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VESUVIUS IN ERUPTION, 1872
THE STORY OF THE
EARTH IN PAST AGES
BY
H. G. SEELEY, F.R.S.
PROFESSOR OF GEOGRAPHY AND LECTURER ON GEOLOGY AND
MINERALOGY IN KING'S COLLEGE, LONDON
WITH FORTY ILLUSTRATIONS
44872
NEW YORK
MCMXII
COPYRIGHT, 1895, 1902.
BY D. APPLETON AND COMPANY.
Printed in the United States of America
O e.
PREFACE.
I HAVE endeavoured to tell the story of the
Earth so that its past history helps to explain its
present condition.
Explanations are given of the nature of. the
common materials which form rocks, of the ways
in which they rest upon each other, and of the
means by which they may be distinguished.
The story of the Earth is divided into epochs
by layers of rock which rest on each other and
rise to the surface of the visible land, and to the
floor of the ocean.
Geological time cannot be defined in years.
The time occupied by an existing river like the
Rhine or the Niagara river, in excavating the
gorge through which it flows, dates back beyond
the antiquity imagined for man by historians.
Yet this incident in sculpture of the Earth's sur-
face is subsequent to the newest of the regular
layers of rock. It is convenient to forget the
human standard of time, and think of a period of
geological time as the age when some rock, such
as coal, accumulated, or when an extinct plant or
animal was dominant on the Earth.
Fossils are the remains of plants and animals
by which each period of by-gone time is distin-
guished.
6 PREFACE.
I. Many kinds of animals, which still live,
date back to the beginning of the Earth's story,
or to an early period.
II. Many groups of animals, such as Trilo-
gies or Ichthyosaurs, endured on the Earth for
long geological ages, varied in form and struc-
ture, and became extinct successively, leaving no
survivor.
The life which now exists on the Earth is a
survival of ancient types of life known from
fossils, which have undergone substantially no
change since first they became known in the
rocks. They are associated now with groups,
like the Mammalia, which are changing rapidly.
The diversity of mammal orders in structure of
the skeleton, is not unlike that which the ancient
Saurians put on before they became extinct.
Animals' orders which vary rapidly last for a
relatively short time.
I have used some scientific names of these
fossils in the story of the Earth, since names
give the easiest identification for fossils as for
our fellow-men. The characteristics or lives of
fossil animals and of living men give interest
to their names. Practical knowledge of fossils
ensures this enduring interest, and is gained by
collecting them in the sea-cliff, quarry, or pit,
and by comparing such specimens with named
examples in museums.
H. G. SEELEY.
KENSINGTON, W., 1895.
CONTENTS.
CHAPTER TAG*
I. INTRODUCTION 9
II. THE EARTH'S INTERNAL HEAT ... 12
III. MATERIALS OF MOUNTAIN CHAINS . . 18
IV. VOLCANIC ROCKS 26
V. THE MATERIALS OF STRATA .... 31
VI. THE SUCCESSION OF STRATA . . . .51
VII. ORIGIN OF STRATIGRAPHICAL GEOLOGY . 58
VIII. FOSSILS 62
- IX. THE CLASSIFICATION OF WATER-FORMED
ROCKS 74
X. THE ARCH/EAN ROCKS 78
XI. CAMBRIAN AND ORDOVICIAN ROCKS . . 81
XII. OLD RED SANDSTONE AND DEVONIAN . . 92
XIII. CARBONIFEROUS STRATA 97
XIV. PERMIAN AND TRIAS 115
XV. LIAS 125
XVI. OOLITES 130
XVII. THE NEOCOMIAN PERIOD . . . .142
XVIII. LOWER CRETACEOUS ROCKS . . . .149
XIX. THE CHALK 156
XX. THE LOWER TERTIARY STRATA . . .162
XXI. THE MIDDLE TERTIARY PERIOD . . .173
XXII. THE CRAG 178
XXIII. GLACIAL PERIOD AND GRAVELS . . 182
LIST OF ILLUSTRATIONS.
Vesuvius in Eruption, 1872 . .
1 Gn?iia ... 3
a, 3. Hertfordshire Pudding Stone . . . .35
4. Laminated band 39
. Ripple-marked Sandstone . .... 41
6. Lithographic Stone ....... 46
7. Carboniferous Limestone ...... 47
8. The Chalk in Yorkshire 56
9. Snowdon to Flintshire 83
10. Inlier at Usk 87
11. Feet of the Trilobite 91
12. To the Forest of Dean 93
13. East of the Pennine Chain loo
14. Productus ...... IOI
15. Pleurotomaria . 102
16. Sigillaria . . . . . . , , . Iio
17. Teniaeopteris . . . . .Hi
IS. Pareiasaurus . . . . . . . .119
19. Lias Outlier ........ 126
20. Gryphaea Incurva 127
21. Cardinia Listeri 128
22. Ichthyosaurus ........ 131
23. Belemnites Oweni ....... 136
24. Shotover Hill 137
25. Skeleton of Archaeopteryx 139
26. Skull of Archaeopteryx ...... 140
27. Hythe to Folkestone 148
28. Ammonites Deshayesii . . . . . .150
29. Section at Hunstanton . . . . . .151
30. Ammonites Planulatus 152
31. Poterocrinus . 153
32. Micraster Coranguinum 159
33. Galerites Subrotundus 160
34. East of Herne Bay '. 164
35. Ostraea Bellovacina ....... 165
36. Cyprina Morrisi 166
37. Strata in Alum Bay ....... 169
38. Planorbis Euomphalus ...... 175
39. Cardita Senilis 179
40. Fusus Antiquus reversed 181
THE STORY OF THE EARTH.
CHAPTER I.
INTRODUCTION.
THE building of the surface layers of the Earth
is recorded in rock materials, which are accumu-
lated upon each other. But there is no trace of a
beginning to their story of the Earth's history.
In the remotest period of past geological time of
which evidence has been found, the earth was in-
habited by types of animals, some of which stilt
survive. There is no evidence that the most
ancient animals which have been discovered were
the first that existed, or that the oldest rocks at
present known mark the beginning of geological
records. It is as unprofitable to enquire for evi-
dences of the origin of the earth, as it is to ask
for proofs of the mode of origin of the life which
has flourished upon it.
Because the earth is a planet we may assume
that it had a similar history in its origin to some
of the heavenly bodies. The light which comes
to the earth from the most distant stars in the
universe, proves, when analysed, to result from
the incandescence of elements which are mostly
identical with those found in the earth. The
small masses of matter, termed meteorites, which
fall from time to time to the earth's surface, con-
&
10 THE STORY OF THE EARTH.
sist of iron and other metals, and of minerals like
those which combine to form crystalline rocks.
The forces which act on the earth are like those
manifested in other heavenly bodies. If the
Earth's surface is not incandescent, as in the
luminous stars, its interior demonstrates in many
ways an internal heat, which has played an im-
portant part in its history. So that, with the mat-
ter and force substantially the same, there is some
justification for the old definition of geology as
that department of astronomy which tells the
story of the Earth.
The geological story differs from that told by
the astronomer in giving results of unceasing ac-
tion of the forces of nature upon the rock materi-
als of the globe. They have worked during a time
which is immeasurably long, when estimated by
such changes on the earth as have happened dur-
ing human history. This time cannot be expressed
in centuries. The work of rivers in carving chan-
nels upon the existing surface of the earth has
been computed at from 15,000 to 30,000 years, in
the case of Niagara river, without reaching the
age when the newer layers of the globe were de-
posited from the sea. This stupendous duration
of time has brought about revolutions in the po-
sitions of oceans and continents ; in the types of
life which were predominant on the earth, as well
as in the distribution of life over the globe, and
in the succession of different kinds of life in the
same region in successive ages, which would be
incredible but for the evidence of fossil animals
and existing animals which are everywhere around
us. These changes have come about, not as result
of catastrophes which have destroyed the fair sur-
face of the land and its life, but as parts of the
INTRODUCTION. II
order of nature, and as conditions of that stability
of government of the world by which the cre-
ations of earlier times have been preserved, and
passed on from one geological age to another to
survive at the present day.
On various parts of the globe, meteorites have
been found which vary in weight from a few ounces
to a few tons. Examples of 400 of them are pre-
served in the British Museum. Some have been
seen to fall. It may therefore be inferred that
ever since the earth has been in existence it has
probably received such additions of material.
Meteorites however do not demonstrate that the
earth has been built up of meteoric matter; but
they are the only clue of a practical kind to the
origin of the globe, which the geologist encoun-
ters.
The iron in meteorites is metallic, usually com-
bined with nickel. In the earth iron is rarely me-
tallic, and rarely crystallized -with nickel. Minute
particles of metallic iron are present in the vol-
canic rock named Basalt, which has flowed over
the north of Ireland. Iron is found combined
with nickel in the Van mine in Denbighshire.
The percentage of nickel in the iron varies in
different localities. There is only one or two per
cent, of nickel in the great masses of iron, some-
times weighing 50,000 Ibs., embedded in Basalt at
Ovifak in Disco Island, on the west of Greenland.
An alloy of these metals found in New Zealand,
yields 67 per cent, of nickel. Both are regarded
as of terrestrial origin.
Although the mineral quartz is one of the most
12 THE STORY OF THE EARTH.
abundant constituents of surface rocks, no true
quartz has been recognised in any meteorite. But
a rare mineral asmanite with many of the proper-
ties of quartz occurs, which somewhat resembles
the variety of quartz found in some volcanic
rocks, which has been distinguished under the
name tridymite.
About ten rare minerals are met with in me-
teorites which have never been recognised in the
rock materials of the globe.
On the other hand, earthy meteorites have
yielded many of the constituents of volcanic and
crystalline rocks.
Two kinds of felspar named labradorite and
anorthite have been recorded in meteorites, and
such minerals as Augite, Bronzite, Enstatite, Oli-
vine, which upon the earth are often combined with
the felspars in mineral union to form crystalline
rocks. But the facts are too few and too obscure
to do more than stimulate interest in the relation
of the earth to the bodies among which it moves.
CHAPTER II.
THE EARTH'S INTERNAL HEAT.
THE earth has an internal heat of its own,
which is not derived from the sun. The temper-
ature of the outer surface layer varies with sum-
mer and winter. In Java and India at a depth of
12 feet the thermometer is constant all the year
round. In London and Paris an unvarying tem-
perature occurs at about 100 feet below the earth's
surface. The earth's heat begins to increase be-
THE EARTH'S INTERNAL HEAT. 13
low this variable surface layer, though the rate of
increase differs with the kinds of rock passed
through, and with the locality. It averages one
degree Fahrenheit for every 55 feet of depth.
In the famous Artesian well at Crenelle near
Paris, the water rose from a depth of 1794 English
feet, with a temperature of nearly 82 F. The
deep boring at Sperenberg near Berlin appears to
show an increase of i F. in 42 feet at the depth
of 1000 feet; i F. in 57 feet, at 2000 feet; and i
F. in 95 feet, at 3000 and 4000 feet. From these
facts the inference has been made that tempera-
ture does not augment appreciably below a mod-
erate external thickness of rock.
The difference between the surface tempera-
ture and the interior temperature, results from the
loss of the earth's internal heat by radiation. On
this circumstance attempts have been made to es-
timate the duration of geological time. By meas-
uring the amount of heat which the earth radiates
from its surface in a year, Lord Kelvin has con-
cluded that in a period of 20,000 millions of years,
more than enough heat would have been lost to
melt the entire bulk of the earth, if the rate of
loss had been always what it is now, and if the
earth had consisted throughout of the same ma-
terials as its surface rocks. This is the time which
the physicist conceives as possible for the earth's
origin and history. Sir John Herschel had doubt-
ed the primitive fluidity of the earth. It is per-
haps possible that the heat which the earth loses
may not be the original heat of an igneous fusion,
but the result of strain due to its rigid state. It
rotates so that its surface experiences the lifting
influence of tidal attraction which reduces the
pressure, although the amount is too small to dis-
14 THE STORY OF THE EARTH.
turb the stability of its surface. By the conver-
sion of this attraction of gravitation upon its
outer layers into heat, at a depth from the surface
sufficient to ensure that the heat so generated
could not be radiated in a day, a store of heat
might accumulate near to the surface of the globe.
The most ancient rocks give no evidence of greater
internal heat, or of greater refrigeration of the
earth, or of tidal action upon its surface having
been in any way different from what it is now.
The greatest depth at which the fractures and
dislocations, termed earthquakes, are known by
actual measurement to originate, is about 30
miles. It has also been calculated that a heat
sufficient to melt granite might occur at a depth
of 20 or 30 miles. This is the maximum depth to
which geological theory extends its inferences.
Attempts have been made to calculate the
pressure under which masses of granite in moun-
tain chains have consolidated. In some cases the
crystal structure appears to indicate a superin-
cumbent pressure equal to no more than 15 miles'
thickness of rock, though the pressure was proba-
bly lateral.
The materials ejected from volcanos give no
indication of having ascended from more than
very moderate depths. The molten matter of
lava streams does not appear to be the primitive
substance of the earth's interior. That heated
material might be rendered liquid by fractures
which penetrate downward so as to remove the
pressure which keeps the heated rock solid. It is
thus manifest that some cause generates heat near
to the earth's surface, which is associated with the
crumpling of the earth's outer layers, with the
changed distribution of level of land from age to
THE EARTH'S INTERNAL HEAT. 15
age, and with the phenomena of volcanic ac-
tivity.
This cause is believed to be the cooling of the
earth ; by which the shrinkage of the deeper lay-
ers crushes the upper layers together, crumpling
them into folds which are directed alternately up-
ward and downward. As these folds are crushed
^closer together, the mechanical energy of com-
pression, resisted by the rock material, becomes
converted into heat along the lines of most intense
squeezing.
The directions of these folds change from age
to age in geological time ; for e\ ery land consists
of masses of rock which extend through it in direc-
tions which were once approximately parallel to
its shores.
The late Mr. Robert Mallet believed that the
energy of volcanic eruptions was developed by
these compressions of the crust. He also urged
that the lateral pressure exerted by the sides of
an arch of continental land upon its supports
would result in crushing along the lines of greatest
weakness; and calculated that the temperature
may be raised locally in this way to a red heat, or
even to the fusing point of the rocky materials
which are crushed. This heat, which is produced
locally, he believed to be consumed locally, and to
be the source of the explosive energy which ejects
the materials of which volcanos are built up.
Active volcanos are commonly met with in
regions undergoing upheaval. This is attributed
to the underground compression of the rocks
which causes upheaval, generating heat. The
water near the shore which penetrates to the
heated region is raised by that heat to an explo-
sive temperature. Volcanos have a linear exten-
1 6 THE STORY OF THE EARTH.
sion ; sometimes in islands rising from the sea,
sometimes in mountain chains formed of islands
united together. The linear arrangement is at-
tributed to the opening of fissures, which pen-
etrate downward along lines, in which the rocks
have been folded and fractured in the process of
upheaval. When rain water, in a region so bent
and strained, is held back upon the land and
hindered from escaping by the pressure of the sea
round its shores, the water descends through the
minor joints and capillary interspaces between the
particles of rock. Then it rises in temperature
with the internal heat of the earth, so as to facil-
itate the melting of rocks, with which it combines.
Some of this water eventually ascends through
the planes of fracture and displacement forming
outlets for explosive energy, discharging steam,
dust, and the rock matter, both solid and molten,
which builds volcanic cones.
The past periods of geological time abound in
evidences of volcanic activity. From the imper-
fect nature of the records which remain upon the
earth their linear arrangement is not always evi-
dent ; but they may be inferred to mark lines of
upheaval which brought islands into existence, or
united them into continental masses of land in
successive epochs of geological time. But be-
sides the volcanos which are marked by beds of
ashes and lava-flows, and the throats up which
the molten matter ascended, there are in many
parts of the world extinct volcanos with' their
cones well preserved, as though the craters had
been recently active.
A little south of the Pyrenees, in the basin of
the Ebro, there are fifteen cones about Olot in
Catalonia, built of cinders, from each of which
THE EARTH'S INTERNAL HEAT. 17
lava has flowed in streams still to be traced, yet
so long since that the existing rivers have cut
passages for themselves through the lava.
The Auvergne is a granite platform in which
some ancient rocks of the carboniferous period
occur. This district appears to have been an is-
land traversed by a line of fracture from N.W. to
S.E., which corresponds to the uplifting of the
crystalline rocks. A second fracture runs from
N. to S. In fhis region are the ruins of the four
grand volcanos known as Mont Dore, Cantal,
Canton d'Aubrac, and Mezen. The lava flowed
from Mont Dore for 20 miles. The minor cones,
of which there are hundreds, range through the
country in a broad band, from N. to S. Many
have the craters burst u^'.vn by the lava which
ascended in them, and overflowed into the neigh-
bouring valleys.
Beautifully preserved volcanic cones are found
to the north of the Moselle river in the district
known as the lower Eifel. It may have been in
this country that the eruption took place which is
mentioned by Tacitus as having affected the
country near Cologne, in the reign of the Roman
Emperor Nero. For a long way up the Rhine
the rocks are volcanic ; and evidences of extinct
volcanos are found west of the Rhine, in many
parts of central Germany; and a series ranges
through Hungary S.W. of the Carpathians into
Servia.
The latest volcanic outbursts in the British
Isles were at the beginning of the Tertiary period
in Skye, Rum, Mull and th r Adjacent mainland of
Scotland, and in the north of Ireland, where
streams of mud due to volcanic dust, washed
down by rains, covered up the vegetation of the
a
1 8 THE STORY OF THE EARTH.
country before it was deluged with the black lava
named basalt. Branches of the conifer Sequoia,
and of plane trees covered with leaves, are pre-
served in the consolidated mud which underlies
these lava-flows.
CHAPTER III.
THE MATERIALS OF MOUNTAIN CHAINS.
THE same cause which produced the local heat
and fractures which led to volcanic outbursts, has
folded the earth's crust. Rocks many thousands
of feet thick have been bent, folded and crumpled.
This structure, which is shown in the succession
of rocks on the surface of every country, in folds
termed saddles and troughs, is most astounding in
its intensity in mountain chains. The upheaving
of the parallel ridges of limestone rock known as
the Jura chain, forming the frontier between
Switzerland and France, is a beautiful example of
troughs which form valleys, parting the elevated
ridges from each other. In that part of the Alps
known as the Orisons, all the geological deposits,
from the tertiary down to the oldest, have been
turned upside down, in the process of folding by
lateral displacement ; which is the sole cause
which lifts mountain ranges. The curved form of
the earth necessitates that every axis of elevation
must be accompanied by spurs at right angles to
itself, or by parallel ranges. The parallel system
is exemplified in the chains of North America,
which lie between the Rocky Mountains and the
Pacific.
THE MATERIALS OF MOUNTAIN CHAINS. 19
These folds once formed remain for all time.
They may be raised higher, or depressed beneath
the sea, and new rocks laid down upon them ;
but as those ancient folds increase in intensity
with the slow succession of geological ages, the
newer rocks become folded with their folds, and
the folds run in the same direction.
In such puckered and crumpled rocks as moun-
tain chains exhibit on their denuded heights, there
is almost invariably evidence of a crystalline tex-
ture. This may be attributed to the influence of
the heat produced by the mechanical power, trans-
formed by the resistance which the rock mass of-
fered to compression.
The rocks which form mountains are chiefly
slaty rocks, and schists, with here and there some
granite masses or sheets of volcanic rock. They
have only been laid bare by the removal of vast
thicknesses of water-formed rock which once ex-
tended above them. If the crystalline materials
are not the necessary products of the upward
thrust of the mountain chain and adjacent land
which supports it, it may be difficult to account
for the uniform character of the rocks of which
the durable central masses of mountain chains are
built. There are stages in this process of change.
The flanks of a mountain range commonly show
the fine microscopic crystalline texture of slate,
while the central masses show the coarse crystal-
line texture of schist, or granite.
Slate. The part which slate plays in the forma-
tion of mountain masses is well seen in the struc-
ture of the mountainous regions of North and
Central Wales, in parts of the Lake District in
Westmoreland and Cumberland, and in the south
of Scotland. It is certain that slate was originally
20 THE STORY OF THE EARTH.
a water-formed rock, a mud which consolidated
into clay. It often shows successive parallel beds
marked by differences of colour. Welsh slates
sometimes contain clay pebbles, such as occur at
the present day on shores where the cliffs are of
compact clay. Many slates contain fossil remains
of animals which lived in the sea when the old
mud was accumulating. Those fossils are often
distorted and squeezed into half their original
breadth or length, showing that the whole moun-
tain mass has undergone compression and con-
densation. The compression has bent the rocks
into synclinal troughs and anticlinal saddles.
The slaty texture is most developed in the troughs.
The effect of this lateral pressure has been in
the first place to turn the films of water contained
between the particles of the old mud at right
angles to the direction from which the pressure
came. The resistance offered by the rock trans-
formed a large part of the motion imparted to its
particles into heat. That heat raised the temper-
ature of the water contained in the rock, enabling
each film, under the pressure, to dissolve some
constituents of the mineral matter in which it was
contained. These slaty rocks often give evidence
of having been fractured through their thickness
by minute dislocations, and subsequently re-united.
Such breakage, relieving the pressure, would cause
the temperature to fall, and the substances which
had been dissolved then crystallize in minute
films, parallel to each other, extending throughout
the mountain mass, and having no relation to the
original planes in which the mud was deposited.
These microscopic crystal films resemble such min-
erals as mica or chlorite. They impart to the
rock the property termed slaty cleavage. This
THE MATERIALS OF MOUNTAIN CHAINS. 21
cleavage causes it to split in layers which cut
across the original folded or faulted planes of
bedding. This microscopic crystalline change of
texture imparts to the rock, now termed slate, a
remarkable durability. Its particles are laced
together by a network of parallel films of micro-
scopic crystals. Slates may be of any antiquity.
Nothing but folding and uplifting of mountainous
masses is needed to form them. In England and
America they belong chiefly to the ancient epochs
of time distinguished as pre-Cambrian, Cambrian,
Silurian, and Devonian.
Schists. The transitions between slate and
schist are common in mountain regions. Crystals
of other minerals are sometimes developed on the
cleavage planes of slate. Some slates are very
micaceous; and it is sometimes difficult to say
where mica slate ends, and mica schist begins.
The original bedding is usually obliterated in
schists; so that the rocks give no evidence of
having been deposited in water. Occasionally,
as in the mica slates south of Bergen in Norway,
beds of limestone, in which fossils are preserved,
are found in such rocks. In the north of Scot-
land fossil-bearing beds, known as the Durness
limestone, occur between schists, where they are
introduced by horizontal dislocations.
A schist presents to the eye an arrangement of
short irregular layers of crystals, which is similar
to the appearance which a thin film of slate shows
under the microscope, although schists differ from
slates in having all their material crystalline.
There is some reason for regarding them as re-
sults of intenser action of such compression as
imparted a slaty texture to ancient beds of very
varied mineral character.
22 THE STORY OF THE EARTH.
A schist thus foliated is typically an alternation
of films of the mineral quartz with some other
minerals. Each quartz film is made up of a num-
ber of crystals matted together, and occasionally
little plates of mica separate the individual crys-
tals from each other. The mineral, which alter.
FIG. i. Gneiss : showing foliated structure, from Gairloch in
Ross-shire.
nates with the quartz, gives its name to the schist,
as mica schist, hornblende schist, chlorite schist.
Some schists, such as gneiss, are identical with
granite in mineral composition ; some are identical
with slates in chemical composition. Schists are
frequently contorted and crumpled, as in the cliffs
round Holyhead, with a minuteness of folding
which is not seen in slates. Like slates they can
be inferred to have been crystallized by the trans-
formation into heat of the pressure which elevated
them. They have been exposed at the surface by
removal under the denuding action of water, of
the rocks which originally covered them.
Schists often alternate with crystalline quartz-
rock, which appears to have been originally sand-
stone, metamorphosed by partial solution and
THE MATERIALS OF MOUNTAIN CHAINS. 23
crystallization which has blended the grains. In
some localities, as on the west coast of Scotland,
limestone occurs in schists and gneiss. Its tex-
ture is frequently compact and crystalline, and
sometimes saccharoid like statuary marble. It
contains many minerals but no fossils. All lime-
stones were originally deposited from water.
Thus the three chief types of water-formed rock
sandstone, clay and limestone appear to be
represented among schists. The process which
has rendered them crystalline is termed metamor-
phism. Metamorphic rocks, which divide into
layers by differences in the mineral character of
their crystalline constituents, are said to be foli-
ated. This foliation may be regarded as closely
comparable with the cleavage of slates.
Schists may be formed of quartz, felspar and
mica in parallel layers, when the rock is termed
gneiss. The crystals of a schist may be thrown
out of their parallelism, as in Anglesea, so as to
present a confused mixture, which has been
termed granite. Some observers, however, take
the converse view, and believe that the original
texture of the rock was granite, and that the
schistose texture has been acquired by shearing
movement acting on a heated plastic rock. In
the south of Cornwall a schistose texture has
been imparted in the metamorphic region of
Cornish schists, to rocks which were originally
volcanic.
Metamorphism is produced in several distinct
ways. When the rocks of an elevated tract be-
come changed in texture throughout their mass,
the expression " regional metamorphism " has
been used to distinguish such wide-spread trans-
formations of rock texture, from the local altera-
24 THE STORY OF THE EARTH.
tions of texture termed "contact metamorphism,"
which result from highly heated rocks acting
upon the sediments over which or through which
they flow. The changes produced by the action
of the atmosphere and infiltrating water, which
break up minerals originated by heat or pressure,
and elaborate others in their place, give rise to
"sub-aerial metamorphism."
In the central regions of mountain chains, such
as the Grampians and the central axis of Devon
and Cornwall, schists sometimes pass into the
condition termed granite; so that there has some-
times seemed to be a relation of cause and effect
between the position in which the granite occurs,
and the way in which its mineral matter is ar-
ranged.
Granites vary so much in the minerals they
include that they form a family of rocks dis-
tinguished by chemical and mineral composition
and texture. The minerals depend upon the
chemical constituents. The silica varies from 55
per cent, to 80 per cent. The alumina from 7
to 20 per cent. So that the quartz is commonly
from a fifth to a third of the bulk of the granite,
though occasionally nearly two-thirds. The mica
may occasionally be only i per cent., though it
is commonly between 5 and 25 per cent. The
felspars form between 40 and 70 per cent, of the
rock. Sometimes a green variety of hornblende
gives rise to hornblendic granite. Granite may
include angular fragments of schists, slate and
limestone, often of immense size. These frag-
ments appear to show that the granite is intru-
sive, and that it tore them away from rocks
through which it passed. Instances have been
recorded of granite resting upon schist. Granite
THE MATERIALS OF MOUNTAIN CHAINS. 25
is also intruded on a smaller scale, forming veins,
which penetrate into other rocks, or sometimes
cut through the granite itself. The only evidence
of the condition and temperature at which the
granite was intruded is afforded by its junction
with slate. In Cornwall, where the slate near to
it has acquired the texture of mica schist and
gneiss, there is no evidence to show whether that
metamorphism was due to the heat of the granite,
or to the pressure which it exerted, or both com-
bined.
A few rocks which are found in mountain
regions resemble granite in texture, but differ
from it in mineral constituents, owing to the
original chemical difference of the material out
of which the crystals are formed. Syenite is well
known in Charnwood Forest and in Guernsey.
Syenite is a rock formed commonly of orthoclase
felspar, hornblende and black mica. They are a
variable group, including mica syenites, augite
syenites, nepheline syenites, zircon syenites and
many others.
A third type of granite rock is named gabbro.
It is familiarly known in the Cuchullin hills in
Skye. Its crystals are as large as those of granite,
and similarly arranged. It is formed of a plagio-
clase felspar like labradorite, associated with some
mineral of a brassy or metallic aspect like diallage,
and often contains black mica and olivine; and
in some localities hornblende.
These granitic rocks have been termed plu-
tonic because they appear to originate in the re-
gion which mythology assigns to Pluto, in the
interior of the earth, consolidating slowly under
great pressure.
26 THE STORY OF THE EARTH.
CHAPTER IV.
VOLCANIC ROCKS.
No clear distinction can be drawn between
plutonic rocks and coarsely crystalline forms of
volcanic rocks. Both are extruded in some in-
stances from deep-seated parts of the earth. In
consequence of the rigid condition of the globe
it is impossible that those rocks came to the sur-
face from an unconsolidated interior by ascend-
ing fissures. Many writers have assumed the
existence of molten areas or lakes in the interior
of the crust, as a source for lava streams, which
sometimes flow on the surface for a hundred
miles.
Others, again, assume that the longitudinal
fissures, along which volcanic cones have been
built, penetrate down to different layers of the
earth, each distinguished by having the mineral
character of the different kinds of volcanic rocks.
Such a fissure allows the atmosphere to penetrate
downwards, and removes from the heated rock
the pressure which had kept it solid. The rock
then liquefies and ascends the fissure like fluid in
a pump, until it comes in contact with water de-
rived from the earth's surface, and so generates
steam, which forms the explosive outbursts. The
steam ascends miles high into the air, carrying
up the rock in the form of dust. The dust from
the volcano Krakatoa, in the Strait of Sunda,
ejected in 1884, remained suspended for more
than a year.
On this hypothesis the difference between
plutonic rocks and volcanic rocks is in the circum-
VOLCANIC ROCKS. 2^
stance that the plutonic rocks consolidate deep
in the earth, while the volcanic rocks consolidate
under the pressure of the atmosphere, or near to
the surface.
The principal types of volcanic rocks are
named Rhyolites, Trachytes, Andesites and Ba-
salts. The basalt has been supposed to be the
last formed ; and to have come from a greater
depth than the others, being commonly the
densest of the volcanic rocks. It frequently rests
upon andesites and rhyolites. These rocks have
been repeated several times in succession in the
history of the earth. Rhyolites are found in the
old pre-Cambrian rocks of Wales; andesites in
the Cambrian rocks of the Lake district, and the
Old Red Sandstone of Scotland ; while in the
later Coal Measures there were countless out-
bursts of basalt. The volcanic rocks of the Ter-
tiary period in Britain are a repetition of those of
the Primary period, basalts succeeding andesites
and rhyolites.
There is at the present day something like a
geographical distribution of the different volcanic
rocks. The volcanos of the Andes pour out the
rock named andesite. The volcanos of Southern
Italy give out varieties of basalt. Metals are
very rarely associated with volcanic eruptions,
though an appreciable quantity of silver has been
found in volcanic ash of eruptions in Chili.
Chemical and mineral composition alike sug-
gest the closest relation between the deep-seated
crystalline rocks and those which flow from vol-
canos. The plutonic granite appears to become
the volcanic rhyolite. Plutonic syenite and dio-
rite on reaching the surface appear to become
andesite. And the rock which cooling under
28 THE STORY OF THE EARTH.
pressure becomes gabbro, after flowing on the
earth's surface become? basalt.
Rhyolite. The name rhyolite indicates the
fluidal structure of the cooled lava, which results
from the movement of minute crystals about
larger crystals in the flow of the molten stream.
