^ ^ \ ■^^o^ ^c^ ;V\: ^c^ ^ % ^^^ ^ rO^ ?:^.9^ ?^ o^ ^ o,. /• ^ / » « s ^ -A" ^ G^^ ^ o^. 9^;'o ?^ ^ : -"^/.o^ 1- r V ^ >■ ' ,. '^ %<^' 'A- C'" ^. Chapter XIV. — Formation of Mists and Clouds. — Height, Thickness, Form, and As- pect of Clouds 280 Chapter XV. — Influence of the Winds on the Formation of Snow and Rain. — Distri- bution of Rain over Plains and Mountains 285 Chapter XVI. — Tropical Rains. — Rainy and Dry Seasons. — Periodicity of Rains 292 Chapter XVII. — Rains beyond the Tropics.^ — ^Winter Rains. — Rains of Spring and Autumn. — Summer Rains.— Rains of the Polar Regions 297 Chapter XVIII. — Countries without Rain. — Geological action of Rains. — Contrast of the two Hemispheres 300 BOOK IV.— THUNDER-STORMS, AURORAS, MAGNETIC CURRENTS. Chapter XIX. — Height of Thunder-clouds. — Distribution of Thunder-storms in vari- ous Regions of the Earth. — Cause of these Phenomena 305 Chapter' XX. — Polar Auroras 314 Chapter XXI. — Terrestrial Magnetism. — Declination, Inclination, and Intensity of the Movements of the Needle. — Magnetic Poles and Equator. — Isogonal Lines and their Secular, Annual, and Diurnal Variations. — Isoclinal Lines. — Isodynamic Lines 324 BOOK v.— CLIMATES. Chapter XXII. — Solar Heat. — Irregularities of Local Climates. — Equalization of the Temperature below the Surface of the Ground 331 Chapter XXIII. — Contrast between the Climates of the Northern and Southern Hemi- spheres, between those of the Eastern and Western Sides of Continents, those of the Coasts and the Interior of Countries, and of Mountains and Plains 335 Chapter XXTV. — Isothermal Lines.^ — ^Thermal Equator. — Poles of Cold. — Increase of Temperature toward the Poles. — Open Seas 341 Chapter XXV. — Extremes of Temperature. — Isochimenal and Isotheral Lines. — Daily and monthly Variations. — Decrease of Warmth in the upper Strata of the Air. — Variations of Climate during the Historical Period 345 # 10 • CONTENTS. PAET III. — LIFE. BOOK I.— THE EARTH AND ITS FLORA: Page Chapter I. — The Assemblage of living Creatures. — Number of Vegetable Species. — Proportion of Dicotyledons, Monocotyledons, and Cryptogams. — Forests and Savan- nas [ [ 356 Chapter II. — Influence of Temperature, Moisture, and Solar Kays on Vegetation. — Distribution of Plants 361 Chapter III. — Particular Habitats of Species. — Salt-water and Fresh-water Plants. — Littoral Species. — Parasites. — Terrestrial Species. — Influence of the Soil on Vegeta- tion. — Plants associated together. — Sea- weed. — Extent of Areas 368 Chapter IV. — Contrast of the Floras in the different parts of the World. — Insular and continental Floras. — Increasing richness of Vegetation in the direction from the Poles to the Equator , 373 Chapter V. — Distribution of Vegetation on the Slopes of Mountains. — Mingling of the different Floras. — Upper limits of the Plants in various parts of the World. — Irregu- larities in the Vertical Distribution of Plants 379 Chapter VI. — Unconnected Species. — Displacement of Areas in consequence of Geo- logical Changes. — Plants of Great Britain. — Naturalization. — Incessant Modification of Floras 386 BOOK II.— THE LAND AND ITS FAUNA. Chapter VII. — Origin of Life. — Species of Animals. — Multitude of Organisms. — Con- trasts of Land and Sea , 393 Chapter VIIL— The Oceanic Fauna 396 Chapter IX. — Influence of Climate and physical Conditions on the Species of Animals 401 Chapter X. — Food of Animal Species. — Contrast of Faunas. — Areas of Habitation.— Changes in the Surface of the Areas. — Birth and Disappearance of Species 406 Chapter XI. — Great Terrestrial Faunas. — Homoiozoic Zones 411 Chapter XII. — Distribution of Species on the Slopes of Mountains and in the Depths of the Sea..... .* 416 Chapter XIII. — Geological Labors of certain Animal Species. — Coral Reefs and Islands 421 BOOK III.— EARTH AND MAN. Chapter XIV. — The Influence of Nature on the Destiny of Mankind. — Antiquity oft th^ Human Race on the Earth. — Monogenists and Polygenists. — Fusion of Human Races 434 Chapter XV. — Influence of Climate. — Tropical Zone. — Frigid Zone. — Temperate Zone 440 Chapter XVI. — Influence of the raised Outline of the Earth on Mankind. — Table- lands, Mountains, Hills, and Plains , 445 Chapter XVII. — Influence of the Sea and running Waters. — Traveling and Commer- cial Nations. — Islands and Islanders...- 452 • CONTENTS. 11 PaRo Chapter XVIII. — Blending of different Climates. — The Influence of Civilization on the Featm-es of a Country 456 Chapter XIX. — The course of History. — Harmony existing between Countries and the Nations inhabiting them 4G1 BOOK IV.— THE WORK OF JIAN. Chapter XX. — Reaction of Man on Nature. — Exploration of the Globe. — Voyages of Discovery. — Ascents of Mountains 466 Chapter XXI. — Reclamation of the Earth by Cultivation. — Ancient and modern Ir- rigation 470 Chapter XXII. — The Culture of Marshes. — Drainage of the Ground in the Country and Towns 474 Chapter XXIII. — The Draining of Lakes and Inlets of the Sea. — The Lake of Copais, the Lake of Fucino, the Sea of Haarlem, the Zuyder Zee. — Polders. — The Purifica- tion of Saline Marshes 478 Chapter XXIV. — Dikes on the Sea-shore. — Points of Defense. — Point-de-Grave 487 Chapter XXV. — Natural and artificial Ways of Communication. — Sea-shores, Des- erts, and Savannas. — Rivers, Canals, and Railways. — Bridges and Viaducts. — The cutting through Isthmuses. — The Suez Canal. — The Isthmuses of Central America... 495 Chapter XXVI. — The industrial Power of Man. — The Electric Telegraph. — Posses- sion taken of the Sea. — Cultivation of Oysters 504 Chapter XXVII. — Comparative Harmlessness of Hurricanes. — Prevision of Weather. — Modification of Climates effected by the Labor of Jian 510 Chapter XXVIII. — Influence of Man on the Flora and Fauna of a Country. — En- croachment effected by the more common Species. — Extension given by Agriculture to certain cultivated Species '. 516 Chapter XXIX. — Influence of Man on the Beauty of the Earth. — Disfigurement and Embellishment of the Land. — The diverse Action of different Nations. — The Appre- ciation of Nature. — The Progress of Mankind 522 ILLUSTRATIONS. [The Colored Maps, indicated in the list by capital letters, were printed in England, and by mistake were in txco instances incorrectly numbered. They are located, hoicever, in their proper places with reference toihe text.'\ Number Page I. Straits OF Dover 21 1. Gulf of Cape Breton 22 2. Depths of the Adriatic 24 ;'.. Profile of Bed of Adriatic 25 II. Submarine Platjiau 26 4. Profile of Bed of North Sea 26 .".. Depths of the English Channel 27 <;. Profile of the greatest Depth 27 III. North Atlantic Ocean 28 7. Section of Atlantic in Tropics 28 H. Depths at the ]\Iouth of the Ganges. . 31 '.). Comparative Saltness of Seas 36 10. Salt Marshes of Bessarabia 38 1 1 . Temperature of Sea-water 44 12. Glacier of La Madeleine 49* 13. Course of the Icebergs 53 IV. Antarctic Land 54 14. Icebergs of the Antarctic Ocean 54 15. Icebergs of tlie Antarctic Ocean 54 16. Route of the Peacock in Ice-pack 65 17. Course of Icebergs 56 18. Rollings of a Ship 60 19. Average Heights of Waves 61 20. Average Amplitude of Waves 62 21. Bay of St. Jean de Luz 65 V. Current of the Gulf Stream. . 70 22. Channel of Florida 72 23. Route of Steam-packets 80 VI. Oceanic Currents 84 24. Straits of Gibraltar 90 25. Profile of Straits of Gibraltar 91 26. LunarTide 96 27. Syzygy Tide, during New Moon 97 28. Syzygy Tide, during Full Moon 98 29. Tide during Quadrature 99 30. Tide at Southampton ■. 100 31. Co-tidal Lines of British Isles 105 32-34. Ckirves of the Tidal Waves 106 :r>. BavofFundv 107 Number Page 36. Mouth of the Avon 108 VII. Bay OF St. Michael 108 37. Straits of Noirmoutiers 109 38. Tides of the English Channel 110 39. Height of the Tides 112 40. Crossing of Tide-swellings 113 41. Course of the Tide in Irish Sea 117 42. Profile of a Tidal Wave 119 43. Height of the Tidal Wave 120 44. Plan of the Tidal Wave 120 45. Plan of two Tidal Waves 120 46. Tides of the Garonne 121 47. Profile of Straits of Messina 124 48. Lysefjord, Norway 128 49. Fjords of Greenland 129 50. Mouths of Cattaro 130 51. Fjords of South America 131 VIII. Fjords OF NoRAv AY 134 52. Ancient Fjords of Northern Italy... . 135 53. Fjords of South-east of Iceland....... 136 54. Filled-up Fjords of Christiansand 137 55. Ancient Fjords of Carentan 138 56. Roads of the Downs 140 57. Map of Abervrac'h 142 58. Giants' Caldrons of Haelstolmen 143 .^>9. Section of Giants' Caldrons 143 60. Tidal Wells 144 61. Clift' on the Mediterranean 148 62. Ocean Cliff. 149 63. Tides'of Inishmore 149 64. Heligoland 1.52 IX. Depths of the Zuyder Zee 154 65. Isleof Borkum in 1738 154 66. Isle of Borkum in 1825 155 67. Coast between Oneglia and Savone... 157 68. Section of Sea-shore 159 69. Mouth of the Liamone 160 70. Mouth of the Bidassoa 161 71. Mouth of the Oi-ne 162 14 ILLUSTRATIONS. NUMBEE TaGB 72. Peninsula of Giens 163 73. Section across Peninsula of Giens... 163 74. Peiiinsula of Cape Sepet 164 75. Chesil Bank 165 76. Miquelon Isles 166 77. Coast-ridges 167 78. Lagunes and Lidi of Venice 168 X. Coast of North Carolina 169 79. Coasts of Dantzic and Pillau 170 80. Cape Ferret from 1768 to 1863 171 81. Road of La Madeleine, California. . . 172 82. Gulf of Carentan 173 83. Bahr-el-Assal and Gulf of Tedjura. 176 84. Clioa-Canzouni 183 85. Nossi-Mitsiou 184 86. Celebes and Gilolo 185 87. Section of Stramboli 185 88. Section of Panaria 186 89. Formation of a Dune 189 90. Formation of Sand Dunes 189 91. Section of a Dune 191 XL Dunes OF La Tkste 192 92. Crescent-shaped Dunes 193 93. Etangs, or Littoral Lakes 197 94. Formation of Etangs 198 95. Isle Thelenji, in Caspian Sea 199 96. Sable Island 199 97. Mirages at Verdon ; 211 98. Mirages at Sea 211 ' 99. Tropical Hours of Equatorial Ocean 218 100. Pressure of dry Air at Apenrade.... 219 101. Variations in atmospheric Pressure. 221 102. Oscillations of the Barometer 222 XII. Showers of Volcanic Ashes . 228 103. Cloud of Cinders 229 104. Island of TeneriflFe 230 105. Theories of Trade-winds .•. . 231 106 Variations in Trade-winds 232 107. Trade-winds and Monsoons 238 108. General Direction of Winds 247 109. Direction of Winds in Fi-ance 248 110. Calm during Hurricane, 1861 254 111. Calm d.uring Hurricane, 1761 255 112. Spirals made by a Ship 258 113. Cyclone in Indian Ocean, 1852 259 114. Cyclone in Indian Ocean, 1860 260 115. Parabola described by a Hurricane. 261 116. Simultaneous Cyclones 264 XIII. Range of Hurricane, 1848... 265 117. Direction of Cyclones 266 118. Tempests of the North Atlantic 269 119. Storm in the Pyrenees 270 120. Storm in the Pyrenees 271 NuMBEE Page 121. Hurricane of Monville 272 122. Whirlwinds of Dust 274 123. Whirlwinds of Dust 274 124. Variations in Hygometric Degrees.. 278 125. States of Thermometer and Hy- grometer 278 126. Winds and Clouds at Teneriflfe 283 127. Rain-fall in Valley of the Saone 287 128. Altitudes in Valley of the Saone... . 287 129. Comparative amounts of Rain-fall . . 289 130. Rains around tlje Gulf of Mexico ... 293 131. Rain-falls at Calcutta and Madras... 294 132. Rain-fall at Anjarakandy.* 295 133. Rain-fall in the Basin of the III 298 134. Rains in France 299 135. Rains in parts of Europe 299 136. Ravines in Craters of Reunion 302 XIV. Rain Map of the World 303 137. Average of Stojms in Europe 806 138. Proportion of Hailstorms 807 139. Storms in May, 1865 308 140. Storm in Plain North of Pyrenees... 309 141. Hailstorms of Orleans 310 142. Hailstorms of Lower Rhine 311 143. Aurora Borealis of August, 1859.... 316 144. Aurora Borealis of Sept. ,1859 317 145. Monthly Distribution of the Aurora 318 146. Monthly Distribution of the Aurora 819 •147. Auroras seen at New Haven, Conn. 320 148. Circumpolar Zone of the Aurora. . . . 321 XV. ISOGONIC AND ISOCLINIC LiNES . 829 149. Isodynamic Lines 330 150. Temperatures of the Saone and Rhone 384 151. Distribution of Temperatures, July. 385 152. Distribution of Temperatures, Oct.. 336 153. Distribution of Temperatures, Jan. . 887 154. Valuation of Temperature at Paris . 338 155. Continental and Oceanic Climates. . 389 XVI. Isothermal Lines 341 XVI. Winter Isothermal Lines... 343 XVIII. Isothermal Lines in the North 347 156. Climate of the British Isles 847 157. Variations of Temperature at Paris. 348 158. Monthly Variations of Temperature 849 159. Temperatures at Brussels 350 160. Variation of Temperature at Halle . 350 161. Different Temperatures at Halle.... 351 162. Succession of Climates on Mont ■ Blanc ......'. 352 163. Treeless Regions around North Pole 358 XIX. Forests OF the VosGES 359 n^LUHTBATIONS. 15 Number Paoe 1G4. Forests of Transylvania 800 165. Northward Distribution of riants... 'MVl 166. Polar Limits of Plants 863 167. Polar Limits of Plants 364 XX. Sargasso Sea 369 168. Mediterranean Flora 375 169. Botanical Map of Java 381 1 70. Stages of Vegetation in Teneritle . . . 38§ 171. Stages of Vegetation on Canigou.... 382 172. Stages of Vegetation on Sulitjelma. 384 173. Height of Plants on Canigou and Alps 385 174. Organisms from the Sea-bottom 399 175. Profile of a Coral Reef. 423 176. Roadstead in Island of Tahiti 424 177. Gambler Island 425 178. Profile of Gambler Island 426 179. Atoll of Menchik'off. 426 180. Brown's Archipelago 427 181. Part of Kingsmill Group 428 182. The Red Sea and its Coral Reefs... 429 183. The Kfiys of Florida 430 XXI. Great Barrier Reefs 431 184. Bahama Archipelago 431 185. Cross-section of Bahama Islands.... 432 186. Eleuthira and New Providence Isl- ands 433 187. Deinsity of Population in Belgium . . 443 Number Page 188. Density of Population in Greece.... 443 189. Valgodemar 446 190. Valley of the Plessur ■ 447 191. Villages of Aliennont 458 192. Monte San-Giulano , 459 XXII. Grecian Archipelago 463 XXIII. •Unexplored Polar Re- gions 467 193. The Lake of Copais ' 479 194. The Polders of Haariem 480 195. The Zuyder Polder 483 196. The Salt-works of Trapani 485 197. Profile of a Sea-dike in Friesland... 487 198. The Dikes of Uithuizen 488 XXIV. Works at Point-de-Grave. 489 199. The Embankments of Westkapelle. 490 200. The Embankments of Petten 491 201. Progressive Depths of the Clyde.... 496 202. The Railways of Lancashire 497 203. Populations of English Cities 498 XXV. Passes of the Maurienne.. 499 204. The Isthmus of Corinth 501 XXVI. Isthmus OF Suez 502 XVII. Isthmus of Central Amer- ica 503 205. The Transatlantic Cables 506 206. The Roadstead of Aiguillon 508 . 207. Shipwrecks in the Mediterranean... 511 • THE OCEAN; THE ATMOSPHERE, METEORS, AND LIFE. PAUT I -THE OCEAN. BOOK I.— THE SEAS. CHAPTER I. GENERAL CONSIDERATION'S. To the majoi'ity of mankind, grouped in crowded jjopulations on the continents, extending over scarcely a quarter of the surface of the globe, the sea is little else than a vast abyss Avithout limits or bottom. Even learned men are inclined, by an illusion of intellectual optics, to give a much greater geographical importance to the phenomena of continental regions than to those of the ocean. Just as our ancestors, beholding infi- nite space filled with stars and nebulse arched over their heads, imagined this immensity to be a dome resting on the vast structure of the earth. Although the influence of the ocean in the general economy of the globe has not been studied with the same care, relatively, as the effect of the rivers which flow through the plains, or of the springs which gush from the clefts of the hills, yet it is still of the first importance, and on it all the phenomena of planetary life depend, " Water is the chief of all !" ex- claimed Pindar, in the early days of Hellenic civilization ; and since then science has revealed to us that the continents themselves are elaborated in the bosom of the seas, and that without them earth, like a metallic sur- face, could give birth to no organic life whatever. Thus, as almost all the cosmogonies of primitive nations poetically declare, earth is "The daugh- ter of ocean." This is not simply a myth, it is a fact. The study of the strata of the earth — rocks, sand, clay, chalk, conglomerates — proves that the mate- rials of the continental masses have in great part been deposited at the bottom of the sea, and have assumed their form and chai'acter there. Many rocks, especially the granites of Scandinavia, which were formerly believed to have emerged in a plastic state from the interior of the earth, are perhaps in reality ancient sedimentary strata slowly transformed by 2 18 TEE OCEAN. mechanical and chemical action,' which operate incessantly in the great laboratory of the globe. Even on the sides and summits of the highest moimtains, now raised thousands of feet above the level of the ocean, may sometimes be found traces of the action of the sea in ancient times. Un- der our very eyes the immense work of creation, commenced by the se^s in the earliest ejDOch, is carried on without relaxation ; with such energy, in fact, that even during this short life man may witness important changes along their shores. If the waves undermine and slowly destroy a penin- sula here, elsewhere they spread out sandy beaches and form islets. New rocks, diifering in arrangement and apj)earance, succeed the ancient rocks demolished by the waves. Thus the promontories of granite are disin- tegrated by the action of the waters, which carry away its various con- stituents, quartz, feldspar, and mica, building them up into new rocks. In the same way the clay resulting from the slow decomposition of the por- phyritic or granitic feldspar is transformed into slate, which becomes sooner or later as hard as the ancient schists. But the dashing waves and the flowing rivers are not the only agents occupied in the formation of new rocks in the bosom of the sea. There is another ever-active agent engaged beneath its waters. This agent is animal life. Shells, corals, and innu- merable animalculse with calcareous or silicious coverings, inhabiting the ocean, are incessantly engaged in consuming and reproducing. They ab- sorb and digest matter which the rivers bring down to the sea, and secrete substances which form their skeletons and cases: as, generation after gen- eration, these swarms perish, their remains are spread out over the bottom of the sea or heaped up on the strand ; and at last form immense banks and submarine plateaux which by some subsequent elevation will be brought to light. Owing to this ceaseless renewal of the rocks, the ocean is constantly creating a world differing from the old one in the appearance and the dis- position of its beds. Thus, to the geologist, the invisible depths of the sea should not be of less importance than the exposed surface of the con- tinents. The ground which to.-day bears us and our cities will disappear, as the continents of former epochs have already entirely or in part disap- peared ; and the unknown spaces which the waters now cover will rise in their turn, and appear as continents, islands, or peninsulas. In the long period of geological centuries or ages during which the lands are bathed, not by the waters of the sea, but solely by the waves of the atmosphere, the ocean does not the less continue to modify the configura- tion of the globe by its clouds, its rains, and all the meteoric influences which take their birth at its surface. All those atmospheric agencies which rage about the summits of mountains, riving them and little by little lowering them, it is the sea which dispatches them. All those gla- ciers which polish the rocks, and carry down into the valleys those piled-up boulders, it is the clouds from the ocean which deposit them in the form of snow on the summits of the mountains. All those waters which pene- trate by fissures into the depths of the ground, which dissolve the rocks. THE PARENT OF WATERS. 19 hollow out the caverns, bring mineral substances to the surface, and cause at times great subterranean subsidences, what are they but marine va- pors returning in a fluid state toward the basin from whence they arose ? Finally, the numerous rivers which spread life over all the globe, and with- out which the continents would be deserts wholly uninhabitable, are noth- ing else than a system of veins and veinlets, which carl*jr back to the great reservoir of the ocean the waters distributed over the soil by the arterial system of clouds and rain. It is, then, to the phenomena of this oceanic life we must attribute the immense geological operations of rivers, and the exceedingly important part which they play in the flora and fauna of diflerent countriesj and in the history of humanity itself The future discoveries of geologists and naturalists will tell us also what share in the production and development of those germs of vegetable and animal life, which reach their greatest beauty on continents, may be referred to the ocean. As for climate, upon the varieties of which all that lives upon the earth depends, does it not follow from movements of the ocean, asgwell as from the position and elevation of the masses of land ? The cold of polar lati- tudes would be more rigorous, and the heat of the tropics more intense, and these extremes would undoubtedly destroy most of the beings now in existence, if the currents of the ocean did not convey water from the poles to the equator, and from the equator to the poles ; thus constantly tend- ing to an equalization of temperature. In the same way the atmosphere of continents would be completely deprived of vapor, and so perhaps ren- dered unfit for breathing, if the humidity it derives from the sea were not spread by the winds all over the globe. Thus the ocean blends the con- trasts of climate, and makes a harmonious whole of all the distinct regions of our planet ; it awakens and preserves life on the earth, which it has de- posited layer by layer, which it waters by its vapors, and renders fertile by its springs and its rivers. 20 THE OCEAN. ^ CHAPTER II. OCEANIC BASINS. — DEPTH OP THE SEAS. — LEVEL OF THE SURFACE OF THE OCEAN. The seas which cover the greater part of this planetary sphere have not comjDletely inclosed basins. They all have their origin in the great common reservoir of the Antarctic Ocean, and cornmunicate with each other by wide straits, or by sheets of water of secondary importance. This partial absence of boundaries, and their enormous extent of surface, deprive the seas of that harmony of form observable in the continental masses. Yet, wherever the water washes the shores of the land, it neces- , sarily reproduces its contour ; and, in consequence, the sea everywhere presents a distribution exactly the opposite of that of the earth. The twofold basin of the Atlantic, with its wide central expansion, corre- sponds to the two continents of America, with their narrow uniting isth- mus. The Pacific itself is divided by its immense Archipelago into two vast distinct seas ; and the Indian Ocean in the south balances the mass of Asia in the north. While limiting with its waves the shores of the land, the ocean penetrates far into the interior, either by large rounded gulfs like those of Guinea and Bengal, or by seas bordered with chains of islands and islets, like the China Sea and that of the Antilles, or by an in- tricate net-work of channels like those of Sunda, and the Polar Archipela- go of America. Certain seas also are almost completely inclosed, and communicate with the remainder of the ocean onl}'- by narrow outlets, as is the case with the Mediterranean and the Red Sea. The bottom of all these seas is not always horizontal or even regularly inclined. It is certain that the bed of the sea has, like our continents, but in a far less degree, plateaux, valleys, and plains. Geology reveals to us that in the course of ages, the highlands of the continents sink be- neath the oceanic expanses, and the abysses formerly hidden by their waters emerge to the light and reveal the inequalities of their surface. Were not the plains and the hills, which now bear our cities and our har- vests, in past ages covered by the waters of the deep ? Do we not see on the flanks of the Himalayas, 18,000 feet above the level of the mouth of the Ganges, shells which the sea has there deposited in the strata ? And do not our navigators search the bottom of the ocean, and, so to speak, investigate its inequalities with those enormous " feelers," their sounding apparatus ? We may well imagine that the submarine surface still preserves all its primitive rudeness ; and that its rocks, cliffs, and fells uniformly present edges unworn and sharp, the marks of fracture, just as on the day when the solid rock was first cleft. And, in fact, in the depths of the sea there The Ocetin.&c. S TRAIT 7° W t 1 n^ 1 *« ^,y ' Soalli foreland a'"' Af. . •'■'l"/ ast,we ai- B ay S ' v< zS ME*^^ rlFOLKESTOifK ^S "^ , aJ *"> 53 .w 2/ ^6" ^. 52 ^ > 22 S "^-^ ^ 2.? 32 <<^ 2(? s5 \ ^Q , 5/; e. .■•■ •Ov J5 57 ^^ . ^:-- <^3t ^^ _ ■ :'/ .:^ /c, ij- ^"^ ^^ 33 <^^^,- 35 ^^riy 4-1 ^^ 5S ' 00 28 - \4 4o 2.0 /■■■^•'^ 5- ^.9 ^^ ■^A/ ^ ; ^, ^ 3* -^^ V. 4/ i^ . ND / j^ . " *v / V /^ ■■2-3 ^/ J^ 0,/ /•■■■ 00 Cupc Griz-JS^ei '■S / ' ■■■' J2 ^/ / r « i li ^^ ■3^ •= 13 0-1 J s; ^ i - Ir 1 ■ . • -U 01 Z 3 4- Profile ■ of the St Eng^■a^redty El-hard , HARPER. -^:<. BRO OF DOVER PLI NEW 70RK SUDDEN CHANGES OF DEPTH. 21 are no frosts to break off projecting peaks, no lightnings to split, no gla- ciers to carry them or crumble them away, no meteoric influences to cor- rode and round them. Nevertheless, if there are not in the sea, as on the land, agencies like these, ceaselessly at work leveling projections, there a»e others which as ceaselessly labor to smooth the asperities of the surface. There are the sedimentary dej^osits brought down by the rivers, and innumerable millions of the skeletons of animalcula3, which live in the deep, or fall like snow from the upper strata of the water and gradually fill up the submarine valleys. Those fantastic mountain chains drawn on the bed of the sea by Buache and other geographers can not, therefore, really exist, since the geological agencies at work under water differ from those which carve out the table-lands and mountains on our continents. If some immense eddy prevented the particles from being- deposited in the deep parts of the ocean, then the rocks and the rifts of the abysses Avould keep their first form, like those peaks and craters of the moon which are not worn away by the inclemencies of an atmosphei'e. There are, indeed, tracts in thq sea where, perhaps from the influence of a submarine counter-cuiTcnt, the rocks of the bottom are not covered by organic alluvium. In the deepest part of that great arm of the sea which separates the Faroe Islands from Great Britain, Wallich drew up from a depth of more than 600 fathoms* a large fragment of quartz detached fronPthe living rock, and several pieces of basalt; it is quite possible, however, that these fragments had been dropped there by an iceberg. In general, the sea-bed extends for wide spaces in long undulations and gentle slopes. Sailors, who are carried swiftly over the water by wind or steam, and who generally take soundings at places far distant from one another, are tempted to exaggerate the magnitude of inequalities in the sea-bed, and to see chasms and precipices, where the declivity is in reality inconsiderable. Escarpments, similar to those of the continental mount- ains, very rarely present themselves; Fitzroy was greatly surprised to find in the neighborhood of the Abrolhos, near Brazil, such rapid slopes, that the lead on one side of the shij? indicated from 4 to 6 fathoms only, while on the other side it marked from 16 to 22 fathoms. Sometimes a special cause explains these abrupt changes of the level. Thus M. de Villeneuve-Flayosc discovered in the Gulf of Cannes, a spring of fresh water springing from the depths of a kind of well, the sides of which sloped at an angle of 27 degrees. But how can we explain that singular gulf which extends immediately in front of Cape Breton, on the coast of the Landes ? Ought we to attribute its formation to the meeting of the tides, which takes place in the channel of the Gulf of Gascony? This is a question which it is not yet possible to decide. We can form some notion of the submarine tracts by surveying the countries that have emerged from under water at a comparatively recent epoch. The Landes of France, the low lands which have replaced the * Marine soundings are always taken in fathoms ; a fathom is equivalent to 2 yards, or 6 feet linear. 22 THE OCEAN. , KXauu Breton" Depths under Sfath. Depths from Bfath. to 54 fath. Depths of more than 54 fath. Fig. 1. Gulf of Cape Breton. Gulf of Poitou, a great part of the Sahara, the pampas of La Plata, fur- nish remarkable examples of the regularity of inclination which generally characterizes the bottom of the sea. Even rocky coasts, like those of Scotland and Scandinavia, have been leveled here and there in their lower parts, that were not long ago covered by the waters of the Atlantic. If earthquakes and fissures of the soil, volcanoes and slow oscillations of the terrestrial crust, did not on their side increase the inequalities of our planet's surface, it is certain that the incessant contribution of fluvial de- posits, the fragments of rocks worn away by the waves, and, above all, those remains of swarming organisms which fill the sea, would have ef- fected, as an inevitable result, the equalization of the ocean-beds, and the transformation of their abysses into scarcely indicated slopes; the waters, on their side, would gradually invade the surface of the continents, till, after the operations of myriads of centuries, the earth would become again what it formerly was, a spheroid with its surface entirely covered by a bed of water of uniform thickness. According to an ancient popular opinion, which, in default of direct observation, was not more contradictory to good sense than many other hypotheses called scientific, the sea was " bottomless ;" and this prover- bial expression is still that which best conveys to many ignorant persons the real state of things. At the commencement of last century Marsigli himself spoke of "the abyss" of the Mediterranean as of a gulf absolutely unfathomable.* On the other side, mathematicians, supported by theo- * Histoire de la Mer, p. 10. ESTIMATED DEPTH OF THE SEA. 23 retical considerations, have attempted to estimate by calculation the av- erage d'epth of the seas. Butibn, who does not quote the Italian author from whom he has borrowed his argument, gave to the ocean a deptli of water equal to 230 toises, or 240 fathoms.* The astronomer Lacaille, whose estimates are no nearer those that recent soundings have rendered probable, allowed from 164 to 273 fathoms of depth to the sea. Laplace, who erroneously estimated the mean elevation of the land at 3280 feet (that is to say, three times the height now approximately determined),! thought that the waters of the sea must also be of about equal depth. Young, drawing his deductions from the theory of the tides, assigned about 2735 fathoms to the waters of the Atlantic, and from about 3250 to 3800 fathoms to those of the South Sea. Arnold Guyot remarked that this depth assigned to the Atlantic would be, in fact, that of the trench formed in this marine valley, between the coasts of South America and Africa, having the plateaux of Bolivia on the one hand, and those of the Lupata Mountains on the other. J This last estimate has, however, only a relative value : if we aj^ply it to the Pacific, continuing westward and eastward the coasts of Asia and America, we should find as the lowest point, and lying (according to this hypothesis) to the east of Easter Isl- and, a depth of about \5^ miles — three times the elevation of the highest mountain in the world. Evidently it is by direct observation that we must hope some day to know all the projections and undulations of the bottom of the ocean ; but the instruments which seamen can command are still imperfect, and, except for inconsiderable depths, do not give re- salts of rigorous accuracy. In those latitudes where the water is many hundreds, or even thousands of fathoms in depth, they can not risk the taking a sounding unless the atmosphere and the waves are in an excep- tional state of tranquillity ; and even then the slenderness of the cord, the weight of the apparatus, the enormous pressure it endures as it de- scends, and which increases at the rate of one atmosphere for every elev- en yards of immersion, and finally, the long hours which must be em- ployed in this delicate operation, greatly endanger the final success. Unless instruments furnished with electrical bells, like those of Schneider or of Gareis and Becker,§ and others more easily employed, more rapid and sure, are used, " bathymetric " observations will be always at great distances from each other, and it will not be possible to construct a sub- marine map in relief, such as is being constructed of the surface of the continents. Besides, it is very rarely that sailors take soundings in the deep seas simply for the scientific pleasure of investigating the depth of the ocean. It is solely for the requirements of navigation, of commerce, and of industry, that they have observed the depth of the sea, either in gulfs like the Adriatic, or in parts that are filled with sand-banks like the North Sea, in the neighborhood of coasts and rocks laid down in ancient * Theorie de la Terre : les Fleuves. t Humboldt. See the section entitled Harmonies and Contrasts. X Earth and Man, pp. 76, 77. § Physiographie des Meeres, 1867. 24 THE OCEAN. Fig. 2 —Depths of the Adriatic. (The parts marked by cross-shading are 270 fathoms and upward in depth.) maps, or in those parts of the ocean which are destined to receive elec- tric cables. In the open sea ships sail almost entirely over nnmeasured depths. Owing to its elongated form, and to the amphitheatre of lofty monnt- ains which all but wholly surround it, the Adriatic offers a very remark- able example of the continuation of the continental slopes below the level of the sea. The bed of the northern part of this gulf, which is a continu- ation under water of the level plains of Venetia, has an exceedingly gen- tle slope, much less, in fact, than that of the plains of Lombardy, which seem horizontal.* The sounding-lead shows only a depth of 54 fathoms beyond the narrows formed by the islands of Zara and the headland of Ancoua ; thus more than a third of the Adriatic is found not to exceed in * G. Collegno, Geologia deW Italia, p. 12. THE ADRIATIC AND THE MEDITERRANEAN. 25 • mean depth rivers like the Mississippi and the Amazons. Farther south the submarine declivity, which continues on one side that of the Apen- nines, on the other that of the Alps of Dalinatia, becomes comparatively- greater, and the sounding-lead descends to about 110 and even 170 fath- oms below the surface. At this spot the sea forms a sort of hollow, bounded on the south by a submarine isthmus uniting the peninsula of Manfredonia with the isolated rock of Pelagosa, and with the islands of the Dalmatian coast, Lagosta, Curzola, and Lesiua. Beyond this isth- mus, and extending as far as the Straits of Otranto, is another and much deeper hollow, toward the middle of which the soundings indicate a depth of nearly 500 fathoms ; and on the east rise the precipices of Montenegro, the roots of which descend very rapidly beneath the waters. Thus the soundings of the Adriatic confirm the observations, made long ago by Dampier and many other navigators, that the sea is generally deep at the base of abru2Jtly sloping mountains, and, on the other hand, that there is but a slight depth of water near low coasts. 1 t XT) a- X df 31 d. t 00 03 o .g- Fig. 3.— Profile of the Bed of the Adriatic. As to the Mediten-anean properly so called, it is almost unknown, ex- cept in those parts which have been explored for the laying of telegraphic cables ; however, on comparing with one another all the soundings, and the various tracks followed by those who have laid the wires, we can at least form a general notion of its submarine surface. If the waters of the Mediterranean were suddenly lowered about 110 fathoms, it would be di-. vided into three distinct sheets of water : Italy would be joined to Sicily, Sicily would be united by an isthmus to Africa, the Dardanelles and the Bosporus would be closed, but the outlet of Gibraltar would remain in free communication with the Atlantic Ocean. If the level was loAvered by about 550 fathoms, the ^gean, the Euxine, and the Adriatic would wholly disappear, or only leave in their beds unimportant pools ; the re- mainder of the Mediterranean would be divided into several seas like the Caspian, either isolated or communicating with each other by narrow channels, and the terminal promontory of Europe would be joined by the isthmus of Gibraltar to the mountains of Africa. A depression of about 1100 fathoms would leave nothing but three inland lakes; to the west a 26 TEE OCEAN. • triangular basin occupying the centre of the depression between France and Algeria ; in the middle, a long cavity extending from Crete to Sicily ; and eastward, a hollow lying in front of the Egyptian coast. The great- est depth of the Mediterranean, exceeding 2200 fathoms, lies to the north of the Syrtes, almost in the geometrical centre of the basin.* It is the same with the North Atlantic Ocean as with the Mediterra- nean. The depth of the central valley, extending from north to south be- tween Europe and the New World, is only known in a general manner. But the gulfs and straits which project from the ocean between the north- ern countries of Europe, such as the Channel, the North Sea, the Categat,' the Baltic, have been almost completely exploited by the sounding-lead. The North Sea in all its northern part, from the 51st to the 57th degree of latitude, presents a mean depth of only about 16 to 27 fathoms, except near Newcastle-upon-Tyne, where the bottom is found to be from about 49 to 65 fathoms below the surface. Vast tracts of sand and mud — the White bank, the Black bank, the Brown bank, the Dogger bank, the Fisher bank — separated from one another by fosses and lateral channels, deejDer by from about 6 to 11 fathoms, almost entirely fill its bed, and stretch as far north as the Shetland Islands. There, as in the centre of a whirlpool, is dej)osited the marine alluvium, while that arm of the ocean follows the precipitous shores of Scandinavia over the rocks and compact clays of the bottom. In these parts the lead descends to about 164 and Scotland ... F Norway g:il:t?:tl:tit:l: I; it; t I: l" I: I: t. 1 1 &: Fig. 4.— Profile of the Bed of the North Sea, from the north point of Scotland to Stavanger, in Norway. even 437 fathoms from the surface of the sea; and in the centre of the Skagerrack, between the sandy beach of Jutland and the bold shores of Norway, nearly 443 fathoms have been reached. One seems to see here, in vaster proportions, a repetition of those narrow and deep trenches which surround isolated rocks left standing out on flat sandy shores. From the Skaggerrack to the Categat, which may be considered as the submarine threshold of the inland waters of the Baltic, the transition is effected somewhat abruptly. The Categat presents nowhere more than 93 fathoms, the mean depth of its channel is only 64 fathoms, and the banks of sand and mud render its navigation difficult. The depth of water is reduced to 16, 11, and even in some places to 5 fathoms, in the Sound and the Great Belt, which form the entrances to the Baltic Sea, properly so called. This vast reservoir, which partakes at the same time of the nature of a gulf by its free communication with the ocean, and of * Bottger, das Mittelmeer ; Mittheilungen von Petermann, 1866. The OceaTi.&c SUBMARINE PLATEAU OF THE BRITISH ISLES. jr^ n. Rn^av^d by EfKard . y%e ttnts irniictit^ the d< ffereni ricplhs in. feet Bra-v™liT-AVuai<>Triii I I S6. DEPTHS OF TEE ENGLISH CHANNEL. 11 J)i^i7vs Tnore^ t/aiur Si-yiUTv' I I Depths under' S^/oI/l.. Fig. 5.— Depths of the English Channel. an inland lake by the slight saltness of its waters, has a mean depth of 22 to 33 fathoms, analogous to that of the Categat. According to Foss, the greatest depth (between the island of Gothland and Esthonia) would be found at only 98 fathoms below the surface of the sea ; but, according to Anton von Etzel, the lead would not reach the bottom at less than 150 fathoms in the deepest hollow. To the south-west, the North Sea communicates by the Straits of Do- ver with the Channel — a narrow arm of the sea which may be considered as a mere accident of the earth's surface, as a kind of maritime trench, so inconsiderable is its depth compared with that of the ocean. In order to form a true notion of the depth of the Channel, compared with its Avidth, one must imagine a miniature of this sea drawn on a scale of one yard for two-thirds of a mile, on a perfectly horizontal surface. This sheet of wa- Fig. 6 Profile following the Line of the greatest Depth, ter would not have less than 547 yards of length, and its width would vary, according to the coast-lines, between 36 and 240 yards. And yet, notwithstanding this considerable surface, the greatest depth would be less than 2 inches at the entrance. In the deepest hollow of the Chan- nel, between the hillock representing Start Point and that of the Sept- 28 THE OCEAN. lies, it would be less than 2J inches. A siDarrow could hop this minia- ture sea.* We see that it is as easy to exaggerate the importance of the depth of the sea as it is the height of mountains. The section an- nexed to Plate I. shows the proportionate depth of water between the shores of Dover and Calais. On leaving the Channel, the parts of the oceanic bed which have been explored by sounding are more and more distant toward the west, and then become quite rare. Finally, many hundred miles out at sea, where the true abysses commence, soundings have been only taken at intervals of about 30 and even 55 miles apart. The points thus marked, which have served for drawing the submarine chart of the North Atlantic, are therefore by no means numerous, but nevertheless we have in it a pretty exact representation of the relief of the ocean-bed. The average depth of Avater which separates the coasts of North America and those of Eu- rope is about 1915 fathoms, but the central valley presents a surface rel- atively uniform, and much less varied than that of Europe or even the United States ; the greatest slopes do not probably exceed those of the river-beds which seem nearly horizontal; and it may be said- that the depth of the sea is concentric with the surface. Hence the name of " the telegraph plateau," given by Maury to these plains some time before the first transatlantic cable was laid. The most considerable depth of this plateau is 4846 yards^— that is to say, about one-sixteen hundred and thirty-ninth of the width of this ocean ; this being a thickness relatively less than that of the finest needle.f The section on Plate III. enables us to compai'e the relief of the continental surface and that of the oceanic depths from the coasts of the United States to those of Europe. It is true that, in order to render the vertical dimensions visible, it has been t^ ■^ ^^ 60° 50* ^ o 30^ %t '0> ■v. Fig. 7.