World-life; or, Comparative geology

Front matter

-bo'

-0- ^

3;

Preface

r mHE reader will find in the following pages a thoughtful view of -*- the processes of world formation, world growth and world decadence. I have gathered together here many of the important facts observed in the constitution and course of nature, and have endeavored to weave them into a system by the connecting threads of scientific inference. I have aimed to incorporate the soundest and latest views published on the various branches of the subject; and have yet felt constrained, in so wide a field, and so unexplored in some of its nooks, to interpose my own conclusions in some cases where, perhaps, due diffidence should have restrained my pen. Inevitably the whole discussion is conducted from the standpoint of nebular cosmogony. This, as will be seen, has shaped the views presented on the accumulation of the materials for world formation, on the evolutions of nebulae, stars and planets, on the all-important influence of tidal action in cosmic history, and on the grand cycle of cosmic existence. Appropriately the treatment ends with a historical sketch of the progress of opinion toward the lofty and inspiring generalization which the work attempts to set forth.

The motives which have prompted to the preparation of the work are four-fold .

1. I felt desirous that the general reader should be able to find within reach some simple, yet complete and connected, account of the development of the world and the system of material things to which we belong. Many of the grandest conceptions of modern science fall within this range. Many of the marked advances of modern investigation have contributed to the enlargement of our view in this field. Yet there is no work in the English language, if, indeed, in any language, bringing into one connected course of discussion all the questions properly incident to the activities of world.

Yl PREFACE.

life. Different persons have ably investigated different branches of the general theme, as the reader will learn in the sequel, but no one has brought together and put in the form of popular statement the chief results of so diversified a range of researches. Many thousands of intelligent listeners have testified their appreci- . at ion of the expositions offered during fifteen years past from the popular platform; but these expositions have been necessarily descriptive and superficial, while many questions and many difficulties raised by the hearer had to be left unanswered. Here the speaker sits down to a sober talk with those who wish to listen further. I hope, therefore, the present work will find a welcome among the multitudes who have caught mere glimpses of the great doctrine, as well as the large class of readers in general who require something more substantial than our popular, fictitious tales of society.

2. I desired to offer the reader a portrayal of the grand system of the universe, and leave him with a profound impression of the omnipresence and supremacy of One Intelligence. The unity and interdependence of all parts of ihs cosmic mechanism, from nebula to river delta ; the universality of nature's forces, and the uniformity of nature's modes of activity, all the way down from the galaxy to the little cascade in the glen, are facts of such stupendous and impressive significance as to stir the imagination and arouse the most torpid soul. This w6nderful concatenation of things when once glimpsed by the timid doubter, must force a conviction of the continuity of material existence ; and whoever has gained that conviction, and will faithfully question his own consciousness, will soon be convinced that that which is interpreted, and can only be interpreted, in terms of mechanism, cannot be self- originated, however remote its origin ; nor self-acting, however vast its extent or incomprehensible its activities.

3. I desired to induct the earnest student of nature, young or old, into the vestibule of celestial mechanics, and leave him with an inspiration which should carry him on to the pursuit of the higher methods of physical investigation. I have hoped, also, to show him that the fields of truth are not fenced off from each other and limited by the narrow definitions of the sciences. The fences are all down, and it is all one domain. The geologist tries to work

PREFACE. VU

out the constitution and life history of our planet. For the study of its accessible parts he needs to use the appliances and results of the whole round of the sciences. To its interior he cannot penetrate; but he finds the planet journeying on a course of change which leads directly from a state of high primitive incandescence ; and, lifting his eyes, he beholds the incandescent state as a common incident in the vicissitudes of worlds. He cannot transport himself across the intervals of geologic aeons, but he can gaze upon other worlds just entering upon states passed millions of years ago by our earth; or states, even, which will be reached by our planet some millions of years in the future. I have attempted to take the reader over the system of evidences from which he may thus reason in laying the foundations of a science which, from one point of view, may be styled the geology of the stars; and, from another, the astronomy of the earth. It is the science of Comparative Geology. It is Astrogeology. It yields to no science in the fruitfulness and fascination of its conceptions.

