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Title: Principles of Geology
       or, The Modern Changes of the Earth and its Inhabitants
       Considered as Illustrative of Geology

Author: Charles Lyell

Release Date: July 22, 2010 [EBook #33224]

Language: English

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  PRINCIPLES

  OF

  GEOLOGY.




[Illustration: VIEW OF THE TEMPLE OF SERAPIS AT PUZZUOLI IN 1836.]


  PRINCIPLES

  OF

  GEOLOGY;

  OR,

  THE MODERN CHANGES OF THE EARTH AND ITS
  INHABITANTS

  CONSIDERED AS ILLUSTRATIVE OF GEOLOGY.

  BY

  SIR CHARLES LYELL, M.A. F.R.S.

  VICE-PRESIDENT OF THE GEOLOGICAL SOCIETY OF LONDON; AUTHOR OF
  "A MANUAL OF ELEMENTARY GEOLOGY," "TRAVELS IN NORTH AMERICA,"
  "A SECOND VISIT TO THE UNITED STATES," ETC. ETC.

  NEW AND ENTIRELY REVISED EDITION.

  ILLUSTRATED WITH MAPS, PLATES, AND WOODCUTS.

  NEW YORK:
  D. APPLETON & CO., 346 & 348 BROADWAY.

  M.DCCC.LIV.


"Vere scire est per causas scire."--BACON.


"The stony rocks are not primeval, but the daughters of Time."--LINNAEUS,
_Syst. Nat._ ed. 5, _Stockholm_, 1748, p. 219.


"Amid all the revolutions of the globe, the economy of nature has been
uniform, and her laws are the only things that have resisted the general
movement. The rivers and the rocks, the seas and the continents have
been changed in all their parts; but the laws which direct those
changes, and the rules to which they are subject, have remained
invariably the same."--PLAYFAIR, _Illustrations of the Huttonian
Theory_, Section 374.

"The inhabitants of the globe, like all the other parts of it, are
subject to change. It is not only the individual that perishes, but
whole species.

"A change in the animal kingdom seems to be a part of the order of
Nature, and is visible in instances to which human power cannot have
extended."--PLAYFAIR, _Illustrations of the Huttonian Theory_, Section
413.




PREFACE TO THE NINTH EDITION.


The Principles of Geology in the first five editions embraced not only a
view of the _modern changes_ of the earth and its inhabitants, as set
forth in the present work, but also some account of those monuments of
analogous changes of _ancient_ date, both in the organic and inorganic
world, which it is the business of the geologist to interpret. The
subject last mentioned, or "geology proper," constituted originally a
fourth book, now omitted, the same having been enlarged into a separate
treatise, first published in 1838, in one volume 12mo., and called "The
Elements of Geology," afterwards recast in two volumes 12mo. in 1842,
and again re-edited under the title of "Manual of Elementary Geology,"
in one volume 8vo. in 1851. The "Principles" and "Manual" thus divided,
occupy, with one exception, to which I shall presently allude, very
different ground. The "Principles" treat of such portions of the economy
of existing nature, animate and inanimate, as are illustrative of
Geology, so as to comprise an investigation of the permanent effects of
causes now in action, which may serve as records to after ages of the
present condition of the globe and its inhabitants. Such effects are the
enduring monuments of the ever-varying state of the physical geography
of the globe, the lasting signs of its destruction and renovation, and
the memorials of the equally fluctuating condition of the organic world.
They may be regarded, in short, as a symbolical language, in which the
earth's autobiography is written.

In the "Manual of Elementary Geology," on the other hand, I have treated
briefly of the component materials of the earth's crust, their
arrangement and relative position, and their organic contents, which,
when deciphered by aid of the key supplied by the study of the modern
changes above alluded to, reveal to us the annals of a grand succession
of past events--a series of revolutions which the solid exterior of the
globe, and its living inhabitants, have experienced in times antecedent
to the creation of man.

In thus separating the two works, however, I have retained in the
"Principles" (book i.) the discussion of some matters which might fairly
be regarded as common to both treatises; as for example, an historical
sketch of the early progress of geology, followed by a series of
preliminary essays to explain the facts and arguments which lead me to
believe that the forces now operating upon and beneath the earth's
surface may be the same, both in kind and degree, as those which at
remote epochs have worked out geological changes. (See Analysis of
Contents of this work, p. ix.)

If I am asked whether the "Principles" or the "Manual" should be studied
first, I feel much the same difficulty in answering the question as if a
student should inquire whether he ought to take up first a treatise on
Chemistry, or one on Natural Philosophy, subjects sufficiently distinct,
yet inseparably connected. On the whole, while I have endeavored to make
each of the two treatises, in their present form, quite independent of
the other, I would recommend the reader to study first the modern
changes of the earth and its inhabitants as they are discussed in the
present volume, proceeding afterwards to the classification and
interpretation of the monuments of more remote ages.


  CHARLES LYELL.

   _11 Harley Street, London_, May 24, 1853.


_Dates of the successive Editions of the "Principles" and "Elements" (or
Manual) of Geology, by the Author._

  Principles, 1st vol. in octvo, published in               Jan. 1830.
  ----------,  2d vol.   do.   do.                          Jan. 1832.
  ----------, 1st vol. 2d edition in octavo                      1832.
  ----------,  2d vol. 2d edition do.                       Jan. 1833.
  ----------,  3d vol. 1st edition do.                      May, 1833.
  ----------, New edition (called the 3d) of the whole work
                in 4 vols. 12mo                             May, 1834.
  ----------, 4th edition, 4 vols. 12mo                    June, 1835.
  ----------, 5th do.  do.  do.                             Mar. 1837.
  Elements, 1st edition in one vol                         July, 1838.
  Principles, 6th do.  3 vols. 12mo                        June, 1840.
  Elements, 2d edition in 2 vols. 12mo                     July, 1841.
  Principles, 7th edition in one vol. 8vo                   Feb. 1847.
  ----------, 8th edition in one vol. 8vo                   May, 1850.
  Manual of Elementary Geology (or "Elements," 3d edition)
            in one vol. 8vo                                 Jan. 1851.
  Manual, 4th edition, one vol. 8vo                         Jan. 1852.
  Principles, 9th edition, now published in one vol. 8vo   June, 1853.




  ANALYSIS OF THE CONTENTS
  OF
  THE PRINCIPLES OF GEOLOGY.


  BOOK I. (CHAPTERS I. TO XIII.)

  HISTORICAL SKETCH OF THE PROGRESS OF GEOLOGY, WITH A SERIES OF
    ESSAYS TO SHOW THAT THE MONUMENTS OF THE ANCIENT STATE OF THE
    EARTH AND ITS INHABITANTS, WHICH THIS SCIENCE INTERPRETS, CAN
    ONLY BE UNDERSTOOD BY A PREVIOUS ACQUAINTANCE WITH TERRESTRIAL
    CHANGES NOW IN PROGRESS, BOTH IN THE ORGANIC AND INORGANIC
    WORLDS.

  CHAPTER I.
  Geology defined--Its relation to other Sciences                  Page 1

  CHAPTER II.
  Oriental and Egyptian Cosmogonies--Doctrines of the Greeks
    and Romans bearing on Geology                                       4

  CHAPTER III.
  Historical progress of Geology--Arabian Writers--Italian,
    French, German, and English geologists before the 19th
    century--Physico-theological school                                17

  CHAPTER IV.
  Werner and Hutton--Modern progress of the science                    46

  CHAPTER V.
  Prepossessions in regard to the duration of past time,
    and other causes which have   retarded the progress
    of Geology                                                         61

  CHAPTER VI.
  Agreement of the ancient and modern course of nature
    considered--Changes of climate                                     73

  CHAPTERS VII. VIII.
  Causes of vicissitudes in climate, and their connection
    with changes in physical geography                            92, 114

  CHAPTER IX.
  Theory of the progressive development of organic life
    at successive periods considered--Modern origin of Man            130

  CHAPTER X.
  Supposed intensity of aqueous forces at remote
    periods--Erratic blocks--Deluges                                  153

  CHAPTER XI.
  Supposed former intensity of the igneous forces--Upheaval
    of land--Volcanic action                                          160

  CHAPTER XII.
  Causes of the difference in texture of older and newer
    rocks--Plutonic and Metamorphic action                            175

  CHAPTER XIII.
  Supposed alternate periods of repose and disorder--Opposite
    doctrine, which refers geological phenomena to an
    uninterrupted series of changes in the organic and inorganic
    world, unattended with general catastrophes,
    or the development of paroxysmal forces                           180


  BOOK II. (CHAPTERS XIV. to XXXII.)

  OBSERVED CHANGES IN THE INORGANIC WORLD NOW IN PROGRESS: FIRST,
    THE EFFECTS OF AQUEOUS CAUSES, SUCH AS RIVERS, SPRINGS,
    GLACIERS, WAVES, TIDES, AND CURRENTS; SECONDLY, OF IGNEOUS
    CAUSES, OR SUBTERRANEAN HEAT, AS EXHIBITED IN THE VOLCANO AND
    THE EARTHQUAKE.

  CHAPTER XIV.
  Aqueous causes--Excavating and transporting power of rivers         198

  CHAPTER XV.
  Carrying power of river-ice--Glaciers and Icebergs                  219

  CHAPTER XVI.
  Phenomena of springs                                                232

  CHAPTER XVII.
  Reproductive effects of rivers--Deltas of lakes and inland
    seas                                                              251

  CHAPTER XVIII.
  Deltas of the Mississippi, Ganges, and other rivers exposed
    to tidal action                                                   263

  CHAPTERS XIX. XX. XXI.
  Denuding, transporting, and depositing agency of the waves,
    tides, and currents--Waste of sea-cliffs on the coast
    of England--Delta of the Rhine--Deposition of sediment
    under the influence of marine currents                  290, 321, 337

  CHAPTER XXII.
  Observed effects of igneous causes--Regions of active
    volcanoes                                                         344

  CHAPTERS XXIII. XXIV.
  History of the volcanic eruptions of the district round
    Naples--Structure of Vesuvius--Herculaneum and Pompeii       360, 375

  CHAPTER XXV.
  Etna--Its eruptions--Structure and antiquity of the cone            396

  CHAPTER XXVI.
  Volcanoes of Iceland, Mexico, the Canaries, and Grecian
    Archipelago--Mud volcanoes                                        424

  CHAPTER XXVII.
  Earthquakes and the permanent changes attending them                451

  CHAPTER XXVIII.
  Earthquake of 1783 in Calabria                                      471

  CHAPTER XXIX.
  Elevation and subsidence of dry land, and of the bed of
    the sea during earthquakes--Evidence of the same afforded
    by the Temple of Serapis near Naples                              493

  CHAPTER XXX.
  Elevation and subsidence of land in regions free from
    volcanoes and earthquakes--Rising of land in Sweden               519

  CHAPTERS XXXI. XXXII.
  Causes of earthquakes and volcanoes--Theory of central
    fluidity of the earth--Chemical theory of volcanoes--Causes
    of permanent upheaval and depression of land                 533, 545


  BOOK III. (CHAPTERS XXXIII to L.)

  OBSERVED CHANGES OF THE ORGANIC WORLD NOW IN PROGRESS; FIRST,
    NATURE AND GEOGRAPHICAL DISTRIBUTION OF SPECIES, AND THEORIES
    RESPECTING THEIR CREATION AND EXTINCTION; SECONDLY, THE
    INFLUENCE OF ORGANIC BEINGS IN MODIFYING PHYSICAL GEOGRAPHY;
    THIRDLY, THE LAWS ACCORDING TO WHICH THEY ARE IMBEDDED IN
    VOLCANIC, FRESHWATER, AND MARINE DEPOSITS.

  CHAPTERS XXXIII. XXXIV. XXXV. XXXVI.
  Whether species have a real existence in nature--Theory
    of transmutation of species--Variability of
    species--Phenomena of hybrids in animals and
    plants                                             566, 578, 591, 600

  CHAPTER XXXVII.
  Laws which regulate the geographical distribution of
    species--Distinct provinces of peculiar species of
    plants--Their mode of diffusion                                   612

  CHAPTER XXXVIII.
  Distinct provinces of peculiar species of
    animals--Distribution and dispersion of
    quadrupeds, birds, and reptiles                                   629

  CHAPTER XXXIX.
  Geographical distribution and migrations
    of fish--Of testacea--Of zoophytes--Of
    insects--Geographical distribution and
    diffusion of the human race                                       646

  CHAPTER XL.
  Theories respecting the original introduction of
    species--Reciprocal influence of species on each other            665

  CHAPTERS XLI. XLII.
  Extinction of species--How every extension of the range
    of a species alters the condition of many others--Effect
    of changes of climate                                        677, 689

  CHAPTER XLIII.
  Creation of species--Whether the loss of certain animals
    and plants is compensated by the introduction of
    new species                                                       701

  CHAPTER XLIV.
  Modifications in physical geography caused by organic beings        708

  CHAPTER XLV.
  Imbedding of organic remains in peat, blown sand,
    and volcanic ejections                                            718

  CHAPTER XLVI.
  Imbedding of the same in alluvial deposits and in caves             730

  CHAPTER XLVII.
  Imbedding of organic remains in aqueous deposits--Terrestrial
    plants--Insects, reptiles, birds, quadrupeds                      742

  CHAPTER XLVIII.
  Imbedding of the remains of man and his works                       753

  CHAPTER XLIX.
  Imbedding of aquatic animals and plants, both freshwater
    and marine, in aqueous deposits                                   765

  CHAPTER L.
  Formation of coral reefs                                            775


  LIST OF PLATES.