Some of the crystals are visible to the eye. The
material between them is named the ground mass.
Under the microscope, this ground mass is seen to
be formed of microscopic crystals, with an un-
crystalline material between them, distinguished
as the base. The visible crystals are principally
quartz, with the glassy variety of orthoclase fel-
spar named sanidine. These minerals may form
the entire mass of a granite rhyolite. But rhyolite
may be free from crystals, forming a glass, such
as obsidian ; or be expanded into a froth like
pumice.
Nearly all crystalline rhyolites are full of con-
cretions with a radiating structure, or alternations
of granular layers with spherulitic layers, and
these are known as spherulites. Besides the
common form of quartz, another variety named
tridymite occurs, in hexagonal plates. A little
mica and sometimes hornblende may be diffused
in the rock. The oldest British volcanic rocks of
St. David's, Bangor and the Wrekin, are rhyolites.
Rhyolites and rhyolitic ashes often occur around
granitic centres, as though they were mutually
related.
Andesite. Andesites contain 55 to 75 per cent,
of silica. As the silica increases, the percentage
of alumina decreases from 20 to about 12 per
cent. The oxide of iron and lime also become
less with the increase of silica. Typical andesites
are formed of oligoclase felspar, and columnar
VOLCANIC ROCKS. 29
nornblende, in a glassy ground mass, with a little
mica and magnetic iron. The quartz hornblende
andesites correspond to syenites in chemical com-
position ; just as syenites correspond chemically
to some Cambrian slates. The hornblende ande-
sites, which are free from quartz, are closely re-
lated to the rocks named diorites. Andesites are
largely quarried on the Rhine, in the Siebenge-
birge, near the Apollinaris spring at Remagen.
Andesite abounds in black concretions rich in
hornblende, like those found in the granite of
Shap in Westmoreland. Phonolite is probably a
volcanic representative of a syenite which con-
tains the mineral nepheline.
Basalt. This is the most familiar volcanic
rock. Its silica is reduced to 35 to 55 per cent.
Oxide of iron, lime, and magnesia are more abun-
dant in it than in other volcanic rocks. It con-
sists chiefly of the minerals labrador-felspar, and
augite, or some similar substance, usually associ-
ated with a little magnetite and olivine. It is
dark in tint, grey-brown, blue-black, or greenish
black when freshly broken. Cooled slowly, it
gains a fine granular texture, and is known as
dolerite.
In the most ancient basalts of Cambrian,
Silurian and Devonian ages the olivine and augite
have been partly decomposed, and converted into
a green mineral like chlorite. The basalt or
dolerite is then known as diabase. The less
altered dolerites, of carboniferous age, have been
termed melaphyres. Occasionally the felspar in
basalt may be replaced by allied minerals. In
Etna and Vesuvius leucite takes its place. There
is also a nepheline basalt.
Olivine may take the place of felspar. That
30 THE STORY OF THE EARTH.
mineral then gives a name, peridotite, to the rocks
in which it is an essential constituent. Those
rocks are frequently converted by decomposition
into serpentines.
Volcanic rocks of the basalt family sometimes
divide into beautifully regular six-sided columns,
such as are familiar in the island of Staffa, and
the Giant's Causeway in the north of Ireland. A
lava flow sometimes cools from its floor and also
from its upper surface ; and two independent sets
of vertical columns of different sizes may then be
formed, separated by a crystalline part in the
middle.
Each of these kinds of lava may also be repre-
sented by fragmental rocks, having the aspect of
cinders, or dust. In past periods of geological
time, beds of volcanic agglomerate, of ashes, and
vesicular lavas are common in association with
compact lavas. In North Wales, among the
Arenig rocks, the ashes are enormously thick in
Cader Idris, Aran Mowddwy and Arenig moun-
tains, and there is little doubt that the ash was
ejected from volcanic throats near Dolgelly and
Arenig.
In the Permian rocks near Exeter, the beds of
volcanic ash at Pocombe are manifestly drifted
by the wind. And at Spence Combe the lava flow
is highly vesicular, with the vesicles filled with
minerals, giving singular evidence of elongation
of the steam cavities by flow in these old lavas of
Devonshire.
There is a close chemical resemblance between
the several types of volcanic and plutonic rocks,
and a marked similarity in their mineral composi-
tion, which suggests a common origin. The evi-
dence is not quite so complete that would tend to
THE MATERIALS OF STRATA. 31
establish a transition from the plutonic rocks
through schists to water-formed deposits. It has
not been fully collected, but deserves examina-
tion, since the earth offers no indication of a be-
ginning in its geological history. If metamor-
phism such as is manifest in the older rocks were
extended over the earth's surface it would oblit-
erate records. And the wearing up of such
metamorphosed rocks into new sediments would
ensure a succession of similar rock materials.
CHAPTER V.
THE MATERIALS OF STRATA.
Terrestrial Rocks.
AROUND many parts of the coast, as in Lanca-
shire and Norfolk, the winds blow up sands from
the sea-bed, laid bare at low tide. These sands
form low ranges of hills, known as sand dunes.
They often show forms of hill contours as varied
as are produced by the work of water and frost in
carving hills out of solid material. These sand
dunes are but an insignificant illustration of the
work done by the wind, in heaping and rounding
the grains of sand which form desert regions.
There, every grain of quartz, which in a sandstone
usually retains some of its angles of crystal form,
is rounded by long continued motion, till it be-
comes a miniature pebble. There is some evi-
dence that desert conditions not altogether dis-
similar to those of Arabia or the Sahara may
have existed in Great Britain at the beginning of
the Secondary period of time, when the rock salt-
32 THE STORY OF THE EARTH.
was in process of accumulation by the evaporation
of land-locked basins of the sea. In Lancashire
and Cheshire, in the lower part of the Trias, there
are some layers known as the " millet seed beds "
because the separate grains of sand flow between
the fingers like millet seed or shot. Those minute
pebbles are not all of quartz but partly of felspar.
They can only be compared to blown sands of
deserts in their pebble-like forms.
The less completely rounded sand grains in
ordinary sandstones have probably acquired their
character from long continued rolling, partly in
rivers, partly on shores, as they have passed from
one geological deposit to another in successive
epochs of time, as a consequence of the construc-
tion of new layers of rock out of the materials of
ancient lands; a process repeated again and again,
and still in progress.
Another terrestrial rock which can scarcely be
termed water-formed, because it is accumulated by
vegetable growth, is seen in the peat, which cov-
ers large parts of the earth's surface where the
mean temperature falls belows 42 F. It is well
known that peat frequently originates in the fall
of forest trees, because they obstruct the surface
drainage on level lands, until bog plants grow and
form a sponge-like covering to the land which
buries the fallen trees, and kills the adjacent for-
est. Such accumulations in Cambridgeshire have
been stated to attain a thickness of 40 feet. In
the East of England, as in Ireland, there are two
successive peats. The older has yew trees at the
base ; and the newer peat covers forests of pine
trees. In the Fens of the Isle of Ely these peats
are often separated by a clay of marine origin,
the " buttery clay " of the Fen-man, the Scrobicu-
THE MATERIALS OF STRATA. 33
taria clay of science, so named from a bivalve
shell found in it, which lives in the swampy inlets
on the east coast of England. In that clay are
occasionally found the remains of walrus and
seal, whale and grampus ; showing that the inlet
known as the Wash extended southward during
the deposition of the clay, over the lower peat in
much of the Isle of Ely. When peat becomes
compressed by the deposition of superincumbent
rock, it is consolidated like the rocks with which
it alternates. There are important geological de-
posits, which have grown in the same way, in the
successive periods of time. At the beginning of
the tertiary period, at Bovey Tracey in Devonshire,
alternations of lignite and clay form a succession
of layers which fill up a lake-basin in the older
rocks : similar growths are seen in the Brack-
lisham beds of the Isle of Wight. In the second-
ary rocks there is a remarkable bed of vegetable
matter five feet thick, at Brora in Sutherland,
which is worked for coal. Thinner beds are found
on the Yorkshire coast, which appear to have
grown like the modern beds of peat, in the posi-
tions in which they are found. Far more impor-
tant are the beds of consolidated vegetable matter
found in the upper carboniferous rocks of the pri-
mary period, which are commonly known as coal.
They often give evidence of change in level of
land during their accumulation ; the same bed
being thick in one place and divided up at a
little distance by intervening sedimentary de-
posits. These accumulations of sediments pre-
serve indications of the plant life of the earth,
and in the associated sediments are occasional-
ly found remains of insects and other terrestrial
animals which lived in the same epochs of time
3
34 THE STORY OF THE EARTH.
Pebble Beds.
Any rock which is sufficiently durable to break
into compact pieces may give rise to a pebble bed
when the fragments are further reduced in dimen-
sions by the action of frost, or the transporting
movement of a flowing river, or the battering ac-
tion of waves upon a shore or shoal. The harder
rocks are not rounded into pebbles without long
continued rolling. The term pebbles is applied
to stones more than half an inch in diameter, so
that they vary in size from Barcelona nuts to co-
coanuts. Stones which are larger than these are
termed boulders. Stones which are smaller are
often termed grits. A river flowing two miles an
hour transports stones as large as eggs, so that
pebbles may be brought by such means from
many kinds of rock which are exposed in the in-
terior of a country. They are mixed and ac-
cumulated either on shores, or where the stream
leaves them behind owing to its slower move-
ment.
The pebble beds around shores are carried
backwards and forwards with the daily movement
of the tidal waters, and they serve to mark, when
covered up by other sediments, ancient shores of
seas which existed in bygone time. Pebbles
which exist in the old geological deposits have
been derived from granites and schists, from con-
solidated quartz rock, and lava streams, from con-
solidated sandstones, and veins of quartz which
infiltrating waters have deposited in the cracks
which upheaval has produced in ancient slates.
Many beds of pebbles have been formed from con-
cretions of flint, and similar substances, which
THE MATERIALS OF STRATA. 35
FlG. 2. Conglomerate of flint-pebbles, from the Hertfordshire
puddingston'e, showing the external surface of the pebbles.
FIG. 3. Fracture through this conglomerate, showing sections of
flint-pebbles imbedded in a siliceous cement.
3<J THE STORY OF THE EARTH.
prove mere durable than the geological deposits
in which they were contained.
Pebble beds indicate the ceaseless action of
water in wasting the earth's surface, which has
gone on without intermission through all the
periods of past time, because tides have never
ceased to flow and ebb or rivers to run.
The positions in which pebble beds accumulate
have changed, because the outlines of the seas
alter with the folding of the rocks during past
ages ; and they frequently come back again age
after age with variation in level of land, at long
intervals to be re- deposited upon a shallow sea-
bed, or shore-line in the same district.
Occasionally the pebbles are scratched, and
some in the Permian rocks of Worcestershire are
regarded as ice-worn fragments.
The pebbles are frequently bound together by
a cement, which converts a loose aggregate of
stones into a compact and durable rock. The
most important of these cements is silica which is
occasionally more durable than the pebbles which
it binds together, as may be seen in the Hert-
fordshire puddingstone. Such rocks, named con-
glomerates, are also formed of pebbles bound
together with a cement of oxide of iron, or of car-
bonate of lime.
Conglomerates and pebble beds are among
the oldest known geological deposits in Britain.
Among the primary rocks they are formed almost
entirely of granite, schists, and lavas. Among
the secondary rocks the pebbles which make up
conglomerates are frequently derived from rocks
that have more obviously had a water-formed
origin. In the tertiary period of time most of the
English pebble beds have been derived from the
THE MATERIALS OF STRATA. 37
grinding up of flints, liberated from the destruc-
tion of the chalk.
Pebble beds frequently mark important divi-
sions of geological time in the country in which
they are found; because their existence implies
that change of level of land which resulted in the
tidal denudation which brought them into exist-
ence. Among examples of great pebble beds and
conglomerates may be mentioned the geological
deposit known as the Llandovery beds, which in
Wales forms the base of the true Silurian rocks,
and extends successively over the upturned edges
of the older Cambrian rocks, which had previously
been planed level by the sea.
Sands.
There is a rapid gradation between pebble-
beds and sands. Beds of intermediate texture,
with many grains as large as peas, are named
grits, and are typically seen in some layers of the
" Millstone grit," which underlies the coal. The
grains are miniature pebbles, often angular, formed
by rounding angular masses of quartz rock on a
sea shore. On a sandy shore, like that of Hast-
ings, Reculvers or Hunstanton, the sands now
being deposited are derived from sandstones
which form the cliffs, broken up first by joints,
and afterwards separated into grains, similar to
the material out of which such sandstones were
originally consolidated. Cambridge green sand
and Neocomian sand contain many rock frag-
ments and fossils derived from ancient deposits.
The particles of quartz are often crystalline,
but are sometimes derived from uncrystalline
forms of silica such as chalcedony, chert, opal,
44872
38 THE STORY OF THE EARTH.
and flint. Under the microscope the source of
the grains can usually be recognised; for if the
quartz was originally crystalline all the crystal
faces are rarely lost, and the mineral may include
hair-like crystals of other minerals, or minute
cavities ki which there may be fluid with a bubble
of air. This is enough to show that the quartz
came originally from the wearing away of schists
or granitic rocks, in times when the level of the
land caused those rocks to be exposed to the de-
stroying influence of the waves. But although a
sandstone is mainly formed of quartz, it rarely
contains more than from 50 to 85 per cent, of
silica the whole of which is not in the crystalline
form of quartz. There are frequently in a sand
grains of water-worn felspar. The felspar, which
is a silicate of alumina combined with a silicate of
soda or potash, may decompose, liberating the
soluble silicate of soda or potash. Felspar crys-
tals abound in the old Cambrian sandstones of
Barmouth, in the Devonian sandstones of South
Devon, and in the Trias sandstones of the South
of England. Sandstones often contain scales of
the mineral mica, as in the Yorkshire sandstones,
used for paving. Sometimes the mica decays, and
then the iron oxide which was one of its constitu-
ents, gives a rusty colour to the sandstone. Many
sandstones are mainly the grains of quartz, which
were constituents of crystalline rocks, liber-
ated by the decay of minerals with which they
were associated, and left behind comparatively
near to the source from which they were derived.
The finer particles associated with them which
resulted from the decomposition of other minerals
have been carried to greater distances. A stream
flowing three miles an hour at its bottom carries
THE MATERIALS OF STRATA. 39
away sand ; but sand may be carried out to a dis-
tance of more than 50 miles from the shore. The
FIG. 4. Laminated vertical sand (Bagshot sand 1 * of Alum Bay in
the Isle of Wight, showing current bedding.
size of the particles of sand when coarse is ^ of
an inch ; but the majority of the grains vary from
-j^-g- of an inch to -j^-y of an inch in diameter.
When a sand is laid down it is incoherent. It
often shows evidence of its shallow-water origin,
in the manner in which currents have brought its
materials from different directions. After a de-
posit of sand is uplifted, and exposed to the action
of rain-water flowing through it, it begins to be
bound together by a cement which determines its
40 THE STORY OF THE EARTH.
durability. There are three chief kinds of ce
ment, which were originally of vegetable or anU
mal origin. First, there is the iron sand which is
commonly red, yellow, or brown; and is rarely
green. The iron was probably collected from the
sea-water by the growth of marine plants, and
liberated by their decay. Oxide of iron is liable
to accumulate in the planes in which water has
flowed underground through the rock, which are
sometimes determined by strain. Examples of
sand so coloured are seen in the Bagshot beds of
Alum Bay, in the Isle of Wight ; and the Wealden
beds of Warbarrow Bay, in the Isle of Purbeck.
The Wealden sands of Kent and Sussex are so rich
in iron that they were for a long time the main
source of the metal out of which English imple-
ments of war and ornaments of art were made.
Sands are often bound into calcareous sand-
stones by a cement of carbonate of lime. It is
sometimes derived originally from the evapora-
tion of water, but more frequently from the fall-
ing to the bottom of organisms which lived in the
water, or by the accumulation of marine shells.
The Kentish Rag, which forms the lower part of the
Lower Greensand, is a familiar example of a cal-
careous sandstone in the S. E. of England. The
shells become dissolved by water flowing through
the rock ; and the carbonate of lime of which they
consisted is re-deposited, so as to fill the inter-
spaces between the grains of quartz, and form
crystals which bind the sand into a sandstone.
The third kind of sandstone as modified by
the cementing material is the siliceous sandstone,
in which the grains of quartz are bound together
by silica. These sandstones are of all geological
ages. The material of the cement appears to be
THE MATERIALS OF STRATA. 41
in most cases, if not always, the minute particles
of the siliceous skeletons of sponges, some of
which resembled the Euplectella speciosa from
eastern seas, sometimes known as Venus's flower
FIG. 5. Ripple-marked sandstone from Permian Rocks in the
Karoo, near Prince Albert, Cape Colony.
basket. The spiculae which form the skeletons
of such sponges, dissolved by the water draining
through the rock, furnished a cement which is
deposited in the same way as the cement of cal-
careous sandstones. Infiltration of this silica
frequently builds, within the sandstone, compact
layers of a flinty rock, known as chert. Such
layers are found in the Lower Greensand, the
Upper Greensand, and especially in the Carbon-
iferous Limestone. In the S. E. of England the
sands and sandstones, secondary and tertiary, are
often coloured green, with the mineral glaucon-
ite. As a rule sands are red, yellow, or brown,
42 THE STORY OF THE EARTH.
coloured with oxides of iron. They are shallow-
water or shore deposits which show current bed-
ding; due to deposition by changing currents, as
well as ripple-marks of wave movement, and foot-
prints of animals.
Clay.
Any substance which is taken up by moving
water so as to cloud it, is popularly termed mud,
and mud when deposited consolidates into clay.
Mud banks abound on parts of the coast where
clay forms the cliffs, because tidal movement of
the water converts the clay into mud. It is
chiefly composed of light flocculent particles of
silicate of alumina, which frost tears apart from
each other, and the lightest shower moves down
a valley. The mud of rivers is carried into the
sea, as far as the fresh water can float over the
ocean. The Yellow Sea is yellow with the mud
of the Hoang-Ho. When the Rhine at Bonn is
turbid and full of water, - 6 fa part of its weight
is mud ; but after continued dry weather the sedi-
, ment falls to -3-^^-5-5- part of the weight. Thus the
^alternation of seasons may give a laminated char-
acter to deposits carried to the sea, marking the
succession of years by changes in the deposit, like
the rings of growth in the wood of a tree.
When clay extends parallel to a shore, in con-
sequence of denudation of the cliffs, it commonly
has a definite relation to coarser sediments which
are deposited nearer to land. This is seen in the
large percentage of sand, sometimes amounting
to 50 or 60 per cent., which may be separated
from clays by washing. The particles of sand
however are extremely fine, so that they are held
in suspension for a long time by moving water.
THE MATERIALS OF STRATA. 43
Under such circumstances, the chemical composi-
tion of a clay is sometimes the same as that of a
sandstone ; and there may be an unbroken tran-
sition from one deposit to the other through an
intervening loam. Almost all the minerals which
enter into the composition of crystalline rocks,
are occasionally found in clays. Often the origin
of a clay is revealed in the abundance of the
flakes of mica which are scattered through it, for
the silicate of alumina corresponds chemically
with decomposed felspar, and the presence of
particles of quartz diffused in it, shows that the
rock has been derived from an old crystalline
material. The presence of mica renders it prob-
able that the schists which were denuded were of
the kind termed gneiss, if the crystalline rock
was not granitic. Some ancient clays have been
found full of needles of the mineral rutile. The
purest clays are formed on land from the decom-
position of white granite. Such a source would
appear to be necessary for the beds of white pipe
clay, found interstratified in the Bagshot sands of
Hampshire and Dorset.
The colours of clay are due to oxides of iron.
Occasionally, as in the Woolwich and Reading
beds at Reading, current bedding is marked by
alternate layers of red and green clay. Such bed-
ding would be unsuspected, but for the colour.
Often a blue clay passes into a brown or yellow
tint. It is then sandy and porous, so as to per-
mit the infiltration of water charged with atmos-
pheric air, which oxidises the iron.
Minor sources for clay are the small percent-
age of silicate of alumina which is the insoluble
residue left when limestones have been dissolved.
This forms the red cave earth in limestone dis-
44 THE STORY OF THE EARTH.
tricts; and the red soil on limestones. Beds of
volcanic ash, exposed upon the surface, may be-
come broken up by atmospheric decomposition
and converted into clay.
The bedding of clays is frequently marked by
the occurrence of thin layers of earthy limestone,
or of concretions termed septaria, which are dis-
tributed in parallel layers, on zones where car-
bonate of lime was abundant. These concretions
probably mark near approach to the limit to which
the ancient mud was carried in the sea, where the
sediment was becoming replaced on the ocean
floor by calcareous layers of organic origin. The
septaria often contain upwards of 50 per cent, of
carbonate of lime, and their occurrence appears
to mark, either oscillations in level of the sea bed
which varied the distance to which sediment was
carried, or indicates that the land area which was
being worn away to form the new deposit became
more calcareous.
One of the most interesting clay deposits in
England is the inflammable clay, known as Kim-
eridge clay, found in Lincolnshire and Cambridge-
shire as well as on the Dorset coast. Some
layers of this clay when distilled yield as much as
40 per cent, of paraffin, naphtha, tar and heavy
oils, which are similar to products of coal tar.
Those chemical substances derived from coal be-
ing of vegetable origin, it is probable that the in-
flammable character of the clay is due to the growth
of marine algae, though no traces of plant remains
are found among the remains of marine shells
which crowd the deposit.
Almost all clays yield the minerals, iron pyrites,
and selenite, which are closely dependent upon
each other. Iron pyrites mineralizes fossils, and
THE MATERIALS OF STRATA. 45
occurs in irregular masses. Both iron and sulphur
may have been liberated in the decay of marine
plants. As the iron pyrites decomposes in con-
tact with the air, its sulphur is converted into an
acid, which dissolves the substance of shells, ex-
pelling the carbonic acid, and forming a hydrated
sulphate of lime, known as selenite. Occasion-
ally phosphate of lime form concretions in clays
and mineralizes fossils. Clays are commonly
formed in deeper water than sands, and further
from the shores which furnished the sediment.
Limestone.
Limestones differ from other water-formed
rocks in not being sediments. Their particles
have grown, as portions of organisms ; and have
become rock substance, when the animals or
plants died, which separated the carbonate of
lime from water. Sometimes limestone is pre-
cipitated by evaporation of water. The carbonate
of lime which forms limestones is usually in the
mineral condition of calcite.
Beds of limestone may be deposited over the
whole sea-bed, whether the water is shallow or
deep. As a rule they are most noticeable in the
open ocean, beyond the limits to which sediments
are carried. Limestone may be formed near into
shore ; and when the rock is dissolved away by
acids, in some cases nothing remains but a vary-
ing percentage of siliceous sand. Rocks of that
kind are termed calcareous grits.
Evidences of the shallow-water origin of some
oolitic limestones in the west of England, are also
seen in current bedding, which characterizes some
oolitic rocks, and is as marked as in sandstones.
4 6 THE STORY OF THE EARTH.
The limestones named oolites, are probably all
formed in moderate depth of water; since there if
e
PIG. 6. Lithographic limestone from Solenhofen, showing circular
staining at the intersection of
gated fracture on the right side.
staining at the intersection of rectangular joints ; and corru-
f ra
some evidence to show that the oolitic grains may
be derived from plants like the Nullipores, and
larger grains, termed Pisolite, show a minute
tubular structure, attributed to an organism
named Girvanella.
Beds of shell limestone are seen in process of
formation on many shores. Shell-haven, in the
Thames, takes its name from the manner in
which shells are drifted together so as to form a
deposit ; and a similar accumulation may be ob-
THE MATERIALS OF STRATA.
47
served at Shell Ness which makes the eastern end
of the Isle of Sheppey. Parts of the forest mar-
ble in Oxfordshire, consist of accumulated growths
of shells; and in Gloucestershire portions of the
same deposit show ripple marks which indicate
shallow conditions of deposition.
Coral reefs are also to be classed as shallow-
iwater limestones since the coral grows most vigor-
ously where the water is aerated by the movement
of the waves near to the surface of the sea. The
FlG. 7. Carboniferous limestone, the surface dissolved by rain,
showing the remains of Encrinite columns, of which it is part-
ly formed.
great brainstone coral Meandrina and the com-
pact coral Forties, associated with Nullipores
build buttresses which constitute the living foun-
dation of the reef. Our English coral limestones
48 THE STORY OF THE EARTH.
all give evidence of shallow-water conditions,
exactly such as are seen in the growths of fring-
ing reefs of coral at the present day.
There is a second group of limestones which
may be termed oceanic, or deep-sea limestones,
made known by exploration of the floors of the
great oceans. They are largely composed of the
minute organisms termed foraminifera, such as
cover so much of the Atlantic, Pacific and Indian
oceans. Among geological deposits due to such
organisms, may be placed the Chalk of Europe;
the Nummulitic limestone, which extends through
Europe, Africa, and Asia; and the Fusulina lime-
stone, which extends from Russia to Japan.
There are other animals which appear to form
deep-water limestones, since they live in some
depth of water at the present day, such as the
group of shells termed Brachiopoda; and Encri-
nites, which make up portions of the Carbonifer-
ous Limestone in this country.
An oceanic limestone is not necessarily built
up in deep water, although such rocks often attain
a great thickness. It is only necessary that the
sea in which the rock accumulates should be be-
yond the limits to which sediments from land can
be transported. Ocean basins often increase in
depth as the deposit increases in thickness, when
limestones may be formed as thick as are the
Carboniferous limestone of Flint and Derbvshire.
Fresh Water Deposits.
Accumulations of sands, clays, and limestones
are brought down from higher land wherever
fresh waters accumulate upon the land surface
If the pond or lake rests upon a limestone the
THE MATERIALS OF STRATA. 49
deposits formed within the lake will be mainly
calcareous. Fresh-water plants like the Chara
precipitate carbonate of lime upon the stem by
absorbing the carbonic acid gas from the water,
so that the carbonate of lime is no longer soluble.
This ensures an accumulation of granular lime-
stone as the plants decay. Such a deposit covers
up the remains of fresh water shells, and fre-
quently the remains of animals derived from land.
The lakes in Cumberland and Westmoreland
are found to have their beds covered with deposits
which consist of volcanic minerals when they lie
in regions occupied by old volcanic rocks; while
the deposits are ordinary sediments when the
lakes are surrounded by rocks formed of such ma-
terials. If the lake is sufficiently large, like the
Lake of Geneva, the sediments may be completely
sorted, successively deposited, and pass from the
condition of coarse pebbles and boulders where
the Rhone coming from the Valais enters the lake,
to the finest sediment where its clear waters leave
it, southward of Geneva. Hence a lake may con-
tain an epitome of all known water-formed rocks
pebble-beds, sands, clays, limestones as well
as layers of plant remains consolidated into
lignite.
Examples of such fresh-water growth of sedi-
ments alternating with lignite, has been already
referred to in the layers known as Coal Measures.
In the lacustrine deposits which are so important
in the northern part of the Isle of Wight, fresh-
water limestones are familiarly seen at Headon
Hill and Bembridge, which were formed in fresh-
water lakes, and give no evidence of sediments
being mixed with the calcareous matter. Other
fresh-water limestones alternating with terrestrial
50 THE STORY OF THE EARTH.
surfaces, on which the remains of coniferous foiest
trees stand erect, are seen in the Purbeck beds of
the Isle of Portland and the Isle of Purbeck in
Dorsetshire. Fresh-water sediments, alternations
of sands and clays are found with numerous rep-
etitions in the Wealden beds of the Isle of Purbeck,
and the Isle of Wight ; and they are associated
into a few deposits, fairly well defined into sands
and clays, in the Wealden strata of Kent and
Sussex.
Recognition of the fresh-water origin of all
such rocks rests upon the presence in them of
animals which lived in fresh water. When these
are shells they are often matted together to form
layers of some thickness. The types or genera
are identical with those which live in every pond,
lake and stream on the surface of the country at
the present day. The bivalve shells are usually
species of Cyclas, or' Unio, or Anodonta. The uni-
valve shells are either the pond shells Planorbis,
Paludina and Ltmncza, or such river shells as Neri-
tina, and the fresh-water limpet.
There is probably no fresh-water limestone
from which the seed-vessels of the plant Chara
are absent. Sometimes the presence of the sili-
ceous spiculae of the fresh-water sponge, Spongilla,
has resulted in fossils being mineralized with silica,
as in the Purbeck beds, or the formation of sili-
ceous layers and concretions in fresh-water lime-
stones, which may be compared to the veins and
concretions of flint found in marine strata like the
Chalk and Carboniferous Limestone.
THE SUCCESSION OF STRATA. 51
CHAPTER VI.
THE SUCCESSION OF STRATA.
Contemporaneous origin of water-formed rocks.
THE conditions under which sediments grad-
ually become finer, as the distance from shore and
depth of water increase, show that all known
varieties of rock may be formed and deposited
adjacent to each other at the same time. Not
only are the beds of peat in Irish bogs contem-
poraneous with the shell marls in the loughs, but
these are contemporaneous with the sands, clays,
and limestones which are forming at the present
time in our seas. Any one type of mineral mat-
ter may be represented by all the other types of
which layers of rock can be formed, in a succes-
sion of different localities. A geological period
of time may be as accurately represented by ter-
restrial lignite, or fresh-water sands, as by any
kind of marine deposit. The chalky muds dredged
a few hundred miles west of Ireland are accumu-
lated in deeper water in association with different
types of life, but manifestly formed contempo-
raneously with the shell beds of Shell Ness, the
muds carried out by the Thames, and the sands
which are spread by the tides off Yarmouth.
In all geological ages there has been the same
contemporaneity of rocks of different mineral
character. Marine rocks must have been laid
down at the same time as the fresh-water sands
and clays of the Weald. An organic limestone
like the chalk formed in the open ocean, necessi-
tates shores where sediments were laid down.
/ea
an
/ TV.
5 S THE STORY OF THE EARTH.
And beyond those shores of the chalk sea were
land surfaces of islands and continents on which
plants and animals survived from age to age.
Lands have never ceased to exist from the
arliest ages. They have changed their forms,
f Their height of elevation above the sea has been
| altered; they have been broken up into islands
and re-united with other islands newly formed.
The lands which exist at the present day are built
up almost entirely of water-formed rocks, which
have been spread out one upon another in the
ocean. Every continent shows this history : a
succession of ancient sea-beds, with the deposits
formed upon them, alternating occasionally with
old land surfaces which make known epochs when
\the sea-bed emerged from the ocean, and became
land as it is now.
The shores, with their pebble beds and other
evidences of tidal movement of the waters, have
persisted from the earliest times, changing their
positions upon the globe, as the lands altered
their forms, never entirely passing away through
the long epochs of geological time, although they
only occasionally come back again to the places
in which shores had previously existed.
The open ocean with its limestones has proba-
bly been equally persistent and as variable in form.