4. It has been a part of my purpose, also, to clear up the most serious difficulties encountered by belief in the nebular origin of our planetary system. At the present day the objections heard do not proceed to any considerable extent from proper representatives of scientific opinion, but from intelligent persons who fear that the interests of religious faith are jeopardized by the acceptance of any form of evolution. Some of these have honored me by very special attentions. They have challenged me to controversy, and their abettors have sometimes jeered me over my assumed inability to rise from the pile of ruins which has been made of me and my theory. I need not disguise the satisfaction which I feel in the arrival of the convenient time when these gentle gladiators shall discover themselves battering their blades against a wall.

While the fundamental conception underlying the course of reasoning here pursued is that of nebular evolution ; and while the general method of the evolution conforms to the celebrated hypothesis of Laplace, it would be an error to conceive the present work an attempt to establish the "hypothesis of Laplace." In the first place, the general principles of nebular cosmogony were the growth of a century and a half ; and the ideas contributed by Kant and Sir

Vlll PREFACE.

William Hersehel were certainly not less guiding and determinative than the services of the Marquis de Laplace. In the next place, the development of the doctrine has continued ever since the Sysfhue di( Monde was published. Since the invention of the spectroscope, the nebular cosmogony has undergone important modifications. A number of the ablest investigators of the present generation have given their best efforts toward putting the general doctrine in a consistent shape. Nor can it be correctly said that the general theory remains still in the status of a hypothesis. In certain points of detail, opinion may still remain divided ; but when a hypothesis has stood the scrutiny of three generations, and has become all but unanimously accepted by those prepared to form original opinions, as the real expression of a method in nature, surely, then, the time has passed when any person can advantageously illustrate his learning and sagacity by continuing to reproach the conception as "a mere hypothesis." If any " mere hypothesis" ever strengthened into the condition of a scientific doctrine, assuredly we find in the scientific world to-day the general features ot a sound nebular doctrine.

In style and treatment the present work possesses a double character. The general reader may confine himself to the body of the discussion, unterrified by the nature of the foot notes, and find a simple, continuous treatment of the theme which. I hope, will satisfy his expectations. But if any one desires to know by what means some of the statements of the text have been established, he will find frequently in the foot notes the indications of simple mathematical operations, which may yield him some additional gratification. And if he feel prompted to pursue still further any branch of the inquiry, the accompanying references to the literature of the subject will enable him to follow the masters of science into their most recondite investigations. Thus, for one class, the book is suited to be read rapidly and laid aside : for another class it is a text book which may be studied.

The general conception of world life here set forth has occupied the author's thoughts for many years ; and by writing and by popular lectures, as well as before university classes, he has endeavored to disseminate truthful and inspiring estimates of the method of the world's growth. He has stood for the defence of nebular theory

PKEFACE. IX

when it had few friends, and when its enemies were prompted as much by sentiment as by good reason. The great idea was fascinating; its magnificence took possession of the imagination, and its symmetry and coherence commanded rational conviction. It now commands the admiration and championship of the scientific world. I feel that it is entirely improbable that all errors of statement have been avoided through all the details of the discussion. The intelligent reader will discover many points where I have had to cut loose from the moorings of high authority and venture among the breakers of independent speculation. It is only Justice to myself, also, to state that all the main positions of the work were taken and reduced to writing more than two years ago. Many of those which at the time were new, or seemed to be new, were presented in public lectures as early as 1878 and 1879. Since these dates many advances in observation and in theory have been made, and not a few along those very lines which I had worked out. Since my first enunciations, Nordenskjold, Tissandier and the British Association have done much to establish the doctrine of disseminated cosmical dust; Sir. W. Siemens has published his speculations on the sources of the sun's heat; M. Faye has investigated the geology of the moon; Mr. (now Professor) G. H. Darwin has published his beautiful analytical investigations of the evolution of a rotating viscous spheroid; and Rev. 0. Fisher has collected in a handsome volume his researches on the physics of the earth's crust. If there remain any thoughts or suggestions which may fairly be ascribed to the author of this work, the scientific reader will find it out ; and I have only to hope that they may be found adequately supported by evidence; and, finally, that the whole discussion may afford the reader a degree of pleasure equal to that experienced by the writer in bringing the discussion to its present shape.

University of Michigan, September, 1883.

