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+*** START OF THE PROJECT GUTENBERG EBOOK 77792 ***
+
+
+  TRANSCRIBER’S NOTE
+
+  Italic text is denoted by _underscores_.
+
+  Footnote anchors are denoted by [number], and the footnotes have
+  been placed at the end of the book.
+
+  Basic fractions are displayed as ½ ⅓ ¼ etc; other fractions were
+  of the form a-b in the original book, for example 1-3000th and
+  7-100ths, and have been left unchanged.
+
+  The text of the heading of Part I of the book (I.--THE EARTH’S
+  CRUST) has been moved to the next page to be directly above the
+  heading of the first Chapter.
+
+  Chapter headings have been made consistent, with the title on a
+  single line and the author on the following line.
+
+  Some minor changes to the text are noted at the end of the book.
+
+  Volume I of this set of four volumes can be found in Project
+  Gutenberg at: https://www.gutenberg.org/ebooks/74571
+
+
+
+
+[Illustration: Jupiter and Minerva Terraces, Hot Springs, Yellowstone
+Park]
+
+
+
+
+                             THE STORY OF
+                             THE UNIVERSE
+
+                       _Told by Great Scientists
+                         and Popular Authors_
+
+                         COLLECTED AND EDITED
+
+                         _By_ ESTHER SINGLETON
+
+     Author of “Turrets, Towers and Temples,” “Wonders of Nature,”
+      “The World’s Great Events,” “Famous Paintings,” Translator
+            of Lavignac’s “Music Dramas of Richard Wagner”
+
+                          _FULLY ILLUSTRATED_
+
+
+                              VOLUME II
+                              
+                              THE EARTH:
+                               LAND AND
+                                 SEA
+
+
+                         P. F. COLLIER AND SON
+                               NEW YORK
+
+
+
+
+                            COPYRIGHT 1905
+
+                        BY P. F. COLLIER & SON
+
+
+
+
+ILLUSTRATIONS
+
+
+  Hot Springs, Yellowstone Park                         _Frontispiece_
+
+  Fingal’s Cave, Staffa                              _Opposite p._ 475
+
+  A Forest of the Carboniferous Period                    ”        523
+
+  The Giant’s Causeway, Ireland                           ”        595
+
+  Stag-Horn Coral Reef, Australia                         ”        643
+
+  The Matterhorn                                          ”        691
+
+  Forms of Snowflakes                                     ”        739
+
+  Forms of Clouds                                         ”        787
+
+  Chart of Winds and Tides                                ”        835
+
+
+
+
+CONTENTS
+
+
+  FORMATION OF THE EARTH. Élisée Reclus                            433
+
+  CLASSES OF ROCKS. Sir Charles Lyell                              439
+
+  GEOLOGICAL CHRONOLOGY. Sir J. William Dawson                     450
+
+  THE SILURIAN BEACH. Louis Agassiz                                456
+
+  CARBONIFEROUS PERIOD. Louis Figuier                              464
+
+  THE PALÆONTOLOGICAL HISTORY OF ANIMALS. Hugh Miller              480
+
+  EUROPEAN AND ASIATIC DELUGES. Louis Figuier                      493
+
+  GLACIERS. Louis Agassiz                                          502
+
+  VOLCANIC ACTION. Sir Archibald Geikie                            516
+
+  THOUGHTS ABOUT KRAKATOA. Sir Robert S. Ball                      527
+
+  VOLCANOES. Sir Archibald Geikie                                  536
+
+  EARTHQUAKES. William Hughes                                      559
+
+  MOUNTAINS. A. Keith                                              566
+
+  LAKES--FRESH, SALT, AND BITTER. Sir Archibald Geikie             573
+
+  UNDERGROUND WATER: SPRINGS, CAVES, RIVERS, AND LAKES.
+      Élisée Reclus                                                588
+
+  RIVERS. A. Keith Johnston                                        621
+
+  SWAMPS AND MARSHES. Élisée Reclus                                628
+
+  LOWLAND PLAINS. William Hughes                                   634
+
+  THE SMELL OF EARTH. G. Clarke Nuttall                            648
+
+  DESERTS. Élisée Reclus                                           654
+
+  THE PRIMITIVE OCEAN. G. Hartwig                                  666
+
+  THE FLOOR OF THE OCEAN. John James Wild                          676
+
+  CORAL FORMATIONS. Charles Darwin                                 689
+
+  MAGNITUDE AND COLOR OF THE SEA. G. Hartwig                       707
+
+  TIDAL ACTION. Sir Robert S. Ball                                 713
+
+  THE GULF STREAM. Lord Kelvin                                     727
+
+  THE PHOSPHORESCENCE OF THE SEA. G. Hartwig                       750
+
+  THE SEASHORE. P. Martin Duncan                                   763
+
+  THE OCEAN OF AIR. Agnes Giberne                                  773
+
+  WEATHER. Sir Ralph Abercromby                                    784
+
+  THE ROMANCE OF A RAINDROP. Arthur H. Bell                        792
+
+  THE RAINBOW. John Tyndall                                        799
+
+  SNOW, HAIL, AND DEW. Alexander Buchan                            807
+
+  THE AURORA BOREALIS. Richard A. Proctor                          813
+
+  CLOUDS. D. Wilson Barker                                         819
+
+  WINDS. William Hughes                                            828
+
+  SQUALLS, WHIRLWINDS, AND TORNADOES. Sir Ralph Abercromby         845
+
+
+
+
+                       THE STORY OF THE UNIVERSE
+                               VOLUME II
+
+
+                     THE EARTH: LAND, SEA, AND AIR
+
+
+
+
+                                 THE
+                        STORY OF THE UNIVERSE
+
+
+
+
+                       _I.--THE EARTH’S CRUST_
+
+
+
+
+  FORMATION OF THE EARTH
+  --ÉLISÉE RECLUS
+
+
+According to Laplace’s ideas, the whole planetary system formed,
+in long past ages, a portion of the sun. This luminary, composed
+solely of gaseous particles much lighter than hydrogen, pervaded
+with its enormous rotundity the whole of the space in which the
+planets, including Neptune, are now describing their immense orbits.
+The diameter of the solar spheroid must then have been 6,500 times
+greater than it now is, and its bulk must have surpassed its present
+volume by more than 860,000 millions of times. In the same way, the
+earth, before it began to get cool and solidify, would have embraced
+the moon within its limits, and its diameter would have been nearly
+six times greater than that of the planet Jupiter. But, unsubstantial
+and aerial as it was, our earth had then nothing but a cosmical
+life which could hardly be called material; it was not until it
+became more solid and its outer crust was hardened that it actually
+commenced its real existence.
+
+This brilliant hypothesis accounts better than any other for the
+uniform translatory motion of the planets in the direction of west
+to east; it also apparently agrees in a remarkable way with certain
+facts in the subsequent history of the earth, as disclosed to us
+by geology; finally, the marvelous rings which surround the planet
+Saturn seem to proclaim the truth of the theory devised by Laplace.
+There have been some experiments on a small scale which appeared to
+reproduce in miniature the magnificent spectacle presented in the
+primitive ages by the origin of the planets. M. Plateau, a Belgian
+_savant_, managed to make a globe of oil revolve in a mixture of
+water and spirits of wine which was of exactly the same specific
+gravity as the oil. When the revolution of the little globe was
+sufficiently rapid, it was noticed to flatten at the poles and to
+swell at the equator; after a time it threw off rings which suddenly
+assumed the shape of globules actuated by a rotatory motion of their
+own, and turning round the central globe.
+
+Another hypothesis connected with Laplace’s brilliant astronomical
+theory must be added, in order to describe the formation of the
+planetary crust. When the gaseous ring became condensed into a globe,
+it would not cease to contract, owing to the continued radiation
+of its caloric. The whole mass, having become liquid through the
+gradual cooling of its molecules, would be changed into a sea of lava
+whirling round in space; but this state was only one of transition.
+After an indefinite term of centuries, the loss of heat was
+sufficient to cause the formation of a light _scoria_, like a thin
+sheet of ice over the surface of the fiery sea, perhaps just at one
+of the poles where nowadays the extreme cold produces icebergs and
+a frost-bound sea. This first _scoria_ was succeeded by a second,
+and then by others; next they would unite into continents floating
+on the surface of the lava, and, finally, would cover the whole
+circumference of the planet with a continuous layer. A thin but solid
+crust would then have imprisoned within it an immense burning sea.
+
+This crust was frequently broken through by the lava boiling beneath
+it, and then, by means of the solidification of the _scoriæ_,
+was again united; the cooling process would tend also to slowly
+thicken it. After a lapse of time, which must have been immensely
+protracted--since the interval during which the temperature of
+the terrestrial crust would be lowered from 2,000° to 200° has
+been estimated, at the very least, at three and a half millions of
+centuries--the pellicle at last became firm, and the eruptions of
+the liquid mass within ceased to be a general phenomenon, localizing
+themselves at those points where the firm crust was the thinnest. The
+surrounding atmosphere, replete with vapors and various substances
+maintained by the extreme heat in a gaseous state, would gradually
+get rid of its burden; all kinds of matter, one after the other,
+would become disengaged from the luminous and burning aerial mass,
+and precipitate themselves on the solid crust of the planet. When
+the temperature was lowered sufficiently to enable them to pass
+from a gaseous to a liquid state, metals and other substances would
+fall down in a fiery rain on the terrestrial lava. Next, the steam,
+confined entirely to higher regions of the gaseous mass, would be
+condensed into an immense layer of clouds, incessantly furrowed by
+lightning. Drops of water, the commencement of the atmospheric ocean,
+would begin to fall down toward the ground, but only to volatilize
+on their way and again ascend. Finally these little drops reached
+the surface of the terrestrial _scoria_, the temperature of the
+water much exceeding 100°, owing to the enormous pressure exercised
+by the heavy air of these ages; and the first pool, the rudiment of
+a great sea, was collected in some fissure of the lava. This pool
+was constantly increased by fresh falls of water, and ultimately
+surrounded nearly the whole of the terrestrial crust with a liquid
+covering; but, at the same time, it brought with it fresh elements
+for the constitution of future continents. The numerous substances
+which the water held in solution formed various combinations with the
+metals and soils of its bed; the currents and tempests which agitated
+it destroyed its shores only to form new ones; the sediment deposited
+at the bottom of the water commenced the series of rocks and strata
+which follow one another above the primitive crust.
+
+Henceforward the igneous planet was externally clothed with a triple
+covering, solid, liquid, and gaseous; it might therefore become the
+theatre of life. Vegetables and lowly forms of animals were called
+into existence in the water, and on the land which had emerged from
+it; and, finally, when the temperature of the surface of the globe
+had become less than 50°, allowing albumen to liquefy and blood to
+flow in the veins, the fauna and the flora would be developed, the
+remains of which are found in the earliest fossil strata. The era
+of chaos was succeeded by that of vital harmony; but in the immense
+series of ages we are dealing with, the life which appeared on the
+refrigerated planet was little else than the “mouldiness formed in a
+day.”
+
+According to the theory generally propounded, the solid crust was not
+very completely formed; it is, indeed, much thinner than the layer
+of air surrounding the globe; for, following the common estimate,
+which, however, is purely hypothetical, at 22 to 25, or, at most, 50
+miles below the surface of the earth, the terrestrial heat would be
+sufficient to melt granite. Compared to the diameter of the earth,
+which is about 250 times greater, this crust is nothing more than
+a thin skin, a just idea of which may be given by a sheet of thin
+cardboard surrounding a liquid sphere a yard in diameter. In the case
+of the earth, this liquid is a sea of lava and molten rocks, having,
+like the ocean above it, its currents, its tides, and perhaps its
+storms.
+
+It is, in fact, very probable that a great part of the rocks which
+form the outer portion of our planet, especially the most ancient
+formations, existed in former times in a state of fusion like that
+of volcanic lava. As most geologists are of opinion, granite and
+other similar rocks, forming the principal building-blocks in the
+architecture of continents, existed once in a soft or semi-soft state.
+
+Neither must it be forgotten that, under the hypothesis admitted by
+those who assume the existence of a central fire, our planet is to
+be considered as actually a liquid mass, as the external crust is
+in comparison but a thin skin. Under these conditions, it would
+be difficult to believe that this great ocean of lava is not, like
+the watery ocean, agitated by the alternating motion of tides, and
+that it does not move twice every day the raft, as it were, which is
+floating on its surface. It is difficult to understand how it is that
+the earth is not much more depressed at the poles than it now is, and
+has not been transformed into a real disk. This flattening of the
+poles is not more considerable than the mere superficial inequalities
+in the equatorial zone between the summits of the Himalayas and
+the abysses of the Indian Ocean. M. Liais attributes the slight
+flattening of the two poles to the erosion which the water and ice
+in those parts, irresistibly drawn as they are toward the equator,
+incessantly cause, year after year and century after century, by the
+enormous quantity of _débris_ torn away from the surface of the soil,
+which they bear with them.
+
+The principal argument of those who look upon the existence of a
+central fire as a demonstrated fact is that, in the external strata
+of the earth, so far as they have been explored by miners, the heat
+keeps on increasing in proportion to the depth of the excavation. In
+descending the shaft of a mine we invariably pass through zones of
+increasing temperature; only the rate of increase varies in different
+parts of the earth, and according to the strata through which the
+shaft is sunk. The heat increases more rapidly in schist than in
+granite, and in metallic veins more even than in schist; in lodes
+of copper more than in those of tin, and in beds of coal more than
+in metallic veins. M. Cordier, being struck by all the objections
+which presented themselves to his mind as to the thinness of the
+terrestrial crust, has admitted that this covering could not be
+stable without having at least from 75 to 175 miles of thickness.
+
+
+
+
+  CLASSES OF ROCKS
+  --SIR CHARLES LYELL
+
+
+Of what materials is the earth composed, and in what manner are these
+materials arranged? These are the first inquiries with which geology
+is occupied, a science which derives its name from the Greek _ge_,
+the earth, and _logos_, a discourse. Previously to experience we
+might have imagined that investigations of this kind would relate
+exclusively to the mineral kingdom, and to the various rocks, soils,
+and metals which occur upon the surface of the earth, or at various
+depths beneath it. But, in pursuing such researches, we soon find
+ourselves led on to consider the successive changes which have taken
+place in the former state of the earth’s surface and interior, and
+the causes which have given rise to these changes; and, what is still
+more singular and unexpected, we soon become engaged in researches
+into the history of the animate creation, or of the various tribes
+of animals and plants which have, at different periods of the past,
+inhabited the globe.
+
+By the “earth’s crust” is meant that small portion of the exterior
+of our planet which is accessible to human observation. It comprises
+not merely all of which the structure is laid open in mountain
+precipices, or in cliffs overhanging a river or the sea, or whatever
+the miner reveals in artificial excavation; but the whole of that
+outer covering of the planet on which we are enabled to reason by
+observations made at or near the surface.
+
+The materials of this crust are not thrown together confusedly;
+but distinct mineral masses, called rocks, are found to occupy
+definite spaces, and to exhibit a certain order of arrangement. The
+term _rock_ is applied indifferently by geologists to all these
+substances, whether they be soft or strong, for clay and sand are
+included in the term, and some have even brought peat under this
+denomination.
+
+The most natural and convenient mode of classifying the various rocks
+which compose the earth’s crust is to refer, in the first place, to
+their origin, and in the second to their relative age.
+
+The first two divisions, which will at once be understood as natural,
+are the aqueous and volcanic, or the products of watery and those of
+igneous action at or near the surface. The aqueous rocks, sometimes
+called the sedimentary or fossiliferous, cover a larger part of the
+earth’s surface than any others. They consist chiefly of mechanical
+deposits (pebbles, sand, and mud), but are partly of chemical and
+some of them of organic origin, especially the limestones. These
+rocks are _stratified_, or divided into distinct layers or strata.
+The term _stratum_ means simply a bed, or anything spread out or
+_strewed_ over a given surface; and we infer that these strata have
+been generally spread out by the action of water, from what we daily
+see taking place near the mouths of rivers, or on the land during
+temporary inundations. For, whenever a running stream, charged with
+mud or sand, has its velocity checked, as when it enters a lake
+or sea, or overflows a plain, the sediment, previously held in
+suspension by the motion of the water, sinks, by its own gravity, to
+the bottom. In this manner layers of mud and sand are thrown down one
+upon another.
+
+If we drain a lake which has been fed by a small stream, we
+frequently find at the bottom a series of deposits, disposed with
+considerable regularity, one above the other; the uppermost, perhaps,
+may be a stratum of peat, next below a more dense and solid variety
+of the same material; still lower a bed of shell-marl, alternating
+with peat or sand, and then other beds of marl, divided by layers
+of clay. Now, if a second pit be sunk through the same continuous
+lacustrine _formation_ at some distance from the first, nearly the
+same series of beds is commonly met with, yet with slight variations;
+some, for example, of the layers of sand, clay, or marl may be
+wanting, one or more of them having thinned out and given place to
+others, or sometimes one of the masses first examined is observed to
+increase in thickness to the exclusion of other beds.
+
+The term _formation_, which I have used in the above explanation,
+expresses in geology any assemblage of rocks which have some
+character in common, whether of origin, age, or composition. Thus we
+speak of stratified and unstratified, fresh-water and marine, aqueous
+and volcanic, ancient and modern, metalliferous and non-metalliferous
+formations.
+
+In the estuaries of large rivers, such as the Ganges and the
+Mississippi, we may observe, at low water, phenomena analogous to
+those of the drained lakes above mentioned, but on a grander scale,
+and extending over areas several hundred miles in length and breadth.
+When the periodical inundations subside, the river hollows out a
+channel to the depth of many yards through horizontal beds of clay
+and sand, the ends of which are seen exposed in perpendicular cliffs.
+These beds vary in their mineral composition, or color, or in the
+fineness or coarseness of their particles, and some of them are
+occasionally characterized by containing driftwood. At the junction
+of the river and the sea, especially in lagoons nearly separated by
+sand bars from the ocean, deposits are often formed in which brackish
+and salt-water shells are included.
+
+In Egypt, where the Nile is always adding to its delta by filling
+up part of the Mediterranean with mud, the newly deposited sediment
+is _stratified_, the thin layer thrown down in one season differing
+slightly in color from that of a previous year, and being separable
+from it, as has been observed in Cairo and other places.
+
+When beds of sand, clay, and marl containing shells and vegetable
+matter are found arranged in a similar manner in the interior of the
+earth, we ascribe to them a similar origin; and the more we examine
+their characters in minute detail, the more exact do we find the
+resemblance. Thus, for example, at various heights and depths in
+the earth, and often far from seas, lakes, and rivers, we meet with
+layers of rounded pebbles composed of flint, limestone, granite, or
+other rocks, resembling the shingles of a sea-beach or the gravel in
+a torrent’s bed. Such layers of pebbles frequently alternate with
+others formed of sand or fine sediment, just as we may see in the
+channel of a river descending from hills bordering a coast, where the
+current sweeps down at one season coarse sand and gravel, while at
+another, when the waters are low and less rapid, fine mud and sand
+alone are carried seaward.
+
+If a stratified arrangement and the rounded form of pebbles are alone
+sufficient to lead us to the conclusion that certain rocks originated
+under water, this opinion is further confirmed by the distinct and
+independent evidences of _fossils_, so abundantly included in the
+earth’s crust. By a _fossil_ is meant any body, or the traces of the
+existence of any body, whether animal or vegetable, which has been
+buried in the earth by natural causes. Now the remains of animals,
+especially of aquatic species, are found almost everywhere imbedded
+in stratified rocks, and sometimes, in the case of limestone, they
+are in such abundance as to constitute the entire mass of the rock
+itself. Shells and corals are the most frequent, and with them are
+often associated the bones and teeth of fishes, fragments of wood,
+impressions of leaves, and other organic substances. Fossil shells
+of forms such as now abound in the sea are met with far inland,
+both near the surface and at great depths below it. They occur at
+all heights above the level of the ocean, having been observed at
+elevations of more than 8,000 feet in the Pyrenees, 10,000 in the
+Alps, 13,000 in the Andes, and above 18,000 feet in the Himalayas.
+
+These shells belong mostly to marine testacea, but in some places
+exclusively to forms characteristic of lakes and rivers. Hence it is
+concluded that some ancient strata were deposited at the bottom of
+the sea, and others in lakes and estuaries.
+
+The division of rocks, which we may next consider, are the volcanic,
+or those which have been produced at or near the surface, whether in
+ancient or modern times, not by water, but by the action of fire or
+subterranean heat. These rocks are for the most part unstratified,
+and are devoid of fossils. They are more partially distributed than
+aqueous formations, at least in respect to horizontal extension.
+Among those parts of Europe where they exhibit characters not to
+be mistaken, I may mention not only Sicily and the country round
+Naples, but Auvergne, Velay, and Vivarais, now the departments of Puy
+de Dôme, Haute Loire, and Ardêche, toward the centre and south of
+France, in which are several hundred conical hills having the forms
+of modern volcanoes, with craters more or less perfect on many of
+their summits. These cones are composed, moreover, of lava, sand,
+and ashes similar to those of active volcanoes. Streams of lava may
+sometimes be traced from the cones into the adjoining valleys, where
+they have choked up the ancient channels of rivers with solid rock,
+in the same manner as some modern flows of lava in Iceland have
+been known to do, the rivers either flowing beneath or cutting out
+a narrow passage on one side of the lava. Although none of these
+French volcanoes has been in activity within the period of history
+or tradition, their forms are often very perfect. Some, however,
+have been compared to the mere skeletons of volcanoes, the rains and
+torrents having washed their sides, and removed all the loose sand
+and scoriæ, leaving only the harder and more solid materials. By this
+erosion and by earthquakes their internal structure has occasionally
+been laid open to view, in fissures and ravines; and we then behold
+not only many successive beds and masses of porous lava, sand, and
+scoriæ, but also perpendicular walls, or _dikes_, as they are called,
+of volcanic rock, which have burst through the other materials. Such
+dikes are also observed in the structure of Vesuvius, Etna, and other
+active volcanoes. They have been formed by the pouring of melted
+matter, whether from above or below, into open fissures, and they
+commonly traverse deposits of _volcanic tuff_, a substance produced
+by the showering down from the air, or incumbent waters, of sand
+and cinders, first shot up from the interior of the earth by the
+explosions of volcanic gases.
+
+Besides the parts of France above alluded to, there are other
+countries, as the north of Spain, the south of Sicily, the Tuscan
+territory of Italy, the lower Rhenish provinces, and Hungary, where
+spent volcanoes may be seen, still preserving in many cases a conical
+form, and having craters and often lava streams connected with them.
+
+There are also other rocks in England, Scotland, Ireland, and almost
+every country in Europe, which we infer to be of igneous origin,
+although they do not form hills with cones and craters. Thus, for
+example, we feel assured that the rock of Staffa and that of the
+Giant’s Causeway, called basalt, is volcanic, because it agrees in
+its columnar structure and mineral composition with streams of lava
+which we know to have flowed from the craters of volcanoes.
+
+The absence of cones and craters, and long narrow streams of
+superficial lava in England and many other countries, is principally
+to be attributed to the eruptions having been submarine, just as
+a considerable proportion of volcanoes in our own times burst out
+beneath the sea. The igneous, as well as the aqueous rocks may be
+classed as a chronological series of monuments, throwing light on a
+succession of events in the history of the earth.
+
+We have now pointed out the existence of two distinct orders of
+mineral masses, the aqueous and the volcanic; but if we examine a
+large portion of a continent, especially if it contain within it a
+lofty mountain range, we rarely fail to discover two other classes
+of rocks, very distinct from either of those above alluded to,
+and which we can neither assimilate to deposits such as are now
+accumulated in lakes or seas, nor to those generated by ordinary
+volcanic action. The members of both these divisions of rocks agree
+in being highly crystalline and destitute of organic remains. The
+rocks of one division have been called plutonic, comprehending all
+the granites and certain porphyries, which are nearly allied in
+some of their characters to volcanic formations. The members of the
+other class are stratified and often slaty, and have been called by
+some the _crystalline schists_, in which group are included gneiss,
+micaceous-schist (or mica-slate), hornblende-schist, statuary marble,
+the finer kinds of roofing-slate, and other rocks afterward to be
+described.
+
+All the various kinds of granites which constitute the plutonic
+family are supposed to be of igneous or aqueo-igneous origin, and to
+have been formed under great pressure, at a considerable depth in
+the earth, or sometimes perhaps under a certain weight of incumbent
+ocean. Like the lava of volcanoes, they have been melted, and
+afterward cooled and crystallized, but with extreme slowness, and
+under conditions very different from those of bodies cooling in the
+open air. Hence they differ from the volcanic rocks, not only by
+their more crystalline texture, but also by the absence of tuffs and
+breccias, which are the products of eruptions at the earth’s surface,
+or beneath seas of inconsiderable depth. They differ also by the
+absence of pores or cellular cavities, to which the expansion of the
+entangled gases gives rise in ordinary lava.
+
+The fourth and last great division of rocks are the crystalline
+strata and slates, or schists, called gneiss, mica-schist,
+clay-slate, chlorite-schist, marble, and the like, the origin
+of which is more doubtful than that of the other three classes.
+They contain no pebbles, or sand, or scoriæ, or angular pieces of
+imbedded stone, and no traces of organic bodies, and they are often
+as crystalline as granite, yet are divided into beds, corresponding
+in form and arrangement to those of sedimentary formations, and
+are therefore said to be stratified. The beds sometimes consist
+of an alternation of substances varying in color, composition, and
+thickness, precisely as we see in stratified fossiliferous deposits.
+According to the Huttonian theory, which I adopt as the most
+probable, the materials of these strata were originally deposited
+from water in the usual form of sediment, but they were subsequently
+so altered by subterranean heat as to assume a new texture. It is
+demonstrable, in some cases at least, that such a complete conversion
+has actually taken place, fossiliferous strata having exchanged an
+earthy for a highly crystalline texture for a distance of a quarter
+of a mile from their contact with granite. In some cases, dark
+limestones, replete with shells and corals, have been turned into
+white statuary marble, and hard clays, containing vegetable or other
+remains, into slates called mica-schist or hornblende-schist, every
+vestige of the organic bodies having been obliterated.
+
+Although we are in a great degree ignorant of the precise nature of
+the influence exerted in these cases, yet it evidently bears some
+analogy to that which volcanic heat and gases are known to produce;
+and the action may be conveniently called plutonic, because it
+appears to have been developed in those regions where plutonic rocks
+are generated, and under similar circumstances of pressure and depth
+in the earth. Intensely heated water or steam permeating stratified
+masses under great pressure have no doubt played their part in
+producing the crystalline texture and other changes, and it is clear
+that the transforming influence has often pervaded entire mountain
+masses of strata.
+
+In accordance with the hypothesis above alluded to, I proposed in
+the first edition of the _Principles of Geology_ (1833), the term
+Metamorphic, for the altered strata, a term derived from meta,
+_trans_, and morphe, _forma_.
+
+Hence there are four great classes of rocks considered in reference
+to their origin--the aqueous, the volcanic, the plutonic, and the
+metamorphic. Portions of each of these four distinct classes have
+originated at many successive periods. They have all been produced
+contemporaneously, and may even now be in the progress of formation
+on a large scale. It is not true, as was formerly supposed, that all
+granites, together with the crystalline or metamorphic strata, were
+first formed, and therefore entitled to be called “primitive,” and
+that the aqueous and volcanic rocks were afterward superimposed,
+and should, therefore, rank as secondary in the order of time. This
+idea was adopted in the infancy of the science, when all formations,
+whether stratified or unstratified, earthy or crystalline, with or
+without fossils, were alike regarded as of aqueous origin.
+
+From what has now been said, the reader will understand that each of
+the four great classes of rocks may be studied under two distinct
+points of view; first, they may be studied simply as mineral masses
+deriving their origin from particular causes, and having a certain
+composition, form, and position in the earth’s crust, or other
+characters, both positive and negative, such as the presence or
+absence of organic remains. In the second place, the rocks of each
+class may be viewed as a grand chronological series of monuments,
+attesting a succession of events in the former history of the globe
+and its living inhabitants.
+
+
+
+
+  GEOLOGICAL CHRONOLOGY
+  --SIR J. WILLIAM DAWSON
+
+
+The crust of the earth, as we somewhat modestly term that portion
+of its outer shell which is open to our observation, consists of
+many beds of rock superimposed on each other, and which must have
+been deposited successively, beginning with the lowest. This is
+proved by the structure of the beds themselves, by the markings on
+their surfaces, and by the remains of animals and plants which they
+contain; all these appearances indicating that each successive bed
+must have been the surface before it was covered by the next.
+
+As these beds of rock were mostly formed under water, and of material
+derived from the waste of land, they are not universal, but occur
+in those places where there were extensive areas of water receiving
+detritus from the land. Further, as the distinction of land and
+water arises primarily from the shrinkage of the mass of the earth,
+and from the consequent collapse of the crust in some places and
+ridging of it up in others, it follows that there have, from the
+earliest geological periods, been deep ocean-basins, ridges of
+elevated land, and broad plateaus intervening between the ridges,
+and which were at some times under water and at other times land,
+with many intermediate phases. The settlement and crumpling of the
+crust were not continuous, but took place at intervals; and each
+such settlement produced not only a ridging up along certain lines,
+but also an emergence of the plains or plateaus. Thus at all times
+there have been ridges of folded rock constituting mountain ranges,
+flat expansions of continental plateau, sometimes dry and sometimes
+submerged, and deep ocean-basins, never except in some of their
+shallower portions elevated into land.
+
+By the study of the successive beds, more especially of those
+deposited in the times of continental submergence, we obtain a
+table of geological chronology which expresses the several stages
+of the formation of the earth’s crust, from that early time when a
+solid shell first formed on our nascent planet to the present day.
+By collecting the fossil remains imbedded in the several layers
+and placing these in chronological order, we obtain in like manner
+histories of animal and plant life parallel to the physical changes
+indicated by the beds themselves. The facts as to the sequence we
+obtain from the study of exposures in cliffs, cuttings, quarries,
+and mines; and by correlating these local sections in a great number
+of places, we obtain our general table of succession; though it is
+to be observed that in some single exposures or series of exposures,
+like those in the great cañons of Colorado, or on the coasts of Great
+Britain, we can often in one locality see nearly the whole sequence
+of beds.
+
+The evidence is similar to that obtained by Schliemann on the site
+of Troy, where, in digging through successive layers of _débris_,
+he found the objects deposited by successive occupants of the site,
+from the time of the Roman Empire back to the earliest tribes, whose
+flint weapons and the ashes of their fires rest on the original
+surface of the ground.
+
+Let us now tabulate the whole geological succession with the history
+of animals and plants associated with it:
+
+  --------------------+---------------------+--------------------------
+        ANIMALS       |SYSTEMS OF FORMATIONS|         PLANTS
+  --------------------+---------------------+--------------------------
+                      | Kainozoic           |
+                      |   Modern            |
+     Age of Man and   |   Pleistocene       |  Angiosperms and
+        Mammalia      |   Pliocene          |       Palms dominant
+                      |   Miocene           |
+                      |   Eocene            |
+  --------------------+---------------------+--------------------------
+                      | Mesozoic            |
+                      |   Cretaceous        |  Cycads and Pines
+    Age of Reptiles   |   Jurassic          |      dominant
+                      |   Triassic          |
+  --------------------+---------------------+--------------------------
+                      | Palæozoic           |
+                      |   Permian           |
+                      |   Carboniferous     |
+   Age of Amphibians  |   Erian             |  Acrogens and Gymnosperms
+       and Fishes     |   Silurian          |      dominant
+  Age of Invertebrates|   Ordovician        |
+                      |   Cambrian          |
+                      |   Huronian (Upper)  |
+  --------------------+---------------------+--------------------------
+                      | Eozoic              |
+                      |   Huronian (Lower)  |
+     Age of Protozoa  |   Upper Laurentian  |  Protogens and Algæ
+                      |   Middle Laurentian |
+                      |   Lower Laurentian  |
+  --------------------+---------------------+--------------------------
+
+It will be observed, since only the latest of the systems of
+formations in this table belongs to the period of human history, that
+the whole lapse of time embraced in the table must be enormous. If
+we suppose the modern period to have continued for say ten thousand
+years, and each of the others to have been equal to it, we shall
+require two hundred thousand years for the whole. There is, however,
+reason to believe, from the great thickness of the formations and the
+slowness of the deposition of many of them in the older systems, that
+they must have required vastly greater time. Taking these criteria
+into account, it has been estimated that the time-ratios for the
+first three great ages may be as one for the Kainozoic to three for
+the Mesozoic and twelve for the Palæozoic, with as much for the
+Eozoic as for the Palæozoic. This is Dana’s estimate. Another, by
+Hull and Houghton, gives the following ratios: Azoic, 34.3 per cent;
+Palæozoic, 42.5 per cent; Mesozoic and Kainozoic, 23.3 per cent. It
+is further held that the modern period is much shorter than the other
+periods of the Kainozoic, so that our geological table may have to be
+measured by millions of years instead of thousands.
+
+We can not, however, attach any certain and definite value in years
+to geological time, but must content ourselves with the general
+statement that it has been vastly long in comparison to that covered
+by human history.
+
+Bearing in mind this great duration of geological time, and the fact
+that it probably extends from a period when the earth was intensely
+heated, its crust thin, and its continents as yet unformed, it will
+be evident that the conditions of life in the earlier geologic
+periods may have been very different from those which obtained
+later. When we further take into account the vicissitudes of land
+and water which have occurred, we shall see that such changes must
+have produced very great differences of climate. The warm equatorial
+waters have in all periods, as superficial oceanic currents, been
+main agents in the diffusion of heat over the surface of the earth,
+and their distribution to north and south must have been determined
+mainly by the extent and direction of land, though it may also have
+been modified by the changes in the astronomical relations and period
+of the earth, and the form of its orbit. We know by the evidence of
+fossil plants that changes of this kind have occurred so great as,
+on the one hand, to permit the plants of warm temperate regions to
+exist within the Arctic Circle; and, on the other, to drive these
+plants into the tropics and to replace them by Arctic forms. It is
+evident also that in those periods when the continental areas were
+largely submerged there might be an excessive amount of moisture in
+the atmosphere, greatly modifying the climate in so far as plants are
+concerned.
+
+Let us now consider the history of the vegetable kingdom as indicated
+in the few notes in the right-hand column of the table.
+
+The most general subdivision of plants is into the two great series
+of Cryptogams, or those which have no manifest flowers, and produce
+minute spores instead of seeds; and Phænogams, or those which possess
+flowers and produce seeds containing an embryo of the future plant.
+
+The Cryptogams may be subdivided into the following three groups:
+
+1. _Thallogens_, cellular plants not distinctly distinguishable into
+stem and leaf. These are the Fungi, the Lichens, and the Algæ, or
+sea-weeds.
+
+2. _Anogens_, having stem and foliage, but wholly cellular. These are
+the Mosses and Liverworts.
+
+3. _Acrogens_, which have long tubular fibres as well as cells
+in their composition, and thus have the capacity of attaining a
+more considerable magnitude. These are the Ferns (_Filices_), the
+Mare’s-tails (_Equisetaceæ_), and the Club-mosses (_Lycopodiaceæ_),
+and a curious little group of aquatic plants called Rhizocarps
+(_Rhizocarpeæ_).
+
+The Phænogams are all vascular, but they differ much in the
+simplicity or complexity of their flowers or seeds. On this ground
+they admit of a twofold division:
+
+1. _Gymnosperms_, or those which bear naked seeds not inclosed in
+fruits. They are the Pines and their allies, and the Cycads.
+
+2. _Angiosperms_, which produce true fruits inclosing the seeds. In
+this group there are two well-marked subdivisions differing in the
+structure of the seed and stem. They are the _Endogens_, or inside
+growers, with seeds having one seed-leaf only, as the grasses and
+the palms; and the _Exogens_, having outside-growing woody stems and
+seeds with two seed-leaves. Most of the ordinary forest trees of
+temperate climates belong to this group.
+
+On referring to the geological table, it will be seen that there is
+a certain rough correspondence between the order of rank of plants
+and the order of their appearance in time. The oldest plants that we
+certainly know are Algæ, and with these there are plants apparently
+with the structures of Thallophytes but the habit of trees, and
+which, for want of a better name, I may call _Protogens_. Plants
+akin to the Rhizocarps also appear very early. Next in order we
+find forests in which gigantic Ferns and Lycopods and Mare’s-tails
+predominate, and are associated with pines. Succeeding these we have
+a reign of Gymnosperms, and in the later formations we find the
+higher Phænogams dominant.
+
+
+
+
+  THE SILURIAN BEACH
+  --LOUIS AGASSIZ
+
+
+The crust of our earth is a great cemetery where the rocks are
+tombstones on which the buried dead have written their own epitaphs.
+They tell us not only who they were and when and where they have
+lived, but much also of the circumstances under which they lived.
+We ascertain the prevalence of certain physical conditions at
+special epochs by the presence of animals and plants whose existence
+and maintenance requires such a state of things, more than by any
+positive knowledge respecting it. Where we find the remains of
+quadrupeds corresponding to our ruminating animals, we infer not
+only land, but grassy meadows and an extensive vegetation; where we
+find none but marine animals, we know the ocean must have covered
+the earth; the remains of large reptiles, representing, though in
+gigantic size, the half aquatic, half terrestrial reptiles of our
+own period, indicate to us the existence of spreading marshes still
+soaked by retreating waters; while the traces of such animals as live
+now in sand and shoal waters, or in mud, speak to us of shelving
+sandy beaches and mud flats. The eye of the Trilobite tells us that
+the sun shone on the old beach where he lived; for there is nothing
+in nature without a purpose, and when so complicated an organ was
+made to receive the light there must have been light to enter it.
+The immense vegetable deposits in the Carboniferous period announce
+the introduction of an extensive terrestrial vegetation; and the
+impressions left by the wood and leaves show that these first forests
+must have grown in a damp soil and a moist atmosphere. In short, all
+the remains of animals and plants hidden in the rocks have something
+to tell of the climatic conditions and the general circumstances
+under which they lived, and the study of fossils is to a naturalist
+a thermometer by which he reads the variation of temperature in
+past times, a plummet by which he sounds the depths of the ancient
+oceans--a register, in fact, of all the important physical changes
+the earth has undergone.
+
+The Silurian beach was a shelving one, and covered, of course,
+with shoal waters; but the parallel ridges trending east to west
+across the State of New York, considered by some geologists as the
+successive shores of a receding ocean, are believed by others to be
+the inequalities on the bottom of a shallow sea. Not only, however,
+does the general character of these successive terraces suggest the
+idea that they must have been shores, but the ripple marks upon
+them are as distinct as upon any modern beach. The regular rise and
+fall of the water is registered there in waving, undulating lines
+as clearly as on the sand beaches of Newport or Nahant; and we can
+see on any of those ancient shores the track left by the waves as
+they rippled back at ebb of the tide thousands of centuries ago.
+One can often see where some obstacle interrupted the course of the
+water, causing it to break around it; and such an indentation even
+retains the soft, muddy, plastic look that we observe on the present
+beaches, where the resistance made by any pebble or shell to the
+retreating wave has given it greater force at that point, so that the
+sand around the spot is soaked and loosened. There is still another
+sign familiar to those who have watched the action of water on a
+beach. Where a shore is very shelving and flat, so that the waves do
+not recede in ripples from it, but in one unbroken sheet, the sand
+and small pebbles are dragged and form lines which diverge whenever
+the water meets an obstacle, thus forming sharp angles on the sand.
+Such marks are as distinct on the oldest Silurian rocks as if they
+had been made yesterday. Nor are these the only indications of the
+same fact. There are certain animals living always on sandy or muddy
+shores which require for their well-being that the beach should be
+left dry for a part of the day. These animals, moving about in the
+sand or mud from which the water has retreated, leave their tracks
+there; and if, at such a time, the wind is blowing dust over the
+beach and the sun is hot enough to bake it upon the impressions so
+formed, they are left in a kind of mold. Such trails and furrows made
+by small shells and crustacea are also found in plenty on the oldest
+deposits.
+
+Admitting it, then, to be a beach, let us begin with the lowest type
+of the Animal Kingdom and see what _Radiates_ are to be found there.
+There are plenty of _Corals_, but they are not the same kind of
+_Corals_ as those that build up our reefs and islands now. The modern
+Coral animals are chiefly _Polyps_, but the prevailing _Corals_
+of the _Silurian_ age were _Acalephian Hydroids_, animals which
+indeed resemble _Polyps_ in certain external features, and have been
+mistaken for them, but which are, nevertheless, _Acalephs_ by their
+internal structure.
+
+Of the _Echinoderms_, the class of _Radiates_ represented now by our
+_Star-Fishes_ and _Sea-Urchins_, we may gather any quantity, though
+the old-fashioned forms are very different from the living ones.
+The _Mollusks_ were also represented then, as now, by their three
+classes, _Acephala_, _Gasteropoda_, and _Cephalopoda_. The _Acephala_
+or _Bivalves_ we find in great numbers, but of a very different
+pattern from the _Oysters_, _Clams_, and _Mussels_ of recent times.
+
+Of the _Silurian Univalves_ or _Gasteropods_, there is not much
+to tell, for their spiral shells were so brittle that scarcely
+any perfect specimens are known, though their broken remains are
+found in such quantities as to show that this class also was
+very fully represented in the earliest creation. But the highest
+class of _Mollusks_, the _Cephalopods_ or _Chambered Shells_, or
+_Cuttle-Fishes_, as they are called when the animal is unprotected by
+a shell, are, on the contrary, very well preserved, and they are very
+numerous.
+
+Of _Articulates_ we find only two classes, _Worms_ and _Crustacea_.
+Insects there were none--for, as we have seen, this early world
+was wholly marine. There is little to be said of the _Worms_, for
+their soft bodies, unprotected by any hard covering, could hardly
+be preserved; but, like the marine _Worms_ of our own times, they
+were in the habit of constructing envelopes for themselves, built of
+sand, or sometimes from a secretion of their own bodies, and these
+cases we find in the earliest deposits, giving us the assurance that
+the _Worms_ were represented there. I should add, however, that many
+impressions described as produced by _Worms_ are more likely to have
+been the tracks of _Crustacea_. But by far the most characteristic
+class of _Articulates_ in ancient times were the _Crustaceans_. The
+_Trilobites_ stand in the same relation to the modern _Crustacea_ as
+the _Crinoids_ do to the modern _Echinoderms_. They were then the
+sole representatives of their class, and the variety and richness of
+the type are most extraordinary. They were of nearly equal breadth
+for the whole length of the body, and rounded at the two ends, so as
+to form an oval outline.
+
+We have found _Radiates_, _Mollusks_, and _Articulates_ in plenty;
+and now what is to be said of _Vertebrates_ in these old times--of
+the highest and most important division of the Animal Kingdom, that
+to which we ourselves belong. They were represented by Fishes alone;
+and the fish chapter in the history of the early organic world is
+a curious and, as it seems to me, a very significant one. We shall
+find no perfect specimens; and he would be a daring, not to say a
+presumptuous, thinker who would venture to reconstruct a fish of
+the _Silurian_ age from any remains that are left to us. But still
+we find enough to indicate clearly the style of those old fishes,
+and to show, by comparison with the living types, to what group of
+modern times they belong. We should naturally expect to find the
+_Vertebrates_ introduced in their simplest form; but this is by no
+means the case: the common fishes, as _Cod_, _Herring_, _Mackerel_,
+and the like, were unknown in those days.
+
+I have spoken of the _Silurian_ beach as if there were but one, not
+only because I wished to limit my sketch and to attempt, at least,
+to give it the vividness of a special locality, but also because a
+single such shore will give us as good an idea of the characteristic
+fauna of the time as if we drew our material from a wider range.
+There are, however, a great number of parallel ridges belonging to
+the _Silurian_ and _Devonian_ periods running from east to west,
+not only through the State of New York, but far beyond, through the
+States of Michigan and Wisconsin into Minnesota; one may follow nine
+or ten such successive shores in unbroken lines from the neighborhood
+of Lake Champlain to the Far West.
+
+Although the early geological periods are more legible in North
+America, because they are exposed over such extensive tracts of land,
+yet they have been studied in many parts of the globe. In Norway, in
+Germany, in France, in Russia, in Siberia, in Kamtchatka, in parts of
+South America, in short, wherever the civilization of the white race
+has extended, _Silurian_ deposits have been observed, and everywhere
+they bear the same testimony to a profuse and varied creation. The
+earth was teeming then with life as now, and in whatever corner of
+its surface the geologist finds the old strata, they hold a dead
+fauna as numerous as that which lives and moves above it. Nor do we
+find that there was any gradual increase or decrease of any organic
+forms at the beginning or close of the successive periods.
+
+I think the impression that the faunæ of the early geological periods
+were more scanty than those of later times arises partly from the
+fact that the present creation is made a standard of comparison for
+all preceding creations. Of course, the collection of living types
+in any museum must be more numerous than those of fossil forms, for
+the simple reason that almost the whole of the present surface of
+the earth, with the animals and plants inhabiting it, is known to
+us, whereas the deposits of the _Silurian_ and _Devonian_ periods
+are exposed to view only over comparatively limited tracts and in
+disconnected regions. But let us compare a given extent of _Silurian_
+or _Devonian_ seashore with an equal extent of seashore belonging
+to our own time, and we shall soon be convinced that the one is as
+populous as the other. On the New England Coast there are about one
+hundred and fifty different kinds of fishes; in the Gulf of Mexico
+two hundred and fifty; in the Red Sea about the same. We may allow
+in present times an average of two hundred or two hundred and fifty
+different kinds of fishes to an extent of ocean covering about four
+hundred miles. Now, I have made a special study of the _Devonian_
+rocks of Northern Europe, in the Baltic, and along the shore of the
+German Ocean. I have found in those deposits alone one hundred and
+ten kinds of fossil fishes. To judge of the total number of species
+belonging to those early ages by the number known to exist now is
+about as reasonable as to infer that because Aristotle, familiar only
+with the waters of Greece, recorded less than three hundred kinds
+of fishes in his limited fishing-ground, therefore these were all
+the fishes then living. The fishing-ground of the geologist in the
+_Silurian_ and _Devonian_ periods is even more circumscribed than
+his, and belongs, besides, not to a living but to a dead world, far
+more difficult to decipher.
+
+Extinct animals exist all over the world; heaped together under the
+snows of Siberia, lying thick beneath the Indian soil, found wherever
+English settlers till the ground or work the mines in Australia,
+figured in the old encyclopedias of China, where the Chinese
+philosophers have drawn them with the accuracy of their nation, built
+into the most beautiful temples of classic lands--for even the stones
+of the Parthenon are full of the fragments of these old fossils, and
+if any chance had directed the attention of Aristotle toward them,
+the science of Paleontology would not have waited for its founder
+till Cuvier was born--in short, in every corner of the earth where
+the investigations of civilized men have penetrated, from the Arctic
+to Patagonia and the Cape of Good Hope, these relics tell us of
+successive populations lying far behind our own, and belonging to
+distinct periods of the world’s history.
+
+
+
+
+  CARBONIFEROUS PERIOD
+  --LOUIS FIGUIER
+
+
+In the history of our globe the Carboniferous period succeeds to
+the Devonian. It is in the formations of this latter epoch that we
+find the fossil fuel which has done so much to enrich and civilize
+the world in our own age. This period divides itself into two great
+sub-periods: 1. The _Coal-measures_; and 2. The _Carboniferous
+Limestone_. The first, a period which gave rise to the great deposits
+of coal; the second, to most important marine deposits, most
+frequently underlying the coal-fields in England, Belgium, France,
+and America.
+
+The limestone mountains, which form the base of the whole system,
+attain in places, according to Professor Phillips, a thickness
+of 2,500 feet. They are of marine origin, as is apparent by the
+multitude of fossils they contain of Zoophytes, Radiata, Cephalopoda,
+and Fishes. But the chief characteristic of this epoch is its
+strictly terrestrial flora--remains of plants now become as common
+as they were rare in all previous formations, announcing a great
+increase of dry land.
+
+The monuments of this era of profuse vegetation reveal themselves in
+the precious Coal-measures of England and Scotland. These give us
+some idea of the rich verdure which covered the surface of the earth,
+newly risen from the bosom of its parent waves. It was the paradise
+of terrestrial vegetation. The grand _Sigillaria_, the _Stigmaria_,
+and other fern-like plants, were especially typical of this age,
+and formed the woods, which were left to grow undisturbed; for as
+yet no living Mammals seem to have appeared; everything indicates
+a uniformly warm, humid temperature, the only climate in which
+the gigantic ferns of the Coal-measures could have attained their
+magnitude. Conifers have been found of this period with concentric
+rings, but these rings are more slightly marked than in existing
+trees of the same family, from which it is reasonable to assume that
+the seasonal changes were less marked than they are with us.
+
+Everything announces that the time occupied in the deposition of the
+Carboniferous Limestone was one of vast duration. Professor Phillips
+calculates that, at the ordinary rate of progress, it would require
+122,400 years to produce only sixty feet of coal. Geologists believe,
+moreover, that the upper Coal-measures, where bed has been deposited
+upon bed for ages upon ages, were accumulated under conditions of
+comparative tranquillity, but that the end of this period was marked
+by violent convulsions--by ruptures of the terrestrial crust, when
+the carboniferous rocks were upturned, contorted, dislocated by
+faults, and subsequently partially denuded, and thus appear now in
+depressions or basin-shaped concavities; and that upon this deranged
+and disturbed foundation a fourth geological system, called Permian,
+was constructed.
+
+Coal, as we shall find, is composed of the mineralized remains of
+the vegetation which flourished in remote ages of the world. Buried
+under an enormous thickness of rocks, it has been preserved to
+our days, after being modified in its inward nature and external
+aspect. Having lost a portion of its elementary constituents, it has
+become transformed into a species of carbon, impregnated with those
+bituminous substances which are the ordinary products of the slow
+decomposition of vegetable matter.
+
+Thus, coal is the substance of the plants which formed the forests,
+the vegetation, and the marshes of the ancient world, at a period
+too distant for human chronology to calculate with anything like
+precision.
+
+It is a remarkable circumstance that conditions of equable and warm
+climate, combined with humidity, do not seem to have been limited to
+any one part of the globe, but the temperature of the whole globe
+seems to have been nearly the same in very different latitudes. From
+the equatorial regions up to Melville Island, in the Arctic Ocean,
+where in our days eternal frost prevails--from Spitzbergen to the
+centre of Africa, the carboniferous flora is identically the same.
+When nearly the same plants are found in Greenland and Guinea; when
+the same species, now extinct, are met with of equal development at
+the equator as at the pole, we can not but admit that at this epoch
+the temperature of the globe was nearly alike everywhere. What we now
+call _climate_ was unknown in these geological times. There seems to
+have been then only one climate over the whole globe. It was at a
+subsequent period, that is, in later Tertiary times, that the cold
+began to make itself felt at the terrestrial poles. Whence, then,
+proceeded this general superficial warmth, which we now regard with
+so much surprise? It was a consequence of the greater or nearer
+influence of the interior heat of the globe. The earth was still so
+hot in itself that the heat which reached it from the sun may have
+been inappreciable.
+
+Another hypothesis, which has been advanced with much less certainty
+than the preceding, relates to the chemical composition of the
+air during the Carboniferous period. Seeing the enormous mass of
+vegetation which then covered the globe, and extended from one pole
+to the other; considering, also, the great proportion of carbon and
+hydrogen which exists in the bituminous matter of coal, it has been
+thought, and not without reason, that the atmosphere of the period
+might be richer in carbonic acid than the atmosphere of the present
+day. It has even been thought that the small number of (especially
+air-breathing) animals, which then lived, might be accounted for by
+the presence of a greater proportion of carbonic acid gas in the
+atmosphere than is the case in our own times. This, however, is
+pure assumption, totally deficient in proof. What we can remark,
+with certainty, as a striking characteristic of the vegetation of
+the globe during this phase of its history, was the prodigious
+development which it assumed. The Ferns, which in our days and in
+our climate are most commonly only small perennial plants, in the
+Carboniferous age sometimes presented themselves under lofty and even
+magnificent forms.
+
+Every one knows those marsh-plants with hollow, channeled, and
+articulated cylindrical stems; whose joints are furnished with a
+membranous, denticulated sheath, and which bear the vulgar name of
+“mare’s-tail”; their fructification forming a sort of catkin composed
+of many rings of scales, carrying on their lower surface sacs full of
+_spores_ or seeds. These humble _Equiseta_ were represented during
+the coal-period by herbaceous trees from twenty to thirty feet
+high and four to six inches in diameter. Their trunks, channeled
+longitudinally, and divided transversely by lines of articulation,
+have been preserved to us: they bear the name of _Calamites_.
+
+The _Lycopods_ of our age are humble plants, scarcely a yard in
+height, and most commonly creepers; but the Lycopodiaceæ of the
+ancient world were trees of eighty or ninety feet in height. It
+was the _Lepidodendrons_ which filled the forests. Their leaves
+were sometimes twenty inches long, and their trunks a yard in
+diameter. Such are the dimensions of some specimens of _Lepidodendron
+carinatum_ which have been found. Another Lycopod of this period, the
+_Lomatophloyos crassicaule_, attained dimensions still more colossal.
+The _Sigillarias_ sometimes exceeded 100 feet in height. Herbaceous
+Ferns were also exceedingly abundant, and grew beneath the shade of
+these gigantic trees. It was the combination of these lofty trees
+with such shrubs (if we may so call them) which formed the forests of
+the Carboniferous period.
+
+How this vegetation, so imposing, both on account of the dimensions
+of the individual trees and the immense space which they occupied, so
+splendid in its aspect, and yet so simple in its organization, must
+have differed from that which now embellishes the earth and charms
+our eyes! It certainly possessed the advantage of size and rapid
+growth; but how poor it was in species--how uniform in appearance! No
+flowers yet adorned the foliage or varied the tints of the forests.
+Eternal verdure clothed the branches of the Ferns, the Lycopods, and
+Equiseta, which composed to a great extent the vegetation of the age.
+The forests presented an innumerable collection of individuals, but
+very few species, and all belonging to the lower types of vegetation.
+No fruit appeared fit for nourishment; none would seem to have been
+on the branches. Suffice it to say that few terrestrial animals
+seem to have existed yet; animal life was apparently almost wholly
+confined to the sea, while the vegetable kingdom occupied the land,
+which at a later period was more thickly inhabited by air-breathing
+animals. Probably a few winged insects (some coleoptera, orthoptera,
+and neuroptera) gave animation to the air while exhibiting their
+variegated colors; and it was not impossible but that many
+pulmoniferous mollusca (such as land-snails) lived at the same time.
+
+The vegetation which covered the numerous islands of the
+Carboniferous sea consisted, then, of Ferns, of Equisetaceæ, of
+Lycopodiaceæ, and dicotyledonous Gymnosperms. The Annularia and
+Sigillariæ belong to families of the last-named class, which are now
+completely extinct.
+
+The _Annulariæ_ were small plants which floated on the surface of
+fresh-water lakes and ponds; their leaves were verticillate, that
+is, arranged in a great number of whorls, at each articulation of
+the stem with the branches. The _Sigillariæ_ were, on the contrary,
+great trees, consisting of a simple trunk, surmounted with a bunch or
+panicle of slender drooping leaves, with the bark often channeled,
+and displaying impressions or scars of the old leaves, which, from
+their resemblance to a seal, _sigillum_, gave origin to their name.
+
+The _Stigmariæ_, according to palæontologists, were roots of
+Sigillariæ, with a subterranean fructification; all that is known of
+them is the long roots which carry the reproductive organs, and in
+some cases are as much as sixteen feet long.
+
+Two other gigantic trees grew in the forests of this period: these
+were _Lepidodendron carinatum_ and _Lomatophloyos crassicaule_, both
+belonging to the family of Lycopodiaceæ, which now includes only very
+small species. The trunk of the Lomatophloyos threw out numerous
+branches, which terminated in thick tufts of linear and fleshy
+leaves. The Ferns composed a great part of the vegetation of the
+Coal-measure period.
+
+The seas of this epoch included an immense number of Zoophytes,
+nearly 400 species of Mollusca, and a few Crustaceans and Fishes.
+Among the Fishes, _Psammodus_ and _Coccosteus_, whose massive
+teeth inserted in the palate were suitable for grinding; and the
+_Holoptychius_ and _Megalichthys_, are the most important. The
+Mollusca are chiefly Brachiopods of great size. The _Bellerophon_,
+whose convoluted shell in some respects resembles the Nautilus of our
+present seas, but without its chambered shell, were then represented
+by many species.
+
+Crustaceans are rare in the Carboniferous Limestone strata; the genus
+Phillipsia is the last of the Trilobites, all of which became extinct
+at the close of this period. As to the Zoophytes, they consist
+chiefly of Crinoids and Corals. We also have in these rocks many
+Polyzoa.
+
+Among the corals of the period we may include the genera
+_Lithostrotion_ and _Lonsdalea_. Among the Polyzoa are the genera
+_Fenestrella_ and _Polypora_. Lastly, to these we may add a group
+of animals which will play a very important part and become
+abundantly represented in the beds of later geological periods, but
+which already abounded in the seas of the Carboniferous period. We
+speak of the _Foraminifera_, microscopic animals, which clustered
+either in one body or divided into segments, and covered with a
+calcareous, many-chambered shell, as _Fusulina cylindrica_. These
+little creatures, which, during the Jurassic and Cretaceous periods,
+formed enormous banks and entire masses of rock, began to make their
+appearance in the period which now engages our attention.
+
+This terrestrial period is characterized, in a remarkable manner, by
+the abundance and strangeness of the vegetation which then covered
+the islands and continents of the whole globe. Upon all points of the
+earth, as we have said, this flora presented a striking uniformity.
+In comparing it with the vegetation of the present day, the learned
+French botanist, M. Brongniart, who has given particular attention
+to the flora of the Coal-measures, has arrived at the conclusion
+that it presented considerable analogy with that of the islands
+of the equatorial and torrid zone, in which a maritime climate and
+elevated temperature exist in the highest degree. It is believed that
+islands were very numerous at this period; that, in short, the dry
+land formed a sort of vast archipelago upon the general ocean, of no
+great depth, the islands being connected together and formed into
+continents as they gradually emerged from the ocean.
+
+This flora, then, consists of great trees, and also of many
+smaller plants, which would form a close, thick turf, or sod,
+when partially buried in marshes of almost unlimited extent. M.
+Brongniart indicates, as characterizing the period, 500 species
+of plants which now attain a prodigious development. The ordinary
+dicotyledons and monocotyledons--that is, plants having seeds with
+two lobes in germinating and plants having one seed-lobe--are
+almost entirely absent; the cryptogamic, or flowerless plants,
+predominate; especially Ferns, Lycopodiaceæ, and Equisetaceæ--but
+of forms insulated and actually extinct in these same families. A
+few dicotyledonous gymnosperms, or naked-seed plants forming genera
+of Conifers, have completely disappeared, not only from the present
+flora, but since the close of the period under consideration, there
+being no trace of them in the succeeding Permian flora. Such is a
+general view of the features most characteristic of the coal-period,
+and of the Primary epoch in general. It differs, altogether and
+absolutely, from that of the present day; the climatic condition of
+these remote ages of the globe, however, enables us to comprehend the
+characteristics which distinguish its vegetation. A damp atmosphere,
+of an equable rather than an intense heat like that of the tropics,
+a soft light veiled by permanent fogs, were favorable to the growth
+of this peculiar vegetation, of which we search in vain for anything
+strictly analogous in our own days. The nearest approach to the
+climate and vegetation proper to the geological period which now
+occupies our attention would probably be found in certain islands,
+or on the littoral of the Pacific Ocean--the island of Chloë, for
+example, where it rains during 300 days in the year, and where the
+light of the sun is shut out by perpetual fogs; where arborescent
+Ferns form forests, beneath whose shade grow herbaceous Ferns, which
+rise three feet and upward above a marshy soil; which gives shelter
+also to a mass of cryptogamic plants, greatly resembling, in its
+main features, the flora of the Coal-measures. This flora was, as
+we have said, uniform and poor in its botanic genera, compared to
+the abundance and variety of the flora of the present time; but the
+few families of plants which existed then included many more species
+than are now produced in the same countries. The fossil Ferns of the
+coal-series in Europe, for instance, comprehend about 300 species,
+while all Europe now only produces fifty. The gymnosperms, which now
+muster only twenty-five species in Europe, then numbered more than
+120.
+
+Calamites are among the most abundant fossil plants of the
+Carboniferous period, and occur also in the Devonian. They are
+preserved as striated, jointed, cylindrical, or compressed stems,
+with fluted channels or furrows at their sides, and sometimes
+surrounded by a bituminous coating, the remains of a cortical
+integument. They were originally hollow, but the cavity is usually
+filled up with a substance into which they themselves have been
+converted.
+
+If, during the coal-period, the vegetable kingdom had reached its
+maximum, the animal kingdom, on the contrary, was poorly represented.
+Some remains have been found, both in America and Germany, consisting
+of portions of the skeleton and the impressions of the footsteps
+of a Reptile, which has received the name of Archegosaurus. Among
+the animals of this period we find a few Fishes, analogous to
+those of the Devonian formation. These are the _Holoptychius_ and
+_Megalichthys_, having jawbones armed with enormous teeth. Scales
+of _Pygopterus_ have been found in the Northumberland Coal-shale at
+Newsham Colliery, and also in the Staffordshire Coal-shale. Some
+winged insects would probably join this slender group of living
+beings. It may then be said with truth that the immense forests and
+marshy plains, crowded with trees, shrubs, and herbaceous plants,
+which formed on the innumerable isles of the period a thick and
+tufted sward, were almost destitute of animals.
+
+Coal, as we have said, is only the result of a partial decomposition
+of the plants which covered the earth during a geological period
+of immense duration. No one, now, has any doubt that this is its
+origin. In coal-mines it is not unusual to find fragments of the very
+plants whose trunks and leaves characterize the Coal-measures, or
+Carboniferous era. Immense trunks of trees have also been met with
+in the middle of a seam of coal. In order to explain the presence
+of coal in the depths of the earth, there are only two possible
+hypotheses. This vegetable débris may either result from the burying
+of plants brought from afar and transported by river or maritime
+currents, forming immense rafts, which may have grounded in different
+places and been covered subsequently by sedimentary deposits; or the
+trees may have grown on the spot where they perished, and where they
+are now found.
+
+Can the coal-beds result from the transport by water, and burial
+under ground, of immense rafts formed of the trunks of trees? The
+hypothesis has against it the enormous height which must be conceded
+to the raft, in order to form coal-seams as thick as some of those
+which are worked in our collieries. If we take into consideration the
+specific gravity of wood, and the amount of carbon it contains, we
+find that the coal-deposits can only be about seven-hundredths of the
+volume of the original wood and other vegetable materials from which
+they are formed. If we take into account, besides, the numerous voids
+necessarily arising from the loose packing of the materials forming
+the supposed raft, as compared with the compactness of coal, this may
+fairly be reduced to five-hundredths. A bed of coal, for instance,
+sixteen feet thick, would have required a raft 310 feet high for its
+formation. These accumulations of wood could never have arranged
+themselves with sufficient regularity to form those well-stratified
+coal-beds, maintaining a uniform thickness over many miles, and that
+are seen in most coal-fields to lie one above another in succession,
+separated by beds of sandstone or shale. And even admitting the
+possibility of a slow and gradual accumulation of vegetable débris,
+like that which reaches the mouth of a river, would not the plants
+in that case be buried in great quantities of mud and earth? Now,
+in most of our coal-beds the proportion of earthy matter does not
+exceed fifteen per cent of the entire mass. If we bear in mind,
+finally, the remarkable parallelism existing in the stratification
+of the coal-formation, and the state of preservation in which the
+impressions of the most delicate vegetable forms are discovered, it
+will, we think, be proved to demonstration that those coal-seams have
+been formed in perfect tranquillity. We are, then, forced to the
+conclusion that coal results from the mineralization of plants which
+has taken place on the spot; that is to say, in the very place where
+the plants lived and died.
+
+It was suggested long ago by Bakewell, from the occurrence of the
+same peculiar kind of fireclay under each bed of coal, that it was
+the soil proper for the production of those plants from which coal
+has been formed.
+
+[Illustration: Fingal’s Cave, Staffa, Coast of Scotland]
+
+The clay-beds, “which vary in thickness from a few inches to more
+than ten feet, are penetrated in all directions by a confused and
+tangled collection of the roots and leaves, as they may be, of the
+_Stigmaria ficoides_, these being frequently traceable to the main
+stem (_Sigillaria_), which varies in diameter from about two inches
+to half a foot. The main stems are noticed as occurring nearer
+the top than the bottom of the bed, as usually of considerable
+length, the leaves or roots radiating from them in a tortuous
+irregular course to considerable distances, and as so mingled with
+the under-clay that it is not possible to cut out a cubic foot of it
+which does not contain portions of the plant.”
+
+It is a natural inference to suppose that the present indurated
+under-clay is only another condition of that soft, silty soil, or
+of that finely levigated muddy sediment--most likely of still and
+shallow water--in which the vegetation grew, the remains of which
+were afterward carbonized and converted into coal.
+
+In order thoroughly to comprehend the phenomena of the transformation
+into coal of the forests and of the herbaceous plants which
+filled the marshes and swamps of the ancient world, there is
+another consideration to be presented. During the coal-period, the
+terrestrial crust was subjected to alternate movements of elevation
+and depression of the internal liquid mass, under the impulse of the
+solar and lunar attractions to which they would be subject, as our
+seas are now, giving rise to a sort of subterranean tide, operating
+at intervals, more or less widely apart, upon the weaker parts of
+the crust, and producing considerable subsidences of the ground.
+It might, perhaps, happen that, in consequence of a subsidence
+produced in such a manner, the vegetation of the coal-period would
+be submerged, and the shrubs and plants which covered the surface
+of the earth would finally become buried under water. After this
+submergence new forests sprung up in the same place. Owing to another
+submergence, the second forests were depressed in their turn, and
+again covered by water. It is probably by a series of repetitions
+of this double phenomenon--this submergence of whole regions of
+forest, and the development upon the same site of new growths of
+vegetation--that the enormous accumulations of semi-decomposed
+plants, which constitute the Coal-measures, have been formed in a
+long series of ages.
+
+But, has coal been produced from the larger plants only--for example,
+from the great forest-trees of the period, such as the Lepidodendra,
+Sigillariæ, Calamites, and Sphenophylla? That is scarcely probable,
+for many coal-deposits contain no vestiges of the great trees of the
+period, but only of Ferns and other herbaceous plants of small size.
+It is, therefore, presumable that the larger vegetation has been
+almost unconnected with the formation of coal, or, at least, that it
+has played a minor part in its production. In all probability there
+existed in the coal-period, as at the present time, two distinct
+kinds of vegetation: one formed of lofty forest-trees, growing on the
+higher grounds; the other, herbaceous and aquatic plants, growing on
+marshy plains. It is the latter kind of vegetation, probably, which
+has mostly furnished the material for the coal; in the same way
+that marsh-plants have, during historic times and up to the present
+day, supplied our existing peat, which may be regarded as a sort of
+contemporaneous incipient coal.
+
+To what modification has the vegetation of the ancient world been
+subjected to attain that carbonized state which constitutes coal?
+The submerged plants would, at first, be a light, spongy mass, in
+all respects resembling the peat-moss of our moors and marshes.
+While under water, and afterward, when covered with sediment,
+these vegetable masses underwent a partial decomposition--a moist,
+putrefactive fermentation, accompanied by the production of much
+carbureted hydrogen and carbonic acid gas. In this way, the hydrogen
+escaping in the form of carbureted hydrogen, and the oxygen in the
+form of carbonic acid gas, the carbon became more concentrated, and
+coal was ultimately formed. This emission of carbureted hydrogen gas
+would, probably, continue after the peat-beds were buried beneath
+the strata which were deposited and accumulated upon them. The mere
+weight and pressure of the superincumbent mass, continued at an
+increasing ratio during a long series of ages, have given to the coal
+its density and compact state.
+
+The heat emanating from the interior of the globe would also
+exercise a great influence upon the final result. It is to these two
+causes--that is to say, to pressure and to the central heat--that we
+may attribute the differences which exist in the mineral characters
+of various kinds of coal. The inferior beds are _drier_ and more
+compact than the upper ones; or less bituminous, because their
+mineralization has been completed under the influence of a higher
+temperature, and at the same time under a greater pressure.
+
+
+
+
+  THE PALÆONTOLOGICAL HISTORY OF ANIMALS
+  --HUGH MILLER
+
+
+However much the faunas of the various geologic periods may have
+differed from each other, or from the fauna which now exists, in
+their general aspect and character, they were all, if I may so speak,
+equally underlaid by the great leading ideas which still constitute
+the master types of animal life. And these leading ideas are four in
+number. _First_, there is the _star-like_ type of life--life embodied
+in a form that, as in the corals, the sea-anemones, the sea-urchins,
+and the star-fishes, radiates outward from a centre; _second_,
+there is the _articulated_ type of life--life embodied in a form
+composed, as in the worms, crustaceans, and insects, of a series of
+rings united by their edges, but more or less movable on each other;
+_third_, there is the bilateral or _molluscan_ type of life--life
+embodied in a form in which there is a duality of corresponding
+parts, ranged, as in the cuttle-fishes, the clams, and the snails,
+on the sides of a central axis or plane; and _fourth_, there is
+the _vertebrate_ type of life--life embodied in a form in which
+an internal skeleton is built up into two cavities placed the one
+over the other; the upper for the reception of the nervous centres,
+cerebral and spinal--the lower for the lodgment of the respiratory,
+circulatory, and digestive organs. Such have been the four central
+ideas of the faunas of every succeeding creation, except, perhaps,
+the earliest of all, that of the Lower Silurian System, in which, so
+far as is yet known, only three of the number existed--the radiated,
+articulated, and molluscan ideas or types.
+
+The fauna of the Silurian System bears in all its three great types
+the stamp of a fashion peculiarly antique, and which, save in a few
+of the mollusca, has long since become obsolete. Its radiate animals
+are chiefly corals, simple or compound, whose inhabitants may have
+somewhat resembled the sea-anemones; with zoophytes, akin mayhap to
+the sea-pens, though the relationship must have been a remote one;
+and numerous crinoids, or stone lilies, some of which consisted of
+but a sculptured calyx without petals, while others threw off a
+series of long flexible arms, that divided and subdivided like the
+branches of a tree, and were thickly fringed by hair-like fibres.
+
+The articulata of the Silurian period bore a still more peculiar
+character. They consisted mainly of the Trilobites--a family in
+whose nicely jointed shells the armorer of the Middle Ages might
+have found almost all the contrivances of his craft anticipated,
+with not a few besides which he had failed to discover; and which,
+after receiving so immense a development during the middle and later
+times of the Silurian period that whole rocks were formed almost
+exclusively of their remains, gradually died out in the times of
+the Old Red Sandstone, and disappeared forever from creation after
+the Carboniferous Limestone had been deposited. The mollusca of
+the Silurians ranged from the high cephalopoda, represented in our
+existing seas by the nautili and the cuttle-fishes, to the low
+brachiopods, some of whose cogeners may still be detected in the
+terebratulæ of the Highland lochs and bays, and some in the lingulæ
+of the Southern Hemisphere. The cephalopods of the system are all of
+an obsolete type, that disappeared myriads of ages ago. At length, in
+an upper bed of the system, immediately under the base of the Old Red
+Sandstone, the remains of the earliest known fishes appear, blended
+with what also appears for the first time--the fragmentary remains
+of a terrestrial vegetation. The rocks beneath this ancient bone-bed
+have yielded no trace of any plant higher than the Thallogens,
+or at least not higher than the Zosteraceæ--plants whose proper
+habitat is the sea; but, through an apparently simultaneous advance
+of the two kingdoms, animal and vegetable--though, of course, the
+simultaneousness may be but merely apparent--the first land-plants
+and the first vertebrates appear together in the same deposit. The
+earliest fishes--first-born of their family--seem to have been all
+placoids. The Silurian System has not yet afforded trace of any other
+vertebral animal. With the Old Red Sandstone the ganoids were ushered
+upon the scene in amazing abundance; and for untold ages, comprising
+mayhap millions of years, the entire ichthyic class consisted, so far
+as is yet known, of but these two orders. During the times of the Old
+Red Sandstone, of the Carboniferous, of the Permian, of the Triassic,
+and of the Oolitic Systems, all fishes, though apparently as numerous
+individually as they are now, were comprised in the ganoidal and
+placoidal orders. The period of these orders seems to have been
+nearly correspondent with the reign, in the vegetable kingdom, of the
+Acrogens and Gymnogens, with the intermediate classes, their allies.