Very little is known of limestones which may have
existed in the earliest geological ages. But from
their thickness and importance in the time named
Devonian and Carooniferous, and in all "subse-
quent times, it is inferred that the open ocean has
persisted, though its depth has varied. There
can have been no breaks in geological time,
though there are breaks in the continuity of land
surfaces, in the continuity of shore lines, and the
THE SUCCESSION OF STRATA. 53
continuity of deposits of the open sea. These
breaks are local, like the breaks which are made
by the islands or lands which divide the sea, and
by the waters which separate lands from each
other.
The Succession of super-imposed Rocks.
A sediment may be followed round a shore
line, so that it has everywhere the same general
character, except in so far as the rocks of the
cliffs vary, which give rise to pebble beds in some
localities and scarcely any sandy particles on the
shore in others. As a rule, tidal work sorts and
sifts the products which the sea carries down to
its depths, so that they are arranged in bands
which are parallel to the coast. The particles
vary in size in those zones of deposit. The finer
particles remain suspended longest; and are there-
fore transported to the greatest distance by the
moving water. Thus there is a horizontal succes-
sion of rocks on successive parts of the same
ocean floor, which may be roughly classed as
sands, clays, and limestones. Sands formed near-
est to shore sometimes pass into grits and pebble-
beds. And the limestones, like the sands, some-
times alternate with clays in vertical succession,
where they pass horizontally into each other. In-
stances may occur where limestones extend con-
tinuously from the shore to the open ocean, with-
out intervening deposits.
The horizontal sequence of water-formed
rocks, observed at the present day, explains the
meaning of the vertical succession of the layers
of rock termed strata, which differ from each
other in mineral character. By their superposi-
tion they build up most of the visible land, as well
54 THE STORY OF THE EARTH.
as of those parts which are hidden under the oceans.
> Their vertical succession depends upon successive
changes in position of the area from which sedi-
ments are brought into the sea.
If the land sinks down so that it becomes
smaller, and its shores recede, each kind of sedi-
ment derived from it, being carried by the moving
water the same distance as before its depression,
is transported for a less distance out to sea as
compared with the deposit formed previously.
Therefore the finer sediments on a sinking sea-
bed rest upon the coarser sediments, which had
been formed previously, when the source of sup-
ply was nearer to the place of deposition. In
other words, clays rest upon sands ; while the new
sands rest upon areas which had previously been
dry land. If this process of depression continues,
then while the clays follow the new sands, and
become super-imposed upon them, limestones are
super-imposed upon clays.
Sandstones occasionally give evidence that
they were deposited between tide marks, in pre-
serving the footprints of animals, as well as in
the ripple marks, sun-cracks and rain-prints which
were formed when the surfaces dried between suc-
cessive tides. Such memorials are preserved in
the Trias Sandstone of Cheshire, and the Hast-
ings Sand. Clays occasionally, in the abundant
remains of terrestrial plants which they yield,
give evidence of estuarine origin, which may not
be strictly comparable to the succession of con-
ditions seen upon a land which is being sub-
merged.
On the other hand some deposits are formed
upon shores which are rising, and advance at the
expense of the sea, and then the deposits which
THE SUCCESSION OF STRATA. 55
result from waste of the land, succeed each other
vertically in reverse order. In the sea which
borders the coast of South America, the sand de-
rived from its cliffs may be carried out to a dis-
tance of from 20 to 150 miles from the shore.
The mud formed at the same time would be car-
ried much further. If then such a land were to
be enlarged by slow upheaval, so that the shore
extended over the area which had previously been
the shallow sea, two sediments which would still
be formed would be carried as great a distance as
they were carried previously, and the sand at its
furthest limit from the shore would gradually ex-
tend beyond the limit of the sand beneath it, and
would thus be super-imposed in part at least upon
clay. In like manner the mud sediment would
be carried further than the mud had gone pre-
viously, so that it would similarly rest upon lime-
stone.
^.Therefore, under the influence of continual
depression, the geological deposits come to be
accumulated in the vertical order of sand, clay
and limestone, in the same place. While under
the influence of continued upheaval the vertical
succession comes to be limestone, clay, sandstone.
# There are constant oscillations of level of
land which are evidenced by successions of sand
and clay, or limestone and clay, which are local.
And occasionally a sediment is derived simul-
taneously from two different sources, as when
ancient cliffs furnish sand, and an ancient river
supplies mud which is deposited at the same time,
over part of the same area.
The layers of water-formed rock which form
every land, succeed each other vertically in some
such order as sand, clay limestone, limestone, clay
56 THE STORY OF THE EARTH.
sand. Their order in Nature, as seen in the cliffs
and on the surface of the land, is evidence of
great upward and downward movements both of
the floor of the ocean and the dry land, which
have been brought about by foldings of the rocks.
Usually these rocks, the strata of sand clay
and limestone, rest evenly upon each other, for
the upward and downward movements are com-
monly so gradual, that while the rocks are dis-
tinguished from each other by mineral character,
and the planes of bedding, which change with
FIG. 8. Geological map of part of Yorkshire, showing the west-
ward extension from Flamboro' Head of the Chalk and Hun-
stanton Limestone, so as to rest unconformably upon the
Kimeridge Clay, Lower Oolites and Lias.
depth of the sea-bed, there is no physical break
in the succession of limestone on clay or clay on
fr sand, and the beds in parallel planes of deposit,
THE SUCCESSION OF STRATA. 57
are said to be conformable to each other. This is
particularly true of an area undergoing depres-
sion. Yet as depression extends, and an area
which had previously been dry land is submerged
so as to be covered with new deposits, worn from
the higher land which is near to the now sub-
merged area, such a new layer begins a new order
of succession in that district, and rests upon the
edges of many older deposits which had been
tilted up and worn level, so that their edges be-
came exposed before the old land was raised from
the sea. Such a succession is said to be uncon-
forma-blf. There is an unrepresented interval of
time between such unconformable strata and the
layers on which they rest; but the unconformity
is local, and does not imply any real break in the
succession of rocks, for the break is a conse-
quence of the submergence of the denuded land,
which had interrupted the even spread of sedi-
ments by the water, so long as it remained above
the sea.
^ On the other hand, when land is undergoing
upheaval, and the shore deposits begin to be
raised out of the water, it must happen that the
newest formed deposits will be worn up and re-
moved before they emerge from the sea. There
is a break formed in this way in the horizontal
sequence, though there is no break in the vertical
sequence of strata. Traced by their mineral
character to the circumstances in which they
originate, the whole succession of water-formed
rocks which is known demonstrates no more than
three or four great oscillations in level of the
earth's surface, which have converted lands into
seas, and seas into lands.
It is obvious that land is disturbed in level in
5 8 THE STORY OF THE EARTH.
some localities, while the level elsewhere is un-
affected, so that the succession of rocks may vary
in mineral character in the disturbed district,
with no indication of change in the succession
felsewhere. On this account, the history of every
part of the earth needs to be told separately from
the other parts, for too little is yet known of the
detailed events which took place in the successive
periods of time, in the different portions of the
globe, to piece the parts of the story together
into a complete history of the earth.
CHAPTER VII.
-# ORIGIN OF STRATIGRAPHICAL GEOLOGY.
GEOLOGY originated in observation of the
earth's surface, by which records were made of
the order and arrangement in which different
rocks occur in England and Wales. -^This knowl-
edge is expressed in two laws. 'The first is the
law of stratification. It affirms that the rocks
which are anywhere exposed on the surface of
the country are usually portions of layers, which
rest successively upon each other. Therefore
they rise from beneath each other, in the order
of their relative antiquity, whenever they are in-
clined to the plane of the horizon. Every such
layer is a stratum. ,\Strata differ from each other
in relative antiquity, in their mineral materials,
thickness, extension, and degree of disturbance
from the original condition of their horizontal
deposition. * The law of succession of the layers
upon each other is named their superposition.
ORIGIN OF STRATIGRAPHICAL GEOLOGY. 59
^The second law is that every stratum may be
identified by means of the included remains of
plants and animals, termed fossils, which lived
when its rock material was being accumulated in
the part of the earth in which it is found. By
these fossils the exposed edge of every stratum
may be traced as it extends through the country.
Therefore the area occupied upon the surface of
the country by each geological deposit may be
drawn upon a map. A map made in this way,
which defines the limits of strata, lava flows,
crystalline and other rocks which form the coun-
try, is a Geological map. It shows how the strata
in a country may be distinguished and classified
by the succession of groups of animals and plants
which have followed each other in occupying the
same portion of the Earth's surface.
These Ja_ws were discovered about 1790 by
fWJliiairL_Smilh. He applied them in travelling
through the country, so as to make the first Geo-
logical Map of England and Wales, which was
completed in 1815. In 1816 his collection of
fossils, which distinguish and identify the several
British Strata, was placed in the British Museum.
It became the foundation of the National Geo-
logical Collection and the beginning of all Geo-
logical Museums.
Other observers had recorded the order of the
strata in different localities, and in some cases
had recorded the occurrence of fossils in a single
stratum ; but without making the discovery that
the strata may be identified by their organic re-
mains.
Dr. Lister, in 1684, proposed to the Royal
Society to make a map of the soils in our coun-
try. This was the first proposal to make a Geo-
60 THE STORY OF THE EARTH.
logical Map. In one of his writings Dr. Lister
gives a drawing of a small fossil, a Belemnite,
and states correctly, that it is found in all the
cliffs along the Yorkshire wolds, for a distance of
more than 100 miles, by Speeton, Londesbro' and
Caistor, -but always in a red ferruginous earth
[now known as the Hunstanton Limestone].
Mr. John Strachey in 1719 laid before the
Royal Society evidence that the upturned and
levelled edges of the Coal Strata in the Somerset-
shire Coal Basin were covered by nearly hori-
zontal beds of the Red Marl, Lias, and Oolite.
The Rev. John Holloway in 1723 described to
the Royal Society the parallelism of the Chalk
of the Gog-Magog and Chiltern Hills, the Sand
Hills of Woburn, and the Clay country drained
by the Cam, Ouse, Nen, and Isis.
The Rev. John Mitchell in 1760 stated to the
Royal Society that " we ought to meet with the
same kinds of earths, stones and minerals appear-
ing at the surface in long narrow strips, and lying
parallel to the greatest rise of any long ridges of
mountains, and in fact we find them [thus ex-
posed]." The ridge in England which influences
the direction of the strata is said to run first
north to south, and then from north-east to
south-west. Travelling between the Chalk hills
of Cambridgeshire and the Coal of Nottingham
and Yorkshire, he observed the succession of the
strata; and in 1788, gave to Smeaton the Engi-
neer, a table of these strata, with their thick-
nesses. They are enumerated in vertical se-
quence as Chalk, Golt, Sand of Bedfordshire,
Northampton lime and Portland lime in several
strata, Lyas, Sand of Newark, Red Clay of Tux-
ford, etc., Sherwood Forest pebbles and gravel
ORIGIN OF STRATIGRAPHICAL GEOLOGY. 61
[fine white sand], Roche Abbey and Brotherton
limes, Coal Strata of Yorkshire. This table was
given to Henry Cavendish, who preserved it.
Mr. John Whitehurst in 1778 gave an account
of the Geological structure of Derbyshire; and
remarks : the strata follow each other in a regu-
lar succession, both as to thickness and quality,
insomuch that by knowing the incumbent stra-
tum, together with the arrangement thereof in
any particular part of the earth, we come to a
perfect knowledge of all the inferior beds, so far
as they have been previously discovered in the
adjacent country.
Smeaton in 1786 expressed his belief that the
Lias extends from Watchet in Somersetshire to
Barrow in Leicestershire, probably with few
breaks in continuity, and through the vale of
Belvoir into Nottinghamshire and Lincolnshire,
beyond Grantham and Long Bennington.
There is no reason to believe that William
Smjlk had heard of any of these observations.
He was born 23rd March 1769, at Churchhill in
Oxfordshire, upon the Oolites. He became a
land surveyor and engineer; and at the age of
twenty-one had found out for himself the succes-
sion of such rocks as he had seen, and had begun
to compare the appearances at one locality with
those observed at a distance. His work was dis--if
tinguished from that of all predecessors by his
method of untiring persistence in observing facts
of stratification ; activity in comparing, extending
and establishing the conclusions to which those
observations led ; and care in recording upon his
map nothing but what he had seen and proved.
This work caused him to be known through the
country as Strata Smith ; recognised among geol-
62 THE STORY OF THE EARTH.
ogists as the Father of Geology ; and honoured as
a great original discoverer in science.
CHAPTER VIII.
Geological and Zoological Aspects of Fossil Plants
and Animals.
IN the early days of geology fossils were re-
garded with interest because some species were
limited in their range in time and only found in
certain rocks. -^Attention was given chiefly to
extinct species which were most abundant in each
of the geological deposits. A large amount of
practical work, in mapping the distribution of the
strata, was done with the aid of very slight knowl-
edge of a few species of animals.
^ It became possible also to group the rocks to-
gether in a rough way by limitation to the vertical
range of a few fossils. -*The oldest rocks were
defined as those containing Trilobites; the mid-
dle group as those containing Ammonites; and
the newest group as containing Nummulites. The
geologist, having to classify the rocks and iden-
tify them, was influenced in making divisions of
the strata occur wherever a difference in life of
any kind would permit the separation of strata, or
groups of strata, from each other.
A dim idea prevailed that the change in life
was in some way connected with the succession
of geological periods of time.J^Hypotheses were
put forward that the groups of strata correspond
FOSSILS. 63
to about six successive epochs, during which the
\life gradually became higher in the details of its
organization. This theory was not suggested by
examination of the rocks and their contents, be-
cause divisions which separate strata in Europe
are differently placed in America. The hypothe-
sis endeavoured to forestall results at which
science might arrive. xThe species of fossils
found in each stratum were supposed to have
been created in the period of time when they
were first met with ; and to have become extinct
when they disappeared with the succession of
newer strata.
Naturalists found that existing life varies with
elevation above the sea level, and that there is a
relation between distribution in height and in
horizontal area. While some of the plants found
in Great Britain are identical with those of Ger-
many, there are a few, living on high ground,
which are Scandinavian types. In the south-west
of Ireland there are a few Spanish a,nd Portuguese
types. The Scandinavian life was accounted for
on the hypothesis that, in a recent period of geo-
logical time, those plants spread over land which
is now the North Sea, when the temperature was
lower than it is now. When the German types of
plants subsequently spread over England, the
Scandinavian species, which could endure greater
cold, survived upon the hills; much as the Celtic
population may have receded to the high ground
before the invading Saxon peoples.
4/ Considerations of this kind indicate two great
laws. ' First, that the existing life which occupies
the earth's surface is grouped in series of geo-
graphical assemblages, each of which may be
termed a life province ; and^secondly, that these
64 THE STORY OF THE EARTH.
provinces occupy changed areas of the earth's
surface, with alterations in the level of land.
In the same way it was found that life in the
sea varies with the depth of the water Sea-shells
which live between tide-marks, and are adapted
to exist more or less exposed in atmospheric air,
are different in genera or species to those in the
deeper water, where the great growths of sea
plants are found. Marine life again changes its
character with greater depth. The shells which
would be indicative of a shore, travel along the
shore; and the shells which are found in clays,
are rarely met with in sand. -^Marine life also
varies geographically in the horizontal direction,
because there are natural history provinces of life
in the sea, which may also change their area,
when the depth of water changes, so as to scatter
or concentrate or combine the life.
About the year 1864 it began to be urged that
the differences found in the fossil life between
two successive geological deposits, were not due
to great denudations of intervening strata, which
had removed the intervening transitional organ-
isms, making breaks in the geological record, but
were the results of geographical migrations of
organisms, so that these animals and plants came
into an area which they had not previously occu-
pied, by moving away from one which had for-
merly been their home. When fossilized, the
remains of such a group indicate a different as-
semblage of animals or plants to those w"hich
lived previously in the area, when the life in the
underlying stratum accumulated and was fossilized
in the same way.
Js^Thus it is intelligible that the distribution of
life in the strata has been brought about in the
FOSSILS. 65
same way as the distribution of life is varied
upon the earth's surface now. And instead of
jffossils in geological formations representing a
multitude of successive creations, there appears
to be but one creation. These types of life sur-
vived from the earliest time by undergoing more
or less adaptation to altered conditions, as a
necessary circumstance for their perpetuation
through all the revolutions which the earth's sur-
face has undergone.
Thus it is known that the elephant, hippo-
potamus, lion, hyaena, rhinoceros, which are now
living in Africa, have been common animals in
Europe and Britain since the time during which
men have lived here ; that those animals have
changed their habitation ; and that the area of
the life province to which they belong is mani-
festly altered. There are no animals more dis-
tinctive of Africa at the present day than the
hippopotamus and ostrich, but in a recent ter-
tiary period of geological time, these animals left
their remains in rocks of Northern India, in asso-
ciation with extinct allies of the giraffe, a type
which is now limited to Africa. And so another
^change in the area occupied by a natural history
province of life is made known by remains of
animals preserved in the rocks.
. ^.All down the sequence of the geological ages
the story is of the same kind. Wherever there
is a change in the material of which rocks are
formed there is a change in the distribution of
life on the earth. The upheaval or depression
which varies the distribution of the mineral mat-
ter and produces the succession of strata is also
the cause which varies the distribution of life.
(^Therefore the fossils found in any geological
66 THE STORY OF THE EARTH.
formation are a portion of a natural history
province, which has been preserved in the condi-
tion in which it existed on the earth's surface at
that particular epoch of time.
If we suppose land and sea at the present
day to be occupied over their areas with natural
history provinces of life, in the manner in which
they have been marked out by naturalists, such
provinces are manifestly the survival of the life
which has existed in the several periods of the
geological record. They have reached their
present positions in consequence of the geolog-
ical circumstances of rock folding in the earth's
crust which have given the earth's surface its
present form. This truth is the only explanation
of the succession of life in the past ages of the
earth's history. It is impossible to imagine any
change in life between the oldest deposit known
and the bed which succeeded it, unless the life
was already different in an adjacent area of the
ocean, so that a new natural history province
could be superimposed upon that which had pre-
viously occupied the ground. The fossils of thei
geological formations are therefore the records of'
the succession of the natural history provinces of
life on the earth. Each province has been formed
by geological changes. They have succeeded
each other like the movements of chess-men upon
the same square of the chess-board. In this pro-
cess many of the old life provinces are broken
up, and their constituent animals and plants scat-
tered and intermixed with others, almost beyond
recognition. Such survivals have not been accom-
plished, however, without the earth losing many
of the kinds of life with which the geological story
begins, and which characterize its greater epochs.
FOSSILS. 67
The Succession of Life.
O The oldest geological deposits in the Cam-
brian period give no indication of a commence-
ment of life on the earth. The assemblage of
fossils, after eliminating the types which have be-
come extinct, is comparable to such as might be
found upon an existing sea-bed. The most an-
cient groups of fossils in the stratified rocks lend
no support to the hypothesis that they are stages
of a process by which animals came successively
into existence, in the order of their grades of
organisation. There are already several groups
of animals co-existing, associated with each other
as they are upon an existing sea-bed. On many
shores at the present day the variety in life is not
greater than the geologist finds in a quarry or
cliff after examining a few yards of rock.
Each of the great divisions of the animal king-
dom has representatives in very old rocks. Man
is limited, so far as is at present known, to the
newest deposits. But geological research has,
pushed further and further backward in time, the-
epoch in which each of the highest types mam-
mals, birds, reptiles, fishes is first met with.
Sometimes the earlier rocks are fancifully
spoken of as the age of fishes; those of the
middle period are named the age of reptiles; and
the latest rocks are termed the age of mammals.
Each of those groups of animals puts on a con-
siderable diversity of organisation in the epochs
which it is supposed to characterize ; and each
includes some extinct groups which are not met
with at the present day ; or subsequent to the
epoch which the group characterizes. On the
other hand, mammals are not only not limited
458 THE STORY OF THE EARTH.
to the tertiary strata, but have been recorded as
extending to the Trias, the beginning of the
secondary rocks. Indications of their existence
occur in connection with each of the old land
surfaces which the strata make known in the
south of England. Birds have been found on
two different horizons in the secondary rocks.
The presence in those secondary rocks of animals
so remarkable as Ichthyosaurs, Plesiosaurs, Or-
nithosaurs, Dinosaurs, and Anomodonts, fully
justifies the term, age of reptiles. The modern
type of crocodiles, lizards, turtles, and snakes,
which are the true reptiles of the present time,
do not extend back to very early parts of the
secondary epoch, so far as is known at present.
Extinct groups of reptiles such as the Anomo-
donts and Labyrinthodonts date back at least as
far as the time in which the Permian and Carbon-
iferous coal was accumulated. The great facts
which life presents to us when examined by means
of fossil remains, preserved in the succession of
strata, are: first, that it has been always changing
in the same locality, in the same way as a fauna
or flora undergoes change at the present day. In
the lifetime of individuals, plants and insects have
disappeared from the fen district of Cambridge-
shire under the influence of embanking and drain-
ing, just as in historic times animals like the wolf,
brown bear, beaver and roebuck, have disappeared
from South Britain. In other parts of the world
the existing fauna has become poorer by the ex-
tinction of birds like the Dodo, and the Moa.
This process of extinction has never ceased. Its
evidences remain in the extinct species which
characterize every geological deposit.
The process of extinction has extended to
FOSSILS. 69
some larger groups, such as in natural history are
termed Orders of Animals. Thus in the old slaty
rocks termed Cambrian and Silurian the entire
group of animals termed Graptolites is extinct.
In the primary rocks there is an extinct group of
corals, termed Rugosa, which have the radiating
shelly partitions termed septa, in multiples of
four. There are small extinct groups of Echino-
derms in the silurian and carboniferous rocks,
allied to the sea urchins, named Cystoidea and
Blastoidea. Among Crustacea there are the ex-
tinct groups Trilobites, comprising more than
fifty genera ; and the Merostomata, comprising
animals which are allied to the king crabs and
scorpions.
Other groups of animals, though not entirely
extinct, are much better represented in the fossil
state than in existing nature. Most of the genera
of the groups of lamp-shells named Brachiopoda,
are extinct, and found only in the Primary rocks;
and the larger number of allies of the Nautilus
are found in a fossil state, partly in the primary,
and partly in the secondary period of time.
A number of the existing groups of animals
date from very remote, if not from the earliest
known geological ages. The genera in which
they are first met with, frequently appear to have
persisted ever since, without undergoing any ap-
preciable change, beyond those minor modifica-
tions which distinguish species. Although the
fruits of the Araucaria, of various pines, and of
Pandanus, are found in the lower Secondary rocks,
it is not until the latter part of the secondary
period that any deposit yields enough fossil leaves
to enable the vegetation of the earth to be com-
pared as a group with living types. The common
70 THE STORY OF THE EARTH.
genera of ferns of the present day are well repre-
sented in strata older than the chalk, by such
types as Pteris, Asplenium, Adiantum, Aspidium,
and Gleichenia. Palms are represented by Nipa.
There are numerous representations of the oak,
willow, beech, fig, laurel, ebony, magnolia. Noth-
ing is known of the origin of this ancient cretace-
ous flora, but there is no ground for believing
that it suddenly came into existence in widely
separated parts of the world, where it is first met
with.
In the oldest group of rocks every class of
animals is represented by many genera which
still live. Thus the Foraminifera, which fill so
large a place in the life of the open ocean at the
present day, are represented in the Silurian period
by the genera Dentalina, Lagena, Nodosaria, Tex-
tularia.
The existing genera of Echinoderms are not
known from so early a period ; but in the begin-
ning of the secondary time Cidaris and many
other genera are found, which abound at the pres-
ent day.
Among shells the Brachiopods Lingula and
Crania, Discina, Rhynconella, Terebratula and oth-
ers survive from the older primary time.
The common bivalve shells, which have few
representatives in the Primary rocks, include such
familiar forms as Pecten, Pinna, Cardiun, Area,
Avicula.
The common Univalve shells begin with such
forms as Patella, Pleurotomaria, Chiton, Natica,
Trochus, Dentalium, which have never since been
absent from the earth. The Nautilus dates from
a very early period.
Thus, although the history of life has left be-
FOSSILS. 7 1
hind enough extinct entombed forms to enable
every deposit to be recognised by their remains,
the great lesson of fossil remains is not so much
extinction, as survival and persistence upon the
earth of the life which has once existed. The
natural inference would be that the variety in
kinds of life has been steadily diminishing from
the earliest time, owing to the loss of the extinct
groups of plants and animals. But with each
group of newer strata, genera and families of
animals are met with among the fossils, which
were not known in the older sets of fossils.
There is perhaps no proof that they were pre-
viously absent from the earth ; and it is possible
that some of them may have come into existence
as modifications of the types which were already
in existence.
The variation which life undergoes as the
condition of its existence.
// There is a principle which affects the history
I of life, which necessitates that new modifications
\ of plants and animals should constantly come into
) existence, under the varying conditions which the
Dearth's surface assumes. -^The different organic
\types are saved from extinction by manifesting
some degree of adaptation to altered circum-
stances. It is this property which enables the
genus to survive from the earliest times. It
undergoes a series of changes by which slight
differences of form or ornament are perpetuated
for a time, eventually giving place to another
similar series of modifications; and these char-
acters distinguish the species of which the genus
consists. Even persons who are not trained to
72 THE STORY OF THE EARTH.
recognise the technical characters by which ani-
mals and plants are classified, are aware that
there are different kinds of scallop shells, and
different kinds of cockles. The change in form
and ornament can often be seen to originate as a
consequence of the home of the shells being a
place where the water is still, or one where it is
exceptionally disturbed, the ribs of shells being
always stronger in rough water. The presence
of fresh water in an estuary would appear to be
a frequent cause of variation, not only in orna-
ment, but in form. Such variations of the com-
mon periwinkle and purple shell are found in
Crag-beds at Norwich, and seen in inlets on the
coast at the present day. Many of these varia-
tions are such as might characterize different
genera if they were persistent and became per-
manent characters, but they do not even consti-
tute species, and are only regarded as local races
due to local causes. If it were possible that after
a local race had come into existence, another set
of circumstances affected it so as to cause varia-
tion to take place in some new direction, it may
be that what was previously but a race character,
would be perpetuated in all the new modifica-
tions, and become the distinctive attribute of a
species, or even of a genus. The capacity of an
animal for variation is usually in the develop-
ment of something new, which did not previ-
ously exist ; but the most remarkable evidences
of variation are in the loss of parts which had
existed in animals in a previous period of time.
The capacity for variation is strikingly seen in
the manner in which the antlers of a deer become
complicated year by year, by the development of
new processes. In the present state of knowledge
FOSSILS. 73
certain fossil deer appear to have had antlers
which were less complicated ; and in others the
antlers were more complicated. It is on such
characters that species of deer are distinguished.
All the higher forms of life which are dis-
tinguished in classification, are records of loss.
Thus there can be no doubt that the common
horse is closely related to the fossil horse named
Hipparion, which had three toes on each foot, and
the existing horse still preserves rudiments of the
lateral toes which have been lost, in the splint
bones, which occur at the sides of each cannon
bone. Attempts have been made to show that
the three-toed horse had ancestors with five toes,
so that by loss of the digits of the feet, which are
consequences of the ways in which the toes are
used, genera may come into existence. At pres-
ent there is very little in the way of fact out of
which such a history could be constructed. Sci-
ence can only be carried pn, on a basis of un-
broken evidence, from facts, which are to the
scientific man what capital is to the merchant.
There is, however, no doubt that the mammals
-have lost the composite structure of the lower
jaw, which is found in reptiles ; and that reptiles
have lost the greater part of the arch of bones
which in fishes intervenes between the brain case
and the lower jaw, if their structures are inherited
from one group to the other.
74 THE STORY OF THE EARTH.
CHAPTER IX.
THE CLASSIFICATION OF WATER-FORMED ROCKS.
IN every country breaks exist in the con-
tinuity of the strata. Such interruptions in se-
quence are in progress at the present day by the
upheaval of land of existing islands, and conti-
nents, which intermits the deposition of marine
strata. Such breaks are evidenced by want of
conformity in the order of succession of the de-
posits. This is one of the main grounds for di-
viding geological deposits from each other. The
breaks which exist in any one country are some-
what limited in the area which they affect. They
can never be world-wide divisions between strata.
Strata are also divided according to their differ-
ences in predominant mineral character. The
changes which take place in the prevalent types
of extinct life which they severally preserve, give
grounds for division of deposits, so that the cessa-
tion of an ancient group of animals, or the in-
coming of a new group, makes a division possible
between the strata.
There is no necessary connection between the
break in stratification, termed unconformity, and
the break in life. Frequently there is a great
change in fossils between two successive strata
without an indication of unconformity. It is
difficult to understand how the life can change
appreciably without a change in the level of
adjacent land, which causes the life of an adja-
cent area to migrate. An unconformity is not of
necessity any greater evidence of an unrepre-
sented interval of time than conformity; because
CLASSIFICATION OF WATER-FORMED ROCKS. 75
the unconformable beds might always be traced
to a district where they become conformable, so
that there is no break in the geological record.
The changes in life between conformable
strata, are no more than the differences which
zones of life assume with depth. As a pebble
bed changes to a sandstone, its life alters from
the fauna of the littoral zone between tide marks,
to the fauna of the deeper laminarian zone. As
the sand is succeeded by a clay the fauna alters
to the life of the coralline zone. Therefore there
is, from the point of view of the existing distribu-
tion of plants and animals, a necessary change of
life, with change in stratification, which has no
important connection with imperfections in the
geological record.
The breaks in life and in stratification were
stated by the late Sir Andrew Ramsay in the
following series: Between the Lingula flags and
the overlying Tremadoc slates there is a nearly
complete break in genera and species; and un-
conformity is probable. There is the same
condition between the Tremadoc slates and the
Arenig rocks; and between the Bala and Caradoc
beds below, and the lower Llandovery above.
There is a great break in species in all these
examples, and probably unconformity as well,
but the unconformity is not seen. Between the
Lower Llandovery and Upper Llandovery beds
a break in life occurs, and marked unconformity ;
and between the Upper Llandovery beds and
Wenlock beds, is similar evidence of a break in
succession. The Old Red-sandstone however
shows no sign of unconformity at the junction
where it succeeds the Ludlow rocks at the top of
the Silurian, and no break in life though both
76 THE STORY OF THE EARTH.
might be expected. Nor does any break occur
between the upper limit of the fresh water old
red sandstone and the marine carboniferous rocks
in the Welsh country. The carboniferous rocks
are usually conformable from top to bottom; but
there is sometimes an unconformable succession
of Millstone grit upon mountain limestone, in the
Forest of Dean. There is a great unconformity
between the Carboniferous rocks and the Per-
mian. This makes a total of ten physical breaks
which are evidenced during the primary portion
of geological time.
There is a complete stratigraphical break, or
unconformity between the Trias and the Permian.
