THE-BO
MATURE- STUD

BR1MAND
HER

THE BOOK OF NATURE STUDY

THE BOOK OF

NATURE STUDY

EDITED BY

J. BRETLAND FARMER

M.A., D.Sc.(OxoN.), F.R.S.

PROFESSOR OF BOTANY, ROYAL COLLEGE OF SCIENCE, LONDON

ASSISTED BY

A STAFF OF SPECIALISTS

FULLY ILLUSTRATED

VOL. VI

LONDON:
THE CAXTON PUBLISHING COMPANY

CLUN HOUSE, SURREY STREET, W.C.

M

CONTENTS OF VOLUME VI

THE PHYSICAL ENVIRONMENT— METEOROLOGY, Etc.

PAGE

PRELIMINARY — FIRST OBSERVATIONS ON THE WEATHER . . i

CHAPTER I
WEATHER AND CLIMATE .... .8

CHAPTER II
PRECIPITATION ....... .18

CHAPTER III
THE RELATION BETWEEN PRECIPITATION AND VEGETATION . . 31

CHAPTER IV
SNOW AND ICE ......... 40

CHAPTER V
THE SKY — SUNSETS — CLOUDS — THUNDERSTORMS ... 51

CHAPTER VI

THE APPARENT MOVEMENTS OF THE SUN . , . .63

CHAPTER VII

DAY AND NIGHT — THE SEASONS . . . -75

CHAPTER VIII
THE MOON ....... -85

THE PHYSICAL ENVIRONMENT— GEOLOGY, Etc.

CHAPTER IX
INTRODUCTION ...... . . 92

357753

VI

DENUDATION

DEPOSITION

CLASTIC ROCKS .

IGNEOUS ROCKS .

MODELS AND MAPS

CONTOUR MAPS .

CONTENTS OF VOLUME VI

CHAPTER X

CHAPTER XI

CHAPTER XII
CHAPTER XIII
CHAPTER XIV

CHAPTER XV

GEOLOGICAL MAPS

HISTORY OF LANDSCAPE

CHAPTER XVI

CHAPTER XVII

CHAPTER XVIII

HISTORY FROM THE ROCKS

CHAPTER XIX

THE GEOLOGICAL RECORD

THE GROWTH OF BRITAIN

CHAPTER XX

CHAPTER XXI

LANDSCAPE, POPULATION, AND OCCUPATION

INDEX

AGE

107

"5

123

130

159
177
189
196

208

213

225

LIST OF PLATES— VOLUME VI

BLACK AND WHITE PLATES

PAGE

THE BLUMLISALP AND OESCHINENSEE, NEAR KANDERSTEG . . .22
TREES NEAR EDINBURGH, SHOWING EFFECT OF PREVAILING WESTERLY WIND 22

THE LAUTERBRUNNEN VALLEY . . . . . . 23

SAND-DUNES ON HOLY ISLAND, NORTHUMBERLAND . . . -23

TULAROSA DESERT, NEW MEXICO . . . . . -36

" BADLANDS " OF NEBRASKA . . . . . . -36

SNOW SCENE ......... 37

LOWER END OF THE UPPER GRINDELWALD GLACIER . . . .46

AN ANTARCTIC ICEBERG . . . . . -47

Ross's ICE BARRIER IN THE ANTARCTIC . . 47

THE MATTERHORN FROM THE HORNLI RIDGE. . 58

AN ICEBERG OFF NEWFOUNDLAND , . -58

CLOUD FORMS ....... -59

FROST ACTION ALONG JOINTS. ILKLEY. . . . .100

THE SCREES, WASTWATER . . . . . . .100

GLOBIGERINA OOZE, ATLANTIC . . . . . . 101

BAXENDALE GORGE, INGLETON . . . . . . 101

MARINE DENUDATION, NEAR SCARBOROUGH . . .102

SELECTIVE MARINE DENUDATION. LULWORTH COVE . . . .102

WORK OF STORMS. PAKEFIELD, LOWESTOFT . .103

WIND EROSION. BRIMHAM ROCKS . . . 103

DELTA IN LOCH LUBNAIG ... .no

SANDS AND GRAVELS. MIDDLETON ON THE WOLDS . . 110

BEDDED LIMESTONES. ISLE OF MAN . . . in

STRATIFIED ROCK . . . . . . in

viii LIST OF PLATES— VOLUME VI

RIPPLE MARKS AND FOOTPRINTS, TRIASSIC SANDSTONE

SAND GRAINS (MAGNIFIED) .......

BOULDER CLAY, NEAR RICHMOND, YORKSHIRE ....

GLACIATED BOULDER. WITHERNSEA ......

CRINOIDAL LIMESTONE, SILURIAN. DUDLEY .....

OLD RED SANDSTONE CONGLOMERATE. FORFAR ....

SILURIAN LIMESTONE, WITH BRACHIOPODS, CRINOIDS, AND A TRILOBITE.

DUDLEY . . . . . . . . . 117

RAISED BEACH. HOPE'S NOSE, TORQUAY . . . . . 117

ANTICLINE AND SYNCLINE, NEAR BOLTON ABBEY . . . .120

FOLDED ROCKS, STARE COVE, LULWORTH . . . . .120

SHAP GRANITE QUARRIES . . . . . . .121

INTRUSIVE ROCKS. CORNWALL. . . . . . .121

JOINTED SANDSTONE. BRIMHAM ROCKS . . . . .128

WIDENED JOINTS IN LIMESTONE. GRANGE-OVER-SANDS . . .129

MODEL OF PART OF SKYE . . . . . . .129

CAM LONG DOWN, A "NAB" OR OUTLIER OF THE COTSWOLDS . .168

ESCARPMENT OF OTATARI LIMESTONE, OAMARU, NEW ZEALAND . .168

RELIEF MAP OF THE WEALD . . . . . . .169

NANT FFRANCON. TOPOGRAPHY APPROACHING MATURITY . . .178

HARDRAW SCAR, NEAR HAWES. IMMATURE TOPOGRAPHY . . .178

Box HILL, SURREY. THE FLAT-TOPPED NORTH DOWNS . . . 179

ISSUE OF A LIMESTONE SPRING. CRUMMACK BECK HEAD . . . 179

A DRY LIMESTONE VALLEY. GORDALE BECK, YORKSHIRE . . .190

LANDSLIP, NEAR CROMER . . . . . .190

HEAD OF A TRILOBITE, SILURIAN . . . . . .191

A FOSSIL TREE, CARBONIFEROUS ... 191

FOSSIL SKELETON OF A PLESIOSAUR .... 202

AN AMMONITE, CRETACEOUS . . . . . -203

EOCENE GASTROPODS . . . . . . . . 203

CARBONIFEROUS LIMESTONE RESTING UNCONFORMABLY ON SILURIAN SLATES . 212

EASDALE TARN: A LAKE DAMMED BY A MORAINE , '. . .212

THE BOOK OF NATURE STUDY

THE PHYSICAL ENVIRONMENT

BY MARION I. NEWBIGIN, D.Sc.(LoncL), Editor of the "Scottish Geographical
Magazine," Lecturer in Zoology and Biology in the School of Medicine for
Women, Edin., etc.

Mais il y a a considerer dans la science la methode et les resultats. Les
resultats, vous en prendrez ce que vous pourrez. La methode, plus
precieuse encore que les resultats, puisqu'elle les a tous produits et qu'elle
en produira encore une infinite d'autres, la methode vous saurez 1'appro-
prier, et elle vous procurez les moyens de conduire surement votre esprit
dans toutes les recherches qu'il vous sera utile de iaire. — ANATOLE
FRANCE.

PRELIMINARY — FIRST OBSERVATIONS ON THE WEATHER

2 .*: •

/:••';•: :/:THE:'B<X)K OF NATURE STUDY

liminary observations may be very well rendered vivid to the
little ones by some simple artifice, as for instance by the display
on the schoolroom wall, day by day, of a human figure chosen to
represent the particular type of weather, such as those which
some journals show in their weather reports. When these obser-
vations have been continued for some little time, an attempt
should be made to analyse the sensations upon which the char-
acterisations have been based, with a view to bringing out the
fact that we have been dealing with four great sets of variables :—
(i) the amount of sunshine, which is again related to the clearness
of the sky ; (2) the temperature ; (3) the amount and nature of the
movement of the air, i.e. the wind ; and (4) the amount of moisture
in the air, or the humidity. By questions and examples it should
be brought out that all our many changes in weather, as observed
by the senses, are due to changes in one or other of these four
points, each of which demands further study.

First, as regards sunshine and temperature, bring out the fact
that on any given day it is always hotter in the sun than out of
it ; that our hottest days are those when the sun shines longest
(roughly speaking, that is) ; that it is colder at night when the sun
does not shine than in the day when it does, and so arrive at the
deduction that the sun is the great source of heat. What then
becomes of the sun on cloudy and foggy days ? The teacher
will be wise to devote much time to the answering of this question,
for the fact of the sun's presence in the sky on dull and cloudy
days, behind the clouds, is by no means clearly realised by children
and uninstructed people.

Some homely examples will help to make the matter clear.
The washhouse darkened on a summer's day by the clouds of
steam, the locomotive at the railway station darkening the sky
as it blows off steam, — such familiar facts as these should not be
neglected in trying to explain the meaning of cloud. If the
school be placed in a narrow valley, or near the seashore in a
district with considerable hills in its vicinity, the formation of
mist and cloud can often be beautifully illustrated on an autumn
or winter morning, when the mists lie low in the valley or on the
seashore, while the sun shines brightly on the hilltops. In this
way it is sometimes possible to illustrate in a very striking fashion

PRELIMINARY 3

that while a day may be marked " cloudy " in the almanack at
the school, it may be " sunny " at a place only a few hundred
feet above. If the district does not render excursions of this
type possible, much can be done with pictures of drifting mountain
mists. Very many of the ordinary Swiss photographs of mountain
peaks show mists pouring over the rock edges at some point,
while other parts of the scene are in bright sunshine. The points
to aim at are the realisation that clouds may, in the first instance,
be compared to the steam from the kettle, the steam from the
locomotive, even to the vapour that arises from the morning plate
of porridge. Of these analogies the safest is perhaps the locomotive
blowing off steam, for one must be careful not to give the idea
that clouds are hot, and the heat of the steam from a locomotive
is not ordinarily felt by an observer on the ground. Second,
strive to make it clear that while in the daytime the sun is always
riding in his majesty in the heavens, the earth is ever producing
mantles of mist and cloud which hide him from our eyes.

Again, make it clear by judicious questions that the clouds
prevent part of the heat no less than part of the light of the sun
from reaching us. Comparisons of very cloudy days with those
where the sky is covered with light drifting mist will show that
the amount of light and of heat absorbed by the cloud mantle
depends upon its thickness, and even at this early stage the days
of drifting mist may be used to show that clouds are not all of
the same height in the air. All this will help to lay the
foundation of a conception of the atmosphere and its load of
vapour.

When, however, these simple observations have been con-
tinued for some time, whether in summer or in winter, we may
notice that although on the same day it is warmer in the sun than
out of it, yet often in winter the cloudy days are warmer than
the sunny ones. In winter the alternation of cold, clear frosty
weather, with little wind and some sunshine, and relatively warm,
windy, cloudy or wet days is so frequent that every winter will give
striking examples of both types. At a very early age a skating
schoolboy learns practically that if after a frost he is wakened at
night by a boisterous westerly wind, then it means that the frost
is gone and the ice breaking up. We thus see that if the sun is the

4 THE BOOK OF NATURE STUDY

heat-giver, and the stretching of a mantle of cloud between us
and him means cold, it is yet true that from one day to another
the temperature is greatly influenced by the nature of the
wind.

It is obvious, then, that whatever simple form of chart, diagram,
or figure we employ for our daily weather observations, we should
not be content to say only " windy " or " calm " ; we should add a
note on the direction of the wind. It will soon be found that in
summer our hottest days generally come with an easterly wind,
while in winter the east wind means often intense cold and frost,
though the weather is possibly dry and as we say " healthy."
When the wind is westerly, again, it is never so cold in winter nor
so hot in summer as with an easterly wind, but it is often wet.
The class will not have continued its observations long before they
will notice that west winds are commonest with us, and that
therefore generally our weather is not very cold in winter, and not
very hot in summer.

As to the fourth point, the dampness or humidity of the air,
it is well to prepare the way for future observations on evapora-
tion and rain formation by simple everyday facts illustrating the
variations in the amount of moisture contained in the air. If the
air is moist the road is muddy ; if it is dry the road is dusty. The
road dries more quickly after rain in summer when the air is warm
than in winter when the air is cold. When the air is very moist,
the trees, the railings, the walls are all dripping with water ;
in summer, especially if it is both windy and warm, the ponds
begin to dry up, and the boggy places in the road are no longer
muddy. Let your class collect for you little facts of this kind,
let them reach themselves the conclusion that sunny days are
dry days, that cloudy days are days when the air is moist, and
that when the air is moist it rains sooner or later, — all these little
commonplaces are valuable to them if they have reached them
themselves, and the observation of them is paving the way for
a fuller treatment later.

When these simple observations have been continued for
some time what have we gained ? We know that it is the sun
which sends heat and light to the earth, but that its rays may
be partly stopped by cloud. We know that clouds are made

PRELIMINARY 5

up of little particles of water, and that we can tell in various
ways that when we see many clouds up in the sky the air round
us is full of water too, and that there will soon be rain. We
know, too, that though all the heat comes from the sun, yet the
wind has a great deal to do with making a day warm or cold,
and we explain that to ourselves by noticing that if we stand in
the passage and let the hot air come to us from the warm school-
room, it feels much warmer than when we open the outer door
and let in the cool air from outside. We know that some winds
are formed of warm air while others are formed of cold air, and
we suspect, therefore, that the warm winds come from a place
where the sun is strong, and the cold winds from some place
where the air is chilled down in some way. We know too that
the sun and the wind dry up the road quickly, while on calm,
cloudy days it is always muddy, — here is at least the beginning
of a rational study of the weather.

At a very early stage something more than this can be done.
Simultaneously with the weather observations simple notes will
of course be taken of plant and animal life as affected by weather.
In the reading lesson and elsewhere the children are learning
that spring is the growing time, summer the flowering time,
autumn the seeding time, and winter the resting time ; but care
should be taken to point out by the daily weather observations
how far removed our normal type of winter, for example, is from
the dead season of the poets. The monthly rose striving to
flower in December ; the birds singing in mid-winter ; the spring
bulbs pushing their little spears through the soil between frosts ;
the yellow aconite piercing the crust with its bent head in mid-
January ; the redwings trooping over to our shores after a cold
spell: these and many other examples should be used to show
what we owe to the south-westerly winds of winter. Make the
class realise by their own observations that our ordinary winter
consists of a series of relatively short periods of frost, with or
without snow, separated by periods of relatively mild weather.
At the same time, whether or not formal lessons in geography
have begun, tell them of the vast snow-covered plains of northern
Europe, of the silent Russian steppes, read them passages of
Tolstoi or Turgeniev describing winter scenes, make them realise

6 THE BOOK OF NATURE STUDY

the contrast between the persistent winter mantle of snow over
the great plains of the Continent, and the brown earth we see
around us.

Tell them of the snow-caps on Mars, and how the astronomers
see them spreading in winter and shrinking in summer, and how
if there are astronomers in Mars with telescopes, they must equally
be able to see the eternal ice and snow of the north Pole slowly
spreading downwards as our winter comes on, until it envelopes
the greater part of northern Europe and Asia. Let them think
of this spreading veil as stretching far over Northern Asia, and
parts of Europe, but failing to conquer, except for short periods,
the western European sea-board, and leaving as it were, a brown
streak uncovered in the region of Great Britain. If this can be
done, if the appeal is made first to the imagination, then the state-
ment in the geography books that Great Britain has " an insular
climate " will not be so meaningless as it is to the majority of
persons who have learnt this fact at school.

Again, in spring, if day by day the children record on the
school almanack their simple observations on the weather, it is easy
to bring out the fact that our spring comes slowly, and is treacher-
ous and fluctuating. Our winters are not cold, but our summers
are not hot, and therefore the contest between the forces of spring
and those of winter is very equal, — now the one now the other gains
the mastery; the buds which were tempted to unfold in March
may be blasted in April, a warm April may be followed by a bitter
May. Again, contrast with the sudden glorious triumph of the con-
tinental spring, victorious once for all over the forces of winter.
Show by a quotation from some great author the deep mantle
of snow which over the northern parts of continental Europe
buries all plant life until the warm wind blows and it melts once
for all, allowing the buds to unfold with a rush ; tell of the bands
of children in the German towns who go round the town singing
when the storks come back. Explain that though we may share
their emotion in seeing the first swallow circle in the air, yet though
we gain some birds in spring we lose many — that those who
have wintered here leave us for the summer. But, and this is the
point, begin with the simple weather observations, and do not
till this has been done take the wider flight. As our object

PRELIMINARY 7

is to prepare the way for more detailed and difficult observa-
tions, aim in these preliminary observations to arouse the interest,
try to get what the French call a tremplin, a point from which
a further flight may be made. For this purpose it is especially
important to emphasise the effect of the periodic changes of
weather upon plants and animals, and upon ourselves. The
spontaneous observation — " it is nice when the sun shines " — is
really a scientific statement of the highest value, and should be
encouraged as such.

CHAPTER I
WEATHER AND CLIMATE

THE BAROMETER AND THERMOMETER : PRESSURE AND
TEMPERATURE. — The path having being prepared by simple
observations of this kind, a more careful study of the elementary
aspects of weather and climate may be begun. Hitherto, without
instruments and without precision, we have noted the frequent
variations in temperature, in the amount and the direction of
the wind, and in the humidity of the air, and our observations
have shown us that though there is some connection between these
different variables, the connection is not a very close one. We
have found that it is generally warmer in summer with an east
wind than with a west one, but colder in winter and spring ; that
our heaviest rains generally come with a westerly wind ; that an
east wind is at least sometimes a very dry wind, and so on. But
all these statements have only a generalised accuracy — it may
rain heavily with an east wind, the air may be dry with a west
one, and so on. There is then probably some other element which
is affecting all the rest which we have not yet studied.

This element is of course pressure, whose variations as measured
by the barometer tell us more about the probable course of the
weather than any direct observation we can make. As the
ordinary child is perfectly familiar with the appearance of a baro-
meter, and probably sees it consulted by some members of his
household daily, his attention should be directed to it at an early
age, and the opportunity may be taken to indicate the value to
mankind of instruments of precision. If in winter the glass is
high we have usually sunshine, often accompanied by considerable
cold or frost, and little wind ; if it is low, we have stormy or windy
and wet weather, probably with a higher temperature. In summer
the high glass means what we call " fine " weather ; the low, rain and
probably wind. Be content at first with simple generalisations

WEATHER AND CLIMATE 9

of this kind, and by drawing frequent attention to the barometer at
times when it is changing rapidly, drive home the fact that though
the changes of the barometer are often associated with changes
in temperature, humidity, and the direction or force of the wind,
which we can perceive with our senses, yet we have no sense per-
ception of that change in pressure to which the barometer responds.

In the same way point out that although our senses register for
us changes of temperature yet their indications are very inexact.
It is easy to bring this out by questions — the same day will be
regarded as warm by some children and cold by others, the sensa-
tions even of the same person altering with hunger and fatigue. To
further emphasise the point insist upon all the children performing
for themselves the old experiment with water of different tempera-
tures. One hand should be plunged into cold water, the other into
hot, and after a few minutes both hands should be plunged into
warm water. The one hand will receive the sensation of warmth
and the other of cold. Each child should be made to do this for
itself, and by judicious questions the meaning of what the psycho-
logist calls the subjectivity of sensations should be clearly brought
out. It is obvious then that if we had no instruments, if we were
shut up exclusively within the limits of our individual sensations,
the scientific study of our surroundings would be impossible.
Before any attempt is made to explain the thermometer and the
barometer, their value should be made clear in this way.

We may next make practical use of these instruments, and
especially of the thermometer, before proceeding to explain them.
The explanation will come much better at a later stage when we
have used them constantly and realised their usefulness. On the
school excursions, then, let us take an aneroid barometer and a
thermometer. From our observations of the first we learn that
while it does not change (during short periods of time that is) on
the level, it begins to go down when we climb a hill, or rises if we
descend. At this stage pictures and stories of Pascal on the Puy de
Dome and de Saussure on Mt. Blanc will be appropriate. In
Whymper's Guide to Chamonix there is an interesting reproduction
of a picture showing one of de Saussure' s excursions on the
Mt. Blanc range, with the huge cavalcade of porters carrying
the impedimenta. If this picture can be shown to the class, and

io THE BOOK OF NATURE STUDY

if the neighbourhood afford a hill which can be taken as a mimic
Mt. Blanc, a great deal of information could be driven home by a
teacher willing to take advantage of the child's joy in pretending.

On a hill of a height suitable for an ordinary school excursion
the fall of temperature with increase of altitude is less easy to
demonstrate. The fall is roughly i° F. for every 300 feet of rise of
altitude. If an attempt is made to show this, arrangements
should be made to have another thermometer read at the same
time at the bottom of the hill. If a direct observation of a fall of
temperature with a rise of altitude cannot be made, snow on the
summit of distant hills, or the snow lying on the uplands while it
has melted on the lower ground, can all be used to suggest the
fact of this fall of temperature.

A mimic ascent of Mt. Blanc, then, whether conducted
wholly in imagination or by means of an actual ascent of a
local hill, has been taken as an opportunity to show that
both the barometer and the thermometer fall as we ascend.
As we stand on the top and look down on the valley below,
we note that if our hill is, say five hundred feet high, then five
hundred more feet of air weigh on the valley than upon us, and
we connect this fact with the slight fall in the aneroid. (The
barometer near sea-level falls rather more than one inch for
every thousand feet of rise.) We remember how de Saussure and
his companions gasped as they reached the top of Mt. Blanc,
and we realise that though the absence of five hundred feet of air
does not affect our breathing, yet when fifteen thousand feet of
air are absent matters are different. If the view from the hill-
top includes the sea it would be a suitable opportunity to suggest
that while we live at the bottom of an ocean of air, the fish in the
depths of the sea live at the bottom of two oceans, one of air and
another of water.

We remember, also, that it is a little colder at the top of our
hill than on the plain, and that it is very much colder on the top
of Mt. Blanc than at Chamonix, so much colder that even in
summer the snow does not melt at the top. We take note, then,
that the air is thinner at the top of a hill than at the bottom, and
that at the same time it is colder, and we resolve to try and find
out if there is any relation between the two facts.

WEATHER AND CLIMATE n

Standing also on the top of our hill we remember that there
are hills even higher than Mt. Blanc, and that the highest of
these have not yet been climbed, because it gets colder and colder
and more and more difficult to breathe as the climber ascends,
until he finds it impossible to go farther. We conclude then that
if the air gets thinner and thinner as we ascend, there probably
comes a time when there is no more air, and if it gets colder and
colder as we go up it will be probably very cold in the region
where the air disappears. Thus we reach the provisional conclusion
that the air has something to do with making the earth warm.

In going farther one must be careful not to attempt too much,
for the problems involved are of course highly complex. A few
simple points should, however, be emphasised. It is so cold on
the top of high hills, in spite of the strong sun, that the snow never
completely melts. It is cold also when people ascend in balloons,
and colder still when they send kites up to heights they cannot
reach. Therefore, though the sun sends his rays through space,
those rays are not warm till they reach the earth, and it is the warm
earth, not directly the sun, which warms the air. But the air
acts like a blanket and prevents the loss of the warmth which the
earth is always radiating into it. One of the reasons why it is cold
on the mountain tops is that there the blanket of air is thin. Air,
especially if it is dry, allows the rays which make the earth warm
to pass through it easily, but, as we have already seen, damp air
stops some of the rays, and therefore, other things being equal,
damp days feel colder than dry ones.

When the sun shines then we have to think of the rays pouring
through space, pouring through our thick blanket of air, and
warming the upper surfaces of the soil. The warm soil again
throws back its heat into the air, and warms its lower layers. If
the soil is dry it warms the air much more than if it is moist, for then,
as we shall see, some of the heat is used for another purpose.

On our excursions an opportunity should be taken to read the
thermometer first in the shade on the bank of a pool or stream,
and then when its bulb is plunged beneath the surface of the water.
We shall of course find by the thermometer what we already know
by our own feelings, that the water is colder than the ground or the
air, though the same sun is shining on both. We notice, then, that

12 THE BOOK OF NATURE STUDY

the surface of the smooth water shines like a mirror, or like the
bright fireirons on the hearth, and we explain that just as the
water is throwing back much of the light into the air, so also it is
throwing back some of the heat. There are of course a good many
other points to be considered, but in the course of the excursion
we may rest content with the proof that water is colder than air
or soil under the same conditions, and also that it has a reflecting
surface which soil has not, leaving further and more difficult points
for indoor work. A boat on a considerable expanse of water, or
the memory of a journey by sea, may also enable us to add to our
notes that air above water is colder than air above dry ground.

If the conditions make it possible it would be well to have the
observations repeated by some one at night, and the results shown
to the class, in order that they may formulate for themselves the
conclusion that the dry ground which warms so quickly with the
sun in the daytime, cools very quickly at night, while the water
cools little. Again, the repetition of the same observations in winter
will show that the winter conditions are similar to those obtaining
at night. The ground loses its summer store of heat much faster
than the sea or than a great mass of water, and the air above dry
ground therefore cools faster than air over the sea or a considerable
area of water. From these very simple observations, by the aid
of judicious questions, bring out the idea that a great mass of water
near a land area will tend to make it warmer in winter and cooler
in summer, cooler also during a summer's day and warmer at
night than it would otherwise be, and get the class to suggest
that this condition is fulfilled on an island, especially a small island,
which has the equalising sea within reach of all its area. Recall
the facts about the winter and summer climates of the plains of
Russia which have been already suggested, and let the class give
the reasons for the extremes of temperature there.

Tell them also of the vast arid plains of Asia, far from any great
masses of water, and get them to realise at once the heat and the
cold. Tell them of the hotel-crowned Alpine hills where the sun
beats down through the clear, thin air all day, until the heat may
seem nearly intolerable in clear weather, and then explain how
chill the air becomes as the sun disappears and the heat is radiated
out into space through the thin blanket of air. But let this be

WEATHER AND CLIMATE 13

after and not before they have made some actual observations of
their own, however simple and even inaccurate these observations
may have been. We want to aim at giving them the joy of dis-
covery, the emotion which carried de Saussure through the hard-
ships of his ascent, which enables the Arctic explorer to endure the
tedium of the winter night.

WIND. — But we have spoken as if the air was perfectly still,
and this though we have already made some simple observations
on wind. Clearly the next point is to show that heated air expands
and rises, and chilled air descends. All books on heat give various
simple experiments to illustrate the expansion of solids, liquids,
and gases with heat, but though some of these will doubtless be
performed by the teacher, they have all the objection of an air of
unreality, which unfits them for the Nature Study course. At this
stage it is better, if possible, to confine oneself to observations which
can be made directly without special apparatus. Our aim is after all
to interpret the existing environment, not to introduce a new one.

The adventurous child who has climbed to the top of a high
bookcase in a heated room knows that the air there is distinctly
hotter than on the floor. Some observation of this simple kind
may be taken as a starting-point, and the stepladder and thermo-
meter used to show that his impression is not imaginary. The
rush of warm air out to the landing when the door of a hot room is
opened may also be used to show that warm air tends to move, while
the previous experiment has shown that its tendency is to move
upward.

With such observations as starting-points a good deal may be
done, and without borrowing tubes, coloured fluids, flasks, etc.,
from the physical laboratory certain minor experiments may be
performed. A bottle half-filled with water or oil and lightly
corked, if put down close to the warm fire can be induced to shoot
out its cork. A piece of bladder also may be tied over the mouth
of a bottle filled with hot water in order to see how the bladder
is sucked in when the water cools. A whole series of trifling
experiments of this kind, chosen as being related as closely as
possible to daily life, should precede any statement as to the effect
of heat upon air.

14 THE BOOK OF NATURE STUDY

From them we deduce the conclusion that as air gets warm it
takes up more space, and therefore becomes lighter, and so rises.
But as it moves even more easily than water does, it does not leave
a space when it moves, fresh air comes in to take its place. Without
stressing too much these theoretical facts we return continually
to our temperature observations, and we say to ourselves, England
is cool in summer because there is sea all round it, and the air is cool
over the sea, and in the daytime that cool air is always streaming
in towards the land to take the place of the warm air which is
continually rising. But at night, and in winter when the land is
cool or cold and the air over the sea not so cold, the sea helps to
keep us warm. At the same time we just think in passing that
over those vast hot plains in Asia in summer the air must always
be streaming out towards the distant sea, but in winter the icy
plains must have over them a thick mass of very cold air, while
we are feeling the mild air from the sea. In a Nature Study course
one would not wish to go much farther than this, but would leave
the thought, the picture, for the teacher of geography to elaborate
and enlarge later. But see to it that long before the child has been
plunged into the airy depths of monsoons and trade winds, deflec-
tion, and so forth, his imagination has been touched, his interest
aroused by contact with actual facts. Strive to make clear that
all this knowledge has been acquired by human beings equipped
with the same senses as himself.

RELATIONS OF TEMPERATURE AND PRESSURE TO WIND. — We
have now got to a point when we may begin to say something
about wind in its relation to pressure. We have learnt that air
is capable of very free movement, and we have suggested that when
it is warmed it always tends to rise and flow away, while fresh,
colder air comes in to take its place. We have shown also that
the difference between sea and land is one great cause of movements
in air. The school locality may even afford some detailed examples
of the effect of the proximity of water. Near large towns there
are usually areas of market gardens especially devoted to early
produce, selected because experience has shown that the particu-
lar locality is not liable to spring frosts. A good example is the
peninsula of the Wirral, whose crops of spring vegetables are

WEATHER AND CLIMATE 15

determined not only by the fertile soil but also by the fact that
the climate is mild owing to the proximity of the two great estu-
aries of the Mersey and the Dee.

On a smaller scale the same phenomenon is frequent. In the
vast area which supplies the market of London, and especially in
Kent and Surrey, it has been shown that the proximity of the
valley of even a small river, has a markedly ameliorating effect
upon the local climate. The teacher should look out for such
local examples, and by encouraging the reading of the thermo-
meter daily by different pupils in their own homes should get at
the fact that in the same district there are frequent minor differ-
ences of temperature. This done, make it clear that every minor
variation, every change between hill and valley, between marsh
and dry soil, between upland moor and fertile plain, is producing
little changes in pressure, and so starting movements in the air.

But if it is true that every trifling change in the local conditions
is producing changes of temperature and therefore of pressure, one
wants to remember that it is infinitely more true when great areas
are considered. When we are in the depth of black winter the shops
are full of bright flowers. If some of these come from hothouses,
many others come from France or from the Channel Islands.

In spring in most parts of Britain, strawberries from a distance
appear long before those of the locality are ripe. Seize facts of this
kind — for after all to the majority of school children the shops
are a very important part of the environment — and get the class to
deduce for themselves the existence of differences of temperature
on the surface of the globe. If the strawberries of Brittany are
red ripe while ours are green, the probabilities are that it is hotter
there than with us. But if the ground is hotter the air is warmer,
therefore it is lighter, and the sun on that peninsula is starting a
circulation of which quite possibly we are feeling the influence.

Children from the south of England who go north to Scotland
for their holidays know that the days are longer in summer there
than in the south. If the direct experience be not available, every
railway station shows advertisements of cruises to see the midnight
sun. But if the sun shine longer in the north than in the south
on a summer's day, then the ground there must be still receiving
heat while that farther south is beginning to pour out its heat —

16 THE BOOK OF NATURE STUDY

here is another cause of air movement. In some such way intro-
duce the subject of pressure, give an idea of the constant changes
of which the air is the seat, always trying to begin with direct
observation.

To sum up, then — we have to realise that whether we think
of our own small locality, or of the great world at large, there
are everywhere differences of temperature in the air, and there-
fore differences of pressure. These differences of temperature are
brought about in two main ways. First, they are due to the
fact that the different parts of the globe do not all get the same
amount of sunshine and therefore of heat. Second, we find that
land and water, dry ground and moist ground, even when subjected
to the same amount of heat, become unequally hot, and heat
unequally the layer of air above them. This is what we learnt
from plunging our thermometer into the pond.

To illustrate the next point the analogy of the bicycle tyre may
well be utilised. Let the members of the class explain from their
own observations that much air can be squeezed into a bicycle
tyre when the arm of the pumper is strong, let them tell how the
air whizzes out when the valve is removed, or the omnipresent thorn
enters, and let this precede the familiar statement that air or any
other gas, when free to move, tends to move from a region of high
pressure to one of low. Let them describe how the air rushes out
faster at first when the tyre is full than later when it is beginning
to empty. Then choose a day of violent wind, and while this
howls round the chimney-pots, point to the low barometer, and
by judicious questioning get the class to see that the low glass,
the shrieking wind, mean that the air from some region of high
pressure is rushing in to fill the gap which the low glass indicates.
On a day of high pressure, point out that then there is relative
calm, the air merely streaming gently out of our area into a more
distant one where pressure is lower. Before any details are given,
however, be sure that the connection of differences of temperature,
of differences of pressure, and of wind is grasped. Every change
of wind means a change of pressure, every change of pressure means
a change of temperature, and this brings us back to the differences
in the amount of heat and to the differential absorption which start
the whole circulation.

WEATHER AND CLIMATE 17

Before beginning observations in detail of the local changes of
wind, it may be well to re-emphasise the fact that Great Britain
is an island, and that the proverbial changeableness of our weather
is in part related to this fact. Tell stories or read passages of
books which give accounts of the constancy of the weather in the
great continents, of the winds which blow in the same direction
day after day and week after week. Tell how in Asia especially
the hot land in summer sucks in the air from the sea, while in winter
the warmer sea sucks out the air from the cold land, so that in
both cases there is great constancy of wind direction. Compare
with this the preliminary observations which have been made,
which show that although winds with a westerly direction pre-
dominate here yet our winds show great variation, and this at all
times of the year.

In passing suggest one or two of the more obvious facts about
our winds. We have already noticed that our hottest days in
summer are often days when the wind, though very light, is
easterly in direction. Now that we have learnt about the differ-
ences in temperature of continents and seas, we note that the
reason is probably that the east wind is then coming to us from
the hot plains of continental Europe. This suggests to us also
that one reason why the east wind is so bitterly cold in early
spring may be that it is then coming from the snow-covered plains
of the continent. Similarly, the strong south-west wind of winter
must be mild because it is coming from the relatively warm sea
to the west of us.

Again, if our winds are most often westerly, it is probable that
somewhere to the west of us the pressure is nearly permanently
low. Some of the above statements, as all those who have studied
meteorology know, are only partially true, but as our object is not
to give the school child a profound knowledge of meteorology but
only to awaken interest, they are justifiable as partial explanations
of the facts of observation. Our object, before proceeding to the
special study of the local winds and their causes, is to emphasise
the fact that we live in a region of variable winds, as opposed to
many regions where there is great constancy. As winds have
much to do with the amount of rain, the inconstancy of our winds
is closely related to the general inconstancy of our weather,

VOL. VI. — 2

CHAPTER II
PRECIPITATION

i. ITS CAUSES. — We have next to consider the various questions
connected with precipitation. The preliminary observations have
given some facts which can be utilised as a starting-point. We
have seen that the road dries quicker on some days than others,
quickest of all on warm windy days with sunshine. We have taken
advantage of such trivialities, from the strictly scientific standpoint,
as the family washing, and we have learnt that the clothes dry
quickest on such days, slowest on damp, sunless, windless days ; we
have seen also that on the same day they dry quicker the more fully
they are exposed to the air, and we have watched the props being
adjusted with the object of raising the line as high as possible in
the air. The clothes are put out wet, they are taken in dry — where
does the moisture go ? Not into the clothes-line, not into the ground,
and therefore it must be into the air, though we can see no differ-
ence in the air. Therefore we conclude that the air can take up
moisture, and that when so taken up the moisture is invisible.
But if the clothes, other things being equal, dry quicker the greater
the movement of the air, then it is probable that the air can only
take up a limited amount of moisture. What becomes of all the
moisture that the air takes up ?

The answer to this question should be given gradually, in
making use of all the simple observations which present themselves
in the course of daily life. In the winter the white cloud of vapour
which one sees issuing from the nostrils of horses standing in the
frosty air ; the similar cloud which escapes from our nostrils in the
open, while it is not visible in the warm room ; the cloud which
forms on the outside of a glass of water taken from a deep well or
a cold spring in summer ; the similar cloud outside a glass of iced
lemonade ; the steam on the windows of a railway carriage or
tram car ; the similar condensation on the windows of the in-

PRECIPITATION 19

sufficiently- ventilated schoolroom — seize such simple facts as
these as the preliminaries to the statement that warm air can hold
much more water vapour than cold air. Again, the heating of the
nozzle of the inflator as the air is forced into the bicycle tyre may
be used as an illustration of the fact that when air is compressed
it becomes warmer, while at the same time we explain that as it
expands it becomes cooler.

If the neighbourhood afford no examples of hills high enough
to show the formation of cloud, pictures must be utilised to
explain that just as the moisture in our breath condenses into
vapour when we leave a warm room for the chill of a winter's
day, so the warm dense air of the lowlands as it rises up against the
cold mountain-side grows chill, and forms a cloud of vapour. If we
hold a bright object in our breath it becomes clouded with vapour,
which form minute drops. In the same way the light vapour which
we see against the mountain is mist or cloud to those who are within
it. In some such ways try to explain the formation of rain-clouds,
try to give an idea of the invisible load of moisture everywhere
present in the air, try to show that the air only requires to be
cooled down enough, and however dry it may appear it will throw
down some moisture.

All air then contains moisture, and air only requires to be
:ooled for this moisture to appear as mist or rain. What cools
the air in natural conditions ? There are two main causes : air
becomes cooled as it expands in ascending, and it also becomes
cooled by passing from a region of higher temperature to one of
lower. Take the first point. We have noticed that in a room
the air is hotter near the ceiling than on the floor. But then the
upper layers are retained by the ceiling. If they had been free to
move they would have risen higher and higher, cooling as they rose,
like the hot air which cools as it rises up a mountain-side. When,
then, in summer we enjoy the pleasant warmth of the turf on
which we are lying, we have to remember that the pleasant warmth
would soon become suffocating heat were it not that the air as it
is warmed by the hot soil is constantly rising, cooling as it rises,
and that it is always new layers which are becoming warm. As
the warmed air rises and cools its moisture may form fleecy clouds
such as those we see in the sky.

20 THE BOOK OF NATURE STUDY

Again, we have noticed that in spring, when the weather is
often dry, east winds are common, and are often cold. We have
seen that they are cold because they come from those plains of
Europe which are not, like our islands, warmed by nearness to
the sea. We now ask ourselves why they are dry. The answer
is of course that, coming from a colder region to a warmer one,
they become capable of taking up more moisture, and have no
tendency to throw dowrn their existing load.

In such ways we suggest that cooling air seems to make it
damper, that heating it seems to make it drier, and that therefore
rain, no less than the appearance of a cloud of vapour when we
breathe, means that warmed air is being chilled down. If the
air be chilled down to a very great extent the moisture may pass
direct from the state of vapour to that of snowflakes, and fall as
snow. On the other hand, if the raindrops in descending fall
through a very cold zone of air, as happens not infrequently in
thunderstorms, freezing takes place, and the drops fall as hail-
stones. In its simplest form this is the explanation of rain, hail,
and snow ; the first and last especially, however, require much
more detailed study.

We have striven to give a picture of the ever-changing mantle
of air which lies over the whole of the surface of the globe. We
have seen that in different parts it is unequally heated, and this
unequal heating starts movements which present themselves to
our senses as wind, and which are determined by those differences
of pressure which the barometer registers. We have learnt also
that all air can take up a certain amount of water, the amount
varying with its temperature, warm air always taking up more
than cold air. Therefore we know that cooling air has always a
tendency to cause the invisible moisture to appear as mist, rain,
snow, or hail, according to the conditions.

We have noticed also, without troubling about Boyle's law,
that air cools when it expands ; that it cools as it rises, while it
becomes warmer as it is compressed, that is, it becomes capable
of holding more vapour as it descends. We have repeated in
imagination or in reality our mountain ascent, and have added to
our first note that it is not only colder on the hill but rain is more
frequent there, because the cold mountain cools the air and makes

PRECIPITATION 21

its moisture appear as a cloud, exactly in the same way as that in
which the frost of winter causes the moisture of our breath to
appear as a vapour cloud. In this second excursion we may go
even a little further. We think of the warm air rising from the
valley, loaded with the moisture which it has gathered from the
river. In imagination we see it cooling as it rises, throwing down
its load of vapour as the mountain mist, and then being displaced
by new gusts of warm damp air coming up from the low ground.

We notice that even though it be perfectly still on the low
ground there is nearly always a breeze on the hill, and we try to
>icture to ourselves the meaning of this breeze, how it is always
trrying the warm damp air upwards. We examine the trees or
mshes on the slopes of our hill, and we try to find from them —
or even from the way the sheepfolds are built — whether or not the
ind blows more frequently from one direction than another.

If our examination is conducted on a real hill, and not an im-
'inary one, we shall probably soon find facts which lead us to
suspect that just as in the valley, so on the hill, the west winds are
tost frequent. That means that the warm damp air blows up one
>ide of the hill more frequently than up the others. As it sweeps
ip it cools and its moisture is condensed. But it sweeps on and
down the other side. As it sweeps down it gets warmer, just as it
got colder in ascending. In ascending it threw down its vapour,
therefore it has but little left to throw down on this side, which
ill be drier than that facing the wind.

All these statements are of course only very partially true for an
isolated hill, but they are sufficiently true for us to pass easily to
the great deduction that if a long range of hilly ground runs north
and south in a country where the prevailing winds are westerly,
then the side which faces the west will be wetter than the side
facing east.

Once again, we stand on our hill and look down to the valley
or plain below. However small absolutely our hill is, we try to
picture to ourselves the air always carrying up moisture from the
river to the top of the hill, always being compelled by the hill to
throw down its burden, and yet always recommencing the task.
But the river remains in spite of the robber who is always at work ;
what becomes of the spoil which the mountain reclaims from the

22 THE BOOK OF NATURE STUDY

thief ? If the hill is not sufficiently extensive to afford an
example of a tiny stream, we can always go back in imagination
to the origin of the river, always suggest that it was born from the
clouds which formed round the peaks of the distant greater hills.
The air then carries the water from the river to the mountain, but
the mountain reclaims this water from the air, which it chills until
its grip relaxes, in order that it may give its own back to the
river.

On the larger scale the same thing happens with the sea. The
river pours its water into the ocean. The air robs the ocean, but
as it flees ever farther and farther inland the mountains seize
its load and return it to the ocean. So the eternal struggle
goes on, while the impassive sun gazes on the combat which
he originates and controls, but the active part in which he leaves
to others.

If the mountain gives back her own to the ocean, however,
it is not without paying a heavy price. With its cold fingers it
grasps the vapour borne by the air, but as if in revenge for being
brought back to earth that vapour makes streams which scar and
scour all the flanks of the mountain. Not the water only is
sent back to the river, but with it the very substance of the
mountain. With its water the river carries this down to the
sea ; and though the water returns, this load of sand and silt must
remain. As the struggle goes on the mountain loses more and
more, it gradually crumbles away, until in imagination we can
look forward to a period when it will have been worn so low that
it can no longer seize the floating vapour, and capture it for the
river. It is then that another party intervenes to redress the
inequality of the combat. The old earth awakes, shakes her-
self, pours back on the land the substances of which it has been
robbed, or raises bodily above sea-level the waste of the land
to make new mountain ranges — and thus the eternal struggle
is renewed. Once again the mountain leagues itself with river
and sea to reclaim the load of vapour which the air would
capture.

Something after this fashion would one wish to suggest the
basal facts of physical geography, long before the very name of
that science has been uttered.

The Bliimlisalp and Oeschinensee, near Kandersteg, showing the formation of cloud
round the summits of the mountains.

(Photo by WEHRLI, Zurich.)

Trees near Edinburgh, showing effect of prevailing westerly wind,
growing towards the east.

(Photo by ANDREW WATT.)

The trees are

The Lauterbrunnen Valley, showing the streams which flow from the mountains
forming the sides of the valley, and give rise to waterfalls.

(Photo by WEHRLI, Zurich.)

Sand-dunes on Holy Island, Northumberland. Note sands-reeds, and the
fact that the surface has no continuous covering of vegetation.

(Photo by LESSUE NEWBIGIN.)

PRECIPITATION 23

In detail, of course, the order of study must depend upon
the general arrangement of the school course, but at an early
stage allusion may be made to the main facts connected with the
structure of Britain, as illustrating on a larger scale the facts
observed locally. Thus, one would point out that all the great
backbone of mountains which runs down through Great Britain
presents a rainy side to the ocean, and a less rainy side to the
east. If the western side be the wetter side, however, there
the streams will be most frequent, there also the mountain sides
will be most deeply carved out by the water, while the wearing
action of the water will be less on the other side.

The next point is of course to indicate in some way the difference
between the steep rocky Atlantic sea-board and the more fertile,
gently-sloping eastern slope, the facts being considered in relation
to rainfall and erosion, and their geographical significance merely
suggested.

2. MEASUREMENTS OF RAINFALL. — To give exactness to
meteorological observations of the type suggested above it will,
however, be necessary that the members of the class should
actually measure the diurnal variations of one or other of the
elements for themselves. In the first place, at least, there is much
to be said for allowing them to measure the rainfall by means of
a rain-gauge, and this for several reasons. If the barometer be
chosen, we have to face the fact that the small daily variations,
except during the passage of considerable cyclones, are not easy
to interpret. For all ordinary purposes, indeed, the terms rising
or falling, high or low, may be said to suffice. Not till the stage
when meteorological charts can be used is more required. The
case is similar with the thermometer. Except when the varia-
tions occur round the freezing point, where they have consider-
able economic importance, variations of a degree or two, up or
down, do not directly affect daily life, and observations must
therefore be kept over a considerable period before the observer
can accumulate a sufficient basis of experience to interpret them,
or find in them any great degree of interest. Although, therefore,
it is a good plan even from an early stage to add occasionally
to notes of the weather a reading of barometer and thermometer,

24 THE BOOK OF NATURE STUDY

some progress should have been made before this is done regularly.
A very cold day, a very warm one, a great storm, a long period
of calm settled weather — all these should be chosen as occasions
to record the temperature and pressure, as texts for special
lessons. Again, to contrast with these one would take more
normal periods, and thus almost unconsciously, and without
special effort, associations would be formed in the minds of the
class between special figures and special conditions of the weather.
From daily observations of the rain-gauge something more might,
however, be learnt.

Before going further it may be well to say something here on
the subject of measurements in the Nature Study course. In the
author's opinion any insistence upon measuring as measuring in
this course is wholly out of place. Our object is to fan the
natural interest in his surroundings which is the birthright of
every healthy child. It is to fan it especially by showing, in the
case of the simplest, most everyday phenomena, that by careful
observation we can discover hidden causal relations, can show
the connection between apparently isolated facts. At the same
time we have to strive to keep ever before us the fact that the
child is growing up in the midst of an ancient and highly complex
civilisation, where the means of satisfying intellectual curiosity
exist abundantly all through life. Our object then is to see not
that he leaves school a little scientist, but that he goes out into
the world with his initial curiosity stimulated, his powers of
observation strengthened, his thirst for knowledge unsated.
Next to the great and pressing danger of forcing facts upon him
before he is ready for them, is the danger of demanding from him
a degree of accuracy which as an undeveloped human being he
is incapable of giving. Both lead to exhaustion, to the suppression
of the curiosity which we want to stimulate.

Many scientists, struck with our national want of exactness,
our national indifference to scientific method, urge the necessity
for attempting to combat this by insisting upon accuracy from
the earliest stages, and especially by making exact measurement
an important part of early education. But both mentally
and physically the child is unfit for the kind of accuracy which
demands delicate muscular adjustments ; even the thought that

PRECIPITATION 25

such accuracy is desirable is no part of his mental equipment.
In our Nature Study course, then, if we measure we measure because
we want to get at certain facts only obtainable in that way.
In the first instance at least the teacher is wise to accept all
results, even slovenly ones. As we go on, and as we proceed to
use our results, we find that if they are inaccurate we become
involved in all sorts of difficulties, and thus slowly, and in the
natural way, the need for care and accuracy dawns. But let
us strive above all things to follow the natural order, not to take
the means for the end, to measure because we want to know,
and not for the sake of measuring, not for an abstract purpose
beyond the child's reach.

The measurements involved in observing rainfall are simple,
and can be carried out without great strain. As we do not propose
to send our results to the rainfall organisation, a standard-pattern
gauge is not necessary — a jam pot, a funnel from the cook, a
measuring glass from some one who goes in for photography will do
to start with. If, as is increasingly the case in schools, the building
is furnished with meteorological instruments on which regular
readings are taken, it will be useful to compare our more or less
haphazard readings with the more formal ones taken by the higher
classes, to find out to what extent the difference, if any, is due to
carelessness, and to what extent to defects in the instruments. If
the school has no meteorological station the neighbourhood will
probably contain one, or at least some interested amateur, who will
not object to give his results for comparison. If both conditions
fail, the daily newspaper will almost certainly give meteorological
notes. These facts are important, because one wants to convey
to the members of the class the idea that what they are doing
many other persons are also doing, one wants to be careful to
remove as far as possible the air of unreality from the Nature
Study course — an air it is only too apt to have.

One would naturally begin rainfall observations at a time of
year when the rainfall is heavy. As a general rule in Great Britain,
October and November are months of high precipitation, while the
spring months, notably April and May, are months of low rainfall.
The autumn is thus a good time to begin. If possible, a spell of
wet weather should be chosen as the date of beginning. At such

26 THE BOOK OF NATURE STUDY

periods the conversation at home and abroad usually deals largely
with the weather, and the members of the class will be delighted
to offer their contributions, in the shape of the observations that
they have made. At the same time the teacher should compare
the local fall with that in other parts of the country, comparing
the local flooding of the streams, if any, with that in other dis-
tricts, until the connection between inches of fall as measured by
a rain-gauge and the rain as seen, and as it affects the streams, is
clearly grasped. One would at the same time note whether the
rain is or is not accompanied by wind, and if so, from what
direction the wind is coming.

In an autumnal rainy period the opportunity would of course
also be taken to point out that all the long summer the warm air
had been taking up water vapour, and that with the cooling of the
air in autumn this vapour descends as rain. As a general rule the
rainy winds come up from the Atlantic, and the rain which descends
has been gathered as vapour from all that great expanse of water
which lies to the west of us. As a contrast one would take a dry
period in spring, when the winds are often easterly and cold. They
have, as we have seen, been sweeping over a land area before they
reached us, and are usually more or less dry as well as cold.

3. BRITISH RAINFALL. — It is no part of our business here to give
in detail the conditions in regard to precipitation which exist in the
British area, but it may be well here to briefly mention some of
the facts to the demonstration of which the school observations
should be directed.

Reference to the literature of the subject (see below) will show
that the mean annual rainfall of the whole British area is about
38 inches per annum, but, as any rainfall map will show, the state-
ment is absolutely useless as affording any guide to the conditions
likely to be observed in any given locality. The whole of the west
coast of Ireland, and all the elevated parts of the west of Great
Britain, have a rainfall considerably exceeding 40 inches, the
annual fall rising at places like Ben Nevis to about 160 inches.
Again, portions of the eastern seaboard, both of England and
Scotland, have a fall below 25 inches, this being especially true
of the " wheat belt " in England. From these statements there

PRECIPITATION 27

results the fact that the rainfall of any particular part of Great
Britain is interesting in relation to the geographical position of
that area, and should be considered in that connection.

It is unlikely that a teacher, however enthusiastic, will succeed
in getting a class to carry out rainfall observations over any con-
siderable period of time, so that the annual rainfall cannot be
studied on the basis of actual observation. On the other hand, the
observations can probably be kept up for a fortnight or even a
month at a time, and this will give an opportunity for explaining
the meaning of the term mean. The local result can also be com-
pared with the recorded averages for other stations, and thus an
idea of the great variations in the British area given, and correlated
with position, elevation, etc. Even if the actual observations
can only be kept up for a very short period, they should not be
neglected, for it is very important to associate directly a measured
amount of rain in the gauge with the observation of rain as it falls,
and, once this association has been firmly established, lessons based
upon official figures can be given without unreality.

Another point of great importance as regards actual observa-
tion is the number of days with rain. For the meteorologist
a day with rain is one in which T^- inch falls. An attempt
to record the days with rain should be made over a considerable
period, for from the climatic point of view this is of great import-
ance. The British climate as a whole is characterised by the great
number of days with rain, and therefore the relative infrequency
of torrential rain. Over the whole area the average is nearly 200
days with rain out of the 365 composing the year, but again the
different parts of the country differ considerably. The average
is about 180 for England and Wales, about 206 for the whole of
Scotland, and 216 for Ireland. The actual figures are only of
importance as enabling us to emphasise the great number of days
with rain in all parts of our area. As in the case of the total rain-
fall, the figures given above are made up by averaging a number
of different figures. The lowest number of days with rain on an
average in England seems to be 153 (at Weymouth), and the
highest 243, in Ireland (at Londonderry). The fact that the days
with rain are distributed throughout the year should be emphasised.
There is no season of the year when rain is not likely to occur.

28 THE BOOK OF NATURE STUDY

The number of rainy days in Great Britain is a point which
requires emphasis. It is a point which becomes commonplace
from so early a stage in the life of the individual that it is difficult
to make its significance realised. Our rainfall is moderate ; it
occurs throughout the year ; the number of days with rain is large —
here are three facts of prime importance. Two important conse-
quences are : first, that long spells of drought are rare, and form no
part of the normal sequence of our weather ; second, that very
heavy falls of rain are also rare.

As regards the second point, falls which exceed 2 inches in
twenty-four hours are regarded by the Rainfall Organisation as
sufficiently exceptional to need special emphasis. Much greater
falls than this do occur, the heaviest individual falls occurring as a
rule in districts where the rainfall is relatively great. The chance
that falls exceeding 2 inches in twenty-four hours will occur
varies so much with the locality that a general statement can
hardly be made. We may mention, merely for purposes of refer-
ence, that in the period between 1882 and 1905 the mean of the
daily rainfall records received by the British Rainfall Organisation
was 2314, and of these 285, or about 12 per cent., recorded falls
exceeding 2 inches in twenty-four hours. Further details will be
found in the yearly volume of the Organisation (British Rainfall).

4. FLOODS. — The first point then is to emphasise the relatively
gentle, diffused nature of our rainfall, using the ordinary observa-
tions for this purpose. But not infrequently, especially perhaps
in autumn, we have exceptional rainfall ; this, as indicated above,
being much more frequent in some places than others. Again,
if droughts do not regularly occur, almost every summer will afford
examples of a temporary limited dryness, which may be used to
illustrate the general phenomena of drought. Let the teacher then
first, by the help of actual measurements and records of rainy days,
emphasise the ordinary character of our rainfall, and then let him
seize exceptional conditions as a basis for lessons which may drive
home the ordinary conditions by emphasising the extraordinary.

We may begin with a heavy rainfall. For example, in October
1906, very heavy rainfall was experienced in parts of Scotland,
especially on Speyside. At Ardclach (Glenferness) , in the county of

PRECIPITATION 29

Nairn, the fall on igth October was 4 inches in twenty-four hours,
while the rainfall for the whole year was 43-28 inches, so that
more than 9 per cent, of the total fell in twenty-four hours.

On the same day heavy rain fell in the upper valleys of the
Spey and the Findhorn. The result was very extensive flooding,
notably at Kingussie, and a considerable interference with traffic.
The season being relatively advanced and the district one of high
mean elevation the precipitation on the higher hills took the form
of snow, but the fall on the low ground, as already stated, was
sufficient to swell the rivers to flood level. Such floods, produced
in this way, are not very uncommon, and whether they occur in
the local district or are merely recorded in the newspapers, should
be used as the starting-point for a lesson on torrential rainfall. If
4 inches of rain in twenty-four hours causes flooding, what must
we expect of countries where, as in the United States, falls of
5-7 inches in twenty-four hours are not infrequent ? At Bombay
24 inches have fallen in one night. All books of reference give
examples of similar heavy falls. The point is not to emphasise
the actual figure, but to correlate torrential falls with floods, to
contrast the frequency of such flooding in certain countries with
its relative rarity on any considerable scale here.

If no examples of considerable flooding are available the fall
in a summer thunderstorm should be measured. One or two
figures may perhaps be useful as a basis of comparison. Thus on
2nd August 1906, it is estimated that about 5 inches of rain fell in
three hours at Moel Hebog in North Wales. In 1887, 2-24 inches
fell in forty minutes at Lednathie, Forfarshire. Much heavier falls
certainly occur in what are called " cloud bursts " in the western
states of North America.

Even more important, however, than the actual amount of
rain which falls at any one spot, is the area over which the torrential
fall is distributed, for this has of course a great influence on the
amount of flooding produced. Thus during a historic flood at
Pennsylvania in 1889, it was estimated that a fall of 8 inches
occurred during three days over an area of 12,000 square miles, with
a smaller fall over a larger area. In England, on 28th and 29th June
1906, i| inches of rain fell over the very large area of 24,000 square
miles, comprising nearly the whole of the southern part of the

30 THE BOOK OF NATURE STUDY

country. The above are given merely as examples which the
teacher may find useful in giving lessons on heavy rainfall ; many
other similar cases will be found detailed in the books of reference
given at the end of this article.

While speaking of the effects of excessive rainfall the teacher
will of course again draw attention to its effects on human life.
Floods destroy life and property ; they interfere with traffic, and
so check the free exchange of commodities, thus leading to indirect
losses ; their effect on agriculture is always injurious — seeds or
young plants may be washed out of the ground ; large amounts of
fertile, well-manured soil are swept into the rivers and thus totally
lost ; ripe or ripening crops may be rendered useless, as was the
case during the continuous wet of the autumn of 1907, when the
cut corn was actually washed from the fields into the rivers.
Again, as a summer thunderstorm will show well, a torrential rain
of short duration produces a smaller beneficial effect on growing
crops than a gentle long-continued fall. This should be em-
phasised by drawing attention to the rapid drying of the roads
after a thunder-shower, and the almost immediate swelling of the
streams, showing that much of the water is running off the land at
once. Explain that Great Britain is remarkable for the high
average yield of the land, and show that one factor in this pro-
ductiveness is the uniform distribution of the rainfall through the
year, and the rarity of heavy falls ; but again, this deduction
should come after, and not before, actual observations have been
made.

CHAPTER III
THE RELATION BETWEEN PRECIPITATION AND VEGETATION

DROUGHT AND DESERTS. — From the consideration of heavy
rainfalls one would pass next to that of drought, and this again
requires to be treated in some detail, for the condition is so foreign
to our experience that the realisation of its importance over the
greater part of the globe is excessively difficult for the child. The
author has repeatedly found that even students capable of giving
clear and precise accounts of the geography of, for instance, the
Sahara desert, will every now and then show by some casual
phrase that they find it impossible to realise the meaning in daily
life of rainlessness.

Drought is so important a subject, if any real progress is to be
made with geography later, that many methods of approach may
be profitably tried. For example, we water the school garden in
summer-time, but does the farmer water his fields ? The very
suggestion will probably raise a smile, so foreign is it to our
experience. Why does he not water his fields ? Two answers
would probably be forthcoming — because it costs too much, and
because generally it is not necessary, there is rain enough. Does
he never lose money then because his crops do not get sufficient
rain ? If the school is one in a country district, or where the chil-
dren have knowledge of country conditions, one may get at such
facts as that where the climate is relatively dry, as in the east of ,
England, the farmer grows a large amount of wheat which does not
need much summer rain ; that where it is wet he grows crops like
turnips or grass which need more rain ; that, our climate being
somewhat uncertain over the greater part of the agricultural regions,
he discounts the possibility of drought by a variety of crops. If
his wheat fail because of excessive rain he has still his root crops,
which have been favoured by the wet summer. If the summer
has been exceptionally dry his grain crops will at least in part

32 THE BOOK OF NATURE STUDY

compensate for his loss on root crops and hay. It is very important
to correlate the variety of crops which country children see around
them with the peculiarities of our climate. The economic geographer
will no doubt say that the fact that England and the lowlands
of Scotland are characteristically " polycultural " is due to more
than one cause, but climate is certainly one of these, and one that
is worth emphasising.

Our climate is very variable, but the variations are small, and
it is possible to discount the minor climatic variations by a judicious
variety of crops. In the general case the risk of prolonged, severe
drought is too small to make it necessary to arrange any method
of bringing water to the crops. With this condition one would
naturally compare others. In the Great Plains of North America
as one travels westward one approaches a region where the rainfall
is just sufficient for crops in normal seasons. From a variety of
causes the cultivated crops are limited, wheat largely predominat-
ing ; in other words the district is largely " monocultural." If a
series of seasons with good rainfall occur, more and more land is put
down to wheat. A series of dry seasons may then occur, and as
the farmer has no other crops to fall back upon total ruin may
result. If a farmer only grows wheat ; if he knows that every
now and again there will come years of prolonged drought ; if in
those years the rain that does fall comes in heavy drenching
downpours, when the water runs off his land before the poor
plants have received much benefit, what would the members of
the class suggest doing ? In some such way one might lead up to
the question of irrigation, obtaining from the class examples of
countries where it is practised. Conversely, show them that if we
know that irrigation is practised in such and such a country, from
this very fact we may deduce a good deal as to the climate of the
country.

RAINFALL AND VEGETATION. — From such conceptions we
want to travel farther in order to investigate the problem as
to the effect of drought, occasional or continued, on vegetation. If
no rain falls for some time and water is not supplied artificially
what becomes of the plants ? Neglected lawns may often be
found to help us to answer this question. Careful persons water

PRECIPITATION AND VEGETATION 33

their lawns in dry weather, and so keep them permanently green
and fresh. If they are not watered and the summer is a dry
one, the grass soon gets brown and withered. As it withers
the earth bakes hard or becomes converted into dust. Watch
such a lawn, especially if placed on a slope, during a thunder-
storm. The rain may not penetrate the baked earth at all,
but simply run off its surface, leaving great furrows as it runs.
At the same time note the contrast between the effect of heavy
rain on a surface covered by vegetation and one which is from
any cause devoid of a plant covering. The latter is worn into
channels and gutters much more readily, the soil is quickly washed
away. On the other hand, soil completely covered with vegetation
is not nearly so readily washed away. We thus see that the plant-
covering has a protective effect.

During dry weather also, observations should be made in the
school garden or elsewhere, to show the depth to which the drying
of the soil extends. That the surface layers of the soil may be
quite dry while the deeper layers are moist ; that shallow-rooted
plants flag more quickly in drought than deep-rooted ones ; that
a number of plants growing together, as plants usually do in
nature, suffer less from drought than solitary plants in a garden
border — such facts as these may be obtained from actual observa-
tion, and have an important bearing on the question of drought.
Similarly, the fact that while we may let our window-boxes get
very dry in cold or frosty weather without harming the plants, yet
they flag at once if we allow the soil to get very dry in summer,
is of importance in considering the connection between rainfall
and vegetation.

Once again, the teacher should try to find local examples
showing how greatly soils differ in their power of holding water.
Over a great part of our country the frequency of boulder clay
as the sub-soil enables us to show how a clay soil holds water.
With this should be contrasted the lighter, sandier soils, which
dry with great rapidity. If the school is near the seashore,
and this shore affords examples of sand dunes, much may be learnt
in regard to desert conditions from a well-planned excursion.
Just as in studying the distribution of temperature over the
surface of the globe much additional interest may be roused by

VOL. VI. — 3

34 THE BOOK OF NATURE STUDY

a real or imaginary mountain ascent, so an excursion to the
shore, elevated in imagination to a desert journey, will yield much
that is of value. Almost all the essential points in regard to
desert conditions are illustrated on many parts of our own coast-
line.

One would, of course, point out that although the same rain
falls on the shore as on the green fields or woods inland, yet the
fact that the sand is excessively porous produces a condition
of drought analogous to that which obtains in the Sahara or
many parts of America where the rainfall is very scanty. Let
the members of the class examine the fleshy-leaved sand spurrey
and other shore plants, noting the long roots which these send down
into the shifting sand in search of water. While they are looking
at these speak to them of the great cactuses of the American
deserts, and let them reconstruct that desert in imagination.
Show them the creeping sand-reed (Ammophila arundinacea)
with its curled-in leaves, and explain how it binds the sand and
makes a beginning of vegetable mould of which other plants are
quick to take advantage. Show them how as we pass inwards
from the shore the sand loses its golden colour, becomes darker
and more soil-like, and that as it becomes soil-like more and
more different kinds of plants can grow upon it. Explain
that the dark matter in the sandy soil (humus) has the power
of holding water, and that where it is present at the surface
the water does not run through as it does through the pure sand.
To make a desert sandhill a grassy field, then, we want first to
stop the sand shifting with the wind, and this is done in nature
by plants with creeping rootstocks. Second, we want to add
some water-holding substance to the soil, to prevent the abundant
rainfall from running through the sand. This is done in nature
by the first hardy plants that get a foot-hold on the sand, which
by their dying leaves, by the small plants that accumulate round
their roots, add vegetable matter to the sterile sand. If these
two conditions can be fulfilled, and there is no excessive amount
of salt in the sand, the dune gradually passes into fertile land.
But this is because in our country there is abundant rainfall,
and with the help of that rainfall the sand-reed conquers the sand
from the ocean, to be conquered in its turn by the other plants which

PRECIPITATION AND VEGETATION 35

oust it from the land it has reclaimed. But in many inland
regions over the world we find great sterile tracts of sand, because
there there is not the rain which is the essential preliminary
condition for vegetation — that is, no constant gentle rainfall
throughout the growing season. In many such regions, if water
can be supplied by irrigation, the process of reclamation is easy
—of this the geography book will furnish many examples.

