Elementary Lessons in Physical Geography

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Preface

A SIMPLE but systematic and yet interesting description of the familiar features of the Earth's surface may be regarded as a natural introduction to the teaching of science. Treated from this point of view, Physical Geography may be made a valuable instrument of education. To give it such importance, the most advantageous method is to make use of the common knowledge and experience of the pupils, and, starting from this groundwork, to train them in habits of observation and in scientific modes of thought and inquiry among every -day phenomena. From the very outset the instruction should be as far as possible practical A shower of rain, the growth and disappearance of a cloud, the flow of a brook, the .muddy water of a river, the shape of a cliff, the outlines of a mountain, the undulations of a plain — these and the thousand other common features of landscape should be eagerly seized by the teacher and used as vivid illustrations of the broad fundamental principles which it will be his main object that his viii PREFACE.

pupils should thoroughly master. Thus employed, Physical Geography is not learnt as an ordinary task, but rather becomes a delightful recreation, in which, however, the observing faculty is exercised, the power of induction cultivated, and the imagination kept constantly active.

Having been long convinced that such a method of instruction would place this branch of science upon a firmer and broader footing in our educational system, and would moreover prove of great service in fostering a spirit of observation and reflection even among children, I projected many years ago the Primer of Physical Geography^ published in the series of Science Primers, The continued sale of large impressions of that little work encourages the hope that the method advocated has been found successful in practice.

The present volume may be regarded as a further development of the same plan of instruction. As its title implies, it still deals mainly with the broad elementary questions of Physical Geography. It would have been impossible to find a place within its Lessons for the treatment of every branch of the wide subject, and as impossible, had it even been desirable, to bestow equal fulness upon every branch for which room has been made. I have devoted most space to

PREFACE. ix those aspects of the science which, in my own experience, have been found best suited for practical instruction. While as much general information as may be feasible should be communicated to them, young pupils cannot of course be expected to find the same interest in all divisions of the subject. It is of far more consequence to awaken in them a taste for such pursuits, and lead them to carry on the study of their own accord, than to try to charge their memories with dry facts and figures which, in the absence of intelligent and suggestive teaching, are too commonly meaningless and repulsive.

While, therefore, adhering to a systematic treatment, I have been led to dwell, for example, on the phenomena of the atmosphere at much greater length than is usual in elementary class-books. These phenomena are among the most familiar and universal features of the globe; examples of them can be constantly adduced, and they may thus be used with singular advantage to illustrate how the facts of science are observed and its laws are deduced.

I acknowledge with pleasure my obligations to my fnend Mr. Buchan, who not only kindly allowed me to make use of his Charts of Atmospheric Pressure

PREFACE.

and Temperature, but who also read over the proofsheets of the first two chapters and gave me valuable suggestions on subjects regarding which he is so high an authority.

The present Edition has been carefully revised throughout Two new Plates have been added, one (from the " Challenger " results) showing the form of the great sea-basins as revealed by recent deep-sea research ; the other (from Professor Loomis' Chart) indicating the general distribution of rain over the globe.

Contents

PAGE I

Chapter I.— THE EARTH AS A PLANET. Lesson

L The Earth's Form 8

n. The Earth's Motions ii

in. The Earth and the Sun .17

IV. Measurement and Mapping of the Earth's

Surface 24

V. A General View of the Earth ... 32

Chapter II. — AIR

Lesson VI. Its Composition

VII. The Height of the Air .

Vin. The Pressure of the Air .

IX. The Temperature of the Air X. The Moisture of the Air .

XI. The Movements of the Air

38 45 47 54 64

Chapter III.— THE SEA

Lesson XII. The Great Sea-basins

XIIL The Saltness of the Sea .

XIV. The Depths of the Sea .

XV. The Temperature of the Sea

XVI. The Ice of the Sea .

XVIII. The Offices of the Sea .

"3 119

137 152 xii CONTENTS.