— Section of the Atlantic in the Tropics. necessary to exaggerate them in the enormous proportion of twenty- fold. To the south the depth of the sea becomes more and more varied. An imaginary section from the plateau of Anahuac to Senegambia, across * Saxby, Nautical Magazine, March, 1864. t Bischof, die Gestalt der Erde und der Meeresflache, p. 6, and following (note). Tie Ocean. &c. NORTH E RN A 45* 40° h:f X isei A T L A 35€6 *«5 H33 NEWPOTIin)LAOT)N 4=1 rinity Ba)( SVJctoii Great Baiik of l*IewfouiidlaTid 3oi8 () c JS57 •?^2>- />^ 6* 50*7 *^7 S CO o ■» 2000 30"° SO n \ _2 13,00( The Scale of hei^Jits is in prop HARPER- 5c BRO NTl C OCEAN PLBl N -*-*5 z63i A 32lff T I 3iM N 384o Sito TpS io26 256b »7*-? ,^^ U76 b^o IVaW, ^ ^50" ioffb t5ji iogS ♦73* 27*3 *320 3524 J2»9 45/4 ^571 1000>>>eU„„ " 2000 rN O "^ 5 o P3 "5 Oc h. .f ^0" 400 5P0 JfiZe^ to the length as 20 lo 1 ^^.-^^J IS. NEW" YORK DEPTH OF THE ATLANTIC. 29 Yucatan, the Caribbean Sea, the Antilles, and the central basin of the tropical Atlantic, presents a much more unequal surface than that of the telegraphic plateau ; but the true oceanic part of the basin equally shows a great uniformity in almost its entire extent. Considered as a whole, the North Atlantic is a depression whose sides descend gradually toward a central hollow situated between the coasts of the United States, the Bermudas, and the Banks of Newfoundland. A fall of the waters of less than 110 fathoms would reveal the submarine groundwork upon which France, Spain, and the British Isles rest. This is, indeed, the true foundation of the European continent, for immediately beyond this basement, which forms the extreme angle of the Old World, the bei of the sea, at an inclination of about eight degrees, descends gradually from 110 fathoms to 1640 and 2187 fathoms below the waves. A fall in its level of 1094 fathoms would diminish the width of the Atlan- tic more than half, would leave the Gulf of Mexico completely dry, and only leave an elongated lake in the central part of the Caribbean Sea. If the present level were lowered by 2187 fathoms, a continent separated from Europe and America by two narrow channels, and extending over a space of from about 1550 to 186(> miles, would stretch into the torrid zone, and, by a remarkable coincidence, would affect that peninsular con- formation and southerly direction presented by Greenland, Scandinavia, Spain, Italy, Greece, Arabia, India, and the three great continents of the South.* A lowering of 3280 fathoms would completely unite Newfound- laud to Ireland, and consequently form a bridge between the Old and New Worlds. Even of the central Atlantic there would only remain a narrow "Mediterranean" sea in front of the, Antilles and Guiana. Final- ly, let the waters be lowered by 4375 fathoms, and the northern part of the Atlantic would be reduced to a small triangular " Caspian," situated between the Azores, the Banks of Newfoundland, and the Bermudas. In the present state of science, it is impossible to draw an approximate chart of the depths of the South Atlantic similar to that which one can construct of the bottom of the northern part. It even appears that many of the soundings made in this part of the ocean must be considered null, because the explorers have not taken into account the deflection of the sounding-line occasioned by submarine currents. The depth of 7600 fath- oms obtained by Captain Denham, R.N., is accepted by M. Bischof and other geologists with all confidence, because this explorer took care to raise the cord several times by a hundred yards, and when thrown again it always stopped at the same point. As to the sounding of 8695 fath- oms, announced by the American Parker, it is certainly erroneous, since later, in the same latitudes, they have found the bottom at 3007 fathoms only. Not knowing the depth of water in the different parts of the South Atlantic, mathematicians have tried at least to calculate the mean depth of the entire basin by the swiftness of the translation of the tidal waves. They have estimated the mean force of the bed of water ia the Atlantic * Sir John Herschel, Physical Geography, p. 35. 30 THE OCEAN. Ocean from the SOtli degree south to the 50th degree north latitude to be about 7330 yards. Now, the mean depth of the north basin being very nearly 2187 fathoms, the depth of the southern basin must be estimated, according to this calculation, at about 4920 fathoms.* However, these figures rest on the very contestable and much contested hypothesis that the tides, instead of forming in a distinct manner in every basin of the ocean, have a common origin in the great South Polar Sea, and roll toward the north like one immense wave, in the double valley of the Atlantic.f As to that part of the Pacific Ocean comprised between Japan and the coasts of California, it is not by the swiftness of the proj^agation of the tides, but by that of the earthquake-waves, that the mean depth may be approximately estimated. In the terrible earthquake of Decemlter 23d, 1854, which j)artially destroyed several Japanese towns, among others Yeddo and Simoda, the vibrations of the marine surface traversed an oceanic space of 6842 miles in twelve hours and a few minutes ; and Prof Franklin Bache was able to calculate, in consequence, the swiftness of the waves and the depth of the ocean across which they were propagated : this depth is an average of 2342 fathoms.J Besides, various authentic soundings taken in the northern basfci of the Pacific between California and the Sandwich Islands confirm the result of this calculation, since they indicate a depth varying from 1968 to 2570 fathoms. Not far from the coast of California 2700 fathoms of depth have been found. § Between the Philippine and the Marianne Islands two other soundings have given 3267 and 3609 fathoms, and even in this last operation the lead has brought up specimens of the submarine soil, and 117 species of minute forms of life. Finally, between the Pacific and the Indian Sea, to the south of the East India Islands, Captain Ringgold found the bottom more than 8f miles below the sui-face. Thus one might throw into this abyss of the sea not only Pelion on Ossa, but Gaourisankar itself, the highest mountain of the globe ; and even if on its peak Mont Blanc were set up, the summit of this colossus of the continent of Europe would not reach to the surface of the water. The Indian Ocean, too, is probably very deep in the greater part of its extent, but we only know those j^arts nearest land, and those in hardly moi'e than an approximate manner. Its gulfs, like those of the Mediter- ranean and the Atlantic Ocean, have relatively a slight depth of water : the Persian Gulf, for instance, having a mean depth of only 54, and the Red Sea of 163 to 273 fathoms. Those parts of the Gulf of Bengal which are adjacent to the Coromandel Coast and the delta of the Ganges in- crease only very gradually in depth, except near the northern extremity of the Gulf, where a prodigious abyss has been discovered, called " the Great Swatch," which is no less than 2187 fathoms deep, and is bounded * Sir John Herschel, Physical Geographj, p. 72. t See below, the section entitled The Tides. % Report of the United States Coast Survey. § Sir John Herschel, Physical Geography, p. 39. DEPTH OF THE ANTARCTIC SEA. 31 oil the north, east, and west by deposits of mud and ooze, which the lead touches at some five or ten fiithoras. The formation of this singular fun- nel is perhaps due to an eddy of tidal waters, commencing precisely at that spot where the alluvium of the Ganges is brought down to mingle with the sea.* Almost all the Indian Archipelago, Sumatra, Java, Borneo, and the ad- jacent, islands, rest on a submarine bank, having on an average only a depth of 33 fathoms, and even at the deepest places only 55 fathoms. This is probably the base of an ancient continent, of which the innumera- ble islands scattered over the sea in these latitudes are the remains. An- Fig. S.— Depths of the Sea at the mouth of the Ganges.t Other bank, extending for 435 miles to the north and north-west of Aus- tralia, suppoi'ts that continent, and all the neighboring islands, including New Guinea. A channel of very deep water, not yet sounded, separates from the Asiatic archipelago those higher Australian levels which also seem to be only the ancient fragments of vanished lands.J It is around these two great continental basements that the Pacific and the Indian Oceans, properly so called, commence. With respect to Antarctic latitudes, 1722 fathoms have been found be- tween the 63d and 64th degrees : near the VSth degree, at the very side of the enormous barrier of ice, which hinders any advance toward the pole. Sir James Ross has touched the bottom at 415 fathoms. And this" is all the information which navigators have given us." The icy sea of the north is better known, at least in some parts. To the north of Sibe- * See the section entitled Rivers. t The part marked by cross-sliading represents the " Great Swatch." i See below, the section entitled Shores and Islands, and The Earth and its Fauna. 32 THE OCEAN. ria, the bed of the sea, continuing the slope of the hardly-inclined " tun- dras,^'' extends toward the pole with such a slight declivity, that at 156 miles from the coast the lead only shows a mean of from 14 to 15 fath- oms. Around Spitzbergen and the western shores of Scandinavia the sea is much deeper, and on the precipitous coast of Norway its abysses join the deep channel which separates Scandinavia from the lesser depths of the North Sea. More to the west, between Scotland and Iceland, the parts explored by McClintock, with the view of laying the telegraphic cable, are rarely more than 328 fathoms, and nowhere present a depth of water of more than 670 fathoms. Between Iceland and Greenland a depth of 1547 fathoms has been sounded, and in Baffin's Straits are abyss- es of nearly 2000 fathoms. This great depression makes Greenland a country quite distinct from the American continent. The plateau upon which this grand island rests presents slopes relatively very steep. On the western side the declivity is in certain places one yard for every five of distance, while the western slopes of the submarine plateau of Ireland, which are among the most rapid in all the ocean, have about one yard of fall for every eight yards of length.* We can see clearly that the state of our knowledge of the subterranean surface is still very limited; yet the sum of the facts which have been already scientifically confirmed gives a great probability to the opinion, very natural on other grounds, that the oceans deepen gradually toward the south, where the waters occupy the greatest extent on our planet. The celebrated chemist and geologist, Bischof, thinks we may conclude, from the comparison of all the soundings, that the bottom of the sea is on an average as near the centre of the globe as the poles themselves. In certain latitudes, and notably toward the VSth degree north, the terres- trial radius drawn to the bottom of the sea is even less than that at the pole, which perhaps is to be attributed to the wearing away of the soil by icebergs. But, on the other hand, in the greater part of the ocean the bottom of the sea is a little more distant from the centre than the poles, which doubtless arises from the alluvium brought down by the rivers and the accumulations of organic remains. Thus the part of the globe cov- ered by the seas might be considered as perfectly round, and Newton's hypothesis, explaining the bulging at the equator by the state of fluid- ity in which the planetary mass had originally been, would become un- necessary.! As to the mean depth of the whole mass of the marine waters, we can hardly estimate it at less than about three miles ; since, as we have already seen, the entire basin of the Atlantic, and that of the Northern Pacific, which border upon the great northern continents, are deeper by many hundreds or even thousands of fathoms. Taking as the total surface of the ocean an extent of more than 145 millions of square miles, we find that the sea forms a volume of about 2^ * Wallich, North Atlantic Sea-bed, p. 18. t Gestalt der Erde und der Meeresfldche. DISTURBANCES OF THE SEA-LEVEL. 33 million billions of cubic yards, that, is to say, the 560th part of the planet itself. Sir John Herschel* gives much higher figures for the same volume of Avater ; but he has taken, as the basis of his calculation, the probable maximum of the depth of the seas, that is to say, four English miles, more than 3738 fathoms. We can not speak yet with certainty, but one day, thanks to the new observations which are added every year to those which science already possesses, it will be possible to give figures more relatively exact for the depth of the marine abysses, and the mass of wa- ter that fills them. One thing is certain, that the highest jjart of the continent raised above the surface of the waters is of much less elevation than the depth of the sea; and we can estimate the land above the level of the sea at only about a fortieth part of the mass of waters. Besides which, the land itself contains within it an enormous quantity of water united either chemically or mechanically with all rocks. The water of the seas, urgied by the force of gravitation, constantly seeks its level, like the water of rivers and lakes. When, in consequence of very rapid evaporation, or of a succession of tempests blowing from the same quarter of the horizon, the surface of the sea is lowered in any gulf, the waters from the adjacent parts rush toward the impoverished space, to fill the void. In the same way, when great rains, the swelling of large rivers, or the action of winds have raised the level of the sea in one point, this local swelling soon subsides, and its superfluity is dis- persed over the surrounding surfaces. We may, therefore, consider the mean height of the sea as the same in eveVy ocean, since the natural movement of water tends ever to re-establish an equality of surface in all parts where an accidental disturbance has occurred. Nevertheless, the diversity of climates, of winds, and of currents, is such, that certain seas, separated from one another by a narrow isthmus, present permanently unequal levels. Thus several German engineers be- lieve that they have established the fact that the Baltic Sea, into which a great numb^er of considerable rivers discharge themselves, is on an aver- age some inches higher (?) than the North Sea.f In the same manner the Atlantic, whose waters spread out on one side into the North Sea, and on the other into the Mediterranean, would have a mean level scarcely high- er than that of the two basins which it supplies ; while the Black Sea and the Gulf of Venice, receiving, like the Baltic, several large rivers, would, like the latter, be proportionably elevated. On the two sides of the Isthmus of Suez the waters are also found at slightly unequal heights. According to the engineer I^urdaloue, the mean level of the Red Sea at Suez exceeds by 31^ inches that of the Mediterranean near Port Said ; at low tides the two sheets of water are perceptibly of the same level, while at high-water the sea is sometimes higher by 3^^ feet in the Bay of Suez than at the northern extremity of the maritime canal. A similar differ- ence, too, occurs between the Bay of Colon and the Gulf of Panama, and * Physical Geography, p. 17. t Woltmann ; Von Hoft', Verdnderungen der Erdoherfldche, t. iii., p. 328. 3 34 , THE OCEAN. there also it is the mass of wat«r in which the tides have the fullest swell, that is to say, the Pacific Ocean, which has the highest level. But the measurements made on the always unstable level of the sea are very delicate operations, as one can so easily make a mistake at starting, through the oscillations of the ebb and flow ; and over spaces of many miles, divided by various obstacles, it is very difficult to avoid slight er- rors. At all events, it is certain that the surface of the sea, unceasingly traversed and perturbed by winds, currents, and tides, is not perfectly horizontal at any point of the globe. SALTNESS OF THE SEA. 35 CHAPTER m. COMPOSITION OF SEA-WATER.— SPECIFIC WEIGHT. — SALT MARSHES, NATURAL AND ARTIFICIAL. — VARIOUS SUBSTANCES, — DIFFERENCES OP SALTNESS. — MARINE SALT. Besides the ooze, the remains of animalculae, and innumerable frag- ments held in suspension, the sea-water is also charged with chemical substances ii^ solution, which give it a specific gravity considerably su- perior to that of fresh water. This varies in all seas, according to the quantity of the substances dissolved, the amount of evaporation, the con- tributions of rain and rivers, the direction of the currents and counter- currents. In the polar seas the specific gravity of the waters is also modified by the formation, or melting, of the ice. Every variation of temperature, every local movement of the sea, causes a more or less per- ceptible modification in the proportion of the salts dissolved, and in the specific gravity of the water. Thus we can only obtain an average for the various conditions of the fluid mass in the diSerent seas. The mean specific gravity of oceans with deep basins is nearly 1028 ; that is to say, sea-water weighs 2 '8 per cent, more than the same bulk of distilled water. In the Mediterranean, where the heat of the sun evap- orates more water than the rivers bring down to it, the average specific gravity exceeds, 1029; in the Black Sea, on the other hand, where very considerable rivers of fresh water discharge themselves, the specific grav- ity is reduced to 1016. And all the intermediate degrees between these exti'cme specific gravities are found, according to the varied physical conditions which exist, in other seas. Furthermore, it seems to be estab- lished that the waters of the ocean in the southern hemisphere are, on an average, lighter than those of the northern hemisphere,* The average quantity of all the salts contained in the sea, or the salt- ness of sea-water, was estimated by Bibra and Bischof at 35*27 parts in 1000 ; but much more complete observations made since by Forchham- mer have reduced this i^roportion to 34'40. Besides, almost all the analy- ses, which up to the present time have been made of sea-water, confirm the general opinion of chemists, that the relative proportion of the mat- ters dissolved is the same in all seas. The quantity of common salt (chlo- ride of sodium) dissolved in sea-water is always a little more than three- (]uarters (75*786) of the total mineral matter held in solution. In the north tropical Atlantic, on the coasts of the Sahara and of Mo- rocco, where the sea receives no tributaries, and where, on the other hand, the evaporation is very rapid, the average of oceanic salts is nearly 38 parts in 1000. In mid-ocean, and more especially in the neighborhood * Homer ; J. Davy. — Bischof, Lehrbtich der chemischen Geologic. 36 THE OCEAN. of America, where the water of many great rivers mingles with that of the sea, the saltness is less by one, two, and even three thousandths ; but it is generally greater in the tepid waters of the great current called the Gulf Stream, which crosses the Atlantic obliquely. The proportion of salts contained in this current always exceeds 35 thousandths,* while the water that flows from the pole toward the equator by Baffin's Bay con- tains only about 33 thousandths. It is to the enormous accumulation of ice that these currents owe the slightly less saltness of their waters. The quantity of cold water which flows from the Antarctic Pole toward the south of Africa and America contains likewise less saline matter than the seas of the temperate and equatorial zones. Fig. 9.— Comparative Saltness of Seas. With regard to basins almost inclosed, like the Mediterranean, the Ca- ribbean Sea, and the Baltic, the saltness ought evidently to be greater or less there than in the ocean, according as the evaporation is in excess of or is inferior to the fresh water brought by the rivers and the clouds. In the Mediterranean, the loss in evaporation being more considerable than the contributions of fresh water, the saltness ought to increase in conse- quence, and the liquid mass would constantly diminish, if a current set- ting in from the Atlantic through the Straits of Gibraltar did not restore the equilibrium. While the less saline waters of the ocean thus pene- trate into the Mediterranean flowing along its surface, a submarine coun- ter-current, composed of heavier and Salter water, flows deep below in an opposite direction, and mingles with the waters of the Atlantic, which contain less salt. The mean saltness of the Mediterranean is nearly 38 * See below, the chapter headed Currents, INEXHAUSTIBILITY OF COMMON SALT. 37 thousandths, and even exceeds 39 thousandths on the coasts of Tripoli, where the parching winds of the Libyan desert blow. In like manner, the Caribbean Sea seems to present a somewhat high relative saltness because of an excess of evaporation over the contribution of fresh water; but the contrary happens in the Gulf of St. Lawrence, in the North Sea, and, above all, in the Baltic and the Euxine. The saltness of the North Sea is in different parts from 30 to 35 thousandths, while that of the Baltic, a shallow sea into which so many rivers flow, and where the least wind disturbs the waters,* does not quite amount to five thousandths ; in the port of Cronstadt it is not even two-thirds of a thou- sandth, which is almost fresh water. As to the Black Sea, it preserves, even more than the Baltic, the character of a gulf of the ocean, for the average saltness is about half that of the Atlantic. These differences of salinity between the central basin of the Atlantic and its tributary seas are not in themselves astonishing ; but we do not yet know why the South Sea and Indian Ocean contain less saline matter in their waters than the Atlantic, unless the enormous quantity of Antarc- tic ice explains this difference. While the latter has a saltness of about 36 thousandths, the water of the Pacific has less by nearly one thou- sandth, and the Indian Ocean contains no more than 35 thousandths of chemical substances. The Atlantic, however*, receives a greater quantity of fresh water than the other oceans, and the evaporation is probably not so great, on an average, as in the Indian Ocean. But nevertheless the gulfs of the Indian Ocean present phenomena analogous to those of the inland seas of the Atlantic. Thus the Red Sea, into which no single per- manent stream of water flows, and where evaporation proceeds with very great intensity, shows the enormous degree of saltness of 43 thousandths; such a proportion as is only found in inland salt-water lakes.f Chloride of sodium or common salt contributes, as we have said, three- quarters of the saltness of sea-water. This is, indeed, the characteristic salt of the ocean which most of all gives it its peculiar flavor, and that odor with Avhich the sea-breezes, laden with the fine spray of the waves, are charged. The air which rests on the sea also contains salt to a con- siderable height ; at an elevation of 2000 feet above the coast on the sides of the mountain which towers above the Peruvian town of Iquique, Mr. BoUaert asserts that any materials washed in distilled water are covered in a few days by a slight incrustation of salt. J The thickness which a layer of chloride of sodium in the open sea would form, if crystallized, would be, on an average, nearly two inches to every fathom of water ; so that if one could imagine the entire evaporation of the waters of the ocean, estimating them to be, on the average, above three miles deep, there would remain at the bottom of its bed a layer of salt of about 230 feet in mean thickness, which would represent for the whole extent of the seas more than a t^usand millions of cubic miles. * Von Sass, Zeitschrift fur die Erdkunde. t Forchhammer, Philosophical Transactions, part i., 1865. f Antiquities, p. 258. 38 THE OCEAN. We can understand how, with such* vast quantities of chloride of sodium in solution, the sea has been sufficient to form those enormous beds of rock-^alt that are found in the earth in various parts of Europe, without I'eckoning many other deposits which still remain to be discovered, and which sooner or later will be repealed to us by the labors of miners, or by Artesian borings. Then, too, we may see the ocean at work on all the low coasts, where it deposits saline beds, destined to become in process of time masses of rock-salt, after they shall have been buried beneath more modern strata. When, in consequence of a tempest or of a high tide, the waters of the ocean are spread in a thin sheet over a flat shore, or in some deeper de- pression, this slight bed of salt water, spread over a vast surface, evapo- rates rapidly under the rays of the sun, and leaves in its place a slight white crust of saline crystals. Other sheets of water, urged by the bil- lows or the tide into the same basin of evaporation, disappear likewise, forming new layers of crystals ; it is thus that real banks of a considera- ble thickness are gradually formed on the borders of the sea, as well as on the shores of inland seas and salt lakes.* Pig. 10. — Salt Marshes of Bessarabia. Even the Black Sea, where the proportion of salt is relatively very in- considerable, is, on the greater part of its shores, bordered with these natural salt marshes. In Bessarabia, to the south of Odessa, three Umans of a total area of many square miles, cease in summer to receive their * See the section entitled Lakes. ELEMENTS CONTAINED IN SEA- WATER. 39 * affluents of fresh water, and all the water which has been brought there in winter evaporates, leaving an incrustation of salt ; toward tlie centre of the basins of crystallization the solid mass attains nearly an inch in thickness.. In 1826, these natural deposits, worked by the natives, pro- duced about 120,000 tons .of pure salt.* In most of the populous coun- tries of Western Europe, man has converted these casual swamps into salt marshes with regular outlines. The unequal depressions, where the water of the sea evaporated accidentally, are transformed into reservoirs, where the water is conducted from compartment to compartment, to sat- urate itself gradually and deposit the pure salt in equal layers. But these are only economical works ; man is confined to regulating the oper- ations of the sea itself.f Besides common salt, many substances which are exceptionally found in inland Avaters and hot springs form a part of the normal composition of sea-water. The various simple substances which science has been able to discover therein (either directly by the analysis of the liquid, or in- directly by the.study of the plants which draw all their nourishment from the ocean) are twenty-eight in number; but doubtless numerous other simple substances are likewise contained in sea-water, many of which will not long escape the piercing researches of chemists. After oxygen and hydrogen, which constitute the liquid mass itself, the principal elements contained in sea- water are : chlorine, nitrogen, carbon, bromine, iodine, fluorine, sulphur, phosphorus, silicon, sodium, potassium, boron (?), aluminium, magnesium, calcium, strontium, barium. The com- mon fucus and other sea-weeds contain the greater part of these sub- stances, as well as several metals. They have discovered copper, lead, and zinc in the ashes of Fucus vesiculosus ; cobalt, nickel, and manganese in those of the Zostera marina. Iron may be obtained directly by an analysis of sea-water, and finally silver is found in a zoophyte, the Po- cillopora. Forchharamer has obtained from a branch of this coral about a three-millionth of silver, mixed with six times the same quantity of cop- per, and eight times of lead. A slight proportion of silver is precipitated on the bottoms of ships, in consequence of the magnetic current estab- lished between the copper sheathing and the «water of the surrounding sea. J And, lastly, arsenic has been found in the boilers of steamers which have been supplied with sea-water.§ It is true that these various sub- stances only exist in infinitesimal proportions in the water, and it is by indirect means alone that chemistry succeeds in revealing them ; but the total mass of silver contained in the ocean is estimated at two millions of tons. The seas having most probably received from the terrestrial strata, which have been unceasingly worn away by the currents of water, all * Bischof, Lehrbuch der chemischen und physikalischen Geologic. t See below, the section entitled The Works of Man. X Philosophical Transactions, part i., 1865. § Bischof, Lehrbuch der chemischen und physikalischen Geologie. 40 THE OCEAN. the substances which they contain in solution, we may conclude that the proportions of these substances have continually varied during the geo- logical eras. The saltness would be modified from age to age, according to the various quantities of soluble substances which the rivers brought down to the ocean, and which it returned again to the land, either direct- ly, by depositing them on the shore, or indirectly, by fixing them in the tissues of its plants, corals, and other organisms which people its expanses. By ingenious comparisons between the conditions of the present day and those which seem to have existed in former times in the sedimentary beds, several geologists have attempted to determine if the substances in solu- tion in sea-water have augmented or diminished. But the conclusions at which they have arrived rest, at present, on data too hypothetical for us to regard them as a new conquest of science. It is only certain that in our day the proportions of the substances dissolved have not ceased to vary in every sea. We can judge of this by the enormous difi"erence that there is between the saltness of the waters of the Caspian and those of the Black Sea — two separate basins which formed a part of the same ocean at a geological epoch still comparatively recent. Sea-water contains also a great quantity of the atmospheric gases, the proportions of Avhich constantly change with heat, light, the motion of the waves, and barometric pressure. Salt water retains dissolved air bet- ter than fresh water, and the bulk which it absorbs is generally greater by a third than that found in rivers. It varies from a fifth to a thirtieth, and gradually increases from the surface to a depth of about 325 to 380 fathoms.* Carbonic acid gas is also contained in a relatively very con- siderable proportion iu sea-water, as might have been expected from the swarming myriads of marine animals. Under the influence of light, plants decompose this gas, which diminishes during the day, and is in- creased again during the night. As to the quantity of dissolved oxygen, it varies inversely ; during the day it increases by degrees, to be again reduced in the hours of darkness. As by a sort of respiration, the great sea — that immensity alive with organisms — absorbs and disengages alter- nately the gases necessary to the maintenance of life, and measures each breath by the daily course of the sun. * Bischof, Lehrbuch der chemischen und physikalischen Geologie. ITS VARIETY OF COLOR. ' 41 CHAPTER IV. VARIOUS COLORS OF SEA- WATER. — REFLECTIONS, TRANSPARENCY, AND PROP- ER COLOR. TEMPERATURE OF THE DEPTHS OP THE SEA. Owing to the double property which water possesses of reflecting liglit and allowing its rays to penetrate to a great depth, it presents suc- cessively the most varied colors, the most delicate tints?, with alternations the most fugitive and changeable that are to be found in nature. The sea produces, and at the same time modifies, the varied face of the heav- ens with all the play and gradation of light and shade. At dawn, the surface of the water is gently brightened by the glimmering of the at- mosphere, as yet pale and faint ; then the sparkling of the waves becomes more brilliant, and the full light of day pours a flood of fire upon the bil- lows. The least movement in the air is betrayed by a change in the as- pect of the water, every cloud in passing mirrors itself with the forms and shades of its vapors, every breath of wind that just curls the waves renews the harmony of the changeable coloring on the face of the ocean. And when evening comes, the sea reflects back to the sky all its splendor of purple and flame. It is then that we see on the horizon "two suns appear, one in front of the other." But the water does not owe its beauty to the splendor of the sky alone, it is beautiful also from its transparency; while the substances suspended in the liquid mass, which are visible to a considerable depth, modify by their own color the general tint of the sea. The animals, fish or cetaceans, which come to the surface or glide swiftly through the waves, cause them suddenly to glitter with changing reflections of gray, rose, green, and silver. The fuci, too, growing beneath the water, vary the aspect of the liquid strata which cover them ; and where these beds of plants alternate with ridges of bare rock, or tracts of sand, the sea pre- sents a wonderful mixtui-e of diflerent shades with blended and tremu- lous outlines. In those latitudes where the water is very transparent, the color of the ground may be thus distinctly seen at 10, 20, or even 25 fathoms below the surface, which navigators have confirmed by scien- tific observations made with the greatest care.* But this transparency does not seem to depend upon the intensity of light received, for in the ^Vrctic Seas floating objects can be perceived at as great depths as in the Caribbean Sea ; and it is indeed in polar latitudes that the eye of man has been able to penetrate to the greatest depth below the surface. According to Scoresby, that conscientious explorer of the polar seas, the sea-bed of the pure waters in these regions is sometimes visible at a * Ciakli, Sid Moto Ondoso del Mare, p. 284. 42 THE OCEAN. depth of 70 fathoms.* It is true that, in consequence of climatic differ- ences and the organic life which depends on them, the bottom of the sea is much more curious to contemplate in the tropical zone than in the neighborhood of the poles. There is nothing more delightful than to sail over one of those seas where, without fear of hidden rocks, one can watch the bed of the sea reveal itself far below the prow of the vessel. Numer- ous algge, green or rose colored, wave gracefully below the surface like the grasses of a brook; the mollusks crawl along the bottom; crustace- ans, fish, star-fishes of brilliant colors, and many other animals of strange form, glide slowly or dai-t like arrows thi'ough the blue water, glistening in a thousand changing hues; while the IsTemertida and other living ribbons softly unroll their transparent rings. One might fancy one's self suspended above another earth, and floating in an aerial ship. The white foam on the waves raised by the keel of the ship, and the irides- cent colors which sparkle in the spray, add fresh charms to this wonder- ful picture. Even when the bed of the sea is not distinctly visible, it does not fail to reveal itself by the peculiar tint it imparts to the water. In general the color of the sea is lighter near the coasts, and even at a depth of above 100 to 150 fathoms, a paler shade of the water at times makes known to the practiced eye of the mariner the relative proximity of the bottom. Not far from the coasts of Peru, De Tessan perceived that the sea had suddenly assumed a tint of dark olive-green, and when he caused a sounding to be taken, it was found that the mud at the bottom was precisely of this color. Numerous navigators have affirmed that in one part of the Lagullas bank, where the mass of water is above 100 fathoms deep, the water passes suddenly from blue to a greenish color.f Lastly, off Loango, the water is always brown, similar to that of the bottom, which Tuckey has found to be of an intense red. Is, then, this coloring owing to the sun's light, which descends through the liquid depths to the bed of the sea, and is reflected again to the surface ; or does it result, as Cialdi thinks, from particles of mud that are floating in the water ?J Another question, difficult to solve, is that of knowing what is the nat- ural color of the sea- water. Not to mention local coloring, resulting, like phosphorescence, from numberless minute living organisms,§ the various parts of the ocean almost always present, whatever may be the state of the atmosphere, a normal tint easy to be distinguished from accidental shades. Thus, to cite one of the most striking contrasts, the water of the Gulf of Gascony is of a sombre green, while in the Gulf of Lyons the water of the Meditei-ranean is of a magnificent azure, deeper than that of the sky. The wonderful blue color which rises from the depths of the water in the grotto of Capri, so frequently visited by travelei-s, is a well-known example of the degree of intensity to which the blue peculiar * Arctic Regions. See also the notice of Arago, (Euvres coinpletes, t. ix. t Arago, ibid. % -SmZ Moto Ondoso del Mare, p. 287. § See below, the section entitled The Earth and its Fauna. TEMPERATURE OF THE SEA. 43 to the waters of the Mediterranean can»attain. In the tropical latitudes of the Atlantic and the South Sea, the azure of the ocean is no less beau- tiful than that of the Tyrrhenian Sea; Avhile in the direction of the poles the water gradually assumes a greenish tint. Naturalists have con- cluded from this fact that the refraction of the rays of light, which are much more vivid under tropical latitudes, play a principal part in the blue coloring of the sea. Maury thinks that the saltness is also one of the causes which contributes the most to give its azure tint to the wa- ter ; and x)bserves that the Gulf Stream of the American coasts, superior in salinity and in temperature to the water around it, is also of a much deeper blue. In the same way the shallow water let into the salt marshes of coasts gains in intensity of color in proportion as the salt is concen- trated there. Still, it is very possible that th^ coloring of the sea is due in great part, like the marvelous tints of the Swiss lakes,* to innumerable corpuscules held in suspension, upon which the light strikes. The law of the distribution of temperature, in the depth of the ocean, is not as yet more determined than that of the coloring of the water. At the surface of the sea it is as easy to make observations as in the air, and it has been determined, without difficulty, that this superficial sheet of water presents, on an average, in all climates, the same degree of heat as the superincumbent atmosphere. Thus, from the polar regions to the equatorial zone, the water becomes warmer with an almost regular grada- tion, and, from the freezing-point under the Arctic circle, the temperature rises to 68 and 77 degrees Fahr. under the tropics, and to 86 and even above 90 degrees Fahr. in the Pacific, the Red Sea, and the Indian Ocean. f With regard to the increase or decrease of heat in a vertical direction, we had till recently only the vaguest notions, in consequence of the want of exact soundings. It is, in fact, very difficult to lower to a depth of several hundred, and even several thousand fathoms, thermometrical ap- paratus strong enough to resist the enormous pressure of one atmos- phere for every 33 feet. Sir James Ross was one of the first who attempted to apply the re- sources of modern science to a systematic exploration of the temperature in the depths of the sea; but he seems to have committed the error of generalizmg too hastily from the incomplete results which he had obtahi- ed ; and, in his eagerness, he believed he had discovered a law which the subsequent researches of navigators have not confirmed. He thought that he could establish the fact that under the equator the temperature of the water diminishes gradually to 1200 fathoms, where it is only 39'2 degrees Fahr. On each side of the equator the upper waters gi-adually cool, and the limit of four degrees is progressively raised toward the sur- face ; it is at the fiftieth degree of latitude, in the southern hemisi^here, that it finally reaches the level of the sea. Farther in the direction of the pole the superficial water continues to grow colder, while the line of four degrees sinks gradually to the depth of 765 fathoms. Thus, as the * See the section entitled Lakes. t Fitzroj, Weather-Bool-, p. 84. 44 THE OCEAN. ::i^^iM&m. Fig. 11. — Sheet f)f Water presumed to be at a teropcrature of .09-2 degrees Fahr. accompanying figure shows, the line of uniform temperature to the south of the equator describes a long curve, touching the surface of the water at one point only. Admitting, with the naturalists of his time, that the sea-water has its greatest density, and in consequence its greatest rela- tive weight, at seven degrees above freezing-point. Sir James Ross con- cluded from this that all the deep waters below this line of 39"2 degrees have the same temperature, and are collected by reason of their conden- sation at the bottom of the oceanic basins, Nevertheless it has since been proved, by the obsei'vations of Neu- mann* and other scientific men, that if the greatest density of fresh water corresponds in reality to 39'2 degrees Fahr., the water of the sea only at- tains this maximum at nearly four degrees below freezing-point (28'4 de- grees Fahi'.), or even at still lower temperatures, and, in consequence, the conclusions at which Sir James Ross arrived are negatived. Experiments made in chemical laboratories, however,' where substances are treated in small quantities, can not give a perfectly exact notion of the phenomena which have nature itself for their theatre, and which take place either in the aerial spaces or in the vast oceanic basins. Thus, as the celebrated meteorologist Mtihry says, the immense sea, and a bucketful of salt water, do not obey absolutely the same laws of temperature and density. But before the difference is established, nothing can authorize us in maintain- ing a superannuated theory against all the experiments of chemists, ac- cording to which the volume of salt water in the sea in cooling presents phenomena identical with those of fresh-water lakes. Moreover, during the past years, numerous observers of polar seas have found at great depths beds of water at a temperature lower than 39'5 degrees Fahr.f That which remains of the researches of the eminent navigator. Sir James Ross, is that in the tropical and temperate seas the heat diminishes graduallj'- and constantly to a considerable depth. This is what has been put beyond all question, by soundings taken by Fitzroy and other marine explorers. To the south of the island of Madagascar, the surface of the water having then a tempei-ature of 1b'2 degrees Fahr., Fitzroy ascer- tained that the thermometer fell in the most regular manner, till at the * Ueher die Dichtigkeit heim Meerwasser. t Fitzroy, Weather-Book, p. 81. TEMPERATURE OF THE SEA. 45 depth of 420 fathoms, where they ceased sounding, the temperature indi- cated hardly cxc(.'eded 5r8 degrees Fahr.