+At length, during the ages of the Chalk, the Cycloids and Ctenoids
+were ushered in, and were gradually developed in creation until the
+human period, in which they seem to have reached their culminating
+point, and now many times exceed in number and importance all other
+fishes. The delicate Salmonidæ and the Pleuronectidæ--families to
+which the salmon and turbot belong--were ushered into being as early
+as the times of the Chalk; but the Gadidæ or cod family--that family
+to which the cod proper, the haddock, the dorse, the whiting, the
+coal-fish, the pollock, the hake, the torsk, and the ling belong,
+with many other useful and wholesome species--did not precede man by
+at least any period of time appreciable to the geologist. No trace of
+the family has yet been detected in even the Tertiary rocks.
+
+Of the ganoids of the second age of vertebrate existence--that of
+the Old Red Sandstone--some were remarkable for the strangeness
+of their forms, and some for constituting links of connection,
+which no longer exist in nature, between the ganoid and placoid
+orders. The Acanth family, which ceased with the Coal-measures, was
+characterized, especially in its Old Red species, by a combination
+of traits common to both orders; and among the extremer forms, in
+which palæontologists for a time failed to detect that of the fish
+at all, we reckon those of the genera Coccosteus, Pterichthys, and
+Cephalaspis. The more aberrant genera, however, even while they
+consisted each of several species, were comparatively short-lived.
+The Coccosteus and Cephalaspis were restricted to but one formation
+apiece; while the Pterichthys, which appears for the first time in
+the lower deposits of the Old Red Sandstone, becomes extinct at its
+close. On the other hand, some of the genera that exemplified the
+general type of their class were extremely long-lived. The Celacanths
+were reproduced in many various species, from the times of the Lower
+Old Red Sandstone to those of the Chalk; and the Cestracions, which
+appear in the Upper Ludlow Rocks as the oldest of fishes, continue in
+at least one species to exist still.
+
+The ancient fishes seem to have received their fullest development
+during the Carboniferous period. Their number was very great: some
+of them attained to an enormous size, and, though the true reptile
+had already appeared, they continued to retain till the close of
+the System the high reptilian character and organization. Nothing,
+however, so impresses the observer as the formidable character of the
+offensive weapons with which they were furnished, and the amazing
+strength of their defensive armature. I need scarce say that the
+palæontologist finds no trace in nature of that golden age of the
+world, of which the poets delighted to sing, when all creatures lived
+together in unbroken peace, and war and bloodshed were unknown. Ever
+since animal life began upon our planet there existed, in all the
+departments of being, carnivorous classes, who could not live but by
+the death of their neighbors, and who were armed, in consequence,
+for their destruction, like the butcher with his axe and knife, and
+the angler with his hook and spear. But there were certain periods
+in the history of the past during which these weapons assumed a more
+formidable aspect than at others; and never were they more formidable
+than in the times of the Coal-measures. The teeth of the Rhizodus--a
+ganoidal fish of our coal-fields--were more sharp and trenchant than
+those of the crocodile of the Nile, and in the larger specimens fully
+four times the bulk and size of the teeth of the hugest reptile of
+this species that now lives. The dorsal spine of its contemporary,
+the Gyracanthus, a great placoid, much exceeded in size that of any
+existing fish; it was a mighty spearhead, ornately carved like that
+of a New Zealand chief, but in a style that, when he first saw a
+specimen in my collection, greatly excited the admiration of Mr.
+Ruskin. But one of the most remarkable weapons of the period was
+the sting of the Pleuracanthus, another great placoid of the age of
+gigantic fishes. It was sharp and polished as a stiletto, but, from
+its rounded form and dense structure, of great strength; and along
+two of its sides, from the taper point to within a few inches of the
+base, there ran a thickly set row of barbs, hooked downward, like
+the thorns that bristle on the young shoots of the wild rose, and
+which must have rendered it a weapon not merely of destruction, but
+also of torture. The defensive armor of the period, especially that
+of its ganoids, seems to have been as remarkable for its powers of
+resistance as the offensive must have been for their potency in the
+assault; and it seems probable that in the great strength of the bony
+and enameled armature of this order of fishes we have the secret of
+the extremely formidable character of the teeth, spines, and stings
+that coexisted along with it.
+
+The oldest known reptiles appear just a little before the close of
+the Old Red Sandstone, just as the oldest known fishes appeared
+just a little before the close of the Silurian System. What seems
+to be the Upper Old Red of Great Britain, though there still hangs
+a shade of doubt on the subject, has furnished the remains of a
+small reptile, equally akin, it would appear, to the lizards and the
+batrachians; and what seems to be the Upper Old Red of the United
+States has exhibited the foot-tracks of a larger animal of the same
+class, which not a little resemble those which would be impressed on
+recent sand or clay by the alligator of the Mississippi, did not the
+alligator of the Mississippi efface its own footprints (a consequence
+of the shortness of its legs) by the trail of its abdomen. In the
+Coal-measures the reptiles hitherto found are all allied, though
+not without a cross of the higher crocodilian or lacertian nature,
+to the batrachian order--that lowest order of the reptiles to which
+the frogs, newts, and salamanders belong. It was not, however, until
+the Permian and Triassic Systems had come to a close, and even the
+earlier ages of the Oolitic System had passed away, that the class
+received its fullest development in creation. And certainly very
+wonderful was the development which it then did receive. Reptiles
+became everywhere the lords and masters of this lower world. When
+any class of the air-breathing vertebrates is very largely developed,
+we find it taking possession of all the three old terrestrial
+elements--earth, air, and water. The human period, for instance,
+like that which immediately preceded it, is peculiarly a period of
+mammals; and we find the class _free_, if I may so express myself, of
+the three elements, disputing possession of the sea with the fishes,
+in its Cetaceans, its seals and its sea-lions, and of the air with
+the birds, in its numerous genera of the bat family. Further, not
+until the great mammaliferous period is fairly ushered in do either
+the bats or the whales make their appearance in creation. Remains of
+Oolitic reptiles have been mistaken in more than one instance for
+those of Cetacea; but it is now generally held that the earliest
+known specimens of the family belong to the Tertiary ages, while
+those of the oldest bats occur in the Eocene of the Paris basin,
+associated with the bones of dolphins, lamantines, and morses. Now,
+in the times of the Oolite it was the reptilian class that possessed
+itself of all the elements. Its gigantic enaliosaurs, huge reptilian
+whales mounted on paddles, were the tyrants of the ocean, and must
+have reigned supreme over the already reduced class of fishes; its
+pterodactyles--dragons as strange as were ever feigned by romancer
+of the Middle Ages, and that to the jaws and teeth of the crocodile
+added the wings of a bat and the body and tail of an ordinary
+mammal--had the “power of the air,” and, pursuing the fleetest
+insects in their flight, captured and bore them down; its lakes and
+rivers abounded in crocodiles and fresh-water tortoises of ancient
+type and fashion; and its woods and plains were the haunts of a
+strange reptilian fauna of what has been well termed “fearfully great
+lizards”--some of which, such as the iguanodon, rivaled the largest
+elephant in height, and greatly more than rivaled him in length and
+bulk. Judging from what remains, it seems not improbable that the
+reptiles of this Oolitic period were quite as numerous individually,
+and consisted of wellnigh as many genera and species as all the
+mammals of the present time. In the cretaceous ages, the class,
+though still the dominant one, is visibly reduced in its standing:
+it had reached its culminating point in the Oolite and then began to
+decline; and with the first dawn of the Tertiary division we find it
+occupying, as now, a very subordinate place in creation. Curiously
+enough, it is not until its times of humiliation and decay that
+one of the most remarkable of its orders appears--an order itself
+illustrative of extreme degradation, and which figures largely in
+every scheme of mythology that borrowed through traditional channels
+from Divine revelation, as a meet representative of man’s great
+enemy, the Evil One. I, of course, refer to the ophidian or serpent
+family. The earliest ophidian remains known to the palæontologist
+occur in that ancient deposit of the Tertiary division known as the
+London Clay, and must have belonged to serpents, some of them allied
+to the Pythons, some to the sea-snakes, which, judging from the
+corresponding parts of recent species, must have been from fourteen
+to twenty feet in length.
+
+Birds make their first appearance in a Red Sandstone deposit of the
+United States in the valley of the Connecticut, which was at one time
+supposed to belong to the Triassic System, but which is now held to
+be at least not older than the times of the Lias. No fragments of
+the skeletons of birds have yet been discovered in formations older
+than the Chalk; the Connecticut remains are those of footprints
+exclusively; and yet they tell their extraordinary story, so far as
+it extends, with remarkable precision and distinctness. They were
+apparently all of the Grallæ or stilt order of birds--an order to
+which the cranes, herons, and bustards belong, with the ostriches and
+cassowaries, and which is characterized by possessing but three toes
+on each foot (one species of ostrich has but two), or, if a fourth
+toe be present, so imperfectly is it developed in most of the cases
+that it fails to reach the ground. And in almost all the footprints
+of the primeval birds of the Connecticut there are only three toes
+exhibited. The immense size of some of these footprints served to
+militate for a time against belief in their ornithic origin. The
+impressions that are but secondary in point of size greatly exceed
+those of the hugest birds which now exist; while those of the
+largest class equal the prints of the bulkier quadrupeds. There are
+tridactyle footprints in the Red Sandstones of Connecticut that
+measure eighteen inches in length from the heel to the middle claw,
+nearly thirteen inches in breadth from the outer to the inner toe,
+and which indicate, from their distance apart in the straight line,
+a stride of about six feet in the creature that impressed them in
+these ancient sands--measurements that might well startle zoologists
+who had derived their experience of the ornithic class from existing
+birds exclusively. In a deposit of New Zealand that dates little
+if at all in advance of the human period, there have been detected
+the remains of birds scarce inferior in size to those of America in
+the Liassic ages. The bones of the _Dinornus giganteus_, exhibited
+by Dr. Mantell in Edinburgh in 1850, greatly exceeded in bulk those
+of the largest horse. The larger thigh-bone referred to must have
+belonged, it was held, to a bird that stood from eleven to twelve
+feet high--the extreme height of the great African elephant. Such
+were the monster birds of a comparatively recent period; and their
+remains serve to render credible the evidence furnished by the great
+footprints of their remote predecessors of the Lias. The huge feet of
+the greatest Dinornus would have left impressions scarcely an inch
+shorter than those of the still huger birds of the Connecticut.
+
+With the Stonesfield slates--a deposit which lies above what is known
+as the Inferior Oolite--the remains of mammaliferous animals first
+appear.
+
+The Eocene ages were peculiarly the ages of the Palæotheres--strange
+animals of, that pachydermatous or thick-skinned order to which the
+elephants, the tapirs, the hogs, and the horses belong. It had been
+remarked by naturalists that there are fewer families of this order
+in living nature than of almost any other, and that of the existing
+genera not a few are widely separated in their analogies from the
+others. But in the Palæotheres of the Eocene, which ranged in size
+from a large horse to a hare, not a few of the missing links have
+been found--links connecting the tapirs to the hogs, and the hogs to
+the Palæotheres proper; and there is at least one species suggestive
+of a union of some of the more peculiar traits of the tapirs and the
+horses. It was among these extinct Pachydermata of the Paris basin
+that Cuvier effected his wonderful restorations, and produced those
+figures in outline which are now as familiar to the geologist as
+any of the forms of the existing animals. The London Clay and the
+Eocene of the Isle of Wight have also yielded numerous specimens of
+these pachyderms, whose identity with the Continental ones has been
+established by Owen; but they are more fragmentary, and their state
+of keeping less perfect than those furnished by the gypsum quarries
+of Velay and Montmartre.
+
+In the Middle or Miocene Tertiary, pachyderms, though of a wholly
+different type from their predecessors, are still the prevailing
+forms. The Dinotherium, one of the greatest quadrupedal mammals that
+ever lived, seems to have formed a connecting link in this middle age
+between the Pachydermata and the Cetaceæ. Each ramus of the under
+jaw, which in the larger specimens are fully four feet in length,
+bore at the symphysis a great bent tusk turned downward, which
+appears to have been employed as a pick-axe in uprooting the aquatic
+plants and liliaceous roots on which the creature seems to have
+lived. The head, which measured about three feet across--a breadth
+sufficient, surely, to satisfy the demands of the most exacting
+phrenologist--was provided with muscles of enormous strength,
+arranged so as to give potent effect to the operations of this
+strange tool. The hinder part of the skull not a little resembled
+that of the Cetaceæ; while, from the form of the nasal bones, the
+creature was evidently furnished with a trunk like the elephant. It
+seems not improbable, therefore, that this bulkiest of mammaliferous
+quadrupeds constituted, as I have said, a sort of uniting tie between
+creatures still associated in the human mind, from the circumstances
+of their massive proportions, as the greatest that swim the sea
+or walk the land--the whale and the elephant The Mastodon, an
+elephantoid animal, also furnished, like the elephant, with tusks
+and trunk, but marked by certain peculiarities which constitute it
+a different genus, seems in Europe to have been contemporary with
+the Dinotherium; but in North America (the scene of its greatest
+numerical development) it appears to belong to a later age. In
+height it did not surpass the African elephant, but it considerably
+exceeded it in length--a specimen which could not have stood above
+twelve feet high indicating a length of about twenty-five feet: it
+had what the elephants want--tusks fixed in its lower jaw, which the
+males retained through life, but the females lost when young; its
+limbs were proportionally shorter, but more massive, and its abdomen
+more elongated and slim; its grinder teeth, too, some of which have
+been known to weigh from seventeen to twenty pounds, had their cusps
+elevated into great mammæ-like protuberances, to which the creature
+owes its name, and wholly differ in their proportions and outline
+from the grinders of the elephant. The much greater remoteness of the
+mastodontic period in Europe than in America is a circumstance worthy
+of notice, as it is one of many facts that seem to indicate a general
+transposition of at least the later geologic ages on the opposite
+sides of the Atlantic.
+
+
+
+
+  EUROPEAN AND ASIATIC DELUGES
+  --LOUIS FIGUIER
+
+
+The Tertiary formations, in many parts of Europe of more or less
+extent, are covered by an accumulation of heterogeneous deposits,
+filling up the valleys, and composed of very various materials,
+consisting mostly of fragments of the neighboring rocks. The erosions
+which we remark at the bottoms of the hills, and which have greatly
+enlarged already existing valleys; the mounds of gravel accumulated
+at one point, and which is formed of rolled materials, that is
+to say, of fragments of rocks worn smooth and round by continual
+friction during a long period, in which they have been transported
+from one point to another--all these signs indicate that these
+denudations of the soil, these displacements and transports of very
+heavy bodies to great distances, are due to the violent and sudden
+action of large currents of water. An immense wave has been thrown
+suddenly on the surface of the earth, making great ravages in its
+passage, furrowing the earth and driving before it débris of all
+sorts in its disorderly course.
+
+To what cause are we to attribute these sudden and apparently
+temporary invasions of the earth’s surface by rapid currents of
+water? In all probability to the upheaval of some vast extent of dry
+land, to the formation of some mountain or mountain range in the
+neighborhood of the sea, or even in the bed of the sea itself. The
+land, suddenly elevated by an upward movement of the terrestrial
+crust, or by the formation of ridges and furrows at the surface, has,
+by its reaction, violently agitated the waters, that is to say, the
+more mobile portion of the globe. By this new impulse the waters have
+been thrown with great violence over the earth, inundating the plains
+and valleys, and for the moment covering the soil with their furious
+waves, mingled with the earth, sand, and mud, of which the devastated
+districts have been denuded by their abrupt invasion.
+
+There have been, doubtless, during the epochs anterior to the
+Quaternary period many deluges such as we are considering. Mountains
+and chains of mountains were formed by upheaval of the crust into
+ridges, where it was too elastic or too thick to be fractured. Each
+of these subterranean commotions would be provocative of momentary
+irruptions of the waves.
+
+But the visible testimony to this phenomenon--the living proofs
+of this denudation, of this tearing away of the soil--is found
+nowhere so strikingly as in the beds superimposed, far and near,
+upon the Tertiary formations, and which bear the geological name of
+_diluvium_. This term was long employed to designate what is now
+better known as the “bowlder” formation, a glacial deposit which is
+abundant in Europe north of the 50th, and in America north of the
+40th, parallel, and reappearing again in the Southern Hemisphere;
+but altogether absent in tropical regions. It consists of sand and
+clay, sometimes stratified, mixed with rounded and angular fragments
+of rock, generally derived from the same district; and their origin
+has generally been ascribed to a series of diluvial waves raised
+by hurricanes, earthquakes, or the sudden upheaval of land from
+the bed of the sea, which had swept over continents, carrying with
+them vast masses of mud and heavy stones, and forcing these stones
+over rocky surfaces so as to polish and impress them with furrows
+and striæ. Other circumstances occurred, however, to establish a
+connection between this formation and the glacial drift. The size and
+number of the erratic blocks increase as we travel toward the Arctic
+regions; some intimate association exists, therefore, between this
+formation and the accumulations of ice and snow which characterize
+the approaching glacial period.
+
+There is very distinct evidence of two successive deluges in our
+hemisphere during the Quaternary epoch. The two may be distinguished
+as the _European Deluge_ and the _Asiatic_. The two European deluges
+occurred prior to the appearance of man; the Asiatic deluge happened
+after that event; and the human race, then in the early days of its
+existence, certainly suffered from this cataclysm.
+
+The first occurred in the north of Europe, where it was produced by
+the upheaval of the mountains of Norway. Commencing in Scandinavia,
+the wave spread and carried its ravages into those regions which
+now constitute Sweden, Norway, European Russia, and the north of
+Germany, sweeping before it all the loose soil on the surface, and
+covering the whole of Scandinavia--all the plains and valleys of
+Northern Europe--with a mantle of transported soil. As the regions
+in the midst of which this great mountainous upheaval occurred--as
+the seas surrounding these vast spaces were partly frozen and covered
+with ice, from their elevation and neighborhood to the pole--the wave
+which swept these countries carried along with it enormous masses of
+ice.
+
+The physical proof of this _deluge of the north of Europe_ exists
+in the accumulation of unstratified deposits which covers all the
+plains and low grounds of Northern Europe. On and in this deposit
+are found numerous blocks which have received the characteristic
+and significant name of erratic blocks, and which are frequently of
+considerable size. These become more characteristic as we ascend to
+higher latitudes, as in Norway, Sweden, and Denmark, the southern
+borders of the Baltic, and in the British Islands generally, in all
+of which countries deposits of marine fossil shells occur, which
+prove the submergence of large areas of Scandinavia, of the British
+Isles, and other regions during parts of the glacial period. Some of
+these rocks, characterized as _erratic_, are of very considerable
+volume; such, for instance, is the granite block which forms the
+pedestal of the statue of Peter the Great at St. Petersburg. This
+block was found in the interior of Russia, where the whole formation
+is _Permian_, and its presence there can only be explained by
+supposing it to have been transported by some vast iceberg, carried
+by a diluvial current. This hypothesis alone enables us to account
+for another block of granite, weighing about 340 tons, which was
+found on the sandy plains in the north of Prussia, an immense model
+of which was made for the Berlin Museum. The last of these erratic
+blocks deposited in Germany covers the grave of King Gustavus
+Adolphus, of Sweden, killed at the battle of Lutzen, in 1632. He was
+interred beneath the rock. Another similar block has been raised in
+Germany into a monument to the geologist Leopold von Buch.
+
+These erratic blocks, which are met with in the plains of Russia,
+Poland, and Prussia, and in the eastern parts of England, are
+composed of rocks entirely foreign to the region where they are
+found. They belong to the primary rocks of Norway; they have been
+transported to their present sites, protected by a covering of ice,
+by the waters of the northern deluge.
+
+The second European deluge is supposed to have been the result of
+the formation and upheaval of the Alps. It has filled with débris
+and transported material the valleys of France, Germany, and Italy
+over a circumference which has the Alps for its centre. The proofs
+of a great convulsion at a comparatively recent geological date are
+numerous. The Alps may be from eighty to one hundred miles across,
+and the probabilities are that their existence is due, as Sir Charles
+Lyell supposes, to a succession of unequal movements of upheaval and
+subsidence; that the Alpine region had been exposed for countless
+ages to the action of rain and rivers, and that the larger valleys
+were of pre-glacial times, is highly probable. In the eastern part
+of the chain some of the Primary fossiliferous rocks, as well as
+Oolitic and Cretaceous rocks, and even Tertiary deposits, are
+observable; but in the central Alps these disappear, and more recent
+rocks, in some places even Eocene strata, graduate into metamorphic
+rocks, in which Oolitic, Cretaceous, and Eocene strata have been
+altered into granular marble, gneiss, and other metamorphic schists;
+showing that eruptions continued after the deposit of the Middle
+Eocene formations. Again, in the Swiss and Savoy Alps, Oolitic and
+Cretaceous formations have been elevated to the height of 12,000
+feet, and Eocene strata 10,000 feet above the level of the sea; while
+in the Rothal, in the Bernese Alps, occurs a mass of gneiss 1,000
+feet thick between two strata containing Oolitic fossils.
+
+Besides these proofs of recent upheaval, we can trace effects of two
+different kinds, resulting from the powerful action of masses of
+water violently displaced by this gigantic upheaval. At first broad
+tracks have been hollowed out by the diluvial waves, which have, at
+these points, formed deep valleys. Afterward these valleys have been
+filled up by materials derived from the mountain and transported
+into the valley, these materials consisting of rounded pebbles,
+argillaceous and sandy mud, generally calcareous and ferriferous.
+This double effect is exhibited, with more or less distinctness, in
+all the great valleys of the centre and south of France. The valley
+of the Garonne is, in respect to these phenomena, classic ground, as
+it were.
+
+The small valleys, tributary to the principal valley, would appear to
+have been excavated secondarily, partly out of diluvial deposits, and
+their alluvium, essentially earthy, has been formed at the expense of
+the Tertiary formation, and even of the diluvium itself. Among other
+celebrated sites, the diluvial formation is largely developed in
+Sicily. The ancient temple of the Parthenon at Athens is built on an
+eminence formed of diluvial earth.
+
+In the valley of the Rhine, in Alsace, and in many isolated parts of
+Europe, a particular sort of _diluvium_ forms thick beds; it consists
+of a yellowish-gray mud, composed of argillaceous matter mixed with
+carbonate of lime, quartzose and micaceous sand, and oxide of iron.
+This mud, termed by geologists _loess_, attains in some places
+considerable thickness. It is recognizable in the neighborhood of
+Paris. It rises a little both on the right and left, above the base
+of the mountains of the Black Forest and of the Vosges; and forms
+thick beds on the banks of the Rhine.
+
+The fossils contained in diluvial deposits consist, generally, of
+terrestrial, lacustrine, or fluviatile shells, for the most part
+belonging to species still living. In parts of the valley of the
+Rhine, between Bingen and Basle, the fluviatile loam or _loess_,
+now under consideration, is seen forming hills several hundred feet
+thick, and containing, here and there, throughout that thickness,
+land and fresh-water shells; from which it seems necessary to
+suppose, according to Lyell, first, a time when the _loess_ was
+slowly accumulated, then a later period, when large portions of it
+were removed--and followed by movements of oscillation, consisting,
+first, of a general depression, and then of a gradual re-elevation of
+the land.
+
+The Asiatic deluge--of which sacred history has transmitted to us
+the few particulars we know--was the result of the upheaval of a
+part of the long chain of mountains which are a prolongation of
+the Caucasus. The earth opening by one of the fissures made in its
+crust, in course of cooling, an eruption of volcanic matter escaped
+through the enormous crater so produced. Volumes of watery vapor or
+steam accompanied the lava discharged from the interior of the globe,
+which, being first dissipated in clouds and afterward condensing,
+descended in torrents of rain, and the plains were drowned with the
+volcanic mud. The inundation of the plains over an extensive radius
+was the immediate effect of this upheaval, and the formation of the
+volcanic cone of Mount Ararat, with the vast plateau on which it
+rests, altogether 17,323 feet above the sea, the permanent result.
+The event is graphically detailed in the seventh chapter of Genesis.
+
+All the particulars of the Biblical narrative here recited are only
+to be explained by the volcanic and muddy eruption which preceded the
+formation of Mount Ararat. The waters which produced the inundation
+of these countries proceeded from a volcanic eruption accompanied
+by enormous volumes of vapor, which in due course became condensed
+and descended on the earth, inundating the extensive plains which
+now stretch away from the foot of Ararat. The expression, “the
+earth,” or “all the earth,” as it is translated in the Vulgate, which
+might be implied to mean the entire globe, is explained by Marcel
+de Serres, in a learned book entitled _La Cosmogonie de Moïse_,
+and other philologists, as being an inaccurate translation. He has
+proved that the Hebrew word _haarets_, incorrectly translated “all
+the earth,” is often used in the sense of _region_ or _country_, and
+that, in this instance, Moses used it to express only the part of
+the globe which was then peopled, and not its entire surface. In the
+same manner “_the mountains_” (rendered “_all the mountains_” in the
+Vulgate) only implies all the mountains known to Moses.
+
+Of this deluge many races besides the Jews have preserved a
+tradition. Moses dates it from 1,500 to 1,800 years before the epoch
+in which he wrote. Berosus, the Chaldean historian, who wrote at
+Babylon in the time of Alexander, speaks of a universal deluge, the
+date of which he places immediately before the reign of Belus, the
+father of Ninus.
+
+The _Vedas_, or sacred books of the Hindus, supposed to have been
+composed about the same time as Genesis, that is, about 3,300 years
+ago, make out that the deluge occurred 1,500 years before their time.
+The _Guebers_ speak of the same event as having occurred about the
+same date.
+
+Confucius, the celebrated Chinese philosopher and lawgiver, born
+toward the year 551 before Christ, begins his history of China by
+speaking of the Emperor named Jas, whom he represents as making the
+waters flow back, which, being _raised to the heavens_, washed the
+feet of the highest mountains, covered the less elevated hills, and
+inundated the plains. Thus the Biblical deluge is confirmed in many
+respects; but it was local, like all phenomena of the kind, and was
+the result of the upheaval of the mountains of western Asia.
+
+
+
+
+  GLACIERS
+  --LOUIS AGASSIZ
+
+
+The long summer was over. For ages a tropical climate had prevailed
+over a great part of the earth, and animals whose home is now beneath
+the equator roamed over the world from the far south to the very
+borders of the Arctics. The gigantic quadrupeds, the mastodons,
+elephants, tigers, lions, hyenas, bears, whose remains are found in
+Europe from its southern promontories to the northernmost limits of
+Siberia and Scandinavia, and in America from the Southern States
+to Greenland and the Melville Islands, may indeed be said to have
+possessed the earth in those days. But their reign was over. A
+sudden intense winter, that was also to last for ages, fell upon
+our globe; it spread over the very countries where these tropical
+animals had their homes, and so suddenly did it come upon them that
+they were embalmed beneath masses of snow and ice, without time even
+for the decay which follows death. The elephant was by no means a
+solitary specimen; upon further investigation it was found that the
+disinterment of these large tropical animals in Northern Russia and
+Asia was no unusual occurrence. Indeed, their frequent discoveries
+of this kind had given rise among the ignorant inhabitants to the
+singular superstition that gigantic moles lived under the earth which
+crumbled away and turned to dust as soon as they came to the upper
+air. This tradition, no doubt, arose from the fact that, when in
+digging they came upon the bodies of these animals, they often found
+them perfectly preserved under the frozen ground, but the moment
+they were exposed to heat and light they decayed and fell to pieces
+at once. Admiral Wrangell, whose Arctic explorations have been so
+valuable to science, tells us that the remains of these animals are
+heaped up in such quantities in certain parts of Siberia that he and
+his men climbed over ridges and mounds consisting entirely of the
+bones of elephants, rhinoceroses, etc.
+
+We have as yet no clew to the source of this great and sudden change
+of climate. Various suggestions have been made, among others that
+formerly the inclination of the earth’s axis was greater, or that
+the submersion of the continents under water might have produced
+a decided increase of cold; but none of these explanations is
+satisfactory, and science has yet to find any cause which accounts
+for all the phenomena connected with it. It seems, however,
+unquestionable that, since the opening of the Tertiary age, a cosmic
+summer and winter have succeeded each other, during which a tropical
+heat and an Arctic cold have alternately prevailed over a great
+portion of the present temperate zone. In the so-called drift (a
+superficial deposit subsequent to the Tertiaries) there are found far
+to the south of their present abode the remains of animals whose
+home now is in the Arctics or the coldest parts of the Temperate
+Zones. Among them are the musk-ox, the reindeer, the walrus, the
+seal, and many kinds of shells characteristic of the Arctic regions.
+The northernmost part of Norway and Sweden is at this day the
+southern limit of the reindeer in Europe; but their fossil remains
+are found in large quantities in the drift about the neighborhood of
+Paris, and they have been traced even to the foot of the Pyrenees,
+where their presence would, of course, indicate a climate similar to
+the one now prevailing in Northern Scandinavia. Side by side with
+the remains of the reindeer are found those of the European marmot,
+whose present home is in the mountains, about six thousand feet
+above the level of the sea. The occurrence of these animals in the
+superficial deposits of the plains of Central Europe, one of which
+is now confined to the high north and the other to mountain heights,
+certainly indicates an entire change of climatic conditions since
+the time of their existence. European shells now confined to the
+Northern Ocean are found as fossils in Italy, showing that, while
+the present Arctic climate prevailed in the Temperate Zone, that of
+the Temperate Zone extended much further south to the regions we now
+call sub-tropical. In America there is abundant evidence of the same
+kind; throughout the recent marine deposits of the Temperate Zone,
+covering the low lands above tide water on this Continent, are found
+fossil shells whose present home is on the shores of Greenland. It is
+not only in the Northern Hemisphere that these remains occur, but in
+Africa and in South America, wherever there has been an opportunity
+for investigation, the drift is found to contain the traces of
+animals whose presence indicates a climate many degrees colder than
+that now prevailing there.
+
+But these organic remains are not the only evidence of the geological
+winter. There are a number of phenomena indicating that during
+this period two vast caps of ice stretched from the northern pole
+southward and from the southern pole northward, extending in each
+case far toward the equator, and that ice fields, such as now spread
+over the Arctics, covered a great part of the Temperate Zones, while
+the line of perpetual ice and snow in the tropical mountain ranges
+descended far below its present limits.
+
+The first essential condition for the formation of glaciers in
+mountain ranges is the shape of their valleys. Glaciers are by no
+means in proportion to the height and extent of mountains. There
+are many mountain chains as high or higher than the Alps which can
+boast of but few and small glaciers, if, indeed, they have any. In
+the Andes, the Rocky Mountains, the Pyrenees, the Caucasus, the few
+glaciers remaining from the great ice period are insignificant in
+size. The volcanic, cone-like shape of the Andes gives, indeed, but
+little chance for the formation of glaciers, though their summits
+are capped with snow. The glaciers of the Rocky Mountains have been
+little explored, but it is known that they are by no means extensive.
+In the Pyrenees there is but one great glacier, though the height
+of these mountains is such that, were the shape of their valleys
+favorable to the accumulation of snow, they might present beautiful
+glaciers. In the Tyrol, on the contrary, as well as in Norway and
+Sweden, we find glaciers as fine as those of Switzerland in mountain
+ranges much lower than either of the above-mentioned chains. But they
+are of diversified forms, and have valleys widening upward on the
+slope of long crests. The glaciers on the Caucasus are very small in
+proportion to the height of the range; but on the northern side of
+the Himalayas there are large and beautiful ones, while the southern
+slope is almost destitute of them. Spitzbergen and Greenland are
+famous for their extensive glaciers, coming down to the seashore,
+where huge masses of ice, many hundred feet in thickness, break off
+and float away into the ocean as icebergs.
+
+At the Aletsch in Switzerland, where a little lake lies in a deep cup
+between the mountains, with the glacier coming down to its brink, we
+have these Arctic phenomena on a small scale; a miniature iceberg
+may often be seen to break off from the edge of the larger mass and
+float out upon the surface of the water. Icebergs were first traced
+back to their true origin by the nature of the land ice of which they
+were always composed, and which is quite distinct in structure and
+consistency from the marine ice produced by frozen sea water, and
+called “ice flow” by the Arctic explorers, as well as from the pond
+or river ice, resulting from the simple congelation of fresh water,
+the laminated structure of which is in striking contrast to the
+granular structure of glacier ice.
+
+Land ice, of which both the ice fields of the Arctics and the
+glaciers consist, is produced by slow and gradual transformation of
+snow into ice; and though the ice thus formed may eventually be as
+clear and transparent as the present pond or river ice, its structure
+is, nevertheless, entirely distinct.
+
+We may compare these different processes during any moderately cold
+winter in the ponds and snow meadows immediately about us. We need
+not join an Arctic exploring expedition, or even undertake a more
+tempting trip to the Alps, in order to investigate these phenomena
+ourselves, if we have any curiosity to do so. The first warm day
+after a thick fall of light, dry snow, such as occurs in the coldest
+of our winter weather, is sufficient to melt its surface.
+
+As this snow is porous, the water readily penetrates it, having also
+a tendency to sink by its own weight, so that the whole mass becomes
+more or less filled with moisture in the course of the day. During
+the lower temperature of the night, however, the water is frozen
+again, and the snow is now filled with new ice particles. Let this
+process be continued long enough and the mass of snow is changed into
+a kind of ice gravel, or, if the grains adhere together, to something
+like what we call pudding-stone, allowing, of course, for the
+difference of material; the snow, which has been rendered cohesive
+by the process of partial melting and regelation, holding the ice
+globules together, just as the loose materials of the pudding-stone
+are held together by the cement which unites them.
+
+Within this mass air is intercepted and held inclosed between the
+particles of ice. The process by which snowflakes or snow crystals
+are transformed into grains of ice, more or less compact, is easily
+understood. It is the result of a partial thawing under a temperature
+maintained very nearly at thirty-two degrees, falling sometimes a
+little below and then rising a little above the freezing-point, and
+thus producing constant alternations of freezing and thawing in the
+same mass of snow. This process amounts to a kind of kneading of
+the snow, and when combined with the cohesion among the particles
+more closely held together in one snowflake, it produces granular
+ice. Of course, the change takes place gradually, and is unequal in
+its progress at different depths in the same bed of fallen snow. It
+depends greatly on the amount of moisture infiltrating the mass,
+whether derived from the melting of its own surface, or from the
+accumulation of dew, or the falling of rain or mist upon it.
+
+The amount of water retained within the mass will also be greatly
+affected by the bottom on which it rests and by the state of the
+atmosphere. Under a certain temperature the snow may only be glazed
+at the surface by the formation of a thin, icy crust, an outer
+membrane, as it were, protecting the mass below from a deeper
+transformation into ice; or it may be rapidly soaked throughout its
+whole bulk, the snow being thus changed into a kind of soft pulp,
+what we commonly call slush, which, upon freezing, becomes at once
+compact ice; or, the water sinking rapidly, the lower layers only
+may be soaked, while the upper portion remains comparatively dry.
+But, under all these various circumstances, frost will transform the
+crystalline snow into more or less compact ice, the mass of which
+will be composed of an infinite number of aggregated snow particles,
+very unequal in regularity of outline, and cemented by ice of another
+kind, derived from the freezing of the infiltrated moisture, the
+whole being interspersed with air.
+
+Let the temperature rise, and such a mass, rigid before, will resolve
+itself again into disconnected ice particles, like grains more or
+less rounded. The process may be repeated till the whole mass is
+transformed into very compact, almost uniformly transparent and blue
+ice, broken only by the intervening air-bubbles. Such a mass of ice,
+when exposed to a temperature sufficiently high to dissolve it, does
+not melt from the surface and disappear by a gradual diminution of
+its bulk, like pond ice, but crumbles into its original granular
+fragments, each one of which melts separately. This accounts for the
+sudden disappearance of icebergs, which, instead of slowly dissolving
+into the ocean, are often seen to fall to pieces and vanish at once.
+
+Ice of this kind may be seen forming every winter on our sidewalks,
+on the edge of the little ditches which drain them, or on the summits
+of broad gate posts when capped with snow. Of such ice glaciers are
+composed; but, in the glacier, another element comes in which we have
+not considered as yet--that of immense pressure in consequence of
+the vast accumulations of snow within circumscribed spaces. We see
+the same effects produced on a small scale when snow is transformed
+into a snowball between the hands. Every boy who balls a mass of snow
+in his hands illustrates one side of glacial phenomena. Loose snow,
+light and porous, and pure white from the amount of air contained in
+it, is in this way presently converted into hard, compact, almost
+transparent, ice. This change will take place sooner if the snow be
+damp at first, but if dry, the action of the hand will presently
+produce moisture enough to complete the process. In this case,
+mere pressure produces the same effect which, in the cases we have
+been considering above, was brought about by alternate thawing and
+freezing, only that, in the latter, the ice is distinctly granular,
+instead of being uniform throughout, as when formed under pressure.
+In the glaciers, we have the two processes combined. But the
+investigators of glacial phenomena have considered too exclusively
+one or the other: some of them attributing glacial motion wholly to
+the dilatation produced by the freezing of infiltrated moisture in
+the mass of snow; others accounting for it entirely by weight and
+pressure. There is yet a third class, who, disregarding the real
+properties of ice, would have us believe that, because tar, for
+instance, is viscid when it moves, therefore ice is viscid because it
+moves.
+
+There is no chain of mountains in which the shape of the valleys is
+more favorable to the formation of glaciers than the Alps. Contracted
+at their lower extremity, these valleys widen upward, spreading
+into deep, broad, trough-like depressions. Take, for instance, the
+valley of Hassli, which is not more than half a mile wide where you
+enter it above Meyringen; it opens gradually upward till, above the
+Grimsel, at the foot of the Finster-Aarhorn, it measures several
+miles across. These huge mountain-troughs form admirable cradles for
+the snow, which collects in immense quantities within them, and as it
+moves slowly down from the upper ranges is transformed into ice on
+its way, and compactly crowded into the narrower space below. At the
+lower extremity of the glacier the ice is pure blue and transparent,
+but as we ascend it appears less compact, more porous and granular,
+assuming gradually the character of snow, till in the higher regions
+the snow is as light, as shifting, as incoherent as the sand of the
+desert. A snowstorm on a mountain summit is very different from
+a snowstorm on the plain on account of the different degrees of
+moisture in the atmosphere. At great heights there is never dampness
+enough to allow the fine snow crystals to coalesce and form what are
+called snowflakes. I have even stood on the summit of the Jungfrau
+when a frozen cloud filled the air with ice-needles, while I could
+see the same cloud poring down sheets of rain upon Lauterbrunnen
+below. I remember this spectacle as one of the most impressive I
+have ever witnessed in my long experience of Alpine scenery. The
+air immediately about me seemed filled with rainbow dust, for the
+ice-needles glittered with a thousand hues under the decomposition of
+light upon them, while the dark storm in the valley below offered
+a strange contrast to the brilliancy of the upper region in which I
+stood. One wonders where even so much vapor as may be transformed
+into the finest snow should come from at such heights. But the warm
+winds creeping up the sides of the valley, the walls of which become
+heated during the middle of the day, come laden with moisture which
+is changed to a dry snow like dust as soon as it comes into contact
+with the intense cold above.
+
+Currents of warm air affect the extent of the glaciers and influence
+also the line of perpetual snow, which is by no means at the same
+level, even in neighboring localities. The size of glaciers, of
+course, determines to a great degree the height at which they
+terminate, simply because a small mass of ice will melt more
+rapidly, and at a lower temperature, than a larger one. Thus the
+small glaciers, such as those of the Rothhorn or of Trift, above the
+Grimsel, terminate at a considerable height above the plain, while
+the Mer de Glace, fed from the great snow-caldrons of Mont Blanc,
+forces its way down to the bottom of the Valley of Chamouni, and the
+glacier of Grindelwald, constantly renewed from the deep reservoirs
+where the Jungfrau hoards her vast supplies of snow, descends to
+about four thousand feet above the sea level. But the glacier of the
+Aar, though also very large, comes to a pause at about six thousand
+feet above the level of the sea; for the south wind from the other
+side of the Alps, the warm sirocco of Italy, blows across it, and it
+consequently melts at a higher level than either the Mer de Glace or
+the Grindelwald. It is a curious fact that, in the Valley of Hassli,
+the temperature frequently rises instead of falling, as you ascend;
+at the Grimsel the temperature is at times higher than at Meyringen,
+below, where the warmer winds are not felt so directly. The glacier
+of Aletsch, on the southern slope of the Jungfrau, and into which
+many other glaciers enter, terminates also at a considerable height,
+because it turns into the Valley of the Rhone, through which the
+southern winds blow constantly. Under ordinary conditions, vegetation
+fades in these mountains at the height of six thousand feet, but,
+in consequence of prevailing winds and the sheltering influence of
+the mountain walls, there is no uniformity in the limit of perpetual
+snow and ice. Where currents of warm air are very constant, glaciers
+do not occur at all, even where other circumstances are favorable to
+their formation.
+
+There are valleys in the Alps far above six thousand feet which have
+no glaciers, and where perpetual snow is seen only on their northern
+sides. These contrasts in the temperature lead to the most wonderful
+contrasts in the aspect of the soil; summer and winter lie side by
+side, and bright flowers look out from the edge of snows that never
+melt. Where the warm winds prevail there may be sheltered spots at
+a height of ten or eleven thousand feet, isolated nooks opening
+southward where the most exquisite flowers bloom in the midst of
+perpetual snow and ice; and occasionally I have seen a bright little
+flower with a cap of snow over it that seems to be its shelter.
+The flowers give, indeed, a most peculiar charm to these high
+Alpine regions. Occurring often in beds of the same kind, forming
+green, blue, or yellow patches, they seem nestled close together in
+sheltered spots, or even in fissures and chasms of the rock, where
+they gather in dense quantities.
+
+Even in the sternest scenery of the Alps some sign of vegetation
+lingers; and I remember to have found a tuft of lichen growing on
+the only rock which pierced through the ice on the summit of the
+Jungfrau. It was a species then unknown to botanists, since described
+under the name of Umbelicarus Higinis. The absolute solitude, the
+intense stillness of the upper Alps is most impressive; no cattle,
+no pasturage, no bird, nor any sound of life--and, indeed, even if
+there were, the rarity of the air in these high regions is such that
+sound is hardly transmissible. The deep repose, the purity of aspect
+of every object, the snow, broken only by ridges of angular rocks,
+produce an effect no less beautiful than solemn. Sometimes, in the
+midst of the wide expanse, one comes upon a patch of the so-called
+red snow of the Alps. At a distance one would say that such a spot
+marked some terrible scene of blood, but as you come nearer the hues
+are so tender and delicate, as they fade from deep red to rose, and
+so die into the pure colorless snow around, that the first impression
+is completely dispelled. This red snow is an organic growth, a plant
+springing up in such abundance that it colors extensive surfaces,
+just as the microscopic plants dye our pools with green in the
+spring. It is an Alga (Protocoites nivalis), well known in the
+Arctics, where it forms wide fields in the summer.
+
+In ordinary times, layers from six to eight feet deep are regularly
+added annually to the accumulation of snow in the higher regions--not
+taking into account, of course, the heavy drifts heaped up in
+particular localities, but estimating the uniform average over wide
+fields. This snow is gradually transformed into more or less compact
+ice, passing through an intermediate condition analogous to the slush
+of our roads, and in that condition chiefly occupies the upper part
+of the extensive troughs into which these masses descend from the
+loftier heights. This region is called the region of the _névé_. It
+is properly the birthplace of the glaciers, for it is here that the
+transformation of the snow into ice begins. The _névé_ ice, though
+varying in the degree of its compactness and solidity, is always very
+porous and whitish in color, resembling somewhat frozen slush, while
+lower down in the region of the glacier proper the ice is close,
+solid, transparent, and of a bluish tint.
+
+In consequence of the greater or less rapidity in the movement of
+certain portions of the mass, its centre progressing faster than its
+sides, and the upper, middle and lower regions of the same glacier
+advancing at different rates, the strata, which in the higher ranges
+of the snow fields were evenly spread over wide expanses, become
+bent and folded to such a degree that the primitive stratification
+is nearly obliterated, while the internal mass of the ice has also
+assumed new features under these new circumstances. There is, indeed,
+as much difference between the newly formed beds of snow in the
+upper region and the condition of the ice at the lower end of a
+glacier as between a recent deposit of coral sand or a mud bed in
+an estuary and the metamorphic limestone or clay slate twisted and
+broken as they are seen in the very chains of mountains from which
+the glacier descended.
+
+
+
+
+  VOLCANIC ACTION
+  --SIR ARCHIBALD GEIKIE
+
+
+Large quantities of water accompany many volcanic eruptions. In some
+cases, where ancient crater-lakes or internal reservoirs, shaken by
+repeated detonations, have been finally disrupted, the mud which has
+thereby been liberated has issued from the mountain. Such “mud-lava”
+(_lava d’aqua_), on account of its liquidity and swiftness of motion,
+is more dreaded for destructiveness than even the true melted lavas.
+On the other hand, rain or melted snow or ice, rushing down the cone
+and taking up loose volcanic dust, is converted into a kind of mud
+that grows more and more pasty as it descends. The mere sudden rush
+of such large bodies of water down the steep declivity of a volcanic
+cone can not fail to effect much geological change. Deep trenches
+are cut out of the loose volcanic slopes, and sometimes large areas
+of woodland are swept away, the débris being strewn over the plains
+below.
+
+One of these mud-lavas invaded Herculaneum during the great eruption
+of 79, and by quickly enveloping the houses and their contents,
+has preserved for us so many precious and perishable monuments of
+antiquity. In the same district, during the eruption of 1622, a
+torrent of this kind poured down upon the villages of Ottajano and
+Massa, overthrowing walls, filling up streets, and even burying
+houses with their inhabitants. During the great eruption of Cotopaxi,
+in June, 1877, enormous torrents of water and mud, produced by
+the melting of the snow and ice of the cone, rushed down from the
+mountain. Huge portions of the glaciers of the mountain were detached
+by the heat of the rocks below them and rushed down bodily, breaking
+up into blocks. The villages all round the mountain to a distance
+of sometimes more than ten geographical miles were left deeply
+buried under a deposit of mud mixed with blocks of lava, ashes,
+pieces of wood, lumps of ice, etc. Many of the volcanoes of Central
+and South America discharge large quantities of mud directly from
+their craters. Thus, in the year 1691, Imbaburu, one of the Andes of
+Quito, emitted floods of mud so largely charged with dead fish that
+pestilential fevers arose from the subsequent effluvia. Seven years
+later (1698), during an explosion of another of the same range of
+lofty mountains, Carguairazo (14,706 feet), the summit of the cone
+is said to have fallen in, while torrents of mud containing immense
+numbers of the fish _Pymelodus Cyclopum_ poured forth and covered
+the ground over a space of four square leagues. The carbonaceous mud
+(locally called _moya_) emitted by the Quito volcanoes sometimes
+escapes from lateral fissures, sometimes from the craters. Its
+organic contents, and notably its siluroid fish, which are the same
+as those found living in the streams above ground, prove that the
+water is derived from the surface, and accumulates in craters or
+underground cavities until discharged by volcanic action. Similar but
+even more stupendous and destructive outpourings have taken place
+from the volcanoes of Java, where wide tracts of luxuriant vegetation
+have at different times been buried under masses of dark gray mud,
+sometimes 100 feet thick, with a rough hillocky surface from which
+the top of a submerged palm-tree would here and there protrude.
+
+A volcano, as its activity wanes, may pass into the Solfatara
+stage, when only volatile emanations are discharged. The well-known
+Solfatara near Naples, since its last eruption in 1198, has
+constantly discharged steam and sulphurous vapors. The island of
+Volcano has now passed also into this phase, though giving vent to
+occasional explosions. Numerous other examples occur among the old
+volcanic tracts of Italy, where they have been termed _soffioni_.
+
+Another class of gaseous emanations betokens a condition of volcanic
+activity further advanced toward final extinction. In these, the
+gas is carbon-dioxide, either issuing directly from the rock or
+bubbling up with water which is often quite cold. The old volcanic
+districts of Europe furnish many examples. Thus on the shores of the
+Laacher See--an ancient crater-lake of the Eifel--the gas issues
+from numerous openings called _moffette_, round which dead insects,
+and occasionally mice and birds, may be found. In the same region
+occur hundreds of springs more or less charged with this gas. The
+famous Valley of Death in Java contains one of the most remarkable
+gas-springs in the world. It is a deep, bosky hollow, from one small
+space on the bottom of which carbon-dioxide issues so copiously as
+to form the lower stratum of the atmosphere. Tigers, deer, and wild
+boars, enticed by the shelter of the spot, descend and are speedily
+suffocated. Many skeletons, including those of man himself, have been
+observed.
+
+As a distinct class of gas-springs, we may group and describe here
+the emanations of volatile hydrocarbons which, when they take fire,
+are known as Fire-wells. These are not of volcanic origin, but arise
+from changes within the solid rocks underneath. They occur in many of
+the districts where mud-volcanoes appear, as in northern Italy, on
+the Caspian, in Mesopotamia, in southern Kurdistan, and in many parts
+of the United States.
+
+In the oil regions of Pennsylvania, certain sandy strata occur at
+various geological horizons whence large quantities of petroleum and
+gas are obtained. In making the borings for oil-wells, reservoirs
+of gas as well as subterranean courses or springs of water are met
+with. When the supply of oil is limited, but that of gas is large, a
+contest for possession of the bore-hole sometimes takes place between
+the gas and water. When the machinery is removed and the boring is
+abandoned, the contest is allowed to proceed unimpeded, and results
+in the intermittent discharge of columns of water and gas to heights
+of 130 feet or more. At night, when the gas has been lighted, the
+spectacle of one of these “fire-geysers” is inconceivably grand.
+
+Eruptive fountains of hot water and steam, to which the general name
+of Geysers (_i. e._, gushers) is given, from the examples in Iceland,
+which were the first to be seen and described, mark a declining phase
+of volcanic activity. The Great and Little Geysers, the Strokkr,
+and other minor springs of hot water in Iceland, have long been
+celebrated examples. More recently another series has been discovered
+in New Zealand. But probably the most remarkable and numerous
+assemblage is that which has been brought to light in the northwest
+part of the Territory of Wyoming, and which has been included within
+the “Yellowstone National Park.” In this singular region the ground
+in certain tracts is honeycombed with passages which communicate with
+the surface by hundreds of openings, whence boiling water and steam
+are emitted. In most cases, the water remains clear, tranquil, and
+of a deep green-blue tint, though many of the otherwise quiet pools
+are marked by patches of rapid ebullition. These pools lie on mounds
+or sheets of sinter, and are usually edged round with a raised rim
+of the same substance, often beautifully fretted and streaked with
+brilliant colors. The eruptive openings usually appear on small, low,
+conical elevations of sinter, from each of which one or more tubular
+projections rise. It is from these irregular tube-like excrescences
+that the eruptions take place.
+
+The term geyser is restricted to active openings whence columns of
+hot water and steam are from time to time ejected; the non-eruptive
+pools are only hot springs. A true geyser should thus possess an
+underground pipe or passage, terminating at the surface in an opening
+built round with deposits of sinter.
+
+At more or less regular intervals, rumblings and sharp detonations
+in the pipe are followed by an agitation of the water in the basin,
+and then by the violent expulsion of a column of water and steam to a
+considerable height in the air. In the Upper Fire Hole basin of the
+Yellowstone Park, one of the geysers, named “Old Faithful,” has ever
+since the discovery of the region sent out a column of mingled water
+and steam every sixty-three minutes or thereabout. The column rushes
+up with a loud roar to a height of more than 100 feet, the whole
+eruption not occupying more than about five or six minutes. The other
+geysers of the same district are more capricious in their movements,
+and some of them more stupendous in the volume of their discharge.
+The eruptions of the Castle, Giant, and Beehive vents are marvelously
+impressive.
+
+In course of time, the network of underground passages undergoes
+alteration. Orifices that were once active cease to erupt, and even
+the water fails to overflow them. Sinter is no longer formed round
+them, and their surfaces, exposed to the weather, crack into fine
+shaly rubbish like comminuted oyster-shells. Or the cylinder of
+sinter grows upward until, by the continued deposit of sinter and the
+failing force of the geyser, the tube is finally filled up, and then
+a dry and crumbling white pillar is left to mark the site of the
+extinct geyser.
+
+Mud-Volcanoes are of two kinds: 1st, where the chief source of
+movement is the escape of gaseous discharges; 2d, where the active
+agent is steam.
+
+Although not volcanic in the proper sense of the term, certain
+remarkable orifices of eruption may be noticed here, to which the
+names of _mud-volcanoes_, _salses_, _air-volcanoes_, and _maccalubas_
+have been applied (Sicily, the Apennines, Caucasus, Kertch, Tamar).
+These are conical hills formed by the accumulation of fine and
+usually saline mud, which, with various gases, is continuously or
+intermittently given out from the orifice or crater in the centre.
+They occur in groups, each hillock being sometimes less than a yard
+in height, but ranging up to elevations of 100 feet or more. Like
+true volcanoes, they have their periods of repose, when either no
+discharge takes place at all, or mud oozes out tranquilly from the
+crater, and their epochs of activity, when large volumes of gas,
+and sometimes columns of flame, rush out with considerable violence
+and explosion, and throw up mud and stones to a height of several
+hundred feet. The gases play much the same part, therefore, in these
+phenomena that steam does in those of true volcanoes. They consist
+of marsh-gas and other hydrocarbons, carbon-dioxide, sulphureted
+hydrogen, and nitrogen, with petroleum vapors. The mud is usually
+cold. In the water occur various saline ingredients, among which
+common salt generally appears; hence the names _Salses_. Naphtha is
+likewise frequently present. Large pieces of stone, differing from
+those in the neighborhood, have been observed among the ejections,
+indicative doubtless of a somewhat deeper source than in ordinary
+cases. Heavy rains may wash down the minor mud-cones and spread out
+the material over the ground; but gas-bubbles again appear through
+the sheet of mud, and by degrees a new series of mounds is once more
+thrown up.
+
+The second class of mud-volcano presents itself in true volcanic
+regions, and is due to the escape of hot water and steam through
+beds of tuff or some other friable kind of rock. The mud is kept
+in ebullition by the rise of steam through it. As it becomes more
+pasty and the steam meets with greater resistance, large bubbles are
+formed which burst, and the more liquid mud from below oozes out from
+the vent. In this way, small cones are built up, many of which have
+perfect craters atop. In the Geyser tracts of the Yellowstone region,
+there are instructive examples of such active and extinct mud-vents.
+Some of the extinct cones there are not more than a foot high, and
+might be carefully removed as museum specimens.
+
+Mud-volcanoes occur in Iceland, Sicily (Maccaluba), in many districts
+of northern Italy, at Tamar and Kertch, at Baku on the Caspian, near
+the mouth of the Indus, and in other parts of the globe.
+
+It is not only on the surface of the land that volcanic action shows
+itself. It takes place likewise under the sea, and as the geological
+records of the earth’s past history are chiefly marine formations,
+the characteristics of submarine volcanic action have no small
+interest for the geologist. In a few instances, the actual outbreak
+of a submarine eruption has been witnessed. Thus, in the early summer
+of 1783, a volcanic eruption took place about thirty miles from Cape
+Reykjanaes on the west coast of Iceland. An island was built up, from
+which fire and smoke continued to issue, but in less than a year the
+waves had washed the loose pumice away, leaving a submerged reef
+from five to thirty fathoms below sea-level. About a month after
+this eruption, the frightful outbreak of Skaptar-Jökull began, the
+distance of this mountain from the submarine vent being nearly 200
+miles. A century afterward, viz., in July, 1884, another volcanic
+island is said to have been thrown up near the same spot, having at
+first the form of a flattened cone, but soon yielding to the power
+of the breakers. Many submarine eruptions have taken place within
+historic times in the Mediterranean. The most noted of these occurred
+in the year 1831, when a new volcanic island (Graham’s Island, Ile
+Julia) was thrown up, with abundant discharge of steam and showers of
+scoriæ, between Sicily and the coast of Africa. It reached an extreme
+height of 200 feet or more above the sea-level (800 feet above
+sea-bottom), with a circumference of 3 miles, but on the cessation of
+the eruptions was attacked by the waves and soon demolished, leaving
+only a shoal to mark its site. In the year 1811, another island
+was formed by submarine eruption of the coast off St. Michael’s in
+the Azores. Consisting, like the Mediterranean example, of loose
+cinders, it rose to a height of about three hundred feet, with a
+circumference of about a mile, but subsequently disappeared. In
+the year 1796 the island of Johanna Bogoslawa, in Alaska, appeared
+above the water, and in four years had grown into a large volcanic
+cone, the summit of which was 3,000 feet above sea-level.
+
+[Illustration: Ideal Landscape of the Carboniferous Period
+
+Showing Lepidodendra and other Giant Ferns and Mosses whose remains
+are found in the Coal-Measures]
+
+Unfortunately, the phenomena of recent volcanic eruptions under the
+sea are for the most part inaccessible. Here and there, as in the
+Bay of Naples, at Etna, among the islands of the Greek Archipelago,
+and at Tahiti, elevation of the sea-bed has taken place, and brought
+to the surface beds of tuff or of lava, which have consolidated
+under water. Both Vesuvius and Etna began their career as submarine
+volcanoes. The Islands of Santorin and Therasia form the unsubmerged
+portions of a great crater-rim rising round a crater which descends
+1,278 feet below sea-level.
+
+Confining attention to vents now active, of which the total number
+may be about 300, the chief facts regarding their distribution over
+the globe may be thus summarized. (1) Volcanoes occur along the
+margins of the ocean-basins, particularly along lines of dominant
+mountain ranges, which either form part of the mainland of the
+continents or extend as adjacent lines of islands. The vast hollow
+of the Pacific is girdled with a wide ring of volcanic foci. (2)
+Volcanoes rise, as a striking feature, from the submarine ridges
+that traverse the ocean basins. All the oceanic islands are either
+volcanic or formed of coral, and the scattered coral-islands have
+in all likelihood been built upon the tops of submarine volcanic
+cones. (3) Volcanoes are situated not far from the sea. The only
+exceptions to this rule are certain vents in Manchuria and in the
+tract lying between Tibet and Siberia; but of the actual nature of
+these vents very little is yet known. (4) The dominant arrangement
+of volcanoes is in series along subterranean lines of weakness,
+as in the chain of the Andes, the Aleutian Islands, and the Malay
+Archipelago. A remarkable zone of volcanic vents girdles the globe
+from Central America eastward by the Azores and Canary Islands to
+the Mediterranean, thence to the Red Sea, and through the chains of
+islands from the south of Asia to New Zealand and the heart of the
+Pacific. (5) On a smaller scale the linear arrangement gives place to
+one in groups, as in Italy, Iceland, and the volcanic islands of the
+great oceans.
+
+In the European area there are six active volcanoes--Vesuvius, Etna,
+Stromboli, Volcano, Santorin, and Nisyros. Asia contains twenty-four,
+Africa ten, North America twenty, Central America twenty-five, and
+South America thirty-seven. By much the larger number, however, occur
+on islands in the ocean. In the Arctic Ocean rises the solitary Jan
+Mayen. On the ridge separating the Arctic and Atlantic basins, the
+group of Icelandic volcanoes is found. Along the great central ridge
+of the Atlantic bottom, numerous volcanic vents have risen above
+the surface of the sea--the Azores, Canary Islands, and the extinct
+degraded volcanoes of St. Helena, Ascension, and Tristan d’Acunha.
+On the eastern border lie the volcanic vents of the islands off the
+African coast, and to the west those of the West Indian Islands.
+Still more remarkable is the development of volcanic energy in the
+Pacific area. From the Aleutian Islands southward, a long line of
+volcanoes, numbering upward of a hundred active vents, extends
+through Kamtchatka and the Kurile Islands to Japan, whence another
+numerous series carries the volcanic band far south toward the
+Malay Archipelago, which must be regarded as the chief centre of
+the present volcanic activity of our planet. In Sumatra, Java, and
+adjoining islands, no fewer than fifty active vents occur. The chain
+is continued through New Guinea and the groups of islands to New
+Zealand. Even in the Antarctic regions, Mounts Erebus and Terror are
+cited as active vents; while in the centre of the Pacific Ocean rise
+the great lava cones of the Sandwich Islands. In the Indian Ocean,
+the Red Sea, and off the east coast of Africa a few scattered vents
+appear.
+
+
+
+
+  THOUGHTS ABOUT KRAKATOA
+  --SIR ROBERT S. BALL
+
+
+Midway between Sumatra and Java lies a group of small islands,
+which, prior to 1883, were beautified by the dense forests and
+glorious vegetation of the tropics. Of these islands Krakatoa was
+the chief, though even of it but little was known. Its appearance
+from the sea must, indeed, have been familiar to the crews of the
+many vessels that navigated the Straits of Sunda, but it was not
+regularly inhabited. Glowing with tropical verdure, such an island
+seemed an unlikely theatre for the display of an unparalleled effect
+of plutonic energy, but yet there were certain circumstances which
+may tend to lessen our surprise at the outbreak. In the first place,
+as Professor Judd has so clearly pointed out, not only is Krakatoa
+situated in a region famous, or perhaps infamous, for volcanoes and
+earthquakes, but it actually happens to lie at the intersection of
+two main lines, along which volcanic phenomena are, in some degree,
+perennial. In the second place, history records that there have been
+previous eruptions at Krakatoa. The last of these appears to have
+occurred in May, 1680, but unfortunately only imperfect accounts
+of it have been preserved. It seems, however, to have annihilated
+the forests of the island, and to have ejected vast quantities of
+pumice, which cumbered the seas around. Krakatoa then remained active
+for a year and a half, after which the mighty fires subsided. The
+irrepressible tropical vegetation again resumed possession. The
+desolated islet again became clothed with beauty, and for a couple of
+centuries reposed in peace.
+
+It was one o’clock in the afternoon of Sunday, August 26, 1883, when
+Krakatoa commenced a series of gigantic volcanic efforts. Detonations
+were heard which succeeded each other at intervals of about ten
+minutes. These were loud enough to penetrate as far as Batavia and
+Buitenzorg, distant 96 and 100 miles respectively from the volcano.
+A vast column of steam, smoke, and ashes ascended to a prodigious
+elevation. It was measured at two P. M. from a ship 76 miles away,
+and was then judged to be 17 miles high--that is, three times the
+height of the loftiest mountain in the world. As the Sunday afternoon
+wore on, the volcanic manifestations became ever fiercer. At 3 P. M.
+the sounds were loudly heard in a town 150 miles away. At 5 P. M.
+every ear in the island of Java was engaged in listening to volcanic
+explosions, which were considered to be of quite unusual intensity
+even in that part of the world. These phenomena were, however, only
+introductory. Krakatoa was gathering strength. Between 5 and 6 P.
+M. the British ship _Charles Bal_, commanded by Captain Watson,
+was about ten miles south of the volcano. The ship had to shorten
+sail in the darkness, and a rain of pumice, in large pieces and
+quite warm, fell upon her decks. At 7 P. M. the mighty column of
+smoke is described as having the shape of a pine tree, and as being
+brilliantly illuminated by electric flashes. The sulphurous air is
+laden with fine dust, while the lead dropped from a ship in its
+anxious navigation astounds the leadsman by coming up hot from the
+bottom of the sea. From sunset on Sunday till midnight the tremendous
+detonations followed each other so quickly that a continuous roar
+may be said to have issued from the island. The full terrors of the
+eruption were now approaching. The distance of 96 miles between
+Krakatoa and Batavia was not sufficient to permit the inhabitants of
+the town to enjoy their night’s sleep. All night long the thunders of
+the volcano sounded like the discharges of artillery at their very
+doors, while the windows rattled with aerial vibrations.
+
+On Monday morning, August 27, the eruption culminated in four
+terrific explosions, of which the third, shortly after 10 A. M.
+Krakatoa time, was by far the most violent. The quantity of material
+ejected was now so great that darkness prevailed even as far as
+Batavia soon after 11 A. M., and there was a rain of dust until
+three in the afternoon. The explosions continued with more or less
+intensity all the afternoon of Monday and throughout Monday night.
+They finally ceased at about 2:30 A. M. on Tuesday, August 28. The
+entire series of grand phenomena thus occupied a little more than
+thirty-six hours.
+
+It seems to be certain that if all the materials poured forth from
+Krakatoa during the critical period could be collected together,
+the mass they would form would be considerably over a cubic mile
+in volume. It is in the other standards of comparison that the
+importance of the explosion of Krakatoa is to be sought. The
+intensity of this outbreak in its last throes was such that mighty
+sounds were heard and mighty waves arose in the sea for which we can
+find no parallel. Every part of our globe’s surface felt the pulse of
+the air-waves, and beautiful optical phenomena made the circuit of
+the globe even more than once or twice. In these last respects the
+eruption of Krakatoa is unique.
+
+It appears to me that the most remarkable incident connected with
+the eruption of Krakatoa was the production of the great air-wave by
+that particular explosion that occurred at ten o’clock on the morning
+of Monday, August 27. The great air-wave was truly of cosmical
+importance, affecting as it did every particle of the atmosphere on
+our globe.
+
+The comprehensive series of phenomena wherein the atmosphere of the
+entire globe participates in an organized vibration has, so far as
+we know, only once been witnessed, and that was after the greatest
+outbreak at Krakatoa, at ten o’clock on the morning of August 27. But
+the ebb and the flow of these mighty undulations are not immediately
+appreciable to the senses. The great wave, for instance, passed
+and re-passed and passed again over London, and no inhabitant was
+conscious of the fact. But the automatic records of the barometer at
+Greenwich show that the vibration from Krakatoa to its antipodes, and
+from the antipodes back to Krakatoa, was distinctly perceptible over
+London not less than six or seven times.
+
+From all parts of Europe, from Berlin to Palermo, from St.
+Petersburg to Valencia, we obtain the same indications. Fortunately
+self-recording barometric instruments are now to be found all over
+the world. Almost all the instruments show distinctly the first great
+wave from Krakatoa to its antipodes in Central America, and the
+return wave from the antipodes to Krakatoa. They also all show the
+second great wave which sped from Krakatoa, as well as the second
+great wave which returned from the antipodes. Thus, the first four of
+the oscillations are depicted on upward of forty of the barograms.
+The fifth and sixth oscillations are also to be distinguished on
+several of the curves, and even the seventh is certainly established
+at some few places, of which Kew is one. Then the gradually
+increasing faintness of the indications renders them unrecognizable,
+from which we conclude that after seven pulsations our atmosphere
+had sensibly regained its former condition ere it was disturbed by
+Krakatoa.
+
+In the whole annals of noise there is nothing which can be compared
+to the records. Lloyd’s agent at Batavia, 94 miles distant, says
+that on the morning of August 27 the reports and concussions were
+deafening. At Carimon, Java Island, reports were heard which led to
+the belief that some vessel offshore was making signals of distress,
+and boats were accordingly put out to render succor, but no vessel
+was found, as the reports were from Krakatoa, at a distance of 355
+miles. At Macassar, in Celebes, explosions were heard all over the
+province. Two steamers were sent out to discover the cause, for
+the authorities did not then know that what they heard came from
+Krakatoa, 969 miles away. But mere hundreds of miles will not suffice
+to exemplify the range of this stupendous siren. In St. Lucia Bay,
+in Borneo, a number of natives, who had been guilty of murder,
+thought they heard the sounds of vengeance in the approach of an
+attacking force. They fled from their village, little fancying that
+what alarmed them really came from Krakatoa, 1,116 miles distant.
+All over the island of Timor alarming sounds were heard, and so
+urgent did the situation appear that the government was aroused, and
+sent off a steamer to ascertain the cause. The sounds had, however,
+come 1,351 miles, all the way from Krakatoa. In the Victoria Plains
+of West Australia the inhabitants were startled by the discharge
+of artillery--an unwonted noise in that peaceful district--but the
+artillery was at Krakatoa, 1,700 miles distant. The inhabitants of
+Daly Waters, in South Australia, were rudely awakened at midnight on
+Sunday, August 26, by an explosion resembling the blasting of a rock,
+which lasted for a few minutes. The time and other circumstances
+show that here again was Krakatoa heard, this time at the monstrous
+distance of 2,023 miles. But there is undoubted testimony that to
+distances even greater than 2,023 miles the waves of sound conveyed
+tidings of the mighty convulsion. Diego Garcia, in the Chagos
+Islands, is 2,267 miles from Krakatoa, but the thunders traversed
+even this distance, and created the belief that there must be some
+ship in distress, for which a diligent but necessarily ineffectual
+search was made. To pass at once to the most remarkable case of all,
+we have a report from Mr. James Wallis, chief of police in Rodriguez,
+that “several times during the night of August 26-27, 1883, reports
+were heard coming from the eastward, like the distant roar of heavy
+guns. These reports continued at intervals of between three and four
+hours.” We have thus the astounding fact that almost across the
+whole wide extent of the Indian Ocean, that is, to a distance of
+nearly 3,000 miles (2,968), the sound of the throes of Krakatoa was
+propagated.
+
+I shall content myself with the mention of three facts in
+illustration of the great sea waves which accompanied the eruption
+of Krakatoa. Of these, probably the most unusual is the magnitude
+of the area over which the undulations were perceived. Thus, to
+mention but a single instance, and that not by any means an extreme
+one, we find that the tide gauge at Table Bay reveals waves which,
+notwithstanding that they have traveled 5,100 miles from Krakatoa,
+have still a range of eighteen inches when they arrive at the
+southern coast of Africa. The second fact that I mention illustrates
+the magnitude of the seismic waves by the extraordinary inundations
+that they produced on the shores of the Straits of Sunda. Captain
+Wharton shows that the waves, as they deluged the land, must have
+been fifty feet, or, in one well authenticated case, seventy-two
+feet high. It was, of course, these vast floods which caused the
+fearful loss of life. The third illustrative fact concerns the fate
+of a man-of-war, the _Berouw_. This unhappy vessel was borne from
+its normal element and left high and dry in Sumatra, a mile and
+three-quarters inland, and thirty feet above the level of the sea.
+
+During the crisis on August 26-27, the volume of material blown into
+the air was sufficiently dense to obscure the coasts of Sumatra
+to such a degree that at 10 A. M. the darkness there is stated to
+have been more intense than it is even in the blackest of nights.
+The fire-dust ascended to an elevation which, as we have already
+mentioned, is estimated to have been as much as seventeen miles.
+Borne aloft into these higher regions of our atmosphere, the clouds
+of dust at once became the sport of the winds and the currents which
+may be found there. If we had not previously known the prevailing
+tendency of the winds at these elevations and in these latitudes, the
+journey of the Krakatoa dust would have taught us.
+
+It seems certain that, having attained their lofty elevation, the
+mighty clouds of dust were seized by easterly winds, and were swept
+along with a velocity which may not improbably be normal at a height
+of twenty miles above the earth’s surface.
+
+It appears that this cloud of dust started immediately from Krakatoa
+for a series of voyages round the world. The highway which it at
+first pursued may, for our present purpose, be sufficiently defined
+by the Tropic of Cancer and the Tropic of Capricorn, though it hardly
+approached these margins at first. Westward the dust of Krakatoa
+takes its way. In three days it had crossed the Indian Ocean and
+was rapidly flying over the heart of Equatorial Africa; for another
+couple of days it was making a transatlantic journey; and then it
+might be found, for still a couple of days more, over the forests of
+Brazil ere it commenced the great Pacific voyage which brought it
+back to the East Indies. The dust of Krakatoa had put a girdle round
+the earth in thirteen days! The shape of the cloud appears to have
+been elongated, so that it took two or three days to complete the
+passage over any stated place.
+
+It remains to give some brief account of the optical phenomena due
+to the presence of dust, unusual both in quantity and in character,
+in the upper atmosphere. Beautiful pictures show the twilight and
+after-glow effects as seen by Mr. W. Ascroft on the bank of the
+Thames a little west of London, on the evening of November 26, 1883.
