Initial commit of ebook 77792 filesHEAD main

author: www-data <www-data@mail.pglaf.org> 2026-01-26 14:12:00 -0800
committer: www-data <www-data@mail.pglaf.org> 2026-01-26 14:12:00 -0800
commit: b0ec5f78336ee6068b9b079f737b85ceb4bb8f15 (patch)
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+      The story of the universe (vol 2 of 4) | Project Gutenberg
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+</head>
+<body>
+<div style='text-align:center'>*** START OF THE PROJECT GUTENBERG EBOOK 77792 ***</div>
+
+
+<div class="transnote">
+<p><strong>TRANSCRIBER’S NOTE</strong></p>
+
+<p>Footnote anchors are denoted by [number], and the footnotes have been
+  placed at the end of the book.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>Chapter headings have been made consistent, with the title on a single
+line and the author on the following line.</p>
+
+<p class="customcover">New original cover art included with this eBook is
+granted to the public domain.</p>
+
+<p>Some minor changes to the text are noted at the <a href="#TN">end of the book.</a>
+<span class="screenonly">These are indicated by a <ins class="corr">dashed blue</ins> underline.</span></p>
+
+<p>Volume I of this set of four volumes can be found in Project Gutenberg at:<br>
+  <a href="https://www.gutenberg.org/ebooks/74571">https://www.gutenberg.org/ebooks/74571</a></p>
+</div>
+
+
+<hr class="chap x-ebookmaker-drop">
+<div class="chapter"></div>
+
+<figure class="figcenter illowp50" id="cover-orig" style="max-width: 30em;">
+  <img class="w100" src="images/cover-orig.jpg" alt="Original cover"
+  title="Original cover">
+</figure>
+
+<hr class="chap x-ebookmaker-drop">
+<div class="chapter"></div>
+
+<figure class="figcenter illowp100" id="i_001" style="max-width: 50em;">
+  <img class="w100" src="images/i_001.jpg" alt="Colorful strata">
+  <figcaption class="caption">Jupiter and Minerva Terraces, Hot Springs, Yellowstone Park
+  </figcaption>
+</figure>
+
+<hr class="chap x-ebookmaker-drop">
+<div class="chapter"></div>
+
+<h1>
+THE STORY OF<br>
+THE UNIVERSE</h1>
+
+<p class="p1 pfs120"><i>Told by Great Scientists<br>
+and Popular Authors</i></p>
+
+<p class="p2 pfs70">COLLECTED AND EDITED</p>
+
+<p class="pfs100"><i>By</i> ESTHER SINGLETON</p>
+
+<p class="p1 pfs60">Author of “Turrets, Towers and Temples,” “Wonders of Nature,”<br>
+“The World’s Great Events,” “Famous Paintings,” Translator<br>
+of Lavignac’s “Music Dramas of Richard Wagner”</p>
+
+<p class="p2 pfs80"><em>FULLY ILLUSTRATED</em></p>
+
+<div class="bbox">
+<div class="bbox2">
+<p class="pfs120 wsp lht"><span class="fs80">VOLUME II</span><br>
+<span class="wsp">THE EARTH:<br>
+LAND AND<br>
+SEA</span></p>
+</div>
+</div>
+<p class="p4 pfs90 lsp2">P. F. COLLIER AND SON</p>
+
+<p class="pfs80">NEW YORK</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<div class="chapter"></div>
+
+<p class="p6 p6b pfs80 smcap lht">
+Copyright 1905<br>
+By P. F. COLLIER &amp; SON</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum" id="Page_i">[Pg i]</span></p>
+<div class="chapter"></div>
+  <h2 class="p4 nobreak" id="ILLUSTRATIONS">
+    ILLUSTRATIONS
+  </h2>
+
+<table class="autotable fs90 wd80">
+<tr>
+<td class="tdl"><a href="#i_001">Hot Springs, Yellowstone Park</a></td>
+<td class="tdr" colspan="2"><i>Frontispiece</i></td>
+</tr>
+<tr>
+<td class="tdl"><a href="#i_056">Fingal’s Cave, Staffa</a></td>
+<td class="tdc wd10"><i>Opposite</i></td>
+<td class="tdr">p. 475</td>
+</tr>
+<tr>
+<td class="tdl"><a href="#i_106">A Forest of the Carboniferous Period</a></td>
+<td class="tdc">”</td>
+<td class="tdr">523</td>
+</tr>
+<tr>
+<td class="tdl"><a href="#i_180">The Giant’s Causeway, Ireland</a></td>
+<td class="tdc">”</td>
+<td class="tdr">595</td>
+</tr>
+<tr>
+<td class="tdl"><a href="#i_230">Stag-Horn Coral Reef, Australia</a></td>
+<td class="tdc">”</td>
+<td class="tdr">643</td>
+</tr>
+<tr>
+<td class="tdl"><a href="#i_280">The Matterhorn</a></td>
+<td class="tdc">”</td>
+<td class="tdr">691</td>
+</tr>
+<tr>
+<td class="tdl"><a href="#i_330">Forms of Snowflakes</a></td>
+<td class="tdc">”</td>
+<td class="tdr">739</td>
+</tr>
+<tr>
+<td class="tdl"><a href="#i_380">Forms of Clouds</a></td>
+<td class="tdc">”</td>
+<td class="tdr">787</td>
+</tr>
+<tr>
+<td class="tdl"><a href="#i_430">Chart of Winds and Tides</a></td>
+<td class="tdc">”</td>
+<td class="tdr">835</td>
+</tr>
+</table>
+
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum"><a id="Page_iii"></a>[iii]</span></p>
+<div class="chapter"></div>
+
+  <h2 class="p4 nobreak" id="CONTENTS">
+    CONTENTS
+  </h2>
+
+<table class="autotable fs90 wd80">
+<tr>
+<td class="tdl"><span class="smcap">Formation of the Earth.</span> &nbsp; Élisée Reclus</td>
+<td class="tdr"><a href="#I-433">433</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Classes of Rocks.</span> &nbsp; Sir Charles Lyell</td>
+<td class="tdr"><a href="#I-439">439</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Geological Chronology.</span> &nbsp; Sir J. William Dawson</td>
+<td class="tdr"><a href="#I-450">450</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Silurian Beach.</span> &nbsp; Louis Agassiz</td>
+<td class="tdr"><a href="#I-456">456</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Carboniferous Period.</span> &nbsp; Louis Figuier</td>
+<td class="tdr"><a href="#I-464">464</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Palæontological History of Animals.</span> &nbsp; Hugh Miller</td>
+<td class="tdr"><a href="#I-480">480</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">European and Asiatic Deluges.</span> &nbsp; Louis Figuier</td>
+<td class="tdr"><a href="#I-493">493</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Glaciers.</span> &nbsp; Louis Agassiz</td>
+<td class="tdr"><a href="#I-502">502</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Volcanic Action.</span> &nbsp; Sir Archibald Geikie</td>
+<td class="tdr"><a href="#I-516">516</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Thoughts About Krakatoa.</span> &nbsp; Sir Robert S. Ball</td>
+<td class="tdr"><a href="#I-527">527</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Volcanoes.</span> &nbsp; Sir Archibald Geikie</td>
+<td class="tdr"><a href="#I-536">536</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Earthquakes.</span> &nbsp; William Hughes</td>
+<td class="tdr"><a href="#I-559">559</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Mountains.</span> &nbsp; A. Keith</td>
+<td class="tdr"><a href="#I-566">566</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Lakes—Fresh, Salt, and Bitter.</span> &nbsp; Sir Archibald Geikie</td>
+<td class="tdr"><a href="#I-573">573</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Underground Water: Springs, Caves, Rivers, and Lakes.</span> &nbsp; Élisée Reclus</td>
+<td class="tdr"><a href="#I-588">588</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Rivers.</span> &nbsp; A. Keith Johnston</td>
+<td class="tdr"><a href="#I-621">621</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Swamps and Marshes.</span> &nbsp; Élisée Reclus</td>
+<td class="tdr"><a href="#I-628">628</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Lowland Plains.</span> &nbsp; William Hughes</td>
+<td class="tdr"><a href="#I-634">634</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Smell of Earth.</span> &nbsp; G. Clarke Nuttall</td>
+<td class="tdr"><a href="#I-648">648</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Deserts.</span> &nbsp; Élisée Reclus</td>
+<td class="tdr"><a href="#I-654">654</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Primitive Ocean.</span> &nbsp; G. Hartwig</td>
+<td class="tdr"><a href="#II-666">666</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Floor of the Ocean.</span> &nbsp; John James Wild</td>
+<td class="tdr"><a href="#II-676">676</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Coral Formations.</span> &nbsp; Charles Darwin</td>
+<td class="tdr"><a href="#II-689">689</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Magnitude and Color of the Sea.</span> &nbsp; G. Hartwig</td>
+<td class="tdr"><a href="#II-707">707</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Tidal Action.</span> &nbsp; Sir Robert S. Ball <span class="pagenum"><a id="Page_iv"></a>[iv]</span></td>
+<td class="tdr"><a href="#II-713">713</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Gulf Stream.</span> &nbsp; Lord Kelvin</td>
+<td class="tdr"><a href="#II-727">727</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Phosphorescence of the Sea.</span> &nbsp; G. Hartwig</td>
+<td class="tdr"><a href="#II-750">750</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Seashore.</span> &nbsp; P. Martin Duncan</td>
+<td class="tdr"><a href="#II-763">763</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Ocean of Air.</span> &nbsp; Agnes Giberne</td>
+<td class="tdr"><a href="#III-773">773</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Weather.</span> &nbsp; Sir Ralph Abercromby</td>
+<td class="tdr"><a href="#III-784">784</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Romance of a Raindrop.</span> &nbsp; Arthur H. Bell</td>
+<td class="tdr"><a href="#III-792">792</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Rainbow.</span> &nbsp; John Tyndall</td>
+<td class="tdr"><a href="#III-799">799</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Snow, Hail, and Dew.</span> &nbsp; Alexander Buchan</td>
+<td class="tdr"><a href="#III-807">807</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">The Aurora Borealis.</span> &nbsp; Richard A. Proctor</td>
+<td class="tdr"><a href="#III-813">813</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Clouds.</span> &nbsp; D. Wilson Barker</td>
+<td class="tdr"><a href="#III-819">819</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Winds.</span> &nbsp; William Hughes</td>
+<td class="tdr"><a href="#III-828">828</a></td>
+</tr>
+<tr>
+<td class="tdl"><span class="smcap">Squalls, Whirlwinds, and Tornadoes.</span> &nbsp; Sir Ralph Abercromby</td>
+<td class="tdr"><a href="#III-845">845</a></td>
+</tr>
+</table>
+
+
+<hr class="chap x-ebookmaker-drop">
+<div class="chapter"></div>
+<p class="p6 pfs135">
+THE STORY OF THE UNIVERSE<br>
+<span class="fs60">VOLUME II</span></p>
+
+<hr class="r15">
+
+<p class="p1 p6b pfs120">THE EARTH: LAND, SEA, AND AIR</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum" id="Page_433">[Pg 433]</span></p>
+<div class="chapter"></div>
+
+<p class="p4 pfs100 lht2">
+THE<br>
+<span class="fs150">STORY OF THE UNIVERSE</span></p>
+
+<hr class="r15">
+
+<h2 class="p4 nobreak" id="I-THE_EARTHS_CRUST">
+  <i>I.—THE EARTH’S CRUST</i>
+</h2>
+
+<h3 id="I-433">
+  FORMATION OF THE EARTH<br>
+  —<span class="smcap">Élisée Reclus</span>
+</h3>
+
+
+<p class="drop-capy">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.</p>
+
+<p>This brilliant hypothesis accounts better than any
+other for the uniform translatory motion of the planets
+<span class="pagenum" id="Page_434">[434]</span>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 <i lang="fr">savant</i>, 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.</p>
+
+<p>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
+<i lang="la">scoria</i>, 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
+<span class="pagenum" id="Page_435">[435]</span>sea. This first <i lang="la">scoria</i> 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.</p>
+
+<p>This crust was frequently broken through by
+the lava boiling beneath it, and then, by means of
+the solidification of the <i lang="la">scoriæ</i>, 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
+<span class="pagenum" id="Page_436">[436]</span>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 <i lang="la">scoria</i>, 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_437">[437]</span>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.”</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_438">[438]</span>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 <i lang="fr">débris</i> torn away
+from the surface of the soil, which they bear with
+them.</p>
+
+<p>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
+<span class="pagenum" id="Page_439">[439]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-439">
+  CLASSES OF ROCKS<br>