* In tlie inclosed basins of inland seas thermoraetrical observations arc much more easily made than in the middle of the great ocean, because the waters there are generally less deep, and the natural gradations of temperature are less disturbed by currents. Thus the water is not very cold in the depths of the Mediterranean, and presents only slight varia- tions of temperature. At about 100 to 275 fathoms below the surface, the fluid .mass has already attained permanently the mean temperature, which it preserves during all the year, and which seems to correspond to the meam annual temperature of the neighboring lands, which are subject to all the abrupt changes of heat and cold.f While in summer the super- ficial sheet of water has about 73 "4 degrees Fahr., the water comprised between 273 fathoms depth and the very bottom of the Mediterranean is found at 59 degrees Fahr., which is pretty nearly the mean annual warmth of the bordering countries. In the Greek Archipelago, the deep waters of which are probably colder in consequence of the current flowing from the Black Sea, the waters of the surface have in summer from 77 to 78 '8 degrees Fahr., and at hardly 98 fathoms' depth the thermometer reveals a constant temperature of from 53*6 to 55*4 degrees Fahr. The Mediter- ranean is divided into distinct basins, separated from one another by in- termediate ridges, which are situated from 98 to 273 fathoms below the surface, the result being that the variations of temperature produced by the movements of currents and counter-currents arc arrested on the tops of the ridges. The water of each basin, being relatively tranquil, thus maintains almost constantly the same thermometrical degree.]; * Adventure and Beagle, vol. ii., Appendix, p. 303. t See below, the section entitled Climates. X Spratt, Nautical Magazine, January, 1860. 46 , THE OCEAN. \ CHAPTER V. FORMATION" OP ICE, — ICE-FLOES, FIELDS OF ICE, AND ICEBEEGS. — ICE IN THE BALTIC AND THE BLACK SEA. In the Polar seas the low temperature results in the formation of ice. During the long winters of these cold regions, the tranquil water of the bays and gulfs freezes round the edge of the coasts, and the crystallized mass gaining incessantly on the sea finally extends to a considei'able dis- tance. This is " ground-ice." The surface of the sea disappears, like that of the lakes, under a solid layer; but the manner of forming the icy crust differs, for in the rivers and basins of fresh water crystals of ice at first appear over almost the entire surface, but in the seas which have no great depth it is generally from the bed itself that the liquid mass congeals. In fact, salt water has not, like fresh water, its greatest density at the temperature of 39*2 degrees Fahr., but it becomes heavier and heavier in proportion as it freezes. The coldest strata of water, being also the heaviest, descend vertically toward the bottom of the sea, and displace the lower strata, which are lighter and of a higher temperature. While the water which descends to the bottom in rivers has a normal heat of seven degrees above freezing-point, the sea-water which falls deeper may have been chilled to 32° Fahr., or even many degrees below it. When the mass is not agitated, it remains liquid, but, on the slightest disturb- ance, it suddenly turns to ice. Sometimes, at the commencement of win- ter, the mariners and fishermen of the Baltic and western coasts of I^or- way find themselves suddenly surrounded by floes of ice, which rise from the bed of the sea and which still contain fragments of fucus. It ap- pears so rapidly that the boats often run great risk of being crushed be- tween the solid masses which are piled around them, and the crews are in imminent danger. Around the rocky coasts of Greenland, Labrador, and Spitzbergen, these* ice-floes often raise huge stones which they have torn from the bed of the sea.* In the open sea ice is also formed. In winter, when the air is calm, the snow falls in large flakes on the tranquil waves, the sea is soon cov- ered with a kind of scum,*which gradually changes into a thin coating of ice. The wind may break this layer when barely formed, and the tiny scattered fragments may be surrounded with water from the melted snow, which does not mix with the salt-water of the sea, and glitters feebly with iridescent hues beneath the rays of an oblique sun; but this does not last long, and the cold soon reforms the layer of ice.f Even in * Edlund, Poggendorf' s Annalen, cxxi. t Gustave Lambert, Expedition au Pole Nord. Bulletin de la Societe de Geographic, December, 1867. FIELDS OF ICE. 4-7 despite of wind and wave, innumerable needles of ice, which give to the surface of the water a pasty appearance, spread their net-work over the sea, and soon consolidate into a thick layer, which constantly increases as the cold of winter becomes more and more rigorous. By the natural chemistry of the sea, which is an immense laboratory, the mass of ice is in a great measure freed from the salt which is found in sea-water; for, according to the observations of Mr. Walker, it contains hardly more than five thousandths; that is to say, about a fifth of its normal quantity. The water nearest to the new ice mixes with the expelled salt, becomes heavier, and as the freezing-point is at the same time lowered it descends deeper in the water without becoming solid. This is the reason why in the open sea the water is rarely frozen for any considerable depth, below the surface, as one might expect.* In consequence of the frequent collision of these fragments of ice toss- ed by the waves, they generally assume the same circular form as the flakes of ice on rivers. They are roundlets of a very inconsiderable di- ameter, slightly raised at the edges ; the English sailors term them " ice- cakes." But the cold becoming more intense, these disks finally adhere to one another, and before long millions of them, united in vast fields, form islands which stretch to the farthest horizon. Sometimes these " ice-fields " have a superficial extent of hundreds of thousands of square miles, and even constitute, by their dimensions, real continents. Those which border upon the eastern coast of Greenland have not been melted for four centuries, and efiectually prevent the approach of navigators to the land ; those connected with the Siberian coasts are still more con- siderable, because of the long extent of shore which serves as their base. In the Polar archipelago of America, ice bars the entrances of the chan- nels almost every year, and raises before the navigator an impassable wall. How many times have the explorers of Arctic seas tried in vain to find a passage through these barriers, and have remained imprisoned in the solid mass, after having ventured into some deceitful opening of the ice-field ! These interminable white surfaces are almost always bordered on the seaward side by blocks and disks rocking or whirling on the billows; these are the scattered islands which announce the neighborhood of con- tinents of ice. Those which are elevated on an average from three to six feet above the water, and the bases of which descend from twenty to twenty-five feet below the surface, have sometimes a tolerable uniformity of aspect, and when at times the snow covers all inequalities, the ice-field seems to be transformed into an even plain like the Russian Steppes. But the ice is much more often rugged ; fantastic hillocks, formed of all the wreck-fragments which the floes of ice have thrown up in dashing against each other, appear here and there several yards high. There are some which one might even confound with the enormous blocks that have fallen from the glaciers of Greenland or of Spitzbergen, and which * Neumann, Ueber die Dichtigkeit heim Meerwasser. 48 THE OCEAN. really can not be distinguished from them but by the slightly saline taste of the ice. These projecting masses are seen from afar above the sea, and remain erect long after the ice-field has melted. In the Siberian seas, where they give them the name of toroses, most of these hillocks, composed of the ice of the preceding winter, are easily melted by the •first warmth of summer ; but there are some which are preserved from year to year, and which remain indestructible during centuries, even un- der the rays of the sun. The Ostiac hunters, who frequently see these toroses run aground on the Siberian coast, designate them "Adam's ice," and, imagining that they are contemporaneous with the origin of the world, assert that even fire itself is powerless against their crystalline masses.* In spring-time and in summer, when the great heat commences in the polar zone, the force of the currents, whose action constantly makes itself felt beneath the ice plains, detaches from the remainder of the mass enormous fields of ice several hundred square miles in extent, and carries them far toward the open sea. The vessels of the explorers or whalers, which have been set fast in the bed of ice, are then carried out of their course with the broken field. Coui\ageous sailors who have penetrated beyond Bafiuln's Bay have often thus been brought back by the current for hundreds and thousands of miles, and have only been able to regain the way they have lost at the price of most painful efforts, or have even been obliged to abandon their enterprise completely. Such was the case in the sea around Spitzbergen in 1777 ; ten Dutch vessels were driven with the ice more than 1500 miles toward the south-west, and shattered on the way. It was a phenomenon of the same nature which prevented CajDtain Parry from reaching the North Pole. He had al- ready approached nearer to this point than all preceding navigators, and had taken a sledge to cross the ice-field ; but each day, notwithstanding the great distance apparently traversed in the direction of the pole, he found himself farther than the day before from the goal toward which he marched — the reason being that the continent of ice which bore him was being itself carried rapidly toward the south. White bears are thus sometimes carried by ice-floes, and landed on the coasts of Lapland.f When once broken, the ice-field soon disappears ; large fragments, driv- en by the currents and the waves, are dashed against each other with the enormous force which a weight of hundreds of thousands or millions of tons gives. Shattered by the terrible shock, these masses are divided into pieces of smaller dimensions ; the cementing ice being destroyed by the fragments of the more anciently-formed ice-field, the turrets and pin- nacles which stand here and there begin to melt and fall, and a few days after the thaw has commenced nothing remains but a few ice-floes and uneven blocks gently rocking with the waves. To account for this rapid disappearance of the ice-fields (in which the infinite tiny organismsj of * r. de Wrangel, Voyage, Appendice, p. 314. + Barto von Lowenigh, Mittheilungen von Petermann, Erganznngsheft xvi. X See below, the section entitled Earth and its Flora. FORMATION OP ICEBERGS. 49 tlie sea also aid) the inhabitants of Greenland imagine that the entire mass is ingulfed iu the depths of the ocean. Even in the Baltic, where this phenomenon is comparatively much less remarkable, the Danish sailors, almost without exception, assert that in spring-time the ice-floes are swallowed* up by the sea, although not one of them has witnessed the immersion.* But what is more easily corroborated is the strange noise that always accompanies the breaking up of the ice. With the crash of the meeting ice, more deafening, more terrible than that of can- non answering to each other, with the roar of the waves, and the groan- ing sound from the breaking disks and the air which escapes from them, is-joined a kind of crackling, similar to drops of rain falling on plates of metal. This noise, which is heard also on mountain glaciers, results, as Tyndall has shown, from the incessant breaking up of the crystals which compose the mass.f • Pig. 12.— Glacier of La Madeleine, ou the Coast of Spitzbergen. Whatever picturesque beauty thei-e may be in the ice of marine forma- tion constituting this field, it is far inferior to that of the masses which are detached from the glaciers of Greenland, Spitzbergen, and other coun- tries of th^ North Pole, Enormous fragments may be separated from the end of the glacier in two different ways, according to the tempera- * Forchhammer, Philosophical Transactions, part i., p, 233, 1865. t See the chapter entitled Snows and Glaciers. 4 50 THE OCEAN AND THE ATMOSPHERE. ture of tlae sea into which they protrude. In Spitzbergen and on the coasts of Southern Greenland, the congealed mass, which often projects far into the sea, is gradually undermined by the comparatively warm waves which beat against it, and the remaining fragments overhanging the water are detached with a terrible noise, and plunge into the ocean. M. Martins and other members of the French expedition to Spitzbergen have observed this at the base of all the glaciers of that archipelago. But in very cold seas, like that of Smith's Strait, the water, being of a still lower temperature, can not melt the glacier, which continues its course into the bay, its extreme end reaching fai? into the depths of the ocean, like an immense plain gliding over the rocks. Though lighter than the water, the enormous frozen mass is kept below because of its cohesion to the mer-ch-glace which drives it along. But the moment comes when that connection breaks, and, obeying at last the force which its buoyancy im- parts to it, it shoots to the surface, and after repeated oscillations from the change in its centre of gravity it rises in huge towers or fantastic peaks.* We can imagine what a chaotic mass all these fragments, mixed with the marine ice and the remains of ice-fields, must produce in narrow bays, or in very contracted arms of the sea. It was across one of these prodig- ious " packs," in Smith's Strait, that the inti-epid Hayes, wuth almost su- perhuman perseverance, passed. These glistening icebergs are the splendor of Arctic seas. Often of colossal dimensions, they present at times forms of almost perfect regu- larity, while at others they assume the most varied and fantastic shapes. Lofty towers, columns in pairs, with groups of sculpture, and statues, like marble divinities, rise above the sea. In comparatively warm seas like those of Spitzbergen, which are a^cted by the Gulf Stream, the ice is constantly worn away ; and those parts of the floating masses which rise above the surface of the sea generally assume the appearance of pil- lars, with more or less overhanging capitals, fringed with stalactites. The summit is white and occasionally covered with snow, Avhile the flut- ing of the column where the more compact ice has been bathed by the waves has an emerald or sapphire hue. The foundations of the columns are pierced with caves, into which the water rushes with a hollow mur- mur ; and at times they are riddled with small holes, from which each wave springs in diA^erging jets. Silvery fountains burst alternately from either side of the column, according to the inclination given to it by the sea,f In very cold water, like that of the Arctic Ai'chipelago, the op- posite phenomena occur. Instead of being worn away and melted by the waves, the blocks fallen from the glaciers at first gradually increase in dimensions, on account of the low temperature of the water iftto which they are plunged, which solidifies around the foot of these enormous floating towers.J * Rink ; Hayes, The Open P.olar Sea. t Bavto von Lowenigh, Mittheilungen von Petermann, Erganzungsheft xvi. X Edlund, Poggendorfs Annalen, 6xxi. SIZE OF THE ICEBERGS. 51 The larger masses detached from the glaciers are known i;nder the name of icebergs. Dr. Wallich was able to measure some of them on the coasts of Greenland, by ascertaining the depth below water of the bank on which several of these moving bergs had been stranded ; and he found that, with the regularly formed blocks, the part above the level of the sea is never more than the fourteenth or sixteenth part of that be- neath the level of the water. With respect to the masses whose exposed portions terminate in a cone or a pyramid, they descend to a less depth, in proportion as they present a more considerable bulk above water. But the total height of the iceberg always exceeds by seven or eight times the visible portion. By these proportions, mariners can judge of the real size of the icy masses which they see stranded on the coasts of Newfoundland, or melt- ing slowly as they float far out into the Atlantic. Enormous blocks have been seen from 800 to 400 feet high, so that these fragments of glaciers measured more than 3000 feet from summit to base — that is to say, an elevation equal to the highest mountains of England or Ireland. One of these masses which was encountered by the ship Acadia off the Banks of Newfoundland, amidst a labyrinth of other floatiag mountains, was about 480 feet high, surmounted by a kind of dome resembling St. Paul's Cathedral in a most singular manner. Twenty days later, when on her homeward voyage, the Acadia found the same iceberg 68 miles more to the south. A great number of these traveling masses have been seen, measuring several miles in length and breadth, whose bulk amounted to tens of thousands of cubic yards. As to fragments of ice-fields, some have been met with measuring not less than from 50 to 100 miles in each direction. TJie slow movement of the block observed by the Acadia^ which only advanced a little more than three miles per day, proves that icebergs offer considerable resistance to the current which carries them. The checks to which they are subject on the way, such as partial strandings, or when the surface and under-currents urge them in opposite directions, retard their speed considerably, and often change them into seemingly stationary islets. Toward the end of 1855 an unexpected circumstance, still moi'e remarkable than that of the berg seen by the Acadia^how^ us exactly what had been the progress of an iceberg during the space of more than a year. An American whaler sailing in Davis's Strait per- ceived a dark mass in the middle of a group of floating peaks ; this mass was the ship Resolute^ which the British Government had sent out in search of Franklin, and which the crew, having ventured into the ice-pack, had abandoned, to continue their way in sledges. When the vessel was found again, it had been already detained in its floating prison for six- teen months, and during that space of time had only been carried about 870 miles, counting the necessary turnings through Barrow's Strait and Lancaster Sound. Thus the ship, abandoned in the Polar Sea, had not exceeded the speed of 130 yards j^er hour in its progress toward the At- 52 THE OCEAN. lantic, which is a hardly perceptible advance. In the history of the great Arctic expeditions thi-ee other vessels are mentioned, which were carried in the same manner toward the ocean, but without having been abandoned by their crews; these were the ships of Sir John Ross, of Lieutenant De Haven, and of McClintock, The last-named navigator was a prisoner for 242 days, and advanced about 1120 miles toward the south, that is to say, about 346 yards per hour. The enormous masses of icebergs, like gigantic ships, are often stranded on shoals, even where the depth of the sea exceeds a hundred fathoms. Arrested in its southward drifting, the immense block gradually dissolves or divides into fragments, which in their turn are stranded on some other bank at a less depth. Day by day the waves melt and destroy great quantities of ice, which then let fall the gravel and stones with which it was charged, and in this manner continually raises the sea-bottom. Ev- ery year new beds of rock, pebbles, and earth from the mountains of Greenland and the archipelago of North America are thus deposited on the Banks of Newfoundland and in the neighboring seas, laying the foundations of a new continent. Doubtless the Great Bank, which ex- tends over a tract of above 55,000 square miles, and which has its foun-, dation in a sea of about four to six miles deep, is composed entirely of this moraine matter of glacial origin. Thus during a long series of ages the ice-floes have been laboring without relaxation to demolish the Arc- tic lands, and to construct new continents in the seas of the temperate zone. From the time of the breaking up of the northern ice — that is to say, from the beginning of March to the month of July and even to the month of August — that part of the Atlantic to the east of the Banks of Newfoundland assumes the appearance of the Arctic Sea. The Polar current, descending from Baffin's Bay parallel to the coasts of Labrador, brings with it in long procession the fragments of the ice-fields and gla- ciers of Greenland. After having rounded the Banks of Newfoundland, the current bends toward the south-west with its burden of ice, in conse- quence of the movement, which carries the earth in an easterly direction, and causes a deviation from its course in every thing coming from the north.* fCarried by this current, which drives them in the opposite di- rection to the Gulf Stream, continuing its course toward the south-west below the surface current of the latter, the icebergs, like ships cutting the waves with their prows, pass majestically through the water which dashes against them. Some fragments of mighty ice-fields, brought from Greenland by Polar currents and then drifted northward by the Gulf Stream, S.re seen here and there proceeding in an opposite direction from the rest. The accompanying map, borrowed from Redfield, indicates the position of all the icebergs and ice-fields recently observed in the western part of the North Atlantic Ocean. • It is principally in this region of the ocean that flotillas of ice are to * See below, p. 68. DANGERS FROM ICEBERGS. 53 Fig. 13. — Course of the Icebergs between Europe and America. be dreaded' by navigators. The sailors of Newfoundland hardly ever approach one nearer than about a mile, and then always keeping to windward of them, for otherwise they would be in danger of drifting upon the terrible mass, toward which, in addition, a somewhat strong current is always flowing to replace the upper ^tratum of water, rendered colder by contact with the floating mountain. Enveloped in fog, in con- sequence of the lowness of their temperature compared with that of the warm, humid air from the south, the gigantic hull of the glacier discovers itself to seamen by strange whitish reflections, and also by the intense cold of the surrounding atmosphere. But sometimes, when this indica- tion of peril has just been recognized, it is too late to avoid the shock. Hundreds of ships overtaken by the ice have thus disappeared, with their crews, in the cold waters of the ocean. At other times, even in clear weather, one meets with a whole archipelago of ice-floes ; and, in or- der to avoid them, it is necessary to steer with the greatest precaution for days together. It Avas thus that, in 1821, the English brig Anne, sur- prised by the ice before Cape Race, not being able to enter a free sea, was obliged to remain twenty-nine days surrounded by towers and threatening peaks. Happily these fragments of glaciers diminish very quickly in number and height as soon as they enter the zone of the Gulf Stream. Worn away at their base by the tepid waters of that cur- 54 THE OCEAN. rent, they capsize, break, and dissolve so completely, that toward the 40th degree of latitude it is rarely that any fragments even remain. However, in June, 1842, the ship Formosa encountered, in 37° 30' of north latitude, a floating iceberg 30 yards high and 50 yards long mov- ing toward the south.* In the Antarctic hemisphere exactly similar phenomena occur. Thus, as is proved by numerous observations, more than 860 of which have been regularly catalogued by Fitzroy and other geographers, the ice- fields and fragments of glaciers of the southern continent float likewise in the direction of the equator. But it seems that the icebergs of the southern hemisphere generally present less variety of form than those of the opposite one. They are not peaks and domes with fantastic out- lines, but rather resemble walls rising like rocky precijDices to an eleva- tion of about 160 to 200 feet; these floating masses are probably, how- ever, on an average of still more considerable dimensions than the masses which fall from Arctic glaciers. The massive form of these floating mountains of the southern seas must doubtless be attributed to the severe cold which prevails in the south jDolar zone, which drives the snow and glaciers of the Antarctic lands farther into the open sea. Even Figs. 14 and 15.— Icebergs of the Autarctic Ocean (after Wilkes). at the 50th degree of south latitude, ships meet with ice-fields of a size equal to those which on the other side of the earth are only found with- in the polar circle. In the northern hemisphere the ice-rivers of Green- land and Spitzbergen are not fed by a sufiicient quantity of snow to car- * Eedfield, Memoir on the Dangers of Ice in the North Atlantic Ocean. The Ort-au.&f. A N T A R j3o Eas A C I I I Engraved ly E rliar d . HARPER. &. B] I C LAND B a ^ s^ _. ^ Ur a i t s T ASM AiV I A . X^?^."'. I 'Hnbart-Townl h& -jj/ji o c PL IV E A N AucAlajui /.' * (iunf.6eZl I\ *«*• so XJ T Tl ^ T I r T o a I if J> A N n RS "T='W Y')RK Diawn by A. VuiUemin ."_ ajLcr Ch .Wilkes THE ANTAECTIC ICE- FIELDS. 55 ly tlieni completely out of the bays into which they flow, and into the open sea. Retained in their course by steep lateral cliffs, promontories, and rocky islets, they assume, in consequence of all these obstacles, a much more irregular form than they would have if they penetrated into the free ocean, like the glaciers of the South Pole. The latter are drift- ed for out of the gulfs, beyond the capes even, and they are only oc- casionally attached to the submarine base of the continent. In front of this ice-sheet float innumerable islands, through which ships can with difliculty find their way. Thus during the exploring voyage of Wilkes, the Peacock had to steer for a long time in a labyrinth of blocks which threatened to crush her. 16.— Route of the Peacock, Commander Wilkes, U. S. Navy, in the Antarctic Ice-paclc. The breaking up of the Antarctic ice occurs in spring and summer, like that of the North Pole, but six months later, in consequence of the opposition of seasons in the two hemispheres, caused by the obliquity of the earth's axis. The scattered pieces of ice met with during winter are only fragments detached from the ice-fields. Vessels traversing the Antarctic Ocean meet with thirty or forty times more ice in December, the height of summer, than in July, which is the coldest time. The niul- 56 THE OCEAN. titude of floating masses varies much in these seas. To the south of Australia and New Zealand icebergs and ice-fields are comparatively rare. To the south of Cape Horn they are met with more frequently, but are never seen between this southernmost point of America and the Falkland Islands ; for, owing to the great Polar current, they all drift toward the north-east. It is to the south of the African continent that the ice is carried in the greatest quantity, and approaches most nearlj^ to the equator. Some has even been perceived from Cape Town in 34 de- grees of south latitude. Thus the Antarctic icebergs are carried about 250 miles nearer the torrid zone than are the Arctic masses. 10 10 20 30 *0 50 60 30 80 00 V;.. r. ^„,.^ ""V* U_^^ f'^hTyTy fA,., tv\a Fr^^™- « ^<3t._ . . . Trep i2..Pt. pajiricorn ... \ ! V /-^^^ h so v^ Sr'^Jy^ ^rUxhurg 'V^ ^ io I.T, istojud'Ac uihcL' ' T-Amsterd, uri/ Ln -■ tc ^ J.Pr mX'EdzDa •i;. ■^. '.,;. ^ •-, so • ':■'::■:'.■ ^ '■ '"' <<«?•• crgaelen - 50 r. ■ " "•' ■i.Ice/-'Ba IS Fig. 17. — Course of Icebergs in tlie Southern Hemisphere. In the inland seas exposed to severe cold, the congelation of the water is produced in the same way as in the ocean ; the phenomena onlj^ differ ^in proportion. Thus the ice of the Baltic is far from presenting such a grand spectacle as the ice-fields of the Polar seas, but its mode of forma- tion is known in a much more complete manner; for dujing a long se- ries of years, conscientious observers have studied its various changes, from the formation of the first ice to the general breaking up. These researches have proved that, after having been formed, the icy bed of the Baltic is subject to the same phenomena as that of lakes, not only in the northern parts of the sea, where the water is almost fresh, but near the entrance also, where the mass of fluid is still strongly saline. The cre- vasses in the ice do not differ essentially in their foi'mation from those of Lake Baikal* or the Lake of Constance. They also open with a thunder- ing noise, letting a great quantity of water escape, which freezes in its ' turn, and thus increases the thickness of the solid bed. Around the isl- and of Oesel the fissures vary from six inches to more than six feet, and are continued for a distance of several miles. But the surf produced by * * See the section entitled Lakes. THE ICE OF THE BALTIC. 57 the cuiTents and the dashuig of the waves, where the sea is not frozen, o-ives the most varied directions to the crevasses ; in some places they are parallel, while in others they intersect one another irregularly, or ra- diate toward all points of the horizon. Ice very rarely covers the surface of the sea while the water is much ao-itated. Tempests or rapid currents retard, or even completely pre- vent, the formation of the ice-sheet. Thus, while on the east, where the sea is calm, the island of Oesel is, on an average, united to the main-land durino- 130 days of the year by a layer of ice sometimes attaining a thickness of more than three feet, and serving as a high-road for sledges, the w^estern cliiTs, against which the surges strike, are, on the contrary, only bordered by a narrow fringe of ice. On the promontory of Muhha 'Ninna the waves always break with fury, and this extreme agitation of the water lasts during the whole winter, preventing the appearance of the least particle of ice ; indeed the peasants of the island say that they have never seen any near this point.* Every year a considerable part of the Baltic is covered with ice. Al- most all the Gulf of Bothnia and the entire coast-line of the Gulf of Fin- land is changed into a white and immovable surface, the island^ and islets are encircled by a zone of ice-floes, more or less wide, while the straits of a slight depth are similarly obstructed. Every winter Finland is reunited to Sweden by a bridge of ice, pierced here and there by the innumerable rocks of the Oeland Archipelago. This solid crust then be- comes for many months the highway between Sweden and Russia. The Baltic, like the Polar ice-fields, has its piled-up masses of ice, resembling turrets, pyramids, and obelisks built upon the sea ; from these fields, also, broad masses are detached from their edges to float toward the south with the current, then, breaking with a loud crash, are similarly reduced into scattered pieces; and in a few days after the commencement of the thaw only thin fragments remain, tossed here and there by the waves. During the last few centuries the Baltic Sea has never been entirely covered with a field of ice. But the chronicles inform us that in 1323 the southern part of the basin was completely frozen over, and during six Aveeks travelers from Copenhagen repaired on horseback to Ltlbeck and Dantzic ; and temporary hamlets were even erected on the ice at the in- tersection of the roads. During the winters of 1333, 1349, 1399, and 1402, the same phenomena of general congelation occurred in the south- ern Baltic, and the icy bed served as a road for commerce between Pom- erania, Mecklenburg, Denmark, and the islands. In 1408 the ice-field completely closed the entrance of the Baltic between Norway and Jut- land, and extended through the Categat, the ^traits of the Sea of Scania, into the Baltic, as far as the large island of Gothland. It is said even that the wolves of Norway, driven from their native forests by hunger, crossed the Skagerrack to invade the villages of Jutland. Since this epoch, several parts of the Southern Baltic have been frozen over again; * Von Sass, Bulletin de F Academic de Saint Petersbourg, t. ix., p. 166, etc. 58 THE OCEAN. but the solid surface has never presented the same extent, nor the same consistency. This fact would seem to prove that the mean temperature has become milder in Northern Europe since the 14th century, while, ac- cording to Adhemar's hypothesis, exactly the contrary is the case.* It is a remarkable fact, that save in a few exceptional years the Black Sea, which is exposed to all the piercing winds which descend from the Polar regions, has never been invaded by ice like the Baltic, During the earlier historic ages the Sea of Marmora and the surface of the Eux- ine have been frequently covered with ice ; which proves that, at least during this period of frost, the temperature of Constantinople was no higher than that of Coj^enhagen. In the year 401 of the present era the Black Sea was almost entirely frozen over, and when the ice broke up, enormous icebergs were seen floating in the Sea of Marmora for thirty days. In 762 the solid layer which covered the Euxine extended from one bank to the other, from the terminal cliifs of the Caucasus to the mouths of the Dniester, Dnieper, and the Danube. Moreover, contempo- rary writei's assert that the j:][uantity of snow which fell on the ice rose to the height of twenty cubits (from 30 to 40 feet?), and completely hid the contour of the shores, so that one kncAV not where the land began or the sea ended. In the month of February, the broken masses of the ice, carried by the current to the entrance of the ^gean Sea, reunited in one immense sheet, between Sestos and Abydos, across the Hellespont. f * See the chapter entitled Harmonies and Contrasts. t P. de Tchihatcheff, Le Bospore et Constantinople. BE&ULAR AND IRREGULAR UNDULATIONS. 59 CHAPTER VI. M'AVES OF THfe SEA. REGULAR AND IRREGULAR UNDULATIONS. HEIGHT OF THE WAVES. — THEIR SIZE AND SPEED. — GROUND-SWELL. COAST-WAVES. The sea rarely presents a glassy surface. When the atmosphere is calm, Avhich however is commonly the case before a tempest, the water is sometimes so very smooth that every object is reflected by it with a perfectly sharp outline ; the only changes which seem to affect the vast motionless sheet of water are those produced by the mirage, which makes the distant horizon glitter like a long band of sUver or steel ; the fishermen then say that " the sea is reflecting itself." But this tranquilli- ty of the water is a very imcommon phenomenon, except in the Mediter- ranean and other seas, where there is only a slight tide. Usually the wind, either in breezes or tempests, now aiding and now retarding the ebb and flow, raises the sea into waves, more or less high, which some- times roll onward regularly, or are dashed against and cross one another. Even during calms, the waves, still obeying the impulse of recent winds, continue to roll across the ocean in long undulations. One of the grand- est spectacles at sea is offered by these regular movements of the waves in perfectly calm weather, when not a breath stirs the sails ; high, blue, and foamless, the liquid masses succeed one another at intervals of 200 to 300 yards, pass under the ship in silence, and, pursued by other waves, are lost in the far distance. One contemplates with a feeling of admi- ration, not unmixed with terror, the calm and majestic wave advancing like a moving rampart, as if about to swallow up all before it, "and ^^et hardly leaving a sign to mark its passage. These waves appear with surprising regularity during the autumnal calms, under the Tropic of Cancer, and almost at every season in the narrower part of the Carib- bean Sea toward the Gulf of Darien ; there the waves are seen silently to advance, and slightly raise the ship, passing onward Avith scarcely a murmur, as regularly as the furrows of a field, and stretching as far as the eye can see. Such perfectly regular waves .as these can only be formed in seas ex- posed to the influence of equable winds, such as the trade-winds. Wher- ever the winds are uncertain and shifty, blowing in gusts, it is evident that the waves driven by them can not assume a regular form or follow in a uniform direction. For aerial currents constantly vary in their speed ; being composed of strata of unequal force, which, moving at a rate different from that of the surface of the sea, alternately increase and diminish in force. Under the influence of these variable atmospheric im- pulses, the waves must necessarily vary in height and speed, and their 60 THE OCEAN. crests can not be developed in a vinifovm line. The wind also frequently changes its direction ; as if urged by some new impulse,* it commences blowing from another point of the compass, and drives the waves in a different direction from that Avhich it had- itself given them. Neverthe- less, the first movement is continued by the succeeding waves even while the second is still making itself felt, and from this double impulse an in- tersection of waves, differing from one another in direction, height, and speed, results. Let the wind shift to another point of the compass, and a third undulation crosses the preceding two. Finally, should the aerial current make the complete circuit of the compass, the ripples of the wa- ter pursue one another in all directions, urged from all points of the im- mense circle. Not a breath is lost on the sensitive surface of the sea, and the variety of its undulations testifies to the diversity of the aerial movements which cause them. From a lofty Ijeadland or from the mast of a ship, whence a vast ex- panse of water can be viewed, the beautiful sight may be often enjoyed of two or three systems of waves intersecting each other at various an- gles. Now they double the natural height of the undulations, by piling one wave upon another, and then again they equalize the surface of the water by throwing billows into the furrows. Sometimes the sea is so agitated that it is impossible to discern the direction of all the waves which have aided in producing the violent commotion. As to the voy- agers, whom the wave-tossed ship incessantly shakes by its rolling and pitching, it is still more difiicult for them to recognize in the intersection of the waves the various impulses communicated to the sea by the at- Prow. Stern. . 18.— Rollings of a Ship upon the Waves. mosphere. The accompanying figure is reproduced from that of an En- glish traveler, of the curves drawn during a single minute by a pencil * See below, the chapter entitled The Air and the Wind. HEIGHT OF WAVES. 61 suspended, vertically in the cabin of a sliip. At the time when the pen- cil traced these lines, the wind was low and tlie motion of the water very moderate. The height of the waves is not the same in all seas ; it is greater when the basin is deeper in proj^ortion to the exposure of its surface to the wind, and also in proportion as the water, being less salt and so lighter, yields more readily to the atmospheric curi-ents. Thus, assuming equali- ty of surface, the water of Lake Superior would be raised in higher waves than that of a gulf of the sea barred on tlie open side by islands and sand-banks. When of equal saltness, the narrowest basins ought to present the shortest and least elevated waves. The waves of the Cas- ' pian Sea are not to be comj^ared Avith those of the Mediten-anean, which, again, are greatly exceeded in height by those of the North Atlantic ; and these latter, in their turn, ai'e surpassed by those of the Antarctic Sea, AvhiCh spreads over an entire hemisphere. According to Admiral Smyth, who was well acquainted with the Med- iterranean, the tempest waves rise from 13 to 18 feet in vertical height above the trough of the sea. He has even seen quite exceptional waves rise to the height of above 30 feet, but the average waves raised by high winds were only from about 10 to 13 feet.* In one passage from Liver-, pool to Boston, Avhich the celebrated navigator Scoresby made in 1847, he measured waves from 26 to 2^^ feet, and the average of all his obser- vations gave a height of about 19 feet for the largest waves. Oh his return in 1848, he fouitd the average to be 30 .feet, and some among the waves he measured rose to about 43 feet above the trouo-h of the sea. JaimaryretouigylVlarch Aprfl Mixy Jmie Jiily An^st Sept^?'' Oct^P Nov^?'' Deo''?^ Fig. 19.— Average Heights of Waves observed at Lybster (Scotland) iu 1S52. Other navigators have given similar estimates for the highest crests of waves in the North Atlantic ; but the mean elevation is much less. One can form a good notion by the preceding diagram, drawn by the engineer Middlemiss to represent the annual variations of the wave at Lybster, on the coast of Scotland. In the South Atlantic the height of the waves is certainly greater than * Cialdi, Sul Moto Ondoso del Mare, p. 142. 62 THE OCEAN. in the northern parts. Many seainen have seen the water rise to be- tween 50 and 60 feet oif the Cape of Good Hope, where the basins of the Atlantic and the Indian Oceans meet. Dumont d'Urville even as- serts that he has seen waves above 108 feet high, to the depths of which the ship descended as into a valley, and M. Fleuriot de Langle attests the truth of this assertion. These are, indeed, the mountains of which poets speak, and wliich, in fact, seem such to those who find themselves at their mercy. It is probable, too, that the highest waves of the sea have not yet been measured. One remarkable thing is, that it is not usually during the most violent tempests that the hugest waves are* formed. On the contrary, the force of the atmosphere which then pre- cipitates itself obliquely on the waves, so to speak, dejjresses and crushes ' them.