Our previous observations have, however, shown us that it is
a continuous supply of water through the growing season which
is necessary for plant-life — occasional torrential showers will do
no good. In some such way we might lead on from the general
subject of deserts to the very interesting conditions which pre-
vail in the " Badlands " of parts of the United States. Here the
rainfall is too small to permit the formation of a continuous cover-
ing of vegetation, but nevertheless there is a not inconsiderable
precipitation which comes mostly in heavy falls of short duration.
The result of these falls on a surface deprived of any protective
covering of vegetation is that the land is carved into extraordinary
forms, like those shown in the illustration. The case is interest-
ing in that it shows that erosion by rain may be actually greater
in a region of limited rainfall than in one of considerable fall,
because the conditions in the former do not permit of a continuous
covering of protective vegetation.

On a much smaller scale the same phenomenon is illustrated
by the increased rapidity of erosion produced in a country by
the destruction of the forests and the draining of marshes. There
is little doubt, for instance, that formerly much of England and
parts of the lowlands of Scotland were covered by marshes.
The effect of these marshes was to hold up the water — as
may be well seen on an excursion to a moor, where the effect
of the moss Sphagnum should be especially pointed out. The
holding up of the water meant a slower and more equable flow-
ing of the streams. The disappearance of the marshes means
that the water reaches the sea more quickly, and it has therefore
greater carrying power. This is well seen in the case of the
Forth, for instance, which appears to be becoming yearly muddier,
that is, has had its power of erosion and transportation increased
by the draining of the country through which it flows.

36 THE BOOK OF NATURE STUDY

The effect of the destruction of the forests in promoting
erosion is not easily illustrated in this country, where the forests
have been so thoroughly destroyed. The teacher who travels
to the Alps in the summer may often see beautiful examples
of the destruction of mountain pasturages by the cutting down
of the trees, though the danger is there being increasingly
recognised.

In the United States the matter is also attracting attention,
and we give an illustration showing the extraordinarily rapid
erosion which follows the cutting down of trees on a mountain
slope. The point to be illustrated is that an adequate supply
of rain is necessary for the establishment of a continuous
covering of vegetation over any area. Once established, this
vegetation increases the fertility of the soil in which it grows by
the addition to the original sand or rock debris of vegetable mould.
If from any cause, however, natural or artificial, this covering
of vegetation be destroyed, then the very rainfall which per-
mitted the establishment of the vegetation may destroy in a
limited period of time the work of ages. If the rainfall is not
of the type which permits of a complete covering of vegetation,
that is, if it is absolutely deficient in amount, if it comes at the
wrong season, or if it comes in torrential downpours of brief
duration, then the waste of the surface takes place with a rapidity
which is unknown in lands where the rainfall is of a different
type.

The significance of the various types of rainfall in relation
both to vegetation and to human activities may, however, be
illustrated by other methods. For instance, if the school course
includes the study of living plants, and if the school excursions
include a study of plant formations as they occur in nature, it is
easy to show that our native plants, with few exceptions, are
not of the water-economising type (xerophytes) . In the summer-
time we may also show that their foliage is such as to allow of
the escape into the air of a great amount of water vapour,
and as indications of drought on any considerable scale among
plants growing under natural conditions are rare, it is obvious
that water is being abundantly supplied to their roots. Again,
we can show that the fall of the leaves in autumn no less than

Tularosa Desert, New Mexico. Note the general resemblance to sand-dunes in this country

" Badlands " of Nebraska, showing the effect of rain on a surface unprotected by vegetation.

Snow scene. Note the much greater weight of snow borne by the evergreens
than by the deciduous trees.

(Photo tf/Reigate Parish Church, by FRITH.)

PRECIPITATION AND VEGETATION 37

the dying down of herbaceous plants is due to the fact that the
temperature in autumn and winter is low.

The botanist would doubtless consider that this statement lacks
the accuracy which comes from a full physiological treatment,
but from our standpoint the essence of the matter is that in our
climate the vegetative rhythm is determined by temperature, and
not by seasonal differences in amount of moisture. But in winter,
when outside all is bleak and bare, our rooms are gay with bulbous
plants, which in the summer of our warm rooms or greenhouses
will flower luxuriantly in the midst of snow. Now, as we all
know, the activity of these winter-flowering bulbs is of very short
duration : they flower, they ripen their bulbs, as the gardeners
say, and they die down. But it is clear that the Freesia or Ixia,
or the more familiar hyacinth, which sleeps throughout our
summer, has not its life rhythm punctuated by changes of tem-
perature as most of our native plants have. Such bulbs actually
pass the warmest part of our year in the resting condition. How
can we explain this anomaly ? If we try to find out in what
countries the greatest numbers of bulbous plants occur naturally, we
find that they occur specially in the Mediterranean region,
in South Africa, in Southern California, and so on, that is, in
countries where the rain only falls in the winter season.

Take the Mediterranean region as nearest to us. Here there
is no temperature check to vegetation as with us ; generally speak-
ing there is warmth enough for vegetative activity throughout
the year. But in the summer-time, when the sun is hottest,
there is no rain, therefore the plants are obliged to take advant-
age of the winter rains for their flowering. They rush through
their activities in a very short space of time, and it is water, not
rising temperature, which wakens them. Those of the plants
of the Mediterranean which are not bulbous have usually
small leathery leaves ; they are often prickly ; generally they
show the desert type of structure. We notice from watching
cactuses in the greenhouse or Botanic Garden that again it is
moisture which induces flowering, not a rise of temperature.
This subject might of course be much further elaborated, but
these few hints may be useful to the teacher in planning lessons
on rainfall and vegetation.

38 THE BOOK OF NATURE STUDY

One other point must, however, be touched upon. Man depends
largely upon the vegetable kingdom for his food. Now, as we
all know by experience, other things being equal, plants, within
limits, grow faster the higher the temperature. But the absence
of summer rains in places with the Mediterranean type of rain-
fall checks growth, and thus, without man's intervention, the
part of the year when growth ought to be most rapid is lost. If
man does not intervene, we say ; but in that vast region round
the Mediterranean, where civilisation rose at a very early period,
man learnt to intervene, learnt to supply the water without
which summer crops were impossible. That great Mediterranean
civilisation, the civilisation from which we inherited ours, was
nourished, in the literal sense, from irrigated land. Then, those
great plains in western North America which now feed Europe
lay uncultivated, and the men of the Old World learnt, slowly
and painfully, the skill, the ingenuity, the foresight, which make
irrigation on a considerable scale possible. The races which have
received their inspiration from that old Mediterranean stock,
have carried on the same tradition, and are noted now for their
engineering skill, the skill which has enabled them to bring the
wheat of the New World to the Old by methods which make
the cost of transport inconsiderable. Various interesting points
in this connection will be found discussed in Mr. Chisholm's pre-
face to The Atlas of the World's Commerce, and in the same author's
Commercial Geography. We need only notice here in passing the
contrasting conditions which occur in the monsoon regions of
the Far East. Here again the rainfall is seasonal, as contrasted
with our uniform type ; but the rainy season is the warm season,
so that the plants find the two necessary conditions — warmth and
moisture — co-existing. The result is that over much of the
area agriculture is a comparatively simple matter, and thus food
is relatively easy to obtain, and the population has thus become
enormously dense. In the East, then, another type of civilisation
arose, different from that of the West. Until quite recently, how-
ever, it was conscious of no inferiority, and no inferiority probably
existed, until the enormous development of machinery and methods
of mechanical transport occurred in the West. It is not perhaps
too fanciful to see in the absence of this development in the East

PRECIPITATION AND VEGETATION 39

a result of the easier victory over nature in the monsoon regions,
which did not produce the same type of ingenuity as was necessi-
tated in the West. That the East has been obliged in these later
days to come and learn humbly from the West, is perhaps then a
consequence of the original difference in the type of rainfall in the
two regions.

This may seem to be a far cry from the study of the local rain-
fall, but the object of its insertion is to emphasise once again
that in a Nature Study course the study of rainfall as rainfall,
as it appears to the meteorologist, is wholly out of place. If the
course is to have any logical coherence at all, the study of any
one technical problem like rainfall can only find place in so far as it
means the study of correlations. The fact that half an inch of
rain fell yesterday is only of interest at the Nature Study stage,
in that we may use it as a basis for a reasoned consideration of
the action and reaction of man and his environment. Without
this, and in the necessary absence of the previous knowledge which
makes it of importance to the meteorologist, it is a fact of no
importance whatever to the child.

CHAPTER IV
SNOW AND ICE

DURING the winter season opportunities should be taken
to make observations on snow. Snowstorms are relatively
infrequent in our area. In other words, they do not occur so
frequently that they cease to interest the child, and with the
help of this interest much can be learnt from them. The snow
should be measured, in some open locality where there has
been no drifting, by means of a stick. That in the rain gauge
should also be melted to show the relative great bulk of snow.
The simplest way of doing this is to add to the snow in a vessel
a measured amount of warm water. When this has caused
melting, the whole should be measured, and the amount of water
added subtracted.

The actual amount of water produced varies greatly with the
type of snow, whether it be light and powdery or dense, but a very
ordinary rough estimate is that one foot of snow makes an inch of
rain. The meaning of this should be emphasised by the help
of actual experiments on different occasions. Careful observa-
tion should also be directed to showing that in this country no
great depth of snow falls, the occasional blocking of roads and rail-
ways being always due to drifting, and not to the actual snowfall.
When the snow is especially light and powdery, the opportunity
should be taken to show, with the help of a lens, the beautiful
crystalline forms which it takes. A calm day must be chosen
for this observation, as on windy days the crystals become matted
together, and are broken and irregular. Further, as each shower
of snow usually only produces one type of snow crystals, the ob-
servations should be repeated frequently, to give an idea of the
number of types which exist. An attempt should be made to show
that the crystals are built up of tiny filaments of ice, and are of
all degrees of complexity. At the same time, attention should

SNOW AND ICE 41

be drawn to other examples of ice crystals, to those in hoar
frost, to the ice needles which form on the pavement, and especi-
ally to the beautiful patterns to be seen on window panes, these
patterns being again due to the tendency of ice to form six-sided
crystals. Show also the needles appearing on ponds as these begin
to freeze, and their subsequent disappearance as the complete
crust of ice forms. The subject may be further illustrated by
dissolving common salt or washing soda in water, and allowing
the solution to slowly evaporate on a plate in the warm room.

As snowstorms are relatively infrequent in our normal winters,
there is no difficulty in obtaining an exact measurement of the
amount of snow which falls throughout the winter period. That
is, the fall on each occasion should be measured, and at the end of
the winter the totals should be added up, and the reckoning of an
inch of rain to a foot of snow used to show how small a part of our
total precipitation falls as snow. In the preliminary lessons the
teacher has already emphasised the fact that Great Britain differs
from many other places in the same or lower latitudes in the absence
of a continuous winter covering of snow. After observations on a
winter's fall have been made, it is a good plan to go back upon this
lesson, and by the help of actual figures point out the contrast
between our conditions and those which prevail elsewhere.

Thus in the New England States generally the average snow-
fall ranges from 4 to 7 feet. On the southern shore of Lake
Superior the winter fall is nearly n feet, while at the point
where the Central Pacific Railway crosses the Sierra Nevada the
winter fall is 30 feet. Seizing some striking figures of this kind
one would in imagination lead the class northward to the region
where all precipitation takes the form of snow, and southward
where it never occurs, striving always to make the facts real by
dwelling on the human side of the facts. Thus the disorganisation
of traffic which often follows a sudden heavy snowfall in this country
should be compared with the conditions which prevail in countries
where a heavy fall is normal, and therefore discounted in advance.
The class should, of course, be encouraged to observe for themselves
such facts as whether snowploughs are or are not familiar objects
in the neighbourhood, for this has an important bearing on the
local climate.. If the whole question of transportation considered

42 THE BOOK OF NATURE STUDY

in relation to the presence or absence of a continuous winter
covering of snow is geographical rather than one for a Nature Study
course pure and simple, yet a great many suggestive points can
be touched upon which will clear the way for the teacher of geo-
graphy later. That while in this country a winter snowstorm of
considerable dimensions impedes transport in every direction, in
the Far North of America the winter is the only time when trans-
port can be carried on with any ease, is, for instance, a point very
well worth emphasising in the course of a lesson on snow.

One would also point out that the locking up of so large an
amount of water in the form of snow means a winter dryness in
many countries very foreign to our experience, while the possibility
of the sudden melting of a large bulk of snow means a liability to
a type of spring flood from which we are as a rule immune here.
Again, in southern and central Florida snow does not fall, and a
wholly exceptional snowstorm recorded in 1774 was described by
the inhabitants as " an extraordinary white rain/' The interest
of the class in atmospheric phenomena will be greatly increased
if the attempt is made in these ways always to attack the subject
first from the human side — in their relation to human beings like
themselves. It is very important to bear constantly in mind that
the abstract " scientific " standpoint is late in development, both
in the case of the individual and of the race. Unless it be rigor-
ously excluded from the earlier stages of the Nature Study
course, no progress from the educational point of view can be
hoped for.

In connection with individual storms, in addition to measur-
ing the amount of water yielded by a given amount of snow at the
time of its first fall, the same observation should be repeated
in the days that follow, as the snow becomes increasingly dense.
A snow ball or the snow man in the playground should be used to
show further how the air which fills the interstices of the snow
can be squeezed out, so as to bring the particles of ice nearer
and nearer together. A heap of snow should also be watered at
night while the frost lasts, and the deeper layers carefully
examined to show how they become more and more ice-like.
At the same time we note that while at the bottom of drifts, and
especially if there is alternation of frost and thaw, the snow

SNOW AND ICE 43

becomes more and more ice-like, on the house roofs, where the
slope is steep, the powdery snow sweeps down in an avalanche.

But our snow does not last long. We soon see it disappear,
except for isolated patches in sheltered situations. As it melts
we note that the most effective melting agent is warm rain. We
compare this with our own observations in the case of the rain
gauge, where we found that the quickest method of turning snow
into water was to add to it a small quantity of warm water.
Knowing as we already do that the air on hills is colder than in the
valleys, we are not surprised to see the snow linger there when it has
disappeared below. If the locality gives a view of distant hills of
some size, we shall see them still covered with a spotless mantle
while the ground near us has returned to its brown tint.

As a general rule in Britain, at least near the populous parts,
the hills are of soft and rounded contours, and are, therefore, in
winter snowstorms more or less continuously shrouded in white.
They are never very high, and with some exceptions their covering
of snow is of relatively short duration. But in some countries
the hills are very much higher and much rockier. Some countries
also are much colder than ours. While the country is under the
influence of a snowstorm, we should then take the opportunity of
speaking of other countries where the snow is permanent, either
on the high hills only, or right down to the low ground. What
happens to snow when it lies for a long time ? We have already
in the playground made observations which help us to answer this
question. If it falls on a steep slope, as the layer gets thicker, and
as the sun comes out when the snowfall ceases, the whole covering
starts to move, and rushes down the slope with increasing force as
an avalanche. We have not only watched this happening on roofs,
but we have noticed that when greenhouses are placed against a
house there is always some arrangement to obviate the risk of such
an avalanche crashing into the glass roof.

But if snow lies long on a surface which is not very steep, what
happens ? As it lies it freezes and thaws, it has the air squeezed
out of it by the weight of the upper layers, it becomes more and
more ice-like, more solid, more firm. Ice is transparent, snow is
pure white, but our observations have shown us that as the air is
squeezed out of snow it becomes more and more transparent,

44 THE BOOK OF NATURE STUDY

more like ice. We suspect, [then, that it is the air in snow that
makes it white, and that if all the air could be squeezed out it would
be transparent like ice. What is snow, then, if not needles of ice
with a great deal of air between the particles ?

Having reached this point, we should show some pictures of
Alpine scenery. The familiar view of the Matterhorn is an excel-
lent one for the purpose. This is a very high hill, so high that
on the top of it the snow never completely melts. But high and
cold as it is we notice that a good deal of it is bare rock, with no
trace of snow. Why is this ? When we look closer we find that
the bare parts are the steep parts, and we suspect that they are
bare, not because snow does not fall there, but because as soon
as it reaches a certain thickness it has no longer the power of
clinging to the steep slope, but begins to glide downwards, moving
faster and faster as it goes, like the snow on a steep roof. When
we look again at the picture, and see how the snow is piled up in the
places where the slope is gentle, we see that this must be so. But
those hollows and gentle slopes must then receive not only their
own snowfall, but also all the accumulations of snow that have slid
off the steep upper slopes. If, at the bottom of a snow drift eight
or ten feet deep, the snow turns into something resembling ice,
what must it be when there are hundreds of feet of snow on top
of it ? It becomes pure solid ice. But this ice and snow never
melt ; they remain there year after year, summer and winter.

We think of our summer excursions to a hill, and we remember
how we saw that the mountain robs the air of the moisture that
that air stole from the sea or the river, and that the use of the
mountain is to give back this moisture to sea and river. But
the snow and ice are just frozen water — is this mountain an excep-
tion, does it never give back to the rivers the water which the air
took from them ? Some of the snow and ice melts, no doubt, in the
hot sun of summer, and so flows downward, but much of it does
not melt at all up on the cold mountain-side. What happens then ?
As the snow is more and more pressed into ice, and as the heaps of
ice and snow get thicker and thicker, the ice begins to creep slowly
downward towards the valley, as a slow-moving river of ice. As
it creeps down and down it loses the cold breath of the mountain,
more and more it feels the warm air of the valley. As it moves,

SNOW AND ICE 45

then, it melts more and more. Little streams form all over its
surface. Warmed by the sun these little streams melt the ice
more and more. They hollow out great cavities in it, and sweep
down into these cavities. Finally, there comes a moment when
the valley conquers the mountain, the ice melts away into a great
river, which pours down the lower slopes of the mountain, in haste
to carry back to the sea the water which has been so long parted
from it. In some such way we might use our observations of a
winter snowstorm to lay the foundations of a conception of glacier
action, which would be further elaborated later by the teacher
of physical geography.

As a contrast with these Alpine conditions, we should on
another occasion consider the special conditions seen in the Arctic
or Antarctic, which are also the conditions which once existed
in our own area.

Thus, after a heavy snowstorm, we might begin a lesson
as follows : —

Once upon a time a great amount of snow fell over Scotland
and part of England. So much snow fell that the sun of
summer never completely melted the snow of winter. At
first only the hills were covered with this permanent mantle,
but gradually it crept down and down, as always more snow
fell than was melted. At last all the land was snow-covered
except just the steep parts of the high mountains, which stuck
like rocks through the great waste of snow. All Scotland
and a great part of England were then much like what Greenland
is now — a great snowfield, with almost no life, but with great
bare rocks sticking out of the snow. In those days, as in the
icy North now, the snow accumulated in the high mountain
valleys was squeezed into ice by the weight of the fresh snow
always falling on the surface, and from those high valleys tongues
of ice began to creep out towards the low ground, just as they
creep down from the Alps now. But in Britain in those days,
just as in the Far North now, as the ice crept slowly down to the
low ground it found very different conditions from those which
exist in the Alps.

In the Alps, though the mountains are cold, the valleys are
very hot. As the ice comes down lower and lower it feels the

46 THE BOOK OF NATURE STUDY

heat of the valley, and begins to melt away, leaving only a great
turbid river, which can be compared to the muddy streams that
we see trickling away from the snow drifts when the thaw comes.
In Britain, in those old days, all the low ground was deadly cold
too. There was nothing then to melt the ice, which pushed its
way downwards to the sea. Those great ice streams probably
pushed their way right out into the sea, just as the great ice
masses in the Antarctic now push their way out into the sea;
just as in the Antarctic at present they probably ended in great
Ice Barriers, huge walls of ice, from which enormous flat-topped
icebergs separated off and floated away.

In the north at the present time the ice behaves a little differ-
ently. Here we have smaller tongues of ice, true glaciers, which
push their way towards the sea, and as they enter it irregular
masses break off, the icebergs of the north, which float away
southwards with the currents.

Some such picture as this we might present, just suggesting
at the same time the different ways in which we recognise the
old work of ice in the existing features of our country.

Many other observations on ice and the work of frost may
also be made, for it should be remembered that while on the
one hand it is difficult to make the conditions existing at other
parts of the earth's surface real to the child unless attention
has been deliberately drawn to the home conditions, on the
other hand it is equally true that once the imagination has been
stimulated by interesting accounts of different conditions, the
home conditions will be studied with renewed zest. We have
spoken, then, of the huge flat-topped icebergs which break off
from the great Ice Barrier in the Antarctic Ocean, we have spoken
also of the smaller, more irregular forms found in the north. We
have shown for what great distances these ice-masses may float
before they are finally conquered by the warm water as they
reach the hotter parts of the ocean. The ice on the rain-water
barrel or in the pond may next be used to make mimic icebergs,
to answer the question why icebergs float. We have reconstructed
in imagination the playground with its little heaps of snow as
Greenland or as Britain in the Ice Age. We have imagined
that from those snow heaps glaciers were slowly creeping out,

Lower end of the Upper Grindelwald Glacier, showing the ice-cave from which

the stream arises.

(Photo by WEHRLI, Zurich.)

SNOW AND ICE 47

find their way out into the cold sea. We have realised that
the sea is too cold to melt the ice, which is carried away by
:urrents to lower latitudes, and bears with it the waste of the
tnd of its birth.

With the help of some broken pieces of ice we have made
;ebergs in a pond or in an open dish. Our mimic icebergs have
lown us that though ice floats it floats with a great part of its
>ulk submerged. Using either the rain-water barrel, or a big
dish of water, and pieces of ice of various shapes, we have tried
to find out how much of the ice is above and how much below
water. By repeated experiments we succeed in showing that
about one-tenth is above water, and nine-tenths below water.
When the frozen pond melts, we watch the great pieces of ice
floating on the surface, and again we notice how much bigger
each piece really is than it appears to be as it lies in the
water.

But we remember that real icebergs float not in ponds but
in the sea, and we resolve to investigate the question whether ice
floats in sea water in the same fashion. If sea water is available
the experiment may be made direct. If not, it may be imitated
by adding common salt to water in the proportion of three and
a half parts by weight to one hundred parts of water. The
result is of course not sea water, which contains other salts as
well as common salt, but it is a near enough imitation for the
purpose. It will be found that the ice will not sink so far in the
water containing salt as in fresh water. If possible the same piece
of ice should be used for the two experiments, which should be
carried out under similar conditions. In the denser salt-containing
water about one-ninth of the volume of the ice will rise above
the surface, while eight-ninths are sunk below the surface. After
such an experiment a picture of an iceberg teaches us more
than it did at first, for we know now that, in addition to the ice
exposed at the surface, there is a much greater bulk below the
water.

The next point to consider is in regard to the melting of the
ice. We think of the icebergs from, for example, the Arctic
Ocean, which are carried down past Newfoundland by the cold
Labrador current. But as these icebergs pass southward they

48 THE BOOK OF NATURE STUDY

come gradually into regions where the water becomes warmer
and warmer. Let us take a dish of warm water and put one
of our miniature icebergs into it, choosing one of irregular shape,
to imitate as far as possible a natural form. If the experiment
is carried out in a glass vessel we shall see the base of the ice-
berg gradually diminish, as its substance is as it were eaten away
by the action of the warm water. Sooner or later probably
the little berg will topple over as it becomes too heavy for its
base. When this has been noticed in the mimic berg, descrip-
tions may be given of the crashing of the real bergs as their lower
submerged portions melt, and they reel over with a tremendous
splash.

Again, we notice as the ice melts how it chills the water,
chills also the air, and how, if there be much ice in proportion
to the water, there probably forms on the outer side of the glass
a misty vapour. One would then repeat what has been already
said as to the effect of cooling the air, and at the same time speak
of the dense mists which occur in the vicinity of icebergs, or where
a current of water cooled by melting ice reaches a region where
the air is comparatively warm. We may also read a passage from
Rudyard Kipling's Captains Courageous to emphasise the danger
to navigation which results. In this way one would pass to
explanations of fog and mist, showing by examples that as the
air above water is always full of water vapour, any chilling down
of it tends to produce fog or mist. The mist which forms in river
valleys on calm evenings helps to illustrate the same fact.

Again, if ice floats in water it is because it is lighter than
water. The question at once arises — how much lighter ? Let
us put into our measuring-glass a certain amount of warm water,
and drop into it a piece of ice. The teacher should find by ex-
periment beforehand the necessary size to cause the water to
rise to a convenient height. The ice of course floats, but nine-
tenths of its bulk is submerged, and this causes the water in the
glass to rise through a certain distance. We allow the ice to
melt, and find that the water stands at the same level as it did
when the ice was floating in it. An attempt should be made
to show that this means that when ice melts the resultant water
represents only about nine-tenths of the bulk of the ice, or in

SNOW AND ICE 49

other words that in becoming ice water undergoes a consider-
able expansion of bulk, and that there is a corresponding
diminution when ice becomes water.

A more striking way of demonstrating the same thing is by
allowing water to freeze in a jampot, to show how the expansion
splits the pot. If desired this experiment can of course be
performed in the schoolroom, when the potful of water should
be surrounded with a freezing mixture made of snow and salt. A
small flask from the chemical laboratory will show the expansion
well, but in some respects the jampot experiment is preferable.

The connection of the expansion of water with the domestic
phenomenon of burst pipes will of course be discussed, and the
action of the frost on the ground noticed. The occurrence of
frost without snow should be utilised to show the effect on the soil
of the expansion of water in becoming ice.

Something has been already said about hoar frost, but more
detailed observations may be usefully made. Notice that hoar
frost does not occur when the temperature is very low, hence
the common distinction between hoar and black frosts. In
the autumn dew formation will have been noticed. By the help
of our thermometer we show that, especially when the sky is clear
and the air calm, the ground becomes rapidly colder after sun-
down. The result of the rapid loss, under the conditions named,
is that the air is chilled down below the point where it can hold
its load of vapour, and drops of moisture appear on the ground.
The appearance of a light mist close to the surface is of course
a phenomenon of precisely the same nature. If the chilling is
excessive the dew may freeze as it forms, producing the phenom-
enon of hoar frost. •

Though any extensive observations either on hoar frost or
on dew formation are not likely to be carried out with children,
yet an attempt should be made to show that both dew and hoar
frost are more noticeable on vegetation than on ground denuded
of vegetation, the vegetation parting with its heat more readily
than stones or dry ground, and also giving off moisture which
assists in the formation of dew.

More feasible than detailed observations on dew formation
are those on methods of protecting from frost. On evenings when
VOL. vi. — 4

50 THE BOOK OF NATURE STUDY

frost may be expected, a light covering should be put upon
cherished plants in the garden, to show that by stopping radia-
tion this protects against frost.

In a region of market gardens also observations should be
encouraged on the extent to which gardens at different levels
are attacked by frost. Sometimes in the same garden it will
be found that the lower branches of a blossoming tree are black-
ened while the upper ones are untouched, this showing that the
chilling of the air is due to loss of heat by the ground, and is
greatest near the ground. Again, as a general rule the gardens
which lie at the bottom of a valley suffer more from frost than
those on the slope above, this being partly due to the tendency
cold air has to accumulate at the bottom of valleys in calm
weather. The upland gardens, on the other hand, feel of course
the effect of strong and cold winds much more than those on
a lower level.

In a good many of the examples mentioned above, care
should be taken not to force an explanation on the child before
the need for one is felt, but the facts should be borne in mind
by the teacher, because they suggest directions in which observa-
tions may be made.

CHAPTER V

THE SKY — SUNSETS — CLOUDS — THUNDERSTORMS

THE SKY. — In addition to simple observations on meteorology
the attention should be directed at an early date to the apparent
movements of the sun, to the alternation of day and night, to
the rhythm of the seasons, and to the correlated phenomena.

If, as has been suggested, the more striking points in regard
to the atmosphere are studied during school excursions, it will
be natural at the same time to direct attention to the great
vault of the sky. To country children this great vault is of
course familiar from the first, but the attention of town-bred
children should be specially directed to it. They should be
made to notice that whenever we have a clear view the horizon
is circular, and that where a portion only is visible this forms
a part of a circle. If the ascent of a hill forms one school ex-
cursion, as from many centres it may conveniently do, emphasise
especially the fact that our view increases in extent as we ascend,
the horizon always keeping its circular form. Take advantage
of short halts for rests to take special note of the approximate
rise since the last halt, and simultaneously of the extent to which
the view has increased. Make the class note roughly, by the aid
of the Ordnance map, which should always be carried on the
excursions, the approximate range of the view in miles at differ-
ent points. This is a very important matter, and one which is
too much neglected. For the teacher's benefit it may be noted
that the distance to which the view should theoretically extend,
allowing for the rotundity of the earth, can be readily calculated.
The accompanying diagram illustrates the principle of the cal-
culation. Let a semi-circle be drawn to represent a section of
the earth. Let A and B represent points on a mountain on the
surface. Lines drawn from these points to touch the surface
of the semi-circle define the limits of the horizon in the two cases,

THE BOOK OF NATURE STUDY

and show that the view from A, the lower point, is necessarily

less extensive than that from B, the higher.

To calculate the radius of the circle of the horizon proceed as

follows (Fig. i). Let P
be the point where the
line of vision drawn
from A touches the sur-
face, and let C be the
centre of the earth.
Join CA and CP. Now
the angle at P being a
right angle, by Euclid
I. 47, AP2 = AC2-CP2,
or calling the earth's
radius r, the height of
the mountain a, and

the required distance ocy we have —

therefore xz = a (zr+a). Taking the earth's radius as roughly
3975 miles, it will be found that a hill 800 feet high should
give theoretically a range of view of about 34 miles in every
direction. The actual view will depend upon the day, the
amount of haze present, and so forth.

While the class is engaged in these observations, the colour
of the sky will naturally come in for study. If the day is fine,
and such a day would naturally so far as possible be chosen, we
should note the clear blue of the sky overhead. We should
also notice that this blue fades towards the horizon, where
the sky becomes whitish. The opportunity might also be taken
for some incidental observations on the meaning of certain
terms. Standing on the summit of a hill we should naturally
notice that if a line were supposed to be prolonged indefinitely
above our heads to reach the sky, this line would pierce the centre
of the great vault. This would be a useful opportunity to ex-
plain the meaning of the term zenith. Such little remarks as that
wherever we stand we are beneath the centre of the arch of
heaven, are then worth making. To attempt to explain the

THE SKY 53

full significance of this from the philosophical standpoint would
be absurd, but children are interested in little puzzles of this
kind. If, as a philosopher has said, even .a little dog is for him-
self the centre of the universe, there seems no reason why we
should not point out the fact in a Nature Study course.

While speaking of the zenith, bring out the fact that no
member of the class has ever seen the sun in the zenith. If the
day is sunny and the shadows of the party clear as they stand
on the summit, bring out also the fact that because the sun is
never exactly overhead there is no time of the year when we have
no shadows. Prescott's statement about Quito (" Quito lay
immediately under the equator, where the rays of the sun threw
no shadow at noon ") may be repeated, and without stopping
to discuss in detail its accuracy, we may bring out that at least
at times at the equator there is no noon shadow, because the sun
is in the zenith.

Returning to the visible sun, we may by reference to it bring
out the meaning of the term altitude ; perhaps, even by suggest-
ing that it is always in the zenith somewhere, we may think
out the meaning of declination. Quite a number of other simple
points may similarly be considered in an informal fashion, and
will clear the way for the teacher of geography afterwards.

If the excursion be taken in the afternoon the sinking sun
as we turn homeward may well be used to bring out the difference
between day and night as regards warmth and light ; the contrast
of a summer day and a winter one may similarly be used to
suggest that the sun's rays are warmer the more nearly direct
they are, and less warm the more they slope.

Among other points which should be studied during excursions
are the colours of the sunset sky, the rainbow and its relation to
rain, and especially to thunder showers, and the forms and
characters of clouds. All these subjects involve, however, con-
siderable detail ; they require both to be studied out of door
whenever occasion permits, and also indoors, when the observa-
tions and deductions made out of doors may be summed up and
conclusions drawn.

SUNSETS. — As opportunities for observing sunsets during

54 THE BOOK OF NATURE STUDY

school hours must necessarily be limited, such observations may
well be prescribed to be done as home work. When this is done
the children should be instructed to observe and note down the
sequence of colours, the time of persistence of the colours after
the disappearance of the sun, the occurrence of colour in the
eastern as well as in the western sky, and also to make rough
calculations, so far as they can, of the area of the sky over which
the sunset colours extend. As the whole series of phenomena
which accompanies the setting of the sun is only rarely observ-
able on the same evening, a considerable number of observations
should be made. The connection between very fine sunsets and
clear summer weather, the absence of the beautiful colouring
when the sky is heavy with clouds, and the reddish appearance
of the sun during periods of evening and morning mist, should
all be noticed. If opportunity offers the sunrise appearances,
which are generally parallel with those of the sunset, should also
be noticed.

Before, however, the special peculiarities of the sunset sky
can be appreciated, attention must be carefully drawn to the
appearances seen when the sun is high. By repeated observations
make it clear that the purity of the blue of the unclouded sky
varies with the amount of moisture in the air, that is with the
" fineness " of the weather. More than this, the purity of the
blue varies with the degree of elevation of the sun. As it sinks
towards evening the sky grows paler ; it is much paler also at
the dawn than in the blaze of noonday. Similarly, our winter
skies never have the bright blue of summer ; at no period do
our skies have the brilliant colouring of more southerly latitudes.
By comparing days when the air is loaded with moisture with clear
days, by comparing hours or seasons when the sun is low with
those when it is high in the heavens, try to get the class to see
that the greater the thickness of air traversed, and the more loaded
is that air with solid particles, the greater the absorption of light
and heat, and therefore the paler the sky, until when it is loaded
with clouds the blue darkens to grey or nearly black.

When speaking of the meaning of the term zenith it is easy to
show that the higher up in the sky the sun is the less the thickness
of air that its rays have to traverse. Autumnal anticyclones

THE SKY 55

often afford opportunities for interesting observations. It will
often be found then that during the middle of the day the sun
penetrates easily through the mist-laden atmosphere, and we
have a characteristic pale autumn sky. As it sinks down
towards evening its rays can no longer easily penetrate the
atmosphere, and the evening mist seems to gather early.

If will hardly be possible to explain the optical reason why
the sky during the day varies from blue to grey according to the
amount of solid matter in suspension, but the fact that it does
contain such particles should at least be demonstrated. The
familiar experiment of allowing a beam of sunlight to penetrate
through a hole in the shutter into a dark room should be per-
formed, and the dancing motes pointed out. Explain that air
always contains such dust particles, and that they are less in the
country than in the town, less on high snow mountains than near
dusty roads, but are always present in greater or less amount.
Try to suggest also that this dust is most plentiful in the lower
layers of the atmosphere, in the layers which the slanting rays of
the setting sun must penetrate. It is for this reason that when
lofty mountains are ascended the sky becomes a deeper and a
purer blue, ultimately darkening almost to indigo. Speak also
of the effect of the minute drops of water or even of the minute
crystals of ice which may be suspended in the upper air.

As to the exact phenomena of sunset, the chief points to
be noted are the following. As the sun sinks the variety of
colour increases, but its intensity diminishes. Two sets of
colours appear ; the one, the glow colours, are arranged round
the sun, while the second or horizon colours spread north and
south of the setting sun. The glow colours centre round a point a
little above the sun, which becomes red or yellow as it sinks instead
of the dazzling white of noonday. The glow colours pass from
silvery white through yellow to rosy pink, the last reaching
to about 25 degrees above the sun. Let the pupils hold a
protractor level with the setting sun, and by aid of a ruler
endeavour to calculate the angular extension of the colours. The
horizon colours, when at their fullest development, may extend
to some 60 or 80 degrees from the sun. An attempt should
be made to measure this point also. The horizon colours

56 THE BOOK OF NATURE STUDY

are at first yellow, passing through green into the pale blue sky
above, but, as the sun sinks, the belt becomes narrower and
passes through orange to red. As this fades a pale light remains,
and during summer nights in our latitudes this pale light does
not completely disappear till the dawn twilight comes, so that we
never have complete darkness.

At the same time that the colours appear in the western
horizon, the eastern sky is also affected. Here on clear evenings
what is called the twilight arch appears, this being a low flat arch
of pinkish colour, below which blue sky can be seen.

In a letter written to Renan, the French chemist Berthelot
gives a very beautiful description of a sunset. We quote here in
translation the relevant passages, to show how nearly an actual
sunset may approach to the ideal conditions as outlined above.
The quotation may further serve as a model for similar descrip-
tions to be written by the pupils from their own observations. It
will be noticed that Berthelot, with a skill more frequent in French
than in British scientists, has contrived to give an accurate
description of the sequence of events, while producing at the
same time a beautiful piece of literary composition. In the
translation only passages which relate to the condition of the
sky have been included : —

" From the Place de la Concorde, with its leaping waters, one
saw in the first place in the western sky the fiery red mass surround-
ing the sun, already sunk to the horizon. It was not that this
light owed its beauty to its dazzling brilliancy, but it had an
indescribably soft and rosy tint, which was very soothing to
the eye, and which was reflected in the clouds of the opposite
sky. Here the reflected rosy tint faded gradually away, so mingling
with the natural colour of the clouds as to take on lovely purplish
tones. ... At this moment the sun, now completely beneath the
horizon, illuminated the western sky with a brighter glow. From
the bosom of this fiery expanse there radiated to north and south
four immense horizontal clouds, and the light was reflected to
the most distant points of the eastern clouds. Soon only the
four clouds remained brilliant, like four columns of fire, in the
centre of a white sky, partly masked throughout by a huge
greyish cloud and by the columns of smoke which rose from the

THE SKY 57

city. Soon even they darkened, the darkening spreading out
laterally from the centre, so that a vast semicircle of light only
remained, of parabolic shape. Even this light faded by degrees,
until the sky came to present only a rosy background, more and
more limited in extent, against which the sombre form of the
Arc de Triomphe stood out."

The teacher will not fail to point out that in this description
the three striking phenomena of sunset, the glow, the horizon
colours, and the twilight arch, are expressly mentioned. The
appearance of horizontal clouds (stratus) at sunset is also, as is
explained below, a frequent phenomenon in clear weather.

The facts connected with refraction at sunset, which have as
result the bringing of the sun up to the horizon when it has really
sunk below it, are too difficult to be dealt with in an elementary
course, but it is worth while to deliberately make the attempt to
prove that, owing to the enlargement of the horizon with increase
of altitude, the apparent time of sunset is not precisely the same
at the top of a hill as it is at the bottom. Encourage the
children to prove this for themselves in the holidays. Further,
especially if any members of the class go far north in the summer
season, they may very well try to prove to themselves that
sunset on the same evening becomes later as one travels westward.
In the latitude of Inverness, for example, a degree of longitude has
only a length of about thirty-seven miles. Roughly, then, sunset
is here a minute later for every nine miles to the westward. Two
boys at this distance from each other, and both furnished with
watches, could without great difficulty prove to themselves that
this difference exists, by noting the exact second of disappearance,
and later comparing their watches and results. During a holiday
in the Highlands of Scotland a clear view of the western sky is
easily obtained, and it may quite well happen that members of the
same family, on steamboat or motor-car excursions or in other ways,
may be ten or twelve miles distant from each other at sunset.
Even if the actual experiment cannot be made, it is well to suggest
the possibility of it, for we want above all to get the class to realise
that sunset is an appearance whose time of occurrence depends upon
the observer's elevation above the surface and upon his position on
it. It seems a sound principle to get at this fact so far as possible

58 THE BOOK OF NATURE STUDY

by observation before detailed consideration of the earth's move-
ments is begun.

CLOUDS. — The general principles of cloud formation have been
considered in the previous chapter, but there are many interesting
points connected with their shapes which are worth notice. When
speaking of the dust particles in air, it will be natural to speak
of the probability that clouds consist of minute particles of water,
each one condensed round a more minute dust particle. The
dust is produced from the earth, and has a limited extension upwards
in the air. For this as well as for other reasons we find that clouds
have a limited upward extension, 50,000 feet, or under ten miles,
being probably the highest level at which they occur. In some
such way one might strive to repeat again the lessons of the previous
chapter, to show that the cloud mantle is earth-produced, that
what the earth gives to the air she gets back again.

The same thing can be well studied on a summer's day. Choose
a clear day and let the class note, before they come to school, and
especially if they have been up early, how clear is the morning
sky. As the sun sweeps onward, little flecks of cloud gather in
the sky. At first quite ragged, they soon acquire a heaped-up form.
The under surface of this cloud mass is more or less level, this
edge occurring at about the same height in the different cloud
groups. The upper edge, on the other hand, is billowy and moun-
tainous. The crests of the billows are usually in motion, often
rolling over and disappearing. On fine summer days such clouds
usually reach their maximum about midday, when the sky may be
largely cloud-covered. As afternoon goes on they usually begin
to decrease in amount, and as they decrease they flatten out until
they form long horizontal sheets of cloud, lying low in the heavens,
and often beautifully illuminated by the rays of the sun at sunset.
In fine summer weather this is so frequent a series of events, that
it may be described as typical. After it has been studied on more
than one occasion, it may be found convenient to give the name
of cumulus to the billowy midday clouds, and stratus to the sunset
layers,1 but no special emphasis should be laid on the names.

1 The special name of alto-stratus is sometimes given to these clouds when they are
high in the air.

The Matterhorn from the Ilornli ridge. Note how the snow slides off the steep slopes
and accumulates in the less steep regions.

(Photo by WEHRLI, Zurich.)

An iceberg off Newfoundland. Note the curious shape, due to melting.

MARES TAJ L

CIRRUS

^7000 T. 5o.OQOjt

CIRRO-STRATUS

AVERAGE Z9500 5*

MACKEREL SKY

CIRRO-CUMULUS

10.000 to 23000^t

ALTO-CUMULUS

10,000 to £3000^

ALTO STRATUS

STRATO CUMULUS

ABOUT

CUMULUS

i»500 to 6000 ft

STORM CLOUD.

CUMULONIMBUS

45*00 to 24000 ft

RA IN CLOUD

NIMBUS

3000 ^ S^OO f.

STRATUS

o •><.- 3 5 o c» -

8

F

I

IMALAYAS\I
[IVIT EVEREST]

A l\| DES

[ACONfACUAl

MONT BLANC

IWA1

'ATTERHORN

KITE. BOSTON

A US.

BEN NEVIS

El PEL TOWER;

< PAUL'S

Cloud Forms.

(By permission from " Weather Lore," by R. INWAKDS (Elliot Stock). The Photos -were taken by Col. H. M. SAUXDERS.)

THE SKY 59

Much more profitable than the naming of the cloud types is the
investigation of the invisible phenomena which are accompanying
the visible one of cloud formation. In the early morning when the
sky is clear, the ground will be found to be soaked with dew, all the
plants and shrubs being dripping with it. As the sun's rays grow
stronger the dew disappears. But we have already noticed that
damp clothes, for instance, even in a warm room, do not dry much
unless the window is opened to let the damp air escape. Therefore
we conclude that the layer of air close to the ground must be moving,
even if there seems to be little wind, because otherwise the drying
process could not be continuous. We know that as the sun beats
down it warms this air, which then rises, to be continually replaced by
fresh air. As it rises up into the clear sky with its load of moisture
it cools, until finally, when it reaches a height of somewhere about
4500 to 6000 feet, it has become too cold to hold its moisture any
longer, and this condenses to form a cloud. The fact that on any
given day the level at which this condensation occurs is more or
less constant, explains the flat lower edge of the clouds. When
cloud-formation has reached considerable dimensions, as happens
usually about midday, then the clouds form a partial screen across
the sky, and so diminish evaporation. This checks the rapidity
of the upward movement of the heated air, and thus a condition
of balance may be more or less obtained, so that the clouds largely
dissolve away at sunset.

The actual conditions are of course much more complex than
this would suggest, but this is the essence of the matter. If,
instead of melting away and flattening out towards sunset, the
cumulus clouds become denser and more massed towards evening,
then the atmosphere has received a greater load of moisture than
it can hold, and rain is likely to follow. Over most of Great Britain
it is unlikely that the teacher will have an opportunity of demon-
strating the formation of cumulus round elevated headlands, lofty
hills, rocky islands, and so on, as an ordinary summer phenomenon,
but if exceptionally such local conditions present themselves,
they should be taken full advantage of. If they are not available,
pictures of Alpine summits, or of the "tablecloth" over Table
Mountain at the Cape of Good Hope, will be found useful.

Very different from the low-lying cumulus and stratus clouds

60 THE BOOK OF NATURE STUDY

are those called cirrus, which are very lofty, varying from five to
nearly ten miles in height, and forming the " mare's tails" of
country people. They are popularly supposed to foretell wind,
but this is rather true of the modification called cirro-stratus.
Scattered cirrus clouds after stormy weather indicate generally the
probability of a return to calmer conditions, while the appearance
of cirrus after settled weather may indicate a break. Notes should
be taken of the appearance of these clouds at different times, if
only to show how difficult it is to lay down any certain predic-
tions of weather from the clouds. They will probably be noticed
to be very frequent in spring, especially in windy weather. The
origin of such cirrus clouds has been explained on the supposition
that the difference between the lower air, which is being warmed
by the sun, and the cold upper air is so great that air currents are
produced which extend upwards to a great height. The result is
that the ascending moist air is carried upwards to a great height
also before it reaches a still region where condensation can take
place. In general, cirrus clouds appear to be the final product of
cooling by ascent of moisture-laden air.

Cumulus, stratus, and cirrus are the three main types of clouds.
A considerable number of other types have been recognised, but
their practical significance, at any rate in teaching, is not very
obvious, and there is not as yet entire agreement as to the names
which should be given to the different types. There are occasions,
however, especially in connection with thunderstorms, when it is
of interest to be able to give names to the different types of cloud
seen. The following are the terms most usually employed. Cirro-
cumulus is the name given to clouds consisting of dense roundish
masses forming what is commonly called a " mackerel" sky. Cirro-
cumulus clouds occur in the middle layer of the atmosphere, as
compared with the lofty cirrus and the relatively low cumulus.
In winter the appearance of such a mackerel sky often denotes the
approach of a thaw ; this is a point which may very well be studied.
In warm summer weather cirro-cumulus clouds sometimes appear
after rain, and then mean heat. If, on the other hand, the cloudlets
are thick and show a tendency to aggregation in hot summer
weather, a thunderstorm is likely to follow.

Cirro-stratus clouds occur at considerable altitudes (average

THE SKY 61

29,500 feet), and take the form of thin, horizontal streamers,
with bent or undulated edges. Such cloud sheets may sometimes
be seen in summer forming above the upward limit of the ordinary
cumulus clouds. They are also generally associated with thunder-
storms, and almost always occur on the advancing side of cyclonic
storms. Thus at all seasons the appearance of much cirro-stratus
may be said to presage rain and probably wind. The mingling
of cirro-stratus clouds with cumulus produces the condition
known as cumulo-stratus (or strato-cumulus) . Such cloud masses
often form heavy banks, and then a part of the cloud descends as
rain, forming the so-called nimbus. Cumulo-stratus clouds often
accompany windy weather with some rain ; the appearance of
masses of these clouds indicates a change in the weather. Some
other cloud modifications are recognised by meteorologists, but
it seems only necessary to speak of nimbus, a somewhat indefinite
name, given to any form of cloud from which rain is descending.
Thus a cumulo-stratus cloud from which rain is descending or is
about to descend is called cumulo-nimbus. In its most char-
acteristic form nimbus accompanies thunderstorms, and is then
seen as a dense black or very dark curtain, topped by cumulus,
or some modification of this form, which is in its turn crowned
by some cirrus modification.

THUNDERSTORMS. — As a general rule it is unlikely that it will
be found possible to make with young children detailed observa-
tions on thunderstorms, sufficient detachment of mind being
rarely available. With minor and distant storms some observa-
tions can, however, be readily made. It should be noted that as a
general rule such storms come in the hottest part of the year and
of the day ; they are generally also commoner in hot summers
than in cold ones. When severe they are frequently associated
with showers of hail. This should be noted, for many people do
not clearly realise that hail is more frequent as a concomitant of
a summer thunderstorm than in winter,

The first sign of the approaching storm is often a layer of
cirro-stratus cloud, followed by heavy masses of storm clouds of
the cumulus type, often called cumulo-nimbus, from the dense
rain which pours from their lower edge. Before the rain falls

62 THE BOOK OF NATURE STUDY

there is often a short squall of wind, which precedes the approach
of the storm. If the storm is very distant, the cloudstmay take
on a peculiar anvil shape. As a general rule the severest lightning
occurs near the beginning of the heaviest rain. Thunderstorms
frequently appear in the west, and travel away towards the east.
As they pass away, and the clouds break, the sun shining on the
posterior part of the rain cloud produces a rainbow, the bow being
more nearly complete the nearer the sun is to the horizon. On the
level, rainbows are not seen in the middle of the day — the sun
must be fairly low either in the western or the eastern sky. Their
association either with thunderstorms, or with those short but
heavy showers which resemble thunderstorms so closely, should
be insisted upon. They are most common in summer, or at
least in the warmer parts of the year, and rarely occur except after
short showers. Note that after long-continued rain we rarely see
a bow, the reason being that the sky is then usually too continuously
covered with cloud for the sun and a rain cloud to appear at
opposite points of the horizon, as is necessary for the phenomenon
to develop. When there are two bows, note that the second is
fainter than the first, and has its colours inverted as compared
with the first. In the case of a school placed near the sea, the
rainbow should be compared to the similar phenomenon often
visible in stormy weather, when the crests of the breakers near
the shore show rainbow lights.

CHAPTER VI

THE APPARENT MOVEMENTS OF THE SUN

WE have now described the simpler forms of observations which
may be made on the physical environment. But it is obvious
that the course would be very incomplete if it did not also include
somewhat more detailed observations on the changes of the
seasons — on that great drama which lies at the back of most of
the historic religions, and has so powerfully moulded the thought
and the literature of all peoples. As these phenomena are less
obvious to town-dwellers than to the shepherds on the hills, the
hunters on the trackless plains, or the sailors on the seas, it is
essential that the attention of school children be directly drawn
to that mighty swing upwards and downwards in the sky of the
great sun, to that rhythm which punctuates all our life. The
Christmas festival when the infant sun begins his upward climb,
the Easter joy near the period when his triumph is assured, the
harvest rejoicing at the work he has accomplished when his
descent is becoming increasingly obvious — all these ancient
ceremonies may be used to suggest the unity of the human race,
the continuity of emotion through all the changes in modes of
life and thought.

Again, another if more prosaic argument for a careful study
of the seasons in the Nature Study period is that their scientific
explanation can never be made easy, and it is therefore of great
educational importance that an association of wonder and interest
be firmly established before the pupils pass to the consideration
of the difficulties involved in their geographical lessons.

As in the case of meteorological problems, various methods
of approach may be profitably tried. It seems, however, a sound
educational method to begin with some of the direct effects of
the sun's (apparent) motion on daily life. The varying lengths
of the days, for instance, is a point to which attention may well

64 THE BOOK OF NATURE STUDY

be directed at an early stage of progress. In these days of the
multiplication of bicycles and motor-cars the time of sunrise and
sunset for the school locally is easily obtained. A local time-
table, a local newspaper, will nearly always give this. If no other
possibility presents itself, the calculation may easily be made
from the sun's declination for the latitude concerned, as given in
a Nautical Almanack. In addition, rough direct observations
may of course also be made, where this is possible, as to the time
of setting, and even of rising during the parts of the year when
this is easy.

Apart, however, from such rough direct observations, it will
be found a good plan, especially at certain seasons, to draw the
attention of the class to the exact times as shown in the almanack.
The importance of the exact figures in connection with " lighting-
up time " may quite well be definitely made the starting-point,
for, above all, we must beware of separating our Nature Study too
far from common life. A child whose elder brother bicycles or
owns a motor-car may quite well be commissioned to produce
the figures for certain given days, and it need hardly be emphasised
that these days should be especially chosen to include the equinoxes
and the summer and winter solstices. At the March and Septem-
ber equinox get the members of the class to draw for you the
deduction that then the night and day are nearly of equal length,
and, by recording the times for some days, get them also to draw
the conclusion that the days grow longer and the nights shorter
after the March equinox, and that the conditions are reversed
after the September one.

Similar observations should of course be made in regard to
the solstices, and in both cases direct rough observations should
be added to the deductions made from the figures. This is of
course all very obvious, but something more may be done with
" lighting-up time " figures. Most of the ornamental calendars,
now so abundant, give the time of sunrise and sunset on the slip
for each day. Being for the most part published in London,
these times are times for London. From the comparison of the
local penny time-table, then, and such a calendar, material for
some interesting lessons can be drawn. On the accompanying
table the comparison for Edinburgh and London at the important

THE APPARENT MOVEMENTS OF THE SUN

seasons of the year has been made to illustrate the differences.
The differences would, of course, be more striking if London and
Aberdeen had been chosen, and less striking if London and a
midland town had been selected.

LENGTH OF DAY AT EDINBURGH AND LONDON AT THE EQUINOXES AND THE SOLSTICES.

Date.

Edinburgh.

London.

Respective
Lengths of
Days.

Sun rises.

Sun sets.

Sun rises.

Sun sets.

Mar. 17
18

19
20

6 hr. 27 min.

6 ,, 24 ,,

6 ,, 22 „

6 „ 19 „

6 hr. 17 min.
6 „ 19 „

6 „ 21 „

6 „ 23 „

6 hr. 12 min.
6 „ 9 „
6 „ 7 »»

6 „ 5 »

6 hr. 6 min.
6 „ 7 „
6 „ 9 „

6 „ ii „

Days of
about
equal
lengths.

June 19

20

21

22

3 » 28 „
3 N 28 „
3 „ 29 „
3 „ 29 „

8 „ 59 „
8 „ 59 „
9 » o „
9 » 0 „

3 » 44 „
3 » 44 »
3 » 44 »

3 » 45 »

8 „ 18 „
8 „ 18 „
8 „ 18 „
8 „ 19 t»

Days about
one hour
longer at
Edinburgh.

Sep. 23

24

a

6 „ o „

6 „ 2 „
6 „ 4 »
6 „ 6 „

6 „ 8 „
6 „ 6 „
6 „ 3 „

6 „ o „

5 » 48 „
5 » 50 „

5 » 52 „
5 „ 53 ..

5 jy 56 „

5 » 54 »
5 „ 52 „
5 » 49 »>

Days of
about
equal
lengths.

Dec. 21

22
23

8 „ 45 „
8 „ 46 „
8 ,, 46 „

3 » 36 „

3 » 37 „
3 „ 37 „

8 „ 6 „
8 „ 6 „
8 „ 6 „

3 » 5i „
3 » 52 „
3 »» 52 „

Days about
one hour
shorter at
Edinburgh.

Figures for Edinburgh taken from Edinburgh Postal Directory, 1 908-9 ; for London
from Whitaker's Almanack, 1908.

Let us note some of the interesting points which may be brought
out by this simple little comparison. In March the time between
sunrise and sunset, i.e. the length of the day, is, in general terms,
the same for Edinburgh and London. We might select one or two
other towns to show that this is true everywhere.

To put the matter in another way : suppose a man is motoring
all night in any part of Britain at the end of March or at the end of
September, he would have to burn his lamps for the same number
of hours everywhere. But, as the figures show us, in Edinburgh he
would not need to light them till about twelve minutes later in the
VOL. vi.— 5

66 THE BOOK OF NATURE STUDY

evening, and to make up he would have to keep them burning
twelve minutes longer in the early morning. (This, of course, is due
to the fact that Edinburgh is west of London, a point which would
naturally come up later.) At the Nature Study stage one does not
want to go into the question of equinoxes, or even to mention the
word, unless it is already known to the class, but the occurrence
of equal days and nights in March and September, and the fact
that there is a difference between the times of sunset and sunrise
in places in a different longitude is an important point. In
September the same points are, of course, to be observed — that
night and day are of the same length in the two towns, but that
in London the sun rises earlier and sets earlier than it does in
Edinburgh. (The reason, as before, is the westerly position of
Edinburgh as compared with London.)

The solstices show, of course, even more important points.
In June the sun rises earlier in Edinburgh and sets later, our
motorist there gains an hour's daylight as compared with his
London friend, but if he motors all the year round he loses the hour
in winter, for in December his lamps must burn for an hour longer
than they need to do in London. If we took figures for Aberdeen
or Shetland, we should find that the nights get longer and longer
in winter as we go north, and shorter and shorter in summer.
Carry this on in imagination, suppose we travel on and on into the
Arctic, what do we find ? Lead up in some such way to the long
Arctic night and the long Arctic day.

In this way, without formal lessons, without any indications
of the difficult problems involved, taking as the means of approach
the simple facts of everyday life, we arrive at quite a number of
important points, which should be checked by simple direct observa-
tions. We know that day and night vary in length throughout
the year, that the longest days are those which immediately precede
and follow 2ist June, and the shortest days those which precede
and follow 22nd December. (Note that it is not strictly accurate to
say, as is often done, that 2ist June is the longest and 22nd Decem-
ber the shortest day ; as the figures show, there is very little
difference in a group of days round the actual turning-points.)
We know further that at the end of March and the end of
September the days and nights are of equal length. We have tried

THE APPARENT MOVEMENTS OF THE SUN 67

to consider these facts in their human relations. Further, by
contrasting London with our own locality, or if London be the
home locality with another town, such as Edinburgh or Aberdeen,
we have shown that the winter days get shorter and the summer
days longer as we go nearer and nearer the Pole. We have illus-
trated this so far as possible by pictures and stories of the Arctic
day and of the Arctic night.

We have travelled, in imagination, from London to the Far
North, and we have seen that as we go north the difference in
length between day and night becomes greater both in summer
and winter. Suppose we reverse our journey. Now we find that
the disproportion in length between the two diminishes as we go
southward, until at London the longest day is about i6| hours,
and the longest night about i6J- hours. Suppose in imagination
we prolonged our journey still further south, we should find that
the disproportion went on diminishing until at last the longest day
and the longest night were each (about) 12 hours long, that is, until
the days and nights were always of the same length. This point is,
of course, the Equator, and once it is passed the disproportion
recommences until we arrive again at the Polar night and Polar
day of the Antarctic region. If we begin, as has been suggested
above, with some of the differences which the variations in length
of night and day make in our daily life, then it is comparatively
an easy matter to make clear the special conditions which prevail
in a region where night and day are always of approximately equal
length.

In the above summary treatment we have taken no note of
twilight, and have regarded the length of day as the period between
sunrise and sunset. This is of course incorrect, for the daylight
lingers after the sun's rim has dipped beneath the horizon, giving
us a longer or shorter period of twilight. Legally, as all bicyclists
know, in this country daylight is regarded as lasting for one hour
after sunset, and as beginning one hour before sunrise. This law
holds everywhere from north to south, though it is of course only
an approximation to the actual conditions. It is a very useful
exercise, whenever this is possible, to make the pupils mark the
actual onset of darkness, as tested by the power to read print
in the open, or to see objects across the road, or in some similar

68 THE BOOK OF NATURE STUDY

fashion. The long twilight of summer should be emphasised,
and the increase in the number of nights where there is never
complete darkness as one passes northwards should be sug-
gested, as far as possible in connection with human life. In the
reading lessons also opportunities should be seized to indicate
the importance in human life of the sudden onset of darkness
in tropical and equatorial countries.

In the summer evenings in this country we watch with un-
concern the disappearance of the sun beneath the horizon, know-
ing that a long stretch of daylight is still before us. Contrast
this with the countries where

" The sun's rim dips ; the stars rush out :
At one stride comes the dark."

No explanation of the differences in twilight can be profitably
attempted at the Nature Study stage, any more than we can hope
to make clear the actual movements of the earth ; but it is much
if the facts of observation can be brought out. Remembering
also that in the history of the race countless observations of the
main phenomena of the seasons were made before a science arose
which tried to correlate and explain these, it seems a sound method
to allow a period of mere collection of facts to precede also in
the history of the individual an attempt to find explanations.

The noting of the changes in the length of the days as deter-
mined by the changes in the times of sunset and sunrise may
of course be done at any season of the year, and does not demand
anything beyond the necessary tables. Direct shadow observa-
tions should, however, be also made whenever the day permits.
If the conditions allow, the comparatively speaking imposing
experiment of a tall stick in the playground has no doubt much
to be said for it, but as so much of the school work must neces-
sarily be done in the schoolroom, open-air experiment may be
well supplemented or even replaced by a window-sill experiment
which permits of much more continuous observation.

Whenever the day permits, take a few shadow observations.
If the room is sunny, this can be very simply effected by putting
a pin or darning needle into the cork of a gum bottle placed upon
the window-sill, or upon a desk if the sun enters the room freely.
Measure the height of the pin above the surface of the table

THE APPARENT MOVEMENTS OF THE SUN 6g

before the experiment is begun, and record this height. Put
the bottle in position, and make a dot with a blue pencil at the
extremity of the shadow, and record the time of observation.
Let the children return to the window at intervals of, say, half
an hour to make a fresh dot each time, recording on the black-
board the hour of observation in each case.

If the room is fully exposed to sunlight, a pretty and easy
way of carrying out the experiment is to place a drawing-board
on the floor, pin to it a large sheet of paper, and stick up a pin
in the middle. The head of the pin helps to give definiteness to
the end of the shadow, and measurements are also much easier
in this way than on a rough and uneven window-sill or playground.
If the room only receives the sunshine for a very short period,
then the drawing-board may quite well be placed in the open.
Again, especially when the room has an exposure such that it
receives relatively little sunshine, and that only at certain
times of the year, careful observations should be made of the
times of day and the date when it enters and disappears. A
little piece of stamp-edge, with the hour and date neatly written
upon it, may be easily gummed on the wall with its edge to the
edge of the shadow, the operation being repeated at longer or
shorter intervals.

In the first instance, it would be a mistake to attempt to
deduce anything but the simplest and most elementary facts
from these shadow and sunshine observations. The shadow
experiment, carried on for a morning, shows us that the shadow
of a pin changes quickly, and that in the morning the shadow
grows shorter and shorter till midday comes. By repeating the
experiment in the afternoon, we find that the shadow grows longer
and longer after noon. We check this by observations made on
the shadows of houses and fences seen on the road. There is
indeed no difficulty in getting the class to mark the shadow of
some object in the playground as they enter at nine, again as they
leave at noon, and again twice in the afternoon, so as to confirm
their schoolroom observations.

Similarly, by marking the place reached by the sunshine either
in the schoolroom or on the outer wall of the school, and doing
this at intervals for weeks or months, we soon learn that as the

70 THE BOOK OF NATURE STUDY

shadows change with the change from morning till evening, so
they also change in position with the change from spring to
summer and from autumn to winter. Try to find in the school
buildings some striking examples to illustrate these changes, for
instance, a wall which receives no sun in the winter months. Let
the last appearance of the sun here in autumn be carefully marked
with the date and hour, and let the class watch in spring for the
first illumination by its rays. They will almost certainly be
greatly interested in such observations, and they are laying the
foundations for a fuller treatment of the sun's movements after-
wards. Add to these observations notes upon the position of the
sun in relation to landmarks in the vicinity. In the morning on
such and such a date it is beside the church, in the evening it
sinks behind such a hill, and so on. In this fashion we may obtain
general notions of its apparent double movements, the diurnal
and the annual.

Again, by repeating the shadow observations at different
seasons, we may easily deduce the fact that the noonday shadow
is shortest in summer and longest in winter — that it changes
throughout the year as it changes in length when watched for a
day. We note also that when the shadows grow long in the evening
the sun's rays are much less bright — we can look at the setting
sun without discomfort, while at midday he is too brilliant for
us to attempt this. In the same way when the shadows grow
long in winter it is a paler, feebler sun than that which casts the
short shadow of summer.

Two little points of practical interest may perhaps be mentioned here. The
first is that children should never, under any circumstances, be encouraged or
permitted to look directly at the sun, either with the naked eye or with any
instrument involving the use of a telescope (i.e. a sextant), unless the eye be
protected in some way. While making observations of short duration a piece of
smoked glass (or dark bottle glass) held between the eye and the sun is a good
protection ; other more effective means are blue " goggles," or, when the telescope
is used, the insertion of special smoked or coloured glasses. The point is one of
great practical importance, and the difficulty of insisting upon it in each individual
case with a considerable 'class must always make shadow observations preferable
when dealing with children to any which render direct observation of the sun
necessary.

The second point, which is of importance if more or less continuous shadow
observations are to be made throughout the year, is to remember the great length

THE APPARENT MOVEMENTS OF THE SUN

of winter shadows, and therefore either to make the object used for the purpose
of measuring the changes very short or to allow ample room. At London the

ZENITH

:§T^ SUMMER SOLSTICE

EQUINOX

FIG. 2.— Diagram showing the variations in length of the shadow of a
stick at London.

noonday shadow of a 6-feet pole varies from a little over 3 feet at the summer
solstice to considerably over 22 feet at the winter solstice (cf. Fig. 2). At
Edinburgh at the winter solstice a similar pole would be more than 32 feet long,
and at the summer solstice nearly 4 feet, while at Aberdeen or Kirkwall it
would be still longer. For the sake of the teacher's convenience, it may be

1ENITH

SUMMC R SOLSTICE

EOU I N OX

FIG. 3. — Variations in length of the shadow of a stick at Kirkwall.

of the shadow in winter.

Note the great length

noted that the length of the shadow at the solstices may be readily calculated
for the latitude of the school in the following way. The formula required, as very

72 THE BOOK OF NATURE STUDY

little consideration will show, is that the tangent of the sun's altitude is equal
to the height of the stick divided by its shadow.