Near Ormskirk the new Red Marl rests uncon-
formably on the new Red Sandstone. There is
no visible unconformity between the Rhsetic beds
and the Lias, which rests upon them, but the
change in life indicates a great break in the
uniformity of previous conditions. There is no
complete unconformity between the Lias and the
overlying Inferior Oolite. But the change in life
to this deposit, and through all the succeeding
divisions of the Oolites, is such as may be asso-
ciated with unconformity in adjacent areas. At
the top of the Oolites there is an insensible pas-
sage from the marine Portland limestone to the
Purbeck beds. But since the Purbeck deposits
include terrestrial surfaces, and are largely of
fresh-water origin, an unconformity must exist
in the south of England in this part of the suc-
cession. The wealden beds may also be uncon-
formable. But in the overlying cretaceous series
of deposits, the apparent unconformity is an
overlap on the older strata which gave increased
geographical extension to the Hunstanton lime-
CLASSIFICATION OF WATER-FORMED ROCKS. 77
stone and Chalk in the north, in Yorkshire; and
to the Greensand and Chalk in the south-west of
England.
There is no other physical break in this coun-
try till that between the chalk and the tertiary
strata, which is partly bridged in Belgium, and
perhaps entirely bridged over in North America.
The upheaval of a succession of land surfaces in
the tertiary period is evidence of remarkable
breaks in the sequence of deposits, and then a
great gap, unrepresented by strata in England,
occurs in the middle tertiary period. The mani-
fest physical breaks in the area in which the Brit-
ish strata were deposited, are much fewer than
the breaks in the succession of life, many of which
are evidently due to the way in which life is dis-
tributed in successive zones in depth. Therefore
there has been no uniform principle in distinguish-
ing the strata from each other by their fossils;
and more attention has been paid to the differ-
ences in life, than to the circumstances by which
the differences were caused.
In England the principal changes in marine
life occur (i) between the Silurian and Devonian
rocks, though the changes in types of life appear
to be unimportant.
(2) Between the Primary and Secondary rocks
there is a great change in both the marine and
terrestrial life.
(3) Between the Oolites and Cretaceous rocks
there is apparently an important change in the
terrestrial life, though the change in the marine
life is less marked.
(4) The gap in the marine succession between
the Secondary and Tertiary is very striking; butthe
gap in the terrestrial plant life appears to be small.
78 THE STORY OF THE EARTH.
It is on evidence of this kind that geological
time is divided into stages, ages, and epochs,
which record a series of transitions and succes-
sions, which the life of a limited part of the globe
has undergone. Sometimes the diffusion of world-
wide species appears to have been as remarkable
in the seas of old geological periods, as any geo-
graphical extension of living species which is
known at the present day.
CHAPTER X.
THE ARCHEAN ROCKS.
THE most ancient rocks are termed Archean.
They consist chiefly of crystalline schists, and
other crystalline substances, such as quartzite,
limestone, graphite. Formerly they were gener-
ally regarded as metamorphic. At the present
day some writers do not believe that they are
crystallized out of ancient strata, which were ac-
cumulated in water. Nevertheless they show in
many localities, and especially in the Laurentian
rocks of Canada, two constituents which may in-
dicate a stratified origin. One is the presence of
layers of crystalline limestone, which is not known
to originate in nature, except by metamorphism of
limestone built up by organisms which lived in
water. Secondly, these Laurentian rocks contain
an amount of graphite, which has been stated to
be equal in bulk, if it were all brought together,
to the quantity of coal found in a coal-field. No
source upon the earth for the carbon of which
graphite consists is known, except the meta-
THE ARCHEAN ROCKS. 79
morphism of vegetable matter such as forms coal.
Existing coal-fields show, in the formation of an-
thracite, what appears to be a transitional step
between coal and graphite, for the percentage of
carbon augments as the other gaseous constitu-
ents of coal are lost under the distilling action of
pressure and heat.
If the Archean limestones and graphite are of
organic origin, they would appear to have been
originally beds of coal and limestone which con-
sisted mainly, if not entirely, of fossils. There-
fore, the other constituents of these rocks, the
schists which form the great mass of the country
north of the St. Lawrence, would appear once to
have been sands and clays in which fossils may
have been distributed as they are in more recent
deposits.
The estimated thickness of the Laurentian and
overlying Huronian rocks is about 50,000 feet,
and in that thickness no fossil is found, unless the
structure named Eozoon canadense which has been
described from Laurentian limestones is correctly
identified as an encrusting reef-building foramini-
fer ; which its mode of occurrence in the rocks
makes not improbable, though the structure is
paralleled in volcanic rocks. Such metamorphism
of ancient sediments all over the globe must be
inferred to have obliterated all records of the
early history of the earth.
The geological story commences at a com-
paratively late period, compared with the unre-
corded epochs which have gone before. Without
such an obliteration of a past record of almost
infinite duration as compared with known geo-
logical time, it is inconceivable that processes of
variation, such as are now known to be in opera-
So THE STORY OF THE EARTH.
tion, can have give,n rise to the diverse types of
life, which the oldest fossiliferous rocks make
known.
The Archean rocks are widely spread on the
surface of Scandinavia, Finland and North-West
Russia, Saxony, and Bohemia, and in Bavaria as
well as in the British Islands. Rocks of this class
will probably be found all over the globe, wher-
ever there is an opportunity of examining the ma-
terial upon which the most ancient fossiliferous
rocks rest.
In the Western Highlands in Scotland, from
Cape Wrath southward, the schists and funda-
mental gneiss of that region are displaced by an
incredible multitude of horizontal thrusts which
break them up into parallel sheets, almost as well
marked as planes of stratification, with which they
were at one time confused. Among these crys-
talline rocks are included great thicknesses of
sandstones, and folded in among them occasion-
ally are fossiliferous bands of limestone.
Other archaean areas are exposed further
southward. The most interesting are the crys-
talline rocks about St. David's, in Pembroke-
shire ; at the Longmynd, in Shropshire ; in the
central axis in Carnarvonshire ; and in Anglesey.
In these most ancient British rocks, evidences
appear to exist of contemporaneous activity of
terrestrial volcanos, so that among the oldest
British rocks, alternating with schists, are the
rhyolite lavas of Bangor, Carnarvon, Llyn -Pa-
darn, associated in some of these localities with
agglomerates. The Wrekin and Ercal Hill make
known rhyolites of pre-Cambrian age which are
associated with indurated volcanic ash. In the
neighbourhood of St. David's the rhyolitic lavas
CAMBRIAN AND ORDOVICIAN ROCKS. 8 1
are in the same way associated with volcanic ash,
interstratified in schists, the whole being affected
by compression to which they have since been
subjected.
The British Geological Record begins with
conditions which indicate volcanic outbursts,
and the shallow water accumulation of grits and
pebble beds. As far as the evidence goes, similar
conditions might exist at the present day ; but
the rocks have been modified from their original
state by slow chemical changes.
CHAPTER XI.
CAMBRIAN AND ORDOVICIAN ROCKS.
THERE is an unconformity between the pre-
Cambrian and Cambrian rocks, which implies a
long interval of time, unrepresented by deposits
in the localities which have been examined. The
Cambrian rocks are of enormous thickness ; and
in Britain are probably not less than 30,000 feet
thick in Wales and the border counties of Eng-
land.
There is difference of opinion as to the use
of the term Cambrian. Some writers make it
include four groups of rocks, named Longmynd
rocks, Menevian beds, Lingula flags, and Tre-
madoc slates. Others carry the name higher
and make it include the succeeding rocks named
Arenig, Llanvirn, Lower Bala and Middle Bala
and Upper Bala, which have also been grouped
as Ordovician.
The overlying strata, termed May Hill rocks,
82 THE STORY OF THE EARTH.
the Denbighshire grits, Wenlock and Ludlow beds,
and the Downton sandstone series, are combined
to form the Silurian group.
From the physical history of the deposits,
there is ground for dividing the rocks in this
way, but from consideration of the life they
contain, the whole might well be combined, and
grouped together as ten successive series, with
ten distinct fauna, which more or less resemble
the life of similar natural history provinces,
superimposed on each other, and preserved suc-
cessively in sediments in the same area.
At first the old rocks which comprise the
Longmynd groups, and the Harlech and Llan-
beris slates, which rise 1600 feet above the sea,
in the Longmynd Hills in Shropshire, consist of
slates, sandstones, grits, and conglomerates; with
very few fossils. The water-worn pebbles in them
prove deposition under ancient shore conditions;
and they are associated with beds which show the
ripples of waves, runnels of rills on the shore, in-
terlacing cracks formed by the heat of the sun,
prints of raindrops, and burrows of sea-worms
closely allied to the living Arenicola. Few fossils
have been found in the Longmynd. They are
scarcely more numerous in the Bangor country of
Carnarvonshire. There the rocks are represented
by green and purple slates, which stretch from the
banks of the Ogwen through the lake of Llanberis,
and the Penrhyn slate quarries. In South Wales,
in the section near St. David's, the interest of
these rocks is greatest. The conglomerates and
sandstones found there, with red, purple, and
green slates, appear to be on the same geo-
logical horizon as the Bethesda and Llanberis
slate quarries Towards the base of this group
CAMBRIAN AND ORDOVICIAN ROCKS. 83
of rocks are found two genera of fossils named
Lingulella and Discina, which may be regarded as
having survived through all subsequent ages of
geological time to the present day without under-
going any notable change, although the surviving
shell is named Lingula instead of Lingulella. The
lowest beds in which they occur, the Caerfai group,
are succeeded by the Solva group, in which genera
of the extinct order of Trilobites appear in profu-
sion.
Here occurs the oldest known sponge named
Protospongia, and a species is met with of the ex-
tinct genus of Pteropod named Theca, which sur-
vived in the ancient seas for a long time. This
assemblage of life, the earliest as yet known in
the earth's history, consists of types which are in
no sense embryonic. It distinctly points to a
line of similar ancestors which has yet to be dis-
covered. With the succession of the overlying
Menevian beds, and the succeeding divisions of
the Lingula flags and Tremadoc slates, a fauna
of 185 species of fossils becomes known in which
FIG. 9. Section through North Wales from the Cambrian slates
of the Snowdon district to the Cheshire Trias.
some of the shells, species of the genera of Brachi-
opoda named Lingula and Orthis, and Oboldla pass
up into the overlying Arenig rocks. With the
Menevian beds the most ancient Echinoderm
appears. It is a far-off relative of the existing
stone-lines and sea-eggs. It belongs to the ex-
tinct group of Cystidea, and is named Protocystites.
84 THE STORY OF THE EARTH.
The most ancient bivalve shells known are found
in the Tremadoc rocks of Wales. They can be
closely paralleled at the present day. Modiolopsis
is probably nothing but Modiola, the horse mussel
under another name ; and Glyptarca, Palcearca, and
Ctenodonta are only forms of the living genus Area,
in which the shell has not developed the habit of
growing in depth along its hinge, as in most of its
living representatives. Pteropods are well repre-
sented : the univalve Gasteropods are represented
by the extinct genus Bellerophon, which appears to
be a symmetrical shell abundant in the primary
rocks, probably allied to the living Pleurotomaria.
The group of many-chambered shells named Ceph-
alopoda is represented by allies of the Nautilus,
one of them the straight horn Otthoceras, and an-
other Cyrtoceras, the curved horn. In the lower
Tremadoc rocks the oldest known starfish is
found, in a species of the genus Palcea sterina ;
and the oldest known Crinoid or Stone-lily, in a
species of the genus Dendrocrinus.
The great Arenig series rests conformably on
the Tremadoc slates. It forms Cader Idris, the
Festiniog Mountains, Aran and Arenig. It in-
cludes a great group of roofing slates worked in
ihe quarries of Festiniog, and an immense quan-
tity of volcanic ash. The total thickness of the
ashes, agglomerates and lavas seen in Cader Idris
is between 5000 and 6000 feet. The throats of
the ancient volcanos which contributed so largely
to form the Arenig rocks in North Wales, were
placed near Dolgelly, and Aran Mowddwy by the
late Sir A. Ramsay.
The Cambrian period was an epoch of vigor-
ous volcanic action. The products of the vol-
canos are seen in the Skiddaw slates of the Lake
CAMBRIAN AND ORDOVICIAN ROCKS. 85
district, where about 12,000 feet of volcanic ash
and Andesite lavas, of Honister Crag and Sea-
thwaite, mark the beginning of volcanic action
which continued through the accumulation of the
Borrowdale series of rocks. In North Wales
Rhyolitic lavas continued to be ejected in the
Bala period which followed. They are seen
about Bettws-y-coed and the Conway falls.
Rhyolitic lavas are seen in the Glyders, on the
north side of the Pass of Llanberis, near Bedd-
Gelert, and about Snowdon.
The most remarkable feature in the life of
these upper Cambrian rocks, is the extraordinary
abundance of the extinct group of Graptolites.
They are found not only in South Wales and the
Lake District, but in as great a diversity of forms
and complexity of branching structure in North
America.
Trilobites increase in number of genera and
species. The genus Pleurotomaria, a Gasteropod
only known at the present day from living species
in the West Indies and verging on extinction, ap-
pears for the first time in the lower Arenig rocks
at Llanvirn, near St. Davids. In this period an-
other Gasteropod Euomphalus, which continues to
be important during the primary period, is found
for the first time.
Several corals make their appearance in the
Llandeilo rocks. They are the most ancient
representatives of the group in Britain. Among
them is the chain coral Halysites, and a species of
Favosites, both of which are important genera
in the primary rocks. The Crinoids increase in
number.
Several genera of Brachiopod shells appear,
two of which, Rhynchonella and Crania, afterwards
86 THE STORY OF THE EARTH.
become much more important and still survive;
while the genus Leptaena, which now first ap-
pears, lives on till the lower part of the second-
ary epoch of time. The common genus Mytilus,
the edible mussel, is first found with the close of
the Cambrian period. Cephalopods become more
numerous and varied, and Cystidians are repre-
sented by a number of genera. The appearance
and abundance of Graptolites, and the increase of
Trilobites in number of genera and species, are
the chief changes which occur in the life of the
Cambrian period of time.
The Silurian.
The Silurian rocks extend unconformably
over the Cambrian Strata. Between the Long-
mynd and Wenlock Edge, they cover up the
whole series of the Cambrian strata, resting upon
their upturned and denuded edges. But when
they are traced into North Wales in Denbigh-
shire, the evidence of Silurian unconformity is
less marked.
The Silurian rocks typically include the May-
hill sandstone, the Wenlock rocks and the Ludlow
rocks. The May Hill series, so named from May
Hill in Gloucestershire, consists chiefly of sand-
stones and conglomerates, yellowish and brown
with oxide of iron, about 1000 feet thick, covered
by the Wenlock group, which in the south is
formed of shales and limestones, and in Denbigh-
shire chiefly of sandstones known as the Denbigh
grits, which overlie the Tarannon shales. Above
these rocks are the Ludlow beds, which also in-
clude shales parted by the Aymestry limestones.
The Silurian group of rocks is capped by the
SILURIAN ROCKS. 87
Downton sandstone, which makes a transition in
rock character to the lower beds of the old red
sandstone. These Wenlock and Ludlow rocks
are the oldest British strata which include con-
siderable beds of limestone. The exposure of
Wenlock limestone at the surface forms the hill
range south-west from Coalbrookdale, known as
Wenlock Edge.
These beds indicate shallow-water conditions
by the May Hill sandstones at their base. The
shales, which are only hardened muds, were pre-
MAP OF AN INLIER.
FIG. 10. Map showing a dome-shaped elevation of Silurian rocks
exposed by denudation of the old red sandstone and carbonif-
erous rocks whteh once extended continuously over the whole
sumably deposited further from shore ; while the
limestones, formed of corals, shells, and crinoids,
were beyond the reach of sediment, but not
necessarily formed in deep water.
The Wenlock limestone includes a large num-
ber of corals, and is the first indication met with
in geological time of a British coral reef, though
many of the beds are largely composed of En-
crinites, and some of Brachiopod shells, showing
the same conditions as are afterwards repeated
88 THE STORY CDF THE EARTH.
in the Carboniferous limestone, which is locally
formed of many different organisms. There are
twenty-five genera and seventy-six species of
corals in the Wenlock rocks alone. And twenty
new genera of crinoids appear, the group being
represented by sixty-eight species in the Wenlock
limestone. This limestone is frequently thin-
, bedded, and alternates with shale, often green, as
is well seen in the dome-shaped exposure in the
Wren's Nest, near Dudley, where it is covered
by coal measures without any intervening rocks.
The thin beds of limestone both in the Wenlock
and Ludlow beds, thin out, first becoming nodu-
lar and concretionary, and then disappearing
altogether.
In Wales and the adjacent parts of England
the Wenlock rocks have been very little meta-
morphosed, and are in this respect in marked
contrast to the cleaved slates of the Cambrian
period. They have probably a wide distribution
under the secondary strata, and were met with
below the chalk and Gault at Ware, in a deep
boring for water. The characteristic fossils are
present. With the exception of the remarkable
' crinoids, corals, and brachiopods, there is noth-
ing very impressive in the character of the Silu-
rian fauna. The remarkable Crustacea Eurypte-
rus, Pterygotus, and Hemiaspis first appear in the
Wenlock rocks.
The oldest fishes in Britain are met with in
the Ludlow rocks, represented by no fewer than
ten species. Among these is the Buckler-headed
Scaphaspis in the Lower Ludlow, while in the
Upper Ludlow are found Cephalaspis, afterwards
known in the old red sandstone, together with
Pteraspis, Auchenaspis, Onchus, and other genera.
SILURIAN ROCKS. 89
The Eurypterida appear to have reached their
maximum development in the Upper Ludlow
period. There were probably more fishes living
then than are yet known, since the Ludlow bone
bed, which is found all round the Woolhope area,
at May Hill, and in many other localities, consists
largely of the remains of fishes matted togeth-
er, with fragments of the great Crustacea, some
plants, and some shells. The Downton sand-
stones and Ledbury shales especially abound
with the remains of Eurypterus and Pterygotus.
With the Ludlow beds, trilobites become less
important, and genera which occur in the upper-
most Ludlow beds are also met with in the
Devonian rocks. The wide-spread crustacean
type, Eurypterus, is largely represented in Scot-
land. All the compound graptolites vanish, and
the group disappears with a few simple species
in the lower Ludlow beds. Ludlow rocks yield
a considerable number of star-fishes, partly from
Westmoreland, partly from Ludlow. Orthoceras
is known from a multitude of species ; and there
are allied genera.
The organisms known in the lower Palaeozoic
rocks make up an enormous fauna, with multi-
tudes of genera of sponges, corals, hydrozoa,
crinoids, cystidians and star-fishes, trilobites,
phyllopods, eurypterida, and every group of
mollusca, as well as many fishes. It is in this
period of time that the "sea-eggs," with flexible
and elastic enveloping shells make their first ap-
pearance iu British rocks, in the genus Palachinus.
They are of spheroidal form, and composed of
numerous plates in rows which overlap each other
obliquely at the edges. The group is always
scantily represented in the geological deposits,
90 THE STORY OF THE EARTH.
but still survives in the deep oceans, where it is
represented by the genus Calveria dredged in 445
fathoms of water.
Trilobites.
Trilobites are a group of Crustacea, entirely
extinct, which appear in the oldest stratified rocks,
and survive till the close of the carboniferous
period. The group is characterised by having
the body divided, first into a head-shield, termed
the cephalo-thorax, which may theoretically con-
sist of five segments of the immature animal,
blended into one plate. In this shield, in a suture
between the central part called the glabella and
the free cheeks, the eyes are placed, when the
eyes have a recognisable development. Some
trilobites appear to be blind, being without eyes.
On the under side of the head is the labrum, from
which the long-jointed antennae extend forward in
a genus named Triarthrus. The middle part of
the animal, known as the abdomen, consists of a
number of separate overlapping plates, like those
in the tail of a lobster, which are capable of mov-
ing freely upon each other, and are sometimes
arranged so that the animal can roll into a
ball, like the living terrestrial crustacean Oniscus,
known as the woodlouse. The number of these
joints in the abdomen, termed somites, varies from
two in Agnostus, to about twenty in genera like
Paradoxides, which is one of the oldest, and Aula-
copleura, which is a Silurian type. Thirdly, there
is a tail-plate, known as the pygidium, which is
sometimes marked with external ornament, cor-
responding to that of the separate plates of the
abdomen, and sometimes smooth. The eyes are
SILURIAN ROCKS.
compound, and the individual facets can be seen
with a lens, and although generally grouped to-
gether and raised in a crescent, as in the genus
Phacops, appear sometimes to be scattered, so as
to cover much of the lateral plates of the cephalo-
thorax, as in the genus Trinudeus. The intestine
is sometimes preserved. On the under side of the
body numerous limbs were developed.
On the head, besides the antennae, there were
appendages for mastication, but only one of them
is preserved. The jointed
limbs on the trunk consist of
two parts, one for locomo-
tion, and the other a gill ; so
that they appear to belong
to the leaf-footed group of
Crustacea termed Phyllo-
pods, notwithstanding their
remarkable external resem-
blance to the king crabs, to-
wards which they approxi-
mate.
The limbs gradually di-
minish in size from front to
back, where the hindermost
are minute and rudimentary.
The two longitudinal
grooves make the three
lobes of a Trilobite.
The most ancient Trilo-
bites include the simplest and some of the most
complex. They vary chiefly in the number of
segments ; the form and size of the cephalo-tho-
rax, and the pygidium ; in the elongation of the
pleurae of the abdomen ; in the external ornament
of the carapace, which sometimes takes the form
TRIAKTHRUS.
FIG. ii. A Trilobite show-
ing feet and antennae.
92 THE STORY OF THE EARTH,
of spines upon all parts of the body. As the
Trilobite grows it is said to shed its shell like
other Crustacea ; and with this growth there come
to be additional plates added to the abdomen, so
that there is a sense in which the ancient types,
like Paradoxides, may be regarded as the most
complex.
Among the Lower Cambrian genera are Para-
doxides, Dikelocephalus^ Olenus, Conocoryphe. In
the middle and Upper Cambrian or Ordovician
rocks, the common genera include Ogygia, Asa-
phus, Trinucleus, Lichas, Acidaspis. Phacops
ranges through the Silurian and Devonian ; and
Illaenus ranges from the Upper Cambrian to the
Silurian.
In the Silurian, Calymene, Encrinurus, Phacops y
and Homalonotus are characteristic genera.
In the Devonian rocks, Phacops, Homalonotus
and Bronteus are commonest.
In the carboniferous, Phillipsia is the best-
known genus.
CHAPTER XII.
OLD RED SANDSTONE AND DEVONIAN PERIOD.
A GREAT unconformity is inferred to divide
the Silurian rocks below from the overlying
strata. North of the Bristol Channel there is no
evidence of marine origin for the deposits which
appear to have been accumulated in great lakes
upon a land surface. South of the Bristol Chan-
nel, and eastward through France and Germany,
the rocks which follow upon the Silurian are
entirely marine. They are remarkable for the
OLD RED SANDSTONE AND DEVONIAN PERIOD. 93
circumstance that the lowest beds exposed give
evidence of shallow-water conditions in con-
glomerates and sandstones, seen in North Devon
and West Somerset, in the beds known as the
Foreland and Linton group. In South Devon
the lowest beds are purple slaty rocks. The
middle or Ilfracombe group, though mainly
formed of slaty rocks, contains a little limestone.
5P^ : - V yy s> LU p ' A '
CARBONIFEROUS
W. E.
FIG. 12. Section from west to east, showing how the Silurian,
Old Red Sandstone, and Carboniferous rocks are folded be-
tween South Wales and Gloucestershire.
The limestone becomes more abundant in South
Devon at Plymouth and Torquay, often taking
the form of great coral reefs and sometimes
thinning off into the shales. The uppermost
Devonian known as the Pilton group in North
Devon becomes sandstone. In Cornwall these
rocks are represented by limestones and slates at
Petherwyn.
The striking feature of these rocks is the
remarkable change which takes place in the
marine life. The multitude of genera which had
survived more or less conspicuously from the
Cambrian to the Silurian time becomes replaced
by new sets of types which are substantially the
same as survive through the marine beds of the
94 THE STORY OF THE EARTH.
carboniferous period. Some layers are character-
ized by a few peculiar genera, such as the conti-
nental deposits in the Middle Devonian known
from the Brachiopod Stringocephalus, as Stringo-
cephalus limestone; and from the coral Calceola
as Calceola slate, which give a distinctive char-
acter to the Devonian period. It is in the
Devonian age that we are particularly impressed
with the abundance on the earth of types of life
which enter largely into the existing fauna.
Fishes have hitherto been few in number, but
some of those remarkable fishes Pterichthys which
occurred at the top of the Ludlow beds, together
with Coccosteus and the great scaled fringe-finned
Holoptychius, are found in the marine Devonian
beds of the continent, as well as in the old red
sandstone of Scotland.
In this period commence several marine uni-
valve shells such as Natica, Nerita, Trochus,
Vermetus, which are so important in the sea-shore
life of the present day.
They are associated with two very interesting
Cephalopods. Nautilus occurs accompanied by
the remarkable Nautiloid shell named Ctymenia,
which has a fold in each septum which divides
one chamber from another, similar to the fold
which is observed in the septa of many tertiary
species of Nautilus, which are similarly com-
pressed from side to side. Those compressed
tertiary species have the little tube named the
siphuncle which passes through the septa placed
in a more inward position than is usual in Nau-
tilus. This genus Clymenia has the siphuncle as
far inward as it could be, so as to be in contact
with the previously formed coil. The genus is
therefore in marked contrast to another remarka-
OLD RED SANDSTONE AND DEVONIAN PERIOD. 95
ble fossil named Goniatites, in which the septa are
angularly folded several times, and the siphuncle
is as far outward as it can be. Goniatites is the
antecedent form of the great group of Cephalopod
shells allied to Ammonites, which is found in the
Secondary strata.
On turning landward to the lacustrine deposits
of Old Red Sandstone age, the first of the great
lakes in the British area on which the old red
sandstone was deposited, is that which extends
from Coalbrookdale southward over Hereford
and Monmouth, and westward into Pembroke-
shire. The sandstone accumulated in it is esti-
mated to be about 8000 feet thick in Hereford
and Brecon ; and in Monmouth it includes thick
conglomerates, full of quartz pebbles, which may
be compared with those which formed the Mill-
stone Grit, in a later period of time. The lower
part of this area of the Old Red Sandstone is
termed the cornstone group.
As might be expected there is an overlap of
these beds upon the Upper Cambrian, which is
well seen near Caermarthen.
Some of the marine fossils found in the De-
vonian of North Devon are also met with in
Pembrokeshire. Hence there is some ground for
believing that the old red sandstone, which is
assumed to have been lacustrine, communicated
with the sea by an estuary. This may account
for the occurrence of some fishes indifferently in
the marine and fresh-water beds, which are now
separated approximately by the Bristol Channel.
All the other old red sandstone deposits are re-
garded as formed in lakes, chiefly in the lower
old red sandstone period. These supposed lakes
have been named from the geographical regions
96 THE STORY OF THE EARTH.
which the rocks occupy. First, Lake Cheviot in-
cludes the Cheviot Hills with considerable thick-
nesses of volcanic rock of the kind named Por-
phyrite or Andesite. Further north a great lake,
termed Lake Caledonia, appears to have extended
southward from the Grampians over the Firth of
Clyde into the North of Ireland. Third, the lake
of Lome covered part of Argyleshire from Loch
Awe, and may have extended northward in the
line of the great glen. Further north still is the
old red sandstone region beyond the Grampians,
which includes Caithness and Sutherland, the Ork-
neys and Shetlands. The lake is named Lake
Orcadie. It is filled with conglomerates, red sand-
stone and grey flagstones, with occasional thin-
bedded limestones, sometimes bituminous in the
upper part.
In these beds there are many terrestrial plants,
some coniferous, and some, such as Lepidodendron
and Ca/amites, like those of the Coal, and similar
to the plants found in the upper Devonian rocks
of North Devon, probably derived from the land
to the north. Pterygotus, which had appeared in
the marine Silurian beds, is well known in the
old red sandstone of Scotland, where it has been
termed by quarrymen "fossil seraphim."
The fishes are of extreme interest. First, there
is the remarkable extinct group of buck'er-headed
fishes represented by Pterichthys and Cephalaspis.
Secondly, the more remarkable series of fringe-
finned fishes termed Crossopterygidse, which are
represented at the present day by Polypterus of the
river Nile. These fishes are covered with bony
armour, and include a great number of types such
as Osteolepis, Holoptychius, Dipterus.
These fishes do not appear to be in any sense
CARBONIFEROUS. 97
embryonic. They have great importance in the
primary period. One of their living representa-
tives, the Ceratodus, has, in addition to the gills
which are common to most fishes, a lung which is
adapted to breathing air under terrestrial condi-
tions, as though it were possible for some fishes
to have developed terrestrial habits of life.
Another interesting circumstance connected
with the old red sandstone is the occurrence in
it, in the Irish locality of Kiltorkan, and near
Caerleon in Monmouth, of a shell, which has not
been distinguished from the common pond mussel,
named Anodonta.
Beds of the same age in Canada make known,
among evidences of terrestrial life, large insects;
and remarkable forms of myriapods, in which
there is only one pair of legs developed on each
segment of the body.
The accumulation of the enormous thicknesses
of the old red sandstone deposits presupposes im-
mense dimensions for a lake in which sediments
three miles thick could be piled up, and a large
area of denudation to furnish it with sediments.
CHAPTER XIII.
CARBONIFEROUS.
THE carboniferous period of time has been so
named because it is the principal geological epoch
in Britain in which coal occurs. The rocks rest
on the Old Red Sandstone in Scotland, and on the
Devonian in the west of England. They are un-
conformable to the older rocks in some districts.
98 THE STORY OF THE EARTH.
The carboniferous period, like the preceding
epoch, gives evidence of conditions which are in
part marine, and in part terrestrial. In the south-
ern area, it is the marine condition which is chiefly
developed in the lower part of the formation.
Whereas, in the northern area, terrestrial condi-
tions are developed towards the base. In travel-
ling southward from Scotland over Britain the
terrestrial beds come to hold a higher and higher
position among the carboniferous strata. The
formation is usually taken to include four or five
chief divisions, which, commencing at the base,
are reckoned as Lower Limestone Shales, Car-
boniferous Limestone, Yoredale beds, Millstone
grit and Coal Measures.
The first point of interest of this epoch, is in
the circumstance that in Scotland, the Calciferous
Sandstone, which attains a thickness of 3,500 feet,
lies at the base of the formation, so that the sand-
stone conditions of the carboniferous period, suc-
ceed to the sandstone conditions of the old red
sandstone. There are occasional beds of lime-
stone and shales, like the Burdiehouse limestone
in the upper part of the group. The fossils in-
clude land plants. There is evidence of consider-
able volcanic activity, especially in the tuffs and
andesite lavas associated with the calciferous pe-
riod, in the Garlton Hills, north of Kaddington.
In the shales are one or two coal seams; and the
shales themselves are sometimes so bituminous as
to be a valuable source of mineral oil. The ter-
restrial conditions, which commenced in this way
in Scotland, appear never to have entirely ceased
in any of the areas in which the coal is found.