  DIRECTIONS TO THE BINDER.


  FRONTISPIECE, View of the Temple of Serapis
    at Puzzuoli in 1836,                            _to face_ title page.

  PLATE 1. Map showing the Area in Europe which
             has been covered by Water since the
             beginning of the Eocene Period              _to face_ p. 121

        2. Boulders drifted by Ice on the Shores
             of the St. Lawrence                                      220

        3. View looking up the Val del Bove, Etna                     403

        4. View of the Val del Bove, Etna, as seen from above         404


PRINCIPLES OF GEOLOGY.


BOOK I.




CHAPTER I.


   Geology defined--Compared to History--Its relation to other
   Physical Sciences--Not to be confounded with Cosmogony.


Geology is the science which investigates the successive changes that
have taken place in the organic and inorganic kingdoms of nature; it
inquires into the causes of these changes, and the influence which they
have exerted in modifying the surface and external structure of our
planet.

By these researches into the state of the earth and its inhabitants at
former periods, we acquire a more perfect knowledge of its present
condition, and more comprehensive views concerning the laws now
governing its animate and inanimate productions. When we study history,
we obtain a more profound insight into human nature, by instituting a
comparison between the present and former states of society. We trace
the long series of events which have gradually led to the actual posture
of affairs; and by connecting effects with their causes, we are enabled
to classify and retain in the memory a multitude of complicated
relations--the various peculiarities of national character--the
different degrees of moral and intellectual refinement, and numerous
other circumstances, which, without historical associations, would be
uninteresting or imperfectly understood. As the present condition of
nations is the result of many antecedent changes, some extremely remote,
and others recent, some gradual, others sudden and violent; so the
state, of the natural world is the result of a long succession of
events; and if we would enlarge our experience of the present economy of
nature, we must investigate the effects of her operations in former
epochs.

We often discover with surprise, on looking back into the chronicles of
nations, how the fortune of some battle has influenced the fate of
millions of our contemporaries, when it has long been forgotten by the
mass of the population. With this remote event we may find inseparably
connected the geographical boundaries of a great state, the language now
spoken by the inhabitants, their peculiar manners, laws, and religious
opinions. But far more astonishing and unexpected are the connections
brought to light, when we carry back our researches into the history of
nature. The form of a coast, the configuration of the interior of a
country, the existence and extent of lakes, valleys, and mountains, can
often be traced to the former prevalence of earthquakes and volcanoes in
regions which have long been undisturbed. To these remote convulsions
the present fertility of some districts, the sterile character of
others, the elevation of land above the sea, the climate, and various
peculiarities, may be distinctly referred. On the other hand, many
distinguishing features of the surface may often be ascribed to the
operation, at a remote era, of slow and tranquil causes--to the gradual
deposition of sediment in a lake or in the ocean, or to the prolific
increase of testacea and corals.

To select another example, we find in certain localities subterranean
deposits of coal, consisting of vegetable matter, formerly drifted into
seas and lakes. These seas and lakes have since been filled up, the
lands whereon the forests grew have disappeared or changed their form,
the rivers and currents which floated the vegetable masses can no longer
be traced, and the plants belonged to species which for ages have passed
away from the surface of our planet. Yet the commercial prosperity, and
numerical strength of a nation, may now be mainly dependent on the local
distribution of fuel determined by that ancient state of things.

Geology is intimately related to almost all the physical sciences, as
history is to the moral. An historian should, if possible, be at once
profoundly acquainted with ethics, politics, jurisprudence, the military
art, theology; in a word, with all branches of knowledge by which any
insight into human affairs, or into the moral and intellectual nature of
man, can be obtained. It would be no less desirable that a geologist
should be well versed in chemistry, natural philosophy, mineralogy,
zoology, comparative anatomy, botany; in short, in every science
relating to organic and inorganic nature. With these accomplishments,
the historian and geologist would rarely fail to draw correct and
philosophical conclusions from the various monuments transmitted to them
of former occurrences. They would know to what combination of causes
analogous effects were referable, and they would often be enabled to
supply, by inference, information concerning many events unrecorded in
the defective archives of former ages. But as such extensive
acquisitions are scarcely within the reach of any individual, it is
necessary that men who have devoted their lives to different departments
should unite their efforts; and as the historian receives assistance
from the antiquary, and from those who have cultivated different
branches of moral and political science, so the geologist should avail
himself of the aid of many naturalists, and particularly of those who
have studied the fossil remains of lost species of animals and plants.

The analogy, however, of the monuments consulted in geology, and those
available in history, extends no farther than to one class of historical
monuments--those which may be said to be _undesignedly_ commemorative of
former events. The canoes, for example, and stone hatchets found in our
peat bogs, afford an insight into the rude arts and manners of the
earliest inhabitants of our island; the buried coin fixes the date of
the reign of some Roman emperor; the ancient encampment indicates the
districts once occupied by invading armies, and the former method of
constructing military defences; the Egyptian mummies throw light on the
art of embalming, the rites of sepulture, or the average stature of the
human race in ancient Egypt. This class of memorials yields to no other
in authenticity, but it constitutes a small part only of the resources
on which the historian relies, whereas in geology it forms the only kind
of evidence which is at our command. For this reason we must not expect
to obtain a full and connected account of any series of events beyond
the reach of history. But the testimony of geological monuments, if
frequently imperfect, possesses at least the advantage of being free
from all intentional misrepresentation. We may be deceived in the
inferences which we draw, in the same manner as we often mistake the
nature and import of phenomena observed in the daily course of nature;
but our liability to err is confined to the interpretation, and, if this
be correct, our information is certain.

It was long before the distinct nature and legitimate objects of geology
were fully recognized, and it was at first confounded with many other
branches of inquiry, just as the limits of history, poetry, and
mythology were ill-defined in the infancy of civilization. Even in
Werner's time, or at the close of the eighteenth century, geology
appears to have been regarded as little other than a subordinate
department of mineralogy; and Desmarest included it under the head of
Physical Geography. But the most common and serious source of confusion
arose from the notion, that it was the business of geology to discover
the mode in which the earth originated, or, as some imagined, to study
the effects of those cosmological causes which were employed by the
Author of Nature to bring this planet out of a nascent and chaotic state
into a more perfect and habitable condition. Hutton was the first who
endeavored to draw a strong line of demarcation between his favorite
science and cosmogony, for he declared that geology was in nowise
concerned "with questions as to the origin of things."

An attempt will be made in the sequel of this work to demonstrate that
geology differs as widely from cosmogony, as speculations concerning the
mode of the first creation of man differ from history. But, before
entering more at large on this controverted question, it will be
desirable to trace the progress of opinion on this topic, from the
earliest ages to the commencement of the present century.




CHAPTER II.

HISTORICAL SKETCH OF THE PROGRESS OF GEOLOGY.


   Oriental Cosmogony--Hymns of the Vedas--Institutes of
     Menu--Doctrine of the successive destruction and renovation of
     the world--Origin of this doctrine--Common to the
     Egyptians--Adopted by the Greeks--System of Pythagoras--Of
     Aristotle--Dogmas concerning the extinction and reproduction
     of genera and species--Strabo's theory of elevation by
     earthquakes--Pliny--Concluding Remarks on the knowledge of the
     Ancients.


_Oriental Cosmogony._--The earliest doctrines of the Indian and Egyptian
schools of philosophy agreed in ascribing the first creation of the
world to an omnipotent and infinite Being. They concurred also in
representing this Being, who had existed from all eternity, as having
repeatedly destroyed and reproduced the world and all its inhabitants.
In the sacred volume of the Hindoos, called the Ordinances of Menu,
comprising the Indian system of duties religious and civil, we find a
preliminary chapter treating of the Creation, in which the cosmogony is
known to have been derived from earlier writings and traditions; and
principally from certain hymns of high antiquity, called the Vedas.
These hymns were first put together, according to Mr. Colebrooke,[1] in
a connected series, about thirteen centuries before the Christian era,
but they appear from internal evidence to have been written at various
antecedent periods. In them, as we learn from the researches of
Professor Wilson, the eminent Sanscrit scholar, two distinct
philosophical systems are discoverable. According to one of them, all
things were originally brought into existence by the sole will of a
single First Cause, which existed from eternity; according to the other,
there have always existed two principles, the one material, but without
form, the other spiritual and capable of compelling "inert matter to
develop its sensible properties." This development of matter into
"individual and visible existences" is called creation, and is assigned
to a subordinate agent, or the creative faculty of the Supreme Being
embodied in the person of Brahma.

In the first chapter of the Ordinances of Menu above alluded to, we meet
with the following passages relating to former destructions and
renovations of the world:--

"The Being, whose powers are incomprehensible, having created me (Menu)
and this universe, again became absorbed in the supreme spirit, changing
the time of energy for the hour of repose.

"When that Power awakes, then has this world its full expansion; but
when he slumbers with a tranquil spirit, then the whole system fades
away..... For while he reposes, as it were, embodied spirits endowed
with principles of action depart from their several acts, and the mind
itself becomes inert."

The absorption of all beings into the Supreme essence is then described,
and the Divine soul itself is said to slumber, and to remain for a time
immersed in "the first idea, or in darkness." After which the text thus
proceeds (verse fifty-seven), "Thus that immutable power by waking and
reposing alternately, revivifies and destroys, in eternal succession,
this whole assemblage of locomotive and immovable creatures."

It is then declared that there has been a long succession of
_manwantaras_, or periods, each of the duration of many thousand ages,
and--

"There are creations also, and destructions of worlds innumerable: the
Being, supremely exalted, performs all this with as much ease as if in
sport, again and again, for the sake of conferring happiness."[2]

No part of the Eastern cosmogony, from which these extracts are made, is
more interesting to the geologist than the doctrine, so frequently
alluded to, of the reiterated submersion of the land beneath the waters
of a universal ocean. In the beginning of things, we are told, the First
Sole Cause "with a thought created the waters," and then moved upon
their surface in the form of Brahma the creator, by whose agency the
emergence of the dry land was effected, and the peopling of the earth
with plants, animals, celestial creatures, and man. Afterwards, as often
as a general conflagration at the close of each manwantara had
annihilated every visible and existing thing, Brahma, on awaking from
his sleep, finds the whole world a shapeless ocean. Accordingly, in the
legendary poems called the Puranas, composed at a later date than the
Vedas, the three first Avatars or descents of the Deity upon earth have
for their object to recover the land from the waters. For this purpose
Vishnu is made successively to assume the form of a fish, a tortoise,
and a boar.

Extravagant as may be some of the conceits and fictions which disfigure
these pretended revelations, we can by no means look upon them as a pure
effort of the unassisted imagination, or believe them to have been
composed without regard to opinions and theories founded on the
observation of Nature. In astronomy, for instance, it is declared that,
at the North Pole, the year was divided into a long day and night, and
that their long day was the northern, and their night the southern
course of the sun; and to the inhabitants of the moon, it is said one
day is equal in length to one month of mortals.[3] If such statements
cannot be resolved into mere conjectures, we have no right to refer to
mere chance the prevailing notion that the earth and its inhabitants had
formerly undergone a succession of revolutions and aqueous catastrophes
interrupted by long intervals of tranquillity.

Now there are two sources in which such a theory may have originated.
The marks of former convulsions on every part of the surface of our
planet are obvious and striking. The remains of marine animals imbedded
in the solid strata are so abundant, that they may be expected to force
themselves on the attention of every people who have made some progress
in refinement; and especially where one class of men are expressly set
apart from the rest, like the ancient priesthoods of India and Egypt,
for study and contemplation. If these appearances are once recognized,
it seems natural that the mind should conclude in favor, not only of
mighty changes in past ages, but of alternate periods of repose and
disorder;--of repose, when the animals now fossil lived, grew, and
multiplied--of disorder, when the strata in which they were buried
became transferred from the sea to the interior of continents, and were
uplifted so as to form part of high mountain-chains. Those modern
writers, who are disposed to disparage the former intellectual
advancement and civilization of Eastern nations, may concede some
foundation of observed facts for the curious theories now under
consideration, without indulging in exaggerated opinions of the progress
of science; especially as universal catastrophes of the world, and
exterminations of organic beings, in the sense in which they were
understood by the Brahmins, are untenable doctrines.

We know that the Egyptian priests were aware, not only that the soil
beneath the plains of the Nile, but that also the hills bounding the
great valley, contained marine shells; and Herodotus inferred from these
facts, that all lower Egypt, and even the high lands above Memphis, had
once been covered by the sea.[4] As similar fossil remains occur in all
parts of Asia hitherto explored, far in the interior of the continent as
well as near the sea, they could hardly have escaped detection by some
Eastern sages not less capable than the Greek historian of reasoning
philosophically on natural phenomena.