Chapter IV.— THE LAND. PAGE

Lesson XIX. Continents and Islands . . .162 XX. The Relief of the Land — Mountains,

Plains, and Valleys . . .173

XXIV. The Waters of the Land— Part I.— Springs and underground Rivers . 222

XXV. The Waters of the Land — Part IL—

Running Water — Brooks and Rivers . 244 XXVI. The Waters of the Land— Part HI.—

Lakes and Inland Seas . . . 258

XXVII. The Waters of the Land— Part IV.— The Work of Running Water . . . 272

XXVIII. The Waters of the Land— Part V.— Frost, Snow- fields, Glaciers . . 293 ft »»

99 99

Chapter V.— LIFE

Lesson XXX. The Geographical Distribution of Plants

and Animals 328

,, XXXI. The Diffusion of Plants and Animals —

Climate — Migration and Transport — Changes of Land and Sea . . 337

LIST OF ILLUSTRATIONS.

PLATES.

TO FACE PAGE

Plate I. The World in Hemispheres 24

II. Pressure of the Atmosphere over the Globe in January . 46

III. Pressure of the Atmosphere over the Globe in July 50

IV. Isothermal Lines over the Globe for January . . 54 V. Isothermal Lines over the Globe for July ... 60

VI. Map showing the mean Annual Rainfall of the Globe . 76

VII. The Ocean Basins .103

VIII. Ocean Currents 144

IX. Distribution of Earthquakes and Volcanoes over the

Globe 200

X. Zoological Provinces of the Globe ..... 328

WOOD-CUTS.

FIG. PAGE

Ocean- Waves Frontispiece

1. Curvature of the Earth's Surface, as shown by ships at sea . . 9

2. The Earth and Moon as seen from space 10

3. The Earth's path round the Sun 24

4. Plan of Volcanic Hills and Craters in the Bay of Naples . . 29

5. A part of the Surface of the Moon, showing Volcanic Craters . 20

6. Measurement and Mapping of a Country by means of Triangu-

lation . . 31

7. What is seen after some raindrops collected in a town are evapor-

ated, and the residue is placed below a microscope ... 40 xiv LIST OF ILLUSTRATIONS.