+  —<span class="smcap">Sir Charles Lyell</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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 <em>ge</em>, the earth, and <em>logos</em>, 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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_440">[440]</span>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.</p>
+
+<p>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 <em>rock</em> 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.</p>
+
+<p>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.</p>
+
+<p>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 <em>stratified</em>, or divided into distinct
+layers or strata. The term <i lang="la">stratum</i> means simply a
+bed, or anything spread out or <em>strewed</em> 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,
+<span class="pagenum" id="Page_441">[441]</span>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.</p>
+
+<p>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 <em>formation</em> 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.</p>
+
+<p>The term <em>formation</em>, 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.</p>
+
+<p><span class="pagenum" id="Page_442">[442]</span></p>
+
+<p>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.</p>
+
+<p>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 <em>stratified</em>, 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_443">[443]</span>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.</p>
+
+<p>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 <em>fossils</em>, so abundantly included
+in the earth’s crust. By a <em>fossil</em> 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,
+<span class="pagenum" id="Page_444">[444]</span>13,000 in the Andes, and above 18,000 feet in the
+Himalayas.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_445">[445]</span>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 <em>dikes</em>, 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 <em>volcanic tuff</em>, 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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_446">[446]</span>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.</p>
+
+<p>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.</p>
+
+<p>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 <em>crystalline schists</em>, in which
+<span class="pagenum" id="Page_447">[447]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_448">[448]</span>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_449">[449]</span></p>
+
+<p>In accordance with the hypothesis above alluded
+to, I proposed in the first edition of the <cite>Principles
+of Geology</cite> (1833), the term Metamorphic,
+for the altered strata, a term derived from meta,
+<i lang="la">trans</i>, and morphe, <i lang="la">forma</i>.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_450">[450]</span>monuments, attesting a succession of events in the
+former history of the globe and its living inhabitants.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-450">
+  GEOLOGICAL CHRONOLOGY<br>
+  —<span class="smcap">Sir J. William Dawson</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.</p>
+
+<p>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
+<span class="pagenum" id="Page_451">[451]</span>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.</p>
+
+<p>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.</p>
+
+<p>The evidence is similar to that obtained by Schliemann
+on the site of Troy, where, in digging through
+successive layers of <i lang="fr">débris</i>, he found the objects deposited
+by successive occupants of the site, from the
+<span class="pagenum" id="Page_452">[452]</span>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.</p>
+
+<p>Let us now tabulate the whole geological succession
+with the history of animals and plants associated
+with it:</p>
+
+<table class="autotable fs80 wd80">
+<tr>
+<td class="bt" colspan="4"></td>
+</tr>
+<tr>
+<th class="tdc">ANIMALS</th>
+<th class="tdc bl" colspan="2">SYSTEMS OF FORMATIONS</th>
+<th class="tdc bl">PLANTS</th>
+</tr>
+<tr>
+<td class="bt" colspan="4"></td>
+</tr>
+<tr>
+<td class="tdl" rowspan="6">Age of Man and Mammalia</td>
+<td class="tdl bl" colspan="2">Kainozoic</td>
+<td class="tdl bl"></td>
+</tr>
+<tr>
+<td class="tdl bl"></td>
+<td class="tdl">Modern</td>
+<td class="tdl bl" rowspan="5">Angiosperms and Palms dominant</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Pleistocene</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Pliocene</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Miocene</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Eocene</td>
+</tr>
+<tr>
+<td colspan="4">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="tdl" rowspan="4">Age of Reptiles</td>
+<td class="tdl bl" colspan="2">Mesozoic</td>
+<td class="tdl bl"></td>
+</tr>
+<tr>
+<td class="tdl bl"></td>
+<td class="tdl">Cretaceous</td>
+<td class="tdl bl" rowspan="3">Cycads and Pines dominant</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Jurassic</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Triassic</td>
+</tr>
+<tr>
+<td colspan="4">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="tdl" rowspan="5">Age of Amphibians and Fishes</td>
+<td class="tdl bl" colspan="2">Palæozoic</td>
+<td class="tdl bl"></td>
+</tr>
+<tr>
+<td class="tdl bl"></td>
+<td class="tdl">Permian</td>
+<td class="tdl bl" rowspan="7">Acrogens and Gymnosperms dominant</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Carboniferous</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Erian</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Silurian</td>
+</tr>
+<tr>
+<td class="tdlt" rowspan="3">Age of Invertebrates</td>
+<td class="tdc bl"></td>
+<td class="tdl">Ordovician</td>
+</tr>
+<tr>
+<td class="tdc bl"></td>
+<td class="tdl">Cambrian</td>
+</tr>
+<tr>
+<td class="tdc bl"></td>
+<td class="tdl">Huronian (Upper)</td>
+</tr>
+<tr>
+<td colspan="4">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="tdl" rowspan="5">Age of Protozoa</td>
+<td class="tdl bl" colspan="2">Eozoic</td>
+<td class="tdl bl"></td>
+</tr>
+<tr>
+<td class="tdl bl"></td>
+<td class="tdl">Huronian (Lower)</td>
+<td class="tdl bl" rowspan="4">Protogens and Algæ</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Upper Laurentian</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Middle&nbsp;Laurentian</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdl">Lower Laurentian</td>
+</tr>
+<tr>
+<td class="bb" colspan="4"></td>
+</tr>
+</table>
+
+
+
+<p>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
+<span class="pagenum" id="Page_453">[453]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_454">[454]</span>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.</p>
+
+<p>Let us now consider the history of the vegetable
+kingdom as indicated in the few notes in the right-hand
+column of the table.</p>
+
+<p>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.</p>
+
+<p>The Cryptogams may be subdivided into the following
+three groups:</p>
+
+<p>1. <i>Thallogens</i>, cellular plants not distinctly distinguishable
+into stem and leaf. These are the Fungi,
+the Lichens, and the Algæ, or sea-weeds.</p>
+
+<p><span class="pagenum" id="Page_455">[455]</span></p>
+
+<p>2. <i>Anogens</i>, having stem and foliage, but wholly
+cellular. These are the Mosses and Liverworts.</p>
+
+<p>3. <i>Acrogens</i>, 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 (<i>Filices</i>), the Mare’s-tails
+(<i>Equisetaceæ</i>), and the Club-mosses (<i>Lycopodiaceæ</i>),
+and a curious little group of aquatic plants
+called Rhizocarps (<i>Rhizocarpeæ</i>).</p>
+
+<p>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:</p>
+
+<p>1. <i>Gymnosperms</i>, or those which bear naked seeds
+not inclosed in fruits. They are the Pines and their
+allies, and the Cycads.</p>
+
+<p>2. <i>Angiosperms</i>, 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 <i>Endogens</i>, or inside
+growers, with seeds having one seed-leaf only, as the
+grasses and the palms; and the <i>Exogens</i>, having outside-growing
+woody stems and seeds with two seed-leaves.
+Most of the ordinary forest trees of temperate
+climates belong to this group.</p>
+
+<p>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,
+<span class="pagenum" id="Page_456">[456]</span>I may call <i>Protogens</i>. 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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-456">
+  THE SILURIAN BEACH<br>
+  —<span class="smcap">Louis Agassiz</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_457">[457]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_458">[458]</span>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.</p>
+
+<p>Admitting it, then, to be a beach, let us begin with
+the lowest type of the Animal Kingdom and see
+<span class="pagenum" id="Page_459">[459]</span>what <i>Radiates</i> are to be found there. There are
+plenty of <i>Corals</i>, but they are not the same kind of
+<i>Corals</i> as those that build up our reefs and islands
+now. The modern Coral animals are chiefly <i>Polyps</i>,
+but the prevailing <i>Corals</i> of the <i>Silurian</i> age were
+<i>Acalephian Hydroids</i>, animals which indeed resemble
+<i>Polyps</i> in certain external features, and have
+been mistaken for them, but which are, nevertheless,
+<i>Acalephs</i> by their internal structure.</p>
+
+<p>Of the <i>Echinoderms</i>, the class of <i>Radiates</i> represented
+now by our <i>Star-Fishes</i> and <i>Sea-Urchins</i>, we
+may gather any quantity, though the old-fashioned
+forms are very different from the living ones. The
+<i>Mollusks</i> were also represented then, as now, by their
+three classes, <i>Acephala</i>, <i>Gasteropoda</i>, and <i>Cephalopoda</i>.
+The <i>Acephala</i> or <i>Bivalves</i> we find in great
+numbers, but of a very different pattern from the
+<i>Oysters</i>, <i>Clams</i>, and <i>Mussels</i> of recent times.</p>
+
+<p>Of the <i>Silurian Univalves</i> or <i>Gasteropods</i>, 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 <i>Mollusks</i>, the <i>Cephalopods</i> or <i>Chambered
+Shells</i>, or <i>Cuttle-Fishes</i>, as they are called when the
+animal is unprotected by a shell, are, on the contrary,
+very well preserved, and they are very numerous.</p>
+
+<p>Of <i>Articulates</i> we find only two classes, <i>Worms</i>
+and <i>Crustacea</i>. Insects there were none—for, as we
+have seen, this early world was wholly marine.
+There is little to be said of the <i>Worms</i>, for their soft
+<span class="pagenum" id="Page_460">[460]</span>bodies, unprotected by any hard covering, could hardly
+be preserved; but, like the marine <i>Worms</i> 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 <i>Worms</i> were represented there. I
+should add, however, that many impressions described
+as produced by <i>Worms</i> are more likely to
+have been the tracks of <i>Crustacea</i>. But by far the
+most characteristic class of <i>Articulates</i> in ancient
+times were the <i>Crustaceans</i>. The <i>Trilobites</i> stand in
+the same relation to the modern <i>Crustacea</i> as the
+<i>Crinoids</i> do to the modern <i>Echinoderms</i>. 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.</p>
+
+<p>We have found <i>Radiates</i>, <i>Mollusks</i>, and <i>Articulates</i>
+in plenty; and now what is to be said of <i>Vertebrates</i>
+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 <i>Silurian</i> age from
+any remains that are left to us. But still we find
+enough to indicate clearly the style of those old fishes,
+<span class="pagenum" id="Page_461">[461]</span>and to show, by comparison with the living types, to
+what group of modern times they belong. We should
+naturally expect to find the <i>Vertebrates</i> introduced
+in their simplest form; but this is by no means the
+case: the common fishes, as <i>Cod</i>, <i>Herring</i>, <i>Mackerel</i>,
+and the like, were unknown in those days.</p>
+
+<p>I have spoken of the <i>Silurian</i> 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
+<i>Silurian</i> and <i>Devonian</i> 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.</p>
+
+<p>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,
+<i>Silurian</i> 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
+<span class="pagenum" id="Page_462">[462]</span>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.</p>
+
+<p>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 <i>Silurian</i> and
+<i>Devonian</i> periods are exposed to view only over comparatively
+limited tracts and in disconnected regions.