We also know that the rulers of Asia were engaged in very remote eras in
executing great national works, such as tanks and canals, requiring
extensive excavations. In the fourteenth century of our era (in the year
1360), the removal of soil necessary for such undertakings brought to
light geological facts, which attracted the attention of a people less
civilized than were many of the older nations of the East. The historian
Ferishta relates that fifty thousand laborers were employed in cutting
through a mound, so as to form a junction between the rivers Selima and
Sutlej; and in this mound were found the bones of elephants and men,
some of them petrified, and some of them resembling bone. The gigantic
dimensions attributed to the human bones show them to have belonged to
some of the larger pachydermata.[5]

But, although the Brahmins, like the priests of Egypt, may have been
acquainted with the existence of fossil remains in the strata, it is
possible that the doctrine of successive destructions and renovations of
the world, merely received corroboration from such proofs; and that it
may have been originally handed down, like the religious traditions of
most nations, from a ruder state of society. The system may have had its
source, in part at least, in exaggerated accounts of those dreadful
catastrophes which are occasioned by particular combinations of natural
causes. Floods and volcanic eruptions, the agency of water and fire, are
the chief instruments of devastation on our globe. We shall point out in
the sequel the extent of many of these calamities, recurring at distant
intervals of time, in the present course of nature; and shall only
observe here, that they are so peculiarly calculated to inspire a
lasting terror, and are so often fatal in their consequences to great
multitudes of people, that it scarcely requires the passion for the
marvellous, so characteristic of rude and half-civilized nations, still
less the exuberant imagination of Eastern writers, to augment them into
general cataclysms and conflagrations.

The great flood of the Chinese, which their traditions carry back to the
period of Yaou, something more than 2000 years before our era, has been
identified by some persons with the universal deluge described in the
Old Testament; but according to Mr. Davis, who accompanied two of our
embassies to China, and who has carefully examined their written
accounts, the Chinese cataclysm is therein described as interrupting the
business of agriculture, rather than as involving a general destruction
of the human race. The great Yu was celebrated for having "opened nine
channels to draw off the waters," which "covered the low hills and
bathed the foot of the highest mountains." Mr. Davis suggests that a
great derangement of waters of the Yellow River, one of the largest in
the world, might even now cause the flood of Yaou to be repeated, and
lay the most fertile and populous plains of China under water. In modern
times the bursting of the banks of an artificial canal, into which a
portion of the Yellow River has been turned, has repeatedly given rise
to the most dreadful accidents, and is a source of perpetual anxiety to
the government. It is easy, therefore, to imagine how much greater may
have been the inundation, if this valley was ever convulsed by a violent
earthquake.[6]

Humboldt relates the interesting fact that, after the annihilation of a
large part of the inhabitants of Cumana, by an earthquake in 1766, a
season of extraordinary fertility ensued, in consequence of the great
rains which accompanied the subterranean convulsions. "The Indians," he
says, "celebrated, after the ideas of an antique superstition, by
festivals and dancing, the destruction of the world and the approaching
epoch of its regeneration."[7]

The existence of such rites among the rude nations of South America is
most important, as showing what effects may be produced by local
catastrophes, recurring at distant intervals of time, on the minds of a
barbarous and uncultivated race. I shall point out in the sequel how the
tradition of a deluge among the Araucanian Indians may be explained, by
reference to great earthquake-waves which have repeatedly rolled over
part of Chili since the first recorded flood of 1590. (See chap. 29,
Book II.) The legend also of the ancient Peruvians of an inundation many
years before the reign of the Incas, in which only six persons were
saved on a float, relates to a region which has more than once been
overwhelmed by inroads of the ocean since the days of Pizarro. (Chap.
29, Book II.) I might refer the reader to my account of the submergence
of a wide area in Cutch so lately as the year 1819, when a single tower
only of the fort of Sindree appeared above the waste of waters (see
Chap. 28, Book II.), if it were necessary, to prove how easily the
catastrophes of modern times might give rise to traditionary narratives,
among a rude people, of floods of boundless extent. Nations without
written records, and who are indebted for all their knowledge of past
events exclusively to oral tradition, are in the habit of confounding in
one legend a series of incidents which have happened at various epochs;
nor must we forget that the superstitions of a savage tribe are
transmitted through all the progressive stages of society, till they
exert a powerful influence on the mind of the philosopher. He may find,
in the monuments of former changes on the earth's surface, an apparent
confirmation of tenets handed down through successive generations, from
the rude hunter, whose terrified imagination drew a false picture of
those awful visitations of floods and earthquakes, whereby the whole
earth as known to him was simultaneously devastated.

_Egyptian Cosmogony._--Respecting the cosmogony of the Egyptian priests,
we gather much information from writers of the Grecian sects, who
borrowed almost all their tenets from Egypt, and amongst others that of
the former successive destruction and renovation of the world.[8] We
learn from Plutarch, that this was the theme of one of the hymns of
Orpheus, so celebrated in the fabulous ages of Greece. It was brought by
him from the banks of the Nile; and we even find in his verses, as in
the Indian systems, a definite period assigned for the duration of each
successive world.[9] The returns of great catastrophes were determined
by the period of the Annus Magnus, or great year,--a cycle composed of
the revolutions of the sun, moon, and planets, and terminating when
these return together to the same sign whence they were supposed at some
remote epoch to have set out. The duration of this great cycle was
variously estimated. According to Orpheus, it was 120,000 years;
according to others, 300,000; and by Cassander it was taken to be
360,000 years.[10]

We learn particularly from the Timaeus of Plato, that the Egyptians
believed the world to be subject to occasional conflagrations and
deluges, whereby the gods arrested the career of human wickedness, and
purified the earth from guilt. After each regeneration, mankind were in
a state of virtue and happiness, from which they gradually degenerated
again into vice and immorality. From this Egyptian doctrine, the poets
derived the fable of the decline from the golden to the iron age. The
sect of Stoics adopted most fully the system of catastrophes destined at
certain intervals to destroy the world. Those they taught were of two
kinds;--the Cataclysm, or destruction by water, which sweeps away the
whole human race, and annihilates all the animal and vegetable
productions of nature; and the Ecpyrosis, or destruction by fire, which
dissolves the globe itself. From the Egyptians also they derived the
doctrine of the gradual debasement of man from a state of innocence.
Towards the termination of each era, the gods could no longer bear with
the wickedness of men, and a shock of the elements or a deluge
overwhelmed them; after which calamity, Astrea again descended on the
earth to renew the golden age.[11]

The connection between the doctrine of successive catastrophes and
repeated deteriorations in the moral character of the human race is more
intimate and natural than might at first be imagined. For, in a rude
state of society, all great calamities are regarded by the people as
judgments of God on the wickedness of man. Thus, in our own time, the
priests persuaded a large part of the population of Chili, and perhaps
believed themselves, that the fatal earthquake of 1822 was a sign of the
wrath of Heaven for the great political revolution just then consummated
in South America. In like manner, in the account given to Solon by the
Egyptian priests, of the submersion of the island of Atlantis under the
waters of the ocean, after repeated shocks of an earthquake, we find
that the event happened when Jupiter had seen the moral depravity of the
inhabitants.[12] Now, when the notion had once gained ground, whether
from causes before suggested or not, that the earth had been destroyed
by several general catastrophes, it would next be inferred that the
human race had been as often destroyed and renovated. And since every
extermination was assumed to be penal, it could only be reconciled with
divine justice, by the supposition that man, at each successive
creation, was regenerated in a state of purity and innocence.

A very large portion of Asia, inhabited by the earliest nations, whose
traditions have come down to us, has been always subject to tremendous
earthquakes. Of the geographical boundaries of these, and their effects,
I shall speak in the proper place. Egypt has, for the most part, been
exempt from this scourge, and the Egyptian doctrine of great
catastrophes was probably derived in part, as before hinted, from early
geological observations, and in part from Eastern nations.


_Pythagorean Doctrines._--Pythagoras, who resided for more than twenty
years in Egypt, and, according to Cicero, had visited the East, and
conversed with the Persian philosophers, introduced into his own
country, on his return, the doctrine of the gradual deterioration of the
human race from an original state of virtue and happiness; but if we are
to judge of his theory concerning the destruction and renovation of the
earth from the sketch given by Ovid, we must concede it to have been far
more philosophical than any known version of the cosmogonies of Oriental
or Egyptian sects.

Although Pythagoras is introduced by the poet as delivering his doctrine
in person, some of the illustrations are derived from natural events
which happened after the death of the philosopher. But notwithstanding
these anachronisms, we may regard the account as a true picture of the
tenets of the Pythagorean school in the Augustan age; and although
perhaps partially modified, it must have contained the substance of the
original scheme. Thus considered, it is extremely curious and
instructive; for we here find a comprehensive summary of almost all the
great causes of change now in activity on the globe, and these adduced
in confirmation of a principle of a perpetual and gradual revolution
inherent in the nature of our terrestrial system. These doctrines, it is
true, are not directly applied to the explanation of geological
phenomena; or, in other words, no attempt is made to estimate what may
have been in past ages, or what may hereafter be, the aggregate amount
of change brought about by such never-ending fluctuations. Had this been
the case, we might have been called upon to admire so extraordinary an
anticipation with no less interest than astronomers, when they endeavor
to define by what means the Samian philosopher came to the knowledge of
the Copernican system.

Let us now examine the celebrated passages to which we have been
adverting:[13]

"Nothing perishes in this world; but things merely vary and change their
form. To be born, means simply that a thing begins to be something
different from what it was before; and dying, is ceasing to be the same
thing. Yet, although nothing retains long the same image, the sum of the
whole remains constant." These general propositions are then confirmed
by a series of examples, all derived from natural appearances, except
the first, which refers to the golden age giving place to the age of
iron. The illustrations are thus consecutively adduced.

1. Solid land has been converted into sea.

2. Sea has been changed into land. Marine shells lie far distant from
the deep, and the anchor has been found on the summit of hills.

3. Valleys have been excavated by running water, and floods have washed
down hills into the sea.[14]

4. Marshes have become dry ground.

5. Dry lands have been changed into stagnant pools.

6. During earthquakes some springs have been closed up, and new ones
have broken out. Rivers have deserted their channels, and have been
re-born elsewhere, as the Erasinus in Greece, and Mysus in Asia.

7. The waters of some rivers, formerly sweet, have become bitter; as
those of the Anigris, in Greece, &c.[15]

8. Islands have become connected with the mainland by the growth of
deltas and new deposits; as in the case of Antissa joined to Lesbos,
Pharos to Egypt, &c.

9. Peninsulas have been divided from the main land, and have become
islands, as Leucadia; and according to tradition, Sicily, the sea having
carried away the isthmus.

10. Land has been submerged by earthquakes; the Grecian cities of Helice
and Buris, for example, are to be seen under the sea, with their walls
inclined.

11. Plains have been upheaved into hills by the confined air seeking
vent; as at Troezene in the Peloponnesus.

12. The temperature of some springs varies at different periods. The
waters of others are inflammable.[16]

13. There are streams which have a petrifying power, and convert the
substances which they touch into marble.

14. Extraordinary medicinal and deleterious effects are produced by the
water of different lakes and springs.[17]

15. Some rocks and islands, after floating and having been subject to
violent movements, have at length become stationary and immovable; as
Delos and the Cyanean Isles.[18]

16. Volcanic vents shift their position; there was a time when Etna was
not a burning mountain, and the time will come when it will cease to
burn. Whether it be that some caverns become closed up by the movements
of the earth, and others opened, or whether the fuel is finally
exhausted, &c., &c.

The various causes of change in the inanimate world having been thus
enumerated, the doctrine of equivocal generation is next propounded, as
illustrating a corresponding perpetual flux in the animate creation.[19]

In the Egyptian and Eastern cosmogonies, and in the Greek version of
them, no very definite meaning can, in general, be attached to the term
"destruction of the world;" for sometimes it would seem almost to imply
the annihilation of our planetary system, and at others a mere
revolution of the surface of the earth.

_Opinions of Aristotle._--From the works now extant of Aristotle, and
from the system of Pythagoras, as above exposed, we might certainly
infer that these philosophers considered the agents of change now
operating in nature, as capable of bringing about in the lapse of ages a
complete revolution; and the Stagyrite even considers occasional
catastrophes, happening at distant intervals of time, as part of the
regular and ordinary course of nature. The deluge of Deucalion, he says,
affected Greece only, and principally the part called Hellas, and it
arose from great inundations of rivers, during a rainy winter. But such
extraordinary winters, he says, though after a certain period they
return, do not always revisit the same places.[20]

Censorinus quotes it as Aristotle's opinion that there were general
inundations of the globe, and that they alternated with conflagrations;
and that the flood constituted the winter of the great year, or
astronomical cycle, while the conflagration, or destruction by fire, is
the summer, or period of greatest heat.[21] If this passage, as Lipsius
supposes, be an amplification, by Censorinus, of what is written in "the
Meteorics," it is a gross misrepresentation of the doctrine of the
Stagyrite, for the general bearing of his reasoning in that treatise
tends clearly in an opposite direction. He refers to many examples of
changes now constantly going on, and insists emphatically on the great
results which they must produce in the lapse of ages. He instances
particular cases of lakes that had dried up, and deserts that had at
length become watered by rivers and fertilized. He points to the growth
of the Nilotic Delta since the time of Homer, to the shallowing of the
Palus Maeotis within sixty years from his own time; and although, in the
same chapter he says nothing of earthquakes, yet in others of the same
treatise he shows himself not unacquainted with their effects.[22] He
alludes, for example, to the upheaving of one of the Eolian islands
previous to a volcanic eruption. "The changes of the earth," he says,
"are so slow in comparison to the duration of our lives, that they are
overlooked ([Greek: lanthanei]): and the migrations of people after
great catastrophes, and their removal to other regions, cause the event
to be forgotten."[23]

When we consider the acquaintance displayed by Aristotle, in his
various works, with the destroying and renovating powers of Nature, the
introductory and concluding passages of the twelfth chapter of his
"Meteorics" are certainly very remarkable. In the first sentence he
says, "The distribution of land and sea in particular regions does not
endure throughout all time, but it becomes sea in those parts where it
was land, and again it becomes land where it was sea: and there is
reason for thinking that these changes take place according to a certain
system, and within a certain period." The concluding observation is as
follows:--"As time never fails, and the universe is eternal, neither the
Tanais, nor the Nile, can have flowed forever. The places where they
rise were once dry, and there is a limit to their operations; but there
is none to time. So also of all other rivers; they spring up, and they
perish; and the sea also continually deserts some lands and invades
others. The same tracts, therefore, of the earth are not, some always
sea, and others always continents, but every thing changes in the course
of time."