FIG. PAGB

8. Diagram showing the influence of the varying thickness of the

atmosphere in retarding the Sun's heat 57

9. Clouds condensed by the Cliff of the Noss Head, Shetland, with

a clear sky and a S.E. wind 73

10. Snow-flakes 80

IX. Position and height of the Snow-line between Equatorial Africa

and the North Polar Seas 81

12. Sand-dunes — ridges of dry sand blown inland off the shore by the

wind 100

13. What is seen when a drop of concentrated sea- water is evaporated

under a microscope 115

14. Some of the Ooze of the Atlantic floor, magnifled .... 124

15. Iceberg at Sea 130

16. The Birthplace of the Arctic Icebergs 132

17. Scene among the disrupted ice of the frozen Arctic Sea . . 134

18. The Ice-foot of Greenland 136

19. Diagram illustrating the origin of the tides 149

ao. Diagram showing the relation of the beach to the lines of high and

low water 152

21. View of the sea-cliffs south of the river Tjme (magnesian limestone

worn away by the waves, and the isolated fragments left) . . 159

22. Steep shore descending abruptly into deep water .... 167

23. Low shore shelving into shallow water 167

24. Section of one side of a Continent 175

25. Section to show the formation of soil and subsoil from rotting away

of rock underneath 183

26. Bedded arrangement of rocks 185

27. Piece of shale containing portion of a fossil fern . . . .186

28. Piece of limestone, showing how the stone is made up of animal

remains 187

29. Some of the grains of a piece of chalk 188

30. A piece of granite, showing the composition of a Crystalline Rock x88

31. View of the geysers of Iceland. Great Geyser in eruption . . 193

32. Plan of the Peak of Teneriffe, showing the large crater, partly

effaced, and smaller craters with lava currents issuing from

them 198

33. View of a Street in Pompeii 199

34. View of Vesuvius as seen from Naples during the eruption of 1872 201

35. Mount Vesuvius as seen from the sea, with the remaining part of

the old crater of Somma behind 202

LIST OF ILLUSTRATIONS. xv

FIG. PAGE

36. Houses surrounded and partly demolished by the lava of Vesuvius,

1872 204

37. View of the extinct volcanoes of Central France, taken from the

Fuy de Pariou 308

38. House rent by earthquake (Mallet) 215

39. Diagram-section to illustrate the propagation of an earthquake-

wave and the mode of calculating the depth of its origin . . 2x5

40. View of an old sea-terrace or raised beach, with sea-worn caves

on its inner margin 217

41. Raised sea-terraces of the Alten Fjord, Norway .... 218

42. Section of an island with a fringing coral reef . . . .2x9

43. Section of an island with a Barrier reef 219

44. Section of an Atoll or coral island built over submerged land . 230

45. View of an Atoll or coral island 220

46. Section across a valley to show how the simplest kinds of springs

arise 228

47. Section to show how deep-seated springs arise .... 229

48. Section to show the intricate underground drainage which issues

in a deep-seated spring 230

49. Section to the position of the water-bearing rocks below the clay

at London 23X

50. Section across the cliff and landslip of Antrim .... 243 5x. View of part of the cliffs and landslip of Antrim .... 342

52. Delta of the Nile . 246

53. Windings of the Mississippi 249

54. Part of the Island of Lewis, illustrating the abundant lakes of the

north-west of Europe 259

55. Section of a lake-basin excavated in solid rock .... 260

56. Section of a lake-basin lying in a hollow of superficial detritus . 261

57. Section of a lake dammed up by a barrier of earth or gravel . 26x

58. Prints made in soft mud or moist sand by rain-drops . . 273

59. Earth pillars of the Tyrol 274

60. View of ravines cut by streams out of a table-land . . 277 6x. Cascade and pot-holes of a water-course 378

62. Section of a waterfall and ravine 379

63. Terraces of gravel, sand, and mud, left by a river . . . 287

64. Delta of the Mississippi 293

65. Snow-field and glaciers of Holands Fjord, Arctic Norway . . 301

66. View of a glacier, with its lines of rubbish (moraines) and the

river which escapes from its end 302 xvi LIST OF ILLUSTRATIONS.

FIG. PAGE

67. Plan of the Mer-de-Glace of Chamouni and its tributary glaciers,

showing the way in which lateral moraines become medial . 305

68. Glacier table — a pillar of ice supporting a block of stone . 308

69. The Pierre-k-Boat, near Neufchitel 309

70. Glacier descending to the sea. Head of Jokuls Fjord, Arctic

Norway 310

71. Stone polished and striated under glacier ice .... 313

72. Quarry in flat stratified rocks 316

73. Section across a mountain-chain to show how the level rocks of

the plains are bent and inverted along the flanks of the mountain, while the lowest and oldest rocks are made to form the central and highest point of the chain 3x8

74. Section across a mountain-chain, showing two successive periods

ofuplift 3x9

75. Section across a mountain-chain showing three successive periods

ofuplift ... 330

76. Scene on the Coast of Caithness 322

77. Portion of the west front of Salisbury Crag, Edinburgh . . 323

78. Vertical distribution of climate on mountains .... 343 r .

ELEMENTARY LESSONS

IN

PHYSICAL GEOGRAPHY.