+Analogous phenomena were seen almost universally during November and
+December in the same year. Who is there that does not remember the
+wondrous loveliness of the twilights and the after-glows during that
+remarkable winter! These appearances at sunrise and sunset are only
+the more generally recognized of a whole system of strange optical
+phenomena. One of the most striking indications of the presence of
+the dust-stream in its first voyage round the earth was given by the
+strange blue hue it imparted to the sun. The dust-stream was also
+visible in its rapid voyages as a lofty haze or extensive cloud of
+cirro-stratus. Then, too, strange halos were often seen, there were
+occasional blue or green moons, and the sun was sometimes glorified
+by a corona that had its origin in our atmosphere. Everywhere in the
+world there were remarkable features in the sky that winter: from
+Tierra del Fuego to Lake Superior; from China to the Gulf of Guinea;
+from Panama to Australia. Wherever on land there were inhabitants
+with sufficient intelligence to note the unusual, wherever on the sea
+there were mariners who kept a careful log, from all such observers
+we learn that in the autumn and winter months following the great
+eruption of Krakatoa, there were extraordinary manifestations
+witnessed in the heavens.
+
+
+
+
+  VOLCANOES
+  --SIR ARCHIBALD GEIKIE
+
+
+The term volcanic action (volcanism or volcanicity) embraces all the
+phenomena connected with the expulsion of heated materials from the
+interior of the earth to the surface. Among these phenomena, some
+possess an evanescent character, while others leave permanent proofs
+of their existence. It is naturally to the latter that the geologist
+gives chief attention, for it is by their means that he can trace
+former phases of volcanic activity in regions where, for many ages,
+there have been no volcanic eruptions. In the operations of existing
+volcanoes, he can observe only superficial manifestations of volcanic
+action. But examining the rocks of the earth’s crust, he discovers
+that amid the many terrestrial revolutions which geology reveals,
+the very roots of former volcanoes have been laid bare, displaying
+subterranean phases of volcanism which could not be studied in any
+modern volcano. Hence an acquaintance only with active volcanoes
+will not afford a complete knowledge of volcanic action. It must
+be supplemented and enlarged by an investigation of the traces of
+ancient volcanoes preserved in the crust of the earth.
+
+The word “volcano” is applied to a conical hill or mountain (composed
+mainly or wholly of erupted materials), from the summit and often
+also from the sides of which hot vapors issue, and ashes and streams
+of molten rock are intermittently expelled. The term “volcanic”
+designates all the phenomena essentially connected with one of these
+channels of communication between the surface and the heated interior
+of the globe. Yet there is good reason to believe that the active
+volcanoes of the present day do not afford by any means a complete
+type of volcanic action. The first effort in the formation of a new
+volcano is to establish a fissure in the earth’s crust. A volcano is
+only one vent or group of vents established along the line of such
+a fissure. But in many parts of the earth, alike in the Old World
+and the New, there have been periods in the earth’s history when
+the crust was rent into innumerable fissures over areas thousands of
+square miles in extent, and when the molten rock, instead of issuing,
+as it does at a modern volcano, in narrow streams from a central
+elevated cone, welled out from numerous small vents along the rents,
+and flooded enormous tracts of country without forming any mountain
+or conspicuous volcanic cone in the usual sense of these terms. Of
+these “fissure-eruptions,” apart from central volcanic cones, no
+examples appear to have occurred within the times of human history,
+except in Iceland, where vast lava-floods issued from a fissure in
+1783. They can best be studied from the remains of former convulsions.
+
+The materials erupted from volcanic vents may be classed as (1) gases
+and vapors, (2) water, (3) lava, (4) fragmentary substances.
+
+Gases and vapors exist dissolved in the molten magma within the
+earth’s crust. They play an important part in volcanic activity,
+showing themselves in the earliest stages of a volcano’s history,
+and continuing to appear for centuries after all other subterranean
+action has ceased. By much the most abundant of them all is
+water-gas, which, ultimately escaping as steam, has been estimated
+to form 999-1000ths of the whole cloud that hangs over an active
+volcano. In great eruptions, steam rises in prodigious quantities,
+and is rapidly condensed into a heavy rainfall. M. Fouqué calculated
+that, during 100 days, one of the parasitic cones on Etna had
+ejected vapor enough to form, if condensed, 2,100,000 cubic metres
+(462,000,000 gallons) of water. But even from volcanoes which, like
+the Solfatara of Naples, have been dormant for centuries, steam
+sometimes still rises without intermission and in considerable
+volume. Jets of vapor rush out from clefts in the sides and bottom
+of a crater with a noise like that made by the steam blown off by a
+locomotive. The number of these funnels or “fumaroles” is often so
+large, and the amount of vapor so abundant, that only now and then,
+when the wind blows the dense cloud aside, can a momentary glimpse
+be had of a part of the bottom of the crater; while at the same
+time the rush and roar of the escaping steam remind one of the din
+of some vast factory. Aqueous vapor rises likewise from rents on
+the outside of the volcanic cone. It issues so copiously from some
+flowing lavas that the stream of rock may be almost concealed from
+view by the cloud; and it continues to escape from fissures of the
+lava, far below the point of exit, for a long time after the rock has
+solidified and come to rest.
+
+Abundant discharges of water accompany some volcanic explosions.
+Three sources of this water may be assigned: (1) from the melting of
+snow by a rapid accession of temperature previous to or during an
+eruption; this takes place from time to time on Etna, in Iceland,
+and among the snowy ranges of the Andes, where the cone of Cotopaxi
+is said to have been entirely divested of its snow in a single night
+by the heating of the mountain; (2) from the condensation of the
+vast clouds of steam which are discharged during an eruption; this
+undoubtedly is the chief source of the destructive torrents so
+frequently observed to form part of the phenomena of a great volcanic
+explosion; and (3) from the disruption of reservoirs of water filling
+subterranean cavities, or of lakes occupying crater-basins; this has
+several times been observed among the South American volcanoes, where
+immense quantities of dead fish, which inhabited the water, have
+been swept down with the escaping torrents. The volcano of Agua in
+Guatemala received its name from the disruption of a crater-lake at
+its summit by an earthquake in 1540, whereby a vast and destructive
+debacle of water was discharged down the slopes of the mountain. In
+the beginning of the year 1817, an eruption took place at the large
+crater of Idjèn, one of the volcanoes of Java, whereby a steaming
+lake of hot acid water was discharged with frightful destruction down
+the slopes of the mountain. After the explosion, the basin filled
+again with water, but its temperature was no longer high.
+
+The term lava is applied generally to all the molten rocks of
+volcanoes. The use of the word in this broad sense is of great
+convenience in geological descriptions, by directing attention to the
+leading character of the rocks as molten products of volcanic action,
+and obviating the confusion and errors which are apt to arise from an
+ill-defined or incorrect lithological terminology.
+
+While still flowing or not yet cooled, lavas differ from each other
+in the extent to which they are impregnated with gases and vapors.
+Some appear to be saturated, others contain a much smaller gaseous
+impregnation; and hence arise important distinctions in their
+behavior. After solidification, lavas present some noticeable
+characters, then easily ascertainable. (1) Their average specific
+gravity may be taken as ranging between 2.37 and 3.22. (2) The
+heavier varieties contain much magnetic or titaniferous iron,
+with augite and olivine, their composition being basic, and their
+proportion of silica averaging about 45 to 55 per cent. (3) Lavas
+differ much in structure and texture. (4) Lavas vary greatly in
+color and general external aspect. The heavy basic kinds are usually
+dark gray, or almost black, though, on exposure to the weather,
+they acquire a brown tint from the oxidation and hydration of their
+iron. Their surface is commonly rough and ragged, until it has been
+sufficiently decomposed by the atmosphere to crumble into soil which,
+under favorable circumstances, supports a luxuriant vegetation. The
+less dense lavas, such as phonolites and trachytes, are frequently
+paler in color, sometimes yellow or buff, and decompose into light
+soils; but the obsidians present rugged black sheets of rock,
+roughened with ridges and heaps of gray froth-like pumice. Some of
+the most brilliant surfaces of color in any rock-scenery on the globe
+are to be found among volcanic rocks. The walls of active craters
+glow with endless hues of red and yellow. The Grand Cañon of the
+Yellowstone River has been dug out of the most marvelously tinted
+lavas and tuffs.
+
+Volcanic action may be either constant or periodic. Stromboli, in the
+Mediterranean, so far as we know, has been uninterruptedly emitting
+hot stones and steam, from a basin of molten lava, since the earliest
+period of history. Among the Moluccas, the volcano Sioa, and in the
+Friendly Islands, that of Tofua, have never ceased to be in eruption
+since their first discovery. The lofty cone of Sangay, among the
+Andes of Quito, is always giving off hot vapors; Cotopaxi, too, is
+ever constantly active. But, though examples of unceasing action may
+thus be cited from widely different quarters of the globe, they are
+nevertheless exceptional. The general rule is that a volcano breaks
+out from time to time with varying vigor, and after longer or shorter
+intervals of quiescence.
+
+It is usual to class volcanoes as _active_, _dormant_, and _extinct_.
+This arrangement, however, often presents considerable difficulty in
+its application. An active volcano can not of course be mistaken, for
+even when not in eruption, it shows by its discharge of steam and
+hot vapors that it might break out into activity at any moment. But
+in many cases it is impossible to decide whether a volcano should
+be called extinct or only dormant. The volcanoes of Silurian age
+in Wales, of Carboniferous age in Ireland, of Permian age in the
+Harz, of Miocene age in the Hebrides, of younger Tertiary age in
+the Western States and Territories of North America, are certainly
+all extinct. But the older Tertiary volcanoes of Iceland are still
+represented there by Skaptar-Jökull, Hecla, and their neighbors.
+Somma, in the First Century of the Christian era, would have been
+naturally regarded as an extinct volcano. Its fires had never been
+known to have been kindled; its vast crater was a wilderness of wild
+vines and brushwood, haunted, no doubt, by wolf and wild boar. Yet in
+a few days, during the autumn of the year 79, the half of the crater
+walls was blown out by a terrific series of explosions, the present
+Vesuvius was then formed within the limits of the earlier crater, and
+since that time volcanic action has been intermittently exhibited up
+to the present day. Some of the intervals of quietude, however, have
+been so considerable that the mountain might then again have been
+claimed as an extinct volcano. Thus, in the 131 years between 1500
+and 1631, so completely had eruptions ceased that the crater had once
+more become choked with copse-wood. A few pools and springs of very
+salt and hot water remained as memorials of the former condition of
+the mountain. But this period of quiescence closed with the eruption
+of 1631--the most powerful of all the known explosions of Vesuvius,
+except the great one of 79.
+
+In short, no essential distinction can be drawn between dormant and
+extinct volcanoes. Volcanic action is apt to show itself again and
+again, even at vast intervals, within the same regions and over the
+same sites. The dormant or waning condition of a volcano, when only
+steam and various gases and sublimates are given off, is sometimes
+called the Solfatara phase, from the well-known dormant crater of
+that name near Naples.
+
+The interval between two eruptions of an active volcano shows a
+gradual augmentation of energy. The crater, emptied by the last
+discharge, has its floor slowly upraised by the expansive force
+of the lava-column underneath. Vapors rise in constant outflow,
+accompanied sometimes by discharges of dust or stones. Through
+rents in the crater-floor red-hot lava may be seen only a few feet
+down. Where the lava is maintained at or above its fusion-point and
+possesses great liquidity, it may form boiling lakes, as in the
+great crater of Kilauea, where acres of seething lava may be watched
+throwing up fountains of molten rock, surging against the walls
+and re-fusing large masses that fall into the burning flood. The
+lava-column inside the pipe of a volcano is all this time gradually
+rising, until some weak part of the wall allows it to escape, or
+until the pressure of the accumulated vapors becomes great enough to
+burst through the hardened crust of the crater-floor and give rise to
+the phenomena of an eruption.
+
+Kluge has sought to trace a connection between the years of maximum
+and minimum sun-spots and those of greatest and feeblest volcanic
+activity, and has constructed lists to show that years which
+have been specially characterized by terrestrial eruptions have
+coincided with those marked by few sun-spots and diminished magnetic
+disturbance. Such a connection can not be regarded as having yet
+been satisfactorily established. Again, the same author has called
+attention to the frequency and vigor of volcanic explosions at or
+near the time of the August meteoric shower. But in this case,
+likewise, the cited examples can hardly yet be looked upon as more
+than coincidences.
+
+At many volcanic vents the eruptive energy manifests itself with
+more or less regularity. At Stromboli, which is constantly in an
+active state, the explosions occur at intervals varying from three or
+four to ten minutes and upward. A similar rhythmical movement has
+been often observed during the eruptions at other vents which are
+not constantly active. Volcano, for example, during its eruption of
+September, 1873, displayed a succession of explosions which followed
+each other at intervals of from twenty to thirty minutes. At Etna and
+Vesuvius a similar rhythmical series of convulsive efforts has often
+been observed during the course of an eruption. Among the volcanoes
+of the Andes a periodic discharge of steam has been observed; Mr.
+Whymper noticed outrushes of steam to proceed at intervals of from
+twenty to thirty minutes from the summit of Sangai, while during his
+inspection of the great crater of Cotopaxi, this volcano was seen to
+blow off steam at intervals of about half an hour. At the eruption of
+the Japanese volcano, Oshima, in 1877, Mr. Milne observed that the
+explosions occurred nearly every two seconds, with occasional pauses
+of 15 or 20 seconds. Kilauea, in Hawaii, seems to show a regular
+system of grand eruptive periods. Dana has pointed out that outbreaks
+of lava have taken place from that volcano at intervals of from eight
+to nine years, this being the time required to fill the crater up to
+the point of outbreak, or to a depth of 400 or 500 feet.
+
+The approach of an eruption is not always indicated by any
+premonitory symptoms, for many tremendous explosions are recorded to
+have taken place in different parts of the world without perceptible
+warning. Much in this respect would appear to depend upon the
+condition of liquidity of the lava, and the amount of resistance
+offered by it to the passage of the escaping vapors through its mass.
+In Hawaii, where the lavas are remarkably liquid, vast outpourings of
+them have taken place quietly without earthquakes during the present
+century. But even there the great eruption of 1868 was accompanied by
+violent earthquakes.
+
+The eruptions of Vesuvius are often preceded by failure or diminution
+of wells and springs. But more frequent indications of an approaching
+outburst are conveyed by sympathetic movements of the ground.
+Subterranean rumblings and groanings are heard; slight tremors
+succeed, increasing in frequency and violence till they become
+distinct earthquake shocks. The vapors from the crater grow more
+abundant as the lava-column in the pipe or funnel of the volcano
+ascends, forced upward and kept in perpetual agitation by the passage
+of elastic vapors through its mass. After a long previous interval of
+quiescence, there may be much solidified lava toward the top of the
+funnel, which will restrain the ascent of the still molten portion
+underneath. A vast pressure is thus exercised on the sides of the
+cone, which, if too weak to resist, will open in one or more rents,
+and the liquid lava will issue from the outer slope of the mountain;
+or the energies of the volcano will be directed toward clearing the
+obstruction in the chief throat, until with tremendous explosions,
+and the rise of a vast cloud of dust and fragments, the bottom and
+sides of the crater are finally blown out, and the top of the cone
+disappears. The lava may now escape from the lowest part of the lip
+of the crater, while, at the same time, immense numbers of red-hot
+bombs, scoriæ, and stones are shot up into the air. The lava at first
+rushes down like one or more rivers of melted iron, but, as it cools,
+its rate of motion lessens. Clouds of steam rise from its surface, as
+well as from the central crater. Indeed, every successive paroxysmal
+convulsion of the mountain is marked, even at a distance, by the rise
+of huge ball-like wreaths or clouds of steam, mixed with dust and
+stones, forming a column which towers sometimes a couple of miles
+or more above the summit of the cone. By degrees these eructations
+diminish in frequency and intensity. The lava ceases to issue, the
+showers of stones and dust decrease, and after a time, which may
+vary from hours to days or months, even in the _régime_ of the same
+mountain, the volcano becomes once more tranquil.
+
+The convulsions which culminate in the formation of a volcano usually
+split open the terrestrial crust by a more or less nearly rectilinear
+fissure, or by a system of fissures. In the subsequent progress of
+the mountain, the ground at and around the focus of action is liable
+to be again and again rent open by other fissures. These tend to
+diverge from the focus; but around the vent where the rocks have been
+most exposed to concussion, the fissures sometimes intersect each
+other in all directions. In the great eruption of Etna, in the year
+1669, a series of six parallel fissures opened on the side of the
+mountain. One of these, with a width of two yards, ran for a distance
+of 12 miles, in a somewhat winding course, to within a mile of the
+top of the cone.
+
+In the deeper portions of a volcanic vent the convulsive efforts of
+the lava-column to force its way upward must often produce lateral as
+well as vertical rifts, and into these the molten material will rush,
+exerting as it goes an enormous upward pressure on the mass of rock
+overlying it. At a modern volcano these subterranean manifestations
+can not be seen, but among the volcanoes of Tertiary and older times
+they have been revealed by the progress of denudation.
+
+Though lava very commonly issues from the lateral fissures on a
+volcanic cone, it may sometimes approach the surface in them without
+actually flowing out. The great fissure on Etna in 1669, for example,
+was visible even from a distance, by the long line of vivid light
+which rose from the incandescent lava within. Again, it frequently
+happens that minor volcanic cones are thrown up on the line of a
+fissure, either from the congelation of the lava round the point
+of emission, or from the accumulation of ejected scoriæ round the
+fissure-vent. One of the most remarkable examples of this kind is
+that of the Laki fissure in Iceland, the whole length of which (12
+miles) bristles with small cones and craters almost touching each
+other.
+
+Apart from the appearance of visible fissures, volcanic energy may
+be, as it were, concentrated on a given point, which will usually be
+the weakest in the structure of that part of the terrestrial crust,
+and from which the solid rock, shattered into pieces, is hurled into
+the air by the enormous expansive energy of the volcanic vapors.
+The history of the cone of Vesuvius brings before us a long series
+of such explosions, beginning with that of A. D. 79, and coming
+down to the present day. Even now, in spite of all the lava and
+ashes poured out during the last eighteen centuries, it is easy to
+see how stupendous must have been that earliest explosion by which
+the southern half of the ancient crater was blown out. At every
+successive important eruption, a similar but minor operation takes
+place within the present cone. The hardened cake of lava forming the
+floor is burst open, and with it there usually disappears much of the
+upper part of the cone, and sometimes, as in 1872, a large segment
+of the crater-wall. The islands of Santorin bring before us evidence
+of a prehistoric catastrophe of a similar nature, by which a large
+volcanic cone was blown up. The existing outer islands are a chain of
+fragments of the periphery of the cone, the centre of which is now
+occupied by the sea. In the year 1538 a new volcano, Monte Nuovo, was
+formed in twenty-four hours on the margin of the Bay of Naples. An
+opening was drilled by successive explosions, and such quantities of
+stones, scoriæ, and ashes were thrown out from it as to form a hill
+that rose 440 English feet above the sea-level, and was more than a
+mile and a half in circumference.
+
+A communication having been opened, either by fissuring or explosion,
+between the heated interior and the surface, fragmentary materials
+are commonly ejected from it, consisting at first mainly of the rocks
+through which the orifice has been opened, afterward of volcanic
+substances. In a great eruption, vast numbers of red-hot stones
+are shot up into the air, and fall back partly into the crater
+and partly on the outer slopes of the cone. According to Sir W.
+Hamilton, cinders were thrown by Vesuvius, during the eruption of
+1779, to a height of 10,000 feet. Instances are known where large
+stones, ejected obliquely, have described huge parabolic curves
+in the air, and fallen at a great distance. Stones eight pounds
+in weight occur among the ashes which buried Pompeii. The volcano
+of Antuco in Chili is said to send stones flying to a distance of
+thirty-six miles, Cotopaxi is reported to have hurled a 200-ton block
+nine miles, and the Japanese volcano, Asama, is said to have ejected
+many blocks of stone measuring from 40 to more than 100 feet in
+diameter.
+
+But in many great eruptions, besides a constant shower of stones
+and scoriæ, a vast column of exceedingly fine dust rises out of the
+crater, sometimes to a height of several miles, and then spreads
+outward like a sheet of cloud. The remarkable fineness of this dust
+may be understood from the fact that during great volcanic explosions
+no boxes, watches, or close-fitting joints have been found to be able
+to exclude it. Mr. Whymper collected some dust that fell sixty-five
+miles away from Cotopaxi, and which was so fine that from 4,000 to
+25,000 particles were required to weigh a grain. So dense is the
+dust-cloud as to obscure the sun, and for days together the darkness
+of night may reign for miles around the volcano. The eruption of
+Cotopaxi, on 26th June, 1877, began by an explosion that sent up
+a column of fine ashes to a prodigious height into the air, where
+it rapidly spread out and formed so dense a canopy as to throw the
+region below it into total darkness. So quickly did it diffuse
+itself, that in an hour and a half a previously bright morning became
+at Quito, thirty-three miles distant, a dim twilight, which in the
+afternoon passed into such darkness that the hand placed before
+the eye could not be seen. At Guayaquil, on the coast, 150 miles
+distant, the shower of ashes continued till the 1st of July. Dr.
+Wolf collected the ashes daily, and estimated that at that place
+there fell 315 kilogrammes on every square kilometre during the first
+thirty hours, and on the 30th of June, 209 kilogrammes in twelve
+hours.
+
+One of the most stupendous outpourings of volcanic ashes on record
+took place, after a quiescence of twenty-six years, from the volcano
+Coseguina, in Nicaragua, during the early part of the year 1835. On
+that occasion, utter darkness prevailed over a circle of thirty-five
+miles radius, the ashes falling so thickly that, even eight leagues
+from the mountain, they covered the ground to a depth of about ten
+feet. It was estimated that the rain of dust and sand fell over an
+area at least 270 geographical miles in diameter. Some of the finer
+materials, thrown so high as to come within the influence of an upper
+air-current, were borne away eastward, and fell, four days afterward,
+at Kingston, in Jamaica--a distance of 700 miles. During the great
+eruption of Sumbawa, in 1815, the dust and stones fell over an area
+of nearly one million square miles, and were estimated by Zollinger
+to amount to fully fifty cubic miles of material, and by Junghuhn
+to be equal to one hundred and eighty-five mountains like Vesuvius.
+Toward the end of the Eighteenth Century, during a time of great
+disturbance among the Japanese volcanoes, one of them, Sakurajima,
+threw out so much pumiceous material that it was possible to walk a
+distance of twenty-three miles upon the floating débris in the sea.
+
+The varying degree of liquidity or viscosity of the lava probably
+modifies the force of explosions, owing to the different amounts
+of resistance offered to the upward passage of the absorbed gases
+and vapors. Thus explosions and accompanying scoriæ are abundant at
+Vesuvius, where the lavas are comparatively viscid; they are almost
+unknown at Kilauea, where the lava is remarkably liquid.
+
+In tranquil conditions of a volcano, the steam, whether collecting
+into larger or smaller vesicles, works its way upward through
+the substance of the molten lava, and as the elasticity of this
+compressed vapor overcomes the pressure of the overlying lava,
+it escapes at the surface, and there the lava is thus kept in
+ebullition. But this comparatively quiet operation, which may be
+watched within the craters of many active volcanoes, does not produce
+clouds of fine dust. The collision or friction of millions of stones
+ascending and descending in the dark column above the crater must
+doubtless cause much dust and sand. But the explosive action of steam
+is probably also an immediate cause of much trituration. The aqueous
+vapor or water-gas which is so largely dissolved in many lavas must
+exist within the lava-column, under an enormous pressure, at a
+temperature far above its critical point, even at a white heat, and
+therefore possibly in a state of dissociation. The sudden ascent of
+lava so constituted relieves the pressure rapidly without sensibly
+affecting the temperature of the mass. Consequently, the white-hot
+gases or vapors at length explode, and reduce the molten mass to the
+finest powder, like water shot out of a gun.
+
+As every shower of dust and sand adds to the height of the ground
+on which it falls, thick volcanic accumulations may be formed far
+beyond the base of the mountain. The volcano of Sangay, in Ecuador,
+for instance, has buried the country around it to a depth of 4,000
+feet under its ashes. In such loose deposits are entombed trees and
+other kinds of vegetation, together with the bodies of animals, as
+well as the works of man. In some cases, where the layer of volcanic
+dust is thin, it may merely add to the height of the soil, without
+sensibly interfering with the vegetation. But it has been observed at
+Santorin that though this is true in dry weather, the fall of rain
+with the dust at once acts detrimentally. On the 3d of June, 1866,
+the vines were there withered up, as if they had been burned, along
+the track of the smoke cloud. By the gradual accumulation of volcanic
+ashes, new geological formations arise which, in their component
+materials, not only bear witness to the volcanic eruptions that
+produced them, but preserve a record of the land-surfaces over which
+they spread. In the third place, besides the distance to which the
+fragments may be hurled by volcanic explosions, or to which they may
+be diffused by the ordinary aerial movements, we have to take into
+account the vast spaces across which the finer dust is sometimes
+borne by upper air-currents. In the instance already cited, ashes
+from Coseguina fell 700 miles away, having been carried all that
+long distance by a high counter-current of air, moving apparently at
+the rate of about seven miles an hour in an opposite direction to
+that of the wind which blew at the surface. By the Sumbawa eruption,
+also referred to above, the sea west of Sumatra was covered with a
+layer of ashes two feet thick. On several occasions ashes from the
+Icelandic volcanoes have fallen so thickly between the Orkney and
+Shetland Islands, that vessels passing there have had the unwonted
+deposit shoveled off their decks in the morning. In the year 1783,
+during the memorable eruption of Skaptar-Jökull, so vast an amount
+of fine dust was ejected that the atmosphere over Iceland continued
+loaded with it for months afterward. It fell in such quantities
+over parts of Caithness--a distance of 600 miles--as to destroy
+the crops; that year is still spoken of by the inhabitants as the
+year of “the ashie.” Traces of the same deposit have been observed
+in Norway, and even as far as Holland. Hence it is evident that
+volcanic accumulations may take place in regions many hundreds
+of miles distant from any active volcano. A single thin layer of
+volcanic detritus in a group of sedimentary strata would not thus of
+itself prove the existence of contemporaneous volcanic action in its
+neighborhood.
+
+At its exit from the side of a volcano, lava glows with a white heat,
+and flows with a motion which has been compared to that of honey or
+of melted iron. It soon becomes red, and like a coal fallen from a
+hot fireplace rapidly grows dull as it moves along, until it assumes
+a black, cindery aspect. At the same time the surface congeals, and
+soon becomes solid enough to support a heavy block of stone. The
+aspect of the stream varies with the composition and fluidity of
+the lava, form of the ground, angle of slope, and rapidity of flow.
+Viscous lavas, like those of Vesuvius, break up along the surface
+into rough brown or black cinder-like slags and irregular ragged
+cakes, bristling with jagged points, which, in their onward motion,
+grind and grate against each other with a harsh, metallic sound,
+sometimes rising into rugged mounds or becoming seamed with rents and
+gashes, at the bottom of which the red-hot glowing lava may be seen.
+In lavas possessing somewhat greater fluidity, the surface presents
+froth-like, curving lines, as in the scum of a slowly flowing river,
+or is arranged in curious ropy folds, as the layers have successively
+flowed over each other and congealed. A large area which has been
+flooded with lava is perhaps the most hideous and appalling scene of
+desolation anywhere to be found on the surface of the globe.
+
+A lava-stream usually spreads out as it descends from its point
+of escape, and moves more slowly. Its sides look like huge
+embankments, or like some of the long mounds of “clinkers” in a great
+manufacturing district. The advancing end is often much steeper,
+creeping onward like a great wall or rampart, down the face of which
+the rough blocks of hardened lava are ever rattling.
+
+In a lofty volcano, lava occasionally rises to the lip of the crater
+and flows out there; but more frequently it escapes from some fissure
+or orifice in a weak part of the cone. In minor volcanoes, on the
+other hand, where the explosions are less violent, and where the
+thickness of the cone in proportion to the diameter of the funnel is
+often greater, the lava very commonly rises into the crater. Should
+the crater-walls be too weak to resist the pressure of the molten
+mass, they give way, and the lava rushes out from the breach. This is
+seen to have happened in several of the puys of Auvergne. But if the
+crater be massive enough to withstand the pressure, the lava may at
+last flow out from the lowest part of the rim.
+
+As soon as the molten rock reaches the surface, the superheated
+water-vapor or gas dissolved within its mass escapes copiously,
+and hangs as a dense white cloud over the moving current. The
+lava-streams of Vesuvius sometimes appear with as dense a steam-cloud
+at their lower ends as that which escapes at the same time from the
+main crater. Even after the molten mass has flowed several miles,
+steam continues to rise abundantly both from its end and from
+numerous points along its surface, and continues to do so for many
+weeks, months, or it may be for several years.
+
+Should the point of escape of a lava-stream lie well down on the
+cone, far below the summit of the lava-column in the funnel, the
+molten rock, on its first escape, driven by hydrostatic pressure,
+will sometimes spout up high into the air--a fountain of molten rock.
+This was observed in 1794 on Vesuvius, and in 1832 on Etna. In the
+eruption of 1852 at Mauna Loa, an unbroken fountain of lava, from 200
+to 700 feet in height and 1,000 feet broad, burst out at the base of
+the cone. Similar “geysers” of molten rock have subsequently been
+noticed in the same region. Thus in March and April, 1868, four fiery
+fountains, throwing lava to heights varying from 500 to 1,000 feet,
+continued to play for several weeks. According to Mr. Coan, such
+outbursts take place from the bottom of a column of lava 3,000 feet
+high. The volcano of Mauna Loa strikingly illustrates another feature
+of volcanic dynamics in the position and outflow of lava. It bears
+upon its flanks at a distance of 20 miles, but 10,000 feet lower,
+the huge crater Kilauea. As Dana has pointed out, these orifices
+form part of one mountain, yet the column of lava stands 10,000 feet
+higher in one conduit than in the other. On a far smaller scale the
+same independence occurs among the several pipes of some of the
+geysers in the Yellowstone region of North America.
+
+The rate of movement is regulated by the fluidity of the lava, by
+its volume, and by the form and inclination of the ground. Hence, as
+a rule, a lava-stream moves faster at first than afterward, because
+it has not had time to stiffen, and its slope of descent is usually
+steeper than further down the mountain. One of the most fluid and
+swiftly flowing lava-streams ever observed on Vesuvius was that
+erupted on 12th August, 1805. It is said to have rushed down a space
+of 3 Italian (3⅔ English) miles in the first four minutes, but to
+have widened out and moved more slowly as it descended, yet finally
+to have reached Torre del Greco in three hours. A lava erupted by
+Mauna Loa in 1852 went as fast as an ordinary stage-coach, or fifteen
+miles in two hours; but some of the lavas from that mountain have in
+parts of their course moved with double that rapidity.
+
+In some cases, lava escaping from craters or fissures comes to rest
+before reaching the base of the slopes, like the obsidian current
+which has congealed on the side of the little volcanic island of
+Volcano. In other instances, the molten rock not only reaches the
+plains, but flows for many miles away from the point of eruption.
+Sartorius von Waltershausen computed the lava emitted by Etna in 1865
+at 92 millions of cubic metres, that of 1852 at 420 millions, that
+of 1669 at 980 millions, and that of a prehistoric lava-stream near
+Randazzo at more than 1,000 millions. The most stupendous outpouring
+of lava on record was that which took place in Iceland in the year
+1783. Successive streams issued from a fissure about 12 miles long,
+filling up river gorges which were sometimes 600 feet deep and 200
+feet broad, and advancing into the alluvial plains in lakes of
+molten rock 12 to 15 miles wide and 100 feet deep. Two currents of
+lava which, filling up the valley of the Skapta, escaped in nearly
+opposite directions, extended for 45 and 50 miles respectively, their
+usual thickness being 100 feet. Bischof estimated that the total
+amount of lava poured forth during this single eruption “surpassed in
+magnitude the bulk of Mont Blanc.”
+
+The varying degrees of liquidity are manifested in a characteristic
+way on the surface of lava. Thus, in the great lava-pools of Hawaii,
+the rock exhibits a remarkable liquidity, throwing up fountains of
+molten rock to a height of 300 feet or more. During its ebullition in
+the crater-pools, jets and driblets a quarter of an inch in diameter
+are tossed up, and, falling back on one another, make “a column of
+hardened tears of lava,” one of which was found to have attained
+a height of 40 feet, while in other places the jets thrown up and
+blown aside by the wind give rise to long threads of glass which
+lie thickly together like mown grass, and are known by the natives
+under the name of “Pele’s Hair,” after one of their divinities. Yet,
+although the ebullition is caused by the uprise and escape of highly
+heated vapors, there is no cloud over the boiling lake itself, heavy
+white vapor only escaping at different points along the edge.
+
+
+
+
+  EARTHQUAKES
+  --WILLIAM HUGHES
+
+
+It appears, from the accurate records of such phenomena which have
+been kept within recent periods, that earthquakes are of much more
+frequent occurrence than is commonly supposed. Upward of three
+thousand earthquakes are recorded as having occurred within the first
+half of the Nineteenth Century--an average of more than one for every
+week throughout the entire period. But not more than one in forty is
+of considerable importance, by far the greater number consisting of
+such slight shocks as are occasionally experienced in Great Britain
+and other countries favored with a like immunity in this regard. An
+important earthquake, however, in some part of the world or other,
+appears, from the above average, to occur once in every eight months.
+In Europe alone, where a more complete record of such occurrences is
+obtainable than in other parts of the world, as many as 320 distinct
+earthquakes are recorded to have occurred within a period of ten
+years (1833-42)--an average of thirty-two annually, and of one such
+shock for every ten days throughout the period.
+
+  [The _geographical area_ within which shocks of earthquakes
+  are experienced is a widely spread one, and does not appear to
+  undergo any material change (if, indeed, any change whatever)
+  as to its limits. At any rate, the regions in which violent
+  earthquakes are recorded to have occurred in former times are
+  those in which such disturbances are of most frequent recurrence
+  at the present day. One of the most striking evidences in favor
+  of the supposition that the volcanic eruption is due to the same
+  deeply seated cause which produces the shock of the earthquake,
+  is afforded by the fact, that all the volcanoes which have been
+  in eruption within the modern period of geology are found within
+  regions liable to earthquakes, and, for the most part, to violent
+  shocks.]
+
+Regarding the earthquake and the volcanic eruption as the
+manifestation, under different conditions, of the earth’s internal
+fires, we readily mark out upon the globe the great regions of
+geographical distribution in the case of such phenomena. The most
+widely extended of these coincides with the circuit of the Pacific
+Ocean. Along the entire western coast of the New World, from Tierra
+del Fuego to the peninsula of Alaska and the neighborhood of the
+Aleutian Islands, shocks of earthquakes are known to occur; and,
+within a large portion of the space, vents of active eruption
+are found. The subterranean igneous force is, indeed, much more
+powerfully displayed in the southern than in the northern half of
+the American continent, and the active volcanoes that occur within
+the limits referred to are nearly all found amid the cordilleras of
+the Andes, or upon the plateaus of the Mexican isthmus. One of the
+Mexican volcanoes--Jorullo--is especially deserving of notice, from
+the circumstance of its having first risen above the surrounding
+plain by the accumulation of volcanic matter during an eruption in
+the year 1759.
+
+The Aleutian Islands connect the volcanic region of the eastern
+Pacific with that which extends along its western shores. In the
+latter case, however, it is upon the peninsular regions, or in the
+chains of islands that adjoin the mainland, that the igneous force
+is displayed. Kamtchatka, the Kurile Islands, Yesso, the Japanese
+group, and the entire region of the Malay Archipelago, exhibit the
+presence of igneous force below the ground. Seven active volcanoes
+occur in Kamtchatka. The Japanese Archipelago is said to contain at
+least twenty-seven active volcanoes, eight of them upon Yesso and
+the adjacent islets. Between Japan and the Loo-choo group is Sulphur
+Island, an insular volcano, from which smoke is constantly emitted.
+
+The Philippine Islands, in which earthquakes are of frequent
+occurrence, prolong the volcanic chain to the southward. Thence it
+is traced, at intervals, along the northern shores of New Guinea,
+and through the prolonged chains of the Solomon Islands, and the
+New Hebrides, to the North Island of New Zealand. Slight shocks
+of earthquake have also been experienced within the southern and
+eastwardly portions of the Australian mainland.
+
+The numerous volcanoes of the Malay Archipelago, the whole area of
+which is liable to frequent earthquake shocks, often of the most
+destructive violence, belong to the eastern portion of this region,
+and display the agency of subterranean heat on the grandest scale.
+The island of Java alone contains forty-three active volcanoes,
+ranging in a linear direction throughout its length. The volcanic
+chain of Java is prolonged to the eastward through the Lesser Sunda
+Islands (Sumbawa, etc.), in which direction it is united with
+that which borders the Pacific waters. There are active volcanoes
+on an island in the Gulf of Siam, besides the well-known crater
+of Barren Island, in the Bay of Bengal. The region adjoining the
+last-named body of water, together with the whole of northern India,
+is of frequent liability to earthquakes, some of them (as that of
+Cutch, in 1819) of the most destructive violence. The volcanic
+island of Mayotta (Comoro group), the active Piton of Réunion or
+Bourbon Island, and the hot springs and extinct craters of St. Paul
+and Amsterdam Islands, in a high southern latitude of the Indian
+Ocean, constitute points which indicate, at distant intervals, the
+continuity of the volcanic chain.
+
+The southwestern portion of Asia, the southern shores of Europe, and
+the northwestwardly portion of the African mainland, fall within
+this region on the one side, as the islands of the West Indies do
+upon the other. The entire breadth of the Atlantic Ocean, as well
+as the circuit of the Mediterranean, is thus included within its
+limits. To the northward, the numerous volcanoes of Iceland, and
+the more distant cone of Jan Mayen Island, lying within the Arctic
+circle, must be regarded as within its area; together with, in an
+opposite direction, the still-burning peak of the Cameroon Mountains,
+adjoining the upper extremity of the Gulf of Guinea. The volcanic
+peaks found within the widely detached groups of the Azores and the
+Cape Verde Islands, with Tenerife, in the Canary group, are among its
+outlying members.
+
+Throughout the wide region thus indicated, earthquakes are of
+frequent occurrence. There are fewer active vents of eruption than
+in the case of the Pacific circuit. But the cones of Etna and
+Vesuvius, with the island of Santorin, in the Mediterranean, and
+the numerous volcanoes of Iceland, attest the destructive violence
+of the subterranean fires. Western Asia, from the Caspian to the
+shores of the Archipelago (including Armenia, Syria, and the Lesser
+Asia), Greece, southern Italy, the Spanish peninsula, and the region
+of Mount Atlas, in Northwestern Africa, are all liable to the
+frequent repetition of such convulsions. The only portion of the
+Mediterranean coasts exempt from such disturbing phenomena is on its
+southern shores, embracing that part of the North African coast which
+stretches from the Lesser Syrtis to the valley of the Nile. We have
+no record of the experience of any shocks of earthquake in Egypt.
+Had it been otherwise, perhaps the pyramids of that land of wonders
+might have proved less enduring monuments of the past.
+
+The movement imparted to the ground during an earthquake may be
+either horizontal or vertical. In the former case, the phenomenon
+consists in an undulating, wave-like movement; in the latter, in
+an upheaval or subsidence of land. The vertical shock affects most
+the relative levels of adjacent objects, and produces the most
+striking permanent changes in the natural aspect of the region in
+which it is experienced. But the undulatory movement is attended
+by more serious consequences to man, since it at once shakes the
+foundations of the strongest edifices, and may overthrow in the
+space of a few seconds the accumulated labors of prior ages. Whole
+tracts of land, with their cities or villages, may be elevated or
+depressed with comparatively little injury to life; but nothing can
+withstand the force of a motion which rocks the solid strata of the
+earth itself. The most solidly constructed buildings are not proof
+against the earthquake any more than the weakest. Indeed, it has in
+many instances been observed that those erections which displayed
+the strongest masonry have suffered more from the effects of an
+earthquake than buildings of slighter structure. The cracking of
+walls, the falling-in of roofs, and the crash of tumbling houses on
+every side, burying their inmates beneath the ruins, are among the
+characteristics of the earthquake in its most violent and frightful
+form.
+
+It has been asserted that a third kind of movement--viz., in a
+rotatory direction--sometimes occurs, and certain phenomena by
+which earthquakes have been attended have favored this belief.
+Thus, isolated columns or statues have been found, after such
+an occurrence, to face a different quarter from that which they
+previously did. This, however, would be sufficiently accounted for
+by a vibratory movement, acting upon a column which was _unequally_
+attached to its base; _i.e._, the fastening of which was of unequal
+strength relatively to the central point of junction. During the
+Chilian earthquake of 1835, vessels moored alongside of one another
+in the harbor of Concepcion were afterward found with their cables
+twisted together.
+
+The duration of any single earthquake shock is seldom more than a few
+seconds, though the terror which it inspires naturally tends to make
+it seem of longer continuance; but in the case of the more violent
+movements, even a few moments serve to destroy the work of ages. In
+the Chilian earthquake of 1835, the great shock which destroyed the
+city of Concepcion was preceded by several tremulous movements of
+minor intensity. During the first half-minute, many persons remained
+in their houses; but the convulsive motion of the earth then became
+so strong that all rushed into the open streets for safety. The
+horrid motion (writes an eye-witness of the scene) increased; people
+could hardly stand; buildings waved and tottered; suddenly an awful
+and overpowering shock caused universal destruction. In less than six
+seconds the city was in ruins!
+
+The earthquake is propagated to enormous distances from the region
+in which the shock originates, the rate at which the motion travels
+varying not merely with the violence of the originating impulse, but
+also with the nature of the formations through which it passes. Rocks
+of solid and homogeneous texture, as granite, favor the transmission
+of the shock; while formations of loose texture, such as sand, most
+retard its speed. The well-known Lisbon earthquake of 1755, by which
+sixty thousand persons are said to have perished within the brief
+space of six minutes, was felt in the British Islands, as well as
+upon the coast of Barbary, and even among the islands of the West
+Indies, on the opposite side of the Atlantic.
+
+
+
+
+  MOUNTAINS
+  --A. KEITH JOHNSTON
+
+
+The number and altitude of the mountains of the globe are so great
+that they form almost everywhere prominent objects, and operate to a
+large extent in modifying the climatic conditions of every country
+in the world. Yet the amount of solid material so raised above the
+ordinary level of the land is not so much as might be expected.
+Remembering that elevated plateaus of great extent occur in several
+regions, and that the general surface of the earth is considerably
+higher than the sea-level, it has been estimated that were the whole
+dry land reduced to a uniform level, it would form a plain having an
+elevation of 1,800 feet above the sea. And were these solid materials
+scattered over the whole surface of the globe, so as to fill up the
+bed of the ocean, the resulting level would be considerably below
+the present surface of the sea, inasmuch as the main height of the
+dry land most probably does not exceed one-fifteenth of the mean
+depth of the bed of the ocean.
+
+Mountains, and especially mountain-chains, subserve important uses in
+the economy of nature, especially in connection with the water system
+of the world. They are at once the great collectors and distributers
+of water. In the passage of moisture-charged winds across them the
+moisture is precipitated as rain or snow. When mountain ranges
+intersect the course of constant winds by thus abstracting the
+moisture, they produce a moist country on the windward side, and a
+comparatively dry and arid one on the leeward. This is exemplified in
+the Andes, the precipitous western surface of which has a different
+aspect from the sloping eastern plains; and so also the greater
+supply of moisture on the southern sides of the Himalayas brings the
+snow-line 5,000 feet lower than on the northern side.
+
+Above a certain height the moisture falls as snow, and a range of
+snow-clad summits would form a more effectual separation between
+the plains on either side than would the widest ocean, were it not
+that transverse valleys are of frequent occurrence, which open up a
+pass, or way of transit, at a level below the snow-line. But even
+these would not prevent the range being an impassable barrier, if
+the temperate regions contained as lofty mountains as the tropics.
+Mountain ranges, however, decrease in height from the equator to the
+poles in relation to the snow-line.
+
+The numerous attempts that have been made to generalize on the
+distribution of mountains on the globe have hitherto been almost
+unsuccessful. In America, the mountains take a general direction more
+or less parallel to the meridian, and for a distance of 8,280 miles,
+from Patagonia to the Arctic Ocean, form a vast and precipitous range
+of lofty mountains, which follow the coast-line in South America,
+and spread somewhat out in North America, presenting everywhere
+throughout their course a tendency to separate into two or more
+parallel ridges, and giving to the whole continent the character of
+a precipitous and lofty western border, gradually lowering into an
+immense expanse of eastern lowlands. In the Old World, on the other
+hand, there is no single well-defined continuous chain connected
+with the coast-line. The principal ranges are grouped together in a
+Y-shaped form, the general direction of which is at right angles to
+the New World chain. The centre of the system in the Himalayas is
+the highest land in the hemisphere. From this, one arm radiates in
+a northeast direction, and terminates in the high land at Behring
+Strait: the other two take a westerly course; the one a little to the
+north, through the Caucasus, Carpathians, and Alps, to the Pyrenees;
+the other more to the south, through the immense chain of Central
+African mountains, and terminating at Sierra Leone. Most of the
+principal secondary ranges have generally a direction more or less at
+right angles to this great mountain tract.
+
+The inquiry into the origin of mountains is one that has received
+not a little attention. Geologists have shown that the principal
+agents in altering the surface of the globe are denudation, which is
+always abrading and carrying to a lower level the exposed surfaces,
+and an internal force which is rising or depressing the existing
+strata, or bringing unstratified rocks to the surface. Whether the
+changes are the small and almost imperceptible alterations now taking
+place, or those recorded in the mighty mountains and deep valleys
+everywhere existing, denudation and internal force are the great
+producing causes. These give us two great classes of mountains.
+
+The extent to which denudation has altered the surface of the globe
+can scarcely be imagined. All the stratified rocks are produced by
+its action; but these do not measure its full amount, for many of
+these beds have been deposited and denuded, not once or twice, but
+repeatedly, before they reach their present state. Masses of rock
+more indurated, or better defended from the wasting currents than
+those around, serve as indices of the extent of denudation. The most
+remarkable case of this kind with which we are acquainted is that of
+the three insulated mountains in Ross-shire--Suil Veinn, Coul Beg,
+and Coul More--which are about 3,000 feet high. The strata of the
+mountains are horizontal, like the courses of masonry in a pyramid,
+and their deep red color is in striking contrast with the cold bluish
+hue of the gneiss which forms the plain, and on whose upturned edges
+the mountain-beds rest. It seems very probable, as Hugh Miller
+suggests, that when the formation of which these are relics (at one
+time considered as Old Red Sandstone, but now determined by Sir
+Roderick Murchison as being older than Silurian) was first raised
+above the waves, it covered with an amazing thickness the whole
+surface of the Highlands of Scotland, from Ben Lomond to the Maiden
+Paps of Caithness, but that subsequent denudation swept it all away,
+except in circumscribed districts, and in detached localities like
+these pyramidal hills.
+
+Mountains produced by internal force are of several kinds. (_a_)
+Mountains of ejection, in which the internal force is confined to a
+point, so to speak, having the means of exhausting itself through an
+opening in the surface. The lava, scoriæ, and stones ejected at this
+opening form a conical projection which, at least on the surface,
+is composed of strata sloping away from the crater. Volcanoes are
+mostly isolated conical hills, yet they chiefly occur in a somewhat
+tortuous linear series, on the mainland and islands which inclose
+the great Pacific Ocean. Vesuvius and the other European volcanoes
+are unconnected with this immense volcanic tract. (_b_) But the
+internal force may be diffused under a large tract or zone, which, if
+it obtain no relief from an opening, will be elevated in the mass.
+When the upheaval occurs to any extent, the strata are subjected to
+great tension. If they can bear it, a soft rounded mountain-chain
+is the result; but generally one or more series of cracks are
+formed, and into them igneous rocks are pushed, which, rising up
+into mountain-chains, elevate the stratified rocks on their flanks,
+and perhaps as parallel ridges. Thus, the Andes consist of the
+stratified rocks of various ages, lying in order on the granite and
+porphyry of which the mass of the range is composed.
+
+The position of the strata on such mountains supplies the means of
+determining, within definite limits, the period of upheaval. The
+newest strata that have been elevated on the sides of the mountain
+when it was formed, give a date antecedent to that at which the
+elevation took place, while the horizontal strata at the base
+of the mountains supply one subsequent to that event. Thus, the
+principal chain of the Alps was raised during the period between the
+deposition of the Tertiary and that of the older recent deposits.
+(_c_) But there is yet another way in which the upheaving internal
+force operates, viz., where it does not act at right angles to the
+surface, but rather obliquely, and, as it were, pushes the solid
+strata forward, causing them to rise in huge folds, which, becoming
+permanent, form parallel ranges of mountains.
+
+The crust of the earth, in its present solid and brittle condition,
+is thus curved, in a greater or less degree, by the shock of every
+earthquake; it is well known that the trembling of the earth is
+produced by the progress of a wave of the solid crust; that the
+destruction of buildings is caused by the undulation; and that the
+wave has been so evident that it has been described as producing
+a sickening feeling on the observer, as if the land were but thin
+ice heaving over water. The Appalachians were thus formed. Many
+other ranges have had a similar origin, as some in Belgium and in
+the Southern Highlands of Scotland, as has been suggested by Mr.
+Carruthers.
+
+It is evident that in the last two classes the parallel ridges
+were produced at the same time. Elie de Beaumont generalized this,
+maintaining that all parallel ridges or fissures are synchronous;
+and on this he based a system of mountain structure which is too
+universal and too geometrical to be true. The synchronism of parallel
+fissures had been noticed by Werner, and it is now received as a
+first principle in mining. The converse is also held to be generally
+true, that fissures differing in direction differ also in age;
+yet divergence from a centre, and consequent want of parallelism,
+as in the case of volcanoes, may be an essential characteristic
+of contemporaneity. Nevertheless, Elie de Beaumont classified the
+mountains of the world according to this parallelism, holding that
+the various groups are synchronous. The parallelism does not consist
+in having the same relations to the points of the compass--for these,
+as regards north and south, would be far from parallel--but is
+estimated in its relation to some imaginary great circle, which being
+drawn round the globe would divide it into equal hemispheres. Such
+circles he calls Great Circles of Reference. But beyond this, he went
+a step further, and proposed a more refined classification, depending
+on a principle of geometrical symmetry, which he believed he had
+discovered among his great circles of reference. It is to be feared,
+however, that his geometrical speculations have little foundation in
+nature.
+
+
+
+
+  LAKES--FRESH, SALT, AND BITTER
+  --SIR ARCHIBALD GEIKIE
+
+
+Depressions filled with water on the surface of the land, and known
+as Lakes, occur abundantly in the northern parts of both hemispheres,
+and more sparingly, but often of large size, in warmer latitudes. For
+the most part, they do not belong to the normal system of erosion in
+which running water is the prime agent, and to which the excavation
+of valleys and ravines must be attributed. On the contrary, they are
+exceptional to that system, for the constant tendency of running
+water is to fill them up. Their origin, therefore, must be sought
+among some of the other geological processes.
+
+Lakes are conveniently classed as fresh or salt. Those which possess
+an outlet contain in almost all cases fresh water; those which have
+none are usually salt.
+
+In the northern parts of Europe and America, as first emphasized by
+Sir Andrew C. Ramsay, lakes are prodigiously abundant on ice-worn
+rock-surfaces, irrespective of dominant lines of drainage. They
+seem to be distributed as it were at random, being found now on the
+summits of ridges, now on the sides of hills, and now over broad
+plains. They lie for the most part in rock-basins, but many of them
+have barriers of detritus. In the mountainous regions of temperate
+and polar latitudes, lakes abound in valleys, and are connected with
+main drainage-lines. In North America and in Equatorial Africa, vast
+sheets of fresh water occur in depressions of the land, and are
+rather inland seas than lakes.
+
+The water of many lakes has been observed to rise above its normal
+level for a few minutes or for more than an hour, then to descend
+beneath that level, and to continue this vibration for some time. In
+the Lake of Geneva, where these movements, locally known there as
+_Seiches_, have long been noticed, the amplitude of the oscillation
+ranges up to a metre or even sometimes to two metres. These
+disturbances may sometimes be due to subterranean movements; but
+probably they are mainly the effect of atmospheric perturbations,
+and, in particular, of local storms with a vertical descending
+movement.
+
+Among the geological functions discharged by lakes the following may
+be noticed:
+
+1st. Lakes equalize the temperature of the localities in which they
+lie, preventing it from falling as much in winter and rising as much
+in summer as it would otherwise do.[1] The mean annual temperature of
+the surface water at the outflow of the Lake of Geneva is nearly 4°
+warmer than that of the air.
+
+2d. Lakes regulate the drainage of the area below their outfall,
+thereby preventing or lessening the destructive effects of floods.
+
+3d. Lakes filter river-water and permit the undisturbed accumulation
+of new deposits, which in some modern cases may cover thousands
+of square miles of surface, and may attain a thickness of nearly
+3,000 feet (Lake Superior has an area of 32,000 square miles;
+Lago Maggiore is 2,800 feet deep). How thoroughly lakes can filter
+river-water is typically displayed by the contrast between the muddy
+river which flows in at the head of the Lake of Geneva, and the
+“blue rushing of the arrowy Rhone,” which escapes at the foot. The
+mouths of small brooks entering lakes afford excellent materials
+for studying the behavior of silt-bearing streams when they reach
+still water. Each rivulet may be observed pushing forward its delta
+composed of successive sloping layers of sediment. On a shelving
+bank, the coarser detritus may repose directly upon the solid rock of
+the district. But as it advances into the lake, it may come to rest
+upon some older lacustrine deposit. The river Linth since 1860 has
+annually discharged into Lake Wallenstadt some 62,000 cubic metres of
+detritus.
+
+A river which flows through a succession of lakes can not carry much
+sediment to the sea, unless it has a long course to run after it has
+passed the lowest lake, and receives one or more muddy tributaries.
+Let us suppose, for example, that, in a hilly region, a stream passes
+through a series of lakes. As the highest lake will intercept much,
+perhaps all, of this sediment, the next in succession will receive
+little or none until the first is either filled up or has been
+drained by the cutting of a gorge through the intervening rock. The
+same process will be repeated until the lakes are effaced, and their
+places are taken by alluvial meadows. Examples of this sequence of
+events are of frequent occurrence in Britain.
+
+Besides the detrital accumulations due to the influx of streams,
+there are some which may properly be regarded as the work of lakes
+themselves. Even on small sheets of water, the eroding influence
+of wind-waves may be observed; but on large lakes the wind throws
+the water into waves which almost rival those of the ocean in size
+and destructive power. Beaches, sand-dunes, shore-cliffs, and other
+familiar features of the meeting-line between land and sea, reappear
+along the margins of such great fresh-water seas as Lake Superior.
+Beneath the level of the water a terrace or platform is formed, of
+which the distance from shore and depth vary with the energy of the
+waves by which it is produced. This platform is well developed in the
+Lake of Geneva.
+
+Some of the distinctive features of the erosion and deposition that
+take place in lake-basins have been admirably laid open for study in
+those basins of vanished lakes which have been so well described by
+Gilbert, Dutton, Russell, and Upham in the Western Territories of the
+United States. They have been treated of in a masterly way by Gilbert
+in his essay on _The Topographic Features of Lake-Shores_.
+
+4th. Lakes serve as basins in which chemical deposits may take place.
+Of these the most interesting and extensive are those of iron-ore,
+which chiefly occur in northern latitudes.
+
+5th. Lakes furnish an abode for a lacustrine fauna and flora,
+receive the remains of the plants and animals washed down from
+the surrounding country, and entomb these organisms in the
+growing deposits, so as to preserve a record of the lacustrine
+and terrestrial life of the period during which they continue.
+Besides the more familiar pond-snails and fishes, lakes possess a
+peculiar pelagic fauna, consisting in large measure of entomostracous
+crustaceans, distinguished more especially by their transparency.
+These, as well as the organisms of shallower water, doubtless furnish
+calcareous materials for the mud or marl of the lake bottoms. But
+it is as receptacles of sediment from the land, and as localities
+for the preservation of a portion of the terrestrial fauna and
+flora, that lakes present their chief interest to a geologist. Their
+deposits consist of alternations of sand, silt, mud, gravel, and
+occasional irregular seams of vegetable matter, together with layers
+of calcareous marl formed of lacustrine shells, _Entomostraca_, etc.
+In lakes receiving much sediment, little or no marl can accumulate
+during the time when sediment is being deposited. In small, clear,
+and not very deep lakes, on the other hand, where there is little
+sediment, or where it only comes occasionally at intervals of flood,
+thick beds of white marl, formed entirely of organic remains, may
+gather on the bottom, as has happened in numerous districts of
+Scotland and Ireland. The fresh-water limestones and clays of some
+old lake-basins (those of Miocene time in Auvergne and Switzerland,
+and of Eocene age in Wyoming, for example) cover areas occasionally
+hundreds of square miles in extent, and attain a thickness of
+hundreds, sometimes even thousands, of feet.
+
+Existing lakes are of geologically recent origin. Their disappearance
+is continually in progress by infilling and erosion. Besides the
+displacement of their water by alluvial accumulations, they are
+lowered and eventually drained by the cutting down of the barrier at
+their outlets. Where they are effaced merely by erosion, it must be
+an excessively slow process, owing to the filtered character of the
+water; but where it is performed by the retrocession of a waterfall
+at the head of an advancing gorge, it may be relatively rapid after
+it has once begun. In a river-course it is usual to find a lake-like
+expansion of alluvial land above each gorge. These plains may be
+regarded as old lake-bottoms, which have been drained by the cutting
+out of the ravines. Successive terraces often fringe a lake and mark
+former levels of its waters. It is when we reflect upon the continued
+operation of the agencies which tend to efface them, that we can best
+realize why the lakes now extant must necessarily be of comparatively
+modern date.
+
+Saline lakes, considered chemically, may be grouped as _salt lakes_,
+where the chief constituents are sodium and magnesium chlorides
+with magnesium and calcium sulphates; and _bitter lakes_, which are
+usually distinguished by their large percentage of sodium carbonate
+as well as chloride and sulphate (natron-lakes), sometimes by their
+proportion of borax (borax lakes). From a geological point of view
+they may be divided into two classes--(1) those which owe their
+saltness to the evaporation and concentration of water poured into
+them by their feeders; and (2) those which were originally parts of
+the ocean.
+
+Salt and bitter lakes of terrestrial origin are abundantly scattered
+over inland areas of drainage in the heart of continents, as in Utah
+and adjacent territories of North America, and on the great plateau
+of Central Asia. These sheets of water were doubtless fresh at first,
+but they have progressively increased in salinity, because, though
+the water is evaporated, there is no escape for its dissolved salts,
+which consequently remain in the increasing concentrated liquid. In
+Ladâkh, extensive lakes formed by the ponding back of valley waters
+by alluvial fans have grown saline and bitter, and have become the
+site of deposits of rock-salt and soda.
+
+The Great Salt Lake of Utah, which has now been so carefully studied
+by Gilbert and other geologists, may be taken as a typical example
+of an inland basin, formed by unequal subterranean movement that
+has intercepted the drainage of a large area, wherein rainfall
+and evaporation on the whole balance each other, and where the
+water becomes increasingly salt from evaporation, but is liable to
+fluctuations in level, according to oscillations of meteorological
+conditions. The present lake occupies an area of rather more than
+2,000 square miles, its surface being at a height of 4,250 feet above
+the sea. It is, however, merely the shrunk remnant of a once far more
+extensive sheet of water, to which the name of Lake Bonneville has
+been given by Gilbert. It is partly surrounded with mountains, along
+the sides of which well-defined lines of terrace mark former levels
+of the water. The highest of these terraces lies about 940 feet
+above the present surface of the lake, so that when at its greatest
+dimensions this vast sheet of water must have stood at a level of
+about 5,200 feet above the sea, and covered an area of 300 miles from
+north to south, and 180 miles in extreme width from east to west.
+It was then certainly fresh, for, having an outlet to the north, it
+drained into the Pacific Ocean, and in its stratified deposits an
+abundant lacustrine molluscan fauna has been found. According to
+Gilbert there are proofs that, previous to the great extension of
+Lake Bonneville, there was a dry period, during which considerable
+accumulations of subaerial detritus were formed along the slopes of
+the mountains. A great meteorological change then took place, and the
+whole vast basin, not only that termed Lake Bonneville, but a second
+large basin, Lake Lahontan of King, lying to the west and hardly
+inferior in area, was gradually filled with fresh water. Again,
+another meteorological revolution supervened and the climate once
+more became dry. The waters shrank back, and in so doing, when they
+had sunk below the level of their outlet, began to grow increasingly
+saline. The decrease of the water and the increase of salinity
+were in direct relation to each other until the present degree of
+concentration has been reached. The Great Salt Lake, at present
+having an extreme depth of less than 50 feet, is still subject to
+oscillations of level. When surveyed by the Stansbury Expedition
+in 1849, its level was 11 feet lower than in 1877, when the Survey
+of the 40th Parallel examined the ground. From 1866, however, a
+slow subsidence of the lake has been in progress, consequent upon a
+diminution of the rainfall. Large tracts of flat land, formerly under
+water, are being laid bare. As the water recedes from them and they
+are exposed to the remarkably dry atmosphere of these regions, they
+soon become crusted with a white saliferous and alkaline deposition,
+which likewise permeates the dried mud underneath. So strongly
+saline are the waters of the lake, and so rapid the evaporation,
+as I found on trial, that one floats in spite of one’s self, and
+the under surfaces of the wooden steps leading into the water at
+the bathing-places are hung with short stalactites of salt from the
+evaporation of the drip of the emergent bathers.
+
+Some of the smaller lakes in the great arid basin of North America
+are intensely bitter, and contain large quantities of carbonate
+and sulphate as well as chloride of sodium. The Big Soda Lake near
+Ragtown in Nevada contains 129.015 grammes of salts in the litre of
+water. These salts consist largely of chloride of sodium (55.42 per
+cent of the whole), sulphate of soda (14.86 per cent), carbonate of
+soda (12.96 per cent), and chloride of potassium (3.73 per cent).
+Soda is obtained from this lake for commercial purposes.
+
+Salt lakes of oceanic origin are comparatively few in number. In
+their case, portions of the sea have been isolated by movements of
+the earth’s crust, and these detached areas, exposed to evaporation,
+which is only partially compensated by inflowing rivers, have shrunk
+in level, and at the same time have sometimes grown much salter than
+the parent ocean.
+
+The Caspian Sea, 180,000 square miles in extent, and with a maximum
+depth of from 2,000 to 3,000 feet, is a magnificent example. The
+shells living in its waters are chiefly the same as those of the
+Black Sea. Banks of them may be traced between the two seas, with
+salt lakes, marshes, and other evidences to prove that the Caspian
+was once joined to the Black Sea, and had thus communication with
+the main ocean. In this case, also, there are proofs of considerable
+changes of water-level. At present the surface of the Caspian is 85½
+feet below that of the Black Sea. The Sea of Aral, also sensibly salt
+to the taste, was once probably united with the Caspian, but now
+rests at a level of 242.7 feet above that sheet of water. The steppes
+of southeastern Russia are a vast depression with numerous salt lakes
+and abundant saline and alkaline deposits. It has been supposed that
+this depression continued far to the north, and that a great firth,
+running up between Europe and Asia, stretched completely across what
+are now the steppes and plains of the Tundras, till it merged into
+the Arctic Sea. Seals of a species (_Phoca caspica_) which may be
+only a variety of the common northern form (_Ph. fætida_) abound in
+the Caspian, which is the scene of one of the chief seal-fisheries of
+the world.[2] On the west side of the Ural chain, even at present, by
+means of canals connecting the rivers Volga and Dwina, vessels can
+pass from the Caspian into the White Sea.[3]
+
+The cause of the isolation of the Caspian and the other saline
+basins of that region is to be sought in underground movements
+which, according to Helmersen, are still in progress, but partly,
+and, in the case of the smaller basins, probably chiefly in a
+general diminution of the water supply all over Central Asia and the
+neighboring regions. The rivers that flow from the north toward Lake
+Balkash, and that once doubtless emptied into it, now lose themselves
+in the wastes and are evaporated before reaching that sheet of water,
+which is fed only from the mountains to the south. The channels of
+the Amur Darya, Syr Darya, and other streams bear witness also to the
+same general desiccation. At present, the amount of water supplied
+by rivers to the Caspian Sea appears on the whole to balance that
+removed by evaporation, though there are slight yearly or seasonal
+fluctuations. In the Aral basin, however, there can be no doubt that
+the waters are progressively diminishing.
+
+Owing to the enormous volume of fresh water poured into it by its
+rivers, the Caspian Sea is not as a whole so salt as the main
+ocean, and still less so than the Mediterranean Sea. Nevertheless
+the inevitable result of evaporation is there manifested. Along the
+shallow pools which border this sea, a constant deposition of salt
+is taking place, forming sometimes a pan or layer of rose-colored
+crystals on the bottom, or gradually getting dry and covered with
+drift-sand. This concentration of the water is particularly marked
+in the great offshoot called the Karaboghaz, which is connected with
+the middle basin of the Caspian Sea by a channel 150 yards wide and
+5 feet deep. Through this narrow mouth there flows from the main sea
+a constant current, which Von Baer estimated to carry daily into
+the Karaboghaz 350,000 tons of salt. An appreciable increase of the
+saltness of that gulf has been noticed; seals, which once frequented
+it, have forsaken its barren shores. Layers of salt are gathering on
+the mud at the bottom, where they have formed a salt bed of unknown
+extent, and the sounding-line, when scarcely out of the water, is
+covered with saline crystals.
+
+The study of the precipitations which take place on the floors of
+modern salt lakes is important in throwing light upon the history
+of a number of chemically formed rocks. The salts in these waters
+accumulate until their point of saturation is reached, or until
+by chemical reactions they are thrown down. The least soluble are
+naturally the first to appear, the water becoming progressively
+more and more saline till it reaches a condition like that of the
+mother-liquor of a salt work. Gypsum begins to be thrown down from
+sea-water, when 37 per cent of water has been evaporated, but 93
+per cent of water must be driven off before chloride of sodium can
+begin to be deposited. Hence the concentration and evaporation of
+the water of a salt lake having a composition like that of the sea
+would give rise first to a layer or sole of gypsum, followed by one
+of rock-salt. This has been found to be the normal order among the
+various saliferous formations in the earth’s crust. But gypsum may be
+precipitated without rock-salt, either because the water was diluted
+before the point of saturation for rock-salt was reached, or because
+the salt, if deposited, has been subsequently dissolved and removed.
+In every case where an alternation of layers of gypsum and rock-salt
+occurs, there must have been repeated renewals of the water-supply,
+each gypsum zone marking the commencement of a new series of
+precipitates.
+
+But from what has now been adduced it is obvious that the composition
+of many existing saline lakes is strikingly unlike that of the sea
+in the proportions of the different constituents. Some of them
+contain carbonate of sodium; in others the chloride of magnesium
+is enormously in excess of the less soluble chloride of sodium.
+These variations modify the effects of evaporation of additional
+supplies of water now poured into the lakes. The presence of the
+sodium-carbonate causes the decomposition of lime salts, with the
+consequent precipitation of calcium-carbonate accompanied with a
+slight admixture of magnesium-carbonate, while by further addition of
+the sodium-carbonate a hydrated magnesium-carbonate may be eventually
+precipitated. Hunt has shown that solutions of bicarbonate of lime
+decompose sulphate of magnesia with the consequent precipitation of
+gypsum, and eventually also of hydrated carbonate of magnesia, which,
+mingling with carbonate of lime, may give rise to dolomite. By such
+processes the marls or clays deposited on the floors of inland seas
+and salt lakes may conceivably be impregnated and interstratified
+with gypseous and dolomitic matter, though in the Trias and other
+ancient formations which have been formed in inclosed saline waters,
+the magnesium-chloride has probably been the chief agent in the
+production of dolomite.
+
+The Dead Sea, Elton Lake, and other very salt waters of the
+Aralo-Caspian depression, are interesting examples of salt lakes
+far advanced in the process of concentration. The great excess of
+the magnesium-chloride shows, as Bischof pointed out, that the
+waters of these basins are a kind of mother-liquor, from which most
+of the sodium-chloride has already been deposited. The greater the
+proportion of the magnesium-chloride, the less sodium-chloride can
+be held in solution. Hence, as soon as the waters of the Jordan and
+other streams enter the Dead Sea, their proportion of sodium-chloride
+(which in the Jordan water amounts to from .0525 to .0603 per cent)
+is at once precipitated. With it gypsum in crystals goes down,
+also the carbonate of lime which, though present in the tributary
+streams, is not found in the waters of the Dead Sea. In spring, the
+rains bring large quantities of muddy water into this sea. Owing
+to dilution and diminished evaporation, a check must be given to
+the deposition of common salt, and a layer of mud is formed over
+the bottom. As the summer advances and the supply of water and mud
+decreases, while evaporation increases, the deposition of salt
+and gypsum begins anew. As the level of the Dead Sea is liable to
+variations, parts of the bottom are from time to time exposed, and
+show a surface of bluish-gray clay or marl full of crystals of common
+salt and gypsum. Beds of similar saliferous and gypsiferous clays,
+with bands of gypsum, rise along the slopes for some height above
+the present surface of the water, and mark the deposits left when
+the Dead Sea covered a larger area than it now does. Save occasional
+impressions of drifted terrestrial plants, these strata contain no
+organic remains. Interesting details regarding saliferous deposits of
+recent origin, on the site of the Bitter Lakes, were obtained during
+the construction of the Suez Canal. Beds of salt, interleaved with
+laminæ of clay and gypsum-crystals, were found to form a deposit
+upward of 30 feet thick extending along 21 miles in length by about
+8 miles in breadth. No fewer than 42 layers of salt, from 3 to 18
+centimetres thick, could be counted in a depth of 2.46 metres. A
+deposit of earthy gypsum and clay was ascertained to have a thickness
+of 367 feet (112 metres), and another bed of nearly pure crumbling
+gypsum to be about 230 feet (70 metres) deep.
+
+The desiccated floors of the great saline lakes of Utah and Nevada
+have revealed some interesting facts in the history of saliferous
+deposits. The ancient terraces marking former levels of these lakes
+are cemented by tufa, which appears to have been abundantly formed
+along the shores where the brooks, on mingling with the lake,
+immediately parted with their lime. Even at present, oolitic grains
+of carbonate of lime are to be found in course of formation along
+the margin of Great Salt Lake, though carbonate of lime has not been
+detected in the water of the lake, being at once precipitated in the
+saline solution. The site of the ancient salt lake which has been
+termed Lake Lahontan displays areas several square miles in extent
+covered with deposits of calcareous tufa, 20 to 60 and even 150
+feet thick. This tufa, however, presents a remarkable peculiarity.
+It is sometimes almost wholly composed of what have been determined
+to be calcareous pseudo-morphs after gaylussite (a mineral composed
+of carbonates of calcium and sodium with water)--the sodium of the
+mineral having been replaced by calcium. When this variety of tufa,
+distinguished by the name of _thïnolite_, was originally formed, the
+waters of the vast lake must have been bitter, like those of the
+little soda-lakes which now lie on its site--a dense solution in
+which carbonate of soda predominated. On the margin of one of the
+present Soda Lakes, crystals of gaylussite now form in the drier
+season of the year. Yet no trace of carbonate of lime has been
+detected in the water. The carbonate of lime in the crystals must
+be derived from water which on entering the saline lakes is at once
+deprived of its lime.
+
+
+
+
+  UNDERGROUND WATER: SPRINGS, CAVES, RIVERS, AND LAKES
+  --ÉLISÉE RECLUS
+
+
+If all soils were absolutely impervious, there would be no springs,
+and the whole of the liquid mass furnished by rain and snow would
+flow away over the surface of the ground like the torrents and
+flood-waters of the mountains. The greater part, however, of the
+water which falls upon the ground sinks in the first place into the
+depths of the earth. There it becomes more or less perfectly purified
+from the foreign bodies with which it was charged, gradually rising
+to the temperature of the strata through which it passes, and
+becoming impregnated with the soluble salts which it meets with.
+Ultimately, when the water, in sinking down, encounters impervious
+beds, it can penetrate no further, and, flowing laterally to the
+outcrop of the beds, makes its escape in the form of springs.
