, evidently by the men who lived there, the picture of
a Mammoth. (There are besides, antlers on which a reindeer is very
cleverly and artistically outlined. Even the tuft of hair below the
chin is shown, and the great feet and the extra toes are correctly
pictured. Clearly the men who drew this reindeer lived with the
reindeer; and besides the reindeer, living near these men in the
south of France, was the great Mammoth.)
The Mammoth was like an Indian elephant, but with a coarse hairy
pelt. It was rather bigger than the big Indian elephant, and its
tusks had a different curvature; but we may dispose of the popular
idea that it was bigger than any elephant. No Siberian Mammoth has
yet been found higher at the shoulders than nine feet six inches,
whereas the African elephant stands eleven feet and sometimes more
at the shoulders. Among the fossil elephants of Southern Europe and
of North America (_Elephas imperator_) there are two which stood from
twelve to thirteen feet high. The remains of the Mammoth are left all
over the north of Europe and Asia and of the countries which were
subjected to glacial influences. Even in England its teeth and tusks
are constantly found, and in the Natural History Museum there is a
whole skull with enormous tusks, which was dug up in a brickfield
at Ilford. Probably this animal continued to exist longer in Asia
and Siberia than in our own part of the world: and the cold and ice
preserved their remains so well that whole carcases have been dug up.
One such instance is historic. In 1799 a native chief near Lake
Onkoul, in Siberia, while seeking for Mammoth teeth, perceived a
great shapeless mass among the ice. He watched it for some years,
till at the end of the fifth year the ice melted and disclosed the
carcase of a whole Mammoth.
In the month of March, 1804, Schumakhoff cut off the horns (the
tusks), which he exchanged with the merchant Bultunof for goods of
the value of fifty roubles (not quite eight pounds sterling). It was
not till two years after this that Mr. Adams, of the St. Petersburg
Academy, who was travelling with Count Golovkin, sent by the Czar of
Russia on an embassy to China, having been told at Yakutsk of the
discovery of an animal of extraordinary magnitude on the shores of
the Frozen Ocean, near the mouth of the River Lena, betook himself
to the place. He found the Mammoth still in the same place, but very
much mutilated. The Yakuts of the neighbourhood had cut off the
flesh, with which they fed their dogs; wild beasts, such as white
bears, wolves, wolverenes, and foxes, had also fed upon it, and
traces of their footsteps were seen around. The skeleton, almost
entirely cleared of its flesh, remained whole, with the exception of
one foreleg. The spine of the back, one scapula, the pelvis, and the
other three limbs were still held together by the ligaments and by
parts of the skin; the other scapula was found not far off. The head
was covered with a dry skin; one of the ears was furnished with a
tuft of hairs; the balls of the eyes were still distinguishable; the
brain still occupied the cranium, but seemed dried up; the point of
the lower lip had been gnawed and the upper lip had been destroyed so
as to expose the teeth; the neck was furnished with a long flowing
mane; the skin, of a dark-grey colour, covered with black hairs and a
reddish wool, was so heavy that ten persons found great difficulty in
transporting it to the shore.
There was collected, according to Mr. Adams, more than thirty-six
pounds weight of hair and wool which the white bears had trod into
the ground while devouring the flesh. This Mammoth was a male, so
fat and well fed, according to the assertion of the Tungusian chief,
that its belly hung down below the joints of its knees. Its tusks
were nine feet six inches in length, measured along the curve, and
its head without the tusks weighed four hundred and fourteen pounds
avoirdupois. Mr. Adams took every care to collect all that remained
of this unique specimen of an ancient creation, and forwarded the
parts to St. Petersburg, a distance of 11,000 versts (7330 miles).
He succeeded in repurchasing what he believed to be the tusks at
Yakutsk, and the Emperor of Russia, who became the owner of this
precious relic, paid him 8000 roubles.
The skeleton is deposited in the museum of the Academy of St.
Petersburg, and the skin still remains attached to the head and the
feet.
A very curious example of the Siberian Mammoth was discovered only a
few years ago by a Lamut of one of the Arctic villages, and through
the energy of Dr. Herz was eventually removed in pieces to St.
Petersburg. In the Zoological Museum there the reconstructed Mammoth
now crawls out of a huge pit, for it was by falling into a pit that
this fine beast met his death hundreds of generations ago. It was
sunk in frozen ground, and this cold-storage treatment had preserved
it in an extraordinary manner. If the Siberian natives who discovered
it partially buried in alluvial deposit had not uncovered it, so that
the sun was able to play on the carcase and produced decay, this
wonderful primeval monster might almost have been got out whole. As
it was the frozen ground had so kept the remains that Dr. Herz found
well-preserved fragments of food between the teeth, and the remains
of a hearty meal in the stomach. There is no doubt that the Mammoth
fell into the crevice or pit and damaged himself so much in the fall
that he could not crawl out. One cannot help feeling some relief that
he died after a short death-struggle. A good deal of the very old
meat of this body was eagerly eaten by the native dogs.