Introduction

1. At night, when the sky is clear, the largest stars seem to stand out in front, with others less in size and brightness crowding behind them. As we gaze into these depths, still remoter and feebler twinkling points appear, until at last our eyes can no longer shape out any distinct specks of light. Such a sight impresses our minds, as nothing else can do so vividly, with the vastness of the Universe. We feel how comparatively small must, after all, be the distance which we can see into that " stardust " which has been sown through the regions of space. And even when, with the aid of a good telescope, we return to these same skies, it is to find more cause than ever to acknowledge how immeasurably vast is that part of the Universe which man can thus explore ; but at the same time, to meet again with* a vague limit, beyond which we cannot see, not because we have reached the utmost verge of creation, but because our instruments can carry our vision no farther. Far beyond that limit, it may be that the regions of space contain other stars and systems, though too remote ever to be brought into

PHYSICAL GEOGRAPHY.

view even by the most powerful telescopes which human skill could construct

Astronomers have calculated the distance of some of the largest and nearest stars. But their figures, expressing sums of many millions of miles, are too vast to carry any definite ideas to our minds. When we reflect that each of those stars, from the brightest to the faintest twinkling point, is really a sun, many of them, no doubt, far vaster in size than our sun, but dwindled into such seeming feebleness by reason of their inconceivable distance, we cannot but feel what a little speck of dust, in comparison, must this dwelling-place of ours really be which we call the Earth.

2. It is useful to get this comparative insignificance of the Earth firmly realised by our minds. And in no way can this be done so well as by watching the starry sky, and learning what has been discovered regarding the motions, sizes, and distances of the heavenly bodies. What, then, is the Earth in relation to these bodies ? Has it always been in the same conditipn as now, or has It perhaps passed through long ages of change and progress .-^ Mankind has had a long and varied history. May not the Earth itself have had one also ? If so, can we learn anything about the story of the Earth ?

3. Again, when, on the other hand, we look upon the face of the Earth by day, how boundless and varied it seems ! From the district in which we may chance to live, we can pass in thought to the country at large, then to other countries, and then to the idea of the whole wide globe, with its continents and oceans, its mountains, valleys, and plains, and all that wonderful diversity of form and colour which makes its surface so unceasingly beautiful.

4. This variety is everywhere associated with life and movement. Consider, for instance, the unvarying succession of day and night ; the orderly march of the seasons ; the constant or fitful blowing of the winds ; the

INTRODUCTION.

regular circling of the ocean tides ; the ceaseless flow of rivers ; the manifold growth and activity of plant and animal life ! Surely it was no strange thought when men in old times pictured this world as a living being. And even though we cannot look on the earth as a living thing in the sense in which a plant or animal is so called, yet in view of all that multitudinous movement which is ever in progress upon its surface, and on which, indeed, we know that our own existence depends, there is evidently another sense in which we may speak of the life of the Earth.

6. Now this Life of the Earth is the central thought which runs through all that branch of science termed Physical Geography. ^ The word geography, as ordinarily used, means a description of the surface of the earth, including its natural sub -divisions, such as continents and oceans, together with its artificial or political sub-divisions, such as countries and kingdoms. But Physical Geography is not a mere description of the parts of the earth. It takes little heed of the political boundaries except in so far as they mark the limits of different races of men. Nor does it confine itself to a mere enumeration of the different features of the surface. It tries to gather together what is known regarding the Earth as a heavenly body, its constitution, and probable history. In describing the parts of the earth — air, land, and sea — it ever seeks so to place them before our minds as to make us realise, not only what they are in themselves, but how they affect each other, and what part each plays in the general system of our globe. Thus Physical Geography endeavours to present a vivid picture of the mechanism of that wonderfully complex and harmonious world in which we live.

6. Many of the facts with which this branch of science deals are familiar to every one. With nothing, for exam-

1 This term as here used is synonymous with Physiography, which has been proposed in its stead.

PHYSICAL GEOGRAPHY.

pie, have we better acquaintance than with the air which surrounds us. We have breathed it every moment of our lives ; we know it at rest as well as in storms ; we have watched the growth in it of mists and clouds, as well as the fall of dew and rain. At first there might seem hardly anything more perfectly known to us, and therefore regarding which we should have so little new to learn. But Physical Geography, taking up the subject as one great whole, strives to show how all the different conditions and changes of the air are connected together, to explain their causes, and to point out the essential part which the air takes in the great movements that affect both sea and land. One of the great advantages of this study lies in the very commonplace character of the phenomena of which it treats. We cannot go anywhere without meeting with illustrations of some of the great lessons which it enforces. When we have once practically learnt these lessons, therefore, we carry an additional source of pleasure in every walk and journey. We get into the habit of using our eyes, and noting an endless variety of things that would otherwise have been passed by unseen, and this habit of observation, besides the pleasure its exercise brings with it, will be found of no slight service in the ordinary affairs of life.