+
+The absorption of the rain and melted snow takes place in various
+ways, according to the nature of the soil. Ordinary vegetable
+earth only allows the water to penetrate to a very slight depth,
+especially when the rain falls in showers and the slope of the
+ground is favorable for drainage. As mould is capable of absorbing
+a very large quantity--indeed, more than half its own weight, it
+prevents the strata beneath from receiving its due share of moisture,
+retaining almost the whole of it for the use of the vegetation which
+it nourishes. In fact, it requires an altogether exceptional rainfall
+to saturate any ordinary arable soil to the extent of a yard below
+the surface. Water passes with much more facility through sandy
+and gravelly beds; but compact loams and clay will not allow it to
+penetrate through them, retaining it in the form of pools or ponds on
+the surface of the ground.
+
+The action of vegetation is not confined merely to imbibing the water
+falling from the clouds; it often, also, assists the superabundant
+moisture in penetrating the interior of the ground. Trees, after
+they have received the water upon their foliage, let it trickle down
+drop by drop on the gradually softened earth, and thus facilitate
+the gentle permeation of the moisture into the substratum; another
+part of the rain-water, running down the trunk and along the roots,
+at once finds its way to lower strata. On mountain slopes, the
+mosses and the freshly growing carpet of Alpine plants swell like
+sponges when they are watered with rain or melted snow, and retain
+the moisture in the interstices of their leaves and stalks until the
+vegetable mass is thoroughly saturated and the liquid surplus flows
+away. Peat-mosses especially absorb a very considerable quantity of
+water, and form great feeding reservoirs for the springs which gush
+out at a lower level. The immense fields of peat which cover hundreds
+and thousands of acres on the mountain slopes of Ireland and Scotland
+may, notwithstanding their elevation and inclined position, be
+considered as actual lacustrine basins containing millions of tons of
+water dispersed among their innumerable leaflets. The superabundant
+water of these tracts of peat-mosses issues forth in springs in the
+plains below.
+
+Rocks, like vegetable earth, also absorb water in greater or less
+quantities, according to their fissures and the density of their
+particles. If the soil is formed of volcanic scoriæ, or porous beds
+of pebbles, gravel, or sand, the water rapidly descends toward the
+underlying strata. Some of the harder rocks, especially certain kinds
+of granite, absorb but a very small quantity of water, on account of
+the small number of their clefts; others, on the contrary, as most
+of the calcareous masses, imbibe every drop of water which falls on
+their surface. There are some rocks which have their layers broken
+and cracked to such an extent that they resemble enormous walls of
+rubble-work; the rain instantly disappears on them as if it had
+fallen into a sieve. But the greater part of the calcareous rocks
+belonging to various geological periods are formed of thick and
+regular strata, cleft at intervals by long vertical crevices. Below
+the surface-beds, perhaps, are layers of soft marl, which the water
+penetrates with difficulty, although it can soften and carry away its
+particles. Here are formed, rill by rill, the subterranean rivulets
+which ultimately spread all over the substratum of marl, following
+the general slope of the bed. After a more or less considerable lapse
+of time, the stratum of marl ultimately becomes saturated, and the
+water then flows out through caverns which are variously modified by
+subsidences--faults in the strata and the perpetual action of the
+streams. The springs which proceed from calcareous rocks of this
+nature are in general the most abundant, owing to the length of their
+subterranean course. The water which falls on vast areas on the
+surface of plateaus is ultimately united in one bed. A liquid mass of
+this kind, which springs up suddenly into sight, just as if it merely
+issued from the soil, drains perhaps an extent of country of many
+hundreds or thousands of square miles.
+
+Thus, according to the nature of the rock on which the rain
+falls, the latter finds its way again to the surface, either at a
+considerable distance from the spot where it fell, or else springs
+out in little rivulets immediately below the place where its drops
+were first gathered. On a great many mountains we are surprised to
+meet with springs gushing out at a few yards from the summit. These
+jets have, indeed, often been considered as the evidence of some
+miraculous intervention. Among others, we may mention the “Sorcerers’
+Spring,” which gushes out on one of the highest points of the
+Brocken, the culminating peak in the Hartz Mountains.
+
+The springs which cause the most astonishment are those which for a
+time flow plentifully, and then all at once cease running, but, after
+an uncertain lapse of time, again make their appearance. One might
+almost fancy that some invisible hand alternately opened and shut the
+secret flood-gate which gave an outlet to the subterranean stream.
+The cause for this phenomenon of intermission is easily explained.
+When the water brought by the underground stream is collected in a
+capacious cavity in the rock, which communicates with the exterior
+surface through a siphon-shaped channel, the liquid mass gradually
+rises in the stone reservoir before it rushes out into the air. It is
+necessary that the reservoir should be filled up to the level of the
+siphon, in order that the latter should be primed, and that the water
+should flow out as a spring into the external basin. If the water in
+the reservoir is not replenished with sufficient rapidity, and is
+unable to keep at least on a level with the external outlet, the jet
+of water will immediately cease, and can not recommence until the
+upper part of the liquid mass has again risen up to the highest point
+of the siphon. After an indefinite period of repose, the spring then
+enters on a new phase of activity.
+
+There are many of these subterranean streams which, before they break
+forth in springs, do not flow over beds continuously sloping in the
+direction of their current, as in the case with the water-courses on
+the surface of the ground. There are some indeed which first descend
+into the bowels of the earth, either by a uniform declivity or by a
+series of cascades or rapids, and ultimately reascend from the depths
+toward the surface, or jet out vertically from the ground.
+
+In obedience to the law which compels liquids to seek the same
+level in all connected reservoirs, a rivulet of water will never
+fail to dart forth as a spring as soon as it finds an outlet below
+the caverns in which the water is collected from which it proceeds.
+Likewise, if the spot where the gushing out takes place is on a much
+lower level than that of the feeding reservoirs situated above, the
+liquid jet must necessarily shoot up in a column above the surface
+of the ground. This is the case at Châtagna, in the department of
+the Jura, where a natural _jet d’eau_ springs up to a height of
+10 or 12 feet. In the grotto of Male-Mort, near Saint-Etienne, in
+Dauphiné, the jet of water is not less than 23 to 26 feet in height.
+But the water of the fountains being always more or less charged with
+sediment, the deposit accumulates in the form of a circular hillock
+around the orifice, thus almost always ultimately raising it to the
+level of the top of the liquid column. As an instance of these rising
+fountains, we may mention the famous springs of Moses (_Aïn Musa_),
+which gush out in a charming oasis not far from the shores of the
+Gulf of Suez. These springs, the temperature of which varies from
+70° to 84° (Fahr.), now flow from the top of several small cones of
+sandy and slimy débris which they have gradually thrown up above the
+level of the plain. They are also shaded by olive and tamarind trees.
+
+In the innumerable multitude of springs, either cold or thermal,
+which rise from the earth, we may observe the whole range of possible
+temperatures from freezing-point up to the boiling-point. A spring
+which flows from the side of the Hangerer, in the Oetzthal, at a
+height of 6,742 feet, is only 1° warmer than ice. On the Alps, the
+Pyrenees, and all the other chains of snow-clad mountains, near
+the summits small rills of water are very frequently met with,
+the temperature of which is scarcely higher than that of melting
+snow. Even at the bases of mountains, and especially those of a
+calcareous nature, a great number of springs are found which are
+much colder than the surrounding soil. This is so because, in
+addition to the water, the air also enters the subterranean channels
+and circulates in all the network of clefts and crevices, and, by
+incessantly gliding over the wet sides of the channels, produces a
+rapid evaporation of moisture, and, in consequence, refrigerates the
+surface of the rocks and even the stream itself. The temperature,
+therefore, of springs which proceed from the interior of cavernous
+mountains is always several degrees lower than the normal temperature
+of the soil.
+
+Springs which have a higher temperature than the soil are called
+_thermal_ springs.
+
+It is to be remarked that nearly all thermal springs which do not owe
+their high temperature to the vicinity of volcanoes issue forth from
+faults which open on the surface of masses of a crystalline nature,
+and principally at the side of modern eruptive rocks which have been
+thrust up through older strata.
+
+The influence of rains and seasons has much less effect upon thermal
+waters than upon cold springs which proceed from the upper layers
+of the soil. A great number of warm springs, however, undergo
+certain changes in their yield of water, which must be without
+doubt attributable, at least partially, to the same causes as the
+variations in the discharges of superficial streams. In Auvergne,
+in the Pyrenees, and in Switzerland, several springs, perfectly
+protected against any infiltration of rain-water, flow in much
+greater abundance at the very same period when the adjacent torrents
+become swollen. At Brig-Baden, in the Valais, the water, the mean
+temperature of which is in autumn and winter from 71° to 72° (Fahr.),
+rises to 113° and 122° (Fahr.) when the breath of spring melts the
+ice on the Jungfrau.
+
+Most thermal springs contain mineral substances in solution;
+there are, however, a certain number which are almost as pure
+as rain-water--such as, for instance, the celebrated waters of
+Plombières, also that of Gastein, Pfeffers, Wildbad, and Badenweiler.
+The springs of Chaudes-Aigues--those in France which have the highest
+temperature, 158° to 176° (Fahr.)--contain only a small amount of
+mineral substances. The inhabitants of Chaudes-Aigues use the water
+to prepare their food, to wash their linen, and to warm their houses.
+Wooden conduits, erected in all the streets of the town, supply, on
+the ground floor of each house, a reservoir which serves to heat it
+during cold weather, and thus dispenses with fires and chimneys.
+
+Among the various substances which spring-water brings to the
+surface, those which are most common proceed from the strata
+which serve to constitute the very framework of the globe. Chalk,
+especially, occurs in different proportions in most springs, either
+under the form of sulphate of lime, or, more often, as carbonate of
+lime. Water which contains carbonic acid in solution is charged with
+calcareous matter dissolved away from the sides of the rocks through
+which it passes; then, by means of evaporation, it redeposits the
+stony substances which it previously held in solution. Hence arise
+all those calcareous concretions which form around so many springs;
+also the stalactites in caverns.
+
+[Illustration: The Giant’s Causeway, Antrim, Ireland]
+
+Nearly all countries of the world possess some of these curious
+springs, which cover with a calcareous crust any object placed
+in their waters. Among these incrusting springs, those of Saint
+Allyre, near Clermont, Rivoli, and San Filippo, not far from Rome,
+have justly become celebrated. These latter have, in a space of
+twenty years, filled up a pond with a bed of travertin 30 feet
+thick, and, in the neighborhood, entire strata of this same rock
+may be seen having a depth of more than 328 feet. The springs of
+Hammam-Mes-Khoutine, in the province of Constantine, are also
+very remarkable on account of the considerable amount of their
+deposits. This water, which rises at a temperature of 203° (Fahr.),
+and from which a high column of steam always rises, is frequently
+compelled to change its point of issue on account of the dense beds
+of travertin which are gradually deposited upon the soil. Most of
+these deposits are of a dazzling white hue, striped here and there
+with bright colors, and are developed in mammillated strata; other
+concretions, accumulating gradually round an orifice, have taken
+the form of cones, and are like small craters near a volcano, some
+of them rising to a height of as much as 33 feet; lastly, there are
+masses of travertin which stretch out in a kind of wall below the
+flow which deposits them. One of these walls, which is interrupted at
+intervals by heaps of earth upon which large trees grow, is not less
+than 4,921 feet long, 66 feet high, and, on an average, from 33 to 49
+feet wide.
+
+The thermal waters of Algeria are, however, surpassed in grandeur and
+beauty by the springs of the ancient Ionian city of Hierapolis (holy
+city), which at the present time flow in the solitary plateau called
+Panbouk-Kelessi (Castle of Cotton), on account of the cotton-like
+aspect of the white masses of travertin of which it is composed. On
+reaching this spot from Smyrna, something like an immense cataract
+may be seen in the distance, 328 feet high and 2½ miles wide; this
+is formed by the walls which the water has gradually constructed,
+column after column, and layer after layer, by flowing over the
+edges of the plateau and gushing out on the slopes. Here and there,
+real cascades glitter in the sun, and their sparkling surfaces
+light up the dead whiteness of the crystal walls. As a spectator
+ascends the declivities, the masses deposited and carved out by the
+water appear in all their strange beauty; one might fancy that they
+were colonnades, groups of figures, and rude bas-reliefs which the
+chisel had not yet perfectly set free from their rough coverings of
+stone. And all these calcareous deposits which have been fashioned
+by the cascades during a succession of ages open a multitude of
+cup-like hollows with fluted edges fringed with stalactites; these
+graceful reservoirs--some of which are shaded with yellow or veined
+with red, brown, and violet, like jasper or agate--are filled with
+pure water. Higher still follow two steps of the plateau on which
+stood the ancient thermal edifice and the Necropolis of Hierapolis.
+There whitish masses cover the ancient tombstones and fill up the
+conduits. The ground is crossed in various directions by the former
+beds of rivulets, which have gradually stopped up their own courses
+by depositing concretions upon them. Above one of the widest of
+these dried-up channels, the magnificent span of a natural bridge
+displays its graceful form, like an arch of alabaster, streaming with
+innumerable stalactites. At what date did this majestic structure
+take its rise, and how many years and centuries did the process of
+its formation last? No one knows. According to Strabo, the channels
+of the baths of Hierapolis were soon filled up by solid masses, and
+if Vitruvius can be believed, when the proprietors of the environs
+wished to inclose their domain, they caused a current of water to run
+along the boundary-line, and in the space of a year the walls had
+risen.
+
+Silica, which is still more important than chalk in the formation
+of terrestrial rocks, is also sometimes deposited on the edge of
+springs, but in very small quantities.
+
+The various dislocations of the terrestrial strata, the cooling of
+the waters, and, perhaps, in many instances, the obstruction of
+channels by deposits of ore, explain why, in the present period,
+so small a number of thermal springs issue from metalliferous
+beds. Nevertheless, many localities might be mentioned where these
+phenomena take place at the present time. A spring at Badenweiler,
+in the Black Forest, issues forth at a few yards from a vein of
+sulphuret of lead. In the granitic plateau of central France other
+springs are likewise found to be associated with this metal. Various
+thermal waters in the Black Forest, like those of Carlsbad and
+Marienbad, are in close connection with veins of iron and manganese.
+Oligiste iron is found in the fissures of the springs of Plombières
+and Chaude-Fontaine. In Tuscany sulphureous fumaroles proceed from
+the veins of antimony. In France and Algeria the waters of Sylvanès
+and Hammam R’ira issue forth from beds of copper. Lastly, near
+Freyberg, a voluminous thermal spring has been discovered in a vein
+of silver.
+
+Among the mineral substances which some springs bring to the surface
+of the soil, the most important, in an economical point of view, is
+common salt. This substance, being one of those which dissolve most
+readily in water, all the liquid veins which pass over saline beds
+become saturated with salt; therefore springs of this kind, which
+flow in great abundance, give rise to salt-works of more or less
+importance. The masses of common salt which make their way every
+year from the interior of the earth may be estimated at thousands
+of tons. The springs of Halle, which rise on the northern slope of
+the Alps of Salzburg (Salt Town), and are managed with the greatest
+care, annually produce 15,000 tons of this mineral. The salt springs
+of Halle, in Prussia, which have been worked from time immemorial by
+a company, furnish 10,000 tons of salt every year. Other parts of
+Germany also yield for consumption thousands of tons of white salt,
+which is produced by the evaporation of saline springs. The mass
+of salt furnished by the single artesian well of Neusalzwerk, near
+Minden, in Prussia, represents every year a cube measuring 78 feet on
+each side.
+
+Though not so rich as Germany in saline springs thus turned to
+account, most of the civilized countries of the world possess
+salt-works which are also very important. France enjoys the springs
+of Dieuze, Salins, and Salies; Switzerland, those of Bex; Italy has
+the springs in the environs of Modena, and many others besides. In
+England, near Chester, there are some mines of rock-salt in which
+numerous liquid veins issue forth which are impregnated with salt.
+Lastly, the United States have the celebrated springs of Syracuse.
+
+Not far from the “spot where Troy once stood” is the valley of
+Touzla-sou, which owes its name (Salt Water) to its numerous salt
+springs. The mountains which rise around its circumference are
+variously shaded with blue, red, and yellow, and the rocks are
+incessantly decomposing under the action of the liquid salt which
+oozes out from and trickles down their sides. The plain itself
+is covered with a variegated crust, while jets of boiling water,
+saturated with salt, burst forth in every direction. Here and there
+pools are found, the moisture of which, by evaporating in the sun,
+leaves upon the soil beds of salt as white as snow. Near the mouth
+of the valley springs become more and more numerous. Lastly, in
+the place where the cliffs approach near together, so as to form a
+defile, a magnificent spout of water jets out from one side of the
+rock. This jet is not less than a foot in diameter at the orifice,
+and falls again after having described a parabola of more than a
+yard and a half. Other springs shoot out on both sides, the constant
+temperature of which is more than 212° (Fahr.); these, together with
+the principal jet, form a rivulet of boiling and steaming water.
+
+Springs of salt water are used for the treatment of diseases as
+well as for the extraction of salt. They constitute one of the most
+important groups of medicinal waters, according to the various
+substances which they contain in solution. The other springs made
+use of, on account of their healing virtues, have been classed under
+ferruginous, sulphureous, and acidulous springs. These waters also
+contain, in different proportions, a variable quantity of gases and
+salts which they have dissolved in their passage over subterranean
+beds of every kind.
+
+Mineral springs are most numerous and abundant in mountain valleys,
+and there, consequently, the great thermal institutions are
+established. In Europe the chain of the Pyrenees is probably the
+richest in mineral, sulphureous, saline, ferruginous, and acidulous
+springs. According to Francis, the engineer, in 1860 more than 550
+mineral springs, 187 of which are used, flowed upon the French
+slopes of the Pyrenees. These waters supplied 83 hot baths in 53
+localities, the principal of which are Bagnères de Bigorre, Luchon,
+Eaux-Bonnes, and Cauterets. The most abundant springs, those of Graus
+d’Olette, form a sort of mineral stream, yielding more than four
+gallons a second, or 2,322 cubic yards a day. In Algeria the spring
+of Hammam-Mes Khoutine yields 6 gallons a second.
+
+There are regions, some volcanic and some not, in which nearly all
+the springs are thermal and mineral; springs of pure and fresh
+water being so rare, they are there considered to be most precious
+treasures. One of these regions comprehends a large part of the
+plateau of Utah. In this place numerous thermal springs issue forth,
+to which have been given the vulgar names of the Beer, Steamboat,
+Whistle Springs, etc., and into one of which the Mormons plunge their
+neophytes. The springs which are not thermal are loaded with saline
+and calcareous matter. It is only in spring, at the time when the
+snow melts, that the springs, which then become very abundant, yield
+comparatively pure water. During the dry season, salt and carbonate
+of lime become concentrated in the nearly exhausted springs, and give
+to the liquid flow an unpalatable taste. Palgrave, the traveler,
+informs us that all the springs of the country of Hasa, in Arabia,
+are also thermal.
+
+It can readily be understood that when all these substances escape
+from the interior of the rocks, together with the water which holds
+them in solution, they must leave empty spaces in the earth. During
+the course of long centuries whole strata are dissolved, and, under
+a form more or less chemically modified, are brought up from the
+depths and distributed on the surface of the soil. The thermal waters
+of Bath, which are far from being remarkable for the proportion of
+mineral substances they contain, bring to the surface of the earth
+an annual amount of sulphates of lime and soda, and chlorides of
+sodium and magnesium, the cubic mass of which is not less than 554
+cubic yards. It has also been calculated that one of the springs of
+Louèche, that of Saint Laurent, brings every year to the surface
+8,822,400 pounds of gypsum, or about 2,122 cubic yards; this quantity
+is enough to lower a bed of gypsum a square mile in extent, more than
+five feet in one century. But this is only one spring, and we have
+reckoned one century only; if we think of the thousands of mineral
+springs which gush from the soil, and of the immensity of time during
+which their waters have flowed, some idea may be formed of the
+importance of the alterations caused by springs. In time they lower
+the whole mass of mountains, and, no doubt, after these sinkings,
+violent oscillations of the earth may often have taken place.
+
+In regions where the strata are pierced with wide and deep caverns,
+and especially in calcareous countries, the waters sometimes
+accumulate in sufficient quantities to form perfect streams with
+long subterranean courses. At their issue from the caverns, these
+waters form a contrast with the rocks and hills around, all the more
+striking because the latter are completely devoid of moisture, and
+fearfully sterile, while on the brink of the limpid stream the fresh
+verdure of plants and trees is at once developed. Like a captive,
+joyous at seeing the light once more, the water which shoots forth
+from the sombre grotto of rocks sparkles in the sun, and careers
+along with a light murmur between its flowery banks.
+
+Among these subterranean streams, the most celebrated, and doubtless
+one of the most beautiful, is the Sorgues of Vaucluse. The vaulted
+grotto from which the mighty mass of water escapes opens at the mouth
+of an amphitheatre of calcareous rocks with perpendicular sides.
+Above the spring rises a high white cliff, bearing on its summit
+a ruined tower of the Middle Ages; the rock is everywhere sterile
+and bare; there is nothing but a miserable fig-tree, clinging to
+the stone like a parasitical plant to the bark of a tree, which has
+plunged its roots into the fissure of the cave, and greedily absorbs
+with its leaves the moisture which floats like a mist above the
+cascades of the spring. After heavy rains, the liquid mass, which is
+then estimated at 26 or even 32 cubic yards a second, flows in a wide
+sheet high above the entrance to the cavern, which is then altogether
+inaccessible. When the waters are low, they flow bubbling across the
+barrier of rocky débris which obstructs the entrance; at that time
+it is quite possible to penetrate under the arch, and to contemplate
+the vast basin in which the blue waters of the subterranean stream
+spread out before they leap into the open air. Soon after its issue
+from the cave and amphitheatre of Vaucluse, the Sorgues is divided
+into numerous irrigation channels, which spread fertility in the
+country over an area of more than 77 square miles. The subterranean
+course of the affluents which form the stream is not ascertained; but
+it is known that most of them commence 12 or 15 miles to the east,
+in the plateaus of Saint Christol and Lagarde, which are pierced all
+over with _avens_ or chasms, into which the rain-water sinks and
+disappears.
+
+In another part of France there is a second important subterranean
+stream, which is much less known but no less remarkable than that of
+Vaucluse; this is the Touvre of Angoulême, continuing the course of
+the Bandiat, the waters of which, like those of the Tardoire, are
+swallowed up in several abysses at distances varying from 3 to 7
+miles to the east and northeast. The three principal springs of the
+Touvre flow slowly out of a deep cave, hollowed out at the base of
+an escarped cliff; another spring bubbles up in a basin of rock; the
+third emerges from a sort of boggy meadow intersected by drains. At
+the outlet of their subterranean courses these three enormous springs
+immediately form three streams, which reunite, leaving between them
+two long peninsulas of reeds and other aquatic plants. Below the
+junction, the Touvre, which is here more than 100 yards wide, passes
+round a rugged hill, and, dividing into several branches, turns
+the numerous mill-wheels of the important gun-foundry of Ruelle;
+then, after a course of five miles, it flows into the Charente at a
+small distance above Angoulême. Among the hundreds and thousands of
+travelers whom steam annually conveys over the bridge of the Touvre,
+there are few who are aware of the curious nature of the source of
+the river of limpid water over which the train passes in its noisy
+career.
+
+Omitting to mention the streams which accidentally pass under the
+strata of rocks during a small part of their course, or of the
+subterranean outlets of certain lakes, a multitude of other instances
+might be brought forward of masses of water, more or less abundant,
+which appear above ground after having traversed a considerable
+distance under the earth. Of this kind is the graceful spring of
+Nîmes, the blue transparent water of which, reflecting the foliage
+of pines and chestnut trees, glides in its gentle ripples over the
+semicircular steps of an old Roman staircase. Of this kind, too, is
+the spring of Vénéran, near Saintes: this spring, which was formerly
+sacred to the Goddess of Love, gushes from the ground in a gorge of
+rocks, and, passing through a mill, the wheel of which it turns, it
+suddenly disappears, being swallowed up in an abyss; thus it appears
+on the earth to work but for an instant.
+
+Numbers of water-courses do not reappear on the surface of the soil
+after being swallowed up in the earth, but flow straight to the sea
+by means of subterranean channels. On nearly the whole extent of the
+continental shores, and principally in localities where the coasts
+are of a calcareous nature, the outlets of submarine tributaries may
+be noticed, some of which are perfect rivers. Most of the springs of
+the department of Bouches du Rhone jet up from the bottom of the sea,
+but at various distances from the shore. One of them, that of Porte
+Miou, near Cassis, forms on the surface of the sea a considerable
+current, which drifts any floating bodies to a great distance.
+At Saint Nazaire, Ciotat, Cannes, San Remo, and Spezzia, other
+streams also issue from the midst of the salt waves, and attempts
+have even been made to measure approximately their discharge. M.
+Villeneuve-Flayosc estimates at 24 cubic yards a second the quantity
+of water discharged into the sea by all the hidden affluents of the
+Mediterranean between Nice and Genoa. Some of the submarine springs
+of Provence and Liguria proceed from enormous depths. The orifice of
+the spring of Cannes is 531 feet below the level of the sea; that of
+San Remo rises from a depth of 954 feet; lastly, at four miles to
+the south of Cape Saint Martin, between Monaco and Mentone, another
+stream of fresh water empties itself under a bed of salt water, near
+2,296 feet deep.
+
+The coasts of Algeria, Istria, Dalmatia, and the Herzegovina also
+present numerous instances of submarine streams; on the eastern
+shores of the Adriatic the traveler may even have the pleasure of
+contemplating the delta of a considerable river, the Trebintchitza,
+visible through the sea-water at the depth of a yard. The abundant
+springs of fresh water which pour out into the open sea to the
+southwest of the Cuban port of Batabano are well known, since
+Humboldt described them, and it is observed that the lamantins,
+or sea-cows, which dread salt water, delight in frequenting these
+parts. Lastly, the Red Sea, which does not throughout its immense
+circumference receive a single permanent stream flowing on the
+surface of the ground, nevertheless receives some which spring
+from the bottom of its bed. The shores of the United States, the
+calcareous soil of which is probably pierced with caverns from the
+very centre of the continent, perhaps are the coasts which pour into
+the sea the most abundant subterranean rivers. Near the mouth of the
+stream of St. John, a submarine stream of perfectly pure water spouts
+in bubbles as far as one to two yards above the level of the sea.
+Off the Carolinas, and Florida, salt water has been known to change
+into brackish water under the influence of the sudden increase of its
+subterranean affluents. In the month of January, 1857, all that part
+of the sea which is adjacent to the southern point of Florida was
+the scene of an immense eruption of fresh water. Muddy and yellowish
+water furrowed the straits, and myriads of dead fish floated on the
+surface and accumulated on the shores. Even in the open sea the
+saltness diminished by one-half, and in some places the fishermen
+drew their drinking-water from the surface of the sea as if from
+a well. It is affirmed by all those who witnessed this remarkable
+inundation of the subterranean river that, during more than a month,
+it discharged at least as much water as the Mississippi itself, and
+spread over all the strait, 31 miles wide, which separates Key West
+from Florida.
+
+On the coasts of Yucatan, the fresh waters which take a subterranean
+course down to the sea do not appear to flow like rivers which have a
+narrow bed and attain considerable speed, but more in the form of a
+wide sheet of liquid with a nearly imperceptible current. _Cenotes_
+open here and there over the surface of the country; they are a
+kind of natural draining-well or hole, not very deep, into which
+the inhabitants descend to draw spring water. At Merida and in the
+environs the subterranean water is found at a depth of 26 to 30 feet;
+but the nearer we approach to the sea the thinner the layer of rock
+becomes which covers the liquid veins; on the seashore fresh water
+is found nearly on a level with the soil. The height of the veins
+varies several inches, according to the quantity of rain; but in
+every season the mass of water descending from the plateau of Yucatan
+is poured into the sea through innumerable outlets. Over a great
+extent of the shore of the peninsula, these hidden springs furnish
+collectively a mass sufficiently large to counterpoise the waters of
+the sea. Under the pressure of the marine current which runs along
+the coast, there is formed, between the open sea and the liquid mass
+which has made its way from the land, a littoral bank like those
+barriers which the waves construct before the mouths of rivers. This
+embankment, which protects the coasts of Yucatan like a breakwater,
+is not less than 171 miles long, and is cut through by the sea at
+two or three points. The channel, which stretches like a wide river
+between the bank of alluvium and the Yucatan coast, is, not without
+reason, designated by the inhabitants by the name of stream or _rio_.
+
+Among the remarkable phenomena which perhaps owe their existence to
+subterranean water-courses, we must mention the sudden or gradual
+appearance of those hillocks of clay (“mud-lumps”) which rise, to
+the great danger of navigators, either in the middle of the bar of
+the Mississippi, or in the immediate vicinity. Like small volcanoes
+of mud, the “mud-lumps” generally appear under the form of isolated
+cones, allowing a rill of dirty water to escape from their summits.
+Some of them are irregular on their surface, on which lateral
+orifices here and there show themselves, some in full activity,
+others abandoned by the springs which formerly gushed from them. The
+water of some “mud-lumps” is loaded with oxide of iron or carbonate
+of lime, which, with the agglutinated sands, form hard masses, having
+the consistence of perfect rocks. These hillocks vary both in their
+height and shape. The greater part remain hidden at the bottom of the
+water, and even their summits do not reach the level of the river
+or sea; others hardly raise their heads above the waves; the most
+considerable, however, rise to a height of 6, 9, or even 19 feet, and
+their base covers an area of several acres. The sudden way in which
+most of these water-volcanoes make their appearance, the anchors of
+vessels, and the remains of cargoes which have been found on their
+surface, their conical form, their terminal craters, and all the
+springs, “which seem to spout out as if from a subterranean sieve,”
+indicate the existence of a subterranean force always at work to
+upheave this band of hillocks.
+
+M. Thomassy is of opinion that the hillocks of these bars are the
+orifices of regular artesian wells naturally formed by a sheet of
+subterranean water descending from the plateaus of the interior and
+flowing below the Mississippi and the clayey levels of Louisiana.
+However this may be, the mode in which these mud hillocks are formed
+is well enough known to render it easy to clear them away from the
+mouths of the Mississippi and to protect the interests of navigation.
+When a cone of clay makes its appearance on the bar, a charge of
+powder is introduced into it and explodes it. Thus, in the year 1858,
+the southwest passage was cleared of a “mud-lump” which formed a
+considerable island; a single charge was sufficient to annihilate
+the whole. The island suddenly sunk; in its place a wide depression
+was formed, the circumference of which resembled that of a volcanic
+crater; at the same time an enormous quantity of hydrogen gas was
+discharged into the atmosphere.
+
+Above the springs the course of subterranean rivulets is generally
+indicated by a series of chasms or natural wells, which disclose
+the stream beneath. The arches of caves not being always strong
+enough to support the weight of the superincumbent masses, they
+necessarily fall in some places, leaving above them other spaces
+into which the upper beds successively sink. The débris of the ruin
+is afterward cleared away by the water, or dissolved, atom by atom,
+by the carbonic acid contained in the stream, and gradually all the
+loose rubbish is carried away. In this manner, above the subterranean
+rivulets, a kind of well is formed, which is designated in various
+countries by very different names.
+
+By means of these natural gulfs it is possible to reach the
+subterranean streams, and to give some account of their system, which
+is exactly like that of rivulets and rivers flowing in the open air.
+These streams also have their cascades, their windings, and their
+islands; they also erode or cover with alluvium the rocks which
+compose their bed, and they are subject to all the fluctuations of
+high and low water. The only important difference which superficial
+waters and subterranean currents present in their phenomena is that
+these streams in some places fill the whole section of the cave, and
+are thus kept back by the upper sides, which compress the liquid
+mass. In fact, the spaces hollowed out by the waters in the interior
+of the earth are only in a few places formed into regular avenues,
+which might be compared to our railway tunnels. Where beds of hard
+stone oppose the flow of the rivulet, all it has done during the
+course of centuries has been to hew out one narrow aperture. This
+succession of widenings and contractions, similar to those of the
+valleys on the surface, forms a series of chambers, separated one
+from the other by partitions of rock. The water spreads widely in
+large cavities, then, contracting its stream, rushes through each
+defile as if through a sluice.
+
+On account of these partitions, it is very difficult, or even
+impossible, to navigate the course of subterranean rivers to any
+considerable distance, even at the time the water is low. When it
+is high, the liquid mass, detained by the partitions, rises to a
+very high level in the large interior cavities, and often reaches
+the roof above. Sometimes when, through the clefts of the rocks, a
+communication exists between the cave and some hollow above, the
+surplus water from the subterranean streams makes its appearance
+there. Thus the Recca, which flows beneath the adjacent plateau
+of Trieste, does not always find space enough to flow freely in
+its lower channels, and Schmidt has seen it ascend in the chasms
+of Trebich to a height of 341 feet. It may be understood that the
+pressure of such a column of water often shatters enormous pieces of
+rock, and thus modifies the course of underground streams.
+
+When the water, impelled by force of gravitation, seeks a new bed in
+the cavernous depths of the earth, and disappears from its former
+channels, these are at first much easier of access than they formerly
+were; but ere long, in most caves, a new agent intervenes, which
+seeks to contract or even completely obstruct them. This agent is
+the snow-water, or rain, which percolates, drop by drop, through
+the enormous filter of the upper strata. In passing through the
+calcareous mass, each one of these drops dissolves a certain quantity
+of carbonate of lime, which is afterward set free on the arch or
+the sides of the cave. When the drop of water falls, it leaves
+attached to the stone a small ring of a whitish substance; this is
+the commencement of a stalactite. Another drop trickles down, and,
+trembling on this ring, lengthens it slightly by adding to its edges
+a thin circular deposit of lime, and then falls. Thus drop succeeds
+drop in an infinite series, each depositing the particles of lime
+which it contains, and forming ultimately a number of frail tubes,
+round which the calcareous deposit slowly accumulates. But the water
+which drops from the stalactites has not yet lost all the lime which
+it held in solution; it still retains sufficient to enable it to
+elevate the stalagmites and all the mammillated concretions which
+roughen or cover the floor of the grotto. It is well known what
+fairy-like decorations some caverns owe to this continuous oozing
+through the vaults of their roofs. There are few sights in the world
+more astonishing than that of these subterranean galleries, with
+their dead-white columns, their innumerable pendants and multiform
+groups, like veiled statues, all yet unstained by the smoke of the
+visitor’s torch.
+
+When the action of the water is not disturbed, the needles and
+other deposits of the calcareous sediment continue to increase with
+considerable regularity. In some cases each new layer which is
+added to the concretions may be studied as a kind of time-measurer,
+indicating the date when the running water abandoned the cave. At
+length, however, the soft concentric layers disappear, and are
+replaced by forms of a more or less crystalline character; for
+in every case where solid particles exist, subject to constant
+conditions of imbibition by water, crystals are readily produced.
+Sooner or later, the stalactites, increasing gradually in a downward
+direction, meet and unite with the needles rising from the surface of
+the ground, and, forming by their number a kind of barrier, obstruct
+the narrower passages and close up the defiles separating the cavern
+into distinct chambers.
+
+One of these Kentucky caves, called the “Mammoth Cave,” is the
+largest which is at present known. The whole of its extent has
+not been as yet fully explored, for it may be almost called a
+subterranean world, having a system of lakes and rivers, and a
+network of galleries and passages without number, which cross and
+recross one another, going down to an immense depth. From the
+chief entrance to the further recesses of the cave, the distance
+is reckoned to be not less than 9¼ miles, and the whole length of
+the two hundred alleys that have been traced out in this enormous
+labyrinth is 217 miles in extent. This “Mammoth Cave” once served as
+a retreat for savage tribes, for skeletons of men of an unknown race
+have been found buried in it under layers of stalactite.
+
+The district which is the most remarkable among all the calcareous
+countries of Europe for its caves, its subterranean streams, and
+its abysses is unquestionably the region of the Carniolan and
+Istrian Alps, which extends to the east of the Adriatic, between
+Laibach and Fiume. The whole surface of the country, as in certain
+plateaus of the Jura in France, is everywhere pierced with deep
+boat-shaped cavities, at the bottom of which the water forms a kind
+of whirlpool, like the water flowing out of the hold of a stranded
+ship. Many mountains are penetrated in every direction with caverns
+and passages, just as if the whole rocky mass was nothing more than
+an accumulation of cells. On one steep cliff-side may be noticed
+all kinds of perforations at different heights--arched portals and
+orifices of fantastic shape; on another there are numbers of springs
+of blue water gushing from the caves, or from the rocks heaped up at
+the foot of the cliff, and forming rivulets which disappear a little
+further on in the fissures of the ground, as if through the holes of
+a sieve. The whole surface of the plateaus, whether bare or covered
+with forests, is scattered over with wells, or funnel-shaped holes
+communicating with subterranean reservoirs.
+
+One of the Istrian rivers, the subterranean course of which, although
+still unknown as regards a great number of points, has given rise to
+a most continuous course of investigations, is the celebrated Timavus
+(Timavo), which falls into the sea near Duino, about twelve miles
+to the north of Trieste. Virgil’s description no longer applies to
+the mouths of the Timavo; at present they do not reach the number
+of nine, because the extermination of the woods of the Carso has
+diminished the mass of the water, or the action of the stream and
+the alluvium of the delta have modified the form of the shore. But
+still it is a magnificent spectacle to see the outlet of the three
+principal torrents of water which rush foaming out of the heart of
+the rocks, and are navigable from their mouths to their very source.
+A river of this importance must certainly receive the drainage of
+a vast basin, and yet all the neighboring valleys seem perfectly
+devoid of rivulets, and their surface presents little else but the
+bare rock; in fact, the whole of the rain and snow-water runs away
+through underground caverns.
+
+The most remarkable network of caverns in this region of the Alps is
+that which spreads out from the southwest to the northeast across
+the Adelsberg group of mountains, between Fiume and Laibach. The
+principal cave is especially curious on account of its size, the
+variety of its calcareous concretions, and the torrent which runs
+roaring through it.
+
+North of the town of Adelsberg the traveler passes along the base of
+a hill with steep and bare sides, bringing into view the sharp edges
+of its highly pitched calcareous beds. On the right the stream of
+the Poik winds peaceably in the valley; and then, its course being
+arrested by a headland, turning suddenly, it flows into the interior
+of the mountain through a kind of high portal, opening between two
+parallel beds of rocks. Unless the water in the stream is very low,
+it is impossible to follow it over the accumulation of rocks upon its
+bed; but on the right, at a height of a few yards, there is another
+entry, through which the traveler may descend dry-shod into a vast
+cavity or chamber, where the Poik again appears issuing from its
+narrow passage of rocks.
+
+At this point the cave divides; on the north the stream, the depth
+of which varies, according to the season, from a few inches to 30 or
+33 feet, buries itself in a winding avenue, which has been traversed
+in a boat as far as a point 1,027 yards from the entrance; on the
+northeast, a higher avenue, discovered only in 1818, pushes its
+way far into the heart of the mountain, branching out in various
+directions into narrow passages and wide compartments. This portion
+of the grotto, which appears to have been the former bed of the Poik,
+is the most curious part of the Adelsberg labyrinth; it affords
+wonderful groups of stalactites, especially in the Salle du Calvaire,
+the vaulted roof of which, having the enormous span of 210 yards,
+has dropped upon a hillock of débris a perfect forest of stalagmitic
+columns and white needles. The full length of the principal cave is
+not less than 2,575 yards; but very probably some other and still
+longer avenues may yet be discovered.
+
+Although it is impossible to go in a boat along the subterranean
+portion of the Poik for a greater distance than 1,027 yards,
+by traversing the surface of the calcareous plateaus we can at
+all events trace out the subterranean stream by means of the
+funnel-shaped holes which open above its course. One of these gulfs,
+the Piuka-Jama, is situated about a mile and a half to the north of
+the entrance of the Adelsberg caves; the only way to descend into
+this is by clinging to the branches of the shrubs and sliding down by
+the assistance of a cord fastened to the top of the rocks. By these
+means the entrance to a kind of air-hole may be reached, from which
+the Poik is visible foaming over its bed of rocks, and only a slope
+of débris is to be descended to reach the edge of the stream. It can
+only be followed in the downstream direction for about 275 yards;
+but it can easily be ascended for a distance of 495 yards by passing
+under a high portal with lofty pillars, and in this way a point can
+be reached which is less than a mile from the place where the stream
+disappeared in the cave of Adelsberg.
+
+Further down the stream the Poik is not visible again until it
+emerges from the mountain, where it is known under the name of the
+Planina; it rushes out through a circular arch at the base of a
+perpendicular bluff crowned with fir-trees. It really is the Poik,
+as is proved by the equal temperature of water and the sudden
+increase of its liquid mass after a storm has burst at Adelsberg;
+but the stream always issues from the cave much more considerable
+in bulk than it is when it enters, owing to the tributaries which
+pour into it on both sides during its subterranean course of five
+to six miles. One of these rivulets, which comes down from the
+plateaus of Kaltenfeld, joins the Poik at a little distance from its
+outlet. Above the confluence the principal stream can be ascended
+in a boat to a distance of more than 3,500 yards, which, with the
+other explored parts of the subterranean river, makes about three
+miles. Below the point of outlet the stream is partially lost in the
+fissures of its bed, and then, joining the Unz, goes on and empties
+itself into the Danubian Save.
+
+About a dozen miles to the southeast of the Adelsberg and Planina
+caves extends a large plain surrounded on all sides by high
+calcareous cliffs, at the base of which nestle seven villages. In
+this hollow, the most elevated portion of which is under cultivation,
+the remainder being covered with rushes and other marsh-plants, there
+are to be found more than 400 funnel-shaped holes resembling those
+in other parts of Carniola. These _dolinas_, the average depth of
+which is from 40 to 60 feet, have each their special name, such as
+the “_Grand Crible_” (great sieve), the “_Crible-à-froment_” (corn
+sieve), the “_Tambour_” (drum), the “_Cuve_” (tub), the “_Tonneau_”
+(cask), pointing out the form or some remarkable peculiarity of
+each abyss. During extremely dry seasons there is only one of these
+cavities which contains any water; but after continuous and heavy
+rain, the water of a stream which is swallowed up in the rocks a
+little above the plain rises with a roaring noise in each of these
+wells. Torrents escaping from all these open “_cribles_” form in the
+wide space hemmed in by the cliffs a sea of blue and transparent
+water. This is the lake of Jessero or Zirknitz, the _lacus Lugens_ of
+the Romans. The surface of the sheet of water extends over an area of
+14,826 acres; at the time of great inundations, this extraordinary
+temporary lake, thus vomited out by the underground river, is not
+less than 24,711 acres. The water runs away through a subterranean
+channel, and, further on, empties itself into the Unz, below the
+Planina.
+
+Lacustrine basins of this sort, first emitted, and then again
+absorbed by a subterranean water-course, are rather rare; there are,
+however, some other remarkable instances of them in Europe. Thus,
+in the Oriental Hartz, in the midst of a beautiful spot surrounded
+by fir-trees, the charming lake called Bauerngraben (Peasants’
+Ditch), or sometimes Hungersee (Lake of Famine), sometimes makes its
+appearance; but when this mass of blue water has filled but for a few
+days its basin of gypsum rock, it is suddenly swallowed up, and flows
+away by subterranean channels into the stream of the Helme. The
+celebrated lake of Copaïs, in Bœotia, may likewise be compared to the
+Zirknitz lake, at least as regards certain portions of its basin.
+
+
+
+
+  RIVERS
+  --A. KEITH JOHNSTON
+
+
+Rivers are the result of the natural tendency of water, as of all
+other bodies, to obey the law of gravitation by moving downward
+to the lowest position it can reach. The supply of water for the
+formation of rivers, though apparently derived from various sources,
+as from rain-clouds, springs, lakes, or from the melting of snow, is
+really due only to atmospheric precipitation; for springs are merely
+collections of rain-water; lakes are collections of rain or spring
+water in natural hollows, and snow is merely rain in a state of
+congelation. The rills issuing from springs and from surface-drainage
+unite during their downward course with other streams, forming
+_rivulets_; these, after a further course, unite to form _rivers_,
+which, receiving fresh accessions in their course from _tributaries_
+(subordinate rivers or rivulets) and their _feeders_ (the tributaries
+of tributaries), sweep onward through ravines, and over precipices,
+or crawl with almost imperceptible motion across wide, flat plains,
+till they reach their lowest level in ocean, sea, or lake. The
+path of a river is called its _course_; the hollow channel along
+which it flows, its _bed_; and the tract of country from which it
+and its subordinates draw their supplies of water, its _basin_, or
+_drainage-area_. The basin of a river is bounded by an elevated
+ridge, part of which is generally mountainous, the crest forming
+the watershed; and the size of the basin, and the altitude of its
+watershed, determine, _cæteris paribus_, the volume of the river. The
+greater or less degree of uniformity in the volume of a river in the
+course of a year is one of its chief physical features, and depends
+very much on the mode in which its supply of water is obtained.
+
+In temperate regions, where the mountains do not reach the limit
+of perpetual snow, the rivers depend for their increase wholly on
+the rains, which, occurring frequently, and at no fixed periods,
+and discharging only comparatively small quantities of water at a
+time, preserve a moderate degree of uniformity in the volume of the
+rivers--a uniformity which is aided by the circumstance that in these
+ones only about one-third of the rainfall finds its way directly over
+the surface to the rivers; the remaining two-thirds sinking into
+the ground, and finding its way to spring-reservoirs, or gradually
+oozing through at a lower level in little rills which continue to
+flow till the saturated soil becomes drained of its surplus moisture,
+a process which continues for weeks, and helps greatly to maintain
+the volume of the river till the next rainfall. This process, it
+is evident, is only possible where the temperature is mild, the
+climate moist, evaporation small, and the soil sufficiently porous;
+and under these circumstances great fluctuations can only occur
+from long-continued and excessive rains or droughts. In the hotter
+tracts of the temperate zones, where little rain falls in summer,
+we occasionally find small rivers and mountain torrents becoming
+completely exhausted; such is often the case in Spain, Italy, Greece,
+and with the Orange, one of the largest rivers of South Africa.
+
+In tropical and semi-tropical countries, on the other hand, the year
+is divisible into one dry and one wet season; and in consequence the
+rivers have also a periodicity of rise and fall, the former taking
+place first near the source, and, on account of the great length of
+course of some of the tropical rivers, and the excessive evaporation
+to which they are subjected (which has necessarily most effect where
+the current is slow), not making itself felt in the lower part of
+their course till a considerable time afterward. Thus, the rise of
+the Nile occurs in Abyssinia in April, and is not observed at Cairo
+till about mid-summer. The fluctuations of this river were a subject
+of perpetual wonderment to the ancient civilized world, and were
+of course attributed to superhuman agency; but modern travel and
+investigation have not only laid bare the reason of this phenomenon,
+but discovered other instances of it, before which this one shrinks
+into insignificance.
+
+The maximum rise of the Nile, which is about 40 feet, floods 2,100
+square miles of ground; while that of the Orinoco, in Guiana, which
+is from 30 to 36 feet, lays 45,000 square miles of savannah under
+water; the Brahmaputra at flood covers the whole of Upper Assam to a
+depth of 10 feet, and the mighty Amazon converts a great portion of
+its 500,000 square miles of selvas into one extensive lake. But the
+fluctuations in the rise of the flood-waters are surpassed by some
+of the comparatively small rivers of Australia, one of which, the
+Hawkesbury, has been known to rise 100 feet above its usual level.
+This, however, is owing to the river-beds being hemmed in by lofty
+abrupt cliffs, which resist the free passage of a swollen stream.
+
+The increase from the melting of snow in summer most frequently
+occurs during the rainy season, so that it is somewhat difficult
+to determine, with anything like accuracy, the share of each
+in producing the floods; but in some rivers, as the Ganges and
+Brahmaputra, the increase from this cause is distinctly observable,
+as it occurs some time after the rains have commenced, while in the
+case of the Indus it is the principal source of flood. When the
+increase from melted snow does not occur during the rainy season, we
+have the phenomenon of flooding occurring twice a year, as in the
+case of the Tigris, Euphrates, Mississippi, and others; but in most
+of these cases the grand flood is that due to the melting of the snow
+or ice about the source.
+
+The advantages of this periodical flooding in bringing down abundance
+of rich fertile silt--the Nile bringing down, it is said, no less
+than 140 millions of tons, and the Irrawadi 110 millions of tons
+annually--are too well known to need exposition here. Islands are
+thus frequently formed, especially at a river’s mouth. Permanent and
+capacious lakes in a river’s course have a modifying effect owing to
+their acting as reservoirs, as is seen in the St. Lawrence; while
+the Red River (North) and others in the same tract inundate the
+districts surrounding their banks for miles. In tropical countries,
+owing to the powerful action of the sun, all rivers whose source is
+in the regions of perpetual snow experience a daily augmentation
+of their volume; while some in Peru and Chili, being fed only by
+snow-water, are dried up regularly during the night.
+
+The course of a river is necessarily the line of lowest level from
+its starting-point, and as most rivers have their sources high up a
+mountain slope the velocity of their current is much greater at the
+commencement. The courses of rivers seem to be partially regulated
+by geological conditions of the country, as in the case of the San
+Francisco of Brazil, which forms with the most perfect accuracy the
+boundary-line between the granitic and the tertiary and alluvial
+formations in that country; and many instances are known of rivers
+changing their course from the action of earthquakes, as well as from
+the silting up of the old bed. The inclination of a river’s course
+is also connected with the geological character of the country; in
+primary and transition formations, the streams are bold and rapid,
+with deep channels, frequent waterfalls and rapids, and pure waters,
+while secondary and alluvial districts present slow and powerful
+currents, sloping banks, winding courses, and tinted waters; the
+incline of a river is, however, in general very gentle--the average
+inclination of the Amazon throughout its whole course being estimated
+at little more than six inches per mile, that of the Lower Nile less
+than seven inches, and of the Lower Ganges about four inches per mile.
+
+The average slope of the Mississippi throughout its whole length is
+more than seventeen inches per mile, while the Rhone is, with the
+exception of some much smaller rivers and torrents, the most rapid
+river in the world, its fall from Geneva to Lyons being eighty inches
+per mile, and thirty-two inches from Lyons to its mouth.
+
+The velocity of rivers does not depend wholly on their slope; much is
+owing to their depth and volume (the latter being fully proved by the
+fact that the beds of many rivers remain unaltered in size and slope
+after their streams have received considerable accessions, owing to
+the greater rapidity with which the water runs off); while bends in
+the course, jutting peaks of rock or other obstacles, whether at the
+sides or bottom, and even the friction of the aqueous particles,
+which, though slight, is productive of perceptible effect, are
+retarding agencies. In consequence, the water of a river flows with
+different velocities at different parts of its bed; it moves slower
+at the bottom than at the surface, and at the sides than the middle.
+The line of quickest velocity is the line drawn along the centre of
+the current, and in cases where this line is free from sudden bends
+or sharp turns, it also represents the deepest part of the channel.
+The average velocity of a river may be estimated approximately by
+finding the surface-velocity in the centre of the current by means of
+a float which swims just below the surface, and taking four-fifths
+of this quantity as a mean. If the mean velocity in feet per minute
+be multiplied by the area of the transverse section of the stream in
+square feet, the product is the amount of water discharged in cubic
+feet per minute. According to Sir Charles Lyell, a velocity of 40
+feet per minute will sweep along coarse sand; one of 60 feet, fine
+gravel; one of 120 feet, rounded pebbles; one of 180 feet (a little
+more than two miles per hour), angular stones the size of an egg.
+
+“Rivers are the irrigators of the earth’s surface, adding alike to
+the beauty of the landscape and the fertility of the soil; they
+carry off impurities and every sort of waste débris; and when of
+sufficient volume, they form the most available of all channels of
+communication with the interior of continents.... They have ever been
+things of vitality and beauty to the poet, silent monitors to the
+moralist, and agents of comfort and civilization to all mankind.” By
+far the greater portion of them find their way to the ocean, either
+directly or by means of semi-lacustrine seas; but others, as the
+Volga, Sir-Daria (Jaxartes), Amu-Daria (Oxus), and Kur (Araxes), pour
+their waters into inland seas; while many in the interior of Asia
+and Africa--as the Murghab in Turkestan, and the Gir in the south of
+Morocco--“lose themselves in the sands,” partly, doubtless, owing
+to the porous nature of their bed, but much more to the excessive
+evaporation which goes on in those regions.
+
+
+
+
+  SWAMPS AND MARSHES
+  --ÉLISÉE RECLUS
+
+
+Marshes proper are shallow lakes, the waters of which are either
+stagnant or actuated by a very feeble current; they are, at least
+in the temperate zone, filled with rushes, reeds, and sedge, and
+are often bordered by trees, which love to plunge their roots into
+the muddy soil. In the tropical zone a large number of marshes are
+completely hidden by multitudes of plants or forests of trees,
+between the crowded trunks of which the black and stagnant water can
+only here and there be seen. Marshes of this kind are inaccessible
+to travelers, except where some deep channel, winding in the midst
+of the chaos of verdure, allows boats to attempt a passage between
+the water-lilies, or under some avenue of great trees with their
+long garlands of creepers waving in the shade. Whatever may be the
+climate, it would, however, be impossible to draw any distinction,
+even the most vague, between lakes and marshes, as the level of these
+sheets of water oscillates according to the seasons and years, and
+as the greater number of lakes, principally those of the plains,
+terminate in shallow bays which are perfect marshes. Some very
+important lacustral basins, among others Lake Tchad, one of the
+most considerable in all Africa, are entirely surrounded by swamps
+and inundated ground, which prohibit access to the lake itself, and
+prevent its true dimensions from being known.
+
+In like manner, a portion of the course of many rivers traverses low
+regions in which marshes are formed, either temporary or permanent,
+the uncertain limits of which change incessantly with the level of
+the current. The borders of great water-courses, when left in their
+natural state, are the localities in which these marshy reservoirs
+principally exist. The most remarkable marshes of this kind are
+perhaps those crossed by the Paraguay and several of its tributaries;
+they consist of wet prairies and interminable sheets of water, which
+stretch away like a sea from one horizon to the other. They have
+received the names of Lakes Xarayes, Pantanal, etc. Further south,
+certain tributaries of the Parana, the Maloya, the Batel, and the
+Sarandi, which cross the State of Corrientes from northeast to
+southwest, are nothing but wide marshes, the water of which overflows
+slowly across the grass on the imperceptible slope of the territory.
+There is, indeed, one of these marshes, the Laguna Bera, which drains
+simultaneously into the two great rivers of Parana and Uruguay.
+
+In the same way as the low river-shores are frequently converted into
+marshes, vast extents of the seacoasts when but slightly inclined
+are also covered over by marshes, which are generally separated from
+the main sea by tongues of sand gradually thrown up by the waves.
+In these marshes, most of which once formed a part of the sea and
+still mark its ancient outline, the water presents the most varied
+proportions of saline admixture. These half dried-up bays are rarely
+deep enough to allow of large vessels sailing in them, and their
+banks are generally overrun by the most luxuriant vegetation. The
+shore constantly keeps gaining upon them, and thus tends to the
+increase of the mainland.
+
+The coasts which surround the Caribbean Sea and the Gulf of Mexico,
+and also the Atlantic shores of North America from the point of
+Florida to the mouth of the Chesapeake, are bordered by a very
+large number of marine marshes, forming a continued series over
+hundreds and thousands of miles in length. In this immense series
+of coast-marshes all kinds of vegetation seem to flourish, and
+threaten to get the better of the mud and water, and to convert
+them into _terra firma_. To the south, upon the shores of Colombia
+and Central America, the mangroves and other trees of like species
+plunge the terminal points of their aerial roots deep into the mud,
+crossing and recrossing in an arch-like form, and retaining all the
+débris of plants and animals under the inextricable network of their
+natural scaffoldings. The shores of the Gulf of Mexico, in Louisiana,
+Georgia, and Florida, are bordered by cypress swamps, or forests of
+cypress (_Cupressus disticha_); these strange trees, the roots of
+which, entirely buried, throw out above the layer of water which
+covers the soil multitudes of little cones, the business of which is
+to absorb the air. For millions of acres nearly all the marshy belt
+along the seashore is nothing but an immense cypress swamp, with
+trees bare of leaves, and fluttering in the wind their long hair-like
+fibres of moss. Here and there the trees and muddy soil give place to
+bays, lakes, or quaking-meadows, formed by a carpet of grass lying
+upon a soil of wet mud, or even upon the hidden water. In Brazil
+these buoyant beds of vegetation are frequently met with, and the
+significant name of _tremendal_ has been given to them: in Ireland
+these are called “quaking-bogs.” The least movement of the traveler
+who ventures upon them makes the soil tremble to some yards’ distance.
+
+To the north of Florida, in the Carolinas and Virginia, the belt of
+cypress swamps continues; but in consequence of the change of climate
+and vegetation, the quaking-meadows are gradually converted into
+peat-mosses. The surface of the marsh is incessantly renewed by a
+carpet of green vegetation, while below, the dead plants, deprived
+of air, carbonize slowly in the moisture which surrounds them: these
+are the beds of peat which form upon the ground just as the layers of
+coal were formed in previous geological epochs.
+
+On the southern side, the first great peat-bog of a well-defined
+character is the “Dismal Swamp,” which extends along the frontiers
+of North Carolina and Virginia. This spongy mass of vegetation rises
+ten feet above the surrounding land. In the centre, and, so to speak,
+upon the summit of the marsh, lies Lake Drummond, the clear water
+of which is colored reddish-brown by the tannin of the plants. A
+canal, which crosses the Dismal Swamp to connect it with the adjacent
+streams, is obliged to make its way along the marsh by means of
+locks. To the north of Virginia peat-bogs proper become more and more
+numerous; and in Canada, Labrador, etc., they cover vast expanses
+of country. All the interior of the island of Newfoundland, inside
+the inclosure formed by the forests on the shore, is nothing but
+a labyrinth--a great part of which is still unknown--of lakes and
+peat-bogs; even on the sides of the hills there are marshes on so
+steep an incline that the water from them would disappear and run off
+in a stream if it was not stopped by the thick carpet of plants which
+it saturates. Many a large peat-bog which may be crossed dry-shod
+contains more water than many lakes filling a hollow of the valley
+with deep water.
+
+Opposite Newfoundland, on the other side of the Atlantic, Ireland
+is hardly less remarkable for the enormous development of its
+peat-mosses or bogs. These tracts of saturated vegetation, in
+which _Sphagnum palustre_ predominates, comprehend nearly two and
+a half millions of acres--the seventh part of the whole island.
+The inhabitants continue to extract from them, every year, immense
+quantities of fuel. The spaces left by the spade in the vegetable
+mass are gradually filled up again by new layers. After a certain
+number of years, which vary according to the abundance of rain, the
+depth of the bed of water, the force of vegetation, and the slope of
+the soil, the turf “quarry” is formed anew. In Ireland it generally
+takes about ten years to entirely fill up again the trenches,
+measuring from nine to thirteen feet in depth, which are made in the
+bogs on the plains, when a fresh digging of turf may be commenced.
+In Holland, crops of this fuel may be gathered, on an average, every
+thirty years. In other peat-moss districts the period of regeneration
+last forty, fifty, and even a hundred years. In France, on the
+borders of the Seugne (Charente-Inférieure), it has been ascertained
+that ditches five feet deep and nearly seven feet wide are completely
+obstructed by vegetation after the lapse of twenty years. As for the
+beds of peat which carpet the sides of mountains, they take centuries
+to form afresh.
+
+In Ireland, the Low Countries, the north of Germany and Russia, heaps
+of trunks of former forest-trees--oaks, beech, alder, and other
+trees--are frequently discovered, which by their decay have made way
+for the peat-mosses. The _Sphagnum_, too, often takes possession of
+ground of which man had previously made himself master, and in many
+places roads, remains of buildings, and other vestiges of human labor
+are found below the modern bed of vegetation by which they are now
+covered. Certain peat-bogs in Denmark and Sweden may be considered,
+on account of the curiosities which have been found in them, as
+perfect natural museums, in which the relics of the civilization of
+ancient nations have been preserved for the _savants_ of our own day.
+
+The air above the peat-mosses of Ireland and other countries in
+the world is not often unhealthy, either because the heat is not
+sufficient to develop miasma, or else because the vegetation, by
+absorbing the water into its spongy mass, impedes the corruption of
+the liquid, and produces a considerable quantity of oxygen. Further
+south, the peat-mosses, which are intermixed with pools of stagnant
+water, and especially marshes properly so-called, generate an impure
+air, which spreads fever and death over the surrounding country.
+Unless marshes are surrounded with dense forests, which arrest
+the dispersion of the gases, the latter exercise a most injurious
+influence on the general salubrity of the district; for during dry
+weather, a vast area of the bed of the marshes becomes exposed, and
+the heaps of organic débris lying on the bottom decompose in the heat
+and infect the whole atmosphere. The average of life is much shorter
+in all marshy countries than in the adjacent regions which are
+invigorated by running water. In Brescia, Poland, in the marshes of
+Tuscany, and in the Roman plains, the wan and livid complexion of the
+inhabitants, their hollow eyes, and their feverish skin, announce at
+first sight the vicinity of some centre of infection. There are some
+marshes in the torrid zone where the decomposition of organic remains
+goes on with a much greater rapidity than in temperate climates; no
+one can venture on the edges of these districts without peril to his
+life. As Frœbel ascertained in his journey across Central America,
+the miasma is occasionally produced in such abundance that not only
+can it be smelt, but a distinct impression of it is left upon the
+palate.
+
+
+
+
+  LOWLAND PLAINS
+  --WILLIAM HUGHES
+
+
+The plateaus and mountain regions of the globe occupy a large
+portion of its surface--perhaps more than half of the whole extent
+of the land--and their influence over its climate and other natural
+conditions affecting mankind is very great. The highlands of the Old
+World--fitted by their physical attributes to be the home of pastoral
+and nomad races--were among the regions earliest occupied by mankind.
+From the banks of the Euphrates and the primeval cities of the
+Assyrian plain, the course of the shepherd-warrior--whether directed
+to the east or the west--led toward some of the elevated regions
+which stretched thence within the same (or nearly the same) degrees
+of latitude, and which, at least in a general sense, are under like
+conditions of climate. The highlands of Persia and Afghanistan,
+in the one direction, of Syria and the Lesser Asia, in the other,
+display abundant evidence, both in traditional and monumental
+records, of their early occupation by man. From the one, the natural
+order of advance leads to the fertile plains of India; from the
+other, to the shores of the Mediterranean, whence is easy transit to
+the peninsula and islands that lie beyond.
+
+But if the highlands of the earth were early the dwelling-place of
+the shepherd-warrior, it was within the adjoining lowland plains and
+fertile river basins that the arts of civilization were first called
+into being, that towns were built, that population became numerous,
+and that systems of social polity were developed. The lowland plains
+of Asia and Europe constitute, in the present day, the most populous
+regions of the globe, and include by far the more numerous portion
+of the human race. The like regions in the New World are fast
+filling with inhabitants, as the redundant population of older lands
+is directed, in an ever-flowing stream, across the waters of the
+Atlantic.
+
+The most important and extensive among the lowland plains of the Old
+World are the following:
+
+IN ASIA.--Plain of the Euphrates and Tigris (the ancient Mesopotamia
+and Babylonia); Plain of Hindustan, or Northern India; Plain
+of China, embracing the northeast part of that country; Plain
+of Siberia; Plain of Turkestan. Among lowland regions of less
+importance are the plains of Pegu, Siam, and Tonquin, all within the
+Indo-Chinese peninsula, or India beyond the Ganges.
+
+IN EUROPE.--The Great Eastern Plain, embracing nearly the whole of
+Russia; Plain of Hungary, embracing the middle portion of the valley
+of the Danube; Plain of Wallachia and Bulgaria, or the Lower Danube;
+Plain of Lombardy, or Northern Italy; Plain of Languedoc, in the
+south of France; Plain of Andalusia, in the south of Spain; Plain of
+Bohemia, or basin of the Upper Elbe.
+
+The limits and direction of these regions may be traced upon any
+ordinary map, by means of their coincidence with the great river
+basins of the Eastern Hemisphere. They include the longer slopes
+of the land, which are directed toward the north and northwest, as
+well as the less extensive low grounds which border the Indian and
+Pacific Oceans. The Siberian plain alone comprehends an area equal
+to that of Europe, and the rivers by which it is watered are among
+the most considerable in the Old World. So vast an area, under
+other conditions of climate, might have become the home of populous
+nations, the seat of civilization and empire. But its high latitudes,
+which involve the rigor of an Arctic sky, condemn a large portion
+of Siberia to the condition of a sterile wilderness, and must
+prevent even its more favored districts from being other than thinly
+inhabited. The dreary swamps and morasses of the _tundras_, which
+replace, during the brief summer of those latitudes, the plain of ice
+and snow, stretch along the shores of the Arctic Sea through a vast
+extent of this widespread region.
+
+Conditions hardly more favorable belong to the extreme northern
+portion of the great plain of Europe, the slope of which is directed
+toward the White Sea and the Arctic basin. But a large portion of
+Eastern Europe is inclined toward a southerly sky, and is watered by
+rivers which have their outfall into the Black and Caspian Seas. The
+Volga, the longest of European rivers, belongs to the Caspian basin,
+the most depressed portion of the entire region.
+
+The southeastern division of the European lowland, and the adjacent
+portions of Asia, constitute the region of the _steppes_. These
+occupy an immense portion of the empire of Russia, and are among
+the most characteristic of the physical features of the Old World.
+The steppes are grassy plains--prairies, or meadows, they would be
+called in the New World--which occupy a vast belt of the European
+and Asiatic continents. They stretch eastward from the banks of
+the Dnieper far into the heart of Asia--along the shores of the
+Caspian and Aral Seas, and as far as the banks of the great river
+Obi. Indeed, in so far as their grassy covering and general level
+expanse--among the prime characteristics of the steppe-land--are
+concerned, a like region may be said to extend to the eastward
+through Central Asia, as far as the Great Wall of China and the
+valley of the Amour. This is the “land of grass” of the Mongol
+shepherd, the true home of the Tartar nations, whose descendants
+yet preserve in their songs the memory of their famous leader
+Timour--the Tamerlane of historic record. So vast is the extent of
+this grass-covered region, that a mounted horseman, it has been said,
+setting out from one of its extremities at the beginning of the year,
+and traveling day and night at his utmost speed, would find the
+season of spring elapse ere he reached its further limits.
+
+The southwestern portion only of the steppe-land falls within
+the limits of Europe. This exhibits an unbroken expanse of level
+plain--fatiguing to the eye from its perfect uniformity--dry and
+burned up by excessive heat in summer, a pathless expanse of snow
+during the opposite season of the year. The steppe is only productive
+during the brief time that the thirsty soil is refreshed by the rains
+of spring and early summer. Its aspect is then, for a time, glowing
+and verdant; grass and wild flowers cover the earth with a carpet of
+varied and attractive hues, and the wild cattle and horses luxuriate
+in the abundant pasture. In the autumn, when the herbage has become
+dry and withered, the steppe sometimes exhibits a vast sheet of
+rolling flame, the grass being occasionally fired by accident, at
+other times intentionally, for the sake of the young crop which
+springs up through the ashes. The illusive phenomena of _mirage_--the
+result of atmospheric refraction, engendered by the intense dryness
+of the air--are of frequent occurrence in the steppe. Sometimes the
+eye is cheated by the semblage of a lake, which vanishes on approach.
+In other instances, the traveler over these wild regions appears to
+see rising before him, and glittering through the dense mist which
+often prevails during the hours of midday heat, the towers and other
+buildings of a distant city. Spires, trees, bridges, rivers, all
+appear in picturesque combination, only to sink into confusion as
+they are approached. When the spot where the city of enchantment
+had seemed to stand is actually reached, there is found only the
+long, dry grass, waving as elsewhere in the surrounding waste. The
+vast accumulation of dry sand on the surface gives rise to another
+phenomenon, of frequent occurrence on the steppe, resembling
+waterspouts upon the sea, excepting that the column is filled with
+dust instead of water. “Suppose the great flat steppe stretched out
+beneath the blue sky--nothing visible--no breath of air apparently
+stirring--the whole plain an embodiment of sultriness, silence, and
+calmness--when gradually rise in the distance six or eight columns of
+dust, like inverted cones, two or three hundred feet high, gliding
+and gliding along the plain in solemn company; they approach, they
+pass, and vanish again in the distance, like huge genii on some
+preternatural errand.”
+
+Such is the region over which the semi-nomad tribes of Tartar
+shepherds, who constitute a fraction of the vast population of the
+Russian Empire, pasture their herds. It is only here, within the
+limits of Europe, that the camel is successfully reared. Odessa, the
+great outport of southern Russia, stands almost on the edge of the
+steppe, and the whirlwinds of dust that pass through its streets, and
+constitute, during a portion of the year, one of its chief drawbacks
+as a place of residence, furnish obvious evidence of this proximity.
+The steppe includes two-thirds of the Crimean peninsula, the extreme
+south of which, however, is traversed by a hill-range of considerable
+elevation, and exhibits widely different features.
+
+Beyond the Dnieper, the Don, and even the Volga, the same region of
+alternate grassy plain and sandy waste stretches far into the Asiatic
+continent. To the east and north of the Caspian and the Aral are the
+steppes over which roam the hordes of the Khirghiz. The names of
+Kara-kum and Kizil-kum, given respectively to the sandy wastes which
+extend upon either side of the river Syr, or Jaxartes, are strikingly
+indicative of the general character of the tracts to which they are
+applied.
+
+Mr. T. W. Atkinson, in his _Travels in Regions on the Upper and Lower
+Amour_, thus describes the journey through these wild regions: “For
+many miles the sand was hard, like a floor, over which we pushed on
+at a rapid pace. After this we found it soft in places, and raised
+into thousands of little mounds by the wind. Our horses were now
+changed, and in an hour these mounds were passed, when we were again
+on a good surface, riding hard.... Hour after hour went by, and our
+steeds had been changed a second time.... In our route there was no
+change visible--it was still the same plain; there was not so much
+as a cloud floating in the air, that, by casting a shadow over the
+steppe, could give a slight variation to the scene.... The whole
+horizon was swept with my glass, but neither man, animal, nor bird
+could be seen.... We rode on for several hours, but there was no
+change of scene. One spot was so like another that we seemed to make
+no progress.... No landmark was visible, no rock protruded through
+the sterile soil; neither thorny shrub nor flowering plant appeared,
+to indicate the approach to a habitable region; all around was
+‘kizil-kum’ (_red sand_).”
+
+The perfect solitude and unbroken silence of the desert are not less
+characteristic than its wearisome monotony of surface. No sound of
+bird or animal breaks the solemn stillness which reigns around;
+no trees expose their foliage to the influence of the wind. The
+course of the traveler is still onward, through the same apparently
+interminable waste. “Fourteen hours had passed, and still a desert
+was before us. The sun was just sinking below the horizon. The
+Kirghiz assured me that two hours more would take us to pastures and
+to water.... It had now become quite dark, and the stars were shining
+brilliantly in the deep blue vault. My guides altered their course,
+going more to the south. On inquiring why they made this change, one
+of them pointed to a star, intimating that by that they must direct
+their course.
+
+“We traveled onward, sometimes glancing at the planets above, and
+then anxiously scanning the gloom around, in the hope of discovering
+the fire of some dwelling that would furnish food and water for our
+animals. Having ridden on in this manner for many miles, one of our
+men stopped suddenly, sprang from his horse, and discovered that we
+had reached vegetation. The horses became more lively and increased
+their speed, by which the Kirghiz knew that water was not far off.
+In less than half an hour they plunged with us into a stream, and
+eagerly began to quench their terrible thirst, after their long and
+toilsome journey.”
+
+The features above described are those of the steppe region, regarded
+as a whole. But this aspect undergoes considerable variation in
+particular localities. The Lower Steppes, as those portions of
+the great plains which immediately border the Caspian are termed,
+exhibit a soil largely impregnated with saline particles, and
+contain numerous salt-water lakes. Some of these lakes furnish a
+large quantity of salt, derived by means of evaporation. This region
+resembles in aspect the dried-up bed of a sea. The Caspian, upon
+which it borders, occupies the lowest part of a depression below the
+general level of the earth’s surface, its waters being 81 feet lower
+than those of the Black Sea. The extent of the Caspian appears to be
+gradually diminishing.
