Physiography

Front matter

I i niiMW Kiw n M i iiM»ii n ww« i» i 11'nnxiii'ir- < ii mm i n ii i i w iii'i'- i fn ' r i r i r ---iiii —

Glass.

Book.

Preface

Nearly nine years ago, I was invited, by the Managers of the London Institution, to take part in a series of courses of Educational Lectures ; which were intended to initiate young people in the elements of Physical Science.

My course was to be the first of the series ; and I made use of the opportunity, thus afforded me, to put into practical shape the ideas, which I had long entertained and advocated, respecting the proper method of approaching the study of Nature.

It appeared to me to be plainly dictated by common sense, that the teacher, who wishes to lead Iiis pupil to form a clear mental picture of the order which pervades the multiform and endlessly shifting phenomena of nature, should commence with the familiar facts of the scholar's daily experience ; and that, from the firm ground of such experience, he should lead the beginner, step by step, to remoter objects and to the less readily comprehensible relations of things. In short, that the knowledge of the child should, of set purpose, be made to grow, in the same

VI PREFACE.

manner as that of the human race has spontaneously grown,

I conceived that a vast amount of knowledge respecting natural phenomena and their interdependence, and even some practical experience of scientific method, could be conveyed, with all the precision of statement, which is what distinguishes science from common information ; and, yet, without overstepping the comprehension of learners who possessed no further share of preliminary educational discipline, than that which falls to the lot of the boys and girls who pass through an ordinary primary school. And I thought, that, if my plan could be properly carried out, it would not only yield results of value in themselves, but would facilitate the subsequent entrance of the learners into the portals of the special sciences.

I undertook, therefore, to deliver twelve lectures, not on any particular branch of natural knowledge, but on natural phenomena in general ; and I borrowed the title of " Physiography," which had already been long applied, in a different sense, to a department of mineralogy, for my subject; inasmuch as I wished to draw a clear line of demarcation, both as to matter and method, between it and what is commonly understood by " Physical Geography."

Many highly valuable compendia of Physical Geography, for the use of scientific students of that subject, are extant ; but, in my judgment, most of the elementary works I have seen, begin at the wrong end, and too often terminate in an omnium gatherzim of scraps of all sorts of undigested and unconnected information ; thereby entirely destroying the educational value of that study which Kant justly termed the "propaedeutic of natural knowledge."

PREFACE. vii

I do not think that a description of the earth, which commences, by telling a child that it is an oblate spheroid, moving round the sun in an elliptical orbit: and ends, without giving him tlie slightest hint towards understanding the ordnance map of his own county ; or any suggestion as to the meaning of the phenomena offered by the brook which runs through his village, or the gravel pit whence the roads are mended ; is calculated either to interest or to instruct. And the attempt to convey scientific conceptions, without the appeal to observation, which can alone give such conceptions firmness and reality, appears to me to be in direct antagonism to the fundamental principles of scientific education.

" Physiography " has very little to do with this sort of " Physical Geography." My heaiers were not troubled with much about latitudes and longitudes ; the heights of mountains, depths of seas ; or the geographical distribution of kangaroos and Compositts. Neglecting such pieces of information — of the importance of which, in their proper places, I entertain no doubt — I endeavoured to give them, in very broad, but, I hope, accurate, outlines, a view of the "place in nature" of a particular district of England, the basin of the Thames ; and, to leave upon their minds the impression, that the muddy waters of our metropolitan river ; the hills between which it flows ; the breezes which blow over it ; are not isolated phenomena, to be taken as understood because they are familiar. On the contrary, I endeavoured to show that the application of the plainest and simplest processes of reasoning to any one of these phenomena, suffices to show, lying behind it, a cause, which again suggests another ; until, step by step, the conviction dawns upon the learner that, to^ altam to even an elementary conception viii PREFACE.

of what goes on in his parish, he must know something about the universe ; that the pebble he kicks aside would not be what it is and where it is, unless a particular chapter of the earth's history, finished untold ages ago, had been exactly what it was.

It was necessary to illustrate my method by a concrete case ; and, as a Londoner addressing Londoners, I selected the Thames, and its basin, for my text. But any intelligent teacher will have no difficulty in making use of the river and river basin of the district, in which his own school is situated, for the same purpose.