* The waves are developed in all their majesty when the wind is at the same time very high and very regular, and blows for a long time from the same point of the compass. Fig. 20. — Average Amplitude of Waves. As to the width of the waves — that is to say, their total breadth, from base *to base — observens have not obtained the same results ; but there ai"e few among them who have found the verticaWieight of the crest of the wave to be less than a twentieth or more than a tenth of the width. On an average the height oi' an undulation of the water is only equal to the fifteenth part of its base ; thus a wave of 4 feet in height measures 40 feet from valley to valley, and a wave 33 feet high is 495 feet in width. This is a much smaller size than would be imagined by the sail- or lost in the midst of the billows, which he sees rising around him in every direction. Moreover, the inclination of the waves varies with the force of the wind, and the movements of the secondaiy undulations which intersect the principal ones. The speed of the waves is only an apparent speed, like that of the folds of a cloth raised by a current of air. Thus, although the water pressed by the wind rises and sinks by turns, it nevertheless hardly changes its place, and objects floating on its surface move but slowly and in an un- dulatory mannei". The real movement of the 'sea is that of a drifting current which gradually forms under the prolonged action of the wind ; but this general movement of the liquid mass is, after all, inconsiderable. The only part which advances with the storni is the foaming crest which, curling over the summit of the waves, dashes down the slope in front. By their incessant movements, the surface of the waves gradually increase in temperature, as has been observed after a succession of violent storms.f * Cialdi, Sul Moto Ondoso del Mare, p. 139. t Joule. Cialdi, Sul Moto Ondoso del Mare, p. 218. DEPTH OF MOVING WAVE. 63 The apparent displacement of the billows (which is rather difficult to measure with exactitude in the open sea) varies in a regular manner, according to the magnitude of its waves and the depth of its waters. Thus, according to the calculations of the astronomer Airey, every Avave of 100 feet in width, traversing a sea of 164 fathoms mean depth, has a velocity of nearly 2100 feet per second, or about 15^ miles per hour; a wave of 674 feet, moving over the surface of a sea 1640 fathoms deep, travels more than 69 feet per second, or nearly 50 miles per hour; this last figure may be considered as an average speed for storm-waves in great seas. Since, therefore, we can by calculation infer the velocity of waves from their width and the known depth of the ocean-bed, it is easy to determine by an inverse opevation what is the ,depth of the ocean it- self, provided that we know the rate of motion of the waves. It is by this method that the mean depths of the South Atlantic and of the Pa- cific Ocean, between Japan and California, have been calculated,* Natural philosophers have frequently discussed the question of the movement of the waves in a vertical direction. To Avhat depth in the abysses of the sea does the action of the superficial wave penetrate, and at how many fathoms can it disturb the sand and debris at the bottom? It was formerly admitted, as a well-ascertained fact, but Avitliout jjroof, that the agitation of the sea ceases to be felt at four to six fathoms below the surface. Direct observations made by seamen in many latitudes have shown that this opinion is erroneous. Sailors have frequently seen the waves break at 10, 16, and even 27 fathoms of depth over hidden rocks, which proves that the rocks were obstacles which abruptly barred the advance of the lowest part of the wave. Still more frequently, dur- ing violent tempests, the water has been seen charged with clay and mud, which had been raised from the bottom at 50, 80, and even 100 fathoms below the surface.f The direct experiments of Weber on the movements of waves have likewise proved that each wave extends its in- fluence in a vertical direction to 350 times its height. Thus every wave of about a foot in height makes itself felt on the bed of the North Sea at a depth of 50 fathoms; while every oceanic billow of 33 feet is felt at about If miles. It is true that at these enormous depths the action of the wave is, so to speak, imaginary, for below the surface it decreases in geometrical proportion ; but at about 25 to 50 fathoms only, the subma- rine waves have still great force, and we can easily understand that when thousands of them are abruptly arrested by submarine rocks, and on the rapid slopes of sand-banks, violent eddies must be produced which, afterwai'd returning to the surface of the water, cause " heavy swells," From these causes arise those turbulent seas which ships encounter at times in calm weather, especially in the neighborhood of submarine banks; also those "ground swells" which suddenly raise the surface of the sea and endanger boats; and those formidable tide- races which, I . * See above, p. 30. + Cialdi, Sul Moto Ondoso del Mare, p. 174. 64 THE OCEAN. springing from the depths of the ocean, advance abi'uj)tly upon its slop- ing beaches, destroying all they encounter on their way. It is along the shgres of continents and around rocky islands that ordi- nary waves and heavy surf appear in all their grandeur and assume di- mensions truly formidable. In accordance with the more or less gradual inclination of the bottom to the shore, a wave coming from the open sea rolls over a bed more and more shallow, and must perforce slacken its speed ; but at the same time, it increases by its own depth the stratum of water which it overflows, and consequently the wave which follows it is subjected to less retardation of the impulsive force. The second wave constantly gains on the first, and finally reaches it, swelling its crest, and, slackening its own speed in its turn, gives a third wave time to distance it also. Finally, near the strand, the liquid mass, swelled by the pursuing waves, and unable to spread out farther at its base along the shore, which is too near, gains in height what it wants in breadth, and, rising like a wall, it bends over with a wide curve in front, and breaks with a thun- dering sound, throwing water, mixed with sand and foam, far along the shore. This surge, which is dreadful indeed during tempests, rises much higher than the waves ; to the ancients the whitening billows of the open sea, whose crests were seen to shine like the fleeces of sheep, were the flocks of Proteus ; while the waves of the shore, still called in our days cavalli and cavalloni by the peojale of the south of Europe, were the foaming horses of Neptune. The lieight to which the crests of some of these waves attain when the configuration of the coast favors the movement, seems sometimes to par- take of the marvelous. The mass of water which rises vertically can then only be compared to an ascending cataract. Spallanzani relates that sometimes, in violent tempests, the waves reach half-way up, or even to the top, of Stromboluzzo, a peak of lava which rises near Stromboli, 318 feet above the mean level of the sea. The Bell Rock light-house, which rises boldly to 112 feet in height on a rock ofl" the Scottish coast, is often enveloped in waves and foam even long after the tempest has ceased to disturb the sea.* Smeaton, too, has seen waves covering the Eddystone light-house, and leaping in a spout of water 82 feet above the lantern ; the mass which is thus raised around the edifice can not be less than from 2616 to 3924 cubic yards, and would weigh as much as a large three-decker. After these great storms, salt pools are scattered here and there on the top of the clifis. The pressure exerted by these masses of water, hurled with such impe- tus, is no less surprising. Thomas Stephenson ascertained that the force of the sea dashed against the. Bell Rock light-house amounted to about 17 tons for every square yard. In the Island of Skerryvore the heaviest calculated pressure is about three tons and a half for every yard — that is to say, more than Q^ lbs. avoirdupois for every 0*16 of a square inch. With such a force the displacement of blocks which seem enormous to u# * Mrs. Somerville, Physical Geography. FORCE OF THE WAVES. 65 is only child's play to the tempest waves. Before all sea-ports and road- steads where great works, such as sea-walls and breakwaters, have been constructed, seamen have been able to observe the prodigious power of the angry water. On all the exposed works at Holyhead, Kingston, Portland, Cherbourg, Port Vendres, Leghorn, the waves have been seen to seize blocks weighing several tons, and hurl them like playthings over the dikes. At Cherbourg the heaviest cannon on the rampart have been displaced ; at Barra Head, in the Hebrides, Thomas Stephenson states that a block of stone of 43 tons was driven more than If yards by the breakers. At Plymouth, a vessel weighing 200 tons was thrown, with- out being broken, to the very top of the dike, where it remained erect as on a shelf beyond the fury of the waves. At Dunkirk, M. Villarceau has ascertained, by the most delicate measurements, that during a heavy sea the ground trembles at nearly one mile from the shore. Fig. 21.— Bay of St. Jean de Luz. 5 66 THE OCEAN. In the Gulf of Gascony, so frequently visited by tempests, the waves, coming from the west and north-west, are drawn into a sort of funnel, and hurl themselves against the shores with a force at least equal to that of the waves in the Channel and the English seas. The works constructed by engineers to protect the roads and ports against this terrible pressure have been frequently swept away, or much damaged by the waves. Man must incessantly continue the strife he is engaged in with the sea, tinder pain of seeing the work of a century destroyed in a day. During the winter of 1867 and 1868, M. Palaa says that blocks of masonry, 36 tons in weight, placed at the extremity of the dike at Biarritz, were thrown horizontally from 11 to 13 yards ; one block was even raised nearly seven feet, carried over the breakwater, then thrown down, and rolled to a great distance during the storm. At St. Jean de Luz the surge is perhaps still mor^ terrible, and some of the masses of stone now employed in con- structing the dike of Socoa, at the entrance to the roadstead, are not' less than from 80 to 90 cubic yards. And yet even this strong wall would not be strong enough, if it was not additionally defended by stones scat- tered loosely here and there, forming a range of protecting rocks in front of the dike upon which the sea expends its fury. The only places where the waves display a still greater power than in the Gulf of Gascony are those that are sometimes ravaged by the torna- does. In the Isle of Reunion there is to be found in the middle of a sa- vanna a massive block of madrej^oric stone, which is no less than 510 cu- bic yards in size. It is a piece that the waves' have detached from a reef and driven before them across the land.* How can we wonder that waves strong enough to hurl such projectiles can alter the shores in such varied ways, demolishing the cliffs here, and forming islands there, or con- structing sand-banks at the entrances to gulfs.f * Zurchei- and Margolle. t See the chapters entitled The Shores and the Islands ; the Work of Man. GENERAL CAUSES OF CURRENTS. 67 I BOOK II.— CURRENTS. CHAPTER VII. GREAT MOVEMENTS OF THE SEA. — GENERAL CAUSES OF CURRENTS. — THE FIVE OCEANIC RIVERS. Currents, that is to say, the real movements of the sea, much less visible to the eye than the apparent displacements which constitute the waves, are notwithstanding of much greater importance in the economy of our planet. By their action enormous volumes of water, thousands of miles wide and hundreds of fathoms deep, move across the oceanic ba- sins; the water of the polar seas is carried to equatorial regions, while these, on their side, send, their waves in the direction of the poles. The liquid mass circulates incessantly, as if in a vast whirlpool, in every ocean of the globe, and we can follow in thought its gigantic circuit from the fields of ice to the warm atraosjihere of the tropics. Currents are indeed only the ocean itself in luotion, and by their action the waters of the sea are successively distributed over all parts of the globe. They are the windings of the great " salt river " of Homer, which rolls around the earth in one immense circuit. Every drop that has not already been raised in vapor to commence its long journey through clouds, mists, glaciers, and rivers, continually changes its place in the abysses of the sea ; it descends to the bottom, or mounts to the surface ; it moves from the equator to the pole, or from the pole to the equator ; and thus trav- erses all parts of the ocean. It is to this continual displacerdent of its innumerable particles that the sea owes its unifofmity in such a surpris- ing manner, under all latitudes, as regards the appearance, composition, and saltness of its waters. Every difference of level which is jiroduced on the liquid surface in consequence of prolonged winds, heavy rains, or very active evaporation, causes, as a necessary result, the formation of a current ; for water, wheth- er salt or fresh, ever seeks its level, and incessantly flows from the more elevated places toward the depressions. Every atmospheric variation lias, for result, a displacement in one direction or another of the superfi- cial water. But the great currents which flow with a regular movement around the basins of the ocean-, between the polar and the equatorial zones, are determined by general causes acting at the same time on the entire planet. These causes are the sun's heat and the rotation of the earth on its axis. The equatorial basin, incessantly heated by the solar rays, loses a great 68 THE OCEAN. quantity of water, which is transformed into vapor, and rises into the higher strata of the atmosphere to be condensed into clouds. Admitting that the annual evaporation is about fourteen feet,* which is probably below the reality, the quantity of fluid raised from the Atlantic in the tropical zone would be nearly 120 trillions of cubic yards, and would con- sequently represent the same value as a cubic mass of water nearly 30 miles in extent. It is true that a considerable part of this vapor, the half perhaps, falls as rain into the sea from which it was taken, yet a great proportion of the clouds are carried by the trade- windsf and other aerial currents, into seas situated beyond the tropics, and over the neigh- boring continents. Near the equator, therefore, much more water is drawn from the ocean by evaporation than is returned to it by the clouds, and, in consequence, an immense void is formed which can only be filled by the waters from the polar basins, vfhere the contributions of snow, rain, and ice exceed the loss in vapor. This superabundant mass of fluid continually flows toward the basin of the torrid zone, and forms the two great currents, which meet one another from the opposite poles in the Atlantic and the Pacific, incessantly describing a regular orbit like the celestial bodies. But the excess of evajjoration which occurs in tropical waters is not the only reason of this great movement of the po- lar seas toward the torrid zone. The trade-winds, attracted by Jhe force of equatorial heat, blow incessantly in the same direction, and always driving the waves before them, thus accelerate the march of the oceanic current. If the mass of water which continually flows from the poles to the equator were exactly equal in quantity to that which is evajDorated by the sun's heat, the arctic currents would be arrested under the tropics, and no return movement would be produced toward the polar oceans. But the waters which flow from the north and south are always in ex- cess, in consequence of the continual impulse of the trade-wind ; and when they arrive in tropical latitudes they are influenced by a new cur- rent, the true cause of which is the rotation of the earth on its axis. In fact, owing to the incoherence of its particles, the ocean does not obey in an absolute manner the rotatory motion of the earth, which carries it from west to east. In descending from the poles to the equator, and thus crossing latitudes whose speed of rotation is greater than their own, they are constantly drawn obliquely toward the west, and this continual retardation of their motion behind that of the rotation of the globe be- comes, in relation to the surface of the sea, an apparent motion from east to west. Upon their meeting in the tropics, the polar currents, being both afifected by a side movement, strike each other obliquely, then reunite in the same oceanic river, and flow directly toward the west in the opposite direction to that of the solid earth. It is thus that the equatorial cur- rent is produced, which, with the two polar currents, determines all the * Mauiy's Geography of the Sea. t See the chapter entitled The Air and the Winds. THE OCEANIC RIVEBS. gg movements of the waters in each oceanic basin. The other rivers of the sea are simply branches from them, caused by the form of the continents. The equatorial current, which is a continuation of the polar currents, and forms with them a vast semicircle, can not be freely develojDed around the circumference of the globe. Arrested in the Atlantic by the American continent, in the Pacific by Asia and the archipelago which unites that continent with New Holland, it breaks against the shores and divides into two halves, which flow back in the direction of the poles, the one descending toward the south, the other ascending to the north. The immense river thus returns to its source, but at the same time the motion of terrestrial rotation, which at its outset caused it incessantly to deviate toward the west, now urges it obliquely in the opposite direction. Under the equator, the angular speed of the terrestrial surface around the axis of the planet being much more considerable than under any oth- er latitude, the waters coming from the tropics into temperate seas are animated by a more rapid movement toward the east than those amidst which they flow. They deviate in consequence in an easterly direction, and when the returning current reaches the polar sea it seems to come from the west. Thus the grand circuit of the waters is completed in each hemisphere. The Atlantic and the Pacific have each their double circulatory system, formed of two immense eddies united in the torrid zone by a common equatorial current. As regai'ds the Indian Ocean, be- ing bounded on the north by the continent of Asia, it has but one simple current, which turns incessantly in its vast basin between Australia and Africa. As a whole, these ocean rivers recall, by their distribution, the divisions of the land. The two great whirlpools of the Atlantic corre- spond to the two continents of Europe and Africa; the huge eddies of the Pacific have a binary division analogous to the two continents of Ameri- ca; and the current of the Indian Ocean reminds one of the enormous mass of Asia, which alone fills half the northern hemisphere. 70 THE OCEAN. CHAPTER VIII. THE GULF STEEAM. — INFLUENCE OP THIS CURRENT ON CLIMATE. — ITS IM- PORTANCE TO COMMERCE. Of all the oceanic rivers, the best known to us is that part of the North Atlantic current which the English and the Americans have named the Gulf Stream, because it makes a long circuit in the Gulf of Mexico before reaching the ocean. In the year 1513 the Spaniards, Ponce de Leon and Antonio de Alaminos, knew of the existence of this current; and six years later Alaminos, setting forth from the Straits of Florida, allowed himself to be carried by the water into the open sea, and thus discovered the great circular route which ships have now to follow in order to return speedily to Europe. Since the time of Varenius, who attempted to describe the Gulf Stream, of Vossius, who traced its immense circuit on a map, Frank- lin 'and Blagden, who were the first to explore it scientifically, this cur- rent has been studied by numerous geographers. Without doubt, there is no marine current which merits to be better known in all its details; none has been of more importance in the commerce of nations or exercises a greater influence upon the climate of the north-west of Europe. It is to the Gulf Stream that the British Isles, France, and the neighboring- countries owe in great part their mild temperature, their agricultural wealth, and, in consequence, a very considerable part of their material and moral power.* . Its history is almost identical with that of the entire North Atlantic Ocean, so important is its hydrological and climatic in- fluence.! The celebrated Maury devotes the most important part of his classical woi'k on the " Geography of the Sea " to the Gulf Stream. It " is a river in the ocean ; in the severest droughts it never fails, in the mightiest floods it never overflows. Its banks and its bottom are of cold water, while its current is of warm. There is in the world no other such ma- jestic flow of waters. Its current is more rapid than the Mississippi or the Amazon, and its volume a thousand times greater." Such is the epic language in which Maury's fine work commences.^ After having made the tour of the Caribbean Sea and the Gulf of Mex- ico in six months, after having driven back upon the shores of Alabama the muddy waters of the Mississippi which border its dark blue waves, the Gulf Stream follows the northern coasts of Cuba, then turns the southern point of Florida, and penetrates the strait which separates the American continent from the islands and banks of Bahama. Swelled by * See the chapter entitled The Earth and Man, t J. G. Kohl, Geschichte des Golfstroms, p. 1. I Physical Geography of the Sea, p. 23. The ( )fe(iii.(S^c THE CURRENT F ii- \ rp \ \ S, % , , \ |¥V A\\V\\v. m\w Draomi'LnrA'Viiillenmi HARPER 8c BR E GULF STREAM PL.v iii^^^]y£ri.aTd •S. l^EW YORK COURSE OF THE GULP STREAM. 71 the mass of water Avhich.the great equatorial current sends directly through the straits of the archipelago, and above all by the old channel of Bahama, the Gulf Stream flows straight to the north, pressing througli the ocean like a river nearly 37 miles wide, and of an average depth of 200 fathoms. Its speed is great, even equaling that of the principal riv- ers of the world, being sometimes from about 4^ to 5 miles an hour; but usually it is about 3|^ miles. The mass of water discharged by the cur- rent may, therefore, be estimated at nearly 45 millions of cubic yards per second — that is to say, at 2000 times the mean discharge of the Missis- sippi; and yet it was to tlje outflow of this North American river that many geographers formerly attributed the existence of the Gulf Stream ! When winds from the south, the west, or even the north-west, Snd the movement of the tides, favor the progress of this current, it rolls toward the Atlantic in much greater volume than usual. But on the other hand, when retarded by tempests that blow from the north-east, it pours a much smaller quantity of water into the ocean. When thus checked, it swells, rises, spreads with fury over the low lands that border it, ravages vast tracts, and causes whole islands to disappear. At its embouchure into the ocean, this marine river resembles those sti'eams which flow through, continents, it erodes on the one side, while it deposits alluvium on the other. And doubtless the Bahama Islands, which are scattered through the sea to the east of the Gulf Stream, and the keys or rocks de- veloped on the north in a long range, rest on a foundation of submarine banks formed in part by the deposits of this gi-and river.* On emerging from the Strait of Bemini, the Gulf Stream expands and spreads over the Atlantic, but at the same time its depth becomes pro- portionately less considerable. While the strata of cold water which serve as its banks'retire on each side and allow it to spread over a great- er breadth, the bed of cold water which bears it and over which it flows, as terrestrial rivers glide over beds of rocks, gradually approaches near- er the surface. At Cape Hatteras the depth of the current is about 120 fathoms, and its speed does not exceed three miles per hour; but it is twice as wide when it emerges from the Strait of Bemini, and spreads over a space of about 78 miles. The thickness of this powerful stream of warm water is constantly diminishing, and when it has crossed the At- lantic it is only a superficial sheet. But even then it covers an immense extent, reaching from the Azores to Iceland and Spitzbergen, The soundings taken since 1845 by the ofiicers of the Coast Surve}'- of North America prove that the Gulf Stream flows along the coast of the United States at some distance from the land. The slight inclination of the low lands of Georgia and Carolina is continued under water till the lead reaches a depth of about 50 fathoms. The bottom then sinks rapid- ly, and forms a long valley parallel to the shore of the United States and the chalky walls of the Appalachians; it is in this valley, hollowed to * Agassiz. E. Thoraassy, Bulletin de la Societe de Geographie, Noverabre, 1860. See the chapter entitled Earth and its Fauna. 72 THE OCEAN. The Soundings are in fathoms. Fig. 22.— Channel of Florida. the east of the sulbmarine basement of America, that the waters of the Gulf Stream flow. Owing to the rotatory motion of the globe, and prob- ably also to the general direction of the coasts, the current follows a con- stant direction to the north-east, and does not touch any of the advanced points of the continent. Off New York and Cape Cod it deviates more and more to the east, and, ceasing to follow at a distance the American MEETING OF HOT AND COLD CURRENTS. . 73 coast-line, rolls across the open Atlantic toward the shores of "Western Europe. Thus, as Maury says, if an enormous cannon had force enough to send a bullet from the strait of the Bahamas to the North Pole, the projectile would follow almost exactly the curve of the Gulf Stream, and, gradually deviating on its way, Avould reach Europe from the west. Between the 43d and 47th degrees of north latitude, in the neighbor- hood of the Banks of Newfoundland, the Gulf Stream, coming from the south-west, meets on the surface of the sea the polar current discovered by Cabot in the year 1497. The line of demarkation between these two oceanic rivers is never absolutely constant, but varies with the seasons. In winter — that is to say, from September to March — the cold current drives the Gulf Stream toward the south ; for during this season all the circulatory system of the Atlantic, winds, rains, and currents, approach more nearly the southern hemisphere, above which the sun travels. In summer — that is to say, from March to September — the Gulf Stream, in its turn, resumes its preponderance, and forces back the line of its conflict with the polar current more and more toward the north. Thus the great river undulates here and there over the seas, and, according to the grace- ful expression of Maury, waves like a pennon in the breeze. But it is probable that the advance of the two opposing currents is often modified only in appearance, in consequence of the superficial expansion of cold or warm water. The Banks of Newfoundland, that enormous plateau sur- rounded on all sides by abysses five to six miles deep, is undoubtedly due in great part to the meeting of these two moving liquid masses. On entering the tepid waters of the Gulf Stream, the icebergs gradually melt and let fall the fragments of rock and loads of earth which they bear into the sea. The bank, which rises gradually from the bottom of the ocean, is a sort of common moraine for the glaciers of Greenland and the polar archipelago.* After encountering the waters of the Gulf Stream, those of the Arctic current cease in great part to flow on the surface, and descend into the depths, in consequence of the greater weight which their low tempera- ture gives them. The direction of this counter-current, exactly opposite to that of the Gulf Stream, is demonstrated by the icebergs which the warm breath of temperate latitudes has not yet melted, which travel toward the south-east, directly against the superficial current, which they divide like the prow of a ship. More to the south, we recognize the ex- istence of this concealed current only by means of sounding apparatus, the cold waters serving as a bed to the warm river flowing from the Gulf of Mexico ; it descends lower and lower as far as the Straits of Ba- hama, where the thei'mometer discovers it at a depth of 220 fathoms. Nevertheless, a part of the waters of the polar current remains at the surface of the sea ; and, gliding along the western coasts of the United States as far as the point of Florida, gives to the Gulf Stream, by contrast, very sharply defined limits. Generally the cold water coming from the * See above, p. 29. '74 • THE OCEAN. Arctic" Sea possesses sufficient force to compel the current from the Gulf to bend sensibly toward the south, and to oppose an insurmountable bar- rier to it in the other direction. The warmest and most rapid part of the Gulf Stream, which forms precisely the left or western side of the cur- I'ent, is found in immediate juxtaposition to a sheet of cold water, which spreads in an opposite direction between the Gulf Stream and the Ameri- can shores. This counter-current, which interposes the waters of the Icy Sea between the coast of Carolina and the warm i-iver flowing from the Gulf of Mexico, bounds the Gulf Stream like a wall of ice.* Sometimes the line of demarkation between the two liquid masses is so precise that it is appreciable to the sight, and the exact moment when a ship leaves one current, to cleave the other with its prow, may be distinguished. The water of the Gulf Stream is of a beautiful azure, that of the counter- current is greenish ; the first is saturated with salt, the latter contains it in a much less proportion. The one is tepid, the other cold; and the ther- mometer, when plunged alternately in the two liquids, instantly marks the difference of temperature. On the boundary line of the currents, the friction of the two masses of water flowing in opposite directions pro- duces a series of eddies, whirlpools, and short waves, which give to these ocean rivers an aspect similar to that of continental rivers. Sometimes one can even hear, like a dull roaring, the noise of the waters contending on the surface of the sea. Floating plants and other fragments are whirl- ed round on the ever-changing boundary of the two contending streams.f The GulftStream, like all other currents, finally mingles with the sea, and thus tends to equalize the proportion of salt and all other substances contained in the liquid mass. The normal salinity of the Caribbean Sea is from 36 to 37 thousandths, except in the neighborhood of the mouths of great rivers. After having received the fresh waters of the Missis- sippi and the visible and subterranean rivers of Florida, the Gulf Stream does not contain quite 36 thousandths of saline substances ; but this is gradually increased as it advances toward the north. Off Newfound- land, where the waters of the St. Lawrence and many other rivers, as well as the melted ice, fogs, and heavy rains, have rendered the waves of the sea more fresh, the Gulf Stream contains less than 34 parts in 1000 of saline matter, but it gradually increases the proportion to 35 thou- sandths as it shapes its course toward the coasts of Western Europe and the polar regions. The currents of cold water which serve as its bed are all less rich in saline substances, as Forchhammer and other chemists have proved. But in consequence of the incessant mixture of the waters, an equalization of saltness between the currents is produced in the vari- ous latitudes.^ Another effect of the Gulf Stream, no less important in the economy of our planet, is that which it accomplishes, in concert with the south-west * Franklin Bache, United States Coast-Survey. t Kohl ; Fitzroy, Adventure and Beagle, Appendix to vol. ii. X Forchhammer, Philosophical Transactions, part i., p. 241, 1865. EFFECT OF THE GULF STREAM ON CLIMATE. 75 winds,* on the climate of Western Europe. While rotating in the Gulf of Mexico as in an immense caldron, the waters of the current are gradu- ally heated : when they escape through the Strait of Bernini to enter the ocean, their temperature is not Jess than 86° Falir,, and exceeds by about 4° Fahr. the natural heat of the neighboring beds of water. The waters of the Gulf Stream lose their warmth but slowly, and during winter they often have, oft' Cape Hatteras and the Banks of Newfoundland, a temper- ature exceeding by 21° or 28° Fahr. that of the rest of the Atlantic un- der the same latitudes. When the Gulf Stream meets the polar current, the former has still a temperature of 36° or even 45° Fahr., while, even at a distance of some hundreds of miles from the coasts of Labrador, the latter is sometimes found to be below freezing-point (24'8° Fahr.) ; thus, in defiance of latitude, the waters of the tropics and of the icy zone are brought into juxtaposition. In its advance toward the north, the up- per strata, which in consequence of radiation have become colder than the subjacent layers, descend to a greater or less depth in the mass of the current, and are replaced by the warmer and lighter water lying im- mediately below. Thus a constant alternation of position is produced in the liquid strata of the Gulf Stream, and one may remark in consequence, in crossing the whole breadth of the current, a series of parallel bands of unequal temperature. f In each of these bands the warm water rises by turns to the chilled surface of the sea. It is a remarkable fact, that if the Gulf Stream did not flow as it does in a bed entirely composed of cold water, but moved along the very bottom of the ocean, it would rapidly lose its high temperature, and would cease in consequence to be a source of heat for Western Europe. In fact, the earth being a better conductor of heat than the water, the warm waters of the current would communi- cate their temperature to it, and would finally lose their whole store. But the cold waters of the polar current, being interposed between the bottom of the sea and the waters of the Gulf Stream, serve as a protect- ing screen to the latter, and hinder their refrigeration. It is by such con- trasts as these that the harmony of the world is established. The qua\itity of heat which the Gulf Stream carries toward the north- ern regions forms a very considerable part of the caloric stored up in its waters under the tropics. The cetaceans, fish, and other inhabitants of the torrid zone follow the course of the Gulf Stream without perceiving that they have changed their country, and often push their adventurous voyages to the Azores, and even to the coasts of Iceland ; the southern birds mount also toward the north in the warm stream of air reposing on the current. The animals of northern seas, on the contrary, are kept • prisoners in the glacial ocean, and the right whales, says Mauiy, recoil before the Gulf Stream as before " a barrier of flame." The total warmth of the current would suflice, if it was centred in a single point, to fuse mountains of iron, and cause a river of metal as mighty as the Mississippi * See the chapter entitled Climates. t Franklin Bache, United States Coast-Survey. 76 THE OCEAN. to flow forth. It would sufiice also to raise from a winter to a constant summer temperature the entire column of air which rests on France and the British Isles. But though it is spread over enormous spaces to the west and north of Europe, the Gulf Stream does nevertkeless exercise a preponderating influence upon the climate of this part of the Old World. Owing to the warmth of its waters, the lakes of the Faroe and Shetland Isles never freeze during winter; Great Britain is enveloped in fogs as in an immense vapor-bath, and the myrtle grows on the shores of Ireland, the " emerald isle of the seas," under the same latitude as Labrador, that land of snow and ice. In green Erin, an island privileged in so many re- spects, the western coasts (the first land which the Gulf Stream encoun- ters after crossing the Atlantic) enjoy a temperature two degrees higher than that of the eastern coasts. In spite of the path of the sun, it is, on an average, as warm in Ireland under the 52d degree of latitude as in the United States under the 38th degree, or about 1025 miles nearer the equator. The Gulf Stream, which conveys the troj)ical warmth to the temper- ate countries of Europe, very often serves as a high-road for tempests. Hence the names of loeather-hreeder and storm-king, which have been given to this current.* The movements of the atmospheric ocean and those of the ocean of waters occur in such complete parallelism -that one would be tempted to regard them as one and the same phenomenon in the ensemble of aerial and nlarine currents.f Thus the Gulf Stream seems to be for the winds, as it really is for the waters, the great medium between the Old and New Worlds. It carries to the seas at the north of Europe the salinity of the Gulf of Mexico ; it bears wnth it the warmth of the tropics for the advantage of the temperate regions, and marks the track which the torrents of electricity, disengaged by the hurricanes of the Antilles, follow. It is, indeed, the great serpent of the Scandinavian poets, which uncoils its immense folds across the ocean, and from its head, which it waves here and there over the shores, wafts a gentle breeze, or pours forth storm and lightning. The Gulf Stream crosses the Atlantic with a mean speed of aboiit 24 miles a day, as has been ascertained either by direct measurement at dif- ferent parts of the ocean or by means of notes, which, having been thrown overboard in bottles carefully closed, have floated for weeks or months at the will of the waves, and then been fished up in other latitudes or found on some sea-shore. In their long passage, the deep waters of the marine river of America transport scarcely any other alluvium than the living frustules of animalcula, which fill the tepid waters of the current, and are constantly falling in a kind of snow to the bottom of the sea. But here and there on the surface of the Gulf Stream float trunks and branches of trees, which are finally thrown on some coast of Europe, and even on the Island of Spitzbergen. It was these remains which ^ur an- * r. Maury, Geography of the Sea. t See the chapter entitled The Air and the Winds. EXTENT OF THE GULF STREAM. 77 cestors of the Middle Ages believed to come from the fabulous Island of St. Brandan or from Autilia, and which furnished matter for thought to daring navigators like the great Columbus.* Seeds carried from the New World by the current have found a favorable soil on the shore of the Azores, and, although many thousand of miles from their native land, have germinated and borne fruit. Often, too, the waves of the Gulf Stream bring to Europe the broken products of human industry and the timber of wrecked ships. During the Seven Years' War, the mainmast of an English ship of war, the Tilbury.^ which had been burned near St. Domingo, was found on the northern coasts of Scotland. In the same way a river-boat, laden with mahogany, was once even driven to the Faroe Islands. The remains of ships wrecked in the latitude of Guinea have been brought to the coast of the British Islands, after having twice crossed the ocean in opposite directions, and Esquimaux have often been carried by the waves to the Orkneys.f It is rather difficult to lay down the precise route of the Gulf Stream in the seas of Western Europe, because of the enormous width of its mov- ing expanse. One may say that in reality it stretches over the whole ocean, from the Azores to Spitzbergen ; but having lost in its onward im- pulse in proportion as it has gained in extent, it is modified and turned aside in its course by a host of local circumstances and the varied con- figuration of the coasts of Europe. Only that part of the current which flows to the north of Ireland and Great Britain maintains its original di- rection. It bathes all the islands between Scotland and Iceland, warms the coasts of Norway ; even in Lapland, it melts the ice at the port of Hammerfast, and then continues its course in the Polar Sea toward Spitz- bergen. Thus, as the Swedish expedition in 1861 ascertained, the cur- rent makes itself felt even on the northern shores of the latter archipela- go; for the seeds of a plant from the Antilles {Entada gigalohium) were found on the shore of Shoal Point, lying at more than 80 degrees north latitude. Indeed, it is certain that the current even bathes the western coasts of Nova Zembla, for bottles that came from a glass factory at Norway, and the nets of Scandinavian fishermen, have been found there. How, then, do these waters, which spread in such a vast sheet over the surface of the Icy Sea, continue their progress toward the Pole ? Here hypothesis commences, since no navigator has yet been able to explore these latitudes and study their hydrological laws. But we know at least in part the origin of the polar current, and by the direction which this mass of water takes may be indicated that which the Gulf Stream itself must follow. Along all the northern coasts of Siberia, as Wrangel and other explorers have told us, a current of cold water flows from east to west. Encountering on its way the large island of Nova Zembla, it covers the strand and rocks with enormous quantities of ice, which ren- der the island quite uninhabitable, and close the straits to navigation. * r. G. Kohl, Geschichte des Golfstroms, p. 17. t Humboldt, A nsichten der Natur (notes). 