COISTTET^TS.

Chapter I. Cosmical Dust

1. Phenomena and Physical Characters _ . , , 3

2. Meteoroidal Orbits 17

§ 2. Zodiacal Light 23

1. Phenomena and Constitution . _ . _ _ 27

2. Connection of Comets and Meteors . _ . _ 33 § 4. Saturnian Rings .._.._. .35 § 5. Nebula 35

1. Their Existence 35

2. The Spectroscope and Its Applications _ _ > 37

3. Forms of Nebula? 42

§ 6. Universal World Stuff _...__ 48

1. Theory of Cosmical Dust ... . . _ .48

2. • Theory of Elemental Atoms 49

(L) History of Opinions 49

(2.) Siemens' Hypothesis Concerning Solar Heat . 56

§ 7. A Cosmical Speculation 65

1. Aggregation of Cosmical Matter _ . _ . 65

2. Cosmical Matter as a Resisting Medium . . .70

3. Genesis of Nebulas and Comets .... 71

4. Vicissitudes of Comets within Our System . . .74

xi

Xll COlsTTENTS.

Chapter II

:nebular life. § 1. Nebular Heat ...__. ..81

1. Heat Produced by Refrigerative Contraction _ _ 81

2. Changes in the Forms of Nebulge . _ .- . .87

3. Heat Arising from the Aggregative Process . . 92 § 2. Nebular Rotation 94

1. Causes of Rotation . . . . . . . 94

2. Causes of Nebular Forms _.■_.. 99

3. Influence of Resisting Medium .... 104

4. Nebular Evolution without Rotation . _ _ , 105 § 3, Nebular Anxulation _ _ _ . . * . 106

1. The Law of Equal Areas lOG

2. Abandonment of a Ring 110

3. Determination of the Width of the Ring ... Ill

4. Non-Annulating Nebula? and Stratified Rings . . 118 § 4. Spheratiox of Rings 119

1. Disruption of a Ring 119

2. Rotation of Resulting Mass . . . . .121

3. Influence of Cosmic Tides 129

4. Ultimate Sjmchronism of Axial and Orbital Motions . 134

5. Summary of Laws of Rotation . . . .134

6. Arrangement of Heavier Matters on the Derived Sphe-

roid 137

7. Orders of Nebulae 139

CONTENTS. Xlll

Part II. Planetology

CHAPTER I.

ORIGIN OF THE SOLAR SYSTEM.

§ 1. Verification of Nebular. Theory from Facts . . 147

1. Phenomena of the Solar System . _ _ . 147

A. Demonstrative Phenomena 147

B. Phenomena Apparently Confirmatory . . 149

2. Phenomena External to the Solar System . _ _ 150 § 2. Objections Based on Relations of Planetary Motions 153

1. Retrograde Motions .._____ 153

(1.) Caused by Perturbative Attractions . _ 154

(2.) Caused by Coalescence of Planetary Constituents . 157 (3.) Caused by a Certain Relation of Rotary Motion of

the Nebula 157

(4.) M. Faye's Explanation _ . _ _ _ 158

2. The Periodic Times Too Long . . . _ .158

(1.) Effect of Subsequent Planetanon _ . .159 (2.) Effect of Great Central Condensation of the Annu-

lating Spheroid 161

3. The Periodic Times Too Short 167

4. The Periodic Time of Phobos Too Short . . .168

5. No Adequate Cause for Rotary Motion ... 170 § 3. Objections Based on Relations of Planetary Positions 171

1. Orbital Inclinations _ . ... . . 171

2. Interplanetary Intervals . . . . - - 173

3. Elliptic Forms of Orbits 173

(1.) Effect of Subsequent Planetation . . .174 (2.) Effect of Perturbative Influences ... 175 § 4. Objections Based on Relations of Planetary Masses AND Densities 175

XIV COKTEKTS.