There is therefore no great break in Scotland in
conformity of physical conditions with the older
CARBONIFEROUS. 99
terrestrial and lacustrine conditions of the old red
sandstone period. As the Calciferous Sandstone
is followed southward, it becomes represented,
first by the Tuedian beds of Northumberland and
Durham, which are alternations of sandstones,
shales and impure limestones. There is no Old
Red Sandstone below the Carboniferous rocks in
the North of England, and from the Cheviot lake
to Coalbrookdale, the Old Red Sandstone is doubt-
fully represented. In the South Wales coal field,
and the Bristol coal field, and the country of the
Mendip Hills, the 400 or 500 feet of Lower Lime-
stone Shale, with the bone bed at or about the
base, consists chiefly of alternations of limestone
and shale, more or less charged with fish remains.
There is little to separate the marine life of this
period from that of the Carboniferous Limestone.
The second division of the carboniferous rocks,
known as the Carboniferous Limestone series,
commences in the Scotch coal fields with sand-
stones, shales, fireclays, coal beds and a thin
bedded limestone. The Scotch beds are grouped
into the lower limestone series, the edge coal
series, and the upper limestone series. The mid-
dle, or edge coal division, is about 600 feet thick ;
and includes among the sandstones and shales
twenty-six seams of coal, now highly inclined,
which grew where they are found, and each is
more than one foot thick. The coal beds are not
entirely absent from the upper limestone series,
so that the representative of the Carboniferous
Limestone in Scotland is important, as indicating
terrestrial conditions which are not quite sharply
marked off from those of the Calciferous Sand-
stone below.
Travelling southward a remarkable physical
100 THE STORY OF THE EARTH.
change takes place. The carboniferous limestone
consists of numerous alternations of limestones
FIG. 13. Section showing the strata on the east of the Pennine
chain.
with shales, which are well exposed in the dales
of Yorkshire, where they are cut through by the
rivers draining eastward into the North Sea.
Above the limestone group, which is known as
the Scar Limestone or Mountain Limestone, there
is a superimposed series termed the Yoredale
beds, which are well represented in Northumber-
land, Yorkshire and Lancashire, and are thickest
on the west side of the Pennine chain. These
beds are partly sandstone, termed Yoredale grit ;
but mainly shales, with impure limestone; so that
they form, essentially, an upper division of the
Carboniferous Limestone in the North of Eng-
land. In Derbyshire and Flint the carboniferous
limestone attains an immense thickness. And
then southward, in the West of England and
South Wales, it is reduced to 1000 or 2000 feet,
with a capping of Upper Limestone Shale, which
represents the Yoredale beds.
Where the limestone is well developed, whether
in the west of Yorkshire or Derbyshire or Bristol,
its organic origin is usually evident. It is formed
in some places of the remains of Encrinites, in
others of Corals, occasionally of Brachiopod
shells, while there are a few localities, especially
in the Bristol area, where the limestone is organic
CARBONIFEROUS. 101
in the same sense as the Oolites are organic, con-
sisting of rounded grains cemented together which
appear to have originated in the growth of marine
Algae allied to existing Nullipores.
Fossils of the Carboniferous Limestone.
The Carboniferous Limestone being in part a
coralline limestone, includes a large number of
corals. Probably the commonest genera found in
Europe are Amplcxus, Cyathophyllum, Lithostrotion,
and Zaphrentis. They
are numerous in species
and abundant in individ-
uals, and are all of ex-
tinct types.
The Echinodermata
are largely represented ;
and propably in no de-
posit is there a greater
number of crinoids. The
principal genera are Ac-
tinocrinus, Cyathocrinus
and Platycrinus.
The shells, however,
are even more distinctive. The two genera Pro-
ductus and Spirifera comprise more than half the
species of Brachiopods. Rhynchonella is well repre-
sented in association with Terebratula. The latter
two survive all subsequent revolutions of the earth.
Among the other shells, the bivalves Pinna,
Lima and Anomia, Avicula, Pecten are associated
with Modiola, Mytilus, Area, Solenopsis, Solemya,
types which appear to survive to the present day,
more common on British coasts than in the car-
boniferous rocks.
FIG. 14. Productus, a brachio-
pod of the carboniferous lime-
stone.
102 THE STORY OF THE EARTH.
Such univalve or Gasteropod shells as Chiton,
Littorina, Natica, Patella, Pleurotomaria, Turritella
and Turbo are surviving genera which are found
in the Carboniferous Limestone. These are not
always the genera richest in species. Aviculo-
pecten, which is regarded as extinct, has more
species than any other bivalve ; and Euomphalus,
also extinct, is one of the best represented genera
of gasteropods.
Fishes abound, the cartilaginous fishes, or
sharks, appear curiously to parallel both in their
fin defences and teeth, the sharks which are sub-
sequently found in the Secondary rocks. The
ganoid fishes are also well represented. As a
group they are unlike the types which lived in
the old red sandstone time.
Millstone Grit.
This rock, mainly formed of quartz grains, is
a shallow-water deposit, which often gives evi-
dence of current bed-
ding, and sometimes di-
vides along planes in
which the mineral mica
is abundantly deposited.
There is perhaps no
good ground for separa-
ting these rocks from
FIG. 15. Pleurotomaria, show- the overlying . coal
ing remains of the original measures ; and the sand-
SZ^s^onf 11 - sto <^ *- hi <* they con,
tain are not more im-
portant than those known as the Pennant sand-
stones, in the coal measures of the West of Eng-
land. They resemble the coal measures of the
CARBONIFEROUS. 103
south in the character of their sandstones and
ironstones, and they yield, in various localities,
some thin beds of coal.
In Scotland this third division of the car-
boniferous group of rocks, is named the Moor
Rock. Its only difference from the Millstone
Grit, is in containing marine fossils. But this
condition probably only indicates that the lacus-
trine basins, in which much of the deposit may
have been formed, were sometimes open to the
sea. Southward in England, the Moor rock
known as the Millstone grit, consists chiefly of
alternations of sandstone and shale. It is only
50 feet thick in Leicestershire but thickens in the
west. In Northumberland it is 400 feet thick. In
the Forest of Dean it is less than 500 feet. It is
1000 feet thick in the Somersetshire coal field.
From this deposit a large part of the flagstones
of Britain is obtained. It forms the wildest scen-
ery of the western side of the Pennine chain. This
is due to the succession of the four principal beds
of grit which rest upon each other in successive
terraces, with the thick Kinderscout grit at the
bottom, and the three less important grits above,
which are all divided from each other by shales
and sandstones. There are many thin beds of
coal in the Millstone Grit. None of them are
worth working, so that the coal miner knows the
deposit in England as the Farewell rock, below
which coal is not to be expected. The existence
of the Millstone Grit indicates an upheaval of
the Carboniferous Limestone sea, by which the
conditions of physical geography became simi-
lar in England to what they were in Scotland.
Such an upheaval exposed the uplifted rocks to
denudation, and probably furnished the material
104 THE STORY OF THE EARTH.
out of which the millstone grit sandstone was
made.
The thick deposits in the south of England
are near to the areas in which the thick masses
of old red sandstone are found. It is possible
that such a cause has governed the thickness of
the deposit, though in the west of Pembrokeshire
the Millstone Grit is only 300 feet thick ; and it
is difficult to see in areas now exposed any source
for the Kinderscout grits, except in such ancient
rocks of Shropshire as form the Longmynd, and
the Denbighshire grits of North Wales. Denu-
dation of the original materials from which such
ancient rocks as those were derived would have
made these sandstones.
The Coal Measures.
The rocks which yield coal are a succession of
sandstones, and shale, ironstones, fire clays and
coal seams, which are repeated over and over
again. They thicken from Northumberland
south-west to South Wales; chiefly owing to in-
crease in quantity of the sand. In the north of
England the thickness is 1500 feet; in the south-
west in Wales it is 11,000 feet.
Fire clays are old soils of the carboniferous
land in which the roots of forest trees often stand
vertical, as they grew; showing that the coal was
in most cases a peaty growth, like Irish bogs, due
to the fall of forest trees, and the accumulation
of vegetable matter where the forest trees had
formerly grown. In South Wales scores of forest
trees of the kinds named Sigillaria and Lepido-
dendron may sometimes be seen crushed flat like
boards, piled one above another in the positions
CARBONIFEROUS. 105
in which they fell, before they became matted
and compressed into a solid mass.
In some cases, the coal growth has been com-
pared to the American swamps and cane-brakes,
where the girdle of surrounding vegetation niters
the muddy waters, so that only clear water
reaches the vegetable matter in the enclosure.
There is no doubt that carboniferous land sur-
faces were constantly undergoing depression of
level, like the Deltas of rivers such as the Po t
and the Mississippi, in many of which a succes-
sion of land surfaces has been found one below
another, indicating accumulation of sediments
which are similar to the coal shales and sand-
stones and resemble them, in the intercalation of
vegetable growths between layers of mud. These
depressions during the growth of the coal often
appear to have been partial and local.
In the Dudley coal field the lo-yard seam is
found, which is the thickest coal bed in England.
When it is traced to the north, it subdivides into
nine seams of coal, each having its own bed of
under clay, on which successive forests grew. At
Essington the nine beds preserve the thickness of
the one bed at Dudley, though they have become
separated from each other, by wedge shaped
layers of 'sandstones and shales, which have an
aggregate thickness of 420 feet.
The Dudley country is also interesting among
English coal-fields on account cf the volcanic
eruption, which appears to have taken place dur-
ing the carboniferous period ; for the basalt at
Rowley Regis, which was ejected through the
coal, is in some places in the condition of cinder
and ash ; and this appears to prove that it was
ejected at or near the surface. Volcanic out-
106 THE STORY OF THE EARTH.
bursts are comparatively rare in the coal of Eng-
land. In the Edinburgh coal-field the volcanic
eruptions are the most impressive feature of the
deposit. The layers of volcanic ash, and vesicu-
lar lavas, such as may be seen in Edinburgh, at
Calton Hill, prove the outbursts to have been
contemporaneous with the sediments. Regions
of volcanic activity are commonly the scene of
changes of level of land, such as the coal strata
demonstrate.
The layers of coal may be compared to the
growth of peat over the flat lands of Holland.
The sea sometimes bursts in, as when the Zuyder
Zee was formed, so that marine beds with marine
shells, rest upon the terrestrial growth. Such
catastrophes occurred in the Dudley coal-field,
and more evidently in that of Coalbrook Dale.
In the lower part of the coal measures is the
layer of clay ironstone known as the Pennystone ;
and in the upper part is the layer known as the
Chance Pennystone; both of these are marine de-
posits with marine fossils, like the shells Goniatites
and Aviculopecten, which had not been seen since
the Carboniferous Limestone was deposited.
They were still existing not far away ; but might
have been thought extinct, but for these incur-
sions of the sea.
There is no means of judging whether the
coal or the intervening sediments occupied the
longer time in forming. The total thickness of
the coal in all the seams added together, varies
from about 100 to 140 feet.
The properties of coal probably vary with the
nature of the juices of the living plants. Thus,
when starch is burnt it gives a vesicular coke or
cinder. When gum arabic is burned, it forms a
CARBONIFEROUS. 107
hard dull coke like an imperfectly coking coal.
When cellulose is burnt, it forms a coke which
does not cohere, like the substance known as
mother of coal. Hence differences which coals
show in burning may depend upon the original
substance of the plants.
The first important variety of coal Anthracite,
which contains the largest percentage of carbon,
is clean to touch, and burns with little smoke.
In some localities anthracite appears to result
from the distilling action of the heat which is
generated underground by the folding of the rocks
in a coal-field. This separates the mineral oil
from the coal, so that the petroleum escapes into
porous rocks like water, and may rise to the sur-
face in springs.
Other coals are often termed bituminous, but
no substance at all like bitumen exists in coal.
Such coal is insoluble in any of the solvents which
dissolve bitumen ; but it softens at a low tempera-
ture. Caking coals partly melt, and make a com-
pact coke.
The non-caking coal, like the steam coal of
South Wales, does not change its form in burning.
The properties of the coals vary with the different
beds, suggesting differences in the species of plants
which formed them.
The group of rocks termed Coal Measures is
commonly divided into three parts. The lower
coal measures, or Canister beds, are usually bar-
ren, or only contain thin coals, which are not often
valuable. Secondly, the middle coal measures
contain most of the thick workable beds of coal.
They correspond to the Pennant group of South
Wales and the Bristol coal-fields. Thirdly, the
upper coal measures yield a good deal of coal in
108 THE STORY OF THE EARTH.
the South of England and Wales, but mostly in
thin beds.
The coal was more widely spread in former
geological ages than it is at the present time,
though there is no reason to suppose that the
vegetable growth ever extended continuously over
the country. The several coal-fields are basin-
shaped depressions, which have been isolated from
each other, sometimes by denudation. First there
has been the compression which elevated the Pen-
nine chain and Wales. This divided the coal-fields
into longitudinal series, stretching south on each
side of the Pennine chain. Then the country was
compressed in the opposite direction, forming
folds which run from east to west. An upward
thrust divides the coal-field of Northumberland
and Durham from that of Yorkshire and Notting-
ham. Its effects are also seen in the separation
of the Cumberland field from the South Lancashire
coal-field. The folds which isolate the South
Wales and Forest of Dean coal-fields and the
Somerset coal-fields lie further south. Afterwards
denudation removed the summits of the anticlinal
folds, and the coal-fields remained in basin-shaped
depressions.
Coal has been found by boring beneath newer
rocks at Burford in Oxfordshire; and at Dover;
so that these east to west folds of the primary
strata beneath the newer rocks, probably extend
continuous with the coal of Belgium.
Coal Plants.
About half-a-dozen terrestrial plants which are
imperfectly known, have been described from
rocks older than the Devonian. The flora of the
CARBONIFEROUS. 109
Devonian period does not differ essentially from
that of the Carboniferous, since both contain the
same genera of ferns, of giant reeds allied to the
living Equisetum, and of club-mosses of the size of
forest trees, which differ from the Quill-wort and
Lycopodiums, more in size than in structure.
The Carboniferous period was an age of ever-
green forest trees of types which did not survive
the Permian period. No example is known of
modern forest trees; but we cannot infer that
they did not exist. The abundance of Eucalyptus,
and of the leafless Acacias in South Australia
shows how largely a few genera may monopolize
the ground ; and the circumstance that both the
Australian and African floras are evergreen at
the present day, proves that the absence of some
types from a district of the Earth or deposit, is
consistent with their existence at the same period
of time in another locality.
Coniferous trees of the coal measures grew to
a large size. In the forms of their fruits they re-
semble some of the yew tribe. The living Salts-
buria of China has fruits which are of nutlike form,
and resemble the Coal Measure fruits known as
Trigonocarpon which are produced by the forest
tree named Dadoxylon. Under the microscope the
wood of this tree shows characteristic coniferous
structure. The tree differs from all conifers of
newer age in having a large central pith, formed
by a succession of thin transverse layers. Casts
of the pith cavity were long supposed to be sepa-
rate plants, and named Sternbergia. Cordaitcs is
another conifer of the yew type. And Araucarites
has been so named from its resemblance to the
living Araucaria.
The club moss tribe, which at the present day
no
THE STORY OF THE EARTH.
rarely grows erect, and never reaches a height of
more than a foot or two, is represented by forest
trees, which grew to a height of fifty to seventy
FIG. 16. Part of the trunk of a Sigillaria from the coal near Hud-
dersfield, showing the thin outer carbonaceous layer with leaf-
feet. Like the conifers they have become known
gradually, and each part of the tree received a
distinct name, before the structure was known
fully. In Sigillaria the trunk is vertically grooved,
with the leaf scars extending round it in a spiral
pattern. In Lepidodendron each leaf scar is en-
closed in a lozenge-shaped area, and since these
CARBONIFEROUS.
areas are in contact, the spiral pattern is more
marked than in Sigillaria. The roots of these
trees bifurcate regu-
larly at each subdi-
vision, and the same
structure is found in
the branches which
crown the trunk.
The roots, formerly
termed Stigmaria,
have an irregular
pitted pattern of
scars to which long
rootlets were at-
tached. The fruits
are cones, developed
like clubs, at the
ends of the branches.
These fruits were
termed Lepidostro-
bus. The existing
Lycopoditim resembles
Lepidodendron in spi-
ral arrangement of
the leaves, fruiting
organs and spores. The internal structure is es-
sentially the same. Lepidodendron has a central
pith, surrounded by woody tissue, which is formed
of elongated vessels. Outside of that is the cam-
bium layer of the bark, formed of large spherical
cells, corresponding to the layer seen in the quill-
worts ; and external to this is the bark, formed of
small cells which are elongated.
Some of the layers of coal which are richest
in hydrocarbons, such as the better bed-coal, are
formed of spores of such plants. These spores
coal, Cape Colony.
112 THE STORY OF THE EARTH.
are usually large macrospores, such as are found
in the lower part of the fruit of the living Selagi-
nella ; and the fossil Triplosporites. The fossil
reeds of the coal, termed Calamites, are closely
related to the living Equisettim, although the
plants grow to a comparatively large size. Ex-
ternally the plant terminates downward in a cone.
The trunk is divided transversely by nodes, and
the internal cast of the internodes is fluted. At
the nodes the stem gives off leaves in circles, and
these leaves supported leaflets arranged in whorls.
The leaves are known as Asterophylites, with needle
shaped leaflets ; Annular ia, with blade-shaped leaf-
lets ; and Sphenophyllum, with wider wedge-shaped
leaflets. There are also several types of fruit,
which closely resemble the fruit of Equisetum,
except that some of the leaves do not bear spo-
rangia, and thus form a protective covering to the
others. The spores are of the same size in the
living and fossil types.
The ferns of the coal known under such
names as Alethopteris, Neuropteris, Odontopteris,
Sphenopteris, closely resemble existing ferns, in so
far as can be determined ; for the fructification is
not often preserved. Four of the eight existing
families of ferns are known in the coal measures.
Tree ferns have been described.
Animals of the Coal Forests.
Terrestrial shells are not preserved in many
geological deposits, and only two genera are
known from the Coal Measures. They are both
small, and were found in a bed of underclay, in
a layer about two inches thick, in Nova Scotia,
probably swept down by the rain, as shells in a
CARBONIFEROUS. 113
forest often are at the present day. One of these
shells is a thin variety of the common hedge
shell of Great Britain, named Helix. The second
appears to be identical with the existing genus
Pupa, which is commonly found about the roots
of trees. They are the oldest terrestrial shells
known.
Associated with the land shells are centipedes.
The group of Myriapods to which they belong is
distinguished by having one pair of antennae, eyes
nearly always simple, no distinct thorax, and no
wings; while limbs are attached to nearly all the
segments. Like insects they have three pairs of
jaws. The respiration, as in insects, is carried on
by tracheae, which open near the articulations of
the legs, except in the living genus Peripatus.
Myriapods live in the loose bark of trees, in
cracks in the rock, and under stones. The oldest
forms were found in the hollow trunks of Sigil-
laria. They are Millipedes rather than centi-
pedes. They are known in the carboniferous
rocks of Canada. A Millipede found in the coal
of Ayrshire, named Euphoberia, is four inches
long, nearly a quarter of an inch broad, formed
of thirty-six body rings, each with two pairs of
legs. These myriapods are distinguished by pos-
sessing branched spines which are hollow. The
American genus Xylobius has been found at Glas-
gow and Huddersfield, in the coal.
The spiders of the coal belong to a group
known as the false scorpions, of which the type
is the living genus Phrynus. Eophrynus Prestwichi
is a well-known, though rare fossil from the iron-
stone of Dudley. It resembles spiders in having
four pairs of legs, and a pair of palpi is seen. On
the under side of the body are the openings of
8
114 THE STORY OF THE EARTH.
six pairs of stomata from the tracheae, which are
developed as in insects. True spiders are found
in the coal measures of Bohemia, Silesia, and of
Illinois.
Another representative of this group of Arach-
nida is the scorpion, which is represented by the
genus Eoscorpius. Scorpions are first found in
the Silurian rocks. Eoscorpius found in the coal
of Illinois, appears to be closely allied to a living
Californian scorpion, of the genus Buthus ; though
the form found in the coal of this country agrees
best with the genus Scorpio.
Insects are well represented in the coal.
Coleoptera are known from beetles named Cur-
culioides and Troxites. Grasshoppers are found,
as are cockroaches. Lithomantis represents the
living leaf-insect Mantis. The white ant occurs;
along with a butterfly. Carboniferous insects are
chiefly known from the coal-fields of the continent.
The fishes found in the coal measures include
a number of sharks, known from their fin defences
and teeth.
Labyrinthodont reptilia are referred to more
than twenty genera. Many of these are from the
Kilkenny coal-field, and Belgian coal-field. The
remarkable genera, Anthracosaurus and Loxomma
from the coal-field of Northumberland are among
the largest of carboniferous genera. They are
distinguished by having the teeth united to the
jaw, without being in sockets. In some families
the palate is covered with a large bone in the
middle, named the para-sphenoid. The skull is
sculptured as in crocodiles, and contains some
bones which are not found in existing reptiles,
especially behind the eye, where bone is absent
in a crocodile.
PERMIAN. 115
CHAPTER XIV.
PERMIAN AND TRIAS.
THE deposits which rest next in succession
upon the Carboniferous series are termed Permi-
an, because they appear to be identical with the
strata found in the Russian government of Perm.
They had been termed Poikilitic, or variegated
rocks; and sometimes the Pontefract rocks, from
occurrence at that town in Yorkshire.
Marine beds in the east of England represent
them between Hartlepool and Nottingham, but
the Permian sandstones have sometimes been
regarded as fresh-water and lacustrine deposits
in the west and south-west of England. They
appear to be unconformable to the underlying
strata in some localities. In other localities
there is no clear separation between the lower
Permian rocks and the Carboniferous. Such
conditions appear in Lancashire and Cheshire,
and are regarded as occurring in Russia, and
in North America.
The lower sandstones in Cumberland yield
the characteristic genera of Carboniferous plants.
It is therefore interesting that near Enville
in Worcestershire, and in other localities, the
Permian rocks contain angular boulders, which
are polished, and scratched apparently by ice;
though the scratched stones may not be evidence
that glacial conditions prevailed in that district
in the Permian period.
The Permian rocks of Great Britain comprise
lower, middle and upper series. The upper and
lower parts are sandstones and conglomerates, or
Il6 THE STORY OF THE EARTH.
sometimes breccia derived from the Carboniferous
limestone. The middle portion is a great wedge of
magnesian limestone, resting upon the marl slate,
600 feet thick in the east of England, and 10 or
20 feet in the west. The upper sandstones and
clays with gypsum, like the lower beds, are thick
in the west and thin in the east : but are only
about one-fifth of the thickness of the lower
sandstone. The lower 3000 feet of variegated
sandstone is identified with the German rothlie-
gende. The marl slate is identified with the
kupferschiefer, and the zechstein with the mag-
nesian limestone. The lower Bunter of Germany
has been compared with the gypseous marls of the
Eden basin in Cumberland.
The magnesian limestone probably was origi-
nally an ordinary limestone formed of calcite, and
the carbonate of magnesia was apparently infil-
trated into it. There is no more singular deposit
anywhere to be seen than the exposure of this
rock at Sunderland, where some of the beds now
consist of radiating concretions of globular form
and variable size, giving the rock an appearance
of being built of shot or cannon-balls.
The Permian age was a time of considerable
volcanic activity, and interstratified beds of vol-
canic ash and lava are well seen in the country
about Exeter, and in Ayrshire, as well as in
Germany.
In other parts of the world the Permian forma-
tion attains a great development in thickness, and
contains important beds of coal. The Gondwana
rocks of India, which are probably comparable to
the Permian of Russia, very closely resemble the
Permian rocks of the Karoo in South Africa. Both
contain coal, and the flora is probably Permian,
PERMIAN. 117
but several of the genera of ferns do not occur
in Great Britain.
Among the fossils in the marine beds between
Hartlepool and Nottingham the foraminifera in-
clude several existing genera. Neither the corals
nor crinoids show any remarkable variation from
carboniferous types, and in a general sense this is
true of the shells, though a large number of the
genera which characterise the primary period are
absent. There are some characteristic genera of
fishes like Acrolepis, but the most abundant fish
type is Palceoniscus.
Fossil Reptiles of the Permian.
The Labyrinthodont reptilia, distinguished by
having teeth blended with the jaw bones without
being in sockets, are found in some British coal-
fields, and are also known from Permian deposits.
In Bohemia and in Saxony many small animals of
diverse forms occur ; some long and snakelike,
and others like land salamanders. Some of these
closely resemble fossils of the Kilkenny coal-field,
as well as similar types from the coal-fields of
Illinois, Ohio, and Nova Scotia, and are referred
to the same genera. One of these Bohemian ani-
mals, named Branchiosaurus, still preserves in the
fossil state a skeleton to the bony arches which
supported gills. This old reptile, like some of
the ancient fishes associated with it, may have
breathed by gills as well as lungs, like certain of
the living amphibia. This terrestrial life makes
a close link between the Permian and Carbonifer-
ous periods.
The Permian rocks contain another extinct
group of animals named Anomodontia, which
Il8 THE STORY OF THE EARTH.
comprises the groups named Theriodontia, Dicy-
nodontia and Pareiasauria. They are animals
with depressed bodies rarely lifted high above
the ground by their limbs, with relatively large
heads, and types of dentition which are anoma-
lous, because they closely resemble the teeth of
different orders of mammals, while preserving
tooth characters of reptiles and fishes. Nor is
this resemblance to mammals limited to the
teeth. It is seen in almost every part of the
skeleton ; and although there is no actual transi-
tion to mammals, isolated parts of the skeletons
have been described as mammalian by different
naturalists.
The Anomodont group is most widely devel-
oped in the Permian rocks of South Africa. It is
well represented in the Permian of Texas, and
other parts of North America. It is recorded from
the Gondwana rocks of India, and from the Per-
mian rocks of Orenburg in Russia. Anomodont
reptiles have also been found in the red sandstones
of Elgin. Those rocks were formerly classed as
Old Red Sandstone, and subsequently as Trias
owing to the affinities of their fossil reptiles, but
on such evidence they may be Permian.
The Theriodont type generally possesses the
three kinds of teeth which characterise mammals.
The canine teeth are strongly developed. This
is seen in the Russian genus D enter osaurus, and in
the South African genus Lycosavrus, both of which
have the teeth in the front of the mouth larger
than the sharp-pointed representatives of the
grinder series placed at the sides. D enter osaurus
finds its place between the Theriodonts and Pareia-
saurus. Some of the South African Theriodonts
have the molar or grinder teeth compressed and
PERMIAN.
120 THE STORY OF THE EARTH.
notched like those of dogs, seals, and other car-
nivorous mammals. There are also types which
have tuberculate crowns to the grinders adapted
for crushing food, during which process the crowns
become ground down, as among Insectivora and
Rodents.
There are in the genus Dicynodon only two teeth
in the upper jaw, which correspond to the tusks of
the walrus.
In Pareiasaurus the surface of the skull is cov-
ered with an arrangement of bones which appears
to be identical with that seen in the Labyrintho-
donts. Labyrinthodonts were formerly grouped
with the Amphibia, but may be closely related to
the Anomodonts. Pareiasaurus appear to be in
many ways transitional between existing reptilia
and mammalia; in so far as can be judged from
the skeleton. It is with existing marsupials and
carnivora, and hoofed or ungulate mammals that
the resemblances in the forms of the bones appear
to be closest.
The Trias.
A glance at a geological map of England and
Wales shows that the Trias, which extends to the
south of the Pennine chain, between Nottingham
and the North Staffordshire coal-field, rests un-
conformably upon the denuded edges of the Per-
mian and Carboniferous strata. Great changes
had taken .place in the earth's surface after th&
deposition of the Permian rocks, and a commence-
ment was made in the definition and uplifting of
the Pennine chain before the Trias was laid down
against its southern termination.
In England the Trias comprises two series of
sandstones. The lower, named Bunter, consists
THE TRIAS. 121
of conglomerates and sands, which are usually
white, but sometimes red. There are some evi-
dences that its upper beds were denuded before
the overlying alternations of marls and sandstones,
named the Keuper beds, were deposited. These
divisions are regarded as corresponding to the
upper and lower divisions of the Trias in Germany,
between which the shell limestone, termed Muschel-
kalk, occurs, yielding numerous marine fossils,
and many peculiar fossil reptiles.
These beds attain a thickness in Lancashire
and Cheshire of 5200 feet. The Keuper is there
twice as thick as the Bunter ; but in Leicester and
Warwickshire the aggregate thickness of both di-
visions of the Trias is less than 1000 feet; and of
that the Bunter forms about one-tenth.
There is a southern thickening of the Trias in
Somersetshire and Devon, where the red rocks
are well exposed on the coast, and are about 2500
feet thick. There are few or no fossils in the
Bunter.
The rock-salt of Cheshire occurs chiefly in the
Keuper marl in two principal beds, as at North-
wich, where each of the principal lenticular masses
of salt is about 100 feet thick. Gypsum is also
found in the marls, and is largely worked in Staf-
fordshire. The occurrence of the salt may be
attributed to the evaporation of an inlet of the
sea; so that the process was substantially the
same as that now going on in the salt-pans on the
shores of the Mediterranean, where salt is obtained
artificially by evaporation of sea-water. There
appear to have been many of these ancient salt-
pans. The lower bed at Northwich is about three-
quarters of a mile in diameter. The salt has been
preserved by the marl in which it is contained,
122 THE STORY OF THE EARTH.
which is impervious to water. The gypsum has
probably been formed out of the carbonate of
lime of calcareous organisms, by the action upon
them of sulphurous waters, such as result from
the decomposition of iron pyrites, for Mr. Charles
Darwin describes gypsum as formed in this way
in lakes on the surface of South America.
In the neighbourhood of Storeton, between
the Mersey and the Dee, an immense number of
impressions of the feet of terrestrial animals are
found, some of which are at present otherwise
unknown. They may comprise the footprints of
Dicynodonts, of Rhynchosaurian reptiles, and per-
haps of Hypetodapedon, bones of which occur in
Keuper beds in other parts of the country. The
Keuper at Warwick yields evidences of the skull
of species of Labyrinthodon. And near Bristol,
carnivorous saurians, termed Palceosaurus, with
piercing and cutting teeth, are found, which are
closely allied to the great saurians of the Trias of
Wurtemberg, named Zandodon.
The Stormberg beds in South Africa are prob-
ably of Triassic age, and contain saurians in some
respects similar to those of Germany, such as
M assospondylus and Euskelesaurus, and are found
above the coal of Cape Colony. They all show
some alliance with the Megalosaurus of a later
age.
The saurians of the Muschelkalk in Germany
include Placodus, which has the palate covered
with large flat crushing teeth ; and Nothosaurus,
which appear to be intermediate between the
Deuterosaurs of the underlying Permian rocks
of Russia, and the long-necked Plesiosaurs of the
Oolitic series above.
In Europe at least the plants of the coal period,
THE TRIAS. 123
with the exception of Catamites, have disappeared
in the Trias ; and various types of Cycads come
into existence, and do not differ appreciably from
surviving forms in mode of growth and fruiting.