-ru £ stick

Therefore, as tan angle a

shadow

shadow

stick
tan angle a

The sun's altitude (i.e. angle a) at the equinoxes may be simply calculated. If
/ be the latitude of the school, then at the winter solstice the sun is distant from
the zenith by / + 23^°, while at the summer solstice it is distant from the zenith
by /-23J°. If the result in either case be subtracted from 90° we have the
sun's height above the horizon, or altitude.

For example, taking the latitude of Edinburgh as roughly 56° N., we find that at
the winter solstice the sun's altitude is 10 J° (56° + 234° = 794° ; 90° - 79i0 = 10 J°) .
The tangent of ioj° (roughly 0*1853) is easily obtained from a table of logarithms,
and if the height of the stick be divided by this tangent the result gives the length
of the shadow. By similar reasoning it will be found that the altitude of the sun
at the summer solstice at Edinburgh is 57!°, and by taking the tangent of this
angle (roughly 1*569) and dividing the length of the stick by it, we can obtain
the minimum length of shadow, as the former calculation gives us the maximum
length. It is prudent to make a rough calculation of this kind, in order to be
quite certain that the place chosen gives space enough for the full demonstration
of the seasonal variations in lengths of shadows.

It would seem well in the first instance to rest content with
shadow and sunlight observations taken from time to time, and
regarded merely as curious facts. If the path of the pin's shadow
on a piece of paper, for instance, or on the window-sill, be carefully
marked, dated, and preserved, it will be natural to refer to these
old records when new ones are made. Comparisons would then
crop up quite naturally, and without excessive effort, and without
having recourse to globes or any pieces of apparatus, we could
make at least the following deductions : Every sunny day we
see the sun low in the early morning, and then its rays are not
very strong, and it casts long shadows ; in the middle of the day
its rays are strongest, and the shadows are shortest. Comparing
summer days with winter days we find that the shadows in the
middle of the day are shorter in summer than in winter, and by
marking the places which the sun reaches in winter and in summer
we may show that it is higher up in the sky in summer than in

THE APPARENT MOVEMENTS OF THE SUN 73

winter, just as it is higher up in the sky in the middle of the
day than in the morning and evening. Therefore we know that
when the sun is high in the sky shadows are short, and when it is
low they are long. We know also that the higher up the sun is,
the hotter are his rays. Every day it becomes cooler or colder
as he sinks down, and in winter when he never rises very high in
the sky it is colder than in summer when he does.

At the same time, simple lessons on the cardinal points will
of course be given, these coming naturally out of the sunshine
and shadow observations. The sun even on a bright day does
not come into all the windows of the school at once. We notice
how it pours into the east windows in the morning, how the south
front gets the full blaze through the midday hours, and how it
illuminates the western windows as it sinks downwards. Try to
find sunshine observations which may help to make it clear to
the class that the sun does not set in the same place throughout
the year. Mark in some way the point where the last rays touch
some wall or building in winter, and then by successive observa-
tions at intervals suggest the creep towards the north as summer
approaches. That is, instead of teaching the only partially true
statement that the sun sets in the west, try to bring out, simul-
taneously with the fact that it sets towards the west, the other
fact that its exact setting place is towards the north-west in
summer and towards the south-west in winter, and true west
only at the equinoxes. Be on the look out throughout the year
for little local points of interest in regard to the periodic move-
ments of our mighty heat-giver.

Those teachers who are so placed that the school has a clear
horizon where the sun can be seen sinking into the sea, behind
a hill, or behind some conspicuous landmark, or so forth, are
fortunate, and should make the best use of their opportunities.
The children should also be encouraged to collect for themselves
observations on the sun's rising or setting, the point being to
insist upon the exact time and date being recorded so that the
observations can be used for comparisons later. A considerable
mass of simple little observations should be collected before any
attempt is made to explain with any fullness the actual movements.
If the facts about sunrise and sunset have been collected from

74 THE BOOK OF NATURE STUDY

almanacks, as suggested above, it is a simple matter to indicate
generally that as the sun travels up towards the north in summer
time he has a longer course to cover and therefore the day is
necessarily longer, and that the process is reversed in winter, when
he travels southward.

CHAPTER VII
DAY AND NIGHT. THE SEASONS

WHEN a considerable number of shadow observations have
been made, and the most elementary points in regard to the
apparent movements of the sun thus made clear, we want to go
a few steps farther. The Nature Study course should give at
least a generalised idea of the two movements of the earth, the
movement of rotation and the movement of revolution, though
we want, of course, to treat these subjects much more simply than
in a geography course.

After we have marked one noon shadow, we want to show
that, in a period of (about) twenty-four hours, the shadow falls
again in the same position, showing that the earth has taken
twenty-four hours to return to the position from which it started.
Similarly, we want to show that if we mark the shortest shadow
at one summer solstice, in about a year from that time the shadow
falls again in the same place, showing that the earth has taken a
year to return to the point from which we started. In the Nature
Study course, however, it would seem that these facts should
be considered rather from the point of view of measures of time,
that is, of their practical importance, than from the astronomical
standpoint.

Day by day we see the sun cross the sky from east to west. We
can easily find the time when he is highest in the heavens by the
fact that the shadow of a stick is then shortest. We call this time
noon, and it takes (roughly) twenty-four hours for the series of
movements whose result is to bring the sun apparently back to
the same place. Here, then, is a convenient measure of time.
Let us suppose that we are shipwrecked mariners cast upon a
desert island. We have no watches, but we must have some
way of dividing our days, and therefore we proceed to construct
a shadow-clock, a sundial. In some such way we might lead

75

76 THE BOOK OF NATURE STUDY

up to the subject, making the members of the class do some
actual constructive work which would interest every one, even
those whose interest in the theory of the matter was weak.

In Simmons, and Richardson's Introduction to Practical
Geography there is a very full treatment of sundials, and some
of the simpler types of those described might be very well con-
structed. It should, however, be carefully noted that while as
shipwrecked sailors we could divide our day as satisfactorily by a
sun-clock as by a watch, as members of a civilised community we
have to note that our sun-clock, however carefully constructed,
does not coincide with the actual clock. The reason is, of course,
twofold. In the first place, clock noon in this country is, except
in Ireland, Greenwich noon, and the school may be considerably
west of Greenwich. Secondly, as clock noon is mean noon, the
correction necessitated by the earth's varying velocity (equation
of time) has to be applied.

In the author's opinion it would be quite unsuitable, at the
Nature Study stage, to attempt to give a full explanation of the
term equation of time. The explanation demands considerable
power of abstraction, and cannot be made clear without diagrams
and apparatus.

If the teacher finds it necessary, and especially if the school is
situated in a port and among seafaring folk who take a natural
interest in navigation, there seems no objection, when attempting
to find noon by a shadow-clock, to applying the necessary correc-
tion from a Nautical Almanack, without explanation, as many a
sailor would apply it, leaving the explanation to come later.

If it is not desired to mention the subject at all, then the attempt
to find the true noon by the sun should be made at a time of
year when the correction is so small that it may be neglected in
the rough experiments performed. For this reason it is well to
make the experiment towards the middle of June, the middle of
April, or the beginning of September. At these times the correc-
tion is a matter of seconds only for some days.1 June is an espe-
cially suitable month, on account of the probability of sunshine.

1 It should be noted that the sun-clock and mean time coincide on four days of the
year, i.e. on four days the equation of time = o. These days are i$th April, i4th June,
ist September, 25th December. -

DAY AND NIGHT— THE SEASONS 77

In regard to the other point, the longitude of the school,
as only a relatively small part of Great Britain lies to the east
of Greenwich, the probabilities are that the sun clock will be
slow by the school clock, i.e. noon will be later. If the difference in
longitude be considerable, it may be quite possible to show it
even by a rough school experiment. At Glasgow, for instance,
which is 4^ degrees west of Greenwich, noon by the sun
is (at times when the equation of time = o) seventeen minutes
later than noon by the clock, a difference which it should be easy
to show.

The experiment of finding local noon may quite well be also
used to find a true north and south line, and may therefore be per-
formed with a little elaboration.

Before beginning the experiment, be sure that the school clock,
or the watch to be used in the experiment, marks correct Greenwich
time, is as we say " right." Choose a fine day as near the I5th June
or i5th April as possible. Fix either a stout pin or a stick on a
level surface, taking care that the object is as nearly vertical as
possible, and that its shadow falls on a smooth surface. About
an hour before noon measure the length of the shadow, and make a
loop of thread or string, whose length is the exact length of the
shadow. The loop should be attached to the stick at one end,
and the other end should bear a piece of chalk, or something
with which a mark may be made. With this chalk describe a
semicircle, the length of the string being the radius, and the
stick the centre. Another method is to describe the semicircle
first, and then mark a point where the shadow touches it for the
first time.

In either case, call the point where the shadow touches the
semicircle A, and the radius AC (see Fig. 4). If the first observa-
tion has been made about an hour before noon, it will be found
that the shadows grow shorter and shorter. Their length should
be marked at short intervals, and the points will be found to lie
within the semicircle. Mark the extremity of the shadow with
special care at the instant when the school clock strikes noon,
and go on making observations at intervals as the shadow creeps
outwards again until once again it touches the circumference of
the semicircle. Call this point B, and join AB. Bisect this

78

THE BOOK OF NATURE STUDY

FIG. 4.

line, which can be done with a measuring tape or ruler. A line
drawn from D, the point of bisection, to the base of the stick

is a true north and south line,
and marks also the position of the
shortest shadow. If the school is in
the longitude of Greenwich, then D
will coincide^with the point at which
the school clock showed noon. If
the school is west of Greenwich,

&L then the point D will be after the

point marked as coinciding with
clock noon. By making the shadow
observations at regular intervals of,
say, ten minutes, it is possible to cal-
culate roughly from them how much
apparent noon is after clock noon.
This experiment, though more laborious, is more satisfactory
than that of trying to find local apparent noon by noting the
point when the shadow is shortest, for it will be found in practice
that it is not easy to determine the exact moment when the
shadow is shortest.

The north and south line so obtained should be marked
permanently, to be used later in geography lessons. The results
obtained in this way should be compared with those obtained
by the rough rule that, if the hour hand of a watch is made to
point to the sun, the direction south lies half-way between the
hour hand and twelve o'clock. The accuracy of the line should
also be tested by means of the compass, allowance being made
for magnetic declination.

It may be necessary to repeat the experiment on several
successive days in order to obtain fair accuracy, and it should
be noted that it is always prudent for the teacher to carry out
experiments of this kind alone beforehand, as various trifling
difficulties present themselves in practice which require care
in overcoming.

If the experiment has been performed on one of the days
specified, the stick, chalk line, etc., should be left in position,
and the observations repeated the next day. It will be found

DAY AND NIGHT— THE SEASONS 79

that, at the moment when the sun once more casts its shortest
shadow, almost precisely twenty-four hours have elapsed since
the last observation. Here, then, is a measure of time ready
for use, and if we were shipwrecked sailors we should know
that it was dinner-time as soon as the shadow came back to
yesterday's mark. Similarly, by noticing that the shadow grows
gradually shorter up to noon, and then lengthens out in precisely
the same fashion as it shortened, it becomes clear to us that
we could make on the ground a series of marks which would
help us to divide our days equally, and make sure that we had
our meals at the same time each day. It seems a sound principle
to look at the movements of the earth in this way in their practical
bearings on daily life, before attempting any wider consideration
of them.

If the class manifests interest in the subject, and shows some
skill in the manipulations involved, it might be well to make
similar observations in November, if the weather conditions
permit. Suppose that in the beginning of that month we are
fortunate enough to be able to make shadow observations at
noon, we shall find that, as compared with our June observation,
noon, as shown by the shortest shadow, occurs sixteen minutes
earlier than it did in June.

This is because the equation of time is large in November,
a correction of sixteen minutes having to be applied to convert
apparent noon into mean noon.

Without going further into these difficult points, it may be
worth while to suggest to intelligent pupils that while the sun
is our great timekeeper, he has the disadvantage of not keeping
perfect time, moving sometimes faster and sometimes slower.
We have therefore to invent a theoretical sun, which keeps
perfect time, and that is one of the reasons why in large towns
Greenwich time is telegraphed from headquarters, instead of
every town simply making observations of the sun for itself.

The questions connected with time and longitude deserve
fuller consideration, for nearly all pupils find them difficult.
It is important to keep as close as possible to the practical side
of the matter, and illustrations from continental or Irish time-
tables should be employed freely.

8o THE BOOK OF NATURE STUDY

We have already attempted to show that sunset is merely
an appearance, and that the farther we go west the later it is
before that appearance develops. Further, by means of our
shadow observations, compared with the clock, we have tried
to show that, supposing our school to be, say, 3 degrees west
of Greenwich, then noon is twelve minutes later. We have
compared this result with the result obtained by studying the
tables showing " ligh ting-up time/' and in this way we have seen
that to persons west of Greenwich the sun rises later, comes
to its highest point later, and sets later than to persons at Green-
wich, this being true for all seasons of the year. For all persons,
then, in Great Britain who live to the west of Greenwich the clock
is fast, just as it is slow to the comparatively few persons who,
in Great Britain, live to the east of Greenwich. Over most of
Great Britain the difference is comparatively small, but we note
that a little boy who lives, say, at Fishguard in Pembrokeshire,
and who goes to bed at eight o'clock, is really going to bed at
twenty minutes to eight by the sun. But then he has the con-
solation of knowing that when he gets up at half -past seven by
the clock, it is really only ten minutes past !

We may notice, also, that so long as there were no railways
it did not matter very much whether people took sun time or
Greenwich time. The extreme difference produced by difference
in longitude in Great Britain is only about twenty-four minutes,
and so long as one has not a train to catch twenty-four minutes
more or less does not make much difference. It was only when
railways became common that Greenwich time came to be
universally adopted in Great Britain. Without the electric
telegraph, also, it would be impossible to have all the clocks in
Great Britain keeping Greenwich time, so that the occurrence
of one time over a country is necessarily a modern development.

One should also notice that while in Great Britain the maxi-
mum difference between sun time and clock time produced by
a difference in longitude scarcely exceeds twenty-four minutes, in
Galway in Ireland, which is 9 degrees west of Greenwich, sun time
is thirty-six minutes slow by Greenwich. Further, there is no
point in Ireland where the difference between sun time
and Greenwich time is less than about twenty-two minutes.

DAY AND NIGHT— THE SEASONS 81

In consequence, we find that in Ireland Greenwich time is not
used, but Dublin time, which is twenty-five minutes slow by
Greenwich time. In discussing these points railway time-tables
should be freely used, and the human side of the question insisted
upon.

The author was much struck recently by a little experience
at the Little St. Bernard Hospice, where an Italian tramp asked
the time. When he was given the information he appeared
to recollect suddenly that his informant was travelling in the
opposite direction to himself, and put the further question — Is
it French time or Central European ? The interesting point was
simply that practical experience had given the tramp a perfectly
clear and definite idea of the difference between the two times,
in spite of the fact that he was apparently without education.
When one recollects that many educated people, unless they have
travelled much, show a more or less hopeless confusion in the
matter of local time and change of time, it seems obvious that the
correct method is to take the practical side of the subject as a
starting-point. One should try, even before the children learn
anything about latitude and longitude, to show them, by
imaginary journeys, how conventional is our measurement of
time.

Shadow experiments then, helped out by the various devices
we have suggested, show us that if we mark the position of the
sun at noon, we find that it takes about twenty-four hours before
he comes back again to the same position. In the words of the
geography book, the earth rotates in twenty-four hours. As we
have seen, the rotation is accomplished in exactly twenty-four hours
only at certain periods of the year. At other times the period
is either a little more or a little less. This rotation forms the
basis of our time, but our days are all of the same length, and
therefore are according to the season a little longer or a little
shorter than the actual time of rotation.

But while at whatever point of the earth we are placed we
find that the earth rotates in twenty-four hours, the day does
not begin at the same moment everywhere. The people to the
east see the sun earlier and lose him earlier than the people to
the west, so that even for people twenty miles apart there is some,

VOL. VI.— 6

82

THE BOOK OF NATURE STUDY

if a small, difference in the time of noon. But round London,
for instance, people sometimes travel twenty miles every morning
into business, and it would be obviously impossible for them
to catch their trains and carry on their business if there was
a different time every few miles. Therefore they agreed that
the time of one particular place should be taken over a wide area,
generally over one country. Thus many countries, unless they
are very large, take their time from their capital, Great Britain
from London, Ireland from Dublin, France from Paris, and so on,
this being done simply as a matter of convenience. One should
go on to point out that the change of time at the frontier of a
country often makes great inconvenience, as when a traveller
goes to Chamonix from Paris through Geneva. Here he finds
that when he gets to Geneva he loses an hour, but as he travels
on towards Chamonix, which is in French territory, he regains
that hour. As he is journeying eastward all the time, this
example is well adapted to show the artificiality of standards
of time.

Shadow experiments may also be used to give some idea of
the meaning of the earth's revolution, though the term itself

should not be mentioned. If
in the previously described
shadow experiments a stick
has been used, a slender lath
should now be taken, and so
placed that one extremity
rests on the top of the stick
and the other end on the
ground (see Fig. 5). In an
indoor experiment with a
stout pin, a piece of card-

FlG.5.-The altitude of the sun at London at the board be used jn

equinoxes, experimentally shown. J

same way. In either case the

lath or card should be adjusted so that the end touching the ground
reaches to the extremity of the noon-tide shadow in one of the
observations already made. If the present observation be made at
noon, make the class notice that when the lath is arranged in this
way it points in the direction of the sun, and in consequence the

DAY AND NIGHT— THE SEASONS

angle between it and the ground is the altitude of the sun, i.e.
its height above the horizon. This angle may be measured
with a protractor, or, more simply, the height of the stick, the
length of the lath, and the distance between the end of the lath
and the foot of the stick may all be measured. These measure-
ments give the three sides of the triangle, and the children may
be shown how to construct a similar triangle to scale, and then
measure the angle between the hypotenuse and the base, i.e.
the altitude of the sun.

At the same time explain to the class that this is the principle
of the gnomen, which was extensively used by the ancients as
a method of obtaining the altitude of the sun and stars.
If the members of the class have an elementary acquaint-
ance with mathematics, they can of course be shown that the
sloping lath is not essential to obtain the altitude of the sun,
for the tangent of the desired angle can be obtained by the

stick perpendicular

ratio - — : — , the equivalent of the of an ordinary

shadow

horizontal

SUMMER SOUSTICC

right-angled triangle. The angle can then be obtained from this
tangent by the aid of a book of logarithms.

By means of the ZE N JTH
sloping lath, or by
calculation, the noon
altitude of the sun
should be obtained
roughly for a series
of dates throughout
the year. In spring,
weekly observations
may well be made,
so that the class can
follow the upward
creep of the sun in
the sky, noting at
the same time the
rise of temperature as the days become longer and the rays less
oblique. They should not be told about the solstice until their

FIG. 6. — The noon altitude of the sun at London at the
equinoxes and solstices. Compare with Fig. 2.

THE BOOK OF NATURE STUDY

own observations have shown how the sun stops its upwards rise,
and turning, begins once more to descend, the days shortening as
he does so. Let them note at the same time that our hottest
weather comes after the sun has turned and is beginning to descend,
the earth having been warmed by the long days of early summer,
whose heat accumulates, as it were, and gives us the blaze of
full summer.

The altitude observations should be continued into winter
whenever the weather permits, so as to give some numerical idea
of the difference between the summer and the winter conditions.
Thus at London the noon altitude at midwinter is only 15°, while

ZENITH

SUMM PR SOLSTICE

INTER

SOLSTICE:

FlG. 7. — The noon altitude of the sun at Kirkwall at the equinoxes
and solstices. Compare wtth Fig. 3.

it is 62° at midsummer, differences which even rough school
observations should make clear. Even if it is not considered
desirable to attempt to obtain exact figures, the experiments
should be so performed as to enable the children to distinguish
by them between the summer conditions when the sun is high
in the sky, and the winter ones when it is low.

CHAPTER VIII

THE MOON

WITH a class of children observations on the moon must
always be of less importance than those on the sun. In the
winter months, however, and especially with country children,
a considerable number of simple observations on the moon may
be readily made. To town children the changes of the moon,
even during the dark months of the year, are not very obvious,
and our satellite is not much noticed except when it is full or
nearly so. To country children, on the other hand, not only is
the moon of more importance, in that winter entertainments are
usually arranged at such times as to permit the dispersing com-
pany to find their way home by moonlight, but also the greater
probability of a clear horizon makes the observation of the waxing
and waning an easier matter. With town children the chance
of seeing the crescent moon at sunset, for instance, must always
be smaller.

Where the school is placed near the sea, it is important to
draw attention to the variations of the moon in relation to the
movements of the tides, a subject which cannot be treated at
an inland school with any success.

The first and most obvious observations to be made are that
the moon appears to us to be the same size as the sun, but while
we cannot look at the sun unless it is veiled in cloud or fog, the
clear white light of the moon does not dazzle our eyes in the
same way. The fact that the markings are the same at every
full moon should be pointed out, for this is one of the reasons
we have for knowing that the moon always turns the same face
towards us. Similarly, the small dark spot which occurs near
the upper portion of the western border of the full moon may
be pointed out. The interesting point is that this spot is seen

on the young crescent moon when it is only a few days old, but

85

86 THE BOOK OF NATURE STUDY

as it is the western border of the full moon that darkens as the
moon wanes, this spot early disappears in the waning moon,
and does not reappear until the new crescent appears. This
spot is the so-called Sea of Crises (Mare Crisium), one of the
numerous " seas " or plains of the moon.

The evidence upon which is based the conclusion that the
moon has no light of her own, but shines by the pale reflected
light of the sun, is based upon somewhat close reasoning, and
the teacher will probably find it necessary simply to take this
conclusion for granted when dealing with elementary classes.
The fact may, however, be suggested in connection with actual
observations, which give it more vividness and reality. Thus
when the full moon is riding high in the heavens on a winter
night, the teacher may suggest the idea of the invisible sun which
she is then facing, and whose glory she reflects in her pale beams.
She is then, as it were, the mirror which tells us that the sun which
we cannot see is still shining in undiminished strength. Simi-
larly, when the slender crescent of the new moon appears in the
western sky, just after the sun has sunk, we may suggest that
the orb, which has been invisible for some nights, is now catching
some of the rays of the western sun, and is thus rendered visible
as a slender rim, whose convex side is turned towards the dis-
appearing sun.

Again, if by a chance observation a pale " crescent " moon
is observed at dawn, we may point out that this is the waning
moon, whose eastern border is illuminated by the rays of the
rising sun, so that the horns are turned in the reverse direction
from those of the waxing moon.

It may also be possible to combine a summer and a winter
observation, so as to show how high the winter moon rides in
the heavens, i.e. how far she is to the north as compared with
the more southerly full moon of June, which lies lower in the
great arch of heaven.

The object of the observations should be to suggest the
double movement of the moon in the heavens, her movement from
west to east, and her other movement from south to north, and
back again to south. The latter movement is chiefly of im-
portance from our standpoint in that it gives us the long moon-

THE MOON 87

light of the winter full moons, when the moon rides high in the
sky.

The facts in regard to the west to east movement are more
important, and deserve fuller treatment. If we begin with the
new moon, the crescent seen after sunset, with the convexity
directed towards the place where the sun has set, we find that it is
then in the western part of the sky. Next night we find that when
. first seen, which happens, if the sky is clear, so soon as the sun-
light has faded sufficiently to make her pale light visible, that the
moon is higher in the sky, i.e. farther towards the east than on the
previous night, and also that her crescent is broader. This goes
on night after night, the moon always shifting farther away
from the sun, and as it shifts its surface becomes fuller and
rounder, more and more of it being illuminated. At last, about
a fortnight after the first pale crescent was seen at sunset, the
moon is at its full. It is now the whole breadth of the sky away
from the sun, and, as it turns the same face to the sun as to the
earth, it is seen as a round disc of pure white light. At this time
the moon rises about the time the sun sets, and sets about the
time he rises.

If there should by chance be a full moon on the 22nd September,
or about this date, then we find that for several successive even-
ings the moon rises in the east just as the sun sets in the west.
The sun at this period, it will be remembered, sets precisely in
the west, so that the two are exactly opposite each other. This
is the phenomenon of harvest moon, which should always be
noticed in the cases when it reaches perfect development. Owing
to its position the harvest moon appears unusually large, and
as it takes over the light-giving task of the sun immediately that
body sets, there is practically no darkness, and we have the long
light nights beloved of harvesters in the days when no mechani-
cal means of rapidly gathering in the corn existed.

But the moon still continues her eastern course, rising later
and later each night as she wanes, and also setting later, so that
her pale crescent may be seen even after sunrise. This process
continues, the shrinking decrescent coming nearer and nearer to
the sun, and rising later and later, until it becomes a mere silver
thread, convex towards the east and visible only just before

88 THE BOOK OF NATURE STUDY

daybreak. Then there come a few nights without any moon,
until again the pale crescent reappears at sunset.

As a guide to the teacher it should be noticed that the crescent
moon is never seen to rise. She rises during the day, but does
not become visible until sufficient light has faded from the sky
for her pale line to be seen. Again, as it may be possible to get
sharp-eyed pupils to observe, though theoretically it may be
said that a period of twenty-nine days elapses between one new
moon and the next, yet in point of fact there is an uncertainty
of a full day, i.e. the period may be twenty-nine or thirty days.
The reason for this is that the question whether or not the new
moon will be visible on a particular evening depends upon the
exact hour at which the conjunction of sun and moon took
place. If this conjunction occurred eighteen hours before sun-
set, then it might be possible to see the crescent moon for a few
minutes. If the conjunction took place less than eighteen hours
before, it would be necessary to wait another day before the new
moon could be seen.

Teachers will find a very interesting little story illustrative
of this point in Fromentin' s Un £te dans le Sahara. The
anecdote has reference to the Mohammedan fast of Ramadan.
As the Mohammedan calendar is lunar, the new month begins
and the fast ends with the first observation of the new moon.
But, as suggested above, this observation is often a delicate
matter. Fromentin, who started on a journey across the desert
at the end of the month of fasting, describes how in the town
from which he started a sharp-eyed member of the faithful
community declared that he had seen the crescent moon. No-
body else had seen it, but as not to see it meant another day
of rigorous fasting, the community in general accepted the state-
ment with alacrity, and proceeded to the holding of the pre-
scribed feast. Fromentin with some difficulty got his caravan
started, but after some hours' marching reached another settlement,
where, to his surprise, he found that the community were still
fasting. His followers also expressed great surprise, and told the
village elders that the fast was over, the new moon had been
seen at their village. But the elders here, of a more devout
frame of mind, poured scorn upon the statement, and intimated

THE MOON 89

that that particular village usually did see the new moon before
any one else. The story is interesting as suggesting some of
the difficulties of a lunar calendar.

It will be found similarly that if an attempt is made to
measure the time between one full moon and the next, or between
the waxing moon being half full until it is half full again, though
the period is about twenty-nine days, there is not perfect con-
stancy, the moon not moving round the earth with equal velocity.
If desired, this might be used to lead up to a consideration
of the different calendars which have been employed. Some
account of these will be found in Johnson's Mathematical Geo-
graphy.

If it is possible to include in the Nature Study course any
observations on the tides, these observations should, of course,
in the first instance be directed towards showing that just as
the moon's phases may be divided into two fortnights, a fort-
night of waxing and a fortnight of waning, so the tides show
fortnightly periods, there being two spring and two neap tides
every month. Very little observation, with the assistance of
the Almanack, will show that the spring tides nearly coincide
with new and full moon, while the neap tides occur in the inter-
vening periods. The full explanation of the relation would
carry the matter beyond the Nature Study stage. At this stage
the teacher should rest content with a mere collection of observa-
tions, and a suggestion of the probable relation between the
tides and the phases of the moon, as shown by the observations.

In conclusion, we may borrow a suggestion from Maunder' s
The Heavens and their Story, and suggest that the teacher be on
the look-out for mentions of the moon and its changes in literature,
especially in poetry. Very often the astronomy in these cases
is very shaky, and the pupils may very well be commissioned
to observe for themselves the " horned moon/' with a view of
trying to find out why it is that the Ancient Mariner must be
regarded as in error when he declared that he had seen it with

"One bright star within the nether tip."

We have already seen that, whatever the poets and novelists
may say, the young crescent moon cannot be seen to rise, for

90 THE BOOK OF NATURE STUDY

it is above the horizon long before dusk. In the same way the
waning "crescent " does not set ; it is only eclipsed by the light
of the rising sun. Neither the crescent nor the decrescent is
ever seen high in the sky.

NOTES ON BOOKS. — In beginning a course on the Physical Environment
the teacher will naturally in the first instance have recourse to the ordinary
school manuals of physical geography. It is unnecessary to give a list
of these, the revised edition of Huxley's Physiography, published as
Physiography by Huxley & Gregory (London, 1904), may be named as a
good example. For reference a text-book of meteorology is useful, such
as Dickson's Meteorology (London, 1893), or Davis' Elementary Meteorology
(Boston, 1894). The Atlas of Meteorology, by Bartholomew, Herbertson, &
Buchan (Edinburgh, 1899), is invaluable, and Hann's Climatology, First Part
translated by Ward as General Climatology (New York and London, 1903), is
also almost indispensable. The raw material of the science of meteorology, no
less than special studies on the subject, is to be found in the publications of the
Meteorological Societies, notably in the Journal of the Scottish Meteorological
Society, where in addition to the monthly records of temperature, rainfall, etc.,
for Scotland, there are numerous valuable papers on climate, temperature,
rainfall, etc., especially the classical papers written by Dr. Buchan. See also
the Quarterly Journal of the Royal Meteorological Society, and the annual volume
of the British Rainfall Organisation (published at London yearly as British
Rainfall), and Symons' Meteorological Magazine. The Royal Meteorological
Society also publishes two little pamphlets which teachers will find useful —
Hints to Meteorological Observers, and Some facts about the Weather, both written
by W. Marriott, assistant secretary, which are revised from time to time.
If any detailed observations are to be made, the Weather Reports of the
Meteorological Office are almost a necessity. Application for these should be
made to the Office, 63 Victoria Street, London, S.W. ; the Daily Report can also
be bought at certain of the railway stations in London.

The facts as regards climate and weather, considered in their geographical
relationships, will be found treated in such books as Britain and the British Seas,
by H. J. Mackinder (second edition, Oxford, 1907), G. S. Chisholm's Commercial
Geography (seventh edition, London, 1908), and The International Geography, edited
by H. R. Mill (London, 1907). In the Scottish Geographical Magazine various
articles have appeared recently on climate and weather ; mention may be made
especially of the author's The Study of the Weather as a Branch of Nature Know-
ledge (xxiii., 1907), and The Climate of the British Isles, by Andrew Watt (xxiv.,
1908). Some useful suggestions as to the best way of including the subject in
a general Nature Study course will be found in Some Suggestions to Teachers for
Seasonal Nature Study in Schools, by J. A. Thomson (Aberdeen, 1908).

For the subjects discussed in the later chapters the following books may be
mentioned : An Introduction to Practical Geography, by Simmons & Richardson
(London, 1907), a little book packed with useful practical suggestions ; Practical

THE MOON 91

Geography for Schools, by Alfred Hughes (Oxford, 1887), which is not "practical "
in the sense of describing experiments, but gives interesting geometrical con-
structions for the problems connected with time, etc. A Nautical Almanack
is indispensable for detailed practical work such as that suggested here ; a useful
one is Brown's Comprehensive Nautical Almanack, published annually at Glasgow.
Many useful points for the teacher are also given in the Royal Geographical
Society's Hints to Travellers, many editions. A pamphlet called The Practical
Teaching of Geography in Schools and Colleges, by Dr. Morgan (London, 1906), is
full of useful suggestions, and there are now many small text-books on practical
geography which deserve to be consulted. A very interesting and simple account
of the movements of the heavenly bodies will be found in The Heavens and Their
Story, by A. & W. Maunder (London, 1908), which has some very instructive
plates. A mathematical treatment of the problems involved will be found in
Mathematical Geography, by Willis G. Johnson (London, 1908).

THE PHYSICAL ENVIRONMENT

BY W. W. WATTS, Sc.D., M.Sc., F.R.S., F.G.S.,
Professor of Geology at the Imperial College of Science and Technology

CHAPTER IX

INTRODUCTION

THE study of the Physical Environment should be begun,
and so far as possible pursued, out of doors, though in most
cases the study of material collected must be carried on
indoors. Even though it may not be possible to carry out
as much of the teaching as is really desirable in the open air, it
is essential that the teacher should keep himself in touch with
first-hand knowledge of his own physical environment, and that
he should come to his pupils fresh from the actual observation,
in their own district, of such earth knowledge as is accessible
to observation in that district.

Before dealing with composition and distribution it seems
to the writer desirable that the dynamics of the earth's crust
should be studied. It is easier of observation, and gives the
student an early insight into the changes and circulation which
the materials of the crust are undergoing ; movement and meta-
bolism analogous to that of a living being. When this has
been brought home from as many points of view as possible,
interest or even enthusiasm will have been stirred sufficient to
spur the student on to make out the structure and composition
of the crust, the history that it has passed through, the dependence
of landscape in these factors, and the reaction of all of them
upon the plant and animal population, and even on man and
his occupations.

Unlike some other branches of nature study, that of the
physical environment is closely dependent upon the exact locality

INTRODUCTION 93

in which the study is carried on. Sometimes one branch and
sometimes another will afford locally special facilities. But there
are few districts in which some branch cannot be pursued with
exceptional success, and it is in discovering the most appropriate
branch that the skill, knowledge, and insight of the teacher is
called out. Sea shores, hill country, abrupt valleys, broad plains,
lakes, alluvial lands, glaciated country, bare rocks, forest land,
mining ground, each presents its own peculiar problems and
each one cannot fail to furnish material for observation and
induction which in the hands of a skilled teacher will lead to
important results, not only in earth knowledge itself, but in giving
a better understanding of the physical environment of life.

The destruction of the surface of the country by some form
or other of denudation is a process which can be studied anywhere.
Facts can be easily collected and reasoned upon, and certain
inevitable consequences so readily foreseen that this branch of
study seems to be naturally marked out as the most convenient
and logical starting-point, and the one most readily available for
all teachers of the subject.

Sir Archibald Geikie, in his admirable Primer of Geology,
made good use of the phenomena of a road as an introduction
to the study of denudation, and the condition of most of the
roads and lanes in the United Kingdom still leaves them quite
as suitable for physiographic study as for bearing the strain of
modern traffic.

A road surface may be regarded as made up of stones, rounded
or edged, packed fairly close together, the remaining interstices
being filled with smaller fragments, grit, and dust. If this
material is packed tightly together, if it is thick enough and rests
on a solid foundation, and if the weather is not too wet, too dry,
or too cold, the coating will remain unbroken, and will stand
the passage of traffic over it. The friction of wheels will, however,
begin to wear away the surface of the stones, and the weight
of traffic will tend to crush down any irregular projections of
them and any softer constituents that they may contain. Both
these causes will be productive of finely crushed rock, which
is known as dust when dry and as mud when wet. The change
of solid, hard stone into dust or mud is known to geologists as

94 THE BOOK OF NATURE STUDY

mechanical disintegration, and the disintegrated material is now
ready for removal by natural agencies or by artificial means.

In dry weather the wind picks up the fine particles, sweeping
them along for a distance, and dropping them as it dies down.
Much of the -dust falls on the road again, some is transported to
the road-side, some deposited on the grass, hedges, and trees, and
some distributed over the bordering fields. On the whole, much
finds its way off the road into the fields, for after a spell of high
winds the roads are found to be scoured clean and to become
quite dustless. Examination of the surface at this stage will
show that the stones project for a fraction of an inch, the dust
having been removed to this depth from between them.

But in wet weather the dust becomes mixed with water, and
if enough rain falls the mixture flows off the road, either directly
down the slope to the side (the " camber " of the road) or for a
time along the wheel tracks, eventually escaping towards the
lower ground at the side. If the rain is heavy, or if the gradient
of the road, or its camber, is steep, the water gathers in little
torrents which flow with considerable velocity. A glass should
be filled with the muddy water and allowed to stand. When
the water has cleared, a layer of sand and mud will be found to
have settled in the glass, and if this is dried and weighed an
estimate can be formed of the amount of material transported
off the road by the rain.

The road should be visited as soon as possible after the rain
has ceased, and attention should be directed to two principal
points ; the course followed by the water, and the bottom of slopes
where its flow has been checked and the transported material
deposited. The general road surface will be found to have been
" washed/' all the mud and dust having been swept off the
surface of the bare stones, and the stones themselves will now
project slightly, some of the "binding" dust between them
having been removed. Besides this, " ruts " will have been cut
by small water courses wjiich have run along or across the road.
The formation of these will mean not only the removal of dust
and mud by the torrents, but also of grit and smaller stones ; while
in the case of heavy rains or steep slopes the heavier metal of the
road surface may have been cut right through. This explains

INTRODUCTION 95

the invariable roughness of roads with high gradients, dust binding
being quite insufficient to hold the road-metal together.

Material swept off the road will be found deposited, unless
the natural or artificial drainage to a stream has been unchecked,
where the gradient slackens, and if such a spot can be found the
deposit should be studied. It will show at the surface sticks,
straws, leaves, organic debris, and anything which could be
floated by the water. Under this will be heavier material too
dense to remain in the water unless it is in swift motion ; this
is said to have been carried in suspension. The upper part of
this deposit will be made of the finest grained material, that which
would take longest to settle through the water. Lower down
the size and weight of the grains will increase ; and lowest of
all, there may be recognisable fragments of the stones used in
mending or making the road, at first tiny, but becoming coarser
and coarser towards the bottom of the deposit.

Opportunity should be taken to observe the action of normal
and gentle showers in contrast to torrential rains ; it is instructive
also to note the action of the same rain on slight and on steep
slopes ; and if the condition of the road has been noted before the
rain it will be valuable to study the effect in relation to the amount
of disintegration which the surface has undergone. The effects
may be co-ordinated with such conditions as the dryness or wetness
of the road, the occurrence of frost or thaw, the breaking up by
heavy traffic, the smoothness of the surface, and perfection of in-
corporation by rolling, the nature of the road metal, and the
composition and amount of binding material between the stones.
These observations will help to bring home the influence of original
consolidation and of prior disintegration as factors in surface
destruction.

It is now known as the result of experiments that wet stone
wears more rapidly than dry stone, but there is compensation
in that a moderate amount of moisture keeps the binding material
together and checks the movement of stones under traffic. Thus
slight watering of the road is on the whole beneficial ; but the
heavy watering usually practised, particularly with intervals of
drying in between, not only makes the stone wear and break up
more easily, but liquefies the binding material, washes it loose,

96 THE BOOK OF NATURE STUDY

and allows the movement of the stones under traffic. This at
once introduces friction between adjacent stones with renewed
wear and the production of still more dust. At the same time
the bonding of the metal breaks down, and it is more easily shifted
by water currents. Such a road soon begins to show cross channels
running down the camber, which are filled with runnels at every
watering and every shower, and are cut gradually deeper until
the road surface is destroyed.

It is in summer that alternate wetting and drying combined
with traffic give rise to most disintegration. But in winter frost
is more effective, and its results may be easily studied. Water
between the grains of the binding material freezes and expands.
This either raises the whole surfacing of the road or else pushes
up the binding material between the stones. The latter effect is
better seen in a garden path. While the frost lasts the ice cements
the whole material together into a hard rock-like mass ; but
directly the ice thaws and is replaced by water the metal is left
in a loose condition and the surfacing is readily ground up by traffic
or washed away by water currents.

A waterproofed road should be studied in contrast with a
surface of imperfect macadam. In this case all dust is first
removed ; the metal is rolled in with rock-chips, not ground to
dust, and the whole is bound together with tar. Water being
thus excluded, frost cannot work between the stones, and the
binding material cannot so easily work up into mud and dust.
Movement of adjacent stones against each other is checked, and
wear is reduced to the direct friction of traffic on the surface.
Disintegrating agents being thus rendered inoperative, the effect of
storm water is very much diminished. Unless traffic breaks through
the waterproof crust, which happens when the foundation on
which it rests is unstable, such a road will last until the surfacing
is absolutely worn away.

A detailed and comparative study of the two types of roads
is capable of furnishing some important conclusions which flow
logically and easily from the observations. The process of de-
struction is seen to be a twofold one, each part of the process
playing into the hands of the other. Disintegration is carried on
by water in the liquid state or when freezing, and by the move-

INTRODUCTION 97

ment and mutual friction of material under traffic. Water action
is partly mechanical, allowing more ready movement of ill-con-
solidated material. It is partly chemical, removing any con-
stituents of the stone or its binding material which are soluble or
capable of decomposition. Frost action and that due to traffic
are entirely mechanical. Transport is almost entirely mechanical,
and is effected by wind or water, the disintegrated matter being
swept off and eventually deposited elsewhere. That removed
must be replaced by periodical surfacing if the road is to be
maintained in usable condition, for the condition of the removed
material when it comes to be deposited by wind or water is not
suitable for further road making or mending, although some
misguided surveyors save it up carefully and eventually use
it as a cheap and very bad binding material.

The faster the surface disintegrates the more rapidly is the
material carried away. On the other hand, the removal of mud
and dust by torrential action continually exposes new surfaces to
disintegration. The checking of either process lengthens the life
of the road, and the ideal road would be one in which there was no
wind or water action and the wear and tear restricted to that
due to the traffic itself, and one built of such hard material that
even this wear was reduced to a minimum. Towards this end
waterproofing is an important step, because it reduces disinte-
gration very considerably. Lessening the camber and gradient
checks the speed and hence the transporting power of running
water, and the construction of immovable, well-drained, founda-
tions diminishes the breaking up of the surface by the weighty
traffic. Further improvements will come in the direction of
lessened watering, avoidance of any hammering or plucking action
on the road, and the interposition of softer and more resilient
substances between the traffic and the road.

The examples thus described serve very well to introduce the
subject of natural denudation. It is only necessary to replace the
surface of a road by that of a landscape, and the same or similar
agencies will be found at work. These should naturally be studied
next, attention being devoted to such parts of the process as the
district allows to be seen in operation.

VOL. vi. — 7

CHAPTER X
DENUDATION

IN studying the denudation of natural surfaces it will be best to
begin so far as possible with disintegration. The work of frost
is perhaps that which lends itself most readily to both ex-
periment and observation.

The fact that water expands on freezing may be demonstrated
by the breaking of a bottle, or even of an iron receptacle, in a
freezing mixture. In most places displacement of stones in walls,
disintegration of roads and paths, and bursting of water pipes,
during frost may be observed. Use can be made of the fact that,
though the damage is done on freezing, the results become apparent
only with the ensuing thaw. In quarries it will be possible to
show that rocks are traversed by natural fissures into which water
can penetrate and then expand with irresistible force on freezing ;
the stages in detachment can be seen in Fig. 8. In a hilly
country there will usually be screes, or heaps and trails of
angular stones broken from the crags by frost (Fig. 9). If these
screes are traced upwards to the crags which feed them evidence
of frost action will generally be apparent ; and it may even be
possible to show that crags and peaks are the residual forms
resulting from the wedging action of frost. The larger stones of
the upper part of the screes will also be found to be split again
and again by the same agency during their downward travel. In
towns flagstones generally demonstrate the action of frost by the
formation of hollow centres. The water saturating the cement
between the grains of the upper layers expands on freezing,
causing the layers to bulge upwards as they are held tightly at
their ends. These layers, then unsupported by the rock beneath,
are easily crushed, and the fragments brushed or blown away.
During rains water settles in the hollows so produced, and the
action is repeated. The disintegrating effect of alternately

DENUDATION 99

freezing and thawing a moistened porous rock like sandstone
might be demonstrated experimentally. Disintegration of this
sort does not affect the composition of the rock, merely its state
of aggregation, and it is hence called mechanical disintegration.

As an example of chemical disintegration, it is best to take
a sandstone or conglomerate, cemented by carbonate of lime, and
submit it to the action of dilute hydrochloric acid. This will
demonstrate that the rock consists of insoluble sand or pebbles,
united by a cement soluble in the acid. Similar action on a
limestone will show that the insoluble portion is insignificant, and
the soluble constituent is in excess. Hydrochloric acid is in
nature replaced by carbonic acid, which is washed out of the air
by rain and held in solution by it. In the field the surface of a
sandstone will often prove to be converted into loose, uncemented
sand, the usual cement, carbonate of lime, being susceptible to
solution by rain-water containing carbonic acid. The exposed
part of a conglomerate will pass into a loose, pebbly gravel under
the same influence. If a limestone is similarly exposed it will be
found to be encrusted or replaced by clay or rotten-stone, the
former the insoluble argillaceous ingredient of some limestones,
the latter the siliceous ingredient of others. If the limestone is
a chalk with nodules of flint, the flint will be left behind and the
chalk dissolved.

Even much harder rocks than these are attacked by carbonic
acid. Granite, basalt, and other volcanic rocks are found to have
some of their ingredients, and especially their most important
one, felspar, decomposed by this weak acid, some of the con-
stituents being dissolved and carried away in solution, and others
left behind in a soft condition resembling clay. The effect on the
rock is like that of removing cement.

Thus hard and solid rocks are found to be broken up by either
mechanical or chemical disintegration, and the resultant material
is left ready to be removed, while the process of removal is rendered
very much easier than if the unaltered rock had to be dealt with.
This second process, the removal of material, is known as transport,
and disintegration and transport together make up the process
of denudation by which the surface of the earth's crust is being
continually changed.

ioo THE BOOK OF NATURE STUDY

Gravitation is the force which is most active in transport,
but it may act through various agents, or it may be operative by
itself alone. For instance, on a mountain side fragments broken
off to make screes are always in unstable equilibrium, and the
least impulse sets them travelling down hill. Even if there is no
other cause, the loading of the upper part by fresh frost-falls is
sufficient, and it is well known that roads crossing screes are very
liable to be blocked in frosty or wet weather. Indeed, there is one
case known to the writer where, when the road needs mending, a
hole is made in the boundary wall and the scree allowed to flow
out on the road. The metal is just spread, the wall mended, and
the deed is done. In the normal course the material travels
down until it reaches a stream, which then undertakes the sub-
sequent transport.

But in many types of country it will only be possible to start
with the material found in a stream, to observe it being carried
downward, and to reason back to its derivation from the place
where the parent rock is exposed. From a stream in spate it will
be possible to collect muddy water and thus to test the power of
running water to carry mud and sand in suspension. The trans-
port of larger fragments by rolling along the bottom is less easily
demonstrated, though it can often be heard; still, the fact that
such fragments are generally present in a stream bed, and that
they are usually rounded and rolled, is quite obvious and may be
reasoned upon. It may thus be inferred that the stream utilises
the products of disintegration, and, knocking off their angles and
edges as they are rolled along, it impresses upon them its own
" tool-mark/' the rounding and rolling of the fragments, until
they pass into pebbles and gravel.

It will also be possible to show the relation in form and size
of pebbles to the hardness of the rock of which they are made,
and the control exercised on their form by the shape of the
original fragments, a consequence of the rocks from which they
are made. At the same time, the share that transported material
must take in deepening the water course may be pointed out,
and it may be possible to show the accelerated rate of work at
certain parts of the stream, such as rapids or waterfalls, where the
velocity is specially great (Fig. 69), or its special type where eddies

FlG. 8. — Frost action along joints. Ilkley.

(Photo by GODFREY BINGLEY.)

FIG. 9. — The Screes, Wastwater.

(Photo l>y A. PETTITT, Keswick.)

FIG. 10. — Globigerina
Ooze, Atlantic.

FIG. n.— Baxendale Gorge, Ingleton.

(Photo by GODFREY UINGLEY.)

DENUDATION .-•- \ : : ,.,^ r .ipl

produce pot-holes or curving hollows and recesses (Fig. u). From
this we can pass to the relation of stream to valley, and show that
the inevitable effect of water running with sufficient velocity will
be to excavate and deepen the course along which it runs ; the
excavation being more rapid where the fall is most abrupt and
the speed of the running water greatest. Thus the work of a
stream is such that, even if there were no valley to start with, but
only a slope, a valley would certainly be excavated, and it is
therefore more likely that the stream has made its valley than
that it found one ready made and took possession of it. This is
one of the many cases where observations like those advised in
the last chapter can be utilised.

Not all the work of a stream is carried out mechanically. A
good deal of it is performed by invisible chemical means. The
evaporation of filtered stream water will show that much dissolved
matter, chiefly consisting of salts of lime, magnesia, iron, and
alkalies, is carried by all rivers.

It will be noted that while a stream is always carrying out a
certain amount of work, this is very much intensified during
storms and floods. At such times more erosive and trans-
porting work may be done than during years of steady flow.
This is an important principle which applies to nearly all forms
of denudation ; a slight increase above the normal power increases
the effect in a geometrical ratio.

In limestone countries the absorption of much of the rainfall
into the ground and its travel along underground channels can be
demonstrated and its work observed or inferred, but it will be
hardly possible at this stage to explain the causes which bring
the water again to the surface. Underground water or that
issuing from springs might, however, be examined for suspended
and dissolved contents to prove that its denuding work is con-
tinued during its underground journey. The issuing of under-
ground waters at springs is one of the most important sources of
streams (Fig. 71).

Neither will it be possible in this country to study directly
the transporting and erosive power of glaciers, which in high
altitudes and latitudes replace the streams with a flow of ice.
That is better deferred until deposition has been studied.

XQ2 1 THE -,BOOK OF NATURE STUDY

But at the sea-side special attention can be given to marine
denudation, because all stages from the rock of the cliffs to the
rounded shingle can be easily observed. The cliffs can easily
be seen to be undergoing both chemical and mechanical dis-
integration, especially the latter. The usual agents are at work,
frost and gravitation send down broken fragments to lower levels ;
rain and carbonic acid remove cement ; the rain mixes with softer
material making mud, which can flow or slip downwards ; and
springs carry out material or undermine rocks and cause land-
slips. But the waves have their own ways of disintegrating, partly
by hurling shingle, stones, timber, or at times ice, at the cliffs,
and partly by driving air into the crevices with a force often
amounting to thousands of pounds per square foot. The com-
pressed air pounded up in this way expands on the retreat of the
waves and is like a charge of explosive inside the rock, causing it
to burst outwards into fragments (Fig. 12).

The transporting effect of the sea is due to its wind-waves,
especially during storms, its tides, tidal currents, and ordinary
currents. Wind-waves are continually picking up and dashing
down all rocks that they can lift. The friction and impact reduce
the size of these rocks, round their corners and angles, reduce
them eventually to pebbles and shingle, and make sand and mud
out of the chips broken from them in the process. All stages of
the work can usually be observed at the sea-side. The rise and
fall of the tide extends the range of the sea's action. The coarser
denuded material is left between tide-marks until it is reduced
to a fine enough condition to be transported by currents, when
the sand is spread out down to and below low tide, and the finer
mud swept some distance out from shore.

It will be observed that it is the harder rocks of the shore from
which pebbles are made, the softer being broken down to sand and
mud and carried away. Further observation will show, if the land
is made of several different kinds of rock, that the contour of the
coast also follows the law of resistance, — the hard rocks jut out as
capes and headlands, the softer are recessed into bays and gulfs.
In other words, the hard rocks project beyond the average contour
of the country into the sea, just as they project above its average
relief into the air as hills (Fig. 13). But in spite of the greater

FlG. 12. — Marine Denudation, near Scarborough.

(Photo byf GODFREY BINGLEY.)

FlG. 13. — Selective Marine Denudation. Lulworth Cove.

(Photo by GODFREY BINGLEY.)

4 : «.*' . " •» J

' v l k - v»% » »* » °c. cC

FIG. 14. — Work of Storms, Pakefield. Lowestoft.

{Photo by S. H. WRIGHTSON.)

FIG. 15. — Wind Erosion. Brimham Rocks.

(Photo by GODFREY BINGLEY.)

DENUDATION 103

resistance of the harder rocks, eventually both hard and soft are
cut back by the sea at approximately the same rate, and the sea
advances steadily upon the land, cutting the cliffs back until, if
left alone to its work, it would mow down the whole of the land
and reduce it to a flat plane below its own surface. Such sub-
marine plains are to be found round most continents and islands,
and are called plains of marine denudation.

The action of the sea in planing down the land before it is
in strong contrast to that of streams in lowering only their own
definite paths. The latter are engaged in producing relief of the
surface, the former in levelling down all outstanding features.
The ultimate effect of the sea must be inevitably to cut down all
land to a plain (Fig. 14), while the stream and its tributaries tend to
accentuate relief of the surface above sea level. It is less easy to
draw any distinction between the fragments denuded by running
water and those prepared by the waves. Both are rolled and
rounded, but the action of the sea produces greater perfection in
these characters than does that of flowing water.

As in the study of a road and of a stream, the powerful effects
of the sea are not so much due to everyday work as to occasional
and infrequent heavy storms (Fig. 14). These phenomena, which
to human reckoning are uncommon and infrequent, are of the
class of irregularly recurring actions, when long periods of time
are in question, and the effect of their recurrence is a matter to
be seriously reckoned with.

Wind is in some places an important transporting and eroding
agent. It acts chiefly on light small materials, such as sand
grains. These when drifted gradually become rounded and
polished, and they react on the rocks that they strike, etching
and undercutting them. Fig. 15 gives a characteristic example of
a projecting rocl: the softer layers of which have been cut into by
wind-drifted sand and dust.

Denudation by the agents so far dealt with is a function of
time and energy. It is most active with heavy rain and winds,
with steep bare slopes, with rapidly moving waters, and in
jointed or soft rocks. It is perhaps less easy to show that at
all times and under all circumstances slow but certain denuda-
tion is being carried out, so long as the slopes of the country are

104 THE BOOK OF NATURE STUDY

sufficient to allow of downward movement under the influence of
gravitation.

In countries where denudation more generally escapes observa-
tion the slopes are gentle and the bare rock is covered with subsoil
and soil. The surface may be cloaked with forest or affected by
cultivation, but until the slopes become so gentle that gravitation
and its agents are rendered inoperative through friction, denuda-
tion will still be carried on under the covering of forest or of field
vegetation.

In order to appreciate this, the soil and subsoil should be
studied. The latter consists of fragments and products derived
from the disintegration of the rock below by frost and rain armed
with carbonic acid. The latter contains the same substances in
a finer state of division mingled with the results of the life of
animals or plants. A section through from the surface of the soil
down to the rock shows that there is a gradual and imperceptible
transition from one to the other. At first the rock has its joints
widened somewhat, then large pieces become detached, and these, in
turn, are broken again and again. This is mainly frost work aided by
carbonic acid. The latter agent partly dissolves and disintegrates
the outer parts of the fragments, rounding them a little, enabling
the outer crusts to scale off, and increasing the proportion of finer
material. The roots of vegetation help in the process, partly
by splitting rocks open, partly by introducing carbonic and
organic acids as they decay. Burrowing animals give new
channels for action, bring material to the surface, and help to mix
the constituents. Worms are very important at this stage.
They pass the fine material through their bodies, extract organic
matter from it, and deposit it in a still more finely divided state at
the entrance to their burrows.

If this all occurred on a flat plain it would afford no aid to
denudation, but practically slopes are everywhere ; and as gravi-
tation will always tend to pull everything downward on a slope,
its power will be increased by whatever brings material into an
easier condition to move. Worm castings and the heaps of soil
thrown out by rats, moles, and rabbits, will be washed flat by rain,
but if on a slope a larger amount of the debris will go in the down-
hill than in the uphill side of the heap. Again, when disused

DENUDATION 105

burrows and the sites of rotting roots collapse, the main movement
of their bounding walls will be downhill. And indeed, settle-
ment of all kinds lubricated by rain and aided by the thrust of
frost will be in that direction. So the whole soil cap, except on
dead levels, will be gravitating downhill, the only check, and that
a temporary one, being provided by the tangle of root fibres.

At the bottom of the slope flows the stream, with banks of
soil and subsoil, whether it reaches the rock below or no. The
banks are continually collapsing into the stream, and the material
is carried away to sea by it. Yet the stream gets no wider, because
the soil of its banks is continually travelling down towards it,
making good the loss. Thus disintegration through soil making is
steadily going on all over even the best cultivated parts of the land,
and throughout such areas this disintegration is providing the
streams with material to transport no less certainly than where
screes carry down the stones obviously broken from bare rock scars.
Only, in the latter case the whole process is easily seen, while in the
former the vegetation masks all movement and change, and the
landscape a thousand years hence may be undistinguishable from
that of to-day. Minute measurement, however, would show that
the entire area of the valley sides had been somewhat lowered in
the interval ; and material taken not from the river's course only,
but from its whole drainage area, would have been carried off by it
to the sea.

This process can, of course, only be carried on so long as the
slope of the country down to the stream is sufficient to allow of
downward movement against friction and obstacles. Gradually
the slope will become more and more gentle ; movement will
become more and more slack, until everything comes practically
to a standstill. When this condition is reached the country will
be one of almost imperceptible slopes, and it will be said to have
been reduced to base-level. When this stage has been reached
denudation will cease, and it can only be renewed if gradients
are increased by an elevation of the land to a higher level. Such
base-levels may often be seen near the coast and less commonly
in flat plains inland.

Part of the function of a stream is to deepen its valley by
means of the load which it rolls along. But while a small part

106 THE BOOK OF NATURE STUDY

of the material it transports is obtained by this erosion, the majority
is but a modified form of that delivered to it by its lateral dis-
integrating agencies, — screes at the higher levels, soil at the lower.
Its main function is to scavenge out the material disinte-
grated and delivered to it by all agencies working all over the
land surface. Thus the rivers will contain, until they are com-
pelled to deposit it, the whole of the material denuded on the
surface of the entire country, and the measure of that material at
the mouth of the river gives the rate at which the whole surface
of the land is being lowered by all types of subaerial denudation.
This rate will, of course, express the rate at which the water course is
being lowered, but each lowering of the river-bed will accentuate
the slope of soil and scree towards the river, and quicken the
downward movement of such material to it. Hence the total
delivery of the river to the sea will measure also the general
lowering of the entire surface of the country by superficial de-
nudation.

The rate of lowering by delivery of debris to the sea varies
considerably under different circumstances. The Mississippi
lowers its basin at the rate of i foot in 6000 years ; the Danube
is somewhat slower, i foot in 6840 years, while the swift-flowing
torrent of the Po is responsible for lowering its basin at an average
rate of i foot in 730 years. To this must be added matter in
solution, which averages the removal of i foot in 13,200 years,
while the work of the sea is about equal to the river average of
i foot in 3000 years.

This study of denuding agents makes it clear that the land of
the world is being steadily destroyed at the rate of about i foot in
1350 years, and the products carried to the sea margins. At the
rates given the whole land of Europe, of an average height of
671 feet above sea level, would be planed down and disappear
in less than a million years, its debris being spread out beneath
the ocean. The inevitable conclusion is either that denudation
could not have been going on for all this time at this rate, or
that new land has been formed to compensate for the continuous
destruction. This proposition must now be discussed in the light
of conclusions drawn from the disposal of denuded material.

CHAPTER XI

DEPOSITION

DUST and mud worn from a road are found to be carried by
the rain torrents so long as the latter have sufficient velocity.
If the water passes off to a drain or brook the debris is carried
away still farther by them. But if hollows occur in the road
surface, or if the gradient flattens out, some or all of the debris
will be deposited, and the deposit may be examined, when it has
dried somewhat, by cutting across it with a knife or spade. The
nature of the material and its arrangement are the two points
to which attention should be especially directed. Coarser matter
will have been the first to drop, then finer sand, and at last the
finest grained mud, the position of each being related to the
slackening velocity of the water current. Thus deposition is
accompanied by sorting. The arrangement of individual frag-
ments, such as water-logged leaves and sticks and bits of slate or
shale, will show that they settle with their flat sides horizontal,
and their long axes in the direction in which the stream was flowing.
Some of the debris swept down by a stream will be found de-
posited wherever the stream slackens in velocity. If it has over-
flowed its banks it will be found to have spread an even coat of
mud or sand over the flooded meadows, laying down a thin sheet of
sediment over the whole area, which in these cases is generally a flat
one (Fig. 68). Digging down below the surface, it may be possible
to show that the soil in which the meadow grass was growing before
the flood is made of earlier deposits of the same kind of stuff
laid down in similar flat layers. If we imagine the same process
to have gone on for a long period, a great thickness of silt will be
thus laid down in successive sheets parallel to one another and to
the surface on which they began to be laid down. Such thin sheets
are called lamince, and the structure as a whole lamination of the
deposit.

io8 THE BOOK OF NATURE STUDY

The delta of the Nile during inundations is similarly covered
with a fine sheet of silt, to which it owes its astonishing fertility,
for this silt has been derived by the river from floods which have
washed away the finest and best of the soil from higher up stream.
But in the dry intervals between the inundations the wind drifts
sand in from the desert, and this is also spread out, by the wind,
into a thin coat. Thus the deposit is a laminated one, and consists
of alternate lamince of silt and sand. As the material dries it
tends to split up into thin layers parallel to the lamination.

Now many fine-grained rocks which make up the earth's crust are
found to exhibit this very type of lamination (Fig. 12). They split
into thin layers which may be merely planes of parting, as in the
silt of an English river, or they may consist of alternating mud and
sand like the Nile deposit, or they may be layers differing in some
degree in colour, texture, or composition. Moreover, the materials
of which such rocks are made are like mud and sand, the only
difference being that the laminated rocks are harder and more
solid than the laminated sediments. Consequently the pre-
sumption arises that these rocks may possibly have been formed
by the deposit of similar sediment which has been subsequently
consolidated.

The deposit just described is called alluvial, and it may generally
be found wherever a river bed flattens out laterally or longitudin-
ally (Fig. 58). Alluvial plains are famous for their fertility, though
there is the inconvenience that they are occasionally flooded. After
a flood it may happen that the water has taken a new course, but
even if it has not done this, the mere fact that a river frequently cuts
into one bank more than another will cause it to shift its position on
its alluvial plain. Travelling at slow speed it is easily turned aside,
and meanders over its plain, at one time at one side or other, and
at another time in the middle of its valley. When it enters a
lake similar debris is spread over the lake bed, and as the supply
of mud to the river fluctuates in amount, depending on the work
of rain at higher levels, the deposit on the lake floor will be inter-
mittent, and hence it is likely to be laminated. The lake may be
ultimately filled up and obliterated in this way, and many lakes are
to be seen not yet quite filled up but with deltas of detritus spread-
ing out from the mouths of the chief silt-carrying rivers (Fig. 16).

DEPOSITION 109

If lake deposits are not available for study a great deal in the same
direction may be learnt from the deposits in a pond if it has been
drained.

In the deposit of this fine-grained material, which is suspended
in water and can be carried great distances by it before sinking,
the prominent characteristic feature is the flatness, regularity,
parallelism, and wide extent of the laminae.

In certain parts of its course a river is capable of depositing
coarser material such as pebbles and sand. While the fine material
is in suspension and may thus be spread over a wide area before
sinking to the bottom and finding rest, the coarser is rolled along
the bed of the stream just so long as the speed of the water is
sufficient. Directly the speed is checked the coarser material
must be dropped and, with further checking, that which is some-
what finer. Now the velocity changes with the gradient of the
river bed, and also as the river winds from side to side. Conse-
quently layers or spits of gravel are formed at these spots, and
the principal facts with regard to such deposits can be easily
observed there. Although pebbles are seen to be laid down with
their flatter sides and longer axes parallel to the surface on which
they are dropped (Fig. 25), such surface is usually inclined, and the
mass is heap-like in general shape. As the river winds from side to
side, or as it cuts its bed down deeper, it tends to destroy such gravel
masses and to move on their constituents to a lower level. Some
of the masses will generally survive, and it will often be found that
gravel pits have been opened in them, both when they are near the
river level and when they occur as terraces above the present level,
the river having deepened its valley since they were deposited.

Examination of one of these gravel pits will show that the
deposit consists of irregularly alternating, bed-like; masses of gravel
and sand (Fig. 17) ; their laminae are generally inclined and in
successive groups not parallel to one another. Such lamination is
called oblique, and it is an almost invariable accompaniment of the
deposit of coarse material rolled along and not held in suspension
by water. The process of formation will be understood if the
making of a quarry tip or a heap of pit waste or an embankment
is watched. The stuff is tipped down from wheel-barrows or
trucks on to the slope of the bank. Its successive layers, each a

no THE BOOK OF NATURE STUDY

truck load, are spread out parallel to the surface at the point
where they are tipped down. In addition to the oblique lamina-
tion, it will be seen that the masses of pebbles and sand considered
as a whole are wedge shaped, not bounded by parallel surfaces,
thinning out in one or more and probably in all directions (Fig. 17).
This phenomenon is called false-bedding.

As such structures are produced by the dropping of material
which has been rolled along, they are naturally the result of deposit
in moving water under the action of currents in shallow depths,
and they will be characteristic of coarse-grained deposits. Similar
structures are to be found in the rocks of the earth's crust, chiefly
among conglomerates and sandstones which yield other evidence
of having been formed under precisely these conditions (Fig. 25).

The deposit of river-borne material on land is only temporary ;
the bulk of it is taken up again and eventually carried out to sea.
Here it is largely deposited in the form of deltas consisting of
fine-grained debris laid on the sea-bed until it is built up to the
water level and can be taken possession of by vegetation. Here
the lamination structures will originate as a result of the alterna-
tion in supply of material, each lamina representing the supply
brought down during a definite interval of time, a spate, a rainy
season, or a period of rapid disintegration. The deltas at the
mouths of the Nile and Ganges cover thousands of square miles,
and represent the deposit of matter denuded from large drainage
basins.

Even this does not account for the whole denuded material,
for much of it, especially in tidal waters and those swept by
marine currents, is carried out to sea and eventually dropped over
a large area of the sea bed. The sea margin is generally edged
with coarse deposits of shingle and sand, which acquire the usual
characters of shallow-water deposits. But the finest material is
carried much farther out and spread over many thousands of
miles of sea bed. As, however, the water gets more and more
still below the surface, it is rare to find mechanically denuded
material more than 300 miles from the shore, and it does not
usually spread more than 200 miles. Dispersed over so wide an
area, the material carried out during any particular interval of
time must be spread very thinly over the sea bed. Hence the

FIG. 16.— Delta in Loch Lubnaig.