+
+The features of the steppe-land, however, are exceptional to the
+general characteristics of the European plain, regarded as a
+whole. Large portions of its middle and western divisions possess
+a rich arable soil, and exhibit annually a waving sea of corn.
+The geographical limits of the lowland region are marked, in the
+direction of north and south, by the Black Sea and the Arctic Ocean.
+The eastwardly portions of this vast level expanse stretch into the
+heart of Asia. In the west it reaches the shores of the Baltic, and
+is thence prolonged, with narrower dimensions, through northern
+Germany and the low flats of Holland, until it subsides beneath the
+water of the German Ocean. Throughout this vast extent, tertiary
+and recent formations prevail, and the abundant clays, sands, and
+gravels give their character to the surface-soil. The plain lying
+to the south of the Baltic consists principally of sandy heaths,
+and contains, toward the seashore, a vast number of small lakes or
+_meers_.
+
+The low shores of Holland--conquered from the sea by the persevering
+industry of the Dutch nation--furnish a conspicuous example of the
+sand-hills, or _dunes_, which are often found on low sandy coasts,
+and which owe their origin to the action of prevailing winds upon
+the loose drift-sand. Where no means are adopted to fix them to
+the soil, the sand-hills become agents of destruction, sometimes
+overwhelming whole villages in their slow but steady advance inland.
+But this is not the case in Holland, where the ingenuity of the Dutch
+has converted them from instruments of destruction into a means of
+national preservation. In some of the provinces of the Netherlands,
+a large portion of the land is actually lower than the level of
+high-water mark, and is therefore exposed (it might appear) to the
+ravages of the adjoining ocean. But from the channel of the Helder
+southward, the coast is protected by a line of broad dunes, or
+sand-hills, which are partially covered with grass or heath, and
+are in some places from forty to fifty feet in height. These have
+been formed by the natural process above adverted to, and still in
+operation; the prevalent sea-winds raise banks or ridges of sand
+at a short distance from the coast, which the inhabitants prevent
+from proceeding further inland by sowing them with a kind of grass
+(_arundo arenaria_), the long roots of which bind the whole mass
+firmly together.
+
+The district of the _Landes_, in the southwest corner of France,
+offers an example of the combined action of sand and sea which is
+widely different from the above in its results. The coast here
+exhibits a line of shifting sand, backed toward the interior by a
+belt of pine-forest. For a length of nearly two hundred miles, from
+the mouth of the Garonne to that of the Adour, there stretches along
+the extreme edge of the sea a range of hills composed of white sand,
+as fine as though it had been sifted for an hour-glass. Every gale
+changes the shape of these rolling masses of drift-sand. A strong
+wind from the land flings millions of tons of sand per hour into
+the sea, to be again washed up by the surf, flung upon the beach,
+and with the first Biscay gale blown in whirlwinds inland. A water
+hurricane from the west has been known to fill up with sand many
+square miles of shallow lake, driving the displaced waters inland,
+dispersing them among the pine-woods, flooding and frequently
+destroying the scattered hamlets of the people, and burying forever
+their fields of millet and rye. The shepherds of the Landes pursue
+their avocation mounted upon stilts, which raise them above the
+reach of the sand-blasts. The pine-forests yield annually a large
+supply of resin, the only harvest of this wild region. Intermixed
+with the pine-forests, a chain of shallow and marshy lakes stretches
+in a direction parallel to the coast, and at a few miles inland.
+
+[Illustration: Great Barrier Coral Reef, Queensland, Australia
+
+This Reef is composed entirely of Stag’s Horn Coral (_Madrepora
+Hebes_)]
+
+The lowland plains of the New World are on a scale of vast magnitude,
+and, if not superior in extent to those of the Eastern Hemisphere,
+yet bear a much larger proportion to the entire area of the land.
+They are watered, moreover, by the longest rivers of the globe, and
+enjoy, for the most part, conditions of situation and climate in the
+highest degree favorable to man. Both in North and South America, the
+whole central expanse of the continent exhibits a vast succession
+of lowland plains, the only division between the different portions
+of which is that formed by the watersheds of its longer rivers--not
+always to be traced without difficulty, owing to the generally
+level nature of the entire plain. In North America, the prairies;
+in South America, the tracts known as llanos, selvas, and pampas,
+are included within the lowland region, and exhibit some of the most
+characteristic among the aspects of nature in the Western world.
+
+The prairies coincide, in a general sense, with the middle and upper
+portion of the Mississippi Valley, embracing the vast region which
+extends from the Great Lakes to the base of the Rocky Mountains. They
+are covered in their natural state with a rich herbage, and exhibit a
+waving sea of grass several feet high. At intervals, toward the banks
+of the rivers, patches of forest vegetation break the uniformity
+of the prospect, but the prairie itself is destitute of trees, and
+(as the name implies) is merely a grassy plain, or meadow. Alternate
+forest and prairie constitute the great features of natural scenery
+in the New World. When the rich soil of the prairie-land is broken
+up by the plow--an operation which is rapidly progressing, year by
+year, within the Western States of America--it yields abundant crops
+of corn. There are, however, within the vast extent of the North
+American continent, immense regions which yet retain the aspect of
+the wilderness. It was within these regions that the buffalo roamed,
+in vast herds, and that the native Indian hunter pursued his game
+ere the advancing footsteps of the white man had driven him from his
+haunts.
+
+The llanos, or savannahs, are vast grassy plains, which occupy nearly
+the whole basin of the Orinoco River, excepting only toward its
+highest portion, when they are succeeded by wooded plains. The llanos
+resemble in general features the prairies of the Mississippi Valley,
+but have for the most part a lower level, and (owing to the abundant
+rains of the torrid zone) are annually inundated by the rivers to
+an immense extent. Whole districts, embracing thousands of square
+miles, are annually converted, within the interior plains of South
+America, into lakes, or temporary seas of fresh water, to be rapidly
+evaporated under the burning rays of a vertical sun. At the close of
+the rainy season the llanos are covered with grass, and form rich
+natural pasture-grounds. During the prolonged season of drought which
+ensues, the verdure is entirely destroyed, and the parched earth
+opens in wide and deep crevices--again to be laid under water with
+the recommencement of the rains.
+
+The selvas, or forest-plains, belong to the valley of the Amazon, and
+include an immense area of Brazil, watered by the lower portion of
+the great stream and its chief tributary, the Madera. Vast regions
+are here covered by an uninterrupted forest, composed of trees of
+giant growth, their boughs interlaced by immense creeping plants, and
+the ground beneath thickly covered with a dense growth of underwood.
+To the southward of the forest region are vast grassy plains, which
+stretch in that direction into the valley of the Paraguay.
+
+The pampas, or plains of the Paraguay and Paraná valleys, exhibit the
+same luxuriant natural growth of herbaceous plants as other lowland
+regions of the New World. They include an immense region, which
+stretches from the neighborhood of the southern tropic far to the
+southward of the river Negro (lat. 39° S.), and from the banks of the
+Paraná to the eastern base of the Andes. The pampas are variously
+covered with long coarse grass, mixed with wild oats, clover, and
+other herbage. The tract of country known by the name of El Gran
+Chaco, immediately to the westward of the upper Paraguay--scarcely
+tenanted excepting by wild beasts--exhibits a luxuriant covering of
+grass, which springs from a soil possessed of the highest natural
+capabilities.
+
+Further south, the plains that extend from Buenos Ayres to the foot
+of the Andes are covered, during a great part of the year, with
+gigantic thistles, which grow to the height of seven or eight feet,
+and are so thick as to render the country almost impassable. For nine
+months of the year the thistles are here the predominant (and almost
+the sole) feature of the vegetable kingdom; but with the heats of
+summer they are burned up, and their tall leafless stems are leveled
+to the ground by the powerful blast of the pampero, or southwest
+wind, which blows from the snowy ranges of the Andes, after which the
+ground is covered for a brief season with herbage. This is destined,
+with the returning spring, again to give place to the stronger
+vegetation which it had succeeded, and for a time supplanted.
+
+
+
+
+  THE SMELL OF EARTH
+  --G. CLARKE NUTTALL
+
+
+A bright fine evening after a day of rain is one of Nature’s
+compensations. The air is peculiarly sweet and fresh, as though
+the rain had washed all evil out of it. The mind, relieved from
+the depressing influence of continuous rain, is exhilarated, and,
+above all, the strong smell of the earth rises up with a scent more
+pleasing than many a fragrant essence. In the town, indeed, this
+earthy smell is often obscured by the bricks and mortar which cover
+the land, and by the stronger, less wholesome, odors of human life,
+but in the country it has full sway, and fills the whole air with
+its presence. Even a slight shower, particularly after drought, is
+sufficient to bring out the sweet familiar smell of the land and
+thrust it upon our notice.
+
+The smell of freshly turned earth is often regarded by country lovers
+as one of the panaceas for the ills of the flesh, and “follow a
+plowshare and you will find health at its tail” has proved a sound
+piece of advice to many a weakly town-sick one, over whose head the
+threatenings of consumption hung like the sword of Damocles, though
+it is possible that it is the fresh air, and more especially the
+sunshine, which are the saving media, and not the mere smell.
+
+But what do we know about this characteristic smell of the soil? Can
+we regard it as the mere attribute of the soil as a simple substance,
+such an attribute as is, for instance, the peculiar smell of leather,
+or the odor of india-rubber; or can we go deeper and find that it is
+really an expression of complexity below?
+
+Strangely enough this is the case, for the smell of damp earth is one
+of the latest sign-posts we have found which lead us into a world
+which, until recently, was altogether beyond our ken. It points us to
+the presence, in the ground beneath us, of large numbers of tiniest
+organisms, and not merely to their presence only, but to their
+activity and life, and reveals quite a new phase of this activity.
+A handful of loose earth picked up in a field by the hedgerow, or
+from a garden, no longer represents to us a mere conglomeration of
+particles of inorganic mineral matter, “simply that and nothing
+more”; we realize now that it is the home of myriads of the smallest
+possible members of the great kingdom of plants, who are, in
+particular, members of the fungus family in that kingdom, plants so
+excessively minute that their very existence was undreamed of until a
+few years ago.
+
+Some faint idea of their relative size, and of the numbers in which
+they inhabit the earth, may be gleaned from the calculations of an
+Italian, Signor A. Magiora, who, a short time ago, made a study of
+the question. He took samples of earth from different places round
+about Turin and examined them carefully. In ordinary cultivated
+agricultural soil he found there would be eleven millions of these
+germs in the small quantity of a gramme, a quantity whose smallness
+will be appreciated when it is remembered that a thousand grammes
+only make up about two and a quarter pounds of our English measure.
+Thus, a shovelful of earth would be the home of a thousand times
+eleven millions of bacteria--but the finite mind can not grasp
+numbers of such magnitude. In soil taken from the street, and,
+therefore, presumably more infected with germs, he calculated that
+there was the incredible number of seventy-eight million bacteria to
+the gramme. Sandy soil is comparatively free from them, only about
+one thousand being discovered in the same amount taken from sandy
+dunes outside Turin.
+
+But though the workers were hidden yet their works were known, for
+what they do is out of all proportion to what they are; in fact they
+perform the deeds of giants, not those of veriest dwarfs. “By their
+works shall ye know them” might be a fitting aphorism to describe
+the bacteria of the soil. And the nature of their deeds is widely
+various, for though the different groups are members of one great
+family, yet, like the individuals of a human family that is well
+organized, they have each of them their special vocation. In the
+spring time, when the sun warms the chilly earth, they act upon the
+husks that have protected the seeds against the rigors of the winter,
+and crumble them up so that the seedling is free to grow; they
+break down the stony wall of the cherry and plum which has hitherto
+imprisoned the embryo; and then, when the young plant starts, they
+attach themselves to its roots, assist it to take in all sorts of
+nutriment from air and soil, and thus help it in its fight through
+life, and when its course has run they decently bury it. They turn
+the green leaves and the woody stem and the dark root back into the
+very elements from which they were built up; they effect its decay
+and putrefaction, and resolve it into earth again. “Dust to dust,
+ashes to ashes,” is the great life work of the earth bacteria.
+
+But up to about 1898 the fresh smell of the earth, the smell peculiar
+to it, had not been in any way associated with these energetic
+organisms, and it was quite a new revelation to find that it was
+a direct outcome of their activity. Among the many bacteria which
+inhabit the soil, a new one, hitherto unknown, has been isolated and
+watched. It lives, as is usual with them, massed into colonies, which
+have a chalky-white appearance, and as it develops and increases in
+numbers it manifests itself by the familiar smell of damp earth,
+hence the name that has been given it--_Cladothrix odorifera_.
+Taken singly, it is a colorless thread-like body, which increases
+numerically by continuous subdivisions into two in the direction of
+its length. It derives its nutriment from substances in the soil,
+which either are, or have been, touched by the subtle influence of
+life, and in the processes of growth and development it evolves from
+these materials a compound whose volatilizing gives the odor in
+question. This compound has not yet been fully examined; it is not
+named, nor have all its properties been satisfactorily elucidated,
+but two facts concerning it stand out clearly. One is that it is the
+true origin of the smell that we have hitherto attributed to earth
+simply; and the other, that it changes into vapor under the same
+conditions as water does. Therefore, when the sun, shining after the
+rain, draws up the water from the earth in vapor form, it draws up,
+too, the odorous atoms of this newly found compound, and these atoms,
+floating in the air, strike on our olfactory nerves, and it is then
+we exclaim so often, “How fresh the earth smells after the rain!”
+
+Though moisture, to a certain extent, is a necessary condition of the
+active work of these bacteria, yet the chief reason why the earthy
+smell should be specially noticeable after the rain is probably
+because this compound has been accumulating in the soil during the
+wet period. We only smell substances when they are in vapor form,
+and since the compound under consideration has precisely the same
+properties in this respect as water, it will only assume gaseous form
+when the rain ceases. The bacteria have, however, been hard at work
+all the time, and when the sun shines and “drying” begins, then the
+accumulated stores commence their transformation into vapor, and the
+strong smell strikes upon our senses. For the same reason we notice a
+similar sort of smell, though in a lesser degree, from freshly turned
+earth. This is more moist than the earth at the surface, and hence,
+on exposing it, evaporation immediately begins which quickly makes
+itself known to us through our olfactory nerves.
+
+It may also have been remarked that this particular odor is always
+stronger after a warm day than after a cold one, and is much more
+noticeable in summer than in winter. This is because moderate warmth
+is highly conducive to the greater increase of these organisms, and,
+in fact, in the summer they are present in far larger numbers and
+exhibit greater vitality than in the winter, when they are often more
+or less quiescent.
+
+Two other characteristics of _Cladothrix odorifera_ are worthy of
+notice as showing the tenacity with which it clings to life. It is
+capable of withstanding extremely long periods of drought without
+injury; its development may be completely arrested (for water in
+some degree is a necessity with all living things, from highest to
+lowest), but its vitality remains latent, and with the advent of
+water comes back renewed activity. But besides drought it is pretty
+well proof against poisons. It can even withstand a fairly large
+dose of that most harmful poison to the vegetable world, corrosive
+sublimate. Hence any noxious matter introduced into the soil would
+harm it little ultimately; the utmost it could do would be to retard
+it for a time.
+
+This, then, is the history of the smell of earth as scientists have
+declared it unto us, and its recital serves to further point the
+moral that the most obvious, the most commonplace things of everyday
+life--things that we have always taken simply for granted without
+question or interest--may yet have a story hidden beneath them.
+Like sign-posts in a foreign land, they may be speaking, though
+in a language not always comprehended by us, of most fascinating
+regions--regions we may altogether miss to our great loss if we
+neglect ignorantly the directions instead of learning to comprehend
+them.
+
+
+
+
+  DESERTS
+  --ÉLISÉE RECLUS
+
+
+The most important group of deserts in the world is that of the
+Sahara, which extends across the African continent from the shores
+of the Atlantic to the valley of the Nile. This immense area is more
+than 3,100 miles from east to west, and is, on an average, more than
+600 miles in breadth; it is, in fact, equal in size to two-thirds
+of Europe. In this region there is only one season, viz., summer,
+burning and merciless. It is but rarely that rain comes to refresh
+these regions, on which the solar rays dart vertically down.
+
+The mean altitude of the Sahara is estimated at 2,000 feet; but the
+level of the soil varies singularly in the different districts. To
+the south of Algeria, the surface of the Chott Mel-R’ir, the remains
+of an ancient sea, which communicated with the Mediterranean, is at
+the present time more than 165 feet below the Gulf of Cabes; while to
+the south and east, the ground rises into plateaus and mountains of
+sandstone or granite to a height varying from 3,300 to 6,660 feet. In
+the centre of the Sahara stands the Djebel-Hogger, the sides of which
+are covered with snow during three months in the year; from December
+to March, its picturesque defiles are traversed by streams which flow
+some distance and lose themselves beneath the surrounding plains.
+This group of lofty mountains is the great landmark which forms the
+boundary between the eastern deserts, or the Sahara proper, and the
+group of western deserts, designated under the general name of Sahel.
+
+The Sahel is very sandy. Throughout the greater part of its extent
+the soil is composed of gravel and large-grained sand, which does
+not give way even under the foot of the camel. Some of the ranges
+of sand-hills which rise in this desert are chains of small hills,
+composed of heavy sand which resists the influence of the wind. But
+in many districts of the Sahel, the arenaceous particles of the
+soil are fine and small. The trade-winds which pass over the desert
+distribute these sandy masses into long waves similar to those of
+the ocean, and here and there raise them into movable sand-hills,
+which overwhelm all the oases which lie across their path. Traveling
+toward the southwest, in which direction they are driven by the wind,
+the sands reach the northern shores of the Niger and Senegal at many
+points of their course, and by their incessant deposits gradually
+drive the waters of these rivers toward the south. To the west, the
+sand of the desert encroaches also upon the ocean. Off the coast
+which stretches between Cape Bojador and Cape Blanco--pointed out
+from afar by the highest dunes in the world--a line of sand-banks
+extends far out into the sea. A current of sand is, therefore,
+constantly passing across the desert from northeast to southwest.
+The débris of rocks in a state of decomposition, and the particles
+brought to the coast of the Gulf of Cabes by the tide, which is very
+powerful at this point, are driven before the wind into the plains of
+the Sahel, and thence, after a journey lasting hundreds and perhaps
+thousands of years, they at last reach the seashore of the Atlantic,
+in order to recommence in the oceanic currents another eventful
+odyssey.
+
+Some parts of the eastern Sahara are equally sandy; but the principal
+parts of the surface of this desert are occupied by plateaus of rock
+or clay, and by groups of grayish or yellowish mountains. The chains
+of sand-hills are numerous, and, like those of the west, they travel
+incessantly under the impulse of the wind in a south or southwest
+direction. The rocky plateaus are crossed and recrossed here and
+there by wide and deep clefts, which are gradually filled by the
+drifted sand, and into which the traveler runs the risk of sinking,
+like the mountaineer into the _crevasses_ of a glacier. In the
+hollows, patches of salt take the place of the lakes which in more
+rainy countries would be found there.
+
+Those districts of the Sahara which are destitute of oases present
+a truly formidable aspect, and are fearful places to travel over.
+The path which the feet of the camels have marked out in the immense
+solitude points in a straight line toward the spot which the caravan
+wishes to reach. Sometimes these faint footmarks are again covered
+with sand, and the travelers are obliged to consult the compass, or
+examine the horizon; a distant sand-hill, a bush, a heap of camels’
+bones, or some other indications which the practiced eye of the
+Touareg alone can understand, are the means by which the road is
+recognized.
+
+Terrible stories are told by the side of the watch-fires of caravans
+being overtaken when amid the sand-hills by a sudden storm of wind,
+and completely buried under the moving masses; they also tell of
+whole companies losing their way in the deserts of sand or rocks,
+and dying of madness after having undergone all the direst tortures
+of heat and thirst. Happily such adventures are rare, even if the
+accounts of them are at all authentic. Caravans, when led by an
+experienced guide and protected by treaties and tribute against the
+attacks of plundering Arabs and Berbers, nearly always arrive at the
+end of their journey without having undergone any other sufferings
+than those caused by the intolerable heat, the want of good water,
+and the coldness of the nights; for the nights which follow the
+burning days in the Sahara are in general very cold. In fact, the air
+of these countries being entirely destitute of aqueous vapor, the
+heat collected during the day on the surface of the desert is, owing
+to the nocturnal radiation, again lost in space. The sensation of
+cold produced by this waste of heat is most acute, and especially
+so to the chilly Arab. Not a year passes without ice forming on the
+ground, and white frosts are frequent.
+
+In all those countries in the Sahara where the water gushes out in
+springs or descends in streams from some group of mountains, there is
+an oasis formed--a little green island, the beauty of which contrasts
+most strikingly with the barrenness of the surrounding sands. These
+oases, compared by Strabo to the spots dotted over the skin of
+the panther, are very numerous, and perhaps comprehend altogether
+an area equal in extent to one-third of the whole Sahara. In the
+greater part of this region, the oases, far from being scattered
+about irregularly, are, on the contrary, arranged in long lines in
+the middle of the desert. The cause of this is either the higher
+proportion of moisture contained in the aerial currents which pass in
+this direction, or, and perhaps principally, the subterranean water
+which follows this slope, and here and there rises to the surface.
+
+The oases are, _par excellence_, the country of date-trees; in
+the neighborhood of Mourzouk there are no less than thirty-seven
+varieties. These trees form the riches of the tribe, for their fruit
+supplies food to man as well as to beast--to dromedaries, horses, and
+dogs. Below the wide fan of leaves, which quiver in the blue air, are
+thickly growing clumps of apricot, peach, pomegranate, and orange
+trees, their branches loaded with fruit, and vines intertwining round
+the trunks; maize, wheat, and barley ripen under the shade of this
+forest of fruit-trees, and, lower still, the modest trefoil fills
+up the very smallest intervals of the soil which is capable of
+irrigation.
+
+To the east of Egypt, which may be considered as a long oasis
+situated on the banks of the Nile, the desert begins again, and
+borders the whole extent of the Red Sea. A large part of Arabia
+presents nothing but sands and rocks, and toward the southeast, in
+the Dahna, there are solitudes which no traveler, either Arab or
+Frank, seems yet to have crossed. To the north and east stretch
+the _Nefouds_, or “daughters of the great desert,” which are much
+smaller than the Dahna, but are nevertheless formidable tracts to
+travel over. One of these regions, which was crossed by Palgrave,
+is that in which the mass of sand, formerly deposited there by the
+marine currents, affords the greatest depth; in certain places it is
+330, 400, and even 500 feet deep. It can be measured by the eye by
+descending to the bottom of the funnel-shaped cavities, which the
+springs of water, spouting out of the adjacent granite or calcareous
+rock, have gradually hollowed out in the bed of sand. This enormous
+bed of material, which represents chains of pulverized mountains,
+does not exhibit an even surface, as one would expect, but,
+throughout its whole expanse, presents long symmetrical undulations,
+similar to those waves which roll in the Caribbean Sea under the
+even influence of the trade-winds. These waves stretch from north
+to south, parallel to the meridian; it is probable that they are
+owing to the movement of the earth round its axis. The solid rocks
+beneath unresistingly obey the impelling force which carries them
+toward the east, but the movable sands which are above them do not
+allow themselves to be carried away with an equal rapidity; each day
+an infinitesimal quantity remains behind and seems to glide toward
+the west, like the waves of the ocean, the atmospheric currents, and
+everything that is movable on the face of the globe. The parallel
+furrows of sand in the Nefouds certainly rise to a greater height
+than those of the other deserts, and differ much in their aspect from
+the smaller waves of sand formed by the wind; but the reason is, that
+the bed of sand in this region is of a very great bulk, and because
+at this point the swiftness of the globe nearly attains its maximum
+on account of its vicinity to the equator.
+
+To the east of the Arabian peninsula, the chain of deserts is
+prolonged obliquely across Asia. The principal part of the plateau
+of Iran, occupying a quadrilateral space, surrounded by mountains
+which stop the rains in their passage, consists of sterile solitudes,
+some covered with saline beds, the remains of dried-up lakes,
+others spread over with shifting sands, which the wind blows up
+into eddies, or dotted over with reddish-colored hills, which the
+mirage renders either nearer or more distant to the eye than they
+really are, incessantly modifying them according to the undulations
+of the atmosphere. This plateau is only separated from the steppes
+of Turkestan by the Elburz Mountains, and is continued toward the
+east by the deserts of Afghanistan and Beloochistan, which are not
+so large, and much easier to travel over. Even the rich peninsula of
+India is protected by a belt of sterile tracts situated on the right
+and left of the Indus. Between each of the five rivers (Punjaub),
+which, by the union of their waters, form the great river, stretches
+a line of steppes in which the torrent-waters of the mountains are
+soon lost. The soil of these steppes is nearly everywhere barren,
+except on the edge of the irrigation canals constructed by the
+inhabitants at a very heavy outlay.
+
+Beyond the mighty central group, whence radiate far and wide
+the mountain-chains of Asia, the steppes and deserts, mutually
+alternating according to the topographical conditions, and the
+abundance or scarcity of water, extend over a space of more than
+1,850 miles between Siberia and China Proper. The eastern part
+of this belt is called, according to the languages, Gobi or
+Chamo, that is to say, the desert _par excellence_, and, from
+its enormous dimensions, corresponds with the Sahara of Africa,
+situated exactly at the opposite extremity of the long chain of
+solitudes which stretches right across the Old World. The mirage,
+the moving sand-hills blown up into eddies, and many other phenomena
+described by African travelers, are found in certain districts of
+the Gobi, just the same as in all other deserts. But the cold here
+is exceptionally intense, on account of the great height of the
+plateaus, which is on an average 4,950 feet, and the vicinity of the
+plains of Siberia, which are crossed by the polar wind. It freezes
+nearly every night, and often during the day. The dryness of the
+atmosphere is extreme; there is hardly any vegetation, and a few
+grassy hollows are the only oases of these regions. From Kiahkta to
+Pekin, there are only five trees for a distance of 400 to 500 miles,
+which is the width of the desert in this part of Mongolia. The Gobi,
+however, like the Sahara, was formerly covered by the waters of the
+ocean; even on the elevated plateaus, old cliffs may be noticed, the
+bases of which are worn away by the waves, and long strands of round
+shingle stretch around the area which was formerly occupied by a now
+vanished gulf.
+
+In North, as in South America, the deserts proper lie to the west of
+the continent, and occupy the basins commanded by the parallel or
+divergent walls of the Rocky Mountains.
+
+The most northerly of these American deserts occupies, to the west
+of Lake Utah, a part of the space called the “Great Basin,” and is
+comprised between the principal chain of the Rocky Mountains and
+the Sierra Nevada of California. The desert of Utah is an immense
+surface of clay, dotted over with thin tufts of artemisia; in certain
+places, however, it exhibits no trace of vegetation, and resembles
+a causeway of concrete, intersected by innumerable clefts, forming
+nearly regular polygons. In the midst of these solitudes no rivulet
+flows, and no water-spring gushes forth; only after journeying for
+many a long hour the traveler sometimes comes upon some field of
+crystallized salt, a white expanse, on which the clouds and blue sky
+are reflected as on the surface of a lake. On the extreme horizon
+some volcanic rocks may be seen, like great scoriæ, half veiled by
+warm atmospheric columns, quivering like the air over the flame of a
+hot brazier. Across these vast plains, inhabited only by a prodigious
+quantity of extraordinarily shaped lizards, the road employed by the
+emigrants used to pass, which was so soon destined to be supplanted
+by the Pacific Railway from New York to San Francisco.
+
+The deserts of North America, crossed here and there by fertile
+valleys, extend eastward toward the basins of the Red River and the
+Arkansas, where they blend with the savannas, and to the south into
+the Mexican states of Chihuahua, Sonora, and Sinaloa. But in the
+tropical zone, which commences beyond these points, the heavy summer
+rains and the much smaller extent of the Mexican territory between
+the two oceans, have prevented the formation of deserts. Regions
+destitute of trees and verdure are only again found on the coasts of
+Peru, to the south of the Gulf of Guayaquil. The trade-winds, after
+having discharged their moisture on the eastern slopes of the Andes,
+pass away through the air far above the seashore on the western side
+of the mountains, and then sweep far out to sea over the surface of
+the Pacific.
+
+The solitudes of the Andes most resembling the desert regions of
+the Old World and of the United States are the elongated plateaus
+which rise one above another between the sea and the principal chain
+of the Andes, in southern Peru and on the frontiers of Bolivia and
+Chili; such as the _pampas_ of Islay and Tamarugal and the desert of
+Atacama. The _pampa_ of Tamarugal, so called from the _Tamarugos_,
+or tamarisks, which grow in the hollows where some moisture oozes
+out of the soil, has a mean altitude of from 2,900 to 3,900 feet. It
+is a plain nearly covered with beds of salt, or _salares_, which are
+worked like rock quarries. The strata of salt are so thick, and rain
+is so rare upon the plateau, that the houses of the village of Noria,
+which are inhabited by the workmen, are entirely constructed of
+blocks of salt. Some deserts, situated to the east of the Tamarugal,
+on more elevated plateaus, contain a still larger quantity of salt.
+The _pampa_ of Sal, which is overlooked by the volcano of Isluga, has
+a mean altitude of not less than 13,800 feet, and its whole extent,
+which is 125 miles long and from nine to twenty-four miles wide, is
+perfectly white. The depth of salt deposited upon this plateau varies
+from five to sixteen inches, according to the undulations of the
+ground.
+
+Whence do these enormous masses of salt proceed? Doubtless from the
+sea or ancient lakes which formerly covered these countries and have
+been gradually emptied by the rising of the soil. Saline matter
+saturates even the rocks and clays, for a film of salt again forms
+by efflorescence on all the ground in the desert from which crops
+have previously been taken. The district of Santa-Rosa, which was
+completely cleared of salt in 1827, was all white again and fit for
+working after a lapse of twenty-three years. Sea-salt is not the
+only production of these immense natural laboratories; but nitrates,
+sulphates, carbonate of soda, borates of soda and lime, are also
+found there and increase every year in thickness, thanks to the
+ephemeral torrents which sometimes descend loaded with débris from
+the adjacent Cordilleras. Saltpetre is also procured from the _pampa_
+of Tamarugal, and is the article which, during all the wars of Europe
+and America, gave such great commercial importance to the town of
+Iquique.
+
+The desert of Atacama, the largest of all those in South America,
+occupies a wide belt of plateaus between the shores of the Pacific
+and the high rampart of the Andes, which separates Bolivia from
+the Argentine Republic. This expanse of reddish-colored rocks, and
+crescent-shaped shifting sand-hills, is so repulsively desolate a
+place that the conquerors of Chili, whether Incas or Spaniards,
+never made up their minds to venture into it, in going along the
+sea-coast; they have been obliged to pass far into the interior, by
+the plateaus of Bolivia, and to twice cross the Andes before entering
+the Chilian valleys. Not long since, men of science were the only
+travelers who dared to enter the desert of Atacama. Nevertheless
+this formidable-looking country also possesses, like the _pampa_ of
+Tamarugal, great natural riches, which will not fail to summon the
+labor of man and all the progress of civilization to these desolate
+regions. Besides salt and saltpetre, this desert produces guano--that
+is, heaps of the almost exhaustless droppings of all the sea-birds
+which settle down in clouds upon the seashore. During the course of
+centuries the ordure has accumulated into perfect rocks which the sun
+dries up, and the surface of which is but rarely softened by rain.
+These masses of detritus, which are, to all appearance, useless upon
+these barren shores, are life itself to the countries of England,
+France, and Belgium, which have become exhausted by the extent of
+cultivation; and, consequently, this substance constitutes a most
+important element of national commerce.
+
+
+
+
+                             II.--THE SEA
+
+
+
+
+  THE PRIMITIVE OCEAN
+  --G. HARTWIG
+
+
+The greatest of all histories, traced in mighty characters by the
+Almighty Himself, is that of the earth-rind. The leaves of this great
+volume are the strata which have been successively deposited in the
+bosom of the sea or raised by volcanic powers from the depths of
+the earth; the wars which it relates are the Titanic conflicts of
+two hostile elements, water and fire, each anxious to destroy the
+formations of its opponent; and the historic documents which bear
+witness to that ancient strife lie before us in the petrified or
+carbonified remains of extinct forms of organic existence--the medals
+of creation.
+
+It is only since yesterday that science has attempted to unriddle
+the hieroglyphics in which the past history of our planet reveals
+itself to man, and it stands to reason that in so difficult a study
+truth must often be obscured by error; but although the geologist is
+still a mere scholar, endeavoring to decipher the first chapters of a
+voluminous work, yet even now the study of the physical revolutions
+of our globe distinctly points out a period when the molten earth
+wandered, a ball of liquid fire, through the desert realms of space.
+In those times, so distant from ours that even the wildest flight
+of imagination is unable to carry us over the intervening abyss,
+the waters of the ocean were as yet mixed with the air, and formed
+a thick and hazy atmosphere through which no radiant sunbeams, no
+soft lunar light ever penetrated to the fiery billows of molten
+rock, which at that time covered the whole surface of the earth.
+What pictures of desolation rise before our fancy at the idea of yon
+boundless ocean of fluid stone which rolled from pole to pole without
+meeting on its wide way anything but itself. Ever and ever in the
+dark-red clouds shone the reflection of that vast conflagration,
+witnessed only by the eye of the Almighty, for organic life could
+not exist on a globe which exclusively obeyed the physical and
+chemical laws of inorganic nature. But while the fiery mass with
+its surrounding atmosphere was circling through the icy region of
+ethereal space (the temperature of which is computed to be lower than
+60° R. below freezing point) it gradually cooled, and its hitherto
+fluid surface began to harden to a solid crust. Who can tell how many
+countless ages may have dropped one after the other into the abyss of
+the past, ere thus much was accomplished; for the dense atmosphere
+constantly threw back again upon the fiery earth-ball the heat
+radiating from its surface, and the caloric of the vast body could
+escape but very slowly into vacant space?
+
+Thus millions of years may have gone by before the aqueous vapors,
+now no longer obstinately repelled by the cooling earth-rind,
+condensed into rain, and, falling in showers, gave birth to an
+incipient ocean. But it must not be supposed that the waters
+obtained at once a tranquil and undisturbed possession of their new
+domain, for, as soon as they descended upon the earth, those endless
+elementary wars began, which, with various fortunes, have continued
+to the present day.
+
+As soon as the cooling earth-rind began to harden, it naturally
+contracted, like all solid bodies when no longer subject to the
+influence of expanding heat, and thus in the thin crust enormous
+fissures and rents were formed through which the fluid masses below
+gushed forth, and, spreading in wide sheets over the surface, once
+more converted into vapors the waters they met with in their fiery
+path.
+
+But after all these revolutions and vicissitudes which opposed the
+birth of ocean, perpetually destroying its perpetually renewed
+formation, we come at last to a period when, in consequence of
+the constantly decreasing temperature of the earth-rind and its
+increasing thickness, the waters at last conquered a permanent abode
+on its surface, and the oceanic empire was definitely founded.
+
+The scene has now changed; the sea of fire has disappeared, and water
+covers the surface of the earth. The rind is still too thin and the
+eruptions from below are still too fluid to form higher elevations
+above the general surface: all is flat and even, and land nowhere
+rises above the mirror of a boundless ocean.
+
+This new state of things still affords the same spectacle of dreary
+uniformity and solitude in all its horrors. The temperature of
+the waters is yet too high, and they contain too many extraneous
+substances, too many noxious vapors arise from the clefts of the
+earth-rind, the dense atmosphere is still too much impregnated with
+poisons to allow the hidden germs of life anywhere to awaken. A
+strange and awful primitive ocean rises and falls, rolls and rages,
+but nowhere does it beat against a coast; no animal, no plant grows
+and thrives in its bosom; no bird flies over its expanse.
+
+But, meanwhile, the hidden agency of Providence is unremittingly
+active in preparing a new order of things. The earth-rind increases
+in thickness, the crevices become narrower, and the fluid or
+semi-fluid masses escaping through the clefts ascend to a more
+considerable height.
+
+Thus the first islands are formed, and the first separation between
+the dry land and the waters takes place. At the same time no less
+remarkable changes occur, as well in the constitution of the waters
+as in that of the atmosphere. The further the glowing internal heat
+of the planet retires from the surface, the greater is the quantity
+of water which precipitates itself upon it. The ocean, obliged to
+relinquish part of its surface to the dry land, makes up for the loss
+of extent by an increase of depth, and the clearer atmosphere allows
+the enlivening sunbeam to gild here the crest of a wave, there a
+naked rock.
+
+And now also life awakens in the seas, but how often has it changed
+its forms, and how often has Neptune displaced his boundaries since
+that primordial dawn?
+
+Alternately rising or subsiding, what was once the bottom of the
+ocean now forms the mountain crest, and whole islands and continents
+have been gradually worn away and whelmed beneath the waves of
+the sea, to arise and to be whelmed again. In every part of the
+world we are able to trace these repeated changes in the fossil
+remains imbedded in the strata that have been successively deposited
+in the sea, and then raised again above its level by volcanic
+agencies, and thus, by a wonderful transposition, the history of the
+primitive ocean is revealed to us by the tablets of the dry land.
+The indefatigable zeal of the geologists has discovered no less
+than thirty-nine distinct fossiliferous strata of different ages,
+and as many of these are again subdivided into successive layers,
+frequently of a thickness of several thousand feet, and each of them
+characterized by its peculiar organic remains, we may form some idea
+of the vast spaces of time required for their formation.
+
+The annals of the human race speak of the rise and downfall of
+nations and dynasties, and stamp a couple of thousand years with
+the mark of high antiquity; but each stratum or each leaf in the
+records of our globe has witnessed the birth and the extinction of
+numerous families, genera, and species of plants and animals, and
+shows us organic Nature as changeable in time as she appears to us in
+space. As, when we sail to the Southern Hemisphere, the stars of the
+northern firmament gradually sink below the horizon, until finally
+entirely new constellations blaze upon us from the nightly heavens;
+thus in the organic vestiges of the Palæozoic seas we find no form of
+life resembling those of the actual times, but every class
+
+      “Seems to have undergone a change
+      Into something new and strange.”
+
+Then spiral-armed Brachiopods were the chief representatives of the
+mollusks; then crinoid star-fishes paved the bottom of the ocean;
+then the fishes, covered with large, thick rhomboidal scales, were
+buckler-headed like the Cephalaspis, or furnished with wing-like
+appendages like the Pterichthys; and then the Trilobites, a
+crustacean tribe, thus named from its three-lobed skeleton, swarmed
+in the shallow littoral waters where the lesser sea-fry afforded them
+abundant food. From a comparison of their structures with recent
+analogies, it is supposed that these strange creatures swam in an
+inverted position close beneath the surface of the water, the belly
+upward, and that they made use of their power of rolling themselves
+into a ball as a defence against attacks from above. The remains of
+seventeen families of Trilobites, including forty-five genera and 477
+species, some of the size of a pea, others two feet long, testify
+the once flourishing condition of these remarkable crustaceans, yet
+but few of their petrified remains, so numerous in the Silurian
+and Devonian strata, are found in the carboniferous or mountain
+limestone, and none whatever in formations of more recent date.
+
+Thus, long before the wind ever moaned through the dense fronds of
+the tree ferns and calamites which once covered the swampy lowlands,
+and long before that rich vegetation began to which we are indebted
+for our inexhaustible coal-fields, now frequently buried thousands of
+feet below the surface on which they originally grew, the Trilobites
+belonged already to the things of the past.
+
+In the seas of the Mesozoic or medieval period, new forms of life
+appear upon the scene. A remarkable change has taken place in the
+cephalopods; for the chambered and straightened Orthoceratites
+and many families of the order have passed away, and the spiral
+Ammonites, branching out into numerous genera, and more than 600
+species, now flourish in the seas, so that in some places the
+rocks seem, as it were, composed of them alone. Some are of small
+dimensions, others upward of three feet in diameter. They are met
+with in the Alps, and have been found in the Himalaya Mountains
+at elevations of 16,000 feet, as eloquent witnesses of the vast
+revolutions of which our earth has been the scene. Carnivorous,
+and resembling in habits the _Nautili_, their small and feeble
+representatives of the present day, their immense multiplication
+proves how numerous must have been the mollusks, crustaceans, and
+annelides, on which they fed, all like them widely different from
+those of the present day.
+
+Then also flourished the Belemnites (Thunder-stones), supposed by
+the ancients to be the thunder-bolts of Jove, but now known to
+be the petrified internal bones of a race of voracious ten-armed
+cuttle-fishes, whose importance in the Oolitic or cretaceous seas
+may be judged by the frequency of their remains and the 120 species
+that have been hitherto discovered. Belemnites two feet long have
+been discovered, so that, to judge by analogies, the animals to
+which they belonged as cuttle-bones must have measured eighteen to
+twenty feet from end to end, a size which reduces the rapacious
+Onychoteuthis of the present seas to dwarfish dimensions. But of all
+the denizens of the Mesozoic seas, none were more formidable than
+the gigantic Saurians, whose approach put even the voracious sharks
+to flight. The first of these monsters that raises its frightful
+head above the waters is the dreadful Ichthyosaurus, a creature
+thirty or even fifty feet long, half fish, half lizard, and combining
+in strange assemblage the snout of the porpoise, the teeth of the
+crocodile, and the paddles of the whale. Singular above all is the
+enormous eye, in size surpassing a man’s head. Woe to the fish
+that meets its appalling glance! No rapidity of flight, no weapon,
+be it sword or saw, avails, for the long-tailed, gigantic Saurian
+darts like lightning through the water, and its dense harness bids
+defiance to every attack. Not only have fifteen distinct species of
+_Ichthyosauri_ been distinguished, but the remains of crushed and
+partially digested fish-bones and scales which are found within their
+skeleton indicate the precise nature of their food. Their fossil
+remains abound along the whole extent of the Lias formation, from the
+coast to Dorset, through Somerset and Leicestershire to the coast of
+Yorkshire, but the largest specimens have been found in Franconia.
+Along with this monster, another and still more singular deformity
+makes its appearance, the Plesiosaurus, in which the fabulous
+chimæras and hydras of antiquity seem to start into existence. Fancy
+a crocodile twenty-seven feet long, with the fins of a whale, the
+long and flexible neck of a swan, and a comparatively small head.
+With the appearance of this new tyrant, the last hope of escape
+is taken from the trembling fishes; for into the shallow waters
+inaccessible to the more bulky Ichthyosaurus the slender Plesiosaurus
+penetrates with ease.
+
+A race of such colossal powers seemed destined for an immortal reign,
+for where was the visible enemy that could put an end to its tyranny?
+But even the giant strength of the Saurians was obliged to succumb to
+the still more formidable power of all-changing time, which slowly
+but surely modified the circumstances under which they were called
+into being, and gave birth to higher and more beautiful forms.
+
+In the Tertiary period, the dreadful reptiles of the Mesozoic seas
+have long since vanished from the bosom of the ocean, and cetaceans,
+walruses, and seals, unknown in the primitive deep, now wander
+through the waters or bask on the sunny cliffs. With them begins a
+new era in the life of the sea. Hitherto it has only brought forth
+creatures of base and brutal instinct, but now the Divine spark of
+parental affection begins to ennoble its more perfect inhabitants and
+to point out the dim outlines of the spiritual world.
+
+During all these successive changes the surface of the earth has
+gradually cooled to its present temperature, and many plants and
+animals that formerly enjoyed the widest range must now rest
+satisfied with narrower limits. The sea-animals of the North find
+themselves forever severed from their brethren of the South by the
+impassable zone of the tropical ocean; and all the fishes, mollusks
+and zoophytes, whose organization requires a greater warmth, confine
+themselves to the equatorial regions.
+
+As the Tertiary period advances toward the present epoch, the species
+which flourished in its prime become extinct, like the numberless
+races which preceded them; new modifications of life, more and more
+similar to those of the present day, start into existence; and,
+finally, creation appears with increasing beauty in her present rich
+attire.
+
+Thus old Ocean, after having devoured so many of his children, has
+transformed himself at last into our contemporaneous seas, with their
+currents and floods, and the various animals and plants, growing and
+thriving in their bosom.
+
+Who can tell when the last great revolutions of the earth-rind took
+place, which, by the upheaving of mighty mountains or the disruption
+of isthmuses, drew the present boundaries of land and sea? or who
+can pierce the deep mystery which veils the future duration of the
+existing phase of planetary life?
+
+So much is certain, that the ocean of the present day will be
+transformed as the seas of the past have been, and that “all that
+it inhabit” are doomed to perish like the long line of animal and
+vegetable forms which preceded them.
+
+We know by too many signs that our earth is slowly but unceasingly
+working out changes in her external form. Here lands are rising,
+while other areas are gradually sinking, here the breakers
+perpetually gnaw the cliffs and hollow out their sides, while in
+other places alluvial deposits encroach upon the sea’s domain.
+
+However slowly these changes may be going on, they point to a
+time when a new ocean will encircle new lands, and new animal and
+vegetable forms arise within its bosom. Of what nature and how gifted
+these races yet slumbering in the lap of time may be. He only knows
+whose eye penetrates through all eternity; but we can not doubt that
+they will be superior to the present denizens of the ocean.
+
+Hitherto the annals of the earth-rind have shown us uninterrupted
+progress; why, then, should the future be ruled by different laws?
+At first the sea only produces weeds, shells, crustacea; then the
+fishes and reptiles appear; and the cetaceans close the vista. But is
+this the last word, the last manifestation of oceanic life, or is it
+not to be expected that the future seas will be peopled with beings
+ranking as high above the whale or dolphin as these rank above the
+giant Saurians of the past?
+
+
+
+
+  THE FLOOR OF THE OCEAN
+  --JOHN JAMES WILD
+
+
+If we wish to form a perfect idea of the distribution of land and
+water, we must consider not only the length and breadth of the areas
+occupied, but also the height of the land and the depth of the water;
+in other words, the volume of those portions of the solid crust
+of the earth which are raised above the level of the sea, and the
+volume of the masses of water which fill up the depressed portions
+of the earth’s crust. We are thus led to regard the surface of the
+solid crust of our planet as composed of heights and hollows, of
+areas of elevation and areas of depression, and, as a next step, to
+discriminate between these areas--not according to the usual standard
+of the level of the sea, but according to their relative distance
+from the centre of the earth. In this sense we may conceive an area
+of elevation--_i. e._, a raised portion of the earth’s surface,
+which may be partially or entirely covered with water, and an area
+of depression--_i. e._, a hollow in the same surface, which may be
+raised above the level of the sea, and from dry land or the basin of
+an inland sea or lake.
+
+If we examine a chart of the world in the light which has been thrown
+upon this question by all the reliable soundings obtained up to the
+present, it will be found that continents and islands which we have
+been in the habit of considering as separated from each other by
+wide seas and deep straits virtually form part of the same area of
+elevation; and, in a similar manner, that certain oceans and seas,
+which we are accustomed to distinguish by separate names, form part
+of the same area of depression. It will also appear that, with the
+exception of the islands scattered over the face of the ocean and of
+the Antarctic region, all the dry land at present existing may be
+reduced to one large area of elevation gravitating to the North Pole,
+as the common centre of the principal land masses; similarly, if we
+except the Arctic region and other inland basins, all the oceans and
+seas compose a single vast area of depression, with the South Pole
+for common centre of the larger accumulations of water on this globe.
+The Arctic region forms a distinct area of depression placed in the
+centre of the great area of elevation, and the Antarctic region,
+according to the evidence we at present possess, is an area of
+elevation, surrounded on all sides by the above-described great area
+of depression. The numerous small islands that crop up in the middle
+of the oceanic basins are generally found associated in groups, and
+they belong to areas of elevation at the present time submerged, that
+is to say, in the condition in which we know the dry land to have
+been at an epoch more or less remote in the history of our planet. In
+support of the above generalization, we may point to the following
+facts as established by recent soundings. The 100-fathom line, as is
+well known, joins the whole of the British Islands, including the
+Hebrides, Orkneys, and Shetland Islands, to the continent of Europe.
+It forms a broad band connecting the Asiatic and American continents
+across Behring Strait. It unites Australia, Papua, and Tasmania in
+a single area of elevation, which, together with the intervening
+archipelago of Java, Sumatra, Borneo, Celebes, the Moluccas, and the
+Philippines, may be looked upon as a prolongation of the continent of
+Asia. It joins Ceylon to Hindostan and the Falkland Islands to the
+South American continent. The 500-fathom line connects North America,
+Greenland, Iceland, the Faroe Islands, and the continent of Europe,
+the only unexplored space being Denmark Strait, between Iceland
+and Greenland, where the soundings may exceed the above depth. The
+1,000-fathom line unites New Zealand with Australia, Madagascar with
+Africa, and nearly exhausts the depth of the more or less landlocked
+seas which lie between Australia and Asia, Africa and Europe, South
+and North America, and of the seas situated within the Arctic and
+Antarctic Circles. The Cape de Verde Islands and the Canaries belong
+to Africa, Madeira to Europe, and less than 500 fathoms divide Norway
+from Spitzbergen.
+
+Depths from 100 to 1,000 fathoms may be considered as shallow in
+comparison with the prevailing depths from 2,000 to 3,000 fathoms
+of the principal oceanic basins, and sufficient to establish a
+connection between islands and continents, the more so as we
+generally find one or more islands occupying the intervening space,
+thus betraying the common link between them.
+
+The result of this examination is that all the larger land masses
+compose an area of elevation which, after nearly completing the
+circuit of the world in the latitude of the Arctic Circle, subdivides
+itself into two parts, an eastern and a western one--the former
+embracing Europe, Africa, Asia, and Australia, the latter North and
+South America. In a similar manner, the different oceans combine
+into an area of depression which, after making the circuit of the
+world along the parallel of lat. 60° S. under the name of the
+Southern Ocean, divides itself into three large basins, respectively
+designated as the Pacific, the Atlantic, and the Indian Oceans. Thus
+the two elements, land and water, starting from opposite hemispheres,
+extend their arms across the equator, holding each other in close
+embrace, like two champions wrestling for the mastery of the world.
+
+A comparison of the deep-sea soundings obtained up to the present
+date shows that, if we omit the seas situated beyond the parallels of
+lat. 60° N. and lat. 60° S.--no depths exceeding 2,000 fathoms having
+as yet been ascertained beyond these latitudes--the average depth of
+the ocean between these parallels may be estimated at about 2,500
+fathoms, or more roughly at three English miles, and the average
+depth of all seas on the surface of the globe at probably two miles.
+
+Contrary to the ideas formerly entertained of the enormous depth of
+the ocean, the soundings of H.M.S. _Challenger_, S.M.S. _Gazelle_,
+and of the U.S.S. _Tuscarora_ and _Gettysburg_, indicate that depths
+of five miles, or even 4,000 fathoms, are but seldom met with, and
+are as exceptional as heights of the same amount on land.
+
+One of the greatest depths ascertained in the Atlantic was found by
+H.M.S. _Challenger_, about eighty miles north of the island of St.
+Thomas in the West Indies. It is 3,875 fathoms, or about four and a
+half miles. In May, 1876, the _Gettysburg_ found 3,593 fathoms only
+eleven miles south of the _Challenger_ sounding. A depth of 3,370
+fathoms obtained by the American ship shows that the deepest area in
+the Atlantic is placed to the northward of the Virgin Islands, and
+extends over 400 miles along the meridian of 65° W.
+
+The greatest depth observed in the Indian Ocean was discovered by the
+_Gazelle_ in May, 1875. Two soundings of 3,020 and 3,010 fathoms were
+taken in the eastern extremity of this ocean between the northwest
+coast of Australia and the line of islands extending from Java to
+Timor.
+
+The greatest of all depths of which we have reliable evidence
+was found by the _Challenger_ on the 23d March, 1875, in the
+comparatively narrow channel which separates the Caroline Islands
+from the Mariana or Ladrone Islands. This sounding amounts to 4,575
+fathoms, or about five miles and a quarter. Several soundings
+exceeding 4,000 fathoms were obtained by the _Tuscarora_ to the
+eastward of the islands of Nippon and Yesso, and another close to
+the most westerly of the Aleutian Islands. Two of these soundings
+are over 4,600 fathoms, but as it appears that no sample of the
+bottom was brought up, there is no evidence of the latter having
+been reached. H.M.S. _Challenger_, shortly after her departure from
+Yokohama, sounded 3,950 and 3,625 fathoms, and in doing so seems to
+have just touched the southern border of this deep but narrow area of
+depression, which runs parallel to the eastern coasts of Japan and
+the Kurile Archipelago as far as the entrance to the Behring Sea.
+
+It will be observed that the above exceptional depths in the
+Atlantic, Indian, and Pacific Oceans are not placed, as one might
+be inclined to conjecture, in or near the centre of these oceanic
+basins, but, on the contrary, upon their confines and in close
+proximity to the land. This remarkable circumstance suggests the idea
+that such areas of maximum depression may be the effect of a sinking
+of the bottom of the sea in compensation for an upward movement of
+the land in their immediate vicinity.
+
+Just as the results of the recent soundings have rendered the
+existence of depths from six to nine miles, as formerly reported,
+highly improbable, so have they modified our ideas of the shape
+of the sea-bottom. The latter was generally represented as a
+repetition of the dry land with its combination of mountain, valley,
+and plain. No doubt the sea-bottom within a short distance of the
+shore naturally forms a continuation of the leading features of the
+adjoining land. Thus a large plain or a low-lying country will, as a
+rule, continue its almost level slopes to a considerable distance out
+to sea, while a range of hills or a chain of mountains often extends
+its steep inclines below the surface of the water.
+
+The alteration of level in mid-ocean between two points as much as
+a hundred miles apart is generally so slight that to an observer
+standing at the bottom of the sea, the latter would appear a perfect
+plain. Thus the bottom of our oceanic basins is composed of gentle
+undulations rising and falling from a few fathoms to two or three
+miles, in distances extending over many hundred miles. This view
+accords with the experience of the geologist who finds that the bulk
+of the dry land consists of sedimentary strata originally laid down
+in a horizontal, or nearly horizontal, position at the bottom of the
+sea, and there can be little doubt but that the depths of the ocean
+are at the present time the scene of the formation of sedimentary
+strata which some day may be converted into dry land, and contain
+imbedded in their folds traces of the animal life with which they
+abound.
+
+One of the most remarkable results in connection with the
+exploration of the sea is the discovery of several extensive
+submarine plateaus, which interrupt what was until lately supposed
+to be an unbroken waste of fathomless abyss. One of these plateaus
+traverses the Atlantic Ocean in its whole length from north to south,
+repeating in its form the S-shaped contour of the eastern and western
+shores of this ocean. After attaching itself by its northern end to
+the plateau which connects Europe and Iceland, and separates the
+Atlantic from the Arctic basin, it runs southward toward the Azores,
+and, gradually contracting in width, sweeps round toward St. Paul’s
+Rocks. Reduced, comparatively speaking, to a narrow ridge, it follows
+the line of the equator as far as the meridian of Ascension Island,
+where, resuming its southward course, it widens out until in lat.
+30° S. it occupies nearly half the space between South America and
+Africa, uniting the island of Ascension with St. Helena in the east,
+Trinidad in the west, and the group of Tristan d’Acunha and Gough
+Island at its southern end.
+
+Considerable portions of this plateau are within 1,500 fathoms, or a
+mile and a half, of the surface of the sea, and most of the islands
+are of volcanic origin. An extinct volcano, 8,300 feet in height,
+forms the island of Tristan d’Acunha; Ascension Island rises to 2,800
+feet, and the summit of Pico in the Azores to 7,600 feet above the
+level of the sea. The northern end of the plateau joins the plateau
+of Iceland with its still active focus of eruption.
+
+By this central plateau, the Atlantic Ocean is divided into two
+longitudinal areas of depression or channels, one following the
+shores of North and South America, the other the shores of Europe
+and Africa. The depths vary from 2,000 to nearly 4,000 fathoms, the
+average depth being about three miles. The deepest portion of the
+eastern channel is situated to the westward of the Cape de Verde
+Islands, and forms an area of depression of over 3,000 fathoms.
+In the western channel there are two such depressions, one placed
+between the Antilles, Bermudas, and the Azores, the other between
+Cape St. Roque, Ascension, and Trinidad. They are divided from each
+other by a submarine elevation, which apparently connects the central
+plateau with the South American continent.
+
+The soundings taken in the Indian Ocean prove the existence of a
+submerged plateau on the limit between the Indian Ocean and the
+Southern Ocean. It rises in many parts to within 1,500 fathoms of
+the sea-surface, and forms the common foundation of all the islands
+situated in this part of the world--viz., Prince Edward Island, the
+Crozet Islands, the Kerguelen group, the Heard Islands, and the
+islands of St. Paul and Amsterdam. The origin of all these islands is
+probably volcanic.
+
+The main basin of the Indian Ocean with an average depth of over
+2,000 fathoms, stretches from the meridian of the Cape of Good Hope
+toward the angle between Java and northwestern Australia, where it
+attains its greatest depths, forming a depression of over 3,000
+fathoms. It communicates with the Arabian Sea by two narrow channels
+situated north and south of the Chagos Archipelago, being nearly
+cut off from that sea by a line of islands and shallow soundings
+which connect Africa, Madagascar, Bourbon, and Mauritius, the Chagos
+Islands and the Maldive Islands with the Asiatic continent. The
+2,500-fathom area of the Indian Ocean crosses the parallel of lat.
+40° S. between St. Paul and Amsterdam Islands and Cape Leeuwin in
+Australia, and forms, between the south coast of Australia and the
+forty-fifth parallel, an area of depression which extends beyond the
+southern end of Tasmania, includes the deepest portion of the basin
+between New South Wales and New Zealand, and probably communicates
+with the depths of the Pacific by a channel situated off the southern
+extremity of New Zealand.
+
+If we divide the Pacific Ocean into an eastern and a western half
+by a line passing from Honolulu to Tahiti, or by the meridian of
+long. 150° W., we observe a remarkable contrast between the two
+portions thus formed. While the eastern half, extending toward
+America, presents a vast unbroken sheet of water, almost devoid of
+islands, the western half, toward Asia and Australia, and inclosed
+between the parallels of lat. 30° N. and lat. 30° S., is composed
+of a labyrinth of seas, separated from each other by chains of
+islands, the projecting points of numerous submarine ridges. Although
+extensive tracts in the Pacific Ocean remain as yet untouched by
+the sounding-line, the observations made by the _Challenger_, the
+_Gazelle_, and the _Tuscarora_ enable us to form an idea of the
+general contours of its bottom. From the shores of North and South
+America, the depths of the eastern half of the Pacific gradually
+increase until, upon the line between Honolulu and Tahiti, they
+attain 3,000 fathoms. The latter depth forms extensive areas of
+depression in the western half of this ocean, and increases to
+4,000 fathoms in the already described hollow extending along the
+Japanese and Kurile Islands toward the entrance of the Behring Sea.
+Thus the idea formerly entertained of the inferior depths of the
+Pacific in comparison with the Atlantic, founded apparently upon the
+large number of islands scattered over its surface, is proved to be
+erroneous. Many of these islands, especially in the northwestern
+half, rise immediately from depths of 3,000 fathoms and more.
+
+In the southeastern portion of the Pacific there are indications
+of a submerged plateau connecting the Society Islands, the Low
+Archipelago, the Marqueses, and the intervening islands of Easter
+Island and Juan Fernandez with the coast of Chili and Patagonia.
+It seems as if an almost uninterrupted area of elevation crossed
+the whole basin of the Pacific in a northwesterly direction from
+Patagonia to Japan. The tendency of most of the submerged ridges of
+this ocean to follow the same direction has been frequently commented
+upon, and, as is the case with the submerged plateaus of the Indian
+and Atlantic Oceans, their association with centres of volcanic
+activity is equally evident.
+
+A line passing from Kamtchatka over Japan, the Ladrone, Caroline,
+Marshall, Gilbert, Ellice, Samoa, Tonga, and Kermadec Islands to
+New Zealand, divides the main basin of the Pacific, of an average
+depth of 3,000 fathoms, from the much shallower seas lying to the
+westward, and may possibly have formed the coast-line of a large
+continent which existed at a remote epoch in the history of the
+surface of our planet, and the boundaries of which have since been
+driven back to the present confines of Asia and Australia.
+
+The Southern Ocean, which makes the circuit of the world along the
+parallel of 60° S., in length equal to half the circumference of
+the earth at the equator, may be considered as occupying the space
+between the Antarctic Circle and the parallel of lat. 40° S. Owing to
+the limited number of soundings as yet obtained within its limits, we
+can only form a general idea of the distribution of its depths.
+
+The boundary-line of the fortieth parallel, which separates the
+Southern Ocean from the Pacific, Atlantic, and Indian Oceans, is
+occupied alternately by areas of depression, with depths ranging
+from 2,500 to nearly 3,000 fathoms, and by areas of elevation, or
+submarine plateaus, approaching to within 1,500 fathoms of the
+sea-surface. With regard to the general distribution of depth in the
+Southern Ocean, its bottom appears to rise gradually from nearly
+3,000 fathoms at the fortieth parallel (with the exception of the
+intervening plateaus) to little over 1,500 fathoms at the Antarctic
+Circle. There are also indications of an area of depression of an
+average depth of 2,000 fathoms, making the circuit of the globe
+between the parallels of 50° and 60° lat. S. The whole surface of the
+Southern Ocean is strewn with masses of floating ice, some of them
+forming islands many miles in extent, and rising from 100 to 300 feet
+above the level of the sea--an imposing spectacle, but fraught with
+much danger to the navigator in these regions. It is this central
+ocean which supplies the masses of cold water that fill up nearly
+two-thirds of the total depth of the Atlantic, Pacific, and Indian
+Oceans.
+
+We are indebted to Sir James Ross for the first soundings procured
+within the Antarctic Circle. They are situated in the wide inlet,
+discovered by that illustrious navigator in the year 1840, which
+extends along the meridian of New Zealand, and terminates at the foot
+of Mount Erebus and Mount Terror. These soundings, which are all
+under 500 fathoms, viewed in combination with the above-mentioned
+gradual rise of the bottom of the Southern Ocean toward the Antarctic
+Circle, justify the assumption that the seas included within the
+latter do not exceed 1,500 fathoms in depth, their average depth
+probably falling below this estimate. The extensive formation of ice
+in this region, as well as the numerous indications of land reported
+by the daring sailors who have penetrated so far south, suggest the
+hypothesis of the existence, if not of an Antarctic continent, at
+all events of a considerable extent of land, rising in the mountain
+ranges and volcanoes of Victoria Land to 10,000 and 15,000 feet above
+the level of the sea.
+
+The region inclosed within the Arctic Circle forms an area of
+depression, almost completely surrounded by the land-masses of the
+great eastern and western continents. A shallow strait of less than
+fifty fathoms in depth connects it with the Pacific Ocean, and it is
+separated from the depths of the Atlantic by the plateau between the
+British Islands and Iceland, which rises to within 500 fathoms of the
+sea-surface. Greenland is probably the largest land-mass belonging to
+this basin, and next in importance we have the group of Spitsbergen,
+of Franz Joseph Land, discovered by the Austrian expedition; Nova
+Zembla, the Liakhov Islands, Kellett Land, off Behring Strait,
+discovered by the Americans in 1867; and finally the extensive
+archipelago, a continuation of the American continent.
+
+The few soundings taken within the Arctic Circle leave much to
+conjecture, but we are tolerably safe in stating that the average
+depth of the Arctic basin is probably under 1,000 fathoms. The
+immense plains of Northern Asia and America seem to continue beneath
+the surface of the Arctic Sea, as indicated by the numerous islands
+which skirt the coasts of these continents, and the greatest depths
+to be found inside the Arctic Circle are probably confined to the
+basin situated between Greenland and Norway, Iceland and Spitzbergen.
+
+
+
+
+  CORAL FORMATIONS
+  --CHARLES DARWIN
+
+
+I will give a very brief account of the three great classes of
+coral-reefs: namely, Atolls, Barrier, and Fringing-Reefs, and will
+explain my views on their formation. Almost every voyager who has
+crossed the Pacific has expressed his unbounded astonishment at the
+lagoon islands, or as I shall for the future call them by their
+Indian name of atolls, and has attempted some explanation. Even as
+long ago as the year 1605, Pyrard de Laval well exclaimed, “C’est une
+meruille de voir chacun de ces atollons, enuironné d’un grand banc de
+pierre tout autour, n’y avant point d’artifice humain.” The immensity
+of the ocean, the fury of the breakers, contrasted with the lowness
+of the land and the smoothness of the bright green water within the
+lagoon, can hardly be imagined without having been seen.
+
+The earlier voyagers fancied that the coral-building animals
+instinctively built up their great circles to afford themselves
+protection in the inner parts; but so far is this from the truth that
+those massive kinds, to whose growth on the exposed outer shores the
+very existence of the reef depends, can not live within the lagoon,
+where other delicately branching kinds flourish. Moreover, on this
+view, many species of distinct genera and families are supposed
+to combine for one end; and of such a combination, not a single
+instance can be found in the whole of nature. The theory that has
+been most generally received is, that atolls are based on submarine
+craters; but when we consider the form and size of some, the number,
+proximity, and relative positions of others, this idea loses its
+plausible character: thus, Suadiva atoll is 44 geographical miles
+in diameter in one line, by 34 miles in another line; Rimsky is
+54 by 20 miles across, and it has a strangely sinuous margin; Bow
+atoll is 30 miles long and on an average only 6 in width; Menchicoff
+atoll consists of three atolls united or tied together. This theory,
+moreover, is totally inapplicable to the northern Maldive atoll in
+the Indian Ocean (one of which is 88 miles in length, and between 10
+and 20 in breadth), for they are not bounded like ordinary atolls by
+narrow reefs, but by a vast number of separate little atolls; other
+little atolls rising out of the great central lagoon-like spaces.
+A third and better theory was advanced by Chamisso, who thought
+that from the corals growing more vigorously where exposed to the
+open sea, as undoubtedly is the case, the outer edges would grow up
+from the general foundation before any other part, and that this
+would account for the ring or cup-shaped structure. But we shall
+immediately see that in this, as well as in the crater theory, a most
+important consideration has been overlooked; namely, on what have
+the reef-building corals, which can not live at a great depth, based
+their massive structures?
+
+Numerous soundings were carefully taken by Captain Fitz Roy on the
+steep outside of Keeling atoll, and it was found that within ten
+fathoms the prepared tallow at the bottom of the lead invariably came
+up marked with the impressions of living corals, but as perfectly
+clean as if it had been dropped on a carpet of turf; as the depth
+increased, the impressions became less numerous, but the adhering
+particles of sand more and more numerous, until at last it was
+evident that the bottom consisted of a smooth sandy layer: to carry
+on the analogy of the turf, the blades of grass grew thinner and
+thinner, till at last the soil was so sterile that nothing sprang
+from it. From these observations, confirmed by many others, it
+may be safely inferred that the utmost depth at which corals can
+construct reefs is between 20 and 30 fathoms. Now there are enormous
+areas in the Pacific and Indian Oceans in which every single island
+is of coral formation, and is raised only to that height to which
+the waves can throw up fragments and the winds pile up sand. Thus
+the Radack group of atolls is an irregular square, 520 miles long
+and 240 broad; the Low Archipelago is elliptic-formed, 840 miles
+in its longer, and 420 in its shorter axis: there are other small
+groups and single low islands between these two archipelagoes, making
+a linear space of ocean actually more than 4,000 miles in length,
+in which not one single island rises above the specified height.
+Again, in the Indian Ocean there is a space of ocean 1,500 miles in
+length, including three archipelagoes, in which every island is low
+and of coral formation. From the fact of the reef-building corals
+not living at great depths, it is absolutely certain that throughout
+these vast areas, wherever there is now an atoll, a foundation must
+have originally existed within a depth of from 20 to 30 fathoms from
+the surface. It is improbable in the highest degree that broad,
+lofty, isolated, steep-sided banks of sediment, arranged in groups
+and lines hundreds of leagues in length, could have been deposited in
+the central and profoundest parts of the Pacific and Indian Oceans,
+at an immense distance from any continent, and where the water is
+perfectly limpid. It is equally improbable that the elevatory forces
+should have uplifted, throughout the above vast areas, innumerable
+great rocky banks within 20 to 30 fathoms, or 120 to 180 feet, of
+the surface of the sea, and not one single point above that level;
+for where on the whole face of the globe can we find a single chain
+of mountains, even a few hundred miles in length, with their many
+summits rising within a few feet of a given level, and not one
+pinnacle above it? If then the foundations, whence the atoll-building
+corals sprang, were not formed of sediment, and if they were not
+lifted up to the required level, they must of necessity have subsided
+into it; and this at once solves the difficulty. For as mountain
+after mountain, and island after island, slowly sank beneath the
+water, fresh bases would be successively afforded for the growth of
+the corals. It is impossible here to enter into all the necessary
+details, but I venture to defy any one to explain in any other manner
+how it is possible that numerous islands should be distributed
+throughout vast areas--all the islands being low--all being built of
+corals.
+
+[Illustration: Matterhorn, Valais Alps, Switzerland]
+
+Before explaining how atoll-formed reefs acquire their peculiar
+structure, we must turn to the second great class, namely,
+Barrier-reefs. These either extend in straight lines in front of the
+shores of a continent or of a large island, or they encircle smaller
+islands; in both cases, being separated from the land by a broad
+and rather deep channel of water, analogous to the lagoon within
+an atoll. It is remarkable how little attention has been paid to
+encircling barrier-reefs; yet they are truly wonderful structures.
+
+Encircling barrier-reefs are of all sizes, from three miles to
+no less than forty-four miles in diameter; and that which fronts
+one side, and encircles both ends, of New Caledonia, is 400
+miles long. Each reef includes one, two, or several rocky islands
+of various heights; and in one instance, even as many as twelve
+separate islands. The reef runs at a greater or less distance from
+the included land; in the Society Archipelago generally from one
+to three or four miles; but at Hogoleu the reef is 20 miles on the
+southern side, and 14 miles on the opposite or northern side, from
+the included islands. The depth within the lagoon-channel also varies
+much; from 10 to 30 fathoms may be taken as an average; but at
+Vanikoro there are spaces no less than 56 fathoms or 336 feet deep.
+Internally the reef either slopes gently into the lagoon-channel, or
+ends in a perpendicular wall, sometimes between two and three hundred
+feet under water in height; externally the reef rises, like an atoll,
+with extreme abruptness out of the profound depths of the ocean.
+What can be more singular than these structures? We see an island,
+which may be compared to a castle situated on the summit of a lofty
+submarine mountain, protected by a great wall of coral-rock, always
+steep externally and sometimes internally, with a broad level summit,
+here and there breached by narrow gateways, through which the largest
+ships can enter the wide and deep encircling moat.
+
+As far as the actual reef of coral is concerned, there is not the
+smallest difference, in general size, outline, grouping, and even in
+quite trifling details of structure, between a barrier and an atoll.
+The geographer Balbi has well remarked that an encircled island is an
+atoll with high land rising out of its lagoon; remove the land from
+within, and a perfect atoll is left.
+
+But what has caused these reefs to spring up at such great distances
+from the shores of the included islands? It can not be that the
+corals will not grow close to the land; for the shores within the
+lagoon-channel, when not surrounded by alluvial soil, are often
+fringed by living reefs; and we shall presently see that there is a
+whole class, which I have called fringing-reefs, from their close
+attachment to the shores both of continents and of islands. Again,
+on what have the reef-building corals, which can not live at great
+depths, based their encircling structures? This is a great apparent
+difficulty, analogous to that in the case of atolls, which has
+generally been overlooked.