CHAPTER XXIV
THE KINGDOM OF MAN
The greatest zoologist of his time, Sir E. Ray Lankester, has said
that man has differed from all other inhabitants of the animal
kingdom in being able to resist the pressure of circumstances which
have altered and destroyed them. In all the cases of the animals
which we have been considering, these creatures have been limited by
the conditions of geography; they have been killed by extremes of
heat and cold; they have been subject to starvation if one kind of
diet were unobtainable; and they have constantly altered in shape,
structure, and appearance, according to the requirements of the new
conditions in which they found themselves. But man's mind and will
have enabled him to cross rivers and oceans by rafts and boats, to
clothe himself against cold, to shelter himself from heat and rain,
to prepare an endless variety of food by fire, and to increase and
multiply as no other animal without change of form, and without
submitting to the terrible axe of selection wielded by ruthless
circumstance over all other living things on this globe. "And as
he has more and more obtained this control over his surroundings,
he has expanded that unconscious protective attitude towards his
mature offspring which natural selection had already favoured and
established among the mammals into a conscious and larger love for
his tribe, his race, his nationality, and his kind. He has developed
speech, the power of communicating, and, above all, of recording from
generation to generation his thought and knowledge. He has formed
communities, built cities, and set up empires; and at every step of
his progress man has receded farther and farther from the ancient
rule exercised by nature over the lower animals."
Whence comes this power? When and how did it arrive? That we do not
know. For the early beginnings of man we can only grope among the
relics of his progress which he has left for the speculation of his
more intelligent descendants, in the shape of the rude implements and
dwellings which he used in the childhood of the race.
From time to time actual remains of early man are found buried
among the uppermost strata, and from them we can make some guesses
at his age. Virtually three links have been found in the chain of
human ancestry. The earliest is represented by the "Trinil Man"
of Java, found by Dubois in 1890, and named the _Pithecanthropos
erectus_, in reference to its likeness both to man as we know him
and to the great anthropoid apes, although it had a much more erect
carriage than any of them. This relic, man or some other creature
as it may have been, stands midway between the chimpanzee and the
more typical "Neandarthal Man," the skull of which was found in a
cave of the Neander Valley, near Dusseldorf, in 1856. Thirty years
later the skulls of the "Spy men" of the same type as this were
found in Belgium. This type lived in what we call the early Stone
Age, and was a low type of meat-eating hunter. The next higher type,
the third type of man, is that identified with what geologists and
anthropologists call the "Gibraltar skull," from the place where
the skull was found. But all we know of these types of man we must
judge from their skulls and from the stone implements and the animals
found near them. The skulls of primitive men and of modern men show
a certain difference in shape. If we take two skulls, that of a man
and a monkey, and draw a line from the region just over the nose to
the place at the back of the skull just above where it joins the
backbone, there is left above the line a great dome in the human
skull, whereas in the monkey the place left above is much flatter
and much shallower. Now the skull of the _Pithecanthropos erectus_
found in Java resembles the monkey's skull in this shallowness; and
the skulls of the Neandarthal and the Spy men also had shallower
brain-pans than the men of to-day. They may, therefore, be either
different creatures or they may merely have had smaller brains. We
can only say that the creature called Man suddenly appears among
the lower animals with a brain some five or six times the bulk (in
proportion to his size and weight) of that of any surviving ape.
Great as is the difference, it is one of the most curious facts in
the history of man's development that the bulk of his brain does not
seem to have continued to increase in any very marked degree since
the early Ages of Stone.
What were the Stone Ages? In the long years before primitive man
learned to weld iron or bronze he formed his weapons and his tools
from stone and flint; and geologists and antiquarians have discovered
several of these "Ages of Stone" of different periods. For example,
the Stone Age which our grandfathers spoke of is now called the
Neolithic Age; and in the second quarter of the last century it
became gradually admitted that man had existed earlier than that and
had swung hammers and chipped edges in what we now call Palæolithic
times. That would put man back to the age of the Mammoth. But in the
last quarter of last century a new claim arose. The Palæolithic stone
weapons and tools were made 150,000 years ago, and were manufactured
with great skill and even artistic feeling. Within the last ten years
much rougher flint implements of peculiar types have been found in
gravels which are 500 to 700 feet above the level of the existing
rivers--in the drift of which Palæolithic implements were found. To
these older, clumsier weapons and tools--if, indeed, implements they
be--the name Eoliths was given by Mr. J. Allen Brown. These Eoliths
of the south of England and of Belgium indicate a race of men of
less developed skill than the makers of the Palæoliths, and carry
the antiquity of man at least as far back beyond the Palæoliths as
these are from the present day. So much for speculation. But are the
Eoliths truly implements, or are they, as a determined school of
anthropologists assert, merely flints which fortuitously resemble
the rougher variety of true Palæolith? The strongest attack made on
their authenticity comes from Professor Boule and M. Laville, of the
French School of Mines, who say that in the flint waste of a cement
factory at Mantes they have discovered "pseudo-Eoliths" which are
made by the action of the water of the mill, and which resemble every
known variety of the so-called "Eolith." Their suggestion is that
Eoliths were not made by man at all but were produced by the action
of running water. To which the Eolithic anthropologists retort that
Eoliths ought surely to be produced by running water now, and that
some Seine-made Eoliths would be more convincing. The differences
between the Mantes specimens and the "true" Eolith cannot be detected
by the untrained eye; but, spite of the French sceptics, the school
of believers in the genuineness of the Eolith is growing.
We need not enter further into these controversies, and we need only
say that flint implements of various kinds are found all over the
world, in Egypt before the Pharaohs, in Australia, in South Africa,
and indeed in every continent. They are being made even to-day by
aborigines in Australasia, and there is even a "flint knapping"
industry which survives to-day at Brandon, in Suffolk, though these
flints are not intended for use as spear-heads or arrow-heads or
anything so primitive. There is little geological evidence to show
the place where man first appeared; but what we know of his frame
and constitution induces us to believe that somewhere in the warm
climate of Southern Asia was his first habitation. From this, or
from some similar tract in that quarter of the globe, there seems to
have been four great migratory movements. These were complicated by
reverse movements, by cross migrations, and by wanderings, which we
shall probably never altogether understand; and so we can only sum up
briefly the chief features of them.