(.Photo by A. S. REID, F.G.S.)

FIG. 17.— Sands and Gravels. Middleton on the Wolds.

(Photo by GODFREY BINGLEY.)

FIG. 18. — Bedded Limestones. Isle cf Man.

(Photo by GODFREY BINGLEY.)

FIG. 19. — Stratified Rock. The rocks being nearly horizontal, the road approximately

follows a contour-line.

(From WELTALL UNO MENSCHHEIT, by permission.)

DEPOSITION in

laminae will be thin and close together and the rate of deposit
extremely slow.

In all waters there is abundance of life, most of the forms being
provided with skeletons, shells, or tests of some kind. When they
die the hard parts fall to the sea bed, and if not destroyed they
will lie flat on this bed until buried up in the accumulating sedi-
ment. Then they may be preserved and their mode of occurrence
in the silt will be exactly the same as that of the well-known
fossils which may so often be collected from beds of sandstone or
shale. The bulk of the organisms so buried and fossilised will be
those which have lived in the water above ; but others will be
drifted or blown in : Thus, mingled with a majority of marine forms
of life, there may be remains of terrestrial plants, fresh-water,
terrestrial, and even aerial animals.

As all mechanically denuded matter is arrested comparatively
near to the shore-line, it might at first be supposed that there would
be nothing to cover the bare sea bed beyond this distance. But
there is no limit to the distance dissolved matter can travel ; and
the composition of sea water shows that it is everywhere present
in about even proportions. Some of it remains permanently
in solution. But some, like carbonate of lime, phosphate of lime,
and silica, is taken out of solution by animals or plants to build
their tests or skeletons. Hence their remains, while mingling with
the mechanical deposits within the " mud line/7 will be the
exclusive possessors of the sea-bed outside that line, and here may
give rise to calcareous, siliceous, or phosphatic, organic deposits.

Many deposits of this class are known. A very large area of
the ocean floor is covered with a pale, sticky, deposit known to
sailors as " ooze." This on examination is found to be chiefly made
of remains of calcareous foraminifera (Fig. 10), mingled generally
with varying proportions of shells, many of floating or free-
swimming forms. Other deposits are formed by corals, others by
dead shells, some by calcareous algae, by Crustacea, sea-urchins,
fish-bones, sponge-skeletons, diatoms, or radiolaria. These are all
organic deposits, having sometimes a calcareous composition like
limestones, sometimes phosphatic, and sometimes siliceous like
cherts or kieselguhr.

The site of organic deposits and of the different varieties of

U2 THE BOOK OF NATURE STUDY

mechanical deposit are connected with the relative stillness, and
hence with the depth of water. If the ocean were to become deeper,
organic deposits would encroach upon the mud and sand of a
previous epoch. On the other hand, a shallowing of the sea, such as
accumulating sediment causes, would result in mechanical deposits
encroaching on and covering organic deposits, and in the coarser
mechanical sediments overlapping the finer grained. At the end
of a long period of such changes we should expect to find an
alternation of large sheets of deposits of these kinds, a phenomenon
precisely similar to that known to geologists as bedding or strati-
fication in the rocks. It will be obvious that the material of any
bed may be laminated, and that the plains of lamination and
bedding will be approximately parallel, except in the case of
false-bedded deposits. This is also the character of rock strati-
fication, which may be defined as the occurrence of the rocks in
successive sheets, inches or feet in thickness, which differ from one
another in a marked degree in colour, character, or composition
(Fig. 18). Evidently this stratification is only a magnified form
of lamination, and it is really not possible to draw an exact line
between the two (Fig. 19). Both laminae and strata may vary
considerably in thickness ; in the case of laminae to the extent
of fractions of an inch, while strata may be a few inches or, in
extreme cases, hundreds of feet in thickness.

The deeper water strata are the most regular in thickness and
extent, as is the case with laminae, a character also borne out
in the rocks. A comparison 6f the structures in sediments and
rocks brings out the fact that they are identical in all vital
particulars, the containing and position of organisms, the lie of
the constituent fragments, and the parallelism of strata to the
laminae they are made of in relation to the coarseness or fineness
of deposit.

Shallow-water deposits, whether formed in the sea, in lakes, or
in rivers, are likely to show peculiarities worthy of observation.
Current or wave action will give rise to a ribbed or ripple-marked
surface of the sand, surfaces exposed in shallow-water or between
tides are likely to show tracks of animals (Fig. 20), casts or burrows
of worms, and there may even be present in exceptional cases the
cracks formed when mud or sand dries under the sun at low tide,

DEPOSITION 113

or the indentations impressed on the drying surface by rain. Thus
shallow water deposits may retain an impression of the sunshine,
the showers, and the breezes of the period when they were formed.
Examples of all these features may be seen in the rocks of the crust.

There is one class of deposit which is conspicuous, because in
it there is neither sorting of ingredients nor stratification. This
used to be known as drift or diluvium, and it was at one time
thought to be the deposit found by a tumultuous deluge. The most
characteristic form of the deposit is called boulder-clay, and it is a
mass of tough clay in which are embedded angular stones of all shapes
and sizes (Fig. 22). The stones have often been transported a long
way from their parent rocks, and the only sign of wear they generally
show is a certain amount of smoothing and polishing, and some-
times scratching and grooving of certain of their surfaces (Fig. 23).
There is no denuding agent now operating in Britain which is cap-
able of producing such material, and yet the boulder-clay is found
scattered all over the country north of the Thames, and is specially
abundant in the mountain districts. On comparison with de-
posits now being thrown down at the termination of Swiss and
Norwegian glaciers, there is found to be agreement in all the
points mentioned above. Glaciers are the drainage of the per-
manent snows of high altitudes and high latitudes, the snow passing
into the form of ice and being driven to flow down the valleys. Ice
flows infinitely more slowly than water, so it banks up in the
valleys and fills them to a great depth, unlike the water of a river,
which is confined to the waterway. Quantities of frost-riven
fragments fall on to a glacier, and are carried on its surface
or fall into its cracks. Armed with the last, the ice becomes
an important eroding agent, and rasps down, polishes, and
scratches its valley floor, wearing off quantities of fine rock flour.
All these materials are shot down when the glacier melts into a
pell-mell mass at its end, called a terminal moraine. During the
height of the Glacial Epoch, of which they give evidence, the
supply of ice was so great that it overflowed from one valley
system to another, and even crossed or ascended valleys and sur-
mounted watersheds which were opposed to its general course.

Acting on a country already much disintegrated by atmos-
pheric action, it soon gathered and transported great masses of

VOL. VI. — 8

n4 THE BOOK OF NATURE STUDY

material, some ground fine by its own action, some coarse and
angular because transported on the surface of the ice. This was
eventually shot down either in single valley moraines (Fig. 83), or
in great sheets of detritus which have filled up valleys or spread
over plains to a thickness of hundreds of feet. This drift covers
hundreds of square miles of lowland in Eastern England and
elsewhere, masking the rocks below and giving rise to new
types of landscape and soil. Among other results the ice has
transported boulders often of considerable size and in great quan-
tities for hundreds of miles from their source, and dropped them
when the ice melted. These travelled blocks, or erratics as they
are called, have been carried from the southern uplands of Scot-
land, from Ailsa Craig, from the Lake District, and from Wales
to many parts of Midland and Western England ; while much of
the Eastern Counties is covered with drift broken from the Chalk
or from other rocks derived from England itself mingled with
others brought from so far as Scotland and Scandinavia.

All denuded matter ultimately makes its way to the sea and
is there deposited. Where deposition is most rapid, on the
margins of the sea, the deposit is gradually brought up to the
level of the sea surface, and, being thus reclaimed, it is added to
the area of the land mass. This occurs in several parts of the
coast of Britain for instance, about Yarmouth and Lowestoft,
at Romney Marsh, on the Chesil Beach near Portland, and on the
Lancashire coast about Southport. The growth of land generally
begins with the deposit of shingle ; sand is then drifted in by the
wind, and eventually great heaps of sand known as dunes are
formed of drift sand, which increase in height and importance and
often gradually travel inland.

This is one way by which the waste of the land is made good,
but it is evident that if rocks in the earth's crust have been
made out of sediments in this way something more is necessary.
The sediment must have been hardened, lifted higher, and in
many cases tilted and broken ; and we have not yet observed any
process by which this might be effected. To this attention will
be directed ; yet it may be well to ascertain, in the first instance,
how close a comparison can be instituted between rocks and
sediments to see if it is worth while to pursue the inquiry further.

FIG. 21. — Sand Grains
(magnified).

(From a Photograph kindly lent
by Dr. C. G. CULLIS.)

FIG. 20. — Ripple Marks and Footprints, Triassic Sandstone.
Storeton.

(Photo by GODFREY BINGLEY.)

FlG. 22.— Boulder Clay, near Richmond, Yorkshire.

(Photo by GODFREY BINGI.EY.)

FlG. 23.— Glaciated Boulder. Withernsea.

(Photo by GODFREY BINGLEY.)

FIG. 24. — Crinoidal Limestone, Silurian. Dudley.

{Photo by F. MARTIN DUNCAN.)

CHAPTER XII
CLASTIC ROCKS

THE examination of specimens of rocks collected from quarries,
mines, or cuttings, or from road metal or building stone, requires
in most cases the use of a magnifying glass, and sometimes
microscopic slides must be prepared. Other observations may be
made by breaking the rock to pieces, washing it in water, acting
on it with acid, and, where necessary, analysing it chemically.
It is found that the ultimate constituents of all rocks are minerals,
chemical compounds capable of crystallising, and sometimes found
in rocks in crystalline shapes. In certain rocks some of the minerals
occur as crystals with their own shapes, and such rocks may be
called crystalline ; others have their minerals, not as perfect
crystals but as broken fragments of what have once been crystals,
and so may be called fragmental or clastic. Granite and basalt
are examples of the first class, sandstone and conglomerate of
the second.

It is best to begin with the consideration of the clastic rocks,
and no better type for the purpose exists than conglomerate
(Fig. 25). This is at once seen to be made of rounded pieces
of all sorts of other stones, granite, basalt, flint, limestone, sand-
stone. The pieces are of all shapes, but their edges and angles are
rounded. If broken out of the rock they are undistinguishable
from shingle or gravel pebbles ; they are made of the same kinds of
rocks and are of about the same shape and size (compare Figs. 25
and 17). They are set amongst finer pebbles and chips of similar
rocks, with sand or mud between, and all is bound up by some
kind of solid cement. The whole thing is very like concrete which
is made of pebbles and sand bound into a solid mass with an arti-
ficial cement prepared from lime. If the fragments of such a rock
are angular, like the fragments found in screes, the rock is called
a breccia.

n6 THE BOOK OF NATURE STUDY

Evidently to make such a rock at least one and usually more
kinds of solid stone must have been broken to pieces, the bits
rounded, and then fastened together. We have already seen
that denuding processes are capable of effecting the first two
results.

Sandstone is merely a conglomerate on a small scale. It is
made of fragments like grains of sand, broken up and rounded, often
stained and coloured, and then cemented together, sometimes
loosely, but often compacted into hard stone. The chief difference
between sandstone and conglomerate, apart from the scale of the
material, is that the fragments, instead of being bits of recognis-
able rocks, are now bits of broken and rounded minerals. The
chief constituents are rounded grains of a clear, transparent sub-
stance, which chemical and microscopical examination proves to
consist of that form of crystalline silica called quartz. Other
broken minerals are present in smaller quantities, such as felspar,
mica, and iron oxides. These constituents are mixed with mud
usually, and the whole cemented by carbonate of lime, silica, or
oxide of iron which gives the rock its colour.

It will be seen later that the disintegration of crystalline
rocks would yield minerals which might be broken up into the
constituents present in sandstone ; and it has already been shown
that ordinary denuding processes result in the production of great
quantities of sand, which may be either river-borne or deposited
on the seashore and below sea level. This sand has precisely the
same chemical and mineralogical character as the sand of sand-
stone (Fig. 21), and the two are identical in every respect, even
to the amount of rounding the grains have undergone and the
staining of them by iron oxide. A similar rock, but made of
angular quartz and felspar grains, is known as a grit, and it bears
the same relation to sandstone that breccia does to conglomerate.

Finer grained rocks are called clay if soft, shale if slightly
hardened and laminated, slate if much indurated. All agree in
the fact that they consist of very fine particles of hydrated
silicate of alumina (china-clay or kaolin) reduced to a fine powder,
and mingled with grit particles very minute in size. Cement may
be present as before, but it is usually not carbonate of lime, nor
is it conspicuous in quantity, the hardening being mostly effected

FlG. 25. — Old Red Sandstone Conglomerate. Forfar.
{Photo by GODFREY BINGLEY.)

FIG. 26. — Silurian Limestone, with Brachiopods, Crinoids, and
a Trilobite. Dudley.

(Photo by F. MARTIN DUNCAN.)

FIG. 27.— Raised Beach. Hope's Nose, Torquay

(Photo by Prof. S. H. REYNOLDS.)

CLASTIC ROCKS 117

by other means. The material is very fine grained, and agrees in
composition and character with the finer marine sediment and
that laid down in the central parts of lakes. If the deposit were
well laminated a shale would be formed, and if strong pressure were
brought to bear on the material it might be converted into a slate.

All the rocks hitherto described agree in being made up of
fragments derived from pre-existing rocks, broken, rounded, or
ground down to various stages of fineness. Any of them may
have been formed in the sea or by rivers or in lakes, and some
may even have been built up on land. The exact method of
origin would have to be decided in each case, mainly from the
fossils contained in the rock. The majority, on application of
this test, prove to have been marine in origin, and the sea may
be looked upon as the chief place of origin of the clastic rocks.

There are other rocks coming into the same category which are
not so obviously derived from pre-existing rocks. Chief amongst
these are limestones. There are many different sorts of lime-
stone. The majority are richly fossiliferous, the fossils being
sometimes seen on a fresh fracture; but they are more easily
collected from weathered rock, and in some cases are only seen
in microscopical slides prepared by grinding thin chips of the
rock till they are transparent. The majority of limestones when
examined in one of those ways prove to be made of broken frag-
ments of organisms provided with a calcareous skeleton or test.
Sometimes these are calcareous algae such as Chara or nullipores :
More usually they are animals such as foraminifera in the Chalk
or Carboniferous Limestone ; corals, crinoids, polyzoa, as at Dudley
(Fig. 24) or Wenlock ; sea-urchins, brachiopods (Fig. 26), as in
some of the Oolites ; lamellibranchs, gastropods, or cephalopods.
Most of them, again, are marine, but there are limestones made of
pond snails or land snails, and shell marls made from fresh-water
shells in lakes. Some few limestones are clearly made from car-
bonate of lime precipitated chemically from springs or in lakes,
and this is also probably the origin of some of the magnesian
limestones, which are usually very poor in fossils. Thus limestones
are rocks made from the carbonate of lime removed by chemical
denudation, precipitated either by the agency of life or by evapora-
tion of water and loss of carbonic acid.

n8 THE BOOK OF NATURE STUDY

Associated with the last class of rocks are the rock-salts and
gypsums, which have also been formed by precipitation occurring
probably in inland salt lakes.

The last of the more important groups of clastic rocks to be
considered are those in which carbon is an important constituent.
The only important deposit of such a character forming now is
peat, which is the result of the growth of numerous bog plants in a
damp climate. The plants grow and die down, and newer plants
grow on their surfaces ; the dead plants lose some of their gaseous
constituents and slowly pass into peat. Coal seams in like
manner are made of plant remains, which have probably grown
where they are found, and their harder and more protective parts
have gradually accumulated. On being buried up by later
sediments they have become compressed and hardened, have
lost some of their volatile constituents, become bituminous and
mineralised, and passed first into lignite, then into bituminous
coal, and lastly into steam-coal and anthracite.

There are, of course, many minor varieties of rocks and many
which stand intermediate between the forms described, but those
mentioned are typical of their classes, and most of the known
clastic rocks belong to one or other of the divisions mentioned,
namely, — pebbly rocks, sands, clays, calcareous rocks, and carbon-
aceous rocks. The crystalline rocks will be considered in the next
chapter.

When we come to compare each of the rocks with the sediment
that it most resembles we at once find important differences
which will be considered later. But already important resemblances
will have been seen in the examination of hard specimens, and other
points of resemblance come out when the mode of occurrence of
the rocks in natural or artificial excavations comes to be studied.

The solid framework of the land can be seen in any kind of
excavation which has been carried beneath the soil and subsoil.
Railway or road cuttings, wells, streams, mines, and quarries, are
the sections which give us our information as to the structure and
composition of this rock framework. Any of these kinds of
exposure which may happen to be available should be next
studied. In the majority of them the rocks will be found arranged
in layers like those of gravel and alluvium, only the layers will

CLASTIC ROCKS 119

be hard and solid instead of soft and loose (Figs, n and 12).
In many cases the relics of plants or animals, fossils, may be
found lying on the lamination planes or in the beds (Fig. 26).
In every particular the arrangement of materials seen in a sand-
stone or conglomerate quarry will be found to correspond with
that in sediment as studied in a previous chapter (compare Figs.
17 and 25). Thus the rock constituents are arranged with their
longer axes parallel to the layers, and the regularity or irregularity
of the layers varies with the coarseness in grain of their con-
stituent substances. The main points of difference will be that
the sandstone or conglomerate is usually consolidated or cemented
into a solid block, and the layers, even if regular, may not
infrequently be inclined to the horizontal.

The several types of solid rocks possess characters which tend
to prove that they were once deposited in river beds or lake bottoms
or on sea floors, the likeness extending even to the types of fossil
animals or plants found in them, which are of kinds restricted to
one or other of these situations. The presence of cockles, mussels,
periwinkles, corals, or foraminfera will indicate that the strata
containing them are of salt-water origin; while fresh-water
mussels, pond snails, fresh-water fishes, abundant plant remains,
and occasional skeletons of land animals are more likely to be
laid down in rivers or lakes. Deposits like the Wealden beds, the
Purbeck rocks, most of the Oligocene rocks, the Old Red Sandstone,
and the strata associated with coal seams, belong to the latter class.
Examples of the former are naturally much more common, and
good types are seen in the London Clay, the Chalk, the Oolitic
limestones or the Lias, and the Carboniferous and Wenlock Lime-
stones. A study should be made of any of these or others which
are available, their structures noted and compared with those of
modern sediments, and their fossils collected in order to ascertain
the exact conditions of deposition.

When it is felt that the comparison of rocks with sediments
is a close and accurate one the question will naturally arise as
to how the rocks, formed at low levels and for the most part under
water, have been lifted to form the skeleton of land and landscape.
Proof of submergence of land beneath the sea, or its elevation
above sea level, will now be required.

120 THE BOOK OF NATURE STUDY

The best available evidence of upward movement of land
will be given by such raised beaches as occur along the Durham
coast or that of Devonshire (Fig. 27). Deposits of beach pebbles
and sand, generally backed by what were evidently cliffs once cut
by the waves, all now at a considerable height above high tide,
may be compared with modern sea-beaches also backed by cliffs
which are reached by the waves of to-day. On the other hand,
old forests which must have grown clear of the water are to be
seen on the Lancashire and Cheshire coasts, in Cornwall, the Bristol
Channel and elsewhere, which are now covered by sea-water at
high tides. The latter furnish evidence of subsidence beneath the
sea. Other direct evidence is not easy to obtain, but enough
may be obtained from direct observation, or the study of maps
and photographs, to ensure the acceptance of the general fact.

This once admitted, it will be seen that the problems of the
stratified rocks require, and give confirmatory evidence of, such
movement in past time. This is given by the succession of strata of
different composition formed under varying circumstances. Lime-
stone full of marine organisms and deposited in clear deep water
will be found resting on or covered by deposits of consolidated mud,
in the form of clay or shale, and these again by beds of sandstone
or pebble beds clearly laid down in shallower water, sometimes
under the influence of shifting marine currents. Seas must have
existed and must have become shallower or deeper with lapse of
time. Coal seams, relics of former forest vegetation, are inter-
bedded with sandstones and shales, and such a succession of coal
seams alternating with shallow-water beds indicates land conditions
alternating with periods of submergence under water.

Strata are often found to be inclined or to dip in various
directions. These must have been originally deposited on flat
sea-beds, and their inclination clearly indicates upward or down-
ward movement after they were laid down. The inclination
seen is part of larger structures ; any dipping rock bed, if traced
far enough, being found to' rise and fall in waves or folds. The
crests of the waves are known as arches or anticlines (up-folds)
and the troughs as synclines (down-folds) (Fig. 28). Such struc-
tures are seldom to be seen in completeness, and their existence
has generally to be inferred from evidence pieced together from a

FIG. 28. — Anticline and Syncline, near Bolton Abbey.

{Photo by GODFREY BINGLEY.)

FIG. 29. — Folded Rocks. Stare Cove, Lulworth.

(Photo by GODFREY BINGLEY.)

FlG. 30. — Shap Granite Quarries.

(Photo by GODFREY BINGLEY.)

FlG. 31. — Intrusive Rocks. Cornwall.

(Photo by G. V. & H. PRESTON, Penzance.)

CLASTIC ROCKS 121

series of neighbouring sections. But here and there the complete
structures may be seen in long cuttings or large quarries (Fig. 29).

Care should be taken to discriminate between strata which owe
their inclination to .the elevation and folding of sediments that
were originally horizontal and these beds which were deposited on
inclined surfaces and built up irregularly under the action of cur-
rents of water. The latter is false bedding, the former is known
as inclined bedding (contrast Fig. 29 with Fig. 17). Inclined beds
can be in imagination stretched out till they are flat again, while
false bedding could not be thus straightened out, the beds having
always been irregular in inclination and wedge-like or lens-like in
shape. Moreover, in false bedding the slope of the layers does
not exceed the "angle of rest " of the material of which they
are made, while " inclined beds " may lie at any angle, because
they have been tilted, in most cases after consolidation. The one
indicates hurried and irregular deposition, the other calm and
quiet deposition on a flat area and the subsequent tilting and
folding of flat strata.

The earth's crust is therefore undergoing not only destruction
by denudation, but renewal by deposition and earth movement.
The debris swept off by streams and the sea is being conserved
in areas of deposition, and eventually it is lifted again to form
new land. In the process great changes in position, height, and
nature of the land are being brought about. Thus none of the
features of the earth are constant in nature or position for any
great length of time. Present denuding agencies are capable of
destroying all the land of the globe in three millions years, and, as
the land has not been destroyed, deposition and elevation must
have been capable of renewing it within the same time. The one
process, that of degradation, is the work of gravitation, dragging
all things to a lower level ; the other process must be attributed
either to the activity of the interior of the earth or to external
energy such as the attractive forces of the sun and moon. These
are in constant antagonism to one another, and their interaction
has prepared and maintained the earth's surface in a condition
suitable for the continued existence of life on it.

The study of different stratified rocks proves that those parts
of the earth's surface in which they occur must have passed

122 THE BOOK OF NATURE STUDY

through very different conditions at different times. The Chalk
must have been formed in deep water, the London Clay in the
delta of a great river, the Triassic Sandstones in a desert and
amongst salt lakes, the Wenlock Limestone in a coral sea, the
Coal Measures in a swampy forest. Such conditions could not
have been synchronous; they must have followed one another
successively. Therefore the physical history of a country is
written in the nature of its rocks, and by reading this history
we learn that a long and varied succession of events must have
followed one another to prepare its present condition, with all
its consequences of landscape, relief, outline, inhabitants, and
occupations.

CHAPTER XIII
IGNEOUS ROCKS

THERE are many rocks in the earth-crust which do not bear
the characters described in the last chapter. They are of
different composition, texture, and structure, differently placed in
the crust, and they evidently originated in some other way than
by deposition. Granite and basalt are examples. They never
yield fossils, they are usually unstratified, and their composition
shows that they are not made up of broken fragments of organisms,
or of sand, mud, or pebbles, broken from pre-existing rocks.

If rocks of this nature are accessible, their characters and rela-
tions should be studied. The absence of stratification and of fossils
in them tends to show that it is not likely that their constituents
have been dropped down on sea beds. Instead they break along
massive rectangular joints (Fig. 30) or into columns or spheroids,
structures comparable to those seen in starch or plaster or in some
other substance which has shrunk on cooling or drying. If their
relations to other rocks can be seen, these will show that they have
the shape of somewhat irregular masses encroaching upon other
rocks as if they had been injected into them when liquid and under
pressure, and that they must have consolidated from a liquid
state in the position where they are now found (Fig. 31). As the
masses expand in breadth downwards, and frequently end off
above by abutting against sedimentary rocks, they would seem
to have come up from below in a liquid condition.

Examination of hand specimens of a rock of this kind, if
coarse grained by the naked eye or a lens, if fine grained in a
thin slice by means of a microscope, will show that, instead of
being made up of broken and rounded grains of sand or pebbles
or bits of organisms, they consist of crystals, some of them
quite perfect and complete in shape, fitting into one another or
into other substances which have the internal structure though

123

124 THE BOOK OF NATURE STUDY

not the exterior shape of crystals. Thus a granite is made of
perfect crystals of the minerals felspar and mica, bound together
by crystalline quartz. The texture in this case is generally coarse,
and the individual minerals can be readily recognised — the felspar
by its white or pink colour and its apparently irregular cleavage
planes, the mica by its brilliant pearly-looking cleavages and its
occasional hexagonal shape, and the quartz by its glassy aspect
and absence of either crystalline shape or cleavage.

Basalt, like that of the Giant's Causeway, is a darker, heavier,
and finer-grained rock, which requires microscopic examination.
It is then found also to consist largely of felspar, with the addition
of olivine, iron-ores, and augite, the last being usually the least
perfect in shape, and the last substance to crystallise. The presence
in these rocks of perfect crystals suggests that they should be
called crystalline rocks, and the crystalline minerals present are
usually silica (quartz), silicates, or oxides. Such minerals are
insoluble in water and not easily decomposed by it, but they are
fusible by heat, and most of them have been experimentally
crystallised from a state of fusion.

It is therefore practically certain that this class of rocks has not
been produced by water but by heat, and that they have been
injected in a fused state into their present position, cooling and
crystallising where they are now found. This supposition is sup-
ported by the fact that frequently sediments and other rocks
with which they come into contact are altered, and sometimes
recrystallised, by reason of the great heat brought to bear on them.
It is well known that the size and perfection of crystals is related to
the time they have taken to grow, and the uniform conditions under
which they have been maintained during growth. Different crystal-
line rocks exhibit marked differences in the size of their constituent
crystals, and it is naturally inferred that those with the largest and
most perfect crystals have solidified most slowly and at a consider-
able depth under the earth's surface, while those with less perfect
and smaller crystals have solidified nearer to the surface.

Melted material having the composition of one or other of the
crystalline rocks is known to reach the surface in volcanoes, where
it is poured out in the form of lava, or shot out by steam in the
form of dust or ashes. When the lava cools it develops crystals,

IGNEOUS ROCKS 125

not very perfect, it is true, of many of the minerals which occur
in the crystalline rocks. It is therefore inferred that masses of
such rocks mark the site of either a once active volcano like Etna
or Vesuvius, or an unsuccessful attempt to establish such a volcano.

Sometimes these crystalline rocks may be traced upwards, and
seen to pass into sheets running parallel to and enclosed between
beds of rock which look somewhat like sediment. The rock of the
sheets may be streaky in aspect, and may show hollows like the
bubbles or steam-holes seen in the lavas of existing volcanoes ;
and such rocks will show columnar or spheroidal shrinkage joints
also linking them with the lavas which they so closely resemble in
composition and texture. The associated beds, in the irregularity
of their bedding, the angularity of their fragments, and the fact
that the latter are either broken crystals or bits of crystalline
rock, may be compared more closely with the beds of ash and tuff
deposited from a modern volcano than with ordinary sediments.

The character and association of the crystalline rocks suggests
that the whole of them are the product of volcanic action. This
is merely the escape of heated molten rock from the interior of
the earth, which either pours out in lava floods, breaks up into
tuff and ash thrown up by steam escaping from the lava, or
consolidates as a crystalline rock in the fissures through which
it is making its way from the interior of the earth to its surface.

The interior of the earth is proved to be in an intensely heated
condition. Hot springs rising from a great depth, and the fact
that the temperature in wells, tunnels, or borings, steadily increases
from above downwards, provide some of the proof required.
Volcanoes testify to further activity, and the fact that volcanic
and crystalline rocks of many different ages form part of the
earth-crust proves that molten matter from the interior con-
tributes to form a considerable and important part of the earth-
crust. Volcanoes are found to be geographically associated with
lines of weakness in the earth-crust — such as coast-lines, or with
mountain chains where the rocks have been lifted to a great
height above the average level. It is in such chains that the
folding of rocks reaches its maximum, showing that the energy
which has manifested itself in crushing the rock together and
folding it, has also squeezed out liquid matter from inside the earth.

126 THE BOOK OF NATURE STUDY

The activity of the earth's interior has therefore a second
influence on the crust. It not only lifts sediments and incorporates
them with the land areas, but it directly contributes new crystalline
rock to the land masses, and this is of course, like the sedimentary
rocks, capable of being disintegrated and transported to lower
levels by denuding agencies. A corollary from the present heated
state of the inside of the earth is that it is now cooling down from
some former intensely heated condition. If this were the case, fluid
water would have been an impossibility at that stage of the earth's
history. Nothing but igneous rocks could be formed at that time,
and the only new additions of solid material must have come from
the cooling of the heated interior matter. Thus all sediments
must be ultimately traceable to crystalline igneous material.

It has been found that the requisite material for clastic rocks
can all be obtained from one or other of the many types of crystalline
rock. Thus granite would provide broken grains of crystalline
quartz to make sand-grains. Any of the felspars would yield grit
fragments if fresh, or if decomposed, silicate of alumina for clay
rocks. Ingredients dissolved from felspathic rocks include salts of
potash, soda, or lime, the last eventually redeposited as limestone.

The vicissitudes passed through by rocks before, during, and
after elevation to form land masses have their effect in inducing
important changes in them, and in giving them the new characters
which they now exhibit in the form of rocks.

First of these comes consolidation. Sediments on their
formation are loaded with water, but the weight of the accumula-
tion squeezes out much of this, drives the particles together making
them to some extent interlock, and thus converts the mass into
a fairly compact substance. Clays pass into shales, and sands
into soft sandstones. During elevation the lateral pressure pro-
duces similar effects in a more important degree, and to this the
making of compact slaty rocks out of clays is to be attributed.
But a more important consolidating agency is the deposition
between the grains of a sediment of crystalline cement from its
solution in water. Carbonate of lime, silica, carbonate and oxide
of iron, are thus deposited. The grains are now held tightly
together, and the mass is converted into a thoroughly solidified
rock which will stand weight and pressure, and will only undergo

IGNEOUS ROCKS 127

disintegration if its cement is redissolved. The process is analogous
to the consolidation of road mud by frost, which converts water
between the dust grains into crystalline ice. The road surface
behaves as a hard rock so long as it remains frozen. Sandstones,
ironstones, and sandy limestones illustrate this process, and the
cement can often be removed by hydrochloric acid or aqua regia,
the rock being thus reduced to its original condition of loose
sediment. Some of the cements, particularly salts of iron and
manganese, are responsible for the coloration of rocks. Modern
calcareous deposits, such as shell beds and coral rock, sometimes
become very thoroughly cemented and compacted by the solution
of part of their carbonate of lime and the deposit of it between the
fragments and in the interstices of the organisms. This chemical
rearrangement is of common occurrence, and is responsible
sometimes for hardening the whole rock, sometimes for solidifying
only certain bands or nodules in it. These latter are known as
concretionary bands or nodules. A striking example is the flint
nodules in Chalk, which are only portions of the chalk
replaced by silica deposited in isolated spots in the chalky
limestone from solution. Such nodules are practically pure
silica, and they are often found to contain organisms like sponges,
which originally had siliceous skeletons, and also fossil shells and
sea urchins, which when living consisted of carbonate of lime but
are now replaced by silica without loss of their original shapes and
structures.

Other effects of elevation and the forces causing it are
mechanical, and there may be mentioned cleavage, jointing,
and faulting. Cleavage is a tendency which certain fine-
grained rocks possess to split into thin layers, called slates, along
planes not usually coincident with the original stratification.
This is the outcome of further application of the same lateral
pressure which began by folding and hardening the rocks, but
was so intense later that the rock constituents were compelled to
set themselves at right angles to the direction of pressure. In
consequence of this a new grain was given to the rock, which now
splits parallel to the up-ended particles into thin elastic slabs
which are of great value for roofing purposes.

Joints are fissures, more or less open, along which the rocks

128 THE BOOK OF NATURE STUDY

break up into blocks in directions usually at right angles to the
bedding and to one another (Figs. 8, 12, 32, and 74). They are very
well seen in lumps of coal. They are sometimes the result of
shrinkage on drying, and when this is the cause they are related
to the hexagonal columns produced by shrinkage in cooling
volcanic rocks. But the more regular jointing of sediments is
probably due to alternate pressure and tension resulting from the
general elevation of consolidated sediments. Joints are of much
importance in roughly shaping blocks for building, and for guiding
the directions along which excavation is easiest in quarries and
mines. Jointing is also very important in giving directions along
which water travels through rocks. In a soluble rock like limestone
the traversing waters often widen out the joints by solution into
open fissures (Fig. 33), and eventually into systems of caves along
which much of the drainage is carried underground. Numerous
examples may be seen in any limestone district, where the sur-
face is often honeycombed with deep hollows, and all the rainfall,
unless in exceptionally rainy seasons, disappears underground
(Fig. 74). Mechanical denudation also works along the joint
planes, and mountain and valley forms are often defined by them.

Often the rock breaks along joints, and under the pressure or
tension one side of the fissure travels up or down relatively to
the other. Such movement planes are known as faults. Folds
often pass into faults, and the two phenomena are closely connected
by causation with one another, and both are related to the causes
which have produced jointing. Faults, too, often produce striking
results in the landscape of the country in which they occur.

At their contact with igneous rocks the clastic rocks are often
found to be much altered in chemical and mineralogical characters ;
they are usually hardened and rendered more compact and less
pervious to water. This is spoken of as metamorphism, and it has
often proceeded so far that the metamorphic rocks have become
crystalline. This is well seen at the margin of granites, or other
large masses of crystalline rocks. Similar effects have often been
produced in large masses of rocks, such as those of the Scottish
Highlands, when these have been brought within the influence of
the extreme heat of the earth's interior. In this case the rocks have
become crystalline throughout, and are known as schists and

FlG. 32. — Jointed Sandstone. Brimham Rocks.

(Photo by GODFREY BINGLEY.)

FlG. 33. — Widened Joints in Limestone. Grange-over-Sands.

(Photo by GODFREY BINGLEY.)

FlG. 34.— Model of part of Skye, constructed by Mr. R. F. Gwinnell of the
Imperial College of Science.

IGNEOUS ROCKS 129

gneisses. These rocks are only found in regions of great earth
movement, such as mountain ranges, or in districts which are
the base of a great mountain range, the higher part of which has
been removed by denudation.

It is only likely that the periods in which sediments were lifted,
folded, and broken, to renew the outstanding parts of the earth-
crust, should show signs of allied activity in the interior of the
earth. Such periods, and the places where there is evidence of
great movement, are connected with the outbreak of volcanoes
and the occurrence of earthquakes. The latter are tremblings
of the surface, often producing damage to buildings, great loss
of life, and disturbance of the atmosphere and the ocean. They
almost invariably accompany the eruption of volcanoes, but
even when the activity is not sufficient to cause volcanic
eruptions, earthquakes may occur. A study of the distribution
of their effects, the direction of transit of the waves they give
rise to, and the class of destruction they produce shows that in
some cases they are due to the fracture of rocks and the production
or intensification of faults. Disastrous as their effects on the
surface often are, the actual permanent movements of the surface
produced by them are often so slight that it is extremely difficult
to detect them at all. Thus the displacement produced along a
fault by any one earthquake may be extremely minute ; and the
production of the larger faults, in which the strata of one side may
have been lifted or lowered hundreds of feet, has probably been
an exceedingly slow process, occupying thousands of years. It
is also probable that this class of movement is proceeding quite
as rapidly at the present day as it ever has done.

VOL. VI. — 9

CHAPTER XIV
MODELS AND MAPS

BEFORE dealing with the relations of rocks to landscape, it is
necessary that the means used for recording and representing
the latter should be known and appreciated. What is needed
is something which shall bring the features of a countryside
into a small compass, so that its broad aspect can be seen at a
glance and either compared with similar features in other dis-
tricts or contrasted with different types. For such a purpose
it is clear that the representation must be on a smaller and more
manageable scale than the original landscape ; and yet the pro-
portion of parts must be exactly preserved. Thus the idea of
scale stands at the head of this branch of the subject, and it is
worth a considerable sacrifice of time to secure a proper com-
prehension of the principle.

A postage stamp might be ruled into quarters or sixteenths,
and then copied by photography, the copies being on the scales
one-half, twice, and four times, the original. An inch divided into
eighths or tenths might be photographed by the side of the stamp.
Pictures and photographs of houses or features familiar to pupils
may next be used. They too should be on one or two scales,
the relation of the scales being shown by lines ruled on the negative
or positive from which the copies are taken. Pictures, however,
can only give one point of view, all that is behind the objects
being out of the picture and invisible. For the purpose we have
in view it is requisite that all should be visible, and that we
should be able to see everything from all possible points of
view.

A model is the obvious way of securing this end, and every
school ought to possess one or two models of a country with fair
relief, and executed with sufficient accuracy to show the landscape
not merely with the aspect of a mud-pie, but with the features

MODELS AND MAPS 131

presenting some approximation to their real shape. The model of
the Weald (Fig. 64) is ideal in this respect, but others are now to
be had (Fig. 34). In default of actual models photographs of them
may be used, but these are usually for some reason rather un-
satisfactory, and it is worth some trouble and expense to secure
at least one really good model. Above all, the fancy and almost
comic models of an earlier generation should be abjured. Need-
less to say, if the features in the school neighbourhood are in sharp
relief, and a model of them can be constructed or obtained, so that
the original may be compared with the model, this is best of all ;
and there can be no better way of imparting an idea of scale.
Heights must necessarily be exaggerated two or three times,
but the vertical scale must not be more than five times the
horizontal, or the model becomes too unreal. There will be
no need to point out the difference in vertical and horizontal
scales at this stage ; that can be left till later on, when the
general character and purpose of the model are thoroughly
understood.

The study of the model will demonstrate the advantage of
the vertical point of view, and will show that, although to
give an idea of the shape of the different features it is neces-
sary to look at each from several points of approximately
horizontal view, some notion of the forms may be gained
from the vertical view-point when the model is obliquely
illuminated.

The next step is from model to map. A photograph of the
model should be taken from the vertical view-point, by placing
the model on its side and illuminating it as nearly as possible
perpendicularly to its surface, so as to eliminate shadow as much
as possible. A blue-print of this photograph should be made, and
all the features expressed on the model by lines, such as streams,
coasts, lake margins, and the human topography, roads, canals,
railways, towns, woods, fields, etc., copied over in Indian ink.
The copy should be immersed in a solution of oxalate of potash
to discharge the blue and leave nothing but the ink lines. This
will then serve as a map of the country shown in the model, and its
use and functions can be demonstrated. The map should be copied
on a larger and on a smaller scale, and, where the model is of the

132 THE BOOK OF NATURE STUDY

school neighbourhood, it should be compared with part of the
country itself. It will thus be brought home to the students
that the map is a more handy thing than the model for storage,
as a guide, and for purposes of measurement of distances. But
it lags far behind the model in that it gives no representation of
relief.

Now relief is a thing which is brought out by shade and
shadow, as may be shown by photographing the model again
from the same point of view, but illuminated with oblique light
from one window (Fig. 34). (Care should be taken that the
usual convention of illumination from the north-west corner is
followed in order to avoid erroneous impressions later on.)
This will give the idea that it may be possible to combine the
features expressed on a plane map with those in a picture, and
a relief, or hill-shaded map produced, which will now be almost
the equal of the model in the one character in which it was
inferior to it.

Having got so far, it might be well to go back a little in
order to prepare plans of the schoolroom and the playground,
or any other readily available area. These should at first be
mere sketches of area, each pupil being allowed a free hand to
make his plan as he likes. Comparison of the several drawings
with each other would show that correctness in detail is in-
dependent of actual scale ; but it would indicate the advisability
of uniformity in certain particulars, and particularly in scale.
The most satisfactory drawing should be selected, its scale deter-
mined by measurement, and, if convenient, adopted in later
drawings.

Incorrect proportion of parts in some of the drawings would
at once suggest testing by measurement, which would then be
applied to the whole plan. Inaccurate placing of objects could
be checked also by measurement ; but a better way would be to get
sighting lines marked by stretched strings, to transfer intersecting
lines to the drawing, and then to insert the correct position of
objects. This will suggest the principle to be employed later in the
use of the plane table. Comparison will necessitate identity of plac-
ing, and thus introduce the advisability of constructing all plans
with identical orientation, and this will lead to the utilisation of

MODELS AND MAPS

133

the midday position of the sun. A few days' observation by the
shadow method will show that this gives a constant direction, one
which it is as well to mark on the plans, and to adopt a name for.
The habit of keeping the plans with their north side upper-
most should be in every way encouraged, and then the idea
of other compass points can be brought out. The compass
itself can be used as supplementary to the observation of the sun
itself.

FIG. 35.— A plane-table.1

Finally, the necessity for the employment of conventional
symbols will become apparent, and a set of symbols will naturally
be selected out of those proposed and adopted. In all exercises
of this kind it is obvious that the use of squared paper should
be encouraged in every way, both for saving of time and also
to encourage accuracy and clearness in work. It will evidently

1 From An Introduction tc Practical Geography (Simmons and Richardson), by permission
of Messrs. Macmillan & Co. Ltd.

134 THE BOOK OF NATURE STUDY

at this stage be applicable to the rough measurement of areas
upon the plans, and thus will further elucidate the meaning
and use of scales.

By this time it should have become evident that the sketch
method of plan-making has inherent defects, and some more
accurate and definite method will be called for, which shall not
require the perpetual correcting and patching requisite in a sketch-
plan. This is the stage at which the plane-table may be intro-
duced, the simplest and most readily applicable of all surveying
instruments. In principle it is merely the application of the
sighting method already advocated for use in the schoolroom, and
in its least elaborate form it is merely a drawing-board mounted
on a tripod and furnished with a ruler (Fig. 35). A base-line
is chosen, measured, and marked in the ground by a stretched
string. The plane table is then placed at one end of this line, and
from the point A, immediately above one end of it, a line is drawn '
upon the paper fixed to the board, exactly in the direction of the
base-line. On the line so drawn the position of the other end,
B, of the base-line is marked, on any scale which may be chosen.
Sighting lines are then taken along the ruler, or strings stretched
from the view-point, A, to a number of objects, and the lines
accurately drawn from the corresponding point A on the plan.
Each line is marked in some way to indicate the object to which
it refers. The board is then moved to the other end, B, of the
base-line, and so placed that the ruled line is exactly in the same
direction as the base line, and the point B of the plan above the
corresponding point on the ground. A second series of lines is
then drawn to the same series of objects, and the position- of
each object marked at the intersection of its two sight-lines
(Fig. 36).

The correctness of the plan so obtained is tested in various
ways. First, by the measured distance of objects from the ends
of the line ; second, by their shortest distance from any part of
the line ; and third, by their distance from one another and their
relative position. It will be useful to choose amongst the objects
one at least which is eclipsed by one of the others from one of
the view-points. During this exercise it will also be well for the
students to pace distances, in order to ascertain the length of

MODELS AND MAPS 135

their steps and the limitation of the accuracy of this method
when tested against tape measurement.

FIG. 36. — To illustrate the use of the plane-table.

When the plane-table method has in this way been
grasped, and confidence been gained in its results, it should be

136

THE BOOK OF NATURE STUDY

FIG. 37.— Reproduced from the 2$-in. Ordnance Survey Map, Surrey (xxvi. 13), with the
sanction of the Controller of H.M. Stationery Office.

MODELS AND MAPS

137

FIG. 38. — Reproduced from the 6-in. Ordnance Survey Map, Surrey (xxvi. S.W.), with the
sanction of the Controller of H.M. Stationery Office. The portion enclosed within
lines, including Broome Park, is the same area as Fig. 37.

138 THE BOOK OF NATURE STUDY

used to prepare a plan of some out-door area like the playground,
and to insert the position of outside objects which may be visible,
in relation to the boundaries of the ground. Work of this
character may be compared with the plan of the same area as
shown in the sheet of the 25-inch ordnance map (Fig. 37). Then
more of the area on that map can be traversed with a view of
verifying the details shown upon it, and ascertaining the meaning
of every symbol employed. It will be soon realised that this map
is excellent as an accurate representation of all the human and
natural topography ; but there is no indication of the slope and
relief of the ground.

The 6-inch map should be the next stage in progress (Fig. 38).
It has the great advantage that it is an absolute copy of the 25-
inch map, with the omission only of the numbering and acreage
of fields. It is true that contouring is also introduced, but this
may for the moment be ignored. The scale is sufficiently large
to make the map extremely easy to read, and the insertion of
hedges, of some of the trees, the exact shape of the roads, and
innumerable other details, makes it possible to ascertain positions
with extreme accuracy. At first attention should be mainly directed
to this exact localisation, to the following of roads and paths
marked upon it, to the verification of objects indicated, and to
the insertion of other objects not recognised by the map. After
this, the map should be used for the purpose of working out
routes from one point to another, the routes being afterwards
verified on the ground. The great object throughout should be
to realise the value of accurate representation of facts, and to
show that an accurate map is the best of all means for recording
them, and for bringing a large collection of topographic data
into a convenient compass, and in a readable form.

If a portion of a 6-inch map be photographed down to the
scale of one-sixth linear, a map on the scale of i inch to the
mile will be produced. But it will be found from inspection
of the photograph that the limit of clearness has been reached
and passed. The details have become too crowded, the roads
are too narrow, and the map cannot be used without a magnifying
glass. This shows that if a map on such a scale is required,
it is necessary to select the most important data only for repre-

MODELS AND MAPS

139

FIG. 39. — Reproduced from the i-in. Ordnance Survey Map (Sheet 286), with the sanction
of the Controller of H.M. Stationery Office. The portion enclosed within lines,
including Broome Park, is the same area as Fig. 38, See also Figs. 40-44.

MODELS AND MAPS 141

sentation, and to omit others, to simplify, and to conventionalise.
That is to say, the work must not be done by a mechanical
process, but by hand, after a careful determination of the
principles guiding selection. Indeed, as a matter of fact, it is
found necessary to issue four styles of these maps, each adapted
for special purposes. One is in plain black, and shows prominently
only the human topography and streams, the relief being indic-
ated by inconspicuous contouring. A second type is the same
map, but in place of contouring the relief is shown by hill-
shading (Fig. 39). The third form has the human topography in
black, and the relief in brown, thus avoiding a certain amount
of confusion in the lines. But the best form of all is now issued
in colour. In this the roads, towns, houses, and other parts of
the " human topography " alone are in black, water is in blue,
contouring in red, and a light hill-shading in brown. In addition
to this first and second class roads are shown in ochre, and woods
in green, two unfortunate additions which have deprived the map,
otherwise one of the best maps issued anywhere in the world,
of some of its usefulness to students of geography.

In maps on this scale the size and relative position of places
are accurately shown, but there is no attempt to retain the exact
size and shape of smaller objects, though their position is kept
correct. Thus the breadth of roads is much exaggerated, and
there is no attempt to render their minor features ; but their
exact directions are rigidly expressed, and they are divided into
three classes according to their breadth, the classes being shown
by different types of lines, so that they are easily read. Correspond-
ing conventions are used for railways, canals, streams, footpaths,
etc., and the greatest care is taken to insert as much information
as possible in the map consistently with retaining clearness and
legibility. The study of part of a large town with a magnifying
glass will show the extraordinary care which has been taken
to secure minute accuracy in detail.

It should be mentioned here that the Ordnance Survey is
prepared to supply maps of the various scales to schools and
other educational institutions in quantity at exceedingly cheap
rates, so that nothing now stands in the way of the liberal use
of them for educational purposes.

142

THE BOOK OF NATURE STUDY

Of the maps described above, the last, or six-colour form, is
undoubtedly the best for students to possess and use. Study
should first be devoted to the kind of features which have already
been dealt with on the higher scales, in order to attain familiarity
with the scale and the methods of representation of various
objects. But attention will soon be called to the new feature of
this map, its conspicuous representation of the relief of the country.
This is done by hachuring, the effect of which is, on the whole,
to give to the eye the appearance of relief. The method will be
most easily grasped if a bit of the map is photographed and enlarged

(Fig. 40). Hachures
are lines drawn in
the direction in
which water would
run down the country
direct from higher to
lower levels. Where
the slope is steep
the lines are drawn
thicker, and closer
together ; as the
slopes soften finer
and thinner lines are
used, until over flat
areas, on very gentle
slopes, on the tops
of plateaus, and on

FIG. 40.-mchuring, enlarged three times from Fig. 39. the actual summits

of hills and ridges, there are no lines at all. This is usually so
well done that it is possible to follow out the drainage of rills and
storm waters down hill-sides into the larger valleys, and it will be
a useful exercise to work out on a part of the map this head-
water drainage, which is too irregular in its occurrence and on too
minute a scale for representation by blue lines on the printed
map. Walking and route-finding exercises may be also made
with the aid of this map, and especial attention should naturally
be directed to the working out of slopes along roads and paths.
While the Mchuring of a map is one of the best ways of picturing

MODELS AND MAPS

143

readily to the eye the general character of the relief of the ground,
and while it brings out the steepness or gentleness of the slopes, it
is only possible to indicate actual heights by the insertion of figures
giving the height in feet, or to infer the approximate height from
a close study of the length, closeness, and thickness of the
hachures. In other words, the relief is expressed in quality

FIG. 41. — Portion of Fig. 39 to show the effect of submerging the country
200 feet. Compare Fig. 44.

rather than in amount, and it is not easy to adopt or adhere
to any method for giving the exact quantitative value of the
relief by this means.

For this purpose another method is required, and that of con-
touring has proved itself to be the best. Great pains should be
taken to secure the thorough understanding of this method.

144

THE BOOK OF NATURE STUDY

The coast-line of the country represents the intersection of the
relief of that country with the flat plane of the sea surface. As
represented in a map, the coast-line gives what is called the
" contour " of the country. If the sea level were to sink, the
contour would alter its shape, and the area inside it would
increase ; while, if the level rose, further alteration in shape and

FIG. 42. — Portion of Fig. 39 to show the effect of a submergence of
400 feet. Compare Fig. 44.

diminution in area would ensue. Suppose the level of the sea
surface were to rise 100 feet, it would intersect the land
everywhere at this higher level, and a new shore-line would be
produced within the original one. The line of this imaginary
shore-line might be drawn on the map, and it would join all
those places which were 100 feet above the original sea level. This
might be called the contour of 100 feet. Suppose the sea level to

MODELS AND MAPS

rise another 100 feet. Again there would be a new shore-line
within the others, including a still smaller area of the country.
This might also be marked on the map, and called the contour
of 200 feet. Further successive submergences to the same
extent might be imagined, and each time the contour-line drawn.

FIG. 43. — Portion of Fig. 39 to show the land which would remain above water
after a submergence of 600 feet. Compare Fig. 44.

The country would become smaller and smaller with each sub-
mergence. The hills would become peninsulas, and then islands,
then the lower ones would be entirely submerged, and at last
no land at all would remain above sea level. On the other hand,
the valleys would successively become gulfs, straits, and seas
during the stages of submergence. (Compare Figs. 41, 42, and 43,
with 39 and 44.)

VOL. VI. — IO

146

THE BOOK OF NATURE STUDY

This method has the advantage of showing precisely how
much land is above and how much below a given level, and
what is the exact shape of the land when followed along any
one level. A map constructed on this plan, with contour lines
drawn at any given intervals (usually, in Britain, 100 feet), is called

A

FIG. 44. — Contour map of part of area shown in Fig. 40. Contour lines are
drawn at 100 feet intervals. A, B and C, D are the lines of section given
on Figs. 46 and 47.

a contour map, and is at once seen to have many uses (Fig. 45).
To take an absolutely level walk, going neither uphill nor downhill,
it is only necessary to follow a contour ; and to construct a canal
without locks, cuttings, or tunnels, it would be necessary that it
should follow a contour line throughout. Crossing from one con-
tour to another will involve going up or down, and the quicker

MODELS AND MAPS

147

one passes from one to another, the steeper must be the slope
along the route taken. The shortest route from one contour to
another will generally be that at right angles to the contour, in
other words, directly down the hill, along the path that water
would flow, or the direction in which hachures would be drawn.
To descend a slope easily one would walk obliquely from the
higher to the lower contour, and the more obliquely the gentler
would be the slope of the path chosen.

Any two contours are not necessarily parallel throughout

FIG. 45.— Sections along the line A, B, Fig. 45. In X the vertical scale is
exaggerated ten times, in Y five times, while in Z there is no exaggeration
and horizontal scales are the same, i inch to a mile.

their whole range. When they approach one another the slope
will be steeper than when they are farther apart. If two contours
touch, the slope must be a vertical precipice. The profile of the
ground should be drawn to scale across contours in several parts
of the map, to obtain a notion of the relief of the country. At
first perhaps, on an exaggerated vertical scale to bring out the
heights and hollows, and, afterwards, on a true scale to get the
exact gradients (Fig. 45). A good deal of practice should be
devoted to section drawing, in order to attain proficiency in the

148

THE BOOK OF NATURE STUDY

work, and to demonstrate the value of contouring in bringing
out the exact shape of features from different points of view
(Fig. 46). It will become clear that, excellent as is the method,
it is only really exact on the contour lines themselves and tells
nothing of the ground between, except that it is of a height
somewhat intermediate between that of the contours. It is here
that hachuring comes in to furnish supplementary aid as to the
profile of slope between contours, whether convex, concave, or
straight.

The first sections would naturally be drawn along straight
lines, but later they can be taken along roads, streams, railways,
etc. They should also be drawn on varying scales, starting naturally

FIG. 46. — Sections along the line C, D, Fig. 44. The lower one is to
natural scale, the upper has the heights exaggerated five times.
Construction lines are ruled in the upper figure.

from the actual scale of the map. The study of several sections
will show that proficiency may be gained in reading the relief
without actually drawing sections, and exercises should be devised
to encourage this. Eventually a scale would be devised for
reading the relief in this way. It would be best expressed by
counting the number of contour intervals in a mile — that is, on the
scale we are considering in a length of i inch on the map. Each
such interval signifies a grade of 100 feet in 5280 feet, or i foot of
height in approximately 50 feet of distance, spoken of as i in 50.
Five contour intervals per mile gives 500 feet in 5280 feet, or
i in 10, and so on.

It will be well also to colour the contour intervals for a part,

MODELS AND MAPS 149

at least, of the map, in order to enable the eye to grasp the relief
more readily. A range of colours, from bluish-green in the hollows,
through yellow-green to yellow, orange, and red on the heights,
will be found a very satisfactory one. Bartholomew's half-inch
map might be shown as an illustration of the application of a
smaller colour range, but one which is very effective for walking
or bicycling maps.

CHAPTER XV
CONTOUR MAPS

THE first contour or sea level of a country sweeps out round
its capes, and back inland at its gulfs and bays (compare Fig. 42
with Fig. 44). Capes exist where hills project out into the sea,
and gulfs where the sea penetrates into low ground or valleys.
The behaviour of the first contour gives a law which other
contours will of course obey, that the bulging out of contours
towards the low ground will signify the existence of a hill, and
the retreat of a contour towards the high ground will indicate the
place of a valley (Fig. 47).

Except in very rugged and very flat country the swings of the
contours which indicate a valley will present a marked contrast to
the hill swings. Along the lowest line of the valley there runs the
course of the stream, its waterway. A contour will necessarily run
up one side of a valley until it meets the waterway ; then it will
double back, just like the coast-line at the end of a gulf, and
run along the opposite side of the valley. Valley swings will
therefore be angular and V-shaped, and the course of the stream
will join the points of the successive Vs. The slopes and shoulders
of hills are usually rounded without marked, angular ridges ;
consequently the hill swings will sweep round them in unbroken
curves of a general U-shape (Figs. 47 and 48). Inspection of a
contour map will thus at once show the situation of hills and
valleys by the shape of the contours, even if the drainage of
the country should not be otherwise indicated. Further, the
contours which form closed curves can only enclose hills and not
hollows — unless the latter contain lakes without outlets (Fig. 44).

Wherever the contours are close together slopes will be steep,
and in precipitous mountains they are so crowded that they
cannot be separately shown. When this is the case the slopes
are generally too steep to walk up ; indeed, they are usually

15°

CONTOUR MAPS 151

rocky precipices, and in such features the crest-lines of the hills
are often angular and the peaks sharp. Under these circum-
stances the mountain contours will usually be angular and V-like,
and care will be requisite to distinguish their swings from those

FIG. 47.— Contour-map of plateau incised by valleys ; " hogs backs " are also shown.

of valleys, and to determine the position of the summits. Where
the slopes are very gentle, on the other hand, the contours will not
only be far apart, but they will pass over the country in sweeping
curves, even across the valleys, and again their succession will not
be quite easy to read.

152 THE BOOK OF NATURE STUDY

The relation of the contouring to canals, roads, and railways
should be studied. Canals must adhere to contours, except
where locks allow them to go over hills, or where hills are cut
through by cuttings or tunnels and valleys bridged. Railways do
not often traverse more than one contour interval in two miles, a
gradient df i in 100 (Figs. 44 and 48). In this case, too, cuttings,
tunnels, and embankments may have to be resorted to. Roads may
cross as many as five intervals in a mile — a grade of i in 10, lanes
and pathways even more. In most cases, however, it will be found
that in more important roads the direction has been carefully
planned to keep the gradients below i in 12, and to secure this
it is often necessary to cross contours obliquely, and even to
wind up valleys and back again. In mountainous country like
the Alps, to secure uniformity and gentleness of gradient, the
system of zigzagging on hill slopes is practised. This is not adapt-
able to railways in which a system of corkscrew tunnels must at
times be employed.

Water will flow straight down the steepest slope it can find ;
that is, across the contours as directly as possible till it reaches
the waterway on a valley floor. It will then still continue to
cross the contours as quickly as possible, i.e. from the point of
one V to the point bf the next. Thus the direction of drainage in
a well-contoured map can be inserted even if the streams have all
been omitted (Fig. 44). The grade of streams can be easily worked
out, and it will be found usually to be steeper at their heads and
to lessen below. The gradient of the valley sides may be either
steep and gorge like, or open and gently sloping, and the contours
along the sides will be nicked where tributaries or storm torrents
come in. Often one side of a valley will be found to be much
steeper than the other (Fig. 48). The cross section of a lowland
valley will be like a U or a very open V, often with the waterway
ill marked and meandering about an almost flat floor. On the
other hand, as a stream winds through a valley amongst hills, the
curve of the concave bank, where the stream swings against the
side of its valley, will be abrupt with crowded contours, while the
other side will be gently sloping with widely spread contours
(Figs. 44 and 46).

Plateau ground will show large areas within its upper contours,

CONTOUR MAPS

153

FIG. 48. — Contour-map of " wolds " with longitudinal and transverse valleys, cols, and

watersheds.

154 THE BOOK OF NATURE STUDY

the lower contours being closer together (Fig. 47). Cuestas or wolds
are hills which have one side — the scarp or escarpment side — steep,
and the other — the dip-slope — falling much more gently (Figs. 44,
45, 48). On the scarp side the contours run exceptionally straight
and parallel to the summit-ridge, which often extends for many
miles, dividing the steep side from the other. If valleys cut across
them they often widen and narrow alternately, the contours crowd-
ing together where the wolds are crossed and spacing out in the
flatter ground between (Fig. 48). Isolated hills, sometimes called
nabs (or buttes) , are surrounded by closed contour curves, and gener-
ally have valleys radiating out from them (Fig. 52). Hogs' backs, or
ridges gently sloping from end to end, but with abrupt sides, are
indicated by contours of a much elongated oval shape (Fig. 47).
Rocky ridges or ar&tes, have elongated contours often with sharp
angles, which might at first be mistaken for valley Vs. Most of
these characters can be verified in the contour maps (Figs. 44-48).

Tracing a valley up to its head, the contour above the highest
V will approach its fellow on the other side of the valley, and then
recede from it again. This marks a col or pass, the depression
across the high ground joining the heads of two valleys, the water
draining in opposite directions from its summit. It is along such
cols that roads will be seen passing through hill ranges from one
valley or low ground to another. Roads traversing high land,
on the other hand, cross cols at right angles to the valley roads, in
order to avoid as much as possible dipping down off the ridge lines
(Fig. 48).

Watersheds and drainage areas may be traced out with exactness
on a contour map, and they should be indicated by coloured lines,
principal and subsidiary watersheds being marked by difference in
width of line. Watersheds are generally situated on high ground
along ridges, scarps, plateaux, and they cross the cols (Figs. 47 and
48). But it does not necessarily follow that the loftiest and most im-
portant hills are principal watersheds, for rivers may rise in ground
of no great average height, and may in their course traverse and
cut deep valleys in considerable hill ranges, of a height now greater
than the summit of the watershed. Valleys of this description
are known as transverse valleys, and they are often in parts of
their course steep sided and gorge like. The valleys tributary

CONTOUR MAPS 155

to them generally run approximately parallel to the hill ranges,
and may be called longitudinal valleys, and one of their most
common characters is that one side of them is usually steeper than
the other. Their rate of fall per mile, or gradient, is also usually
less than that of transverse streams, for a reason which will become
apparent later. Several excellent examples will be seen in
Figs. 44 and 48.

Many exercises, in addition to the section drawing already
advocated, suggest themselves with a view of teaching students
how to get out of a map the chief part of the information conveyed
by it. Routes should be worked out for direction, directness, and
slope, from place to place, the routes being suitable for walking,
bicycling, or driving. Gradients of water-courses and the shapes
of their cross section at different points should be worked out.
The run of the roads and railways in relation to the principal
physical features can be made out ; and suggestions might be
invited and worked out for new ones, their gradients and curves
being taken from those already shown on the map. The situation
of towns and villages should be noted in their relation to slope,
aspect, waterways, gaps through hills, highways, bridges, road
or railway junctions. The distribution of farms, woods, parks,
marshes, and moorland, should be observed, in order to see whether
the map gives any suggestions as to the reason for these things.

A map enables one to tell whether any one point is visible from
any other, or if it is eclipsed by some near or distant natural object.
Carrying out this idea further, it will be possible to sketch the
view from any point, to put in the rough outline of the hills as
observed, their relative position, and the extent to which one
is hidden from sight by a nearer one. Whenever possible, testing
and verification should be carried out on the ground itself, thus
adding a new zest to the work and giving it a reality which could
not otherwise be attained. At the same time, the students' minds
will become stored with a stock of knowledge as to the actual
appearance of the geography and topography.

It is a very valuable exercise, though unfortunately it takes up
a great deal of time, to construct a sheet model of part of the
country by either tracing the contours on paper or pasting a
series of maps on cardboard and then cutting one along each

156 THE BOOK OF NATURE STUDY

contour line. The cardboard sheets are then built up one above
the other, and mounted on a board in their correct position. Such
a model differs from the actual country in the fact that it consists
of steps and terraces which would have to be filled in with wax
or clay in order to make the slopes approach the natural relief
of the ground. Even without the last process, however, the sheet
model is of value in bringing home the general relief, the direction
of drainage, and a host of other features. It is of further use in
enabling students to realise that it is possible to conceive of such
a country being actually built up — as many countries are — of
horizontal sheets of stratified rocks, placed one above the other
and " outcropping " in a way analogous to the cardboard sheets.

After the i-inch map has been made use of it will be a good
thing to obtain the J-inch sheet, including the same area and its
surroundings. The extension of the features over a larger area of
country will thus be seen, the drainage towards bigger rivers, the
purpose of the main highways, and the situation and relations of
the larger towns.

Finally, it will be possible to take small-scale maps of the whole
country, always, if possible, with the relief indicated in the most
lucid way possible. On these, after finding the general plan of
the features of hill, valley, and plain, the drainage and outline of
the country, attention should be given to the distribution of the
human factors of the map. The roads should claim first attention,
from the Roman roads up to the main coaching roads. The latter,
constructed along the simplest and easiest routes that could be
found from one important town to another, the former with an
excellent general grasp of the country, sufficient to seize upon the
easier routes; but when these had been roughly settled, never
deviating to right or left for minor or even considerable obstacles,
but going straight for the direction that had been decided upon

(Fig. 47).

The Roman roads were built by men who had discovered the
primary needs of the country in the way of transport. They were
constructed to bring help to all the strategic points as speedily as
possible, and to keep all parts of the country in ready touch with
one another, so that it might be held in subjection and its frontiers
intact with as small a garrison as possible. Many of the towns

CONTOUR MAPS 157

which were important in those days are important still, though
a few have died out, degenerated into mere villages, or been
replaced by other towns situated in their neighbourhood.
Although later and present-day needs are on the whole different,
the main lines of communication remain much the same, the
shortest, quickest, and most convenient from one point to another.
In certain cases the old roads have degenerated or even dis-
appeared, but in the majority they have been followed, first by
coach roads, then by modern roads, and lastly by railways.