It seems, then, that the Greeks had not only derived from preceding
nations, but had also, in some slight degree, deduced from their own
observations, the theory of periodical revolutions in the inorganic
world: there is, however, no ground for imagining that they contemplated
former changes in the races of animals and plants. Even the fact that
marine remains were inclosed in solid rocks, although observed by some,
and even made the groundwork of geological speculation, never stimulated
the industry or guided the inquiries of naturalists. It is not
impossible that the theory of equivocal generation might have engendered
some indifference on this subject, and that a belief in the spontaneous
production of living beings from the earth or corrupt matter, might have
caused the organic world to appear so unstable and fluctuating, that
phenomena indicative of former changes would not awaken intense
curiosity. The Egyptians, it is true, had taught, and the Stoics had
repeated, that the earth had once given birth to some monstrous animals,
which existed no longer; but the prevailing opinion seems to have been,
that after each great catastrophe the same species of animals were
created over again. This tenet is implied in a passage of Seneca, where,
speaking of a future deluge, he says, "Every animal shall be generated
anew, and man free from guilt shall be given to the earth."[24]

An old Arabian version of the doctrine of the successive revolutions of
the globe, translated by Abraham Ecchellensis,[25] seems to form a
singular exception to the general rule, for here we find the idea of
different genera and species having been created. The Gerbanites, a sect
of astronomers who flourished some centuries before the Christian era,
taught as follows:--"That after every period of thirty-six thousand four
hundred and twenty-five years, there were produced a pair of _every_
species of animal, both male and female, from whom animals might be
propagated and inhabit this lower world. But when a circulation of the
heavenly orbs was completed, which is finished in that space of years,
_other genera and species_ of animals are propagated, as also of plants
and other things, and the first order is destroyed, and so it goes on
forever and ever."[26]

_Theory of Strabo._--As we learn much of the tenets of the Egyptian and
Oriental schools in the writings of the Greeks, so, many speculations of
the early Greek authors are made known to us in the works of the
Augustan and later ages. Strabo, in particular, enters largely, in the
second book of his Geography, into the opinions of Eratosthenes and
other Greeks on one of the most difficult problems in geology, viz., by
what causes marine shells came to be plentifully buried in the earth at
such great elevations and distances from the sea.

He notices, amongst others, the explanation of Xanthus the Lydian, who
said that the seas had once been more extensive, and that they had
afterwards been partially dried up, as in his own time many lakes,
rivers, and wells in Asia had failed during a season of drought.
Treating this conjecture with merited disregard, Strabo passes on to the
hypothesis of Strato, the natural philosopher, who had observed that the
quantity of mud brought down by rivers into the Euxine was so great,
that its bed must be gradually raised, while the rivers still continue
to pour in an undiminished quantity of water. He, therefore, conceived
that, originally, when the Euxine was an inland sea, its level had by
this means become so much elevated that it burst its barrier near
Byzantium, and formed a communication with the Propontis; and this
partial drainage, he supposed, had already converted the left side into
marshy ground, and thus, at last, the whole would be choked up with
soil. So, it was argued, the Mediterranean had once opened a passage for
itself by the Columns of Hercules into the Atlantic; and perhaps the
abundance of sea-shells in Africa, near the Temple of Jupiter Ammon,
might also be the deposit of some former inland sea, which had at length
forced a passage and escaped.

But Strabo rejects this theory, as insufficient to account for all the
phenomena, and he proposes one of his own, the profoundness of which
modern geologists are only beginning to appreciate. "It is not," he
says, "because the lands covered by seas were originally at different
altitudes, that the waters have risen, or subsided, or receded from some
parts and inundated others. But the reason is, that the same land is
sometimes raised up and sometimes depressed, and the sea also is
simultaneously raised and depressed, so that it either overflows or
returns into its own place again. We must, therefore, ascribe the cause
to the ground, either to that ground which is under the sea, or to that
which becomes flooded by it, but rather to that which lies beneath the
sea, for this is more movable and, on account of its humidity, can be
altered with greater celerity.[27] "_It is proper_," he observes in
continuation, "_to derive our explanations from things which are
obvious, and in some measure of daily occurrence, such as deluges,
earthquakes, and volcanic eruptions,[28] and sudden swellings of the
land beneath the sea_; for the last raise up the sea also; and when the
same lands subside again, they occasion the sea to be let down. And it
is not merely the small, but the large islands also, and not merely the
islands, but the continents which can be lifted up together with the
sea; and both large and small tracts may subside, for habitations and
cities, like Bure, Bizona, and many others, have been engulphed by
earthquakes."

In another place, this learned geographer, in alluding to the tradition
that Sicily had been separated by a convulsion from Italy, remarks, that
at present the land near the sea in those parts was rarely shaken by
earthquakes, since there were now open orifices whereby fire and ignited
matters, and waters escape; but formerly, when the volcanoes of Etna,
the Lipari Islands, Ischia, and others, were closed up, the imprisoned
fire and wind might have produced far more vehement movements.[29] The
doctrine, therefore, that volcanoes are safety-valves, and that the
subterranean convulsions are probably most violent when first the
volcanic energy shifts itself to a new quarter, is not modern.

We learn from a passage in Strabo,[30] that it was a dogma of the
Gaulish Druids that the universe was immortal, but destined to survive
catastrophes both of fire and water. That this doctrine was communicated
to them from the East, with much of their learning, cannot be doubted.
Caesar, it will be remembered, says that they made use of Greek letters
in arithmetical computations.[31]

_Pliny._--This philosopher had no theoretical opinions of his own
concerning changes of the earth's surface; and in this department, as in
others, he restricted himself to the task of a compiler, without
reasoning on the facts stated by him, or attempting to digest them into
regular order. But his enumeration of the new islands which had been
formed in the Mediterranean, and of other convulsions, shows that the
ancients had not been inattentive observers of the changes which had
taken place within the memory of man.

Such, then, appear to have been the opinions entertained before the
Christian era, concerning the past revolutions of our globe. Although no
particular investigations had been made for the express purpose of
interpreting the monuments of ancient changes, they were too obvious to
be entirely disregarded; and the observation of the present course of
nature presented too many proofs of alterations continually in progress
on the earth to allow philosophers to believe that nature was in a state
of rest, or that the surface had remained, and would continue to remain
unaltered. But they had never compared attentively the results of the
destroying and reproductive operations of modern times with those of
remote eras, nor had they ever entertained so much as a conjecture
concerning the comparative antiquity of the human race, or of living
species of animals and plants, with those belonging to former conditions
of the organic world. They had studied the movements and positions of
the heavenly bodies with laborious industry, and made some progress in
investigating the animal, vegetable, and mineral kingdoms; but the
ancient history of the globe was to them a sealed book, and, although
written in characters of the most striking and imposing kind, they were
unconscious even of its existence.




CHAPTER III.

HISTORY OF THE PROGRESS OF GEOLOGY--_continued_.


  Arabian writers of the tenth century--Avicenna--Omar--Cosmogony
    of the Koran--Kazwini--Early Italian writers--Leonardo da
    Vinci--Fracastoro--Controversy as to the real nature of
    fossils--Attributed to the Mosaic deluge--Palissy--Steno
    --Scilla--Quirini--Boyle--Lister--Leibnitz--Hooke's
    Theory of Elevation by Earthquakes--Of lost species of
    animals--Ray--Physico-theological writers--Woodward's Diluvial
    Theory--Burnet--Whiston--Vallisneri--Lazzaro
    Moro--Generelli--Buffon--His theory condemned by the Sorbonne
    as unorthodox--His declaration--Targioni--Arduino--Michell
    --Catcott--Raspe Fuchsel--Fortis--Testa--Whitehurst--Pallas
    --Saussure.


_Arabian writers._--After the decline of the Roman empire, the
cultivation of physical science was first revived with some success by
the Saracens, about the middle of the eighth century of our era. The
works of the most eminent classic writers were purchased at great
expense from the Christians, and translated into Arabic; and Al Mamun,
son of the famous Harun-al-Rashid, the contemporary of Charlemagne,
received with marks of distinction, at his court at Bagdad, astronomers
and men of learning from different countries. This caliph, and some of
his successors, encountered much opposition and jealousy from the
doctors of the Mahometan law, who wished the Moslems to confine their
studies to the Koran, dreading the effects of the diffusion of a taste
for the physical sciences.[32]

_Avicenna._--Almost all the works of the early Arabian writers are lost.
Amongst those of the tenth century, of which fragments are now extant,
is a short treatise, "On the Formation and Classification of Minerals,"
by Avicenna, a physician, in whose arrangement there is considerable
merit. The second chapter, "On the Cause of Mountains," is remarkable;
for mountains, he says, are formed, some by essential, others by
accidental causes. In illustration of the essential, he instances "a
violent earthquake, by which land is elevated, and becomes a mountain;"
of the accidental, the principal, he says, is excavation by water,
whereby cavities are produced, and adjoining lands made to stand out and
form eminences.[33]

_Omar--Cosmogony of the Koran._--In the same century, also, Omar,
surnamed "El Aalem," or "The Learned," wrote a work on "The Retreat of
the Sea." It appears that on comparing the charts of his own time with
those made by the Indian and Persian astronomers two thousand years
before, he had satisfied himself that important changes had taken place
since the times of history in the form of the coasts of Asia, and that
the extension of the sea had been greater at some former periods. He was
confirmed in this opinion by the numerous salt springs and marshes in
the interior of Asia,--a phenomenon from which Pallas, in more recent
times, has drawn the same inference.

Von Hoff has suggested, with great probability, that the changes in the
level of the Caspian (some of which there is reason to believe have
happened within the historical era), and the geological appearances in
that district, indicating the desertion by that sea of its ancient bed,
had probably led Omar to his theory of a general subsidence. But
whatever may have been the proofs relied on, his system was declared
contradictory to certain passages in the Koran, and he was called upon
publicly to recant his errors; to avoid which persecution he went into
voluntary banishment from Samarkand.[34]

The cosmological opinions expressed in the Koran are few, and merely
introduced incidentally: so that it is not easy to understand how they
could have interfered so seriously with free discussion on the former
changes of the globe. The Prophet declares that the earth was created in
two days, and the mountains were then placed on it; and during these,
and two additional days, the inhabitants of the earth were formed; and
in two more the seven heavens.[35] There is no more detail of
circumstances; and the deluge, which is also mentioned, is discussed
with equal brevity. The waters are represented to have poured out of an
oven; a strange fable, said to be borrowed from the Persian Magi, who
represented them as issuing from the oven of an old woman.[36] All men
were drowned, save Noah and his family; and then God said, "O earth,
swallow up thy waters; and thou, O heaven, withhold thy rain;" and
immediately the waters abated.[37]

We may suppose Omar to have represented the desertion of the land by the
sea to have been gradual, and that his hypothesis required a greater
lapse of ages than was consistent with Moslem orthodoxy; for it is to be
inferred from the Koran, that man and this planet were created at the
same time; and although Mahomet did not limit expressly the antiquity of
the human race, yet he gave an implied sanction to the Mosaic
chronology, by the veneration expressed by him for the Hebrew
Patriarchs.[38]

A manuscript work, entitled the "Wonders of Nature," is preserved in
the Royal Library at Paris, by an Arabian writer, Mohammed Kazwini, who
flourished in the seventh century of the Hegira, or at the close of the
thirteenth century of our era.[39] Besides several curious remarks on
aerolites, earthquakes, and the successive changes of position which the
land and sea have undergone, we meet with the following beautiful
passage which is given as the narrative of Kidhz, an allegorical
personage:--"I passed one day by a very ancient and wonderfully populous
city, and asked one of its inhabitants how long it had been founded. 'It
is indeed a mighty city,' replied he; 'we know not how long it has
existed, and our ancestors were on this subject as ignorant as
ourselves.' Five centuries afterwards, as I passed by the same place, I
could not perceive the slightest vestige of the city. I demanded of a
peasant, who was gathering herbs upon its former site, how long it had
been destroyed. 'In sooth a strange question!' replied he. 'The ground
here has never been different from what you now behold it.'--'Was there
not of old,' said I, 'a splendid city here?'--'Never,' answered he, 'so
far as we have seen, and never did our fathers speak to us of any such.'
On my return there 500 years afterwards, _I found the sea in the same
place_, and on its shores were a party of fishermen, of whom I inquired
how long the land had been covered by the waters? 'Is this a question,'
said they, 'for a man like you? this spot has always been what it is
now.' I again returned, 500 years afterwards, and the sea had
disappeared; I inquired of a man who stood alone upon the spot, how long
ago this change had taken place, and he gave me the same answer as I had
received before. Lastly, on coming back again after an equal lapse of
time, I found there a flourishing city, more populous and more rich in
beautiful buildings, than the city I had seen the first time, and when I
would fain have informed myself concerning its origin, the inhabitants
answered me, 'Its rise is lost in remote antiquity: we are ignorant how
long it has existed, and our fathers were on this subject as ignorant as
ourselves.'"