7. In completing its picture of the Life of the Earth, Physical Geography must necessarily draw its illustrations from all parts of the world. It thus brings before us phenomena of which we may have no experience in our own country, and which, very probably, we may never have any opportunity of seeing for ourselves. In the study of it we journey, so to speak, all over the world, and learn in a short time far more about the world than we should be able to do from reading a few ordinary books of travel. Indeed, a good treatise on Physical Geography may be regarded as a condensed and wellarranged book of travels in all countries, with this dis-

INTRODUCTION.

tinction, that although it has no personal adventures to describe, it enables us to understand how one region of the earth differs from another, and it explains these differences by connecting them all together and showing their relation to the general principles or laws on which they depend. So that, although a man may never have been in India or Africa, or the Arctic regions, he may, from the study of Physical Geography, have a far better notion of the general features of these countries, and why they differ from each other so much in climate, than many other men who have travelled to, or even have lived for years in them. It is a matter of no little encouragement for all of us to know that the more we watch what takes place around us in our own country, and the more thoroughly we understand it, the more easily do we realise what goes on in other and distant parts of the world.

8. By taking up the study of Physical Geography, not merely as a subject to be learnt from books, but as a practical pursuit to be followed out by our own observations, as opportunity offers in the course of our daily occupations, we make most progress in it and get the largest amount of pleasure out of it. This is the spirit in which the following chapters are written. They are not meant merely to describe the different parts of the earth in such a way that these may most easily be learnt by heart, but rather to incite the learner to use his own eyes, and to examine, compare, and contrast what he sees to take place from day to day. They are so arranged as to begin, where practicable in each sub-division, with our common knowledge. Then they point out what can be ascertained on the subject by our own simple observation and experiment. Lastly, they present such further information as may be acquired from the observations and travels of men who have given much time and thought to the collection and investigation of the facts. In the case of the Air, for example, starting from what each one of us knows by everyday experience, we proceed to con-

PHYSICAL GEOGRAPHY.

sider what we can ourselves easily find out about the air, and from this basis of knowledge we follow what has been still further discovered by prolonged investigation in all parts of the world.

O. At the outset it may be well to group together in due order the different subjects which, coming within the scope of Physical Geography, will have to be attended to in these Lessons.

10. First of all we shall consider what the Earth is, as a heavenly body, how it is related to other heavenly bodies, and specially to the Sun, as the source of light and heat.

11. Secondly, looking at the Earth in itself, we find it wrapped round with an outer envelope of Air, which will next deserve our attention. What this envelope consists of, and the part it takes in the phenomena of the Earth's surface, furnish materials for much interesting inquiry.

12. Thirdly, beneath the surrounding shell of air, and covering the greater part of the surface of the solid globe, lies that vast expanse of water known as the Ocean. We shall follow its tides and currents, and trace the vapour which, ascending from its surface, is carried through the air until it ^Is as rain and snow upon the land, whence it is borne by rivers back again into the ocean. The wonderful beauty and high importance of this circulation will claim our attention.

13. Fourthly, the solid Land will be considered, with its continents and islands, its mountains and valleys, its earthquakes and volcanoes. The evidences of continual change on the surface of the land will lead us back to the action of the air and of water, and we shall find how largely the forms even of " the everlasting hills " have been determined by that action.