The lectures on Physiography were delivered at the London Institution in 1869 ; and I repeated them, at South Kensington, in 1870. Verbatim reports were taken on the former occasion, as it was my intention to publish the course. But I am sorry to say that, in this, as in other cases, I have found a great gulf fixed between intention to publish and its realization.

Seeing a book through the press is a laborious and timewasting affair ; greatly aggravated, in cases such as the present, by the necessity of superintending the execution of maps and figures. And, as I never could muster up the courage, or find the time, to undertake the business, the manuscript remained untouched until last year.

I then had the good fortune to be able to obtain the services of my friend Mr. Rudler, with whose extensive knowledge of various branches of physical science, I was well acquainted ; and, in whose conscientious accuracy, as an editor, I knew I could place implicit confidence.

In preparing the substance of the lectures for the press.

PREFACE. ix

Mr. Rudler has entirely fulfilled my expectations, and has made many valuable suggestions and additions. I have entirely re-written such parts of the work as I thought I could improve ; I have added to others ; and I have carefully revised the proofs of every ciiapter.

I trust therefore that the book maybe useful to both learners and teachers ; but, I am most concerned, that the latter should find in it the ground-work of an introduction to the study of nature, on which their practical experience will enable them to erect a far better superstructure than that which I have been able to raise.

T. H. H.

London,

Is! cnj ember, 1 877.

Preface To The Third Edition

The large demand for this work for educational purposes, during the last three years, has suggested the issue of a new and cheaper edition, which has been carefully revised.

I beg leave to offer my thanks to various correspondents who have called my attention to errors of the pre:-s, or ambiguities of expression in the former editions.

T. H. H.

London, June, iSSo.

Chapter I. Page

THE THAMES . . . . „ I

CHAPTER n.

SPRINGS .......... 21

CHAPTER in.

RAIN AND DEW 39

CHAPTER IV.

THE CRYSTALLISATION OF WATER: SNOW AND ICE . . ^S

CHAPTER V.

EVAPORATION . . » , . . . . 66

CHAPTER VI.

xii CONTENTS.

CHAPTER VII.

KAGH

THE CHEMICAL COMPOSITION OF PURE WATER . . . lOO CHAPTER VIII.

THE CHEMICAL COMPOSITION OF NATURAL WATERS. . IIS

CHAPTER IX.

THE WORK OF RAIN AND RIVERS , I30

CHAPTER X.

ICE AND ITS WORK -. . . . 150

CHAPTER XI.

THE SEA AND ITS WORK 166

CHAPTER XII.

EARTHQUAKES AND VOLCANOES 185

CHAPTER XIII.

SLOW MOVEMENTS OF THE LAND 205

CHAPTER XIV. - ,

LIVING MATTER AND THE EFFECTS OF ITS ACTIVITY ON THE DISTRIBUTION OF TERRESTRIAL SOLIDS, FLUIDS, AND GASES — DEPOSITS FORMED BY THE REMAINS OF PLANTS . 217

CONTENTS. ziii

CHAPTER XV.

FAGB

THE FORMATION OF LAND BY ANIMAL AGENCIES —

CORAL LAND 246

CHAPTER XVI.

THE FORMATION OF LAND BY ANIMAL AGENCIES —

FORAMINIFERAL LAND 260

CHAPTER XVH.

THE GEOLOGICAL STRUCTURE OF THE BASIN OF THE THAMES ; AND THE INTERPRETATION OF THAT STRUCTURE 272

CHAPTER XVni.

THE DISTRIBUTION OF LAND AND WATER 299

CHAPTER XIX.

THE FIGURE OF THE EARTH — CONSTRUCTION OF MAPS. 3^7

CHAPTER XX.

CHAPTER XXI.

THE SUN ....-, 359

LIST OF ILLUSTRATIONS.