+But let us compare a given extent of <i>Silurian</i> or
+<i>Devonian</i> 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 <i>Devonian</i> 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
+<span class="pagenum" id="Page_463">[463]</span>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
+<i>Silurian</i> and <i>Devonian</i> periods is even more circumscribed
+than his, and belongs, besides, not to a
+living but to a dead world, far more difficult to decipher.</p>
+
+<p>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.</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum" id="Page_464">[464]</span></p>
+
+<div class="chapter">
+<h3 id="I-464">
+  CARBONIFEROUS PERIOD<br>
+  —<span class="smcap">Louis Figuier</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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 <em>Coal-measures</em>;
+and 2. The <em>Carboniferous Limestone</em>. 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.</p>
+
+<p>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.</p>
+
+<p>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 <i>Sigillaria</i>, the <i>Stigmaria</i>, and other fern-like
+<span class="pagenum" id="Page_465">[465]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_466">[466]</span>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.</p>
+
+<p>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.</p>
+
+<p>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 <em>climate</em> 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
+<span class="pagenum" id="Page_467">[467]</span>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.</p>
+
+<p>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.</p>
+
+<p>Every one knows those marsh-plants with hollow,
+channeled, and articulated cylindrical stems; whose
+joints are furnished with a membranous, denticulated
+<span class="pagenum" id="Page_468">[468]</span>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 <em>spores</em> or seeds. These humble
+<i>Equiseta</i> 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 <i>Calamites</i>.</p>
+
+<p>The <i>Lycopods</i> 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 <i>Lepidodendrons</i> 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 <i>Lepidodendron carinatum</i>
+which have been found. Another Lycopod of this
+period, the <i>Lomatophloyos crassicaule</i>, attained dimensions
+still more colossal. The <i>Sigillarias</i> 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_469">[469]</span>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.</p>
+
+<p>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.</p>
+
+<p>The <i>Annulariæ</i> 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
+<span class="pagenum" id="Page_470">[470]</span>with the branches. The <i>Sigillariæ</i> 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, <i>sigillum</i>, gave origin
+to their name.</p>
+
+<p>The <i>Stigmariæ</i>, 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.</p>
+
+<p>Two other gigantic trees grew in the forests of
+this period: these were <i>Lepidodendron carinatum</i>
+and <i>Lomatophloyos crassicaule</i>, 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.</p>
+
+<p>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,
+<i>Psammodus</i> and <i>Coccosteus</i>, whose massive teeth inserted
+in the palate were suitable for grinding; and
+the <i>Holoptychius</i> and <i>Megalichthys</i>, are the most important.
+The Mollusca are chiefly <ins class="corr" id="tn-470" title="Transcriber’s Note—Original text: 'Brachipods'">Brachiopods</ins> of
+great size. The <i>Bellerophon</i>, whose convoluted shell
+in some respects resembles the Nautilus of our present
+seas, but without its chambered shell, were then
+represented by many species.</p>
+
+<p><span class="pagenum" id="Page_471">[471]</span></p>
+
+<p>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.</p>
+
+<p>Among the corals of the period we may include
+the genera <i>Lithostrotion</i> and <i>Lonsdalea</i>. Among the
+Polyzoa are the genera <i>Fenestrella</i> and <i>Polypora</i>.
+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 <i>Foraminifera</i>,
+microscopic animals, which clustered either in
+one body or divided into segments, and covered
+with a calcareous, many-chambered shell, as <i>Fusulina
+cylindrica</i>. 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_472">[472]</span>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.</p>
+
+<p>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 <ins class="corr" id="tn-472" title="Transcriber’s Note—Original text: 'familes'">families</ins>. 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.
+<span class="pagenum" id="Page_473">[473]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_474">[474]</span>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.</p>
+
+<p>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 <i>Holoptychius</i>
+and <i>Megalichthys</i>, having jawbones armed
+with enormous teeth. Scales of <i>Pygopterus</i> 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_475">[475]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_476">[476]</span>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.</p>
+
+<p>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.</p>
+
+<figure class="figcenter illowp100" id="i_056" style="max-width: 50em;">
+  <img class="w100" src="images/i_056.jpg" alt="Steep rocky cliffs at the shoreline with large cave">
+  <figcaption class="caption">
+      Fingal’s Cave, Staffa, Coast of Scotland
+  </figcaption>
+</figure>
+
+<p>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 <i>Stigmaria
+ficoides</i>, these being frequently traceable to the main
+stem (<i>Sigillaria</i>), 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
+<span class="pagenum" id="Page_477">[477]</span>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.”</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_478">[478]</span>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.</p>
+
+<p>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.</p>
+
+<p>To what modification has the vegetation of the ancient
+world been subjected to attain that carbonized
+state which constitutes coal? The submerged plants
+<span class="pagenum" id="Page_479">[479]</span>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.</p>
+
+<p>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 <em>drier</em> 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.</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum" id="Page_480">[480]</span></p>
+
+<div class="chapter">
+<h3 id="I-480">
+  THE PALÆONTOLOGICAL HISTORY OF ANIMALS<br>
+  —<span class="smcap">Hugh Miller</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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. <em>First</em>, there is the <i>star-like</i> 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; <em>second</em>, there is the
+<i>articulated</i> 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; <em>third</em>, there is the
+bilateral or <i>molluscan</i> 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 <em>fourth</em>, there is the <i>vertebrate</i> 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,
+<span class="pagenum" id="Page_481">[481]</span>in which, so far as is yet known, only three of the
+number existed—the radiated, articulated, and molluscan
+ideas or types.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_482">[482]</span>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
+<span class="pagenum" id="Page_483">[483]</span>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.</p>
+
+<p>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 <ins class="corr" id="tn-483" title="Transcriber’s Note—Original text: 'constituing'">constituting</ins> 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
+<span class="pagenum" id="Page_484">[484]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_485">[485]</span>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
+<span class="pagenum" id="Page_486">[486]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_487">[487]</span>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 <em>free</em>, 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
+<span class="pagenum" id="Page_488">[488]</span>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.</p>
+
+<p><span class="pagenum" id="Page_489">[489]</span></p>
+
+<p>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
+<span class="pagenum" id="Page_490">[490]</span>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 <i>Dinornus giganteus</i>, 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.</p>
+
+<p>With the Stonesfield slates—a deposit which lies
+above what is known as the Inferior Oolite—the remains
+of mammaliferous animals first appear.</p>
+
+<p>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,
+<span class="pagenum" id="Page_491">[491]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_492">[492]</span>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,
+<span class="pagenum" id="Page_493">[493]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-493">
+  EUROPEAN AND ASIATIC DELUGES<br>
+  —<span class="smcap">Louis Figuier</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.</p>
+
+<p><span class="pagenum" id="Page_494">[494]</span></p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<em>diluvium</em>. This term was long employed to designate
+what is now better known as the “bowlder” formation,
+<span class="pagenum" id="Page_495">[495]</span>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.</p>
+
+<p>There is very distinct evidence of two successive
+deluges in our hemisphere during the Quaternary
+epoch. The two may be distinguished as the <em>European
+Deluge</em> and the <em>Asiatic</em>. 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_496">[496]</span>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.</p>
+
+<p>The physical proof of this <em>deluge of the north of
+Europe</em> 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 <em>erratic</em>,
+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 <i>Permian</i>, and its presence there
+<span class="pagenum" id="Page_497">[497]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_498">[498]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_499">[499]</span>Garonne is, in respect to these phenomena, classic
+ground, as it were.</p>
+
+<p>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.</p>
+
+<p>In the valley of the Rhine, in Alsace, and in many
+isolated parts of Europe, a particular sort of <i>diluvium</i>
+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 <em>loess</em>,
+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.</p>
+
+<p>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 <em>loess</em>, 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 <i>loess</i> was slowly accumulated,
+<span class="pagenum" id="Page_500">[500]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_501">[501]</span>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 <cite lang="fr">La
+Cosmogonie de Moïse</cite>, and other philologists, as
+being an inaccurate translation. He has proved that
+the Hebrew word <em>haarets</em>, incorrectly translated “all
+the earth,” is often used in the sense of <em>region</em> or
+<em>country</em>, 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
+“<em>the mountains</em>” (rendered “<em>all the mountains</em>”
+in the Vulgate) only implies all the mountains known
+to Moses.</p>
+
+<p>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.</p>
+
+<p>The <cite>Vedas</cite>, 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 <cite>Guebers</cite> speak of the same event as having
+occurred about the same date.</p>
+
+<p>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 <em>raised to the
+<span class="pagenum" id="Page_502">[502]</span>heavens</em>, 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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-502">
+  GLACIERS<br>
+  —<span class="smcap">Louis Agassiz</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_503">[503]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_504">[504]</span>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
+<span class="pagenum" id="Page_505">[505]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_506">[506]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_507">[507]</span>striking contrast to the granular structure of glacier
+ice.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_508">[508]</span>of the pudding-stone are held together by the cement
+which unites them.</p>
+
+<p>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_509">[509]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_510">[510]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_511">[511]</span>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
+<span class="pagenum" id="Page_512">[512]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_513">[513]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_514">[514]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_515">[515]</span>(Protocoites nivalis), well known in the Arctics,
+where it forms wide fields in the summer.</p>
+
+<p>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 <i lang="fr">névé</i>. It is properly the birthplace
+of the glaciers, for it is here that the transformation
+of the snow into ice begins. The <i lang="fr">névé</i> 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_516">[516]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-516">
+  VOLCANIC ACTION<br>
+  —<span class="smcap">Sir Archibald Geikie</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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” (<i lang="fr">lava d’aqua</i>),
+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.</p>
+
+<p>One of these mud-lavas invaded Herculaneum
+during the great eruption of 79, and by quickly
+enveloping the houses and their contents, has preserved
+<span class="pagenum" id="Page_517">[517]</span>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 <i>Pymelodus Cyclopum</i>
+poured forth and covered the ground over a space
+of four square leagues. The carbonaceous mud
+(locally called <em>moya</em>) emitted by the Quito volcanoes
+sometimes escapes from lateral fissures, sometimes
+from the craters. Its organic contents, and
+<span class="pagenum" id="Page_518">[518]</span>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.</p>
+
+<p>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
+<em>soffioni</em>.</p>
+
+<p>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 <em>moffette</em>, round
+which dead insects, and occasionally mice and birds,
+<span class="pagenum" id="Page_519">[519]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_520">[520]</span>of 130 feet or more. At night, when the gas has been
+lighted, the spectacle of one of these “fire-geysers”
+is inconceivably grand.</p>
+
+<p>Eruptive fountains of hot water and steam, to
+which the general name of Geysers (<i>i. e.</i>, 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.</p>
+
+<p>The term geyser is restricted to active openings
+<span class="pagenum" id="Page_521">[521]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_522">[522]</span>then a dry and crumbling white pillar is left to mark
+the site of the extinct geyser.</p>
+
+<p>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.</p>
+
+<p>Although not volcanic in the proper sense of the
+term, certain remarkable orifices of eruption may be
+noticed here, to which the names of <em>mud-volcanoes</em>,
+<em>salses</em>, <em>air-volcanoes</em>, and <em>maccalubas</em> 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 <em>Salses</em>.