14. Fifthly, we shall inquire what Climate is, how different kinds of climate are distributed over the globe, and whether any causes can be assigned to account for

INTRODUCTION.

such differences. This will lead us to note that as there is a geographical distribution of climates, so likewise is there one of plants and animals. Each great region of the earth's surface which has a peculiar climate of its own, has also its own distinguishing assemblage of peculiar plants and animals. Even in the way in which the races of man are grouped over the earth there is evidence of the same connection between the distribution of climates and of life. Thus the geographical distribution of Life over the earth's surface will form the concluding part of these Lessons.

Chapter 1. The Earth As A Planet

Lesson L — The EartKs Form.

1. What then is this Earth on which we live ? The answer to this question must be chiefly given by astronomy, but there are some familiar features in the earth itself which, if rightly considered, help to make the answer more vividly realised. Evidently there is much advantage in obtaining a clear idea of what the earth is as a whole, before we begin to trace the events which take place upon its surface.

2. In the first place, then, the earth, like the sun and moon, is a globe. This may be proved in various ways.

(i) If we set sail from England, and steer westward without turning back, we shall eventually find ourselves in England again. This is called Circuxnnavi^atin^r the "world. It would not be practicable unless the earth were really a globe.

(2) Standing by the margin of the sea, and looking seawards, we observe that a ship which is moving away from us, by and by seems to sink into or under the sea. (Fig. I.) The hull first disappears, and then by degrees the sails. So, on the other hand, when a vessel approaches us, we can first, with a telescope, make out the tops of the sails and masts just peeping above the distant surface of the ocean. Little by little the sails rise as it were out of the water, until at last the hull and the whole vessel come into sight. This could not happen ij THE EARTH'S FORM. 9

unless the surface of the sea instead of being flat were really curved, that is, part of the curved surtace of a

(3) If the suriace of the earth were flat, as men once supposed it to be, the sun would rise at the same time at all places on the eanh. But this is not the case ; sunrise takes place later or earlier as we travel west or east. Again, on ascending a mountain we should see the whole of the earth's surface if that surface were really a plain. But the extent to which we see depends on the height to

Fig. I.— Cimalureof ihe Eanb'B Surface, uihown by (hips u sea.

which we climb. This shows that the earth must be a globe,

(4) When the earth comes directly between the sun and moon, so as to cut off the light of the former from the latter, the moon is said to be eclipsed. Now, the earth's shadow as it creeps over the moon's sur&ce, is seen to be circular, and hence the real form of our planet must be that of a globe.

3. Were it possible for us to quit the earth and look back upon it from a. distance of a few millions of miles, it would appear as a large bright moon, hanging in space, with the stars twinkling on all sides of iL lis suriace would shine like that of the moon, with the light falling on it from the sun, and would be seen to be marked by lo niYSICAL GEOGRAPHY. [i.kss.

irregular bright and dark strips and patches. There would be two specially bright parts on opposite sides of the earth's body, marking the great regions of snow and ice at the north and south poles. Between these two areas certain bright irregular bands would indicate the

Fig. s.^-Tlw Earth and Hoon u E«n from Epace.

position of the dry land, while the intervening darker portions would show the extent of the seas (Fig. 2). If we could transport ourselves still farther away ; if, for instance, we could get as far off as the sun, that is to say more than ninety-two millions of miles from where we are living at this moment, our earth would be seen shining merely as a bright star. And were it possible

II.] THE EARTH'S MOTIONS. ii

for us to reach one of the nearest fixed stars, our globe would be no longer visible, while the sun itself, if seen at all, would appear merely as a twinkling star.

4. But the earth is not a perfectly regular sphere. In particular it is somewhat flattened on two opposite sides, so as to resemble an orange in shape. How this is known and measured will be seen from Lesson IV. A line from the middle of one of these flattened sides passing through the centre of the planet to the middle of the opposite flattened side, is called the Axis, and the points at which it reaches the surface are known respectively as the North Pole and South Pole. A line drawn ipidway between the poles round the bulging part of the earth is termed the Equator.