FIG. PAGE

1. How to find the North point 8

2. Magnetic Declination . lo

3. Hill-shading by means of hachures 12

4. Contour-lines round a lull 14

5. Section across the Thames basin, showing the form of the

ground 16

6. Formation of a spring 23

7. Section of Hampstead Heath 26

8. Horizontal permeable and impermeable strata 29

9. Inclined permeable and impermeable strata 29

10. Effect of a fault on the position of a spring or ^^■ell ... 30

11. Diagrammatic Section across the London basin 31

12. Rain-gauge 49

13. Daniell's hygrometer 52

14. Ice in water 57

15. Rock crystal . . - 58

16. Snow-crystals 61

17. Ice-flowers 63

18. Hair hygrometer 70

19. Dry and wet bulb thermometers . , 71

20. Decomposition of red oxide of mercury . . , . , 77

21. Torricelli's experiment . go

22. Times weather chart 93

23. Z>«//y iVirzf/5 ^barometer chart ... 96 xvi LIST OF ILLUSTRATIONS.

FIG. FAGB

24. Daily Telegraph barometer chart 97

25. Decomposition of water by electricity loi

26. Oxygen and hydrogen from decomposition of water . . . 103

27. Decomposition of water by means of sodium 107

28. Decomposition of water by means of heated iron .... 108

29. Formation of water by combustion of dry hydrogen . . . 112

30. Bridge of travertine at Clermont, Auvergne 12.1

31. Stalactites and stalagmites, Isle of Cakly 123

32. The Grand CaKon, Colorado 137

33. Self-established drainage system 138

34. River-valley worn through gravel and LonJon clay . , . . 139

35. Delta of the Nile 144

36. Catchment-basin and delta of a river 145

37. Delta of the Mississippi 146

38. Hope's experiment on the contraction of water 152

39. Glacier of Zermatt 156

40. Motion of a glacier 157

41. Lateral and medial moraines 160

42. Roches Moutonnees Creek, Colorado 162

43. The Needles, Isle of Wight 169

44. Map of the Atlantic, showing course of the Gulf Stream . . 174

45. Section of the Atlantic Ocean between Sandy Hook (near

New York) and Bermuda, a distance of 700 nautical miles. 175

46. Currents in water by heat 177

47. Currents in water by cold .177

48. Chart of the estuary of tlie Thames between the Nore and

Margate 182

49. Plain of marine denudation 183

50. Diagrammatic Section of a Volcano 190

51. Diagi'ammatic Section of a Cinder Cone ' . 191

52. Breached Volcanic Cones, Auvergne ....'.,... 194

53. Diagrammatic Section of a Volcano, with Dykes and Minor

54. Summit of Vesuvius in 1756 . 195

55. Summit of Vesuvius in 1767 196

56. Vesuvius and Monte Somma . . . . 198

LIST OF ILLUSTRATIONS. xvii

FIG. TACn

57. Graham Island, 1831 19^

58. Beehive Geyser, Yellowstone Park, Colorado 201

59. Marble Column from Temple of Jupiter Serapis .... 207

60. Strata deposited in a basin 214

61. Strata thrown into a basin-shape 214

62. Section from Abingdon to the Isle of Wight 215

63. Fossil fruit {Nipadites ellipticus) from the London clay,

Sheppey 230

64. Microscopic section of diatomaceous deposit, Mourne Moun-

tains, Ireland 231

65. Section of coal measures . . 235

66. Sdgniaria ficoixies ; a coal measure fossil 236

67. Sigillaria attached to stigmarian roots 237

68. Cuboidal block of coal split along natural planes .... 238

69. Microscopic section of Better Bed coal, Yorkshire . . . 239

70. Caryophyllia Stnithii, a coral-polype from the coast of Devon-

shire 250

71. Diagrammatic section of a single cup-coral, to show the

general structure of the polype, and the relation of the

skeleton to the soft parts 251

72. Thecopsammia socialis, Pourtales 252

73. Diagrammatic section of an island surrounded by a fringing-

reef 258

74. Diagrammatic section of an island surrounded by a barrier-

reef, with intervening lagoon 258

75. Diagrammatic section of a coral island, or atoll 258

76. 77. Deep-sea sounding apparatus used by the Challenger . . 262

78. Section of the Atlantic sea-bed between Newfoundland and

Ireland 264

79. Globigerina bulloides, D'Orb. ; Orbulina universa, D'Orb. ;

a coccosphere ; a coccolith, two views • . . . . . 265

80. Section exposed in Cannon Street, London, 185 1 .... 275

81. Map of the Valley of the Thames, between Kingston and

Woolwich 279

82. Section across the Valley of the Wandle, sho"iving high-lsv°l

gravels and valley-gravel .... „ 280

b xviii LIST OF ILLUSTRATIONS.