+Naphtha is likewise frequently present. Large
+<span class="pagenum" id="Page_523">[523]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_524">[524]</span>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
+<span class="pagenum" id="Page_525">[525]</span>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.</p>
+
+<figure class="figcenter illowp100" id="i_106" style="max-width: 50em;">
+  <img class="w100" src="images/i_106.jpg" alt="Painting of prehistoric landscape">
+  <figcaption class="caption">
+      Ideal Landscape of the Carboniferous Period<br>
+    <span class="fs90">Showing Lepidodendra and other Giant Ferns and Mosses whose remains
+    are found in the Coal-Measures</span>
+  </figcaption>
+</figure>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_526">[526]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_527">[527]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-527">
+  THOUGHTS ABOUT KRAKATOA<br>
+  —<span class="smcap">Sir Robert S. Ball</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_528">[528]</span>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.</p>
+
+<p>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 <span class="allsmcap">P. M.</span> from a ship 76
+miles away, and was then judged to be 17 miles high—that
+<span class="pagenum" id="Page_529">[529]</span>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 <span class="allsmcap">P. M.</span> the sounds were loudly heard in a town 150
+miles away. At 5 <span class="allsmcap">P. M.</span> 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 <span class="allsmcap">P. M.</span> the British
+ship <i>Charles Bal</i>, 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 <span class="allsmcap">P. M.</span> 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.</p>
+
+<p>On Monday morning, August 27, the eruption culminated
+<span class="pagenum" id="Page_530">[530]</span>in four terrific explosions, of which the third,
+shortly after 10 <span class="allsmcap">A. M.</span> 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 <span class="allsmcap">A. M.</span>, 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 <span class="allsmcap">A. M.</span> on Tuesday,
+August 28. The entire series of grand phenomena
+thus occupied a little more than thirty-six hours.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_531">[531]</span></p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_532">[532]</span>had sensibly regained its former condition ere it was
+disturbed by Krakatoa.</p>
+
+<p>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.
+<span class="pagenum" id="Page_533">[533]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_534">[534]</span>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 <i>Berouw</i>. 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.</p>
+
+<p>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 <span class="allsmcap">A. M.</span> 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.</p>
+
+<p>It seems certain that, having attained their lofty
+elevation, the mighty clouds of dust were seized by
+<span class="pagenum" id="Page_535">[535]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_536">[536]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-536">
+  VOLCANOES<br>
+  —<span class="smcap">Sir Archibald Geikie</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_537">[537]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_538">[538]</span>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.</p>
+
+<p>The materials erupted from volcanic vents may be
+classed as (1) gases and vapors, (2) water, (3) lava,
+(4) fragmentary substances.</p>
+
+<p>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
+<span class="pagenum" id="Page_539">[539]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_540">[540]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_541">[541]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_542">[542]</span>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.</p>
+
+<p>It is usual to class volcanoes as <em>active</em>, <em>dormant</em>,
+and <em>extinct</em>. 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
+<span class="pagenum" id="Page_543">[543]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_544">[544]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_545">[545]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_546">[546]</span>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_547">[547]</span>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 <i lang="fr">régime</i> of the same
+mountain, the volcano becomes once more tranquil.</p>
+
+<p>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.</p>
+
+<p>In the deeper portions of a volcanic vent the convulsive
+<span class="pagenum" id="Page_548">[548]</span>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.</p>
+
+<p>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_549">[549]</span>beginning with that of <span class="allsmcap">A. D.</span> 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_550">[550]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_551">[551]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_552">[552]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.
+<span class="pagenum" id="Page_553">[553]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_554">[554]</span>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.</p>
+
+<p>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.
+<span class="pagenum" id="Page_555">[555]</span>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_556">[556]</span></p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_557">[557]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_558">[558]</span>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.</p>
+
+<p>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.”</p>
+
+<p><span class="pagenum" id="Page_559">[559]</span></p>
+
+<p>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-559">
+  EARTHQUAKES<br>
+  —<span class="smcap">William Hughes</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_560">[560]</span>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.</p>
+
+<blockquote>
+<p>[The <em>geographical area</em> 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.]</p>
+</blockquote>
+
+<p>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
+<span class="pagenum" id="Page_561">[561]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_562">[562]</span>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.</p>
+
+<p>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.</p>
+
+<p>The southwestern portion of Asia, the southern
+shores of Europe, and the northwestwardly portion
+of the African mainland, fall within this region on
+<span class="pagenum" id="Page_563">[563]</span>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 <ins class="corr" id="tn-563" title="Transcriber’s Note—Original text: 'Camaroons'">Cameroon</ins> 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 <ins class="corr" id="tn-563a" title="Transcriber’s Note—Original text: 'Teneriffe'">Tenerife</ins>,
+in the Canary group, are among its outlying
+members.</p>
+
+<p>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.
+<span class="pagenum" id="Page_564">[564]</span>Had it been otherwise, perhaps the pyramids of that
+land of wonders might have proved less enduring
+monuments of the past.</p>
+
+<p>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.</p>
+
+<p>It has been asserted that a third kind of movement—viz.,
+<span class="pagenum" id="Page_565">[565]</span>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 <em>unequally</em> attached
+to its base; <i>i.e.</i>, 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.</p>
+
+<p>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!</p>
+
+<p>The earthquake is propagated to enormous distances
+<span class="pagenum" id="Page_566">[566]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-566">
+  MOUNTAINS<br>
+  —<span class="smcap">A. Keith Johnston</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_567">[567]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_568">[568]</span></p>
+
+<p>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.</p>
+
+<p>The inquiry into the origin of mountains is one
+<span class="pagenum" id="Page_569">[569]</span>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, <ins class="corr" id="tn-569" title="Transcriber’s Note—Original text: 'denundation'">denudation</ins>
+and internal force are the great producing causes.
+These give us two great classes of mountains.</p>
+
+<p>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
+<span class="pagenum" id="Page_570">[570]</span>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.</p>
+
+<p>Mountains produced by internal force are of
+several kinds. (<i>a</i>) 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. (<i>b</i>) 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.
+<span class="pagenum" id="Page_571">[571]</span>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.</p>
+
+<p>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. (<i>c</i>) 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_572">[572]</span>Belgium and in the Southern Highlands of Scotland,
+as has been suggested by Mr. Carruthers.</p>
+
+<p>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.</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum" id="Page_573">[573]</span></p>
+
+<div class="chapter">
+<h3 id="I-573">
+  LAKES—FRESH, SALT, AND BITTER<br>
+  —<span class="smcap">Sir Archibald Geikie</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_574">[574]</span>sheets of fresh water occur in depressions of the
+land, and are rather inland seas than lakes.</p>
+
+<p>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 <em>Seiches</em>, 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.</p>
+
+<p>Among the geological functions discharged by
+lakes the following may be noticed:</p>
+
+<p>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.&#x2060;<a id="FNanchor_1_1" href="#Footnote_1_1" class="fnanchor">[1]</a> 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.</p>
+
+<p>2d. Lakes regulate the drainage of the area below
+their outfall, thereby preventing or lessening the destructive
+effects of floods.</p>
+
+<p>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
+<span class="pagenum" id="Page_575">[575]</span>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_576">[576]</span></p>
+
+<p>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.</p>
+
+<p>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 <cite>The Topographic Features of Lake-Shores</cite>.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_577">[577]</span>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, <i>Entomostraca</i>, 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.</p>
+
+<p>Existing lakes are of geologically recent origin.
+Their disappearance is continually in progress by
+infilling and erosion. Besides the displacement of
+<span class="pagenum" id="Page_578">[578]</span>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.</p>
+
+<p>Saline lakes, considered chemically, may be
+grouped as <em>salt lakes</em>, where the chief constituents
+are sodium and magnesium chlorides with magnesium
+and calcium sulphates; and <em>bitter lakes</em>, 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.</p>
+
+<p>Salt and bitter lakes of terrestrial origin are abundantly
+<span class="pagenum" id="Page_579">[579]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_580">[580]</span>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
+<span class="pagenum" id="Page_581">[581]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_582">[582]</span>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 (<i>Phoca caspica</i>) which may
+be only a variety of the common northern form (<i>Ph.