_Early Italian writers._--It was not till the earlier part of the
sixteenth century that geological phenomena began to attract the
attention of the Christian nations. At that period a very animated
controversy sprang up in Italy, concerning the true nature and origin of
marine shells, and other organized fossils, found abundantly in the
strata of the peninsula. The celebrated painter Leonardo da Vinci, who
in his youth had planned and executed some navigable canals in the north
of Italy, was one of the first who applied sound reasoning to these
subjects. The mud of rivers, he said, had covered and penetrated into
the interior of fossil shells at a time when these were still at the
bottom of the sea near the coast. "They tell us that these shells were
formed in the hills by the influence of the stars; but I ask where in
the hills are the stars now forming shells of distinct ages and species?
and how can the stars explain the origin of gravel, occurring at
different heights and composed of pebbles rounded as if by the motion of
running water; or in what manner can such a cause account for the
petrifaction in the same places of various leaves, sea-weeds, and
marine-crabs?"[40]

The excavations made in 1517, for repairing the city of Verona, brought
to light a multitude of curious petrifactions, and furnished matter for
speculation to different authors, and among the rest to Fracastoro,[41]
who declared his opinion, that fossil shells had all belonged to living
animals, which had formerly lived and multiplied where there exuviae are
now found. He exposed the absurdity of having recourse to a certain
"plastic force," which it was said had power to fashion stones into
organic forms; and with no less cogent arguments, demonstrated the
futility of attributing the situation of the shells in question to the
Mosaic deluge, a theory obstinately defended by some. That inundation,
he observed, was too transient; it consisted principally of fluviatile
waters; and if it had transported shells to great distances, must have
strewed them over the surface, not buried them at vast depths in the
interior of mountains. His clear exposition of the evidence would have
terminated the discussion forever, if the passions of mankind had not
been enlisted in the dispute; and even though doubts should for a time
have remained in some minds, they would speedily have been removed by
the fresh information obtained almost immediately afterwards, respecting
the structure of fossil remains, and of their living analogues.

But the clear and philosophical views of Fracastoro were disregarded,
and the talent and argumentative powers of the learned were doomed for
three centuries to be wasted in the discussion of these two simple and
preliminary questions: first, whether fossil remains had ever belonged
to living creatures; and, secondly, whether, if this be admitted, all
the phenomena could not be explained by the deluge of Noah. It had been
the general belief of the Christian world down to the period now under
consideration, that the origin of this planet was not more remote than a
few thousand years; and that since the creation the deluge was the only
great catastrophe by which considerable change had been wrought on the
earth's surface. On the other hand, the opinion was scarcely less
general, that the final dissolution of our system was an event to be
looked for at no distant period. The era, it is true, of the expected
millennium had passed away; and for five hundred years after the fatal
hour when the annihilation of the planet had been looked for, the monks
remained in undisturbed enjoyment of rich grants of land bequeathed to
them by pious donors, who, in the preamble of deeds beginning
"appropinquante mundi termino"----"appropinquante magno judicii die,"
left lasting monuments of the popular delusion.[42]

But although in the sixteenth century it had become necessary to
interpret certain prophecies respecting the millennium more liberally,
and to assign a more distant date to the future conflagration of the
world, we find, in the speculations of the early geologists, perpetual
allusion to such an approaching catastrophe; while in all that regarded
the antiquity of the earth, no modification whatever of the opinions of
the dark ages had been effected. Considerable alarm was at first excited
when the attempt was made to invalidate, by physical proofs, an article
of faith so generally received; but there was sufficient spirit of
toleration and candor amongst the Italian ecclesiastics, to allow the
subject to be canvassed with much freedom. They even entered warmly into
the controversy themselves, often favoring different sides of the
question; and however much we may deplore the loss of time and labor
devoted to the defence of untenable positions, it must be conceded that
they displayed far less polemic bitterness than certain writers who
followed them "beyond the Alps," two centuries and a half later.


CONTROVERSY AS TO THE REAL NATURE OF FOSSIL ORGANIC REMAINS.

_Mattioli--Falloppio._--The system of scholastic disputations,
encouraged in the universities of the middle ages, had unfortunately
trained men to habits of indefinite argumentation; and they often
preferred absurd and extravagant propositions, because greater skill was
required to maintain them; the end and object of these intellectual
combats being victory, and not truth. No theory could be so far-fetched
or fantastical as not to attract some followers, provided it fell in
with popular notions; and as cosmogonists were not at all restricted, in
building their systems, to the agency of known causes, the opponents of
Fracastoro met his arguments by feigning imaginary causes, which
differed from each other rather in name than in substance. Andrea
Mattioli, for instance, an eminent botanist, the illustrator of
Dioscorides, embraced the notion of Agricola, a skilful German miner,
that a certain "materia pinguis," or "fatty matter," set into
fermentation by heat, gave birth to fossil organic shapes. Yet Mattioli
had come to the conclusion, from his own observations, that porous
bodies, such as bones and shells, might be converted into stone, as
being permeable to what he termed the "lapidifying juice." In like
manner, Falloppio of Padua conceived that petrified shells were
generated by fermentation in the spots where they are found, or that
they had in some cases acquired their form from "the tumultuous
movements of terrestrial exhalations." Although celebrated as a
professor of anatomy, he taught that certain tusks of elephants, dug up
in his time in Apulia, were mere earthy concretions; and, consistently
with these principles, he even went so far as to consider it probable,
that the vases of Monte Testaceo at Rome were natural impressions
stamped in the soil.[43] In the same spirit, Mercati, who published, in
1574, faithful figures of the fossil shells preserved by Pope Sixtus V.
in the Museum of the Vatican, expressed an opinion that they were mere
stones, which had assumed their peculiar configuration from the
influence of the heavenly bodies; and Olivi of Cremona, who described
the fossil remains of a rich museum at Verona, was satisfied with
considering them as mere "sports of nature."

Some of the fanciful notions of those times were deemed less
unreasonable, as being somewhat in harmony with the Aristotelian theory
of spontaneous generation, then taught in all the schools.[44] For men
who had been taught in early youth, that a large proportion of living
animals and plants was formed from the fortuitous concourse of atoms, or
had sprung from the corruption of organic matter, might easily persuade
themselves that organic shapes, often imperfectly preserved in the
interior of solid rocks, owed their existence to causes equally obscure
and mysterious.

_Cardano_, 1552.--But there were not wanting some who, during the
progress of this century, expressed more sound and sober opinions. The
title of a work of Cardano's, published in 1552, "De Subtilitate"
(corresponding to what would now be called Transcendental Philosophy),
would lead us to expect, in the chapter on minerals, many far-fetched
theories characteristic of that age; but when treating of petrified
shells, he decided that they clearly indicated the former sojourn of the
sea upon the mountains.[45]

_Cesalpino--Majoli_, 1597.--Cesalpino, a celebrated botanist, conceived
that fossil shells had been left on the land by the retiring sea, and
had concreted into stone during the consolidation of the soil;[46] and
in the following year (1597), Simeone Majoli[47] went still farther;
and, coinciding for the most part with the views of Cesalpino, suggested
that the shells and submarine matter of the Veronese, and other
districts, might have been cast up upon the land by volcanic explosions,
like those which gave rise, in 1538, to Monte Nuovo, near Puzzuoli. This
hint seems to have been the first imperfect attempt to connect the
position of fossil shells with the agency of volcanoes, a system
afterwards more fully developed by Hooke, Lazzaro Moro, Hutton, and
other writers.

Two years afterwards, Imperati advocated the animal origin of fossilized
shells, yet admitted that stones could vegetate by force of "an internal
principle;" and, as evidence of this, he referred to the teeth of fish
and spines of echini found petrified.[48]

_Palissy_, 1580.--Palissy, a French writer on "The Origin of Springs
from Rain-water," and of other scientific works, undertook, in 1580, to
combat the notions of many of his contemporaries in Italy, that
petrified shells had all been deposited by the universal deluge. "He was
the first," said Fontenelle, when, in the French Academy, he pronounced
his eulogy, nearly a century and a half later, "who dared assert," in
Paris, that fossil remains of testacea and fish had once belonged to
marine animals.

_Fabio Colonna._--To enumerate the multitude of Italian writers, who
advanced various hypotheses, all equally fantastical, in the early part
of the seventeenth century, would be unprofitably tedious; but Fabio
Colonna deserves to be distinguished; for, although he gave way to the
dogma, that all fossil remains were to be referred to the deluge of
Noah, he resisted the absurd theory of Stelluti, who taught that fossil
wood and ammonites were mere clay, altered into such forms by
sulphureous waters and subterranean heat; and he pointed out the
different states of shells buried in the strata, distinguishing between,
first, the mere mould or impression; second, the cast or nucleus; and,
thirdly, the remains of the shell itself. He had also the merit of being
the first to point out that some of the fossils had belonged to marine
and some to terrestrial testacea.[49]

_Steno_, 1669.--But the most remarkable work of that period was
published by Steno, a Dane, once professor of anatomy at Padua, and who
afterwards resided many years at the court of the Grand Duke of Tuscany.
His treatise bears the quaint title of "De Solido intra Solidum
naturaltier contento (1669)," by which the author intended to express,
"On Gems, Crystals, and organic Petrifactions inclosed within solid
Rocks." This work attests the priority of the Italian school in
geological research; exemplifying at the same time the powerful
obstacles opposed, in that age, to the general reception of enlarged
views in the science. It was still a favorite dogma, that the fossil
remains of shells and marine creatures were not of animal origin; an
opinion adhered to by many from their extreme reluctance to believe,
that the earth could have been inhabited by living beings before a great
part of the existing mountains were formed. In reference to this
controversy, Steno had dissected a shark recently taken from the
Mediterranean, and had demonstrated that its teeth and bones were
identical with many fossils found in Tuscany. He had also compared the
shells discovered in the Italian strata with living species, pointed out
their resemblance, and traced the various gradations from shells merely
calcined, or which had only lost their animal gluten, to those
petrifactions in which there was a perfect substitution of stony matter.
In his division of mineral masses, he insisted on the secondary origin
of those deposits in which the spoils of animals or fragments of older
rocks were inclosed. He distinguished between marine formations and
those of a fluviatile character, the last containing reeds, grasses,
or the trunks and branches of trees. He argued in favor of the original
horizontality of sedimentary deposits, attributing their present
inclined and vertical position sometimes to the escape of subterranean
vapors heaving the crust of the earth from below upwards, and sometimes
to the falling in of masses overlying subterranean cavities.

He declared that he had obtained proof that Tuscany must successively
have acquired six distinct configurations, having been twice covered by
water, twice laid dry with a level, and twice with an irregular and
uneven surface.[50] He displayed great anxiety to reconcile his new
views with Scripture, for which purpose he pointed to certain rocks as
having been formed before the existence of animals and plants: selecting
unfortunately as examples certain formations of limestone and sandstone
in his own country, now known to contain, though sparingly, the remains
of animals and plants,--strata which do not even rank as the oldest part
of our secondary series. Steno suggested that Moses, when speaking of
the loftiest mountains as having been covered by the deluge, meant
merely the loftiest of the hills then existing, which may not have been
very high. The diluvian waters, he supposed, may have issued from the
interior of the earth into which they had retired, when in the beginning
the land was separated from the sea. These, and other hypotheses on the
same subject, are not calculated to enhance the value of the treatise,
and could scarcely fail to detract from the authority of those opinions
which were sound and legitimate deductions from fact and observation.
They have served, nevertheless, as the germs of many popular theories of
later times, and in an expanded form have been put forth as original
inventions by some of our contemporaries.

_Scilla_, 1670.--Scilla, a Sicilian painter, published, in 1670, a
treatise, in Latin, on the fossils of Calabria, illustrated by good
engravings. This work proves the continued ascendancy of dogmas often
refuted; for we find the wit and eloquence of the author chiefly
directed against the obstinate incredulity of naturalists as to the
organic nature of fossil shells.[51] Like many eminent naturalists of
his day, Scilla gave way to the popular persuasion, that all fossil
shells were the effects and proofs of the Mosaic deluge. It may be
doubted whether he was perfectly sincere, and some of his contemporaries
who took the same course were certainly not so. But so eager were they
to root out what they justly considered an absurd prejudice respecting
the nature of organized fossils, that they seem to have been ready to
make any concessions, in order to establish this preliminary point. Such
a compromising policy was short-sighted, since it was to little purpose
that the nature of the documents should at length be correctly
understood, if men were to be prevented from deducing fair conclusions
from them.

_Diluvial Theory._--The theologians who now entered the field in Italy,
Germany, France, and England, were innumerable; and henceforward, they
who refused to subscribe to the position, that all marine organic
remains were proofs of the Mosaic deluge, were exposed to the imputation
of disbelieving the whole of the sacred writings. Scarcely any step had
been made in approximating to sound theories since the time of
Fracastoro, more than a hundred years having been lost, in writing down
the dogma that organized fossils were mere sports of nature. An
additional period of a century and a half was now destined to be
consumed in exploding the hypothesis, that organized fossils had all
been buried in the solid strata by Noah's flood. Never did a theoretical
fallacy, in any branch of science, interfere more seriously with
accurate observation and the systematic classification of facts. In
recent times, we may attribute our rapid progress chiefly to the careful
determination of the order of succession in mineral masses, by means of
their different organic contents, and their regular superposition. But
the old diluvialists were induced by their system to confound all the
groups of strata together instead of discriminating,--to refer all
appearances to one cause and to one brief period, not to a variety of
causes acting throughout a long succession of epochs. They saw the
phenomena only as they desired to see them, sometimes misrepresenting
facts, and at other times deducing false conclusions from correct data.
Under the influence of such prejudices, three centuries were of as
little avail as a few years in our own times, when we are no longer
required to propel the vessel against the force of an adverse current.