The greatest movement appears to have been north-eastward between
the great desert and mountain tract of Central Asia on the one hand,
and the Pacific on the other, attended by divergences eastward to
many islands (as they are now) of the Pacific. When the emigrants
got too far north to wish to explore further, they spread out to
east and west, forming a belt below the Arctic regions and sending
a branch down the whole length of the American Continent. This
movement embraced the Mongoloid races, and included the old American
Indians and the Malayan races. Before the disturbing influences of
man's later development, this branch had three notable centres of
civilisation: the Chinese in Asia, the Mexican in North America, and
the Peruvian in South America.
A second and much less numerous band of emigrants struck out to the
south-east, and reaching the southern hemisphere gave rise to the
Australian and New Zealand aboriginal races--all peoples who never
rose very much or developed notable power.
To a third movement to the south-west is assigned the peopling of
Africa south of the Sahara with the negro and similar races, which
have become very numerous but never very powerful or intelligent.
The fourth movement was north-westward across or around the barriers
of desert and mountain to Western Asia, Europe, and North Africa.
These emigrants were the true adventurers, hardy, progressive, and
energetic; and their descendants have developed into the strongest
and most vigorous of the human family. The less progressive of them
remain still on the further side of the mountains of Western Asia.
The three passage-ways used by the original emigrants seem to have
been (1) the Red Sea Nile-Valley path, in which the dusky white and
the Ethiopian races mingled; (2) the Euphrates Valley, down which
the Semitic races moved; and (3) the tracts of the more northerly
plateau, across which moved the ancestral Aryan races. It is also
quite certain that some races moved backwards by this route and
returned to India to give rise to the Brahmins, the most learned race
of that country.
We have thus traced, so far as our limited knowledge will allow
us, the geographical spread of man's dominance. But we cannot
associate him with the history that in previous chapters we have
roughly traced, of the development of the lower members of the
animal kingdom. The qualities which have developed in Man are of
such an unprecedented power and so far dominate everything else in
his characteristics and surroundings that they justify the view that
he forms a new departure in the gradual unfolding of this world's
predestined scheme. Knowledge, Reason, Self-consciousness, Will,
are the attributes of Man. He goes on from strength to strength,
and in the Divine purpose which created him may lie the possibility
that in the future he may attain a fuller knowledge than any he yet
possesses. The great poet of the Victorian Age wrote of Knowledge:--
Flower in the crannied wall
I pluck you out of the crannies;
I hold you there, root and all, in my hand,
Little flower--but if I could understand
What you are, root and all, and all in all,
I should know what God and man is.
The nearer approach to that understanding is the greatest and truest
aim of scientific investigation.
The End
INDEX
Adelsberg, Caverns of, 195
_Æpyornis_, The, 252
"Age of Lakes," The, 257
Air, how it may become solid, 84
Aleutian Islands, Volcanoes of the, 97
Algæ, 103
Alluvium, 54
America in the Devonian Period, 217;
in the Glacial Period, 271
Ammonites, 210
Amœba, The, 100
Andes, Volcanoes of the, 97
Andesite, 184
Andromeda, 92
Animal Life, The first, 104
Animal Species of the Carboniferous Period, 229
Ant, White, The work of the, 44
Anthracite, 133
Apes, The first, 268
_Apteryx_, The, 252
Archæan Era, 129, 199
_Archæopteryx_, The, 243
_Archelon, The_, 249
Arches, The strain on, 25
Aristotle and Earthquakes, 176
Armadillos, 275
Arrhenius, Prof., Theory of, 88
_Arsinoitherium_, The, 266
Assam, Earthquake in, 155
Atmosphere, has the Moon one? 123;
of Mars, 126
Atmospheric pressure, 80, 101
Attraction of bodies, 102
Austen, Sir W. R., his experiment, 85
Avalanches, 69
Babylon, 45
Bacteria in Devonian Period, 217
Baikal, Lake, effects of earthquake, 140
Baltic, Ice in the, 74
Barometer, The use of the, 24
Basalt Rocks, 132
"Beds of Passage," 236
Birds of the Jurassic Period, 243
Bogoslof Islands, 162
Borings, Deep, 79
Boulder-clay deposited by glaciers, 73
_Brachiosaurus_, The, 241
Brahmaputra, The delta of the, 60
Britain in the Silurian Period, 211;
in the Mesozoic Period, 231
British Isles, Ice in the, 75
_Brontosaurus_, The, 240
Cainozoic Period, The, 199
Calabria, Earthquake in, 149
_Calamites_, 222
Calumet and Hecla Mine, Temperature of, 82
Cambrian Hills, The, 200
Cambrian Period, 117;
life in the, 202;