+fætida</i>) abound in the Caspian, which is the scene
+of one of the chief seal-fisheries of the world.&#x2060;<a id="FNanchor_2_2" href="#Footnote_2_2" class="fnanchor">[2]</a> 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.&#x2060;<a id="FNanchor_3_3" href="#Footnote_3_3" class="fnanchor">[3]</a></p>
+
+<p><span class="pagenum" id="Page_583">[583]</span></p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_584">[584]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_585">[585]</span>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_586">[586]</span>the magnesium-chloride has probably been the chief
+agent in the production of dolomite.</p>
+
+<p>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
+<span class="pagenum" id="Page_587">[587]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_588">[588]</span>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 <em>thïnolite</em>, 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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-588">
+  UNDERGROUND WATER: SPRINGS, CAVES, RIVERS, AND LAKES<br>
+  —<span class="smcap">Élisée Reclus</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_589">[589]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_590">[590]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_591">[591]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_592">[592]</span>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_593">[593]</span></p>
+
+<p>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.</p>
+
+<p>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 <i lang="fr">jet d’eau</i>
+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 (<i>Aïn Musa</i>), which gush out
+in a charming oasis not far from the shores of the
+<span class="pagenum" id="Page_594">[594]</span>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.</p>
+
+<p>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.</p>
+
+<p>Springs which have a higher temperature than the
+soil are called <em>thermal</em> springs.</p>
+
+<p><span class="pagenum" id="Page_595">[595]</span></p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_596">[596]</span>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.</p>
+
+<p>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.</p>
+
+<figure class="figcenter illowp100" id="i_180" style="max-width: 50em;">
+  <img class="w100" src="images/i_180.jpg" alt="Hexagonal rock pillars">
+  <figcaption class="caption">
+      The Giant’s Causeway, Antrim, Ireland
+  </figcaption>
+</figure>
+
+<p>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
+<span class="pagenum" id="Page_597">[597]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_598">[598]</span>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
+<span class="pagenum" id="Page_599">[599]</span>the boundary-line, and in the space of a year the
+walls had risen.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_600">[600]</span>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.</p>
+
+<p>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.</p>
+
+<p>Not far from the “spot where Troy once stood” is
+the valley of Touzla-sou, which owes its name (Salt
+<span class="pagenum" id="Page_601">[601]</span>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_602">[602]</span></p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_603">[603]</span>liquid flow an unpalatable taste. Palgrave, the
+traveler, informs us that all the springs of the country
+of Hasa, in Arabia, are also thermal.</p>
+
+<p>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.</p>
+
+<p>In regions where the strata are pierced with wide
+<span class="pagenum" id="Page_604">[604]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_605">[605]</span>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 <em>avens</em> or
+chasms, into which the rain-water sinks and disappears.</p>
+
+<p>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,
+<span class="pagenum" id="Page_606">[606]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_607">[607]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_608">[608]</span>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
+<span class="pagenum" id="Page_609">[609]</span>over all the strait, 31 miles wide, which separates
+Key West from Florida.</p>
+
+<p>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. <i lang="es">Cenotes</i> 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
+<span class="pagenum" id="Page_610">[610]</span>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 <i lang="es">rio</i>.</p>
+
+<p>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,”
+<span class="pagenum" id="Page_611">[611]</span>indicate the existence of a subterranean force always
+at work to upheave this band of hillocks.</p>
+
+<p>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_612">[612]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_613">[613]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_614">[614]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_615">[615]</span>a kind of barrier, obstruct the narrower passages
+and close up the defiles separating the cavern into
+distinct chambers.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_616">[616]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_617">[617]</span>whole of the rain and snow-water runs away through
+underground caverns.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_618">[618]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_619">[619]</span>mile from the place where the stream disappeared
+in the cave of Adelsberg.</p>
+
+<p>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.</p>
+
+<p>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 <em>dolinas</em>, the average
+<span class="pagenum" id="Page_620">[620]</span>depth of which is from 40 to 60 feet, have each their
+special name, such as the “<i lang="fr">Grand Crible</i>” (great
+sieve), the “<i lang="fr">Crible-à-froment</i>” (corn sieve), the
+“<i lang="fr">Tambour</i>” (drum), the “<i lang="fr">Cuve</i>” (tub), the “<i lang="fr">Tonneau</i>”
+(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 “<i lang="fr">cribles</i>” 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
+<i lang="la">lacus Lugens</i> 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_621">[621]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-621">
+  RIVERS<br>
+  —<span class="smcap">A. Keith Johnston</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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 <em>rivulets</em>; these, after a further course, unite
+to form <em>rivers</em>, which, receiving fresh accessions in
+their course from <em>tributaries</em> (subordinate rivers or
+rivulets) and their <em>feeders</em> (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 <em>course</em>; the hollow channel along which
+it flows, its <em>bed</em>; and the tract of country from which
+it and its subordinates draw their supplies of water,
+its <em>basin</em>, or <em>drainage-area</em>. The basin of a river is
+<span class="pagenum" id="Page_622">[622]</span>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, <i lang="la">cæteris paribus</i>, 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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_623">[623]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_624">[624]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_625">[625]</span>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_626">[626]</span></p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_627">[627]</span>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.</p>
+
+<p>“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.</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum" id="Page_628">[628]</span></p>
+
+<div class="chapter">
+<h3 id="I-628">
+  SWAMPS AND MARSHES<br>
+  —<span class="smcap">Élisée Reclus</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.</p>
+
+<p><span class="pagenum" id="Page_629">[629]</span></p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_630">[630]</span>the most luxuriant vegetation. The shore constantly
+keeps gaining upon them, and thus tends to the increase
+of the mainland.</p>
+
+<p>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 <i lang="la">terra firma</i>. 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 (<i lang="la">Cupressus disticha</i>);
+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
+<span class="pagenum" id="Page_631">[631]</span>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 <i lang="la">tremendal</i>
+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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_632">[632]</span>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.</p>
+
+<p>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 <i lang="la">Sphagnum
+palustre</i> 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,
+<span class="pagenum" id="Page_633">[633]</span>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.</p>
+
+<p>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 <i>Sphagnum</i>, 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 <i lang="fr">savants</i> of our own day.</p>
+
+<p>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
+<span class="pagenum" id="Page_634">[634]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-634">
+  LOWLAND PLAINS<br>
+  —<span class="smcap">William Hughes</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_635">[635]</span>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_636">[636]</span></p>
+
+<p>The most important and extensive among the lowland
+plains of the Old World are the following:</p>
+
+<p><span class="smcap">In Asia.</span>—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.</p>
+
+<p><span class="smcap">In Europe.</span>—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.</p>
+
+<p>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
+<span class="pagenum" id="Page_637">[637]</span>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 <em>tundras</em>,
+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.</p>
+
+<p>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.</p>
+
+<p>The southeastern division of the European lowland,
+and the adjacent portions of Asia, constitute the
+region of the <em>steppes</em>. 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
+<span class="pagenum" id="Page_638">[638]</span>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.</p>
+
+<p>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
+<i lang="fr">mirage</i>—the result of atmospheric refraction, engendered
+<span class="pagenum" id="Page_639">[639]</span>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.”</p>
+
+<p>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.
+<span class="pagenum" id="Page_640">[640]</span>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.</p>
+
+<p>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.</p>
+
+<p>Mr. T. W. Atkinson, in his <cite>Travels in Regions
+on the Upper and Lower Amour</cite>, 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
+<span class="pagenum" id="Page_641">[641]</span>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’
+(<em>red sand</em>).”</p>
+
+<p>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.</p>
+
+<p>“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
+<span class="pagenum" id="Page_642">[642]</span>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.”</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_643">[643]</span>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 <em>meers</em>.</p>
+
+<p>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 <em>dunes</em>, 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
+<span class="pagenum" id="Page_644">[644]</span>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
+(<i>arundo arenaria</i>), the long roots of which bind the
+whole mass firmly together.</p>
+
+<p>The district of the <i>Landes</i>, 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
+<span class="pagenum" id="Page_645">[645]</span>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.</p>
+
+<figure class="figcenter illowp100" id="i_230" style="max-width: 50em;">
+  <img class="w100" src="images/i_230.jpg" alt="Portion of the reef above the surface">
+  <figcaption class="caption">
+      Great Barrier Coral Reef, Queensland, Australia<br>
+    <span class="fs90">This Reef is composed entirely of Stag’s Horn Coral (<i>Madrepora Hebes</i>)</span>
+  </figcaption>
+</figure>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_646">[646]</span>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_647">[647]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>Further south, the plains that extend from Buenos
+Ayres to the foot of the Andes are covered, during a
+<span class="pagenum" id="Page_648">[648]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-648">
+  THE SMELL OF EARTH<br>
+  —<span class="smcap">G. Clarke Nuttall</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_649">[649]</span>sufficient to bring out the sweet familiar smell of the
+land and thrust it upon our notice.</p>
+
+<p>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.</p>
+
+<p>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?</p>
+
+<p>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
+<span class="pagenum" id="Page_650">[650]</span>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.</p>
+
+<p>Some faint idea of their <ins class="corr" id="tn-650" title="Transcriber’s Note—Original text: 'relativ'">relative</ins> 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_651">[651]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_652">[652]</span>has been given it—<i>Cladothrix odorifera</i>. 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!”</p>
+
+<p>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
+<span class="pagenum" id="Page_653">[653]</span>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.</p>
+
+<p>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.</p>
+
+<p>Two other characteristics of <i>Cladothrix odorifera</i>
+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
+<span class="pagenum" id="Page_654">[654]</span>it little ultimately; the utmost it could do would be
+to retard it for a time.</p>
+
+<p>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="I-654">
+  DESERTS<br>
+  —<span class="smcap">Élisée Reclus</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.</p>
+
+<p>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
+<span class="pagenum" id="Page_655">[655]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_656">[656]</span>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.</p>
+
+<p>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 <em>crevasses</em> of a glacier. In the hollows, patches of
+salt take the place of the lakes which in more rainy
+countries would be found there.</p>
+
+<p>Those districts of the Sahara which are destitute of
+oases present a truly formidable aspect, and are fearful
+<span class="pagenum" id="Page_657">[657]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_658">[658]</span>especially so to the chilly Arab. Not a year passes
+without ice forming on the ground, and white frosts
+are frequent.</p>
+
+<p>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.</p>
+
+<p>The oases are, <i lang="fr">par excellence</i>, 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
+<span class="pagenum" id="Page_659">[659]</span>intervals of the soil which is capable of irrigation.</p>
+
+<p>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 <i>Nefouds</i>, 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
+<span class="pagenum" id="Page_660">[660]</span>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.</p>
+
+<p>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),
+<span class="pagenum" id="Page_661">[661]</span>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.</p>
+
+<p>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
+<i lang="fr">par excellence</i>, 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.
+<span class="pagenum" id="Page_662">[662]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_663">[663]</span>used to pass, which was so soon destined to be
+supplanted by the Pacific Railway from New York
+to San Francisco.</p>
+
+<p>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.</p>
+
+<p>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 <em>pampas</em> of Islay and
+Tamarugal and the desert of Atacama. The <i>pampa</i>
+of Tamarugal, so called from the <i>Tamarugos</i>, 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 <em>salares</em>, which are worked
+like rock quarries. The strata of salt are so thick,
+<span class="pagenum" id="Page_664">[664]</span>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 <i>pampa</i> 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.</p>
+
+<p>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 <i>pampa</i> 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.</p>
+
+<p><span class="pagenum" id="Page_665">[665]</span></p>
+
+<p>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 <i>pampa</i> 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.</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum" id="Page_666">[666]</span></p>
+<div class="chapter">
+
+  <h2 class="p4 nobreak" id="II-THE_SEA">
+    II.—THE SEA
+  </h2>
+</div>
+
+<h3 id="II-666">
+  THE PRIMITIVE OCEAN<br>
+  —<span class="smcap">G. Hartwig</span>
+</h3>
+
+
+<p class="drop-capy">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.</p>
+
+<p>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
+<span class="pagenum" id="Page_667">[667]</span>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?</p>
+
+<p>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
+<span class="pagenum" id="Page_668">[668]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_669">[669]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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?</p>
+
+<p>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
+<span class="pagenum" id="Page_670">[670]</span>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.</p>
+
+<p>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</p>
+
+<div class="poetry-container">
+  <div class="poetry">
+      <div class="verse indentq">“Seems to have undergone a change</div>
+      <div class="verse indent0">Into something new and strange.”</div>
+  </div>
+</div>
+
+<p><span class="pagenum" id="Page_671">[671]</span></p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_672">[672]</span></p>
+
+<p>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 <i>Nautili</i>,
+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.</p>
+
+<p>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