+
+Are we to suppose that each island is surrounded by a collar-like
+submarine ledge of rock, or by a great bank of sediment, ending
+abruptly where the reef ends? If the sea had formerly eaten deeply
+into the islands, before they were protected by the reefs, thus
+having left a shallow ledge round them under water, the present
+shores would have been invariably bounded by great precipices; but
+this is most rarely the case. Moreover, on this notion, it is not
+possible to explain why the corals should have sprung up, like a
+wall, from the extreme outer margin of the ledge, often leaving a
+broad space of water within, too deep for the growth of corals. The
+accumulation of a wide bank of sediment all round these islands, and
+generally widest where the included islands are smallest, is highly
+improbable, considering their exposed positions in the central and
+deepest parts of the ocean. In the case of the barrier-reef of New
+Caledonia, which extends for 150 miles beyond the northern point of
+the island, in the same straight line with which it fronts the west
+coast, it is hardly possible to believe that a bank of sediment could
+thus have been straightly deposited in front of a lofty island, and
+so far beyond its termination in the open sea. Finally, if we look
+to other oceanic islands of about the same height and of similar
+geological constitution, but not encircled by coral-reefs, we may
+in vain search for so trifling a circumambient depth as 30 fathoms,
+except quite near to their shores; for usually land that rises
+abruptly out of water, as do most of the encircled and non-encircled
+oceanic islands, plunges abruptly under it. On what then, I repeat,
+are these barrier-reefs based? Why, with their wide and deep
+moat-like channels, do they stand so far from the included land? We
+shall soon see how easily these difficulties disappear.
+
+We come now to our third class of fringing-reefs, which will require
+a very short notice. Where the land slopes abruptly under water,
+these reefs are only a few yards in width, forming a mere ribbon or
+fringe round the shores: where the land slopes gently under the water
+the reef extends further, sometimes even as much as a mile from the
+land; but in such cases the soundings outside the reef always show
+that the submarine prolongation of the land is gently inclined. In
+fact, the reefs extend only to that distance from the shore at which
+a foundation within the requisite depth from 20 to 30 fathoms is
+found. As far as the actual reef is concerned, there is no essential
+difference between it and that forming a barrier or an atoll: it is,
+however, generally of less width, and consequently few islets have
+been formed on it. From the corals growing more vigorously on the
+outside, and from the noxious effect of the sediment washed inward,
+the outer edge of the reef is the highest part, and between it and
+the land there is generally a shallow sandy channel a few feet in
+depth. Where banks of sediment have accumulated near to the surface,
+as in parts of the West Indies, they sometimes become fringed with
+corals, and hence in some degree resemble lagoon-islands or atolls;
+in the same manner as fringing-reefs, surrounding gently sloping
+islands, in some degree resemble barrier-reefs.
+
+No theory on the formation of coral-reefs can be considered
+satisfactory which does not include the three great classes. We
+have seen that we are driven to believe in the subsidence of those
+vast areas, interspersed with low islands, of which not one rises
+above the height to which the wind and waves can throw up matter,
+and yet are constructed by animals requiring a foundation, and that
+foundation to lie at no great depth. Let us then take an island
+surrounded by fringing-reefs, which offer no difficulty in their
+structure; and let this island with its reef slowly subside. Now
+as the island sinks down, either a few feet at a time or quite
+insensibly, we may safely infer, from what is known of the conditions
+favorable to the growth of coral, that the living masses, bathed by
+the surf on the margin of the reef, will soon regain the surface.
+The water, however, will encroach little by little on the shore,
+the island becoming lower and smaller and the space between the
+inner edge of the reef and the beach proportionally broader. Coral
+islets are supposed to have been formed on the reef; and a ship
+is anchored in the lagoon-channel. This channel will be more or
+less deep, according to the rate of subsidence, to the amount of
+sediment accumulated in it, and to the growth of the delicately
+branched corals which can live there. We can now see why encircling
+barrier-reefs stand so far from the shores which they front. We can
+also perceive, that a line drawn perpendicularly down from the outer
+edge of the new reef, to the foundation of solid rock beneath the
+old fringing-reef, will exceed, by as many feet as there have been
+feet of subsidence, that small limit of depth at which the effective
+corals can live: the little architects having built up their great
+wall-like mass, as the whole sank down, upon a basis formed of other
+corals and their consolidated fragments. Thus the difficulty on this
+head, which appeared so great, disappears.
+
+If, instead of an island, we had taken the shore of a continent
+fringed with reefs, and had imagined it to have subsided, a great
+straight barrier, like that of Australia or New Caledonia, separated
+from the land by a wide and deep channel, would evidently have been
+the result.
+
+As the barrier-reef slowly sinks down, the corals will go on
+vigorously growing upward; but as the island sinks, the water will
+gain inch by inch on the shore--the separate mountains first forming
+separate islands within one great reef--and finally, the last and
+highest pinnacle disappearing. The instant this takes place, a
+perfect atoll is formed: I have said, remove the high land from
+within an encircling barrier-reef, and an atoll is left, and the land
+has been removed.
+
+We can now perceive how it comes that atolls, having sprung from
+encircling barrier-reefs, resemble them in general size, form, in the
+manner in which they are grouped together, and in their arrangement
+in single or double lines; for they may be called rude outline charts
+of the sunken islands over which they stand. We can further see how
+it arises that the atolls in the Pacific and Indian Oceans extend in
+lines parallel to the generally prevailing strike of the high islands
+and great coast-lines of those oceans. I venture, therefore, to
+affirm that, on the theory of the upward growth of the corals during
+the sinking of the land, all the leading features in those wonderful
+structures, the lagoon-islands or atolls, which have so long excited
+the attention of voyagers, as well as in the no less wonderful
+barrier-reefs, whether encircling small islands or stretching for
+hundreds of miles along the shores of a continent, are simply
+explained.
+
+It may be asked whether I can offer any direct evidence of the
+subsidence of barrier-reefs or atolls; but it must be borne in mind
+how difficult it must ever be to detect a movement the tendency of
+which is to hide under water the part affected. Nevertheless, at
+Keeling atoll I observed on all sides of the lagoon old cocoanut
+trees undermined and falling; and in one place the foundation-posts
+of a shed, which the inhabitants asserted had stood seven years
+before just above high-water mark, but now was daily washed by
+every tide: on inquiry I found that three earthquakes, one of them
+severe, had been felt here during the last ten years. At Vanikoro
+the lagoon-channel is remarkably deep, scarcely any alluvial soil
+has accumulated at the foot of the lofty included mountains, and
+remarkably few islets have been formed by the heaping of fragments
+and sand on the wall-like barrier-reef; these facts, and some
+analogous ones, led me to believe that this island must lately have
+subsided and the reef grown upward: here again earthquakes are
+frequent and very severe. In the Society Archipelago, on the other
+hand, where the lagoon-channels are almost choked up, where much low
+alluvial land has accumulated, and where in some cases long islets
+have been formed on the barrier-reefs--facts all showing that the
+islands have not very lately subsided--only feeble shocks are most
+rarely felt. In these coral formations, where the land and water
+seem struggling for mastery, it must be ever difficult to decide
+between the effects of a change in the set of the tides and of a
+slight subsidence: that many of these reefs and atolls are subject
+to changes of some kind is certain; on some atolls the islets appear
+to have increased greatly within a late period; on others they have
+been partially or wholly washed away. The inhabitants of parts of the
+Maldive Archipelago know the date of the first formation of some
+islets; in other parts the corals are now flourishing on water-washed
+reefs, where holes made for graves attest the former existence of
+inhabited land. It is difficult to believe in frequent changes in the
+tidal currents of an open ocean; whereas we have, in the earthquakes
+recorded by the natives on some atolls and in the great fissures
+observed on other atolls, plain evidence of changes and disturbances
+in progress in the subterranean regions.
+
+Not only the grand features in the structure of barrier-reefs and
+of atolls, and of their likeness to each other in form, size, and
+other characters, are explained on the theory of subsidence--which
+theory we are independently forced to admit in the very areas in
+question, from the necessity of finding bases for the corals within
+the requisite depth--but many details in structure and exceptional
+cases can thus also be simply explained. I will give only a few
+instances. In barrier-reefs it has long been remarked with surprise
+that the passages through the reef exactly face valleys in the
+included land, even in cases where the reef is separated from the
+land by a lagoon-channel so wide and so much deeper than the actual
+passage itself that it seems hardly possible that the very small
+quantity of water or sediment brought down could injure the corals
+on the reef. Now, every reef of the fringing class is breached by
+a narrow gateway in front of the smallest rivulet, even if dry
+during the greater part of the year, for the mud, sand, or gravel,
+occasionally washed down, kills the corals on which it is deposited.
+Consequently, when an island thus fringed subsides, though most of
+the narrow gateways will probably become closed by the outward and
+upward growth of the corals, yet any that are not closed (and some
+must always be kept open by the sediment and impure water flowing out
+of the lagoon-channel) will still continue to front exactly the upper
+parts of those valleys at the mouths of which the original basal
+fringing-reef was breached.
+
+We can easily see how an island fronted only on one side, or on
+one side with one end or both ends encircled by barrier-reefs,
+might after long-continued subsidence be converted either into a
+single wall-like reef, or into an atoll with a great straight spur
+projecting from it, or into two or three atolls tied together by
+straight reefs--all of which exceptional cases actually occur. As the
+reef-building corals require food, are preyed upon by other animals,
+are killed by sediment, can not adhere to a loose bottom, and may be
+easily carried down to a depth whence they can not spring up again,
+we need feel no surprise at the reefs both of atolls and barriers
+becoming in parts imperfect. The great barrier of New Caledonia
+is thus imperfect and broken in many parts; hence, after long
+subsidence, this great reef would not produce one great atoll 400
+miles in length, but a chain or archipelago of atolls, of very nearly
+the same dimensions with those in the Maldive Archipelago. Moreover,
+in an atoll once breached on opposite sides, from the likelihood of
+the oceanic and tidal currents passing straight through the breaches,
+it is extremely improbable that the corals, especially during
+continued subsidence, would ever be able again to unite the rims: if
+they did not, as the whole sank downward one atoll would be divided
+into two or more. In the Maldive Archipelago there are distinct
+atolls so related to each other in position, and separated by
+channels either unfathomable or very deep (the channel between Ross
+and Ari atolls is 150 fathoms, and that between the north and south
+Nillandoo atolls is 200 fathoms in depth), that it is impossible to
+look at a map of them without believing that they were once more
+intimately related. And in this same archipelago, Mahlos-Mahdoo atoll
+is divided by a bifurcating channel from 100 to 132 fathoms in depth,
+in such a manner that it is scarcely possible to say whether it ought
+strictly to be called three separate atolls or one great atoll not
+yet finally divided.
+
+I will not enter on many more details; but I must remark that the
+curious structure of the northern Maldive atolls receives (taking
+into consideration the free entrance of the sea through their broken
+margins) a simple explanation in the upward and outward growth of
+the corals, originally based both on small detached reefs in their
+lagoons, such as occur in common atolls, and on broken portions of
+the linear marginal reef, such as bounds every atoll of the ordinary
+form. I can not refrain from once again remarking on the singularity
+of these complex structures--a great sandy and generally concave disk
+rises abruptly from the unfathomable ocean, with its central expanse
+studded, and its edge symmetrically bordered with oval basins of
+coral-rock just lipping the surface of the sea, sometimes clothed
+with vegetation, and each containing a lake of clear water!
+
+One more point in detail: as in two neighboring archipelagoes
+corals flourish in one and not in the other, and as so many
+conditions before enumerated must affect their existence, it would
+be an inexplicable fact if, during the changes to which earth,
+air, and water are subjected, the reef-building corals were to
+keep alive for perpetuity on any one spot or area. And as by our
+theory the areas including atolls and barrier-reefs are subsiding,
+we ought occasionally to find reefs both dead and submerged. In
+all reefs, owing to the sediment being washed out of the lagoon
+or lagoon-channel to leeward, that side is least favorable to the
+long-continued vigorous growth of the corals; hence dead portions of
+reef not infrequently occur on the leeward side; and these, though
+still retaining their proper wall-like form, are now in several
+instances sunk several fathoms beneath the surface. The Chagos group
+appears from some cause, possibly from the subsidence having been
+too rapid, at present to be much less favorably circumstanced for
+the growth of reefs than formerly: one atoll has a portion of its
+marginal reef, nine miles in length, dead and submerged; a second
+has only a few quite small living points which rise to the surface;
+a third and fourth are entirely dead and submerged; a fifth is a
+mere wreck, with its structure almost obliterated. It is remarkable
+that in all these cases the dead reefs and portions of reefs lie at
+nearly the same depth; namely, from six to eight fathoms beneath the
+surface, as if they had been carried down by one uniform movement.
+One of these “half-drowned atolls,” so called by Captain Scoresby (to
+whom I am indebted for much invaluable information), is of vast size;
+namely, ninety nautical miles across in one direction and seventy
+miles in another line; and is in many respects eminently curious. As
+by our theory it follows that new atolls will generally be formed
+in each new area of subsidence, two weighty objections might have
+been raised; namely, that atolls must be increasing indefinitely in
+number; and, secondly, that in old areas of subsidence each separate
+atoll must be increasing indefinitely in thickness, if proofs of
+their occasional destruction could not have been adduced. Thus have
+we traced the history of these great rings of coral-rock, from their
+first origin through their normal changes, and through the occasional
+accidents of their existence, to their death and final obliteration.
+
+Authors have noticed with surprise that, although atolls are the
+commonest coral structures throughout some enormous oceanic tracts,
+they are entirely absent in other seas, as in the West Indies: we
+can now at once perceive the cause, for where there has not been
+subsidence, atolls can not have been formed; and in the case of the
+West Indies and parts of the East Indies, these tracts are known
+to have been rising within the recent period. The larger areas are
+all elongated; and there is a degree of rude alternation, as if
+the rising of one had balanced the sinking of the other. Taking
+into consideration the proofs of recent elevation both on the
+fringed coasts and on some others (for instance, in South America)
+where there are no reefs, we are led to conclude that the great
+continents are for the most part rising areas; and from the nature
+of the coral-reefs, that the central parts of the great oceans are
+sinking areas. The East Indian archipelago, the most broken land in
+the world, is in most parts an area of elevation, but surrounded
+and penetrated, probably in more lines than one, by narrow areas of
+subsidence.
+
+Bearing in mind the statements made with respect to the upraised
+organic remains, we must feel astonished at the vastness of the areas
+which have suffered changes in level either downward or upward,
+within a period not geologically remote. It would appear, also,
+that the elevatory and subsiding movements follow nearly the same
+laws. Throughout the spaces interspersed with atolls, where not a
+single peak of high land has been left above the level of the sea,
+the sinking must have been immense in amount. The sinking, moreover,
+whether continuous, or recurrent with intervals sufficiently long for
+the corals again to bring up their living edifices to the surface,
+must necessarily have been extremely slow. This conclusion is
+probably the most important one which can be deduced from the study
+of coral formations; and it is one which it is difficult to imagine
+how otherwise could ever have been arrived at. Nor can I quite pass
+over the probability of the former existence of large archipelagoes
+of lofty islands, where now only rings of coral-rock scarcely break
+the open expanse of the sea, throwing some light on the distribution
+of the inhabitants of the other high islands, now left standing so
+immensely remote from each other in the midst of the great oceans.
+The reef-constructing corals have indeed reared and preserved
+wonderful memorials of the subterranean oscillations of level; we see
+in each barrier-reef a proof that the land has there subsided, and in
+each atoll a monument over an island now lost. We may thus, like unto
+a geologist who had lived his ten thousand years and kept a record of
+the passing changes, gain some insight into the great system by which
+the surface of this globe has been broken up, and land and water
+interchanged.
+
+
+
+
+  MAGNITUDE AND COLOR OF THE SEA
+  --G. HARTWIG
+
+
+Of all the gods that divide the empire of the earth, Neptune rules
+over the widest realms. If a giant hand were to uproot the Andes and
+cast them into the sea, they would be engulfed in the abyss, and
+scarcely raise the general level of the waters. The South American
+Pampas, bounded on the north by tropical palm-trees, and on the south
+by wintry firs, are no doubt of magnificent dimensions, yet these
+vast deserts seem insignificant when compared with the boundless
+plains of earth-encircling ocean. Nay! a whole continent, even
+America or Asia, appears small against the immensity of the sea,
+which covers with its rolling waves nearly three-fourths of the
+entire surface of the globe.
+
+The length of all the coasts which form the boundary between sea and
+land can only be roughly estimated, for who has accurately measured
+the numberless windings of so many shores? The entire coast-line of
+deeply indented Europe and her larger isles measures about 21,600
+miles, equal to the circumference of the earth; while the shores of
+compact Africa extend to a length of only 14,000 miles. The coasts of
+America measure about 45,000 miles, those of Asia 40,000, while those
+of Australia and Polynesia may safely be estimated at 16,000. Thus
+the entire coast-line of the globe amounts to about 136,000 miles,
+which it would take the best pedestrian to traverse from end to end.
+
+How different is the aspect of these shores, along which the
+ever-restless sea continually rises or falls! Here steep rock-walls
+tower up from the deep, while there a low sandy beach extends its
+flat profile as far as the eye can reach. While some coasts are
+scorched by the vertical sunbeam, others are perpetually blocked up
+with ice. Here the safe harbor bids welcome to the weather-beaten
+sailor, the lighthouse greets him from afar with friendly ray; the
+experienced pilot hastens to guide him to the port, and all along the
+smiling margin of the land rise the peaceful dwellings of civilized
+man. There, on the contrary, the roaring breakers burst upon the
+shore of some dreary wilderness, the domain of the savage or the
+brute. What a wonderful variety of scenes unrolls itself before
+our fancy as it roams along the coasts of ocean from zone to zone!
+What changes, as it wanders from the palm-girt coral island of the
+tropical seas to the melancholy strands where, verging toward the
+poles, all vegetable life expires! And how magnificently grand does
+the idea of ocean swell out in our imagination, when we consider that
+its various shores witness at one and the same time the rising and
+setting of the sun, the darkness of night and the full blaze of day,
+the rigor of winter and the smiling cheerfulness of spring!
+
+The sea is not colorless; its crystal mirror not only reflects the
+bright sky or the passing cloud, but naturally possesses a pure
+bluish tint, which is only rendered visible to the eye when the light
+penetrates through a stratum of water of considerable depth. In the
+Gulf of Naples, we find the inherent color of the water exhibited to
+us by Nature on a most magnificent scale. The splendid “Azure Cave,”
+at Capri, might almost be said to have been created for the purpose.
+
+All profound and clear seas are more or less of a deep blue color,
+while, according to seamen, a green color indicates soundings. The
+bright blue of the Mediterranean, so often vaunted by poets, is found
+over all the deep pure ocean, not only in tropical and temperate
+zones, but also in the regions of eternal frost. Scoresby speaks with
+enthusiasm of the splendid blue of the Greenland seas, and all along
+the great ice-barrier which under 77° S. lat. obstructed the progress
+of Sir James Ross toward the pole, that illustrious navigator found
+the waters of as deep a blue as in the classical Mediterranean. The
+North Sea is green, partly from its water not being so clear, and
+partly from the reflection of its sandy bottom mixing with the
+essentially blue tint of the water. In the Bay of Loanga the sea has
+the color of blood, and Captain Tuckey discovered that this results
+from the reflection of the red ground-soil.
+
+But the essential color of the sea undergoes much more frequent
+changes over large spaces, from enormous masses of minute _algæ_,
+and countless hosts of small sea-worms, floating or swimming on its
+surface.
+
+“A few days after leaving Bahia,” says Mr. Darwin, “not far from
+the Abrolhos islets, the whole surface of the water, as it appeared
+under a weak lens, seemed as if covered by bits of hay with their
+ends jagged. Each bundle consisted of from twenty to sixty filaments,
+divided at regular intervals by transverse septa, containing a
+brownish-green flocculent matter. The ship passed several bands
+of them, one of which was about ten yards wide, and, judging from
+the mud-like color of the water, at least two and a half miles
+long. Similar masses of floating vegetable matter are a very common
+appearance near Australia. During two days preceding our arrival at
+the Keeling Islands, I saw in many parts masses of flocculent matter
+of a brownish-green color floating in the ocean. They were from half
+to three inches square, and consisted of two kinds of microscopical
+confervæ. Minute cylindrical bodies, conical at each extremity, were
+involved in large numbers in a mass of fine threads.”
+
+“On the coast of Chili,” says the same author, “a few leagues north
+of Concepcion, the _Beagle_ one day passed through great bands of
+muddy water; and again a degree south of Valparaiso, the same
+appearance was still more extensive. Mr. Sullivan, having drawn up
+some water in a glass, distinguished by the aid of a lens moving
+points. The water was slightly stained, as if by red dust, and after
+leaving it for some time quiet a cloud collected at the bottom.
+With a slightly magnifying lens, small hyaline points could be
+seen darting about with great rapidity and frequently exploding.
+Examined with a much higher power, their shape was found to be oval,
+and contracted by a ring round the middle, from which line curved
+little setæ proceeded on all sides, and these were the organs of
+motion. Their minuteness was such that they were individually quite
+invisible to the naked eye, each covering a space equal only to the
+one-thousandth of an inch, and their number was infinite, for the
+smallest drop of water contained very many. In one day we passed
+through two spaces of water thus stained, one of which alone must
+have extended over several square miles. The color of the water was
+like that of a river which has flowed through a red clay district,
+and a strictly defined line separated the red stream from the blue
+water.”
+
+In the neighborhood of Callao, the Pacific has an olive-green color,
+owing to a greenish matter which is also found at the bottom of the
+sea in a depth of 800 feet. In its natural state it has no smell, but
+when cast on the fire it emits the odor of burned animal substances.
+
+Near Cape Palmas, on the coast of Guinea, Captain Tuckey’s ship
+seemed to sail through milk, a phenomenon which was owing to an
+immense number of little white animals swimming on the surface and
+concealing the natural tint of the water.
+
+The peculiar coloring of the Red Sea, from which it has derived its
+name, is owing to the presence of a microscopic alga, _sui generis_,
+floating at the surface of the sea and even less remarkable for its
+beautiful red color than for its prodigious fecundity.
+
+I could add many more examples, where, either from minute _algæ_, or
+from small animals, the deep blue sea suddenly appeared in stripes
+of white, yellow, blue, brown, orange, or red. For fear, however,
+of tiring the reader’s patience, I shall merely mention the _olive
+green_ water which covers a considerable part of the Greenland seas.
+It is found between 74° and 80° N. lat., but its position varies with
+the currents, often forming isolated stripes, and sometimes spreading
+over two or three degrees of latitude. Small yellowish Medusæ, of
+from one-thirtieth to one-twentieth of an inch in diameter, are the
+principal agents that change the pure ultramarine of the Arctic Ocean
+into a muddy green.
+
+When the sea is perfectly clear and transparent, it allows the
+eye to distinguish objects at a very great depth. Near Mindora,
+in the Indian Ocean, the spotted corals are plainly visible under
+twenty-five fathoms of water.
+
+The crystalline clearness of the Caribbean Sea excited the admiration
+of Columbus. “In passing over these splendidly adorned grounds,” says
+Schöpf, “where marine life shows itself in an endless variety of
+forms, the boat, suspended over the purest crystal, seems to float in
+the air, so that a person unaccustomed to the scene easily becomes
+giddy. On the clear sandy bottom appear thousands of sea-stars,
+sea-urchins, mollusks, and fishes of a brilliancy of color unknown
+in our temperate seas. Fiery red, intense blue, lively green, and
+golden yellow perpetually vary; the spectator floats over groves of
+sea-plants, gorgonias, corals, alcyoniums, flabellums, and sponges
+that afford no less delight to the eye, and are no less gently
+agitated by the heaving waters, than the most beautiful garden on
+earth when a gentle breeze passes through the waving boughs.”
+
+
+
+
+  TIDAL ACTION
+  --SIR ROBERT S. BALL
+
+
+Every one is familiar with the fact that the moon raises tides on the
+earth; these tides ebb and flow along our coasts, and in virtue of
+them the satellite exercises a certain control on the movements of
+our globe. If the moon had liquid oceans on its surface there can not
+be a doubt that the attraction of the earth would generate tides in
+the oceans on the moon just as the attraction of the moon generates
+tides in the oceans of the earth. But there would be a fundamental
+difference between the two cases; the shores of the lunar seas would
+be periodically inundated by tides far vaster than any tides which
+the moon can create on the earth. But it may be said that as the
+moon contains no water it seems idle to talk of the tides that might
+have been produced in oceans if they had existed. It is no doubt
+true that the moon contains no visible liquid water on its surface
+at the present time; it is, however, by no means certain that our
+satellite was always void of water; it is not at all impossible
+that spreading oceans may have once occupied a large part of that
+surface now an arid wilderness. The waters from those oceans have
+vanished, but the basins they presumably filled are still left as
+characteristic features on our satellite. For our present argument,
+however, it is really not material that the moon should ever have had
+oceans as we understand them. The water at those remote periods must
+have been suspended in the form of vapor around the more solid parts
+of the glowing globe. But tides can be manifested in other liquids
+besides that which forms our seas. In fact if the basins of our great
+oceans were filled with oil or with mercury, or even with molten iron
+instead of water, the moon would still cause tides to ebb and flow,
+no matter what the material might be, so long as it possessed to some
+extent the properties of a liquid. It need not be a perfect liquid,
+for any material which is in some degree viscous, like honey or
+treacle, would still respond to tidal influence, though not, it may
+be well believed, with the same alacrity and freedom of movement as
+would a fluid of a more perfect character. In the molten moon itself,
+throughout the very body of our satellite, the tidal influence of the
+earth must have been experienced in these primitive ages.
+
+There can not be a doubt that in ancient days when the moon was
+sufficiently fluid, the action of the tides tended without ceasing to
+the establishment of such an adjustment between the rotation of the
+moon around its axis and the revolution of the moon around the earth,
+that the two should be brought to have equal periods. Friction would
+incessantly operate until this adjustment had been effected, and
+owing to the preponderating mass of the earth such strenuous tides
+must have been evoked in the moon that our satellite was brought
+under tidal control with comparative facility. Hence it arose that
+in those early days the habit of bending the same face incessantly
+toward the earth around which it revolved was established on our
+satellite.
+
+Time passed on, the moon gradually dispensed its excessive heat by
+radiation into space, and it gradually became transformed from a
+molten globe to a globe with a solid crust. It may be that the water
+was condensed from vapor and then collected together into oceans on
+the newly formed surface; if so, these oceans would not have any
+ebbing tide or flowing tide, for it would be constant high tide at
+some places and constant low tide at others. Such a state of things
+would at all events endure so long as the adjustment of equality
+between the moon’s rotation and its revolution continued. In fact,
+should any departure from this adjustment have manifested itself,
+corresponding tides would have begun to throb in the lunar oceans,
+and their tendency would be to restore the adjustment which was
+disturbed. This arrangement between the two movements was necessarily
+stable when tidal control was always at hand to check any tendency to
+depart from it.
+
+It may be that the moon has now cooled so thoroughly that not only
+is it hard and congealed on the exterior as we see, but it seems
+highly probable that the heat may have so entirely forsaken even
+the interior that there is no longer any fluid in the globe of our
+satellite to respond to tidal impulse. There is, therefore, in all
+probability, no longer any actual tidal control. On the other hand,
+however, there is nothing to disturb the adjustment. It was, as
+we have seen, caused by the tides which have done their work; the
+consequences of that work are still exhibited in the constant face of
+the moon, which, now that it has been brought about, seems likely to
+exist permanently as a stable adaptation of the movement.
+
+The tendency of the tides on a tide-disturbed globe is to adjust the
+movements of that globe in such a way that the tides shall no longer
+ebb or flow, but that permanent high tide shall be established in
+some places and permanent low tide in others. If the rotation of the
+body be not fast enough the tide will pull the body round in order to
+effect this object. If the rotation of the body be too rapid, then
+the influence of the tide will tend to check the movement and bring
+down the speed of rotation until the desired adjustment is obtained.
+At present the earth is spinning too fast to permit the high tides to
+remain at permanent localities, and consequently tides are applied
+with the effect of checking the rotation. The earth is, however, so
+vast, and the tides generated by so small a body as the moon are
+relatively so impotent, that their effects in reducing the speed of
+the earth’s rotation are insignificant. Nevertheless, small though
+they are, they unquestionably exist, and there can not be a doubt
+that to some extent the earth is affected by the unremitting action
+of the tides; the consequence is that the rapidity with which the
+earth rotates upon its axis is gradually declining.
+
+One result of this can be stated in a very simple manner. The
+length of the day must be increasing. It is true that this gradual
+stretching of the day is very slow; it is indeed quite inappreciable
+in so far as our ordinary use of the day as a measure of time is
+concerned. The alteration almost eludes any means of measurement
+at our disposal. Even in a thousand years the change is so small
+that the increase in the length of the day is only a fraction of a
+second. We can doubtless afford to disregard so trifling a variation
+in our standard of time so far as the period contemplated in mere
+human affairs is concerned. In fact the change is absolutely devoid
+of significance within such periods as are contemplated since the
+erection of the Pyramids, or indeed since any other human monument
+has been reared. We must not, however, conclude that the change in
+the length of the day has no significance in earth history.
+
+The significance of the gradual elongation of the day by the tides
+arises from the circumstance that the change always takes place in
+one direction. In this form of effect the tide differs from other
+more familiar astronomical phenomena which sometimes advance in one
+direction and then after the lapse of suitable periods return in
+the opposite direction, and thus restore again the initial state of
+things. But the alteration of the length of the day is not of this
+character, it is not periodic, its motion is never reversed, is never
+even arrested. Only one condition is therefore necessary to enable
+it to obtain tremendous dimensions, and that is sufficient time in
+which it can operate.
+
+There are many lines of reasoning which show the extreme antiquity
+of our globe: the disclosures of geology are specially instructive
+on this head. Think, for instance, of that mighty reptile the
+Atlantosaurus, which once roamed over the regions now known as
+Colorado. The bones of this vast creature indicate an animal
+surpassing in proportions the greatest elephant ever known. No one
+can count the æons of years that have elapsed since the Atlantosaurus
+whose bones are now to be seen in the museum at Yale University
+breathed its last. A still more striking conception of time than
+even the antiquity of this creature affords is derived from the
+consideration that his mighty form was itself the product of a long
+and immeasurable line of ancestry, extending to a depth in the remote
+past far beyond the limits of computation. I have mentioned this
+illustration of the antiquity of the earth for the purpose of showing
+the ample allowance of time that is available for tides to accomplish
+great work in earlier stages of our globe’s history.
+
+As the evidence of the earth’s crust proves that our globe has
+lasted for incalculable ages, it becomes of interest to think how
+far the gradual elongation of the day may have attained significant
+proportions since very early time. It may be that even in a thousand
+years the effect of the tides is not sufficient to alter the length
+of the day by so much as a single second. But the effect may be
+very appreciable or even large in a million years, or ten million
+years. We have the best reasons for knowing that in intervals of time
+comparable with those I have mentioned, the change in the length of
+the day may have amounted not merely to seconds or minutes, but even
+to hours. Looking into the remote past, there was a time at which
+this globe spun round in twenty-three hours instead of twenty-four;
+at a still earlier period the rate must have been twenty hours, and
+the further we look back the more and more rapidly does the earth
+appear to be spinning. At last, as we strain our gaze to some epoch
+so excessively remote that it must have been long anterior to those
+changes which geology recognizes, we see that our globe was spinning
+round in a period of six hours or five hours, or possibly even less.
+Here then is a lesson which the tides have taught us: they have shown
+that if the causes at present in operation have subsisted without
+interruption for a sufficiently long period in the past, the day must
+have gradually grown to its present length from an initial condition
+in which the earth seems to have spun round about four times as
+quickly as it does at present.
+
+We should, however, receive a very inadequate impression of what
+tides are able to accomplish if we merely contemplated this change in
+the length of the day, striking and significant though it doubtless
+is. The student of natural philosophy is well aware that there is
+no action without a corresponding reaction, and it is instructive
+to examine in this case the form which the reaction assumes. Our
+reasoning has been founded on the supposition that it is the
+attraction of the moon on the waters of our globe that gives rise to
+the tides. It is, therefore, the influence of the moon which checks
+the speed of the earth’s rotation and adds to the length of the day.
+
+As the moon acts in this fashion on the earth, so, by the general
+law that I have mentioned, the earth reacts upon the moon. The form
+which this reaction assumes expresses itself in a tendency to allow
+the moon gradually to move further and further away from the earth
+than the earth’s attraction would permit if our globe were a solid
+mass void of all liquid capable of being distracted by tides. It
+is, therefore, certain that the distance of the moon, which is at
+present about two hundred and forty thousand miles, must be gradually
+increasing; but we need not look for any appreciable change in the
+moon’s distance arising from this cause when only an interval of
+a few centuries is considered. We need not expect to measure the
+difference due to tides between the size of the moon’s orbit this
+month and the size of the orbit last month. In fact, there are so
+many periodic causes of change in the dimensions of the moon’s orbit
+that it becomes impossible to detect the tidal influence even in
+the course of centuries. Here, again, we have to remember that in
+dealing with the history of our earth we are to consider not merely
+the thousands of years that include the human period, not merely the
+millions of years that are required by the necessities of geology,
+but also those unknown periods anterior to geological phenomena to
+which we have already referred.
+
+In the course of such vast ages the reaction of the earth on
+the moon’s orbit has not only become perceptible, it has become
+conspicuous; it has not only become conspicuous, but it has become
+the chief determining agent in making the moon’s orbit as we find it
+at the present day. We have seen that as we look into the past the
+length of the day seems ever shorter and shorter; and concurrent with
+this decline in the day is the diminution in the moon’s distance from
+the earth. There was a time when the moon, instead of revolving at
+a distance of two hundred and forty thousand miles, as it does at
+present, revolved at a distance of only two hundred thousand miles.
+As we think of epochs still earlier we discern the moon ever closer
+and closer to the earth, until at last, at that critical time in
+the history of the earth-moon system, when the earth was quickly
+revolving in a period of a few hours, our satellite seems to have
+been quite close to the earth; in fact, the two bodies were almost in
+contact
+
+The study of the tides has therefore conducted us to the knowledge
+of a remarkable configuration exhibited in the primitive earth-moon
+system. The earth was then spinning round rapidly in a day which
+was only a few hours long, while close to the earth, or almost in
+contact with it, the moon coursed around our globe, the period of
+its revolution being shorter to such an extent that the satellite
+completed its circuit in the same time as the earth required for one
+turn round its axis.
+
+We must remember that the materials destined to form the pair of
+allied planets did not then form two solid bodies as they do at
+present; they were both, in all probability, incandescent masses
+glowing with fervor, and soft, if not actually molten, or incoherent,
+or even gaseous. These aggregations were close together, and one of
+them was whirling around the other in a period of a few hours, the
+duration of that period being equal to the time in which the larger
+mass revolved on its axis. In fact, the two objects, even though
+distinct, seem to have revolved the one around the other as if they
+had been bound together by rigid bonds. The rapid rotation with which
+they were animated suggests a cause for this state of things. It is
+well known that a fly-wheel, when driven at an unduly high speed,
+is liable to break asunder in consequence of its rapid motion. If a
+grindstone be urged around with excessive velocity the force tending
+to rend the stone into fragments may overcome its cohesion, and it
+will fly into pieces, often projected with such violence that fearful
+accidents have been the consequence.
+
+Viewing the earth as a rotating body, it must be subject to the law
+that there is a speed which can not be exceeded with safety. With
+the present period of rotation of once in every twenty-four hours
+the tendency to disruption is but small and consequently the earth
+retains its integrity, though no doubt the protuberance at the
+equator is the result of the accommodation of the shape of the globe
+to the circumstances attending its revolution. But let us suppose
+that the length of the day was greatly diminished, or, what comes to
+the same thing, that the speed with which the earth rotates on its
+axis was greatly increased; it is then conceivable that the tension
+thus arising might be too great for the coherence of the material
+to withstand. We believe that the earth could turn round with double
+the speed that it has at present before this tension approached the
+point at which disruption would ensue. But supposing the day were to
+be so much shortened that the period of rotation was only a very few
+hours instead of twenty-four, there is then good reason to know that
+the tension in the earth arising from this rapid rotation would be so
+great that a rupture of the globe would be imminent.
+
+Provided with this conception, let us think of the initial stage
+when the moon was quite close to the earth. Our globe was then, as
+we know, spinning round so rapidly that its materials were almost on
+the point of breaking up in consequence of the strain produced by
+the rotation. It is interesting to note that the tidal action of the
+sun would also conduce to the rupture of our globe in the critical
+circumstances we have supposed. It seems hardly possible to doubt
+that such a separation of the glowing mass did actually take place, a
+small fragment was discarded, and gradually drew itself by the mutual
+attraction of its particles into a globular form and thus became the
+moon.
+
+We have seen that at the present moment the day is becoming gradually
+longer and the moon is steadily receding further and further from the
+earth. At present these changes take place with extreme slowness,
+but in the primitive periods of which we have already spoken, the
+changes in the length of the day, and the changes in the distance
+of the moon, proceeded at a rate far more rapid than at present.
+As the moon has receded further from the earth its efficiency as a
+tide-producer has declined, and consequently the rate at which the
+consequences of tidal action have proceeded is continually lessening.
+It must therefore be expected that the progress of tidal evolution
+in the future will be ever getting slower and slower, so that the
+periods of time required for the further development of the phenomena
+far exceed those which have elapsed in the course of the history
+already given. We can, however, foreshadow what is to happen in the
+following manner. The length of the day will slowly increase; and
+we can indicate a state of things in the excessively remote future
+toward which it may be said the system is tending. The day will grow
+until it becomes not merely twenty-five or twenty-six hours, but
+until it becomes as long as two or three of our present days. In
+fact, as we stretch our imagination through ages so inconceivable
+that I forbear to specify any figures which might characterize them,
+we seem to discern that the length of the day may go on ever getting
+longer and longer until at last a stage is reached when the day is
+about fifty or sixty times as long as our present day.
+
+All this time, in accordance with the general law of action and
+reaction, the moon must be gradually retreating. As the orbit of
+the moon is gradually enlarging, the time that the moon takes to
+revolve around the earth must be continually on the increase; from
+the present month of twenty-seven days the length of the month will
+gradually augment as the ages roll by until at last when the moon
+has reached a certain distance the period of its rotation will have
+become double what it is at present, or indeed rather more than
+double, and we shall have the day and the month equal, each being
+about fourteen hundred hours long. When this state of things is
+reached, the earth will always turn the same face toward the moon,
+just as the moon at present always turns the same face toward the
+earth.
+
+We have already explained how the constant face of the moon can
+be accounted for by the action of tides raised in the moon by the
+attraction of the earth. Owing to the small size of the moon the
+tides have already wrought all that they were capable of doing, and
+have compelled the moon to succumb to the conditions they imposed.
+Owing to the great mass of the earth and the comparatively small
+mass of the moon the tides on the earth raised by the moon have
+required a much longer period wherein to accomplish their effects
+than was the case when the earth raised tides on the moon. But small
+though our satellite may be, yet the tides raised on the earth have
+incessantly tended to wear down the speed of our globe and reduce it
+to conformity with the law that the two bodies shall bear the same
+face toward each other. At present the earth turns round twenty-seven
+times while the moon goes round once, so the tides have still a
+gigantic task to accomplish. With unflagging energy, however, they
+are incessantly engaged at the work, and they are constantly tending
+to bring down the speed of the earth; constantly tending toward that
+ultimate condition of things in which the earth and moon are destined
+to revolve in a period of fourteen hundred hours as if they were
+connected with invisible bonds.
+
+If such a state of things as this were established then it is plain
+that tides would no longer ebb and flow, that is, at least, if we
+exclude from our consideration the intervention of any other body.
+High tides must prevail at some parts of the earth, and low tides at
+other parts, but the position of these tides will remain fixed. Where
+it is high tide it will always be high tide; where it is low tide
+it will always be low tide. When this state of things is reached,
+the moon will be constantly visible in the same part of the sky from
+one half of our globe, while the other half of our globe will never
+be turned toward the moon. In fact, the moon would always appear
+to us in a fixed position as the earth would always appear to be
+if viewed by an observer stationed on the moon. If there were any
+Lunarians whose residence was confined to the opposite side of the
+moon, they could never see this earth at all, while those who lived
+on this side of our satellite would always be able to see the earth
+apparently fixed in the same part of the sky. An observatory located
+at the middle of the moon’s disk, say near the crater Ptolemy, would
+always have the earth in its zenith or very near thereto, while the
+astronomer, let us say, in the Mare Crisium, would always find the
+earth low down near his horizon.
+
+In order to facilitate our reasoning I have assumed that the moon
+is the only tide-producing agent; this is, however, not the case.
+No doubt the ebb and the flow around our coasts is generated mainly
+by the attraction of the moon. It must not, however, be forgotten
+that a portion of the tide is originated by the attraction of the
+sun. These solar tides will still continue to ebb and flow quite
+independently of the lunar tides, so that even if the accommodation
+between the earth and the moon had been completed some further tidal
+disturbance would not be wanting. The effect of the solar tides will
+be to abate still further the velocity with which the earth turns
+round on its axis, and consequently a time must ultimately arrive
+when the length of the day will be longer than the time which the
+moon takes to revolve around our earth.
+
+
+
+
+  THE GULF STREAM
+  --LORD KELVIN
+
+
+I mean by the Gulf Stream that mass of heated water which pours from
+the Strait of Florida across the North Atlantic, and likewise a wider
+but less definite warm current, evidently forming part of the same
+great movement of water, which curves northward to the eastward of
+the West Indian Islands. I am myself inclined, without hesitation,
+to regard this stream as simply the reflux of the equatorial
+current, added to no doubt during its northeasterly course by the
+surface-drift of the anti-trades which follows in the main the same
+direction.
+
+The scope and limit of the Gulf Stream will be better understood if
+we inquire in the first place into its origin and cause. As is well
+known--in two bands, one to the north and the other to the south
+of the equator--the northeast and southeast trade-winds, reduced
+to meridional directions by the eastward frictional impulse of the
+earth’s rotation, drive before them a magnificent surface current of
+hot water 4,000 miles long by 450 miles broad at an average rate of
+thirty miles a day. Off the coast of Africa, near its starting-point
+to the south of the Islands of St. Thomas and Anna Bon this
+“equatorial current” has a speed of forty miles in the twenty-four
+hours, and a temperature of 23° C.
+
+Increasing quickly in bulk, and spreading out more and more on both
+sides of the equator, it flows rapidly due west toward the coast
+of South America. At the eastern point of South America, Cape St.
+Roque, the equatorial current splits into two, and one portion
+trends southward to deflect the isotherms of 21°, 15°.5, 10°, and
+4°.5 C. into loops upon our maps, thus carrying a scrap of comfort
+to the Falkland Islands and Cape Horn; while the northern portion
+follows the northeast coast of South America, gaining continually
+in temperature under the influence of the tropical sun. Its speed
+has now increased to sixty-eight miles in twenty-four hours, and
+by the union with it of the waters of the river Amazon, it rises
+to one hundred miles (6.5 feet in a second), but it soon falls off
+again when it gets into the Caribbean Sea. Flowing slowly through
+the whole length of this sea, it reaches the Gulf of Mexico through
+the Strait of Yucatan, when a part of it sweeps immediately round
+Cuba; but the main stream, “having made the circuit of the Gulf of
+Mexico, passes through the Strait of Florida; thence it issues
+as the ‘Gulf Stream’ in a majestic current upward of thirty miles
+broad, two thousand two hundred feet deep, with an average velocity
+of four miles an hour, and a temperature of 86° Fahr. (30° C.).”
+The hot water pours from the strait with a decided though slight
+northeasterly impulse on account of its great initial velocity. Mr.
+Croll calculates the Gulf Stream as equal to a stream of water fifty
+miles broad and a thousand feet deep flowing at a rate of four miles
+an hour; consequently conveying 5,575,680,000,000 cubic feet of water
+per hour, or 133,816,320,000,000 cubic feet per day. This mass of
+water has a mean temperature of 18° C. as it passes out of the gulf,
+and on its northern journey it is cooled down to 4°.5, thus losing
+heat to the amount of 13°.5 C. The total quantity of heat therefore
+transferred from the equatorial regions per day amounts to something
+like 154,959,300,000,000,000,000 foot-pounds.
+
+This is nearly equal to the whole of the heat received from the
+sun by the Arctic regions, and, reduced by a half to avoid all
+possibility of exaggeration, it is still equal to one-fifth of the
+whole amount received from the sun by the entire area of the North
+Atlantic. The Gulf Stream, as it issues from the Strait of Florida
+and expands into the ocean on its northward course, is probably the
+most glorious natural phenomenon on the face of the earth. The water
+is of a clear crystalline transparency and an intense blue, and long
+after it has passed into the open sea it keeps itself apart, easily
+distinguished by its warmth, its color, and its clearness; and with
+its edges so sharply defined that a ship may have her stem in the
+clear blue stream while her stern is still in the common water of the
+ocean.
+
+Setting aside the wider question of the possibility of a general
+oceanic circulation arising from heat, cold, and evaporation, I
+believe that Captain Maury and Dr. Carpenter are the only authorities
+who of late years have disputed this source of the current which
+we see and can gauge and measure as it passes out of the Strait
+of Florida; for it is scarcely necessary to refer to the earlier
+speculations that it is caused by the Mississippi River, or that it
+flows downward by gravitation from a “head” of water produced by the
+trade-winds in the Caribbean Sea.
+
+Captain Maury writes that “the dynamical force that calls forth the
+Gulf Stream is to be found in the difference as to specific gravity
+of intertropical and polar waters.” “The dynamical forces which are
+expressed by the Gulf Stream may with as much propriety be said to
+reside in those northern waters as in the West India seas: for on
+one side we have the Caribbean Sea and Gulf of Mexico with their
+waters of brine; on the other the great polar basin, the Baltic and
+the North Sea, the two latter with waters which are little more than
+brackish. In one set of these sea-basins the water is heavy; in the
+other it is light. Between them the ocean intervenes; but water is
+bound to seek and to maintain its level; and here, therefore, we
+unmask one of those agents concerned in causing the Gulf Stream. What
+is the power of this agent? Is it greater than that of other agents?
+and how much? We can not say how much; we only know it is one of the
+chief agents concerned. Moreover, speculate as we may as to all the
+agencies concerned in collecting these waters, that have supplied the
+trade-winds with vapor, into the Caribbean Sea, and then in driving
+them across the Atlantic, we are forced to conclude that the salt
+which the trade-wind vapor leaves behind it in the tropics has to be
+conveyed away from the trade-wind region, to be mixed up again in
+due proportion with the other water of the sea--the Baltic Sea and
+the Arctic Ocean included--and that these are some of the waters, at
+least, which we see running off through the Gulf Stream. To convey
+them away is doubtless one of the offices which in the economy of the
+ocean has been assigned to it.”
+
+Dr. Carpenter attributes all the great movements of ocean water to a
+general convective circulation, and of this general circulation he
+regards the Gulf Stream as a peculiarly modified case. Dr. Carpenter
+states that “the Gulf Stream constitutes a peculiar case, modified by
+local conditions,” of “a great general movement of equatorial water
+toward the polar area.” I confess I feel myself compelled to take a
+totally different view. It seems to me that the Gulf Stream is the
+one natural physical phenomenon on the surface of the earth whose
+origin and principal cause, the drift of the trade-winds, can be most
+clearly and easily traced.
+
+The further progress and extension of the Gulf Stream through the
+North Atlantic in relation to influence upon climate has been,
+however, a fruitful source of controversy. The first part of its
+course, after leaving the strait, is sufficiently evident, for its
+water long remains conspicuously different in color and temperature
+from that of the ocean, and a current having a marked effect on
+navigation is long perceptible in the peculiar Gulf Stream water.
+“Narrow at first, it flows round the peninsula of Florida, and, with
+a speed of about 70 or 80 miles, follows the coast at first in a
+due north, afterward in a northeast direction. At the latitude of
+Washington it leaves the North American coast altogether, keeping
+its northeastward course; and to the south of the St. George’s and
+Newfoundland banks it spreads its waters more and more over the
+Atlantic Ocean, as far as the Azores. At these islands a part of it
+turns southward again toward the African coast. The Gulf Stream has,
+so long as its waters are kept together along the American coast, a
+temperature of 26°.6 C.; but, even under north latitude 36°, Sabine
+found it 23°.3 C. at the beginning of December, while the sea-water
+beyond the stream showed only 16°.9 C. Under north latitude 40-41°
+the water is, according to Humboldt, at 22°.5 C. within, and 17°.5 C.
+without the stream.”
+
+Opposite Tortugas, passing along the Cuban coast, the stream is
+unbroken and the current feeble; the temperature at the surface is
+about 26°.7 C. Issuing from the Strait of Bemini the current is
+turned nearly directly northward by the form of the land; a little
+to the north of the strait, the rate is from three to five miles
+an hour. The depth is only 325 fathoms, and the bottom, which in
+the Strait of Florida was a simple slope and counter-slope, is now
+corrugated. The surface temperature is about 26°.5 C., while the
+bottom temperature is 4°.5; so that in the moderate depth of 325
+fathoms the equatorial current above and the polar counter-current
+beneath have room to pass one another, the current from the north
+being evidently tempered considerably by mixture. North of Mosquito
+inlet the stream trends to the eastward of north, and off St.
+Augustine it has a decided set to the eastward. Between St. Augustine
+and Cape Hatteras the set of the stream and the trend of the coast
+differ but little, making 5° of easting in 5° of northing. At
+Hatteras it curves to the northward, and then runs easterly. In the
+latitude of Cape Charles it turns quite to the eastward, having a
+velocity of from a mile to a mile and a half in the hour.
+
+A brief account of one of the sections will best explain the general
+phenomena of the stream off the coast of America. I will take the
+section following a line at right angles to the coast off Sandy Hook.
+From the shore out, for a distance of about 250 miles, the surface
+temperature gradually rises from 21° to 24° C.; at 10 fathoms it
+rises from 19° to 22° C.; and at 20 fathoms it maintains, with a few
+irregularities, a temperature of 19° C. throughout the whole space;
+while at 100, 200, 300, and 400 fathoms it maintains in like manner
+the respective temperatures of 8°.8, 5°.7, 4°.5, and 2°.5 C. This
+space is, therefore, occupied by cold water, and observation has
+sufficiently proved that the low temperature is due to a branch of
+the Labrador current creeping down along the coast in a direction
+opposite to that of the Gulf Stream. In the Strait of Florida this
+cold stream divides--one portion of it passing under the hot Gulf
+Stream water into the Gulf of Mexico, while the remainder courses
+round the western end of Cuba. Two hundred and forty miles from the
+shore the whole mass of water takes a sudden rise of about 10° C.
+within 25 miles, a rise affecting nearly equally the water at all
+depths, and thus producing the singular phenomenon of two masses of
+water in contact--one passing slowly southward and the other more
+rapidly northward, at widely different temperatures at the same
+levels. This abutting of the side of the cold current against that
+of the Gulf Stream is so abrupt that it has been aptly called by
+Lieutenant George M. Bache the “cold wall.” Passing the cold wall,
+we reach the Gulf Stream, presenting all its special characters of
+color and transparency and of temperature. In the section which we
+have chosen as an example, upward of 300 miles in length, the surface
+temperature is about 26°.5 C., but the heat is not uniform across
+the stream, for we find that throughout its entire length, as far
+south as the Cape Canaveral section, the stream is broken up into
+longitudinal alternating bands of warmer and cooler water. Off Sandy
+Hook, beyond the cold wall, the stream rises to a maximum of 27°.8
+C., and this warm band extends for about 60 miles. The temperature
+then falls to a minimum of 26°.5 C., which it retains for about
+30 miles, when a second maximum of 27°.4 succeeds, which includes
+the axis of the Gulf Stream, and is about 170 miles wide. This
+is followed by a second minimum of 25°.5 C., and this by a third
+maximum, when the bands become indistinct. It is singular that the
+minimum bands correspond with valley-like depressions in the bottom,
+which follow in succession the outline of the coast and lodge deep
+southward extensions of the polar indraught.
+
+The last section of the Gulf Stream surveyed by the American
+hydrographers extends in a southeasterly direction from Cape Cod,
+lat. 41° N., and traces the Gulf Stream, still broken up by its
+bands of unequal temperature, spreading directly eastward across the
+Atlantic; its velocity has, however, now become inconsiderable, and
+its limits are best traced by the thermometer.
+
+The course of the Gulf Stream beyond this point has given rise
+to much discussion. I again quote Professor Buff for what may
+be regarded as the view most generally received among physical
+geographers:
+
+“A great part of the warm water is carried partly by its own motion,
+but chiefly by the prevailing west and northwest winds, toward the
+coast of Europe and even beyond Spitzbergen and Nova Zembla; and
+thus a part of the heat of the south reaches far into the Arctic
+Ocean. Hence, on the north coast of the Old Continent, we always
+find driftwood from the southern regions, and on this side the
+Arctic Ocean remains free from ice during a great part of the year,
+even as far up as 80° north latitude; while on the opposite coast
+(of Greenland) the ice is not quite thawed even in summer.” The two
+forces invoked by Professor Buff to perform the work are thus the
+_vis à tergo_ of the trade-wind drift and the direct driving power
+of the anti-trades, producing what has been called the anti-trade
+drift. This is quite in accordance with the views here advocated.
+The proportion in which these two forces act, it is undoubtedly
+impossible in the present state of our knowledge to determine.
+
+Mr. A. G. Findlay, a high authority on all hydrographic matters, read
+a paper on the Gulf Stream before the Royal Geographical Society,
+reported in the 13th volume of the Proceedings of the Society. Mr.
+Findlay, while admitting that the temperature of Northern Europe is
+abnormally ameliorated by a surface-current of the warm water of the
+Atlantic which reaches it, contends that the Gulf Stream proper--that
+is to say, the water injected, as it were, into the Atlantic through
+the Strait of Florida by the impulse of the trade-winds--becomes
+entirely thinned out, dissipated, and lost opposite the Newfoundland
+banks about lat. 45° N. The warm water of the southern portion of
+the North Atlantic basin is still carried northward; but Mr. Findlay
+attributes this movement solely to the anti-trades--the southwest
+winds--which by their prevalence keep up a balance of progress in a
+northeasterly direction in the surface layer of the water.
+
+Dr. Carpenter entertains a very strong opinion that the dispersion of
+the Gulf Stream may be affirmed to be complete in about lat. 45° N.
+and long. 35° W. Dr. Carpenter admits the accuracy of the projection
+of the isotherms on the maps of Berghaus, Dove, Petermann, and Keith
+Johnston, and he admits likewise the conclusion that the abnormal
+mildness of the climate on the northwestern coast of Europe is due to
+a movement of equatorial water in a northeasterly direction. “What I
+question is the correctness of the doctrine that the northeast flow
+is an extension or prolongation of the Gulf Stream, still driven on
+by the _vis à tergo_ of the trade-winds--a doctrine which (greatly to
+my surprise) has been adopted and defended by my colleague, Professor
+Wyville Thomson. But while these authorities attribute the whole or
+nearly the whole of this flow to the true Gulf Stream, _I_ regard a
+large part, if not the whole, of that which takes place along our
+own western coast, and passes north and northeast between Iceland
+and Norway toward Spitzbergen, as quite independent of that agency;
+so that it would continue if the North and South American Continents
+were so completely disunited that the equatorial currents would be
+driven straight onward by the trade-winds into the Pacific Ocean,
+instead of being embayed in the Gulf of Mexico and driven out in a
+northeast direction through the ‘narrows’ off Cape Florida.” Dr.
+Carpenter does not mean by this to indorse Mr. Findlay’s opinion
+that the movement beyond the 54th parallel of latitude is due solely
+to the drift of the anti-trades; he says, “On the view I advocate,
+the northeasterly flow is regarded as due to the _vis à fronte_
+originating in the action of cold upon the water of the polar area,
+whereby its level is always tending to depression.” The amelioration
+of the climate of northwestern Europe is thus caused by a “modified
+case” of the general oceanic circulation, and neither by the Gulf
+Stream nor by the anti-trade drift.
+
+Although there are, up to the present time, very few trustworthy
+observations of deep-sea temperatures, the surface temperature of
+the North Atlantic has been investigated with considerable care.
+The general character of the isothermal lines, with their singular
+loop-like northern deflections, has long been familiar through the
+temperature charts of the geographers already quoted, and of late
+years a prodigious amount of data have been accumulated.
+
+In 1870, Dr. Petermann, of Gotha, published an extremely valuable
+series of temperature charts, embodying the results of the reduction
+of upward of 100,000 observations.
+
+Dr. Petermann has devoted the special attention of a great part of
+his life to the distribution of heat on the surface of the ocean, and
+the accuracy and conscientiousness of his work in every detail are
+beyond the shadow of a doubt.
+
+In the North Atlantic every curve of equal temperature, whether for
+the summer, for the winter, for a single month, or for the whole
+year, instantly declares itself as one of a system of curves which
+are referred to the Strait of Florida as a source of heat, and the
+flow of warm water may be traced in a continuous stream--indicated
+when its movement can no longer be observed by its form--fanning out
+from the neighborhood of the Strait across the Atlantic, skirting
+the coasts of France, Britain, and Scandinavia, rounding the North
+Cape, and passing the White Sea and the Sea of Kari, bathing the
+western shores of Nova Zembla and Spitzbergen, and finally coursing
+round the coast of Siberia, a trace of it still remaining to find its
+way through the narrow and shallow Behring’s Strait into the North
+Pacific.
+
+Now, it seems to me that if we had only these curves upon the
+chart, deduced from an almost infinite number of observations which
+are themselves merely laboriously multiplied corroborations of
+many previous ones, without having any clew to their rationale,
+we should be compelled to admit that whatever might be the
+amount and distribution of heat derived from a general oceanic
+circulation--whether produced by the prevailing winds of the region,
+by convection, by unequal barometric pressure, by tropical heat, or
+by arctic cold--the Gulf Stream, the majestic stream of warm water
+whose course is indicated by the deflections of the isothermal lines,
+is sufficiently powerful to mask all the rest, and, broadly speaking,
+to produce of itself all the abnormal thermal phenomena.
+
+The deep-sea temperatures taken in the _Porcupine_ have an important
+bearing upon this question, since they give us the depth and volume
+of the mass of water which is heated above its normal temperature,
+and which we must regard as the softener of the winds blowing on
+the coasts of Europe. In the Bay of Biscay, after passing through a
+shallow band superheated by direct radiation, a zone of warm water
+extends to the depth of 800 fathoms, succeeded by cold water to a
+depth of nearly two miles. In the Rockall channel the warm layer
+has nearly the same thickness, and the cold underlying water is 500
+fathoms deep. Off the Butt of Lewis the bottom temperature is 5°.2
+C. at 767 fathoms, so that there the warm layer evidently reaches
+to the bottom. In the Faroe channel the warm water forms a surface
+layer, and the cold water underlies it, commencing at a depth of 200
+fathoms--567 fathoms above the level of the bottom of the warm water
+off the Butt of Lewis. The cold water abuts against the warm--there
+is no barrier between them. Part of the warm water flows over the
+cold indraught, and forms the upper layer in the Faroe channel. What
+prevents the cold water from slipping, by virtue of its greater
+weight, under the warm water of the Butt of Lewis? It is quite
+evident that there must be some force at work keeping the warm water
+in that particular position, or, if it be moving, compelling it to
+follow that particular course. The comparatively high temperature
+from 100 fathoms to 900 fathoms I have always attributed to the
+northern accumulation of the water of the Gulf Stream. The amount of
+heat derived directly from the sun by the water as it passes through
+any particular region, must be regarded, as I have already said, as
+depending almost entirely upon latitude. Taking this into account,
+the surface temperatures in what we were in the habit of calling the
+“warm area” coincided precisely with Petermann’s curves indicating
+the northward path of the Gulf Stream.
+
+[Illustration: Typical Forms of Snowflakes
+
+Showing the Tendency to take the Form of Six-Pointed Figures]
+
+The North Atlantic and Arctic seas form together a _cul de sac_
+closed to the northward, for there is practically no passage for
+a body of water through Behring’s Strait. While, therefore, a large
+portion of the water, finding no free outlet toward the northeast,
+turns southward at the Azores, the remainder, instead of thinning
+off, has rather a tendency to accumulate against the coasts bounding
+the northern portions of the trough. We accordingly find that it
+has a depth off the west coast of Iceland of at least 4,800 feet,
+with an unknown lateral extension. Dr. Carpenter, discussing this
+opinion, says: “It is to me physically inconceivable that this
+surface film of _lighter_ (because warmer) water should collect
+itself together again--even supposing it still to retain any excess
+of temperature--and should burrow downward into the ‘trough,’
+_displacing colder and heavier water_, to a depth much greater than
+that which it possesses at the point of its greatest ‘glory’--its
+passage through the Florida Narrows. The upholders of this hypothesis
+have to explain how such a recollection and dipping-down of the
+Gulf Stream water is to be accounted for on physical principles.” I
+believe that, as a rule, experimental imitations on a small scale are
+of little use in the illustration of natural phenomena; a very simple
+experiment will, however, show that such a process is possible. If we
+put a tablespoonful of cochineal into a can of hot water, so as to
+give it a red tint, and then run it through a piece of India-rubber
+tube with a considerable impulse along the surface of a quantity of
+cold water in a bath, we see the red stream widening out and becoming
+paler over the general surface of the water till it reaches the
+opposite edge, and very shortly the rapidly heightening color of a
+band along the opposite wall indicates an accumulation of the colored
+water where its current is arrested. If we now dip the hand into the
+water of the centre of the bath, a warm bracelet merely encircles the
+wrist; while at the end of the bath opposite the warm influx, the hot
+water, though considerably mixed, envelops the whole hand.
+
+The North Atlantic forms a basin closed to the northward. Into the
+corner of this basin, as into a bath--with a northeasterly direction
+given to it by its initial velocity, as if the supply pipe of the
+bath were turned so as to give the hot water a definite impulse--this
+enormous flood is poured, day and night, winter and summer. When the
+basin is full--and not till then--overcoming its northern impulse,
+the surplus water turns southward in a southern eddy, so that there
+is a certain tendency for the hot water to accumulate in the northern
+basin, to “bank down” along the northeastern coasts.
+
+It is scarcely necessary to say that for every unit of water which
+enters the basin of the North Atlantic, and which is not evaporated,
+an equivalent must return. As cold water can gravitate into the
+deeper parts of the ocean from all directions, it is only under
+peculiar circumstances that any movement having the character of
+a current is induced; these circumstances occur, however, in the
+confined and contracted communication between the North Atlantic and
+the Arctic Sea. Between Cape Farewell and North Cape there are only
+two channels of any considerable depth, the one very narrow along
+the east coast of Iceland, and the other along the east coast of
+Greenland. The shallow part of the sea is entirely occupied, at all
+events during summer, by the warm water of the Gulf Stream, except
+at one point, where a rapid current of cold water, very restricted
+and very shallow, sweeps round the south of Spitzbergen and then dips
+under the Gulf Stream water at the northern entrance of the German
+Ocean.
+
+This cold flow, at first a current, finally a mere indraught, affects
+greatly the temperature of the German Ocean; but it is entirely
+lost, for the slight current which is again produced by the great
+contraction at the Strait of Dover has a summer temperature of 7°.5
+C. The path of the cold indraught from Spitzbergen may be readily
+traced by the depressions in the surface isothermal lines, and in
+dredging by the abundance of gigantic amphipodous and isopodous
+crustaceans, and other well-known Arctic animal forms.
+
+From its low initial velocity the Arctic return current, or
+indraught, must doubtless tend slightly in a westerly direction, and
+the higher specific gravity of the cold water may probably even more
+powerfully lead it into the deepest channels; or possibly the two
+causes may combine, and in the course of ages the currents may hollow
+out deep southwesterly grooves. The most marked is the Labrador
+current, which passes down inside the Gulf Stream along the coasts
+of Carolina and New Jersey, meeting it in the strange abrupt “cold
+wall,” dipping under it as it issues from the Gulf, coming to the
+surface again on the other side, and a portion of it actually passing
+under the Gulf Stream, as a cold counter-current, into the Gulf of
+Mexico.
+
+Fifty or sixty miles out from the west coast of Scotland, I believe
+the Gulf Stream forms another, though a very mitigated, “cold wall.”
+In 1868, after our first investigation of the very remarkable cold
+indraught into the channel between Shetland and Faroe, I stated my
+belief that the current was entirely banked up in the Faroe Channel
+by the Gulf Stream passing its gorge. Since that time I have been led
+to suspect that a part of the Arctic water oozes down the Scottish
+coast, much mixed, and sufficiently shallow to be affected throughout
+by solar radiation. About sixty or seventy miles from shore the
+isothermal lines have a slight but uniform deflection. Within that
+line types characteristic of the Scandinavian fauna are numerous in
+shallow water, and in the course of many years’ use of the towing net
+I have never met with any of the Gulf Stream pteropods, or of the
+lovely Polycystina and Acanthometrina which absolutely swarm beyond
+that limit. The difference in mean temperature between the east and
+west coasts of Scotland, amounting to about 1° C., is almost somewhat
+less than might be expected if the Gulf Stream came close to the
+western shore.
+
+While the communication between the North Atlantic and the Arctic
+Sea--itself a second _cul de sac_--is thus restricted, limiting the
+interchange of warm and cold water in the normal direction of the
+flow of the Gulf Stream, and causing the diversion of a large part
+of the stream to the southward, the communication with the Antarctic
+basin is as open as the day; a continuous and wide valley upward of
+2,000 fathoms in depth stretching northward along the western coasts
+of Africa and Europe.
+
+That the southern water wells up into this valley there could be
+little doubt from the form of the ground; but here again we have
+curious corroborative evidence in the remarkable reversal of the
+curves of the isotherms. The temperature of the bottom water at 1,230
+fathoms off Rockall is 3°.22 C., exactly the same as that of water
+at the same depth in the serial sounding, lat. 47° 38′ N., long.
+12° 08′ W. in the Bay of Biscay, which affords a strong presumption
+that the water in both cases is derived from the same source; and
+the bottom water off Rockall is warmer than the bottom water in the
+Bay of Biscay (2°.5 C.), while a cordon of temperature soundings
+drawn from the northwest of Scotland to a point on the Iceland
+shallow gives no temperature lower than 6°.5 C. This makes it very
+improbable that the low temperature of the Bay of Biscay is due to
+any considerable portion of the Spitzbergen current passing down
+the west coast of Scotland; and as the cold current to the east of
+Iceland passes southward considerably to the westward, as indicated
+by the successive depressions in the surface isotherms, the balance
+of probability seems to be in favor of the view that the conditions
+of temperature and the slow movement of this vast mass of moderately
+cold water, nearly two statute miles in depth, are to be referred to
+an Antarctic rather than to an Arctic origin.
+
+The North Atlantic Ocean seems to consist first of a great sheet of
+warm water, the general northerly reflux of the equatorial current.
+Of this the greater part passes through the Strait of Florida, and
+its northeasterly flow is aided and maintained by the anti-trades,
+the whole being generally called the Gulf Stream. This layer is of
+varying depths, apparently from the observations of Captain Chimmo
+and others, thinning to a hundred fathoms or so in the mid-Atlantic,
+but attaining a depth of 700 to 800 fathoms off the west coasts of
+Ireland and Spain. Secondly, of a “stratum of intermixture” which
+extends to about 200 fathoms in the Bay of Biscay, through which the
+temperature falls rather rapidly; and, thirdly, of an underlying mass
+of cold water, in the Bay of Biscay 1,500 fathoms deep, derived as
+an indraught falling in by gravitation from the deepest available
+source, whether Arctic or Antarctic. It seems at first sight a
+startling suggestion, that the cold water filling deep ocean valleys
+in the Northern Hemisphere may be partly derived from the southern;
+but this difficulty, I believe, arises from the idea that there is a
+kind of diaphragm at the equator between the northern and southern
+ocean basins, one of the many misconceptions which follow in the
+train of a notion of a convective circulation in the sea similar to
+that in the atmosphere. There is undoubtedly a gradual elevation
+of an intertropical belt of the underlying cold water, which is
+being raised by the subsiding of still colder water into its bed
+to supply the place of the water removed by the equatorial current
+and by excessive evaporation; but such a movement must be widely
+and irregularly diffused and excessively slow, not in any sense
+comparable with the diaphragm produced in the atmosphere by the
+rushing upward of the northeast and southeast trade-winds in the zone
+of calms. Perhaps one of the most conclusive proofs of the extreme
+slowness of the movement of the deep indraught is the nature of the
+bottom. Over a great part of the floor of the Atlantic a deposit
+is being formed of microscopic shells. These with their living
+inhabitants differ little in specific weight from the water itself,
+and form a creamy flocculent layer, which must be at once removed
+wherever there is a perceptible movement. In water of moderate depth,
+in the course of any of the currents, this deposit is entirely
+absent, and is replaced by coarser or finer gravel.
+
+It is only on the surface of the sea that a line is drawn between the
+two hemispheres by the equatorial current, whose effect in shedding a
+vast intertropical drift of water on either side as it breaks against
+the eastern shores of equatorial land may be seen at a glance on the
+most elementary physical chart.
+
+The Gulf Stream loses an enormous amount of heat in its northern
+tour. At a point 200 miles west of Ushant, where observations at the
+greatest depths were made on board the _Porcupine_, a section of
+the water of the Atlantic shows three surfaces at which interchange
+of temperature is taking place. First, the surface of the sea--that
+is to say, the upper surface of the Gulf Stream layer--is losing
+heat rapidly by radiation, by contact with a layer of air which is
+in constant motion and being perpetually cooled by convection, and
+by the conversion of water into vapor. As this cooling of the Gulf
+Stream layer takes place principally at the surface, the temperature
+of the mass is kept pretty uniform by convection. Secondly, the
+band of contact of the lower surface of the Gulf Stream water with
+the upper surface of the cold indraught. Here the interchange of
+temperature must be very slow, though that it does take place is
+shown by the slight depression of the surface isotherms over the
+principal paths of the indraught. But there is a good deal of
+intermixture extending through a considerable layer. The cold water
+being beneath, convection in the ordinary sense can not occur,
+and interchange of temperature must depend mainly upon conduction
+and diffusion, causes which in the case of masses of water must
+be almost secular in their action, and probably to a much greater
+extent upon mixture produced by local currents and by the tides. The
+third surface is that of contact between the cold indraught and the
+bottom of the sea. The temperature of the crust of the earth has been
+variously calculated at from 4° to 11° C., but it must be completely
+cooled down by anything like a movement and constant renewal of cold
+water. All we can say, therefore, is that contact with the bottom can
+never be a source of depression of temperature. As a general result
+the Gulf Stream water is nearly uniform in temperature throughout the
+greater part of its depth; there is a marked zone of intermixture at
+the junction between the warm water and the cold, and the water of
+the cold indraught is regularly stratified by gravitation; so that
+in deep water the contour lines of the sea-bottom are, speaking
+generally, lines of equal temperature. Keeping in view the enormous
+influence which ocean currents exercise in the distribution of
+climates at the present time, I think it is scarcely going too far to
+suppose that such currents--movements communicated to the water by
+constant winds--existed at all geological periods as the great means,
+I had almost said the sole means, of producing a general oceanic
+circulation, and thus distributing heat in the ocean. They must have
+existed, in fact, wherever equatorial land interrupted the path of
+the drift of the trade-winds. Wherever a warm current was deflected
+to north or south from the equatorial belt a polar indraught crept in
+beneath to supply its place; and the ocean consequently consisted,
+as in the Atlantic and doubtless in the Pacific at the present day,
+of an upper warm stratum and a lower layer of cold water becoming
+gradually colder with increasing depth.
+
+I must repeat that I have seen as yet no reason to modify the opinion
+which I have consistently held from the first, that the remarkable
+conditions of climate on the coasts of Northern Europe are due in a
+broad sense solely to the Gulf Stream. That is to say that, although
+movements, some of them possibly of considerable importance, must be
+produced by differences of specific gravity, yet the influence of the
+great current which we call the Gulf Stream, the reflux of the great
+equatorial current, is so paramount as to reduce all other causes to
+utter insignificance.
+
+
+
+
+  THE PHOSPHORESCENCE OF THE SEA
+  --G. HARTWIG
+
+
+He who still lingers on the shore after the shades of evening have
+descended not seldom enjoys a most magnificent spectacle; for lucid
+flashes burst from the bosom of the waters, as if the sea were
+anxious to restore to the darkened heavens the light it had received
+from them during the day. On approaching the margin of the rising
+flood to examine more closely the sparkling of the breaking wave, the
+spreading waters seem to cover the beach with a sheet of fire.
+
+Each footstep over the moist sands elicits luminous star-like points
+and a splash in the water resembles the awakening of slumbering
+flames. The same wonderful and beauteous aspect frequently gladdens
+the eye of the navigator who plows his way through the wide deserts
+of ocean, particularly if his course leads him through the tropical
+seas.