FIG. PAGR

83. Cyrena {^Corbicula) fluminalis 281

84. The Mammoth {Elephas primigenius) 283

85. A palaeolithic implement, from Gray's Imi Lane .... 285 Z6. A neolithic implement from the Thames at London . . . 285

87. Nautilus centralis, from the London clay 289

88. Microscopic section of chalk from Sussex 292

89. Atlantic ooze from a depth of 2,250 fathoms .... 292

90. Map showing the efTect of an upheaval of the sea-bottom

around the British Isles, to the extent of lOO fathoms . . 302

91. Map of the World, showing direction of the principal chains

of mountains 304

92. Diagrammatic section across Eurasia 306

93. Diagrammatic section across North America 312

94. Diagrammatic section across South America 312

95. Map of the Arctic regions 314

96. Continental or land hemisphere 315

97. Oceanic or water hemisphere 3^5

98. Disappearance of a ship at sea 318

99. Ship approaching shore. Curvature of the sea . . . . 319 100. Enlargement of the horizon by ascending a hill . . . . 321 xoi. The earth within the star-sphere , 322

102. Difference between polar and equatorial diameters of the

earth 326

103. Coordinates of a point ... 327

104. Parallels of latitude 328

105. Lines of longitude 328

io6. Orthographic projection . . 332

107. Globular projection 333

108. Conical development 334

109. Mercator's projection 335 .

1 10. Polar projection 336

111. Diagram to illustrate the effect of changing the position of the

earth's axis in relation to the sun 339

112. Diagram showing the earth's relation to the sun at different

seasons . , . 3C0

113. The earth at the summer solstice . ■ ... . 35^

LIST OF ILLUSTRATIONS. xix

(■ lO. PAOB

114. The earth at an equinox .... , 353

115. Diagram to illustrate perihelion and aphelion 354

116. Zones of the earth's surface 357

117. Figure to show that apparent magnitude depends upon the

visual angle 360

118. Comparative sizes of the sun and the earth 363

119. The great sun-spot of 1865 as it appeared on Oct. 15 . . 364

1 20. Apparent paths of sun spots at different times of the year . 366

121. The corona and solar prominences as seen during a total

eclipse in 1851 367

122. The formation of the solar spectrcm . . . ... 369

COLOURED PLATES.

PLATE

1. Contoured Map of the Thames Basin Frontispiece.

II. Map of Great Britain and Ireland divided into

River-basins facing page 2o

III. Typical forms of Clouds „ 42

IV. Hyetographical or Rain Map ot England and

Wales „ 48

W, Geological Map of the Basin of the Tiiames . . ,, 288

PHYSIOGRAPHY.

CHAPTER I.

THE THAMES.

No spot in the world is better known than London, and no spot in London is better known than London Bridge. Let the reader suppose that he is standing upon this bridge, and, needless of the passing stream of traffic, looks down upon the river as it runs below. It matters little on which side of the bridge lie may chance to stand ; whether he look up the river or down the river, above bridge or below bridge. In either case he will find himself in the presence of a noble stream measuring, when broadest, nearly a sixth of a mile from bank to bank. The quantity of water under London Bridge varies considerably, however, at different seasons, and even at different hours on the same day. When the water is highest, the greatest depth is about thirty feet and the width 800 feet ; when the water is lowest, the greatest depth is something like tweLe feet and the width only 650 feet. This variation in the volume of water shows that the river is not at rest, and that its surface is, in fact, alternately rising and falling. Moreover, apart from the local agitation due to traffic, apart too from the surface ripples

^ R raised by the passing breeze, the whole body of water is in a constant state of motion. At one time in the day the water sweeps down below bridge in the direction of Greenwich and far onwards to the Nore ; after this movement has been continued for some hours, it gradually slackens, and the water comes almost to a stand-still; then the motion begins afresh, but its direction is reversed, the water flowing this time towards Westminster and far away up the river ; but, after a while, this motion slowly subsides, and is followed once more by renewed movement in a contrary direction.