1. The Aggregate Asteroidal Mass Too Small _ . 175

2. Disrupted State of the Asteroidal Mass . _ _ 176

(1.) Contingencies of a Stratified Ring ... 176 (3.) Possible Fate of an Intra-Jovian Ring . _ 177

(3.) Effect of Excessive Undulations in a Fluid Ring 177

3. Low Densities of the Exterior Planets .... 177 § 5. Objection Based on Relation to Terrestrial Duration 179 § 6. Objections Based on Relations of Comets, Stars and

1. The Comets Irreconcilable with the Theory . . 181

(1.) Neither Laplace nor Other Astronomers have Included Comets in Our System's Nebular History . 182

(2.) Some Comets must Approximate Planetary Conditions 183

(3.) The Physical Relations of Comets to Our System are Acquired _ . 183

2. Matter of Requisite Tenuity could Not Exist . . 184

3. The Separation of a Ring Improbable .... 186

(1.) Reason and Observation Affirm the Possibility . 186 (2.) M. Faye's Objections Considered . _ . .187

4. The Diverse Constitution of the Fixed Stars . . 191

(1.) No Universal Homogeneity of Matter Assumed . 191 (2.) Stellar Spectra Testify the Opposite of the Claim 191

5. Nebular Spectra Indicate Too Low a Pressure _ - 192

(1.) Nebular Theory is Not Staked on Spectra of Neb-

ulfe 192

(2.) The Spectra do Testify a Self-luminous, Tenuous

(3.) Adverse Spectral Evidence Outweighed . . 193 § 7. What the Nebular Theory does Not Imply _ . . 196 § 8. Proposed Modified Forms of Nebular Theory . _ 198

1. M. Faye's Proposed Modification 198

Critical Remarks on M. Faye's Theory . . . 208

2. Spiller's Proposed Modification 213

CONTENTS. XV

CHAPTER II.

GENERAL COSMOGONIC CONDITIONS ON A COOLING PLANET.

§ 1. Relative Ages of Planets ix a System . _ . _ 315

§ 2. Passage to the Molten Phase _ . . _ . 217

§ 3. Superficial Solidification From Cooling . . . 218

§ 4. Internal Solidification From Pressure _ . _ 220

§ 5. Maximum Internal Temperature on an Incrusted Planet 221

§ 6. Tidal Action and Its Consequences . _ . . 222

1. Some Elementary Principles 222

2. General Effects of Tidal Action in Planetary Life . 230

(1.) Rotational Retardation Caused by Lagging Tide 232 (2.) Recession of Tide-Producer Resulting from Same 239 (3.) Increased Inclination of Axis of Tide-Bearer Resulting from Same 243

3. Tendency to Synchronism of Rotary and Orbital Motions 248

4. Predetermination of Submeridional Trends . _ . 252

5. Outflow of Molten Matter 255

6. Crushing Effects of Tidal Deformation . , .255

7. Marine Tides in the Early History of a Planet . . 256

§ 7. Liquefaction of Water 270

§ 8. Transformations of the Planetary Crust . _ _ 274 § 9. Planetographic Effects of Certain Changed Astronomical Conditions ._.._.. 278

1. Changes in Velocity of Rotation . . _ . 278

2. Retarded Orbital Motion 281

3'. Increase of Obliquity of Axis to Plane of Orbit . 282

4. Change in Relative Positions of Apsides and Equinoxes . 285

5. Changes of Orbital Eccentricity . . . _ 288 § 10. Orogenic Forces 291

1. Theory of Upheaval by Aeriform Agents . . . 292

2. Theory of a Molten Nucleus and a Wrinkling Crust . 294

3. Theory of Copious Sedimentation along Geosynclinals 314

XVI CONTENTS.

4. Theory of Mashing Togetlier 319

5. Statement of Separate Constructive Conceptions Rela-

tive to Mountain Making .__... 323

6. Final Conception of Orogenic History . . . 326

7. Analytical Conspectus of Orogenic Speculations _ _ 331 § 11. Unequal Thickness of Planetary Crust . _ . 335

CHAPTER III. SPECIAL planetology; or, present condition and

COSMOGONIC HISTORY OF THE PLANETARY BODIES OF OUR SYSTEM.