+
+“When a vessel,” says Humboldt, “driven along by a fresh wind,
+divides the foaming waters, one never wearies of the lovely spectacle
+their agitation affords; for, whenever a wave makes the ship incline
+sidewise, bluish or reddish flames seem to shoot upward from the
+keel. Beautiful beyond description is the sight of a troop of
+dolphins gamboling in the phosphorescent sea. Every furrow they draw
+through the waters is marked by streaks of intense light. In the Gulf
+of Cariaco, between Cumana and the peninsula of Maniquarez, this
+scene has often delighted me for hours.”
+
+But even in the colder oceanic regions the brilliant phenomenon
+appears from time to time in its full glory. During a dark and stormy
+September night, on the way from the Sealion Island, Saint George,
+to Unalashka, Chamisso admired as beautiful a phosphorescence of
+the ocean as he had ever witnessed in the tropical seas. Sparks of
+light, remaining attached to the sails that had been wetted by the
+spray, continued to glow in another element. Near the south point
+of Kamtchatka, at a water temperature hardly above freezing point,
+Ermann saw the sea no less luminous than during a seven months’
+sojourn in the tropical ocean. This distinguished traveler positively
+denies that warmth decidedly favors the luminosity of the sea.
+
+At Cape Colborn, one of the desolate promontories of the desolate
+Victoria Land, the phosphoric gleaming of the waves, when darkness
+closed in, was so intense that Simpson assures us he had seldom
+seen anything more brilliant. The boats seemed to cleave a flood of
+molten silver, and the spray, dashed from their bows before the fresh
+breeze, fell back in glittering showers into the deep.
+
+Mr. Charles Darwin paints in vivid colors the magnificent spectacle
+presented by the sea while sailing in the latitude of Cape Horn on
+a very dark night. There was a fresh breeze, and every part of the
+surface, which during the day is seen as foam, now glowed with a
+pale light. The vessel drove before her bows two billows of liquid
+phosphorus, and in her wake she was followed by a milky train. As
+far as the eye reached, the crest of every wave was bright, and
+the sky above the horizon, from the reflected glare of these livid
+flames, was not so utterly obscure as over the rest of the heavens.
+
+While _La Venus_ was at anchor before Simon’s Town, the breaking
+of the waves produced so strong a light that the room in which the
+naturalists of the expedition were seated was illumined as by sudden
+flashes of lightning. Although more than fifty paces from the beach
+when the phenomenon took place, they tried to read by this wondrous
+oceanic light, but the successive glimpses were of too short duration
+to gratify their wishes.
+
+Thus we see the same nocturnal splendor which shines forth in the
+tropical seas and gleams along our shores burst forth from the Arctic
+waters, and from the waves that bathe the southern promontories of
+the Old and the New Worlds.
+
+But what is the cause of the beautiful phenomenon so widely spread
+over the face of the ocean? How comes it that at certain times flames
+issue from the bosom of an element generally so hostile to their
+appearance?
+
+Without troubling the reader with the groundless surmises of ancient
+naturalists, or repeating the useless tales of the past, I shall at
+once place myself with him on the stage of our actual knowledge of
+this interesting and mysterious subject.
+
+It is now no longer a matter of doubt that many of the inferior
+marine animals possess the faculty of secreting a luminous matter,
+and thus adding their mite to the grand phenomenon. When we
+consider their countless multitudes, we shall no longer wonder at
+such magnificent effects being produced by creatures individually so
+insignificant.
+
+In our seas it is chiefly a minute gelatinous animal, the _Noctiluca
+miliaris_, most probably an aberrant member of the infusorial group,
+which, as it were, repeats the splendid spectacle of the starry
+heavens on the surface of the ocean. In form it is nearly globular,
+presenting on one side a groove, from the anterior extremity of which
+issues a peculiar curved stalk or appendage marked by transverse
+lines, which might seem to be made use of as an organ of locomotion.
+Near the base of this tentacle is placed the mouth, which passes into
+a dilatable digestive cavity, leading, according to Mr. Huxley, to
+a distinct anal orifice. From the rather firm external coat proceed
+thread-like prolongations through the softer mass of the body, so as
+to divide it into irregular chambers. This little creature, which is
+just large enough to be discerned by the naked eye when the water
+in which it may be swimming is contained in a glass jar exposed to
+the light, seems to feed on diatoms, as this loricæ may frequently
+be detected in its interior. It multiplies by spontaneous fission,
+and the rapidity of this process may be inferred from the immensity
+of its numbers. A single bucket of luminous sea-water will often
+contain thousands, while for miles and miles every wave breaking on
+the shore expands in a sheet of living flame. It was first described
+by Forster in the Pacific Ocean; it occurs on all the shores of the
+Atlantic; and the Polar Seas are illumined by its fairy light.
+“The nature of its luminosity,” says Dr. Carpenter, “is found by
+microscopic examination to be very peculiar; for what appears to the
+eye to be a uniform glow is resolvable under a sufficient power into
+a multitude of evanescent scintillations, and these are given forth
+with increased intensity whenever the body of the animal receives any
+mechanical shock.”
+
+The power of emitting a phosphorescent light is widely diffused,
+both among the free-swimming and the sessile _Cœlenterata_. Many
+of the _Physophoridæ_ are remarkable for its manifestation, and a
+great number of the jelly-fishes are luminous. Our own _Thaumantias
+lucifera_, a small and by no means rare medusid, displays the
+phenomenon in a very beautiful manner, for, when irritated by
+contact of fresh water, it marks its position by a vivid circlet of
+tiny stars, each shining from the base of a tentacle. A remarkable
+greenish light, like that of burning silver, may also be seen to glow
+from many of our Sertularians, becoming much brighter under various
+modes of excitation.
+
+Among the _Ctenophora_ the large _Cestum Veneris_ of the
+Mediterranean is specially distinguished for its luminosity, and
+while moving beneath the surface of the water gleams at night like a
+brilliant band of flame.
+
+The Sea-pens are eminently phosphorescent, shining at night with a
+golden-green light of a most wonderful softness. When touched, every
+branchlet above the shock emits a phosphoric glow, while all the
+polyps beneath remain in darkness. When thrown into fresh water
+or alcohol, they scatter sparks about in all directions, a most
+beautiful sight; dying, as it were, in a halo of glory.
+
+But of all the marine animals the Pyrosomas, doing full justice to
+their name (fire bodies), seem to emit the most vivid coruscations.
+Bibra relates in his _Travels to Chili_ that he once caught half a
+dozen of these remarkable light-bearers, by whose phosphorescence
+he could distinctly read their own description in a naturalist’s
+vade-mecum. Although completely dark when at rest, the slightest
+touch sufficed to elicit their clear blue-green light. During a
+voyage to India, Mr. Bennett had occasion to admire the magnificent
+spectacle afforded by whole shoals of Pyrosomas. The ship, proceeding
+at a rapid rate, continued during an entire night to pass through
+distinct but extensive fields of these mollusks, floating and
+glowing as they floated on all sides of her course. Enveloped in a
+flame of bright phosphorescent light, and gleaming with a greenish
+lustre, the Pyrosomas, in vast sheets, upward of a mile in breadth,
+and stretching out till lost in the distance, presented a sight the
+glory of which may be easily imagined. The vessel, as it chased
+the gleaming mass, threw up strong flashes of light, as if plowing
+through liquid fire, which illuminated the hull, the sails, and the
+ropes with a strange, unearthly radiance.
+
+In his memoir on the Pyrosoma, M. Péron describes with lively
+colors the circumstances under which he first made its discovery,
+during a dark and stormy night, in the tropical Atlantic. “The
+sky,” says this distinguished naturalist, “was on all sides loaded
+with heavy clouds; all around the obscurity was profound; the wind
+blew violently; and the ship cut her way with rapidity. Suddenly we
+discovered at some distance a great phosphorescent band stretched
+across the waves, and occupying an immense tract in advance of the
+ship. Heightened by the surrounding circumstances, the effect of this
+spectacle was romantic, imposing, sublime, riveting the attention of
+all on board. Soon we reached the illuminated tract, and perceived
+that the prodigious brightness was certainly and only attributable to
+the presence of an innumerable multitude of largish animals floating
+with the waves. From their swimming at different depths they took
+apparently different forms--those at the greatest depths were very
+indefinite, presenting much the appearance of great masses of fire,
+or rather enormous, red-hot cannon-balls; while those more distinctly
+seen near the surface perfectly resembled incandescent cylinders of
+iron.
+
+“Taken from the water, these animals entirely resembled each other
+in form, color, substance, and the property of phosphorescence,
+differing only in their sizes, which varied from three to seven
+inches. The large, longish tubercles with which the exterior
+of the Pyrosomas was bristled were of a firmer substance, and
+more transparent than the rest of the body, and were brilliant
+and polished like diamonds. These were the principal scene of
+phosphorescence. Between these large tubercles, smaller ones,
+shorter and more obtuse, could be distinguished; these also were
+phosphorescent. Lastly, in the interior of the substance of the
+animal, could be seen, by the aid of the transparency, a number of
+little, elongated, narrow bodies (viscera), which also participated
+in a high degree in the possession of phosphoric light.”
+
+In the Pholades or Lithodomes, that bore their dwellings in hard
+stone, as other shell-fish do in the loose sands, the whole mass of
+the body is permeated with light. Pliny gives us a short but animated
+description of the phenomenon in the edible date-shell of the
+Mediterranean (_Pholas dactylus_):
+
+“It is in the nature of the pholades to shine in the darkness with
+their own light, which is the more intense as the animal is more
+juicy. While eating them, they shine in the mouth and on the hands,
+nay, even the drops falling from them upon the ground continue to
+emit light, a sure proof that the luminosity we admire in them is
+associated with their juice.”
+
+Milne-Edwards found this observation perfectly correct, for, wishing
+to place some living pholades in alcohol, he saw a luminous matter
+exude from their bodies, which, on account of its weight, sank in
+the liquid, covering the bottom of the vessel, and there forming a
+deposit as shining as when it was in contact with the air.
+
+Several kinds of fishes likewise possess the luminous faculty. The
+sunfish, that strange deformity emits a phosphoric gleam; and a
+species of Gunard (_Trigla lucerna_) is said to sparkle in the night,
+so as to form fiery streams through the water.
+
+With regard to the luminosity of the larger marine animals, Ermann,
+however, remarks that he so often saw small luminous crustacea in
+the abdominal cavity of the transparent _Salpa pinnata_ that it may
+well be asked whether the phosphorescence of the larger creatures is
+not in reality owing to that of their smaller companions.
+
+According to Mr. Bennett--_Whaling Voyage Round the Globe_--a
+species of shark first discovered by himself is distinguished by
+an uncommonly strong emission of light. When the specimen, taken
+at night, was removed into a dark apartment, it afforded a very
+interesting spectacle. The entire inferior surface of the body and
+head emitted a vivid and greenish phosphorescent gleam, imparting
+to the creature by its own light a truly ghastly and terrific
+appearance. The luminous effect was constant, and not perceptibly
+increased by agitation or friction. When the shark expired (which
+was not until it had been out of the water more than three hours),
+the luminous appearance faded entirely from the abdomen, and more
+gradually from other parts, lingering longest around the jaws and on
+the fins.
+
+The only part of the under surface of the animal which was free from
+luminosity was the black collar round the throat; and while the
+inferior surface of the pectoral, anal, and caudal fins shone with
+splendor, their superior surface (including the upper lobe of the
+tail fin) was in darkness, as were also the dorsal fins and the back
+and summit of the head.
+
+Mr. Bennett is inclined to believe that the luminous power of this
+shark resides in a peculiar secretion from the skin. It was his
+first impression that the fish had accidentally contracted some
+phosphorescent matter from the sea, or from the net in which it
+was captured; but the most rigid investigation did not confirm
+this suspicion, while the uniformity with which the luminous gleam
+occupied certain portions of the body and fins, its permanence during
+life, and decline and cessation upon the approach and occurrence
+of death, did not leave a doubt in his mind but that it was a
+vital principle essential to the economy of the animal. The small
+size of the fins would seem to denote that this fish is not active
+in swimming; and, since it is highly predaceous and evidently of
+nocturnal habits, we may perhaps indulge in the hypothesis that the
+phosphorescent power it possesses is of use to attract its prey, upon
+the same principle as the Polynesian islanders and others employ
+torches in night-fishing.
+
+Some of the lower sea-plants also appear to be luminous. Thus, over
+a space of more than 600 miles (between lat. 8° N. and 2° S.), Meyen
+saw the ocean covered with phosphorescent _Oscillatoria_, grouped
+together into small balls or globules, from the size of a poppy-seed
+to that of a lentil.
+
+But if the luminosity of the ocean generally proceeds from living
+creatures, it sometimes also arises from putrefying organic fibres
+and membranes, resulting from the decomposition of these living light
+bearers. “Sometimes,” says Humboldt, “even a high magnifying power is
+unable to discover any animals in the phosphorescent water, and yet
+light gleams forth wherever a wave strikes against a hard body and
+dissolves in foam. The cause of this phenomenon lies then most likely
+in the putrefying fibres of dead mollusks, which are mixed with the
+waters in countless numbers.”
+
+Summing up the foregoing in a few words, it is thus an indisputable
+fact that the phosphorescence of the sea is by no means an electrical
+or magnetic property of the water, but exclusively bound to organic
+matter, living or dead. But although thus much has been ascertained,
+we have as yet only advanced one step toward the unraveling of
+the mystery, and its prominent cause remains an open question.
+Unfortunately, science is still unable to give a positive answer, and
+we are obliged to be content with a more or less plausible hypothesis.
+
+We know as little of what utility marine phosphorescence may be. Why
+do the countless myriads of Mammariæ gleam and sparkle along our
+coasts? Is it to signify their presence to other animals, and direct
+them to the spot where they may find abundance of food? So much is
+certain, that so grand and widespread a phenomenon must necessarily
+serve some end equally grand and important.
+
+As the phosphorescence of the sea is owing to living creatures, it
+must naturally show itself in its greatest brilliancy when the ocean
+is at rest; for during the daytime we find the surface of the waters
+most peopled with various animals when only a slight zephyr glides
+over the sea. In stormy weather, the fragile or gelatinous world of
+the lower marine creatures generally seek a greater depth, until the
+elementary strife has ceased, when it again loves to sport in the
+warmer or more cheerful superficial waters.
+
+In the tropical zone, Humboldt saw the sea most brilliantly luminous
+before a storm, when the air was sultry and the sky covered with
+clouds. In the North Sea we observe the phenomenon most commonly
+during fine, tranquil autumnal nights; but it may be seen at
+every season of the year, even when the cold is most intense. Its
+appearance is, however, extremely capricious; for, under seemingly
+unaltered circumstances, the sea may one night be very luminous
+and the next quite dark. Often months, even years, pass by without
+witnessing it in full perfection. Does this result from a peculiar
+state of the atmosphere, or do the little animals love to migrate
+from one part of the coast to another?
+
+It is remarkable that the ancients should have taken so little
+notice of oceanic phosphorescence. The _Periplus_ of Hanno contains,
+perhaps, the only passage in which the phenomenon is described.
+
+To the south of Cerne the Carthaginian navigator saw the sea burn, as
+it were, with streams of fire. Pliny, in whom the miracle (miraculum,
+as he calls it) of the date-shell excited so lively an admiration,
+and who must often have seen the sea gleam with phosphoric light,
+as the passage proves where he mentions in a few dry words the
+luminous gurnard (_lucerna_) stretching out a fiery tongue, has
+no exclamation of delight for one of the most beautiful sights of
+nature. Homer also, who has given us so many charming descriptions of
+the sea in its ever-changing aspects, and who so often leads us with
+long-suffering Ulysses through the nocturnal floods, never once makes
+them blaze or sparkle in his immortal hexameters. Even modern poets
+mention the phenomenon but rarely. Camoens himself, whom Humboldt,
+on account of his beautiful oceanic descriptions, calls, above all
+others, the “poet of the sea,” forgets to sing it in his _Lusiad_.
+Byron in his _Corsair_ has a few lines on the subject:
+
+      “Flash’d the dipt oars, and, sparkling with the stroke,
+      Around the waves phosphoric brightness broke;”
+
+but contents himself, as we see, with coldly mentioning a phenomenon
+so worthy of all a poet’s enthusiasm. In Coleridge’s wondrous ballad
+of _The Ancient Mariner_ we find a warmer description:
+
+      “Beyond the shadow of the ship
+        I watch’d the water-snakes:
+      They moved in tracks of shining white,
+      And, when they rear’d, the elfin light
+        Fell off in hoary flakes.
+
+      “Within the shadow of the ship
+        I watch’d their rich attire--
+      Blue, glossy green, and velvet black:
+      They coiled and swam, and every track
+        Was a flash of golden fire.”
+
+These, indeed, are lines whose brilliancy emulates the splendor of
+the phenomenon they depict, but, even they are hardly more beautiful
+than Crabbe’s admirable description:
+
+      “And now your view upon the ocean turn,
+      And there the splendor of the waves discern;
+      Cast but a stone, or strike them with an oar,
+      And you shall flames within the deep explore;
+      Or scoop the stream phosphoric as you stand,
+      And the cold flames shall flash along your hand;
+      When, lost in wonder, you shall walk and gaze
+      On weeds that sparkle, and on waves that blaze.”
+
+Or the graphic numbers of Sir Walter Scott:
+
+      “Awak’d before the rushing prow,
+      The mimic fires of ocean glow,
+        Those lightnings of the wave;
+      Wild sparkles crest the broken tides,
+      And dashing round, the vessel’s sides
+        With elfish lustre lave;
+      While, far behind, their vivid light
+      To the dark billows of the night
+        A blooming splendor gave.”
+
+
+
+
+  THE SEASHORE
+  --P. MARTIN DUNCAN
+
+
+The seashore is the debatable ground where the sea is constantly
+striving to wear away the land. It is the present limit to the ocean
+and sea, and a little beyond, for it reaches inland further than the
+wildest waves and the highest tides can attain.
+
+Where the seashore begins and ends is a matter of opinion; but all
+of it is influenced in some way or other by the sea. In some places,
+high cliffs or rocks keep the sea from driving in upon the land;
+they are lofty, and may reach for miles along the coast. The high
+tide comes up their steep faces for many yards, and when it retires
+a rocky strip is seen at their feet, and thence a breadth of rock,
+shingle, or sand leads down with a greater or less slope to the
+water’s edge. Here there can be no doubt how far the shore reaches
+inland, for the cliffs limit it. In other parts of our own and other
+maritime countries, there may be no high land on the coast; but
+marshes and low lands, with, or without sand-hills, form barriers to
+the incursion of the sea. The highest tides have their limit in those
+places, but the wash of the sea and the spray, together with the
+drainage of the sea into the land, make the water saltish for some
+distance inland, and the earth close by is sodden with salt. Then,
+long stretches of mud or of sand form the slope, over which the sea
+rolls up to the land, and which is exposed and remains more or less
+wet at low tide.
+
+In these low-lying parts of the coast the shore is not very
+distinctly separated from the land, and often miles of swamp, marsh,
+and sand-banks are invaded by the sea during storms and very high
+tides. The ditches near the sea contain salt or brackish water, and
+the whole of this kind of coast-line has a peculiar and desolate
+appearance. If these two kinds of coast are taken as the extremes,
+all the varieties of seashores will fit in between them; but still it
+will appear that while in some the limit between the land and the sea
+is very decided, in others it is not so.
+
+Seaward the shore is very variable in its extent. In some places
+it may barely exist, or may only be a ledge of rock, between the
+cliff, the high land, and the water; and in others, miles of sand,
+shingle, and mud may be between the furthest reach of the waves and
+the limit of the low tide. The commonest examples of shores are
+those which are between these extremes. Some seashores slope very
+gradually to the sea and their extent is then usually great; and
+others, which are limited in their breadth, are more precipitous.
+Perhaps it is best to say that a seashore is the part of a coast
+which, at some time or other, is covered or uncovered by the sea;
+and that it has an extension inland, where the spray and wind are
+felt and act on the land, and also seaward, where some shore is only
+uncovered during excessively low tides. According to this view, it
+is possible to portion out a seashore into a greater or less number
+of breadths, which may be placed, side by side, from the land to the
+sea. First, a breadth will pass along the coast, and will contain
+the marshy, swampy land, or the hard rock down to the edge of the
+highest tide-mark. It may be miles across, or only a few feet in
+extent. Secondly, a breadth will be found between this last and the
+sea, where it is highest during common tides and storms. Thirdly, a
+breadth will exist four times in the twenty-four hours as dry land,
+and for the rest of the time it will be beneath the waves, and this
+is situated between ordinary high and low-tide marks. Finally, a
+breadth will be between this last and the everlasting sea; it is
+narrow, and is only uncovered for a few hours, in the months of the
+year when there are what are called “low spring tides.” These four
+breadths are termed zones, or belts; and in common language the first
+is the beach and coast-line, the second is the shore, the third is
+the tide-shore, and the fourth is “low spring shore.”
+
+Differing in their extent, and in the nature of their surface,
+in every few miles of the coast of a maritime country like Great
+Britain, the zones have their peculiar animals and plants, and
+waifs and strays--the wreckage of the sea, of its floor, and of the
+coast-line. When the whole of the shore slopes very rapidly to the
+sea, the third and fourth zones are small in extent, but when the
+slope is gradual, they are large. And when the tide rises much and
+falls correspondingly, the third zone is usually uncovered but for
+a short time. The tide usually moves along the shore, and does not
+simply come in on to the land and recede; for one tide moves in one
+direction and the next in the opposite. Thus floating substances are
+carried along the coast for miles by the rising tide, and come back
+again, more or less, with the falling tide.
+
+Tide, wind, and wave forever act on the surface of the zones, but
+their action is the greatest on those which are landward. There are
+other wreckers of the coast; for the heat of the sun, the winter’s
+frost, the rain, and the chemical action of the air, one and all
+crumble and break off pieces of rock or earth. These fall on to the
+tidal shore, and are rolled here and there, and up and down, to be
+turned into mud, sand, and pebbles. The cliffs and bold headlands are
+worn year by year, and during centuries they lose much, and retire
+landward. Needles and “no man’s lands” stand out on the shore, or out
+at sea, testifying to the former extension of the land; and shore
+exists where there was once high solid rock. The shore consists
+of the worn surface of the old land, rock, or earth, and this is
+usually hidden by stone or stuff which has fallen from the cliffs,
+and by sand, or mud, or pebble and stone, which the tide has swept
+along. But often the jagged or rounded remains of the former rock
+project out of the sand, mud, and stone on the shore, and they may
+be bare, or covered with sea-weed. In other spots, the hard rock is
+hollowed out into places which let the water stand in them like so
+many puddles, pools, and ponds, when the tide has gone down. These
+are often crowded with marine plants and animals of the shore. The
+rolling stones, the wash of the tide, and the rush and drawback of
+the waves, are ever wearing off the surface of the shore and grooving
+it, or planing it flat, and in some places where the stones do not
+collect, this is very evident; but where they form great masses of
+pebbles or shingle, it can not be readily seen.
+
+There are many shores around Great Britain, where the rock is hard,
+which are rarely covered with pebbles, bowlders, and sand; and the
+sea-weed grows on them and protects them against the sea. But usually
+the rock is only exposed here and there, and the stones which collect
+and cover much of it come from a distance, and are on the move at
+every tide. In some places, where the coast is composed of clay or
+soft sandstone, the shore is muddy, soft, and may be uncovered or
+covered by stones.
+
+The wear of the sea is but little seen in such places as this, and
+still less so where the coast is low and flat, and the shore is very
+extensive and the water is shallow for a long distance. In fact,
+on many of these flat shores, instead of erosion taking place, the
+sea is adding to the land by depositing. This is particularly the
+case at the entrance of great, and of many small rivers. Their mud
+collects in the shallows at their mouths, and is added to by sand
+and shingle, so that land grows seaward, instead of the reverse. The
+seashore is then, usually, uninviting and often consists of large
+mud flats. Again, in some localities, where much sand collects on
+the surface of the rock forming the seashore, it may be “quick” in
+many places. The rising tide gets under the sand, which suddenly
+becomes like so much sand and water, and the falling tide leaves it
+hard for a while. The ordinary condition of a sandy shore is either
+that of a number of very slightly rounded stretches of sand, with
+drainage-streams between them, or it is pretty hard, readily dug
+into, and marked on the surface by ripples. The ripple-mark on sand
+always strikes the observer; it represents little ripple-like waves,
+wonderfully regular, and each has a ridge and a valley. They are very
+lasting, but disappear on the slightest movement of the wet sand as
+the tide comes in. These little ridges and valleys are not found
+when the water covers the sand at a considerable depth, but they are
+especially seen between high and low spring-tide limit. Such marks
+can be made, artificially, with sand, for instance, on the bottom
+of a large basin. If some sand is placed on the bottom, and water
+be poured in, and the edge of the basin be pushed, a to-and-fro
+movement of the water will occur, and it will be continued down to
+the sand. As the motion ceases, the sand will be seen to collect
+in ridges, side by side, and they will be perfect when the motion
+stops. Motion of the sea-water in one direction over soft sand will
+not produce ripple-mark well, but a slight to-and-fro movement will
+do it to perfection. Infinitely more wonderful than these ripples
+are the pebble beaches, for they often extend for many miles, and
+have a very considerable thickness. Worn, in the first instance,
+from distant rocks, born of huge bowlders, which the mighty waves
+laden with rolling stones have broken down, the pebble is formed
+by rolling against others, and the result of its wear and tear is
+carried off in the form of sand. They travel miles and miles along
+the coast with the tide, and therefore it is very common to find one
+kind of rock forming the coast-line, and the shore close by having
+pebbles made up of stone which is not known to be near at hand. Thus,
+on the coast of South Devon, the red rocks form the coast-line;
+they are sandy, and are covered in some places by a beautiful green
+vegetation. The sea is often of the brightest blue, or gray, when the
+sky is not much tinted with color. But the sea covering the shore at
+high tide looks whitish, and this is produced by the white and light
+slate-colored pebbles which reach up close to the red rocks. They are
+not made up of red sand; on the contrary, they are of gray and bluish
+limestone, and come from rocks which are situated miles to the west.
+Further east, the Chesil Bank is seen, and it is an enormous shore
+of pebbles, which have been carried along the coast and have found
+an uncertain resting-place there. Every tide makes more sand out of
+the hardest pebbles, as they knock one against the other and wear
+away, and the sand already made scrubs them as it is hurried hither
+and thither by the waves. In some places where the sea is giving up
+rather than taking off land, the sand which is cast up may be the
+result of the wear of distant pebble-making, or it may be composed of
+myriads of broken tiny shells which once lived in shallow water.
+
+It has been already stated that the sea is encroaching on the land
+in some parts of England, and that it does not do so in others,
+while it appears to be giving place to land elsewhere. In the first
+instance, the seashore must grow, as it were, must increase landward,
+and it really does so at different rates, in different parts of the
+country. In some parts of the coast a yard is lost every year and the
+sea comes in on the land so much the more. But all the space once
+occupied by cliff and rock is soon worn by the sea and is covered
+gradually by the tide, and after years have elapsed this _fore-shore_
+is deepened seaward by the rolling stone and rushing waves, so that
+the visible beach or shore diminishes in size, unless a corresponding
+landward extension takes place. Although the cliffs and rocks fall,
+and their remains are swept away from the level of the shore, by
+currents, tides, and waves; yet, as has already been noticed, much
+of the ruined surface, leveled down as it has been, is covered up by
+relics of their wear and tear or by stone brought from a distance. It
+is only after some severe gale of wind, accompanied by a very high
+tide, that these stones and covering-up relics are swept away and the
+old rock-surface comes in view. All these matters are of importance,
+for the living creatures of the seashore depend upon the state of
+things, in each of the zones, for their ability to exist and flourish.
+
+Where the coast has been low and the sea has gradually encroached,
+the remains of stumps of trees are often exposed after a gale. Then
+what is called part of a submarine forest is opened to the sight.
+There are many of them around England and especially on the coast of
+Norfolk and Essex, on the east; in many places on the south coast
+as far as Torbay; and on the west they are found in the Bristol
+Channel, and about Holyhead and the river Mersey. Sometimes it
+appears that the sunken forest has not been altogether produced by
+the encroachment of the sea on the land, and that sinking of the
+coast, or slipping of part of it, has caused the event. When the sea
+comes in on the land, it wears everything before it, and any forest
+land would in most instances be completely wrecked and the roots of
+the great trees would be worn and torn out of the soft earth and
+carried off to sea by the waves, tides, and currents. On looking at
+some smaller forests which are laid bare at very low tides, it is
+found that they consist of stumps of trees of great size, whose roots
+are still in the clay in which they grew, and a quantity of mud and
+sand is between the stumps and protects them from the usual action of
+water on submerged land. It appears that some movement of the earth’s
+crust had caused the coast to sink down, and then the sea invaded
+without wearing off the land. The trees were ruined by the sea-water,
+and broken off, and the mud, sand, and stone collected around the
+stumps.
+
+It is not uncommon to see collections of stone and shells high up on
+the face of a rock or cliff, and when they are carefully examined
+they are found to resemble a bit of a shore or a piece of the beach,
+hoisted up many feet above the present line of the waves and tides.
+
+They are called raised beaches, and they were formed by an upheaval
+of part of the coast with its shore during movements in the crust of
+the globe. There was a shore and a cliff, as there may be now, and
+the whole was pushed up some twenty, thirty, or more than a hundred
+feet beyond the reach of the highest tides and waves. In years past
+the waves broke upon the cliff beneath the upraised portion, and wore
+it away bit by bit; and then the air and sun acted with the rain in
+wearing it, and now only a portion remains.
+
+Every coast-line is subject to these sinkings-down and upheavals,
+and of course a seashore is produced rapidly, and is made broad and
+shallow during the first kind of occurrence, and is stopped and has
+to be formed afresh during the last. As these remarkable movements
+of the outside of the globe are not universal, and affect some parts
+of a coast more than others, they will tend to give great variety
+to the seashores of a country. Together with the varying action of
+the tides, waves, and currents upon cliffs and rocks of different
+stones and earths, and of many hardnesses, these movements have made
+the shores of Great Britain very curiously varied in their size and
+character.
+
+It must be remembered that as new shores are formed, or old ones
+are extended, the zones are kept within their bounds, and that as
+one zone creeps in on the land, those to the seaward move up also;
+so that where there was once a between-tide zone there may now be
+deep water. This change in the position of zones is very important;
+for certain animals and plants of the shore only live in certain
+zones, and their increase or decrease in numbers depends upon the
+corresponding state of their special locality.
+
+
+
+
+                         III.--THE ATMOSPHERE
+
+
+
+
+  THE OCEAN OF AIR
+  --AGNES GIBERNE
+
+
+Our earth has many robes. Closely-fitting garments come first, of
+brown soil or gray rock and green grass, with wide liquid underskirts
+of deep blue filling up the spaces between. Outside these are
+coverings more wonderful still; fragile, yet strong, transparent,
+almost invisible, folded around layer upon layer, or, as one
+might say, veil upon veil, each more gossamer-like than the last.
+These form earth’s surrounding atmosphere--a substance pervading
+everything, found everywhere. One may travel from the equator to the
+poles, one may journey by sea or by land, one may soar high in a
+balloon or descend deep into a mine, but one can never in this world
+go to a place where the atmosphere is not.
+
+A substance--for air can be felt; air has weight; air occupies space;
+air, like any other body, can be made hot or cold; air is composed of
+particles of substantial matter. Air has a faint bluish tint, which
+on a sunshiny day becomes in the sky a very pure and deep blue. This
+tint is not believed to be the natural color of the atmosphere. Were
+it so, the air would merely act the part of a blue pane of glass,
+rendering the white light of the sun blue as it reaches our eyes;
+but the blue of the atmosphere is known to be a reflected blue.
+
+If reflected, there must be something in the atmosphere to reflect
+it; and such indeed is the case. Perfectly pure air would doubtless
+be without color, but perfectly pure air we do not find. The whole
+atmosphere is full of multitudinous minute specks, so small as to be
+in themselves invisible, so light as to remain aloft. To the presence
+of these the blue tint is believed to be due. They scatter the light
+of the sun, and produce the blue effect.
+
+A beam of strong white light, caused to pass through a liquid which
+contains a large supply of minute floating particles, is affected
+by them in a like manner. The short blue waves are more abundantly
+reflected than the long red waves; and so the water seems to be blue.
+This explanation serves for the deep-blue color of the ocean, as well
+as for the blue of the atmosphere.
+
+The whole earth is surrounded by this marvelous air-ocean; an
+ocean of gaseous matter, at least one hundred times as deep as the
+water-ocean. At the bottom of the gaseous ocean we small human
+creatures crawl about, commonly on flat lower levels--the ocean
+bottom, in fact. Sometimes, with much toil and trouble, we climb the
+little ridges and mounds called “mountains”; little compared with the
+depth of the atmosphere, though not little compared with ourselves.
+The highest mountain-peaks of even the vast Himalayas lie low down
+near the bottom of the ocean of air.
+
+But the very extent of the ocean of air adds to our difficulty
+in studying its nature. All observations that we can make must be
+limited by the state of the atmosphere just around ourselves. We
+can never get out of and beyond the atmosphere, so as to see it as
+a whole. At any time a slight local fog is enough to put a stop
+altogether to such observations, beyond the unpleasant experience of
+the fog itself.
+
+It used to be supposed that the atmosphere reached only to a height
+of about fifty miles above earth’s surface. Of late years the opinion
+has gained ground that the atmosphere reaches to a height certainly
+of two or three hundred miles, probably of four or five hundred,
+possibly a good deal more. But the condition of the air far above is
+different from that of the air in lower levels, where we live and
+breathe. The higher we ascend, the more thin or “rare” becomes the
+air. A less quantity fills a certain space up there than down here.
+The particles float further apart one from another.
+
+This difference in the density of the air is chiefly due to
+attraction. Each separate air-particle is drawn steadily earthward by
+the force of gravitation, and that force is stronger on the surface
+of earth than at a distance. The closer to earth, the heavier the
+pull; the further from earth, the less the pull. Besides the actual
+attraction of the earth drawing the air-particles downward, there is
+the great weight of the whole atmosphere above, caused by the same
+attraction. Miles and miles of air overhead press mightily downward,
+packing tightly together the lower layers of air near to earth’s
+surface.
+
+Without this pressure of the overlying atmosphere, the air down
+here would not be nearly so dense as it is; and, indeed, would not
+be fitted to support life. A man ascending a mountain or rising in a
+balloon leaves heavy layers of air below, and has an ever-lightening
+weight above, so that the atmosphere around him becomes constantly
+more thin, more difficult to breathe.
+
+In the beginning of the last century Humboldt made a vigorous attempt
+to scale Chimborazo, one of the loftiest of the Andes. He and his
+party suffered severely from sickness, giddiness, and difficulty in
+breathing, and the attempt proved a failure. Not till over seventy
+years later was the ascent actually accomplished by Mr. Whymper.
+
+Carried upward passively in a balloon, without effort, men have risen
+higher than the highest mountains. Mr. Coxwell and Mr. Glaisher in
+their celebrated aerial voyage of 1862 are believed to have mounted
+seven miles above the sea. No little peril and suffering were
+involved, alike from the extreme thinness of the air, and from the
+bitter cold.
+
+The voyagers suffered from severe “sea-sickness,” though not from
+bleeding of the nose or singing in the ears, popularly expected on
+such occasions. They had enough to bear without these additions.
+Mr. Glaisher held manfully to his task, observing and noting down
+the state of the atmosphere minute by minute, despite sickness,
+brain-pressure, violent headache, and a pulse at 108 per minute, all
+due to the rarity of the air.
+
+In those lofty regions of the air-ocean no living creatures exist.
+The voyagers passed through boundless silent solitudes--silent
+except for the hurried beating of their own hearts, the sound of
+their own panting breath, the sharp ticking of their watches, and the
+“clang of the valve door.”
+
+On leaving earth the thermometer stood at 59°. Soon afterward the
+balloon passed through masses of cloud, thousands of feet in depth,
+then came out into dazzling sunshine, with deep-blue sky above and
+countless mountain masses of billowy cloud below.
+
+As they rose, they released at intervals a captive pigeon. One set
+free at a height of nearly five miles “fell downward like a stone.”
+Of two others taken higher, one died of the cold and the other
+was stupefied. When they reached five miles above the sea, the
+temperature was below zero.
+
+Still upward, further upward, rose the resolute pair. Then blinding
+darkness and insensibility seized Mr. Glaisher. Had he been alone, he
+could never have revived. With no one to open the valve, the balloon
+must have carried him onward into yet higher and deathlier regions,
+where for lack of air he would have perished. Even then Mr. Coxwell
+did not at once give in; but he was strictly on the watch. At the
+seven miles’ level, a tremendous height, he too felt signs of failing
+consciousness. In a few minutes more all would have been over with
+them both, and at last he yielded. It was indeed time that he should.
+His hands were powerless to act, but he seized the valve rope in his
+teeth and pulled. The gas rushed out; the balloon steadily sank. Both
+lives were saved, and a mighty feat had been accomplished.
+
+Yes, a mighty feat, and a tremendous height--in consideration of
+human powers! Seven miles high would seem to be the outside limit at
+which animals generally can exist for even a short time. Birds may
+be to some extent an exception. Certain birds are believed to soar
+occasionally two or three miles higher still.
+
+But what are seven miles--what are even ten miles--compared with the
+four or five hundred miles of atmosphere-depth? With all our utmost
+efforts, we and the birds still find ourselves only able to creep and
+flutter on or near the floor of the ocean of air.
+
+What earth would be without her surrounding ocean of air, we can
+scarcely imagine. The atmosphere plays so extraordinary and essential
+a part in all around, that to picture its entire absence is not easy.
+We see faintly on the moon something of what an airless world must
+be. Yet since we only “see” from a distance of two hundred and forty
+thousand miles, that does not mean much. Imagination has to come in,
+and imagination is apt to play us curious tricks when running after
+affairs which lie outside the range of human experience.
+
+Without air, man and beast can not breathe. Without air, plants and
+trees can not grow. Without air, life as we know it--the lower animal
+life common to man and beast--is a thing impossible. Without air, our
+world would be, as we suppose the moon to be, a world of lifelessness.
+
+Air is earth’s outer robe, “for use and for beauty”--for use in modes
+uncountable; for beauty, not so much in itself as in the softening,
+the diffusing, the controlling effects of its presence. Air is a
+mighty ocean, in which all things living must dwell. Even the living
+things of the sea are not exceptions to this rule, for water itself
+is pervaded by air. A man, going into and under water, does not get
+beyond the touch of air; only, not being provided, like fishes,
+with breathing gills, he can not make use of what is there--he can
+not separate the air from the water, and so keep himself alive by
+breathing it.
+
+Some animals living in the water-ocean are as dependent upon the
+air-ocean as man himself for “the breath of life.” Whales are a
+remarkable example of this. They are not fishes, though often
+mistakenly called so, but belong to the same “family” of creatures as
+men and land-quadrupeds generally. A whale is warm-blooded, has no
+gills, and breathes atmospheric air, coming to the surface for it.
+A whale kept forcibly for a long while under water would be drowned
+exactly as a man would be. If a whale is thrown upon the shore, it
+does not die of suffocation, but of inanition. A fish’s gills are
+no more fitted to breathe air in bulk than a man’s lungs are fitted
+to breathe air diffused in minute particles through water. The fish
+out of water is suffocated by getting air too rapidly: the man under
+water by exactly the reverse. A whale breathes like a man, and on
+land it simply starves fast from lack of the incessant food required
+by such a huge carcass.
+
+There is a difference certainly between man and whale in the matter
+of breathing. A man has to take in fresh supplies of air constantly,
+and if he is beyond reach of air for more than a few minutes he dies.
+A whale comes to the surface for about ten minutes, spouting out
+enormous supplies of used-up air and taking in enormous supplies of
+fresh air, after which it can remain under water for half an hour or
+more: some say an hour. Then a fresh bout of noisy breathing becomes
+an absolute necessity. This, however, is merely a matter of internal
+arrangement. The whale has an immense reservoir of blood, which,
+being thoroughly purified by the air during ten minutes of vigorous
+breathing, serves slowly to supply the creature’s requirements while
+below. But the need for air, and the effect of that air upon the
+blood, are much the same in man and whale.
+
+Small creatures, as well as big ones, spending much time under water,
+and yet breathing air, have to come regularly to the surface.
+
+If our world had no ocean of air, there could be on earth no men, no
+quadrupeds, no whales or fishes, no birds or insects, no forms of
+life.
+
+Like the ocean of water, the ocean of air knows no repose or
+stagnation. What we call stillness on the most sultry of summer days
+does not mean absolute stillness. Though not enough wind may stir
+to lift a feather, yet the air is in ceaseless motion, to and fro,
+hither and thither. The whole atmosphere is a vast and complicated
+system of air-currents, and each lesser portion of air has its own
+lesser circulation. You can not lift your hand without causing a tiny
+breeze; you can not turn a wheel without making a minute whirlwind;
+and every separate air-movement draws other movements in its train.
+
+There is water enough on earth for all needed purposes; but we
+should find ourselves in direful straits if the whole water-carrying
+from lakes and rivers for men and animals had to be performed by
+human agencies.
+
+Far from this, a mighty apparatus is provided. The scanty aid that
+man can give only shows how little he is capable of. The entire
+atmosphere is a tremendous pumping engine, an enormous watering
+machine, always at work; always receiving supplies of liquid from the
+ocean, from seas, lakes, rivers; always showering this water down
+again upon the land, as needful drink for plants and animals, as
+needful cleansing for all things.
+
+Air, the great carrier of water, in its wonderful strength and
+restlessness, bears vast layers of cloud to and fro, wafts away
+superfluous damp, drenches the dry and thirsty earth, fills ponds and
+lakes, feeds--nay, actually makes--the rivers, never flags in its
+ceaseless energy. If clouds hang low or fogs arise, we are glad of
+the moving air which sweeps them elsewhere. If the soil is caked and
+plants droop, we are glad of the moving air which brings rain. Thus
+our wants are supplied, and the wide water circulation of earth is
+carried on. Without circulation, without motion, stir, change, there
+can not be life. Stagnation must mean death. Our earth, without her
+ocean of moving air, would be a world of death.
+
+Without air, earth would be in great measure a soundless world.
+Silence would reign here, as probably it does reign on the moon.
+Sound, as it commonly reaches our ears, depends for its very
+existence upon air. Let the concussion of two bodies be ever so
+mighty, if there were no air to bear away the vibrations of that
+concussion, there could be no crash of sound. True, sound-waves can
+be conveyed through a liquid or through a solid as well as through
+air; and we might be conscious of the ground’s vibrations, but our
+ears would hear no noise.
+
+So an airless world would be a silent world. Without air, supposing
+we could ourselves exist, we should hear no trickling brooks, no rush
+of waterfalls, no breaking ocean waves, no sighing of the wind, no
+whisper of leaves, no singing of birds, no voices of men, no music,
+no thunder, no one of the thousand concomitant sound-waves which
+together make up the babble and murmur of country and town. Those
+only who are perfectly deaf can know what such silence means.
+
+Without air our world would not be in darkness; for light does
+not, like sound, depend mainly upon air for its transmission.
+Light travels through regions where air is not; and if light is
+communicated by waves, they are not waves of air. But though the
+absence of air would not deprive the earth of light, it would make a
+very great difference in the kind and degree of light received.
+
+Without air the blue sky would be black as ink; stars would glitter
+coldly in the daytime beside a glaring sun; deep shadows would
+alternate with blinding dazzle, and all the soft tints of sunrise
+and sunset would be wanting. Earth would be like the almost airless
+moon--all fierce whiteness and utter blackness--with no gray shades,
+no rosy gleams, no golden evening clouds; nay, without air there
+could be no clouds. On the moon is no twilight; for no air-particles
+float about, reflecting the sunlight from one to another, and forming
+a soft veil of brightness, to reach further than the direct sunlight
+alone can reach.
+
+Sunbeams travel straight to earth, unbending as arrows in their
+flight, and unaided they can not creep any distance round a solid
+body, though they may be reflected or turned back from it. But the
+air breaks up the sunbeams, bends them, diffuses them, spreads them
+about, surrounds us with a delicate lacework of woven light. A
+sunbeam traveling through space is invisible till it strikes upon
+some object. If that object is solid, the light of the sunbeam is
+partly absorbed, partly reflected; if the object is transparent,
+the sunbeam passes through and onward. Few substances, if any, are
+perfectly transparent. We call air transparent, yet it is so only in
+a measure. Each sunbeam passing through the atmosphere loses part
+of its brightness by the way, and so the great glare of the sun is
+softened before it reaches the lower depths of the air-ocean.
+
+The sun’s rays are rays of heat as well as of light. While the
+atmosphere softens the glare, giving us shade and twilight, it also
+modifies the extremes of temperature, from which, without air, we
+should suffer.
+
+When the sun goes down, although we are often conscious of a chill,
+it is not the instant and overwhelming chill which we should feel but
+for the atmosphere. All day long the sun has been warming the earth
+and air. When his direct rays are withdrawn, the warm air for a while
+keeps its warmth, and gives over of that warmth to us.
+
+
+
+
+  WEATHER
+  --SIR RALPH ABERCROMBY
+
+
+The earliest records of weather among every nation are to be found in
+those myths, or popular tales, which, while describing rain, cloud,
+wind, and other natural phenomena in highly figurative language,
+refer them to some supernatural or personal agency by way of
+explanation.
+
+The most interesting thing about these mythical stories is the
+remarkable fidelity with which they reflect the climate of the
+country that gave them birth. For example, from the mythologies of
+Greece and Scandinavia we can almost construct an account of the
+climate of those two countries by simply translating the figurative
+phraseology of their legends into the language of modern meteorology.
+
+Many survivals of mystic speech are still found among popular
+prognostics, and especially in cloud names.
+
+In England and Sweden “Noah’s Ark” is still seen in the sky, while
+in Germany the “Sea-Ship” still turns its head to the wind before
+rain. In Scotland the “Wind-Dog” and the “Boar’s Head” are still the
+dread of the fisherman, while such names as “Goat’s Hair” and “Mare’s
+Tails” recall some of the shaggy monsters of antiquity.
+
+At a rather later period of intellectual development, the premonitory
+signs of good or bad weather become formulated into short sayings,
+or popular prognostics. A large number of these are still current in
+every part of the world, but their quality and value are very varied.
+Some represent the astrological attitude of mind, by referring
+weather changes to the influence of the stars or phases of the moon;
+others, on the contrary, are very valuable, and, in conjunction with
+other aids to weather forecasting, prognostics will never be entirely
+superseded, especially for use on board ship. Till within a very
+recent period, their science and explanation had hardly advanced
+since they were first recorded. In many cases the prognostics came
+true; when they failed, no explanation could be suggested why they
+did so; neither could any reason be given why the same weather was
+not always preceded by the same signs. A halo sometimes precedes a
+storm; why does it not always do so? Why is rain sometimes preceded
+by a soft sky and sometimes by hard clouds?
+
+About one hundred and fifty years ago the barometer was invented.
+Very soon after that discovery, observation showed that, in a general
+way, the mercury fell before rain and wind, and rose for finer
+weather. Also that bad weather was more common when the whole level
+of the barometer was low, independent of its motion one way or the
+other, than when the level was high. But as with prognostics, so
+with these indications, many failures occurred. Sometimes rain would
+fall with a high or rising barometer, and sometimes there would be a
+fine day with a very low or falling glass. No reason could be given
+for these apparent exceptions, and the whole science of barometric
+readings seemed to be shrouded in mystery.
+
+The science of probabilities came into existence about the
+commencement of the Nineteenth Century, and developed the science of
+statistics. By this method the average readings of meteorological
+instruments, such as the height of the barometer or thermometer, or
+the mean direction and force of the wind, at any number of places
+were calculated, and the results were sometimes plotted on charts so
+as to show the distribution of mean pressure, temperature, etc., over
+the world.
+
+By this means a great advance was made. Besides giving a numerical
+value to many abstract quantities, the plotting of such lines as the
+isothermals of Dove conclusively showed that many meteorological
+elements hitherto considered capricious were really controlled by
+general causes, such as the distribution of land and sea.
+
+Still more fruitful were these charts as the parents of the more
+modern methods of plotting the readings of the barometer over large
+areas at a given moment, instead of the mean value for a month
+or year. Then by tabulating statistics the relative frequency of
+different winds at sea, many ocean voyages--notably those across
+the “doldrums,” or belt of calms near the equator--were materially
+shortened.
+
+Statistics also of the annual amount of rainfall became of commercial
+value as bearing on questions of the economic supply of water for
+large towns, and much valuable information was acquired as to
+the dependence of mortality on different kinds of weather. Of
+more purely scientific interest were the variations of pressure,
+temperature, wind, etc., depending on the time of day, or what are
+technically known as diurnal variations, which were brought to light
+by these comparisons.
+
+This branch of the subject is known as “Statistical Meteorology,” and
+has advanced very little since it was first developed by Dove and
+Kaemtz.
+
+When the attempt was made to apply statistics to weather changes
+from day to day, it was found that average results were useless.
+The mean temperature for any particular day of the year might be
+50°, if deduced from the returns of a great many years, but in any
+particular year it might be as low as 40°, or as high as 60°. The
+first application of the method was made by the great Napoleon, who
+requested Laplace to calculate when the cold set in severely over
+Russia. The latter found that on an average it did not set in hard
+till January. The emperor made his plans accordingly; a sharp spell
+of cold came in December, and the army was lost.
+
+It has now been thoroughly recognized that statistics give a
+numerical representation of climate, but little or none of weather,
+and that large masses of figures have been accumulated, to which
+it is difficult to attach any physical significance. The misuse of
+statistics has done much to bring the science of meteorology into
+disrepute.
+
+But within the last thirty years a new treatment of weather problems
+has been introduced, known as the synoptic method, by which the
+whole aspect of meteorology has been changed. By this method, a
+chart of a large area of the earth’s surface is taken, and after
+marking on the map the height of the barometer at each place,
+lines are drawn through all stations at which the barometer marks
+a particular height. Thus a line would be drawn through all places
+where the pressure was 30.0 inches, another through all where it
+was 29.8 inches, and so on at any intervals which were considered
+necessary. These lines are called “isobars,” because they mark out
+lines of equal pressure. When these charts were first introduced,
+the estimation of the value of the mean pressure was so great that,
+instead of drawing lines where pressure was equal at the moment,
+they were drawn through those places where the pressure was equally
+distant from the mean of the day for each place. These lines were
+called “is-abnormals”; that is, equal from the mean. After the
+isobars have been put in, lines are usually drawn through all places
+where the temperature is equal at the moment. These are called
+“isotherms,” or lines of equal temperature. Then arrows to mark
+the velocity and direction of the wind are inserted; and finally
+letters, or other symbols, to denote the appearance of the sky, the
+amount of cloud, or the occurrence of rain or snow. Such a chart is
+called a “synoptic chart,” because it enables the meteorologist to
+take a general view, as it were, over a large area. Sometimes they
+are called “synchronous charts,” because they are compiled from
+observations taken at the same moment of time.
+
+[Illustration: Typical Forms of Clouds
+
+1, Squall Cumulus; 2, Pillar Cumulus; 3, Cirrus; 4, High Stratus and
+Cumulus]
+
+When these came to be examined, the following important
+generalizations were discovered:
+
+1. That in general the configuration of the isobars assumed one of
+seven well-defined forms.
+
+2. That, independent of the shape of the isobars, the wind always
+took a definite direction relative to the trend of those lines, and
+the position of the nearest area of low pressure.
+
+3. That the velocity of the wind was always nearly proportional to
+the closeness of the isobars.
+
+4. That the weather--that is to say, the kind of cloud, rain, fog,
+etc.--at any moment was related to the shape, and not the closeness,
+of the isobars, some shapes inclosing areas of fine, others of bad,
+weather.
+
+5. That the regions thus mapped out by isobars were constantly
+shifting their position, so that changes of weather were caused by
+the drifting past of these areas of good or bad weather, just as on
+a small scale rain falls as a squall drives by. The motion of these
+areas was found to follow certain laws, so that forecasting weather
+changes in advance became possible.
+
+6. That sometimes in the temperate zone, and habitually in the
+tropics, rain fell without any appreciable change in the isobars,
+though the wind conformed to the general law of these lines.
+
+Observation also showed that, though the same shapes of isobars
+appear all over the world, the details of weather within them, and
+the nature of their motion, are modified by numerous local, diurnal,
+and annual variations. Hence modern weather science consists in
+working out for each country the details of the character and motion
+of the isobars which are usually found over it; just as the geologist
+finds crumplings and denudation all over the world, and works out the
+history of the physical appearance of his own scenery by studying the
+local development of these agencies.
+
+So far the science rests on pure observation--that such and such
+wind or weather comes with such and such a shape of isobars. But it
+has been found, still further, that the seven fundamental shapes
+of isobars are, as it were, the product of so many various ways in
+which an atmosphere circulating from the equator to the poles may
+move. Just as the motion of a river sometimes forms descending eddies
+or whirlpools, sometimes back-waters in which the water is rising
+upward, or yet at other times ripples in which the circulation is
+very complex, so it now appears that the general movement of the
+atmosphere from the equator to the pole sometimes breaks up into a
+rotating and descending movement round that configuration of isobars
+known as an anticyclone, sometimes into a rotating and ascending
+movement round that known as a cyclone, or at other times quite in a
+different way during certain kinds of squalls and thunderstorms.
+
+_Isobars, therefore, represent the effect on our barometers of the
+movements of the air above us, so that by means of isobars we trace
+the circulation and eddies of the atmosphere._
+
+By carrying the general laws of physics into the conception of a
+circulating gas, we find that a cold mixed atmosphere of air and
+vapor descending into a warmer soil would remain clear and bright;
+while a similar atmosphere rising into cooler strata would condense
+some of its vapor into rain or cloud. It is by reasoning of this
+nature that the origin of some of the most beautiful and complex
+forms of clouds has been discovered.
+
+Following out these lines of research, a new science of meteorology
+has grown up, which entirely alters the attitude of mind with which
+we regard weather changes, and gives rise to an entirely new method
+of weather forecasting that far surpasses all previous efforts, and
+which explains and develops all that was known before.
+
+On the one hand, the new method not only explains why certain
+prognostics are usually signs of good or bad weather, and the reason
+why the indications sometimes fail; but also the reason why rain, for
+instance, is sometimes foretold by one prognostic and sometimes by a
+totally different one.
+
+On the other hand, it not only gives a more extended meaning to all
+the statistics which partially represent the climate of a place, and
+to the relation of the diurnal to the general changes of weather; but
+it also enables new inferences to be drawn, which had hitherto been
+impossible from some observations, and explains why other sets of
+figures must always remain without any physical significance.
+
+We may notice here an attempt which has been made by one school of
+meteorologists to deduce all weather _à priori_ from changes in the
+radiative energy of the sun; that is to say, that from a knowledge of
+greater or less heat being emitted by the sun, they would treat the
+consequent alteration of weather as a direct hydrodynamical problem.
+Given an earth surrounded by fifty miles of damp air, and a sun at
+varying altitude, and of varying radiative energy, deduce from that
+all the diverse changes of weather. This is doubtless a very tempting
+ideal, for there is no doubt that the sun’s heat is the prime mover
+of all atmospheric circulation; but when we have explained what the
+nature of weather changes is, we see that there is little hope that
+this method will ever lead to satisfactory results.
+
+Other meteorologists, who lay less stress on the varying power of
+the sun, have taken up the indications of synoptic charts, and
+endeavored to construct a mathematical theory of cyclones and the
+general circulation of the atmosphere. Ferrel, Mohn, Gulberg, Sprung,
+and others have all started with the analysis of the motion of a
+free mass of air on the earth’s surface, first given by Professor
+Ferrel, and worked out, from that and other general principles,
+schemes of the nature and propagation of cyclones, and of the general
+distribution of pressure over the world.
+
+
+
+
+  THE ROMANCE OF A RAINDROP
+  --ARTHUR H. BELL
+
+
+Depth of rainfall is, of course, ascertained by means of a
+rain-gauge, which measures the amount of water precipitated from
+the atmosphere during certain definite periods--usually twenty-four
+hours. Sir Christopher Wren has the credit of constructing the
+first rain-gauge; but they have been made in various shapes and
+sizes since his time; and perhaps none of the instruments in the
+meteorologist’s armory is so familiar to the general public as the
+rain-gauge. The methods of using the instrument and the meaning of
+rainfall statistics are also thoroughly understood nowadays. However,
+behind these statistics and the methods of obtaining them, there
+are questions of great interest that obtrude themselves when we are
+watching the falling rain, and we desire to learn about the history
+of the raindrop--for example: Why is a raindrop round? How are
+raindrops formed? At what particular time does vapor become visible
+as mist? And what are the causes which change this mist into cloud
+and subsequently into rain?
+
+The two prime causes of rain are, of course, the sun and the ocean;
+and since these two factors do not appreciably vary from year to
+year, it follows that the annual rainfall on the earth as a whole,
+if it could be measured, would also be found to be invariable. It
+is obvious, however, that the rainfall at all places is not equal.
+In London, for instance, the average yearly rainfall is twenty-two
+inches; but on the Khasi Hills in India it is no less than six
+hundred inches. Similar contrasts are observable in other parts of
+the world, the differences being due to local geographical conditions.
+
+The starting points in the history of rain are, therefore, heat
+and moisture. From the surface of land and water tiny globules or
+vesicles of moisture are continually rising into the atmosphere by
+the force of the sun’s heat; and the warmer the air the greater the
+number of these globules of water the atmosphere is able to absorb.
+In this respect the atmosphere may be likened to a sponge, for it
+is from the moisture thus retained that the subsequent raindrops
+are formed. Most persons are well acquainted with the very familiar
+phenomenon which is to be noticed when a glass of very cold water is
+brought into a warm room: the drops of moisture which form on the
+outside of the glass being among the commonest phenomena in what may
+be termed domestic meteorology. There is a similar transformation in
+the outside atmosphere; so that when the warm, moist currents of air
+flow against the sides of a cold mountain, or it may be against a
+body of cold air, there is a reduction in temperature, the atmosphere
+is squeezed like a sponge, and the particles of moisture are forced
+out of it. The particles then assume the form of cloud, fog, mist,
+rain, snow, and hail, as the case may be.
+
+Now, as regards the globules of moisture, the most recent experiments
+and observations point to the conclusion that before the drops of
+vapor can form, there must be a tiny nucleus of dust upon which the
+condensed water may settle. At the centre of every drop of vapor in
+a cloud there is probably a little core of dust; and without these
+little atoms there could be no rain. These atoms of dust are visible
+only under the strongest microscopes; and so minute are they that in
+a cubic foot of saturated air it has been calculated that they number
+one thousand millions, their total weight being only three grains.
+
+It is commonly considered that the particles of moisture within
+a cloud are quite motionless; and when looking at a huge cloud
+floating serenely in a summer sky it is difficult not to think of its
+constituent parts as being quite at rest. The apparently stationary
+cloud is all commotion and movement, the particles within it being
+always on the move, some going up and others down. The particles of
+moisture, moreover, being probably only about the four-thousandth
+part of an inch in diameter, the resistance offered by the air to
+their movement is very slight; indeed, as soon as they are condensed
+they immediately begin to fall downward, and were it not for the
+atoms of dust waiting to catch them the particles would at once
+fall to the ground. It is often asked why the vapor, if so readily
+condensed in the atmosphere, does not continually fall to the earth.
+The answer to this question, it will be seen, is that the moisture,
+instead of always pouring down on the earth, settles on the surface
+of the atoms of dust. Thus the first downward movement of the
+incipient raindrop is arrested by the dust-nuclei which swarm in all
+parts of the atmosphere; so that instead of being destroyed as soon
+as it is formed, the particle of moisture is preserved and stored for
+future use. In realizing the fact that a cloud is always in motion,
+the first step has been taken in discovering how a raindrop is formed.
+
+It might be supposed that the raindrops would evaporate as quickly as
+they were condensed; but observation of the drops of moisture running
+down a window-pane and forming larger drops gives a good idea of
+what occurs in the clouds; as also does the fact that in a bottle of
+soda-water the bubbles of air overtake one another and, colliding,
+make larger bubbles.
+
+One of the principal causes of the manufacture of a raindrop is
+to be found in the circumstance that there is a similar process
+of amalgamation at work in every part of the atmosphere. It often
+happens that a drop of moisture falls downward through a cloud for a
+distance of a mile or more; and although it may pass through strata
+of very warm air, thus running a great risk of being evaporated
+and destroyed, it has also many collisions by which its bulk is
+considerably increased, and eventually becomes so heavy that its rate
+of progress is very much accelerated. Then, no longer able to float
+in the air, it plumps down to the earth as a full-grown raindrop.
+
+Supposing it were possible for an observer to occupy a position
+immediately below a cloud, and close enough to see all that was
+taking place, he would notice raindrops of all sizes leaping from the
+under side of the cloud and plunging toward the earth. The simplest
+experiment to get some idea concerning the variation in raindrops
+is to expose an ordinary slate for a few minutes during a shower of
+rain, and it will be seen by the different-shaped blotches on the
+slate that, although the raindrops have all made a similar journey,
+they have, nevertheless, contrived to acquire an individuality during
+their downward passage. That the raindrops are round admits of a
+very simple explanation. They are this shape owing to the action of
+capillarity, which in the case of the raindrop acts equally in all
+directions.
+
+In many parts of the world the very curious phenomenon of colored
+rain sometimes occurs, and in many instances it is due to very simple
+causes. In some cases the coloring matter is found to be nothing but
+the pollen-dust shaken out of the flowers on certain trees at such
+times as a strong wind happened to be blowing over them. Fir trees
+and cypress trees, when grouped together in large forests, at certain
+seasons of the year give off enormous quantities of pollen, and this
+vegetable dust is often carried many miles through the atmosphere by
+the wind, and frequently falls to earth during a shower of rain. The
+microscope clearly reveals the origin of such colored rain, which has
+on more than one occasion puzzled and mystified the inexperienced.
+Pollen is, therefore, very largely responsible for the reports sent
+from different parts of the world of golden, black, and red rain.
+Fish and insects also descend to earth during showers of rain; but
+since it is probable that these and other unwonted visitors to the
+atmosphere were originally drawn up into the air during the passage
+across the country of a whirling storm, with powerfully ascending
+currents of air, there is no need to look for any far-fetched
+explanation of what, after all, is a very simple occurrence.
+
+The history of a raindrop, then, has some very romantic and
+interesting episodes connected with it; but, wonderful as are the
+incidents in what is really a very remarkable career, it is not until
+the raindrops fall on the earth that the full purport of the work
+they do is wholly realized. Contemplated by itself, a raindrop seems
+a very insignificant thing; but when the drops combine in a heavy
+downpour of rain the result is truly wonderful. The information
+that one inch of rain has fallen over a certain area is not very
+impressive; the amount does not seem very great. A fall of one inch
+of rain means, however, that no less than one hundred tons of water
+have fallen on each acre of surface, or no less than sixty thousand
+tons on each square mile. Instead of expressing the amount of water
+in tons, it may be thus stated in gallons, taking the Thames basin
+as a convenient area for reference: a rainfall of three inches over
+that area means that one hundred and sixty thousand million gallons
+of water have been precipitated from the atmosphere. At times, too,
+when the rainfall is still heavier, rivers overflow their banks and
+floods occur, and still further evidence is then forthcoming of the
+power and the might of the raindrops working toward one common end.
+Sooner or later the raindrop, whether it runs off the surface of the
+earth in a river or in a disastrous flood, finds its way, under the
+influence of evaporation, back into the atmosphere, and is then ready
+to start on another journey, which, like all its predecessors, will
+be full of incident from start to finish.
+
+
+
+
+  THE RAINBOW
+  --JOHN TYNDALL
+
+
+The oldest historic reference to the rainbow is known to all: “I do
+set my bow in the clouds, and it shall be for a token of a covenant
+between me and the earth.... And the bow shall be in the cloud; and
+I will look upon it, that I may remember the everlasting covenant
+between God and every living creature of all flesh that is upon the
+earth.”
+
+To the sublime conceptions of the theologian succeeded the desire for
+exact knowledge characteristic of the man of science. Whatever its
+ultimate cause might have been, the proximate cause of the rainbow
+was physical, and the aim of science was to account for the bow on
+physical principles. Progress toward this consummation was very slow.
+Slowly the ancients mastered the principles of reflection. Still more
+slowly were the laws of refraction dug from the quarries in which
+Nature had imbedded them. I use this language because the laws were
+incorporate in Nature before they were discovered by man. Until the
+time of Alhazan, an Arabian mathematician, who lived at the beginning
+of the Twelfth Century, the views entertained regarding refraction
+were utterly vague and incorrect. After Alhazan came Roger Bacon and
+Vitellio, who made and recorded many observations and measurements on
+the subject of refraction. To them succeeded Kepler, who, taking the
+results tabulated by his predecessors, applied his amazing industry
+to extract from them their meaning--that is to say, to discover
+the physical principles which lay at their root. In this attempt
+he was less successful than in his astronomical labors. In 1604,
+Kepler published his _Supplement to Vitellio_, in which he virtually
+acknowledged his defeat by enunciating an approximate rule, instead
+of an all-satisfying natural law. The discovery of such a law, which
+constitutes one of the chief corner-stones of optical science, was
+made by Willebrod Snell, about 1621.
+
+A ray of light may, for our purposes, be presented to the mind as a
+luminous straight line. Let such a ray be supposed to fall vertically
+upon a perfectly calm water-surface. The incidence, as it is called,
+is then perpendicular, and the ray goes through the water without
+deviation to the right or left. In other words, the ray in the air
+and the ray in the water form one continuous straight line. But the
+least deviation from the perpendicular causes the ray to be broken,
+or “refracted,” at the point of incidence. What, then, is the law
+of refraction discovered by Snell? It is this, that no matter how
+the angle of incidence and with it the angle of refraction may vary,
+the relative magnitude of two lines, dependent on these angles,
+and called their sines, remains, for the same medium, perfectly
+unchanged. Measure, in other words, for various angles, each of these
+two lines with a scale, and divide the length of the longer one by
+that of the shorter; then, however the lines individually vary in
+length, the quotient yielded by this division remains absolutely the
+same. It is, in fact, what is called “the index of refraction” of the
+medium.
+
+Science is an organic growth, and accurate measurements give
+coherence to the scientific organism. Were it not for the antecedent
+discovery of the law of sines, founded as it was on exact
+measurements, the rainbow could not have been explained. Again and
+again, moreover, the angular distance of the rainbow from the sun
+had been determined and found constant. In this divine remembrancer
+there was no variableness. A line drawn from the sun to the rainbow,
+and another drawn from the rainbow to the observer’s eye, always
+inclosed an angle of 41°. Whence this steadfastness of position--this
+inflexible adherence to a particular angle? Newton gave to De
+Dominis[4] the credit of the answer; but we really owe it to the
+genius of Descartes. He followed with his mind’s eye the rays of
+light impinging on a raindrop. He saw them in part reflected from
+the outside surface of the drop. He saw them refracted on entering
+the drop, reflected from its back, and again refracted on their
+emergence. Descartes was acquainted with the law of Snell, and taking
+up his pen, he calculated, by means of that law, the whole course
+of the rays. He proved that the vast majority of them escaped from
+the drop as _divergent_ rays, and, on this account, soon became
+so enfeebled as to produce no sensible effect upon the eye of an
+observer. At one particular angle, however--namely, the angle 41°
+aforesaid--they emerged in a practically _parallel sheaf_. In their
+union was strength, for it was this particular sheaf which carried
+the light of the “primary” rainbow to the eye.
+
+There is a certain form of emotion called intellectual pleasure which
+may be excited by poetry, literature, nature, or art. But I doubt
+whether among the pleasures of the intellect there is any more pure
+and concentrated than that experienced by the scientific man when a
+difficulty which has challenged the human mind for ages melts before
+his eyes, and re-crystallizes as an illustration of natural law. This
+pleasure was doubtless experienced by Descartes when he succeeded in
+placing upon its true physical basis the most splendid meteor of our
+atmosphere. Descartes showed, moreover, that the “secondary bow” was
+produced when the rays of light underwent two reflections within the
+drop, and two refractions at the points of incidence and emergence.
+
+Descartes proved that, according to the principles of refraction, a
+circular band of light must appear in the heavens exactly where the
+rainbow is seen. But how are the colors of the bow to be accounted
+for? Here his penetrative mind came to the very verge of the
+solution, but the limits of knowledge at the time barred his further
+progress. He connected the colors of the rainbow with those produced
+by a prism; but then these latter needed explanation just as much as
+the colors of the bow itself. The solution, indeed, was not possible
+until the composite nature of white light had been demonstrated by
+Newton. Applying the law of Snell to the different colors of the
+spectrum, Newton proved that the primary bow must consist of a series
+of concentric circular bands, the largest of which is red and the
+smallest violet; while in the secondary bow these colors must be
+reversed. The main secret of the rainbow, if I may use such language,
+was thus revealed.
+
+I have said that each color of the rainbow is carried to the eye by
+a sheaf of approximately parallel rays. But what determines this
+parallelism? Here our real difficulties begin. Let us endeavor to
+follow the course of the solar rays before and after they impinge
+upon a spherical drop of water. Take, first of all, the ray that
+passes through the centre of the drop. This particular ray strikes
+the back of the drop as a perpendicular, its reflected portion
+returning along its own course. Take another ray close to this
+central one and parallel to it--for the sun’s rays when they reach
+the earth are parallel. When this second ray enters the drop it is
+refracted; on reaching the back of the drop it is there reflected,
+being a second time refracted on its emergence from the drop. Here
+the incident and the emergent rays inclose a small angle with each
+other. Take, again, a third ray a little further from the central
+one than the last. The drop will act upon it as it acted upon its
+neighbor, the incident and the emergent rays inclosing in this
+instance a larger angle than before. As we retreat further from the
+central ray the enlargement of this angle continues up to a certain
+point, where it reaches a maximum, after which further retreat
+from the central ray diminishes the angle. Now, a maximum resembles
+the ridge of a hill, or a watershed, from which the land falls in a
+slope at each side. In the case before us the divergence of the rays
+when they quit the raindrop would be represented by the steepness
+of the slope. On the top of the watershed--that is to say, in the
+neighborhood of our maximum--is a kind of summit-level, where the
+slope for some distance almost disappears. But the disappearance of
+the slope indicates, as in the case of our raindrop, the absence of
+divergence. Hence we find that at our maximum, and close to it, there
+issues from the drop a sheaf of rays which are nearly, if not quite,
+parallel to each other. They are the so-called “effective rays” of
+the rainbow.
+
+But though the step here taken by Descartes and Newton was a great
+one, it left the theory of the bow incomplete. Within the rainbow
+proper, in certain conditions of the atmosphere, are seen a series of
+richly colored zones, which were not explained by either Descartes
+or Newton. They are said to have been first described by Mariotte,
+and they long challenged explanation. At this point our difficulties
+thicken, but, as before, they are to be overcome by attention. It
+belongs to the very essence of a maximum, approached continuously
+on both sides, that on the two sides of it pairs of equal value may
+be found. The maximum density of water, for example, is 39° Fahr.
+Its density, when 5° colder and when 5° warmer than this maximum, is
+the same. So also with regard to the slopes of a watershed. A series
+of pairs of points of the same elevation can be found upon the two
+sides of the ridge; and, in the case of the rainbow, on the two
+sides of the maximum deviation we have a succession of pairs of rays
+having the same deflection. Such rays travel along the same line,
+and add their forces together after they quit the drop. But light,
+thus reinforced by the coalescence of non-divergent rays, ought to
+reach the eye. It does so; and were light what it was once supposed
+to be--a flight of minute particles sent by luminous bodies through
+space--then these pairs of equally deflected rays would diffuse
+brightness over a large portion of the area within the primary bow.
+But inasmuch as light consists of _waves_, and not of particles, the
+principle of interference comes into play, in virtue of which waves
+alternately reinforce and destroy each other. Were the distance
+passed over by the two corresponding rays within the drop the same,
+they would emerge as they entered. But in no case are the distances
+the same. The consequence is that when the rays emerge from the drop
+they are in a condition either to support or to destroy each other.