surface of the globe in, 205
Carbonate of Lime, 40, 48
Carbonic Acid, The action of, 47
Carboniferous or Mountain Limestone, 218
Carboniferous Period, The atmosphere of, 219;
insects, mollusca, vegetation, 220;
fish, 224;
strata, 226;
animal species, 229
Carboniferous System, Extent of the, 227
_Cariama_, The, or Screamer, 251
Carinthia, Earthquake in, 141
Carrara marble, 134
Cephalopod types, 207
_Ceratosaurus_, The, 240
Chalk, what it is, 21, 248
_Chelonians_, The, 233
Climate, The changes of, 33
Coal, 219
_Coccosteus_, The, 215
Collision of planets, A, 93
Constructive work of earthquakes, 181
Coral Islands, 66
Coral reefs, 63
Coral reefs in the Silurian Age, 210
_Coryphodon_, The, 259
Cracks in the crust of the Earth, 97
Crater Lakes, 109
_Crinoids_, The, 210
Crustacea, 131, 202
Crust of the Earth, The study of the, 198
Cyclones, 42
Dead Sea, The, 58
Deltas of rivers, 20
Deposits, how they are made, 20, 45
Depths of the sea, 189
Devonian Period, 212; fishes of the, 216;
vegetation, 216;
insects, 216;
Europe and America, 217
Diamonds, how they are produced, 132
_Dinoceras_, The, 266
_Dinosaurus_, The, 240
_Diplodocus_, The, 241
_Dolichosaurs_, 249
Dover, The chalk cliffs of, 21
Dredging, The necessity for, 20
_Dryopithecus_, The, 268
_Dryptosaurus_, The, 253
Dwina, Fossils in the banks of the, 232
Dykes, 105
Earth, The, not so solid as it looks, 23;
its resemblance to a golf ball, 25;
its uneven surface, 31
Earth, Weighing the, 88
Earthquake districts, 171
Earthquake, The sensation of an, 137;
the cause of an, 166, 170
Earthquake waves, 174
Earthquakes, 23;
San Francisco, 140;
New Madrid, 140;
Lake Baikal, 140;
Iceland, 141;
Carinthia, 141;
Japan, 141;
Ocean, 143;
Lisbon, 148;
Sicily, 149;
Chili, 150;
Assam, 156;
Jamaica, 157;
the Mississippi, 158;
Sonora, 160;
Yakutat Bay, 160
Earthquakes, "Great" and "Small," 172;
their constructive and destructive work, 181
Earthworm, The work of the, 44
_Edentata_, The, 275
"Egg-stone," 236
Eifel District, Crater Lakes of the, 109
_Elasmotherium_, The, 265
Elephant, The, 260
_Elephas Imperator_, 280
Emu, The, 260
Encroachment of the sea on the shores of the British Isles, 17
Eocene Period, The, 257
_Eohippus_, The, 263
Eoliths, 287
Era of the First Plants, 103
Erosion, Sea, 19
"Erratic" blocks deposited by glaciers, 72
Eulalie, Lake, effect of earthquake on, 142
Europe in the Devonian Period, 217
Evolution, 115
Excavations and what they reveal, 34
"Faults," 167
Fish in the carboniferous period, 224
Flint, 248
Flint implements, 288
Florida, Encroachment of the sea on the coast of, 18
Flying Reptiles, 242
"Foliated" rocks, 200
_Foraminifera_, 247
Forests covered by the sea, 19
Fossils, 131;
in the banks of the Dwina, 232
Fossil records, 56
Fumaroles, 185
Ganges, The Delta of the, 20
Gases, How metals may be converted into, 84
"General Metamorphism," 133
Geologist, The work of the, 37
Geology, 37
Germany, Sand-dunes in, 46;
Ice in, 74
Geysers, 141
Giant's Causeway, 132
"Gibraltar Skull," The, 286
Ginkgo Tree, 228
Glacial Period, The, theories concerning, 272
Glaciers, 69, 270
_Globigerina bulloides_, 247
_Glyptodon_, The, 275
Gneiss, 200
Grand Cañon of the Colorado, 54
Graphite, 133
Great Barrier Reef, 66
Great Salt Lake, 57
_Hadrosaurus_, The, 253
Harwich, Encroachment of the sea at, 17
Hawaii, Lava eruptions in, 105, 187
Heat and Cold, 68
Heligoland, Encroachment of the sea on, 18
_Hesperornis_, The, 249
Horse, The, 259, 264
Hurricanes, 43
Ice in Scandinavia, Scotland, Germany, 74, 270
Iceland, Eruptions in, 106;
Earthquakes in, 141, 154
_Ichthyornis_, The, 250
_Ichthyosaurs_, The, 234, 239
Igneous rocks, 104
_Iguanodon_, The, 245
_Inostransevia_, The, 233
Insect life in the Ordovician Period, 206;
in the Devonian Period, 216
"Inter-glacial epochs," 273
Interior of the Earth, Theories concerning the, 87
Isle of Wight, Encroachment of the sea in, 17
Jamaica, Earthquake in, 157
Japan, Earthquake in, 141, 153
Jupiter, 91;
as an abode of life, 119
Jupiter Serapis, The Temple of, 181
Jurassic Period, Reptiles of the, 237
Kelvin, Lord, Theory of, 87;
concerning Life, 113
Kern, River, Effect of earthquake on, 141
Kingston, Jamaica, Earthquake at, 176
Kipling, Rudyard, 62
_Kiwi_, The, 252
Krakatoa, The eruption of, 45
Lago di Tolfilo, 152
Lakes, Deposits in, 56
Lakes produced by earthquakes, 152, 159
Land and Water, The distribution of, 31
_Lariosaurus_, The, 234
Laurentian Rocks, 133, 201
Lava eruptions, 105;
in N. America, 106;
plains, 107
Layers of strata which show the history of a place, 37
Leakage of the sea bottom, 190
Leonids, Lyrids, or Perseids, 99
Lias formation, The, 235, 237
Life, The simplest forms of, 111;
theories concerning its origin, 113;
early forms, 114;
in the Cambrian Period, 202;
in the Silurian Period, 203;
in the Ordovician Period, 204
Lisbon, Earthquake at, 148