It may be well, therefore, to forewarn the reader, that in tracing the
history of geology from the close of the seventeenth to the end of the
eighteenth century, he must expect to be occupied with accounts of the
retardation, as well as of the advance, of the science. It will be
necessary to point out the frequent revival of exploded errors, and the
relapse from sound to the most absurd opinions; and to dwell on futile
reasoning and visionary hypothesis, because some of the most extravagant
systems were invented or controverted by men of acknowledged talent. In
short, a sketch of the progress of geology is the history of a constant
and violent struggle of new opinions against doctrines sanctioned by the
implicit faith of many generations, and supposed to rest on scriptural
authority. The inquiry, therefore, although highly interesting to one
who studies the philosophy of the human mind, is too often barren of
instruction to him who searches for truths in physical science.

_Quirini_, 1676.--Quirini, in 1676,[52] contended, in opposition to
Scilla, that the diluvian waters could not have conveyed heavy bodies to
the summit of mountains, since the agitation of the sea never (as Boyle
had demonstrated) extended to great depths;[53] and still less could
the testacea, as some pretended, have lived in these diluvian waters;
for "the duration of the flood was brief, and _the heavy rains must have
destroyed the saltness of the sea!_" He was the first writer who
ventured to maintain that the universality of the Mosaic cataclysm ought
not to be insisted upon. As to the nature of petrified shells, he
conceived that as earthy particles united in the sea to form the shells
of mollusca, the same crystallizing process might be effected on the
land; and that, in the latter case, the germs of the animals might have
been disseminated through the substance of the rocks, and afterwards
developed by virtue of humidity. Visionary as was this doctrine, it
gained many proselytes even amongst the more sober reasoners of Italy
and Germany; for it conceded that the position of fossil bodies could
not be accounted for by the diluvial theory.

_Plot--Lister_, 1678.--In the mean time, the doctrine that fossil shells
had never belonged to real animals maintained its ground in England,
where the agitation of the question began at a much later period. Dr.
Plot, in his "Natural History of Oxfordshire" (1677), attributed to a
"plastic virtue latent in the earth" the origin of fossil shells and
fishes; and Lister, to his accurate account of British shells, in 1678,
added the fossil species, under the appellation of _turbinated and
bivalve stones_. "Either," said he, "these were terriginous, or, if
otherwise, the animals they so exactly represent _have become extinct_."
This writer appears to have been the first who was aware of the
continuity over large districts of the principal groups of strata in the
British series, and who proposed the construction of regular geological
maps.[54]

_Leibnitz_, 1680.--The great mathematician Leibnitz published his
"Protogoea" in 1680. He imagined this planet to have been originally a
burning luminous mass, which ever since its creation has been undergoing
refrigeration. When the outer crust had cooled down sufficiently to
allow the vapors to be condensed, they fell, and formed a universal
ocean, covering the loftiest mountains, and investing the whole globe.
The crust, as it consolidated from a state of fusion, assumed a
vesicular and cavernous structure; and being rent in some places,
allowed the water to rush into the subterranean hollows, whereby the
level of the primeval ocean was lowered. The breaking in of these vast
caverns is supposed to have given rise to the dislocated and deranged
position of the strata "which Steno had described," and the same
disruptions communicated violent movements to the incumbent waters,
whence great inundations ensued. The waters, after they had been thus
agitated, deposited their sedimentary matter during intervals of
quiescence, and hence the various stony and earthy strata. "We may
recognize, therefore," says Leibnitz, "a double origin of primitive
masses, the one by refrigeration from igneous fusion, the other by
concretion from aqueous solution."[55] By the repetition of similar
causes (the disruption of the crust and consequent floods), alternations
of new strata were produced, until at length these causes were reduced
to a condition of quiescent equilibrium, and a more permanent state of
things was established.[56]

_Hooke_, 1688.--The "Posthumous Works of Robert Hooke, M. D.," well
known as a great mathematician and natural philosopher, appeared in
1705, containing "A Discourse of Earthquakes," which, we are informed by
his editor, was written in 1668, but revised at subsequent periods.[57]
Hooke frequently refers to the best Italian and English authors who
wrote before his time on geological subjects; but there are no passages
in his works implying that he participated in the enlarged views of
Steno and Lister, or of his contemporary, Woodward, in regard to the
geographical extent of certain groups of strata. His treatise, however,
is the most philosophical production of that age, in regard to the
causes of former changes in the organic and inorganic kingdoms of
nature.

"However trivial a thing," he says, "a rotten shell may appear to some,
yet these monuments of nature are more certain tokens of antiquity than
coins or medals, since the best of those may be counterfeited or made by
art and design, as may also books, manuscripts, and inscriptions, as all
the learned are now sufficiently satisfied has often been actually
practised," &c.; "and though it must be granted that it is very
difficult to read them (the records of nature) and _to raise a
chronology out of them_, and to state the intervals of the time wherein
such or such catastrophes and mutations have happened, yet it is not
impossible."[58]

Respecting the extinction of species, Hooke was aware that the fossil
ammonites, nautili, and many other shells and fossil skeletons found in
England, were of different species from any then known; but he doubted
whether the species had become extinct, observing that the knowledge of
naturalists of all the marine species, especially those inhabiting the
deep sea, was very deficient. In some parts of his writings, however,
he leans to the opinion that species had been lost; and in speculating
on this subject, he even suggests that there might be some connection
between the disappearance of certain kinds of animals and plants, and
the changes wrought by earthquakes in former ages. Some species, he
observes, with great sagacity, are "_peculiar to certain places_, and
not to be found elsewhere. If, then, such a place had been swallowed up,
it is not improbable but that those animate beings may have been
destroyed with it; and this may be true both of aerial and aquatic
animals; for those animated bodies, whether vegetables or animals, which
were naturally nourished or refreshed by the air, would be destroyed by
the water," &c.[59] Turtles, he adds, and such large ammonites as are
found in Portland, seem to have been the productions of hotter
countries; and it is necessary to suppose that England once lay under
the sea within the torrid zone! To explain this and similar phenomena,
he indulges in a variety of speculations concerning changes in the
position of the axis of the earth's rotation, "a shifting of the earth's
centre of gravity, analogous to the revolutions of the magnetic pole,"
&c. None of these conjectures, however, are proposed dogmatically, but
rather in the hope of promoting fresh inquiries and experiments.

In opposition to the prejudices of his age, we find him arguing against
the idea that nature had formed fossil bodies "for no other end than to
play the mimic in the mineral kingdom;"--maintaining that figured stones
were "really the several bodies they represent, or the mouldings of them
petrified," and not, as some have imagined, 'a lusus naturae,' sporting
herself in the needless formation of useless beings."[60]

It was objected to Hooke, that his doctrine of the extinction of species
derogated from the wisdom and power of the omnipotent Creator; but he
answered, that, as individuals die, there may be some termination to the
duration of a species; and his opinions, he declared, were not repugnant
to Holy Writ: for the Scriptures taught that our system was
degenerating, and tending to its final dissolution; "and as, when that
shall happen, all the species will be lost, why not some at one time and
some at another?"[61]

But his principal object was to account for the manner in which shells
had been conveyed into the higher parts of "the Alps, Apennines, and
Pyrenean hills, and the interior of continents in general." These and
other appearances, he said, might have been brought about by
earthquakes, "which have turned plains into mountains, and mountains
into plains, seas into land, and land into seas, made rivers where there
were none before, and swallowed up others that formerly were, &c., &c.;
and which, since the creation of the world, have wrought many great
changes on the superficial parts of the earth, and have been the
instruments of placing shells, bones, plants, fishes, and the like, in
those places where, with much astonishment, we find them."[62] This
doctrine, it is true, had been laid down in terms almost equally
explicit by Strabo, to explain the occurrence of fossil shells in the
interior of continents, and to that geographer, and other writers of
antiquity, Hooke frequently refers; but the revival and development of
the system was an important step in the progress of modern science.

Hooke enumerated all the examples known to him of subterranean
disturbance, from "the sad catastrophe of Sodom and Gomorrah," down to
the Chilian earthquake of 1646. The elevating of the bottom of the sea,
the sinking and submersion of the land, and most of the inequalities of
the earth's surface, might, he said, be accounted for by the agency of
these subterranean causes. He mentions that the coast near Naples _was
raised during the eruption of Monte Nuovo_; and that, in 1591, land rose
in the island of St. Michael, during an eruption: and although it would
be more difficult, he says, to prove, he does not doubt but that there
had been as many earthquakes in the parts of the earth under the ocean,
as in the parts of the dry land; in confirmation of which, he mentions
the immeasurable depth of the sea near some volcanoes. To attest the
extent of simultaneous subterranean movements, he refers to an
earthquake in the West Indies, in the year 1690, where the space of
earth raised, or "struck upwards," by the shock, exceeded, he affirms,
the length of the Alps and Pyrenees.

_Hooke's diluvial Theory._--As Hooke declared the favorite hypothesis of
the day, "that marine fossil bodies were to be referred to Noah's
flood," to be wholly untenable, he appears to have felt himself called
upon to substitute a diluvial theory of his own, and thus he became
involved in countless difficulties and contradictions. "During the great
catastrophe," he said, "there might have been a changing of that part
which was before dry land into sea by sinking, and of that which was sea
into dry land by raising, and marine bodies might have been buried in
sediment beneath the ocean, in the interval between the creation and the
deluge."[63] Then follows a disquisition on the separation of the land
from the waters, mentioned in Genesis; during which operation some
places of the shell of the earth were forced outwards, and others
pressed downwards or inwards, &c. His diluvial hypothesis very much
resembled that of Steno, and was entirely opposed to the fundamental
principles professed by him, that he would explain the former changes
of the earth _in a more natural manner_ than others had done. When, in
despite of this declaration, he required a former "crisis of nature,"
and taught that earthquakes had become debilitated, and that the Alps,
Andes, and other chains, had been lifted up in a few months, he was
compelled to assume so rapid a rate of change, that his machinery
appeared scarcely less extravagant than that of his most fanciful
predecessors. For this reason, perhaps, his whole theory of earthquakes
met with undeserved neglect.

_Ray_, 1692.--One of his contemporaries, the celebrated naturalist, Ray,
participated in the same desire to explain geological phenomena by
reference to causes less hypothetical than those usually resorted
to.[64] In his essay on "Chaos and Creation," he proposed a system,
agreeing in its outline, and in many of its details, with that of Hooke;
but his knowledge of natural history enabled him to elucidate the
subject with various original observations. Earthquakes, he suggested,
might have been the second causes employed at the creation, in
separating the land from the waters, and in gathering the waters
together into one place. He mentions, like Hooke, the earthquake of
1646, which had violently shaken the Andes for some hundreds of leagues,
and made many alterations therein. In assigning a cause for the general
deluge, he preferred a change in the earth's centre of gravity to the
introduction of earthquakes. Some unknown cause, he said, might have
forced the subterranean waters outwards, as was, perhaps, indicated by
"the breaking up of the fountains of the great deep."

Ray was one of the first of our writers who enlarged upon the effects of
running water upon the land, and of the encroachment of the sea upon the
shores. So important did he consider the agency of these causes, that he
saw in them an indication of the tendency of our system to its final
dissolution; and he wondered why the earth did not proceed more rapidly
towards a general submersion beneath the sea, when so much matter was
carried down by rivers, or undermined in the sea-cliffs. We perceive
clearly from his writings, that the gradual decline of our system, and
its future consummation by fire, was held to be as necessary an article
of faith by the orthodox, as was the recent origin of our planet. His
discourses, like those of Hooke, are highly interesting, as attesting
the familiar association in the minds of philosophers, in the age of
Newton, of questions in physics and divinity. Ray gave an unequivocal
proof of the sincerity of his mind, by sacrificing his preferment in the
church, rather than take an oath against the Covenanters, which he could
not reconcile with his conscience. His reputation, moreover, in the
scientific world placed him high above the temptation of courting
popularity, by pandering to the physico-theological taste of his age. It
is, therefore, curious to meet with so many citations from the
Christian fathers and prophets in his essays on physical science--to
find him in one page proceeding, by the strict rules of induction, to
explain the former changes of the globe, and in the next gravely
entertaining the question, whether the sun and stars, and the whole
heavens, shall be annihilated, together with the earth, at the era of
the grand conflagration.

_Woodward, 1695._--Among the contemporaries of Hooke and Ray, Woodward,
a professor of medicine, had acquired the most extensive information
respecting the geological structure of the crust of the earth. He had
examined many parts of the British strata with minute attention; and his
systematic collection of specimens, bequeathed to the University of
Cambridge, and still preserved there as arranged by him, shows how far
he had advanced in ascertaining the order of superposition. From the
great number of facts collected by him, we might have expected his
theoretical views to be more sound and enlarged than those of his
contemporaries; but in his anxiety to accommodate all observed phenomena
to the scriptural account of the Creation and Deluge, he arrived at most
erroneous results. He conceived "the whole terrestrial globe to have
been taken to pieces and dissolved at the flood, and the strata to have
settled down from this promiscuous mass as any earthy sediment from a
fluid."[65] In corroboration of these views he insisted upon the fact,
that "marine bodies are lodged in the strata according to the order of
their gravity, the heavier shells in stone, the lighter in chalk, and so
of the rest."[66] Ray immediately exposed the unfounded nature of this
assertion, remarking truly that fossil bodies "are often mingled, heavy
with light, in the same stratum;" and he even went so far as to say,
that Woodward "must have invented the phenomena for the sake of
confirming his bold and strange hypothesis"[67]--a strong expression
from the pen of a contemporary.