+By such alternate reinforcement and destruction, which occur at
+different places for different colors, the colored zones are produced
+within the primary bow. They are called “supernumerary bows,” and
+are seen, not only within the primary, but sometimes also outside
+the secondary bow. The condition requisite for their production is
+that the drops which constitute the shower shall all be of nearly the
+same size. When the drops are of different sizes, we have a confused
+superposition of the different colors, an approximation to white
+light being the consequence. This second step in the explanation of
+the rainbow was taken by a man the quality of whose genius resembled
+that of Descartes or Newton, and who in 1801 was appointed Professor
+of Natural Philosophy in the Royal Institution. I refer, of course,
+to the illustrious Thomas Young.
+
+But our task is not, even now, complete. The finishing touch to
+the explanation of the rainbow was given by the eminent Astronomer
+Royal, Sir George Airy. Bringing the knowledge possessed by the
+founders of the undulatory theory, and that gained by subsequent
+workers, to bear upon the question, Sir George Airy showed that,
+though Young’s general principles were unassailable, his calculations
+were sometimes wide of the mark. It was proved by Airy that the
+curve of maximum illumination in the rainbow does not quite
+coincide with the geometric curve of Descartes and Newton. He also
+extended our knowledge of the supernumerary bows, and corrected
+the positions which Young had assigned to them. Finally, Professor
+Miller of Cambridge and Dr. Galle of Berlin illustrated with careful
+measurements with the theodolite the agreement which exists between
+the theory of Airy and the facts of observation. Thus, from Descartes
+to Airy, the intellectual force expended in the elucidation of the
+rainbow, though broken up into distinct personalities, might be
+regarded as that of an individual artist, engaged throughout this
+time in lovingly contemplating, revising, and perfecting his work.
+
+The white rainbow (_l’arc-en-ciel blanc_) was first described by the
+Spanish Don Antonio de Ulloa, lieutenant of the Company of Gentleman
+Guards of the Marine. By order of the King of Spain, Don Jorge Juan
+and Ulloa made an expedition to South America, an account of which
+is given in two amply illustrated quarto volumes to be found in the
+library of the Royal Institution. The bow was observed from the
+summit of the mountain Pambamarca, in Peru. The angle subtended by
+its radius was 33° 30′, which is considerably less than the angle
+subtended by the radius of the ordinary bow.
+
+The white rainbow has been explained in various ways. The genius of
+Thomas Young throws light upon this subject, as upon so many others.
+He showed that the whiteness of the bow was a direct consequence of
+the smallness of the drops which produce it. The smaller the drops,
+the broader are the zones of the supernumerary bows, and Young proved
+by calculation that when the drops have a diameter of 1-3000th or
+1-4000th of an inch, the bands overlap each other, and produce white
+light by their mixture.
+
+
+
+
+  SNOW, HAIL, AND DEW
+  --ALEXANDER BUCHAN
+
+
+Snow is the frozen moisture which falls from the atmosphere when the
+temperature is 32° or lower. It is composed of crystals, usually in
+the form of six-pointed stars, of which about 1,000 different kinds
+have been already observed, and many of them figured, by Scoresby,
+Glaisher, and others. These numerous forms have been reduced to
+five principal varieties: Thin plates, the most numerous class,
+containing several hundred forms of the rarest and most exquisite
+beauty; spherical nucleus or plane figure studded with needle-shaped
+crystals; six or more rarely three-sided prismatic crystals; pyramids
+of six sides; prismatic crystals, having at the ends and middle thin
+plates perpendicular to their length. The forms of the crystals
+in the same fall of snow are generally similar to each other. The
+crystals of hoar-frost being formed on leaves and other bodies
+disturbing the temperature are often irregular and opaque; and it has
+been observed that each tree or shrub has its own peculiar crystals.
+
+Snowflakes vary from an inch to 7-100ths of an inch in diameter, the
+largest occurring when the temperature is near 32°, and the smallest
+at very low temperatures. As air has a smaller capacity for retaining
+its vapor as the temperature sinks, it follows that the aqueous
+precipitation, snow or rain, is much less in polar than in temperate
+regions. The white color of snow is the result of the combination of
+the different prismatic rays issuing from the _minute_ snow-crystals.
+Pounded glass and foam are analogous cases of the prismatic colors
+blending together and forming the white light out of which they had
+been originally formed. It may be added that the air contained in
+the crystals intensifies the whiteness of the snow. The limit of
+the fall of snow coincides nearly with 30° N. lat., which includes
+nearly the whole of Europe; on traversing the Atlantic, it rises to
+45°, but on nearing America descends to near Charleston; rises on
+the west of America to 47°, and again falls to 40° in the Pacific.
+It corresponds nearly with the winter isothermal of 52° Fahr. Snow
+is unknown at Gibraltar; at Paris, it falls 12 days on an average
+annually, and at St. Petersburg 170 days. It is from 10 to 12 times
+lighter than an equal bulk of water. From its loose texture, and its
+containing about 10 times its bulk of air, it is a very bad conductor
+of heat, and thus forms an admirable covering for the earth from
+the effects of radiation--it not infrequently happening, in times
+of great cold, that the soil is 40° warmer than the surface of the
+overlying snow. The flooding of rivers from the melting of the snow
+on mountains in summer carries fertility into regions which would
+otherwise remain barren wastes.
+
+The word hail in English is unfortunately used to denote two
+phenomena of apparently different origin. In French, we have the
+terms _grèle_ and _grésil_--the former of which is hail proper; the
+latter denotes the fine grains, like small shot, which often fall
+in winter, much more rarely in summer, and generally precede snow.
+The cause of the latter seems to be simply the freezing of raindrops
+as they pass in their fall through a colder region of air than that
+where they originated. We know by balloon ascents and various other
+methods of observation that even in calm weather different strata
+of the atmosphere have extremely different temperatures, a stratum
+far under the freezing point being often observed between two others
+comparatively warm.
+
+But that true hail, though the process of its formation is not yet
+perfectly understood, depends mainly upon the meeting of two nearly
+opposite currents of air--one hot and saturated with vapor, the
+other very cold--is rendered pretty certain by such facts as the
+following. A hailstorm is generally a merely local phenomenon, or at
+most, ravages a belt of land of no great breadth, though it may be
+of considerable length. Hailstorms occur in the greatest perfection
+in the warmest season, and at the warmest period of the day, and
+generally are most severe in the most tropical climates. A fall of
+hail generally _precedes_, sometimes accompanies, and rarely, if
+ever, follows a thunder-shower.
+
+When a mass of air, saturated with vapor, rising to a higher level,
+meets a cold one, there is, of course, instant condensation of vapor
+into ice by the cold due to expansion; at the same time, there is
+generally a rapid production of electricity, the effect of which upon
+such light masses as small hailstones is to give them in general
+rapid motion in various directions successively. These motions are in
+addition to the vortex motions or eddies, caused in the air by the
+meeting of the rising and descending currents. The small ice-masses
+then moving in all directions impinge upon each other, sometimes with
+great force, producing that peculiar rattling sound which almost
+invariably precedes a hail-shower. At the same time, by a well-known
+property of ice, the impinging masses are frozen together; and this
+process continues until the weight of the accumulated mass enables
+it to overcome the vortices and the electrical attractions, when it
+falls as a larger or smaller hailstone. On examining such hailstones,
+which may have any size from that of a pea to that of a walnut, or
+even an orange, we at once recognize the composite character which
+might be expected from such a mode of aggregation.
+
+A curious instance of the fall of large hail, or rather ice-masses,
+occurred on one of her Majesty’s ships off the Cape in January, 1860.
+Here the stones were the size of half-bricks, and beat several of
+the crew off the rigging, doing serious injury. We may conclude by
+a description (taken from _Mem. de l’Acad. des Sciences_, 1790) of
+one of the most disastrous hailstorms that has occurred in Europe
+for many years back. This storm passed over Holland and France in
+July, 1788. It traveled _simultaneously_ along two lines nearly
+parallel--the eastern one had a breadth of from half a league to
+five leagues, the western of from three to five leagues. The space
+between was visited only by heavy rain; its breadth varied from three
+to five and a half leagues. At the outer border of each, there was
+also heavy rain, but we are not told how far it extended. The length
+was at least a hundred leagues; but from other reports it may be
+gathered that it really extended to nearly two hundred. It seems to
+have originated near the Pyrenees, and to have traveled at a mean
+rate of about sixteen and a half leagues per hour toward the Baltic,
+where it was lost sight of. The hail only fell for about seven and
+a half minutes at any one place. The hailstones were generally of
+irregular form, the heaviest weighing about eight French ounces. This
+storm devastated 1,039 parishes in France alone, and the damage was
+officially placed at 24,690,000 francs.
+
+For any assigned temperature of the atmosphere, there is a certain
+quantity of aqueous vapor which it is capable of holding in
+suspension at a given pressure. Conversely, for any assigned quantity
+of aqueous vapor held in suspension in the atmosphere, there is
+a minimum temperature at which it can remain so suspended. This
+minimum temperature is called the dew-point. During the daytime,
+especially if there has been sunshine, a good deal of aqueous vapor
+is taken into suspension in the atmosphere. If the temperature in the
+evening now falls below the dew-point, which after a hot and calm
+day generally takes place about sunset, the vapor which can be no
+longer held in suspension is deposited on the surface of the earth,
+sometimes to be seen visibly falling in a fine mist. This is one
+form of the phenomenon of dew, but there is another. The surface of
+the earth, and all things on it, and especially the smooth surfaces
+of vegetable productions, are constantly parting with their heat by
+radiation. If the sky is covered with clouds, the radiation sent
+back from the clouds nearly supplies an equivalent for the heat thus
+parted with; but if the sky be clear, no equivalent is supplied, and
+the surface of the earth and things growing on it become colder than
+the atmosphere.
+
+If the night also be calm, the small portion of air contiguous to
+any of these surfaces will become cooled below the dew-point, and
+its moisture deposited on the surface in the form of dew. If this
+chilled temperature be below 32° Fahr., the dew becomes frozen and is
+called _hoar-frost_. The above two phenomena, though both expressed
+in our language by the word dew, which perhaps helps to give rise to
+a confusion of ideas on the subject, are not necessarily expressed
+by the same word. For instance, in French, the first phenomenon--the
+falling evening-dew--is expressed by the word _serein_; while the
+latter--the dew seen in the morning gathered in drops by the leaves
+of plants, or other cool surfaces--is expressed by the word _rosée_.
+
+The merit of the discovery of the “Theory of Dew” has been commonly
+ascribed to Dr. William Charles Wells, who published in 1814 his
+_Essay on Dew_, which obtained great popularity. The merit should,
+however, be divided between him and several others. M. Le Roi of
+Montpellier, M. Pictet of Geneva, and especially Professor Alexander
+Wilson of Glasgow, largely contributed by experiment and inducement
+to its formation.
+
+
+
+
+  THE AURORA BOREALIS
+  --RICHARD A. PROCTOR
+
+
+The aurora is one of those phenomena of nature which are
+characterized by exceeding beauty, and sometimes by an imposing
+grandeur, but are unaccompanied by any danger, and indeed, so far
+as can be determined, by any influence whatever upon the conditions
+which affect our well-being. Comparing the aurora with a phenomenon
+akin to it in origin--lightning--we find in this respect the most
+marked contrast. Both phenomena are caused by electrical discharges;
+both are exceedingly beautiful. It is doubtful which is the more
+imposing so far as visible effects are concerned. When the auroral
+crown is fully formed, and the vault of heaven is covered with the
+auroral banners, waving hither and thither silently, now fading from
+view, anon glowing with more intense splendor, the mind is not less
+impressed with a sense of the wondrous powers which surround us than
+when, as the forked lightnings leap from the thundercloud, the whole
+heavens glow with violet light, and then sink suddenly into darkness.
+The solemn stillness of the auroral display is as impressive in its
+kind as the crashing peal of the thunderbolt.
+
+The reader is no doubt aware that auroras or polar streamers, as they
+are sometimes called, are appearances seen not around the true poles
+of the earth, but around the magnetic poles which lie very far away
+from those geographical poles which our Arctic and Antarctic seamen
+have in vain attempted to reach. The formation of auroral streamers
+around the magnetic poles of the earth shows that these lights are
+due to electrical discharges of electricity, which, though only
+visible at night, take place in reality in the daytime also.
+
+Remembering that the aurora is due to electrical discharges in the
+upper regions of the air, it is interesting to learn what are the
+appearances presented by the aurora at places where the auroral
+arch is high above the horizon--these being, in fact, places nearly
+_under_ the auroral arch. M. Ch. Martins, who observed a great number
+of auroras in Spitzbergen in 1839, thus writes: “At times they are
+simple diffused gleams or luminous patches; at others, quivering rays
+of pure white which run across the sky, starting from the horizon
+as if an invisible pencil were being drawn over the celestial vault;
+at times it stops in its course, the incomplete rays do not reach
+the zenith, but the aurora continues at some other point; a bouquet
+of rays darts forth, spreads into a fan, then becomes pale, and
+dies out. At other times long golden draperies float above the head
+of the spectator, and take a thousand folds and undulations as if
+agitated by the wind. They appear to be but at a slight elevation
+in the atmosphere, and it seems strange that the rustling of the
+folds as they double back on each other is not audible. Generally, a
+luminous bow is seen in the north; a black segment separates it from
+the horizon, the dark color forming a contrast with the pure white
+or bright red of the bow, which darts forth rays, extends, becomes
+divided, and soon presents the appearance of a luminous fan, which
+fills the northern sky, and mounts nearly to the zenith, where the
+rays, uniting, form a crown, which in its turn darts forth luminous
+jets in all directions. The sky then looks like a cupola of fire; the
+blue, the green, the yellow, the red, and the white vibrate in the
+palpitating rays of the aurora. But this brilliant spectacle lasts
+only a few minutes; the crown first ceases to emit luminous jets,
+and then gradually dies out; a diffused light fills the sky; here
+and there a few luminous patches, resembling light clouds, open and
+close with incredible rapidity, like a heart that is beating fast.
+They soon get pale in their turn, everything fades away and becomes
+confused, the aurora seems to be in its death-throes; the stars,
+which its light had obscured, shine with a renewed brightness; and
+the long polar night, sombre and profound, again assumes its sway
+over the icy solitudes of earth and ocean.”
+
+The association between auroral phenomena and those of terrestrial
+magnetism has long been placed beyond a doubt. Wargentin in 1750
+first established the fact, which had been previously noted, however,
+by Halley and Celsius. But the extension of the relation to phenomena
+occurring outside the earth--very far away from the earth--belongs
+to recent times. The first point to be noticed, as showing that the
+aurora depends partly on extra-terrestrial circumstance, is the
+fact that the frequency of its appearance varies greatly from time
+to time. It is said that the aurora was hardly ever seen in England
+during the Seventeenth Century, although the northern magnetic pole
+was then much nearer to England than it is at present Halley states
+that before the great aurora of 1716 none had been seen (or at least
+recorded) in England for more than eighty years, and no remarkable
+aurora since 1574. In the records of the Paris Academy of Sciences no
+aurora is mentioned between 1666 and 1716. At Berlin one was recorded
+in 1707 as a very unusual phenomenon; and the one seen at Bologna
+in 1723 was described as the first which had ever been seen there.
+Celsius, who described in 1733 no less than three hundred and sixteen
+observations of the aurora in Sweden between 1706 and 1732, states
+that the oldest inhabitants of Upsala considered the phenomenon as a
+great rarity before 1716. Anderson of Hamburg states that in Iceland
+the frequent occurrence of auroras between 1716 and 1732 was regarded
+with great astonishment. In the Sixteenth Century, however, they had
+been frequent.
+
+Here then we seem to find the evidence of some cause external to
+the earth as producing auroras, or at least as tending to make
+their occurrence more or less frequent. The earth has remained
+to all appearance unchanged in general respects during the last
+three centuries, yet in the Sixteenth her magnetic poles have been
+frequently surrounded by auroral streamers; during the Seventeenth
+these streamers have been seldom seen; during the last two-thirds of
+the Seventeenth Century auroras have again been frequent; and during
+the Eighteenth Century they have occurred sometimes frequently during
+several years in succession, at others very seldom.
+
+Connected as auroras are with the phenomena of terrestrial magnetism,
+we may expect to find some help in our inquiry from the study of
+these phenomena. Now it appears certain that magnetic phenomena are
+partly influenced by changes in the sun’s condition. We may well
+believe that they are in the main due to the sun’s ordinary action,
+but the peculiarities which affect them seem to depend on _changes_
+in the sun’s action.
+
+Many of my readers will doubtless remember the auroras of May 13,
+1869, and October 24, 1870, both of which occurred when the sun’s
+surface was marked by many spots, and both of which were accompanied
+by remarkable disturbance of the earth’s magnetism.
+
+It may, then, fairly be assumed that the occurrence of auroras
+depends in some way, directly or indirectly, on the condition of the
+sun. But what the real nature of that connection may be is not easily
+determined.
+
+Angström was the first to observe the spectrum of the aurora
+borealis. He found that the greater part of the auroral light, as
+observed in 1867, was of one color, yellow, but three faint bands of
+green and greenish blue color were also seen. The aurora of April 15,
+1869, was seen under very favorable conditions in America. Professor
+Winlock, observing it at New York, found its spectrum to consist of
+five bright lines, of which the brightest was the yellow line just
+mentioned. One of the others seems to agree very nearly, if not
+exactly, in position with a green line, which is the most conspicuous
+feature of the spectrum of the solar corona. During the aurora of
+October 6, 1869, Flögel noticed the strong yellow line and a faint
+green band. Schmidt, on April 5, 1870, made a similar observation.
+He saw the strong yellow line, and from it there extended toward the
+violet end of the spectrum a faint greenish band, which, however, at
+times showed three defined lines, fainter than the yellow line.
+
+It was not till the magnificent aurora of October 24-25, 1870,
+that any red lines were seen in the spectrum of an aurora. On that
+occasion the background of the auroral light was ruddy, and on the
+ruddy background there were seen three deep red streamers very well
+defined. The ruddy streamers, on the night of October 25, converged
+toward the auroral crown, which was on that occasion singularly well
+seen. Förster of Berlin failed to see any red line or band despite
+the marked ruddiness of the auroral light. But Capron at Guildford
+saw a faint line in the red part of the spectrum; and Elger at
+Bedford observed a red band in the light of the red streamers, the
+band disappearing, however, when the spectroscope was directed on the
+white rays of the aurora.
+
+As yet the auroral spectrum has not been interpreted. The reason
+probably is, that the conditions under which the light of the aurora
+as of the corona is formed are not such as have been or perhaps can
+be attained or even approached in laboratory experiments.
+
+
+
+
+  CLOUDS
+  --D. WILSON BARKER
+
+
+Those who are professionally engaged in the scientific work of
+weather bureaus recognize the importance of accurate observations
+of cloud forms and nature, and much good work has been done in this
+connection in recent years by scientific observers in England,
+Australia, and the United States; but as a popular study, nephology
+is almost entirely overlooked, and this notwithstanding the fact
+that, perhaps, no branch of knowledge offers greater facility and
+ease of acquisition. Each cloud has its history fraught with meaning;
+its open secret is writ on its face, and may be read by any one who
+will, give himself a little trouble, nor need he go deeply into the
+study in order to make observations interesting to himself, and
+perhaps of great use in the furthering and perfecting of weather
+lore. To the ancients, the sky was doubtless an object of constant
+remark and interest, and possibly their intuitive knowledge of
+weather forecasting was much more accurate than ours. The dwellers
+in our modern cities see little of the sky, clouds have no interest
+for them beyond the personal consideration as to the advisability
+of taking out an umbrella or not. But farmers, fishermen, sailors,
+and others following open-air avocations are dependent on the
+weather, and to be wise in its forecast is of importance to them.
+To these, especially, cloud study should appeal; it can not fail to
+be profitable to them in their personal work, and they have all the
+opportunity, if the will be there, to forward the general knowledge
+of the subject by careful painstaking observations, which they may
+transmit to those scientifically engaged in dealing with weather
+laws, and thus assist in the elucidation of questions on which we are
+at present but very imperfectly informed.
+
+In this article the broad distinctions of clouds will be dealt with.
+There are two well-defined types--Stratus and Cumulus--so distinct
+in actual appearance and in physical formation that they may be
+taken as the basis of classification. Sometimes both types appear to
+merge into each other, in which case no variety of classification
+suffices to describe them satisfactorily, as any one who has studied
+cloud-forms must allow. “Stratus” is a sheet-like formation of
+cloud. “Cumulus” is recognizable by its heaped-up appearance and
+vertical thickness. Numerous varieties of cloud-forms may be observed
+graduating from one of these types to the other, but when an
+observer can clearly distinguish Stratus from Cumulus he has already
+acquired valuable knowledge.
+
+The presence of either type of cloud alone indicates a more or
+less set condition of the atmosphere, and generally foretells a
+continuance of the existing weather. The simultaneous presence of
+both types indicates a coming change, the gradation of Stratus
+into Cumulus foreboding worse weather, and of Cumulus into Stratus
+heralding good. Again, as we shall show later on, the vertical
+thickening of the stratiform clouds is a distinctly bad indication.
+
+Up to quite recently, Luke Howard’s division of clouds, formulated
+in 1802, held first place; even now it is in constant use, for
+though attempts have been made at a more scientific classification,
+all of them, with the single exception of that proposed by the
+late Rev. Clement Ley, can only be termed make-shifts. Mr. Ley’s
+classification, unfortunately, is long, and not well adapted to the
+use of any but professional investigators, or enthusiasts with ample
+time on their hands. There exists a so-called “international” system
+of cloud nomenclature, but, for all that, each country has its own
+especial system, with the result that vast collections of cloud
+statistics are of little value as helps to a classification, and are
+useful only as records of clouds present at certain times.
+
+Clouds owe their existence to two causes:
+
+1. Through the passing of warm, moist air into colder, when, owing to
+condensation, a certain proportion of the moisture becomes visible in
+the form of a cloud.
+
+2. Through changes occurring in the atmosphere as it rises
+into higher regions of atmosphere, where decrease in pressure
+and expansion and consequent loss of heat take place and cause
+condensation of moisture.
+
+The first process may be described as the condensation formation of
+clouds, and the second as the adiabatic formation of clouds. As a
+matter of fact, no hard and fast line separates these two operations;
+they act in unison, and the combination of vertical and horizontal
+currents goes to make up the diversity of forms which clouds assume.
+
+In settled states of the atmosphere, Stratus clouds are common, or
+the sky may be clear. In unsettled conditions, Cumulus or Heap clouds
+are formed.
+
+We shall now describe a few familiar forms of cloud, giving them
+simple names and endeavoring to compare them with other nomenclatures.
+
+Of Cumulus clouds there are five well-defined varieties.
+
+_Rain Cumulus_, of which there are two sub-varieties:
+
+(_a_) Shower-cumulus, when rain falls from the cloud without
+increment of wind. The edges of this cloud are not cirrus-topped.
+
+(_b_) Squall-cumulus, when the rain is accompanied by wind, or by
+wind with hail and snow falling from this cloud.
+
+In these cases the Cumulus cloud is generally much serrated, having
+a cirriform edging. In some cases this cirriform edging extends far
+over the sky and forms halos, particularly at the rear.
+
+Two rarer varieties of Cumulus are:
+
+_Pillar-cumulus_, generally noticed over the calm belts of the
+ocean, and distinguishable by its slender forms, which rise to great
+altitudes.
+
+_Roll-cumulus_ generally accompanies strong winds, particularly polar
+west winds, which succeed cyclonic disturbances. Here we have the
+ordinary Cumulus cloud so blown along by the wind as to assume the
+roll formation from which it is named.
+
+A still rarer form of Cumulus appears in scattered patches over the
+sky, and is indicative of an electrical state of the atmosphere.
+
+Cumulus clouds form at a low altitude, but they frequently tower
+upward to great heights.
+
+It should be noticed that in these clouds the fine weather form is of
+soft, smooth outline, and has a quiet appearance.
+
+_Stratus Clouds_ may be divided into four varieties as follows:
+
+1. _Fog_, so well known as not to need description. It is, in fact, a
+Stratus cloud resting on the earth’s surface.
+
+2. _Stratus_, a cloud sheet which covers the whole sky at a
+moderate elevation. Here and there the cloud is thin, and under
+surfaces appear as parallel lines all round the horizon. This is
+the characteristic cloud of anti-cyclonic, or dry, fine weather
+conditions. It may continue to cover the sky for several days in
+succession.
+
+3. _High Stratus_, including all the varying forms of Cirro-cumulus
+from the mackerel skies to the Cirro-macula of Clement Ley. Many
+beautiful varieties of this cloud of minute cumuliform appearance
+are caused by the changes taking place in the atmosphere. We notice
+waves, wavelets, stipplings, and flecks. To it are due the coronas
+sometimes seen round the sun, as also iridescent clouds occasionally
+noticed in the same vicinity. The wave-like appearance of the clouds
+is due to the passage of a more rapidly moving air current over a
+slower one, or of a wave current crossing a motionless portion of the
+air. When two air currents pass over one another at an angle, the
+particles of clouds tend to fall into different shapes, hence our
+mackerel skies. But this cloud, although beautiful, is essentially
+one of warning, more especially when the flecks are of a thin, scaly
+appearance (resembling the scales of certain fishes so closely that
+I have called it the scale cloud). Sometimes these detached flecks
+appear in lines, and very striking is the effect produced.
+
+4. _Cirrus._--The highest form of cloud and the most important as a
+factor in the science of weather forecasting. Cirrus, ordinarily,
+appears as wisps and feather pieces scattered over the sky, and its
+significance is then of no import.
+
+When, however, this cloud takes the form of lines parallel to the
+horizon, or of lines appearing to radiate as wheel-spokes from any
+one part of the horizon, it should be carefully noted as indicative
+of approaching weather. Its movement and propagating transition
+should be observed. This cloud is composed of ice-dust or crystals.
+
+When a cyclonic disturbance is about to pass over an observer, Cirrus
+generally appears first in parallel lines, or at a radiant point;
+the threads gradually increase and interlace until a complete sheet
+of Cirro-stratus covers the sky, causing a halo. The cloud further
+thickens, the halo disappears, all becomes overcast, and rain comes
+on. The cloud is now known as Nimbus, and after it has endured some
+time, the wind shifts, the Nimbus clears off, and it is succeeded by
+a polar west wind.
+
+In addition to these forms of clouds, we may often notice,
+particularly during high winds, fragments of clouds hurrying across
+the sky. These are known as “scud”; they are generally pieces carried
+off by the winds from the main bodies of clouds.
+
+Occasionally two forms of cloud are present at the same time. This
+is ordinarily taken as a case of Cumulus and Stratus, and has become
+known as Cumulo-stratus; but, if observed in the zenith, it may
+readily be noted that the two forms of cloud are distinct, and they
+had better be dealt with separately. The appearance of Cumulo-stratus
+is an effect of perspective.
+
+Clouds float at varying altitudes, according to the latitude and
+elevation of the ground; the vertical temperature and adiabatic
+gradients determining the level at which the vapor becomes visible as
+cloud. It is desirable in all cloud observations, that note should
+be made of the approximate relative altitudes of clouds and of their
+velocity of motion. This is particularly desirable when dealing with
+the stratiform clouds, whether as ordinary Cirro-cumulus or as very
+high Cirro-macula.
+
+The beautiful coloring of clouds results from the breaking up of
+light beams in passing through them or along their edges. This
+phenomenon is caused by diffraction, and to it is due our lovely
+sunrises and sunsets. When the sun is high in the heavens, the light
+is white, but as the orb nears the horizon, and its rays pass through
+thicker layers of atmosphere, the smaller light waves get gradually
+cut off, until the sun sinks as a red ball below the horizon. The
+largest waves of light produce the red rays and the after glow
+which are so beautiful. Sunrise and sunset effects are matters of
+much interest, but are of too complicated a nature to be fully gone
+into here; we must, however, notice them briefly, because of their
+importance in weather forecasts. Soft sunset colors indicate fine
+settled weather; fiery brilliant hues denote change to stormy or wet
+weather.
+
+Other color effects in clouds are due to phenomena, known as halos
+and coronas. Halos appear as rings round the sun and moon; they
+are caused by the shining of the orb through very high Stratus or
+Cirrus clouds, and have a diameter of 42°. Sometimes shades of
+color, resembling those of a rainbow, are visible--red appears on
+the inside and blue on the outside. These rings of color are due
+to the reflection and refraction of light passing through the fine
+ice crystals of which high Stratus or Cirrus clouds are composed.
+Occasionally a complicated series of beautifully colored rings is
+noticeable. Generally speaking, these rings are due to the thinness
+of the high cloud through which the light is passing. Still more
+curious arrangements of halos sometimes occur.
+
+Coronæ are broader rings seen quite close to the sun or moon, and are
+due to the shining of light through the edges of loose Cumulus or
+Stratus clouds. They have red on the outside and blue on the inside
+of the ring; the colors are, generally, easily distinguishable.
+The more brilliant hues occasionally seen, as has been said, in
+the vicinity of the sun and moon, would appear to be incomplete
+sections of circles intermediate in size between coronæ and halos. An
+interested observer will be well repaid if he chooses to study more
+closely the many curious optical phenomena connected with clouds, but
+it would be beyond the scope and object of this paper to go into them
+more fully here.
+
+Whoever wishes to be weatherwise, and who has time to study the
+weather charts published daily, may easily acquire such knowledge
+of local characteristics as will enable him to forecast fairly
+accurately. Cirrus clouds, as a rule, are reliable guides; they
+form, as we have said, in parallel threads, from the position and
+movements of which forecasts may be made. Should the threads appear
+on, and parallel to, the west horizon, and moving from a northerly
+point, a depression is approaching from the west, but, although
+causing some bad weather, it will probably pass to the north of
+the observer. Should the lines appear parallel to the southwest or
+south-southwest horizon, and be moving from a northwesterly point,
+the depression will very likely pass over the observer and occasion
+very bad weather. These are two of many possible prognostics. Weather
+forecasting is much helped by a study of the daily weather charts.
+Again, weather is often very local, and to predict with fair accuracy
+a knowledge of local conditions is necessary.
+
+
+
+
+  WINDS
+  --WILLIAM HUGHES
+
+
+Among the secondary causes affecting climate, probably none is of
+greater importance than the direction of prevailing winds. The
+currents of air are warm or cold, wet or dry, according as they
+have had their origin in warm or cold latitudes, and have traversed
+inland tracts, or the expanse of ocean, in their advancing course.
+With us, and in the northern half of the globe in general, north
+and east winds are cold and dry, while south and west winds are
+warm, and often accompanied by moisture. Within the Southern
+Hemisphere these conditions are reversed, and the hottest currents
+of air come from a northwardly direction. The prevailing winds of
+western Europe are from the west and southwest; and it is to this
+fact that we must mainly ascribe the high winter temperature, as
+well as the comparative freedom from extremes of heat and cold
+which distinguishes the countries of western Europe. The same cause
+explains the abundant moisture which belongs to those regions in
+general, and which distinguishes the western shores of our own
+islands in a remarkable degree. Such winds have traversed the immense
+expanse of the Atlantic, and come to the western seaboard of Europe
+laden with the moist vapors gathered on their course. These vapors,
+condensed upon the high grounds which line the western side of the
+British Islands, or, further to the northward, upon the long chain of
+the Scandinavian Mountains, fall to the earth in copious torrents of
+rain. In the process of condensation, a vast quantity of latent heat
+is disengaged, and the temperature is correspondingly raised. Warmth
+and moisture are, indeed, speaking generally, concomitant conditions
+of European climate, and are especially so in the case of western
+Europe.
+
+Even in the case of lands which nearly approach the tropic, the
+influence of prevailing winds in raising or lowering the temperature
+is strikingly seen. At New Orleans, bordering on the Mexican Gulf,
+and throughout the adjacent portions of the United States, the
+winters are often of excessive severity. Cold winds, generated in
+the higher latitudes of the New World, and blowing for weeks in
+succession from the northern quarter of the sky, are the cause of
+this. The generally level interior of the North American Continent--a
+vast lowland plain, bounded only to the east and west by the
+Alleghanies and the Rocky Mountains--presents no obstacle to the
+advance of these cold northerly blasts. The middle and eastwardly
+parts of North America are subject to like influences, in this
+regard, to the plains of eastern Europe. To the westward of the
+Rocky Mountains, on the other hand, the conditions affecting climate
+present greater analogy to those that belong to western Europe.
+
+In the case of many countries, some local wind, of occasional
+prevalence, forms a marked characteristic of climate. The most
+remarkable of these local winds are the simoon, the sirocco, the
+föhn, the harmattan, and the mistral.
+
+The often-described _simoon_ of the desert is an intensely heated
+and dry wind, which raises the temperature like the blast of a
+furnace, and fills the air with particles of sand, of suffocating
+quality. The same wind is known in the deserts of Turkestan as the
+_tebbad_ (fever-wind), the terrible conditions of which are thus
+described by the pen of a traveler. “The kervanbashi (_leader of the
+caravan_) and his people drew our attention to a cloud of dust that
+was approaching, and told us to lose no time in dismounting from the
+camels. These poor brutes knew well enough that it was the _tebbad_
+that was hurrying on; uttering a loud cry they fell on their knees,
+stretched their long necks along the ground, and strove to bury their
+heads in the sand. We intrenched ourselves behind them, lying there
+as behind a wall; and scarcely had we, in our turn, knelt under their
+cover, than the wind rushed over us with a dull, clattering sound,
+leaving us, in its passage, covered with a crust of sand two fingers
+thick. The first particles that touched me seemed to burn like a
+rain of flakes of fire. Had we encountered it when we were deeper
+in the desert we should all have perished. I had not time to make
+observations upon the disposition to fever and vomiting caused by
+the wind itself, but the air became heavier and more oppressive than
+before.”
+
+The _sirocco_ of the Mediterranean coasts is the hot wind of the
+African desert, tempered, before reaching the coasts of southern
+Europe, by its passage across the great expanse of inland waters.
+The enervating influences of this wind are well known to the resident
+on the shores of Sicily, the Italian mainland, or the islands of the
+Archipelago. The same wind, when it reaches the high mountain regions
+of the Apennines and the Alps, is known as the föhn.
+
+The _föhn_, or warm south wind, is an important agent in modifying
+the climate of the higher Alpine region, where its prevalence for a
+few days in succession causes the snow-line to recede, and is often
+accompanied by inundations occasioned by the suddenly melted snows.
+Its absence during a longer period than usual is attended, on the
+other hand, by a prolongation of the glaciers into a lower region
+of the mountain valleys. The Swiss peasants have a saying, when
+they talk of the melting of the snow, that the sun could do nothing
+without the föhn.
+
+The _harmattan_ of Senegambia and Guinea is a cold and intensely dry
+wind, which blows from the northeast during the months of December
+and January.
+
+The _mistral_ of southern France possesses similar qualities to the
+last-named wind, and blows, for days together, down the valley of the
+Rhone.
+
+Winds transport particles of dust, and, with them, the minuter forms
+of vegetable and animal life, to vast distances. The phenomena known
+to sailors as _red fogs_ and _sea-dust_ are evidence of this. In
+the Mediterranean, and also in the neighborhood of the Cape Verde
+Islands, showers of dust, of brick-red or cinnamon color, are
+sometimes experienced in such quantity as to cover the sails and
+rigging hundreds of miles away from land. Among this sea-dust,
+examination with the microscope has detected infusoria and other
+organisms native to the tropical regions of South America.
+
+The prevailing currents of the atmosphere, or _winds_, constitute an
+important feature in the climate of any country, and it belongs to
+Physical Geography to explain the prevalent winds which distinguish
+great regions of the globe. Such explanation is more easily made
+in regard to the warmer latitudes of the earth, where alone the
+direction of the wind is constant, than might be at first supposed
+by those whose personal experience is limited to such countries as
+Britain, and other temperate lands, where the variable condition
+of the atmosphere is the well-known subject of common observation
+and remark. But within those parts of the globe which experience
+a vertical sun, and for a few degrees beyond the exact line which
+marks the limit of the sun’s vertical influence on either side of
+the equator, the conditions either of perennial calm, or of currents
+of air that constantly blow in one given direction, are the uniform
+characteristics of climate.
+
+Throughout a zone of a few degrees in breadth, which extends round
+the globe in the neighborhood of the equator, and the limits of which
+undergo a certain amount of variation, dependent on the sun’s passage
+of the equinox, the variation of temperature throughout the year
+is confined within very narrow limits, and the result is a general
+prevalence of calms--that is, of undisturbed atmosphere. Wind is air
+set in motion, mainly by the existence of different conditions of
+temperature between adjacent bodies of air--of colder and denser air
+pressing against warmer and lighter air, and taking the place which
+is left vacant by the latter, as it rises into the higher regions
+of the entire aerial sea. Between the heated air of the tropics in
+general, and the comparatively cooler air of the regions lying some
+distance north and south of the tropics, for example, there is a very
+manifest difference as to temperature, as well as in regard to other
+conditions; but for a few degrees in the immediate neighborhood of
+the equator there is no such obvious difference, and, consequently,
+nothing to occasion disturbance (temperature alone being considered)
+in the general equilibrium of the atmosphere. Hence the prevalence
+of calms in that region. Within the parallels of 8° or 10° on either
+side of the line, the angle at which the solar rays reach the earth
+is at no time more than a few degrees from the perpendicular, for
+the equator divides the total amount of angular difference which is
+involved in the entire yearly path of the sun.
+
+The average breadth of the calm latitudes--or the _Zone of Calms_,
+as it is the custom, in books and maps, to term it--may be stated
+at about six or seven degrees. The mid-line of this zone does not
+coincide with the equator, for the reason that the equator does
+not represent the line of the earth’s highest temperature, owing
+to the preponderance of land in the Northern Hemisphere. Hence
+the Zone of Calms is, for the most part, to the northward of the
+equator--extending, with varying seasonal limits, from about the
+first to the seventh or eighth parallel of north latitude. But the
+limits oscillate with the sun’s passage of the equinox and consequent
+place in the heavens vertically over either side of the equator.
+
+The calm latitudes are the dread of the mariner, whose ship is often
+delayed for weeks together within their limits. The wearisome and
+tantalizing nature of this delay can, perhaps, only be adequately
+appreciated by those who have experienced the monotony attendant on
+a calm in mid-ocean, when, with a still and glassy sea around, a
+glittering atmosphere, and a burning sun overhead, the sails hang
+idly by the yards, and the vessel makes no appreciable progress.
+
+Between the oscillating limit of the Zone of Calms and the parallel
+of 28° in the Northern Hemisphere, on one side of the globe, and
+between the correspondent limit and the parallel of 25° south
+latitude, on the opposite hemisphere, there prevail through above
+two-thirds of the earth’s circumference, steady winds, blowing
+with almost undeviating uniformity from the eastward. These are
+the trade-winds. More precisely, _the trade-wind of the Northern
+Hemisphere is a wind blowing from the northeastward_--that is, a
+_northeast wind_. _The trade-wind of the Southern Hemisphere blows
+from the southeastward_, and is _a southeast wind_.
+
+The trade-wind belts stretch round more than two-thirds of the
+earth’s surface. They comprehend (within the latitudinal limits
+already defined) the Atlantic and Pacific Oceans, with the countries
+that lie adjacent to those vast areas of water. In the Pacific,
+however, their limits are less distinctly marked, and their influence
+less powerful, to the southward of the equator than to the north of
+that line. Over the Indian Ocean and its shores, the atmospheric
+currents follow, during portions of the year, an opposite course.
+
+The trade-winds of the Atlantic and Pacific--blowing constantly,
+and with almost undeviating steadiness, from the eastward--regulate
+the course of the mariner across those oceans. They, of course,
+facilitate the passage of either ocean in a westerly direction--that
+is, from the shores of the Old World to the eastern seaboard of
+America, or from the western coast of the New World to the eastern
+shores of the Asiatic and Australian Continents. It was the
+trade-wind of the Northern Atlantic that carried Columbus to the
+westward, on the adventurous voyage which resulted in the discovery
+of the New World, inspiring terror in the breasts of his companions,
+while in the mind of the great navigator himself it strengthened the
+assurance of reaching land by pursuing the direction in which his
+vessels’ prows were turned. On a like great occasion, the trade-wind
+of the Pacific carried Magellan’s ship steadily forward through the
+ocean which he was the first to cross, and facilitated the earliest
+circumnavigation of the globe. On the other hand, the same winds
+compel the return voyage across either ocean to be made in higher
+latitudes, where westerly winds prevail.
+
+The explanation of the trade-winds is found in the different measure
+in which the sun’s heat is experienced by regions within or nearly
+adjacent to the tropics, and by those of higher latitudes. They
+are currents of air set in motion by the differences of density
+consequent upon such various conditions of temperature--conditions
+which are of uniform prevalence, and the result of which is also
+constant.
+
+To sum up, we may say that the trade-winds, like the currents of
+the ocean, are due, _first_, to the sun,--that is to the different
+measure in which the solar heat is distributed on the globe’s
+surface; and, _secondly_, to the earth’s axial rotation, which
+affects the direction of currents in the aerial ocean in manner
+precisely analogous to that in which it affects the like currents
+in the aqueous ocean. In truth, the ocean of water, and the ocean
+of air--in contact with one another, and possessing many properties
+in common--act and react upon one another, mutually imparting their
+respective temperatures, movements, and other conditions. This is
+only one among the instances of mutual harmony--one of the many mute
+sympathies--which abound in the natural world.
+
+The monsoons are winds which blow over the Indian Ocean, and the
+countries adjacent to its waters. In general terms, it may be said
+that they prevail within the same latitudes as those over which the
+trade-winds of the Atlantic and Pacific blow. But the monsoons differ
+from the trade-winds of the two greater oceans in the fact that they
+are _periodical winds_, not perennial. The monsoon blows for half the
+year from one quarter of the heavens, and for the other half from an
+opposite quarter.
+
+[Illustration: Charts Showing the General Directions of Wind and Tide
+Currents]
+
+Over the northerly portion of the Indian Ocean--from the
+neighborhood of the equator to the shores of the Asiatic Continent,
+including the Malay Archipelago and the adjacent China Sea--a
+northeast monsoon blows during the winter months of the Northern
+Hemisphere; that is, from October to March, inclusive. During the
+summer months--April to September--and within the same limits,
+the southwest monsoon blows. Southward from the equator to the
+neighborhood of the tropic of Capricorn, the southeast monsoon
+blows during the winter of those latitudes (April to September):
+this is exchanged, during the other half of the year, for a
+northwest monsoon in the neighborhood of the Australian coasts,
+and for a northeast monsoon along the line of the African shores.
+The term _monsoon_--derived from a Malay word which signifies
+“season”--expresses the periodical nature of these winds, and
+indicates to how large an extent the climate of Indian seas and lands
+is dependent upon their periodical recurrence.
+
+The change from the one monsoon to that from an opposite quarter
+is not accomplished at once. The breaking-up of the monsoon, as it
+is termed, is attended by thunderstorms and other meteorological
+phenomena, which prevail during some weeks, until the setting-in
+of the coming monsoon is fairly accomplished. The nature of these
+changes, and the general characteristics of the monsoon itself, are
+admirably depicted in the following passage, by a master hand:
+
+“Meanwhile the air becomes loaded to saturation with aqueous vapor
+drawn up by the augmented force of evaporation acting vigorously
+over land and sea; the sky, instead of its brilliant blue, assumes
+the sullen tint of lead, and not a breath disturbs the motionless
+rest of the clouds that hang on the lower range of hills. At length,
+generally about the middle of the month, but frequently earlier, the
+sultry suspense is broken by the arrival of the wished-for change.
+The sun has by this time nearly attained his greatest northern
+declination, and created a torrid heat throughout the lands of
+southern Asia and the peninsula of India. The air, lightened by its
+high temperature and such watery vapor as it may contain, rises into
+loftier regions, and is replaced by indraughts from the neighboring
+sea, and thus a tendency is gradually given to the formation of a
+current bringing up from the south the warm humid air of the equator.
+The wind, therefore, which reaches Ceylon comes laden with moisture,
+taken up in its passage across the great Indian Ocean. As the monsoon
+draws near, the days become more overcast and hot, banks of clouds
+rise over the ocean to the west, and in the peculiar twilight the eye
+is attracted by the unusual whiteness of the sea-birds that sweep
+along the strand to seize the objects flung on shore by the rising
+surf.
+
+“At last sudden lightnings flash among the hills and shoot through
+the clouds that overhang the sea, and with a crash of thunder the
+monsoon bursts over the thirsty land, not in showers or partial
+torrents, but in a wide deluge, that in the course of a few hours
+overtops the river banks and spreads in inundations over every level
+plain.
+
+“All the phenomena of this explosion are stupendous: thunder, as we
+are accustomed to be awed by it, affords but the faintest idea of
+its overpowering grandeur in Ceylon, and its sublimity is infinitely
+increased as it is faintly heard from the shore, resounding through
+night and darkness over the gloomy sea. The lightning, when it
+touches the earth where it is covered with the descending torrent,
+flashes into it and disappears instantaneously; but when it strikes a
+drier surface, in seeking better conductors, it often opens a hollow
+like that formed by the explosion of a shell, and frequently leaves
+behind it traces of vitrification. In Ceylon, however, occurrences
+of this kind are rare, and accidents are seldom recorded from
+lightning, probably owing to the profusion of trees, and especially
+of cocoanut palms, which, when drenched with rain, intercept the
+discharge, and conduct the electric matter to the earth. The rain at
+these periods excites the astonishment of a European; it descends
+in almost continuous streams, so close and so dense that the level
+ground, unable to absorb it sufficiently fast, is covered with one
+uniform sheet of water, and down the sides of acclivities it rushes
+in a volume that wears channels in the surface. For hours together,
+the noises of the torrent as it beats upon the trees and bursts upon
+the roofs, flowing thence in rivulets along the ground, occasions an
+uproar that drowns the ordinary voice and renders sleep impossible.”
+
+The monsoons of the Indian Ocean are not divided by any such
+distinctly defined belt of calms as separates the opposite
+trade-winds of the northern and southern Pacific and Atlantic. The
+southeast monsoon of the southern Indian Ocean passes gradually
+into the southwest monsoon, which prevails at the same time in the
+northern half of that ocean. Nor is the season of change from the
+one monsoon to the other precisely the same over all parts of that
+ocean. Indeed, the Indian Ocean, from the geographical conditions
+already adverted to, is exposed in much higher measure than either
+of the other oceans to the disturbing influences consequent upon
+proximity to land, and its winds are hence affected in a vastly
+greater degree by local conditions. Thus the Indian monsoon, the
+Arabian and East African monsoon, and the monsoon of northwestern
+Australia, assume in each case a direction which is dependent upon
+the geographical position and contour of the lands whence they derive
+their distinguishing names. In the Red Sea, the monsoons follow
+the direction of its shores, and blow, for six months of the year,
+alternately, up and down its long and trough-like valley, confined
+and guided in their passage by the mountain-chains which bound it
+upon either side.
+
+We have hitherto spoken of the monsoons only in connection with the
+Indian Ocean. But, in truth, a monsoon, or season-wind--which is what
+the word monsoon means--is experienced upon a large portion of the
+West African coasts, and thence far out into the mid-Atlantic, within
+the proper region of the Atlantic trades. The evidence of this is one
+among the many valuable results due to the Wind and Current Charts
+of Maury, and the cause of it is precisely the same as that which
+occasions the monsoon of the Indian coasts. Between the equator
+and the parallel of 13° north, the intense heat of a vertical sun,
+acting upon the western coasts and adjacent interior of the African
+Continent, occasions a reversal of the ordinary wind of that region.
+The intensely heated atmosphere of the land, owing to superior
+rarity, ascends, and the cooler air of the neighboring sea sets in to
+fill its place. The monsoon thus generated lasts as long as the sun
+remains to the northward of the equator. Further to the south a like
+phenomenon accompanies, in those localities, the passage of the sun
+into south declination. The influence of these monsoons extends to
+a distance of a thousand miles or more from land, the entire space
+within which they prevail forming a cuneiform (or wedge-shaped)
+region in the midst of the Atlantic, the base of which rests upon the
+African Continent, while its apex is within ten or fifteen degrees of
+the mouth of the Amazon.
+
+A similar reversal of the trade-winds of the North Pacific occurs
+off the western shores of Central America, capable of explanation
+in precisely like manner--due, that is, to the excess of heat which
+the summer sun brings to the adjacent lands, and the consequent
+rarefaction and rising of the currents of air over those lands.
+This, and the like instance of the West African monsoons, show in
+the most striking manner how powerfully the land is affected by the
+sun’s heat, and to how wide a distance the atmospheric movements
+which are generated by such influences extend over the adjacent
+seas. Even such limited tracts of land as the Society and Sandwich
+Islands have a marked influence upon the winds experienced over the
+surrounding waters. They interfere, says Maury, with the trade-winds
+of the Pacific very often, and even turn them back, for westerly and
+equatorial winds are common at both groups, in their winter time.
+
+Upon the coasts of most countries that are within the warmer
+latitudes of the globe, there occur daily, at or shortly before the
+hour of early dawn, and toward the approach of sunset, breezes that
+blow respectively _off the shore_ or from _off the adjacent waters_.
+The former is known as the land-breeze; the latter as the sea-breeze.
+
+These refreshing movements of the air are not confined to countries
+within, or even very near to, the tropics, though they are more
+powerful in the case of countries that are within the torrid zone
+than in the case of other lands. But they are felt upon the coasts
+of the Mediterranean, and in even much higher latitudes than those
+of the Mediterranean, during the warmer portions of the year. The
+hour at which they begin to be perceptible is not the same in all
+localities; but, speaking generally, the land-breeze begins to be
+felt about an hour before sunrise, and the sea-breeze toward the
+early evening, as the time of sunset approaches. During the midday
+hours the intense heat of the atmosphere, accompanied by general calm
+and almost perfect repose of the animal world, is painfully felt by
+all residents in warm countries, and the cooling sea-breeze which
+sets in as the sun approaches the horizon is welcomed with intense
+delight. To the sojourner in Indian lands, it is the signal for
+outdoor exercise, and is accompanied by a general reawakening of
+the outer world of nature. The dweller on the African or Australian
+coasts equally rejoices in its refreshing power. The mariner within
+Indian seas, frequently becalmed during the stillness of the
+night-watch, finds like relief in the breeze which blows off the land
+with the approach of early morning.
+
+The land and sea-breezes are due to a cause strictly analogous
+to that which produces the monsoon of eastern seas--that is, the
+influence of the sun heating in various measures the lands and
+seas, and with them the superincumbent air. Successive movements
+are generated in the atmosphere according as different portions of
+the whole acquire, with difference of temperature, various degrees
+of density. During the hours of midday heat, the air over the land
+becomes relatively hotter, by many degrees, than the air which is
+above the adjacent water, for it is the well-known attribute of land
+to experience much greater extremes of temperature than water does.
+As afternoon, with its sultry temperature, advances, this continued
+heat occasions the land-air to form an ascending current, while the
+cooler (and relatively denser) air from the neighboring waters flows
+in to take its place. This cooling breeze is an effort of nature to
+restore equilibrium in the atmosphere, the heavier portions of the
+whole body of air assuming the place of lower strata, and the higher
+portions spreading over the superior regions. This effort continues
+until the desired balance is attained, and, with the approach of
+midnight, the air is again calm and settled. But during the night,
+while the water retains a nearly uniform temperature, the land
+rapidly parts with the heat, so that the air over the land becomes
+at length colder than that over the water. This latter, therefore,
+relatively the warmer of the two, tends to rise, while the cooler air
+of the land fills its place. A wind blowing from off the land is thus
+generated. In some localities this blows during great part of the
+night. But the period of its commencement varies in different places,
+and the intervals of calm between both land and sea-breezes are often
+of uncertain duration.
+
+The land and sea-breezes repeat, on a scale of diurnal variation, the
+phenomena shown by the monsoons on a scale of yearly change. They
+show how readily the atmosphere yields to the slightest pressure,
+and how powerful an influence on the laws of climate, and, with
+them, on the condition of mankind, is exercised by every change,
+of temperature, or otherwise, to which it is subject. Similar
+winds--alternating from opposite quarters of the heavens--are
+experienced in inland districts, as on the banks of the Tapajos
+River, in South America.
+
+The rotary storms which occur, at uncertain intervals, in particular
+latitudes, are to be included among the exceptional phenomena of
+atmospheric change. They prevail, however, over larger areas than
+was formerly supposed, and perhaps belong to a general system of
+atmospheric movements in which electric and magnetic influences fill
+an important place. The hurricanes of the West Indies, the tornadoes
+and cyclones of the Indian Ocean, and the typhoons of the China Sea,
+are winds of this description. Within the Southern Hemisphere, the
+direction of the rotating circle is always found to correspond to the
+movement of the hands of a watch (_i. e._, from west to north, east,
+and south): to the north of the equator, the circle of wind follows
+an opposite direction (or west to south, east, and north). By a
+knowledge of this law, combined with careful observation of the track
+usually taken by such storms, mariners are enabled to avoid some of
+the dangers incident to their occurrence. The destruction which they
+occasion, however, within maritime tracts exposed to their influence,
+as well as upon the high seas, is at times fearfully great.
+
+Waterspouts are another form in which the rotary movements of the
+air are manifested. In the case of these phenomena, a taper column
+of cloud, descending from above, is joined by a spiral column of
+water which winds upward from the agitated surface of the sea, the
+two together forming, by their union, a continuous column which moves
+over the sea. Waterspouts seldom last longer than half an hour. They
+are more frequent near the coast than on the high seas, and more
+commonly seen in warm climates.
+
+
+
+
+  SQUALLS, WHIRLWINDS, AND TORNADOES
+  --SIR RALPH ABERCROMBY
+
+
+If we watch the stages of gradually increasing wind, we find that as
+the strength rises the tendency is more and more to blow in gusts.
+Gradually these gusts get still more violent, and in their highest
+development come with a boom like the discharge of a piece of heavy
+ordnance. This is what sailors call “blowing in great guns,” and
+these are the gusts which blow sails into ribbons, and dismast ships
+more than any amount of steady wind. These gusts only last a few
+minutes, but they seem to be very closely allied to the simplest form
+of squalls. In a true, simple squall the wind generally need not be
+of the exceptional violence which causes “guns”; but after it has
+rather fallen a little, the blast comes on suddenly with a burst,
+and rain or hail, according to intensity, or other circumstances,
+while the whole rarely lasts more than five or ten minutes. At sea
+one often sees two or three squalls flying about at a time. Then we
+readily observe that over the squall there is firm, hard, cumulus
+cloud; that the disturbance only reaches a short distance above the
+earth’s surface; that the squall moves nearly in the same direction
+as the wind; and that there is little or no shift of the wind before
+or during the squall. We also see that the shape of the squall is
+merely that of an irregular patch, with a tendency rather to be
+longer in the direction of the wind than in any other quarter; and
+that the motion of the squall as a whole is much slower than that
+of the wind which accompanies the first blasts. If, at the same
+time, we watch our barometer closely, we find that if the squall
+is sufficiently strong, the mercury invariably rises--sometimes as
+much as one-tenth of an inch--and returns to its former level after
+the squall is over. No difference is observed in this sudden rise,
+whether the squall is accompanied with rain, hail, or thunder and
+lightning; and though we are unable exactly to explain why the wind
+sometimes takes this irregular method of blowing, we have still to do
+with a comparatively simple phenomenon.
+
+The simplest kind of thunderstorm may more properly be described as
+a squall accompanied by thunder and lightning, instead of only with
+wind and rain. On a wild, stormy day, with common squalls, one or two
+of these, which are exceptionally violent, will be accompanied by one
+or two claps of thunder with lightning. The principal interest which
+attaches to this type of thunderstorm consists in the proof which
+is afforded that there is no essential difference between a common
+squall and another which may be associated with electrical discharge,
+except intensity. The look and motion of the clouds, and the sudden
+rise of the barometer, are identical in both cases. In western Europe
+this class of thunderstorm is much more common in winter than in
+summer, which is the reverse of what takes place with all other kinds
+of thunderstorm. So much is this the case that in Iceland there are
+no summer thunderstorms, but only winter ones, of this simple squall
+type. In Norway both types occur; and the winter ones are there
+found to be the most destructive, because they are lower down, and
+therefore the lightning is the more likely to strike buildings. In
+that country, however, the summer thunderstorms are not nearly so
+violent as in more southern latitudes.
+
+We must now just mention a class of thunderstorms which are more
+complicated than a simple squall, and yet differ in many ways from
+line-thunderstorms. They are associated with secondary cyclones,
+and are much commoner in England than line-thunderstorms, but none
+have been tracked over a sufficiently long area to allow us to say
+anything about their shape or motion. All we know is, that as surely
+as we see a secondary on the charts in summer, so certainly will
+thunderstorms occur during the day, though we can not say in what
+portion of the small depression.
+
+The special features of this class of thunderstorm are the calm
+sultry weather with which they are associated, so different from
+the squall of a line-thunderstorm, and the limited rotation of
+the surface-wind during the progress of the storm. Another very
+remarkable feature is that this surface circling of the wind extends
+only a very short distance upward, and whenever a glimpse can be
+caught of the drift of the upper clouds, they are found to move in
+the same direction throughout the whole period of the disturbance.
+This is the familiar class of thunderstorm which we associate with
+sultry weather, and with the thunder coming against the wind.
+
+One of the first things which must strike everybody is, that even
+in the temperate zone some countries are far more ravaged by
+thunderstorms than others. For instance, France suffers more than any
+other part of Europe, and England the least. We may probably find at
+least two causes which modify the development of thunderstorms. In
+the first place, the geographical position of the country relative to
+the great seasonal areas of high and low pressure. From this point
+of view we can readily see that France is far more exposed to the
+influence of small secondaries, which come in from the Atlantic,
+and which die out before they reach central Europe, than any other
+portion of that continent.
+
+In Great Britain, though the bulk of winter rain is cyclonic, a
+great deal of summer rainfall is non-isobaric; in Continental Europe
+a still larger proportion is of the latter character; so are most
+tropical rains, except the downpour of hurricanes; while the whole of
+the heavy rain on the equator, and all that falls in the doldrums, is
+also absolutely non-isobaric.
+
+A moderate whirlwind may be two hundred feet high, and not above ten
+feet in diameter. The dimensions, however, are very variable, for a
+whirlwind may vary in intensity from a harmless eddy in a dusty road
+to the destructive tornado of the United States.
+
+But by far the most striking non-isobaric rain in the world is the
+burst of the southwest monsoon in the Indian Ocean. The quality of
+the rain, if nothing else, distinguishes the monsoon from cyclonic
+precipitation. The rain in front of a Bengal cyclone seems to grow
+out of the air, while that of the monsoon falls in thunderstorms and
+from heavy cumulo-form clouds. The only rational suggestion which has
+been made to account for this burst of rain would look to a sudden
+inrush of damp air from the region of the doldrums as the source
+of the change in weather, but not of the direction of the wind, or
+of the shape of the isobars; for the burst is apparently almost
+coincident with the disappearance of the belt of high pressure to
+the south of the Bay of Bengal.
+
+The word “pampero” is, unfortunately, used in a very vague manner
+in the Argentine Republic and neighboring states. Every southwest
+wind which blows from off the pampas is sometimes called a pampero;
+and there is a still further confusion caused by calling certain dry
+dust-storms _pamperos sucios_, or dry pamperos. The true pampero
+may be described as a southwest wind, ushered in by a sudden short
+squall, usually accompanied by rain and thunder, with a very peculiar
+form of cloud-wreath.
+
+The barometer always falls pretty steadily for from two to four days
+before the pampero, and always rises for some days after the squall.
+Temperature is always very high before the squall, and then the
+sudden change of wind sends the thermometer rapidly down, sometimes
+as much as 33° in six hours. Thunder accompanies about three out of
+four pamperos; but more or less rain always falls, except in the
+rarest cases. The wind before this class of pampero almost invariably
+blows moderately or gently for some days from easterly points, and
+then with a sudden burst the southwest wind comes down with its full
+strength, and, after blowing thus from ten to thirty minutes, either
+ceases entirely or continues with diminished force for a certain
+number of hours. In all cases but one the upper wind-currents have
+been seen to come from the northwest before, during and after the
+pampero.
+
+The general appearance of a pampero will be best understood by a
+description of an actual squall. “In the early morning of a day
+in November, the wind blew rather strongly from the northeast. The
+sky was cloudy, but not overcast, save in the southwest horizon.
+The clouds were moving very slowly from the west, or a little
+south of it, throwing out long streamers eastward. About 8 A. M.
+the threatening masses in the southwest had advanced near enough
+to show that at their head marched two dense and perfectly regular
+battalions of cloud, one behind the other, in close contact, yet
+not intermingling, and completely distinguished by their striking
+difference of color, the first being of a uniform leaden gray, while
+the second was as black as the smoke of a steamer. On arriving
+overhead, it was seen that the front, although slightly sinuous, was
+perfectly straight in its general direction, and that the bands were
+of uniform breadth. As they rushed at a great speed under the other
+clouds without uniting with them, preserving their own formation
+unbroken, their force seemed irresistible, as if they were formed of
+some solid material rather than vapor. The length of these wonderful
+clouds could not be conjectured, as they disappeared beneath the
+horizon at both ends, but probably at least fifty miles of them
+must have been visible, as the ‘Cerro’ commands a view of twenty
+miles of country. Their breadth was not great, as they only took
+a few minutes to pass overhead, and appeared to diminish from the
+effects of perspective to mere lines on the horizon. At the instant
+when the first band arrived, the wind--which was still blowing, and
+something more than gently, from the northeast--went round by north
+to southwest; at the same time a strong, cold blast fell from the
+leaden cloud, and continued to blow till both bands had passed.”
+
+A whirlwind may be described as a mass of air whose height is
+enormously greater than its width, rotating rapidly round a more or
+less vertical axis.
+
+A tornado is simply a whirlwind of exceptional violence; if it were
+to encounter a lake or the sea, it would be called a waterspout.
+Its most characteristic feature is a funnel, or spout, which is the
+visible manifestation of a cylinder of air that is revolving rapidly
+round a nearly vertical axis. This spout is propagated throughout the
+northern temperate zone in a northeasterly direction at a rate of
+about thirty miles an hour, and tears everything to pieces along its
+narrow path.
+
+The diameter of the actual spout often does not exceed a few yards,
+and the total area of destructive wind is rarely more than three
+or four hundred yards across. The height of the spout is that of
+the lowest layer of clouds, which are then never high; and, as in
+thunderstorms, the upper currents are unaffected by the violent
+commotion below.
+
+The spout as a whole has four distinct motions:
+
+1. A motion of translation generally toward the northeast at a
+variable rate, but which may be taken to average thirty miles an hour.
+
+2. A complex gyration. The horizontal portion of this rotation is
+always in a direction opposite to that of the hands of a watch--that
+is to say, in the same manner as an ordinary cyclone. But in addition
+to this there is a violent upward current in the centre of the
+cylinder of vapor or dust which constitutes the spout, and sometimes
+small clouds seem to dart down the outer sides of the funnel whenever
+these float in close proximity. There are, however, no authentic
+instances of any object being thrown to the ground by the individual
+effort of a downward current. The slight downward motion of a few
+small clouds is probably only a slight eddying of a violent uprush.
+
+3. A swaying motion to and fro like a dangling whip, or an elephant’s
+trunk, though the general direction of the spout is always vertical.
+
+4. A rising and falling motion, that is to say, that sometimes the
+end of the funnel rises from the surface of the ground and then
+descends again, and so on. Owing to this rise and fall, the general
+appearance of the tornado changes a good deal. When the bottom of
+the spout is some distance above the ground, the whole is somewhat
+pointed, and does comparatively little harm as it passes over any
+place. As the spout descends, a commotion commences on the surface of
+the ground. This latter gradually rises so as to meet the descending
+part of the spout, and then the whole takes the shape of an
+hour-glass. This is the most dangerous and destructive form, because
+the ground gets the whole force of the tornado.
+
+The general appearance of the cloud over a tornado or whirlwind is
+always described as peculiarly smoky, or like the fumes of a burning
+haystack. The tornado is also never an isolated phenomenon; it is
+always associated with rain and electrical disturbance.
+
+The destructive effects of the tornado are very curious, from the
+sharp and narrow belt to which the injury is confined. It appears
+that in the passage of some tornadoes wind-pressures of various
+amounts, from eighteen to a hundred and twelve pounds per square
+foot, have been demonstrated by destruction of bridges, brick
+buildings, etc. The upward pressures are sometimes as great as the
+horizontal, and even greater. Downward pressures or movements of
+wind have not been clearly proved. Upward velocities of 135 miles
+per hour seem not to be unusual, and horizontal velocities of eighty
+miles have been recorded with the anemometer. The destructive
+wind-velocities are confined to very small areas. A destruction of
+fences, trees, etc., is often visible over a path many miles long and
+a few hundred yards wide, but the path of greatest violence is very
+much narrower. The excessive cases above referred to are observed
+only in small isolated spots, less than a hundred feet square,
+unequally distributed along the middle of the track. Thus, in very
+large buildings, only a small part is subject to destructive winds.
+In different parts of this area of _maximum_ severity, the winds are
+simultaneously blowing in different, perhaps opposite, directions,
+the resultant tending not to overturn or carry off or crush in, but
+rather to twist round a vertical axis. Buildings are generally lifted
+and turned round before being torn to pieces. As the chances are very
+small that a building will be exposed to the violent twisting action,
+it is evidently the average velocity of rectilinear winds within the
+path of moderate destruction that it is most necessary to provide
+against in ordinary structures. These winds may attain a velocity
+of eighty miles an hour over an area of a thousand feet broad, and
+generally blow from the southwest; the next in frequency blow from
+the northwest. The time during which an object is exposed to the
+more destructive winds varies from six to sixty seconds. An exposed
+building experiences but one stroke, like the blow of a hammer, and
+the destruction is done. Hence, in a suspension-bridge, chimney,
+or other structure liable to be set into destructive rhythmic
+vibrations, the _maximum_ winds do not produce such vibrations. The
+duration of the heavy southwest or northwest winds over the area
+of moderate destruction is rarely over two minutes. The motion of
+translation of the central spout of a tornado, in which there is a
+strong vertical current, is, on ah average, at the rate of thirty
+miles an hour.
+
+Tornadoes mostly occur on sultry days and either in the southeast or
+right front of cyclones, or in front of the trough of V-depressions.
+
+The general character of all tornadoes is so similar that the
+description of one will do for all. We shall therefore give some of
+the description furnished by an eye-witness to the United States
+Signal Office, which is described in the reports as the “Delphos
+tornado”:
+
+“On Friday morning, May 30, 1879, the weather was very pleasant,
+but warm, with the wind from the southeast, from which direction it
+had blown for several days. The ground was very dry, and no rain
+had fallen for a number of weeks. About 2 P. M. threatening clouds
+appeared very suddenly in the west (against the wind), attended in a
+few minutes by light rain, the wind still in the southeast It stopped
+in about five minutes, and then commenced again, wind still the same,
+accompanied by hail, which was thick and small at first, but rapidly
+grew less in quantity and larger in size, some stones measuring
+three and a half inches in diameter, and one was found weighing
+one-fourth of a pound. This last precipitation continued for about
+thirty minutes, after which a cloud in the shape of a waterspout
+was seen forming in the southwest, and moving rapidly forward to
+the northeast. The cloud from which the funnel depended, seen at a
+distance of eight miles, appeared to be in terrible commotion; in
+fact, while the hail was falling, a sort of tumbling in the clouds
+was noticed as they came up from the northwest and southwest, and
+about where they appeared to meet was the point from which the funnel
+was seen to descend. There was but one funnel at first, which was
+soon accompanied by several smaller ones, dangling down from the
+overhanging clouds like whiplashes, and for some minutes they were
+appearing and disappearing like fairies at a play. Finally one of
+them seemed to expand and extend downward more steadily than the
+others, resulting at length in what appeared to be their complete
+absorption. This funnel-shaped cloud now moved onward, growing in
+power and size, whirling rapidly from right to left, rising and
+descending, and swaying from side to side. When within a distance
+of three or four miles, its terrible roar could be heard, striking
+terror into the hearts of the bravest.” The eye-witness judged that
+the funnel itself would reach a height of about five hundred feet
+from the ground. As the storm crossed a river, a cone-shaped mass
+came up from the earth to meet it, carrying mud, débris, and a large
+volume of water. The cloud then passed the observer’s house very
+near to 4 P. M. The progressive velocity at the time was considered
+to be about thirty miles per hour, although at Delphos, three and a
+half miles distant, it had slackened down to near twenty miles. A few
+minutes previous to and during the passage of the funnel, the air was
+very oppressive; but ten minutes after the wind was so cold from the
+northwest that it became necessary to wear an overcoat when outside.
+
+The actual diameter of this storm appears to have been only
+forty-three yards. On the right of the track, destructive winds
+extended to a further distance of from one to two miles, sensibly
+deflected winds for another mile and a half, beyond which only the
+usual wind of the day was experienced. On the left or northern side
+of the tornado path, the damage did not extend quite so far, for the
+width of the belt of destructive winds was not more than twenty-eight
+yards across and that of sensibly deflected winds one mile and a
+quarter.
+
+As a specimen of the damage done a large two-horse sulky plow,
+weighing about seven hundred pounds, was carried a distance of twenty
+yards, breaking off one of the iron wheels attached to an iron axle
+one and three-quarter inches in diameter. A woman was carried to the
+northwest two hundred yards, lodged against a barbed-wire fence, and
+instantly killed. Her clothing was entirely stripped from her body,
+which was found covered with black mud, and her hair matted with it.
+A cat was found half a mile to the northwest of the house, in which
+she had been seen just before the storm, with every bone broken.
+Chickens were stripped of their feathers, and one was found three
+miles to the northwest.
+
+A few miles further on, another eye-witness says, “the dark, inky,
+funnel-shaped cloud rapidly descended to the earth, which reaching,
+it destroyed everything within its grasp. Everything was taken up and
+carried round and round in the mighty whirl of the terrible monster.
+The surrounding clouds seemed to roll and tumble toward the vortex.
+
+“The funnel, now extending from the earth upward to a great height,
+was black as ink, excepting the cloud near the top, which resembled
+smoke of a light color. Immediately after passing the town, there
+came a wave of hot air, like the wind blowing from a burning
+building. It lasted but a short time. Following this peculiar
+feature, there came a stiff gale from the northwest, cold and bleak,
+so much so that during the night frost occurred, and water in some
+low places was frozen.”
+
+
+END OF VOLUME TWO
+
+
+FOOTNOTES:
+
+[1] The lakes of Sweden, which cover one-twelfth of the surface of
+the country, exercise an important influence on climate according as
+they are frozen or open.
+
+[2] Another variety or species of seal inhabits Lake Baikal.
+
+[3] Count von Helmersen, however, has stated his belief that for this
+extreme northern prolongation of the Aralo-Caspian Sea there is no
+evidence. The shells, on the presence of which over the Tundras the
+opinion was chiefly based, are, according to him, all fresh-water
+species, and there are no marine shells of living species to be met
+with in the plains at the foot of the Ural Mountains.
+
+[4] Archbishop of Spalato and Primate of Dalmatia.
+
+
+
+
+  TRANSCRIBER’S NOTE
+
+  Obvious typographical errors and punctuation errors have been
+  corrected after careful comparison with other occurrences within
+  the text and consultation of external sources.
+
+  Some hyphens in words have been silently removed, some added,
+  when a predominant preference was found in the original book.
+
+  Except for those changes noted below, all misspellings in the text,
+  and inconsistent or archaic usage, have been retained.
+
+  Pg 470: ‘chiefly Brachipods of’ replaced by ‘chiefly Brachiopods of’.
+  Pg 472: ‘these same familes’ replaced by ‘these same families’.
+  Pg 483: ‘constituing links’ replaced by ‘constituting links’.
+  Pg 563: ‘Camaroons Mountains’ replaced by ‘Cameroon Mountains’.
+  Pg 563: ‘with Teneriffe in’ replaced by ‘with Tenerife in’.
+  Pg 569: ‘existing, denundation’ replaced by ‘existing, denudation’.
+  Pg 650: ‘their relativ  size’ replaced by ‘their relative size’.
+  Pg 718: ‘incalulable ages’ replaced by ‘incalculable ages’.
+  Pg 722: ‘greatly diminshed’ replaced by ‘greatly diminished’.
+
+
+*** END OF THE PROJECT GUTENBERG EBOOK 77792 ***