Llama, The, 273
London, What excavations have revealed concerning the site of, 35
Luray, Caverns of, 196
_Lycopods_, 222
_Lyginodendrons_, 223
Mammals, The development of, 234, 258
Mammoth, The, 279
Mammoth Cave of Kentucky, 196
Man, 284
Marble, how it is produced, 133
Marl in lakes, 57
Mars, 91;
as an abode of life, 119;
atmosphere, 126
Marsupials, 237
Martinique, Devastation of, by volcano, 186
_Mastodon_, The, 260
_Megatherium_, The, 275
Mercury as an abode of life, 118
_Meritherium_, The, 261
Mesozoic Period, The, 199, 231
Metals may be converted into gases, 84
Meteorites, 96
Microbes and Bacteria, 111
_Microlestes_, 237
Migrations of the human race, 290
Miller, Hugh, 213
Millstone Grit, 218
Miocene Period, The, 257
Mississippi, The Delta of the, 20;
sediment deposited, 51;
earthquake in region of, 159
_Moa_, The, 252, 260
Monsoons, 42
Moon, The, 90;
its birth, 100, 120;
volcanoes in, 106;
as an abode of life, 119;
weight, 120;
temperature, 124
Moraines, 70
Moraine-stuff, 70
Mountain formation, 167
Mud-banks, how they are made, 19
Mussels, 210
_Mylodon_, The, 276
Myths concerning earthquakes, 177
_Naosaurus_, The, 230
Neandarthal man, 285
Nebulæ, 92
Negroes, Nature's reason for the dark pigmentation of, 116
Neolithic Age, The, 287
Neptune, 119
New Chum Mine, Temperature of, 83
New Madrid, Earthquake at, 140
Niagara Falls, The work of the, 52
Nile, The Delta of the, 20
Nineveh, 45
North America, Ice in, 76
North Garden Gully Mine, Temperature of, 83
North Sea, The, how it was formed, 19
North Sea, Ice in the, 75
Ocean deposits, 61;
life, 114
Oceanic Era, The, 101
Old Red Sandstone, 212
Oolite, 66, 238
Ordovician Period, Life in the, 204;
surface of the earth in the, 206;
insect life in the, 206;
fish in the, 207;
the Trilobite, 207
Ordovician rocks, 202
_Oreopithecus_, The, 268
Organisms, Multicellular and Unicellular, 111
Orion, 92
_Ostracoderm_ group, The, 215
Ostrich, The, 260
Oxygen, The action of, 47
Palæolithic Age, The, 287
_Palæomastodon_, The, 261
Palæozoic Period, The, 199
Palæozoic Alps, The, 219
_Pareiasaurus_, The, 232
Parsons, Hon. Charles, on the difficulties of deep boring, 79
"Pea-grit," 238
Peak Cavern in Derbyshire, 195
Pearl-oyster, The, 210
Peat-water, The action of, 48
Pelée, Mount, 86, 108;
the obelisk, 184
Permian or Dyas formation, 227
Peroxide of Iron, 40
Perseids, 99
_Pharorachus_, The, 251
_Pithecanthropos erectus_, 285
Planetismals or Meteorites, 99
Plant life in the Silurian Period, 210
Plants, Era of the first, 103
Pleiades, The, 91
Pleistocene Period, The, 269
_Plesiosaurus_, The, 234, 239
Pliny on the upheaval of land, 192
Pliocene Period, The, 257
Po, Sediment deposited by the River, 20
Polyps, Coral, 65
"Pot-holes" in Yorkshire, 195
Pre-Cambrian, 201
Pressure, of air, 80;
of the ocean, 190
Pressure and weight of rocks, 85;
astounding effects of, 134
Pribylof Islands, 164
_Proboscideans_, The, 273
_Proterozoic era_, The 130
Pteraspes, The, 215
_Pterichthyds_, The, 215
_Pterodactyls_, 242
_Pterosaurs_, The, 255
Quartzite, 200
Quaternary Period, The, 199
Quebec, Collapse of the bridge of, 25
Rag-stone, 238
Rain, The influence of, 47
Rainfall on the British Isles, 128
Raised Beaches, 151
Red clay deposit in the ocean, 61
Red Sandstone Formation, 212
Reptiles and Amphibians of the Triassic Period, 232;
of the Jurassic Period, 237
Reptiles in the Carboniferous Period, 229
Rhinoceros, The, 265
Rhizopods, The, 224
Rhætic beds, 237
Rivers and Streams in the Silurian Age, 209
River Terraces, 55
Rivers, Work done by, 20;
records left by, 50
Rocks, how they are made, 79;
igneous and sedimentary, 104, 129;
"foliated," 200
Rocks, Pressure and weight of, 85
Roestone, 238
Romney Marsh, 60
Rorqual, The, 275
Royal Commission on Sea Erosion, 19
Sabre-toothed Cat, The, 273
Saharan desert, The, 22
St. Pierre, Destruction of, by volcano, 186
Salt Lakes, 57
Sambon, Dr., 116
_Samotherium_, The, 266
San Francisco, Earthquake at, 140, 161
San Gabriel River, effect of earthquake on, 141
Sand-banks and mud-banks, how they are made, 20
Sand-dunes, how they are made, 45
Saturn as an abode of life, 119
Scaly Saurians, 248
Scandinavia, Ice in, 74
Schist, 200
Scotland, Ice in, 74
Sea, depths of the, 189;
in the Silurian Age, 210
Sea, The, encroachment on land, 17;
Isle of Wight, 17;
British Isles, 17;
Florida, 18;
Heligoland, 18;
Erosion, 19;
its work, 19
Seaquakes, 143;
Chilian coast, 144;
the _Florence Nightingale_, 145;
sensation of, 145;
origin of, 147
Sea-water, The action of, 65
Sediment deposited by rivers, 20, 51
Sedimentary rocks, 104, 129
See, Dr. J. J., his theory concerning the interior of the earth, 88
Seismology, 23;
in Japan, 153
Seismometers, 24, 153
Shape of the Earth, The, 31
Sharks, 216
Shingle, how it accumulated, 60
Shells found on dry land, 19;
forests covered by, 19
Shells in lakes, Deposit of, 57;