The Oldest Known Mammal.
The oldest known mammal is found in the
upper part of the Trias or in the Rhaetic beds.
There are several species referred to the genus
Microlestes. They are only known from isolated
teeth and are referred to mammals because the
roots of the teeth are divided. They occur in
Wurtemberg, and at Frome, and Watchet in
Somersetshire. The great milk tooth from Watchet
is marked with seven ribs, like those on the pre-
molar tooth of the living kangaroo-rat named
Hypsiprymnus. The animal has therefore been re-
garded as a marsupial mammal. Animals with
this type of tooth are found in subsequent periods
of geological time. The lower jaw of a little
mammal named Plagiaulax found in the terrestrial
Purbeck beds at the close of the Oolites, has sim-
ilar teeth. This type is repeated in the genus
Neoplagiaulax, found at Rheims in the lower ter-
tiary beds of the Paris basin. There is therefore
reason to believe that very little change has taken
place in the oldest type of mammal since its first
occurrence in the Trias; and that it was essen-
tially a Kangaroo-rat.
Peculiar marine fossils appear in the Muschel-
kalk. One of these is the Cephalopod shell Cera-
tites, which is exactly intermediate between the
Carboniferous Goniatites which has the septa angu-
larly folded and the newer Ammonites which has
the folds of the septa digitated on both the front
124 THE STORY OF THE EARTH.
and back margins. Subsequently, in the Austrian
Alps, especially at Hallstadt on the north, and St.
Cassian on the south, the Upper Trias abounds in
shells which are a remarkable mixture of those
which survive from the Primary period, such as
Orthoceras, Gontatites, Euomphalus, Murchisonia,
with the shells which are found in the overlying
strata, such as Ammonites, Belemnites, NerinKa,
Trigonia, Cardita, Thecidium. Therefore the sepa-
ration in life between the Trias and the Permian,
although most marked, is not so absolute as it
would have appeared to be if those Alpine deposits
had been unknown. And the occurrence of genera
which had characterised the primary strata, is the
more interesting because other examples occur of
similar survival of types of life from the primary
time, in the occurrence of the genus Leptaena in
the Lias, and of Spirifera in the Lias and Lower
Oolites. Such occurrences prove that the change
in life was a local change, and that the primary
types became extinct gradually.
Newer than the Keuper is a series of beds in
the west of England not more than TOO feet thick,
known as the Penarth beds or Rhaetic beds, from
their great development in the Rhaetic Alps. They
are included in the Trias by many writers. William
Smith referred to them as the White Lias, which
is a compact limestone forming the top of the
Rhaetic series, in marked contrast to the Blue Lias
above. The White Lias has occasionally been
used as a substitute for lithographic slate, which
it resembles in appearance. Dragon-flies, Cock-
roaches, Grasshoppers, and other insects are pre-
served in the White Lias.
Fossils are plentiful in the underlying black
shales, at the base of which is the Rhaetic bone
THE LIAS. 125
bed, full of the remains of fishes and reptiles. Be-
neath the black shale are the tea-green marls,
which pass down through other marls into the
Keuper beds. Species of the existing Australian
fish Ceratodus evidenced by teeth here occur ; as-
sociated with extinct genera of sharks, such as
Hybodus and Acrodus which characterise the
Oolites.
The common sea-shells of Rhaetic age include
a Cockle and a Pecten, such as might occur on
our own shores at the present day, associated with
a species of Avicula, a horse-mussel and an oyster.
At least one large terrestrial Saurian with teeth
like Megalosaurus occurs in Rhaetic beds in Somer-
set. The Ichthyosaurs and Plesiosaurs, which
are found for the first time in this stratum in this
country, do not differ from those of the newer
beds.
Rhaetic strata occur in most European coun-
tries in which the Trias is developed; but are no-
where more grandly exhibited than in the Rhaetic
Alps of Lombardy and Austria.
CHAPTER XV.
THE LIAS.
IN the Jura range between France and Switz-
erland, which furnishes the continental type for
rocks like our Lias and Oolites, the Jurassic beds
are commonly divided into three parts, named
Black, Brown and White. -The Black Jura corre-
sponds generally with the Lias; the Brown Jura
with the lower Oolites ; and the White Jura with
126
THE STORY OF THE EARTH.
MAP OF AN OUTLIER.
FIG. 19. Map of an outlier of Lias be-
tween Market Drayton and Whit-
church, proving that the Lias was
spread over the West of England.
the upper Oolites of England. These three divi-
sions in this country are greatly subdivided by
differences in min-
.:._^ . eral character, as
well as by fossils.
The Lias is gen-
erally recognised
by the great
breadth of country
that it covers be-
tween Whitby and
Lyme Regis, by
its thickness, and
its many sub-divis-
ions which are
^"f ^^ the
Country. It IS, as
a rule, a blue-black
clay alternating
with thin, regular layers of earthy limestone, so
that the alternations of clay and limestone which
characterise the Rhaetic beds are continued, with
a multitude of repetitions. The Lias limestones
have sometimes a tendency to be brown. The
thickness of the Lower Lias varies between 500
feet at Lyme Regis and 800 feet on the Yorkshire
coast. The common Lias Oyster is the Gryphaea
incurva. Occasionally, in the country towards
Frome the Lias almost thins away where it rests
against the Carboniferous limestone, and it is
probable that the different beds vary in thickness
locally. The marine and terrestrial saurians are
found chiefly in the lower beds of the Lower Lias,
in the south of England. They include both
Ichthyosaurs and Plesiosaurs. Nearer the top
of the Lower Lias Scelidosaurus, a terrestrial ar-
THE LIAS.
127
moured saurian is found, which in many ways re-
sembles the Iguanodon of a later period, and is
the type of a
family with ver-
tically serrated
teeth named
Scelidosauridse.
The fossils
which are most
abundant are a
multitude of ex-
tinct species of
Ammonites and
Belemnites, to-
gether with an FIG. 20. Gryphaea incurva : Lias,
oyster with an
involute mode of growth, known as the genus
Gryphtza incurva, the devil's toe-nail of the Dogger
fishermen. But with such exceptions the great
multitude of the fossils belong to existing gene-
ra. Among which are the bivalves Lima, Pecten y
Pinna, Pholadomya, Astarte, Avicula, Modiola, Tri-
gonia, Plicatula ; and the Univalve shells Litto-
rina and Pleurotomaria are abundant. Species of
the genus Ammonites give names to sub-divisions
or zones of the Lias. Some genera such as Car-
dinia and Hippopodium are only found in the Lias.
There is perhaps no sharp separation to be
drawn between the Lower and Middle Lias. The
two beds are conformable to each other, although
the fossils distinguish them, and there is some
difference in their mineral character. The Mid-
dle Lias comprises the marl stone, which forms
an escarpment in the middle of England; and it
also includes the ironstone series, which is well
developed in the Cleveland district of Yorkshire,
128 THE STORY OF THE EARTH.
and southward through Lincolnshire into Oxford-
shire. The Middle Lias is about 250 feet thick
on the south coast ; and 140 feet thick on the
Yorkshire coast. Near Cheltenham the lower
part includes some grey sand, and is about 150
feet thick. The difference from the Lower Lias
in fossils is chiefly in the species of Ammonites
and Belemnites. Some
of its upper beds are
known as the Belem-
nite beds, from the
abundance of this fos-
sil. In these beds
many star fishes of
the genus Ophioderma
are found, both on
FIG. 2i. Carxlima Listeri : Lias. the Yorkshire coast,
and near Charmouth.
The Upper Lias is usually very thin on the
coast of Dorsetshire, about 70 feet, including the
associated sands near Charmouth. But it thick-
ens northward to 300 feet near Cheltenham, and
400 feet further north in Bredon Hill ; maintain-
ing a thickness of 300 feet in Leicestershire, but
thinning in Lincolnshire and Yorkshire to 200
feet or less. On the Yorkshire coast it is often
known as alum shale, alum having formerly been
obtaiied from the cliffs and manufactured from
the shale. Near the base there are beds of jet,
in which the rings of growth of the coniferous
trees out of which it was formed, may occasion-
ally be observed. In the Upper Lias at Ilminster
many Ichthyosaurs, Plesiosaurs, and crocodiles of
the group Teleosauria are met with. A little
higher up, in the zone of the Ammonites communis
and Ammonites bifrons near Whitby, the same
THE LIAS. 129
genera occur, though they are sometimes met
with in the underlying zone of Ammonites serpen-
tinus, which yields the jet.
The Upper Lias of Gloucestershire and War-
wickshire contains a considerable number of in-
sect remains, probably derived from the forests
in which the coniferous trees grew, which appear
to have been allied to the living Araucaria.
There are also the remains of Cycads, such as
Zamia, and of a few ferns; so that, although
there is no such evidence of a land surface as in
the Triassic period, the occurrence of insects in
districts which, in the previous period of the
Trias, yield the remains of terrestrial animals,
appears to show that the physical change which
brought the Lias to an end, and caused the Mid-
ford sands to be superimposed upon it, was
substantially a bringing back again in part, by
means of upheaval, of the shallow water condi-
tions which prevailed in the Trias period.
The yellow sands, 200 feet in thickness at
Bridport, which pass northward into Somerset-
shire and Gloucestershire, under the name of
Midford sands, gradually thin away. But since
they indicate the same conditions as afterwards
reappear in the Northampton sands in the mid-
dle of England, they may be grouped with the
Oolites rather than with the Lias.
130 THE STORY OF THE EARTH.
CHAPTER XVI.
THE OOLITES.
THE Oolites are granular limestones of limited
extent, contained between clays, which in Great
Britain range between Dorsetshire and the north
coast of Yorkshire. They form three limestone
terraces in the south of England, each of which
rests on a clay, and hence have sometimes been
named Lower, Middle, and Upper. It is more
convenient to adopt two divisions. The Lower
Oolites include every bed above the Lias to the
Cornbrash. The Upper Oolites extend from the
Oxford Clay to the Portland Oolite.
Lower Oolites.
The Midford Sands are seen near Bath making
the base of the Oolites. The sand appears to have
been derived from the south, because the whole
of the Lower Oolites are represented by sands in
Dorsetshire. The Midford Sands disappear to
the north of the Cotswold Hills, probably because
they are represented there by clay which is not
distinguished from the Lias.
The beds named Northampton Sands occur in
the same geological position in Northampton-
shire. They are about 70 feet of brown sands
and yellow sandstone, with ironstone, which is a
valuable iron ore. They are capped by grey and
white sand, containing beds of lignite, which may
have accumulated in an estuary. Their fossils
are mainly those of the Inferior Oolite; and they
are probably a geographical continuation of the
Midford Sands.
THE OOLITES.
132 THE STORY OF THE EARTH.
In Yorkshire the beds which rest on the Lias
are known as Dogger. They are about 90 feet
of yellow sand covered by concretions of Oolitic
ironstone, usually sandy. Like the Northampton
sands, they are capped by current-bedded sands
and shales among which are beds of impure coal.
The fossils of those estuarine sands include ferns,
a large Equisetum often found erect among the
blown sand, and the Cycad Zamia. They indi-
cate an old land surface. The beds which rest
upon these sands show a similar want of conti-
nuity where they are exposed at the surface of
the country.
The Inferior Oolite is limited to the west of
England. In the Cotswold Hills it is about 250
feet thick, mainly limestone. At its base is the
pea grit, with concretions about the size of peas.
Above it are the Oolite limestones with texture
like the hard roe of fish, known to builders as
freestone, termed Roe-stone, which alternate with
marl. A little sand remains when the limestone
is dissolved. The rock thins away to the east
beyond Woodstock. Its fossils include Terebra-
Jula fimbria, Pholadomya fidicula, Ostrea Marshii,
Clypeus plotii.
In Northamptonshire the beds are replaced,
first, at the base by a thin bedded, shelly lime-
stone used for roofing, known as Collyweston
Slate. It is sometimes 20 feet thick. The great
mass of the Inferior Oolite is represented by a
limestone known as Lincolnshire limestone, which
thins away to the north and south. It is 200
feet thick at its maximum, and forms an escarp-
ment terrace in Northamptonshire and Lincoln-
shire.
In Yorkshire this period of time is repre-
THE OOLITES. 133
sented by the middle estuarine beds with bands
of coal and plants, seen in Gristhorpe Bay;
above which is the marine Scarborough lime-
stone, with the Inferior Oolite fossil Ammonites
Jfumphreystanus.
The Fuller's Earth in the south of England
caps the Inferior Oolite, and divides it from the
great Oolite. It is a series of clays, marl, and
earthy limestone known as Fuller's Earth rock.
The stratum, sometimes blue, sometimes yellow
of Fuller's Earth of commerce is only a few
feet thick. The Fuller's Earth in Dorsetshire is.
estimated at 400 feet in thickness. In the Mid-
land counties the Upper Estuarine beds represent
it with 30 feet of sands, clays and limestones. On
the Scarborough coast their thickness is 200 feet,
and, besides remains of terrestrial plants, they
contain the fresh water pond shell Anodonta.
The Great Oolite is more local than the Infe-
rior Oolite. At Minchinhampton it includes
shelly beds. At Bath it is a freestone 50 feet
thick, sometimes with oolitic texture, sometimes
marly. It is seldom oolitic to the north of the
Cotswold Hills.
To the north-east, the Bath oolite is repre-
sented by the Stonesfield slate, a concretionary
thin-bedded limestone, formed in part by the de-
struction of older beds of oolitic rock. It indi-
cates near proximity to land. Its fossils are the
fronds of ferns, foliage and fruits of cycads,
branches of coniferous trees. There are beetles,
dragon-flies, butterflies, and other insects. Lower
jaws of four kinds of mammals have been found,
named Amphitherium, Amphilestes, Phascolotherium y
and Stereognathus, which, on the evidence of their
t*eth, appear to be allied to Marsupials, though a
134 THE STORY OF THE EARTH.
thigh bone resembles that of the Australian duck
bill Ornithorhynchus. Flying saurians are named
Rhamphocephalus. Long snouted types of croco-
dile occur, and remains of the great terrestrial
carnivorous Megalosaurus, which appeared first
in the Inferior Oolite. All these fossils are in a
bed full of marine shells.
About Bath and in Dorsetshire the Great
Oolite is succeeded by a brown clay crowded
with the Apiocrinus, or pear encrinite, which has
a cylindrical stem. This clay, named Bradford
clay, separates the Great Oolite from the thin-
bedded Forest marble above it. That shelly lime-
stone at Enslow Bridge near Oxford, at Chipping
Norton, and other localities yields the remains of
Cetiosaurus, which is the largest terrestrial fossil
reptile found in England.
In Northamptonshire and Lincolnshire there
is a clay above the Great Oolite limestone, in the
position of the Forest marble and Bradford clay,
called the Blisworth clay.
All these irregularities in mineral character of
the Lower Oolites as they are traced through
England may result from the sinuous contours
of bays and promontories of the shores at the
time of their depositure, which did not corre-
spond with the line along which the several de-
posits come to the surface of the country at the
present day.
Cornbrash is the name given to a shelly lime-
stone which closes the Lower Oolitic period. It
is rarely more than 10 to 15 feet thick. Many of
its fossils are like those of the Inferior Oolite.
The most characteristic species is the Avicula
echinata. It is the first deposit since the Lias
which extends continuously through England,
THE OOLITES. 135
and is seen between Scarborough and Weymouth.
It is evidence of a change in the tilt of the sea-
bed, which makes a break in the succession of
the strata.
Upper Oolites.
There is no break in the order of succession
of the Oolitic rocks above the Cornbrash, which
would divide them into Middle and Upper Oolites.
The differences in mineral character between the
several beds are such as may be attributed to
changes in level of the old land from which the
sediments were derived, which removed the source
of the deposited material from time to time, to
greater distances.
The first effect of such an upheaval is seen
in the Kelloway Rock, which forms concretionary
sandy beds, and yellow sands and limestones 80
feet thick on the Yorkshire coast. It is said to
occur in Bedfordshire. It is named from occur-
rence at Kelloway Bridge in Wiltshire. This dis-
tribution may be connected with proximity to the
Mendip ridge in the latter case, and connected
with the Pennine chain in the former. The con-
ditions which produced the Stonefield slate prob-
ably produced the Wiltshire Kelloway rock ; and
the conditions of the sand beds in the Yorkshire
Lower Oolites are approximated to by the York-
shire Kelloway rock. This deposit is more im-
portant in France.
The Oxford day is manifestly the consequence
of a depression which prevented the coarse sandy
sediment from reaching so far out from its source
as in the previous age. This clay, which is 170
feet thick in Yorkshire, and 600 feet thick in
Dorset, is therefore superimposed upon the
13 6 THE STORY OF THE EARTH.
Kelloway rock. Near its base, about Peter-
borough, the Oxford clay abounds in remains of
timber trees, apparantly coniferous. Its plant
remains also include Cycads. It yields the ter-
restrial reptiles Cetiosaurus and Omosaurus, with
Teleosaurian crocodiles, Ophthalmosaurus, which
is an Ichthyosaur with three bones in the fore-
arm instead of two. The big headed Pliosaurus
is common ; Muraenosaurus is a long-necked plio-
siosaurian with single headed ribs to the neck,
.and two bones in the forearm. The common
shells in the Oxford clay are the oyster Gryphcea
dilatata, Belemnites hastatus, Ammonites Duncani
and Ammonites cordatus. The Ampthill Clay and
Oxford Oolite rest upon the Oxford clay. The
Ampthill clay is seen between Ampthill in Bed-
fordshire and Acklam Wold in Yorkshire.
The Coralline Oolite interlaces with the clay
in Bedfordshire by a number of thin beds of blue
FIG. 23. Belemnites Oweni, an internal shell of a kind of cuttle-
fish. The " Guard " is broken to show the conical phragma-
cone which penetrates into it. Oxford Clay.
earthy limestone. Traced southward by Shot-
over, it forms two divisions ; and at Weymouth
there is the sandy lower calcareous grit well de-
fined, and an upper grit or sand which passes up
to the Kimeridge clay. In Yorkshire this Oolite
extends through the Howardian Hills by Malton,
through the Vale of Pickering to Filey. At Up-
ware on the river Cam, a small reef full of corals
appears to result from the Carboniferous lime-
stone having furnished calcareous matter to the
THE OOLITES. 137
neighbouring sea. The reptiles of this age, Omo-
saurus and Pliosaurus, are like those of the Oxford
clay, but a great Megalosaurian, named Strepto-
spondylus, has also been found at Weymouth and
Malton in Yorkshire.
The Kimeridge Clay. The reef of limestone at
Upware appears to be a dividing point for the
Kimeridge clay, which comes next in vertical suc-
cession. In Cambridgeshire it is about 40 feet
thick, but thickens south-west to Dorsetshire to-
more than 600 feet thick, and its northern thick-
ening to Yorkshire is almost as great. This clay
contains inflammable beds known as Kimeridge
coal, which divide into thin sheets like paper, and
are full of marine fossils. In Dorsetshire the clay
is used as fuel, and has been used in making
paraffin candles, and to produce gas for illumina-
FIG. 24. Section showing the succession of strata east of Oxford.
tion of the neighbouring villages. These clays
are full of beds of concretions of earthy lime-
stone, named septaria, which are each 2 or 3 feet
in diameter.
The oldest known representative of the Iguan-
odon is found in this clay at Cumnor. And be-
tween Ely in Cambridgeshire and Swindon many
fossil reptiles are found, such as Teleosaurian
crocodiles, peculiar turtles and Ichthyosaurs.
Colymbosaurus is a long necked Plesiosaur with
single heads to the neck ribs, distinguished by the
massiveness of its arm bones, and by having three
138 THE STORY OF THE EARTH.
bones in the forearm instead of two. Omosaurus
is a large land saurian found at Swindon. The
common shells of the clay include Ostrea delto dea,
Exogyra virgula, Lingula ovalis and Ammonites
biplex.
The Solenhofen slate of Bavaria makes known
numerous insects and other forms of terrestrial
life of this period, including the oldest known bird.
The Oldest Known Bird.
A bird is known by its feathers ; though there
is no reason why the covering to the skin should
not be as variable in this group of animals as
among reptiles or mammals. It is therefore re-
markable that the oldest known bird named
Archceopteryx has feathers as well developed as in
the existing representatives of the class and simi-
larly arranged. It is found in the lithographic
slate of Solenhofen in Bavaria, which is of about
the age of the Kimeridge clay, in the Upper part
of the Oolites. The animal is an elegant slender
bird which is chiefly remarkable for showing teeth
in the jaws. About twelve, short and conical, oc-
cur on each side in the upper jaw. The skull is
about two inches long, shaped like the skull in
many existing birds, with a circle of sclerotic bones
defending the eye.
The neck and back are each about 2f inches
long, and there is a slender rat-like tail, of more
than twenty elongated vertebrse, which is 6 inches
long. The fore limbs are as well developed as the
hind limbs. But they differ from existing birds in
the bones of the metacarpus not being blended
together, and in the three digits terminating in
sharp claws. The number of the phalanges in the
THE OOLITES. 139
three fingers is 2, 3, 4. They are thus similar to
the digits of the hind limb, and are apparently
_,
FIG. 25. Skeleton of the oldest-known bird, Archaoi>teryx macru-
ra, showing impressions of the feathers on the wings, legs, and
tail. From the lithographic stone of Solenhofen (after Dames).
capable of being applied to the ground like the
fore limbs of a quadruped, although the great
development of the feathers attached to the
arm bones demonstrates that the wings were
140 THE STORY OF THE EARTH.
constructed on the same plan as in existing
birds.
The femur or thigh bone is about two inches
long ; the drum stick is more than two inches and
a half. And the slender metatarsus is about an
inch and a quarter long. The three points of dif-
FIG. 26. Skull of the oldest-known bird with teeth. Archae-
opteryx raacrura (after W. Dames). A. orbit of the eye. B.
pre-orbital vacuity. C. nostril. Scl. circle of bony plates
round the eye. h. tongue bones, mi. lower jaw. m and im.
jaw bones. /. tear-bone, n. nose-bone. (After Dames.)
ference from existing birds are, the elongated tail
bearing feathers on each vertebra, the teeth, and
the claws on the three digits of the hand.
Close of the Oolitic period.
A great change in life took place between the
Kimeridge clay and the Portland Oolite which
rests upon it. And although the granular Oolitic
THE OOLITES. 14!
texture, which the Portland limestone shows in
the south of England, has caused it to be asso-
ciated with the older Coralline Oolite, and Lower
Oolites, it yet marks the beginning of a great up-
rising of the sea-bed, which extended eastward
from the Mendip Hills during the succeeding
periods of time. Many of its fossils may justify
its position in the Oolitic series, but the physical
conditions of upheaval, and representation by
limestone and sand, appear also to link it with the
great terrestrial epoch of Purbeck and Wealden
beds, which form a portion of the Neocomian
period of time.
The Portland strata are almost limited in a
recognisable form to the south of England,
though the horizon is defined by fossils in the
clay beds at the top of the Kimeridge clay in
Filey Bay. A thin sandy layer with characteristic
Portland fossils caps the Kimeridge clay through
Lincolnshire, Norfolk, and Cambridgeshire. It is
not always possible to draw a line between this
feeble representative of the Portland sand and
the overlying sand termed Neocomian, so that the
Portland sand appears like the beginning of the
shore conditions, which lasted in the area of South
Britain till the close of the Lower Greensand.
On the Yorkshire coast there is no break
whatever in mineral character from the Kimer-
idge clay to the Hunstanton Red Limestone at
the base of the chalk.
Among the fossils of the Portland beds several
species of Perna, Astarte, etc., are found which re-
semble fossils of the Kimeridge clay, but there
are also species of Cyprtna, Pecten, Cerithiutn, etc.,
which resemble Neocomian forms. Lucina Port-
landica is one of the characteristic bivalve fossils.
142 THE STORY OF THE EARTH.
CHAPTER XVII.
NEOCOMIAN.
THE Neocomian period of geological time is
completely represented in Great Britain in the
Speeton clay, which is about 300 feet thick, and
seen to the north of Flamborough Head. The
basement bed of this deposit is the Coprolite
bed which divides it from the Kimeridge clay
on which the Speeton clay rests. That bed is a
layer of nodules of phosphate of lime, which ap-
parently were formed about fossils, like similar
beds of phosphate of lime in newer deposits in
Bedfordshire and Suffolk. This layer of phos-
phates marks a change in the life; so that the
shells which characterise the Kimeridge clay be-
low do not pass above it. It was formerly sup-
posed to occur at the top of the Portland beds,
but the Ammonites regarded as Portlandian oc-
cur above this junction bed.
There is therefore some ground for regarding
the Speeton clay above the Coprolite bed as
representing in unbroken marine sequence the
geological ages which in the south of England
are partly lacustrine, partly terrestrial, and partly
marine, and known as the Portland beds, the Pur-
beck, and the Wealden beds, and the Lower Green-
sand.
The lowest division of the Speeton clay is
known as the zone of Belemnites lateralis. The
Lucina Portlandica is found in the Coprolite bed,
and a variety of the Exogyra sinuata appears some-
what higher up. The next division is the zone of
Belemnites jaculum, which ranges through about
NEOCOMIAN. 143
120 feet of clay in which there is a large number
of characteristic Ammonites, with species of Tere-
bratula and Rhynchonella. The third zone is that
of the Belemnites semi-canaliculatus. In this zone
in the Ammonites Deshayesii found in the Lower
Greensand of the south of England. The upper-
most zone of the Speeton clay is that of Belemnites
minimus. This fossil which in the south of Eng-
land abounds in the Gault, here occurs in asso-
ciation with Inoceramus concentricus, Inoceramus
sulcatus and Nucula pectinata, which are also com-
mon gault species. The clays, which are mostly
dark blue, and blue black, become red at the top,
so that there appears to be a transition from the
red clay to the argillaceous red limestone, known
as the Hunstanton Limestone, or red chalk of
early writers.
The top beds of the Speeton clay may there-
fore be newer than the Neocomian of which the
upper limit is the Lower Greensand of the south
of England. The other beds give a threefold
division. So that the Portland and Purbeck lime-
stones of Swindon correspond to the Belemnites
lateralis beds, which are represented by the Up-
per Volga beds of Russia. The middle beds,
apparently, would correspond to the Wealden
period of the south of England, Belgium, and
Hanover, while the zone of Belemnites semi-cana-
liculatus corresponds to the Lower Greensand.
While these beds were being laid down in a
region which underwent but little change of level,
so that an uninterrupted deposit of clay was ac-
cumulated, the land was upheaved, further south,
into those shallow water conditions, ot wmch tne
Portland beds are evidence, which pass without
an appreciable break into the lacustrine and ter-
144 THE STORY OF THE EARTH.
restrial Puibeck series. There is nothing to show
that the terrestrial surface was more or less than
an enlargement of the land which in previous ages
of secondary time had supplied the insects, mam-
mals, plants and terrestrial reptiles which are
found in various beds of the Upper and Lower
Oolites, and which, by its varying elevation,
had effected the distribution and nature of the
sediments, all through the lower secondary pe-
riod.
The limestone beds appear to have owed their
existence largely to the influence of the Carbon-
iferous limestone, for many evidences are found
that it was repeatedly denuded, while the sand-
stones and clays were supplied partly by sedi-
ments derived from denudations of older slatey
and schistose rocks. The existence of the Pur-
beck beds, which in Dorsetshire are alternations
of thin-bedded white limestone, with bands of
dark-coloured clay, shows that the streams of
fresh water coming from off the land into the
lake, charged the fresh water with carbonate of
lime, just as they had previously charged the
sea; while the uplifting of the earth's surface
above the sea-level was so gradual that there is
no break between the marine and fresh water
beds. Near the base of the Purbeck beds in
Dorsetshire an old land surface is found, known
to the quarrymen as the Dirt Bed. It is well
seen in the cliffs of Lulworth Cove in the Isle of
Purbeck, and in the Isle of Portland. Here co-
niferous trees, sometimes a foot or two in diame-
ter, lie prostrate, but the roots and lower parts
of the trunk remain erect as they grew. Some
of the coniferous trees show nearly 200 rings of
annual growth and a length of sixty feet. Among
NEOCOMIAN. 145
them are the short stems of Cycads, which resem-
ble the living Cycas revoluta.
The Lower Purbeck also contains a multitude
of insect remains, on several different horizons.
They are chiefly in cream-coloured marl, and
include the wing cases and bodies of beetles,
dragon-flies, and other insects.
A terrestrial surface at the base of the Middle
Purbeck is evidenced by many jaws, and a few
other remains of small mammals. They appear
to be little insectivorous marsupials, such as
Truonodon, Spalacotherium, and the type like the
kangaroo-rat, which is named Plagiaulax.
The Middle Purbeck includes some marine
layers with cockle shells, oysters and pectens,
with occasional ripple-marked sandstone. The
marine beds alternate with the fresh-water beds,
in which the common shells which live in exist-
ing ponds, Paludina y Planorbis, Physa, etc., appear
for the first time.
The Upper Purbeck beds are interesting, first,
for yielding the grey, Paludina marble, anciently
used for decorative carving and monuments in
the interior of churches; and, secondly, for the
number of its fresh-water tortoises, named Pleuro-
sternon, which differ from their living allies in
having an extra pair of bones, stretching over
the middle of the breast-plate, known as the
plastron.
In Swanage Bay the overlying Wealden beds
differ from the Purbeck beds in being sands and
clays. In the boring near Battle in Sussex, the
Purbeck beds, formerly known as the Ashburn-
ham beds, contain some important layers of gyp-
sum, but no other calcareous deposits ; and are
like the Wealden beds in mineral character.
146 - THE STORY OF THE EARTH.
The Wealden strata exhibit two types. In
Dorsetshire and in the Isle of Wight they com-
prise alternations of numerous beds of grit, sand
and clay, frequently of the most brilliant red
colour. A few marine shells, species of Pecten,
occur in the lower Wealden beds of the Isle of
Purbeck. In the Isle of Wight they have yielded
multitudes of vegetable remains, among which
are pine cones, and especially the fossil forest of
Brook, where, however, the great forest trees ap-
pear to be drifted and water-logged. In these
beds have been found the remains of many
extraordinary terrestrial reptiles. The Ornitho-
cheirus type of Pterodactyl appears, which has the
earlier joints of the backbone blended together,
as in the frigate bird. There is a terrestrial
saurian named Polacanthus, which had the lower
part of the body covered with a complete shield
like that of an armadillo. Associated with it is
the Belgian Iguanodon, the great Cetiosaurian
named Ornithopsis, and the genera named Hypsile-
phodon, Sphenospondylus, Vectisaurus, etc.
Further to the north, in the typical Wealden
country of Kent, Surrey, and Sussex, these beds,
instead of being multitudinous and irregular, be-
come separated into great divisions of tolerably
uniform mineral character. The Ashdown Sand
is in the main a hard yellow sandstone. The
Wadhurst Clay above it is a number of alterna-
tions of shale and hardened sand frequently
ferruginous, with plant remains. The Tunbridge
Wells Sand is about 150 feet of sandstone more
or less divided by thin beds of clay, which may
thicken locally. Above these beds, which are
named Hastings Sand, comes the Weald Clay,
which is 900 feet thick in the south-east of Kent,
NEOCOMIAN. 147
and 400 feet thick in the west of Surrey. It is
full of bands of fresh-water limestone, formed of
fresh-water shells, especially Paludina.