1. Condition of the Earth's Interior .... 339

(1.) Fluidity of a Certain Zone 344

(2.) Fluidity Resulting from Relief of Pressure . 345 (3.) Tidal Deformation and Volcanic Phenomena . 346

2. Submeridional Trends in the Earth's Primitive Structure 350

3. The Earth's Age, with Methods of Estimation . . 355

(1.) Time Required for Contraction of the Sun . 355 (2.) Time Required for Cooling of the Sun . . 356

(3.) Time Required for Cooling of the Earth . . 356 (4.) Time Required for Deposition of All the Rocky

Sediments 356

(5.) Method Based on Disturbance from Continental

Elevation 366

(6.) Calculation Based on Secular Variation of Eccentricity ... 368

(7.) Estimates Based on Rates of Erosion and Deposition 369 (8.) The Rate of Terrace Formation . . . .374 (9.) Under-rate of Increase of Internal Heat beneath Regions Anciently Covered by an Ice Cap . . 376

g 2. The Moon 379

1. Planetological Retrospect 379

CONTENTS. xvn

2. .Tidal Forces on the Moon . . - . .383

3. Physical Aspects of the Moon 385

4. Tidal Evolution of the Moon 395

5. The Atmospheric Factor in Lunar History . . . 410 § 3. Mars 415

1. Phenomena of Mars, and Their Interpretation . .. 415

2. Tidal and Atmospheric Influences on Mars . . . 417 § 4. The Inferior Planets 420

1. Venus 420

2. Mercury .423

1. Physical Relations _...... 425

2. Jupiter's Retarded Development .... 429

3. Tidal Action on Jupiter 434

4. Tidal Effects and Densities on Jupiter's Satellites . 438 § 6. The Ultra-Jovian Planets 442

Chapter IV

PLANETARY DECAY; OR, COSMIC CONDITIONS MORE ADVANCED THAN THE TERRESTRIAL STAGE.

1. Shrinkage and Acceleration of Axial Motion . . 459

2. Absorption of Water and Atmosphere . _ _ 460

(1.) Index of Rock Absorption by Volume . . _ 460 (2.) The Volume of the Ocean . . _ . 466 (3.) Calculation of Absorptive Capacity of the Planetary Pores ...--._. 467 § 3. Synchronistic Motions and Tidal Finalitos . . 473 § 4. Influence of Interplanetary Matter .... 477 § 5. General Refrigeration 484

1. Planetary Refrigeration 484

2. Solar Refrigeration 484

XVlll CO^iTTENTS.

(1.) Inductive Evidences of Lowered Terrestrial Temperature - . _ 485

(a) In Historic Times 485

(6) In Prehistoric Times . . . - .485 (c) Cause of Secular Deterioration of Climates . 486

(2.) Deductive Considerations Touching Secular Cooling 489 3. Revivification of a Dead Universe - . . . 491

Chapter V. Ha.bitability Of Other Worlds

§ 1. Some Referexces to Literature ox the Subject . . 496 § 3. The Humax Staxdard of Habitability Not Absolute . 497 § 3. Habitability uxder the Humax Staxdard . . _ 500

Chapter I

FIXED STARS AND XEBUL^. § 1. COXDITIOXS OF THE FiXED StARS 511

1. Double, Triple and Multiple Stars . . , . oil

2. Temporary Stars 513

3. Variable Stars 518

4. Gradations of Stars 522

5. Indications of Incipient Stellation .... 530 § 2. CosMOGOxic Conditions of Nebula _ .- . .531

Chapter II. The Cosmic Cycle

§ 1. The Keys of Comparative Geology .... 534

§ 2. The Final Generalization 538

1. Stages of World Life ....-.- 538

2. Some Final Deductions ..--.. 544

CONTEi^"TS. XIX

Part IV. Evolution Of Cosmogonic Doctrine

CHAPTER I.

PRE-KANTIAN SPECULATIONS.

§ 1. Greek Philosophers , . 551

§ 2. Speculations of Kepler 553

§ 3. The Vortical Theory of Descartes . . . _ 554

3. His Planetogeny 564

§ 5. The Vortical Theory of Swedenborg .... 566 § 6. The Speculations of Thomas Wright . . . 573

CHAPTER n.

rant's general history of nature.