_Burnet, 1690._--At the same time Burnet published his "Theory of the
Earth."[68] The title is most characteristic of the age,--"The Sacred
Theory of the Earth; containing an Account of the Original of the Earth,
and of all the general Changes which it hath already undergone, or is to
undergo, till the Consummation of all Things." Even Milton had scarcely
ventured in his poem to indulge his imagination so freely in painting
scenes of the Creation and Deluge, Paradise and Chaos. He explained why
the primeval earth enjoyed a perpetual spring before the flood! showed
how the crust of the globe was fissured by "the sun's rays," so that it
burst, and thus the diluvial waters were let loose from a supposed
central abyss. Not satisfied with these themes, he derived from the
books of the inspired writers, and even from heathen authorities,
prophetic views of the future revolutions of the globe, gave a most
terrific description of the general conflagration, and proved that a new
heaven and a new earth will rise out of a _second chaos_--after which
will follow the blessed millennium.

The reader should be informed, that, according to the opinion of many
respectable writers of that age, there was good scriptural ground for
presuming that the garden bestowed upon our first parents was not on the
earth itself, but above the clouds, in the middle region between our
planet and the moon. Burnet approaches with becoming gravity the
discussion of so important a topic. He was willing to concede that the
geographical position of Paradise was not in Mesopotamia, yet he
maintained that it was upon the earth, and in the southern hemisphere,
near the equinoctial line. Butler selected this conceit as a fair mark
for his satire, when, amongst the numerous accomplishments of Hudibras,
he says,--


  "He knew the seat of Paradise,
   Could tell in what degree it lies;
   And, as he was disposed, could prove it
   Below the moon, or else above it."


Yet the same monarch, who is said never to have slept without Butler's
poem under his pillow, was so great an admirer and patron of Burnet's
book, that he ordered it to be translated from the Latin into English.
The style of the "Sacred Theory" was eloquent, and the book displayed
powers of invention of no ordinary stamp. It was, in fact, a fine
historical romance, as Buffon afterwards declared; but it was treated as
a work of profound science in the time of its author, and was
panegyrized by Addison in a Latin ode, while Steele praised it in the
"Spectator."

_Whiston, 1696._--Another production of the same school, and equally
characteristic of the time, was that of Whiston, entitled, "A New Theory
of the Earth; wherein the Creation of the world in Six Days, the
Universal Deluge, and the General Conflagration, as laid down in the
Holy Scriptures, are shown to be perfectly agreeable to Reason and
Philosophy." He was at first a follower of Burnet; but his faith in the
infallibility of that writer was shaken by the declared opinion of
Newton, that there was every presumption in astronomy against any former
change in the inclination of the earth's axis. This was a leading dogma
in Burnet's system, though not original, for it was borrowed from an
Italian, Alessandro degli Alessandri, who had suggested it in the
beginning of the fifteenth century, to account for the former occupation
of the present continents by the sea. La Place has since strengthened
the arguments of Newton, against the probability of any former
revolution of this kind.

The remarkable comet of 1680 was fresh in the memory of every one when
Whiston first began his cosmological studies; and the principal novelty
of his speculations consisted in attributing the deluge to the near
approach to the earth of one of these erratic bodies. Having ascribed an
increase of the waters to this source, he adopted Woodward's theory,
supposing all stratified deposits to have resulted from the "chaotic
sediment of the flood." Whiston was one of the first who ventured to
propose that the text of Genesis should be interpreted differently from
its ordinary acceptation, so that the doctrine of the earth having
existed long previous to the creation of man might no longer be regarded
as unorthodox. He had the art to throw an air of plausibility over the
most improbable parts of his theory, and seemed to be proceeding in the
most sober manner, and, by the aid of mathematical demonstration, to the
establishment of his various propositions. Locke pronounced a panegyric
on his theory, commending him for having explained so many wonderful and
before inexplicable things. His book, as well as Burnet's, was attacked
and refuted by Keill.[69] Like all who introduced purely hypothetical
causes to account for natural phenomena, Whiston retarded the progress
of truth, diverting men from the investigation of the laws of sublunary
nature, and inducing them to waste time in speculations on the power of
comets to drag the waters of the ocean over the land--on the
condensation of the vapors of their tails into water, and other matters
equally edifying.

_Hutchinson, 1724._--John Hutchinson, who had been employed by Woodward
in making his collection of fossils, published afterwards, in 1724, the
first part of his "Moses's Principia," wherein he ridiculed Woodward's
hypothesis. He and his numerous followers were accustomed to declaim
loudly against human learning; and they maintained that the Hebrew
Scriptures, when rightly translated, comprised a perfect system of
natural philosophy, for which reason they objected to the Newtonian
theory of gravitation.

_Celsius._--Andrea Celsius, the Swedish astronomer, published about this
time his remarks on the gradual diminution and sinking of the waters in
the Baltic, to which I shall have occasion to advert more particularly
in the sequel (ch. 29).

_Scheuchzer, 1708._--In Germany, in the mean time, Scheuchzer published
his "Complaint and Vindication of the Fishes" (1708), "Piscium Querelae
et Vindiciae," a work of zoological merit, in which he gave some good
plates and descriptions of fossil fish. Among other conclusions he
labored to prove that the earth had been remodelled at the deluge.
Pluche, also, in 1732, wrote to the same effect; while Holbach, in 1753,
after considering the various attempts to refer all the ancient
formations to the flood of Noah, exposed the inadequacy of this cause.

_Italian Geologists--Vallisneri._--I return with pleasure to the
geologists of Italy, who preceded, as has been already shown, the
naturalists of other countries in their investigations into the ancient
history of the earth, and who still maintained a decided pre-eminence.
They refuted and ridiculed the physico-theological systems of Burnet,
Whiston, and Woodward;[70] while Vallisneri,[71] in his comments on the
Woodwardian theory, remarked how much the interests of religion, as well
as those of sound philosophy, had suffered by perpetually mixing up the
sacred writings with questions in physical science. The works of this
author were rich in original observations. He attempted the first
general sketch of the marine deposits of Italy, their geographical
extent, and most characteristic organic remains. In his treatise "On the
Origin of Springs," he explained their dependence on the order, and
often on the dislocations, of the strata, and reasoned philosophically
against the opinions of those who regarded the disordered state of the
earth's crust as exhibiting signs of the wrath of God for the sins of
man. He found himself under the necessity of contending, in his
preliminary chapter, against St. Jerome, and four other principal
interpreters of Scripture, besides several professors of divinity, "that
springs did not flow by subterranean siphons and cavities from the sea
upwards, losing their saltness in the passage," for this theory had been
made to rest on the infallible testimony of Holy Writ.

Although reluctant to generalize on the rich materials accumulated in
his travels, Vallisneri had been so much struck with the remarkable
continuity of the more recent marine strata, from one end of Italy to
the other, that he came to the conclusion that the ocean formerly
extended over the whole earth, and after abiding there for a long time,
had gradually subsided. This opinion, however untenable, was a great
step beyond Woodward's diluvian hypothesis, against which Vallisneri,
and after him all the Tuscan geologists, uniformly contended, while it
was warmly supported by the members of the Institute of Bologna.[72]

Among others of that day, Spada, a priest of Grezzana, in 1737, wrote to
prove that the petrified marine bodies near Verona were not
diluvian.[73] Mattani drew a similar inference from the shells of
Volterra and other places; while Costantini, on the other hand, whose
observations on the valley of the Brenta and other districts were not
without value, undertook to vindicate the truth of the deluge, as also
to prove that Italy had been peopled by the descendants of Japhet.[74]

_Moro_, 1740.--Lazzaro Moro, in his work (published in 1740) "On the
Marine Bodies which are found in the Mountains,"[75] attempted to apply
the theory of earthquakes, as expounded by Strabo, Pliny, and other
ancient authors, with whom he was familiar, to the geological phenomena
described by Vallisneri.[76] His attention was awakened to the
elevating power of subterranean forces by a remarkable phenomenon which
happened in his own time, and which had also been noticed by Vallisneri
in his letters. A new island rose in 1707 from deep water in the Gulf of
Santorin, in the Mediterranean, during continued shocks of an
earthquake, and, increasing rapidly in size, grew in less than a month
to be half a mile in circumference, and about twenty-five feet above
high-water mark. It was soon afterwards covered by volcanic ejections,
but, when first examined, it was found to be a white rock, bearing on
its surface living oysters and crustacea. In order to ridicule the
various theories then in vogue, Moro ingeniously supposes the arrival on
this new island of a party of naturalists ignorant of its recent origin.
One immediately points to the marine shells, as proofs of the universal
deluge; another argues that they demonstrate the former residence of the
sea upon the mountains; a third dismisses them as mere _sports of
nature_; while a fourth affirms that they were born and nourished within
the rock in ancient caverns, into which salt water had been raised in
the shape of vapor by the action of subterranean heat.

Moro pointed with great judgment to the _faults_ and dislocations of the
strata described by Vallisneri, in the Alps and other chains, in
confirmation of his doctrine, that the continents had been heaved up by
subterranean movements. He objected, on solid grounds, to the hypothesis
of Burnet and of Woodward; yet he ventured so far to disregard the
protest of Vallisneri, as to undertake the adaptation of every part of
his own system to the Mosaic account of the creation. On the third day,
he said, the globe was everywhere covered to the same depth by fresh
water; and when it pleased the Supreme Being that the dry land should
appear, volcanic explosions broke up the smooth and regular surface of
the earth composed of primary rocks. These rose in mountain masses above
the waves, and allowed melted metals and salts to ascend through
fissures. The sea gradually acquired its saltness from volcanic
exhalations, and, while it became more circumscribed in area, increased
in depth. Sand and ashes ejected by volcanoes were regularly disposed
along the bottom of the ocean, and formed the secondary strata, which in
their turn were lifted up by earthquakes. We need not follow this author
in tracing the progress of the creation of vegetables and animals on the
other days of creation; but, upon the whole, it may be remarked, that
few of the old cosmological theories had been conceived with so little
violation of known analogies.

_Generelli's illustrations of Moro_, 1749.--The style of Moro was
extremely prolix, and, like Hutton, who, at a later period, advanced
many of the same views, he stood in need of an illustrator. The Scotch
geologist was hardly more fortunate in the advocacy of Playfair, than
was Moro in numbering amongst his admirers Cirillo Generelli, who, nine
years afterwards, delivered at a sitting of Academicians at Cremona a
spirited exposition of his theory. This learned Carmelitan friar does
not pretend to have been an original observer, but he had studied
sufficiently to enable him to confirm the opinions of Moro by arguments
from other writers; and his selection of the doctrines then best
established is so judicious, that a brief abstract of them cannot fail
to be acceptable, as illustrating the state of geology in Europe, and in
Italy in particular, before the middle of the last century.

The bowels of the earth, says he, have carefully preserved the memorials
of past events, and this truth the marine productions so frequent in the
hills attest. From the reflections of Lazzaro Moro, we may assure
ourselves that these are the effects of earthquakes in past times, which
have changed vast spaces of sea into terra firma, and inhabited lands
into seas. In this, more than in any other department of physics, are
observations and experiments indispensable, and we must diligently
consider facts. The land is known, wherever we make excavations, to be
composed of different strata or soils placed one above the other, some
of sand, some of rock, some of chalk, others of marl, coal, pummice,
gypsum, lime, and the rest. These ingredients are sometimes pure, and
sometimes confusedly intermixed. Within are often imprisoned different
marine fishes, like dried mummies, and more frequently shells,
crustacea, corals, plants, &c., not only in Italy, but in France,
Germany, England, Africa, Asia, and America;--sometimes in the lowest,
sometimes in the loftiest beds of the earth, some upon the mountains,
some in deep mines, others near the sea, and others hundreds of miles
distant from it. Woodward conjectured that these marine bodies might be
found everywhere; but there are rocks in which none of them occur, as is
sufficiently attested by Vallisneri and Marsilli. The remains of fossil
animals consist chiefly of their more solid parts, and the most rocky
strata must have been soft when such exuviae were inclosed in them.
Vegetable productions are found in different states of maturity,
indicating that they were imbedded in different seasons. Elephants,
elks, and other terrestrial quadrupeds, have been found in England and
elsewhere, in superficial strata, never covered by the sea. Alternations
are rare, yet not without example, of marine strata, with those which
contain marshy and terrestrial productions. Marine animals are arranged
in the subterraneous beds with admirable order, in distinct groups,
oysters here, dentalia or corals there, &c., as now, according to
Marsilli,[77] on the shores of the Adriatic. We must abandon the
doctrine, once so popular, which denies that organized fossils were
derived from living beings, and we cannot account for their present
position by the ancient theory of Strabo, nor by that of Leibnitz, nor
by the universal deluge, as explained by Woodward and others; "nor is it
reasonable to call the Deity capriciously upon the stage, and to make
him work miracles for the sake of confirming our preconceived
hypothesis." --"I hold in utter abomination, most learned Academicians!
those systems which are built with their foundations in the air, and
cannot be propped up without a miracle; and I undertake, with the
assistance of Moro, to explain to you how these marine animals were
transported into the mountains by natural causes."[78]

A brief abstract then follows of Moro's theory, by which, says
Generelli, we may explain all the phenomena, as Vallisneri so ardently
desired, "_without violence, without fictions, without hypothesis,
without miracles_."[79] The Carmelitan then proceeds to struggle against
an obvious objection to Moro's system, considered as a method of
explaining the revolutions of the earth, _naturally_. If earthquakes
have been the agents of such mighty changes, how does it happen that
their effects since the times of history have been so inconsiderable?
This same difficulty had, as we have seen, presented itself to Hooke,
half a century before, and forced him to resort to a former "crisis of
nature:" but Generelli defended his position by showing how numerous
were the accounts of eruptions and earthquakes, of new islands, and of
elevations and subsidences of land, and yet how much greater a number of
like events must have been unattested and unrecorded during the last six
thousand years. He also appealed to Vallisneri as an authority to prove
that the mineral masses containing shells, bore, upon the whole, but a
small proportion to those rocks which were destitute of organic remains;
and the latter, says the learned monk, might have been created as they
now exist, _in the beginning_.