in the ocean, 63
Shetland Islands, Action of the sea on the, 59
_Sigillarias_, 222
Silchester, 45
Silica, 40
Silurian Period, Scorpions and insects in the, 203;
surface of the earth in the, 208;
rivers and streams, 209;
coral reefs, 210;
fish, 210;
plant life, 210;
Britain, 211
Silurian rocks, 202
_Sivatherium_, The, 266
Snail-shells in lakes, 57
Snakes, First appearance of, 255
Snow and Ice Age, 68
Sonora, Earthquake at, 160
Sperm Whale, The, 274
_Sphenodon_, The, 230
"Spy men," 286
Stars, The, 91
Steam a cause of earthquakes
_Stegosaurus_, The, 242
Stone Age, The, 287
Stones smoothed by water, 55
Strata, The earth's, 78
_Strokkur_ geyser in Iceland, 141
Submarine volcanoes, 187
Subterranean caves, how caused, 195
Sun, The, 90;
as an abode of life, 118
Tapir, The, 273
Temperature of borings, The, 83;
of the Moon, 124;
of Mars, 126
Temperature, Changes of, 33
Terminal moraines, 76
Tertiary Period, The, 257
_Tetrabelodon Mastodon_, The, 260
Thames, Sediment deposited by the, 21
Tides, 87, 102
_Titanotherium_, The, 265
Tornadoes, 43
Torrents, The action of, 52
Torridonian Sandstones, 130
Trade Winds, 42
Triassic Period, The, 231
_Triceratops_, The, 253
Trilobite, The, 204;
in the Ordovician Period, 207
"Trinil Man," The, 285
Typhoons, 43
_Ultima Speranza Cave_, The, 276
Upheaval of land, 151, 181
Uranus, 119
Valais Mountains glacier, 72
Valparaiso, Earthquake at, 160
Vegetation on the Moon, 124;
of the Devonian Period, 216;
of the Carboniferous Period, 220;
of the Jurassic Period, 245
Venus as an abode of life, 118
Vertebrates, Evolution of the, 225
Volcanoes of the Andes, 97;
in the Moon, 106
Water, The action of, 47;
its power, 51
Water, The formation of, 109
_Wateree, The_, carried inland by a vast wave, 144
Waterspouts: how they are caused, 44
Waves caused by earthquakes, 143, 144, 145;
the Chilian coast, 144;
Hakodate, 144;
the ship _Wateree_, 144;
Arica, 144;
Samoa, 145;
N. Zealand, 145;
Japan, 145;
speed of, 145;
Lisbon, 148
Weather, The influence of the, 40
Whales, 267
Weighing the earth, 88
Wind-stakes for stopping sand, 46
Wind, The work of the, 40
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| systems in all parts of the world| of the World |
| | |
| By ARCHIBALD WILLIAMS | By ARCHIBALD WILLIAMS |
| B.A., F.R.G.S. | B.A., F.R.G.S. |
| | |
| _With twenty-five Illustrations_ | _With twenty-four illustrations_ |
| | |
| "Crisply written, brimful of | "We cannot praise this book too |
| incident. To intelligent lads | highly."--_British Weekly_ |
| should be as welcome as a | |
| Ballantyne story." | |
| _Glasgow Herald_ | |
+----------------------------------+----------------------------------+
| THE ROMANCE OF | THE ROMANCE OF |
| POLAR EXPLORATION | THE MIGHTY DEEP |
| | |
| Adventures Arctic and Antarctic, | A popular account of the Ocean, |
| from the Earliest Times to the | the Laws by which it is ruled, |
| Voyage of the "Discovery" | its wonderful powers and strange |
| | inhabitants |
| By G. FIRTH SCOTT | |
| | By AGNES GIBERNE |
| _With twenty-four illustrations | |
| Extra Crown 8vo. 5s._ | _With illustrations_ |
| | |
| "Thrillingly interesting." | "Most fascinating; admirably |
| _Liverpool Courier_ | adapted for the young." |
| | _Daily News_ |
+----------------------------------+----------------------------------+
SEELEY & COMPANY LIMITED
=THE ROMANCE OF SAVAGE LIFE=
DESCRIBING THE HABITS, CUSTOMS, EVERYDAY LIFE, &c., OF PRIMITIVE MAN
By Prof. G. F. SCOTT ELLIOT, M.A., B.Sc., &_c._
_With Thirty Illustrations. Extra Crown 8vo. 5s._
"Mr. Scott Elliot has hit upon a good idea in this attempt to set
forth the life of the primitive savage. On the whole, too, he has
carried it out well and faithfully.... We can recommend the book as
filling a gap."--_Athenæum._
"A readable contribution to the excellent series of which it
forms a part. Mr. Scott Elliot writes pleasantly...he possesses a
sufficiently vivid imagination to grasp the relation of a savage to
his environment."--_Nature._
"There are things of remarkable interest in this volume, and it makes
excellent reading and represents much research."--_Spectator._
=THE ROMANCE PLANT LIFE=
DESCRIBING THE CURIOUS AND INTERESTING IN THE PLANT WORLD
By Prof. G. F. SCOTT ELLIOT, M.A., B.Sc, &_c._
_With Thirty-four Illustrations. Extra Crown 8vo. 5s._
"The author has worked skilfully into his book details of the facts
and inferences which form the groundwork of modern Botany. The
illustrations are striking, and cover a wide field of interest, and
the style is lively."--_Athenæum._
"In twenty-nine fascinating, well-printed, and well-illustrated
chapters, Prof. Scott Elliot describes a few of the wonders of plant
life. A very charming and interesting volume."--_Daily Telegraph._
"Mr. Scott Elliot is of course a well-known authority on all that