+<span class="pagenum" id="Page_673">[673]</span>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 <i>Ichthyosauri</i> 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
+<span class="pagenum" id="Page_674">[674]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_675">[675]</span>whose organization requires a greater warmth, confine
+themselves to the equatorial regions.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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?</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_676">[676]</span></p>
+
+<p>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.</p>
+
+<p>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?</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="II-676">
+  THE FLOOR OF THE OCEAN<br>
+  —<span class="smcap">John James Wild</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_677">[677]</span>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>i. e.</i>,
+a raised portion of the earth’s surface, which may be
+partially or entirely covered with water, and an area
+of depression—<i>i. e.</i>, 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_678">[678]</span>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
+<span class="pagenum" id="Page_679">[679]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_680">[680]</span></p>
+
+<p>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.</p>
+
+<p>Contrary to the ideas formerly entertained of the
+enormous depth of the ocean, the soundings of
+H.M.S. <i>Challenger</i>, S.M.S. <i>Gazelle</i>, and of the
+U.S.S. <i>Tuscarora</i> and <i>Gettysburg</i>, 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.</p>
+
+<p>One of the greatest depths ascertained in the Atlantic
+was found by H.M.S. <i>Challenger</i>, 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 <i>Gettysburg</i> found 3,593
+fathoms only eleven miles south of the <i>Challenger</i>
+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.</p>
+
+<p>The greatest depth observed in the Indian Ocean
+was discovered by the <i>Gazelle</i> in May, 1875. Two
+soundings of 3,020 and 3,010 fathoms were taken in
+the eastern extremity of this ocean between the northwest
+<span class="pagenum" id="Page_681">[681]</span>coast of Australia and the line of islands extending
+from Java to Timor.</p>
+
+<p>The greatest of all depths of which we have reliable
+evidence was found by the <i>Challenger</i> 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 <i>Tuscarora</i> 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. <i>Challenger</i>, 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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_682">[682]</span></p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>One of the most remarkable results in connection
+<span class="pagenum" id="Page_683">[683]</span>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.</p>
+
+<p>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.</p>
+
+<p>By this central plateau, the Atlantic Ocean is divided
+into two longitudinal areas of depression or
+<span class="pagenum" id="Page_684">[684]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_685">[685]</span>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.</p>
+
+<p>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 <i>Challenger</i>,
+the <i>Gazelle</i>, and the <i>Tuscarora</i> 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,
+<span class="pagenum" id="Page_686">[686]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_687">[687]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_688">[688]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_689">[689]</span>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.</p>
+
+<p>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="II-689">
+  CORAL FORMATIONS<br>
+  —<span class="smcap">Charles Darwin</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_690">[690]</span>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,
+<span lang="fr">“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.”</span> 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_691">[691]</span>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?</p>
+
+<p>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
+<span class="pagenum" id="Page_692">[692]</span>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
+<span class="pagenum" id="Page_693">[693]</span>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.</p>
+
+<figure class="figcenter illowp100" id="i_280" style="max-width: 50em;">
+  <img class="w100" src="images/i_280.jpg" alt="View of the peak in summer">
+  <figcaption class="caption">
+      Matterhorn, Valais Alps, Switzerland
+  </figcaption>
+</figure>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_694">[694]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_695">[695]</span>of its lagoon; remove the land from within, and a
+perfect atoll is left.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_696">[696]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_697">[697]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_698">[698]</span>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.</p>
+
+<p>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.</p>
+
+<p>As the barrier-reef slowly sinks down, the corals
+will go on vigorously growing upward; but as the
+<span class="pagenum" id="Page_699">[699]</span>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.</p>
+
+<p>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_700">[700]</span>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
+<span class="pagenum" id="Page_701">[701]</span>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_702">[702]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_703">[703]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_704">[704]</span>just lipping the surface of the sea, sometimes clothed
+with vegetation, and each containing a lake of clear
+water!</p>
+
+<p>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
+<span class="pagenum" id="Page_705">[705]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_706">[706]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_707">[707]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="II-707">
+  MAGNITUDE AND COLOR OF THE SEA<br>
+  —<span class="smcap">G. Hartwig</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.</p>
+
+<p><span class="pagenum" id="Page_708">[708]</span></p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_709">[709]</span>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!</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_710">[710]</span>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.</p>
+
+<p>But the essential color of the sea undergoes much
+more frequent changes over large spaces, from enormous
+masses of minute <em>algæ</em>, and countless hosts
+of small sea-worms, floating or swimming on its
+surface.</p>
+
+<p>“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.”</p>
+
+<p>“On the coast of Chili,” says the same author, “a
+few leagues north of Concepcion, the <i>Beagle</i> one day
+passed through great bands of muddy water; and
+<span class="pagenum" id="Page_711">[711]</span>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.”</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_712">[712]</span>of little white animals swimming on the surface
+and concealing the natural tint of the water.</p>
+
+<p>The peculiar coloring of the Red Sea, from which
+it has derived its name, is owing to the presence of
+a microscopic alga, <i lang="la">sui generis</i>, floating at the surface
+of the sea and even less remarkable for its beautiful
+red color than for its prodigious fecundity.</p>
+
+<p>I could add many more examples, where, either
+from minute <em>algæ</em>, 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 <em>olive green</em> 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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_713">[713]</span>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.”</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="II-713">
+  TIDAL ACTION<br>
+  —<span class="smcap">Sir Robert S. Ball</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_714">[714]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_715">[715]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_716">[716]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_717">[717]</span>consequence is that the rapidity with which the earth
+rotates upon its axis is gradually declining.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_718">[718]</span>necessary to enable it to obtain tremendous dimensions,
+and that is sufficient time in which it can
+operate.</p>
+
+<p>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.</p>
+
+<p>As the evidence of the earth’s crust proves that
+our globe has lasted for <ins class="corr" id="tn-718" title="Transcriber’s Note—Original text: 'incalulable'">incalculable</ins> 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
+<span class="pagenum" id="Page_719">[719]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_720">[720]</span>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.</p>
+
+<p>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.</p>
+
+<p>In the course of such vast ages the reaction of the
+<span class="pagenum" id="Page_721">[721]</span>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</p>
+
+<p>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_722">[722]</span>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.</p>
+
+<p>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 <ins class="corr" id="tn-722" title="Transcriber’s Note—Original text: 'diminshed'">diminished</ins>, 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
+<span class="pagenum" id="Page_723">[723]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_724">[724]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_725">[725]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_726">[726]</span>revolve in a period of fourteen hundred hours as if
+they were connected with invisible bonds.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_727">[727]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="II-727">
+  THE GULF STREAM<br>
+  —<span class="smcap">Lord Kelvin</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.</p>
+
+<p>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
+<span class="pagenum" id="Page_728">[728]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_729">[729]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_730">[730]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_731">[731]</span>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.”</p>
+
+<p>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_732">[732]</span>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.”</p>
+
+<p>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
+<span class="pagenum" id="Page_733">[733]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_734">[734]</span>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
+<span class="pagenum" id="Page_735">[735]</span>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.</p>
+
+<p>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.</p>
+
+<p>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:</p>
+
+<p>“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
+<span class="pagenum" id="Page_736">[736]</span>by Professor Buff to perform the work are thus the
+<i lang="fr">vis à tergo</i> 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.</p>
+
+<p>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_737">[737]</span>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 <i lang="fr">vis à tergo</i> 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, <em>I</em> 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
+<i lang="fr">vis à fronte</i> 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
+<span class="pagenum" id="Page_738">[738]</span>caused by a “modified case” of the general oceanic
+circulation, and neither by the Gulf Stream nor by
+the anti-trade drift.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_739">[739]</span>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.</p>
+
+<p>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.</p>
+
+<p>The deep-sea temperatures taken in the <i>Porcupine</i>
+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
+<span class="pagenum" id="Page_740">[740]</span>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.</p>
+
+<figure class="figcenter illowp75" id="i_330" style="max-width: 50em;">
+  <img class="w100" src="images/i_330.jpg" alt="Twenty examples of snowflake shapes">
+  <figcaption class="caption">
+      Typical Forms of Snowflakes<br>
+    <span class="fs90">Showing the Tendency to take the Form of Six-Pointed Figures</span>
+  </figcaption>
+</figure>
+
+<p>The North Atlantic and Arctic seas form together
+a <i lang="fr">cul de sac</i> closed to the northward, for there is
+<span class="pagenum" id="Page_741">[741]</span>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
+<em>lighter</em> (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,’ <em>displacing colder and heavier
+water</em>, 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
+<span class="pagenum" id="Page_742">[742]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_743">[743]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_744">[744]</span>under the Gulf Stream, as a cold counter-current,
+into the Gulf of Mexico.</p>
+
+<p>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.</p>
+
+<p>While the communication between the North Atlantic
+and the Arctic Sea—itself a second <i lang="fr">cul de sac</i>—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
+<span class="pagenum" id="Page_745">[745]</span>day; a continuous and wide valley upward of 2,000
+fathoms in depth stretching northward along the
+western coasts of Africa and Europe.</p>
+
+<p>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.</p>
+
+<p>The North Atlantic Ocean seems to consist first of
+<span class="pagenum" id="Page_746">[746]</span>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
+<span class="pagenum" id="Page_747">[747]</span>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.</p>
+
+<p>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.</p>
+
+<p>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 <i>Porcupine</i>, 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
+<span class="pagenum" id="Page_748">[748]</span>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
+<span class="pagenum" id="Page_749">[749]</span>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.</p>
+
+<p>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.</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum" id="Page_750">[750]</span></p>
+
+<div class="chapter">
+<h3 id="II-750">
+  THE PHOSPHORESCENCE OF THE SEA<br>
+  —<span class="smcap">G. Hartwig</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.</p>
+
+<p>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.</p>
+
+<p>“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
+<span class="pagenum" id="Page_751">[751]</span>the peninsula of Maniquarez, this scene has often delighted
+me for hours.”</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_752">[752]</span>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.</p>
+
+<p>While <i>La Venus</i> 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.</p>
+
+<p>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.</p>
+
+<p>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?</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_753">[753]</span>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.</p>
+
+<p>In our seas it is chiefly a minute gelatinous animal,
+the <i>Noctiluca miliaris</i>, 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
+<span class="pagenum" id="Page_754">[754]</span>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.”</p>
+
+<p>The power of emitting a phosphorescent light is
+widely diffused, both among the free-swimming and
+the sessile <i>Cœlenterata</i>. Many of the <i>Physophoridæ</i>
+are remarkable for its manifestation, and a great
+number of the jelly-fishes are luminous. Our own
+<i>Thaumantias lucifera</i>, 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.</p>
+
+<p>Among the <i>Ctenophora</i> the large <i>Cestum Veneris</i>
+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.</p>
+
+<p>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
+<span class="pagenum" id="Page_755">[755]</span>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.</p>
+
+<p>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
+<em>Travels to Chili</em> 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_756">[756]</span>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.</p>
+
+<p>“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
+<span class="pagenum" id="Page_757">[757]</span>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.”</p>
+
+<p>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 (<i>Pholas dactylus</i>):</p>
+
+<p>“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.”</p>
+
+<p>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.</p>
+
+<p>Several kinds of fishes likewise possess the luminous
+faculty. The sunfish, that strange deformity
+emits a phosphoric gleam; and a species of Gunard
+(<i>Trigla lucerna</i>) is said to sparkle in the night, so
+as to form fiery streams through the water.</p>
+
+<p>With regard to the luminosity of the larger marine
+animals, Ermann, however, remarks that he so
+<span class="pagenum" id="Page_758">[758]</span>often saw small luminous crustacea in the abdominal
+cavity of the transparent <i>Salpa pinnata</i> that it may
+well be asked whether the phosphorescence of the
+larger creatures is not in reality owing to that of
+their smaller companions.</p>
+
+<p>According to Mr. Bennett—<em>Whaling Voyage
+Round the Globe</em>—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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_759">[759]</span>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.</p>
+
+<p>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 <i>Oscillatoria</i>, grouped
+together into small balls or globules, from the size
+of a poppy-seed to that of a lentil.</p>
+
+<p>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
+<span class="pagenum" id="Page_760">[760]</span>fibres of dead mollusks, which are mixed with the
+waters in countless numbers.”</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>In the tropical zone, Humboldt saw the sea most
+<span class="pagenum" id="Page_761">[761]</span>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?</p>
+
+<p>It is remarkable that the ancients should have
+taken so little notice of oceanic phosphorescence.