§ 1. Firmamental Organization , 574

§ 3. Planetogeny _ _ 577

§ 3. The Cosmos in Its Totality 583

§ 4. Our Sun and Other Suns 587

§ 5. The Mechanical Constitution of the World . . 589

§ 6. Deductions Touching Habitability and Unity in the 591

System of Worlds 593

§ 7. Synopsis of Points in the Cosmogonic Theory of Kant

1. Points Considered Well Taken 593

3. Points Considered Incorrectly Taken _ . - 595

Chapter III

DR. LAMBERT AND SIR WILLIAM HERSCHEL.

t* 1. Lambert's Cosmological Letters 597

XX . CO]S^TElirTS.

1. The Structure of the Heavens 528

2. Nebular Studies . . _ . . > .601

Chapter IV

§ 1. Prelimixary Views ox Xebulje axd General Physical Astronomy 606

§ 2. Hypothesis Touching the Genesis of the Solar System 611

1. Former Expansion of the Solar Atmosphere . . . 612

2. Formation and Abandonment of Zones of Vapor . 613

3. Rupture and Planetation of Rings _ . _ .614

4. Relations of Comets and Zodiacal Liglit . , . 615

5. Lunar Synchronistic ^Motions . . - _ . 615

Chapter V. Systematic Resume Of Opixioxs

LIST OF ILLUSTRATIONS.

1. Corpuscles of Magnetic Iron from the Snow on Mont Blanc

at the Altitude of 2,710 Metres X500 . . - .10 From Tissandier.

2. Corpuscles of Magnetic Iron Collected from Rain Water at

Sainte Marie du Mont X500 _ _ ... 10

From Tissandier.

3. Corpuscles of Magnetic Iron from the Dust Collected in the

Unfrequented Towers of Notre Dame de Paris . . 10

From Tissandier.

4. Fall of a Bolide at Queengouck, India _ . _ _ 12

From a Drawing by Lieutenant Aylesbury.

5. The Positions of the August and November Meteoroidal

Swarms _ _--19

Compiled by the Author.

6. The Great Nebula in Orion. Central Part . . „ 42

From a Drawing by Trouvelot.

7. Siekl^-shaped Nebula. Herschel 3,239 . . o . 43

After Schellen.

8. Spiral Nebula in Canes Venatici. Herschel 1,622 . .44

After Schellen.

9. Spiro-annular Nebula. Herschel 604 . _ _ _ 44

After Schellen.

10. Spiro-annular Nebula. Herschel 854. Indications of Several Rings . _ 45

After Schellen.

11. Annular Nebula in the Lyre 46

From a Drawing by Professor Holden.

12. Planetary Nebula, without a Nucleus. Herschel 2,241 . 46

After Schellen.

13. Planetary Nebula with two Nuclei. Herschel 838 . - 47

After Schellen.

14. Ideal Illustration of the Streams of Outflowing and Inflowing Matter on the Sun 60

After Siemens.

xxi

XXU LIST OF ILLUSTRATIONS.

15. Motion of a Body in the Presence of Two Other Bodies . 67

Original.

16. The Omega Nebula in Sagittarius . , . . . 89

From a Drawing by Lasell in 1862.

17. The Omega Nebula . . . . . . .90

From a Drawing by Trouvelot and Holden in 1875.

18. The Trifid Nebula " 91

From a Drawing by Trouvelot.

19. Motion of Three Nebulae in Space, Case I, Sub-case I .95

Original.

20. Motion of Three Nebulae in Space, Case I, Sub-case II _ 96

Original.

21. Motion of Three Nebulae in Space, Case II ... 97

Original.

22. Rotation Resulting without Actual Impact . . .98

Original.

23. Possible Origin of the Falcate Form of Nebula . . 103

Original.

24. Coagulating Nebula, or "Curdling Fire mist" _ . 105

Original.

25. Formation of Local Nuclei in a Nebula . . . 106

Original.

26. The " Law of Equal Areas " 108

Original.

27. Nebula in Process of Annulation 113

Original.

28. Illustrating the Determination of the Width of a Nebulous Ring - ... 114

Original.

29. Nebula Becoming Annular 117

Original.

30. Stratification of a Nebulous Ring 119

Original.

31. Nebulous Ring Undergoing Rupture . . _ . 120

Original.

32. Spheration of a Nebulous Ring 120

Original.

33. Prolateness and Rotation of the Derived Spheroid . . 130

Original.

34. Inversion of the Orbit of a Satellite . ^ o - 155

Original.