Every one knows that this regular backward-and-forward movement of the great mass of water is due to tidal action. For about seven hours, during ebb-tide, the water of the Thames runs down towards the sea ; and for about five hours, during flood-tide, the movement takes place in th& opposite direction, the water being then driven up the river. At the end of the ebb-tide the river is shallowest , at the end of the flood tide it is deepest. The water at London Bridge is consequently twice in every four-and twenty hours at its highest and twice at its lowest level.

As we go up the river, we find the efi'ect of the tide gradually diminishing, until at length it ceases to be felt. In point of fact, the tidal movement has no influence beyond Teddington Weir, some nineteen miles above London Bridge. The very name Teddington is indeed said to be a corruption of " Tide-end-ton," the town where the tide ends. Up to Teddington, then, the Thames is a tidal river, the water rising, and falling, and moving, fiist in one direction and then contrariwise, at definite intervals. The flood tide occupies about two hours in coming up from the Nore to London, a distance of about 40 miles ; that is to say, it is high water at London Bridge two iiours later than at the Nore. Then it takes two hours more for the gradual rise of the \^ater to its highest level, to travel onwards from London to Teddington, though the distance between these two points is less than twenty miles. The rise of the level of the surface of the Thames, which thus passes with great rapidity from the Nore towards Teddington, is accompanied by a much slower general motion of the water in the same direction, which constitutes the upward current of the tide ; while a downward current in the opposite direction attends the fall of the water during the ebb.

Floating bodies are therefore carried towards Teddington, during the flood, and towards the Nore, during the ebb. It is almost needless to add that this tidal action is of vast service to the port of London, since barges, lighters, and other boats are thus enabled at certain periods of the day to float up or down the river with little or no expenditure of power on the part of the boatmen.

Above Teddington Weir the motion of the river is totally different from that which is observed at London Bridge. There is no alternate backward-and-forward motion, no regular rise and fall of the water, but the river flows onwards in one constant direction, always running down towards London. Careful observations at Teddington have shown that, with the water at ordinary summer-level, about 380 million gallons ' flow over the weir every four-and-twenty hours. This vast volume of water is swept down past London, and ultimately carried out to sea. As the ebb-tide runs for about seven hours, whilst the flood lasts only five, it is clear that much more water runs down than flows up ; and it is in this way that the vast volume of water sent down from above Teddington drains away seawards.

1 Many of the statistical data relating to the Thames have been obligingly furnished by Mr. Leach, of the Thames Conservancy Board.

B 2

In seeking the origin of the water thus brought down by the Thames, it is necessary to trace the river to what is commonly called its " source." On ascending, it is observed that the river grows smaller, the volume of water becoming less and less. Thus, at Teddington, the Thames is only 250 feet wide at high water, whilst its width at London Bridge is about 800 feet. Follov/ing the many windings of the river past Windsor, Reading, and Oxford, we observe the stream still growing more narrow and more shallow, until at Lechlade, in Gloucestershire, 146 miles from London, the Thames ceases to be navigable. At Lechlade the quantity of water running down the river has been roughly estimated at something like a hundred million gallons per day, or only about one-fourth the quantity flowing over Teddington Weir. The main stream splits up at Lechlade into a number of smaller streams, forming the " head-waters " of the river, and it is by no means easy to say which of these streams should be followed up in seeking the true source of tlie Thames. Nor does it much matter, for the origin of any one of them is much the same as the origin of any of the others. It is usual, however, to single out one of these streams, which takes its rise in a spring near Cirencester, about 170 miles from London Bridge, and is dignified with the name of Thames Head.

Although the spring at Thames Head is thus popularly called the "source" of the river, it should be remembered that the quantity of water delivered by this spring is quite insignificant when compared with that derived from the numerous streams which flow into the Thames at various points along its course. Every tributary helps to swell the bulk of the river by discharging its water into the main stream ; yet it does not follow that the river is necessarily increased in width by the influx of this water, for it often happens that the additional supply is carried off by increased rapidity of flow. As the Thames rolls along, it receives a number of these feeders, or affluents,^ which empty themselves into the river, some on one side and some on the other.