concerns plants, and the number of facts he has brought together
will not only surprise but fascinate all his readers."--_Westminster
Gazette._
SEELEY & CO., Ltd., 38 Great Russell Street
=THE ROMANCE OF THE ANIMAL WORLD=
DESCRIBING THE CURIOUS AND INTERESTING IN NATURAL HISTORY
By EDMUND SELOUS
_With Sixteen full-page Illustrations_
"Mr. Selous takes a wide range in Nature, he has seen many wonders
which he relates. Open the book where we will we find something
astonishing."--_Spectator._
"It is in truth a most fascinating book, as full of incidents and as
various in interest as any other work of imagination, and, beyond
the pleasure in the reading there is the satisfaction of knowing
that one is in the hands of a genuine authority on some of the most
picturesque subjects that natural history affords. Mr. Selous method
is strong, safe, and sound. The volume has numerous illustrations
of a high order of workmanship and a handsome binding of striking
design.--_School Government Chronicle._
"This is a very fascinating volume, full of picturesquely written
descriptions of the life, habits, and customs of a number of birds
and beasts, including beavers, seals, bears, penguins, crocodiles,
and a host of other creatures."--_Graphic._
"A fund of information and amusement will be found in the pages of
this handsomely bound book. From the lowest animals of all, the
Infusoria, to the lion and the elephant, all come within the range of
Mr. Selous' observation, and he builds up out of the vast material
at his disposal a very readable narrative. The illustrations are
carefully drawn, and are very true to nature."--_Education._
"The volume would make an excellent present for an intelligent boy,
being full of interesting and sometimes thrilling stories from the
wide field of natural history. It is well written in a clear, easy
style which is to be commended. Mr. Edmund Selous has made a most
interesting collection of striking facts, and the book has one of the
prettiest covers that I have seen."--_Daily News._
=THE ROMANCE OF MODERN EXPLORATION=
WITH DESCRIPTIONS OF CURIOUS CUSTOMS, THRILLING ADVENTURES, AND
INTERESTING DISCOVERIES OF EXPLORERS IN ALL PARTS OF THE WORLD
By ARCHIBALD WILLIAMS, B.A. (Oxon.), F.R.G.S.
_With Twenty-six Illustrations_
"A mine of information and stirring incident."--_Scotsman._
"Mr. Williams is most catholic in his choice, taking his readers to
soar in a balloon with the luckless Andree, to wander in African
forests and Australian deserts, to seek for the North Pole with
Nansen, and even to note such an up-to-date expedition as that of the
'Discovery' in the Antarctic Regions, to cite but the most prominent.
Mr. Williams has done this work most judiciously,...a book which will
delight both young and old alike."--_Graphic._
"The book unites strong natural attractiveness with valuable
geographical information to a degree probably unequalled by any other
that might be offered as appropriate for the purpose of a gift book
or the recreative library."--_School Government Chronicle._
"It is a kind of epitome of the best travel books of our time, and is
exceedingly well done."--_Academy._
SEELEY & CO., Ltd., 38 Great Russell Street
=THE ROMANCE OF INSECT LIFE=
DESCRIBING THE CURIOUS & INTERESTING IN THE INSECT WORLD
By EDMUND SELOUS
AUTHOR OF "THE ROMANCE OF THE ANIMAL WORLD," ETC.
_With Sixteen Illustrations._ _Extra Crown 8vo._ _5s._
"An entertaining volume, one more of a series which seeks with much
success to describe the wonders of nature and science in simple,
attractive form."--_Graphic._
"Offers most interesting descriptions of the strange and curious
inhabitants of the insect world, sure to excite inquiry and to
foster observation. There are ants white and yellow, locusts and
cicadas, bees and butterflies, spiders and beetles, scorpions
and cockroaches--and especially ants--with a really scientific
investigation of their wonderful habits, not in dry detail, but in
free and charming exposition and narrative. An admirable book to put
in the hands of a boy or girl with a turn for natural science--and
whether or not."--_Educational Times._
"Both interesting and instructive. Such a work as this is genuinely
educative. There are numerous illustrations."--_Liverpool Courier._
"With beautiful original drawings by Carton Moore Park and Lancelot
Speed, and effectively bound in dark blue cloth, blazoned with
scarlet and gold."--_Lady._
"Admirably written and handsomely produced. Mr. Selous's volume shows
careful research, and the illustrations of insects and the results of
their powers are well done."--_World._
=THE ROMANCE OF MODERN MECHANISM=
INTERESTING DESCRIPTIONS IN NON-TECHNICAL LANGUAGE OF WONDERFUL
MACHINERY, MECHANICAL DEVICES, & MARVELLOUSLY DELICATE SCIENTIFIC
INSTRUMENTS
By ARCHIBALD WILLIAMS, B.A. (Oxon.), F.R.G.S.