78 THE OCEAN. Arrested by this barrier, the waters of the glacial current are forced to bend to the north, and flow in a north-westerly direction toward Spitz- bergen, round the northern archipelago of which they finally turn, in or- der to enter the seas around Greenland. It is here that they begin to take a direct road toward the equatorial seas; and all the navigators who have ventured to the north-west of Iceland have recognized the ex- istence of this stream, flowing along the coast-line as far as Cape Fare- well. Its average speed, according to Graah and Scoresby, is from, three to four miles a day. ■ To the south of Greenland the lessened sheet of the Gulf Stream must meet this transverse current ; and doubtless, in consequence of the great- er weight which its stronger proportion of saline substances imparts to it, it plunges into the depths and is changed into a submarine current, which finishes by mixing completely with the cold waters of the northern seas, and flows back at last toward the equator in an opposite direction to that which it at first pursued. Thus the river of warm water from the Gulf of Mexico feeds, by its incessant contributions, the polar counter- current, and the great circuit is established between the zone of heat and that of ice. Perhaps, too, the reflux of the Gulf Stream is partially ac- complished, under the pressure of water from the north by an abrupt turn. This would explain the strong salinity of 35 thousandths, which Forchhammer found in the waters of the polar current to the east of Greenland. It is not only in the wide extent of the North Atlantic, from Nova Zembla to Iceland, that the Gulf Stream takes a submarine course ; the same is the case, it apj)ears, in Baffin's Bay to the west of Greenland. In fact, from Cape Farewell to eight degrees farther north the existence of a coast current has been ascertained, which carries the ice in an exactly contrary direction to that of the current which follows on the west the coasts of Labrador, and which serves as a high-road for the fragments of the ice-fields.* This current was formerly considered as the continuation of the one which flows along the eastern coast of Greenland from north to south, and which would thus have abruptly turned round Cape Fare- well. But it is much more natural to think that the polar current con- tinues its route directly toward the great centre in the tropical seas. In this case, the current on the western coast of Greenland would be simply a branch of the Gulf Stream, which is rendered almost certain by its waters being comparatively warm. The sea very seldom freezes on the shore which it bathes, and the climate there is on an average nine de- grees (Fahi-.) warmer than on the coast looking toward the east. To- ward the '78th degree of latitude, this river -like curi-ent completely ceases, and it is undoubtedly . there that it becomes submarine, perhaps to flow on the surface again in the open sea of Kane.f On the other hand, if in the icy seas the various branches of the Gulf Stream change into smaller counter-currents, the polar currents do the * See p. 52. t Graah ; Miihrj', Mittheilungen von Petermann, t. ii., 1867. COURSE OF THE GULF STREAM. 79 same more to the south, and become the bed for the waters which flow to the north. These contain, it is true, more saline substances, but they are also warmer; rendered heavy by the salt, they are lightened by their hio-h temperature, so that a slight difference of w^armth or of salinity can modify their equilibrium and make them change their position with the polar current. In the temperate seas, where they are still warm and strongly saline, they flow on the surface ; but sink, on the contrary, in the icy seas, Avhere they are chilled, or where the admixture of Salter water is effected. This explains the intersection of the currents. To the north of Spitzbergen and Nova Zembla, the Gulf Stream is a submarine sheet ; to the south of Iceland, it is the waters from the pole which flow below. Not far from the Faroe Islands the sounding-lead can even indicate the direction followed by the icy counter-current, owing to the layer of vol- canic remains which have been brought from the coasts of Iceland, and spread over a space of 25 degrees of longitude between the 47th and 52d degree north latitude. This hidden river must flow, at least in certain places, on the very bottom of the sea, for various soundings taken by McClintock to the south-east of Iceland show that all the light detritus has been swept away by its waters.* If the Gulf Stream throws out various branches toward the north, which contribute to form the vast circunipolar whirlpool in the same way, an- other branch flowing toward the south goes to swell the eomatorial cur- rent. This offshoot of the Gulf Stream, of which one brauOT penetrates into the Bay of Biscay and forms the coast current called Rennell's,f flows along the coasts of the Iberian peninsula, follows the outline of Africa to the south of the Canaries and Cape Verd Islands, where lateral counter-currents occur, and enters the great marine river which moves the waters from east to west, " following the course of the heavens." Thus is completed the immense* circuit of the Atlantic, in the centre of which the sea-meadows of wrack| extend in clusters like an ai'chiiDelago. It is owing to this perpetual circuit that navigators in sailing-vessels have been able to reach the New World from Western Europe. If Co- lumbus had not made use of the semicircular current which flows from the coasts of Spain to the Antilles, he certainly would not have discover- ed America. If the pilot Alaminos, and, since his first voyage, the great- er part of the na«gators returning from the Antilles and United States, had not, either wuhout knowing it, or else well understanding the cause, followed the course of the Gulf Stream, the coasts of America would have remained practically far more distant from Europe than they really ai'e. The colonies, now become so prosperous as independent republics, Avould be still in deplorable isolation ; and civilization would have been greatly retarded, or even completely arrested, for want of new im^tus. As to commerce, properly so called, one can judge of the influence exercised upon it by the movement of the waters of the Atlantic, when one ex- * Wallich, North Atlantic Sea-bed. t See chapter entitled Earth and its Flora. % Ibid. 80 THE OCEAN. amines on a map the position of the great centres of trade. Havana and New Orleans, two principal markets of the Antilles and Mississippi States, are, so to say, at the source of the Gulf Stream. New York is situated facing the principal bend of this current, at the spot where the vast river flowing from the Antilles bends toward Europe. Finally, Liverpool, among so many other considerable ports washed by the Gulf Stream on its arrival at the coasts of the Old World, is the one which is most direct- ly in the path of its waters. When Franklin discovered, in 1775, that the mariner has only to plunge a thermometer in the water of the Atlantic to discover if he is sailing over the Gulf Stream or outside its course, the illustrious savant imme- diately perceived the importance of this fact for navigation. He even thought for a long time he must conceal it, from a fear that the English Government, then at war with the American Colonies, would profit by this discovery to send ships and men more rapidly against the revolted provinces. After the definite establishment of American Independence, no peril of this kind being any longer to be feared, all navigators were enabled for the future to know precisely the high-road which they had to follow in the open sea to reach Europe most expeditiously from Amer- ica, and what particular line to avoid in order to effect the journey in an opposite direction. Toward the middle of the last century, the whalers fig. 23.— Koute of Steam-packets, after Maury. of Nantucket and the skippers of Rhode Island had already, from experi- ence, come to choose two difiTerent routes for going and returning. In order to "descend" on England, they allowed themselves to be carried with the Gfflf Stream, and on their return crossed this current at the Banks of Newfoundland, and " mounted " the Arctic counter-current ;* on these voyages they distanced vessels from other sea-ports on an aver- age by 74 miles per day. The progress of navigation permits us now to * J. G. Kohl, Geschichte des Golfitroms, p. 103. USE OF THE GULF STREAM TO SHIPS. 81 utilize the impelling force of the cuvrents of the North Atlantic far better than the sailors of Providence could. The normal duration of the passage lias been reduced to half. Eight weeks were formerly reckoned for a voyage from England to the United States; now four weeks suffice for sailing-vessels, and some have even made the journey in seventeen days only. Steamers, which also have a double route too, in order to avail themselves of tlie current, accomplish the passage in nine or ten days. For commerce, civilization, and the brotherhood of peoples, such a result is not less important than as if the continents themselves were shifted, so as to reduce by three-quarters the width of the ocean which separates them. 6 82 THE OCEAN. CHAPTER IX. CUKEENTS OF THE SOUTH ATLANTIC AND THE INDIAN OCEAN. — DOUBLE EDDY OP THE PACIFIC OCEAN. The circuit of the waters which occurs to the south of the equator, in the southern basin of the Atlantic, is much less known than that of which the Gulf Stream forms a part; but all that has been observed of it by navigators proves that the movements of the liquid mass are analogous in the two hemis]3heres. A current of cold water, coming from the Ant- arctic seas, dashes against the Lagullas Bank to the south of the African continent and divides into, two branches, one of which re-enters the In- dian Ocean, while the other flows along the western coast of Africa, pen- etrates into the Gulf of Guinea, and, in consequence of the motion of the earth, bends toward the west in a wide semicircle. To the south of the Cape Verd Islands, the waters coming from the southern seas join those which flow from the icy sea of the north, and uniting into one river of 500 to 1000 miles wide, move slowly in the direction of South America and the Antilles. The greater mass of water approaches the continent to the north of Cape St. Roque, the advanced promontory of Brazil, and, flowing to the north-west along the coasts of Guiana and Columbia, en- ters the Caribbean Sea, there to form the Gulf Stream, A less consid- erable fraction of the equatorial current bends to the south of Cape St. Roque, and follows the Brazilian coast-line to the south-west. But in descending toward latitudes nearer and nearer the southern pole, the warmer current from the equator incessantly gains on the rotatory move- ment of the earth ; consequently, it bends more to the south than to the south-east, and forming a sort of gulf stream in an opposite direction, it strikes the polar current to the east of the Falkland Isles, whose position in the southern hemisphere corresponds to that of ]Sre\^foundland in the northern hemisphere. There the warm current, after having deposited drift-wood, taken from tlie Brazilian coast, on the shores of the Falkland Islands, sinks below the lighter strata of the glacial current ; while the latter directs its course to the north-east toward St. Helena, where it joins the great equatorial river. The whole circuit is accomplished in a period which may be estimated at about two or three years.* Dissimilar, and often contradictory, observations recorded by various navigators who have studied the phenomena of the waters in the South Atlantic, seem to put it beyond doubt that the currents of this basin have not the same regidarity, of course, as those of the Northern Atlantic. It frequently happens that the water does not flow in the direction indi- cated on ma|)s, or even tends in an opposite direction to the normal move- * Mittheilungen von Petermann, t. x., 1866. CURRENTS OF THE SOUTH ATLANTIC. 83 ment. The reason of this difference between the two basins is quite nat- ural. While the North Atlantic is a very regular sea in its general form, bounded on each side by almost parallel shores, the marine area lying be- tween Africa and South America expands very widely from the coast of the southern polar land. It may be considered simply as a gulf of the great ocean, which extends around the globe to the south of the extremi- ties of the three southern continents. As a consequence of this irregular disposition of the coasts, the variations from the normal circumstances of the waters can not fail to be very great. The cold waters from the Ant- arctic Pole, charged with fragments of ice-fields and icebergs, flow, it is true, Avith a continuous motion to replace the vapors which rise incessant- ly from the equatorial Atlantic ; but the regular play of the currents is modified, now at one point now at another, according to the greater or less activity of evaporation in those parts of the sea. Besides, the chang- ing coast winds, which blow alternately from the ocean to the land and from the land to the ocean, impress their varying movements on its sur- face. The Indian Ocean has likewise its great circuit of water. There, too, the mass of fluid, chilled by its sojourn in the icy zone, is incessantly flowing toward the equator, in order to fill up the vacancy produced by the annual evaporation of thirteen to sixteen feet. It flows along the western coast of Australia, and afterward unites with the waters that come from the Pacific Ocean, through Torres Straits and the East Indian Archipelago. But there the regular current seems to lose itself; and we only see in the gulfs of Bengal and Oman marine rivers changing their course with the monsoons. Nevertheless, it must really be that the gen- eral movement of the waters is continued from the east to the west around the vast basin ; for on the eastern coast of Africa a current of warm water, iflcessantly supplied by the seas which bathe Hindostan and Arabia, flows to the south-west, and, under the name of the Mozambique Current, passes between the Island of Madagascar and the continent, touches the edge of the great submarine bank of Lagullas, and spreads into the Antarctic Ocean, after having mingled a part of its waters in the great whirlpool of the Atlantic. At the part whereitt is narrowest, the Mozambique Current is almost as rapid as the Gulf Stream, and moves with a speed of about A^ miles an hour. In the centre of the eddy in the waters of the Indian Ocean, as in the North Atlantic, Avhole meadows of sea- weed spread over the calm waters. The circuit of the currents commences in the great Pacific Ocean in the same manner as in the other basins. An immense river of cold water of unknown breadth strikes the Island of Magellan, at the south of America, and divides into two partial currents, one of which, penetrating into the Atlantic to the east of the Falkland Isles, where ice never comes, joins in the great round of waters between Africa and Brazil, while the other flows directly to the north along the coasts of Patagonia, Chili, and Peru; this is Humboldt's Current, thus named after the celebrated traveler who 84 THE OCEAK first recognized its existence. It carries with it large icebergs, often la- den with stones and fragments that have fallen from the Antarctic mount- ains, and by the coldness of its waters produces a remarkable lowering of the temperature in all the countries whose shores it bathes. This liq- uid mass, which has a depth of no less than 670 fathoms on the coast of Chili, gives to the vegetation of the country a remarkable analogy with that of St. Helena, which at a distance of 4000 miles is washed by anoth- er branch of the Antarctic current. Humboldt and Duperrey state, that off the coasts of Callao and Guayaquil — that is to say, in one of the driest climates and most exposed to the rays of the sun — the current is on an average at from 59° to 60° Fahr., while the adjacent seas are about 20° warmer. Not a branch of coral can take root on the rocks and shores washed by this current of cold water: the polar current changes every thing on its passage — the flora, fauna, climate, and even the history of mankind. If the air was not constantly refreshed by the contact of cold water coming from the pole, Peru, which is so rarely watered by rain, would be transformed into another Desert of Sahara, and human life would become almost impossible there. By this current, too, the dis- tances are notably diminished, and Valparaiso, Coquimbo, Arica, Callao, are, in reality, less distant from Europe than they appear on the map ; for after having rounded Cape Horn, the ships sailing along the western coasts of South America are carried about fifteen to twenty miles a day by this current. Widening more and more on the side of the open sea, Humboldt's Cur- rent ends by abandoning the coast-line, and, bending toward the west, to mix its waters with those of the equatorial current tending from east to west across the Pacific. This liquid moving mass is undoubtedly the most powerful oceanic river of our planet. According to Duperrey, it has a mean width of no less than 3500 miles, from the twenty-sixth de- gree of south latitude to the twenty-fourth degree of north latitude, and on its immense journey in a straight line round the world, it traverses from 130 to 140 degrees of longitude — that is to say, more than a third of the circumference of the globe. Its average speed is, like that of Hum- boldt's Currentfabout 19 miles per day; but in certain places, according to the seasons, an advance twice as rapid has been ascertained. What the quantity of this enormous mass of water can be that is thus displaced from one end of the sea to the other, is unknown ; for it would be first necessary to know the mean depth of the current, but this the sounding- lead has not yet discovered. It is only known that at the point where the water from the pole turns toward the west to enter the great equa- torial stream, it proceeds " en masse " in one direction, with a dejDth of not less than a mile. In the midst of the innumerable islands which are scattered over the Pa- cific, the general regularity of the great current is frequently disturbed, at least on the surface, in consequence of evaporation, rains, and even by the incessant labors of the coral-building zoophytes, which in various ways Tkc OroMiiX-. OCEANIC En^^bjETharcL. HAMPER 5<^ B; R R ENTS PL VI o |c: K )a ."is:// / Dravra "by AVuiliemin. 5. NEW YHRK THE GREAT EQUATORIAL CURRENT. 85 disturb the cquilibriura of the ocean. But undei" the thveefokl influence of the terrestrial rotation, the trade-winds, and the great tidal wave which is propagated from east to west across the ocean,* the quantity of water moved each day toward the west is certainly several tens of thou- sands of cubic miles. The only anomaly in this prodigious movement of the waters of the Pacific which seems inexplicable is the existence of an oceanic river flowing in an opposite direction to the principal current. This reflux has been observed to the north of the equator over a mean breadth of upward of 300 miles ; elsewhere its speed is variable, and its advance is not always in the direction of due east. In the absence of measurements and positive experiments which permit us to give an ex- act account of the progress of this counter-current in the difierent sea- sons, several hypotheses have been suggested to explain its origin. The common opinion is that it is masses of water turned aside on their course and thrown back by submarine plateaus.f Nevertheless, it is much sim- pler to admit that this is a normal phenomenon, for in the Atlantic Ocean it has also been established that some lateral eddies tend in an opposite direction from the great liquid mass flowing from east to west. When it has arrived at the end of its voyage across the Pacific, the equatorial current must of necessity change its direction. A portion of its waters, driven now in one direction and now in another by the mon- soons which succeed one another on the borders of the continents of Asia and Australia, flows into the Indian Ocean by the shallow straits of the East India Islands. But the greater mass of the current is thrown back either to the south or to the north, by the resistance of the shores against which it «lashes and breaks. The half of the current which strikes the coasts of Australia diverges toward the south, and flows in the direction of the Antarctic lands. It thus flows in the opposite direction to the po- lar current, which it finally encounters to the south of New Zealand, and plunges beneath its colder waters, which by their freshness are rendered lighter. To the east and north-east the current of the Antarctic seas completes the enormous circuit described by the waters in the southern basin of the Pacific. The other half of the equatorial current, diverted by New Guinea, the Philippmes, and that long barrier of islands lying to the east of China, bends gradually toward the north and flows along the outer coasts of Japan. It is the Gulf Stream of the Pacific Ocean, called also Tessan's Current, after the navigator who revealed its existence to the savants of Europe. But for centuries, and perhaps thousands of years, the Japa- nese have known and prized it highly for their coast-navigation. They give it the name of Kuro-Sivo, or " Black River," doubtless because of the deep blue of its waters. Less rapid than the Gulf Stream, its ad- vance is nevei'theless, on an average, more than 1^ miles per hour, and in many places very much exceeds this speed. Before Yeddo its mean tem- perature is '75"2° Fahr. — that is to say, about 10° to 12° Fahr. higher than * See p. 102. t Herschel, Physical Geography. 86 THE OCEAN. the Still waters beside it. Furthermore, the Kuro-Sivo, like the Gulf Stream, is com]josecl of liquid bands of unequal temperature flowing be- side each other like two distinct rivers in the same bed. In passing the largest island of Japan,* the Black River, obedient to the impelling force which the rotation of the earth has communicated to it nnder troj)ical latitudes, already commences to bend toward the north- east, and, spreading over a vast extent, loses in depth what it gains in surface. To the north of Japan, it meets obliquely a current of cold wa- ter emerging from the Sea of Okhotsk, to replace in part the void caused by the evaporation in the equatorial seas. Tliick fogs, similar to those of the Banks of Newfoundland, rest above the spot, of contact between the warm and cold waters. Shoals of fish, the object of pursuit to fisher- men, i^eople this maritime zone, which serves as a limit between the, two currents, and where the mass of animalcula and remains brought from the trojDics is joined to those which are conveyed in the waves coming from the north. Still, the phenomena presented by the meeting of the two currents have not the same grandeur in the North Pacific as under the corresponding latitudes of the Atlantic. For the mass of water flowing from the Sea of Okhotsk is relatively less considerable, and the opening of Behring's Straits, 31 miles wide and 50 fathoms deep, is of too small dimensions to allow much water from the icy ocean to penetrate into the Pacific. Only small coast currents, carrying the pines and firs from the shores of Siberia, and rounded ice-floes from along the two coasts, cross from one sea to the other. In summer the current which comes from the north, both on the eastern and western bank of the strait, is only a super- ficial current. On the other hand, the slight portion of the waters of the Black River which passes beyond the range of the Aleutian Islands to enter Behring's Straits is a submarine current, at least during the sum- mer season. Arriving in the icy sea, still warm and strongly saline, it mingles with the cold and light water which descends into the Atlantic by Bafiin's Bay.f The great mass of the Kuro-Sivo traverses the Northern Pacific from east to west with a graceful curve, no less beautiful than that formed by the islands that are washed by its waters; then bends gradually to the south-west and south, to coast the shores of California; finally, in the neighborhood of the tropics, it changes its direction again, and is lost in the equatorial current, inclosing in its circuit a floating forest of sea-weed hardly less extensive than that of the Pacific. Contrary to Humboldt's Current, which rolls its cold watei's and drives before it icebergs to refresh the dry and burning atmosphere of Peru, the Gulf Stream of the Japanese carries along the coasts of Sitka and Van- couver's Island a mass of waters warmed by a long sojourn under tropical heat, and by its vapors brings spring to regions which without it would have a very severe winter. It bears on its waves the fragments which it * De Kerhallet, Considerations sur V Ocean Pacijique. t De Haven ; Miihiy ; Gustave Lambert. THE ''KUItO-SIVO;' Oli TESSAN'8 CURRENT. 87 lias received from the coasts of the Moluccas, the Philippinesj and Japan. To the inhabitants of the Aleutian Islands and Alaska it gives, as fuel, camphor-wood, and other odoriferous trees from southern countries; it serves, too, as a highway for all kinds of waifs, carries away disabled ships, and numberless traditions relate how Ja^nese sailors were drifted afar and landed against their will on the coasts of America?. And it is per- liaps to au adventure of this kind that the Chinese navigators owe their discovery of the New World ten centuries before Columbus, if it is true that the country of Fusang, mentioned in the annals of China, is in fact the countries of Mexico and Guatemala. Messrs. Neumann, d'Eichthal, and other learned scholars do not doubt the authenticity of this historical fact. THE OCEAN. CHAPTER X. LATERAL EDDIES. — EENNELl's CTJEEENT. — COUNTEK-CUEEENT IN THE SEA OP THE ANTILLES. EQUILIBEIUM OP THE WATEES IN THE BALTIC, THE BOSPOEUS, AT THE ENTEANCES TO THE MEDITEEEANEAN AND THE BED SEAS. — EXCHANGE OP WATEE AND SALT BETWEEN THE SEAS, None of those great currents which wind through the oceanic basins show, in their exterior contours, the same sinuosities as the seas through which they flow. While most of the shores present a succession of prom- ontories and gulfs, the currents stretch in long regular curves, which in their vast sweep indicate but generally the form of the depression which contains them. Every considerable gulf which is separated from the ocean by any projecting land remains outside the whirlpool of waters, unless it should be in the very axis of the current, like the sea of the An- tilles. Yet even in those parts, which do not share in the general circu- lation, the waters do not remain perfectly stationary. They also have their circulatory system, and it is from the gi-eat maritime current that each secondary eddy receives its impulsion. A remarkable example of these currents of the secondary order is pre- sented on the west of Europe, in the semicircular basin formed by the coasts of Spain, France, England, and Ireland. A portion of the waters of the Gulf Sti'eam coming from the north and north-west strikes the coasts of Galicia and the Asturias ; it turns east toward the extremity of the Gulf of Gascony, flows along the shore of the Landes, then that of Saintonge, Poitou, Bretagne, and, returning in a north-west and west direction, forms a sort of liquid barrier across the Channel. To the south of Cape Clear, this oceanic river, known under the name of Rennell's Cur- rent, after the English savant who discovered its existence, finally enters the Gulf Stream, and returns to the south with the waters of the ocean. Thus a complete circuit, is made around the basin, analogous to that which occurs in each of the great oceans of the world. Rennell's Current, in its turn, coasting at a greater or less distance the shores of the continent, sends out into the little bays currents of a third order, which also com- plete their circular movement, like the Gulf Stream and the Kuro-Sivo ; and so, by lateral transmission, the circulation of the waters is continued from oceans to gulfs, from gulfs to bays, and from these to the creeks. These secondary currents, howevei", are usually much less regular than the general currents, and navigators have ascertained that at times Rennell's Current has flowed in a completely reversed way to its normal direction.* Secondary currents generally move in a course exactly oppQsite to that of the principal stream, of which they are only a branch bent back on it- * Gareis and Becker, Physiographie des Meeres. EQUILIBRIUM OF WATERS IN THE BALTIC, ETC. 89 self. Either permanently or temporarily they are found in all seas, open . or inland, in all gulfs and bays of the ocean. Even the sea of the vVn- tilles, the waters of which are carried almost en masse toward the Gulf of Mexico, presents at its western extremity a permanent current, which tends from the shores of the isthmus to those of Colombia. A vessel drifted by the principal current into the neighborhood of Nicaragua would only have to ascend to Colon, and then abandon itself to the waves in order easily to accomplish its return voyage, born^ by the waters which flow incessantly in the direction of Carthagena ancl Santa Marta. Many lazy seamen never pass from the ports of the isthmus to those of terra firma in any other way. Regardless of time, they let themselves be rocked by the billows without even taking the trouble to hoist the sails. Their bark, slower than a tortoise, advances at the most but a mile an hour, and, after eight or ten days spent on the passage, they finally per- ceive the bluish mountains of New Granada, and its sandy shores shaded by cocoa-nut trees. ' There are some currents which are evidently produced by a disturbance of equilibrium between two levels. Thus the Baltic Sea, which receives more water by the contributions of rivers than it loses by evaporation, must necessarily distribute its superfluity in the North Sea through the straits of the Sound and the two Belts. Nevertheless, these outlets being large and deep enough to difi'use the superabundant water in a little time, the current is not permanent. Waves from the North Sea, driven into the Baltic by the westerly winds, frequently meet it, and from this conflict of waters arise local and unexjDCCted movements dangerous to ships. Every four days the waters on the surface flow on an average for forty-eight hours toward the Categat, then flow back into the Baltic for one day, and during another day there is no sensible movement in either direction. Often, too, according to Forchhammer, the two contrary cur- rents glide one above the other ; the lighter on the surface, coming from the Baltic, and the other from the North Sea, heavier by reason of the salt it contains, flowing beneath. At the other extremity of Europe similar phenomena occur in the Bos- porus, at the outlet of the Black Sea. This strait, which receives the superabundant waters of the Euxine, presents a mean breadth of more than a mile, with a depth of 15 fathoms ;* so that if the waters of the sea flowed there in a continuous manner as in the bed of a river, and the swiftness of the current were only about \^ miles per hour, it would not discharge less than nearly 36,000 cubic yards per second. But it is prob- able that all the united afiluents of the Black Sea and the Sea of Azof supply hardly the half of this quantity; and, besides, a great part of the water brought by them is carried ofl" again by evaporation. The Bos- porus is, therefore, too large to serve -as the bed of a single current flow- ing from the Black Sea into the Sea of 'Marmora. It has been observed that the waters ordinarily descend toward the Mediterranean, with a * Tchihatchef, Asie Mineure. 90 THE OCEAN. speed of from two to four miles an hour ; but the existence of tolerably- rapid lateral counter-currents has also been established; and sometimes the winds blowing from the west cause the principal current to flow back through the strait. A submarine movement of the waters in the direc- tion of the Black Sea also exists, as already ascertained by Marsigli in the last century. At the western part of the Mediterranean, between Gibraltar and Ceu- ta, the normal current is that coming from the ocean. In fact, the Med- iterranean has not many considerable tributaries. It only receives a sin- gle river having a really great mass of water, namely, the Danube ; its other affluents of any importance — the Rhone, the Po, the Dniester, the Dnieper, the Don, and the Nile — bring, on an average, not more than 19,620 cubic yards of water per second.* On the other hand, evaporation is very ^ A'S-J T//c^ .rondj'nt/s are Pig. '24.— The Straits of Gibraltar. rapid in the basin of the Mediterranean, especially on the coasts of Egypt and Tripoli. We may admit that the quantity of water taken from this basin by the solar rays, and not directly restored bj'- rain, annually repre- sents a section of about 4|- feet; which is probably near enough to the * See the section entitled Rivers. CURRENTS OF THE RED SEA. 91 trutli, as in the neighborhood of Genoa, Beaucaire, Aries, and Perpignan, on tl)e northern shores of tlie sea, tlie evaporation exceeds four-tentlis of an inch per day in the great heat, and nearly two feet during the three summer months,* while the amount of rain during the year is about 1 9^ inches. The result is that the Mediterranean constantly loses three times as much water as it receives by its tributaries. It is the ocean, then, Avhich must fill up the void ; a portion of the current which flows from north to south along the coasts of Portugal and Spain enters by the Straits of Gibraltar, and spreads far into the Mediterranean in superficial sheets. Nevertheless, if this inland sea did not also send a counter-cur- rent to the Atlantic^ it w^ould sooner or later be changed into an immense plain of salt. Incessantly losing fresh water by evaporation, and always receiving salt water from the ocean, its liquid mass would become in the end completely saturated, and the crystals of salt would line the marine bed in ever-increasing layers. In order that the equilibrium of saltness between the two seas should not be interrupted, it is necessary that the Mediterranean should send its saltest waters to the Atlantic. This is, in fact, what takes place. Besides the lateral eddies that occur along the shores an each side of the current coming from the Atlantic, a Mediter- ranean counter-current flows below the lighter superficial waters, and Fig. 25..— Profile of the Straits of Gibraltar. takes its direction toward the ocean. This submarine river, which passes the Straits of Gibraltar to be lost in the open sea, is, as chemical analyses have shown, a current of heavy water almost saturated with salt. Thus an exchange is accomplished through that nari-ow passage ; the Atlantic gives to the Mediterranean the waters wdiich it needs, and receives in re- turn its superfluity of salt to diff'use through the ocean. The sea endeav- ors incessantly to re-establish its constantly disturbed equality at the boundary of the two marine basins, at a depth of about 546 fatlioms. This harmony of the forces of nature is shown in a still more striking manner at the entrance to the Red Sea. This elongated gulf, which is nearly 1480 miles in length from the Straits of Babel-Mandeb to Suez, re- ceives from the atmosphere and the bordering countries so slight a quan- tity of Avater that it may be considered as absolutely nothing. It rains but very rarely (jver the sheet of water lying between the two deserts of Egypt and Arabia, and not a single torrent brings down its waters to it. * Regy, Annates des Fonts et Chaussees, 18G3. Vigan, ibid., 186G. 92 THE OCEAN. The Red Sea is therefore only an immense basin of evaporation, and the annual loss is all the greater that the rays of the sun shine almost always from a cloudless sky. The portion of fluid transformed into vapor is es- timated at about eight-tenths of an inch per 24 hours — that is to say, nearly 23 feet per year; so that if the gulf was completely closed, the wa- ter, whose mean depth does not exceed 220 fathoms, would be entirely dried up in the space of sixty years. Owing to their higher level, the waves of the Indian Ocean are carried into the Arabian Gulf by the Straits of Babel-Mandeb ; and this flow, superficial or submarine, must make itself felt with all the more force, because during eight ^months of the year the winds blow from the north to the south precisely in the axis of the Red Sea, and would thus tend to empty the gulf, if the Taws of gravity per mitted. But whatever be the swiftness of the current coming from the Indian Ocean, a portion of its water evaporates on the way, and, in con- sequence, the liquid mass, diminished by a certain quantity from evapo- ration,, must become Salter and salter in proportion as it advances to the north. In fact, it has been established by direct analyses that the quan- tity of salt contained in the same volume of water increases gradually from Aden to Suez. From a little more than 39 parts in a thousand at the entrance to the gulf, it rises to 41 and even 43 parts in the thousand at the northern extremity.* Dr. Buist, a scholar of Bombay, has cal- culated that if the Red Sea did not return to the ocean the salt that is concentrated there in consequence of evaporation, it would end in being changed into a solid mass of salt in a space of time certainly less than three thousand years, and perhaps in only fifteen or twenty centuries»f Now the Red Sea has already existed for thousands and thousands of years, and its waters (more salt than those of other seas, it is true) are still very far from being in a state of saturation. We therefore come to this inevitable conclusion, that a very salt submarine current flows through the Straits of Babel-Mandeb into the Indian Ocean in an oppo- site direction, and below^ the superficial current which supplies the Ara- bian Gulf As in houses each door serves at the same time as a passage for two contrary currents — that of the warmer and lighter air which es- capes above, and that of the colder and heavier air penetrating below — so in the seas each strait is traversed by two streams diiferent in tempera- ture and in their saline contents. All these phenomena of exchange, which occur in such a striking man- ner at th^ entrance to the Red Sea, the Mediterranean, and the Baltic, are reproduced in the vast space of the seas wherever the equilibrium of level, warmth, or saltness is disturbed by any cause whatever. Thus the Atlantic, much better supplied than the South Sea as regards rains and aflluents, is nevertheless not more elevated; and on its side the Pa- cific does not contain a greater quantity of salt than the other oceans. On all parts of the planet, seas bathing the shores of countries most di- verse in appeai'ance and geological formation have a tendency to resem- * See p. 36. t Mauiy, Geography of the Sea. INTERCHANGE OF WATER AND SALT. 93 ble each other iu their composition, saltuess, and in most of the other phenomena of tlieir waters. The currents are the great agents in pro- ducing this equilibrium in the seas ; but by their very mobility, their de- pendence on the seasons, winds, configuration of the coasts, and, finally, by reason of the submarine part of their course, they are exceedingly difficult to observe in a systematic manner; and among the numerous general and partial currents, there is not a single one, not even the Gulf Stream, whose normal course can be traced with complete precision. Happily, scientific observations are now being multiplied over all the seas; they add to and unite with one another; and, little by little, ap- proach the truth by approximations which result from the comparison of facts. Every new sounding, every new thermometrical reading, is an ac- quisition to science, and allows us to follow with a clearer eye the com- plicated circulation of the waters in the immeu'se labyrinth of the ocean. 94 THE OCEAN. BOOK III— THE TIDES. CHAPTER XI. OSCILLATIONS OP THE LEVEL OP THE SEAS. — THEORY OP THE TIDES. Another movement which keeps the waters of the sea in a constant agitation is that of the tides. While the currents cany the waves from one pole to the other, and -stir the very mass of the ocean, the tides inces- santly modify the level by the alternations of ebb and flow^ which they impart to its waters. They raise or depress without relaxation the mass of waves on all the shores of the globe ; the strand, which by turns they invade and lay bare, becomes debatable ground between the two elements, and successively forms a part of the oceanic basin and the continental surface. Twice a day vast plains of sand- like those of Mount St. Michael are invaded by the waves, deej) bays are formed far into the land, and barks glide with sails spread above the path which the pedestrian has just quitted. Twice a day the same tidal wave causes the waters brought to it from the continents to return back again, transforms simj)le rivulets into large rivers, changes basins filled with mud into vast inland harbors, and carries fleets of ships over sand-banks and hidden rocks. Six hours afterward all is changed. The tidal ports are strewn with ships stranded and lying in the mud, the mouths of rivers allow their islands of alluvium to emerge, and great bays are no more than plains of sand. Thus the outline of continents incessantly changes in appearance; the girdle of estuaries and ports, beaches, rocks, and sand-banks, which surrounds their coasts, continually alters, and changes the geography of the shores in the same proportion. Besides, movements so considerable can not occur without being accompanied by very powerful currents, flowing alternate- ly from the open sea toward the coast, and from the coast to the open sea, and contributing greatly to the general circulation and mingling of the waters in the ocean. The influence which the ebb and flow of the tides exercises indirectly on the commerce and civilization of nations is immense ; it is to these movements of the sea that England owes in great part her power and glory. In all times the people dwelling on the borders of the ocean have un- derstood, without being able to account for.it, that the alternate j^henom- ena of ebb and flow depend on the position of the moon and sun relatively to the earth. The coincidences that they saw renewed each day between the movements of the tides and those of the large heavenly bodies could not leave them in any doubt of this. Sailors and fishermen, accustomed THEORY OF THE TIDES. 