Several of the trunk railways follow on the whole the broad
direction of the Roman roads, especially those radiating out from
London ; but they differ in detail, either finding easier routes
to avoid the principal obstacles, or dealing with them by means of
bridges and viaducts, embankments, cuttings, and tunnels. Note
should be taken of the lines taken by the chief northern and
western railways to deal with such obstacles as the Chiltern
range, the Edge Hills or Cotswolds, the Pennine range, the
Lake district, the North Welsh mountains, and the southern
uplands of Scotland ; the rivers Severn, Humber, and Mersey,
Tay and Forth ; and the Menai Straits. Equally instructive is
it to study the course of the southern lines in dealing with the
North and South Downs and other ranges in south-eastern
England. The different routes from London to Brighton are full
of interest, the earlier avoiding obstacles by passing round them,
the later going more and more direct as greater speed was required
and increased engineering skill was available in dealing with these
obstacles. Such a study brings out the influence of physical
features in giving importance to towns situated in places
on which lines of transport must inevitably converge. In this
light such places as Basingstoke, Horsham, Lewes, and Tonbridge
might be considered in the south ; and such towns as Crewe,
Normanton, Derby, Didcot, Oxford, Shrewsbury, and Carlisle in
the north.

In the same way the routes of water transport may be studied.
First the navigable rivers, those which have a gentle gradient and
abundant water, which flow in wide open valleys and pass through
regions capable of producing wealth in some form or other. Then
the canals, which either supply the place of navigable rivers or

158 THE BOOK OF NATURE STUDY

shorten their tortuous course, or else join the upper waters of
rivers in distinct basins so as to facilitate intercommunication
between them. And finally, the harbours which facilitate transport
to countries outside, and depend very closely on the natural
facilities given where old river valleys have subsided and been
" drowned " by the sea, so that deep water penetrates far into the
land and has not yet been filled up by the deposits brought down
by the river.

CHAPTER XVI

GEOLOGICAL MAPS

THE surface of landscape is formed by soil resting on subsoil,
but under the latter, at varying distances, more or less solid
rock will always be found. Its situation and the extent of any
well-marked mass of it is called the outcrop of the rock. A
geological map is designed to show the outcrops of the various
rock masses as they would be seen if soil, subsoil, and a few other

numuim

FIG. 49. — Geological map of a small coalfield, showing outcrop of a coal-
seam. At the side is the section shown by the shaft of the colliery.

superficial materials were to be removed. These different rocks
are expressed by varying tints or shading, and numerous con-
ventional signs are employed to enable the reader of the map to
understand the relations of the rocks to one another.

For instance, a strong black line on the map (Fig. 49) is intended
to indicate the outcrop of a seam of coal, a stratum or bed 4 or 5 feet
thick. This plunges underground on one side or other of the line,

'59

i6o

THE BOOK OF NATURE STUDY

and coal workings will probably show on which side this occurs, the
workings being carried down from the surface until they meet the
coal below. Working then proceeds on all sides from the bottom of
the shaft, and as much of the seam as it is safe to remove is taken
out and brought to the surface. Other strata of rock will have
been pierced by the coal shaft before reaching the coal, and they
will come to the surface between the outcrop of the coal seam and
the pit's mouth (Fig. 49). Still other rocks will be met with below
if the shaft pierces through the coal seam, and they in their turn
will outcrop beyond the coal crop. This will be true whether

:V;|Oligoc«ne
Eoceno
Chalk

I Gaul t

Lower
Greenaand

Waaldan
Beds

FIG. 50. — Geological Map of the Isle of Wight.

the beds of rock are horizontal or inclined. If inclined, the bed
is said to dip at so many degrees to the horizontal, and the direction
of dip is measured along the line down which water would run on
its surface. This direction is observed by its compass-bearing,
and a knowledge of it is vital if we wish to understand the rock
sequence and relations at any locality.

The line drawn at right angles to the dip, as thus defined, along
the surface of the bed will always be found to be horizontal, and
a special name is given to it, the strike of the stratum. It will,
of course, be a contour line of the bed. It is easy to see that if
the rocks are dipping and the ground is horizontal the outcrop

GEOLOGICAL MAPS

161

of successive beds will be in parallel bands, all running in the
same direction as the strike. But if the surface of the ground
is more irregular than this, the outcrop will become irregular too
(Fig. 50). The best way to illustrate these two points is to form
a rough model of hills and valleys in clay, and then to plunge a
bit of slate or tin plate into it in various positions and at various
angles. On withdrawing the plate its intersection with the ground-
line of the model may be studied. On the whole, this line of
outcrop will be found to increase in irregularity as the bed
approaches the horizontal, and as the relief of the clay surface
becomes more varied.

Just as from outside we only see the ends and edges of the
bricks and timber of which a house is constructed, so, in the case
of the earth-crust, the surface which is mapped only reveals the
ends and edges of its component rocks; that is, the broken-off

MN.W

FIG. 51. — Geological section across the Isle of Wight.

ends of the rock masses, the rest of which plunge into the earth-
crust out of sight. The majority of these are stratified rocks,
either horizontal or inclined in various ways, but usually according
to a regular plan in any one district. The relation of outcrop to
structure inside the earth's crust is like that seen on the surface
and on the cross-cut of a piece of well-grained wood. Cuts across
the rocks indicated in a geological map are often available in
railway cuttings or large quarries, and they may be called geolo-
gical sections (Fig. 51). Such sections enable us to examine the
composition and character of the rocks exposed, and in addition
show the order of the strata and their angle of dip. They make
clear that those lowest in the sequence must be the oldest, and
those resting on their surfaces newer, because each stratum when
formed must have had a foundation to rest upon. The results
of observations so made are placed on the map, some on the
legend or explanation, others upon the map itself. Thus arrows,

VOL. VI. — H

162 THE BOOK OF NATURE STUDY

pointing in the direction of dip (Fig. 49), and marked with its
amount in degrees, are placed so that their points are exactly
at the place where observations have been made. A map now
becomes not merely a record of the outcrop of certain rocks, but
it shows the run of the rocks in the crust beneath, that is, the
rock structure of that crust (Figs. 50 and 51). The importance
of such symbols will be seen if it is realised, for instance, that a
seam of coal is not generally in good condition for working at its
actual outcrop. If the direction of dip is known, the side of the
line on which a shaft should be sunk is at once indicated, while
the angle of dip will tell the depth to which the shaft must be
sunk.

Outcrops in some cases consist of precipices, the strata being
broken right across, more or less perpendicular to their surfaces.
The sea, on the other hand, would plane off the projecting strata
to a horizontal surface. Average denudation on land comes
between these two extremes, producing varying slopes, those in
hard or porous rocks being generally steeper, and those in soft
rocks gentler : Resistant rocks usually make hills ; less resistant,
valleys.

As the outcrop of a band runs along the strike-line across a
country, the hill it gives rise to will similarly tend to stretch as
a chain or ridge parallel to the strike (Figs. 64 and 65). The
importance, height, breadth, and relief of the ridge will depend on
several factors — the resistance of the rock, its thickness, its angle
of dip, and on the relative softness of the strata above or below it.
Excavation of valleys by streams along the strike of the soft rocks
above and below a hard band, and parallel to the ridge formed
by it, will give rise to the longitudinal valleys already noticed :
these may be alternatively named strike-valleys (Figs. 44 and 48).
Typically the intervening ridges will become wolds or cuestas. The
soft stratum, being stripped by denudation from the top surface
of the hard bed, will allow that surface to govern the outline of
one slope, which will therefore correspond in angle with the dip
of the bed : hence it is called the dip-slope. The denudation of
the outcrop of the softer bed below, on the other hand, will
undermine the hard rock, and cause it to break away across the
stratum. Thus there will be formed a steep slope, tending to be

GEOLOGICAL MAPS 163

nearly at right angles to the under-surface of the hard bed ; and
the more resistant that bed, the nearer will the actual slope con-
form to the theoretical. This is the scarp or escarpment, and,
though usually grass-covered, it sometimes presents a cliff of bare
hard rock (Fig. 53). The soft rock which occurs beneath it is
generally denuded back until protected by the overhang of the
hard rock, and so its slope may also be steep, and it will sweep
upwards to the hard rock cornice in a beautiful parabolic curve.
This is the typical scarp outline.

Valleys may generally be found cutting across wolds in the
direction of the dip of the rock, and the streams usually flow in the
same direction as the dip arrow points, e.g. from strata lower to those
higher in the sequence. These transverse valleys, or, as they may
now be termed, dip-valleys, will be much steeper-sided when travers-
ing hard rock, and more open and V-like in crossing softer rocks.
The tributaries of these streams will be the longitudinal streams
flowing down the strike-valleys until they join their own trans-
verse stream (Fig. 48). Thus the transverse valleys are often the
most striking features in the landscape of a wold country, and
their behaviour at first seems anomalous, because they appear to
cut deep, steep-sided, valleys through hard rocks when there often
seems to be an easier path round the obstruction. A still more
curious feature is the fact that in many cases the land at the head
waters of this type of stream is less conspicuous than the ridge
or ridges they traverse (Fig. 64).

Still a third type of valley comes down the face of the escarp-
ments, flowing in the opposite direction to the dip of the beds.
These are obviously related to the scarp slope itself, and must
have arisen after the scarp was formed, and, starting down its
steep slope, must have cut their way back into it. Their valleys are
comparatively steep, and the streams short and rapid ; in extreme
cases they form rapids and waterfalls (Figs. 40 and 69). It is to them
that the slight curves and recesses in the straight line of the scarp
are due (Fig. 44), and their denuding work is carried on chiefly at
their head waters, which are constantly eating back and thus
lengthening the streams. They might be called counter-dip streams.

It will be seen that if the hard and soft rocks are responsible
for defining the features of a country, and if the whole country

164

THE BOOK OF NATURE STUDY

face is being denuded away, all kinds of scarp slopes will be in
slow retreat, but if the succession of rock-types remains constant,
their outlines will remain permanent in shape. In the case of
dipping strata the retreat will be in the direction of the dip of the
beds, and the features will tend to decrease in height as they retreat.

FIG. 54. — An anticline denuded by the sea as it rises, producing in succession the

surfaces, aa, bbt cc^ dd.

Retreat is more rapid than it would be if dependent on the resist-
ance of the hard bands alone, because the denudation of softer beds
underneath undercuts them. If retreat is unequal at various points
along the line of the scarp, as must be the case where counter-dip
streams run down it, portions will be left behind, at first as penin-

FIG. 55. — Plan and section of planed anticline with transverse streams, ab, ac, flowing

across the strike of the beds.

sulas, later as islands, of rock protected by a capping of the hard
bed (Fig. 52). The lower the angle of dip the more likely this is
to occur. These ^06-shaped hills capped by outlying patches of
hard rock are of frequent occurrence, and may sometimes be a long
way from the main outcrop of their protecting rock, indicating

FlG. 56. — Widening of transverse valleys when crossing soft beds.

the enormous amount of material removed by denudation and
the profound results due to this agency.

Plateaux are an extreme case of wold-hills where the dip
and consequently the " dip-slope " are horizontal. Their scarps are
often extremely steep, as shown by crowded contour-lines. On

GEOLOGICAL MAPS

165

the other hand, where the strata dip steeply, the distinction in
slope between the two sides diminishes until hogs' backs and ridges
with front and back slopes at about the same angle are produced.

FIG. 57. — Incipient longitudinal valleys.

It has already been shown that the dip of rocks is the result
of the originally horizontal strata being thrown into folds, or
alternating arches and troughs. As the folding was taking place,
the arches must have been those parts of the crust which were
rising, and the troughs the sinking parts. Thus the chief slopes

FIG. 58.— Section along transverse stream, ac, of Fig. 57. Lm is the floor of this
stream, and under / and c are given the successive enlargements of two of the
longitudinal valleys.

must have at this time led directly from the arches to the troughs.
When the strata were elevated in this way from the sea bed, rain
water would immediately begin to flow down the slopes produced,
that is, directly from arches to troughs. Thus the first valleys
would be naturally of transverse character, crossing the direction
of strike, and running down the flanks of the arches in the
direction of the dip. This would be the case even if the strata

FIG. 59. — Outline produced by processes at work in Fig. 58.1

were to some extent denuded by the sea during the process of
emergence, indeed the process would be rendered more simple
and direct if this were the case. During emergence there would
be a battle between the denuding sea tending to plane the rocks
down, and the rising fold tending to form an arch. If the former

1 The blocks on this and the preceding page are from the Author's Geology for Beginners
(Macmillan).

i66 THE BOOK OF NATURE STUDY

force were in the ascendant, the arch would not emerge at all ;
if the latter, the arch would emerge, but its upper layers would
be removed during emergence. In spite of this the position of the
axis of the arch would be the highest primitive ground on which
transverse drainage would be initiated (Fig. 54).

These streams would flow across hard and soft strata alike,
and would cut into both (Fig. 50). But the rate of erosion would
be governed by the resistance afforded by the harder beds, as
any slackening of slope across the softer beds would diminish
the erosive power of that part of the stream crossing them. In
this way hard beds would begin to be trenched, and the walls of
this part of the valley would stand up steeply because of the
resistance of the hard bed to weathering. Where softer beds
were traversed, the valleys would widen out (Fig. 56) by the effect
of rain, frost, wind, and soil-making, and rills and eventually
streamlets would begin to flow into the transverse valleys at these
points (Fig. 57). Falling into the cross streams with considerable
velocity, these streams would cut back their head waters along
the strike of the softer beds, and thus lower the level of that
part of the country, that is, along the outcrop of the softer rock.
As the transverse streams deepened their valleys, the longitudinal
ones would also both deepen and lengthen theirs, removing soft
rock from both sides of the hard bands and giving them the wold
outline, with dip-slope and scarp. Further denudation by them
would clear off most of the soft material from the dip-slopes, and
undercut the hard bed in their other side, causing retreat of the
scarps and gradual movement of the stream beds in the same direc-
tion (Fig. 58). All this denuding work would be kept in activity
by the deepening of the cross-cut gorge of the transverse stream.

Thus the relief of the wold, resulting from the resistance of the
hard bed when its softer neighbours have been in part removed
by denudation of strike streams, would be entirely dependent on
the deepening and keeping open of the breach through it by the
transverse streams into which longitudinal streams are draining
and carrying their denuded material (Fig. 59).

If anything were to happen to the strike stream, such as
damming up or loss of erosive power, the fall of the longitudinal
streams into it would diminish, the velocity of its water would

GEOLOGICAL MAPS 167

slacken, its erosive power would be checked, its course would
become choked with its own debris, and the deepening and cutting
back of its valley would be in abeyance, until the transverse
stream got rid of its obstruction and was again in full working
order. Thus the rate of denudation of the tributary streams,
including the longitudinal ones, — that means to say, the denudation
of the country as a whole, — is regulated by the erosion and deepening
of the main and primitive transverse gorges, and that again is
dependent on the resistance of the hard rocks to erosion. In
other words, the rate of denudation of the country as a whole
is regulated by its resistant rocks.

Provided the transverse gorges are kept open, the denudation
of the whole country will be in activity, and as a consequence
the head waters of all the tributaries, and even the rocks on the
crown of the arch from which the original drainage started,
will be steadily lowered, especially if made of soft rock. On the
other hand, the ridges along the hard rock bands between the
transverse gorges will undergo much less erosion, and will only
become slowly lower by the general retreat of the scarp con-
sequent on undercutting. Consequently these ridges will be
the part of the country undergoing least rapid denudation, and
eventually they may come to stand out, not only high above the
floors of the transverse gorges by which they are cut, but above
the very drainage ground from which come the streams cutting
these gorges. Thus we have the paradox that at the present
day the drainage of an important section of the country may
rise at an inconspicuous height, may proceed outwards and plunge
straight at ridge after ridge, whose crests may be higher than the
source of the streams, trench them by steep-sided, deep gorges,
and escape by this difficult path out to the sea or to an outside
drainage system. The paradox, however, ceases to be one when
we follow out the history of the system, and realise the three
main factors. First, that the sources were originally the highest
ground ; secondly, that the relief of the ridges and wolds is due
to the lowering of the intervening bands of softer rock ; and thirdly,
that all the denuded matter has been carried out through the
transverse trenches, and that the keeping open and downward
cutting of these has been a condition without which the general

i68

THE BOOK OF NATURE STUDY

denudation of the country behind would have slackened down
and ceased. It is needless to emphasise the fact that the head
waters will always be higher than the floors of the transverse
gorges, so that the streams maintain sufficient downward
gradient to ensure their flow and work.

The general outcome of the system of denudation just outlined
will be, that the average landscape will be an echo of the resistance
of the rocks. The streams will be adjusted to the structure, the
majority of them situated in soft rocks, flowing off the harder

FIG. 60. — Map of two transverse streams with their longitudinal tributaries.

ones by the shortest possible route, but still in many places
trenching these hard rocks. These trenches are the chief apparent
exceptions to the law of adjustment, but, if the foregoing line of
argument has been followed, it will be clear that they are the
prime cause of all the adjustment, and that they supply the
motive power by which the adjustment is maintained.

A country which possesses the simple tectonic relations
postulated, an arch with alternating harder and softer beds, should
have impressed upon it sufficient transverse streams to carry

FIG. 52. — Cam Long Down. A " Nab" or Outlier of the Cotswolds.

(From a Photograph taken and kindly lent by Miss E. HENDRIKS.)

FIG. 53.— Escarpment of Otatari Limestone, Oamaru, New Zealand.

(Front a Photograph taken and kindly Itnt by Mr. A. C. GIFFORD.)

GEOLOGICAL MAPS

169

out the drainage, each one fed by longitudinal tributaries at
every intersection with a softer bed. But the maintenance of
this state of things would demand a wonderful balance in erosion
and resistance, which is never likely to occur. Suppose, for example,
that a single one of the transverse streams carries out exceptionally
rapid erosion of its bed (Fig. 60). This may result from the rainfall
being excessive in its basin, from the hard rocks which it traverses
being softer where crossed by it than elsewhere, from its primitive
slope being greater than that of the others, or from the stream

FIG. 61. — Capture of the head waters of one stream by those of another.

being supplied with a greater amount of gravel and stones with
which to carve its bed downwards. If its gorge in this way
becomes deeper than those of the other streams, its tributaries
will be at once quickened in consequence of their steeper fall
into the transverse stream. Hence their erosive power will
increase, they will cut back their head waters more rapidly, and
will quickly grow longer. In doing so, they may encroach upon
the side of another transverse stream, and may eventually divert
its waters and capture that portion, the head, of the other stream

170

THE BOOK OF NATURE STUDY

(Fig. 61). This will give the capturing stream more water, greater
velocity, and more eroding material. Thus its channel will be
further deepened, and its other tributaries stimulated until they too
capture the heads of other transverse streams and still more increase
the volume, importance, and power of the transverse stream to
which they flow (Fig. 62). The renewed power of the longitudinal
streams will enable them to cut back the scarp slopes overlooking
their valleys, and, as these retreat, the heads of dip streams rising

FIG. 62.— Second Stage of capture by the stronger stream.

in them will be shortened and starved, and the rain water which
previously fed them will in turn drain to the captor. Thus,
little by little, the stronger streams will grow stronger and more
important, the smaller ones being one after the other diverted
and captured, or starved out, until the final result will be the
survival of two or three important rivers, each with a complex
set of tributaries, the majority of them being longitudinal, but
each of the latter fed by numerous small transverse head streams
which they have captured. The result of capturing may be

GEOLOGICAL MAPS 171

such as to leave portions of the old valleys dry and function-
less, and in others to leave mere streamlets to occupy important
valleys whose size and depth were the work of larger streams now
beheaded and captured by the stronger streams. There is plenty
of evidence of this work in the past in almost every river system,
and the process is still going on, so that no drainage system can
be said to be stable or completed. It is all part of the life process

FIG. 63. — The Severn and Avon, by widening their valley, are causing the
retreat of the Cotswold escarpment, and thus beheading the tributaries
of the Thames.

of the landscape ; but it will be observed that it is all in the
direction of adjustment of drainage to rock structure and history.
The Severn in Gloucestershire, and the Avon in Worcestershire and
Warwickshire, are longitudinal streams flowing at the foot of the
great escarpment of the Cotswolds and Edge Hills (Fig. 63). The
dip-slopes of these wolds are the head waters of the chief tributaries
of the Thames. But the Severn and Avon are under-cutting

172 THE BOOK OF NATURE STUDY

the scarp, and causing it to retreat towards the south and east,
thus shortening the length of these tributaries by cutting back
the ground on which they rise, and themselves growing in size
and importance with the ground and water they are capturing.
The Yorkshire Ouse has captured numerous transverse streams
flowing down from the Pennine dip-slopes, and is carrying them
along a longitudinal path to the Humber. The Trent and the
Mersey are doing similar work.

Instances to illustrate this part of the subject can be found
in any river system, but the finest one described as a connected
whole, and still one of the best for study of the principles, is that
of the south-eastern part of England. This area comprises part-
of Kent, Surrey, and Sussex, and is known as the Weald.

The topographical features may be summarised as follows
(Fig. 64) : — i. There is a central knot of hills about Ashdown Forest
and Tunbridge Wells, culminating at over 700 feet on Crowborough
Beacon, and reaching the sea at Hastings ; these are the Wealden
Heights. 2. A horse-shoe shaped valley, beginning at Romney,
passing inland to beyond Horsham, and back again to the sea at
Pevensey; this is the Wealden Valley. 3. The Ragstone Range,
again horse-shoe shaped, coming out of the sea at Folkestone, over-
topping 950 feet at Leith Hill, sweeping round at Hindhead and
Blackdown, and dying down towards the sea about Hailsham.

4. The Gault Valley running parallel to the last from north of
Folkestone to Farnham, and back to the sea at Eastbourne.

5. The Chalk Downs from Dover to Box Hill and Guildford, round
by Alresford, and so to the sea again at Brighton and Beachy
Head, attaining a maximum height of 880 feet near Oxted. The
steeper faces of these hill ranges all look towards the inside of
the horse-shoe. The two concentric valleys mentioned are not
occupied by single streams, but by innumerable longitudinal
streams, nearly all draining to eight principal transverse streams,
which rise in the central tract, and cut gorges through both
Ragstone Range and Downs, and so escape direct to the sea or
to the Thames. These streams are the Stour, Medway, Mole, and
Wey, cutting through the North Downs, and the Arun, Adur,
Ouse, and Cuckmere through the South Downs. All of these,
except the Wey; have some head-waters coming from the Wealden

GEOLOGICAL MAPS

173

1 1 k I

'f

'o
O

174 THE BOOK OF NATURE STUDY

Heights ; and all have important longitudinal tributaries flowing
along either the Gault or the Wealden Valley, or along both. The
Medway, Arun, and Wey have especially important longitudinal
tributaries.

The general geological map of the Weald is equally simple
(Fig. 65). The Wealden Heights correspond with the outcrop of
a set of hard sands called the Wealden Sands ; the Wealden
Valley is the outcrop of a thick seam of clay — the Weald Clay ; the
Ragstone Range is the outcrop of hard sandstones and chert beds
of the Lower Greensand ; the Gault Valley the outcrop of a clay
seam called the Gault ; and the Downs are the outcrop of the Chalk,
a thick seam of white, pure, absorbent limestone. All the rocks
dip outwards from the central area. The gentle outer face of the
hills are dip-slopes, the steep, inward-looking slopes are escarp-

K^aseegs

'&fs^>*&

tf' v"r" **

FIG. 66. — Geological Section across the Weald.

ments. A geological section across the area (Fig. 66) shows that
the oldest rocks are the Wealden Sands, and the newest the Chalk ;
that the rocks are bent into an arch, or rather into an elongated
dome, like half an egg, the long axis of which runs from a little
north of west to a little south of east. The centre of the dome,
probably to some extent planed by the sea in the way suggested
earlier in this chapter, formed the primitive high ground from
which the transverse streams radiated. There may have been
dozens of these, each with its own set of tributaries ; but, by a
process of capture, the eight strongest ones have survived.
Amongst the last to be captured were the head-waters of the
Darent, and the streams which flowed through Smitham Bottom
and the Caterham Valley to Croydon (Fig. 67). These at present
cut only the Chalk escarpment, but not the Greensand behind,

GEOLOGICAL MAPS

175

their tributaries in the Gault Valley having been captured by
the Medway and the Mole. The end is not yet reached, for the

a,

rt

I

'§
1

Medway is capturing parts of the Mole and Stour drainage, and
the Wey that of the Mole. So this last river is gradually shrinking.

176 THE BOOK OF NATURE STUDY

In the south the Arun and Ouse are gaining on the Adur, while
the Cuckmere has been reduced to little more than a single trans-
verse stream. The balance between even the north-flowing and
south-flowing streams does not appear to have been yet reached,
for to the south the Arun seems to be gaining at the expense of
the Wey and Mole, and to the north the Medway at the expense
of the Ouse and Cuckmere.

Some such process of river development, dating back to the first
making of the arch and the emergence of it from the sea in which the
Chalk was formed, seems to account for the principal facts of the
case ; the outward radiation of the rivers, their neglect of the
now easy path in the great valleys, their passage through the
hard rock ranges, the gorges which they cut through them, their
low head-waters, and the fact that the ranges attain a greater
altitude than the present height of Crowborough and its associates.

CHAPTER XVII
HISTORY OF LANDSCAPE

IT is sometimes found that there are unexpected irregularities
in the run of landscape features, which appear at first to contradict
the law of adjustment. Thus in the Weald there are sometimes
hills rising along the line of the Weald Clay or other soft beds ;
on the other hand, the Ragstone Range attains very great im-
portance at certain spots, and dwindles down to nothing else-
where (Fig. 64). These exceptional occurrences are found on
closer examination to emphasise rather than contradict the law
of adjustment, for they are due to local and exceptional causes.

The dying out of the Ragstone Range as it approaches East-
bourne from the west is due to the thinning and wedging out of the
hard beds, and their replacement by clays which do not differ in
resistance from the Weald Clay below and the Gault above.
The marked development of the same range at Leith Hill and
Hindhead is due partly to the thickening of the hard rocks,
partly to the more complete cementing and hardening of the
individual beds, and in part to the nearly horizontal position
of the rocks, which form a long, flat dip-slope, where the Gault
has been denuded from above them, and a very abrupt scarp,
where the Weald Clay has been undercut beneath them.

The occurrence of occasional hill ranges along the Wealden
Valley is due to the existence of beds of fresh-water limestone in
the neighbourhood of Horsham and Petworth, which are much
more resistant than the Weald Clay with which they are inter-
bedded. Similar occurrences are to be noted in the thickening,
thinning, or dying out of shales and grits amongst the escarp-
ments on the east and west sides of the Pennine Chain.

Other irregularities are found to be caused by smaller and
subsidiary wrinkles on the larger rock folds. Each becomes
denuded in its special way according to the rocks of which it is

VOL. VI. 12

178 THE BOOK OF NATURE STUDY

composed and their relation to one another ; only they are usually
traversed by a single river belonging to the principal system.
Thus a miniature set of features may be locally developed along
the lines occupied mainly by the broad features of the greater
system of folds and drainage.

At times both the major system of folds and the minor system
of wrinkles may be broken by faults, which will destroy the
symmetry of the sides of a fold ; and introduce in parts of the
area unmatched beds of resistant rocks. These bands will be
in part the repetition of those found in normal position, but they
will react on denudation as if they were independent beds. Thus
there may arise two or more parallel scarps, each one resulting
from the repetition of the same rock by faulting. Again, faults or
folds crossing the strike of the rocks may cause this strike to
bend out of its normal course, and thus make the scarp feature
bend in a similar fashion. Facts like these do much to relieve any
monotony in landscape which might result from the development
of a too simple tectonic system, and too great consistency in the
composition of the rocks.

The fissures, joints, and cleavage which traverse rocks often
have a marked influence on the details of landscape. Thus a
joint system running in definite directions will indicate the
direction of easiest erosion to the streams. These will tend to
settle along the joint planes, and either to cut trenches parallel
to them, or to wind from one system to another. This is often
very noticeable in limestone country, where, as will shortly be
seen, another influence comes into play. The outlines of buttresses,
gullies, and ridges of rock mountains are markedly influenced by
joint faces, as may be seen in limestone, grit, or granite countries.
The production of cleavage is often responsible for very irregular
and very sharp ridges, like some of those on Snowdon and its
neighbours.

Crystalline rocks, especially the intrusive ones, being much
less regular than strata in their direction, and in the rocks with
which they come into contact, being devoid of bedding, and tra-
versed by peculiar types of joints, give rise to very strongly-
marked scenery, but of a type which rarely falls into line with
that produced by the denudation of strata. Most of these rocks

FIG. 68.— Nant Ffrancon. Topography approaching maturity.

(Photo by GODFREY BINGI.EY.)

FIG. 69. — Hardraw Scar, near Hawes. Immature Topography.

(Photo by GODFREY BINGLEY.)

FIG. 70. — Box Hill, Surrey. The Flat-topped North Downs.

FIG. 71. — Issue of a Limestone Spring. Crummack Beck Head.

(Photo by GODFREY BINGLEY.)

HISTORY OF LANDSCAPE 179

are much harder than those they come into contact with, and so
stand up as hills, which may be lumpy and massive like Dartmoor,
or extended into lines like many in Wales, or sometimes may form
terraced and stepped slopes like those of some of the Western Isles
of Scotland and the north-east of Ireland.

While adjustment to rock structure is the chief determining
factor of the broad features of landscape, the details, and also to
a less extent some of the principal features themselves, depend
upon the nature and the date of the latest denudation to which
they have been subjected.

While the summit crags of our mountains have plainly been
riven by frost, the valleys and lower shoulders of the peaks are
often rounded and smoothed in a remarkable manner. The
rocks may even show polishing and grooving of precisely the same
character as that exhibited by the rocks from which the Swiss
glaciers have recently retreated. Thus the Glacial Epoch has
left a conspicuous mark upon the scenery of the country, although
the ice-sheets and glaciers disappeared from it many thousands
of years ago. This is an instance of a special form of denuda-
tion, whose influence has not yet been destroyed by the agencies
at work at the present day. In contrast to this we may study
the effect of long-continued water denudation. This can be best
illustrated in the case of a typical river.

In the upper part of its basin innumerable torrents come down
steep slopes with abundant erosive energy and plenty of transported
material. They join one another usually at an acute angle, and
group themselves into a number of larger streams, each with
considerable erosive power, and capable of excavating a valley
along which it flows downwards, carrying most of the material
brought to it, but usually dropping some, at least temporarily,
in the form of gravel banks on its bed or flanks. Gradually the
slope decreases, but the incoming of larger trunk tributaries keeps
up the flow, velocity, and most of the transporting power. The
valley generally widens out, and as it does so the river meanders
along its floor, now depositing and now removing gravel.
Sometimes it floods its lower ground and lays alluvium down over
the gravel. As the valley opens wider, floods become more
frequent, and the alluvium - covered flat wider and more con-

i8o THE BOOK OF NATURE STUDY

spicuous in comparison to the volume of the stream; and here
more and more of the transported material is dropped. The valley
at last opens out into a plain, and here the deposited debris so
chokes and clogs the stream that it readily divides into distributaries
which are constantly changing their courses and ever finding new
exits to the sea. This last portion is the delta of the river which
it has built up to and above sea-level and is constantly pushing
out into the sea.

The extent to which a river conforms to this type is dependent
upon the factors just mentioned, and especially on its age as a
whole or in part. Its main function in its upper part, so long as it
has sufficient fall, water, velocity, and excavating material, is to
incise or saw a trench along its water-way. But the fact that it
makes thus a slope down to its own bed gives power to numerous
lateral agencies capable of opening out the sides of its gorge-like
valley. Rain, springs, frost, wind, and the numerous other
denuding agencies will tend to disintegrate the rock of the flanks
of the trench, and rain, wind, and streamlets will wash some of
the material into the main stream. The effect of this is to cut
back the sides of the trench and to reduce them gradually to a
slope on which soil can form and rest. Soil-making agents
will then work up the rock surface into subsoil and soil which,
resting on an unstable slope, will inevitably travel steadily
downward towards the river, allowing new subsoil and soil to
form and travel down behind it. The river will continue to
scavenge away the material travelling down to it, thus keeping
up the movement and the action of the lateral agencies. So, if
time is allowed, the sides of all valleys will be opened out, at a rate
depending on the hardness or softness of the rock of the valley sides.
When the average slopes have become softened down by these
means, the shape and outline of the valley are spoken of as mature
(Fig. 68). When, on the other hand, the river's downward
erosion has outstripped the work of the lateral agencies, and
the valley sides are abrupt, and all slopes sharp and angular,
the topography is spoken of as youthful or immature. Counter-
dip streams are usually less mature than others, because they
necessarily originate after the main relief of the land has been
sketched out (Fig. 69). Not only are they usually steep sided,

HISTORY OF LANDSCAPE 181

but their gradients are steep, and rapids often occur in their
course.

At any given period the maturity of a river will express the
difference between the power of the river itself and the activity
of the lateral agencies. In rainless countries lateral agencies,
such as rain and frost, are in abeyance on a river's course, though
the river may bring water and stones from distant mountains,
sufficient to carve out a course which may remain gorge-like for
a long period. The rapid torrent of a mountain district will also
easily outstrip lateral agents, until its gradient has been lessened
and its erosive power diminished In the low grounds the gently
flowing river is doing little or no downward cutting, and all the
work is that of the lateral agencies.

As, however, the valley widens and its slopes become more
gradual, the travel of soil and subsoil slackens, and finally it stops :
friction is too great and erosion has come to a standstill. The
river gradient is too gentle to give the water sufficient velocity
to carry any denuded material at all ; the slope of its flanks too
gentle to provide it with any new material to carry or use as an
erosive agent. The system has passed through maturity to old
age and death. A country in which rivers have reached this
stage is said to be at base-level ; its slopes have become so gentle
that they can hardly be distinguished from a plain, or from the
plane which is the ultimate result of marine denudation. It will
not be reduced absolutely to sea-level, but very nearly, and no
further denudation can take place on it unless some important
change occurs. It is at the end of the cycle of denudation,
which began when its rocks were first lifted above the area where
they were formed, when the first rain fell on it and the first
water flowed off it.

If now the region were lifted or tilted, the streams would be
rejuvenated and would begin to flow with renewed velocity. In
consequence they would probably, as a general rule, start afresh
in their old courses and would begin to deepen their old valleys
again. As they did so they would first have to remove and carry
out to sea the bulk of their gravel and alluvia, before reaching
down to the solid rock below. It is extremely probable that
patches or terraces of these materials would be left behind, which

182 THE BOOK OF NATURE STUDY

would indicate that they had been formed in an earlier cycle of
denudation, when the land stood at a lower level. At the same
time the river courses would be the site of the earliest and most
rapid denudation, and, until the lateral agencies caught them up,
some trace of the old base-level in the heights between the valleys
would be left to tell the story of an earlier cycle of denudation.

The landscape of any large country invariably gives evidence
of one or more reductions to base-level, followed by rejuvenation
of the denuding agencies. The base-levelling may have sometimes
been effected under the sea, at other times by rivers and atmo-
spheric denuding agents ; but with each new uplift the rivers have
incised new or old courses and developed drainage systems which
have gradually passed through the stages of youth and maturity
to old age. Traces of such a phase will for a time be found in the
existence of plateaus (the former base-levels) into which the new
streams are incising their valleys. But by degrees the valleys
widen and deepen, reducing the amount of intervening plateau
until nothing is left but a ridge separating the new valleys, and
even this is gradually consumed from both sides by further valley
widening.

As an example we may again turn to the Weald, which bears
evidence of an earlier cycle of erosion preceding that to which its
present hills and valleys are mainly due. One of the most striking
features of the Weald is the level lines given by the summit of
the chief escarpments. A plane 900 feet high, if placed on the top
of the Weald, would nearly touch all the summits of the Downs,
the Ragstone Range, and the Wealden Heights. It is below
some such plane that the valleys are cut. Their sides; where they
cut one or other of the ranges, rise abruptly on either hand up to
nearly this height, and then the ridge sweeps away right and left
at that level (Fig. 70). This would not occur if the country had
been carved out from an unbroken arch, say of Chalk, spreading
right over the whole country. If that had been the case the Chalk
outcrop would run steadily inward and upward from each valley,
and then downward and backward to the next. Instead of that,
it rises onward and upward to a height of 600 to 700 feet, and then
passes away in a nearly straight line to the next valley, when it
plunges down, forward, and back again to about the same 600 or

HISTORY OF LANDSCAPE 183

700 feet level. Numerous other instances might be given where
traces of the old base-level may be detected in such a position as
to show that the work of making the present landscape was
started on it.

In porous and pervious rock a good deal of the denuding work
is carried on underground. Thus in the case of limestone rocks,
systems of caves and underground channels are dissolved out
along the widened joints of the rock. The erosive work is carried
on underground without the formation of valleys on whose sides
the lateral agencies can work. When these underground channels
become very much widened they must eventually collapse, giving
rise to steep-sided, youthful topography until the lateral agencies
which then come into play can smooth down the abrupt slopes.

The travel of underground water is worthy of further study.
Of the rainfall, an average of about one-third is evaporated, a
second third flows over the surface as streams, and the last third
sinks underground into porous rocks. The relative amounts
vary according to the absorptive character of the rocks. Highly
absorbent and porous ones, such as chalk or open sandstone or
conglomerate, absorb a much larger proportion, while non-porous
rocks like clay absorb very little, and the ground is wet and the
streams are full. Even when a rock is not porous between its
grains, like compact limestones and igneous rocks, water may still
travel underground along fissures. Gravitation will carry the water
downward until it meets either with rock already saturated with
as much water as it can hold or with impervious rock. Its direct
downward journey is then stopped, but it may travel obliquely
downward if the surface of saturation in the rock or the imper-
vious layer slopes in any direction. This travel may bring the
water out again if the surface in question outcrops at a lower level.
The escape of this water thus forms a spring, and if the travel of
the water has been continuously downward it is called a surface
spring (Fig. 72). The place where water is absorbed, i.e. the
higher outcrop of the pervious rock, is called the gathering ground
or drainage area, and water will be delivered by the spring in pro-
portion to the area of gathering ground, the distance the water has
to travel, the slope down which it runs, and the resistance offered
to its passage by the closeness of grain or fissures of the rock

i84

THE BOOK OF NATURE STUDY

through which its journey passes. If the travel is fast, variations
in the spring will follow close on variations in rainfall, and the
spring may run dry soon after rain ceases. But if the travel is slow
the yield of the spring will be more steady and it will only run dry
during seasons of exceptional drought (Fig. 71). Thus surface
springs are often intermittent, the dry periods being ultimately
dependent on variations in rainfall.

One of the most remarkable of the intermittent springs are
those known in Chalk districts as " bournes/' These are surface
springs issuing generally at the junction of the Chalk with the
beds above it. Some such springs are permanent, and water
may issue in sufficient quantity to form good sized streams, and

Drainage Area

/mperrious Stocks. The rest are porous.

FlG. 72. — Surface Springs, S. Deep-seated Spring, D.

by them the saturation level of the Chalk is kept down to a certain
point. If the rainfall of any season is exceptionally heavy the
saturation level rises higher, and this produces two effects. In
the first place, the regular springs discharge an unusual quantity
of water ; and, in the second place, new springs burst out along
the same rock junction, but at a higher level. These latter are
the bournes, which only flow after exceptionally rainy seasons,
occurring at fairly regular intervals. After flowing for some
weeks or months they gradually dry up and disappear till the
next excess of rainfall. The amount of water now pumped from
wells in the Chalk has lowered its saturation level so much that
outbreaks of the bournes occur at longer intervals than in former
years.

If the disposition of the strata is such that a great mass of

HISTORY OF LANDSCAPE 185

rock becomes saturated with water before an outlet is reached
the water will be stored up under hydraulic pressure, and under
favourable circumstances perennial springs, often issuing with con-
siderable force, will be produced (Fig. 73). 'This is the case when the
permeable stratum is both underlain and overlain by impermeable
strata, the three strata being either bent into a trough or brought
by faults into contact with another mass of impervious rock.
In the latter case natural fault-springs are common (Fig. 73, D).
Or if the junction remains impervious to water, a well or boring
may be sunk on the right side of the fault to obtain the spring
water, which will rise to a height dependent on the height of its
gathering ground. When a trough or basin in the strata occurs
it is generally necessary to pierce the upper impervious bed by
boring through it down into the porous rock. The water may
then rise up to or even above the surface. Such wells are called

fiocAs impervious Rocks

FIG. 73.— Fault Spring, D. Artesian Wells, A.

artesian wells (Fig. 73, A). The arrangement of strata under Lon-
don, the London Basin, is of this nature, the Chalk being folded into
a basin with impervious Gault below it, and impervious London
Clay above it. Large supplies of water have been obtained by
wells of this description; indeed, so much that the water level
and its" pressure have been lowered, and the water no longer
rises to the surface.

This class of springs is known as deep-seated, springs, because
the water has sunk to a considerable depth, has saturated
a great mass of rock and travelled a long distance through it,
and has then been forced again to the surface by hydraulic
pressure. This class of wells and springs affords water supplies
which are especially valuable for several reasons. There is a
vast reservoir of water to draw upon in times of drought and
the wells or springs rarely or never become dry, the wrater is

186 THE BOOK OF NATURE STUDY

driven along steadily under pressure and the amount received is
fairly constant from day to day, and the water travelling through
the pores of the pervious rock becomes admirably filtered and
purified. When the water travels very deep down into the rocks
it may emerge heated and form hot springs.

The water of both deep-seated and surface springs passing
through the body of the rock comes into contact with any soluble
ingredients there may be, and takes them into solution. Carbonate
of lime, magnesia, or iron are thus taken up by water containing
carbonic acid; sulphate of lime, and certain other salts of iron,
magnesia, and alkalies are taken into solution by all waters, and
brought out by them where they issue as springs. Small quan-
tities of such salts give to spring waters their pleasantness, and
deprive them of the " flat " taste of rain water. Larger quantities
turn the water into strong solutions, and they are then known
as mineral springs and are named calcareous, magnesium, alkaline,
saline, chalybeate, etc., according to their prominent ingredients.

The most important dissolved substances in ordinary springs,
which do not contain enough to entitle them to be " mineral
springs," are sulphate and carbonate of lime. Either of these
salts gives to the water the property known as hardness. A
water is soft if it dissolves soap and forms a lather with it.
Distilled water, rain water, or water flowing off areas of granitic
or siliceous rocks are soft. But a hard water forms a precipitate
with soap, and continues to do so until all the calcareous (or
magnesian) salts are extracted. The water has then become
soft, and will form a lather. Water containing carbonate of
lime precipitates this in kettles, boilers, or pipes when heated,
and especially when boiled, because the carbonate of lime is
only held in solution by the carbonic acid contained in the water,
and this acid is partly driven off by heating and completely
expelled by boiling. Hence boiling is a second method of
softening water hardened by carbonate of lime, and in conse-
quence of this property such water is said to be temporarily hard.

On the other hand, if sulphate of lime is the principal salt
in solution, the water will not be softened by boiling, because
the sulphate is held in solution by water alone without the aid
of the carbonic acid. Hence it is called permanently hard water.

HISTORY OF LANDSCAPE 187

Hard water, if not too hard, is pleasanter for drinking than soft,
and has the advantage that it does not corrode lead or iron pipes
so readily as soft water does. But it is not so good for most
manufacturing purposes, such as dyeing, or for steam raising:
Consequently, it is often softened wholly or partially by water
companies. Permanently hard waters are especially valuable
for brewing.

A temporarily hard water, if it contains very much carbonate
of lime in solution, may be compelled to deposit some of this
substance in consequence of its natural loss of carbonic acid,
when the spring first reaches the open air. This is the origin
of petrifying springs. The " turning into stone " of objects
placed in these springs is merely an incrustation of lime thrown
down upon them. The objects usually employed for petrifaction,
like moss and birds' nests, are such as break the water up and
encourage rapid evaporation of the carbonic acid. Sometimes
springs deposit enough carbonate of lime to form considerable
rock masses, and in Rome " travertine " thus deposited is largely
used as a building stone.

The dissolved material carried by springs is taken out of the
rocks traversed, and therefore springs are powerful disintegrating
and transporting agencies. Often, and especially in limestone dis-
tricts, they dissolve the sides of the cracks along which they
travel, widening them out into systems of caves. These are often
so important that they carry the whole of the drainage of the
area along underground channels, which are often of considerable
complexity. Old valley systems formed in earlier days, before the
water had opened out its underground channels, are often left
dry above (Fig. 74), or are only occupied by water during seasons
of heavy rainfall, when the rock below is saturated and its cracks
filled with water. Eventually the caves fall in and a new surface
drainage exists for a while, until the water has found a still lower
set of channels through the rocks.

Even when caves are not formed, solution of the cement
of a compact rock disintegrates it and prepares it for removal
by running water. The consequences are even more serious
when the water travels along the junction of two rocks and
removes the cement from the upper of them. If the junction crops

i88 THE BOOK OF NATURE STUDY

out on a valley side or at a sea cliff, and especially if the strata
are inclined towards the low ground, there is a great tendency for
the upper pervious rock to slide forward on the unstable junction
between the two, and a landslip is thus formed. This causes
serious . damage and destruction to rocks on the surface of the
ground, and it passes down to lower levels great quantities of
rock in a broken-up condition, and ready to be dealt with by
the stream in the valley or the sea at the foot of the cliff (Fig. 75).
Whether the springs drain to the sea or to rivers, a vast amount
of solid matter is taken away by them in solution from the land,
and the height of the land is lowered eventually by the amount
thus chemically removed. To this must be added dissolved matter
taken up and carried by surface water. Some of the dissolved
constituents, like common salt, remain in solution in the sea
water, and appear to be slowly but steadily accumulating in
amount therein. But other constituents, especially carbonate,
sulphate and phosphate of lime, are made use of by animals,
like shellfish, corals, foraminifera, and fishes, and to some extent
by plants, in building up their shells, tests, or skeletons. At the
death of these organisms the materials are returned again to the
earth-crust on the sea bed, in the form of deposits of carbonate
or phosphate of lime, ready to make limestone rocks and phos-
phatic deposits. If the water does not reach the open sea, but
finds its way to inland lakes instead of the sea, where the only outlet
for water is by evaporation, the pure water alone is carried off,
and its dissolved salts are precipitated on the lake bed as deposits
of carbonate and sulphate of lime or magnesia, or as deposits of
rock salt. Some of the limestones, especially the magnesian
limestones and the chief gypsums and rock salts, found as con-
stituents of the earth-crust, have doubtless had this origin.

CHAPTER XVIII

HISTORY FROM THE ROCKS

AN inference of great importance can be drawn from the occur-
rence of lamination in a stratified rock. Each layer is made
of denuded material spread out on a sea bed. It in turn is the
sea bed, on which a new layer is spread out. Thus a stratum
made up of many laminae must preserve the deposits of many
successive sea beds resting one upon the other. It will contain
the history of a considerable period of quiet deposition under
water. In order to read this history in chronological order, it
will be necessary to begin at the beginning, that is, at the lowest
lamina ; and this will be the case not only when the beds remain
in the horizontal position in which they were laid down, but even
after they have been tilted and folded. This important principle is
known as the order of superposition, and when it is read correctly
the sequence of the laminae gives the sequence of events during
which the rocks were laid down. The alternation of coarse and
finer laminae, for example, will tell of the successive deepening
and shallowing of the sea, just as the alternation of layers of
sand and mud on the delta of the Nile tells of a succession of
inundations and sand storms.

Evidently the principle will apply not only to laminae, but to
the larger beds or strata. If a bed of clay rests on one of chalk,
the latter will be the older, and the interpretation of the rock
succession will indicate that a clear sea with deposit of calcareous
organisms was followed by a muddy sea, to which rivers or currents
swept in quantities of fine denuded matter. The duration of the
two periods will be roughly expressed by the relative thickness
of the two beds. By the application of this principle to all strati-
fied rocks found in juxtaposition it is possible to ascertain the
relative ages of them all, and to construct a time scale out of
them in which all the strata, such as the Lias, the Coal Measures,

igo THE BOOK OF NATURE STUDY

and the Chalk, shall have their correct historical position. All
the " historical documents " which may be contained in the
strata can be dated by means of this time-scale. Then when the
" documents " are deciphered and interpreted they will furnish
some contribution to the history of the region in which they
occur, and thus give a part of the history of the world during
the time occupied in the formation of the stratified rocks.

By piecing together a record in this way from various parts
of the world, it is found that if all known strata were at any place
to be seen lying horizontally one over the other, they would be
350,000 ft. thick, and a boring to pierce them would have to be 66
miles deep . Records of the oldest history would be brought up from
the bottom of the borings, and of later history from nearer to the
surface. It is very occasionally necessary to resort to boring to
acquire evidence of this kind. But the geologist takes advantage
of the tilting of rocks to study the older ones, where by folds and
denudation they have been brought near the surface. He reads
the succession by means of the dip, and so works out the sequence
of events from the records preserved in the rocks. Thus the
popular impression that things buried very deeply in the earth are
necessarily very old, and those near the surface very new, is
wrong, but it is so prevalent that much care must be taken to
eradicate it.

The records in the rocks fall into two main groups, biological
and physical. The biological records are obtained from the fossil
animals or plants which may chance to have been preserved.
The physical records depend on the nature and composition of
the rock, its position and structure, its relations to others, its
range, and to a very considerable extent on the interpretation of
its fossil contents. A vast amount of detail on both these heads has
been patiently collected and laboriously recorded and described,
and some important general conclusions have been drawn from
it.

Physically, it has been shown that practically all rocks have
been formed by agencies such as may now be seen somewhere or
other in operation ; that vast physical changes in land, water, and
climate have occurred in the past, but they have been exceed-
ingly slow and gradual in operation ; that the story of destruction

FIG. 74. — A Dry Limestone Valley. Gordale Beck, Yorkshire.

(Photo by GODFREY BINGLEY.)

FIG. 75. — Landslip, near Cromer.

(Photo by S. H. WRIGHTSON.)

FlG. 76. — Head of a Trilobite, Silurian.
(Photo by F. MARTIN DUNCAN.)

FIG. 77. — A Fossil Tree, Carboniferous.

by GOUFRKY BlNGLEY.)

HISTORY FROM THE ROCKS 191

and renewal of land observed in the present has been going on
throughout geological time ; and that the changes the earth
has gone through have taken up very many millions of years.

Biologically, we find that the further we go back in time the
more unlike were the animals and plants to those living to-day ;
that they have steadily progressed towards existing types ; that the
progress was from simpler to more complex and more highly special-
ised forms ; that the progress was along evolutionary lines ; and
that there has been a constant relationship between progress in
the kingdoms of life and their environment.

Fossils should be collected from any rocks which contain
them. They will usually be obtained better from weathered
rocks and spoil-banks than from the rock exposure itself. As
might be expected from the fact that the sea is the great repository
of sediment, the majority of stratified rocks are of marine origin,
and they will show this by the types to which their fossils belong.
It may be possible to ascertain by comparison with modern genera,
not only that the organisms were marine, but the approximate
depth or conditions under which they lived ; whether between tide
marks, in shallow water, in deep water; or whether they were
free-swimming and liable to be deposited at all depths. They
may also give an indication of the climatal conditions under which
they lived. It must be remembered that only those with hard
skeletons or shells are likely to survive in the fossil state, and it
may be shown that even then their preservation is generally
due to chemical replacement or alteration of their substance.
Sometimes we have only external moulds or casts of the exterior
of hollow bodies to judge by, and there may be cases where only
certain structures, like the nacre of shells or the vascular tissue
of plants, have been preserved.

The fossils of other strata may prove that they were laid down
in lakes or by rivers, in deltas or even on land areas. In the
first two cases we shall have only the remains of fresh-water
animals and plants, pond snails, river mussels, and the like, with
a certain number of land forms that have been washed in. In
deltas similar remains will be mingled with brackish water and
marine forms. Land deposits will sometimes consist of vegetable
agglomerations, like peat or coal and lignite seams, or of barren

192 THE BOOK OF NATURE STUDY

deposits of blown-sand, alluvium, or glacial debris, all of which
will typically contain land animals and plants alone, or no fossils
at all.

When fossils are collected the nature of the containing rock
should be noted in order to see whether it confirms or contra-
dicts the conclusions drawn from the fossils. Pelagic forms are
usually found in clays or limestones ; shore-living forms are
associated with coarser grained deposits ; terrestrial and fresh-
water forms not often with limestones, unless these have been
deposited in tufaceous form from springs. Seams of coal and
lignite will be found resting on old alluvial soils, penetrated by
rootlets, and containing only land and fresh-water forms ; fossil
footprints, usually with ripple-marked sandstones, made up
of rounded grains, and associated with thin clay beds. Evidences
of shallow-water deposits are easily detected by ripple marking,
tracks of worms and other animals (Fig. 20), false bedding, and
the arrangement of the coarser materials (Figs. 17 and 24) ; while
terrestrial deposits are usually tumultuous and unsorted (Fig. 22),
and singularly barren of fossils.

The units of geological history are those strata which are
of sufficient individuality and importance to be called Formations.
No better example can be chosen than the Chalk, a pure, earthy,
white limestone about 1000 feet thick (Fig. 66), easily recognised
and retaining its characters not only all over England, but through-
out Northern Europe. It would be a justifiable inference that
it is approximately contemporaneous in origin throughout its
extent, and that beds immediately preceding and succeeding it
in England would be of the same age as those next below and
above it in Russia. There are many similar Formations in
British geology, and it will be sufficient to remark the Old Red
Sandstone, the New Red Sandstone, the Coal Measures, the
Mountain Limestone, the Great Oolite, and the London Clay.

Originally the geological record was pieced together in single
districts or countries, and it was then sufficient to find the order
of conspicuous Formations and to discover the nature and
thickness of the less conspicuous Formations in between them.
Gradually it was discovered that Formations were not so sharply
marked off from one another as they at first seemed to be, but

HISTORY FROM THE ROCKS 193

that there was transition from one to the next. The lines of
division became more arbitrary and more difficult to fix, and
it became the custom to divide the rock succession into steps
which, although founded to some extent on the broad characters
of the Formations, took note more particularly of the inter-
pretation of the conditions under which they were formed. Thus
some of the old Formation names were retained, like Carboni-
ferous, Old Red Sandstone, Cretaceous. But in other cases it was
necessary to select other types of names, the most convenient
being chosen from the places where the rocks of the division
could be most easily and typically studied. Thus we have such
names as Cambrian, Devonian, Jurassic, all derived from place-
names.

When correlation of succession over wider areas was attempted
it was found that no Formation, however well marked its
character, was world-wide in distribution, but that its character
gradually changed from point to point. Thus the Old Red
Sandstone Formation of Scotland, with its conspicuous colour
and its sandy composition, its fossil fishes and giant Crustacea,
is of the same age as marine slates and limestones in Devonshire,
and it would not be appropriate to extend the Formational
name to cover different rock types in Devonshire. It would be
less objectionable to use the term Devonian for the Scottish
sandstones, but even this can only be regarded as a temporary
expedient. As geological history grows out of the stage of the
history of local areas into the general history of the earth-crust,
the necessity for a wider nomenclature becomes pressing, and
attempts, some of them successful, are being made in this
direction, but the difficulties are at least as great as those found
in any attempt to divide the human history of the world into
convenient divisions applicable to the whole world.

When fossils have been collected from the whole of the rock
succession, and compared with one another, it is found that the
older ones differ very widely from those living at the present
day, but that throughout the succession there is a gradual
approach, accelerated or retarded it may be at different times
and in different places, up to the faunas and floras of the present.
The oldest fossiliferous rocks contain only invertebrate remains ;

VOL. VI. — 13

194 THE BOOK OF NATURE STUDY

the earliest vertebrates are fishes ; these are followed later by
amphibia and reptiles ; and these by birds and mammals. In
each division of the animal kingdom there is progress from lower
to higher forms, a thing which may be especially recognised
in the brachiopoda, the Crustacea, the fishes, the birds, and
the mammals. Thus it becomes possible to determine from the
status of the highest organisms present in any particular stratum,
and from the general grade of the fossils, each in its own division
of the plant or animal kingdom, the approximate position of
the stratum in the geological scale. Progress of this kind has
occurred, not at the same rate or absolutely in the same direction,
all over the world. But over the open oceans, always occupying
a larger area than the land masses, and always more largely
represented in the strata than fresh water or land deposits, the
progress has been more uniform. Thus correlation even over
great distances becomes a possibility.

Historical nomenclature founded on the progress of life is
therefore the type which will be the most exact, the most minute,
the widest in its application, and every effort is being made
in geology to obtain in this way a time-scale which shall be of
world-wide application. Towards such a system words like
Eocene and Miocene, Paradoxidian Division, Pentamerus Beds,
are contributions, but the tendency at present is to attach to
the place-names an exact biological significance, and to continue
the use of them in this new sense. Thus the word Silurian attains
a new significance, and many other words, such as Valentian,
Bathonian, Cenomanien, Ypresian, have been coined from
place-names to serve the same purpose.

Apart from their use in giving us the most convenient and
widely applicable way of dividing the entire record into sections
and chapters, fossils are capable of extended use as date indexes
of wonderful exactness, and as means of minute correlation.
It is found that the fossils of a stratum include usually four
types in varying proportion : — (i) Those confined to the bed
itself and not found above or below ; (2) those found also in beds
below ; (3) those found also in the beds above ; (4) those found both
above and below. All four types are useful in enabling an estimate
to be formed of the age of the rock containing them, but those

HISTORY FROM THE ROCKS 195

first mentioned are of course of the greatest service, and it is
a common practice to name the bed from one or more of its
characteristic and exclusive fossils. The recognition in a new
district of one or more beds containing fossils characteristic of
strata in a known position elsewhere gives a clue to the age of
the rocks in the new district from which their position, succession,
and relations can be worked out. Indeed, it is to this discovery
by William Smith at the end of the eighteenth century that all
modern progress in historical geology is due ; and the early
pursuit of the method in Britain rendered the names given to
members of the British succession applicable to their equivalents
not in Europe only, but in many other parts of the world. Such
terms as Silurian, Devonian, Carboniferous are of world- wide use.
In collecting fossils from successive beds, sometimes the life
change from bed to bed is rapid and complete, but more usually
it is gradual and less decisive. The first condition indicates a
rate of deposition which is slow even compared to the rate of
organic change ; the second indicates more rapid deposition,
and convenient divisions of the strata are much less easy to
locate and define, and are necessarily much less natural in
character. The first condition is associated with deep, clear
water, to which the supply of sediment is brought only in very
small quantities. Confirmatory evidence is usually given by
the fineness in grain of the deposits, the relative abundance of
fossils, and the association with deposits such as are now known
to be forming slowly in the ocean. On the other hand, the more
rapidly deposited rocks are coarser in grain, more irregular in
structure, deposited in shallower water nearer to a coast-line,
and in proximity to regions of more rapid denudation. Thus
more evidence is given as to the physical condition of the area
during the period under consideration. As might be expected,
the slowly deposited rocks will be of wide geographical extension ;
they will be most easy to correlate from place to place ; and they
will form the main ties linking together the general succession
in one place with that in another.

CHAPTER XIX

THE GEOLOGICAL RECORD

THE table given below expresses the chief of the Periods into
which the geological history of the earth-crust is divided, and their
grouping under three great life stages, the Eozoic, Palaeozoic, and

ERAS.

Neozoic

SUB-ERAS.

Cainozoic

Palaeozoic

^Mesozoic

'Deuterozoic

.Protozoic

Eozoic .

PERIODS.

fPleistocene.
Pliocene.
Miocene.
Oligocene.
.Eocene.

[Cretaceous.
•j Jurassic.
iTriassic.

fPermian.

•[ Carboniferous.

[Devonian.

fSilurian.
•j Ordovician.
I Cambrian.

/Torridonian.
I Longmyndian.
1 Dalradian.
ILaurentian.

Neozoic Eras. Of the life of the Eozoic era practically nothing is
known, but there is evidence to show that life had dawned on the
earth at least before the end of the Era. The life of the Palaeozoic
is strikingly old-fashioned and very different in every particular
from that now existing. At first there were no vertebrates, and

when these appear they are slowly succeeded by amphibia and

196

THE GEOLOGICAL RECORD 197

then by reptiles, the last being the highest life forms present in the
Palaeozoic rocks. The vegetation is confined at first to crypto-
gams, but towards the end of the Era gymnosperms have made
their appearance. It is a remarkable fact that representatives of
all the invertebrate sub-kingdoms have been found in the earliest
Palaeozoic rocks, appearing, it is true, in rudimentary forms,
but still with a considerable amount of specialisation. This points
to the existence of many yet undiscovered faunas in the Eozoic
rocks. Vast numbers of genera and even whole classes appeared
and became extinct within the Palaeozoic Era. For instance, the
graptolites, blastoidea, cystidea, trilobites, and armoured ganoids
flourished and became extinct. Others, like the merostomata,
the rugose corals, the spire-bearing brachiopods, the articulated
echinoidea, and the nautiloid cephalopods, flourished in great
numbers and died down later to small numbers of degenerate
forms.

Neozoic life is at first characterised by abundance of reptiles,
and afterwards by abundance of mammals. The reptiles occupied
the sea, the land, and even the air. The mammals give the best
evidence of evolution and progressive specialisation hitherto
obtained from the rocks. The abundant brachiopods are gradually
replaced by lamellibranchia, holostomatous by siphonostomatous
gastropods, regular by irregular echinoidea, the reptile-like
birds of the Mesozoic by the normal types of the Cainozoic.
Cycads and conifers give place to angiosperms, cartilaginous to
teleostean fishes. But again, many forms, either originating during
the Era or surviving from the preceding Era, flourish exceedingly
and then diminish or die out. Thus the ammonites and belemnites
among the cephalopods, the nummulites among the foramini-
fera, the hippurites among the lamellibranchia; the dinosaurs,
ichthyosaurs, and plesiosaurs among the reptiles ; the creodonts
and dinocerata among the mammals become wholly extinct,
while the mud fishes, terebratulae, trigoniae, nautili, the edentata,
and the marsupials have all become vastly reduced in numbers
and importance at the present day. On the other hand, the snakes
and turtles, the apes and herbivora, the birds, the dicotyledons
and grasses, the lamellibranchs and gastropods, increase in pro-
portion as the others diminish.

ig8 THE BOOK OF NATURE STUDY

In what follows an attempt is made to give a brief description
of the successive rock Systems, so as to bring out their broader
characters. What is said with regard to the life is not confined
to the British Isles, but any description of the physical character
of the rocks will necessarily apply chiefly, and often exclusively,
to the British Islands.

The rocks of the Eozoic Group are only seen in limited localities
where newer rocks have been stripped off. They are usually
much altered from their original condition, and are in the form
of gneisses and schists. Associated with these are many igneous
rocks, either poured out as lavas (with their accompanying tuffs
and ashes) or intruded into others at various depths. There are
also sediments, conglomerates, felspathic grits, and slates, with
rare limestones. In the sediments have been found traces of
worms and a few other organisms. The rocks are found some-
times in great plateaux, at others along the core of modern moun-
tain chains or of more ancient chains which have now been
deeply cut into by denudation. The rocks yield rich supplies
of metals such as iron and copper, gem stones, marbles, and stones
for building and roofing. The landscape on their surface is some-
times undulating and monotonous, but at times mountainous and
beautiful.

The Cambrian Rocks are typically seen in Wales. They
consist of slates, quartzites, and grits, the deposition having taken
place in deep seas only shallowed occasionally and over a limited
area. The life of the period consisted mainly of trilobites and
horny brachiopods, with few lamellibranchs and gastropods ;
cephalopods, crinoids, and phyllopods have been found. The
rocks yield slate and road metal, manganese and gold locally.
Their landscape is not usually of much interest, but the great
exception is the Harlech and Tremadoc region in Wales, where the
harder bands form lofty mountains of very massive structure.

The Ordovician Period was one of deep seas sprinkled with
volcanic peninsulas and islands. The rocks are fine shales or
slates, with flagstones and limestones, generally interbedded with
volcanic ashes and lavas, and having innumerable masses of igneous
rock intruded into them. Some of the rocks, like the intensely
fine-grained shales, showing an apparently rapid life-succession,

THE GEOLOGICAL RECORD 199

and the cherts bearing radiolaria, give evidence of excessively
slow deposition in quiet deep oceans, a conclusion borne out by
the wide distribution of floating forms of life like the graptolites.
In addition to these there is a great advance in numbers and
organisation of the trilobites, abundance of spire-bearing and
horny brachiopods, and increasing development of cephalopods.
But the steadfast advance in the graptolites gives at once an
impressive picture of the evolution of the group and an admirable
key to the age of the deposits. Ores of lead, zinc, and barium,
occur in the veins of the rocks, which also yield supplies of building
stone, road metal, and roofing slate. The beautiful landscapes
of the Lake district (Fig. 2), North Wales (Fig. 68), and Shrop-
shire, are due to the presence of bands and masses of igneous rocks
associated with the softer sediments, and the contrasting scenery
of the Southern Uplands of Scotland is the result of the minor
importance or absence of igneous rocks there.

The Silurian System is made up either of alternations of shales
and limestones or of slates and grits. Its landscape in the former
case consists of edges (or wolds) and vales ; in the latter of pastoral
uplands or rugged moorlands. The rocks were laid down either
in continuous areas of shallow water with shifting currents, or in
calmer areas in which calcareous organisms furnished supplies of
shells and tests for limestones, occasionally interrupted by in-
cursions of fine sediment . Volcanic activity was in abeyance . The
life includes trilobites (Figs. 76 and 26) and graptolites, the former
reaching a high stage of perfection, the latter dying out at the
end of the period. Corals are abundant, forming limestone reefs ;
indeed, the period might almost be spoken of as that of corals
and crinoids (Fig. 24). Brachiopods are very numerous, especi-
ally Pentamerus, cephalopoda important, polyzoa abundant, and
there are numbers of lamellibranchs and gastropods. The earliest
fishes appeared at the end of the Period, cartilaginous and
armoured for the most part ; and about the same horizon have
been found the earliest land plants (cryptogams), and a giant
group of the merostomata, the eurypterids. Few Formations
yield more fossils or better preserved. The limestones have been
extensively quarried for lime-burning and for smelting.