AUTHOR OF "THE ROMANCE OF MODERN EXPLORATION," ETC.
_With Twenty-six Illustrations._ _Extra Crown 8vo._ _5s._
"No boy will be able to resist the delights of this book, full to the
brim of instructive and wonderful matter."--_British Weekly._
"This book has kept your reviewer awake when he reasonably expected
to be otherwise engaged. We do not remember coming across a more
fascinating volume, even to a somewhat blasé reader whose business
it is to read all that comes in his way. The marvels, miracles they
should be called, of the modern workshop are here exploited by Mr.
Williams for the benefit of readers who have not the opportunity
of seeing these wonders or the necessary mathematical knowledge to
understand a scientific treatise on their working. Only the simplest
language is used and every effort is made, by illustration or by
analogy, to make sufficiently clear to the non-scientific reader
how the particular bit of machinery works and what its work really
is. Delicate instruments, calculating machines, workshop machinery,
portable tools, the pedrail, motors ashore and afloat, fire engines,
automatic machines, sculpturing machines--these are a few of the
chapters which crowd this splendid volume."--_Educational News._
"It is difficult to make descriptions of machinery and mechanism
interesting, but Mr. Williams has the enviable knack of doing so, and
it is hardly possible to open this book at any page without turning
up something which you feel you must read; and then you cannot stop
till you come to the end of the chapter."--_Electricity._
"This book is full of interest and instruction, and is a welcome
addition to Messrs. Seeley and Company's Romance Series."--_Leeds
Mercury._
"A book of absorbing interest for the boy with a mechanical turn, and
indeed for the general reader."--_Educational Times._
"An instructive and well-written volume."--_Hobbies._
SEELEY & CO., Ltd., 38 Great Russell Street
=THE ROMANCE OF MODERN ELECTRICITY=
DESCRIBING IN NON-TECHNICAL LANGUAGE WHAT IS KNOWN ABOUT ELECTRICITY
& MANY OF ITS INTERESTING APPLICATIONS
By CHARLES R. GIBSON, A.I.E.E.
AUTHOR OF "ELECTRICITY OF TO-DAY," ETC.
_Extra Crown 8vo._ _With 34 Illustrations and 11 Diagrams._ _5s._
"Everywhere Mr. Charles R. Gibson makes admirable use of simple
analogies which bespeak the practised lecturer, and bring the matter
home without technical detail. The attention is further sustained by
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the ohm, and especially the ampere, is better than we have found in
more pretentious works."--_Academy._
"Mr. Gibson's style is very unlike the ordinary text-book. It is
fresh, and is non-technical. Its facts are strictly scientific,
however, and thoroughly up to date. If we wish to gain a thorough
knowledge of electricity pleasantly and without too much trouble on
our own part, we will read Mr. Gibson's 'Romance.'"--_Expository
Times._
"A book which the merest tyro totally unacquainted with elementary
electrical principles can understand, and should therefore especially
appeal to the lay reader. Especial interest attaches to the
chapter on wireless telegraphy, a subject which is apt to 'floor'
the uninitiated. The author reduces the subject to its simplest
aspect, and describes the fundamental principles underlying the
action of the coherer in language so simple that anyone can grasp
them."--_Electricity._
"Contains a clear and concise account of the various forms in which
electricity is used at the present day, and the working of the
telephone, wireless telegraphy, tramcars, and dynamos is explained
with the greatest possible lucidity, while the marvels of the X-rays
and of radium receive their due notice. Now that electricity plays
such an all-important part in our daily life, such a book as this
should be in the hands of every boy. Indeed, older people would learn
much from its pages. For instance, how few people could explain
the principles of wireless telegraphy in a few words if suddenly
questioned on the subject. The book is well and appropriately
illustrated."--_Graphic._
"Mr. Gibson sets out to describe in non-technical language the
marvellous discoveries and adaptation of this pervasive and powerful
essence, and being a most thorough master of the subject, he leads
the reader through its mazes with a sure hand. Throughout he
preserves a clear and authoritative style of exposition which will be
understood by any intelligent reader."--_Yorkshire Observer._
"A popular and eminently readable manual for those interested in
electrical appliances. It describes in simple and non-technical
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applications. There are a number of capital illustrations and
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book."--_Record._
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=Books for Young People=
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=THE LIBRARY OF ROMANCE=
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[Illustration: RAT KANGAROOS BUILDING THEIR HOME
_From "Romance of Animal Arts & Crafts"_]
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Transcriber Note
Minor typos have been corrected. To prevent illustrations from
splitting paragraphs, they were moved. Three very long paragraphs
(pp. 158, 170 and 185) were split to accommodate placement of
anillustration. The two pages of advertising which were placed at
the front of the printed volume have been moved just below the end
of the text with the remaining advertisements. Formatting within the
advertisements has been standardized.
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