+The <cite lang="la">Periplus</cite> of Hanno contains, perhaps, the only
+passage in which the phenomenon is described.</p>
+
+<p>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
+(<em>lucerna</em>) 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
+<span class="pagenum" id="Page_762">[762]</span>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 <cite>Lusiad</cite>. Byron in his <cite>Corsair</cite>
+has a few lines on the subject:</p>
+
+<div class="poetry-container">
+  <div class="poetry">
+      <div class="verse indentq">“Flash’d the dipt oars, and, sparkling with the stroke,</div>
+      <div class="verse indent0">Around the waves phosphoric brightness broke;”</div>
+  </div>
+</div>
+
+<p>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 <cite>The Ancient
+Mariner</cite> we find a warmer description:</p>
+
+<div class="poetry-container">
+  <div class="poetry">
+    <div class="stanza">
+      <div class="verse indentq">“Beyond the shadow of the ship</div>
+      <div class="verse indent2">I watch’d the water-snakes:</div>
+      <div class="verse indent0">They moved in tracks of shining white,</div>
+      <div class="verse indent0">And, when they rear’d, the elfin light</div>
+      <div class="verse indent2">Fell off in hoary flakes.</div>
+    </div>
+    <div class="stanza">
+      <div class="verse indentq">“Within the shadow of the ship</div>
+      <div class="verse indent2">I watch’d their rich attire—</div>
+      <div class="verse indent0">Blue, glossy green, and velvet black:</div>
+      <div class="verse indent0">They coiled and swam, and every track</div>
+      <div class="verse indent2">Was a flash of golden fire.”</div>
+    </div>
+  </div>
+</div>
+
+<p>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:</p>
+
+<div class="poetry-container">
+  <div class="poetry">
+    <div class="stanza">
+      <div class="verse indentq">“And now your view upon the ocean turn,</div>
+      <div class="verse indent0">And there the splendor of the waves discern;</div>
+      <div class="verse indent0">Cast but a stone, or strike them with an oar,</div>
+      <div class="verse indent0">And you shall flames within the deep explore;</div>
+      <div class="verse indent0">Or scoop the stream phosphoric as you stand,</div>
+      <div class="verse indent0">And the cold flames shall flash along your hand;</div>
+      <div class="verse indent0">When, lost in wonder, you shall walk and gaze</div>
+      <div class="verse indent0">On weeds that sparkle, and on waves that blaze.”</div>
+    </div>
+  </div>
+</div>
+
+<p><span class="pagenum" id="Page_763">[763]</span></p>
+
+<p>Or the graphic numbers of Sir Walter Scott:</p>
+
+<div class="poetry-container">
+  <div class="poetry">
+    <div class="stanza">
+      <div class="verse indentq">“Awak’d before the rushing prow,</div>
+      <div class="verse indent0">The mimic fires of ocean glow,</div>
+      <div class="verse indent2">Those lightnings of the wave;</div>
+      <div class="verse indent0">Wild sparkles crest the broken tides,</div>
+      <div class="verse indent0">And dashing round, the vessel’s sides</div>
+      <div class="verse indent2">With elfish lustre lave;</div>
+      <div class="verse indent0">While, far behind, their vivid light</div>
+      <div class="verse indent0">To the dark billows of the night</div>
+      <div class="verse indent2">A blooming splendor gave.”</div>
+    </div>
+  </div>
+</div>
+
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="II-763">
+  THE SEASHORE<br>
+  —<span class="smcap">P. Martin Duncan</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_764">[764]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_765">[765]</span>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.”</p>
+
+<p>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
+<span class="pagenum" id="Page_766">[766]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_767">[767]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_768">[768]</span>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
+<span class="pagenum" id="Page_769">[769]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_770">[770]</span>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 <em>fore-shore</em> 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.</p>
+
+<p>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;
+<span class="pagenum" id="Page_771">[771]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.
+<span class="pagenum" id="Page_772">[772]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum" id="Page_773">[773]</span></p>
+<div class="chapter">
+
+  <h2 class="p4 nobreak" id="III-THE_ATMOSPHERE">
+    III.—THE ATMOSPHERE
+  </h2>
+</div>
+
+<h3 id="III-773">
+  THE OCEAN OF AIR<br>
+  —<span class="smcap">Agnes Giberne</span>
+</h3>
+
+
+<p class="drop-capy">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.</p>
+
+<p>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
+<span class="pagenum" id="Page_774">[774]</span>our eyes; but the blue of the atmosphere is known to
+be a reflected blue.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>But the very extent of the ocean of air adds to our
+<span class="pagenum" id="Page_775">[775]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>Without this pressure of the overlying atmosphere,
+<span class="pagenum" id="Page_776">[776]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>In those lofty regions of the air-ocean no living
+creatures exist. The voyagers passed through boundless
+<span class="pagenum" id="Page_777">[777]</span>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.”</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_778">[778]</span></p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_779">[779]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_780">[780]</span>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.</p>
+
+<p>Small creatures, as well as big ones, spending
+much time under water, and yet breathing air, have
+to come regularly to the surface.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>There is water enough on earth for all needed
+<span class="pagenum" id="Page_781">[781]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_782">[782]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_783">[783]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_784">[784]</span>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="III-784">
+  WEATHER<br>
+  —<span class="smcap">Sir Ralph Abercromby</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.</p>
+
+<p>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.</p>
+
+<p>Many survivals of mystic speech are still found
+among popular prognostics, and especially in cloud
+names.</p>
+
+<p>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.</p>
+
+<p>At a rather later period of intellectual development,
+the premonitory signs of good or bad weather
+<span class="pagenum" id="Page_785">[785]</span>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?</p>
+
+<p>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
+<span class="pagenum" id="Page_786">[786]</span>be given for these apparent exceptions, and the whole
+science of barometric readings seemed to be shrouded
+in mystery.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_787">[787]</span>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.</p>
+
+<p>This branch of the subject is known as “Statistical
+Meteorology,” and has advanced very little since it
+was first developed by Dove and Kaemtz.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_788">[788]</span>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.</p>
+
+<figure class="figcenter illowp100" id="i_380" style="max-width: 50em;">
+  <img class="w100" src="images/i_380.jpg" alt="Four quadrants with different cloud types">
+  <figcaption class="caption">
+      Typical Forms of Clouds<br>
+    <span class="fs90">1, Squall Cumulus; 2, Pillar Cumulus; 3, Cirrus; 4, High Stratus and Cumulus</span>
+  </figcaption>
+</figure>
+
+<p>When these came to be examined, the following
+important generalizations were discovered:</p>
+
+<p><span class="pagenum" id="Page_789">[789]</span></p>
+
+<p>1. That in general the configuration of the isobars
+assumed one of seven well-defined forms.</p>
+
+<p>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.</p>
+
+<p>3. That the velocity of the wind was always nearly
+proportional to the closeness of the isobars.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_790">[790]</span>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.</p>
+
+<p>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.</p>
+
+<p><em>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.</em></p>
+
+<p>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
+<span class="pagenum" id="Page_791">[791]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>We may notice here an attempt which has been
+made by one school of meteorologists to deduce all
+weather <i lang="la">à priori</i> 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
+<span class="pagenum" id="Page_792">[792]</span>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.</p>
+
+<p>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="III-792">
+  THE ROMANCE OF A RAINDROP<br>
+  —<span class="smcap">Arthur H. Bell</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_793">[793]</span>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?</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_794">[794]</span>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_795">[795]</span></p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_796">[796]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_797">[797]</span>to the action of capillarity, which in the case of the
+raindrop acts equally in all directions.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_798">[798]</span>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.</p>
+
+
+<hr class="chap x-ebookmaker-drop">
+<p><span class="pagenum" id="Page_799">[799]</span></p>
+
+<div class="chapter">
+<h3 id="III-799">
+  THE RAINBOW<br>
+  —<span class="smcap">John Tyndall</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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.”</p>
+
+<p>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,
+<span class="pagenum" id="Page_800">[800]</span>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 <cite lang="la">Supplement
+to Vitellio</cite>, 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_801">[801]</span>the same. It is, in fact, what is called “the index of
+refraction” of the medium.</p>
+
+<p>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&#x2060;<a id="FNanchor_4_4" href="#Footnote_4_4" class="fnanchor">[4]</a> 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
+<em>divergent</em> 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
+<span class="pagenum" id="Page_802">[802]</span>emerged in a practically <em>parallel sheaf</em>. In their
+union was strength, for it was this particular sheaf
+which carried the light of the “primary” rainbow
+to the eye.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_803">[803]</span>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.</p>
+
+<p>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,
+<span class="pagenum" id="Page_804">[804]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_805">[805]</span>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 <em>waves</em>, 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,
+<span class="pagenum" id="Page_806">[806]</span>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.</p>
+
+<p>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.</p>
+
+<p>The white rainbow (<i lang="fr">l’arc-en-ciel blanc</i>) was first
+<span class="pagenum" id="Page_807">[807]</span>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.</p>
+
+<p>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="III-807">
+  SNOW, HAIL, AND DEW<br>
+  —<span class="smcap">Alexander Buchan</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_808">[808]</span>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.</p>
+
+<p>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 <em>minute</em>
+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
+<span class="pagenum" id="Page_809">[809]</span>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.</p>
+
+<p>The word hail in English is unfortunately used to
+denote two phenomena of apparently different origin.
+In French, we have the terms <i lang="fr">grèle</i> and <i lang="fr">grésil</i>—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.</p>
+
+<p>But that true hail, though the process of its formation
+is not yet perfectly understood, depends
+<span class="pagenum" id="Page_810">[810]</span>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 <em>precedes</em>, sometimes accompanies, and
+rarely, if ever, follows a thunder-shower.</p>
+
+<p>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
+<span class="pagenum" id="Page_811">[811]</span>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.</p>
+
+<p>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 <cite lang="fr">Mem. de
+l’Acad. des Sciences</cite>, 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 <em>simultaneously</em>
+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.</p>
+
+<p><span class="pagenum" id="Page_812">[812]</span></p>
+
+<p>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.</p>
+
+<p>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 <em>hoar-frost</em>. The above
+two phenomena, though both expressed in our language
+<span class="pagenum" id="Page_813">[813]</span>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 <i lang="fr">serein</i>; 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 <i lang="fr">rosée</i>.</p>
+
+<p>The merit of the discovery of the “Theory of
+Dew” has been commonly ascribed to Dr. William
+Charles Wells, who published in 1814 his <cite>Essay on
+Dew</cite>, 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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="III-813">
+  THE AURORA BOREALIS<br>
+  —<span class="smcap">Richard A. Proctor</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_814">[814]</span>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.</p>
+
+<p>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.</p>
+
+<p>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 <em>under</em> 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
+<span class="pagenum" id="Page_815">[815]</span>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
+<span class="pagenum" id="Page_816">[816]</span>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.”</p>
+
+<p>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
+<span class="pagenum" id="Page_817">[817]</span>Iceland the frequent occurrence of auroras between
+1716 and 1732 was regarded with great astonishment.
+In the Sixteenth Century, however, they had been
+frequent.</p>
+
+<p>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.</p>
+
+<p>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 <em>changes</em> in the
+sun’s action.</p>
+
+<p>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.</p>
+
+<p>It may, then, fairly be assumed that the occurrence
+<span class="pagenum" id="Page_818">[818]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.