The rocks of the Devonian System in Devon and Cornwall are

200 THE BOOK OF NATURE STUDY

sandstones, slates, and limestone, the fossils that are present being
marine types. In Ireland, the Welsh border, and Scotland, they
are in the form of red sandstones and marls with very few fossils,
and those of lacustrine and fresh-water types (Fig. 25). They
were formed in lakes to the north and in a sea to the south of
Britain. Volcanoes were active in Scotland and Devonshire
(Fig. 32). The chief life event is the enormous number of fishes
living at this time, almost all of cartilaginous type with an im-
perfectly ossified skeleton and an armour of bony scales or plates.
Giant eurypterids are also common, many entomostraca, and
some fresh-water mussels have been found. The marine life is
characterised by special types of brachiopods, and large numbers
of corals and crinoids. Trilobites are on the wane. The vegeta-
tion consists of ferns and of lepidodendra, the latter giant repre-
sentatives of the modern club moss. The rocks in Scotland are
quarried for paving flags at Caithness and Arbroath, and they are
also employed as building stones. Fossiliferous limestones con-
taining corals or brachiopods are polished and used for orna-
mental marbles in Devonshire. The most interesting landscape is
where there are hard volcanic bands, as in the Ochil and Sidlaw
Hills ; but generally the country is undulating, and on the Welsh
Borders it is covered with orchards and hop gardens.

The Carboniferous System is the most important in Britain
from an economic point of view. The older rocks are generally
limestones (Figs. 18, 71, and 74), followed by grits, and those by
alternations of clay or shale, coal, sandstone, and ironstone,
known as the Coal Measures (Fig. 50), because they are the rocks
which, not only in Britain, but in Europe, Asia, and America,
yield the chief supplies of coal in the world. The British area
seems to have been in the first place a sea of considerable depth,
in which the limestones were laid down; the succeeding Mill-
stone Grit gives evidence of widespread shallowing of the sea
(Figs. 8 and 32) ; and the Coal Measures with their fresh-water
fossils and abundant plant remains, their ironstones, and the
association of their component strata, indicate a period of deposi-
tion in a great river delta which was, on the whole, undergoing
subsidence while being filled up with deposits. The coal seams,
which vary in thickness from a fraction of an inch to 20 or 30

THE GEOLOGICAL RECORD 201

feet, but are usually from 2 to 10 feet, thick, were formed by the
compression and partial decomposition of vegetation which grew
on the swampy surface of the delta whenever it was built up to
sea level, their thickness depending upon the duration of con-
ditions favourable for growth and preservation of the plants.
The presence of upright trees in and above the coal seams, resting
upon an old clay soil which is penetrated by rootlets and fibres
proceeding from their roots, shows that the coal grew where it is
now found, and was not as a rule drifted into place. Seams of
cannel coal, however, seem to be made of vegetation drifted and
waterlogged. Whenever subsidence of the delta recommenced,
growth of vegetation was stopped for a time, and the plant-remains
were buried up and gradually mineralised and converted into
coal. The alternations of plant growth and subsidence were
repeated hundreds of times.

The vegetation of the period was almost exclusively crypto-
gamic, but the plants, whose only living representatives are
ferns, lycopods, selaginella, and equisetum of lowly size and little
importance, then attained great size (Fig. 77). Some few higher
plants were present, conifers and cycado-filices, but it is doubtful
if there were either monocotyledons or dicotyledons. Microscopic
examination of the coal often proves it to consist of bark, epi-
dermis, and vascular tissue of the plants, and sometimes entire
seams are made up of nothing but spores and spore cases. Air-
breathing mollusca and insects of various kinds have been found
in the Coal Measures, and remains of the earliest known amphibia
have been obtained from the same beds. Fishes and fresh-water
shells are abundant, marine shells being more seldom found, and
then only in particular bands. The ironstones may have been
formed, like the bog iron ores in Sweden, from the growth of ferrug-
inous algae.

The marine fauna of the lower beds is chiefly characterised
by brachiopods, corals, and crinoids. There are many foramini-
fera, lamellibranchs, gastropods, and cephalopods ; but trilobites
are few in number and species, and are on the point of extinction.
Volcanoes were active in Scotland, Ireland, and Devonshire.
Besides coal and iron, the rocks of this System yield refractory
materials such as fireclay and ganister ; clay for pottery and

202 THE BOOK OF NATURE STUDY

bricks; petroleum; lime for mortar, cement, and smelting;
sandstone and grits for building, paving, and the making of
millstones and grindstones; as well as ores of lead and
zinc. The typical moorland landscape of the Pennine Chain
is due to the outcrop of the grit beds of the Millstone Grit,
while the limestone country is either grass-covered and cut into
abrupt valleys, once perhaps caves, or is barren and terraced,
scarred with great cracks running along the joints widened by
solution, and waterless because the drainage finds its way down
these cracks into caves and underground channels (Figs. 33 and 74).
The Coal Measure landscape was doubtless once beautiful, and is
even now at times interesting when forest covered, as much of it
doubtless originally was.

The Permian Rocks consist of sandstones, conglomerates, and
breccias, generally stained deep red with oxide of iron. There is
often present a peculiar limestone containing magnesium carbonate
as well as calcium carbonate. It yields few fossils, those present
belonging to few species. These are of marine type, but stunted
and dwarfed in development, as though living in a most un-
favourable environment. It is generally thought that this
indicates formation in a salt lake in a dry climate. This is
borne out by the nature and unfossiliferous character of associated
deposits, by the nature of the scree-like breccias; and by com-
parison of the British rocks with marine deposits of this age
known on the continent of Europe. The most important new-
comers in the life are the earliest reptiles. The rest of the
fauna is an impoverished descendant of that of the Carboni-
ferous without any remarkable new ingredients. The plants are
the last survivors of Carboniferous types with a few Cycads.
But in Europe outside Britain, in addition to the Palaeozoic types
of life, there are found also the first representatives of those
types which are soon to become abundant and give its character
to the Mesozoic life. The sandstones and magnesian limestones
are used for building, but there is little else of economic interest,
and the landscape of the rocks calls for no remark. In a few
places there are volcanic rocks of this date, but this was the
last effort of the Palaeozoic volcanoes, and the country was quite
quiescent in this respect during the Mesozoic Era.

^/^ '

FIG. 79. — An Ammonite, Cretaceous.

(Photo by F. MARTIN DUNCAN.)

FIG. 80.— Eocene Gastropods.

(Photo by F. MARTIN DUNCAN.)

THE GEOLOGICAL RECORD 203

The Triassic Rocks continue the story begun by the Permian.
They are sandstones, conglomerates, and marls, with the remark-
able addition of beds of rock-salt and alabaster or gypsum The
coarse deposits indicate rapid denudation, the well-rounded sand
grains (Fig. 18) and unfossiliferous rocks point to desert conditions
and deposit under terrestrial conditions, and the rock-salt and
gypsum to the evaporation of such inland salt lakes as are often
found in desert regions. As would be expected, evidence of life is
rare, being confined to a few rare plants, entomostraca, scorpions,
and reptiles. The last are represented not only by bones and
teeth, but by tracks (Fig. 20), some of them of dinosaurs remark-
ably birdlike in their organisation and footprints. But the most
remarkable fossils hitherto obtained are portions of what is
probably the oldest known mammal. In this connexion it is
important to notice that in South Africa and elsewhere remains
of two extinct orders of reptiles presenting many affinities with
the mammals have been found. The vegetation is characterised
by an increased proportion of cycads. In the Alps the strata
occupying the position of the Trias are of marine character with
abundant and well-preserved shells, crinoids, corals, and foram-
inifera, mostly of types which become more common in the
succeeding Formations, but including not a few survivors of
Palaeozoic types. The sandstones of the Trias give excellent
building stones, and they yield one of our most important supplies
of water. The salt beds and brine springs are our chief source
of salt, and the gypsum beds are worked for plaster and impure
alabaster. The rocks occur for the most part in great plains
like those of Chester, York, and the Midlands, which are some-
times deeply trenched by rivers. The land upon them is gener-
ally fertile, and occupied by arable, forest, and gardens.

The rocks of the Jurassic System are mostly alternations of
oolitic limestone and clay (Figs. 13 and 29), the former much
quarried for freestone, the latter excavated for brick-making.
They were deposited in a warm sea of Mediterranean type, at first
deepening on the whole, but afterwards shallowing and eventually
becoming dry. Fossils are abundant and well preserved. The
most conspicuous types are ammonites and belemnites belonging to
the cephalopods ; abundant reptiles like ichthyosaurs and plesio-

204 THE BOOK OF NATURE STUDY

saurs (Fig. 28) in the sea, dinosaurs on the land, and pterodactyls in
the air. Loop-bearing brachiopods compete with abundant lamelli-
branchs and gastropods, and many of the limestones are coral reefs
abounding in sea urchins and a few genera of crinoids. Certain
shallow-water or terrestrial beds yield the remains of small
mammals, and an important vegetation consisting of ferns,
equisetums, conifers, cycads, and monocotyledons. The fishes are
still cartilaginous. Remains of the earliest known fossil bird
found at Solenhofen show that it had wing and tail feathers, but
was closely related to reptiles in the form of its tail, the shape
of its skull, the possession of four digits in addition to the " wing
finger/' and in having jaws furnished with teeth instead of a
beak.

In addition to the economic products mentioned above, the
rocks furnish lime and hydraulic cement, alum, jet, roofing slabs,
iron-ore, sand, and water. There is even inferior coal in shallow-
water beds of this age in Yorkshire (Fig. 12). The scarped wolds
of the limestones with intervening clay vales sweep north and
southward from the Cotswolds (Figs. 52 and 63), and form a bar
which must be crossed by all roads and railways running from
London towards the north or west.

The Cretaceous System was so named because the Chalk
Formation was one of its chief members. The other divisions
consist of alternations of clay and sand with some conglomerates :
In South Britain the lower beds are of fresh-water origin, and are
well developed in the Weald (Figs. 50 and 65) : The higher beds,
called " Greensands," are marine, and usually contain green
specks which are casts of the interior of foraminifera. The
Chalk itself is a pure white limestone composed chiefly of
foraminifera and shell particles, and it seems to have been laid
down in a fairly deep sea, as it has much in common with the
foraminiferal oozes of modern oceans. It carries bands or nodules
of flint, which are concretions of silica generally aggregated
round skeletons of sponges. Again, reptiles and ammonites
(Fig. 79) of various forms are conspicuous fossils, the former
including turtles and snakes, associated with extinct orders.
Mammals have not been found in Europe, but both mammals
and birds occur in America, the latter still possessing the reptilian

THE GEOLOGICAL RECORD 205

character of teeth in the jaws, although they have now typical
avian tails, wings, and skulls. Teleostean fishes and angiosperms
make their appearance, but the life is on the whole more closely
linked with that of the Mesozoic than of the Cainozoic rocks.
Sea urchins are common and brachiopods still prominent. The
rocks yield iron-stone, once much worked in the Weald, a fresh-
water limestone worked for marble, firestones, glass and filtering
sand, fullers' earth, brick clays, phosphatic nodules used for
manure, and flints used sometimes for building and road-making.
The Chalk is a very important source of lime for mortar and
cement, and it and the Greensands yield also considerable supplies
of underground water. The landscape consists of parallel scarps
and valleys like those of the Weald, and the Chalk Downs form
one of the most conspicuous features of southern and eastern
England. The soft chalk is capable of forming hill ground (Fig. 70),
partly because it is relatively harder than the clays above and
below it, and partly because most of the rain water is absorbed
readily by it and does not often form denuding streams on its
surface. Valleys in a chalk country are almost invariably dry.

The Eocene System of rocks is confined to the London and
Hampshire Basins. The rocks are mainly clays, sands, and
shelly marls, deposited in the estuary of a tropical river. The
fossils are mainly marine, though fresh- water and estuarine bands
occur, and both animals and plants begin to show affinities with
forms still living, most of them in tropical latitudes. During
part of the Period, volcanoes became unusually active in many
parts of the world, and especially on the west coast of Scotland
and the north-east of Ireland.

Brachiopods are no longer conspicuous, their place being
taken by lamellibranchs and great abundance of gastropods
(Fig. 74), which show affinities with those now living in the
Indian Ocean. Crinoids, sea urchins, and cephalopods are
much less conspicuous. Foraminifera are common, and some,
like nummulites, exceptionally large, and building whole masses
of limestone. The great profusion of Mesozoic reptiles dis-
appears, leaving only crocodiles, turtles, and snakes. Birds are
almost normal. The method of formation of the rocks has
allowed the preservation of numerous mammalia. Marsupials

206 THE BOOK OF NATURE STUDY

are common, and so are links between marsupials and carnivora,
while most of the forms are not to be exactly referred to
existing orders, but are ancestral forms or links between them.
The vegetation is mainly dicotyledonous, but there is an
abundance of palms, and most of the plants are such as live in
subtropical latitudes.

The rocks provide sands and clays for brick making, but
little else of economic value is obtained. The landscape is flat
or gently undulating, some of the sand beds giving rise to heaths
and commons like those about Bagshot, Aldershot, Hampstead,
and the New Forest.

The Oligocene System is found only in the Hampshire Basin,
including the Isle of Wight. The rocks are estuarine, fluviomarine,
or fresh water in origin, and consist of sands, shelly marls, and
ill-consolidated limestones. The common fossils are fresh and
brackish water shells, with bones and teeth of land animals.
While the invertebrate fossils approach very closely to existing
forms, and are sometimes identical with them, the mammals
still present wide differences. The vegetation still indicates a
climate warmer than Britain of the present, and shows such forms
as fan-palms, feather-palms, and cinnamons.

The Miocene System is not found in Britain. On the
continent it indicates a Period of shallow water, lakes, and much
earth movement.

The Pliocene Rocks are found only in Eastern England. They
are mainly sands and shell-beds full of fossils. The shells are
at first such as live in latitudes a little south of Britain, later
they are closely linked with British forms, and in the end they
include many arctic types. Few of the shells have become
absolutely extinct, though many have left British waters. This
indicates a gradual refrigeration in the climate. The mammalia
shows a close approach to living types, and a few species which
still survive have made their appearance. They include the
extinct mastodon and the living horse and hippopotamus. The
vegetation differs only in a few respects from that at present
living in the same area. The landscape is usually flat and not
very interesting, and the economic application of the rocks is
almost limited to the marling of fields.

THE GEOLOGICAL RECORD 207

Pleistocene Deposits are found in many parts of the country.
They are usually unconsolidated, and have mostly been formed
on land. Their most striking member is the boulder-clay
(Figs. 22 and 23), formed by the action of glaciers and ice sheets,
the climate having been sufficiently cold to allow these to
extend over the whole country north of the Thames. Fossils
are not common, but they include arctic shells, and mammalia
which could live in a cold climate, such as the woolly elephant
or mammoth and the woolly rhinoceros. The vegetation also
was sparse and of an arctic character, including the dwarf birch
and willow.

After the Glacial Epoch the climate gradually ameliorated,
and such materials as raised beaches, cave-earths, river gravels
and alluvia, blown sands, peat, lake, and fen-deposits were laid
down. The most important fossils are the remains of man and
his contemporaries, the former in the shape of stone weapons
made at first of flint rudely chipped into shape. Eventually
man learned to finish stone implements by grinding them to an
edge, later still to work in bronze, and at last in iron.

CHAPTER XX
THE GROWTH OF BRITAIN

THE preceding chapter has shown that the study of the
rock succession in any country reveals that that country
must have passed through numerous geographical changes. In
order, however, that our knowledge of each geographical phase
may be complete, we require to know two things : — (i) The nature
and composition of each geological Formation throughout its entire
extent ; and (2) the changes which each one has undergone since
its formation. This has been summed up by Professor Lapworth
as " knowledge of the Formation and of its Deformation/'

We can never hope to know the entire extent of a Formation,
because not only is a large part of it usually buried beneath
newer strata, but almost always much of it has been denuded
to provide material for the building of subsequent Formations.
Thus our knowledge is almost limited to the outcrop. Inside
this it is hidden ; outside, it has been destroyed. We can, how-
ever, make use of every exposure of a rock along its outcrop in
order to see whether any variation in character can be detected.
Outliers saved from the general denudation, beyond the main
outcrop, will give us an idea of its former extension in that direction,
and borings through newer strata will tell of its nature on its
underground continuation.

All three sets of observations along and across the outcrop
give evidence in many cases of variations from the normal.
A limestone will become less pure and mingled with mud in
certain directions ; it may even pass completely into a shale or
sand. Sands are found to pass into clays in one direction, and
into conglomerates in the other. This is precisely the type of
variation we should expect from the conditions under which
we know the strata to have been laid down. No sea is world-
wide ; somewhere its clear waters and beds covered with organic

208

THE GROWTH OF BRITAIN 209

remains must pass towards the land, from which mud is carried out
by currents and deposited ; while following in the same direction,
we shall pass to the sand and pebbles of the shore, and beyond
that again to the land, where denudation and not deposition
was taking place.

Whenever, therefore, we find a limestone passing into a
deposit of mechanically denuded matter we are approaching
the margin of the sea in which it was deposited, and we may
hope, on proceeding farther in the same direction, to reach the
shore line, and eventually the land of the period. There is no
more striking instance of this than the Carboniferous Limestone,
which is pure, thick, and oceanic in Derbyshire. Traced north-
wards, beds of clay are associated with it, and become thicker
in a northward direction. Then sands come in, then seams of
coal, and in Scotland there are even fresh-water limestones and
shore deposits on the same horizon. The Carboniferous Lime-
stone sea had its main coast-line to the north, and its land was
what is now the Highlands of Scotland. Again, tracing the
limestone southwards from South Wales and Bristol, where it
has much the same character as in Derbyshire, we find it passing
into deeper-water beds, such as radiolarian cherts in Devon,
and therefore we conclude that this was the deepest part of the
British sea in this period. Something similar to this can be
worked out for most British Formations, and even the marine
Chalk can be traced into shallow-water beds and shore deposits
in Scotland. Thus it becomes possible to work out the general
outlines of the seas and land areas of past time.

In this line of inquiry one of the most valuable classes of
evidence is derived from the relation of a stratum to those on
which it rests. If the surfaces of the older and newer strata are
parallel to one another they are said to be conformable (Figs. 18
and 19), the sea bed on which deposit was taking place in the
second period remaining parallel to its position in the first period,
though it may have moved upwards or downwards. But often
the dip or strike of a Formation may differ from that which
underlies it, and the lowest bed of the second series may rest
successively on one member after another of the older series
(Fig. 81). This is called unconformity, and it indicates that the

VOL. VI. — 14

2IO

THE BOOK OF NATURE STUDY

older rock was folded and denuded before the newer was laid
down on its denuded edges (Fig. 82). The deposition of the
older bed must have occurred under water in an area of rest.
It must have been folded by earth movement to give it its dip,
and it must have been lifted up within the area of denudation,
that is into shallow water or to form a land surface. After de-
nudation it must have been again lowered beneath the water into
a new area of deposition. Much time must therefore have elapsed
between the two sets of strata, possibly represented by deposits
elsewhere. There is a gap in the succession, and, what is of more
importance from our present point of view, earth-movement must
have occurred in the interval.

Now, it is such earth-movement which lifts sea beds to form
continental masses, and elevates plateaux and mountain chains.
Consequently the occurrence of unconformities between strata

FlG. 81. — Unconformable junction of beds b with beds a.

enables us to date the origin of the features which result from
earth-movement, while it furnishes new information as to the
boundaries of sea and land after and during the movement. From
such evidence we know that there have been four great and
several minor periods of earth-movement in Britain. Moreover,
we know that each period of earth-movement was a prolonged
cycle, taking sometimes several geological Periods for its com-
pletion.

Each earth-movement contributed new landscape features to
the country ; some of them were transient, but many have
survived to this day and still form conspicuous and important
features in the geography of the country. The movements must
necessarily have reacted on the progression of animal and plant
life ; they must have stimulated or retarded evolution ; and must
have had much effect on the climate and denudation, and on the
drainage and relief of the country. The earliest earth-movement
of which we have knowledge preceded the Cambrian Period ; the

THE GROWTH OF BRITAIN 211

second followed the Ordovician, but was not completed till the
middle of the Devonian Period ; the third was late Carboniferous,
and lingered till the Trias ; and the last began after the deposition
of the Chalk, and was not completed till the beginning of the
Pliocene, if indeed it is yet complete.

Each period of movement is likely to have resulted in the
uplift of continental masses and mountain chains, accompanied
by folding and faulting of the strata, the metamorphism of the
rocks, and the outburst of volcanoes. Each intervening period
of rest or subsidence is likely to have given rise to incursions of
the sea and the formation of marine deposits. This sequence of
events is to some extent traceable in British geological history.

The earliest movement began well before Cambrian times,
but the land and mountains of the period can at present only be
doubtfully traced. The pre-Cambrian volcanoes were an outcome
of the movement in many parts of Wales and the Midlands, and
possibly the Longmyndian and certainly the Torridonian strata
were made of materials rapidly denuded from newly elevated
lofty land. Later came the marine deposition of the Cambrian
strata.

The next period of movement began during the deposit of
the Ordovician rocks, and the site of the volcanoes of this period
was determined by it. There is striking unconformity between
Ordovician and Silurian rocks, but the land seems to have attained
its most remarkable relief during Old Red Sandstone times.

The continental conditions and the great lakes of this Period
were the most important results of this movement, to which we
owe the Scandinavian chain of Europe, of which the Highlands
and Uplands of Scotland, the mountains of Lakeland and Wales,
and those of northern and western Ireland are a part. The nature
of the Old Red Sandstone material, the relation of its strata to
the older rocks on which they rest, and the presence of massive
conglomerates and breccias at the base of the Formation, resting
unconformably on Archaean, Cambrian, and Ordovician rocks,
are the evidences by which this movement and its effects are dated.

The period of rest was comparatively short, but in it the
lower rocks of the Carboniferous System were deposited in a sea
which was shallowed later by the beginning of the next earth-

212 THE BOOK OF NATURE STUDY

movement. This ridged up the strata in lines running either
north and south in the Pennine Chain, or east and west in the
Mendips and South Welsh mountains, a line which was con-
tinued, though the continuation is now hidden, eastward under
the Weald and across to France and Belgium. Such features as the
Pennine and Pendle Ranges, the higher ground of the Midlands, the
South Welsh mountains, the Mendips, and the region of Dartmoor,
Exmoor, and the mountains of Southern Ireland, were added to
British geography. And, associated with them come the remark-
able terrestrial, shallow water, and lacustrine deposits of the
Permian Period, and the river and salt-lake deposits of the Trias.
The mountains were denuded by frost and torrents, and breccias
and conglomerates deposited. The obstruction of rain-bearing
winds by the southern range converted the continental area into
a rainless one with deserts and salt lakes, deprived it of marine
deposits and life, and was responsible for the remarkable character
of such rocks as were deposited. The volcanoes of the Permian
and the vast amount of granite intruded into the earlier rocks of
Southern England at this period are further consequences of the
great earth-movement.

The marine deposits of the Jurassic and Cretaceous Systems
which follow are the natural consequence of the period of rest,
which was on the whole an extremely quiet one. But these
Formations when traced from place to place prove to have their
shore deposits in association with the features just outlined, the
Pennine, and the great southern (or Armorican) ridge running
east and west. Part of the shore-lines were, however, made of the
relics of the still earlier features resulting from the Caledonian
movement, which, indeed, survive to this day in sufficient pro-
minence to form our chief mountain ranges.

The last great movement, the Alpine or Wealden movement,
was responsible for lifting the sea in which the Chalk was formed
into the shallow water in which the Tertiary rocks were laid down.
But the movement reached its maximum after the Oligocene
Period, when all Britain was lifted above the sea and the great
east and west fold of the Weald and Salisbury Plain was formed,
together with the London and Hampshire Basins. At the same
time, but along lines determined mostly by earlier movements,

FlG. 82. — Carboniferous Limestone resting unconformably on Silurian
Slates. Arco Wood, Yorkshire.

(Photo by GODFREY BINGLEY.)

FlG. 83. — Easdale Tarn ; a lake dammed by a moraine.

(Photo by GODFREY BINGLEY.)

THE GROWTH OF BRITAIN 213

the succession of Jurassic and Cretaceous Rocks was folded and
exposed to denudation, so that their wolds and downs are the
result of the denudation of the folded rocks (Figs. 51, 64, and 66).
Thus the main features of eastern and southern England date to
this period. Connected with the movement are the volcanic
rocks of the Inner Hebrides, the result of a tremendous outburst
of energy in these regions, the effects of which spread far and
wide in the intrusion of dykes and sheets of igneous rocks as far
south as the Land's End, as far east as the Yorkshire coast, and as
far west as Donegal.

Deposits of Miocene age, the height of the movement, are
wanting in Britain, but on the continent they recall curiously the
character of such terrestrial deposits as the Old and New Red
Sandstones. In this country no deposits appear to have been
made, or what may have been formed were afterwards destroyed,
but strata of older date were folded and overthrust as the
consequence of the movement.

Thus the landscape of our country is found to be the outcome
of two great processes. The deposition of marine strata with their
fossils and other characteristics during periods of rest and quiet ;
and the elevation and folding of the rocks so formed during
periods of activity in the earth-crust. The landscape does not
depend upon a single epoch of deposition or denudation, but is
the result of several periods of each class of activity, and it may be
said to have been slowly evolved by the interaction of the two
processes. The older strata and the landscape dependent on
them may have had very different levels and may have been
influenced by the different types of denudation resulting from
each of them. Thus many parts of the landscape are ancient,
others have been rejuvenated, others again are in their first
juvenile stage. But all bear out the great principle of evolution
which is applicable to the geography, the landscape, and indeed
the climate of the country, as much as to its populations of animals
or plants.

The occurrence of an Alpine plant in a Welsh mountain re-
quires not only the explanation that it is a survival of an Arctic
flora which occupied the country in Glacial times. It requires
that geographical conditions should have been favourable during

214 THE BOOK OF NATURE STUDY

the Glacial Epoch for the occurrence of glaciers at that place,
and that the climate of succeeding ages should never have been
so much improved as to kill off the survivors of that Epoch.

In a similar way the story of life must have been strongly
influenced by geographical changes taking place in geological
times. Evolution steadily proceeding must have been at times
steadfast and regular as a consequence of stability in geographical
conditions throughout long periods. At other times changes
must have been accelerated by rapidly changing environment,
migration must have been expedited, and the conditions of
existence rendered so stringent that only the types with the most
elastic organisations could have survived.

The study of fossils in association with the position, structures,
and relationships of the rocks has already given, and will continue
to give, new data with reference to those factors in organisa-
tion which make for survival, improvement, or extinction. And
a complete knowledge of the organisms of the past and the
environment in which they lived has become essential to
students of the life of the present day.

CHAPTER XXI

LANDSCAPE, POPULATION, AND OCCUPATION

IN the foregoing chapters particular attention has been
devoted to the reaction of rock structure upon drainage, and
the development of valley and hill systems. It remains to make
a few general remarks upon other landscape features.

Plains may result from deposition of strata in a horizontal
position and elevation of the area above the sea level, without
disturbance in horizontality or sensible denudation. Of this
character is the eastern plain of England, the fen country, and,
with slight modification, the Basins of London and Hampshire.
Other plains result from denudation of strata, however they
may be situated, sufficient time not having elapsed for differential
effects, or else the denudation has been carried so far that a
base-level resulted. The first is generally the effect of marine
denudation. The second is the result of the river systems
reaching base-level, and an approach to this condition may be
seen in the surface of the Weald Clay, and in the plains of
Cheshire, York, and the Midlands which are situated on Triassic
rocks.

Plateaux are little more than plains which have reached a
greater elevation, and they may have been plains of deposition
or of denudation. The great plateau traversed by the Colorado
River belongs to the first group. And to the second, the traces
of several British plateaux, like those of the Longmynd in
Shropshire (Fig. 47), and areas recognised by Ramsey and
Fearnsides, in South and North Wales.

In both cases the plateaux are now being cut into by rivers.
In the earlier stages the plateau form is still easily recognisable
by the flat, elevated, areas between the river valleys ; but later,
the valleys eat their way backward and outward, consuming
the intervening flats, and gradually converting them into ridges

215

216 THE BOOK OF NATURE STUDY

and peaks, which will, however, for a time remain at a height
approximating to that of the original plateau.

Mountain chains are the result of localised earth-movement
on a very intense scale. Along lines of weakness in the earth-
crust the strata have been intensely folded and crumpled (Figs. 29
and 30), tilted to all angles, often overthrust and inverted, broken
by faulting, cleaved and jointed, intruded upon by igneous rocks,
and often, in part at least, subjected to important chemical
changes. Denudation acting on such a chain finds a great complex
of rocks of very varying hardness and composition brought
into j uxtaposition. The whole ground having been much elevated,
selective denudation has been in full activity and adjustment
is speedily obtained. So a mountain chain soon becomes the
site of a vast number of scarps and dip-slopes brought close
together, separated by longitudinal valleys and cut by trans-
verse gorges. Thus a series of broken, but on the whole parallel,
ranges are produced, in which the rock character and structure is
closely related to the relief (Fig. 48). The active denuding agencies,
having produced this type of relief, cut back into the ridges, pro-
ducing cwms or corries, isolating spurs, aretes, and peaks, and
obscuring to some extent the relation between structure and relief.
Examples of this are to be seen in all our chief mountain ranges,
and particularly in those of North Wales, Lakeland, and the
Highlands of Scotland and Ireland. They may even be seen in
numerous separated and isolated ranges which come out through
newer rocks elsewhere, such as the Malverns, in the Scottish
Uplands, and in isolated areas in Ireland.

A feature in valley scenery not hitherto alluded to is that of
lakes, which are either situated high up in the mountain hollows,
when they are called tarns, or along the course of the major
valleys, such as Bala Lake and Windermere. Attention has
often been drawn to the association of these lakes with glaciated
regions, and numerous explanations have been given of them.
The irregular deposit of glacial moraines on a plain has often
given rise to hollows capable of holding water. Again, moraines
dropped across the course of a valley may dam up the rivers
which follow the disappearance of ice from a country, and form
lakes (Fig. 83). In some cases the lakes will drain over the

LANDSCAPE, POPULATION, AND OCCUPATION 217

moraines, but if the latter are lofty and massive the water may
be ponded up to such a height that it will escape over rock in
some other direction, and give the appearance of being entirely
confined by a rock bar. If, however, these lakes are really
moraine-dammed they will drain out of their sides rather than
their ends, through narrow, gorge-like valleys often with rapids
and waterfalls.

Some of these lakes are, however, certainly contained in
real hollows in the solid rock, and not held up by moraine
material. Their basins appear to have been excavated out
of the rock. Now, water could obviously not excavate such
hollows, for the still waters which would result would eventually
fill up the hollow with transported debris. It is possible that
moving ice may have been the excavating agent. But there
is another explanation which may sometimes be applied, that
of earth-movement. If movement occurs while water is the
main denuding agent, it will either cut through the barriers as
they are elevated, or fill up the hollows formed behind the bars
with the sediment it carries. If, however, the country is occupied
by ice it will continue to transport its material as before, and
will only fill up the hollows produced with ice without clogging
them with detritus. When the ice disappears, and is replaced
by water the latter will discover the hollows and fill them with
water ; they will be lakes for a time, until filled up with debris
carried by the water, when they will be replaced by alluvial flats
(Fig. 68). If at any point in a valley system either downward
or upward movement occurs while the valley is filled with ice,
a lake will be an inevitable consequence. This may in part
explain the association of rock basins with glaciation. They will
sum up the result of all the earth-movement which occurred
during the Glacial Epoch.

Study of the geological map of any country will bring out the
relation of relief to geological structure. In England the oldest
rocks are to the west and north, the newer rocks succeeding
regularly to the east and south. The two main exceptions to
this are the arches of the Pennine Chain and the Weald (Figs.
65 and 66), in both of which there is introduced a repetition of
the features resulting form the arched and denuded rocks. On

218 THE BOOK OF NATURE STUDY

the whole the map of relief corresponds with the geological map,
particularly if the latter is so planned as to bring out the contrast
between resistant and non-resistant rocks (compare Figs. 64
with 65).

The oldest rocks, and those which have suffered most from
earth-movement, constitute the chief mountain ground of the
country. North and South Wales, the Welsh Borders, and
the Lake District are our chief examples, made of highly folded,
jointed, and cleaved rocks of Cambrian, Ordovician, and Silurian
ages. Anglesea and the Scottish Highlands are made of the
same or older rocks denuded down more deeply. Our chief hills
are of newer rocks, and in this class may be placed first those
ranges like the Pennine, the South Welsh Hills, the Mendips, and
those of Devon and Cornwall, which result from the denudation
of the generally gentle folds of Pennine and Armorican type
elevated after the Carboniferous Period (Fig. 28). These are edged
or surrounded by the New Red Sandstone Plain, and to the east
and south-east of that rises a hill group which might be called
the Wolds after their chief heights in the Cotswolds. They are
made of Jurassic rocks, whose limestone beds stand out as scarps
between their clay vales (Fig. 63). The range reaches its maximum
in the Cotswolds and in the " Yorkshire Moors/' Elsewhere
it tends to die down, when some of the hard limestones pass
into softer clays between Oxford and Lincolnshire. The last great
range is that of the Chalk Downs (Figs. 66 and 70), which passes
with varying height from Flamborough Head to St. Alban's
Head, sometimes with minor ranges and foot hills due to the
Lower and Upper Greensands. Owing to the Wealden arch the
Downs pass out north-east and south-east from Salisbury
" Plain " to the North Downs and the South Downs, each accom-
panied by the minor ranges described in a previous chapter.

Thus the general structure of the entire country is related
to the broad tectonic arrangement of its rocks. It remains to
note the reaction of the rocks, and the factors which result from
them, on the inhabitants living on their surface. In considering
this relationship, we must bear in mind not only the composition,
position, and association of the rocks themselves, but the outline,
slopes, aspects, and soils that result from the action of denudation

LANDSCAPE, POPULATION, AND OCCUPATION 219

upon them. On the other hand, at this stage we find that results
are dependent upon the composition of rocks and their relation-
ship to those bordering them, but independent of their age except
so far as the latter factor influences their character.

Sandstones give rise to well drained, moderately fertile soils,
suitable for garden cultivation and general agriculture if not
too porous and dry. The rocks are freely covered with soil, on
which grow elms, hollies, chestnuts, and oaks, rhododendrons,
azaleas, heather, bracken, and bilberry. The relief of the land-
scape varies in abruptness according to the amount of cement
in the sandstone ; and the older rocks of this type, like the grey-
wackes are craggy and mountainous. The red sandstones are
the site of orchard ground ; they provide grazing for cattle, and
yield ample dairy produce.

Conglomerates, highly siliceous sandstones, and quartzites
form land which is usually too well drained, so that it is a
common saying that the garden soils require watering one
day and manuring the next throughout the year. The slopes are
often abrupt, and summit crags frequently occur. The land is
often common, park, and moorland, used rather for golf and
sporting than for agriculture. Scotch firs, larches, and birches
are the chief trees ; heather, cranberry, and bracken grow freely ;
the woods are full of wild hyacinths, garlic, and wood anemones,
and even the valleys are barren and bare.

Clays and shales show little bare rock, the soil being usually
deep and rich, not well drained except near the junction with
sands or limestones. The crops are wheat and turnips, grass
grows freely, and the trees include the elm, oak, and ash.

Where the clay is calcareous it is said to be a marl, and marly
soils are about the richest in mineral food for plants. At the
same time, the soils are not too close and impermeable for drainage,
so that they comprise some of the most fertile regions in the
country.

Limestones often give rise to abrupt valleys terraced with
scars of bare rock. The ready passage of water underground
prevents the formation of soil, or carries it away too readily
along the cracks, so that sometimes there are large rocky barren
areas with the vegetation confined to the joints. But more

220 THE BOOK OF NATURE STUDY

usually there is a thin, rich, well-drained soil on which a sweet
grass grows, forming an excellent pasturage. The different
limestones vary considerably in this respect. Usually they are
employed for sheep farming, and there are several different breeds
with local names, like the Cotswold and the South Downs breeds.
The Chalk is a special example of a soft limestone with peculiar
features ; the absence of rocky but the presence of steep and
dimpled grass slopes, waterless hollows, and steep -sided but
grassy combes. The soils are too dry for gardens, but many
trees, especially yews and beeches, flourish on them. Heaths and
commons occur chiefly where the Chalk is covered with sandy
or clayey deposits, so that the influence of the composition of
the chalk but not its physical effects are felt. The limestone
flora is an extremely rich one, and includes a number of charac-
teristic plants, such as the green spleenwort, Anthyllis, Campanula
glomerata, Clematis, Helianthernum vulgare, Reseda, some of the
orchids, and many other species which only flourish in a
calcareous soil.

Alluvial soils made up of the richest pickings carried from an
extensive land surface by river denudation are naturally the
richest in plant food and the most fertile in the country. They
are suitable for all types of agriculture and for gardens ; their only
drawbacks resulting from considerations of flooding and drainage.

The Glacial Epoch has had an important influence in bringing
together the denudation results from all kinds of rocks, and has
covered much of the country with material yielding rich mixed
soils. Here again the chief drawback results from the clayey
nature of the subsoil and the necessity for thorough drainage.

The chief demands made by mankind upon his environment
may be summed up as food, drink, health, wealth, and recreation,
and the sites of his dwelling and lines of transport will be found
to be largely governed by consideration of these factors. Food
was formerly a question mainly of agriculture, but is now chiefly
one of transport. Water in villages and isolated places is still
related to the immediate environment, although in the larger
towns a certain amount of independence has been reached by
bringing good water from a distance. Health and wealth are
both related in a marked degree to the nature of the earth-crust,

LANDSCAPE, POPULATION, AND OCCUPATION 221

and the necessity for recreation has rendered tolerable, and even
desirable, tracts which have little else to recommend them.

When food was more indigenous and less exogenous than is
at present the case the distribution of population showed aggrega-
tions in the richer agricultural districts. Most important towns
were market-towns situated at the outlet to agricultural districts,
and flourished on the handling of commodities produced in these
areas. Now that food is brought in so largely from outside, these
towns are no longer of the same importance, and others in in-
dustrial regions have taken their place. The present areas of con-
centration of population are related to the production of mineral
wealth, and especially coal and iron, to the manufacture of
commodities by means of them, and to the convenient handling
and transport of the manufactured articles or the raw materials.
Thus we find the great centres of population aggregated at, or
migrating to, the coal fields which provide supplies of iron and
steel as well as coal. This explains the position of such towns as
Manchester, Birmingham, Sheffield, Newcastle, Nottingham, and
many others. We find, too, that industries like those of wool and
cotton, previously carried on in the upland regions where water
power was available because of the juvenile topography of the
country, have migrated to the coalfields where the modern sources
of power are to be got from the underground coal. It also
explains the concentration of railways, the modern means of trans-
port, and it will be interesting to study the distribution of railways
as shown on a map with the geological map of the country. While
the South Wrales coalfield, the " Black Country," the Yorkshire
and Durham coalfields, are crossed by innumerable lines of railway,
the heart of the Pennine, the Lake District, Central Wales, and
Devon, are almost devoid of them, except a few trunk lines which
cross those areas in order to reach the industrial tracts. Other
important towns are situated at the outlet of these industrial
areas to the sea, and in this category are such examples as Liver-
pool, Preston, Hull, Bristol, and London itself.

But although the great centres of population have been
attracted towards the areas producing mineral wealth, the
exact site of towns has been settled by considerations of
health and water. Few of the great towns are situated actually

222 THE BOOK OF NATURE STUDY

on the coalfields themselves. They are generally near their
borders, where the soil is better, the conditions more healthy,
and where good supplies of water may be obtained from springs
and wells which draw their water from uncontaminated sources.
Numerous examples will be found from the inspection of any
geological map, but there are few more striking instances than
those towns situated in rings round the Midland Coalfields. The
two lines of southern villages situated at the junctions of the
Chalk, with the Thanet Sand to the north and with the Upper
Greensand to the south, furnish another striking instance of the
attraction possessed for primitive populations of easily obtained
and pure supplies of water. A still more striking instance is afforded
by the growth of London itself. This was originally founded
as near the open sea as was possible before reaching the marshes
which occupied the mouth of the river. Here the main rock
Formation, the London Clay, was covered with brick earths and
gravels, and the latter site was naturally chosen for dwellings
because it both provided the water to wells and carried away the
drainage. The earlier growth of the twin cities of London and
Westminster was confined to the outcrop of the gravels, and it
was not till supplies of water were brought from outside that the
unoccupied areas of brick-earth, and finally of London Clay, were
taken up. Even now the chief recreation grounds, the public
and royal parks, represent the least desirable of the land left;
for they are mostly founded on London Clay or alluvial clays
on which building would still possess considerable disadvantages.
Looking over the country generally, it is found that much
of the land that would otherwise be waste ground on account
of the infertility of its soil, its imperfect drainage, or the character
of the rock on which it is founded, is that which is occupied by
commons, heath, sporting estates, and forest. Thus land which
would be unsuitable for residence, has little agricultural value,
and yields little or no industrial resources, is brought into use for
recreation.

GENERAL INDEX

GENERAL INDEX

Absorption and digestion of
plants, iii. 73.

Acacia, spines of, iii. 2, 51,
82.

Acorn, hard cup of, iv. 148.

Acorn-shells, ii. 132, 151, 170,
175, 176, 181.

Actinia mesembryanthemunt, ii.
128, 162, 176.

Adder, ii. 116, 214, 217.

Adderstongue, iv. 93, 94, 98.

Adventitious buds, iii. 44.

Aerial and parasitic roots, iii.
31 ; fauna, ii. 217.

African pangolin, i. 57.

Agricultural regions, vi. 31.

Agrimony, v. 66, 162.

Agrionidtz, ii. 114.

Agrostis, associations of, v. 63 ;
species of, v. 60, 114, 214.

Air, cause of movement, vi.
1 6 ; dampness and humidity
of, vi. 4, 8 ; in relation to
water, vi. 20 ; necessity of,
iii. 19 ; aerial fauna of,
ii. 169.

Air-sacs, i. 73, 77, 78.

Aira grass, v. 217.

Ajuga reptans, iii. 217.

Albatrosses, i. 86.

Albuminous and exalbuminous
seeds, iii. 9.

Alcyonarians, ii. 170.

Alcyonium digitatum, ii. 164.

Alder, iv. 144, 160, 173, v. 46 ;
Buckthorn, naked buds of,
iii. 43 ; bud scales, iii. 40,
43 ; flowers of, iv. 160 ;
identification of, iii. 39.

Alga cells, iv. 132, 133, 139,
v. 22.

Algaj, fertilisation of, v. 49;
and coloration of water,
v. 52 ; marine and fresh-
water, ii. 82, 83, v. 21, 26.

Alimentary system of birds,
i- 75-

Alisma Plantago, ii. 88, v. 45.

Alismaceae, v. 45.

Allium, species of, iii. 66, v.
141.

Alluvial soils, v. 193, 217;
typical plants of, v. 217.

Almond, iv. 173, v. 167.

Alopecurus, species of, v. 57,
77. 114-

VOL. VI. — 15

Alpine pasture, v. 69, 70 ;
plants, iii. 2, iv. 197, 204,
v. 69 ; plants in Wales,
meaning of, vi. 213.

Alsike clover, v. 58.

Altitude in relation to cold,
iv. 162, vi. 20 ; of the sun,
method of obtaining, vi. 83.

Amaryllideae, iv. 70.

American cockroach, i. 173, 176 ;
water-weed, v. 22.

Ammonite, cretaceous, text-fig.,
vi. 203.

Ammophila arundinacea, v. 115 ;
vi. 34.

Amoeba, ii. 188, 200.

Amphibians, i. 120, 158, 159, ii.
96, 200, 220 ; blood vessels of,
i. 120, 121 ; lungs of, i. 120.

Amphibious plants, v. 47 ; poly-
gonum, v. 47.

Amphipxus, i. 151, 155.

Amphipods, ii. 175, 181, 188.

Anacharis canadensis, ii. 89.

Anagallis, species of, v. 35, 82.

Anchusa italica (Dropmore
variety), v. 171.

Anchylus, species of, ii. 106, 191.

Anemone (animal), ii. 128, 129;
kinds of, ii. 162, 163, 167,
171 ; cave-dwelling, ii. 163,
ii. 167; tentacles of, ii. 164;
thick-horned, ii. 163 ; (plant),
wild, iii. 80 ; wood, v. 16 ;
varieties of, ii. 163 ; bulbs of,
v. 177-

Anemone japonica (plant), v.
171 ; pulsatilla (plant), iii. 80.

Angelica, iv. 158.

Angiosperms, iii. 87, iv. 62,
68, 72.

Angler, ii. 183.

Anguilla vulgaris, i. 147, 150.

Anguis fragilis, i. no, 112,
ii. 214.

Animals in winter dress, i. 62 ;
of the fresh-water aquarium,
ii. 94 ; of the marine
aquarium, ii. 128-168 ;
prickly-skinned, ii. 153.

Annual creepers, v. 178 ; Mer-
cury, iv. 185.

Annuals, cultivation of, v. 168.

Anodonta, ii. 58, 59, 68, 191.

Antarctic icebergs, vi. 46.

Antelopes, i. 38.

Antennanus, i. 147.

Antheridia, iv. 106.

Anticline and syncline text -fig,
vi. 1 20.

Ants, ii. ip, 1 6, 216, y. 33 ;
construction of nests, ii. n ;
economy of, ii. 12, 13, 211 ;
eggs of, ii. 10, 2ii ; heaps,
ii. 2ii, iv. 204 ; male,
female, and worker of, ii. 14 ;
nest of, ii. 10, ii ; pupa of,
ii. 10, 2ii ; queens of, ii. ii.

Aphida3, ii. 12, 15, 17, v.
181, 182.

Apis mellifica, ii. 204.

Apparent movements of the
sun, vi. 63-74, 75 ; noon, vi.
79-

Apple, iv. i, 38, 48, 49, 58, 78 ;
fertilisation of, v. 153; graft-
ing, v. 154, 155, 156, 157 ;
illustration of, iv. 50 ; life
history, cultivation, etc., v.
153-160 ; moss, iv. 107, 108 ;
trees, iii. 31 ; varieties of, v.
150, 153; constituents of, v.
126.

Apricot, y. 148.

Apteria, i. 69.

Aquarium, ii. 70-81.

Aquatic flowering plants, ii. 86 ;
plants, dispersion of fruits
and seeds, v. 49, 50 ; plants,
practical work on, v. 53 ;
plants, submerged, v. 22 ;
vegetation, iv. 199, v. 21.

Arabis, v. 179.

Arable land, v. 86, 194.

Arachnids, ii. 108, 124, 200.

Archegonia, iv. 85.

Arctic days and nights, vi. 66,
67 ; fox, ii. 219 ; floras, iv.
190, 195 ; plant bed, iv. 191 ;
region, vi. 67.

Arion ater, ii. 53, 54, 55, 210;
minimus, ii. 55.

Aristotle's lantern, ii. 154, 176.

Armadillos, i. 20, 58.

Armeria, species of, v. 3, 13, 171.

Arrowhead, v. 29, 45, 50 ;
peculiar seeds of, v. 51.

Arrow-worms, ii. 186.

Arthropods, ii. 108, 145, 152.

Artichoke galls, ii. 18 ; Jeru-
salem, iii. 67 ; tubers of, iii. 70.

Artificial pasture, v. 64.

226

THE BOOK OF NATURE STUDY

Arum, iii. 30 ; anthers of, iii.
78 ; carpels of, iii. 78 ; con-
spicuous bract of, iii. 55, 78.

Ascidia, i. 151.

Ascidian, structure of, ii. 182 ;
larva of, i. 156 ; mouth of,
ii. 182.

Ascidians, habits of, i. 156.

Asellus, ii. 151 ; aquaticus, ii.
108.

Ash, iii. 35, iv. i, 55, 69, 71,
76, 147, I59> 162, 163, 172,
173, 180, 184, v. 73; age
of, iv. 59 ; apical buds of,
iii. 39 ; bark of, iv. 172 ;
compound leaves of, iii. 44 ;
illustrations of, iv. 57 ; pol-
lination of, iv. 57 ; uses of,
iv. 166 ; winter buds, iii.
39, 40, 43.

Asia, arid plains, temperature
of, vi. 12.

Aspidium, iv. 179.

Asptdium Thelypteris, v. 21.

Aspleniunt, species of, iv. 90,
91, 98.

Asses, callosities of, i. 34.

Aster, species of, v. 2, 171.

Asterias rubens, ii. 155, 180.

Astrantia, bracts of, iii. 55.

Astronomers, in relation to
Mars, vi. 6.

Astronomy, literature of, vi.

90, 91-

Atlantic in relation to rain,

vi. 26; sea-board of Great

Britain, vi. 23.
Atlas of the world's commerce,

vi. 38.

Atmosphere, study of, vi. 51.
Aubrietia, v. 169, 176, 179.
Aurelia, ii. 185.
Auricula, v. 179.
Autumn and spring plumages,

i. 87, 88 ; Gentian, iv. 198 ;

seed-time, vi. 5 ; sky, vi. 55.
Autumnal anticyclones, vi. 54 ;

Lady's Tresses, v. 69 ; rainy

period, vi. 26.
Avens, species of, iv. 69, 77,

iii. 80.
Avocet, method of feeding, i.

91, 92.

Awlwort, v. 23, 24, 29, 50.
Awns, iii. 80.

Axillary buds, section of, iii. 57.
Azalea, Trailing, iv. 196.

Bacteria, minute plants, iv. 142 ;
uses, 142 ; blood-red, purple,
etc., iv. 141.

Badger, i. 32, 67.

" Badlands," vi. 35.

Balanoglossus, i. 157.

Balanus, ii. 170, 175.

Baleen, i. 49.

Bamboos, v. 167.

Barberry plant, iii. 82 ; pro-
pagation of, v. 1 1 8.

Bark beetles, iv. 154.

Barley, iii. 25, v. 78, 79 ; and
sandy soil, v. 215, iii. 4;
development of the seed,
iii' 7» 9» 12 ; grown on
blotting-paper, iii. 16.

Barn owl, young (Illustration),
showing first traces of wing
and tail feathers, i. 80.

Barnacles, ii. 166, 175.

Barometer and thermometer,
vi. 8, 9 ; reading of, vi. 23.

Bartsia, iv. 180.

Bat, fore-limb of, i. 44 ;
hibernation of, i. 45 ; species
of, i. 44, 45 ; ears of, 45.

Bats, ii. 218 ; mode of feeding,
i. 46 ; mode of resting, i. 45 ;
wings of, i. 43.

Beach, raised, figure of, vi. 117.

Beadlet, ii. 176, 179.

Beaked parsley, v. 60, 61.

Beaks of birds, structure of,
i. 90.

Beam tree, v. 216.

Bean, iii. 13, 14, 36 ; varieties
of, v. 130, 145, 146 ; plant,
iii. 4, 5, 34 ; development
of the seed, iii. 7 ; exal-
buminous seeds of, iii. 12.

Beans, v. 78, 84 ; cultivation of,
v. 144,214.

Bear, polar, ii. 219.

Beard-Moss, iv. 137, 178; with
fruits, iv. 137.

Bears in Britain, ii. 221.

Beaver, ii. 221.

Bed-bug, ii. 15.

Bedeguar gall, ii. 208 ; rose-gall,
ii. 204, 205.

Bedstraws, iv. 202, v. 9, 36,

Bee, brood of, ii. 6 ; diagram
of comb, ii. 6 ; diagram of
hind leg, ii. 4 ; eggs of, ii.
6,7-

Beech, iii. 3, iv. 144, 147, 156,
160, 164, 171, 172, 173 ;
bark of, iv. 172 ; branching
of, iii. 46 ; buds of, iii. 38,
40 ; bud scales and stipules,
iii. 43 ; exalbuminous seeds
of, iii. 12 ; exposed roots of,
iii. 1 8 ; fruit of, iv. 153 ;
illustration of, iv. 153 ; in
winter, iii. 41 ; uses of, iv.
166 ; seedling of, iii. 12, 36 ;
shape of leaf, iii. 37 ; flowers
of, iv. 153 ; on calcareous
soil, v. 216 ; ferns, iv. 179.

Beech-nut, iii. 36.

Bees, ii. i, iv. 73 ; drone,
queen, and worker, ii. 14 ;
drones, ii. 6 ; nuptial flight,
ii. 8 ; queens, ii. 7 ; royal
jelly, ii. 7 ; solitary, ii. 204 ;
swarming of, ii. 7 ; wild, ii.
204.

Beet, v. 17, 130 ; varieties of,
v. 139 ; constituents of, v.
126 ; history of cultivation,
v. 138.

Beetles, ii. 29, 208, v. 33 ;
ground, ii. 217 ; injurious, v.
182 ; whirligig, ii. 121.

Beetroot, iii. 28, 29, 32.

Begonia, iii. 60.

Begonias, iii. 71, 72, v. 117.

Bell-animalcules, ii. 198.

Bell Heather, iv. 192, 204.

Bellis perennis, iii. 175, v. 62.

Ben Lawers, Alpine plants of,
iii. 2.

Ben Nevis, rainfall of, vi. 26.

Bent, common, v. 59 ; grass,
v. 60, 77, 214.

Berthelot, his description of a
sunset, vi. 56, 57.

Beta, species of, v. 17, 115, 138 ;
vulgaris, v. 115.

Betony, iv. 162.

Bibliography of British am-
phibians, i. 135 ; of bees, ii.
9 ; of British birds, i. 107 ;
of British reptiles, i. 119 ; of
butterflies, i. 190 ; of centi-
pedes and millipedes, ii. 37 ;
of cockroach, i. 176 ; of
earthworms, i. 170 ; of ear-
wig, i. 1 80 ; of ferns, iv. 99 ;
of fresh-water animals, ii.
126, 168 ; of gall-flies and
plant-lice, ii. 18 ; of garden-
ing, etc., v. 186, 187 ; of
gnats, ii. 28 ; of mammals,
i. 67 ; of mammals and
birds, i. 108 ; of mussels, ii.
69 ; of plants, etc., iii. 84,
iv. 187, v. 55 ; of spiders,
ii. 47 ; of The Soil, v. 88 ;
of trees, iv. 176 ; of vegeta-
tion, etc., iv. 210, v. 20 ; of
wasps, i. 212 ; of water-
beetles, ii. 34.

Bicycle, analogy of, vi. 16 ; tyre,
illustrating compressed air,
vi. 19.

Biennial plants, iii. 95.

Biennials, v. 169.

Big bud, v. 185.

Bilberry, iii. 2, iv. 188, 191,
196, 197, 201, 202, 210 ;
fruit of, iv. 195, 196.

Bindweed, v. 38.

Birch, iv. 147, 154, 157, 165,
172, 173, 207 ; bark of, iv.
172 ; absence of hard wood in,
iv. 150 ; illustration, iv. 162 ;
trees, iv. 178 ; Polypore,
hoof-shaped fruit of, iv. 130.

Birch-wood, iv. 193.

Birch-woods, iv. 177.

Birds, i. 55, 158, 159, 200, 218 ;
anatomy of, i. 68 ; desert-
dwelling, i. 79 ; eggs, i. 100,
ii. 196 ; essential characters
of, i. 68 ; fore-limb of, i. 44 ;
feathers of, 70-72 ; insect -
eating, i. 83 ; nest, iv. 181,
182 ; nests, descriptions of,
i. 98, 99 ; of the meadow,
ii. 207 ; of the moor, ii.
213 ; of the pond, ii. 190 ;
of the woods, ii. 210 ; shapes
of, i. 83 ; singing in mid-
winter, vi. 5 ; food and feed-
ing, i. 90.

Bird's-Eye Primrose, iv. 203.

Bird's-Foot Trefoil, iii. 166,
170 ; life-history and figure
of, iii. 172; seeds of, iii. 174,
iv. 25, 26, 76, 206, v. 6, 59,
60, 61, 62, 63, 74.

Bird's Nest Orchis, iii. 46, iv.

157-
Birgus latro, ii. 200.

GENERAL INDEX

227

Bisection of figure, vi. 78.
Bison, ii. 221.
Bites of snakes, i. 118.
Bithynia, eggs of, ii. 107 ; ten-

taculata, ii. 106.
Bitter Cassava, v. 83 ; Cress, v.

40.
Bitterling, economy of, ii. 68,

192 ; young of, ii. 68.
Bivalves, ii. 105, 138, 158, 170,

175, 176, 188.
Black-beetle, i. 171.
Blackberry, iii. 77, iv. 156,

183, 195, v. 72, 73, 148, 161.
Blackbird, colour of young, i.

82.
Black Bryony, iii. 57 ; twining

stems of, iii. 57 ; growing in

hedges, iii. 58 ; illustrations

of, iii. 72, v. 72, 73» 74-
Black-cock, ii. 214.
Black Currant mite, v. 151.
Black-fly, ii. 15.
Black frost, vi. 49 ; Bent Grass,

v. 77, 86, 214; Grouse, figure

of foot, i. 95 ; Goby, ii. 132 ;

headed gull, ii. 190 ; heath,

iv. 188 ; Mullein, iii. 79.;

poplar, iii. 31, 42, 81 ; rat, i.

30, 31 ; sheep, i. 64 ; thorn,

iii. 82, iv. 173 ; Knapweed,

v. 59, 62, 63 ; Knapweed,

figured, v. 60, 61 ; Medick,

figure of, v. 77 ; slug, ii. 54,

210.

Bladder Campion, v. 13, 84, 86.
Bladderwort, iii. 73» v. 31 ;

species of, ii. 90, v. 32.
Bladder-wrack, ii. 82, 84, 151 ;

Brown, v. 9.
Blade-bones, i. 22.
Blatta orientalist i. 176.
Blea Tarn, v. 34.
Blennius pholis, ii. 132.
Blight, ii. 15.
Blood Geranium, v. 6, 160 ;

hounds, i. 26, 28 ; worm,

ii. 25, 27.
Bluebell, v. 17, 159, 208, 210 ;

early flowering, iv. 157 ;

propagation of, iii. 66.
Blue Garden Crocus, life history

of, iii. 161 ; Moor Grass, v.

69, 201, 204 ; mountain hare,

ii. 216 ; sky, explanation of,

vi. 55-

Boar, wild, i. 39.
Bog-Asphodel, iv. 193, 203,

209, v. 34 ; Cinquefoil, v.

34, 35 ; Equisetum, v. 21 ;

Malaxis, v. 35.
Bog-moss, ii. 217, iv. 41, 101,

155, 188, 190, 193, 195, 203,

v. 35 ; illustration of, iv. 101 ;

leaf highly magnified, iv. 102.
Bog-Myrtle, iv. 192, 193, v. 34.
Bog Orchids, v. 34, 35.
Bog Pimpernel, v. 34, 35 ;

figure of, v. 35.

Bog plants, xerophytic char-
acter of, iv. 149, 199, v. 33.
Bog or Sphagnum, v. 21.
Boggy soils, v. 218.
Bogs and fens, plant of, v. 29.
Boletus edulis, iv. 126.

Bombus, ii. 204, 205.

Bones of birds, i. 73 ; of foot of
man, i. 34.

Borage, iii. 83.

Border, herbaceous, v. 175,
176.

Borecole, v. 130, 131.

Botanical surveys, iv. 184.

Bottle brush coralline, ii. 178.

Bottom grass, v. 58 ; growth, v.
64.

Bougainvillea, purple bract of,
iii- 55-

Boulder, glaciated, text-fig., vi.
115-

Boulder-clay, text-fig., vi. 114.

Box, iv. 164, 184, v. 216.

Bracken, iii. 69, 70, iv. 80,
158, 159, 179, 207, v. 72,
86 ; pinnate leaf, iv. 81 ;
rhizome, iv. 208 ; spores of,
iv. 83 ; and sandy soils, v.
216.

Bracket Fungi, iv. 130 ; fungus
on tree-trunk, iv. 127, 132,
141.

Bract, iv. 148.

Bracts in UmbelliferaD, iii. 55.

Branched Bur-Reed, figured, v.
43-

Branches, development of, iii.
45-

Branching, tufted or rosette-
like, iii. 46.

Brandling, i. 169.

Brassica, varieties of, v. 115 ;
oleracea, y. 17, 115, 130, 131 ;
sinapis, iii. 209.

Breast - bone of birds, i. 73,
86.

Bristle-footed worms, ii. 161,
179, 1 88 ; Mosses, capsules
of, iv. in.

Bristles on fruit, iii. 73.

Britain, growth of, vi. 23, 208.

British amphibians, i. 122 ;
birds, i. 79 ; cicadid, ii. 203 ;
oak, its uses, iv. 150 ; rain-
fall, vi. 26, 28 ; reptiles, i
no.

Brittle-star, ii. 156, 180, 181 ;
distinctions between arms
and disc, ii. 156 ; lost parts
of, ii. 156.

Brittle-stars, i. 158, ii. 153.

Broad bean, iii. 9, 12, 21, v.
35, 130, 145, 146; seed of,
v. 113.

Broad clover, v. 58.

Broccoli, v. 17, 130, 131.

Brome grass, v. 58.

Brooding, i. 100.

Brook-lime, v. 39, 54 ; weed,
v. 52.

Broom, iv. 76, v. 167 ; fork-
mosses, iv. 108, 158 ; rape,
iii. 46, iv. 41, 151, 1 80.

Brown Bladderwrack, v. 9 ;
rat, i. 30, ii. 189, 190, 196 ;
seaweed, v. 10 ; seaweeds,
uses of, iv. 9.

Brussels sprouts, buds of, iii.
45, v. 130, 131.

Bryony, black and white, il-
lustration of, iii. 72.

Bryopsis plumosa, ii. 82, 84*
85-

Bryozoa, ii. 179.

Buccinum undatum, ii. 166.

Buckbean, ii. 88, v. 34, 35.

Buckie, egg-capsules of, ii. 176.

Buckwheat, seeds of, iii. 4, 5, 6,
12 ; germination of, iii. 5.

Bud, growth of, iii. 33 ; of the
beech with stipules removed
(Illustration), iii. 42 ; scales,
iii. 39, 43, 74, iv. 72.

Budding, v. 117.

Buds, structures of, iii. 44 ;
of flowering plants, iii. 92.

Buffalo-grass, iv. 205.

Bugle, iii. 166, 217 ; life
history of and plant figured,
iii. 218 ; flower figured, iii.
219, iv. 69, 74.

Bulb, v. 116.

Bulbils, iii. 63, iv. 99.

Bulbous buttercup, iii. 90 ;
plants, place of origin of,
vi. 37 ; flowering in winter,
vi. 37.

Bulbs, iii. 62, 69, iv. 175
contractile roots of, iii. 65
cultivation of, v. 171, 172
178 ; of hyacinths, iii. 67
of tulips, iii. 67.

Bull-dogs, i. 26.

Bull-head, ii. 104, 131, 183.

Bulrush, v. 43, 44, 45.

Bunting, Snow, ii. 217.

Burdock, iii. 80.

Burnet, v. 59, 60, 61, 62, 216.

Bur -reed, v. 43, 44, 45, 76 ;
dispersal of seed, v. 51 ;
illustration of, v. 34.

Burrowing beetles, ii. 216 ;
molluscs, ii. 128.

Butcher's Broom, v. 167.

Butter-Bur, v. 46.

Buttercup, iii. 60, 86, 89, 90,
98, 115, 116, 119, 122, 169,
iv. 68, 69, 73, 74, v. 16, 61,
62, 63, 64, 74, 214 ; flower
of, iii. 99 ; nectar of, 100 ;
carpels of, 101, 107 ; cross-
pollination, 1 02 ; diagram
of whorl, 103 ; diagram of
fruit, 107 ; fruitlet of, 107 ;
embryo plant, 107 ; plant
figured, iii. 89 ; water, iv. 199.

Butter-fish, ii. 133, 184.

Butterflies, ii. 204, 217, iv. 74.

Butterfly, abdomen of, i. 184 ;
claspers of, i. 185 ; eggs of,
i. 184 ; false-legs of, i. 185 ;
full-grown larva of, i. 184 ;
head of, i. 181 ; large
cabbage-white, i. 181, 184 ;
life history of, i. 184 ; male
and female organ, i. 188 ;
pupa of, i. 184, 186 ; wing
scales of, i. 183 ; Small
Tortoiseshell, ii. 204 ; ter-
minal segments of male, i.
188 ; thorax of, i. 182.

Butterwort, iii. 73, 74, iv. i,
41, 69, v. 31, 33, 36;
branch figured, v. 32 ;
common, iv. 43, 44 ; in
flower, illustrated, iv. 44.

228

THE BOOK OF NATURE STUDY

Cabbage, buds of, iii. 45 ; seed

of, v. 114 ; varieties of, v.

17,130-132 ; sprouts, varieties

of, v. 132.
Cacti, iii. 51, v. 9.
Cactuses of American deserts,

vi. 34.
Caddis fly, breathing organs of,

ii. 112 ; cases, ii. 112, 194 ;

larva} of, ii. no, 112 ;

nymph of, ii. 113; pupa of,

ii. 194 ; ii. 109, 113, 194, 195,

198 ; eggs of, ii. 114.
Calcareous purse sponge, ii.

178 ; soils, v. 216 ; plants of,

v. 216, 217 ; pests of, v. 216.
Caledonia, iv. 144.
Calluna, iv. 190 ; vulgaris, iv.

13. 14-

Camomile, v. 15.
Campanula, iii. 32, 170 ;

effect of light on, iii. 58 ;

nettle-leaved, iii. 32 : per-

sicifolia, var. Grandiflora, v.

171.