95 to look to the sky for the signs of the weather, and indications of the route which they ought to follow, had no trouble in ascertaining that the return of every second tide corresponds exactly to the passage of the moon over the same degree of the heavens — that is to say, to the com- mencement of a new lunar day. Following the phases of the moon — at new, half-moon, or full — they saw the tides •change in a regular manner, and become successively higher and higher, and afterward, from day to day, lower, till the end of the lunar month. Finally, the movements of the sun also announced to them beforehand the approaching state of the waves, for the equinoxes of March and September are always accom- panied by very high tides. These coincidences between the jihenomena of the sea and the movements of the moon and sun are so striking, that all barbarous maritime tribes have remarked them, and have rudely sym- bolized the idea in their songs. Thus the Scandinavian sagas represent Thor, the god of winds, blowing the water with a horn which he plunges into the depths of the ocean, and by his powerful breath causing the waves to rise and fall by turns. What can this strange legend signify, if not that the regular oscillations of the tide depend oft the cosmical forces to which the planet itself is subject? Nevertheless, these symbolic tales of the ancient Scandinavians are far removed from that scientific theory of the tides which the researches and sagacity of Newton and Laplace have established. Even Pliny, when he affirmed clearly that the tides are due "to the combined influences of the sun and moon," restricted himself to summing up in precise terms what all the dwellers on the shores of the ocean knew ; but he could not ex- plain in what manner this influence was exercised. The explanation of the mysterious phenomena of the periodical swelling of the waters could only be attempted, in modern times, with the aid of the knowledge ob-^ tained by astronomers on the motion of the celestial bodies, and with the powerful means of investigation which mathematicians have supplied them with. Kepler first indicated the course to be followed; and Des- cartes, and then Newton, each gave his theory explaining the tides — the one by pressure, the other by the attraction exercised by the sun and moon on the mobile waters of the sea. It is the latter theory, that of Newton, which was developed later, much modified by Bernouilli, Euler, and Laplace, and which Lubbock, Whewell, Chazallon, and so many oth- er natural philosophers have since compared with observations made on the. shores of the ocean. Being very satisfactory in most respects, it is now very generally accepted : but it still has eminent opponents, among whom F. Bouchei^orn* must be named ; many of the secondary facts are still to be elucidated, and many local phenomena are not yet understood. To follow the tides in their progress and fluctuations across the seas, it is not sufficient to know the law^ of gravitation, and to calculate with the most I'igorous exactitude the movement and position of the heavenly bodies; one must also know all the facts relative to the movements of • * Philosophic Naturelle, pp. 1-205. 96 ■ THE OCEAN. fluids, and know liow to apply to all their phenomena of acceleration, retardation, increase, interference, and equilibrium the most complicated and most minute formulae of high mathematics. It would also be indis- pensable to know eyery fact respecting the form of the shore, and the inequalities of the bed of the sea. Reduced to its principal 'elements, the theory of tides set forth by Laplace, and generally adopted since, is very simple. The earth is not an isolated body in sj)ace; it is attracted by all the nearer heavenly bodies, and it is, indeed, in great part this force of gravitation which causes it to turn round the sun, and retains the moon as its satellite. Let us imagine for an instant the earth to be covered with water over all its surface, and subject to the attraction of the moon alone. This sujjerficial part of the planet would be more strongly attracted than the solid por- tion, since it is nearer to the moon which attracts it; and owing to the facility with which liquid particles glide one over the other, it would swell, so to say, toward the moon till its weight would be in equilibrium with the attracting force. It would then form an intumescence, the sum- mit of which would be exactly on the ideal line which unites the centre of the earth to that of the moon. On the other side of the planet, accord- ing to the general theory, the w^aters ought to swell in a corresponding wave, and that from a precisely contrary cause. The liquid strata on this part of the earth being farther from the moon than the solid kernel, are less atti'acted than it, and in consequence must remain slightly behind, Fisr. 26.*— Lunar Tide. thus forming a new intumescence, the summit of which will be found on a prolongation of the line uniting the planet with its satellite. Considered as a whole, the mass of marine waters woifld thus assume the form of an ellipsoid, having its greater axis directed toward the moon, which is the * This illustration, as well as Tigs. 27 and 29, have been borrowed from the fine work by M. Ame'dee Gnillemin, entitled Le del. THEORY OF THE TIDES. 97 i-entrc of attraction. It results from tliis, that the tide ought to be noth- ing at all, or very slight, at the poles; since, in its revolution, the moon, wliile moving to the north and south of the equator, maintains itself at the zenith of tropical or sub-tropical regions. If the earth remained immovable, these two waves would advance slowly, following the course of the moon ; but in consequence of the ro- Fig. 27. — Syzygy Tide, during the New Moon. # tation of the earth, they ought to move rapidly in pursuit of one another over its circumference — the wave of the greatest attraction moving in- cessantly over the part lighted by the rays of tlie moon, while the wave of the weakest attraction is propagated from the other side of the eartli on the part farthest from the satellite. In the space of a lunar day — that 98 THE OCEAN. is to say, within the 24 hours 50 minutes during which the earth has suc- cessively presented all parts of its surface to the planet which accompa- nies it — the two waves ought each to accorajjlish a complete circuit around the globe, and each should have a total duration of 12 hours 25 minutes. This is, in fact, what takes place over all seas. As to the numerous vari- ations presented by this phenomenon, in its height and the precise mo- Fig. 28.— S\ 7ygy Tide, dariug Full Moon. ment of its appearance, they depend on the obstacles of every kind which the rocks, islands, continents, oceanic currents, and winds oppose to the free circulation of the waters. Nevertheless, the moon is not the only heavenly body whose attraction is manifested in a sensible manner on the waves of the ocean. The sun, which draws the moon in its immense orbit across the heavens, is near enough to our planet to raise the liquid particles of our ocean also. The DIFFERENCE OF ATTEACTION. 99 total attraction exercised by the sun on the earth is even 162 times great- er than the total attraction of the moon ; and in consequence it would raise the tides into real mountains as high as the Cevennes,* if the true cause of the tides was not to be found in the difference of attraction exercised on tlie waters of the different parts of the earth. The distance from the moon being equal to 60 terrestrial radii only, the action of the satellite is much stronger over the nearer oceanic regions than over the waters situ- ated thousands of miles farther off. The sun, on the contrary, acts near- ly in the same manner on the watery particles of the whole surface of all the seas. According to the results obtained by the calculations of mathematicians, the attractive force exercised by the sun in elevating the waves is, as compared to that of the moon, in the proportion of about a third. JmiiiL;- l^)iiiicir;Uiire. Two tidal weaves, the lunar wave and the solar wave, are thus raised on the surface of the sea. They ought to revolve, the one in the space of 24 hours 50 minutes, and the other in 24 hours. But these two waves, so distinct in their origin, are not separated in their course around the globe ; owing to the incessant mobility of the waters, they mix and are confused, and it is by calculation alone that we can discriminate in their common mass the part that is to be referred to each of the two heavenly bodies. These two united intumescences moVe together around the earth in a di- * 5000 to 6000 feet high. 100 THE OCEAN. vection from east to west — that is to say, in the opposite direction to the rotation of the globe. Serving thus as a drag upon the planet, they must, in the long run, lead to that slackening of its speed which the calcula- tions and deductions of Meyer, Tyndall, Joule, Adams, and Delaunay lead us to consider as inevitable.* When the moon, called new, turns it dark face toward us, and is thus in nearly the same direction as the sun relatively to the earth, the attrac- tions of the two great celestial bodies join together, and the two tidal waves, i-aised at the same time toward the same point of space, are ex- actly superposed. They form those tides of syzygy, or high water, called spring-tides, which rise to such great heights along our shores. At the time of full moon — that is to say, when the satellite, entirely lighted, is in direct opposition to the sun — new tides of syzygy not less elevated than the first are formed ; for, under the influence of the heavenly bodies situ- ated opposite to each other, a double intumescence is simultaneously pro- duced on both sides of the earth. During none of the other phases of the moon does this coincidence exist ; at the time of quadrature, the two great movements of the waves oppose one another, and the tidal wave, which represents then the lunar wave diminished by the entire solar wave, is less elevated than during the other phases of the moon. If the two attracting forces were equal in power, the neutralization of the tide would be complete, and the level of the sea would remain undisturbed. To give an idea of the fluctuations which occur during the course of an entire tide under the influence of the heavenly bodies, and which are va- riously modified by the atmospheric currents, the form of the coast, and inequalities of the bed of the sea, we borrow the following figure from Beardmore. TI Ti Til vm 5y?3 ■■*/-^ 3-f? ..2j«-= ...J4 ^ii Tm n X XI Mdi 1 tt la IV T Fig. 30.— Tide at Southampton, 2d August, 1859. The periods of the tides are exactly those of the bodies which raise them. The semi-diurnal period of 12 hours 25 minutes is comprised be- tween the passage of the moon over the two opposite meridians of the * See the section entitled The Earth in Space. FLUCTUATIONS OF THE TIDES. 101 earth. The diurnal period, dnring which the ocean swells and subsides twice, corresponds exactly to the duration of one apparent rotation of the satellite around our planet. There is the same coincidence for the serai- monthly period ; the return of the spring-tides occurs from fortnight to fortnight with the return of the full or new moon, and the monthly period is completed when the series of lunar phases recommences. Nor is this all ; the tides have also their semi-annual period, from the equinox of March to that of September ; for the sun, being then directly above the terrestrial equator, exercises a stronger attraction on the liquid masses, and the Avaves of the spring-tides rise to a greater height than usual. Finally, an annual period is marked for the tides by the epoch when the earth is nearest the sun. This epoch falls during the winter of the north- ern hemisphere, and it is then, indeed, that the spring-tides rise with most force on the coasts of our continents. Thus the phenomena of the tides are intimately connected with the ce- lestial movements, and every change in the relative position of the bodies which attract our planet^ manifests itself by a corresponding change in the level of the seas. Knowing beforehand the route which the earth follows in space, astronomers foresee thereby even the future oscillations of the Avave, and can trace their curve for centuries to come. Never- theless, it must be admitted, this curve is only true in theory ; for if the tides in their origin be due to astronomical causes, they are also subject to variations from terrestrial phenomena. Like the winds, currents, and all the other manifestations of planetary life, they present incessant vari- ations, and are, so to say, in a continual genesis. 102 THE OCEAN. CHAPTER XII. THEORY OP WHEWELL ON THE ORIGIN AND PROPAGATION OP TIDAL WAVES. — ORIGIN OP THE TIDE IN EACH OCEANIC BASIN. "ESTABLISHMENT" OF PORTS.—" CO-TIDAL " LINES. The English natural philosopher, Whewell, who during long years made laborious researches on the phenomena of ebb and flow, was the first to apply the name of "cradle of the tides" to the great continuous sheet of water which covers almost all the surface of the southern hemi- sphere. It is in this vast basin, of which all the other oceans are mere ramifications, that the combined attraction of the sun and moon would first raise that wave which from shore to shor-e dashes at length against the coasts of Greenland and Scandinavia. It is there that the water, a few instants after the passage of the moo-n over the meridian, would it- self attain the level of its highest •elevation, and would form that first regulating intumescence which the surface of all the seas would obey one after the other, as a coi'd shaken at one of its extremities oscillates to the other end in rhythmical vibrations. According to this theory, the tidal wave circulates incessantly through- out the Antarctic Ocean, to the south of the extremities of the three con- tinents of Australia, Africa, and South America. It follows from east to west the apparent course of the moon, and thus describes a real orbit round the" earth similar to that of the celestial bodies. Even in the Cen- tral Pacific and the Indian Ocean, the tide obeys this normal impulse to- ward the west. It strikes the coasts of Australia and New Guinea almost simultaneously ; then, thirteen or fourteen hours afterward, it dashes on the eastern coast of Africa, from the Bank of Lagullas to Cape Guarda- fui; finally, seven or eight hours later, the coast of South America is struck, in its turn, from Terra del Faego to the estuary of La Plata. To the north of those large oceanic tracts of the South Sea, the tides, not having the same facilities for developing themselves in a normal man- ner, would be obliged to change their direction. But, in spite of this de- viation, they would not the less be, Whewell thinks, continuations -of the primitive swelling. Arrested by the American continent, which bars its passage, the tidal wave would rebound toward the north, and follow the contoui's of the oceanic valley, like a torrent inclosed in a mountain gorge. Striking the coasts of America and those of the Old World, under the same latitude, at the same time, and at an equally oblique angle, it reaches almost simultaileously, on either side of the Atlantic, the Bay of Fundy and the Irish Channel, where its highest known elevation is observed. The tidal wave accomplishes this passage of about 6000 miles, from the Cape of Good Hope to the British Isles, in about fifteen hours. But its VARIATION OF THE TIDES. 103 entire voyage, from the centre of the Antarctic Ocean, must have lasted ' more thau a day ; and, in consequence of the gradual slackening of speed of the waters on the shores of Great Britain, it is only after two days and a half that the tidal wave reaches the mouth of the Thames. Thus the moon would have had time to raise five successive tides in the Pacific Ocean before the motion of the liquid mass would have been propagated to the en^-ance of the North Sea. Such is the theory which the labors of Whewell have caused to be long considered as the very expression of truth. Nevertheless, it is not cer- tain that things occur in this way In fact, it is ascertained that in each oceanic basin the tide seems to start from the centre, and to be propagated in all directions parallel to the general direction of the coasts. We may naturally conclude from this that each great division of the ocean, con- sidered as an isolated sea, is really the cradle of the tides which break upon the surrounding shores. What confirms this idea, too, which ap- pears so probable at first, is that the various oceans are separated from one another by spaces where the regular tide is hardly perceptible. Thus between the South and North Atlantic, whose precise boundary may be defined by the promontory of St. Roque and Cape Verd, there exists a wide zone where the tide hardly changes the maritime level more than about 23 to 27 inches, as at the islands of Ascension and St. Helena. Be- sides, according to the theory of Whewell, the tidal wave on the coasts of the Argentine Republic and Brazil ought to propagate itself from south to north ; while, on the contrary, the movement proceeds from north to south, from Pernambuco to the mouth of the La Plata.* When we see a tidal wave rise oiF the Banks of Newfoundland, in the deepest part of the Northern Atlantic, it is not therefore necessary to consider this as the same wave which twelve hours before was raised near the Bank of LaguUas, at the entrance to the South Atlantic, It is, perhaps, better to regard the oscillations which occur at the same time in both hemispheres as coincident but independent phenomena. Nevertheless, in each isolated basin the movements of the sea are much as Whewell has described them. On the coasts of France and the Brit- ish Isles the tide certainly comes from the open sea, and in its progress along the shores, the original motion which the attraction of the sun and moon produced in the middle of the open sea continually decreases. On penetrating into the shallower seas which surround Ireland and Great Britain, the tidal wave gradually slackens. After having struck Cape Clear and the promontory of Land's End, it is propagated with such slow- ness around the two islands, that nineteen hours elapse before it arrives at the Straits of Dover, where it meets with another livave newer by twelve hours, which has come by the shorlier route of the Channel. Whence comes this slackening of the wave? The researches of astron- omers and natural philosophers inform ns that the speed of the tidal wave is proportioned to the depths of the ocean ; driven by an equal * Fitzioy, Adventure and BeagJe. Appendix to vol. ii. 104 THE OCEAN. force, the circumference of a wheel turns the faster the greater its diame- ter ; in the same way the tide hastens or slackens its movement, accord- ing to the depth of the watery mass which it traverses. In those lati- tudes where the bed. of the ocean is 5000 fathoms from the surface, the speed of the wave is about 528 miles an hour; where the depth is only about 50 fathoms, the tide is not propagated more than about 60 miles in the same space of time; finally, when the bottom is at about fi\^ fathoms below the marine surface, the movement of the waters is greatly retard- ed, and does not exceed fifteen miles per hour — that is to say, 440 yards per minute. In consequence of the delay which the tidal wave experiences, the " es- tablishment " — that is to say, the time which elapses between the passage of the moon over the meridian and the moment of full tide — varies sin- gularly in difierent ports situated near each other. Thus, while at Gib- raltar there is usually a coincidence between the astronomical and marine phenomena, and the establishment is reduced in consequence to zero, this interval is about an hour and fifteen minutes in the port of Cadiz, and four hours at Lisbon. At Bayonne, as at Lorient, it is three hours thirty minutes; at the mouth of the Gironde and at Cherbourg, it is seven hours forty minutes; at Havre, nine hours fifteen minutes; at Dieppe, ten hours forty minutes ; at Dunkirk, eleven hours forty-five minutes. The estab- lishment varies on every shore, according to the speed of propagation of the tide across the open seas and in the gulfs and estuaries. The sinuous line which unites all the points in the ocean where the full tide occurs exactly at the same hour, has received from Whewell the name oi co-tidal line; it indicates the curve which the crest of the tidal wave forms at any one moment on the surface of the sea. It is around the British Isles that these lines of simultaneous swelling or of equal establishment have been most carefully traced. By calculation and di- rect observation, that part of the oscillation on the mobile and almost always agitated surface of the sea, which is to be referred to the phenom- ena of ebb and flow, has been detected ; and much more exact maps of these swellings and depressions, which are invisible on the open sea, have been drawn, than of the vast continental regions which ai'e at present but little known. Thanks to the labors of Whewell, Airy, Lubbock, and Beechey, one can,now follow the whole series of co-tidal lines which suc- ceed one another from hour to hour around these two great islands, from the crest coming in from the open sea, at the entrance of the English Channel and the Irish Sea, four hours after the passage of the moon over the meridian, to the swelling, which nineteen hours later reaches to the south of the Ge*man Ocean and penetrates into the funnel of the Straits of Dover, where it meets the other tidal wave coming directly by the Channel. The general form of these curves demonstrates in a striking manner that the speed of propagation of the tide is in proportion to the depth of the seas. Everywhere we see the co-tidal lines develop their convex part above the deeper valleys of the marine bed; everywhere PROGRESS OF TIDAL WAVES. 105 Fig. 31.— Co-tidal Lines of the British Isles. w6 see the wave slacken its speed in the neighborhood of shallow rocks and shores. One could even, by an inspection of these lines of equal in- tumescence, indicate exactly those parts where the lead would descend lowest, so intimate is the connection of cause and effect between the depth of the sea and the progress of the tide. 106 THE ocean: CHAPTER XIII. APPAEENT IREEGULAEITIES OF THE TIDES. — EXTEAOEDINAEY SIZE OF THE TIDAL WAVE IN CEETAIJST BAYS. INTEEFEEENCE OF EBB AND FLOW, DIUENAL TIDES. INEQUALITIES OF SUCCESSIVE TIDES. Innumeeable are the apparent inequalities which occur in the phe- nomena of the tides, in consequence of the inequalities of the submarine surface, the thousand indentations of the shore, and the alternations of winds and currents. Though the cause of the movement be the same everywhere, we can still say that at no point of the sea do the ebb and flow present a perfect agreement in their progress. Each promontory, each islet, each rock is bathed by waters having a distinct rule in the J h I / i J [ ( *}i« Figs. 32-34.— Irregularities in the Curves of tlie Tidal Waves resulting from the Form of the Sea-bed, projecting Eocks, etc. (after Lubbock). propagation of their tides ; every obstacle which breaks the regular course of the oscillations modifies the whole of the graceful curves which bend around it. The above figures, borrowed from Lubbock, give an idea of these variations in the march of the waves. The diflTerence which most strikes the minds of navigators and inhab- itants of the coast is that of the height of the tides. In one part of the coast the tide hardly makes itself felt, even during the equinoctial syz- ygies; while elsewhere every tide is a real deluge, spreading as far as the eye can see over vast tracts, which emerge again at the time of ebb. This astonishing contrast in the amplitude of the tides results from differ- ences of speed in the progress of the oscillations in the seas and bays of the coast-line. In fact, the great swelling caused by the heavenly bodies may be considered as formed of a great number of successive waves oc- cupying a considerable breadth on the surface of the sea. In the open ocean all these waves move with great speed ; but in proportion as they approach the shores they slacken their movement, and consequently must gain in height what they lose in rapidity. From the mere sight of a tidal chart we can affirm that the tide will rise several feet hisfh in all the a'ulfs SIZE OF THE TIDAL. WAVE. 107 Avhero we see the co-tidal lines crowded together, in consequence of the ivradual retardation of the wave of intumescence. In this respect, facts fully confii-ni theory. The gulfs of Bengal and Oman, the Chinese Sea, the indentations of the eastern coast of Patagonia, the Bay of Panama, that of Fundy, between New Brunswick and Nova Scotia, the Channel and the Irish Sea, are parts where the waves of equal intumescence follow each other very closely, and it is there too that a greater extent of coast is alternately covered and revealed by the tide. In the port of Panama the tides rise nearly twenty-three feet, concealing and discovering by turns an immense strand in their diurnal movements, while at hardly thirty-seven miles distant on the other coast of the isthmus the ebb and flow are scarcely perceptible. In the Persian Gulf and the Chinese Sea the amplitude of the equinoc- tial tide is nearly thirty-six feet at the extrejnity of the gulfs. In the mouth of the Severn and the French bay of Mount St. Michael the dif- ■ ference of height between the spring-tides and low-water is from forty- five to forty-eight feet. To the south of the American Continent, in the gulfs of San Jorge and Santa Cruz, at the entrance of the Straits of Magel- lan, Fitzroy has measured tides of from forty-eight to nearly sixty-six feet Fig. 35.— Bay of Fuudy. high; finally, in the Bay of Fundy, so well calculated, by the contour of its coasts and the surface of its bed, to retard progressively the march of the tide, tl^e difference between high an(f low water, which is about nine feet at the entrance, gradually increases to nearly sixty-nine feet toward 108 THE OCEAN. the extremity of the channel. This is probably the part of the coast M^here the regular oscillations of the waters are accomplished in the grandest manner. Twice a day immense neutral shores, which are neither land nor sea, change into deep gulfs, and stranded ships rise and float with sails spread, while towns lost in the interior of the land find them- selves seated on peninsulas invested by the sea. At St. John's, New Brunswick, a cascade is seen to glisten at the bottom of the port at low water; but when the tide reaches the foot of the cliff", the height of the fall gradually diminishes, and it is at last entirely drowned in the salt waters, which, spreading far over the upper terrace, permit vessels to pen- etrate into the natural basin formed above the cascade. Fig. 36— Mouth of the Avon (after Beardmore). Similar phenomena occur in the two bays of Mount St. Michael and the Severn. There, too, I'ivers and rivulets are periodically changed into gulfs ; there, too, the harbors are tidal ports, where ships, with the ex- ception of those which ai'e inclosed within the basins, lie on their sides in sand or mud at the time of low water. In the same way the space ex- tending between Noirmoutiers and the coast of La Vendee is alternately an isthmus and a strait ; a high-road traversed by vehicles winds through the sandy plain between pools of Avater, and a few hours afterward ves- sels with sails spread pass over the same route. Sailors are often seen walking quietly on the shore at a slight distance from their stranded ves- sel, or else digging in the ground in search of shells; but let the distant rolling of the tide be heard, and in the space of a few seconds the crew is on board, prej)arations are made for a new embarkation, and the vessel, raised by the tide, sails rapidly over the sea. It is in the Bay of St. Michael, on the western coast of Europe, that the rising tide presents the grandest spectacle, for in the centre of the bay rises a black granitic rock — "abbey, cloistez', fortress, and prison" at the same time — which by its abrupt precipices and its " titanic pile, rock upon rock, century after century, but always dungeon over dungeon," contrasts Avith the dreary extent of the shore.* At low water, the immense sandy plain, above 150 square miles in extent, resembles a bed of ashes. But when the tide, swifter than a h(fi'se at full gallop, rises foaming over the * Michelet, La Mer, p. 18. riie Oci'au Ac BAY OF S"^ MICHEL PI VII. ' )Y '4- Drauwn by AAnjilleiuiii 38000C t s ■* 6 e 1 a Erii^ra-ved byl^rhard TIDES IiV THE BA Y OF ST. MICHAEL. 109 scarcely perceptible slope, a few hours are sufficient to transform the whole bay into a sheet of g'rayish water, penetrating far up the nioutlis of the rivers as far as the quays of Avranches and Pontorson. At the ebb, the waters retire with the same speed to nearly six and a quarter miles from the shore, and lay bare the great desert strand, which is intersected Dcjjtli andieated m feet Fig. 37.— Straits of Noirmoutiers. by the subterranean deltas of tributary rivulets, forming here and there treacherous abysses of soft mud, into which travelers are in danger of sinking. At the time of spring-tides the liquid mass which penetrates into the bay is estimated at more than 1470 millions of cubic yards, and even at neap-tides the deluge, which pours over the beach twice in the 110 THE OCEAN. four-and-twenty hours, is not less than about 765 millions of cubic yards.* Is it astonishing that such torrents should have been able in former times, when driven by tempests, to break through the chain of sand-hills which protected the rocks of Tombelene and St. Michael on the north, and to transform into sterile wastes the beautiful country and vast forests which extended to the foot of the peninsula of Cotentin ?f Beechey's observations of the tides of the Channel and the Irish Sea cause it to be regarded as certain that the enormous amplitude of the ebb and flow at the mouth of the Severn, and in the bays of Cancale and St. Malo, arises, not only from the gradual elevation of the bottom, but also from the sujjerposition of two waves, which encounter each other. In fact, the crest of the tide which penetrates into the Irish Channel meets, at the end of the gulf where the'Severn discharges itself, another wave older by twelve hours, which has just made the entire circuit of Ireland. These two Avaves, united into one, take the common direction which re- sults from their original impulsion, and flow together into the Gulf of the Fig. 3S.— Tides of the English Chaunel. Severn. In the same manner, the tide which enters the Channel meets ofi" Jersey with another wave, Avhich has made the tour of the British Isles in twenty-four hours, and the two joining each other, dash their enormous liquid mass against the strand and rocks of Brittany. If two tides coming from opposite points, and ineeting at the time of high tide, are thus combined in one, they, on the contrary, neutralize and suppress each other, when the ebb of the one crosses the flow of the other. A phenomenon of interference occurs then comparable to that of two luminous vibrations extinguishing each other. Fitzroy was the first who *■ Marchal, Annales des Fonts et Chaussees, 1854. t See the section entitled The slow Oscillations of the Land. MEETING OF THE TIDES. m pointed out a rcg-ion of the ocean where contrary tides maintain the snr- Ihce of the water in equilibrium. This region is the estuary of La Plata. At sight of this gulf, which is no less than 15Q miles at the entrance, one Avould be tempted to believe that the amplitude of the ebb and flow would be as enormous there as in the Bay of Fundy or the Gulf of St. Malo. But, on the contrary, the tides there are scarcely any thing. The strong oscillations of the level that have been observed in that estuary are due almost wholly to the regular breezes and the tempests, which depress the Avaves on one side and raise them on the other. ^Then, too, as the land Avinds generally predominate during the morning, and are replaced in the evening by the sea-breezes, the ebb and flow, obedient to the alternating impulses of the atmosphere, succeed each other every twelve hours ; the tide rises in the afternoon and falls the next morning.* This apparent anomaly is easily explained by the meeting of high and low water at the entrance of the estuary. The tidal waves which flow to the south on the Brazilian side, and to the north on the side of Patagonia, do not strike the coasts at the same instant daily. They follow each other at an interval of several hours, and the lateral currents which diverge from tl\era suc- ceed one another at the mouth of the estuary of La Plata, so as to main- tain the liquid mass at nearly the same level. At the moment Avhen the ebb of the northern tide is about to occur, the southern flow takes place, the pressure of which, exercised in the contrary direction, prevents the waters from falling ; then, when a new tide from the coasts of Brazil pre- sents itself, the surface of the sea is already lowered in the southern lati- tudes. The swellings would intersect each other, and on the line of inter- ference the water would be subject to no oscillations. It is probable that to causes of a similar kind we must attribute the formation of those diurnal, and always very slight, tides which occur at the mouth of the Mississippi, on the coasts of New Ireland, at Port Dal- rymple in Tasmania, to the south of Australia, near King George's Gulf, in the Gulf of Tonquin, in the Bay of Bahr-el-Benat, in the Persian Gulf, in the White Sea, and in many other parts of the ocean. These slow changes of level, the ebb and flow of which each lasts twelve hours, pre- sent, like ordinary tides, the greatest diversity in their phenomena, ac- cording to the direction of the winds and the currents, the respective po- sitions of the sun and moon, and the parts of the sea where this equilib- rium of the waters is established. On the moving surface of the ocean, all the undulations, whatever may be their cause, are mixed and con- founded, and in this ceaseless changing and mingling of the waves it is impossible to discern, without long and patient research, the part taken by each agent in disturbing the perfect repose of the sea-level. The problem can be solved in a general manner only, without taking account of details that have been as yet imperfectly observed. Thus it is known that in the port of Vera Cruz and on the neighboring coast the winds have a marked preponderance, for they sometimes maintain the surfoce * Martin de Moussy, Confederation Argentine, t. i., p. 78. 112 THE OVEAK of the sea at the same level during whole days. At the mouths of the Mississippi, where the daily tide has a rise of little more than fourteen inches, it is not less regular in its progress* and its total height each day represents exactly the difference of level between the two composing- waves which have crossed each other. Finally, the tide at Tahiti, nearly twelve inches high, is the result of many more oscillations; for four tides, 39.— Height of the Tides in St. George's Chaunel. TIDELSS AREAS IN THE SEA. 113 coming from the four cardinal points, meet each other there, all differing in their speed and their hour of high water. It is not surprising that, in the middle of this general intersection of the tides of the Pacific Ocean, that of Tahiti is almost completely neutralized.* The Irish Channel, so well studied by Beechey, presents a very curious example of a perfect equilibrium of waters, and that almost opposite the Bristor Channel, Avhere the sea rises and falls alternately above 48* feet. That part of the Channel whose surface remains at rest borders on the Irish coast not far from the little town of Courtown, to the south of Ark- low. There neither rise nor fall in the waters has ever been observed, though the currents of the ebb and flow run along the coast alternately, with a speed of nearly four and a half miles per hour. The point where the waters are always in equilibrium may be considered as a kind of " hinge " on which the tides turn. Their amplitude is greater and greater in proportion as they are distant from this tranquil region — to the north- east toward Holyhead and Liverpool, to the south-east toward Milford Haven and Bristol. In the North Sea, the aieeting of high and low water, nor far from the Straits of Dover, is marked by another centre of equilibrium, which seems to oscillate between the coasts of Holland and those of England, according to the atmospheric and marine currents, and the movements of the heavenly bodies. In this place Hewitt has ascer- tained that the tide rises two feet only ; and it is in this region, where the waters keep almost always at the same level, that the largest and most numerous sand-banks are deposited. ifours l cnv- waUr.levcl ■^ The.hmmsS.6.j8.g.io,aarcrxufu»ved' Fig. 40.— Crossing of the Swellings of the Tides in the English Channel and the North Sea, from the Scilly Isles to the Mouth of the Humber. It appears that the two tidal currents which meet near the Straits of Dover — the one coming directly from the Atlantic, the other from the North Sea — do not follow the centre of the Channel, and consequently do not encounter each other directly. The rotation of the earth, which in the northern hemisphere displaces all moving bodies toward the right, causes each of the tidal waves to diverge in this direction. In the Chan- nel the tidal wave, which is directly propagated, constantly leans toward the right — that is to say, toward the south ; its force is, therefore, much greater on the coasts of France than on those of England, and when it has passed the Straits it keeps its preponderance on the coasts of the con- tinent as far as the mouths of the Meuse ; the tide coming from the north, * Fitzroy, Adventure and Beagle, Appendix to vol. ii., p. 290. 114 THE OCEAN. on the other hand, deviates likewise to the right, and flows along the coasts of England. The crossing of these two contrary currents gives rise to numerous gyratory movements off* the coast of France and Great Britain, the incessantly changing curves of which form a veritable laby- rinth.* In the roadstead of Havre the meeting of the tides results in a remark- able phenomenon, which is at the same time one of the most useful for navigation. Instead of falling immediately after having attained its point of highest tide, the sea remains steady for three hours, and thus permits vessels to sail all over the road, and to penetrate with ease into the port, floating constantly over deep water. The seamen saw in this fact a sort of miracle, before its true cause had been revealed. When the tide from the Atlantic rolls toward the east to the middle of the Channel, it is arrested in its course by the peninsula of Cotentin, and can only ad- vance freely to the north of the Gulf, toward the mouth of the Seine. The marine level is thus more elevated at the centre than on its shores, and its waters are spread laterally toward the road of Havre and the other parts of the coast. At the time of low watei", when fhe ebb pre- vails in the centre of the Channel, the inclination is changed; but before the waters of Havre can descend toward the central course of the Chan- nel, which carries such an enormous mass of fluid to the ocean, they are kept back by the wave which, after having struck the Cape of Antifer, flows along the shores from north-east to south-west, to the Cape of La Heve. Then, when the force of this partial tide fails, another river-tide, which has followed the coast of ISToi'mandy from St.Vaast to Trouville, still maintains the level for a time.f In almost all river-ports, as we can easily understand, the ebb lasts longer than the flow, for the fluvial current neutralizes the tide during a shorter or longer period, and then, adding to the ebb, can not but augment its duration.^ A fact more difficult to explain is that, while in the greater number of ports remote from any river's mouth, the rising tide is shorter than the falling, numerous instances of the opposite are to be seen ; and especially the port of Holyhead. According to the hypoth- esis generally adopted, this longer duration of ebb ought to be attributed to the rotation of the earth in the direction of west to east. The tidal wave being propagated in the contrary direction — that is to say, from east to west — would meet a certain resistance in the waters which are spread before it. It would rise up, and become steeper and more rapid toward the west ; while its other slope, that of the ebb, would lengthen itself to- ward the east. This will explain why the phase of the flow does not last so long as that of the ebb. The inequalities which are observed in certain parts between two suc- cessive tides are likewise a strange and, in some respects, unexplained phenomenon. These various inequalities, now in the duration, and now * Annales des Fonts et Chaussees, 1863, first week. t Baude, Revue des Deux Mondes. t See p. 121. INEQUALITIES OF THE TIDES. 115 in the respective heights of the two tides of morning and evening — or which even aifect every oscillation in its entire course — arise in part from the declination of the moon ; that is to say, from its varying distance to the south or north of the equinoctial line. But in many cases the dii- ferences between two successive tides are relatively enormous, and this explanation is not sufficient. Thus at Port Essingtou, on the northern coast of Australia, differences in height of nearly four feet between thf oscillation of evening and morning have been observed. At Singapore, where the mean tide during the time of highest water is ilearly seven feet, the difference between two succeeding tides is sometimes nearly five feet. At Kurrachee the daily variation is no less, and in the Gulf of Cam- bay it attains to nearly seven feet. At Bassadore, at the entrance of the Persian Gulf, the duration of one oscillation of the sea sometimes exceeds by two hours that which follows it ; and, finally, it has happened at Pe- tropaulowski, in the Northern Pacific, that expected tides have never ap- peared at all. » We can explain these singular anomalies only by the in- tersection of several reflex waves, diurnal and semi-diurnal, which interfere with one another ; and the confused oscillations of which are produced by the meeting of moving liquid masses of diverse origin. It is thus that on the surface of a jjond, the waves that have risen at dj^erent points form an immense' net- work of intersecting lines, which the breeze mingles in undecided wavelets. 