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.