+<span class="pagenum" id="Page_819">[819]</span>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.</p>
+
+<p>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="III-819">
+  CLOUDS<br>
+  —<span class="smcap">D. Wilson Barker</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_820">[820]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_821">[821]</span>when an observer can clearly distinguish Stratus
+from Cumulus he has already acquired valuable
+knowledge.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>Clouds owe their existence to two causes:</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_822">[822]</span></p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>We shall now describe a few familiar forms of
+cloud, giving them simple names and endeavoring to
+compare them with other nomenclatures.</p>
+
+<p>Of Cumulus clouds there are five well-defined varieties.</p>
+
+<p><em>Rain Cumulus</em>, of which there are two sub-varieties:</p>
+
+<p>(<i>a</i>) Shower-cumulus, when rain falls from the
+cloud without increment of wind. The edges of this
+cloud are not cirrus-topped.</p>
+
+<p>(<i>b</i>) Squall-cumulus, when the rain is accompanied
+by wind, or by wind with hail and snow falling from
+this cloud.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_823">[823]</span></p>
+
+<p>Two rarer varieties of Cumulus are:</p>
+
+<p><em>Pillar-cumulus</em>, generally noticed over the calm
+belts of the ocean, and distinguishable by its slender
+forms, which rise to great altitudes.</p>
+
+<p><em>Roll-cumulus</em> 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.</p>
+
+<p>A still rarer form of Cumulus appears in scattered
+patches over the sky, and is indicative of an electrical
+state of the atmosphere.</p>
+
+<p>Cumulus clouds form at a low altitude, but they
+frequently tower upward to great heights.</p>
+
+<p>It should be noticed that in these clouds the fine
+weather form is of soft, smooth outline, and has a
+quiet appearance.</p>
+
+<p><em>Stratus Clouds</em> may be divided into four varieties
+as follows:</p>
+
+<p>1. <em>Fog</em>, so well known as not to need description.
+It is, in fact, a Stratus cloud resting on the earth’s
+surface.</p>
+
+<p>2. <em>Stratus</em>, 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.</p>
+
+<p>3. <em>High Stratus</em>, including all the varying forms
+of Cirro-cumulus from the mackerel skies to the
+Cirro-macula of Clement Ley. Many beautiful varieties
+<span class="pagenum" id="Page_824">[824]</span>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.</p>
+
+<p>4. <em>Cirrus.</em>—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.</p>
+
+<p>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.</p>
+
+<p>When a cyclonic disturbance is about to pass over
+an observer, Cirrus generally appears first in parallel
+<span class="pagenum" id="Page_825">[825]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>The beautiful coloring of clouds results from the
+<span class="pagenum" id="Page_826">[826]</span>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" id="Page_827">[827]</span></p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_828">[828]</span>of the daily weather charts. Again, weather is often
+very local, and to predict with fair accuracy a
+knowledge of local conditions is necessary.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="III-828">
+  WINDS<br>
+  —<span class="smcap">William Hughes</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_829">[829]</span>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.</p>
+
+<p>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.</p>
+
+<p>In the case of many countries, some local wind, of
+occasional prevalence, forms a marked characteristic
+of climate. The most remarkable of these local
+<span class="pagenum" id="Page_830">[830]</span>winds are the simoon, the sirocco, the föhn, the harmattan,
+and the mistral.</p>
+
+<p>The often-described <em>simoon</em> 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
+<em>tebbad</em> (fever-wind), the terrible conditions of which
+are thus described by the pen of a traveler. “The
+kervanbashi (<em>leader of the caravan</em>) 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 <em>tebbad</em> 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.”</p>
+
+<p>The <em>sirocco</em> of the Mediterranean coasts is the hot
+wind of the African desert, tempered, before reaching
+the coasts of southern Europe, by its passage
+<span class="pagenum" id="Page_831">[831]</span>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.</p>
+
+<p>The <i lang="de">föhn</i>, 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.</p>
+
+<p>The <i>harmattan</i> of Senegambia and Guinea is a
+cold and intensely dry wind, which blows from the
+northeast during the months of December and
+January.</p>
+
+<p>The <i lang="fr">mistral</i> of southern France possesses similar
+qualities to the last-named wind, and blows, for days
+together, down the valley of the Rhone.</p>
+
+<p>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
+<em>red fogs</em> and <em>sea-dust</em> 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
+<span class="pagenum" id="Page_832">[832]</span>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.</p>
+
+<p>The prevailing currents of the atmosphere, or
+<em>winds</em>, 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.</p>
+
+<p>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
+<span class="pagenum" id="Page_833">[833]</span>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.</p>
+
+<p>The average breadth of the calm latitudes—or the
+<i>Zone of Calms</i>, 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,
+<span class="pagenum" id="Page_834">[834]</span>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.</p>
+
+<p>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.</p>
+
+<p>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,
+<em>the trade-wind of the Northern Hemisphere
+is a wind blowing from the northeastward</em>—that is,
+a <em>northeast wind</em>. <em>The trade-wind of the Southern
+Hemisphere blows from the southeastward</em>, and is
+<em>a southeast wind</em>.</p>
+
+<p>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
+<span class="pagenum" id="Page_835">[835]</span>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.</p>
+
+<p>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.</p>
+
+<p>The explanation of the trade-winds is found in the
+different measure in which the sun’s heat is experienced
+<span class="pagenum" id="Page_836">[836]</span>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.</p>
+
+<p>To sum up, we may say that the trade-winds, like
+the currents of the ocean, are due, <em>first</em>, to the sun,—that
+is to the different measure in which the solar
+heat is distributed on the globe’s surface; and,
+<em>secondly</em>, 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.</p>
+
+<p>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 <em>periodical
+winds</em>, not perennial. The monsoon blows for half
+the year from one quarter of the heavens, and for
+the other half from an opposite quarter.</p>
+
+<figure class="figcenter illowp75" id="i_430" style="max-width: 50em;">
+  <img class="w100" src="images/i_430.jpg" alt="Global winds and currents">
+  <figcaption class="caption">
+      Charts Showing the General Directions of Wind and Tide Currents
+  </figcaption>
+</figure>
+
+<p>Over the northerly portion of the Indian Ocean—from
+<span class="pagenum" id="Page_837">[837]</span>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 <em>monsoon</em>—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.</p>
+
+<p>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:</p>
+
+<p>“Meanwhile the air becomes loaded to saturation
+with aqueous vapor drawn up by the augmented
+<span class="pagenum" id="Page_838">[838]</span>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.</p>
+
+<p>“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.</p>
+
+<p><span class="pagenum" id="Page_839">[839]</span></p>
+
+<p>“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.”</p>
+
+<p>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
+<span class="pagenum" id="Page_840">[840]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_841">[841]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_842">[842]</span>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.</p>
+
+<p>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 <em>off the shore</em> or from <em>off the adjacent
+waters</em>. The former is known as the land-breeze;
+the latter as the sea-breeze.</p>
+
+<p>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
+<span class="pagenum" id="Page_843">[843]</span>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_844">[844]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_845">[845]</span>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>i. e.</i>, 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.</p>
+
+<p>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.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h3 id="III-845">
+  SQUALLS, WHIRLWINDS, AND TORNADOES<br>
+  —<span class="smcap">Sir Ralph Abercromby</span>
+</h3>
+</div>
+
+
+<p class="drop-capy">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
+<span class="pagenum" id="Page_846">[846]</span>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
+<span class="pagenum" id="Page_847">[847]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.
+<span class="pagenum" id="Page_848">[848]</span>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_849">[849]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_850">[850]</span>belt of high pressure to the south of the Bay of
+Bengal.</p>
+
+<p>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 <em>pamperos sucios</em>,
+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.</p>
+
+<p>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.</p>
+
+<p>The general appearance of a pampero will be best
+understood by a description of an actual squall. “In
+<span class="pagenum" id="Page_851">[851]</span>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 <span class="allsmcap">A. M.</span> 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
+<span class="pagenum" id="Page_852">[852]</span>same time a strong, cold blast fell from the leaden
+cloud, and continued to blow till both bands had
+passed.”</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>The spout as a whole has four distinct motions:</p>
+
+<p>1. A motion of translation generally toward the
+northeast at a variable rate, but which may be taken
+to average thirty miles an hour.</p>
+
+<p>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
+<span class="pagenum" id="Page_853">[853]</span>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>The destructive effects of the tornado are very curious,
+<span class="pagenum" id="Page_854">[854]</span>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 <em>maximum</em> 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
+<span class="pagenum" id="Page_855">[855]</span>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 <em>maximum</em>
+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.</p>
+
+<p>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.</p>
+
+<p>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”:</p>
+
+<p>“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 <span class="allsmcap">P. M.</span>
+threatening clouds appeared very suddenly in the
+<span class="pagenum" id="Page_856">[856]</span>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.”
+<span class="pagenum" id="Page_857">[857]</span>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 <span class="allsmcap">P. M.</span> 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.</p>
+
+<p>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.</p>
+
+<p>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
+<span class="pagenum" id="Page_858">[858]</span>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.</p>
+
+<p>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.</p>
+
+<p>“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.”</p>
+
+
+<p class="p4 pfs90">END OF VOLUME TWO</p>
+
+
+<div class="chapter"></div>
+<div class="footnotes">
+<h2 class="nobreak">FOOTNOTES:</h2>
+
+<div class="footnote"><p><a id="Footnote_1_1" href="#FNanchor_1_1" class="label">[1]</a> 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.</p></div>
+
+<div class="footnote"><p><a id="Footnote_2_2" href="#FNanchor_2_2" class="label">[2]</a> Another variety or species of seal inhabits Lake Baikal.</p></div>
+
+<div class="footnote"><p><a id="Footnote_3_3" href="#FNanchor_3_3" class="label">[3]</a> 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.</p></div>
+
+<div class="footnote"><p><a id="Footnote_4_4" href="#FNanchor_4_4" class="label">[4]</a> Archbishop of Spalato and Primate of Dalmatia.</p></div>
+</div>
+
+<hr class="chap x-ebookmaker-drop">
+<div class="chapter"></div>
+
+<div class="p4 transnote">
+<a id="TN"></a>
+<p><strong>TRANSCRIBER’S NOTE</strong></p>
+
+<p>Obvious typographical errors and punctuation errors have been
+corrected after careful comparison with other occurrences within
+the text and consultation of external sources.</p>
+
+<p>Some hyphens in words have been silently removed, some added,
+when a predominant preference was found in the original book.</p>
+
+<p>Except for those changes noted below, all misspellings in the text,
+and inconsistent or archaic usage, have been retained.</p>
+
+<p>
+  <a href="#tn-470">Pg 470</a>: ‘chiefly Brachipods of’ replaced by ‘chiefly Brachiopods of’.<br>
+  <a href="#tn-472">Pg 472</a>: ‘these same familes’ replaced by ‘these same families’.<br>
+  <a href="#tn-483">Pg 483</a>: ‘constituing links’ replaced by ‘constituting links’.<br>
+  <a href="#tn-563">Pg 563</a>: ‘Camaroons Mountains’ replaced by ‘Cameroon Mountains’.<br>
+  <a href="#tn-563a">Pg 563</a>: ‘with Teneriffe in’ replaced by ‘with Tenerife in’.<br>
+  <a href="#tn-569">Pg 569</a>: ‘existing, denundation’ replaced by ‘existing, denudation’.<br>
+  <a href="#tn-650">Pg 650</a>: ‘their relativ  size’ replaced by ‘their relative size’.<br>
+  <a href="#tn-718">Pg 718</a>: ‘incalulable ages’ replaced by ‘incalculable ages’.<br>
+  <a href="#tn-722">Pg 722</a>: ‘greatly diminshed’ replaced by ‘greatly diminished’.
+</p>
+</div>
+
+<div style='text-align:center'>*** END OF THE PROJECT GUTENBERG EBOOK 77792 ***</div>
+</body>
+</html>
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author	www-data <www-data@mail.pglaf.org>	2026-01-26 14:12:00 -0800
committer	www-data <www-data@mail.pglaf.org>	2026-01-26 14:12:00 -0800
commit	b0ec5f78336ee6068b9b079f737b85ceb4bb8f15 (patch)
tree	40fa73f7da5118f42cffbdd6e16bcf6c5eec240c /77792-h