It is obviously convenient to have some ready means of distinguishing the two banks of a river. For this purpose, geographers have agreed to call that bank which lies upon your right side as you go down towards the sea the right bank, and to call the opposite side the left bank. All that you have to do then, in order to distinguish the two sides, is to stand so that your face is in the direction of the mouth of the river, and your back consequently towards its source, when the right bank will be upon your right hand and the left bank upon your left hand. At Gravesend, for example, the right bank is that which forms the Kentish shore, while the left bank is on the Essex side. With reference therefore to the rivers tributary to the Thames, it is said that the Churn, the Colne, the Leach, the Windrush, the Evenlode, the Cherwell, the Thame, the Coin, the Brent, and the Lea empty themselves into the Thames on the left bank; and the Rey, the Cole, the Ock, the Kennet, the Loddon, the Wey, the Mole, and the Darent, open into the river on its right bank. The relative positions of these affluents^ and their relation to the Thames, may be seen in the map given in Plate I.

If a person in a balloon passed at a great height over any

'^ Affluent, from the Latin ad zxiAfuo, " to flow." The junction of an affluent with the main stream is termed the confiuence, or place where they "flow together." Thus, the town of Coblenz takes its name from the Latin form Confine ntes, in allusion to its position at the junction of the Moselle and the Rhine.

part of the earth's surface, and sketched in outUne what he saw directly below, his sketch on a flat surface like this page would be called a ma/>. When the portion of country thus delineated is but small, the sketch is generally termed d. plati ; and if the area depicted consist chiefly of water instead of land, it is called a chart Hence we commonly speak of the plan of an estate, the map of a country, the chart of an ocean. A map of the Thames, then, is simply an outline-sketch of the river and neighbouring portion of the earth's surface, as would be seen from a balloon passing at a great height directly over the country. It is the common practice to draw maps in such a position that the north is towards the top, and the south towards the bottom ; while the east lies on the right hand of the person who looks at the map, and the west lies on his left hand. By simply looking then at the map, forming Plate I., it is seen at once that the Thames, though taking — like most rivers — an irregular course, winding first in one direction and then in another, nevertheless has, on the whole, a westand-east course ; it flows, in short, from the west towards the east. At the same time it is seen that the left shore of the river is its northern bank, and the right shore its southern bank. It is clear, too, that the tributaries on the left or north side flow generally from north to south, whilst those on the riglit or south side run generally from south to north.

These terms — north and south, east and west — are terms which have a meaning quite independent of local circumstances, and indicate definite directions which can be determined in any part of the world and at all times. Wlien, in the early part of this chapter, we used the local expressions "up the river" and "down the river," "above bridge " and " below bridge." it was assumed that the reader was familiar with the Thames. But to a perfect stranger, one who had never seen the river and knew nothing of London Bridge, such a method of description would be unintelligible. By employing, however, the terms north and south, east and west, we are using expressions that are familiar to all educated people, since they refer to standards of direction universally recognised. It is desirable to explain how these cardinal points may be be determined.

Of the four points, the south is perhaps the most easily found, at least on a sunshiny day. Every morning the sun appears to rise slowly in the sky, and mounts to its greatest height at noon. At the instant of reaching its greatest height, or in other words at exact noon, the sun is precisely in the south. If, then, you place yourself in such a position as to have the sun shining full in your face at that particular time, you must be facing south ; and you will consequently have your back to the north, your right hand towards the west, and your left towards the east.

As true noon does not always coincide with 12 o'clock, as indicated by an ordinary timekeeper, it is necessary to explain how it may be determined. Thrust a stick vertically into the ground, and observe, at different hours of the day, the length and direction of its shadow cast by the sun. When the sun is rising in the sky, the shadow is thrown towards the west ; and when the sun is going down, it is thrown towards the east; at noon, however, it inclines neither to the east nor to the west, but falls exactly in a north- and -south line ; and, moreover, the shadow is then shorter than at any other time. If, therefore, you observe when the shadow is shortest, that time will be exactly noon. The line indicated by the shadow at noon is known as the

PHYSIOGRAPHY.

[chap.

meridian line or mid-day line. That end of the shadow-line which is towards the sun points to the south, and the opposite end to the north. If then a Hne be drawn anywhere at right angles across the shadow, the right-hand end of the cross-line, as you look to the south, points towards the west, and the left hand towards the east.

POLE STAR

GREAT SEAR

Fig. I — How to find the North point.