116 THE OCEAN. CHAPTER XIV. TIDAL CURRENTS. T-EACES AND WHIRLPOOLS. — TIDAL EDDIES. — RIVER TIDES. The popular belief is that the oscillations of the tides are always ac- companied iby currents changing regularly with the ebb and flow, and tending alternately in one direction or the other. This is, it is true, a pretty frequent phenomenon, especially at the mouths of rivers. Usually, when the- water rises, a tidal current rushes at the same time toward the shore and into the estuaries of rivers ; then, when the level of the liquid mass falls, a return or low-water current, swelled by the fresh water from inland, flows again toward the open sea. Nevertheless, this coincidence of the horizontal currents with the vertical oscillations of the ocean is far from being reproduced with regularity in all parts. The tide, being mere- ly a swelling of the sea, can rise without the least movement occurring in one direction or the other. A remarkable example of this is seen in the Irish Sea, so rich in maritime phenomena. In the middle of the channel which separates the Isle of Man from Ireland, the sheet of *water keeps perfectly tranquil between the contrary currents, though the water at this place rises more than eighteen feet during the spring-tides. On the other hand, as one can see at Courtown, on the coast of Arklow, the cur- rent determined by the meeting of opposing tides can have a great speed where the surface of the sea neither rises nor falls,* Finally, the same wave can follow a constant direction across two contiguous regions of the sea, one of which is at ebb and the other at flow. The currents which occur in straits in consequence of differences of lev- el are sometimes extremely violent ; and by their abrupt changes, their eddies and whirlpools may be classed among the most dangerous' phenpm- ena of the ocean. Thus the entrance to the Gulf of Normandy and the Channel Islands is rightly dreaded by navigators because of the terrible speed which the tidal currents attain there. The Blanchard Race, a strait w hieh separates the Cape of La Hogue from the Island of Alderney, is the fi^^ of these terrible marine defiles where the ebb and flow, re- strained between chains of xock^ and shallows, move at the time of high water with a speed of nearly ten miles per hour. Then comes the strait which bears the significant name of the Deroute Passage, and in which the currents flowing along the rugged western coast of Cotentin meet those which come directly from the open sea by the! breach opened between the islands of Jersey and Guernsey ; there the marine rivers, less rapid, are nevertheless animated by a speed of nearly ten feet per second. f Since the disaster of La Hogue, where Tourville, unable to sail against the formidable current of Blanchard Race, lost so many of his ships, how * See p. 113. t Mounier, Memoire sur les Courants de la Manche. TIDAL CURRENTS. m many vessels have been wrecked, how many crews have perished, in these terrible straits, which Victor Hugo has chosen as the theatre for his t^loomy drama of "The Toilers of the Sea!" Fig. 41.— Course of the Tide in tlie Irisli Sea. The mariile defiles which separate the British Isles from the continent, and especially those of the Hebrides, the Orkney, the Shetland, Faroe, and Lofoten Islands (whose rocks and shelving banks confusedly stud a very uneven sea-bed, full of abysses), are also traversed by alternate tid- al currents all the more rapid and tumultuous, because of the difference of level between the two sheets of water which meet in the strait. The most formidable of these passages is perhaps the Great Gulf, or " Coire- bhreacain,"* between the islands of Jura and Scarba, on the western coast of Scotland. At each change in the tide a current, flowing alternately * Gaelic, "Caldron of the Snotted Seas." 118 THE OCEAN. toward the main-land and toward the open sea, is produced. The English Admiralty chart estimates its speed at nearly eleven miles per hour, but sailors affirm that it is at least nearly twelve and a half miles — that is to say, more rapid than the stream of any continental river. No vessel can venture, in strong tides, into such a terrible race ; especially when the wind blows in the contrary dii-ection to the tide, for the Coirebhrea- cain is then in its entire extent a foaming " caldron," without any visible limits.* Other tidal conflicts are hardly less terrible ; such, for example, is that observed in the straits of the Pentland Firth, between Scotland and the Orkneys, and which ends in the formation of currents estimated at more than ten'miles per hour. But the most celebrated of all these encounters between two tides .of different levels is the Moskoestrom, toward the southerly extremity of the archipelago of the Lofoten Islands, called also by seamen the Maelstrom. The sombre imagination of northern peoples, always tending to the creation of monsters, saw in the strait of the Mos- koestrom a polype Avith arms several hundred yards in length, which caused the waters to whirl in an immense eddy, in oi'der to draw ships into it and ingulf them. From this ancient legend there has even re- mained with many the idea that this cun-ent is a sort of abyss in the form of a funnel,.which floating objects approach by degrees, forming narrower and narrower circles, till they finally plunge forever into this revolving well. But it is nothing of the sort. The only eddies are. small lateral ones, produced by the meeting of the cui'rents, and hardly two or three yards deep. The principal phenomenon consists, as in the Coire- bhreacain and the Blanchard Race, of a rapid movement of the waters tending ■ alternately in one or the other direction at the time of the change of the tides. When in the open sea the flow rises in the direction from south to north, a part of its mass spreads with force into the strait opening to the south, between the two islands of Moskoe and Moskoe- naes. In proportion as the surface approaches a state of equilibrium, the current, gradually weakened, tends toward the south-west, and then to the west. A period of calm follows these different movements of the waves when the level is perfectly established; but soon the ebb com- mences, and tends in an inverse direction, at first toward the north, then toward the north-east and east. Thus, in the space of one tide the waters are alternately carried, though with varying force, toward all the points of the compass. The tidal currents, which occur at the entrance to rivers, frequently give place to tumultuous movements less terrible, it is true, than those of the races in archipelagoes, but sometimes of an equally striking as- pect. These phenomena are known under the name of the " bore," barre, " eager," or mascaret. In penetrating into the estuary of a river, the tidal wave, retarded by the shallows, and narrowed by its banks, must necessarily swell, because * AthencEum, August 26, 1864; Mittheilungen von Petermann, t. ix., 1864. Rimil OF THE TIDE UP lilVEIiS. II9 of the restriction of the liquid mass in its bed. All the inlets and bays into which the tide penetrates present thus the spectacle of the "bore;" but in many passages the regular inclination of the bed, the uniformity of the shores, or else an intersection of various currents, diminish the first undulation of the tidal wave, or permit it to be confused with other ir- regularities of the surface. Elsewhere, on the contrary, all the topo- graphical conditions are found united to give a great height to the " bore," and it then rises, like a moving wall, from one shore to the other of the estuary. At the mouths of certain rivers, such as the Amazon, the Hooghly, the Seine, the Dordogne, the Elbe, and the Weser, the waves of the "bore" assume enormous proportions at the tirne of high tides, and become formidable phenomena. In the Amazon, the " bore," called poro- roca because of the roaring of its waters, rises, it is said, in three success- ive waves, attaining together from thirty to fifty feet in height ; and ves- sels surprised by this sudden flood are in great risk of capsizing, as in the open sea. At the mouth of the Ganges the " bore" is also very formidable. As the old Hindoo legend says, in symbolic language, Bagharata having taken the divine (jranga as his spouse in the midst of snows, raised her in his arms, and, mounting his chariot, traced with its two large wheels the banks of the wide bed of the goddess. But, when they arrived at the sea-shore, Ganga recoiled with aff'right before the impure and monstrous ocean ; she fled abruptly by a thousand channels, and since that epoch she comes and goes by turns, now venturing to descend, and now fleeing again toward the mountains, twice a day.* Fig. 42.— Profile of a Tidal Wave observed iu the Bay of tlie Seine (after M. Partiot)j» It is in the bay of the Seine that the mascaret, or " eager," has been most regularly and carefully observed. Flowing from the open sea with a speed of from fifteen to twenty feet per second, the liquid wall remains curved toward the centre, under the pressure of the fluvial current. The two points of the enormous crescent break in foam on the shores; while in the middle of the concavity, the even, rounded wave advances without even rippling the water before it. It seems to turn on the river like a gigantic serpent ; rising from six and a half to ten»feet above the liquid plain ; while behind it rise waves or eteules in concentric undulations quite as high, the advanced guard of the tidal mass. All the obstacles placed in the way of the mascaret irritate it by increasing its impetus; at length the tide, entering a wider and deeper part of the bed, gradually calms and moderates its height till it meets with another shallow or promontory. Moreover, each tide-wave is distinguished from the pre- * Carl Ritter, Von Hoff, Verdnderungen der Erdoberjidche, t. i., p. 378. 120 THE OCEAN. DiJce Korfh Fig. 43.— Height of the " Mascaret," or Tidal Wave, observed between Caudebec and Meilleraye (after M. Partiot). ceding by reason of the difference of winds, currents, and the masses of water put in motion. There is nothing more curious than to see, from the height of a promontory, two waves repelled obliquely by the banks crossing their furrows, and their eteules. Fig. 44 Plan of the ivscaret," or Tidal Wave, observed in the Narrows of the Seine (after M. Partiot). The sole means of diminishing the force of the masearet, which in sev- eral estuaries, and especially in the bay of the Seine, is sometimes danger- ous to small vessels, is to regulate the channel by deepening the shallows X ,^: /'■ Pig. 45.— Plan of two Tidal Waves crossing each other's course on the Banks of the Bay of the Seiuc (after M. Partiot). ' and straightening the banks. The works, which insure a freer and deeper channel for navigation, are those which prevent the injuries caused by the great violence of the tidal waves.* The mascaret of the Seine disap- peared recently for some years, owing to the elevation of a bank of sand * Partiot, Annates des Fonts et Chaussees, t. i., 1861, EFFECT OF THE TIDES OH BIVERS. 121 like a dike, which prevented the entrance of the tide into the bed of the river. The encounter of the mascaret and the fluvial current have again raised this bank of sand at a little distance. On striking against this new obstacle, the tidal wave rises up to surmount it. Different hydraulic works, undertaken in the beds of the Garonne and the Dordogne above-the Bec-d'Ambez, have also often modified the phenomena of the mascaret there. The sudden appearance of the tide in estuaries raises the fluvial waters very rapidly from the level of low to that of high water. At Tancarville, which is the precise spot where the Seine discharges itself into the bay, and where the tide exceeds a mean amplitude of about thirteen feet, the entire rising of the waters is accomplished in two hours, while the fall of the liquid mass, driven back by the tide, occupies about ten hours. The river having to discharge during the period of ebb not only that Avhich the flow had brought to it, but also the fresh waters from higher up, must follow its normal course toward the sea during a space of time longer than that in which it is driven back by the rising tide. For each point of the river-bed the duration of. the flow is generally the shorter the farther that point is from the sea: the force of the tide is gradually exhausted, and toward the end of its course it only momentarily retards the speed of the fluvial current. ^ 0° S jm^. -5=iS2 7y^ 4y^ Fig. 46.— Tides of the Garonne. The amplitude of the tides diminishes, likewise, in proportion to their progress up the stream in rivers. The mass of fresh water flowing inces- santly within the channel prevents the low tide from sinking, as it does on the sea-shore ; and as to the high tide, its shorter duration does not allow it to rise to a much higher level than that which it attains on the strands and cliffs by the ocean. Thus, in the Garonne, the difference be- tween the ebb and flow diminishes gradually above the Bec-d'Ambez; and near Castets, at about ninety-five miles from the sea, it is finally re- duced to zero. In certain places, it is true, particular circumstances may cause apparent exceptions to this general law ; a promontory rising be- fore the tidal wave like that of Tancarville, in the bay of the Seine, bars the way to the marine waters, and gives them, in consequence, a greater relative height above low water. But in spite of these abrupt projec- tions, the mean amplitude of the tide diminishes from the lower to the upper course, and finally it becomes imperceptible. 122 THE OCEAN. CHAPTER XV. EBB AND FLOW IN LAKES AND INLAND SEAS. — CUEEENTS OF THE EUEI- PUS. — SCYLLA AND CHAETBDIS. The attraction of the sun and moon acts no less on inclosed seas than on the great ocean; but in basins of small extent the tide has not the necessary space to rise and develop itself in an appreciable manner. Lake Michigan, whi®h, although not less than 56,000 square miles in. ex- tent, is the smallest surface we are acquainted with where the regular return of the ebb and flow have been established with precision ; the am- plitude of the tide there is, according to Lieutenant Graham, less than three inches. Still, it is undoubted that the smaller lake basins also experience normal oscillations every twelve hours : measures carefully made will probably reveal them one day. Even in the vast Mediterranean the tides are very little perceived, ex- cepting in the Gulfs of Syrtes, between the ancient Pentapolis and Tunis. In this part the phenomenon of the ebb and flow occurs with the greatest regularity, and one can study its progress as in the ocean. At the mouth of Oued-Gabes, almost at the end of the Lesser Syrtes, the water alter- nately rises and falls at least six and a half feet. More to the north, in the port of Sfax, the average difference between high and low water is about five feet, but at the epoch of the equinoxes this difference attains to nearly eight feet. Finally, at the Island of Djerbah, the ancient island of the Lotophagi, the mean amplitude of the tide is not less than nine feet ten inches.* This remarkable height of the tide on the shores of the Syrtes doubtless arises from the Mediterranean presenting in its southern part, from Port Said to Ceuta, a single basin, with a slightly sinuous bank, while on the coast of Europe it is divided into a number of smaller seas, those of Sardinia, the Adriatic Gulf, the Ionian Sea, and the Archi- pelago. Besides, the winds being much more regular on the African coast, the alternate play of the tides is not disturbed there, as on the coasts of Europe, which belong to the zone of variable winds. However, an attentive examination of the movement of the waves has equally revealed to observers the existence of the tidal wave in the par- tial basins of the northern shores of the Mediterranean. Beyond Malaga, where the tides of the Atlantic are still propagated, the level of the sea hardly changes ; but on the coasts of Italy the oscillations begin to be perceptible again. At Leghorn, the tide rises less than twelve inches ; at Venice, the difference between the high and low Avaters varies from one to three feet.f At the mouths of the Po the tide does not attain the same * Victor Guerin, Voyage Archeologique en Tunisie, 1. 1. t G. Collegno, Geologia delV Italia, p. 280. CURRENTS OF THE MEDITERRANEAN. 123 height. On the coasts of Zante, in the Ionian Sea, it is less than six inch- es ; tiually, at Corfu, it does not exceed an inch.* In the Oriental basin of the Mediterranean, the tide is likewise very slight; nevertheless, the al- ternate osciiration of the sea is not ignored by the people living on the 'shores. Omar spoke, doubtless, of the tide when he said, " The sea stands very high, and day and night it entreats the permission of God to inun- date the land." Not only has the Mediterranean its ebb and flow like the ocean, but it has also its currents and eddies, and among these phenomena there are some which, without being as formidable as the Moskoestrom or Blanch- ard Race, are not less celebrated, because of the glory with which clas- sical antiquity has invested them. Thus the Euripus, or Strait of Egripos, which separates the Island of Negropont from Continental Greece, is said to be traversed by extraordinary currents, which produce with regularity their surprising phenomena. Up to the eighth day of the lunar month, the ebb and flow, whose mean amplitude is less than a foot, follow one another in a normal manner, only Avith one hour's delay ; but from the ninth to the thirteenth day the movement of oscillation is suddenly has- tened, and during the twenty-four hours no less than twelve, thirteen, or fourteen tides may be counted, each one having its flow, its period of stability, and its ebb. From the fourteenth to the twentieth day a nor- mal state of things prevails ; then, from the twenty-first to the twenty- sixth, everj^ day will again be marked by a series of a dozen high and low tides. Such is the result of the experiences of the millers, who see the wheels of their mills turn alternately one way and the other, accord- ing to the direction of the current. f On their side, the Mussulmans main- tain, as an article of faith, that the five waves of the Euripus regularly follow the five hours of prayer ;J finally, the rapid observations of several travelers describe in still another manner the oscillations of the sea in the narrow channel. The fact is, that the currents of the Strait of Negropont are unexplained, and if they succeed one another in as strange a mannen as the inhabitants of those shores affirm, one would really comprehend the legend, according to which Aristotle, after having vainly sought to divine the mystery, plunged in despair into the whirlpools of the EurijDUS. Still more famous than the currents of the Strait of Euboea were the abysses of Scylla and Charybdis, braved for the first time by the wise Ulysses. According to the Homeric chants, the two howling monsters which guarded the entrance to the Straits of Messina drew into their submarine caverns immense whirlpools of water, which they afterward discharged in furious currents, and all the ships which approached those formidable caverns were inevitably ingulfed. At present there are no straits in the Mediterranean more frequented than those of Messina, and, owing to the soundings effected in these pretended abysses where the ancients saw the navel of the sea, the monsters have lost their terrible * Von HofF, Verdnderungen der Erdoberfldche, t. iii., p. 256. t Berghaus von Kloden, Handbuch der Erdkunde. % J^atur, t. viii., 1864. 124 THE OCEAN. prestige. It is now known that the whirlpools of Charybdis and Scylla are nothing else than lateral movements produced by the ebb and flow, in their passage through a too narrow channel, whose width is hardly two miles, and which the conquerors of Sicily have more than once crossed by swimming on their horses. At the time of the rising tide the isurrent tends to the north, from the Ionian to the Tyrrhenian sea ; at the fall of the tide, the stream coming from the north assumes the preponderance, and drives the contrary current toward the south.* But there is a strife between the two liquid masses, and the field of battle moves incessantly from Messina to Scylla. On the confines of the currents, where the min- gling of the waters is effected with violence, narrow eddies are formed, where the waves are more agitated than elsewhere; these are the "eye- lets," or garofali. Ships avoid them, for fear of being too violently shaken ; but they run no danger unless the wind blows strongly in a contrary di- rection to the tide. The strait is a curious spectacle, seen from the height of the mountains of Messina or Reggio, with the undulations and eddies that the conflicting waters describe ; every instant sheets of water of a darker tint than those of the surface are seen to change their form, in- dicating the ebb and flow. SidKa'^ I ^. ^. ^^ ^ CalabrG CO Mg. 47. — Profile oi ihe MiaiN ol Ivle^sina. In the other inclosed seas of Europe the tides are likewise little felt. They are less than sixteen inches on an average in the Zuyder Zee, and during the days of the equinox or of tempests they hardly attain three feet six inches. The Baltic, which is much narrower, and more strewn with islands than the Mediterranean, is subject in consequence to much slighter oscillations ; it was even called in former times morimarusa {mor y marb) — that is to say, in Celtic language, "Dead Sea."f The sailors pay no at- tention to the variations of the surface produced by the ebb and flow : for them the winds, the currents, and the meteorology of the atmosphere are the only phenomena which they have to observe. In fact, on the western coast of Jutland the tide is on an average less than twelve inch- es;- at the entrance to the Categat it loses still more in force and regu- larity ; and in the straits of the Sound and the two Belts it is difficult to recognize. In the harbor of Copenhagen an oscillation of about one or two inches can still be sometimes distinguished, but only when the w^eath- er is perfectly calm and the surface of the water hardly rippled. At Wis- mar the phenomena of the tide are still more uncertain ; and it is only by * Spallanzani; Von Itoff ; Smyth. t Von Maack, Zeitschrift fur die Erdhmde, I860. DIFFERENCE IN TIDES. 125 a series of observations on the surface of the Avaters pursued during sev- eral years that the probable existence of a total variation of little more than three inches between high and low water can be ascertained. Near Stralsund the difference is only one and a half inches, and near Merael it hardly exceeds an inch. The much more considerable variations which occur in the level of the sea arise from the winds, the currents, or the pressure of the atmosphere. Rapid oscillations of nearly three feet have been sometimes seen to occur ; but these are the seiches, similar to those of the Lake of Genoa.* The force of the winds alone is sometimes suf- Hcient to lower by little more than three feet the level of the sea in cer- tain straits, as well as in the gulfs of Esthonia and Finland.f The laws of the phenomena of the mouths of rivers difler entirely in the seas with strong tides, as the Northern Atlantic, and in those with insen- sible oscillations, like the Baltic and the Mediterranean. L> the estuaries, where the sea rises regularly twice a day to a great height, it passes over every obstacle, bars, or sand-banks accumulated at the entrance to the mouths of rivers ; while in those places where the level of the sea remains always the same, the dikes of mud or sand dej^osited parallel to the coasts between the fresh and salt waters always close the entrance^ the river. Thus the Rio Magdalena and the Arato, in the Antilles ; the Rhone, the Po, and the Nile, in the Mediterranean, spread their liquid mass over bars which are often hardly a yard at the lowest part ;J while the river of the Amazons, the St. Lawrence, the Gironde, and the Thames, allow free pas- sage to ships at all hours. This diversity of fluvial laws, according to the height of the oscillations of the tide, has the most important consequences for the commerce of regions watered by great rivers. In general, the ports of the rivers with- out tide can not be established at the mouth itself, because of the want of water, and merchants are obliged to choose a locality situated on the sea-coast at a certain distance from the sandy mouths of the river for tfieir emporiums. Thus Marseilles, Avhere almost all the commerce of the great basin of the Rhone is transacted, is constructed on the shores of a deep bay of the Mediterranean, far from the peninsulas of mud between which the river discharges itself Alexandria, the great port of the Egyp- tian delta, lies to the west of the alluvial delta of the Nile ; Venice is far from the mouths of the Po ; Leghorn protects its port from the approach of the Arno ; Barcelona is not at the entrance to the Ebro ; and Cartha- gena, in the West Indies, and Santa Maria are only in communication with the great Magdalena by means of hardly navigable canals. The excep- tions to this rule ai*e not very numerous ; still we may cite Dantzig on the Vistula, Stettin on the Oder, and Galatz on the Danube. § In seas with high tides the principal ports are found, on the contrai'v, * See the chapter entitled Lakes. f Von Sass, Bulletin de rAcadeinie de St. Petersbourg, t. viii., 6. t See the chapter entitled Rivers. § Ernest Desjardins, De l embouchure du Rhone. 126 THE OCEAN. not on the maritime coast-line, but on the rivers, and even at a certain distance from the mouth, not far from the place where the tide rises twice a day, thus changing the river into a true maritime gulf. London, Ham- burg, Nantes, Bordeaux, Rouen, and many other great commercial cities, have been gradually built, in consequence of the necessities of commerce^ as far as possible inland at the precise spot where the depth of water and the force of the tide allow ships to approach easily. Nevertheless, since the ships of the present day draw much more water than those of our ancestors, the result is that a number of ports on rivers have become in- sufficient. It is thus that Rouen has been gradually replaced by Havre as the port for international commerce. Thus Nantes, too, has. seen in these days a rival city grow up in the village of St. Nazaire, so modest but a few yeai'S ago. Perhaps the hamlet of Verdon, provided sooner or later with docks, basins, and jetties, will become likewise the real com- mercial Bordeaux. DEPOSITS AT TUE BOTTOM OF THE SEA. i27 BOOK IV.— THE SHORES AND ISLANDS. CHAPTER XVI. INCESSANT MODIFICATIONS OF THE COAST LINE. — THE FIORDS OF SCANDI- NAVIA AND OTHER COUNTRIES NEAR THE POLES. The sea, every wave of which contains perhaps thousands of living organisms, seems itself to be animated by a vast and mighty life. Ever- changing hues, dark as fog o^ brilliant as the sun, pass over its immense extent, its surface ripples in long undulations, or rises in bristling waves ; its shores are touched with a border of foam, or disappear under the white mass of breaking surf Sometimes it breathes a scarcely audible murmur, and again it combines in very thunder the roarings of allots waves dashed and broken by the tempest. By turns it is smiling and terrible, gracious or formidable. Its aspect fascinates us ; and as we walk along its shores, it is impossible to avoid contemplating and inter- rogating it ceaselessly. Ever moving, it symbolizes life, in distinction to the silent and passive earth which it assaults with its waves. And besides, is it not always untiringly at work to modify the contour of the continents, after having once formed them layer by layer in the depth of its waters? The most important part of the geological labors of the ocean is hid- den from our eyes ; for it is at the bottom of its abysses that the sea de- posits the silica, limestone, chalk, and conglomerates of every kind which will one day constitute new lands. But at least we can witness the con- tinual modifications to which the incessant movement of the sea subjects the shores. These modifications are considerable, and during the his- torical ages a number of coasts have already completely changed their form and aspect. Promontories have been razed, while at other parts points have advanced into the waves ; islands have been transformed into reefs; others have been entirely swallowed up; others again joined- to the main-land. The sinuous line of the shore has not ceased to oscil- late, encroaching here on the waters of the ocean, and there on the con- tinental surface. The action of the sea is double ; it is constantly re- touching the contours of its basin, either by wearing away the rocks that border it anS carrying away the strand, or by casting uj) on its coast the alluvium and wreck of every kind that it tosses in its waves. All that it ingulfs on one side it gives back elsewhere under another form. Before the sea had modified its shores by destroying peninsulas and filling up bays and estuaries, the form of the coast was certainly much 128 THE OCEAN. less regular than it is now in the outline of most countries. If the ma- rine waters were raised by a sudden revolution to 100 or 200 yards above their present level, the ocean, inundating all the river valleys to a very great distance from the present shores, would suddenly enter in elongated gulfs into the depressions of the continent, and change. all the valleys and lateral gorges into bays. In the place of each of those river- mouths which hardly indent the normal line of the coast, deep hollows would be opened, dividing into numberless ramifications. But a work in the opposite direction will instantly be commenced when this change in the outline of the shores is accomplished. On the one side, the water- courses, bringing down their alluvium, will gradually fill the upper val- leys, and little by little restrict the domain of the maritime conquests. On the other side, the ocean will also labor by its dunes along the coast, its banks of sand or shingle, to take away from its surface all those new bays that the sudden increase of its watei^s had given it. After an in- definite lapse of centuries, the shore would finally re-assume the gently undulated form that the greater number of coasts now present. Fig. 48. — Lysefjord, Norway. There are still many counti'ies where this double work of the sea and the continental waters has hardly commenced. Those lands whose coast- line, thus preserving its first form, is still deeply indented, are all situated •at a great distance from the equator, in the neighborhood of the Polar zone. In Europe, the western coasts of Scandinavia, from the promontory of Lindesnaes to the North Cape, are jagged by a series of these j^'ort?^,* or ramified gulfs, and not only the shore of the continent, but all those isl- ands also which form a sort of chain parallel to the Norwegian plateau, are fringed with peninsulas and cut into by small fjords, winding in im- mense passages. Among these indentations, which increase the length of the coast tenfold, and give to the coast-line a border of innumerable peninsulas, more or less parallel, some are pretty uniform in aspect, and * Called in Scotland ^ri/is. SEA-LOCHS AND FJORDS. 129 resemble enormous trenches, hollowed out in the;^thickness of the conti- nent ; others are divided into several lateral fjords, which make the in- land waters an almost inextricable labyrinth of channels, straits, and bays. The total development of the coasts is so much increased by these indentations, that the western shore of the peninsula, whose length in a straight line is about 1180 miles, is increased to above 8000 miles by the bends and turnings of the shore, Avhich is more than the distance from Paris to Japan. ChrLitiausliaai '/ •^i^le-Jjordy Fig. 49.— Fjords of Greenland. The plateaux of Scandinavia, terminating abruptly above the North Sea, the slopes which command the somljre defiles of the fjords, are al- most always very steep; there are some which rise in perpendicular or even overhanging walls, serving as a pedestal to high mountains. It is thus that the Thorsnuten, situated to the south of Bergen, on the shores f)f thg Hardanger Fjord, attains an elevation of above 5250 feet at less than two and a half miles from the shore. In many a bay of Western Norway cascades are seen to leap from the top of the cliff, and precipi- 9 130 THE OCEAN. tate themselves in onejet into the sea, so that vessels can glide between the walls of the rocks and the parabola of the roaring cataracts. Below the water the escarpments are continued also in most of the gulfs, so that in certain defiles of rocks, whose breadth from cliif to cliif is only from 300 to 600 feet, the lead must be thrown to a depth of from 272 to 32*7 fathoms before touching the rocky bottom.* In the " Toilers of the Sea," Victor Hugo correctly cites the Lysefjord as most fearful to con- template among its gloomy approaches, many of which are forever de- prived of a ray of sun by the high walls of rocks which inclose them. Mouths of Cattaro. This enormous putting, of an almost perfect regularity, penetrates above 26 miles into the interior of the continent, though in several places it hardly exceeds 1965 feet in breadth; its walls rise to 3270 and 3600 feet in height, and near the edge the lead only touches the ground at about 220 fathoms.f Doubtless the first seaman who sailed over the dark, tranquil waters of this abyss must have advanced with a sort of hor- ror, asking at each new turn of the approach whether he was not going to see some terrible god rise before him. Even now it is not without a shudder that one penetrates into this gloomy defile, where the ancients would doubtless have seen the entrance to the infernal regions. ^ ' * Berghaus, Was man von der Erde weiss, p. 280. t Vibe, Kiisten und Meer Norwegens, Mittheilungen von Petermann, 1860. FJOBDS OF SOUTH AMERICA. 131 The islands of Spitzbergen, Faroe, and Shetland present also in their outline hundreds of fjords, like those of Scandinavia. The coasts of Ice- land, Labrador, and Western Greenland, those of the islands of the Polar Archipelago, and finally the American coast-line of the Pacific, from the long peninsula of Alaska to the labyrinth of Vancouver's Islands, are no less rich in indentations than the coast-line of Norway. The shores of Scotland are deeply cut in the same way, but only on the western side, where there are besides numerous islands reproducing in miniature the maze of promontories and bays of the main-land. That part of Ireland turned toward the open sea develops itself also into a succession of rocky peninsulas, separated by narrow gulfs; but to the south and east the coasts of the British Islands are much less varied, in form, and sweep in long, regular curves. In France we hardly find a vestige of indentations like those of the Norwegian fjords, except at the extremity of Brittany ; and ther.e does not even exist a word in the language to designate them. Fig. 51.— Fjords of South America. In Spain, in the same way, the part of the peninsula turned toward the north-west, and where the ports of Ferrol and Coruiia open, is the only one which presents some lines of fjords half filled up. Two countries on 132 THE OCEAN. the borders of the Mediterranean have their coasts also cut into fjords, partially obliterated by alluvium; these are Asia Minor and Dalmatia, whose high mountains, formerly covered with glaciers, overlook narrow bays with fantastic outlines like the mouths of Cattaro ; but along these two shores the peninsulas of the coast-line are still uaiformly turned to- ward the west. To the south of the Adriatic and the Archipelago, on the coast-line of warm or torrid countries, no more fjords are seen. To find a similar formation of shores we must traverse the entire continent of America to its southern extremity. The fjords only commence beyond the uniform coast-line of Chili, with the Island of Chiloe, its numerous bays, and the net-work of straits in the Archipelago of Magellan and Terra del Fuego. This is the only region in the southern hemisphere where the astonishing phenomenon of tortuous and deep valleys filled by the waters of the sea is witnessed. As to the countries of the Antarctic continent, no inden- tations can be recognized in them, since the contours of the bays and capes, the gulfs and peninsulas, are all filled by the snouts of glaciers and by continuous ice-fields. FILLING UP OF FJORDS. 133 CHAPTER XVII. FILLING UP OF THE FJORDS BY MARINE AND FLUVIAL ALLUVIUM. The comparative study of all the shores leads thus to the confirmation of this fact, that fjords are only met with on the coasts of cold countries, and tl]§,t, with equality of temperature, they are much more numerous and better developed on the western coasts than on those turned to the east. Why does this strange geographical contrast occur between the various shores, according to the position which they occupy to the north or south, to the west or east? Why have the strands, and even the cliffs, bathed by a warm or temperate atmosphere, assumed in the outline of their curves such a great regularity, while the valleys, opened in the thickness of the plateaux of Scandinavia, Greenland, and Patagonia, have preserved their primitive form? A cause whose effects are produced at the same time and in the same manner at the two extremities of the continents, in the northern islands of America and Europe and in the Magellanic Isles, must necessarily have been a great geological phenome- non, acting during an entire age of our planet. This phenomenon was the special climate which during the glacial pe- riod made itself felt on the surface of the globe, and transformed the mountain snows into long.rivers of ice. The map speaks for itself, so to say ; it relates clearly how the fjords, those ancient indentations of the coast-line, have been maintained in their primitive state by the prolonged sojourn of glaciers.* In fact, the cold period, the unequivocal witnesses of which are still to be seen even in the tropics and under the equator, at the foot of the Andes and in the valley of the Amazon, naturally lasted longer in the vicinity of the poles than under the torrid zone, and in the temperate regions. This glacial period, which terminated perhaps thou- sands of centuries ago on the burning shores of Brazil and Colombia, has ceased at a relatively recent epoch on the coasts of France and England. At an age still nearer our historical time, the fjords of Scandinavia have been in their turn freed from the glaciers that filled them ; while quite in the extreme north and in the Antarctic regions there are countries where the rivers of ice still descend into the sea, and stretch far into the gulfs. The glacier of the Bay of Magdalene, which Messrs. Martins and Bravais have explored, projects far into a fjord which is fifty-five fathoms deep; and the terminal cliff of ice, driven out by the weight of the upper snows, presents a curved line, turning its convexity toward the open sea. On still colder coasts, such as the north of Greenland, and at the South Pole, the outline of the Antarctic countries, even the bays are entirely filled up with ice, and this running into the sea gives a regular * See the chapter entitled Snow and Glaciers ; Oscar Peschel, Ausland, 1866. 134 THE OCEAN. outline to the whole coast. The waves of the open sea dash against a long wall of crystal, and the icy layers disguise the true form of the ar- chitecture of the continents, as the fluvial alluvium and marine sand-banks do in other climates. Nevertheless, deep valleys, hidden by the ice-fields, are also cut into the line of these polar coasts too, and in a future geo- logical period, when the ice shall have disappeared, these incisions of the continent Avill become in their turn fjords, similar to those of Scandinavia. At the epoch when the bays of Scandinavia were filled with ice, as those of Northern Greenland are in our days, they preserved their primi- tive form, excepting that the lateral walls and the rocks at the|f)ottom were grooved and polished by the friction of the mass in movement and the fragments which it carried with it. The blocks of stone fallen on the snow and on the surface of the glacier, the heaps of pebbles and eai'th torn by storms and thaws from the sides of the mountain, formed moraines exactly similar to those which are now seen on the diminished glaciers of the Scandinavian mountains. But these moraines, instead of crumbling away with the ice, in some valleys thousands of feet above the sea, were carried to the very mouths of the fjords in the open sea, and plunged into the middle of the waves with the pieces detached from the glacier itself The successive debris of rocks and pebbles must nec- essarily gradually raise the frontal submarine moraine ; and, in fact, at the entrance of all the Scandinavian fjords heaps of deposit are found ris- ing like ramparts out of the deep water. The seamen of Norway give the name of " sea-gates " to these natural barricades, which serve as limit • to the ancient glaciers, and where the fish from the neighboring waters assemble in myriads. Ofi" the coasts of Western Scotland, as at the en- trance to the small gulfs of Finisterre, the ridges of submarine banks and reefs are observed, which are probably nothing else than ancient terminal glacial moraines. After the period which preceded the present era, the glaciers of Scandi- navia retreated little by little into the interior of the fjords, then ceased to touch the level of the sea, and their lower extremity mounted higher and higher in the open valleys on the sides of the mountains. It was then that the immense geological labor of filling up the bays commenced for the torrents and the sea. The fluvial waters brought their alluvium, and deposited it as an even strand at the foot of the mountains, while the sea leveled with sheets of sand or mud all the fragments of rocks which it had worn away by its waves. Already in a great number of Norwegian fjoi'ds this work of transforming the domain of the waters into firm land has made very sensible progress, and if we knew the amount per century of the augmentation to the shores, we should be able to calculate approximately the epoch at which the valley was free from ice. On the inclined eastern side, toward the open country of Sweden, an analogous work is accomplished; there the glaciers have been re- placed, not by the waves of the sea, but by the lacustrine waters divided into different basins, and these waters also retreat gradually before the The Ocean. <^c. FJORDS OF NORWAY. PL. V III. , ' l^" ' /V . '"^ '■ <" s x,J\'*^'" ^M »^'ii v.\ 'Engra.vBcl.Jy'ErhaL li 1.250000 Mies o a w VOAST-LJNES MODIFIED BY CLIMATE. 