Campion, v. 84.
Canadian waterweed, ii. 89.
Canariensis, v. 178, 179.
Candytuft, y. 169, 179.
Cane-sugar, iii. 29.
Canterbury Bells, v. 169.
Capercailzie, ii. 210.
Caprella, ii. 151.
Caprifoliacece, iv. 69.
Capsella bursa-pastoris, iii. 212.
Carapace of crab, ii. 147.
Carbohydrates, v. 126.
Carbon assimilation, iii. 47;

dioxide, iii. 49, 50.
Carcinus mcenas, ii. 128, 145,

171, 181.
Cardamine pratensis, iii. 120,

188, v. 48, 49-
Carder-bee, ii. 204.
Cardium, ii. 170.
Carex, v. 34, 63 ; arenaria, v.

6 ; pendula, iv. 194 ; pseudo-

cyperus, v. 38.
Carices, iv. 202, v. 36.
Carnation grass, v. 217.
Carnations, iii. 71 ; layering

of, v. 123.

Carnivorous buckies, ii. 170.
Carp, ii. 197.
Carpet shell, exhalant siphon

of, ii. 140 ; foot of, ii. 140.
Carrot, iii. 29, 32, 50, v. 80,

130 ; history and cultivation

of, v. 135-137 ; original

home of, v. 17 ; seed of,

v. 114 ; varieties of, v.

137 ; wild, v. 135, 215.
Caryophyllacea?, v. 14.
Cassava cakes, v. 83.
Castor-oil plant, v. 83.
Cat, tree-climbing, i. 67.
Caterpillars, i. 186 ; to destroy,

v. 184 ; of winter moth, v.

184-

Catfish, i. 141.
Cathartic Flax, v. 67.
Cats, i. 21 ; various breeds of,

i. 59-
Catkins, iii. 81, iv. 46, 47,

48, 147, 160, v. 46.

Cattle, varieties of, i. 39.
Cauliflower, varieties of, v.

17, 130, 131.
Celandine, v. 16, 27 ; Lesser,

iii. 70, 90, iv. 68, 69.
Celery, cultivation of, v. 142.
Cell- walls, iii. 23.
Cellar-slug, ii. 53.
Centaur ea montana, v. 171 ;

nigra, v. 61.
Centaury, v. 7, iv. 158.
Centipede, ii. 14, 35, 215, iv.

154 ; eggs of, ii. 36.
Central Pacific Railway, snow-
fall of, vi. 41.
Centrum, i. 22.
Ceratpphyllum, ii. 90, 92.
Certhia familiaris, ii. 210.
Cervus dama, ii. 213 ; elaphus,

ii. 213.

Chaetopod worms, ii. 199.
Cha?topods, ii. 188, 200.
Chalk, v. 19 ; economic uses of,

vi. 205.

Chamomile, v. 7.
Chara, ii. 82, v. 28, 29.
Characteristics of different

soils, v. 208-218.
Charlock, iii. 212, iv. 68, 69,

76, v. 78 ; life history of, iii.

209 ; flowering branch figured,

iii. 210 ; fruit figured, iii.

212.

Chat or click, ii. 202.
Cheek-teeth, i. 21.
Chenopodiacea?, v. 13, 138.
Cherries, propagation of, v. 160 ;

varieties of, v. 148, 151.
Cherry, iv. 77, 172.
Chickweed, y. 85, 86, 217 ;

common, iii. 74 ; figured, iii.

74-

Chicory, v. 86, 216.
Chironomus, ii. 19, 25, 117 ;

diagram of larva and pupa,

ii. 26 ; eggs of, ii. 25 ; male

and female antennae figured,

ii. 27.

Chiton, ii. 143.
Chlorophyll, iii. 49, 50, 51 ;

development of, iii. 47, 48.
Chrysalids, v. 182.
Chrysanthemum frutescens, iii.

52.

Cicadid, British, ii. 203.
Cinclus aquaticus, ii. 196.
Cinquefoil, iv. 207.
Circle of horizon, radius of, vi.

52.

Civilisation of the Mediter-
ranean, vi. 38.
Cladonia, species of, iv. 138,

140.

Clams, ii. 68, 139.
Clarkia, v. 169, 179.
Classification of leaves, iii. 54 ;

of soils, v. 79.

Claw, horny sheath of, i. 27.
Clay soils, v. 213.
Cleavers, iv. 202.
Clematis, iii. 77, 80, iv. 188,

208, v. 72, 73, 216 ; method

of climbing, iii. 54.
Cliffs, vegetation of, v. 12, 20.
Click-beetle, ii. 37.

Climate, iv. 155; and weather,
vi. 8 ; of England, variability
of, vi. 32.

Climatic variations, vi. 3.

Climbing Nasturtium, v. 178 ;
plants, iii. 72, 77, iv. 184.

ding-fish, i. 147.

Cloudberry, iv. 195.

Cloud bursts, in North America,
vi. 29.

Cloud, formation of, vi. 19.

Cloudlets, vi. 60.

Cloud sheets, vi. 61.

Clouds, general principles of,
vi. 58, 59, 60 ; kinds of, vi.
6 1 ; compared to steam
kettle, vi. 3 ; composition of,
vi. 5 ; formation of, Figs.
22 and 59 ; height of, vi. 3 ;
meaning of, vi. 2.

Cloudy days, comparisons of,
vi. 3.

Clove pink, v. 121.

Clover, iii. 25, 32, iv. 36, 207,
v. n, 58, 60, 64, 78, 79 ; sleep
movements, iii. 56 ; structure,
v. 58 ; kinds of yellow, v. 58,
78.

Clovers, nature of, v. 58.

Club-moss, species of, iv. 99.

Clubmosses, iv. 79, 94, 98,
100, 202.

Coal period forests, iv. 94.

Cochlearia officinalis, iv. 198,
v. 14.

Cockles, ii. 68, 170, 128.

Cockroach, anatomy of, 171
et seq. ; eggs of, i. 174 ; egg-
capsule of, i. 176, 178 ; wings
extended, i. 178 ; young of,
i. 176.

Cock-roads, ii. 210.

Cock's-foot, v. 66 ; grass, v.
57. 58.

Cocoanut crab, ii. 200 ; eggs of,
ii. 200.

Cocoanut, seeds of, and its dis-
tribution, v. 50 ; of the
Seychelles Islands, v. 50 ;
tree, v. 17.

Cocoons, ii. 211.

Cod, i. 147, ii. 135.

Codling moth and caterpillar,
v. 159-

Coelentera, ii. 126, 162-168,
179.

Cold in relation to altitude, vi.
20.

Coleoptera, ii. 29, 195.

Collecting plants, hints on, iii.
no.

Coloration of mammals, i. 59,
65 ; warning, i. 63.

Colour of plants in spring and
autumn, iv. 208 ; of water
influenced by vegetation, v.
52.

Colours of setting sun, explana-
tion of, vi. 55, 56.

Colt's-foot, iv. 206, y. 16, 30.

Columbapalumbus, ii. 210.

Comb-worms, habits of, ii. 160 ;
structure of, ii. 160.

Commercial geography, vi. 38.

Common Arum, v. 43.

GENERAL INDEX

229

Common Avens, life history of,
iii. 166, 168, 214 ; illustra-
tion of, iii. 216, iv. 69.

Common Bent Grass, v. 60 ;
brittle-star, ii. 156 ; buckie,
ii. 172 ; Butterwort, iv. 43 ;
Cinquefoil, iii. 61 ; Club-
moss, iv. 99 ; Crowberry, iv.
193 ; Earwig, i. 177 ; flower-
ing plants, iii. 85 ; Fungi,
iv. 128 ; gnat, ii. 116 ;
Gorse, iv. 192; Hair Moss,
illustrated, iv. 112, 113 ;
Wild Geranium, iii. 196 ;
Heather, iv. 191 ; Ivy,
iv. 30, 31 ; Lady's Mantle,
iv. 198 ; land, v. 215 ;
limpet, ii. 143 ; Ling, iv. 202 ;
Mallow, v. 14 ; winter moth,
life history of, v. 181 ; newt,
ii. 101, 102; Field Poppy,
v. 80 ; Polypody, iv. 86 ;
prawn, ii. 150; Red Poppy,
iv. i, 21, v. 76 ; Reed, v. 27,
29, 76 ; figure of, v. 37 ; Rush,
v. 36 ; scallop, ii. 139 ;
seal, colour of the young,
i. 66 ; shore-crab, ii. 128,
145, 176 ; spider-crab, ii.
146; starfish, ii. 155, 180 ;
trumpet-moss, iv. 138 ;
vapourer moth, figure with
caterpillar and wingless
female moth, v. 181.

Commons of Surrey, iv. 188.

Commons, vegetation of, iv. 188,
206.

Comparative psychology, ii.
209.

Composite, iii. 79, 80, iv. 69.

Compound leaves, iii. 93.

Condensation on windows,
cause of, vi. 18.

Condyle of skull, i. 21.

Coney, of the Bible, i. 25.

Coniferae, iv. 70 ; bud scales
of, iii. 42, 43.

Coniferous trees, iv. 145.

Conifers, v. 215 ; characteristic
of dry soil, iii. 51, v. 215.

Contour-feather, figures of, i.
69, 70, 71, 72.

Convolvulaceae, iv. 69.

Convolvulus, v. 7, 73, 178, 179 ;
hawkmoth, v. 38 ; Larger,
v. 38 ; Polygonum, v. 86 ;
twining stems of, iii. 58.

Cooking apples, v. 150 ;
cherries, v. 151 ; goose-
berries, v. 151 ; pears, v.
150 ; plums, v. 151.

Coot, ii. 190.

Coppice, iv. 147, 148, 156.

Copses, iv. 159.

Coracoids, i. 74.

Corals, i. 158.

Coral- Root Orchids, iv. 181,
182.

Cord-moss, iv. 100, 103, 104.

Cord-mosses, capsules of, iv. 105.

Corded poodles, i. 26.

Coreopsis, v. 170, 179 ; Drum-
mondii, v. 169 ; lanceolata,
v. 171.

Corixa, ii. 123.

Corm of Crocus and Gladiolus,
v. 116.

Corm, nature of, iii. 63.

Cormlets, iii. 71.

Corms, iii. 63, 69, 70, iv. 175.

Corn, v. 78 ; bunting, ii. 203 ;
Buttercup, v. 84, 86 ; Cockle,
v. 76 ; crake, ii. 207 ; Grom-
well, figure of, v. 85 ; Mari-
gold, v. 81, 86, 216 ; reaping
of, v. 88 ; Spurrey, v. 81.

Cornflower, v. 16, 80, 81, 86, 169.

Coronella lavis, i. no, 114, 116.

Cotton, ff9m Africa and
America, iii. 81 ; grass, iii.
2, 80, iv. 183, 188, 196, 200,
208, v. 34, 36 ; grass,
highest altitude of, iv. 197 ;
grass bog, iv. 192 ; grass
moors, iv. 193 ; tail, ii. 202.

Cottony filaments of leaves, iii.
77-

Coitus bubalis, ii. 130, 170 ;
gobio, ii. 104 ; scorpius, ii.
130, 131, 183.

Cotyledons, iii. 5, 33 ; differences
of, iii. 56.

Couch-grass, iii. 61.

Cowberry, figure of, iv. 191, 196.

Cow grass, v. 58.

Cow-parsnip, iv. i, 69, 71, 73,
77 ; flowers of, iv. 5 ; fruit
of, iv. 5 ; pollination of, iv.
5 ; shoot of, iv. 3 ; umbel
of, iv. 4.

Cowslip Orchis, v. 63.

Cowslips, iii. 130, iv. 186, v.
63, 210.

Cow-wheat, ii. 209, 211, iv.
155, 162, 180.

Crab apple, v. 73 ; cocoanut,
ii. 200 ; species of, ii. 128,
145, 146, 147 ; hermit, iii. 186.

Crab stock, v. 150, 160, ii. 186.

Crab, young of, ii. 145.

Crabs, ii. 170.

Cranberry, iv. 195.

Crayfish, ii. 108.

Creeping Buttercup, iii. 90,
114, v. 62 ; illustration of,
iii. 96.

Creeping Crowsfoot, v. 117 ;
Plume Thistle, iii. 61 ; rhiz-
omes, v. 8 ; Scirpus, v. 29 ;
stems, above ground, iii. 69 ;
willow, v. 8.

Crepis biensis, iii. 76 ; fcetida,
iii. 76 ; hairy leaf of, iii. 51.

Crescent moon, vi. 85 ; never
seen to rise, vi. 88.

Cress, cultivation of, v. 144.

Cresses, v. 42.

Crested Dogstail Grass, v. 217.

Crested Newt, ii. 101, 102.

Crickets, i. 176.

Crithmum maritimum, v. 12, 13.

Crocodilians, i. 109.

Crocus, iii. 30, 114, 115, 160,
iv. 69, y. 116, 172, 175 ;
aureus, iii. 161 ; contrac-
tile roots of, iii. 70 ; corm,
stages of development in,
figured, iii. 64, v. 116 ; life
history of, iii. 63, 64, 65 ;
species of, iii. 161.

Crocus verni, v. 116.

Crop of birds, i. 76.

Crops, rotation of, v. 87, 125.

Crossbill, ii. 210 ; type of
beak, i. 92, figure 5.

Cross-fertilisation, ii. 204.

Cross-leaved Heath, iv. 192, 195.

Cross pollination, iii. 78, iv.
7i-

Crosswort, iii. 77, v. 86.

Crowberry, iv. 193, 196, 197.

Crowsfoot, creeping, v. 117.

Crucifer, iv. 185, v. 14.

Cruciferae, iv. 68, 182, v. 3, 42.

Crumb-of -bread sponge, ii. 178,
179.

Crust -lichens on granite rocks
at Dartmoor, iv. 136, 140.

Crustacea, ii. 108, 145, 150, 181.

Crustacean parasite, ii. 181.

Crustaceans, i. 158, ii. 170,
171, 184, 186, 188, ii. 212.

Cryptogamic plants, v. 23.

Cryptogams, fresh-water, v. 21.

Crystals of ice, suspended in
the air, vi. 55.

Crystals, six-sided, vi. 41.

Ctenophores, ii. 186.

Cuckoo Flower, ii. 203, iii. 83,
120, 166, iv. 69, v. 27, 42, 48 ;
life history of, iii. 188.

Cuckoo-spit, ii. 15, 203, 208.

Cucumber, v. 148 ; seedling of,
iii. 10.

Cud-chewing animals, i. 41.

Cudweed, iii. 76, iv. 158.

Culex, ii. 19 ; diagram of egg-
raft, ii. 20 ; diagram of
larvae, ii. 22 ; diagram
of pupa, ii. 23 ; diagram of
respiratory tube, ii. 23 ;
imago emerging from pupa,
ii. 24, figure 13 ; pipiens, ii.
116.

Cultivated crops, vi. 32.

Cultivation, practical observa-
tions, v. 86 ; principles of, v.
218-224 ; weeds of, v. 75.

Culture, vegetable, v. 125-129.

Cultures of soil organisms, v.
204, 206.

Cup fungi, iv. 127, 128, 134,
141, 178.

Cup-lichens on bark, iv. 133,

134-

Cup-moss lichen, growing on
hedge-bank, iv. 140.

Cup-mosses, iv. 138.

Curlew, ii. 203, 214.

Currant, cultivation, propaga-
tion of, v. 162 ; varieties of, v.
148, 149, 151 ; gall mite, life
history and habits of, v. 185 ;
gall mite, preventive treat-
ment of, v. 185.

Currant-galls, ii. 212.

Cuttings, v. 117, 1 18; potting
of, v. 121.

Cuttle, colour change, ii. 137.

Cuttle fish, i. 158, ii. 105, 157,
170, 184; habits of, ii. 173;
suckers of, ii. 138.

Cycloptents lumpus, ii. 131, 183.

Cyclostomes or round-mouths,
i. 151. 157-

230

THE BOOK OF NATURE STUDY

Cymose diagrams, iii. 98.
Cynipid, female ovipositor, ii.

17 ; larva of, ii. 17.
Cynips kollari, ii. 18, 212.
Cypress, naked buds of, iii. 43.
Cypselus apus, ii. 218.

Dabchick, ii. 190, 214.

Dachshunds, i. 26.

Daffodil, iii. 115, iv. 158, 159,

v. 1 6, 63, 70 ; life history

of, iii. 156, 159 ; diagram of,

158 ; illustration of, 160 ;

fertilisation of, 161.
Daisy, iii. 86, 166, iv. 69,

v. 1 6, 64 ; figure of life history,

iii. 175 ; small, v. 62.
Damsons, v. 148.
Dandelion, iii. 86, 115, 179.

iv. 24, 69, 72, 77 ; life history

of, iii. 144 ; fruits of, illustra-
tion of, iii. 80, figure 46 ; time

of opening and closing, iii. 54.
Danes, i. 26.
Darwin on dispersal of seeds,

v. 51 ; on the movements of

plants, iii. 9.

Dassies, of South Africa, i. 25.
Daucus Car ota, v. 115, 135.
Day and night, vi. 75-84; in

relation to warmth and

light, vi. 53.
Day, division of, vi. 76.
Daylight, duration of, vi. 67.
Dead men's fingers, polyps of,

ii. 164.
Dead-nettle, iii. 47, 75, 106,

186, iv. 69, 72, 74; figure

of flower, iii. 79 ; internode

of, iii. 52.
Deadly White Amanita, iv.

218.

Decapod Crustacea, ii. 151.
Decrescent moon, vi. 90.
Dee, estuary of, vi. 15.
Deep-rooted plants, vi. 33;

system, iii. 18.
Deep-sea, abyssal fauna of, ii.

169, 187.
Deer, ii. 216.
Deerhounds, i. 26.
Deinosaurs, i. 109.
Delphiniums, v. 170.
Demoiselle dragon-fly, nymph,

figured, ii. 115.
Denudation, checks on, vi. 105 ;

of peat, illustration of, iv.

190.

Desert, conditions of, vi. 34.
Desert-dwelling birds, i. 79.
Desmids, ii. 83.
Dessert fruit, kinds of, v. 150,

151-
Diagram showing variations

of shadow in London, vi. 71.
Diagrams, illustrating princi-
ples of calculations, vi. 51, 52.
Dicotyledons, ii. 89, iii. 20,

iv. 68, v. 38.
Digestion and absorption of

plants, iii. 73 ; of birds, ii. 76 ;

of ruminants, i. 38.
Dipper, ii. 196 ; eggs of, ii.

197 ; food of, ii. 197 ; nest

of, ii. 197.

Diptera, ii. 195.

Disintegration, by frost, vi.

98 ; by chemical action, vi. 99.

Dispersion of fruit and seeds, iii.

79-

" Displaying " of Ruffs, illustra-
tion of, i. 86.

Diurnal birds of prey, i. 83.

Diverticula or pouches, i. 77.

Division of days, vi. 75.

Docks, iv. 185, v. 45.

Dodder, iv. i, 35, 36, 37, 69,
1 80 ; v. 78 ; flower illus-
trated, iv. 37 ; fruit of, iv. 38.

Dog, foot of, i. 35 ; fish, i.
140, 142, 143, 146 ; eggs of,
ii. 177 ; rose, iv. i, 52, 53,
69, 188, v. 74 ; rose,
coloured illustration of, iv.
52 ; rose, flower of, iv. 54 ;
violet, iii. 124, 128 ; whelk,
ii. 141, 143, 170, 175 ; whelk,
eggs, ii. 172, figure 85 ; wood,
v. 73, 216. .

Dogs, i. 25.

Dog's Mercury, iv. 159, 185.

Dolphins, i. 20, ii. 95.

Domesticated cat, i. 59.

Donkeys, stripes of, i. 67.

Doris, ii. 141, 142, 144; Iarva3
of, ii. 142.

Doto coronata, spawn of, ii. 166.

Dottrel, ii. 217.

Dove's-foot Geranium, v. 86.

Downy Oat Grass, v. 59.

Dragon-flies, i. 188, ii. 195.

Dragon-fly larvae, ii. no.

Dragon-fly, metamorphosis of,
ii. 114, figure 51.

Drainage of grassland, v. 70.

Dray-horse, i. 39.

Drift, how formed, vi. 113.

Drifting mountain mist, vi. 3.

Dropper of tulip, iii. 66, 67, 70.

Dropwort, v. 216.

Drosera, species of, iv. 41, 42,
v. 32, 33-

Droseraceae, iv. 69.

Drought, effect on vegetation,
vi. 32, 33-

Dublin time, vi. 81.

Duck, figure of foot, i. 95.

Ducks, beaks of, i. 90.

Duckweed, ii. 87, v. 26, 29.

Dune pasture, v. 7.

Dunes, ii. 200, 201.

Dunlin, summer and winter
plumages of, i. 88, 89,
ii. 170.

Dust particles, in relation to
sun, vi. 55.

Dwarf apple trees, v. 160.

Dwarf Bean, cotyledons of
figured, iii. 12, v. 130.

Dwarf Furze, iv. 192, 201 ;
Larkspurs, v. 176 ; Nastur-
tium, v. 169 ; Roses, v. 176 ;
shoots, iii. 38 ; Thistle, iv.
206.

Dyers Weed, y. 214.

Dyticus marginalis, ii. 29, 30,
117, 118, 120; female and
larva (text Fig.), ii. 118, 193.

Dytiscus beetle, male and
female (text Fig.), ii. 193.

Eagle, ii. 217 ; method of

feeding (text Fig.), i. 68 ;

type of beak, i. 92.
Eared-seals, i. 51.
Earth, movements of, vi. 75,

79 ; radius of, vi. 52.
Earthworm, cocoons of, i. 163.
Earthworms, i. 160, 163, 166,

169, ii. 199, 205, 208, 209,

210, 215, 216; male and

female, organs of, i. 163.
Earwig, nest and eggs of, i. 178,

180.
East wind, coldness of, in

spring, vi. 17.
Echinoderms, i. 158, ii. 153,

i57> i7i» 180, 184.
Economic geographer, vi. 32.
Economy, rural, ii. 209.
Edelweiss, iii. 76.
Edible Boletus, iv. 128; crab,

ii. 146 ; fungi, iv. 126 ; mussel,

ii. 138,141,175.
Edinburgh, in relation to length

of day, vi. 65, 67.
Eel-fare, i. 149.
Eel, scale of, i. 147, figure 52.
Eel-worms, ii. 17.
Eels, in captivity, ii. 104.
Egg-capsules, ii. 176, ; pockets,

iv. 85, 107, '116; ribbons of

sea-slugs, ii. 141.
Eggs of amphibians, i. 121 ;

of birds, and illustrations of,

i. 98, ipo; of dogfish, ii. 177;

ofreptiles, i. 112, 114, 115, ii.

94 ; of salmon, i. 148 ; of

winter moth, v. 184.
Electric fishes, i. 147.
Elephants, colour of young,

i. 66 ; in Britain, ii. 221.
Elm, iv. 172, 174, 184, v. 73,

217 ; branches of, iii. 46 ;

suckers of, iii. 46 ; bark of,

iii. 46 ; leaf, figure of, iii. 75.
Elvers, ii. 197.

Embryo of young plant, iii. 4.
Enchanter's night-shade, ii. 209,

iv. 161, 181.

Encrusting lichens, iv. 139.
Endosperm, iii. 9, 36.
Enemies of garden crops, v. 180.
Ephemeridae, ii. 195.
Epicotyl, iii. 29.
Epigeal cotyledons, iii. 12.
Epiiobium angusti folium, iv. 17,

v. 171.
Equation of time, vi. 76, 77,

79-

Equator, vi. 53, 67.
Equinox, vi. 64, 71, 83.
Erica cinerea, iv. 17, 192 ;

corolla of, 192.
Ericaceae, iv. 69.
Ermine moth and caterpillar,

v. 182, figure 74.
Erosion and transportation, vi.

35-
Escarpment, illustration of,

vi. 168.

Eschscholtzia, v. 169.
Eucalyptus, iii. 2.
Euphorbia, species of, v. 4, 81,

83-
Euphorbiaceae, v. 84.

GENERAL INDEX

231

Evaporation and rain forma-
tion, vi. 4.

Evening mists, vi. 55 ; rays, of
the sun, vi. 55.

Evergreen oak, iii. 37.

Evergreens, iv. 164.

Evernia, species of, iv. 133, 138.

Exalbuminous seeds, iii. 9.

Expansion of water, effects of,
vi. 49.

Eyebright, iv. 180, 181, 207,
v. 66 ; semi -parasitic, iii. 31.

Eyes of birds, i. 71, 75 ; of
snakes, i. 118.

Fairy-rings, iv. 126, 128.

Falcon, Greenland, ii. 219.

Fallow-deer, ii. 213.

False Mushroom, iv. i28;Truffle,
iv. 141.

Farming operations, v. 87.

Farnham East Street School
Gardens, illustration of, v.
184.

Father-lasher, ii. 130, 170, 183.

Fawn, i. 32, ii. 213.

Feather-mosses, iv. 100, 117,
155-

Feathers of birds, i. 69.

Feathery mosses, iv. 115.

Fen plants, v. 38.

Fermented jam, iv. 141.

Fern Moss, iv. 179, v. 21.

Ferns, iv. 79, 88, 92, 98, 125,
158, 179, 207, v. 21, 38.

Fescue, iv. 204 ; red or creep-
ing, v. 67.

Festuca, species of, v. 63, 114.

Feverfew, iii. 166, 175, 179 ;
life - history, flower figured,
iii. 177, iv. 6g<

Field Alchemil, iii. 2; Cerastium,
v. 29 ; Gentians, iv. 198 ;
Horsetail, iv. 94 ; Madder, v.
74 ; Mint, v. 84, 86, 214 ;
Pansy, v. 76 ; Pennycress,
figured, v. 83, 84 ; Speed-
well, v. 86 ; Thistle, v. 69 ;
vole, ii. 202, 207 ; Wood-
rush, iii. 115, 152 ; illustration
of flower and fruit, 154, 155,
v. 67 ; fare, i. 83.

Fifteen-spined stickleback, ii.

133. 134-

Fig, v. 148.

Figwort, iii. 83, y. 82.

Fiji Islands, natives of, i. 41.

Filmy Fern, iv. 98.

Filo-plumes, i. 70, 71.

Fir Club-Moss, iv. 98, 99.

Fish, age of, i. 146 ; move-
ments of, i. 137 ; air bladder
of, i. 137-

Fish-eating ducks, i. 91.

Fishes, i. 140, 158, 159, ii.
103, 130-136 ; breathing of,
i. 139, 142 ; life-history of,
i. 148 ; scales of, i. 145.

Fishing frog, ii. 183.

Fissidens, iv. 107, 108.

Flag, yellow, iii. 221, v. 43.

Flamingo, type of beak, i. 92,
figure 9.

Flat-fish, ii. 134, 135.

Flat fork-moss, iv. 107, 108.

Flax, figure of, iii. 104, iv.
36, 162, v. 66, 67, 78, 170.

Fleabane, v. 42.

Flies, v. 33.

Flight, i. 84, 87,

Flight-feathers, i. 72, 73.

Floating-leaf, v. 46.

Floods, vi. 28, 30.

Flora of the sea and seashore,
v. 21.

Flounder,!. 137, 145, ii. 134,135;
development of eyes, ii. 135.

Flower of Butterwort figured,
iv. 45 ; of Garden Pea il-
lustrated, iv. 27 ; of Grass,
v. 57 ; of Ling, iv. 191 ; of
Orchid figured, v. 68.

Flower-buds, iv. 148.

Flowering Currant, v. 167 ;
plants, below water, v. 22 ;
plants, common, iii. 85, 109 ;
plants, fertilisation of, v. 49.
50 ; parasitic, iv. 180.

Flowering Rush, v. 29, 45, 51.

Flowers, v. 166-179 ; cultiva-
tion of, iii. 35, v. 1 66.

Flustra, ii. 161, 179.

Fly Agaric, iv. 128, 154, 178.

Flying mammals, i. 54.

Foals, striped, i. 66.

Foliage-leaf, iii. 35, 66.

Food of birds, i. 90.

Foraminifera, ii. 170, 185.

Forelegs, i. 22.

Forest of Dean, iv. 150; of
Ancient Britons, iv. 144.

Forests, destruction of, vi. 35,
36.

Forget-me-nots, iii. 83, iv. 186,

v. 54-

Fox, i. 32, 62, ii. 196, 216;
colour of the young, i. 66;
Arctic, ii. 219.

Foxglove, iii. 32, iv. i, 10, 69,
74, 157-159, v. 169; illustra-
tion of, iv. 10 ; and sandy
soils, v. 216.

Foxtail grass, v. 57.

Fragana, species of, iii. 166,
v. 148, 163.

Fragrant Habenaria, v. 68.

Free-living worms, ii. 158.

French Willow or Rose Bay, iv.
i7-

Frigate bird, figure of, i. 96.

Fringe-mosses, iv. 109.

Frog, development of, i. 127,
129, ii. 96, 97, 130 ; how tc
keep in captivity, ii. 96 ;
hibernation of, i. 126 ; catch-
ing fly, illustration of, ii. 207 ;
spawn of, i. 127, 128, 129, ii.
195 ; year's life of, i. 126.

Frogbit, figure of, v. 49 ;
hoppers, ii. 15, 203 ; Orchis,
v. 68 ; spit, ii. 203.

Frogs, i. 120, 123, 125, ii. 96,
194, 208, 217.

Frost, action of, vi. 49, 98 ;
relation to gardens, vi. 50.

Fruit culture, v. 148-165 ;
dispersal, iv. 74 ; plantation,
summer treatment, v. 183 ;
of Willow, figured, iii. 81.

Full moon, vi. 86, 87.

Frullania dilatata, iv. 120, 122,
123 ; showing capsule with
its elaters, iv. 123.

Fuller's Earth, v. 30.

Fulmar, i. 83.

Futnaria officinalis, v. 79, 80.

Fumitory, figured, v. 79, 80,
86 ; characteristic of corn-
fields, v. 80.

Funaria, iv. 100-106.

Fungi, ii. 17, iv. 79, 125,
I77» i79» 1 80, 190 ; coloured
spores of, iv. 178 ; life-
history of, v. 181 ; rusts,
smuts, and mildews of, iv.
141 ; treatment of, v. 183.

Fungus, iv. 133, 154 ; Cup, iv.
127 ; flora, iv. 178 ; illus-
tration, iv. 141 ; on fish, iv.
141.

Furze, iv. 36, 204, v. 12 ;
Dwarf, iv. 201.

Gadus, species of, i. 140, 143.

Gall-flies, ii. 15, 18.

Gall-making Hymenoptera, ii.
205.

Gall-wasp, ii. 212.

Game-birds, i. 86.

Gammarus, species of, ii. 108,
175, 181.

Gannets, i. 86.

Garden Acacia, spines of, iii.
82 ; drains, v. 99 ; hedges,
v. 102 ; manure, v. 103 ;
Nasturtium, iii. 54 ; Pea, iv.
i, 24, 25, 69 ; Sage, iii. 69,
166, 184 ; life-history of,
diagram of flower, 185 ; snail,
ii. 14, 48; spider, ii. 40;
spider, web of, ii. 43, 44 ;
spider, apex of abdomen
figured, ii. 42 ; cultivation
methods, v. 108-112; trench-
ing, v. loi ; turnip, v. 139.

Gardens, sites for, vi. 114.

Garlic, contractile roots of,
iii. 66 ; mustard, v. 74 ;
bulb reproduction of, iii. 66 ;
wild, iv. 159 ; wood, iv.

159-
Gastropod, i. 158, ii. 48, 83,

105, 140, 165, 170, 176, 186 ;

fossils, vi. (80), p. 203 ; free

swimming young, ii. 165 ;

spawning and hatching of,

ii. 143.
Gastrostetts, species of, i. 138,

ii. 103, 104, 134, i44» 197,

198.

Gemmules, ii. 199.
Gentian, Little Snow, iv. 198.
Gentians, iv. 182, 198, v. 216.
Geological character of rocks,

v. 19 ; periods, vi. 196 ;

sections, nature of, vi. 161.
Geometers, i. 186.
Geotome, iv. 154.
Geraniaceae, iy. 69.
Geranium, iii. 71, y. 74 ;

common wild, iii. 196 ;

cultivation, v. 175 ; kinds

of, iii. 196 ; v. 79, 80, 171,

177 ; propagation of, v.

175-

232

THE BOOK OF NATURE STUDY

Germander Speedwell, iii. 166,
iv. 69, v. 39, 74 ; figure of, v.
82 ; life-history of, iii. 225 ;
flower figured, iii. 226.

Germinating seeds, iii. 4, 6, 19,
21.

Geum, species of, iii. 80, 214, 217.

Giant Campanula, iv. 161 ;
horsetail, iv. 96.

Gill-breathers, ii. 191 ; fila-
ments, i. 143, 144 ; sacs, i.
155 ; toadstools, iv. 127.

Gizzard of a fowl, i. 76.

Glacial epoch, v. 193.

Glacier action, foundation of,
vi. 45.

Glaciers and formation of
streams, vi. text Fig. 46.

Glaciers, kinds of, vi. 113, 115,
123.

Gladioli, iii. 70, 71, v. 171.

Gladiolus, conn of, v. 116.

Glass-eels, i. 150.

Glasswort, iii. 51, 84, v. 2, 3, 9.

Glaux maritima, v. 3.

Globe-fish, i. 137.

Glochidia, ii. 192.

Gloxinias, v. 117.

Glyceria, species of, 2, 7, 45 ;
plant association, v. 3.

Gnat, ii. 19, 114, 196 ; eggs and
larvae of, ii. 19, 110-116;
egg-rafts of, ii. 116 ; respira-
tory organs of, ii. 117.

Gnawing animals or rodents,
i. 28.

Goat Willow, iv. i; illus-
trated, iv. 45.

Goats, i. 39 ; Beard, iii. 54.

Gobius, species of, ii. 132.

Godetia, v. 169.

Gold-crest, ii. 210 ; wren, i. 80.

Golden Eagle, method of feed-
ing, i. 68.

Golden English yew, v. 167 ;
Plover, ii. 214, 217 ; Rod,
iv. 159; Samphire, v. 13, 42;
Saxifrage, v. 40, 41, iv. 161.

Goldfish, breeding in captivity,
ii. 103 ; locomotion of, ii.
ipi.

Goliath Poppy, v. 171.

Gooseberries, varieties of, v.
148, 149, 151.

Gooseberry, life-history, culti-
vation, propagation, iii.
62, v. 161 ; Sawfly, life-
history of, v. 184 ; method
of destroying, v. 184.

Goosefoot, v. 2, 9, 13, 15.

Goose-grass, iv. 202, v. 86, 217.

Gorse, iii. 37, 51, iv. 183, 188,
207, 209, v. 16, 69, 80, 215;
exalbuminous seeds of, iii.
12; seedling of, iii. 82.

Grafting, v. 117.

Grain-eating birds, i. 76.

Gramineae, iv. 70.

Granite, v. 19 ; shap, vi. 121.

Grapes, constituents of, v. 126,
148.

Grape-sugar, iii. 29.

Graphis, species of, iv. 133, 136,
140, 178.

Grass associations, v. 86.

Grass heaths, iv. 188, 191, 200,
204.

Grass, inflorescence of, v. 56 ;
glumes of, v. 57 ; of Parnas-
sus, v. 34 ; quaking, v. 59,
62 ; sheep's fescue, y. 59 ;
snake, i. no, 118, ii. 214 ;
snake, slough of, i. 118 ;
wrack, v. 24, 50.

Grasses, iii. 12, 29, iv. 158, 159,
177, 186, 199, v. 36, 45, 52,
70 ; dominant in meadows
and pastures, v. 56 ; seashore
and moor, v. 57.

Grasshoppers, i. 176.

Grassland, drainage of, v. 70 ;
effect of manures on, v. 58 ;
sandy soil, v. 215.

Grassy Naiad, found only in
Lancashire, v. 24.

Grazing meadow, v. 64.

Great Britain, average amount
of snow in, vi. 41 ; insular
climate of, vi. 6 ; water
courses of, vi. 23 ; mountains
of, vi. 23 , number of rainy
days in, vi. 28 ; changeable-
ness of weather in, vi. 17 ;
high average yield of land in,
vi. 30.

Great Reed-Mace, v. 44.

Great-spotted Woodpecker, ii.
210.

Great Water-Moss, iv. 115, 116.

Greater Bird's-Foot Trefoil, iii.
170 ; illustration of, iii. 172.

Greater Plantain, iii. 166, 205 ;
life-history of, plant figured,
iii. 206 ; Periwinkle, iii. 133,
136 ; section of flower figured,
description of, 137 ; fruit fig-
ured, 138 ; Spearwort, v. 38 ;
Water Plantain, v. 45.

Grebe or dab-chick, ii. 190 ;
figure of foot, i. 95.

Greek tortoise, i. 115.

Green algas, v. 49 ; fly, ii. 15 ;
laver, ii. 84 ; lizard, i. in ;
woodpecker, habits of, ii. 210.

Greenland falcon, ii. 219 ;
whale, i. 49.

Greenwich noon, vi. 76 ; time,
vi. 77, 80.

Green-winged orchis, v. 63.

Grey-hen, ii. 214.

Greyhound, i. 28.

Grey wagtail, ii. 217.

Gromwell, v. 85.

Ground ivy, self-propagation,
iii. 61 ; lichen, iv. 135.

Groundsel, v. ii, 30, 80, 85, 86,
148, 217 ; figure of, v. 81, 82.

Grouse, ii. 216 ; red, ii. 213 ;
willow, ii. 214.

Growth of plants independently
of seeds, iii. 60 ; of radicle,
iii. 12, 1 6 ; of seedlings, iii.
7 ; of the shoot from the
bud, iii. 33.

Guelder-Rose, iv. 208, v. 73.

Guest-bees, ii. 205.

Gull, ii. 170 ; black-backed,
plumages of, i. 89 ; black-
headed, ii. 190, 196.

Gullery, ii. 196.

Gullet or oesophagus, i. 76.
Gunnel, ii. 133, 170, 184.
Gurnard, streaked, ii. 186.
Gymnosperms, iii. 87, iv. 70.

Habits of feeding of birds, i.
90.

Habits of the rattle-snake, i.
119.

Haddock, i. 141, 143, ii. 135 ;
external characters of, i.
140 ; gill chambers of, i. 143.

Hcematopus ostralegus, ii. 196.

Hag, i. 154 ; piston-like tongue
of, i. 154.

Hail, explanation of, vi. 20.

Hailstones, causes of, vi. 20.

Hairless dogs, i. 26.

Hair moss, iv. 112, 157, 179,
v. 36 ; in fruit, iv. 116 ;
mosses, peculiar peristome
teeth of, iv. 112, 113, 114.

Hairs developed for protection
of the plants, iii. 75 ; differ-
ent forms of, iii. 82 ; multi-
cellular and unicellular, iii
8 1 ; in plant life, importance
of, iii. 73-

Hairy porcelain crab, ii. 147 ;
thread mosses, iv. 109.

Hale continuation school gar-
dens, Farnham, v. 144 ;
day school gardens, illustra-
tions of, v. 176.

Halichondria panicea, ii. 178,
179.

Halictus, ii. 204.

Halobates, ii. 195.

Halophytes, v. 16, 17.

Hampstead Heath, iv. 188.

Hanoverian rat, i. 30.

Hard fern, iv. 89, 92, 178, 179 ;
fescue, v. 67 ; heads, v. Co ;
woods, trees producing, iv.
150.

Hardy annuals, v. 167, 168 ;
ferns, v. 179 ; perennials,
fifty of the best, v. 171 ;
perennials, treatment of, v.
170.

Hare, i. 29, 53 ; summer dress
of, i. 62 ; variable, ii. 219 ;
winter dress of, i. 62.

Harebell, iv. 206, 207.

Hare's-foot clover, v. 29.

Harlequin-flies, ii. 196.

Hartstongue, leaves of, iv. 92.

Harvest moon, vi. 87.

Haslemere, commons of, iv.
208.

Haunt of the dragon-fly, ii.
114.

Haunts of animals, ii. 169-222.

Hawfinches, i. 80.

Hawk, raptorial foot, i. 95.

Hawkbit, iii. 76, v. 59, 62.

Hawkweed, hairy leaf of, iii.

5i-
Hawkweeds, iii. 76, iv. 159,

v. 66.
Hawthorn, iii. 44, 58, 82, iv.

51, 165, 184, 204, v. 73 ;

hedge, illustration of, v. 72,

217."
Hay, date of cutting, v. 88.

GENERAL INDEX

233

Hazel, iv. 144, 147, 148, 172,
180, 184, v. 72, 73 ; various
uses of, iv. 149 ; nut, involucre
of, iv. 149 ; nuts dispersed
by Nuthatch, iv. 149.

Head-ganglia, ii. 208.

Heart of birds, i. 78 ; of
mammals, i. 22.

Heart-urchin, ii. 154, 155, 175.

Heat in various parts of the
globe, vi. 1 6, 20 ; formation
of, vi. 124.

Heath, iv. 192 ; bedstraw, iv.
201, 202, v. 69 ; kinds of,
iv. 17, 195 ; rush, iv. 196,
201, 204.

Heather, iii. 188, iv. i, 36,
69, 177, 183, 191, 192, 193,
204, 207, 209, y. 33, 86, 215 ;
illustration of, iv. 14 ; moor,
iv. 190, 192, 196, 199, 200,
202 ; pistil of, iv. 15 ; seed-
lings of, iv. 1 6.

Heaths, iii. 51, iv. 196, v.
n, 217 ; vegetation of, iv.
188.

Heavens and their story, vi. 89.

Hedge garlick, v. 74 ; mustard,
iv. 185.

Hedgehog, i. 54 ; toadstools,
spiny projections of, iv. 128.

Hedgerow, iv. 148 ; in spring,
illustration of, v. 74 ; vege-
tation, effect of running water
on, v. 54 ; illustration of,
v. 72.

Hedgerows, iv. 185.

Helix, species of, ii. 14, 48,
49, 211.

Hellebore Viridis, iv. 160.

Hemiptera, ii. 15.

Hemp agrimony, v. 40.

Henbit, v. 86.

Herbaceous and rose borders,
illustration of, v. 128 ;
border, v. 175 ; cuttings, v.
120 ; plants, iv. 156, v.
170 ; plants in relation to
low temperature, vi. 37 ;
undergrowth, observations
on, iv. 157.

Herb-Robert, iii. 166, 196, 197 ;
life - history of, flowering
shoot figured, fruit figured,
iii. 198, iv. 69, 76, v. 70, 74.

Hermit crab, ii. in, 128, 173,
149, 150, 166, 171, 179, 181 ;
habits of, ii. 149, 150 ;
inhabiting shells, ii. 150 ;
tail of, ii. 149.

Heron, figure of foot, i. 95.

Herons, carriage of neck, i. 87.

Herring, i. 145, 147 ; gull, plum-
ages of, i. 89.

Highland animals in winter, i.
62.

Hills covered with snow, vi. 43.

Hills, how formed, vi. 162.

Hind, i. 32, 213.

Hindhead, commons of, iv. 208.

Hind-limbs, i. 22.

Hints as to shore excursions, ii.
173-

Hints on collecting plants, iii.
no.

Hip-girdle, i. 22.

Hippuris, ii. 92.

Hips, iv. 55.

Hoar frost, vi. 49.

Hoary cress, iv. 185.

Hog-weed, iv. i.

Holcus grass, iv. 208.

Holcus lanatus, v. 60.

Hollow - horned ruminants, i.
38.

Holly, iv. 164, 165, 208 ;
composition of leaves, iii. 51 ;
exalbuminous seeds of, iii. 12.

Hollyhocks, v. 171. •

Holly-leaved Naiad, localities
of, v. 24.

Holly, Sea, v. 10, n ; smooth
bark of, iv. 178; teeth of,
iii. 75 ; typical tree of sandy
soils, v. 215 ; with two
cotyledons, iii. 12.

Holm Oak, iv. 164.

Honeysuckle, iv. i, 32, 69, 74,
78, 156, 208 ; bud scales, iii.
40, 43 ; calyx of, iv. 33 ;
illustrated, iv. 34 ; pollina-
tion of, iv. 35.

Hoofed animals, i. 32, 40.

Hop, iii. 77, v. 178, 179 ; twining
stems of, iii. 58.

Horizon, circular form of, vi. 51 ;
colours, vi. 57.

Horizontal clouds, vi. 57.

Hornbeam, iv. 153, 171, v.
215 ; leafy involucre, iv. 149.

Hornbill, type of beak, i. 92.

Horned moon, vi. 89 ; poppy,
v. 10, 2ii ; poppy, illustra-
tion of, V. 12.

Hornet, i. 210.

Horns, branched, i. 38 ; in the
" velvet," i. 38 ; hollow, i.
38 ; structure of, i. 38.

Hornwort, ii. 90, v. 24, 25 ;
free swimming form, v. 23.

Horse, i. 32, 40 ; bones of the
foot, i. 34 ; callosities of, i.
34 ; colour of, i. 60 ; skeleton
of, i. 33 ; stripes of, i. 67 ;
chestnut, i. 34, iii. 39, 43,
iv. 169, 173 ; chestnut,
cotyledon of, iii. 9 ; chestnut,
exalbuminous seeds of, iii. 12 ;
chestnut, largest buds of any
tree, iii. 40 ; chestnut, with
two cotyledons, iii. 12 ; foot
of, i. 35 ; leech, ii. 125 ;
radish, v. 17 ; starfish, madre-
pore of, ii. 181.

Horse-shoe bat, i. 44 ; vetch,
v. 216.

Horsetail, v. 86 ; Field, iv. 94 ;
Ferns, description of, iv. 95,
96 ; Giant, iv. 94, 96, 97.

Hot-bed, for cuttings, v. 120.

Hudson Bay lemming, ii. 219.

Humble-bees, ii. 204, 205, 208,
iii. 79.

Humidity of air, vi. 2, 8.

Humming-birds, i. 65, 91, 92.

Humus, depth of, iv. 154, 155.

Hyacinth, iii. 70, v. 171, 179,
vi. 37 ; Blue, ii. 209 ; bulb
of, v. 116 ; Wild, iii. 104 ;
diagram of, iii. 105.

Hysena-dog, i. 64.
Hydra, ii. 126.
Hydroids, ii. 175.
Hydrometra stagnorum, ii. 195.
Hymenoptera, ii. 10, 17, 203,

212.
Hypogeal cotyledons, iii. 9.

Ice age, iv. 144 ; barriers, vi.

46 ; nature of, vi. 49 ; action
of, vi. 48 ; crystals, in the
air, vi. 41, 55 ; in proportion
to water, vi. 48 ; in relation
to rivers, vi. 46 ; specific
gravity of, vi. 48 ; needles,
vi. 41 ; pushing its way to
the sea, vi. 46 ; streams, vi.
46.

Iceberg, vi. 47 ; experiment
with, vi. 48 ; peculiarities of
Antarctic, vi. 46, text Fig.

47 ; peculiarities of melting,
vi. 46, text Fig. 58 ;
irregular shape of, vi. 48.

Ice-floats, vi. 47.

Iceland Moss, v. 10 ; Poppy, v.

169.

Ichneumon fly, i. 189.
Ichthyosaurs, i. 109.
Incompletae, iv. 69.
Incubation, i. 101.
Inflorescence of grass, v. 56.
Infusorians, ii. 170, 185, 187,

1 88.
Ink-cap, spore-print of, iv.

127.

Inkstone, i. 76.
Insect and fungoid enemies of

garden crops, v. 180.
Insect pollinated flowers, iii. 1 2 8 .
Insectivorous birds, i. 83, v.

181.
Insectivorous plants, iv. 41, 43 ;

characteristic of peat-bogs,

v. 30, 31 ; habits of, v. 31.
Insects, i. 158, 160 ; ii. 108 ;

entrapped by hairs, iii. 78 ;

injurious, ii. 209.
Instruments, practical use of,

vi. 9.
Intermediate associations, v.

10.
Intermediate Bladderwort, v.

32-
Internodes of flowering plants,

iii. 92.

Inula, species of, v. 42.
Inverness, latitude of, vi. 57.
Invertebrates of fresh-water

aquarium, ii. 105-127.
Irideae, iv. 69.

Iris. iii. 69, v. 28, 175, 179 ; self-
propagation, iii. 6 1 ; yellow,

iv. 70, v. 43.
Iris pallida Dalmatica (Princess

Beatrice), v. 171 ; pseuda-

corus, iii. 221.

Irish or Carrageen Moss, v. 10.
Irish time-tables, vi. 79.
Irregular flowers, iii. 106.
Irrigated land, vi. 38.
Isoetes lacustris, v. 24.
Isopod crustaceans, ii. 188,

200.
Italian rye grass, v. 57, 63.

234

THE BOOK OF NATURE STUDY

Ivy, iv. i, 30, 69, 78, 165, v.
179 ; cross pollination of, iv.
32 ; fruit of, iv. 32 ; illus-
trated, iv. 31 ; Geranium, v.

177-
Ixia or Freesia, vi. 37.

ack-by-the-hedge, v. 74.

acob's Ladder, v. 170.

aguar, i. 63.

apanese spaniels, i. 26.

as tone montana, iv. 192.

ay, ii. 210.

eily-fish, i. 158, ii. 126, 166,

184-186.
Jerboas, i. 53.

Jerusalem Artichoke, iii. 67.
John-go-to-bed-at-noon, iii. 54.
'ointed Rush, iv. 194.
onquils, v. 171.
umping spiders, ii. 38.
unceao, iv. 69.

Juncus, v. 67, 70 ; articulatus,
iv. 194 ; associations, v. 2, 4 ;
species of, iv. 196, 201, v.
3, 7, 36 ; Sphagnum associa-
tion, v. 36.

Juniper, iv. 62, 188, v. 216 ;
absence of bud scales in, iii.
43-

Kale, v. 17.

Kangaroo, i. 52, 53.

Keel, i. 86.

Kent, commons of, iv. 208.

Kestrels, stationary hovering,
i. 87.

Kidney of birds, 77 ; Bean, iii.
9, v. 145 ; hypogeal cotyle-
dons, iii. 12 ; twining stems
of, iii. 58, 59.

Kidney-shaped spore cases, iv.
98.

Kingfisher, i. 81, ii. 196 ;
figure of foot, i. 95.

King of the Brocoli, v. 131.

Kingussie, extensive flooding,
vi. 29.

Knapweed, iii. 75, 80, iv. 162,
v. 1 6, 66 ; black, v. 60.

Knawel, v. 216.

Kohlrabi, v. 130.

Labiatas, iv. 69.
Laburnum, buds of, iii. 59.
Lacerta, species of, i. no, 112,

ii. 217.

Lady Fern, iv. 88, 90, 179.
Lady's Fingers, v. 15, 66.
Lady's Mantle, figured, v. 66,

67 ; species of, iv. 197, 198.
Lady's Smock, illustration of,

iii. 120 ; flower of, 123 ;

iv. 68, 69.

Lagopus, species of, ii. 213, 217.
Lake, and moraine illustration

of, vi. 212.
Lake Superior, average winter

fall of snow, vi. 41.
Lakes, formation of, vi. 216 ;

obliteration of, vi. 108.
Lambs' tails, iv. 148.
Lamellibranchs, ii. 68.
Lamination, meaning of, vi.

107, 112.

Lamperns, i. 153, ii. 197.

Lamprey, i. 149, 151, ii. 197.

Lancelet, notochord, i. 155 ;
lateral view of, i. 155 ; repro-
ductive organs of, i. 155.

Land crabs, ii. 200.

Land, movements of, vi. 119.

Land-plants, iv. 177.

Landscape, how modified, vi.
164, 168 ; history of, vi.
I77» I99» 210, 215.

Landslip, illustration of, vi. 190.

Land surface, rate of destruc-
tion of, vi. 106.

Lapwing, changes of plumage of,
ii. 203.

Larch, iv. 145, 147, 149, 151 ;
transverse section, heart
wood, sap wood, bark, iv.
150 ; uses of, iv. 167.

Larkspur, v. 169, 179.

Larvae of large cabbage white
butterfly, i. 184.

Larva? of pear sawfly upon leaf,
v. 183.

Laurel, propagation of, v. 118,
119.

Lavender, v. 176 ; propagation
of, v. 48, 119 ; sea, v. 13.

Laver, species of, ii. 84, v. 10.

Lawns in relation to rain, vi.
32, 33-

Lawyer's-wig toadstool, iv. 127.

Layering, method of, v. 123.

Lead arseniate, for destroying
insects, v. 183.

Leaf-base of flowering plants,
iii. 92,

Leaf-blade of flowering plants,
iii. 92.

Leaf-blade, transverse section,
iii. 48 ; bud, ii. 205 ;
general structure of, iii. 53,
55 ; scars, iii. 62 ; stalk of
flowering plants, iii. 92 ;
position of stomata, v. 6 ;
worms, parapodia of, ii.

159-

Leaf of Psamma, v. 6.
Leafy Lichen, spore fruits of,

iv. 135-
Leafy Liverwort, illustrated,

iv. 124.
Leaves of bulbs, sugar in, iii.

70 ; radical or cauline, iii. 55 ;

register their own move-
ments, iii. 56 ; sensitiveness

of, iii. 55.
Lecanora, commonest Lichens,

iv. 136.
Lecidea, commonest crust -

lichens, iv. 136.
Leeches, ii. 188, 198, 199, 200.
Leek, cultivation of, v. 141.
LeguminosaB, iii. 20, iv. 69,

v. 144 ; tendrils and sleep

movements of, iii. 54, 56 ;

roots of, iii. 32, v. 59, 60, 61,

130-

Lemming, Hudson Bay, ii. 219.
Lent Lily, iii. 156.
Leopard, i. 63.
Lepidodendrons, iv. 94.
Lepidoptera, i. 183, ii. 17.
Leptoplanatremellarisj'n. 179.

Lesser bladderwort, ii. 90.

Lesser Celandine, iii. 63, 70,
90, 115, 122, iv. 69, 157;
figure of flower, tuberous
roots of, carpels of, 119 ;
flower figured, fruitlet of,
120.

Lesser Periwinkle, iii. 115, 133;
description of, figure of, iii.
134-

Lesser Spearwort, figure of, iv.
158, 193, v. 28, 36.

Letter-wort, iv. 136.

Lettuce, iii. 29 ; kind of, v.
143 ; cultivation of, v. 143 ;
sea, v. 10.

Libellula, antennas of, ii. 114 ;
habits of, ii. 115 ; larva? of,
ii. 114 ; respiratory organs
of, ii. 115.

Lichen, iv. 133 ; fungus, iv.
133 ; habitats, iv. 139 ;
Reindeer Moss, iv. 138 ; re-
production of, iv. 133, 134.

Lichens, iv. 79, 102, 132, 134,
139, 177, 197 ; on oak twig,
iv. 133 ; rock-encrusting, iv.
136 ; Trumpet or Cup, iv.
134-

Life and growth of seedlings,
iii. i.

Life-history of winter moth, v.
181 ; of fishes, i. 148 ; of
fungi, v. 181 ; of pests, pre-
ventive treatment of, v. 184 ;
of eel, i. 149.

Lifting and dividing, figures of,
v. 122.

Light, influence of, iii. 33.

Lignite, iv. 189.

Ligule of grass, v. 58.

Lilac, v. 167 ; buds of, iii. 40, 43,
46, 59 ; propagation of, iii.
118, 119.

Liliaceae, iv. 70.

Lilies, bulbils of, iii. 63.

Lilium, species of, v. 114, 171.

Lily, bulb, iii. 70.

Lily-of-the-Valley, iv. 160, 196.

Limacidae, ii. 54, 55.

Limax, species of, ii. 54, 55,

211.

Lime, iv. 172.

Limestone, v. 19 ; bedded, illus-
tration of, vi. 117 ; crin-
oidal, vi. 117, illustration
of, vi. 115 ; joints of, vi. 117,
illustration of, vi. 129 ; Silu-
rian, vi. 117, illustration of, vi.
117; stratification of, vi. 117,
illustration of, vi. 212 ; valley
of, vi. 117, illustration of, vi.
168, 190; associations, v. 15 ;
Heath, iv. 204, 205 ; pasture,
v. 66.

Limna2a, spawn of, ii. 191.

Limpet, ii. 143, 170, 171, 175.

Ling, iv. 13, 14, 191, 192, 204,
v. 36 ; common, iv. 202 ;
flower of, iv. 191 ; highest
altitude of, iv. 197.

Linnaeus, observations of, iii. 54.

Linum, species of, v. 67, U5>
171.

Lions in Britain, ii. 221.

GENERAL INDEX

235

Liveries and their meaning, i.

59, 65, 89.
Liverwort, iv. 100, 102, 117,

118, 125, 132, 134, 140, 177,

179, 180, 189, v. 38 ; water-
pitchers of, iv. 123 ; fruits

of, iv. 117 ; sperm -pockets, iv.

118 ; pocket-like cavity, iv.

117 ; air-chambers of, iv. 118 ;

lobes of, iv. 1 1 8 ; species of, iv.

I2i, 122, 124.

Living fish, first study, i. 136.
Lizard, i. 109, in, ii. 214; species

of, i. in, 217.
Lizard, sand, i. no.
Loach, ii. 197.
Loam, v. 79.
Lobelia, v. 25, 120, 170.
Lobster, ii. 145, 146.
Locusts, i. 176.
Loganberries, v. 148, 161.
Loligo, ii. 137.
London Pride, iii. 166, iv. 69 ;

life-history of, illustration of,

iii. 192.
London, length of days at

equinoxes, vi. 65.
Long-leaved Sundew, v. 32.
Long shadows, vi. 72.
Long twilight of summer, vi. 68.
Looper, i. 186, v. 184.
Loosestrife, Yellow, v. 45.
Lords and Ladies, iii. 55, 78.
Lotus, sleep movements, iii. 56.
Lotus, species of, iii. 170, v. 115.
Louse wort, iv. 181.
Love-in-a-mist, v. 169.
Lower greensand, v. 188.
Lower vertebrates, i. 151-159.
Lowland oak woods, iv. 159 ;

plants above 2000 feet, v. 70 ;

of Scotland, culture of, vi.

32 ; of Scotland, marshes of,

vi. 35-

Low-lying alluvial soils, v. 217.
Lucerne, v. 79, 216.
Lucky Proach, ii. 130.
Lumpsucker, ii. 131, 132 ;

Sectoral and pelvic fins of,
. 183 ; young of, ii. 132.
Lunar calendar, vi. 89.
Lung-breathers, ii. 191.
Lungs of amphibians, i. 120;

of birds, i. 77 ; of mammals, i.

23«

Lupin, v. 80, 169, 179.
Lupines, sleep movements of,

iii. 56.

Lupinus, species of, v. 115.
Lurid Boletus, iv. 130.
Lychnis, species of, iii. 188, 190,

v. 26, 84.

Lycoperdon, iv. 141.
Lycopodium clavalum, iv. 98,

99, 100, 197, 202.
Lycopodium powder, iv. 98.
Lycopods, iv. 94, 98.
Lyme grass, v. 5.

Machinery and methods of, vi.

38.

Mackerel, i. 145 ; sky, vi. 6.
Madonna lily, v. 171.
Madrepore of starfish, ii. 180.
Magnetic declination, vi. 78.

Magpie, ii. 210.

Maize, iii. 4, 29, 32 ; starch of,

iii. 50 ; development of seed,

iii. 7, 9, 12.
Mallow, v. 6.
Maltese terrier, i. 26.
Malva, species of, v. 170, 171.
Mammal skeleton, i. 20.
Mammalia, i. 55 ; flight in, i.

45. 53. 54-
Mammals, i. 158, 159, ii. 200,

220 ; coloration of young, i.

59, 65 ; clothing of , 1. 55 ; of

the moor, ii. 213.
Mammoth, hair-clad, i. 66.
Mammoths in Britain, ii. 221.
Man, environment of, vi. 39 ;

skeleton of, i. 33, 34, 35, 44 ;

foot of, i. 35.
Manetti stock, v. 172.
Mangel Wurzel, v. 17.
Mangolds, v. 84 ; typical crop of,

v. 214.

Man-of-war, Portuguese, ii. 185.
Mantle of cloud, vi. 4.
Manure for vegetable culture,

v. 127, 128, 129 ; for cuttings,

v. 120.
Manures on grassland, effect of,

v. 58.

Manuring, v. 87.
Manx-shearwater, i. 84.
Maple, distinguished from

sycamore, iii. 39.
Maps, Geological, vi. 159 :

Ordnance, illustration of, vi.

139 ; how to make them, vi.

131, 150 ; use of, vi. 130.
Marble gall, ii. 18, 212.
Marbled angler, i. 148.
Marchantia, with fruits, iv. 116,

120 ; with gemma cups, iv.

116.

Marestail, ii. 92.
Marigold, Corn, v. 81, 179;

marsh, iv. 199.
Marine aquarium, ii. 78 ;

animals of, ii. 128-168 ;

plankton, ii. 188 ; worms, ii.

158-161.
Market of London, supplies of,

vi. 15.
Marl, v. 79.
Marram grass, v. 4, 5, 6, 7 ;

modifications of structure,

v. 8.

Mars, snow-caps, vi. 6.
Marsh Fern, v. 21.
Marsh-hen, ii. 190.
Marsh Horsetail, iv. 97 ;

Marigold, iii. 104 ; diagram

of, iii. 105, iv. 199, v. 38 ;

Pea, v. 38 ; Pennywort, iv.

203, v. 35 ; plants, iv. 193,

v. 28 ; seeds conveyed by

cattle, v. 52 ; Samphire, iii.

5i» v. 9.

Marshes, draining of, vi. 35.
Marshwort, v. 39 ; branch

figured, v. 39.
Marsupials, ii. 220.
Martins, ii. 207.
Mastiffs, i. 26.
Mat Grass, iv. 204.
Matches, iv. 138.

Materials for collecting plants,

iii. no.
Matterhorn, characteristics of,

vi. 44.

May-flies, ii. 109, 195.
May Hill Common, iv. 207.
Meadow Buttercups, propaga-
tion of, iii. 6 1 ; Clovers, v. 28 ;

coloured illustration of, v. 64 ;

Foxtail, v. 59 ; Grass, v. 57,

58, 64; land, ii. 200, 203; moor,

v. 70 ; Pipit, ii. 203, 207 ;

Saxifrage, iv. 198 ; figured,

v. 62 ; Sweet, iii. 76, 83, iv.

158, 161, v. 40, 41, 54.
Meadows and pastures, vegeta-
tion of, v. 56.
Mealy-bugs, ii. 15.
Mealy Guelder Rose, y. 216.
Measurements of rainfall, vi.

23» 25-

Measures of time, vi. 75, 79.
Mechanical transport, vi. 38,

v. 77, 115.
Mediterranean, rainfall of, vi.

38.

Medlars, v. 148.

Medusoids, i. 158, ii. 185, 186.
Melilot, sleep movements, iii. 56.
Merganser, i. 91, 92.
Mermaid's hair, ii. 84 ; purses, ii.

176, 177-

Mersey, estuary of, vi. 15.
Mesophytes, iv. 182, 183.
Metamorphosis, i. 188 ? of

dragon-fly, ii. 114.
Meteorology, observations on,

vi. 51.
Meteorological instruments, vi.

25 ; observations, exactness

of, vi. 23.
Mice and trees, iv. 146 ; and

acorns, 146.

Michaelmas Daisy, v. 171.
Midges, small, ii. 217.
Midriff, i. 23.
Mignonette, v. 169, 179.
Migration of birds, i. 104, 105,

106, 107 ; of fishes, i. 136 ;

of plants, v. 20.
Milchdieb (milk thief), iv. 181.
Mildews, iv. 125.
Milk-teeth, i. 21 ; wort, iv. 207,

v. 66.

Miller's Thumb, ii. 104, 197.
Millipede, ii. 14, 35 ; breeding

of, ii. 37 ; stink-glands of,

ii- 37;

Mimic icebergs, vi. 47.
Mimosa, iii. 55, 56 ; sleep

movements, iii. 55.
Miniature icebergs, vi. 48.
Minnow, i. 136, ii. 104, 197, 198.
Mire-hen, ii. 190.
Missel-thrush, i. 83.
Mist, formation of, vi. 2.
Mist-laden atmosphere in rela-
tion to the sun, vi. 55.
Mistle-thrush, ii. 210.
Mistletoe, iv. i, 35, 39, 40, 69,

78 ; parasitism of, iii. 31 ;

dispersal of berries of, iii. 31 ;

illustrated, iv. 40, 44 ; and

dodder, iv. 38 ; seedling of,

iii. 31-

236

THE BOOK OF NATURE STUDY

Mists in vicinity of icebergs,

vi. 48.

Mites, ii. 17, 198.
Mixed woods, iv. 151.
Mnium, species of, iv. 105, 106,

108.

Mohammedan calendar, yi. 88.
Moisture, effect of, hi. 15,

iv. 1 60 : observations on,

vi. 1 8 ; of the air, amount of,

vi. 2.
Mole, i. 46, 48, ii. 190, 202 ;

habits of, i. 47 ; ii. 206 ;

hills, i. 47 ; shovel-like

hands, i. 47.

Moles, optic nerves of, ii. 208.
Molinia, species of, iv. 159, 200,

204, 205, v. 38.
Molluscs, i. 158, ii. 105, 137,

144, 176, 184.

Monkswood, figure of, iii. 104.
Monocotyledon, ii. 92.
Monocotyledons, ii. 89, iii. 20,

iv. 69, v. 38.
Monocultural, vi. 32.
Monsoon regions of Far East,

vi. 38, 39.
Montbretia, corm, root, and

underground stem of, iii. 65.
Months in which rainfall is

heavy, vi. 25.
Moon, crescent after sunset, vi.

87 ; in relation to tides, vi.

89 ; light, vi. 85 ; Moham-
medan observations of, vi. 88 ;
movement from west to east,
vi. 86, 87 ; movement south
to north, vi. 86 ; number of
days between each, vi. 88 ;
reflected light of, vi. 86 ;
seas or plains of, vi. 86 ;
waxing and waning, vi. 89,

90 ; wort, iv. 93, 98.