LIST OF ILLUSTRATIONS. XXlll

35. Process of Lengthening the Periodic Time and Acquiring

an Elliptic Orbit .160

Original.

36. Increase of Density toward the Centre of the Nebulous Spheroid . ..._--. 164

Original.

37. Deformative Tide 226

Original.

38. Compound Tide 226

Original.

39. Film Tide 227

Original.

40. Quantitative Relations of Tides . - _ . . 228

Original.

41. Illustrating a Lagging Tide 282

Original.

42. Illustrating the Secular Effects of Tides in a Rotating Viscous Spheroid 236

Original.

43. Discordant Tides of a Nucleus and Film . . „ 239

Original.

44. Varying Reaction Resulting from Varying Viscosity . 242

Original.

45. Tidal Increase and Diminution of Obliquity ... 245

Original.

46. The Tide-Bearer Viewed as Tide-Producer . . .246

Original.

47. Ascent of Isothermal Planes in a Planet's Crust . . 276

Original.

48. Climatic Effect of Increased Obliquity of a Planetary Axis 283

Original.

49. Climatic Effect of Change in Relative Positions of Apsides and Solstices . -_.--.. 287

Original.

50. Illustrating the Formation of Mountain Wrinkles . . 299

After M. Alphonse Favre.

51. Formation of Wrinkles in a Planetary Crust, with Parallel Contiguous Furrows . 300

Original.

52. Section through the Alps, Showing the Effects of Lateral Pressure 310

After Heim.

XXIV LIST OF ILLUSTRATIOis^S.

53. Diagram of Niagara Gorge, Old and Xew . > . 370

After Belt.

54. Map of the Moon .__ 386

After M. Faye.

55. Section across the Crater Copernicus . _ . . 387

After M. Faye.

56. Map of the Crater Theophilus, and Surrounding Region - 388

After Xeison.

57. Action of an Internal Tide against the Crust . _ . 398

Original.

58. Effect of Discordant Lagging Tides .... 398

Original.

59. The Disappearance of the Land = _ - . . 455

Original.

Part I. World-stuff

WORLD-LIFE.

CHAPTEE I.

COSMICAL DUST.

I know no recent observation in pliysical geograpliy more calculated to impret's deeply the imagination than the testimony of this presumably meteoric iron frona the most distant abysses of the ocean. To be told that mud gathers on the floor of these abysses at an extremely slow rate conveys but a vague notion of the tardiness of the process. But to learn that it gathers so slowly that the very star-dust which falls from outer space forms an appreciable part of it, brings home to us, as hardly anything else could do, the idea of undisturbed and excessively slow accumulation.— Archibald Geikie.

WHENCE comes the "Dust of Time?" There is nothing around which the dust of time does not gather. It accumulates among the shelters of the mountain cliffs. It falls upon ivy-mantled towers and ruined walls, and creates a rooting place for many a hardy herb, and a nidus for countless living germs. It clogs the water-passages from our roofs, and fills our cisterns with soils yielded by the atmosphere. It gathers about deserted structures; it buries the foundations of columns and temples; and new temples are built upon foundations which have older foundations beneath them. The ancient cities of the East and of the West lie slumbering beneath the accumulations of this dust. Nineveh is recognized only as a mound of earth. Troy lies almost beneath the reach of Schliemann's spade. The cities of

Cyprus, the Morea, and the Roman Peninsula are but slowly undergoing fresh exposure to the light of day.

Whence the dust which has buried walls and towers and cities ? Let us answer the question with soberness. The crumbling of wooden beams, and even of the solid stones, has supplied the larger portion of the debris which mantle the foundations of the ancient cities. Much of the soil w^hich gathers upon roofs and in the crevices of old walls has been lifted by the winds from bare field and dusty street. Even the snowy summits of the Alps * become stained by terrestrial particles borne by upward currents into the mountain air. And yet I will venture the opinion that some dust comes to the earth daily ichich had never belonged to the earth before. Out from the depths of space — beyond the clouds — beyond the atmosphere — from a granary of material germs which stock the empire of the blue sky, comes a perpetual but invisible rain of material atoms — like the evening dew, emerging from the transparency of space into a state of growing visibility.f