185 alluvium of the torrents. In the same way, in the great chain of the Swiss Alps, several deep depressions, formerly the beds of immense gla- ciers, have become a sort of continental fjord, such as the lakes of Mag- giore Iseo, Lugano, Como, and Garda.* These lacustrine basins are closed at the south by large moraines, like the sea-gates of Norway, and their waters, like those of the fjords, are gradually displaced by the al- luvium brought down by Alpine torrents. Fig. 52.— Ancient Fjords of Northern Italy. Situated more to the south than the fjords of Scandinavia, and nearer the source of the warm current flowing from the Antilles, the western bays of Scotland must have been free from ice long before the coasts of Norway, and it was still earlier that the indentations of the coast-lines of Ireland and Brittany ceased to serve as beds to the solidified snows of the surrounding mountains. As to the shores of the British Islands turned to the east toward the North Sea, they have certainly long been freed from ice, for then, as now, the winds from the west and south-west prevailed in Europe, and carried the rains over the slopes of the mount- ains inclined toward the Atlantic ; on the opposite slope the glaciers are sooner melted, because of the want of the necessary moisture. This is the reason of the striking contrast presented in the British Isles and Ice- * Oscar Peschel, Ausland, 1866. 136 THE OCEAN. land by the western coasts all cut into deep bays, and the eastern shores whose fjords are less deep, or even completely obliterated by alluvium. In the same way, at the south of America, the rains being much more abundant on the western slope of the mountains of Patagonia, the gla- ciers have descended much lower into the valleys, and the fjords, pre- served by the ice in their primitive state, make all this part of the Amer- ican coast-line a real labyrinth. The form of the continents themselves must be explained by the movements of the atmosphere. Fig. 53.— Fjords of the Sonth-east of Iceland. After the retreat of the glaciers, the work of rendering the shores reg- ular goes on in the various countries with more or less rapidity, accord- ing to the form of the continents, the depth of the fjords, and all the phe- nomena which constitute their geographical circumstances. In certain countries where the rivers are of little importance, as in the peninsulas of Denmark and in Mecklenburg, the fjords are first closed on the sea- ward side, and then become long and narrow lagunes, separated from the salt waves by the sandy beaches. Those gulfs, on the contrary, where great rivers discharge themselves, are gradually filled up by alluvium in those parts the farthest from the ocean, and are changed little by little into estuaries. Finally, many shores, ainong others those of eastern Ice- land, present a great number of fjords, one beside the other, which are FILLING UP OF FJORDS. 137 luxn-owcd at tlie same time above and below by the deposit from the sea, and that of the streams from the interior. It is thus tliat a multitude of ancient gulfs in Scandinavia, England, and France have been gradually changed into dry laud. The gulfs of Christiansand, in Norway, of Ca- rentan, in France, formerly projected in all directions from deep abysses, the place of which is occupied now by fields and marshes. ^r& Fig. 54.— Filled-up Fjords of Christiansand. Whatever may be the diversity of means employed by nature in filling np the ancient glacial bays, the labor is accomplished in due time, and we may state that from the temperate to the equatorial zone the curves of the shore increase in regularity. The innumerable ports which pene- trate deep into the northern lands are succeeded in the south by more and more inhospitable maritime shores, because of destitute indentations. And on the coasts of the torrid zone, which are destitute of the mouths of rivers, vessels must sail along for hundreds of leagues before finding a harbor of refuge. It is the three southern continents, South America, Africa, and Australia, which present in their outline a most uniform de- velopment of coast and are most destitute of bays. If we can rightly consider each glacier as a natural thermometer, indi- cating by its advance and retreat all the changes of local temperature, we may in the same way regard the general character of the coasts, from the fjords of Greenland and Norway to the' long shores of Equatorial Africa, as a visible representation of the changes of temperature which have taken place on the surface of the globe since the glacial epoch. If 138 THE OCEAN. Pig. 55.— Ancient Fjords of Carentan. by long and patient study we succeed in measuring the time which is necessary for the alhivium of the sea and rivers thus to modify the forms of valleys once filled with ice, we can then estimate the amount of time which has elapsed since the glacial epoch. This vague period, which ac- cording to various geologists comprehends thousands or millions of years, will assume, at least for the times nearest to us, a more precise meaning, and will arrange itself like the centuries in the chronology of mankind. ENCROACHMENT OF THE SEA. 139 CHAPTER XVin. DESTRUCTION OF CLIFFS.' — THE COASTS OF THE CHANNEL. THE STRAITS OP DOVER. ACTION OF SHINGLE AND SAND. GIANTS' CALDRONS. SPOUTING WELLS ON THE COASTS. — TIDAL WELLS. Although there is necessarily an equilibrium between the work of dem- olition and that of reconstruction, we would nevertheless, at first sight, be tempted to believe that the sea took the greatest pleasure in destruc- tion. On contemplating the cliffs, those perpendicular walls which on various coasts rise many hundreds of yards above the level of the sea, we are struck with awe to see how the repeated assaults of the waves have been sufiicient thus to cut the mountains and hills whose bases were formerly gently sloped to the water. From the top of these cliffs, we see the tumultuous ocean spread at their feet like a ^^lane surface, and we no longer distinguish the billows but by their reflections, or the ' breakers but by their garland of foam; the multiplied sound of the waves melts into one long murmur, which dies away and rises to die away again. And yet this water, which we see below at such a great depth, and which seems powerless against the solid rock, has thrown down piece by piege all that part of the hill or mountain, of which the cliff is but a gigantic memorial . then, after having thrown down these enormous masses, it has reduced them to sand, and perhaps caused the very trace of them to disappear. Often not even a rock remains where promontories once jutted out. The phenomena ascertained even during the short life of man are facts so grand in their progress, and so remark- able in their effects, that an English savant, Captain Saxby, has proposed to make of them a special science, Ondavorology.'^ To gain some idea of the destructive force exercised by the waves of the ocean, it is sufficient to contemplate them on a tempestuous day from the height of the chalky cliffs of Dieppe or Havre. At our feet we see the army of whitening billows rush to the assault of the rocks. Driven at the same time by the wind, the tide, and the lateral current, they leap over the rocks and shelves of the shore, and strike the base of the cliffs obliquely. Their shock causes the enormous walls to tremble to the veiy summit, and the roar reverberates in all their angles with an incessant thunder. Dashed into the fissures of the rock with terrible force, the water sweeps away all the clayey and chalky matter, and gradually M,ys bare the solid beds, wrenches large blocks out of them, I'olls them on the strand, and breaks them into shingle, which it drives along with a dread- ful noise. Through the eddy of boiling foam which besieges the shore, one can only now and then perceive the work of demolition ; bivt the * Nautical Magazine, January, 1864. 140 TH^ OCEAN. Fig. 56.— Eoads of tlie Downs. waves are so laden with fragments that they present a blackish or earthy color, as far as the eye can reach. When the storm has ceased, the encroachments of the sea can be meas- ured, and we can calculate the millions of cubic yards of stone ingulfed or ENCROACHMENT OF THE SEA. 141 transformed into shingle and sand. Toward the end of the year 1862, during one of the most terrible tempests of the century, M. Lennier saw the sea batter down the rocks of La Ileve to a thickness of more than fifty feet. Since the year 1100, the waters of the Channel, aided by rain, frost, and other agents, that act strongly on the upper strata, have cut down this cliff by more than 1500 yards — that is to say, more than two yards per year. The spot where the village of Sainte Adresse formerly stood has given way before the flood, and is replaced by the bank of I'Eclat.* ]M. Bouniceau, one of those savants who have specially studied the phenomena of erosion of shores, estimates the fraction of cliff which is carried away by the sea on the coasts of Calvados at above a quarter of a yard on an average yearly, while on the coasts of Seine Inferieure the annual erosion may be considered as nearly a foot. In some places on the southera and eastern coasts of England, the in- vasions of the sea take place with an equal or even superior rapidity, for the farmers generally count on the loss of about a yard per year along the cliff.f To the east of the peninsula of Kent, the waters have ad- vanced more than three miles toward the west since the Roman period. In their successive invasions, they have subnlerged the vast domains of the Saxon Earl Goodwin, and have replaced them by the terrible Good- win Sands, where so many ships are lost every year; and they have transformed the narrow lagune of the Downs into great open roads. Ac- cording to the calculations of M. Marchal,J the total amount of denuda- tion which the waters of the eastern part of the Channel carry on every year is equal to above thirteen millions of cubic yards. The Straits of Dover are being continually enlarged by the action of atmospheric influences, the waves, and the current which flows from the Channel into the North Sea, The patient researches of M. Thome de Gamond, an engineer to whom we owe the fine project of the interna- tional tunnel between France and England, have proved that the cliff of Gris-Xez, the nearest point of the French coast to Great Britain, loses on an average more than twenty-seven yards per century. If in former ages the progress of erosion was not more rapid, it would be about 60,000 years before the present epoch that the isthmus connecting England with the continent was broken by the pressure of the waves. Xevertheless, it is impossible to indicate any date, since at this place the ground has sunk and risen at various intervals: ancient beaches four or five yards above the present level of the sea, as well as submerged forests, testify to these successive oscillations.§ Along the coast of France, to the east of Cape Antifer,the pebbles re- sulting from the denudation of the cliffs are continually advancing to- ward the mouth of the Somme. Arrested at about six miles beyond these ^ * Lamblardie, Bande, Revve des derix Mondes. " t Beete Jukes, School Manual of Geology, p. 90. \ Annales des Fonts et Chaussees, ler sem., p. 201. § Day, Geological Magazine, 186G. 142 TEH OCEAN. last flinty cliffs, by the promontory of Hourdel, so named from the dash {heu7^t, Fr.) of the waves, they are subsequently taken up by the current which runs toward the strait. Ti-iturated more and more, they travel from sand-bank to sand-bank, and after having passed the strait, are de- posited in beds of mud either on the surface of the innumerable banks of the North Sea, or on the coasts of Flanders, Holland, and eastern En- gland, It is these deposits which are called by the expressive name of gain de flot (" winnings from the waves "), in the neighborhood of the G'-wAV'-ofParfe nil)] ki^^a^ _ w G^J5 W.of Pairis Fig. 57.— Map of Abervrac'h. Channel. The ten millions of cubic yards of fragments taken annually from the cliffs of- Sussex and Kent, as well as from those of Calvados and the Pays de Caux, are carried back to the coasts of the northern coun- tries, and it is at the expense of the shores of the Channel that the pol- ders of Holland and the Fens of Norfolk and Lincolnshire are formed. In consequence of this double work of erosion at one point and deposit on another, the shores situated to the north of the straits pr^ent a perfect contrast with the coasts of the Channel. While the cliffs of France and England, on the borders of this sea, are cut into concave bays, the beaches EROSION OF CLIFFS. 143 which stretch to the north of the Straits of Dover uniformly exhihit a convex arrangement. The waves give back in sand and mud what they have taken in rocks and boulders.* We must not think that it is the force alone of the breakers that de- molishes the cliffs along the shore. The sea Avould be almost powerless* against the hard rocks ■ if, on approaching the shore, it was not charged with all kinds of debris, blocks and pebbles, sand and shells — projectiles which are hurled by every wave against the cliffs which oppose them. Fig. 58.—" Giants' Caldrons " of Haelstolmen. Using thus the stones that have fallen as so many battering-rams, the billows roll them over the strand to the foot of the cliffs, dash them against the projecting points, and finally break off masses and reduce them to sand. The sand itself, incessantly washed against the rocks, weai'i away the most solid layers little by little, and thus continues the work of destruction commenced by the shingle : it is in great part the fragments of the promontory itself which serve to further its destruc- tion. On all the rocky coasts of Scandinavia, Scotland, Ireland, and Brit- tany, the multitude of reefs that extend seaward for a great distance from the shore are nothing else than the ancient foundations of the conti- nent, which have been gradually razed by denudation to a level with the Fig. 59.— Section of the "Giants' Caldrons," of Haelstolmen, taken aloug the line a b, in Fig. 58. water. From the top of any hill on the coasts of Paimpol, Morlaix, and Abervrac'h, we may thus distinguish at low tide what was the primitive form of the shore. ■" Marchal, AnnaJes des Fonts et Chause'es, ler sem., p. 204. 144 THE OCEAK The deep and regular excavations known under the name of "Giants' Caldrons " are the most curious of the geological feats accomplished by the scattered blocks. Every stone reposing on a ledge of the rock where the waves break hollows out during the course of ages a kind of well, the walls of which are polished, and planed by the friction. Finally, these cavities, where the gradually rounded stone does not cease to oscil- late, acquire a depth and width of several yards, and these are then, ac- cording to tradition, the caldrons where the giants prepared their repasts in former times. Very remarkable excavations of this kind exist on the coasts of Scandinavia, where blocks of granite, rolled along by a furious sea, are retained by abrupt rocks in a great number of cavities. A phenomenon not less interesting than the revolving of the stones in the giants' caldrons is the sudden a|)pearance of columns of sea-water, which spring in jets through the fissures of the rock. When a large wave is swallowed up in one of the fissured caverns on the coast, its force is sometimes so great that the rock resounds as with the discharge of artillery. The mass of water drives the air before it, and, not finding in the" walls that surround and compress it a large enough space to develop itself, springs through the crevices of the vault. Most of these fissures, gradually sculptured anew by the waters which escape from th%m, at length assume the appearance of real wells, where each return of the wave is signalized by a sort of geyser of variable dimensions. There are some which spring several yards high, and can be seen at a great dis- tance, like the jet of water by which the whale betrays himself afar off; hence arises the name of blowers {souffleurs) given in many countries by sailors to these phenomena on the shore. Fig. CO.— Tidal Wells. The pressure of .the tide does not make itself less felt than the force of the waves in the interior of the fissured rocks of the coast. It does not, it is true, cause magnificent fountains to spring far above the sea, but it lowers the level of the water in all the wells near enough to the shore; even in those that are filled with fresh water. And this is what theory could have indicated beforehand ; the mass of water that penetrates far into the crevices of the rock retains the waters which infiltrate from the interior; the latter, salt or fresh, remain in their reservoirs, and rise at the same time as the tide ; then, when the ebb commences, they flow into the MARINE GROTTOES. I45 sea, find overflow again as soon as the pressure of the ^sing water ceases. Where the rocks of the coast are much fissured, which is ahiiost every- where the case with cliffs composed of calcareous strata, there exist these "tidal" wells, which rise and fall alternately with the tide. We may specially cite those of Finland, near Wasa, those in the environs of Roy- an, on the right bank of the Gironde, and, above all, those of the Bahama Islands. In many of these islands, all the wells, without exception, are I'egulated by the flow of the sea,* There are even certain coasts opening so deeply into large hollows, on the side toward the sea, that the waves penetrate to a great distance into the interior of the continent. A curious example of this is seen in that part of Louisiana known under the name of the Attakapas. There the prairies of the coast, protected against the tempests of the Gulf of Mexico by chains of sand-banks and long islands parallel to the shore, incessantly gain upon the ocean. But they are only solid on the surface, for their roots are bathed by the sea-water, which advances far into a bay with invisible outlines. The fishermen do not fear to venture on these float- ing meadows, resembling fens in every respect, and it is by piercing the ground xinderneath their feet that they procure the fish hidden in these retreats. Nevertheless, such floating shores can only exist on a small number of coasts, where the physical circumstances are quite exceptional ; usually it is by grottoes and caverns hollowed out of the solid rock that the wa- ters of the ocean penetrate fa^j into the land. It is not to be doubted that there are below the level of* the sea multitudes of those rocky gal leries, but only those are known that are open to the strike of the waves, like the azure grotto of Capri. Lower down, the water closes the en- trance to the lateral caverns, which will doubtless long remain unknown to us. But if we can not explore grottoes still filled by the sea, we can at least see on elevated coasts like those of Scandinavia immense caverns which the waves once freely traversed. One of the most impos- ing grottoes in the whole world is that which penetrates the splendid rock of Torghatten, rising like an enormous pyramid to more than 900 feet, on an island of Northern Norway. This gallery, through which sea- men see the light glimmering, is of an astonishing regularity. The thresholds of the immense jDortals, one of which has an arch of nearly 234 feet, and the other of nearly 144 feet span, are found on each side to htve the same elevation of 375 feet above the level of the sea. The ground, covered with fine sand, is almost level, and formed like the floor of a tunnel, where carriages might roll. The lateral walls present almost throughout a polished surface, as if they had been cut by the hand of man, and rise vertically to the spring of the arch ; only toward the cen- tre of the grotto the vault is less elevated than at the two extremities. Seen through this gigantic telescope, 900 feet long, the promontories, islets, innumerable reefs, and the thousand white crests of the breakers, * R. Thomassy, Bulletin de la Societe de Geographie, 18G4. 10 146 THE OCEAN. form a spectacle ^f incomparable beauty, especially when the sun illu- mines the whole landscape with its rays.* When the waves of the sea can not enter into the caverns remote from the shore except by narrow channels, it often happens that a rivulet of salt water regularly flows toward the interior of the land, without ever returning to the ocean. This strange fact, which may seem at first sight a reversal of the laws of nature, may be observed on various points on the coast of calcareous countries, and especially on the coasts of Greece and the neighboring islands. Near Argostoli, a commercial town in the island of Cephalonia, four little torrents of sea-water, rolling on an average fifty-five gallons of water per second, penetrate into the fissures of the clifis, flow rapidly among the blocks that are scattered over the rocky bed, and gradually disappear in the crevices of the soil. Two of these water-courses are sufiiciently powerful to turn throughout the year the wheels of two mills constructed by an enterprising Englishman. Though the subterranean cavities of Argostoli are in constant communication with the sea, and the entrance to the canals is carefully freed from the sea-weed that could ob- struct the passage, or at least retard the current, the waters are not the same height in the grottoes as in the neighboring gulf. This is because the calcareous rocks of Cephalonia, dried on the surface by the sea-breeze and the heat of the sun, are pierced and cracked throughout by innu- merable crevices, which are so many flues aiding the circulation of the air, and the evaporization of the hidden oaoisture. We can compare the entire mass of the hill& of Argostoli, -with all their caverns, to an im- mense Alcaraza, the contents of which are gradually evaporated through the porous clay. In consequence of this constant loss of liquid, the level of the water is always lower in the caverns than in the sea, and to restore the equilibrium, the brooklets, which are fed by the waves, descend in- cessantly by all the fissures toward the subterranean reservoirs. It is probable that the constant evaporation of the salt water has resulted in the accumulation in the cavities of the island of enormous saline masses. Professor Ansted has calculated that the discharge of the two great ma- rine streams* of Argostoli would be sufiicient to form each year a block of more than 1800 cubic yards of salt.f * Vibe, Kiisten und Meer Norwegens., Mittheilungen von Petermann, 1860. t The Ionian Islands in the year 1863. UNDEMMINING OF ROCKS. 147 CHAPTER XIX, UNDERMININfi OP ROCKS. VARIED ASPECT OP CLIPPS. PLATPORMS AT THEIR BASES. RESISTANCE OP THE COASTS. BREAKWATERS PORMED BY THE RUBBISH. HELIGOLAND. DESTRUCTION OP LOW SHORES. All the rocky promontories exposed to the violence of storms, or sim- ply washed by a current, are undermined at their base. The wearing away is accomplished in a more or less rapid manner, according to the progress of the waves, the distribution and inclination of the strata, the hardness of the rocks, and their chemical composition. The method of destruction depends, at the same time, on various hydrological and geo- logical conditions. Strange as this assertion may appear, the water of the sea can even in certain cases destroy the rocks on its borders by combustion. Thus, the cliffs of Ballybunion, on the western coast of Ire- land, long presented the appearance of a rampart of smoking lava. Those rocks which the waves of the Atlantic have pierced with grottoes, and sculptured in massive and fantastic forms, having one day fallen down very extensively, the alum and iron pyrites, which is contained in considerable proportion in the rocks, were exposed to the action of the atmosphere and the sea-water. A rapid oxydation took place, and produced a heat sufficiently intense to set the whole cliff on fire. For weeks the rocks were burning like a vast coal fire, and masses of vapor and smoke rose like clouds above the high wall besieged by the surf Scattered around the space where the fire had prevailed, a heap of melt- ed scoriae, and clay transformed into brick by the violence of the fire, was to be seen. Since such is the diversity of destructive agents employed by nature, that, as we can easily understand, the aspect and form of the rocky coasts varies likewise in a remarkable manner. Thus the cliffs of England and Normandy, which are composed of somewhat friable rocks, fall when their lower strata are eaten away, and their sides being occasionally in- terrupted by " valleuses " (narrow openings where temi^orary or perma- nent brooks flow), they resemble enormous walls from 150 to 300 feet high. In the islands of the Baltic Sea, the chalky rocks, less exposed to the fury of the tempests than those of Western Europe, are also less abrupt, and forests of beech-trees descend like sheets of verdure over the ruins of the cliffs. Elsewhere, especially on the coasts of Liguria, the promontories, formed of limestone rocks harder than chalk, do not fall in when their lower strata are carried away by the sea, and the waves, in- cessantly excavating the bases of these rocks, may carve them into colon- nades, arched gate-ways, winding galleries, and vast grottoes, where the trembling water lights up the vaults with its azure hues. Other cliffs, of 148 THE OCEAN. which the promontory of Socoa, near StJ^^an de Luz, may be considered as a type, are composed of slate rocks, variously inclined toward the sea. Worn away by the waves, some of the layers of schist are detached, oth- ers bend and part from each other, like the pages of an open book, allow- ing the water to glide in long, foaming sheets into the very heart of the cliff, to spring up again from it in immense spouts. Finally, on other coasts the rocks cut by vertical fractures are gradually isolated from one another, and separated into distinct groups by the action of the waters. Surrounded by a roaring sea, they rise on their rocky bases like towers, monstrous obelisks, gigantic arcades, or crumbling bridges. Such are the innumerable rocks which tower above the waves in the archipelago of the Orkney and Shetland islands. Black, slender, and enveloped with spray as with smoke, these wrecks of ancient cliffs justify the name of " chim- ney-rocks," which the English have given to many of them. On the northern coasts of Norway, not far from the polar circle, a rock rises in the midst of the waves, more than 900 feet high, which resembles a giant cavalier; hence its name of Hestmanden. We see that the rocks which the sea-wave has eaten away are very various in form. Still, we may say, as a general rule, that the inequali- ties of cliffs are in direct proportion to the hardness of the strata. The grooves that the waves slowly hollow out in the surface of the rock, the cavities that they scoop out in it, the arcades and grottoes which they excavate there, are the deeper the harder the stone is, for the beds of less solid formation fall in as soon as the lower layers are eroded. That part of the cliff which is only wetted by the foam and the mist of minute drops is less cut up than the base, and the grooves are less numerous there ; but no vegetation as yet appears. Higher up a few lichens give a tint of greenish gray to the stone. Finally, those bushes which delight in breathing the salt air of the sea make their appearance in the angles and on the cornices of the rocks. It is at 100 or 120 feet high that this vegetation begins to show itself on the cliffs at the border of the Medi- terranean.* Fig. 61.— Cliflf on the Mediterranean. Notwithstanding the astonishing variety of aspect presented by cliff's composed of various substances — chalk, marble, granite, or porphyry — we can still observe one trait of singular resemblance in the form of the * Boblaye et Virlet. G. CoUegno, Geologia dell' Italia. FORMATION OF CLIFFS WITH PLATFORMS. I49 rocks which are covered by the' waters of the sea at the foot of the ab- rupt walls. This feature consists in the existence of one or two plat- forms of varying dimensions, situated at the base of the escarpments. FiK- 62.— Oceap Cliflf. On the coasts of the Mediterranean and other seas with a very slight tide, where the level of the waters hardly varies excepting under the in- fluence of the winds and storms, there is but a single one of these plat- forms ; while on the shores of the ocean, where the tides attain a height of at least several yards, two steps, one above the other, extend below the wall of the cliffs. When the rock is very hard the platforms present but a few yards in width, and perhaps may then be compared to a nar- row cornice, suspended at midway between two abrupt walls — that of the cliff, and that which plunges into the abyss of the water. On the other hand, when the rocks are easily cut, the terrace of one or several stages over which the waves roll has sometimes many hundreds of yards in width. ^^1 Fig. 63 — Tides of Inishmore. (Kinahan.) a. Deposit of tempests. h. Terrace of equinoctial tides. c. Terrace of ordinary high tides. dd. Intermediary terraces, e. Terrace of ordinary low tides. /. Low equinoctial tides. At Inishmore, on the western coast of Ireland, the cliff j^resents a succes- sion of regular steps like those of a staircase cut out for giants. The highest step, all incumbered with blocks, is that attained by the waves during a tempest ; lower down are those bathed by the spring-tides, and then that where the ordinary tides are arrested. Still lower are the inter- mediary terraces, and the last two steps of the staircase are those where the water breaks during ordinary ebb, and at the low tides of the equinoxes.* * Kinahan, Geological Magazine, August, 1866. 150 THE ocean: * It will be easily understood that thes^ submarine ledges were formerly- embedded in the thickness of the rock; they have resisted the assault of the waves, while the higher strata, sapped at their base more or less slow- ly, have fallen into the water. As the force of the waves is felt much less in the mass of waters than on the surface of the sea, the rock only allows itself to be cut into at the place where the breakers dash. But its sub- merged slopes remain relatively intact, and maintain more or less exactly • the ancient outline of the coast. This is the reason why there exists on the shores of the Atlantic and other seas, the level of which oscillates alternately with the ebb and flow, two platforms, one above the other, which correspond, the one with the level of low water, the other with that of high water. At the time of flow, the waves, urged by the tides, and more often too by the wind which accompanies the tide,* dash im- petuously against the rocky walls, and push on vigorously their labors of destruction. During the period of the ebb, on the contrary, the water which breaks on the shore is retained by the current of low water, and is as though attracted toward the open sea : neither does it attack the clifi" with as much energy as the rising tide. The difierence which exists be- tween the force of the waves of the flow and those of the ebb can be measured by the respective extent of the intermediary platforms. If the waves march constantly to the assault of the shore to transform into clifis the heights of the coast, the latter, on their side, are not satis- fied with merely resisting by their mass, and by the greater or less hard- ness of their strata, but many of them besides take care, one might say, to protect their threatened base against the waves. A thick vegetation of sea-weed, like floating hair, drapes the cornices, breaks the force of the surf, and changes into torrents of eddying foam the enormous rollers which rush to attack the rocks with great speed. Besides, all that por- tion of the rocks comprised between the levels of high and low water is covered with balani and other shells, numerous enough to give the stone the appearance at certain hours of a swarming mass, and to form it after- ward into an immense immovable carapace. f ' The coasts thus protected are precisely those which, by the solidity of their rocks, would best resist the attacks of the sea. As to the cliffs, composed throughout their thickness, or only at their base of less resist- ing materials, they gave way too often for the mollusks and sea-weed to venture in great numbers on that part of the rock which the waves have just assailed. Great blocks detach themselves from the upper strata, and fall on the beach. Afterward, under the action of the waves, they break into smaller pieces, then into pebbles, which the surge rolls and chafes incessantly. Under these fragments, constantly moved by the wave, no germ of animal or plant can develop itself, no living organism brought from the open sea can exist there. A desert is made even in the waters which dash against the roaring mass. * See the section entitjed The Air and the Winds. t See the sections entitled The Earth and its Flora, and The Earth and its Fauna. NATURAL BREAKWATERS. 151 When this is the case, it is the crumbling masses and the pebbles of the strand which themselves serve ao bulwarks of defense to protect the wall of the cliffs from fresh damage. Supported in a slope on the lower part of the rock, or else scattered in the waves and transformed into shelves, the iixllen blocks break the force of the waves, and retard the progress of erosion. It is thus that on the coasts, of the Mediterranean, near Vintimillia, the lower strata of the cliffs are composed of a sandy clay, which the rain alone suffices to wash away, and this gives rise to a talus of masses of solid conglomerate detached from the upper layers, which thus protects the cliffs from the fury of the waves. In the same way, on the sterile shores of Brittany, the blocks of granite, cracked in all direc- tions, and converted into shingle which the sea carries away and returns again, maintain intact during centuries the walls of rocks of which they formerly made a part. The cliffs of Normandy, composed of materials much less hard than those of the promontories of Brittany, are also more easily worn away ; still, we must attribute their rapid erosion principally to the coastal cur- rent which carries away the shingle accumulated at the base of the rocks. The talus of fallen blocks constitutes at first a perfectly sufficient defense against the fury of the waves ; but little by little the chalky part of the rock is dissolved and deposited here and there on the mud-banks, while the masses of flint disengaged from the substance of the stone cease to present a sufficient resistance to the waves, and are carried away into the neighboring bays in immense processions parallel to the shore. On the south coast of England the current of the coast is much less energetic, and the talus can, in consequence, long resist the attacks of the sea. A few years ago the waters undermined with a threatening rapidjty the base of the cliff which rises not far from Dover, on the western side, and which the English have consecrated to Shakspeare, in remembrance of the beautiful description which he has given of it in King Lear. To preserve this historical promontory, the houses that it supports, and the railroad which runs through it in a tunnel, they formed the plan of blow- ing down the upper part. In the presence of an immense crowd, assem- bled to see this new spectacle, they fired hundreds of pounds of powder buried in a mine, and enormous masses of rock fell with a crash from the top of the hill ; and now the force of the waves is broken on their talus. Mr. Beete Jukes thinks that during eighteen centuries this cliff and the neighboring rocks have been worn away by nearly one mile.* In the North Sea there is an island which, by a singular misapprehen- sion, was believed to have been consecrated to Freya, the goddess of Love and Liberty, and whose ancient name of Halligland (land with the inun- dated banks) has been transformed for foreigners into that of Heligoland (Holy Land). The island, composed entirely of mottled stone, formerly surrounded by cretaceous beds, presents to the sea all round a cliff about 200 feet high, worn away at the base by the waves. By employing the * School Manual of Geology, p. 89. 152 THE OCEAIS'. heroic means which the English engineers; have applied to the defense of Shakspeare's Cliff, and which the garrison of Heligoland had also inaugu- rated in the year 1808, by bombarding a crumbling cliff,* the inhabitants might surround their island with a great circular breakwater. But this dike would not last long, for the strata of mottled stone do not contain 64.— Heligoland. those beds of pebbles which serve to form shingle for a beach. All the blocks would soon be dissolved by the waves, and not a single fragment remaining to protect the lower strata of the cliff against the destructive action of the waves, the work of erosion would freely resume its course. * Hallier, Nord-See Studien, p. 73, INUNDATIONS OF TEE COASTS. 153 Devoted to certain destruction, the island is gradually melting in the waters, like an immense crystal of salt. The learned do not all give the same degree of confidence to the docu- ments relative to the ancient extent of Heligoland. Some, such as Wie- bel,* regard those testimonies of the past as if destitute of sufficient au- thenticity, and think that the lessening of tlie island is accomplished very slowly. Others, on the contrary ,f more respectful to the affirmations of the chroniclers, believe that in the space of five centuries the island has diminished by at least three-quarters. However it may be, it is cerflfcin that the partially inundated lands, to which the island owes its name, have long since ceased to exist. It is equally certain that, toward the end of the seventeenth century, an isthmus still^nited Heligoland to an- other islet, the cliffs of Avhich rose to about 100 feet in height, like the principal island : two excellent ports, which gave the island a great stra- tegical importance, opened to the north and south between the two rocky masses and their submarine extensions. The eastern island has now dis- appeared, and its cliffs are replaced by a few dunes and sand-banks, un- covered at low water : the ports no longer exist, and the ships of war drawing most water can sail freely where the isthmus still existed less than a century and a half ago. Who would now recognize in this rock of Heligoland, hardly a mile and a half long, and about 2000 feet broad, the land of which Adam de Bremse speaks in 1072, and which was then " very fertile, rich in corals, in animals, and birds," and which extended, says Karl Miiller, " over a space of 900 square kil0metres."J In the pres- .ent day, a few rows of potatoes and a few meagre pastures are the only remains that testify to the ancient fertility of Heligoland. If the sea thus destroys countries bordered all round with rocky prom- ontories, it respects still less the low strands which, in consequence of some modifications in the geography of the coasts, or in the relief of the submarine banks, are situated across the currents. In the very front of Heligoland, the shores of Hanover, Friesland, and Holland, which former- ly seemed to sink gradually,§ offer the most striking example of this de- structive power of the sea. During sixteen hundred years — that is to say, ever since written history commenced in these countries — the life of the inhabitants of the shores has been nothing but an incessant strife against the encroachment of the waters. During this period the great irruptions of the sea may be counted by hundreds, and among these there are some which, according to the chronicles, must have drowned whole populations of fifty and a hundred thousand souls. During the course of the third century, tradition tells us that the island of Walche- ren was separated from the continent; in 860 the Rhine rose, inundating the country ; the palace of Caligula {arx Brita7i7iica) remaining in the * Die Insel Helgoland. t Von Maack, Z^itschrift fur die algemeine Erdkunde, 1860. X Die Gefahren der schleswigschen West kuste: Natur, March, 18G7. § See the section entitled The Slow Oscillations of the Terrestrial Soil. 154 THE OCEAN. midst of the waves. Toward the middle of the twelfth century the sea made a new irruption, and the lake Flevo was changed into a gulf, which was still more enlarged in 1225, forming the Zuyder Zee, that vast laby- rinth of sand-banks, which, from a geological point of view, is still a de- pendency of the continent, and is separated by a long row of islands and dunes from the domain of the ocean. In the first years of the thirteenth century the Gulf of Jahde was opened at the expense of the land, and never ceased to enlarge itself during two hundred years. In 1230 the tewible inundation of Friesland took place, which is said to have cost the life of a hundred thousand men. The following year the lakes of Haarlem overflowed the ground, then, gradually increasing, united with each other to expand injp) an inland sea toward the middle of the seven- teenth century. In 1277 the gulf of the Dollart, which is nearly twenty- two miles long and seven miles wide, began to be hollowed out at the expense of the fertile and populous countries, and transformed Friesland into a peninsula. It was only in 1537 that they could arrest the inva- sions of the sea, which had devoured the town of Torum and fifty vil- lages. Ten years after the first invasion of the waters in the Dollart, an overflowing of the Zuyder Zee drowned 80,000 persons, and changed the configuration of the Dutch coast-line. In 1421, seventy-two villages were submerged at once, and the sea, on retiring, left only an archipelago of marshy islands and islets, covered with reeds and banks of mud, in the place of fields and groups of habitations: this is the country known un- der the name of Biesbosch (forest of reeds). Since this epoch many other hardly less terrible catastrophes have taken place on the coasts of Hoi-; land, Friesland, Schleswig, and Jutland.* • iig. 06.— Isle of Borkum in 173a. Of the row of twenty-three islands, which extended along the shore fifteen centuries ago, only sixteen fragments remain, and many are noth- ing else than simple ridges, of sand. The Island of Borkum, as is shown by maps with less than a century's interval, has been singularly lessened ; the Island of Wangerooge, the wreck of the antique country of Wanger- land, which was once united to the continent, and extended far into the sea, was in 1840 still a flouinshing and populous island, and during the * Von HofF; Von Maack ; Beyer ; Baudissin ; Karl Miiller, ete. ITieOceau.Ar DEPTHS OF THE ZUIDER-ZEE. PL. LV. 3°£«Bt of Pax i