In various localities in Sussex, particularly
near Hastings, the footprints of Iguanodon have
been found, and both there and at Cuckfield a
multitude of bones occur. They include small
species of Plesiosaur of the genus Cimoliosaurus
and an Ichthyosaur possibly estuarine, together
with a group of terrestrial saurians, entirely dif-
ferent from those of the Isle of Wight. These
remains include Pelorosaurus, the Iguanodon Man-
telli, Suchosaurtis and Megalosaurus, as well as
fresh-water tortoises. Many plants are met with
on this horizon, including some ferns, like Sphe-
nopteris, with the fronds well preserved ; and nu-
merous Cycads. Fresh-water shells include the
existing Unto. The terrestrial fauna is very im-
perfectly known in comparison with that buried
in the deep valleys near Mons in Belgium, from
which entire skeletons of Iguanodon and other
reptiles have been obtained. Along the northern
outcrop of the Neocomian strata, by Farringdon,,
Potton and Upware, numerous remains have oc-
curred of Iguanodon, Megalosaurus, and other
terrestrial saurians like those of the Weald, and
with them are remains of Cycads, Pandanus and
Pines. On this outcrop the Neocomian Sand
rests successively on the Kimeridge Clay, Ampthill
Clay, and Oxford Clay as at Sandy and Woburn
in Bedfordshire, showing that an unconformity
separates the Neocomian strata from the Oolites
in the middle of England.
The Lower Greensand is a marine bed which
extends over the fresh-water series of the Weald.
But beyond the Wealden area the sands are
148 THE STORY OF THE EARTH.
termed Neocomian ; because, although they ex-
hibit a threefold division, it is difficult always to
prove that these parts correspond to the Portland
and Purbeck, Weald, and Lower Greensand re-
spectively. In the Isle of Wight, the Lower
Greensand consists of a large number of alter-
nating beds of sand and clay, more than 900 feet
thick. More than eighty distinct layers have
been grouped into sixteen beds. So that the
conditions of deposition of the Weald seem to
have continued through the succeeding epoch of
time ; and occasionally the remains of an Jguan-
odon became floated into the Lower Greensand
from land diminished by depression of its level.
There is the same correspondence of the Lower
Greensand to the Wealden beds in stratigraphical
succession in the typical Wealden area of Sussex.
The Lower Greensand is divided, in the section
W. ^~" E.
FIG. 27. Section from Folkestone to Hythe, showing above the
fresh-water Wea'.d Clay, the divisions of the marine Lower
Greensand, named Atherfield beds, Hythe beds, Sandgate
beds, Folkestone beds.
between Hythe and Folkestone, into the Ather-
field Clay at the base, which is sometimes a ma-
rine clay resting on the Weald Clay, and some-
times loose sharp sand. Secondly, the Hythe
beds (or Kentish rag) are alternations of thin
bedded limestone and sand with beds of chert.
Thirdly, the Sandgate beds are sandy clays not
very coherent, often green, like the underlying
LOWER CRETACEOUS STRATA. 149
beds. And fourthly, the Folkestone beds are
usually yellowish, unconsolidated, and appear to
correspond to the ferruginous sands of Shanklin
in the Isle of Wight. Fuller's earth occurs at
many horizons in the Sandgate beds. The Hythe
beds occasionally contain beds of chert, derived
from the growth and breaking up of. siliceous
sponges. Near Maidstone it has yielded boulders
of granite, which may have been the anchor stones
of marine plants like Fucus. Remains of terres-
trial plants and of Iguanodon indicate near prox-
imity of the Maidstone area to land, which is
paralleled in the Isle of Wight.
CHAPTER XVIII.
LOWER CRETACEOUS STRATA.
EVER since the Carboniferous period the influ-
ence of a dividing line extending east to west, due
to elevation of the rocks between Worcestershire
and Lincolnshire, has been more or less persistent.
It has influenced the mineral character of strata
and distribution of life. It has given a distinct
character to the Oolitic rocks south of Banbury,
to that shown by the succession of rocks further
north. The same geographical conditions separate
the Neocomian rocks north and south of the land
barrier indicated on the south by the Purbeck and
Wealden rocks. A like physical difference is seen
in some of the Cretaceous rocks.
In so far as can be judged by fossils, the change
from Speeton clay to Hunstanton limestone took
place in the middle of the Gault ; since the fossils
150 THE STORY OF THE EARTH.
in the bottom beds of the red limestone include
the same Gault species as are found in the top
beds of the underlying clay.
A similar transition in physical character is
seen in Norfolk from the brown sands, locally
termed Carstone at Hunstanton, to the sandy
Hunstantpn limestone which there rests upon it.
This succession has sometimes led to the belief
that the upper part of those sands is of the age of
the Lower Gault.
But while there is an apparent conformity of
the Cretaceous to the Neocomian beds on the east
coast of England, at Speeton there was a manifest
change in the tilt of the land further west, which
caused the sea at that time to extend over the
edges of the
older Secon-
dary strata.
This is seen in
land in the
district which
is now East
Yorkshire by
the deposit of
the Hunstan-
ton limestone
which covers
ear the edges of
the base of the Lower Greensand, Ather- ,v >\ i-.-
geld. the Oolitic
rocks. There
appears to have been a similar depression of land
at the same time to the west, in Dorsetshire and
Devonshire, which resulted in the deposition of
sands, known as the Blackdown Greensand, over
the whole of the Lower Secondary rocks, and
partly upon the Carboniferous rocks about Exeter,
FIG. 28. Ammonite
LOWER CRETACEOUS STRATA. 151
at the time when these cretaceous beds began to
be formed. There are thus sands in the west in
Dorset and Devon, which appear to represent a
part, if not the whole, of the Gault; perhaps the
Upper Gault, and the Upper Greensand. There
is a Red Limestone in the north-east from Norfolk
to north of Flamborough, which is a similarly un-
divided deposit. Placed geographically between
these sands in the south-west and limestone in the
north-east, are the strata known as Gault and
Upper Greensand.
The Gault rests on Lower Greensand and Neo-
comian Sands. It is a blue micaceous clay, dark
in colour in the lower part, where it is rich in fos-
sils, and full of layers of concretions of phosphate
of lime, which contains a large amount of iron
pyrites in some localities. Its thickness in the
south of England is about 150 feet, but it thickens
to more than 200 feet at Hitchin ; and one boring
at Soham is said to have passed through 450 feet
E. W.
FIG. 29. Cliff section, Hunstanton, Norfolk. Upon the brown
Neocomian Sandstone is the red Hunstanton Limestone, four
feet thick. The Lower Chalk rises from the beach to the top
of the cliff, the dip being east.
without piercing it. Yet it thins away in the south
of Norfolk, and there develops calcareous beds in
THE STORY OF THE EARTH.
its upper part, which probably show that the Hun-
stanton limestone, which first begins to be recog-
nised near Sandringham, includes the Upper Gault.
The Gault extends as a clay all round the Weald,
and through the Isle of Wight ; so that its distri-
bution is connected with the area occupied by the
Wealden beds ; and the changes of level by which
.that district was effected.
The Upper Greensand generally follows the dis-
tribution of the Gault ; but there are certain areas
from which it is absent as a recognisable sand. It
is well developed in the Isle of Wight, and extends
from Eastbourne through the South Downs and
through the greater part of the North Downs; but
there is no deposit of a sandy nature in the Maid-
stone country, found
between the Gault and
the chalk, which pass
insensibly into each
other. From Wiltshire
the Upper Greensand
extends to Tring, as a
green sand, which is
there about 30 feet
thick; east of Tring
its sandy character is
lost. It has been found
by a well boring again
to put on the character
of a green sand under
Norwich. All the intervening country, which
Professor Hull regards as having been land, dur-
ing the deposition of the Carboniferous limestone,
is covered with a thin bed known as the Cambridge
Greensand, which is not more than a foot or two in
thickness, and consists of nodules of phosphate of
FlG. 30. Ammonites planulatus,
Cambridge Greensand.
LOWER CRETACEOUS STRATA. 153
lime embedded in a paste of green grains of glau-
conite and marl, which entombs the most remark-
able assemblage of fossils yielded by any forma-
tion in Britain.
When this bed is traced north it is lost ; and in
so far as can be judged from physical evidence,
and its fossils, it has merged in the Hunstanton
I limestone, which divides into three thin beds. The
middle layer of that rock is largely formed of
concretions of phosphate of lime. At the base of
the chalk wolds the limestone augments from 4
feet at Hunstanton to a considerable thickness at
Speeton, where its upper beds become very irreg
ular, and pass in
to the white
chalk without
strati graphical
planes of sepa-
ration. The ir-
regular diffusion
of the red Col- FIG. 31. Part of the stem of an Encrinite
ni- in nortc n( (screw-stone ), derived from the Car-
OUr in parts Of boniferous limestone found in the
the chalk would Cambridge Greensand.
appear to indi-.
cate that the colour has an organic origin.
The succession of the Upper Greensand upon
the Gault is manifestly a consequence of upheaval
of the old land from which the Upper Greensand
was derived, bringing the source of the sediment
nearer; so that it became coarser. The Gault at
Ware rests directly upon the Wenlock limestone.
At Cheshunt it rests upon the purple Devonian
mudstones. Therefore this eastern country of
England gives no evidence of having been sub-
merged during all the Secondary ages till the
Gault sea spread over it, and Gault was laid upon.
154 THE STORY OF THE EARTH.
it. And since some fossils, like those of the Car-
boniferous limestone, obviously derived, have oc-
curred in the Neocomian beds of Upware, and in
the Cambridge Greensand (Fig. 31), it is probable
that the upheaval which brought about the forma-
tion of the Upper Greensand, raised the area of
ancient rocks beneath the Gault. It became too
shallow for the accumulation of anything but the
phosphatic products of marine animal and vege-
table life, boulders of the parent rocks, slates,
schists, quartzites, granites, of the neighbouring
land; and the multitudinous remains of Cimo-
liosaurus and Ichthyosaurs, and Chelonians ; to-
gether with true lizards, allied to the monitor;
and crocodiles of existing types. There are many
terrestrial saurians allied to the armoured Sceli-
dosaurus of the Lias, a score of Pterodactyls of
all sizes of the genus Ornithochirus. One Ptero-
dactyle, at least, is toothless. This type, which
has smooth jaws like the jaws of a bird, is named
Ornithostoma. The oldest known British bird is
found in this bed. It is allied to the divers.
Cretaceous Birds.
The oldest British fossil bird is found in the
Cambridge Upper Greensand. The bones indi-
cate an animal as large as the red-throated Diver.
Some bones are like the living genus Colymbus;
others show resemblances to Grebes and Cormo-
rants ; and possibly, in the hip girdle, to penguins.
The skull is singularly like that of the red-throated
Diver in size and form, and the joints of the back-
bone are similar, but not identical. The femur, the
thigh-bone, was more than i inch long; and the
drumstick bone of the leg develops a process like
LOWER CRETACEOUS STRATA. 155
a patella at the knee-joint, but it is much smaller
than in the Grebes. The bone may have been 4
inches long. The metatarsus differs from the
bone in all existing birds, because it shows no
sign of the tarsal bones being blended with it.
It was probably about 2^ inches long, so that
the animal may not have exceeded a height of 15
inches. It is unknown whether these birds pos-
sessed wings. The saddle-shaped mode of union
between the vertebrae of the neck is as well devel-
oped as in existing birds ; but it is either absent
in the back, or imperfectly developed, since joints
of the back-bone have the ends cup-shaped. There
is no evidence that the tail was short. It is cer-
tain that this bird was a water-bird, and it prob-
ably fed under the water, like the divers. It is
named Enaliornis. In the Greensand of New
Jersey birds have also been found which show
strong affinities with the living divers; and since
those birds possess teeth, it is not improbable that
teeth were also present in the jaws of the bird
from the Cambridge Greensand. The bi-concave
condition of the dorsal vertebrae of Enaliornis is
also found in one of the American genera.
The existence of these fossils goes to show
that the family of divers already existed in the
cretaceous seas ; and that their jaws were armed
with teeth, which are not found in any birds of
more recent date. Birds have also been found
in the Chalk of Seania in Sweden but the bones
are few.
156 THE STORY OF THE EARTH.
CHAPTER XIX
CHALK.
THE superposition of the chalk upon the
Upper Greensand, and the rocks which repre-
sent it, was the consequence of a rapid depres-
sion of old continental land from which the sedi-
ments had been denuded which built up the lower
cretaceous beds. Land did not entirely disappear
at once. There are a few places in Europe in
which the cretaceous flora is met with, such as
Aix-la-('hapelle. Halden in Westphalia, Quedlin-
burg and Blankenburg in the Harz, Molletin in
Moravia, and Niederschcena in Saxony. The
fossil plant-life found in these localities differs
a little, but includes similar types to those in
the cretaceous rocks of Greenland, and North
America. At Aix, the cretaceous basin consists
of hands and sandstones about 300 feet thick,
which rest upon the old primary rock which had
been a land surface. The sands have been re-
garded as of the age of the Upper Chalk, though
they contain some shells of the age of the Upper
Greensand.
The chalk abounds in scattered fragments of
ancient crystalline rocks in its lower part. la
some localities in the south-east of England its
lower beds contain enough clay to give it an
aluminous odour; while, in the west of England,
its lower beds frequently contain grains of quartz.
Proximity to land is indicated almost as definitely
by the preservation of branches of Sequoia, in the
lower chalk of Cambridgeshire, and all through
the chalk period large timber trees are found
CHALK. 157
which have sunk water-logged, more or less de-
stroyed by the borings of the ship worm Teredo.
The presence of the remains of animals, like th^
flying Ornithosaurs and the long-bodied lizard
Dolichosaurus, also indicate proximity to land.
The larger part of the chalk is supposed to have
been accumulated in moderate depth of water,
because the rock almost everywhere shows evi-
dence of slow changes of currents on the sea-bed.
The chalk is divided into four deposits, partly
on the evidence of its physical characters, and
partly from the nature of its fossils. The lower
part of the rock, often termed Chalk Marl, com-
prises the Grey Chalk of Dover, which is coloured
with clayey matter, and is known as the Chalk
Marl and Totternhoe Stone. The bottom beds
contain many univalve shells, and many survivors
of the remarkable series of Cephalopods, named
Scaphites (boat-shaped), Turrilites (spirally tur-
reted), Baculites (staff-like), etc., which are so
characteristic of the Gault and Upper Greensand.
The Lower Chalk, which succeeds the Chalk
Marl, terminates upward in the bed known as
the zone of Holaster sub-globosus. It is thin in
the eastern counties, but becomes thicker in
the south of England. It is covered by the
Melbourne rock, a bed formed of chalk boulders,
embedded in a paste of chalk, and resting upon
a plane of erosion as marked as that by which
the Cambridge Greensand rests on the Gault,
indicating a change of level, which uplifted the
underlying deposit.
The overlying beds are the Middle Chalk.
This part of the chalk lies between the Mel-
bourne Rock below, and a hard phosphatic bed
above, known as the Chalk Rock, which rings
158 THE STORY OF THE EARTH.
under the hammer. Between these limits the
Middle Chalk is about 350 feet thick in Bucking-
hamshire and Bedfordshire, and more than 200
feet thick in Cambridgeshire. It is thinner in
the North Downs. It contains some thin beds
of flint in the Upper part, which is known as the
zone of Holaster planus. The Middle Chalk is a
great lenticular deposit, which is frequently marly,
as though a quantity of clay had been deposited,
while the chalk was being built up, by the growth
of its characteristic organisms. This portion of
the chalk has been thought to derive its clay
from the old land, of which the Cambridge Green-
sand is evidence in the previous period of time,
the intermixed clay being the finer river mud
carried out into the ocean from a region of an-
cient and crystalline rocks removed to a greatef
distance in the depression of land. On this hori-
zon there are multitudes of cup-sponges with
siliceous skeletons, of the genus Ventriculites.
The Middle Chalk is chiefly conspicuous for
wanting most of the peculiar Cephalopods of the
Lower Chalk, and for wanting the sea-urchins and
starfishes of the Upper Chalk.
The Upper Chalk, which is only about 250
feet thick in the North Downs near Croydon, at-
tains its maximum thickness north and south. At
Norwich it is about 500 feet thick ; and in the
Isle of Wight its thickness may be 1000 feet. At
Lyme Regis its thickness appears to be reduced
to 50 feet. It is whiter and softer than the chalk
below. The flint which characterises it occurs
sometimes in horizontal tabular layers, in the
planes of bedding. Sometimes they are in con-
cretionary nodules, fantastically irregular in form,
which are not absolutely limited to the planes of
CHALK. I59
bedding; occasionally these concretions are con-
nected together by tabular flint. The flint nod-
ules have grown since
the upheaval of the
chalk, and they are, as
a rule, scantily devel-
oped on the opposite
side of a slight disloca-
tion wherever the chalk
has been strained and
fractured, as along the
valley of the Thames.
The vertical layers of
flint which have been
deposited in such fis-
SUreS have CUt Off the guinum, from the Upper Chalk.
water supply; so that
the flints are large on one side of such a barrier
and small on the opposite side.
When the chalk is examined under the micro-
scope about one-half of its bulk appears to
consist of microscopic organisms, of the group
foraminifera, some of which appeared in the old-
est rocks and survive at the present day. The
more important of these foraminifera comprise
the heavy shell, shaped something like a nautilus,
named Cristellaria, the broader shell more like an
Ammonite, named Planorbulina, the spiral shell
resembling a pond snail Bulimina, and the little
Globigerina formed of spheres, which succeed each
other in a depressed spire. The other half of the
chalk consists of a multitude of fragments, large-
ly formed of the prisms which compose shells of
moilusca, flakes of the shells of Terebratula and
Rhynchonella, and minute fragments of corals and
Bryozoa ; and when these organisms cannot be
160 THE STORY OF THE EARTH.
recognised, the material is amorphous and a
product of decomposition of organisms. This
may be evidence that a large part of the sub-
stance of the chalk not only
consists of the remains of
animals which preserve their
forms, but that the remain-
der of it passed through the
bodies of animals which have
left little other record of their
existence.
_ The fishes are the chief
FIG. 33. The base of Gal- li 11 ^ between the Chalk and
erites sub-rotundus, the Upper Greensand, a large
sS ng of the the ent ^ mb er of small sharks of
from the Upper Chalk, the two deposits being iden-
tical. There is the greatest
contrast between the beds in mineral character;
and in the principal types of fossils, because the
Upper Greensand gives a record of conditions of
the shore where sediment was accumulating ; and
the chalk gives evidence of conditions in the open
sea, almost beyond the limit to which sediment
was carried, thus demonstrating how great the
difference in fossils may be with a slight interval
in time. The conditions compared are such, in
the two deposits, as may be found on the one
hand on the south-west shores of Ireland at the
present day, and on the other hand on the ocean
floor 400 or 500 miles to the west in the Atlantic,
where an organic deposit is now accumulating
which closely resembles the chalk. But the sharks
on the Irish coast are not limited to the shore,
and leave their remains in the open ocean as well ;
exactly as happened in the ages of the Upper
Greensand and chalk. Just as sea-urchins occur
CHALK. l6l
scattered through the chalk, so they are found
living on the chalky floor of the Atlantic Ocean ;
and the modern representative is sometimes very
closely allied to the ancient fossil.
The chalk is no exception to the law that the
fossils change with every few feet of a deposit
from its base to the top. Thus there are nu-
merous genera of sea-eggs of the order termed
Echinoidea, some living and others extinct found
in the Lower Chalk such as Salenia, P seudodiadema
and Holaster. Ananchytes, Galerites, Micraster and
Cyphosoma characterise the Upper Chalk. This
succession of fossils in the several beds of chalk
is traced through the country.
There is no evidence in the chalk itself, at
least in England, of its deposition coming to an
end. Its newest beds at Norwich give no sign
of shallow water conditions. Its highest beds in
Holland, however, are the yellow granular lime-
stone of Maestricht, which indicates a nearer ap-
proach to a shore than the chalk of England. In
Denmark univalve shells, which from time to time
lived in the chalk sea on definite horizons, like
the Totternhoe Stone and the Chalk Rock, are
found in the newest chalk to include shells which
are not known otherwise till the tertiary period,
such as the genera Cyprcea Oliva and Mitra. They
indicate that the shore conditions of the chalk
sea are returning in its newest beds in conse-
quence of a general upheaval of the sea-bed into
land in the European region-
1 62 THE STORY OF THE EARTH.
CHAPTER XX.
LOWER TERTIARY.
THE tertiary rocks occupy the basins drained
by many of the rivers of Europe. And although
they sometimes occur far inland, and at con-
siderable elevations above the sea, as in the Alps,
Atlas, and many of the mountain chains of the
old world, they are necessarily among the most
recently elevated parts of the earth's surface.
Occasionally there is a possibility that one de-
posit extends continuously from the upper creta-
ceous to the lower Tertiary. The evidence of
this continuity in time is only found in North
America, in the " Laramie formation." in which
there are no marine fossils; but which in Texas,
California and British North America abounds in
plant remains, and yields some vertebrata which
favour that conclusion. It would therefore ap-
pear that in some parts of the earth there is no
break between the secondary and tertiary rocks
in time, any more than between the other rocks
which give records of geological time. The ter-
tiary beds, when followed in their succession from
the oldest to the most recent, show an increasing
number of the species of fossils to be still living,
while the number of genera which are extinct
becomes successively smaller. The geographical
distribution of the surviving life, however, is al-
ways different from that of the fossil life. There
is a succession of tertiary floras ; the older are
Oriental and Malayan and Australian in their
affinities ; succeeded by others which have a
greater analogy with the existing flora of the
LOWER TERTIARY. 163
western part of North America. There is a simi-
lar geographical relation of the fossil shells in
the lower Tertiary rocks. They are at first es-
sentially the shells of the south coast of Asia,
but afterwards include many forms which can
only be paralleled at the present day at our Antip-
odes, so that the life which is now found in many
distant regions, passed in successive ages over
the same area of the earth, and furnished fossils
to the rocks which were laid down upon succes-
sive portions of the sea-bed as it slowly moved
onward.
The oldest tertiary strata in Europe are those
of Mons in Belgium, where the chalk is bent down
into a trough, which received the waters of a shal-
low sea at an earlier period than the chalk of
Great Britain, so that it carries an older deposit of
tertiary age. In like manner the east of England
was depressed at an earlier period than the coun-
try in the meridian of Reading, so that the beds
in the eastern part of the Thames basin are the
oldest in the British tertiary series. The Mon-
tian fossil shells of Belgium include many which
are common to the deposits of the lower tertiary
period.
Thanet Sands.
The Thanet Sands are the oldest tertiary bed
in Great Britain. They are a wedge-shaped de-
posit of sand which occurs in the east of the
trough known as the London basin. It is 90 feet
thick at Canterbury and Herne Bay, and thins
westward, being absent to the west of a.linc from
Leatherhead to Hertford. It is a marine de-
posit, abounding in shells, most of which live on
into the London clay. There is a Pholadomya, a
164 THE STORY OF THE EARTH.
genus which survives in the West Indies, and the
Nautilus Sowerbii, a species met with in the Lon-
don clay, but most of the other fossils are of
such genera as occur upon the British shores at
Otdhavcn
Woo Uick Beds
E. W.
FIG. 34. Cliff section of the Lower Tertiary Strata ; east of Herne
Bay in Kent.
the present day. The commonest are species
of Cyprina which resemble the living Cypriana
Islandica. The sands are nowhere consolidated ;
usually of a yellow colour, almost free from any
mixture of pebbles, but sometimes yielding, in
the east of Kent, a few rounded flints which show
that the chalk had begun to be denuded, and con-
tributed some particles to the crystalline grains
of quartz which form the sand. Under the name
Landenien inferieur, the Thanet Sands are traced
into Belgium, being well seen about Brussels.
They are also traced into France by way of
Calais, but it is not certain that they extend into
the Paris basin. The land surface which occurs
at Gelinden, near Liege, makes known a large
flora similar in some respects to that of Aix, with
oaks like those of the mountain districts. of Asia,
with laurels, willow, ivy, and other familiar types
of vegetation.
Above these beds succeed the Woolwich and
Reading beds 25 feet in east Kent and 90 feet
under London. They are the upper Landenien
of Belgium and the north of France, sometimes
LOWER TERTIARY. 165
known as the zone of Ostrea bellovacina, and
Pectunculus terebratularis. Ascending the Thames
these beds are at first marine sands, differing but
little from the Thanet Sands. At Upnor, near
Rochester, they become estuarine, and consist
of layers of rounded pebbles and alternations of
clay, sands and shell beds. This condition con'
tinues up the Thames valley, and the marine
shells, which were scarcely distinguishable from
the shells of the Thanet Sands at Herne Bay,
give place to fresh-water shells under London.
At Loampit Hill re-
mains of terrestrial
plants and insects also
occur. At Reading
there is a flora of
matted leaves, referred
to species of fig and
laurel and allies of the
evergreen oak, in the
lower part of the sands.
These deposits, which
were formed in fresh
water, alternate with
beds containing ma-
rine shells which have
o 1^ .- r,-^ : +;rv,^ FIG. 35. Ostrea bellovacina, fro
a long range Uptime, the Thanet Sands. The shell h
Some Occurring in the grown on a branch of a tree.
Montian beds and sur-
viving to the London clay. It is therefore shown
by these Woolwich and Reading beds and their
fossils that the dome of the Wealden district, be-
tween the Thames and the English Channel, was
raised into land; and that the chalk which once
covered it furnished the flints which were rolled
into completely rounded pebbles before they were-
166 THE STORY OF THE EARTH.
swept down into these tertiary beds, which are
now exposed on the northern slope of the North
Downs.
With the oscillations in level a part of this
land area at least supported the vegetation which
furnished those beds of lignite which extend by
Woolwich and Bromley, and the forest trees, which
show by their leaves a marked resemblance to
those of Gelinden. This indicates that the an-
cient connection, by continuous land, between
the south-east of what is now England and Bel-
gium and Hanover, was maintained in the tertiary
period just as it had been in the older epoch of
the Weald.
In one locality, near Rheims in France, the
lower tertiary beds have yielded many remains
of mammals which fore-
shadow lemurs and ro-
dents. Among these oc-
curs the Neoplagiaulax
which seems like a sur-
vival of the P lagiaulax of
the Purbeck beds. This
is worth recalling on ac-
count of the resemblance
FIG. 3 6.-Cyprina Morrisi in , f . the tertiary plants of
Thanet Sand. this horizon with the cre-
taceous flora. The Lon-
don clay indicates depression which banished the
shores of the tertiary land to some distance.
There are oscillations in its level which varied
both the mineral character of the stratum and
the fossil life.
At the base there is usually a bed of small
rounded flint pebbles known as the basement
bed, with sharks' teeth. The clay gives evi-
LOWER TERTIARY. 167
dence at its base of terrestrial life, and near
proximity to land, in the presence of a few
mammals, some of which are allied to the exist-
ing tapirs. With these are found crocodiles of
the type now living, and fresh-water tortoises,
such as frequent estuaries at the present day.
The middle of the clay abounds in crabs and
lobsters. While the top bed, about 50 feet thick,
is rich in plants represented by the fruits of a
large flora. The upper beds, like the basement
beds, are sandy. At Bognor the sand at the base
is calcareous and concretionary, with many marine
fossil shells.
The London clay is 500 feet thick in Essex and
Sheppey. It thins to the west and south-west ; be-
ing 400 feet under London, 300 at Southampton,
200 at Alum Bay and 100 at Studland Bay on the
opposite coast. To the south-east it is thickened
with the sands in its lower part. Its fossil shells,
such as Cyprea, Murex, Conus, Pleurotoma, fusus,
are of types which abound in the seas to the south
of Asia. The plants which occur in its uppermost
part also have an Asiatic character. The conifers
are well represented by Cypresses, the Sequoia,
Pines, and the Yew Salisburia. The lilies include
the so-called American aloe, Agave. A species of
Smilax represents the Sarsaparilla tribe. Bananas
are known from the genus Musa. The ginger
order is represented by Amomum which yields
Cardamoms. Nipa, a screw pine common on the
banks of the Ganges and in the Malay peninsula,
is by far the most abundant fruit. It is associated
with many palms, among which the areca palm, the
nutmeg type, the fan palm of the south of Europe
Chamerops, and the great palm Sabal are conspicu-
ous. The oak, hazel, walnut, liquid amber, laurel,
1 68 THE STORY OF THE EARTH.
magnolia, ebony and spurge are present, as are
representatives of some medicinal plants like
SfrycknoSj which yields nux vomica, and of Cin-
chona, which yields quinine. There are represent-
atives of the tomato and melon. Apples are
represented by Cotoneaster, and associated with
almonds and plums. The cocoa is represented
by a species of Theobroma. There are several
limes and maples. Water-lilies are represented
by the Lotus, and the Victoria lily of tropical
America.
The London clay is well developed in Belgium
and in the north of France. It does not reach the
Paris basin in a recognisable form ; though it may
be represented by the lignites and sands of the
Soissonnais. But neither the lignites in France,
nor the Ypresien beds which represent the London
clay in Belgium, yield the abundance of fruits
which is met with in the Isle of Sheppey. Some
of the Belgian specimens of Nipa are much better
preserved than the macerated and compressed
fruits of Sheppey, as though they were deposited
without being so long in the water.
Above the London clay are the sands which
cap the hills at Harrow, Hampstead, Highgate,
High Beech, Haveringate and many places in
Essex, having formerly been spread continuously
all over the London clay, as they still are between
Egham and Aldershot. They form Ascot Heath
and Bagshot Heath, and are known as the Bagshot
Sands.
The lower part, termed Lower Bagshot Sands,
thickens in the Isle of Wight to about 800 feet,
and forms the brilliantly coloured vertical sands
of Alum Bay. They are laminated with films of
clay at Woking, where the thickness is about
LOWER TERTIARY. 169
ioo feet. Beds of pipeclay frequently occur;
and occasionally, as at Newbury, the pipeclay
contains fossil leaves like those at Bournemouth.
In the Isle of Wight the bands of pipeclay are
exceptionally pure, as though they had been de-
rived from white felspar, but never extend far.