Moor, excursion to, vi. 35 ;

grasses, iv. 186, 188 ; mat-

grass, iv. 182, 200, 201 ; hen,

ii. 190, 214 ; land, ii. 200,

213, iv. 188.
Moss, Broom-fork, iv. 158 ;

Campion, iv. 197 ; Fern, iv.

179 ; Four-toothed, iv. 107 ;

gall, ii. 205 ; Hair, iv. 157,

179 ; Irish or Carragean, v.

10 ; \Vavy Hair, iv. 114.
Mosses, iv. 79, 100, 121, 125,

132, 155, 158, 177, 178, i79»

180, 188, 189, 195, 197, v.

21, 23, 70 ; side-fruiting, iv.

115 ; top-fruiting, iv. 107 ;

wall-inhabiting, iv. 109.
Moth, injurious, v. 180 ; small

ermine, figured, v. 182.
Mother Carey's chicken, i. 83.
Moths, v. 33.
Mould-like fungi, iv. 141 ; with

two fruits, magnified, iv. 141.
Moulds, iv. 125, 141.
Moults of young birds, i. 88.
Mount Blanc, de Saussure's

excursion on, yi. 9, 10 ;

temperature of, vi. ii.
Mountain ash, arosaceous tree,

iv. 160 : buckler - fern, iv.

178 ; chains, meaning of,

vi. 216 ; growth of, il-

lustration of, vi. 178 ; hare,
i. 63 , ii. 216 ; pastur-
ages, destruction of, vi. 36 ;
points on the surface of, vi.
51 ; side, ii. 200, 216 ;
St. John's -wort, iv. 160 ;
temperature of, vi. 3.

Mouse-ear hawkweed, iii. 55,
76, v. 74.

Mowing meadow, v. 64.

Mucor, iv. 141.

Mud-haunting animal, ii. 168.

Mud, how formed, vi. 93, 102 ;
line, meaning of, vi. in ;
plants of estuaries, v. i ;
rush, v. 3.

Muddy streams, vi. 46.

Multicellular hairs, iii. 81.

Multiplication of plants, v. 113.

Mus, species of, ii. 189, 196, 207.

Mushroom, iv. 133 ; common,
iv. 126 ; like toadstools,
iv. 127 ; spawn, iv, 125, 126.

Mussel, ii. 138 ; byssus of, ii.
66, 138 ; diagram of glochi-
dium, ii. 66, 67 ; diagram of
section, ii. 63 ; eggs of, ii. 66 ;
exhalant siphon, ii. 138 ;
foot of, ii. 63, 138 ; parasitic
young of, ii. 192 ; mantle
of, ii. 139 ; sensory organs
of, ii. 67 shell teeth of,
ii. 67 ; pearls of, ii. 191, 192.

Mustard, iii. 21 ; and cress,
exalbuminous seeds of, iii.
7, 12.

Mycelium, iv. 133.

Myriopods, i. 158, ii. 35.

Naiadacese, ii. 88.
Naiads, ii. 200, v. 24.
Naked buds, iii. 43.
Narcissus, varieties of, iii. 114 ;

v. 172-179 ; bulb and

flower structure, iii. 63.
Narcissus, species of, iii. 156,

160, v. 177.
Nardus, varieties of, iv. 182-

204.
Nasturtium, varieties of, iii. 59,

v. 42, 179 ; illustration of,

iii. 72.

Nautical almanack, vi. 64, 76.
Navigation in relation to mists,

vi. 48, 76.
Neap tide, vi. 89.
Nectarine, v. 148.
Nekton, ii. 184.
Nematodes, ii. 199, 200.
Nemertea, ii. 161.
Nemophila, v. 169.
Nereis, ii. 179.
Nerittna, ii. 191.
Nerve physiology, ii. 209.
Nesting places, i. 100.
Nestling birds, i. 68-72.
Nests of birds, i. 98-104.
Nettle-leaved campanula, iii. 32.
Nettles, iii. 75, iv. 36, 185.
Newfoundland dogs, i. 26.
Newt, eggs of, i. 123, ii. 194 ;

habits of, i. 120-123.
Nightjar, type of beak, i. 92.
Night-shade, enchanter's, ii. 209.
Nine-eye, i. 152.

Nocturnal birds of prey, i. 83.
Nodes of flowering plants, iii.

92.

Non-flowering plants, iv. 178.
Noon-tide shadow, vi. 75, 82.
North Pole, ice and snow of,

vi. 6.
Norway lobster, ii. 146 ; rat,

i. 30.

Nudibranchs, ii. 144, 170.
Nuthatch, ii. 210 ; method of

feeding on nuts, iv. 149.
Nuts of hazel, iv. 149.

Oak, life-history of, ii. 212,
iii. 3, 86, iv. 144, 145, 147,
148, 150, 157, 162, 164, 172,
179, 208, v. 215 ; illustrations
of, iv. 59 ; varieties of, iv.
152 ; flowers of, illustrated,
iv. 152 ; apple gall-fly, ii. 18,
19; fern, iv. 87, 179 ; galls,
ii. 212 ; spangles, ii. 212.

Oarsmen, ii. 15.

Oarweeds, v. 10.

Oat fields, v. 87 ; belt, v. 87 ;
grass, v. 56.

Oats, iii. 12, 25, 29, 30, v. 78,
86, 88.

Observatory hives, ii. 8.

Octopus, ii. 137.

Olive tree, iv. 165.

Onion, iii. 10, 63, 70, v. 116,
130, 141 ; history and cul-
tivation of, v. 140.

Ooze, composition of, vi. in.

Ooze, globigerina, figure of, vi.
101.

Open sea, pelagic fauna of, ii.
169, 187.

Openbill, type of beak, i. 92.

Open-field system, v. 71, 72.

Opium poppy, iv. 24.

Orchids, iii. 31, 106, 199, iv.
71, 74, 76, 178, 186, v.
68, 216.

Orchis, v. 46, 63.

Orchis maculata, iii. 198, 199,
iv. 69, v. 68.

Origin of soils, v. 188-195.

Osmunda regalis, iv. 89, 93.

Ostrich, figure of foot, i. 95.

Otter, ii. 196.

Otter-shells, ii. 128.

Outcrop, meaning of, vi. 159.

Outer fringe of sand hills,
illustration of, v. 4.

Ovary, two-celled, iv. 148, 160.

Owl-parrot, i. 86 ; owl, snowy, i.
83, ii. 210, ii. 219.

Ox, horns of, i. 38 ; stomach of,
i. 38 ; teeth of, i. 41.

Oxen, i. 32, 39.

Ox-eye daisy, v. 81.

Oxlip, iv. 209 ; pastures of
Leicestershire, v. 65.

Oyster-catcher, ii. 170, 171, 196.

Oysters, ii. 68, 170.

Paddles of penguins, i. 86.
Paddle-worm, leafy plates of,

ii. 159-

Faeony (the Bride), v. 171-
Pangolin, African, i. 57.
Pansies, iii. 124, v. 76, 77, 176.

GENERAL INDEX

237

Papilionaceac, v. 144.
Pappus, iii. 80.
Paradise stock, v. 150.
Parasites, iv. 141, 180.
Parietal bone, i. 21.
Paris, time of, vi. 82.
Parrot, i. 92 ; figure of foot, i. 95.
Parsley, beaked, v. 60, 61 ;

cultivation, v. 143.
Parsnip, history and cultiva-
tion of, v. 137 ; varieties of,

iii. 170, v. 114, 126, 138.
Passeres or perching birds, i. 80.
Pasture associations, v. 20 ; land,

v. 64; grasses, iv. 186.
Patella vulgata, ii. 170, 175.
Peach, v. 148.
Pear, cultivation, life-history

and varieties of, iv. i, 48, 60,

v. 126, 148, 150, 160, 183 ;

blossom of, illustrated, iv.

48.
Peas, life-history, cultivation,

and varieties of, iii. 4, 7, 8, 9,

10, 12, 13, 21, 32, 54, 104,

114, iv. i, 24, 28, 29, 30,

76, v. 78. 113. 130, I44» 145,

147, 148.
Peat-bog, iv. 100, 144, 188,

189, 190, 191.
Peat soils, v. 218.
Pebble beaches, v. 18.
Peewit, ii. 214.
Pelargoniums, iii. 52, v. 117.
Pelecypods, ii. 69.
Pelican, i. 92, 94, 95.
Pellia, iv. 116, 118, 121, 134,

135-

Pendulous carex, iv. 194.
Penguins, i. 86, 159.
Peninsula of the Wirral, vi. 14.
Perch, i. 136, ii. 186, 197.
Peregrine falcon, ii. 217.
Perennial clover, v. 58 ; plants,

iii. 95 ; rye grass, iii. 166, 180 ;

life-history of, flower figured,

iii. 181.

Perianth, iv. 148.
Peristome of four teeth, iv.

in ; of hair moss magnified,

iv. 114; of screw mosses,

iv. no.
Periwinkles, ii. 105, 128, 142,

143, 144, 170, 175, 182, iv.

24. 69, 73, v. 167.
Petrels, i. 83, 84.
Petromyzon, species of, i. 151,

155. 197. "• 197-
Petty spurge, figured, v. 83, 86.
Pheasant, i. 66, 80, ii. 210, 212.
Pheasant's eye narcissus, flower

figured, iii. 160.
Phlox (Coquelicot), v. 171 ;

Drummondii, v. 169.
Pholas, ii. 140.
Phosphates and potash, v. 208,

209.
Phragmites communis, iv. 177,

v. 29, 37, 38, 45. 76.
Phyllodoce lamelligera, ii. 159,

175-
Physical environment, vi. i ;

geography, basal facts of,

vi. 22.
Phytophthera infestans, v. 185.

Pied wagtail, ii. 207.

Pigeon, domesticated varieties

of, i. 76.
Pignut, iii. 70.
Pigs, domesticated breeds of,

i. 40, 64 ; skull, teeth, and

tusks of, i. 20, 39, 41.
Pike, i. 136, ii. 197.
Pillwort, v. 21, 22, 23.
Pimpernel, v. 86, 217.
Pincushion starfish, ii. 180.
Pine, cultivation and life-
history of, iii. 43, 87, iv.

62, 63, 66, 67, 145, 163, 177,

179, 207 ; woods, iv. 178.
Pink, varieties of, v. 121, 171,

176, 179-

Pinus sylvestris, iii. 18, iv. 62.
Pipe-fish, i. 139 ; eggs of, ii.

136.

Pipewort, v. 26.
Pipit, meadow, ii. 207.
Pistillate flowers, iv. 148, 160.
Pisum, species of, iv. 24, 30,

v. 115, 146.
Pitcher-plant, iii. 73.
Plaice, i. 137, 142, ii. 135.
Planarians, ii. 188, 199, 200.
Plane, iv. 171.
Plankton, ii. 184.
Planorbis, ii. 107, 191.
Plant associations, iv. 177, 187.

205, 209, v. i, 6, 19, 53, 87.
Plant (flowering) life-history of,

iii. 109 ; and animal life

as affected by weather, vi. 5 ;

ecology, iv. 180 ; formations,

v. 4, 19, 20, vi. 36 ; bugs,

ii. 203 ; lice, ii. 15, 16 ;

life, iii. i, vi. 35.
Plantago, species of, iii. 205,

v. 14, 115.
Plantain, iii. 166, 205, iv.

69, 76, v. 7.

Planting, notes on, v. 152.
Plants, cultivation, life-history,

and varieties of, ii. 82, iii.

i, 48, 51, 54, 71, 95. 112,

v. 20, 23, 79. i7o, 171. 176,

vi. 33. 37-
Plesiosaur, i. 109 ; illustration

of, vi. 202.

Pleuronectida3, ii. 134.
Ploughing, v. 87.
Ploughman's spikenard, v. 42.
Plum mushroom, iv. 128.
Plumages of birds, nestlings

and seasonal, i. 72, 81, 87,

88, 89.

Plumose anemone, ii. 163.
Plums, cultivation and varieties

of, iv. 77, v. 117, 148, 151,

160.
Plumule, structure of, iii. 13,

33-
Poa, species of, v. 58, 63, 114,

US-
Poinsettia, scarlet bract of,

iii. 55-

Pointer, i. 28.

Poison gland of snakes, i. 117.
Poisoner, iv. 128.
Polar bear, ii. 219.
Polar night and day, vi. 67.
Pollard willows, v. 46.

Pollen grains, iii. 78 ; shedding,
iv. 72 ; tube, iii. 78.

Pollination, iii. 77, iv. 70.

Polyanthus, v. 179.

Polygonum, species of, v. 47,
US-

PolypetalaB, iv. 68.

Polypody, iv. 86, 87, 89, 158,
179-

Polytrichum, species of, iv.
106, 112, 114, 158, 179, v.
36.

Polyzoa, ii. 125, 161, 179.

Pond mussels, ii. 192 ; skaters,
ii. 194, 195; tortoise, life-
history of, ii. 94, 95, 96,
99'

Ponds, vegetation of, v. 26.

Pondweeds, ii. 88, v. 22, 27,
29.

Poodles, corded, i. 26.

Poor man's weather-glass, v. 83.

Poplar, iii. 40, 43, iv. 38, 147,
1 80, v. 46.

Poppy, cultivation, illustration,
life-history, and varieties of,
iv. i, 21, '22, 23, 24, 73. 74.
76, v. 10, n, 76, 80, 86,
171, 210.

Porcelain crab, ii. 147, 148, 149.

Pore toadstools, iv. 128, 130.

Porpoises, i. 20, 48, 53, ii. 95.

Portuguese man-of-war, ii. 185.

Position of feet during flight,
i. 87.

Potamogeton, species of, ii. 88,
91, v. 22, 27, 29, 88, 92.

Potato, cultivation, life-history,
and varieties of, iii. 50, 60,
67, 70, 86, 114, iv. i, 6, 7,
9, 69, v. 78, 80, 116, 126,
130, 132, 133, 134, 135, 185,
186.

PotentUla, species of, iii. 61,
iv. 159, 206, v. 171.

Pot-herb, iii. 184.

Practical geography, introduc-
tion to, vi. 76.

Practical observations on culti-
vation, v. 86.

Practical work, iii. 31, 109, v. 17.

Prawns, ii. 150, 151.

Precipitation, vi. 18-30.

Prehistoric age, iv. 144.

Pressure, variations of, vi. 8, 16.

Prickly-skinned animals, ii. 153.

Primary quills, i. 85.

Primeval forest, iv. 144, 145.

Primrose, iii. 115, 128, 129,
iv. 69, 158, 186, 203, v 25.
41, 210, 215 ; description of,
130 ; pin-eyed, thrum-eyed,
long - styled, diagrams of,
131 ; diagram of, iii. 105.

Principles of cultivation, v. 218-
224.

Privet, iv. 165, 184, v. 73,
118, 119.

Properties of soils, v. 195-208.

Propagation by cuttings, figure
of, v. 120 ; by division, v.
122 ; method of, v. 118-124.

Protective covering of vegeta-
tion, vi. 35 ; resemblances,
i. 60, ii. 210.

238

THE BOOK OF NATURE STUDY

Prothalli, male and female,

iv. 84, 88, 96.
Protococcus and coloration of

water, v. 53.

Protopterus, habits of, ii. 100.
Protozoa, ii. 126, 185, 188, 200.
Proventriculus of birds, i. 77.
Prunus, species of, v. 148, 160.
Psamma arenaria, iii. 61, v.

4. 5. 7-

Psychology, comparative, ii.
209.

Ptarmigan, summer and winter
plumage of, i. 62, ii. 216, 217.

Puff-ball, iv. 131, 141.

Pumpkin, iii. 10, 12.

Pupation, i. 186.

Purpurea, ii. 170.

Purple dead nettle, v. 30 ; fork-
moss, iv. 109 ; laver, ii.
84, v. 10 ; loosestrife, v. 40,
41, 52 ; molinia, iv. 200, 209 ;
sea-snake, ii. 179 ; tipped
sea-urchin, ii. 153, 180.

Purse sponge, ii. 179.

Purslane, sea, v. 10, ii.

Pyrola, species of, iv. 145.

Pyrus, species of, iv. 48, 50, v.
148.

Quaking grass, v. 59, 60. 62.

Quarry in theHythe beds, illus-
tration of, v. 1 88, showing
glacial drift, 192.

Queen wasp hibernating, i. 178.

Queens and drones, ii. 204.

Quercus, species of, iii. 37, iv.
152, 164.

Quill or calamus, i. 70, 71.

Quillwort, v. 21—24, 29.

Quince stocks, v. 160.

Rabbit, habits and varieties of,

i. 28, 30, 32, ii. 201, 221, iv.

146.

Racehorse, i. 39.
Racemose, diagrams of, iii. 98.
Radicle, growth in the soil, iii.

12, 13, 16, 18.
Radiolarians, ii. 184.
Radish, iii. 7, 12, 21, 29, 32, 34,

35, v. 17, 76, 86, 140.
Radula, iv. 121, 140.
Ragged Robin, iii. 83, 188, 191.
Ragwort, iv. 185, 210, v. 7, 86.
Railways, in relation to time,

yi. 80.
Rain, in relation to wind, vi. 1 7 ;

effect on landscape ; illustra-
tion, vi. 36.
Rainbows, vi. 62 ; clouds,

formation of, vi. 19 ;

fall, average at the various

stations, vi. 23, 26, 27, 28, 29,

30, 32, 35. 36, 37. 38, 39 ;

gauge, vi. 23, 24, 40, 43-
Rainy season, vi. 38.
Ramadan. Mohammedan feast

of, vi. 88.
Rana, species of, i. 122, 123,

128, ii. 96.

Ranunculaceae, iv. 68, v. 38.
Ranunculus, species of, iii. 60,

66, 89, 90, 93, 96, 115, iv.

186, 187, v. 36, 48, 62, 74, 84.

Rape, v. 78.

Raphnus, species of, v. 17, 140.

Raspberries, cultivation, life-
history, and varieties of, iii.
62, 66, v. 117, 126, 148, 131,
160.

Ratel, of Africa, i. 60.

Rats, varieties of, i. 30, ii. 196,
216.

Rattle, red and yellow, iii. 31 ;
snake, habits of, i. 116, 119.

Rattles, iv. 180, 181.

Raven, i. 80, ii. 217.

Razor-shells, ii. 128.

Razor-strop fungus, iv. 130.

Recapitulation theory, ii. 101.

Red Campion, life-history and
illustration of, iii. 166, 188,
190, 191, iv. 69, 71, 73, 74,
76, 161, v. 74 ; clover, v.
58 ; cup-moss, iv. 138 ;
currants, v. 151 ; deer, i. 32,
67, ii. 201, 213 ; grouse, ii.
213, 217 ; poppy, iv. 21, 68,
69 ; rattle, iv. 181, v. 36 ;
seaweeds, v. 10 ; throated
diver, ii. 217 ; wing, i. 83,
vi. 5 ; wood-ant, ii. ii.

Reed, iv. 177, 193, v. 27, 28,
45. 76 ; association, v. 29 ;
bunting, ii. 190 ; maces, v.
44, 45 ; poa, v. 45.

Reeves, plumages of, i. 89.

Regular flowers, iii. 106.

Reindeer in Britain, ii. 221 ;
moss, iv. 139 ; moss lichen,
iv. 138.

Reproduction and dispersion
of aquatic plants, v. 49.

Reproduction, vegetative or
asexual, iii. 96.

Reproductive organs of flower-
ing plants, iii. 95.

Reptiles, i. 68, 109-119, 158,
159, ii. 170, 200, 218.

Respiration, iii. 53.

Rest-Harrow, iii. 76, 83, v. 214 ;
figured, v. 69.

Rhinoceros, i. 40, 57 ; in
Britain, ii. 221.

Rhizome, iii. 60, iv. 175, 182.

Rhizopods, ii. 188.

Rhodites, species of, ii. 205.

Rhododendrons, v. 217.

Rhynchota, ii. 195, 203.

Rhythm of the seasons, vi. 51.

Ribbon-ferns, iv. 80 ; worms,
ii. 161, 179.

Ribes, species of, v. 148, 161,
162.

Ribwort plantain, iii. 155, 166,
205, 208 ; life-history of, iv.
72 ; illustration of, v. 14, 60,
61.

Rice, contain starch, iii. 50.

Ringed plover, method of
covering its eggs, i. 100.

Ripple marks, on sandy sea-
shores, v. 17; illustration of,
vi. 114.

Rivers, ii. 169, v. 54, 193,
vi. 106, 109, up, 170, 179.

Riverside birds, ii. 196.

Roach, ii. 197.

Road, lessons of, vi. 93-97.

Robin, i. 82, 83.

Robin's pin-cushion, ii. 205.

Rockcress, v. 30.

Rocks, iv. 136, 208, v. 112,
vi. 115, 123, 127, 128,
189, 190, 204, 218 ; folded
illustration, vi. 120 ; intru-
sive illustration, vi. 121 ;
stratification of illustration,
vi. in.

Rodents or gnawing animals,
i. 28.

Roe-deer, ii. 213.

Roman snail, ii. 49, 56.

Rooks, ii. 210.

Root, root crop, and root
systems, iii. 12, 14, 17, 18, 22,
26, 28, 31, 32, 68, 73, 91, 92,
vi. 31.

Rosaceae, v. 60.

Rosaceous trees, bud scales of,
iii. 43.

Rose, varieties of, iii. 71, 77, 82,
iv. i, 17, 52, 69, 72, 73» 74, 78,
156, 158, v. 40, 55, 72, 73,
117, 118, 172, 173, 176.

Rosebay, v. 72.

Rosemary, v. 176.

Rosette plants, cylindrical
leaves of, v. 23.

Rotation of crops, v. 78, 87 ;
of movement, vi. 75 ; of the
earth, vi. 81.

Rothampsted Experimental
Station, v. 58, 60, 77, 208,
209.

Rotifers, ii. 126, 187, 188.

Round-leaved sundew, iv. 41,
42, v. 32.

Round-mouths, i. 155, 158.

Rowan, iv. 160.

Royal fern, iv. 89, 93.

Ruff and reeve in autumn, plum-
ages of, i. 86, 89.

Ruminant, stomach of, i. 38.

Runner, iii. 96, v. 117.

Rural economy, ii. 209.

Rushes, iv. 182, 183, 192, 196,
199, 201, 202, v. 28, 33, 52,
67, i94» 217-

Russian steppes, winter scenes
of, vi. 5.

Rusts, iv. 125.

Rye, v. 78 ; grass perennial, iii.
166, iv. 70, v. 57, 217.

Sacculina, ii. 182.
Saddle-back fungus, iv. 154.
Saffron crocus, iii. 161 ; plant

figured, iii. 163.
Sage, iv. 74-
Sagitta, ii. 186.
Sagittaria, v. 45.
Sahara desert, vi. 31.
Sainfoin, v. 79, 216.
Salad Burnet, iv. 206 ; wind

pollinated, v. 60, 61, 66.
Salad plants, mustard, cress,

radishes, lettuces, v. 130.
Salamanders, i. 120.
Salicornia plant association,

illustration of, v. 2.
Salix, species of, iv. 46, 100,

v. 2, 8, 46.
Sallow, iv. 47, r6i.

GENERAL INDEX

239

Salmon, i. 136, 147 ; colour
changes of, i. 149 ; early
development of, i. 149 ; eggs
of, i. 148, ii. 197 ; habits of,
i. 149, ii. 197.

Salsola-Cakile plant association,
v. 7.

Salt-loving plants, v. 15.

Salt marsh pasture, v. 7, 20.

Salt spurrey, iii. 84.

Saltwort, iii. 51, 84, v. 5, 6, 7.

Sand-borers, ii. 128 ; burrowers,

11. 129 ; colour of, vi. 34 ;
crab, ii. 173, 181 ; dab, ii.
135 ; dunes, v. 5, 18, 20,
vi. 33 ; formation of, vi. 102 ;
hills, ii. 200 ; hopper, ii. 108,
151, 170, 171, 182 ; hopper
feigns death, ii. 173 ; lizard,
i. no, in ; lyme grass, iii.
61, v. 5, 6 ; mason, ii. 159 ;
mason, gills, tentacles, hooks
of, ii. 159, 160 ; pipers, ii.
170 ; pride, i. 151 ; reed, vi.
34 ; sage, v. 6 ; spurry, v.

12. 29, 80, vi. 34 ; star,
habits of, ii. 156 ; star,
little, ii. 156 ; stone, v. 19 ;
stone, new red, v. 192 ;
wort, v. 6, 14, 15 ; wort
spurrey, v. 81, 86 ; worts, v.
n.

Sand and gravel, relation of,
figured, vi. no, 114.

Sand-dunes and vegetation,
figured, vi. 23.

Sandstone, Old Red, figured,
vi. 116; jointed, figured, vi.
128.

Sandy pasture, v. 69 ; sea-
shores, practical work on, v.
17 ; water-holding capacity
of, vi. 34 ; soils, typical
plants of, v. 216 ; soils, v.
215-

Saprophyte, iv. 182.

Saprophytes, iv. 180, 181.

Sargasso Sea, iv. 177.

Savoy, v. 130, 131 ; sprouts —
Drumhead, Perfection, v.
132-

Sawfish, i. 146.

Sawflies, ii. 10 ; injurious,
v. 182 ; time of hatching,
v. 184.

Saxicava, ii. 140.

Saxifragagranulata, iii. 192, 194,
195, v. 62.

Saxifrage, meadow, v. 62 ;
white meadow, iii. 166, iv.
69.

Saxifrages, iv. 69, 197, v. 176.

Scabious, iv. 207, v. 86, 179 ;
cinquefoil, iv. 206.

Scale-insects, ii. 15, v. 182.

Scales of buds, iii. 38.

Scallops, ii. 139.

Scaly spleenwort, iv. 90.

Scar, Hardrow, figured, vi.
178.

Scarlet pimpernel, v. 82 ;
runner, iii. 58, 59, v. 113,
130, 145, 146 ; runner, illus-
tration of, iii. 72.

Scentless mayweed, v. 12, 14.

School garden, v. 89-95, 144.

Scillas, v. 172, 177.

Scirpus lacustris, iv. 177, v.
28, 29, 45-

Scissor-bill, feeding habits, i.
91. 92-

Scorpions, ii. 108.

Scotch fir, exposed roots of, iii.
18.

Scotland, excessive rainfall, vi.
28.

Scots pine, illustrations of, iv.
62, 63, 64, 70, 145, 162, 163,
171 ; wood, illustration of,
iv. 156.

Screw mosses, peristomes of, iv.
109, no.

"Scree," Wastwater, vi. 100.

Scripture-wort, vi. 136.

Scrophulariacece, iv. 69, v.
82.

Scurvy grass, iv. 197, 198, v.
3, 12, 14, 15-

Sea-anemones, i. 158, ii. 162-
168, 170, 179; arrowgrass,
v. 2, 3 ; artemisia, v. 15 ;
aster, v. 2, 12, 15 ; beet, v.
12, 13 ; butterflies, ii. 186 ;
campion, v. 12, 13 ; cucumber,
habits of, ii. 157 ; cucumbers,
i. 158, ii. 153, 157 ; fir, ii.
164, 165, 178 ; grass, ii. 84;
holly, v. 10, ii, 15; holly,
bracts of, iii. 55 ; horses, i.
139, ii. 136 ; lavender, v.
13 ; lettuce, ii. 84, v. 84 ;
lilies, ii. 153 ; lions, i. 51 ;
mat, ii. 161, 176, 179 ; mat-
grass, iii. 6 r ; milkwort, v.
3, 4, 52 ; of crises, vi. 86 ;
pens, ii. 126, 176 ; pink, v.
12, 13 ; plantain, v. 4, 9, 12,
14, 15 ; purslane, v. 5, 6, 10,
n ; rocket, v. 5, 7, 15 ;
samphire, figure of, v. 13 ;
scirpus, v. 29 ; scorpion, ii.
130^ 131 ; slater, ii. 176 ;
slug, spawn of, ii. 141, 166 ;
slugs, ii. 141, 170 ; snakes,
i. 159 ; spiders, ii. 152,
170, 182 ; spurge, v. 46 ;
spurrey, v. 4 ; squirts, i. 151,
156, ii. 170 ; starwort, v. 2,
4 ; transporting action of, vi.
102 ; thrift, v. 3, 15, 16 ;
urchin, burrowing method,
ii. 155 ; urchin, teeth of,
ii. 154 ; urchin, test of, ii.
154 ; urchins, i. 158, ii.
129, 153, 170, i75» 176-

Seal, common, i. 50 ; flippers
of, i. 50 ; method of swim-
ming, i. 50 ; teeth of, i. 51.

Seashore, fauna, ii. 169, 170 ;
vegetation, v. i.

Seasonal changes of plumage,
i. 79, 87, 88.

Seaweeds, iv. 177, v. 21 ;
colours of, v. 9, 49.

Sea wheat-grass, v. 5, 7.

Sea-worms, ii. 175.

Secondary quills, i. 85.

Sedge, v. 38, 45.

Sedgemoor, iv. 189.

Sedge -warbler, ii. 190.

Sedges, iv. 158, 161, 182, 183,
193, 194, 199, 201, v. 28, 33,
52, 70, 217; fruit enclosed in
utricle, v. 51.

Seed-coat, iii. 5 ; leaves, iii. 12,
13-

Seedling of beech, iii. 36 ; of
cucumber, iii. 10 ; of gorse, iii.
37 ; of oak, iii. 37 ; of onion,
iii. 10 ; of radish, iii. 35 ; of
sycamore, iii. 36 ; of pea, iii.
8 ; of wheat, iii. 10.

Seedlings, iii. 33 ; of bean, iii.
15 ; life-history and growth
of, iii. i, 7; of wallflower,
iii. 24.

Seeds, albuminous, iii. 9 : dis-
persal, iv. 74 ; v. 52 ;
germination, v. 113 ; grown
in moist air, iii. 15 ; struc-
ture of, iii. 4, 12, v. 113.

Segmented worms, i. 158.

Self -fertilisation, iv. 71.

Selfheal, iv. 158, v. 16; illus-
tration of, v. 62.

Self-pollination, iv. 70.

Semicircle, measure of, vi. 77.

Semi-parasitic plants, iii. 31.

Sense organs of snakes, i. 118.

Senses, i. 24.

Sepals, iii. 79.

Sepia, ii. 137-

Serpula, ii, 166, 179.

Serpulid worms, ii. 160, 161.

Sertularia abietina, ii. 178.

Severn, iv. 144.

Sexual reproduction, iii. 97.

Shadow-clock, yi. 75, 76.

Shadow experiments, vi. 82 ;
long and short, vi. 2 ; obser-
vations on, yi. 70.

Shallott, cultivation, v. 141,
142 ; bulb of, iii. 63.

Shallow-rooted plants, vi. 33.

Shanny, habits of. ii. 132, 133.

Shapes of birds, i. 83.

Sharks, i. 140, 141, 146.

Sheep, varieties of. i. 39, 41,
64 ; keeping, v. 75.

Sheep's fescue, v. 59 ; figured,
v. 64, 65, 66 ; grass, v. 57 ;
scabious, iv. 192, v. 216 ;
sorrel, v. 36.

Shellfish, ii. 132.

Shell plates of Chiton, ii. 143.

Shepherd's needle, figure of, v.
76, 77, 85, 86 ; purse, iii.
166, 212; life - history of
plant figured, iii. 213 ; fruit
figured, iii. 214, iv. 68, 69,
70.

Shield-fern, male, iv. 179.

Shingle beaches, v. 18, 19 ;
vegetation of, v. 9.

Shipbarnacle, ii. 176.

Shirley poppy, v. 169.

Shoebill stork, type of beak, i.
92.

Shoots of flowering plants, iii.
92.

Shore-crab, ii. 101, 171, 176,
181.

Shore excursions, ii. 173 ;
fauna, characteristics, ii. 170 ;
plants, long roots of, vi. 34.

240

THE BOOK OF NATURE STUDY

Short -legged puffins, i. 87.
Shoulder-girdle of birds, i. 73 ;

and limbs of mole, i. 47.
Shoveller duck, shape of beak,

i. 92.
Shrew, ii. 208 ; food of, ii.

206, 207 ; habits, ii. 206.
Shrimps, ii. 108, 134, 135, 150.
Shrubby spireas, v. 167 ;

undergrowth, iv. 156, 159.
Side-fruiting mosses, iv. 115.
Sigillarias, iv. 94.
Silurids, i. 147.
Silver-beetle, eggs of, ii. 121 ;

larva of, ii. 121.
Silver birch and sandy soils,

v. 215 ; grass, iv. 207.
Silverweed, iv. 202.
Silvery thread moss, pear-
shaped capsules, iv. 109.
Singworms, v. 183.
Siphonophora, ii. 185.
Siskin, ii. 210.
Skate, i. 137, 138, 146, ii.

142 ; dorsal surface of, i. 141 :

eggs of, ii. 142 ; organs of

locomotion, i. 141 ; young

of, ii. 142.
Skeleton of birds, i. 73 ; of

horse, i. 33 ; of mammal, i. 20 ;

of man, i. 33 ; of mole, i. 47 ;

of the wing, i. 84.
Skeleton - shrimp, respiratory

plates of, ii. 151 ; rudimentary

abdomen of, ii. 151.
Skua-gulls, plumage of the

young, i. 66.
Skull of dog, i. 21 ; of pig, i.

20.

Skunk, i. 63.
Sky, model of, figured, vi. 129 ;

observations, vi. 51, 52, 55;

sunsets, clouds, thunder-
storms, vi. 51-62.
Skye, model of island, vi. 129.
Skye terriers, i. 26, 28.
Skylarks, ii. 203, 207.
"Slaters," ii. 212.
Slender Naiad, v. 23, 24 ;

St. John's wort, v. 70.
Sloths, i. 20.
Slough of snakes, i. 118.
Slow-worm, i. no, in, 112,

ii. 214.
Slugs, ii. 48, 200, 208, 210, 212,

216, 217; eggs of, ii. 2ii ;

foot of, ii. 2ii ; large black,

ii' 53 ; tentacles, ii. 211 ;

troublesome to crops, v. 216.
Small bur-reed, v. 38, 44 ;

daisy, v. 62 ; ermine moth

and caterpillar, v. 182 ;

fleabane, v. 42.
Smooth anemone, ii. 128, 162 ;

horsetail, iv. 97 ; snake, i.

110.
Snail, ii. 48, 200, 208, 216,

217 ; description of, ii. 49 ;

diagram of radula, ii. 52 ;

eye of, ii. 48 ; fertilisation

of eggs, ii. 52 ; foot of, ii.

48 ; freshwater, ii. 188 ;

genital opening, ii. 48 ;

hibernating, ii. 14 ; lines of,

growth, ii. 48 ; mouth of,

ii. 48 ; pedal gland of, ii.

48 ; pulmonary opening, ii.

48 ; slug, ii. 55.
Snakes, varieties of, i. 109, no,

112, 113, 116, 117, 118, 119,

ii. 208.
Snow, vi. 6, 17, 20, 40, 50 ;

ball, vi. 42 ; drift, vi. 44 ;

fall, on Matterhorn, vi. 44 ;

in New England States, vi.

41 ; ploughs, vi. 41 ; storms,

vi. 40, 41 ; bunting, ii. 217 ;

drop, iii. 70, v. 172, 175, 177,

179 ; drop, structure of leaves,

iii. 63; and trees, text-fig.,

vi. 37.

Snowy owl, vi. 219.
Soap-berry, seeds carried by

Gulf Stream, v. 50.
Soft brome, v. 215.
Soil, varieties of, v. 79, 86, 120,

121, 188, 192, 195-208, 211,

213, 215, 216, 217. vi. 33.
Solanacea, iv. 69.
Solanum tuberosum, iv. 6, v.

132-

Sole, i. 137, 147, ii. 135.
Solen, ii. 175.
Solitary plants, vi. 33.
Solomon's seal,self -propagation,

iii. 61, 62, iv. 160.
Solstices, vi. 65, 66.
Solution for spraying, v. 183.
Sorex vulgaris, ii. 206.
Sorrel, v. 60, 61, 64; dock, v.

216.

South Downs, v. 75.
Sow thistle, v. 76, 81, 82, 86,

217.

Spaniel, Japanese, i. 26.
Spanish chestnut and sandy

soils, v. 215.
Sparrow, seasonal changes of

plumage of, i. 87, 88 ; hawk,

ii. 210 ; hawks, nestlings of. i.

102, 103.

Sparrows, in America, ii. 221.
Spawn, iii. 71.
Spawning of salmon, i. 149.
Spear thistle, iv. 206.
Spearwort, lesser, iv. 193, v.

28.

Spearworts, v. 45.
Speedwells, iv. 208, v. 82, 217.
Sperm-whale, i. 49.
Spey and Findhorn, its rain-
falls, vi. 29.
Sphagnum,iv. 100, 101, 102, 108,

190, 193 ; association, v. 35 ;

bogs, iv. 197 ; moss, observa-
tions on, vi. 35.
Sphenodon, i. 109.
Spider, diagram of foot, ii. 43 ;

diagram of head, ii. 41 ;

diagram of pedipalp, ii. 41 ;

falces of, ii. 40 ; respiratory

organ of, ii. 42 ; crab, ii.

146.
Spiders, i. 158, 160, ii. 17, 38, 108,

208, 215, 217, v. 33 ; economy

of, ii. 46, 215 ; egg-cocoon of,

ii. 43, 46; nests, ii. 215;

reproductive functions of, ii.

41 ; web, construction of,

ii. 43.

Spiked milfoil, v. 25.
Spikelets of grass, v. 56, 57, 58.
Spinach, iii. 29, 32 ; cultivation

of, v. 143.

Spinal cord of mammal, i. 20.
Spindletree, v. 73.
Spiny restharrow, v. 6 ; spider

crab, ii. 152.
Spirorbis, ii. 179.
Spleen wort, black, iv. 91 ;

maiden-hair, iv. 91.
Sponge, crumb-of -bread, ii. 178,

179; freshwater, ii. 199.
Sponges, i. 158 ; calcareous, ii.

178 ; skeletons of lime or flint,

ii. 170.

Spongilla, i. 199.
Spongillida?, ii. 188.
Spoonbill, feeding habits, i. 91,

92.

Sporangia, iv. 88, 202.
Spore-cases, iv. 86 ; mass, iv.

86, 90 ; production of, iv.

126, 133, 138.

Spores, where formed, iv. 133.
Spotted orchis, life-history of,

iii. 1 66, 198 ; plant figured,

iii. 200.
Spotted or fire salamander, i.

1 20.

Spout -fish, ii. 175.
Spraying as a prevention of

insect pest, v. 182.
Spring and autumn plumages

i. 87, 88, 89.
Spring bulbs, shooting in

January, vi 5 ; flowers,

iii. 115 ; growing time, vi. 5 ;

onions, v. 141 ; records of

weather, vi. 6 ; tide, vi. 89.
Springs, how found, vi. 183.
Spruce, iv. 156 ; bud scales of,

iii. 43.
Spurge, y. 9, 76, 81, 217 ;

laurel, iv. 164, 165.
Spurreys, v. 80.
Spurry, v. 14, 86, 216.
Spur-winged goose, i. 97 ; plover,

i. 97-

Squat-lobster, ii. 148, 166.
Squid, ii. 137.
Squill, iii, 66, v. 16, i75-
Squirrel, habits of, ii. 210.
Squirreltail grass, v. 217.
St. Bernard, i. 28.
St. John's-wort, iv. 162.
St. Julien plum, v. 160.
Stachys, iii. 20.
Stag, i. 32.
Staghorn moss, iv. 197, 201,

202.
Stags on the crest of a hill, ii.

216.

Stamens, iv. 160.
Staminate flower, iv. 148, 160.
Starch grains, iii. 50.
Starfish, ii. 173, 176 ; madre-
pore of, ii. 1 80 ; method of

crawling, ii. 155.
Starfishes, i. 158, ii. 153, 155,

170.

Starlings, i. 83, 84, v. 181.
Starwort, v. 16.
Staiice auricula/alia, v. 13 ;

latifolia, v. 171.

GENERAL INDEX

241

Steel-coat, ii. 193.

Stellaria media, iii. 74, v. 81,
86.

Stem of potamogeton, trans-
verse section figured, v. 27.

Stem-tubers, iii. 67.

Stems of flowering plants, iii. 92 ;
of plants, colour of, iii. 57.

Stick shadow, vi. 72, 83.

Stickleback, i. 138, 139, 145,
ii. 133, 134, 192 ; economy
of, ii. 198 ; nest-building
of, ii. 103, 104 ; species of,
ii. 103, 104.

Stilt, figure of, i. 96.

Stinging animals, i. 158, ii.
179 ; nettle, iii. 75, 82, v.
30, 74-

Stinking-bishops, ii. 15 ; hay-
weed, v. 86, 217.

Stipa pinnata, iii. 80, iv. 205.

Stipes of cockroach, i, 172.

Stipules, iv. 172 ; of flowering
plants, iii. 92 ; of oak or
beech, iii. 74.

Stoat, ii. 202, 216 ; winter
dress of, i. 62.

Stomach, dissection of, i. 38.

Stomata, protection of, iii. 55,
75 ; number of, in leaf of
water lily, v. 28.

Stone-chat, ii. 214.

Stonecrop, iii. 55, v. 69.

Stone fern, iv. 90.

Stone, wearing properties of, vi.
95-

Stork's bill, iii. 2, v. 6, 8, 9,
29, 69 ; carriage of neck,
i. 87 ; spring migration of,
vi. 6.

Storms, effect of, vi. 103.

Storm-petrel, i. 83.

Stratiotes, v. 23, 25.

Strawberry.life-history, cultiva-
tion, distribution, propaga-
tion, v. 163-165 ; varieties
of, iii. 62, 69, 71, iv. 69,
78, v. 49, 117, 126, 148,
149, 151, 163.

Stream, transporting action of,
vi. 100 ; formation of valley
by, text-fig., vi. 23.

Streams, adjustment of, vi. 166 ;
how formed, vi. 23, 45.

Sturgeon, i. 140, 141, 147.

Submerged aquatic plants,
structure of, v. 22, 23 ; leaf
associations, v. 46.

Subsoil, v. 33, 195.

Subterranean clover, v. 74.

Sucker, v. 117.

Sugar-cane, iii. 60.

Summer days, length of, vi.
53, 66 ; flowering time, vi.
5 ; solstice, vi. 71, 83, 84 ;
spraying, v. 183.

Sun, vi. 4, 5, 51, 53, 54, 63 ;
altitude of, solstices of,
shadows of, setting of, vi. 72,
73-

Sundew, iii. 73, iv. i, 41-44,
69, 208, v. 30, 31, 32, 33,
36 ; plant figured, v. 33.

Sundials, treatment of, vi. 75,
76.

VOL. VI. 1 6

Sunflowers, iii. 24, 32, 59, v.
169, 179.

Sunrise, vi. 66, 67.

Sunset, an appearance, vi. 55,
80.

Sunshine, duration of, vi. i, 2 ;
amount of, 2 ; observations,
vi. 69.

Sun-star, ii. 155, 180.

Supra-occipital bone, i. 21.

Swallow, i. 83.

Swallows, i. 86, ii. 207, vi. 6.

Swan-mussel, ii. 58.

Swans, down-feathers of, i. 69,
ii. 190.

Sward-forming plants, v. 7.

Swede turnips, v. 139.

Sweet alyssum, v. 169, 176,
179; briar, v. 216; chestnut,
fruit of, involucre, iv. 149 ;
cicely, iv. 161 ; cassava, v.
83 ; flag, v. 28, 29, 43 ; peas,
iii. 29 ; peas, varieties of, v.
169, 174, 179 ; peas, cultiva-
tion of, v. 173, 174 ; scabious,
v. 169 ; sultan, v. 169 ;
Williams, v. 169 ; vernal
grass, v. 57, 58 ; violet, iii.
115, 124, iv. 69 ; violet, plant
figured, iii. 124; violet, flower
of, cross-pollination of, 125 ;
violet, sepals of, 126 ; violet,
pollination of, 127.

Swift, i. 83, 86, ii. 218.

Swimming-bells, ii. 165, 166,
185, 186.

Swine, i. 32.

Sycamore, iii. 35, 36, 37, 38,
41, 43, iv. 60, 76, 147, 172 ;
transverse section of bud, iii.
44.

Symbiosis, ii. 185.

Syringa, propagation of, v.
118, 119, 167.

Tacitus, iv. 144.

Tadpole, development of, i.
131, ii. 98, 195 ; breathing
of, i. 134 ; food of, i. 134.

Talpa europea, ii. 206.

Tapioca, v. 83.

Tapir, pig-like, i. 40.

Tap-root system, iii. 28, 29, 32.

Taraxacum officinale, iii. 80, 144.

Tarn, illustration of, vi. 212.

Tawny owl, i. 86.

Tay, iv. 144.

Tealia, ii. 167 ; crassicornis,
ii. 128, 163, 179 ; variety of,
ii. 128.

Teazle, v. 215.

Teeth, cheek, i. 21 ; cutting,
i. 20, 21 ; milk, i. 21 ; pre-
molars, i. 21.

Temperature, iii. 21, vi. -2, ;
and pressure, vi. 8 ; differ-
ences on continents and seas,
vi. 17 ; distribution of, vi.
33 ; influence on children,
vi. 9 ; influenced by wind,
vi. 4 ; in relation to vegeta-
tion, vi. 37 ; of the arid
plains of Asia, vi. 12 ; rise
and fall of, vi. 8, 10, 15;
observations on, vi. 14.

Tentacles of plants, iii. 74.

Terebella, ii. 179 ; conchilega,
ii. 159-

Terebeliids, ii. 160.

Terns, ii. 170.

Terrestrial worms, ii. 199.

Terrier, Maltese, i. 26.

Terriers, skye, i. 26, 28.

Testacella, ii. 51, 53, 55.

Testudo, species of, i. 115.

Tetrao tetrix, ii. 214.

Theoretical sun, vi. 79.

Thermometer and barometer,
vi. 8, 9.

Thermometer, reading of, vi. 23.

Thermometers, iv. 155.

Thistle, iii. 80, 148, iv. 157, 158,
185, 206, 207; down, iv. 77 ;
field, v. 69.

Thread-worms, ii. 188.

Three -branched polypody, iv.
87, 98.

Three-lobed scale of horn-
beam, iv. 148.

Three-spined stickleback, i. 144.

Thrift, sea, v. 15.

Thrush, common, i. 82, 83 ;
feather tracts of young, i. 68.

Thunderstorms, explanation of,
accompaniments of, shape of
clouds, direction of, vi. 33,
60, 61, 62.

Thyme, iv. 36, 207, v. 7, 66,
74 ; thread moss, illustrated,
iv. 105 ; sperm and egg-
pockets, iv. 106, 107.

Thymus serpyUum, iv. 207.

Tides, observations of, vi. 89.

Tiger, i. 62.

Timber, iv. 149 ; suggestions
for practical work, iv. 176.

Time, experiments on the
measure of, vi. 78, 79.

Titmouse, v. 181.

Tits, ii. 210.

Toad, hibernation of, i. 122 ;
natter-jack, i. 122 ; useful-
ness of, i. 122 ; spawn, i. 122,
128, ii. 194 ; stools, ii. 2, 10,
iv. 125, 126, 141, 178 ; tad-
poles of, ii. 194 ; glands of, i.
122.

Tobacco plant, figure of, iii. 104.

Tolstoi, describing winter
scenes, vi. 5.

Toothwort, iii. 46, iv. 157, 180.

Top -shell, ii. 128.

Tormentilla, iv. 201, 202, 206.

Torrential rainfall, vi. 29, 36.

Tortoises, i. 109.

Tortoiseshell butterfly, ii. 204.

Tortoise-shell limpet, ii. 143.

Tortoise-shell, small, ii. 208.

Torlula, iv. 109.

Town gardening, v. 179.

Trachea or wind-pipe, i. 76.

Tradescantia virginica, v. 171.

Trailing azalea, iv. 196.

Transpiration, iii. 51, 76.

Transport, how affected by
snow, vi. 42.

Tree, bole of, iii. 45.

Tree-climbing cat, i. 67.

Tree-creeper, ii. 210.

Tree mallow, v. 12, 14.

242

THE BOOK OF NATURE STUDY

Tree-sparrow, i. 81.

Trees, iv. 147, 149, 151, 167,
i75» 176, 177 ; bibliography
of, iv. 176 ; action of wind on,
vi. 22 ; fossil, vi. 191.

Trematode worm, larva of, ii.
192.

Tri folium, species of, v. 115.

Trilobite, Silurian, vi/ii7, 191.

Triticum junceum, y.~4, 5.

Triton, species of, i. 122, 144,
ii. 101.

Trop&olum, iii. 54.

Tropidonotus natrix, i. no, 112,

H3» "4-
Trout, i. 136 ; ii. 197 ; hatching

of, ii. 198.
Trumpet or cup lichens, iv. 134,

178.

Trumpet-mosses, iv. 138.
Tube-worms, ii. 179.
Tuber, y. 116.
Tubers, iii. 67, 69, 70.
Tubifex, ii. 200 ; rivulorum, ii.

199.

Tubularian polyps, ii. 174.
Tufted or foliose lichen, iv. 140.
Tufted scirpus, iv. 193.
Tulip, iii. 66, 86, 104, 114, 115,

156-159, iv. 70 ; bulb, iii.

67, v. 116 ; life-history of, iii.

148.

Tulipa, species of, iii. 148.
Tumere, iii. 67.
Tunicates, i. 151, 156, 157,

158.

Turf, examples of, v. 208.
Turgenov, describing winter

scenes, vi. 5.
Turnip, iii. 25, 29, 32, v. 78, 79,

130 ; history and cultivation

of, v. 139.

Turnip beetle, v. 139.
Twilight, vi. 67 ; arch, colours of,

vi. 56, 57-
Twite, ii. 214, 217.
Two-spotted goby, ii. 132.
Two-winged flies, ii. 195.
Typha, species of, v. 44, 76.

Ulex europaus, iv. 192, v. 115.
Ulva latissima, ii. 84.
Umbel, compound, iv. 4.
Umbelliferae, iv. 6, 69, v. n,

13, 35, 77,135-
Under-fur of

mammals, i. 69.
Undergrowth, iii. 46, iv. 156.
Underplanting, iv. 151.
Under-wood, iv. 147, 148.
Ungulata, i. 40.
Unicellular hairs, iii. 81.
Unio, ii. 58, 59, 191.
Univalves, ii. 105.
Unsegmented worms, i. 158.
Upright buttercup, figured, iii.

89.

Upright -leaf, v. 46.
Urchin, purple-tipped, ii. 153,

154-

Usnea, iv. 133, 138, 178.
Utricularia, species of, ii. 90, 91,

v. 3i» 32-

Vaccinium moors, iv. 191, 197,
199.

Vaccinium, species of, iv. 195,

196.

Valisneria spiralis, ii. 92, 93.
Valleys, how formed, vi. 162 ;

in relation to streams, vi.

101, 105.
Valvata, ii. 191.
Vanessa urticce, ii. 204.
Vapour, causes of, vi. 21, 22 ;

observations on, vi. 49.
Vapourer moth, figure of, v.

181.
Variable hare, ii. 216, 219 ;

winds, vi. 17.

Variation of climate, vi. 32.
Vegetable beds, arrangement of,

v. 129, 130.
Vegetable brimstone, iv. 98 ;

culture, v. 125-129 ; feeders,

i. 32 ; garden, management

of, v. 125-129 ; kingdom, in

relation to man, vi. 38 ;

marrow, v. 148 ; mould, vi.

36 ; constituent parts of, v.

125.
Vegetation, aquatic, v. 21 ;

cliff, v. 12 ; of commons, iv.

206 ; destruction of, vi. 36 ;

of Gloucestershire, v. 4 ; of

meadows and pastures, v. 56 ;

of muddy shore, illustration

of, v. 2 ; of running water,

v. 38 ; seashore, v. i, 4 ;

xerophytic, v. i ; of shingle,

v. 9 ; of still water, v. 26 ;

of swiftly flowing water, v.

42.
Vegetative organs of flowering

plants, iii. 95.
Vegetative rhythm, determined

by temperature, vi. 37.
Velvet fiddler crab, ii. 186.
Venus's comb, v. 77 ; girdle,

ii. 186.
Veronica, species of, iii. 225,

v. 82, 171.

Veronicas, v. 39, 81, 82.
Vespa, species of, i. 210,

211.

Vertebra, parts of, i. 22.
Vertebrates of the freshwater

aquarium, ii. 94-105.
Vetches, v. 16, 73, 216;

tendrils of, iii. 54.
Vicia, species of, iii. 133, v. 115,

146.
Viola, species of, iii. 124, 128,

v. 76, 171.
Violaceae, iv. 69.
Violas, v. 176.
Violet, iii. 106, iv. 69, v. 17 ;

diagram of, iii. 105.
Viper a berus, i. no, 113, 116.
Viper's bugloss, iii. 75, 83.
Virginia creeper, v. 179.
Virginian stock, v. 169, 179.
Viscous senocio, illustration of,

V. II, 12.

Vis cum album, iv. 35, 44.
Viviparous lizard, ii. 217.
Volcanoes, action of, vi. 128.
Vole-plagues, ii. 202.
Voles, ii. 216.
Von Baer's law, ii. 101.
Vorticella, ii. 199.

Wagtail, species of, ii. 203, 208,
217-

Wallflower, v. 169, 179; seed-
lings of, iii. 24 ; stem of, iii. 59.

Wall rue, iv. 91, 98.

Walnut, iii. 36 ; cotyledon of,
iii. 9.

Waning moon, vi. 85, 86.

Warning coloration, i. 63.

Wartlet, ii. 179.

Wasp, abdomen of, i. 201 ;
breathing of, i. 203 ; cardo of,
i. 195 ; compound eye of, i.
194 ; diagram of front leg, i.
201 ; diagram of nest, i. 209 ;
diagram of sting apparatus,
i. 202 ; diagram of under side
of head, i. 196 ; mouth parts
of, i. 194, 195 ; life-history
of, i. 204 ; nest of, i. 205 ;
social economy of, i. 204.

Water, in different soils, v. 200.

Water avens, iii. 80, 83, 217, iv.
161, v. 70.

Water-beetle, dilation of legs
of, ii. 118 ; eggs and larva? of,
ii. 120; elytra of, ii. 118; life-
history of, ii. 33 ; methods of
swimming and breathing, ii.
119 ; respiration of, ii. 32.
Water-beetles, ii. 188, 193,

194.

Water-boatman, ii. 122, 123,
194; eggs of, ii. 123 ; feeding
of, ii. 123.

Water-bugs, ii. 124, 195.
Water buttercup, iv. 199; club-
moss, iv. 99 ; composition of,
vi. 186 ; cress, v. 46, 39, 52 ;
crowfoot, ii. 87, 92, v. 27, 54 ;
crowfoot, branch figured, v.
48 ; fleas, ii. 109, 187, 189 ;
forget-me-nots, iii. 83 ; hog
house, ii. 108 ; horsetail, ii.
88 ; lily, ii. 87 ; lily associa-
tion, v. 29 ; lily, species of,
v. 29, 51 ; lilies, rhizomes of,
v. 28 ; lobelia, v. 23, 25, 26 ;
milfoil, ii. 92 ; mint, iv. 158 ;
mites, ii. 188 ; ouzel, ii. 196 ;
parsnip, v. 29 ; plantain, v.
29, 45, 50 ; plantains, disper-
sal of seed, v. 51 ; petrifac-
tion, vi. 187 ; plants, ii, 189 ;
plants, absence of hairiness,
v. 54 ; plants, air spaces of, v.
23 ; plants, structure of leaf, v.
28 ; polygonum, ii. 92 ; pepper
polygonum, v. 47 ; rail, ii.
190 ; rat, ii. 189, 196 ;
scorpion, method of breathing
ii. 124 ; scorpions, ii. 15 ;
shrew, ii 189, 190, 196 ;
skaters, ii. 15 ; snails, ii. 191,
194, 198 ; soldier, life-history
of, v. 23, 25 ; spider, ii. 124,
215 ; spider, eggs of, ii. 125,
215; sprites, ii. 194; star-
wort, ii. 87, 89, v. 46;
supply, iv. 147 ; tortoise, ii.
91 ; underground movement
of, vi. 183 ; various colours
of, v. 53 ;' violet, life-history
of, v. 25 ; vole, ii. 189, 190,
196 ; weed, ii. 126.

GENERAL INDEX

243

Wavy-hair grass, v. 213 ; moss,
illustrated, iv. 115.

Wayfaring tree, iii. 43, v. 216 ;
naked buds of, iii. 43.

Wayside-grasses, iv. 186.

Weald, lessons of, vi. 169, 172,
182.

Weasel, ii. 202, 207, 216.

Weather and climate, vi. 8.

Weather changes, effect on
plants and animals, vi. 7.

Weather; observations on, vi. i,
6, 17-

Weeds characteristic of certain
soils, v. 60, 79 ; of cultiva-
tion, v. 75.

West coast of Ireland, in
relation to rainfall, vi. 26.

West Indian bean, distribution
of seeds, v. 50.

West winds in England, vi. 4.

Whalebone, i.'49-

Whales, 1.48,53, 159; paddles
of, i. 49 ; skeleton of, i.
48.

Wheat, iii. 21, 32, v. 79, 84;
an indicator plant, v. 76 ;
starch of, iii. 50 ; cultivation,
v. 85 ; deterioration of, v. 210 ;
development of the seed,
iii. 4, 7, 9, 10 ; growing,
v. 75, 76, vi. 32 ; remarkable
cultivation of. v. 210 ; of the
New World, vi. 38, plots,
experiments of, v. 87 ; pro-
duction in the east of England,
vi. 31 ; ripening of, v. 88 ;
typical crop of, v. 214 ; zone,
v. 76, 85, 87.

Wheatear, nest and eggs of, ii.
202.

Wheats, v. 86.

Whelk, common, ii. 166 ; great,
ii. 172 ; number of eggs of,
ii. 141 ; young of, ii. 142.

Whin, iv. 76.

Whinchat, note of, ii. 208.

Whirligig beetles, eggs and
larvae of, ii. 122 ; description
of, ii. 194.

White beam tree, iii. 76, iv.
i73-

White bryony, iii. 58 ; illustra-
tion of, iii. 72.

White clover, v. 58 ; currants,
v. 151 ; campion, v. 84.

White dead-nettle, iii. 115;
description of, iii. 139 ;
plant figured, 140 ; flower
figured, 141 ; pollination of,
143-

White-leaved fork - moss, iv.
108.

White meadow saxifrage, iii.
166, iv. 69; life-history of,
iii. 192 ; flower figured, iii.
193 ; bulbils figured, iii.
195.

White poplar, v. 46.

White-spored species, iv. 178.

White thorn, propagation of, v.
118.

White turnip, v. 139.

Whorled milfoil, v. 23, 28.

Whortleberry, red, iv. 196.

Wild anemone, downy fruits of,
iii. 80 ; angelica, iv. 158, v.
46, 70 ; apple, iv. 49 ; bees,
ii. 204 ; beet, v. 17 ; boars in
Chartley Forest, i. 42 ; boar,
colour of young of, i. 66 ;
boars, final extermination of,
i. 42 ; cabbage, v. 130 ; carrot,
iv. 162, v. 86, 135, 215 ; carrot,
bracts of, iii. 55 ; cat, i. 32 ;
cherry, v. 160, 216 ; crab,
v. 153 ; cleavers, iii. 77 ;
currant, v. 162 ; dog, ii. 196 ;
duck, ii. 190 ; garlic, iv. 159 ;
hyacinth, iii. 104 ; hyacinth,
diagram of, iii. 105 ; pansy,
iii. 124, 128, iv. 76; parsnip,
v. 216 ; pig of India, i. 40 ;
poppy, v. 86; radish, v. 17,
76 ; roses, iv. 156, v. 72,
172 ; squill, v. 15.

Wild strawberry, life - history
of, iii. 1 66 ; illustration of,
iii. 1 68 ; flower figured, iii.
168 ; fruit figured, iii. 170.

Wild strawberries, iv. 69, 73,
161, v. 163 ; thyme, v. 9, 67.

Willow, iv. 69, 71, 184, v. 55,
72 ; creeping, v. 8 ; goat, iv.
i ; grouse, ii. 214, 217 ; stami-
nate flower, pistillate flower,
iv. 161 ; uses of, iv. 167.

Willow-herb, iii. 81, iv. 77, 161,
i73» 177, y. 40, 46, 55. 72 ;
illustrated in detail, iv. 19 ;
petals of, iv. 18 ; rose bay.
iv. 17, 20, 21 ; self -fertilisa-
tion, iv. 20.

Wimbledon Common, iv. 188.

Wind, vi. 13 ; in connection
with rain, vi. 17 ; direction
of, vi. 8, 26 ; eroding action
of, vi. 103 ; hover, v. 87 ;
in relation to temperature,
vi. 5 ; in relation to the sun,
vi. 5 ; local changes of, vi.
17 ; movement of, vi. 2 ;
observations on, vi. 13 ; pres-
sure of, vi. 1 6 ; relations of
temperature and pressure to,
vi. 14 ; transporting agency
of, vi. 103 ; inconstancy of,
vi. 17.

Window gardening, v. 176,
178.

Wing-bars, i. 81.

Wing of bird, figured, i. 74.

Wingless insects, ii. 176.

Winter days, length of, vi. 66 :
flowering bulbs, vi. 37 ; moth,
caterpillars of, v. 184 ; moth,
habits of, v. 184; moth, life-
history of, v. 184 ; moth,
method of destruction, v.
184 ; resting time, vi. 5 ;
snowstorm, observations of,
vi. 43, 45 ; solstice, vi. 71, 83,
84 ; wash, v. 182 ; wash, con-
stituents of, v. 183 ; white
brocoli, v. 131.

Wirral, pensinula of, vi. 14.

Witches broom on birch, ii.
18.

Woburri Experimental Fruit
Station, v. 152.

Wolf spiders, ii. 38.

Wood anemone, v. 210; ane-
mone, early flowering, iv. 157 ;
beetles, ii. 210 ; betony, iv.
158.

Woodbine, iv. 32.

Woodcock, ii. 210 ; difference of
the young, i. 66 ; method of
feeding, i. 91, 92.

Wood garlic, iv. 159 ; grasses,
iv. 186 ; horsetail, iv. 96.

Woodland, ii. 200, 209 ; birds,
ii. 210; ferns, iv. 88; vege-
tation, iv. 144.

Wood-lice, ii. 108, 109, 202, 212,
iv. 154 ; air-passages of, ii.
200.

Woodpecker, dissection of head,
i- 93 ; species of, ii. 210 ;
method of feeding, i. 93.

Wood-pigeon, notes of, ii. 210.

Woodruff, iv. 158, 159, 161.

Woodrush, iii, 159, iv. 70, 72,
v. 66 ; field, iii. 152, v. 67.

Wood sage, iv. 74, 75, 158 ;
sanicle, iv. 158, 161 ; snail,
ii. 210 ; sorrel, iv. 159, y. 70 ;
sorrel, movements of, iii. 55,
56 ; spurge, iv. 158 ; violets,
iv. 161.

Woods, iv. 155; mixed, iv.
151 ; suggestions for practi-
cal work, iv. 165, 175.

Woody night-shade, v. 73.

Woody plants, propagation of,
v. 118.

Woolly fringe moss, iv. 109.

Work of leaves, iii. 46 ; of the
soil, v. 188.

Worm, breeding habits, i. 162 ;
casts, i. 1 60 ; cingulum of,
i. 163 ; cocoons of, i. 163 ;
leaf-like, ii. 179; shape of , i.
162.

Worms, i. 160, ii. 170, 171,
198, see also Earthworms ;
free-living, ii. 158 ; fresh-
water, ii. 199 ; marine, ii.
158 ; segmented, i. 158 ;
tube-inhabiting, ii. 158, 159 ;
unsegmented, i. 158.

Wracks, v. 9.

Wren, i. 86.

Wriggler, ii. 27.

Wych elm, iii. 75, iv. 174.

Xerophilous, iv. 90.
Xerophytes, vi. 36, 182, 183,

v. 70.
Xerophytic vegetation, iv. i,

199.

Yaffle, ii. 210.

Yarrow, iv. 162, v. 60, 61, 63.

Yeast, iv. 141 ; use in brewing
and bread-making, iv. 142 ;
produces spores, 142.

Yeasts, iv. 125, 142.

Yellow flag, v. 43 ; garden
crocus, iii. 161 ; corn figured,
iii. 162 ; horned poppy, v.
ii, 210 ; horned poppy,
illustration of, v. 12 ; iris,
iii. 166, iv. 70, v. 43 ; iris,
life-history of, iii. 221 ; illus-

244

THE BOOK OF NATURE STUDY

tration of, iii. 224 ; flower
figured, iii. 224 ; loosestrife,
v. 41 ; meadow rue, v. 38, 46 ;
rattle, iv. 180 ; wagtail, ii.
208 ; wort, v. 66 ; figured,
v. 68.

Yew, iv. 62, 164, 184 : bud
scales of, iii. 43 ; golden
English, v. 167 ; typical tree
of calcareous soil, v. 216.

Yews, age of, iv. 150.

Yorkshire fog, v. 60.

Young barn owl, showing first
traces of wing and tail
feathers, i. 8p ; birds and
their moults, i. 88 ; pheas-
ants showing striped down,
i. 80 ; robins in first plumage,
i. 82.

Yucca filamentosa, v. 171.

Zea mays, v. 115.
Zebra, i. 61, 62.
Zebra-antelope, i. 62.
Zebras, callosities of, i. 34.
Zenith,vi. 71.83, 84; explanation

of, vi. 52, 53. 54-
Zoophytes, i. 158, ii. 144, 170,

176, 178, 179.
Zostera, ii. 82, 89, v. 50.
Zostera marina, ii. 88.

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