They are usually only a few inches thick, though
occasionally thick beds are found. From them a
flora has been obtained, which, although known
only from the leaves of plants, indicates many of
the types at the top of the London clay which are
MEADOW HIUL
N. S.
PIG. 37. Cliff-section, Alum Bay, Isle of Wight, showing the rela-
tion between the vertical eocene beds of Alum Bay and the
more horizontal oligocene strata of Headon Hill.
known only from fruits; so that they may well be
regarded as a surviving part of the vegetation of
the London clay. Among these Alum Bay plants
are some of the Cypresses and Sequoia, Smilax and
the palm Sabal is identified in both. There is the
same arum named Aronium. The oak, walnut,
laurel, cinchona, ebony, magnolia, maple, the
soapworts Sapindlus and Cupania, the allspice
and Eucalyptus, the almond and plum, and the
170 THE STORY OF THE EARTH.
mimosas are common to both deposits. Besides
these, the Alum Bay beds make known many new
types, of which the London clay gives no evi-
dence. Among them are the beech, elm, fig, bread
fruit, willow, poplar, sandalwood, the Mezereon,
Aristolochia, olive, ash, convolvulus, verbena, bil-
berry, some heaths, the aralia, dogwood, white
water-lily, custard apple, holly, buckthorn, vine,
sumach and pistachio. These are among the more
important new plants introduced in the Bagshot
Sands ; and with them are a number of Proteaceae,
referred to genera now living in Australia, as well
as a representative of the type genus Proteoides,
the sugar bush of South Africa. One of the most
striking features in the flora is the small number
of palms, and the absence of the Nipa, which in
Sheppey is the predominant fruit and is present
in the newer beds at Bournemouth. The fruits
and leaves, like the shells in the associated strata,
indicate affinities with the life of far-off regions of
the earth. It is a generation since Unger, a Vien-
nese student of the fossil plant-life of the lower
tertiaries, impressed with the occurrence of nu-
merous genera in Austria, which live at the pres-
ent day in Australia, regarded the eocene flora as
indicating a migratory passage of the ancient
plants from Europe into the Australian region.
The plane of junction where the Bagshot Sands
come to an end, and the succeeding marine
Bracklesham beds begin is not easy to draw ; be-
cause the Bracklesham beds contain locally thick
layers of lignite, which have the aspect of a coal
seam, and indicate the persistence of terrestrial
conditions and some oscillations of that terres-
trial surface in level.
Low down in these beds is found the large
LOWER TERTIARY. 171
foraminiferous shell named Nummulites Icsvigatus.
It does not form a thick bed ; but probably marks
the geological horizon of the Nummulitic Lime-
stone, which is one of the most important lime-
stones in the old world, and extends from the
Alps and Carpathians into Thibet, and from Mo-
rocco, Algeria and Egypt through Cabul and the
Himalayas to China.
In Great Britain the Bracklesham beds in Sus-
sex and the Isle of Wight are alternations of
green sands and sandy clays, which are separated
from the overlying Barton clay by a conglomerate
formed of rounded flint pebbles. At Bournemouth
their character has changed. They are foxy-brown
esiuarine sands with beds of pipeclay, in which
occurs another flora, with many ferns, palms, cac-
tus, eucalyptus, figs, willows, beech, and nipa.
The cactus is an American type. Subsequently
the North American type of vegetation became
more abundant in Europe in the middle Tertiary
period, and better defined by many genera. The
Barton clay succeeds the Bracklesham beds. It is
a blue clay, about 300 feet thick, with an extraor-
dinary number of fossil shells, many of which are
similar in genera to those found in the London
clay and Bracklesham beds, though the clay is
characterised by the abundance of individuals of
the genera Chama, Crassatella, Fusus, and Valuta,
and by the presence of some peculiar genera like
Typhis, a univalve similar to Murex, except that
the spines are tubular. There is no such fauna
anywhere to be met with at the present day. It
is not unlike a blending of the existing Malayan
and New Zealand forms of marine life ; and
many of the shells, like the Crassatella, Typhis,
Chaina, Pecten, Pectunculus, are very similar to
172 THE STORY OF THE EARTH.
species now living in or about the New Zealand
seas.
The Bracklesham beds have generally been re-
garded as represented by the Calcaire grossier of
the Paris basin, while the Barton clay corresponds
to the grits with the Nummulites variolarius, and
some newer deposits, such as the Gres de Beau-
champ. These beds ate well represented in Bel-
gium. The Bracklesham beds have yielded some
interesting serpents of the genus Palceophis though
not so large as those of the London clay. In the
Barton clay occurs a marine mammal, of the genus
Zeuglodon shown by its back bone to be a true
whale, which has the teeth double-rooted and ser-
rated in a way that is seen in no other animal,
though resembling some seals.
The Barton period comes to an end with a
deposition of 200 feet of sand, in which fossils
are rare.
Theoretically, the Bracklesham and Barton
beds together are an immense expansion of the
middle 50 feet of the Bagshot sands at Aldershot,
which contain, in some of the clayey layers, im-
pressions of fossils which appear to be identical
with those found at Barton in Hampshire, and
Bracklesham in Sussex. On this hypothesis the
Bracklesham and Barton beds indicate in the
Hampshire area a depression of the old sea-bed,
into which peculiar faunas successively moved.
The upper Bagshot or Barton sands bring back
again the conditions of a shoal, or shore, due
to a general uprising of the land. The few
shells which have been found in them are Barton
species.
The sea-bed continued to be elevated until
it passed into a land surface, in the succeeding
MIDDLE TERTIARY. 173
period of time termed Oligocene, which is the only
part of the middle Tertiary represented in Great
Britain.
CHAPTER XXI.
, MIDDLE TERTIARY.
THE Middle Tertiary period, usually termed
Miocene, makes a more striking approximation in
its life to the animals and plants which exist at
the present day. In the European area it is a
record of terrestrial and lacustrine conditions,
alternating with the deposits of shallow seas.
In Great Britain only a portion of the earlier
part of the Miocene period is represented by de-
posits which now cover the northern part of the
Isle of Wight, much of the New Forest, and are
exposed in the cliffs at Hordwell, Tollands Bay,
at Bembridge and Hempstead. These strata are
grouped together as Oligocene.
Headon Beds.
The oldest oligocene beds, known as the
Headon series, are 130 feet thick at Headon Hill,
in the Isle of Wight, are in the main fresh-water
strata. They comprise first, about 70 feet of
brackish water marls, and fresh-water limestones,
superimposed upon the marine sands above the
Barton series. This proves that the shallow sea,
with the Upper Bagshot Sands for its floor, had
become converted into dry land, upon which
lakes were formed by fresh waters draining into
the bottom of the trough from a limestone region
such as the chalk or the oolites.
174 THE STORY OF THE EARTH.
The strata and their fossils show that the
level of the land fluctuated. The lakes became
sometimes occupied with brackish water, so that
marine life divides up the fresh-water deposits.
After the lower fresh-water beds were formed,
the land was submerged, so as to give rise to the
Middle Headon beds, which are essentially ma-
rine. There are great banks of oysters with nu-
merous marine shells, most of them similar to the
types which had previously been known in the
Barton clay. These marine beds became better
developed at Brockenhurst in the New Forest,
where some corals are found, together with the
vertebral column of Zeuglodon, a marine mammal
of the whale type, with teeth like seals, already
known from the Barton clay. These marine beds
are widely spread in Germany. After they were
deposited the land was raised once more, and the
Upper Headon beds formed, which reach a con-
siderable thickness. They are fresh-water de-
posits, consisting of marls frequently green, full
of the large Paludina lenta, the Cyrena obovata and
the extinct Potomomya plana^ which alternate with
thick limestones, commonly full of fresh-water
shells of the genera Planorbis and Limncea. These
limestones are almost entirely the product of the
growth and decay of the fresh-water plant Chara
which precipitates carbonate of lime upon its
tissues by absorbing carbonic acid gas from the
water charged with carbonate of lime. In these
limestones remains are found of terrestrial mam-
mals of the types present in the Gypseous beds
at Paris, although they are not so numerous as in
the Bembridge beds.
When the Headon beds are followed to the
coast of Hampshire, the limestones disappear,
MIDDLE TERTIARY.
leading to the conclusion that the upheaval of
the chalk, which now runs in a nearly vertical
position through the Isle of Wight, had already
begun to supply the calcareous matter, which the
streams brought into the lakes of the Headon
period.
The beds which rest upon the Upper Headon
strata are termed the Osborne or St. Helens series.
They are sandstones and marls, much thicker
than any of the sandstones and marls in the
Headon beds, and therefore in contrast to them.
Some of the sandstones become calcareous, and
pass into concretion-
ary limestones. The
shells are all of fresh-
water types. The
sandstones are some-
times ripple -marked,
probably by the wind.
The Osborne beds
are about 80 feet
thick, and divide the
Headon from the Bern-
bridge beds. The
Bembridge Limestones
thick, very like the
Headon limestones,
rather creamy in colour, full of the same types
of fresh-water shells, and containing many land
shells, especially examples of the genera Helix,
Bulimus, and Glandina. These land-shells have a
marked affinity with species now living in North
America, with which one or two may be identical.
The Bembridge limestone abounds in seed-vessels
of the plant Chara, which formed it. Remains
occur in it of several species of the extinct mam-
Headon limestone.
176 THE STORY OF THE EARTH.
mal Palaotherium which in some ways approxi-
mated in structure to existing tapirs.
Where this limestone caps Headon Hill it is
about 15 feet thick. The Bembridge marls rest
upon it successively in the section at Hempstead.
They are grouped into a number of sandy beds
and shaly clays, full of estuarine shells, among
which are the genera Melania and Melanopsis,
which alternate with beds containing Cyrena and
other bands in which the shells are of fresh water
species.
The top of the marls is the remarkable thin
deposit known as the Black Band which is usually
grouped with the overlying Hempstead series.
The Hempstead Beds.
Hempstead Hill lies to the east of Yarmouth
in the Isle of Wight, on the shore of the Solent.
It is formed of about 170 feet of fresh-water and
estuarine marls, capped by a marine stratum.
The marls have a general resemblance to the
Bembridge marls. The Black Band at the base
is about two feet of clay, coloured with vegetable
remains, among which Sequoia and water-lilies
have been recognised, together with the teeth of
Palczotherium and other mammals and remains of
tortoises and crocodiles. It is an old terrestrial
surface on which rest, first, the lower marls with
Melania muricata ; secondly, the middle marls
with Cerithium Sedgwicki; and thirdly, the upper
marls with Cerithium plicatum. At the top are the
Corbula beds which contain several marine shells
in addition to the estuarine forms, among them
Valuta Rathiera, Natica, Corbula, and a species
of oyster. The characteristic mammal of these
MIDDLE TERTIARY. 177
beds is the Hyopotamus. These are the newest
British deposits in the Isle of Wight of oligocene
age.
The lignites alternating with clays which fill
up the basin at Bovey Tr^cey in Devonshire are
probably of the same age. They form deposits
about 300 feet thick ; probably once thicker.
With the exception of a single beetle, the remains
found in them are about fifty species of plants.
The lignite itself is chiefly the flattened trunks of
the Sequoia Couttsice. About half the plants are
regarded as of peculiar species and the remain-
ing twenty-five occur in the Miocene of Germany
and Switzerland. Among these trees are species
of fig, oak, laurel, cinnamon, the sour gum tree
Nyssa, a palm, vine, and some ferns such as
Lastrea.
On the Continent the Miocene beds attain
singular importance. Not only from the part
they take in forming the basins drained by so
many rivers, and in the structure of the Alps, but
also on account of the remarkable mammalian
remains which they yield.
The Dinotherium, which appears to have been
a sort of Mastodon with tusks in its lower jaw,
is one of these. The three-toed horse, named
Hipparion, is even more interesting, while the
fossils obtained at Pikermi, near Athens, include
giraffes and many other animals which have long
passed away from Europe. Perhaps the most
extraordinary Miocene fauna is found fossil in
the Siwalik Hills in India, which lie between the
Jumna and the Ganges, and rise to a height of
2000 or 3000 feet. The species of Hippopotamus,
and allies of the giraffe and other African types
which are there found, testify that change of
178 THE STORY OF THE EARTH.
area in the distribution of genera on land in the
Tertiary period, continued as persistently as the
migrations of marine life in the Primary period.
CHAPTER XXII.
THE CRAG.
AFTER the great terrestrial epoch of the newer
Miocene period had passed away entirely unrepre-
sented by strata, in Great Britain, deposits, named
the Crag, are found, which fringe the coast in
Norfolk, Suffolk, and Essex, occur in a few places
in Kent ; and in Belgium.
The relative age of these beds was first deter-
mined by the method of counting the number of
existing species in each of the tertiary strata. On
that basis the tertiary epoch had been divided into
Eocene, or lower Tertiary, Miocene, or middle
Tertiary, and Pliocene, or upper Tertiary. Sub-
sequently the Lower Miocene was named Oligo-
cene. In the Pliocene the fossils include more
than 35 per cent, of living species.
In this great period the Crag finds a place.
The older beds, named Coralline Crag, have 84
per cent, of the shells still living; and in the
newer or Red Crag 92 per cent, of the shells still
exist.
The Coralline Crag rests unconformably upon
the London clay. Its lower part consists of yel-
low false bedded sands, which sometimes form a
building stone about 30 feet thick. This sand
appears to have been derived from denudation of
the Bagshot sands which once extended over the
THE CRAG. 179
whole area of the London clay. The shelly beds
include a number of kinds of life which are now
only represented in southern seas. As many as
two hundred species are said to be found living
in the Mediterranean, and a few are paralleled off
the coasts of Japan, Mexico and the West Indies.
But while about sixty-five of the species are
known only in southern seas, fourteen only in
northern seas, and seventeen have been met with
in no other deposit, there are as many as 185
Coralline Crag shells still found in the British
seas.
The rock is named Coralline Crag from the
large extent to which its upper beds consist of
the remains of Polyzoa which were formerly
termed corallines. Of those Polyzoa which are
still living, 26 out of 30 are met with in British
seas, but the majority of the fossils belong to the
two extinct types Ah'eolaria semioiata, and Fasicu-
laria aurantium with which are some species of
the genera Rttcpora Idmonea and Eschara. The
fishes of this crag include
the common cod, green
cod, power cod, the pol-
lack, whiting, and whiting
pout, with which have been
found the great teeth of
the shark Carcharoden, and
of Otodus.
At the base of the Cor-
alline Crag, in places where
the shark's teeth are found, Xf _ aa ^ ^
is a bed of nodules of the Coralline Crag,
phosphate of lime, in which
bones of the dolphin Choneziphius occur with teeth
of the whale Balanodon, associated with teeth of
l8o THE STORY OF THE EARTH.
deer, rhinoceros and Mastodon which were obvi-
ously derived from a land surface, and perhaps
from an older deposit. In this bed are multitudes
of fossils from the London clay, and a few croco-
diles and Plesiosaurs derived from the older Sec-
ondary rocks.
The characteristic shells of the Coralline Crag,
besides the comparatively rare species of Valuta,
Cassidaria, Pyrula and Lingula, include many spe-
cies of the genus Astarte. That genus which now
characterises northern regions, is here repre-
sented by multitudes of individuals. The Cypri-
ana islandica, Terebratula grandis, Cardita senilis,
Buecinum dalei are typical fossils.
The Red Crag.
After the Coralline Crag was formed in some
tranquil depth of water, the shores appear to have
been upheaved. And on the eroded surface about
20 feet of false bedded sands and comminuted
shells were laid down, as shore deposits, which
fringe the island-like masses of white or coralline
crag. This newer deposit, named Red Crag, indi-
cates three or four successive depositions. Each
of its beds was planed level by denudations, which
left thin layers of pebbles and nodules of phos-
phate of lime at the junctions.
It has been observed that the older Red Crag
at Walton on the Naze, has fossils more like the
species of the Coralline Crag than are found else-
where. At Butley a zone abounds in northern
species, and on this is a newer crag still. The
Red Crag along the river Deben contains a larger
number of terrestrial mammals than has been
found at the base of the Coralline Crag. The
THE CRAG. l8l
additional types comprise species of tapir, the
Siwalik Hycenarctos, hyaena, Hipparion^ besides
deer, bear, and among marine animals a Halithe-
FlG. 40. Fusus antiquus reversed variety, from the Red Crag.
Hum and a walrus with large tusks. The shells
are interesting from the dominance of a few
types, such as the reversed variety of the Fusus
antiquus , which is associated with the common
whelk, the European cowrie, the common purple
shells, and species of the genera JVassa, Emargi-
nula.) Pectuneulus, Mya y Lucina and Cardium. At
Norwich the Red Crag becomes estuarine. The
Forest Bed of the Norfolk coast may be a part of
its land surface. A patch of Crag is found north
of Penzance, at St. Erth, 98 feet above the
sea. A more interesting deposit on the summit
of the Chalk descends into pipes in the Chalk
at Lenham in Kent, indicating that denudation
has removed the Crag from the surface of the
country.
All through the crag the temperature on the
east coast was becoming colder. This is evinced
by the presence of stones in the newer crag which
appear to have been floated southward in ice;
and it may be indicated by the increasing number
of shells which at the present day characterise
1 82 THE STORY OF THE EARTH.
northern and arctic seas. Eventually the crag
land was covered with boulder clay, and the
whole country experienced glacial conditions.
The cold is attributed by some to change of
form in the earth's orbit, by which the winters
increased in length. Others attribute it to up-
heaval of land. Upheaval of Scandinavia and
the North Sea would displace the shells south-
ward, and lead to a condensation of vapour, from
which glaciers would result large enough to cross
the plain of the North Sea and reach Britain.
CHAPTER XXIII.
GLACIAL PERIOD AND GRAVELS.
So manifest a break in the succession occurs
with the superposition of the Glacial deposits
upon the Crag, that some geologists regard
them as beginning a fourth great division of
the strata which is named Quaternary or Post-
tertiary. Others place them in a division of the
Tertiary period, which is named Pleistocene.
The singular feature of the formation which
justifies a separate name is the wide spread of
the glacial conditions over the Earth. In many
countries where ice now is only a passing inci-
dent of Winter, clays are found, blue, purple, or
brown, full of fragments of rocks which are
mostly local, though many have travelled from
distant places. These boulders, which cause the
deposit to be named Boulder Clay, are often
smoothed and grooved or scratched on one side
GLACIAL PERIOD AND GRAVELS. 183
like stones which have travelled in the sides or
bed of a Glacier. The deposit is often indis-
tinguishable from the clay found in Alpine val-
leys, from which Glaciers have retired which once
covered the country. The high ground in every
land in which Boulder Clay is found supports this
inference with evidences of the work of ice.
The Mountains of Scotland, the Lake district
of England, and the Snowdon district in Wales
are smoothed and grooved by sheets of ice which
have passed away. Small joints in the old slates
have been widened and deepened in the valleys,
until rounded structures have been produced like
the backs of huddled sheep at rest. This condi-
tion known as Roches moutonnfas is sometimes
exposed by a retreating glacier in the Alps, and
is manifestly due to the work of frost and
glacier ice.
Above many a mountain valley, such as the
Pass of Llanberis, angular stones are perched in
positions where water could never have left
them. They are regarded as having been the
stones of moraines once carried on the surface
of a glacier, and left behind in their present
places when the ice melted beneath them. The
great blocks of crystalline rock above Neuchatel
are of the same substance as the Mont Blanc
chain, and could only have reached their present
position upon the limestone chain of the Jura by
crossing the central valley of Switzerland. On
such evidence Glacial conditions for a country
may be inferred even though boulder clay is not
seen.
In North America Sir J. W. Dawson has
described the evidences of the Canadian ice-age
as comprising, (i.) a Lower Boulder Clay, which
1 84 THE STORY OF THE EARTH.
rests upon a glaciated and grooved surface of
rock ; (ii.) The Lower and Upper Leda-clay with
marine shells and drift plants ; and (iii.) an
Upper Boulder Clay with the shell Saxicava, and
gravel. The Lower Boulder Clay forms the
basins of the great Canadian lakes. The boul-
ders are mostly of Laurentian gneiss. Their
striation is attributed to the grating of pebbles
included in shore-ice upon the rocky floor be-
neath, when moved by the tide.
In Britain the glacial deposits are spread
irregularly. They consist of Upper and Lower
Boulder Clays on the east coast, divided by
Middle Glacial Sands with marine shells.
The granite of Criffel in Kirkcudbrightshire
is found in the boulder clay over Lancashire and
North Wales. Boulders of Volcanic rocks from
Cumberland are scattered over Cheshire. Dis-
tinct streams of glacial drift extended down both
the east and west sides of Britain. The boulders
of Westmoreland Shap granite found over the
plain of York and between Whitby and Scar-
borough on the coast, prove that boulders were
also distributed eastward from local centres, not-
withstanding the Scandinavian source of many
rocks in the Boulder Clay on the Norfolk Coast
at Cromer. The Boulder Clay found near Lon-
don at Finchley, and at Hornchurch in Essex, is
full of travelled ice-grooved rocks, with fossils
from the secondary strata of Yorkshire and Lin-
colnshire. Glacier ice transported the rock mat-
ter, but probably shore-ice and icebergs were
partly concerned in depositing it, so as to fill up
the old valleys and leave the clay on the surface
of the country. The denudation since the glacial
period has been very great, and the glacial beds
GLACIAL PERIOD AND GRAVELS. 185
are cut through by modern valleys which are ex-
cavated in the underlying deposits.
In many parts of the east of England a series
of gravel beds occurs beneath the Boulder Clay,
and in these pre-glacial gravels, chipped flint im-
plements of the Palaeolithic type are said to be
found.
In the east of England the Boulder Clay which
caps hills is itself capped by coarse hill gravel
which has the aspect of being boulder clay from
which the clay has been washed out. The gravels
descend to lower and lower levels till they occupy
the broad shallow troughs through which exist-
ing rivers flow, from which we may infer that ele-
vation of the land has gradually contracted the
width of existing rivers. Chipped flint imple-
ments are found in both the high and low level
gravels, with remains of mammals, which are
mostly African in their affinities, and mostly ex-
tinct. They include species of Hippopotamus,
Rhinoceros, Elephas, Lion, Bear. Deer, Horse, and
Ox survive in Britain.
Evidences of severer frosts are found in the
broken rock fragments, and of periodic floods
due to melting of the snows. The leaves of the
dwarf birch and dwarf willow are preserved in
clay seams, with the land and river shells which
now exist.
As hunter or as husbandman the rude fore-
fathers of the British people left in rock shelters
and caves simple works of art which show that
people had gained a primitive civilization who
lived when the post-glacial gravels were formed,
and the influence of glacial conditions was still
felt.
The dominance of man over animal and plant
1 86 THE STORY OF THE EARTH.
may mark the beginning of a new geological pe-
riod; but there is no gap in time or change in life
to announce the human period, or to distinguish
it in kind from earlier epochs in the story of the
Earth,
INDEX.
A.
Age of earth, 9.
Alethopteris, 112.
Alps, 18.
Cave earth, 43-
Cephalopoda, 94.
Ceratites, 123.
Chalk, formation of, 48.
Chalk period, the, 156.
Ammonites, 62, 95, 123, 127, 128.
Clay, 42, 53, 54; colouring n
ia-
Andesites, 27, 28.
ter of, 43: inflammable,
4;
Annularia, 112.
Scrobicularia, 33.
Anodonta, 50, 97.
Cleavage, slaty, 30.
Anomodontia, 117.
Clymcnta, 94.
Anorthite in meteorites, 12.
Coal, 33, 98, 104.
Anthracite, 107.
Conformity of strata, 56, 75.
Araucarites, 109.
Conglomerates. 36.
Archtfopteryx, 138.
Coralline Crag, 178-
Archean rocks, 78.
Ash, volcanic, 26, 30, 85.
Coral reefs, 47.
Corals, 85, 87.
Asmanite, 12.
Asterophylites, 112.
Astronomy, relation to geology,
Cordaites, 109.
Crag, the, 178.
Cretaceous rocks, 149.
10.
Crinoidal limestone, 47, 48.
Augite in meteorites, 12.
Curctihides, 114.
Current-bedding in clay, 43;
in
sandstone, 39.
B.
Basalt, 11, 27; varieties of, 29;
Cyclas, 50.
Cystoidea, 69.
columnar structure in, 30.
Belemnites, 60, 127, 128, 142.
Birds, fossil, 138, 154-
D.
Dadoxylon, 109.
Bituminous coal, 107.
Blastoidea, 69.
Deserts, 31.
Devonian period, 92.
Boulders, 34.
Brachiopoda, 69, 83, 85, 101.
Branchiosaurus, 117.
Diabase, 29.
Dinotherium, 177.
Diorite, 27, 29.
Bronzite in meteorites, 13.
Dodo, the, 68.
Dolerite, 29.
Dust, volcanic, 26, 30, 85.
c:
Catamites, 112.
E.
Calcareous sandstone, 40.
Cambrian period, 67, 81.
Carboniferous period, 97-
Earthquakes, 14.
Enaliornis, 155-
187
1 83
THE STORY OF THE EARTH.
Encrinites, 87, TOO.
Enstatite m meteorites, xa.
Iron, in meteorites, xi ; in sand-
stone, 38, 40.
Eocene, or Lower Tertiary pe-
Iron pyrites in clay, 44.
riod, 162, 178.
Eophrynus Prestwichi, 1x3.
J.
Eoscorpius, 114.
Eozoon canadense, 79.
Etna, lavas of, 27, 29.
Jura mountains, 18.
Euphoberia, 113.
K.
urypterus, 88, 89,
F.
Kelvin, Lord, on geological
Felspar in sandstone, 38.
Kimerldge clay, 44.
Krakatoa, eruption of, a&,
Fishes, fossil, 88, 94, g<5, ice,
117, 125, 179.
Folding m rocks, 15, 18, 22.
**
Foraminifera of chalk, 159.
Fossils, v, 20, 59, 62.
Puller's Earth, 133.
Labradorite to meteorites, 19,
Labyrinthodonts, 114, 1x7, 120.
Laurentian period, 78.
Lava, formation of, 14.
G.
Lepidodendron, 104, xxo.
Lencite in basalt, 29.
Gabbro, 25, 28.
Lias period, 125.
Gasteropoda^ 102.
Life, distribution of, on the
Giant's Causeway, 30.
earth, 63.
Glacial period, 182.
Lignite, 33, 49.
Gneiss, 22, 23.
Limestone, 45, 52, 53; Archean,
Goniatites, 95, 106, 123.
Granite, formation, 14, 97 ; meta-
78 ; fresh-water, 49 ; occurrence
with schists, 21, 23.
morphism, 23 ; composition, 34.
Graphite, 78.
Graptolites, 69, 85.
Greensand, Lower, 41, 131.
Ltmncea, 50.
Linffula, 83.
Lister, Dr., 59.
Lithomantis, 114.
Greensand, Upper, 41, 150.
Grisons, 18.
1C,
Grits, 34, 37, 53.
Grypfuza, 126.
Mammals, earliest fossfl, 123,
H.
133, 145.
Man, glacial, 185.
Heat of the earth, 12.
Maps, geological, 59.
Meandrina, 47.
Hemiaspis, 88.
Herschel, Sir John, on fluidity
of the earth, 13.
Hipparion, 73.
Megalosauria, 122, 134, 147.
Melaphyre, 29.
Merostomata, 69.
Metals in volcanic rocks, 87.
Holloway, Rev. John, 60.
Metamorphism, 23.
Horse, fossil development of, 73.
Hunstanton Limestone, 60.
Meteorites, n.
Mica in sandstone, 38.
Huronian rocks, 79.
Hypsiprymus^ 133.
Microlestes, 123.
Millepedes, fossil, 113.
"Millet seed beds," 32.
L
Millstone grit, 37, 95, 102.
Ichthyosaurus, n$, taO,
Miocene period, 173, x?8.
Mitchell, Rev. John, 60.
Jnguanodon, 146, 147.
Insects, fossil, 114, 124, 133, 145.
Moa, the, 68.
Mountain forming rocks, 18,
INDEX.
I8 9
Mountain limestone, 100.
Q.
Mud, 42.
Myriapoda, 113.
ifyMu, 86.
Quartz in meteorites, it.
R.
N.
Rain-prints, 54.
Nautilus, 69.
Neocomian rocks, 142.
Ramsey, Sir Andrew, 75.
Reptiles, fossil, 117, 125.
Neoplagiaulax, 123, 166.
Neritina, 50.
Neuropteris, 112.
Niagara river, v, 10.
Nickel in meteorites, II.
Rhyolite, 27, 28.
Ripple marks, 41, 54.
Roches montonnees, 183.
Rocky Mountains, 18.
Rugosa, 69.
Nummulites, 62.
Ryncliosauria, 122.
O.
S.
Obsidian, 28.
Odontopteris, 112.
Old red sandstone, 92.
Oligocene period, 178.
Olivine in meteorites, 12.
Oolite period, 43, 130.
Ordovician period, 81.
Origin of earth, 9.
Sand, 37, 53.
Sand dunes, 31.
Sand grains, rounding of, 31.
Sandstones, 54; colouring of, 38.
40; occurrence with schists, u.
Scelidosaurus, 126.
Schists, 21.
Scorpions, fossil, 114.
Sea-eggs, 89.
p.
Selemte, 44.
Palceosaurus, 122.
Septaria, 44.
Sequoia, 18.
Palaotherium, 176.
Paludina, 50.
Serpentine, 30.
Shrinkage of earth's crust* 10.
Pareiasauria, nS, 120.
Peat, 32.
Sigillaria, 104, no.
Siliceous sandstone, 40.
Pebble beds, 34, 53.
Silurian period, 86.
Pennystone, 106.
Slate, 19.
Peridolite, 30.
Smeaton, 60, 61.
Permian period, 115.
Smith, William, 59, 61.
Phonolite, 29.
Sphenophyllum, 112.
Pipe clay, 42.
Sphenopteris, 112.
Plagiaulax, 123, :66.
Spherulites, 28.
Planorbis, 50.
Spiders, fossil, 113.
Plants, fossil, 69, 96, 108, 129,
Spongilla, 50.
144, 149, 167, 169, 177.
Plesiosauria, 125, 128.
Pleurosternon, 145.
Stigmaria, in.
Strachey, John, 60.
Strata, 53; classification of, 74.
Pliocene period, 178.
Stratification, contemporaneous
Plutonic rocks, 25, 26.
Polyzea, of Coralline Crag, 179-
Porites, 47.
51; laws of, 58.
Sun-cracks, 54.
Superposition of strata, 58.
Protocystites, 83.
Syenite, 25, 27.
Protospongia, 83.
Pterodactyl, 146.
T.
Pteropoda, 83, 84.
Pterygotus, 88, 96.
Temperature of the earth, 12.
Puddingstone, 36.
Pum-ce, 28.
Terrestrial rocks, 31.
Tertiary period, 160.
THE STORY OF THE EARTH.
Theriodontio, 118.
Time, geological, v, 10, 13.
Trachytes, 27.
Trias period, 120.
Tridymite, 12, 28.
Trilobites, 62, 69, 85, 90.
Troxites, 114.
U.
Unconformity of strata, 57, 74.
Unio, 50.
Variation in species, 71.
Vesuvius, lavas of, 27, 29.
Volcanic ash, 26, 30, 85.
Volcanic rocks, 26.
Volcanoes, 14; extinct, 16.
Water, agency of, in volcanic
action, 16, 26.
Wenlock limestone, 87.
Whitehurst, John, 61.
Wind as a geological agency, 31.
Xylobius, 113.
Zeuglodon, 174.
(11)
THE END.
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