Generelli then describes the continual waste of mountains and
continents, by the action of rivers and torrents, and concludes with
these eloquent and original observations:--"Is it possible that this
waste should have continued for six thousand, and _perhaps_ a greater
number of years, and that the mountains should remain so great, unless
their ruins have been repaired? Is it credible that the Author of Nature
should have founded the world upon such laws, as that the dry land
should forever be growing smaller, and at last become wholly submerged
beneath the waters? Is it credible that, amid so many created things,
the mountains alone should daily diminish in number and bulk, without
there being any repair of their losses? This would be contrary to that
order of Providence which is seen to reign in all other things in the
universe. Wherefore I deem it just to conclude, that the same cause
which, in the beginning of time, raised mountains from the abyss, has
down to the present day continued to produce others, in order to restore
from time to time the losses of all such as sink down in different
places, or are rent asunder, or in other way suffer disintegration. If
this be admitted, we can easily understand why there should now be found
upon many mountains so great a number of crustacea and other marine
animals."

In the above extract, I have not merely enumerated the opinions and
facts which are confirmed by recent observation, suppressing all that
has since proved to be erroneous, but have given a faithful abridgment
of the entire treatise, with the omission only of Moro's hypothesis,
which Generelli adopted, with all its faults and excellences. The reader
will therefore remark, that although this admirable essay embraces so
large a portion of the principal objects of geological research, it
makes no allusion to the extinction of certain classes of animals; and
it is evident that no opinions on this head had, at that time, gained a
firm footing in Italy. That Lister and other English naturalists should
long before have declared in favor of the loss of species, while Scilla
and most of his countrymen hesitated, was perhaps natural, since the
Italian museums were filled with fossil shells belonging to species of
which a great portion did actually exist in the Mediterranean; whereas
the English collectors could obtain no recent species from such of their
own strata as were then explored.

The weakest point in Moro's system consisted in deriving _all_ the
stratified rocks from volcanic ejections; an absurdity which his
opponents took care to expose, especially Vito Amici.[80] Moro seems to
have been misled by his anxious desire to represent the formation of
secondary rocks as having occupied an extremely short period, while at
the same time he wished to employ known agents in nature. To imagine
torrents, rivers, currents, partial floods, and all the operations of
moving water, to have gone on exerting an energy many thousand times
greater than at present, would have appeared preposterous and
incredible, and would have required a hundred violent hypotheses; but we
are so unacquainted with the true sources of subterranean disturbances,
that their former violence may in theory be multiplied indefinitely,
without its being possible to prove the same manifest contradiction or
absurdity in the conjecture. For this reason, perhaps, Moro preferred to
derive the materials of the strata from volcanic ejections, rather than
from transportation by running water.

_Marsilli._--Marsilli, whose work is alluded to by Generelli, had been
prompted to institute inquiries into the bed of the Adriatic, by
discovering, in the territory of Parma (what Spada had observed near
Verona, and Schiavo in Sicily), that fossil shells were not scattered
through the rocks at random, but disposed in regular order, according to
certain genera and species.

_Vitaliano Donati_, 1750.--But with a view of throwing further light
upon these questions, Donati, in 1750, undertook a more extensive
investigation of the Adriatic, and discovered, by numerous soundings,
that deposits of sand, marl, and tufaceous incrustations, most strictly
analogous to those of the Subapennine hills, were in the act of
accumulating there. He ascertained that there were no shells in some of
the submarine tracts, while in other places they lived together in
families, particularly the genera Arca, Pecten, Venus, Murex, and some
others. He also states that in divers localities he found a mass
composed of corals, shells, and crustaceous bodies of different species,
confusedly blended with earth, sand, and gravel. At the depth of a foot
or more, the organic substances were entirely petrified and reduced to
marble; at less than a foot from the surface, they approached nearer to
their natural state; while at the surface they were alive, or, if dead,
in a good state of preservation.

_Baldassari_.--A contemporary naturalist, Baldassari, had shown that the
organic remains in the tertiary marls of the Siennese territory were
grouped in families, in a manner precisely similar to that above alluded
to by Donati.

_Buffon_, 1749.--Buffon first made known his theoretical views
concerning the former changes of the earth, in his Natural History,
published in 1749. He adopted the theory of an original volcanic
nucleus, together with the universal ocean of Leibnitz. By this aqueous
envelope the highest mountains were once covered. Marine currents then
acted violently, and formed horizontal strata, by washing away solid
matter in some parts, and depositing it in others; they also excavated
deep submarine valleys. The level of the ocean was then depressed by the
entrance of a part of its waters into subterranean caverns, and thus
some land was left dry. Buffon seems not to have profited, like Leibnitz
and Moro, by the observations of Steno, or he could not have imagined
that the strata were generally horizontal, and that those which contain
organic remains had never been disturbed since the era of their
formation. He was conscious of the great power annually exerted by
rivers and marine currents in transporting earthy materials to lower
levels, and he even contemplated the period when they would destroy all
the present continents. Although in geology he was not an original
observer, his genius enabled him to render his hypothesis attractive;
and by the eloquence of his style, and the boldness of his speculations,
he awakened curiosity, and provoked a spirit of inquiry amongst his
countrymen.

Soon after the publication of his "Natural History," in which was
included his "Theory of the Earth," he received an official letter
(dated January, 1751) from the Sorbonne, or Faculty of Theology in
Paris, informing him that fourteen propositions in his works "were
reprehensible, and contrary to the creed of the church." The first of
these obnoxious passages, and the only one relating to geology, was as
follows:--"The waters of the sea have produced the mountains and valleys
of the land--the waters of the heavens, reducing all to a level, will at
last deliver the whole land over to the sea, and the sea successively
prevailing over the land, will leave dry new continents like those which
we inhabit." Buffon was invited by the College, in very courteous terms,
to send in an explanation, or rather a recantation of his unorthodox
opinions. To this he submitted; and a general assembly of the Faculty
having approved of his "Declaration," he was required to publish it in
his next work. The document begins with these words:--"I declare that I
had no intention to contradict the text of Scripture; that I believe
most firmly all therein related about the creation, both as to order of
time and matter of fact; and _I abandon every thing in my book
respecting the foundation of the earth_, and, generally, all which may
be contrary to the narration of Moses."[81]

The grand principle which Buffon was called upon to renounce was simply
this,--that the present mountains and valleys of the earth are due to
secondary causes, and that the same causes will in time destroy all the
continents, hills, and valleys, and reproduce others like them. Now,
whatever may be the defects of many of his views, it is no longer
controverted that the present continents are of secondary origin. The
doctrine is as firmly established as the earth's rotation on its axis;
and that the land now elevated above the level of the sea will not
endure forever, is an opinion which gains ground daily, in proportion as
we enlarge our experience of the changes now in progress.

_Targioni_, 1751.--Targioni, in his voluminous "Travels in Tuscany, 1751
and 1754," labored to fill up the sketch of the geology of that region
left by Steno sixty years before. Notwithstanding a want of arrangement
and condensation in his memoirs, they contained a rich store of faithful
observations. He has not indulged in many general views, but in regard
to the origin of valleys, he was opposed to the theory of Buffon, who
attributed them principally to submarine currents. The Tuscan naturalist
labored to show that both the larger and smaller valleys of the
Apennines were excavated by rivers and floods, caused by the bursting of
the barriers of lakes, after the retreat of the ocean. He also
maintained that the elephants and other quadrupeds, so frequent in the
lacustrine and alluvial deposits of Italy, had inhabited that peninsula;
and had not been transported thither, as some had conceived, by Hannibal
or the Romans, nor by what they were pleased to term "a catastrophe of
nature."

_Lehman_, 1756.--In the year 1756 the treatise of Lehman, a German
mineralogist, and director of the Prussian mines, appeared, who also
divided mountains into three classes: the first, those formed with the
world, and prior to the creation of animals, and which contained no
fragments of other rocks; the second class, those which resulted from
the partial destruction of the primary rocks by a general revolution;
and a third class, resulting from local revolutions, and in part from
the deluge of Noah.

A French translation of this work appeared in 1759, in the preface of
which, the translator displays very enlightened views respecting the
operations of earthquakes, as well as of the aqueous causes.[82]

_Gesner_, 1758.--In this year Gesner, the botanist, of Zurich,
published an excellent treatise on petrifactions, and the changes of the
earth which they testify.[83] After a detailed enumeration of the
various classes of fossils of the animal and vegetable kingdoms, and
remarks on the different states in which they are found petrified, he
considers the geological phenomena connected with them; observing, that
some, like those of OEningen, resembled the testacea, fish, and plants
indigenous in the neighboring region;[84] while some, such as ammonites,
gryphites, belemnites, and other shells, are either of unknown species,
or found only in the Indian and other distant seas. In order to
elucidate the structure of the earth, he gives sections, from Verenius,
Buffon, and others, obtained in digging wells; distinguishes between
horizontal and inclined strata; and, in speculating on the causes of
these appearances, mentions Donati's examination of the bed of the
Adriatic; the filling up of lakes and seas by sediment; the imbedding of
shells now in progress; and many known effects of earthquakes, such as
the sinking down of districts, or the heaving up of the bed of the sea,
so as to form new islands, and lay dry strata containing petrifactions.
The ocean, he says, deserts its shores in many countries, as on the
borders of the Baltic; but the rate of recession has been so slow in the
last 2000 years, that to allow the Apennines, whose summits are filled
with marine shells, to emerge to their present height, would have
required about 80,000 years,--a lapse of time ten times greater, or
more, than the age of the universe. We must therefore refer the
phenomenon to the command of the Deity, related by Moses, that "the
waters should be gathered together in one place, and the dry land
appear." Gesner adopted the views of Leibnitz, to account for the
retreat of the primeval ocean: his essay displays much erudition; and
the opinions of preceding writers of Italy, Germany, and England, are
commented upon with fairness and discrimination.

_Arduino_, 1759.--In the year following, Arduino,[85] in his memoirs on
the mountains of Padua, Vicenza, and Verona, deduced, from original
observations, the distinction of rocks into primary, secondary, and
tertiary, and showed that in those districts there had been a succession
of submarine volcanic eruptions.

_Michell_, 1760.--In the following year (1760) the Rev. John Michell,
Woodwardian Professor of Mineralogy at Cambridge, published in the
Philosophical Transactions, an Essay on the Cause and Phenomena of
Earthquakes.[86] His attention had been drawn to this subject by the
great earthquake of Lisbon in 1755. He advanced many original and
philosophical views respecting the propagation of subterranean
movements, and the caverns and fissures wherein steam might be
generated. In order to point out the application of his theory to the
structure of the globe, he was led to describe the arrangement and
disturbance of the strata, their usual horizontality in low countries,
and their contortions and fractured state in the neighborhood of
mountain chains. He also explained, with surprising accuracy, the
relations of the central ridges of older rocks to the "long narrow slips
of similar earth, stones, and minerals," which are parallel to these
ridges. In his generalizations, derived in great part from his own
observations on the geological structure of Yorkshire, he anticipated
many of the views more fully developed by later naturalists.

_Catcott_, 1761.--Michell's papers were entirely free from all
physico-theological disquisitions, but some of his contemporaries were
still earnestly engaged in defending or impugning the Woodwardian
hypothesis. We find many of these writings referred to by Catcott, a
Hutchinsonian, who published a "Treatise on the Deluge" in 1761. He
labored particularly to refute an explanation offered by his
contemporary, Bishop Clayton, of the Mosaic writings. That prelate had
declared that the deluge "could not be literally true, save in respect
to that part where Noah lived before the flood." Catcott insisted on the
universality of the deluge, and referred to traditions of inundations
mentioned by ancient writers, or by travellers, in the East Indies,
China, South America, and other countries. This part of his book is
valuable, although it is not easy to see what bearing the traditions
have, if admitted to be authentic, on the Bishop's argument, since no
evidence is adduced to prove that the catastrophes were contemporaneous
events, while some of them are expressly represented by ancient authors
to have occurred in succession.

_Fortis--Odoardi_, 1761.--The doctrines of Arduino, above adverted to,
were afterwards confirmed by Fortis and Desmarest, in their travels in
the same country; and they, as well as Baldassari, labored to complete
the history of the Subapennine strata. In the work of Odoardi,[87] there
was also a clear argument in favor of the distinct ages of the older
Apennine strata, and the Subapennine formations of more recent origin.
He pointed out that the strata of these two groups were _unconformable_,
and must have been the deposits of different seas at distant periods of
time.

_Raspe_, 1763.--A history of the new islands, by Raspe, a Hanoverian,
appeared in 1763, in Latin.[88] In this work, all the authentic accounts
of earthquakes which had produced permanent changes on the solid parts
of the earth were collected together and examined with judicious
criticism. The best systems which had been proposed concerning the
ancient history of the globe, both by ancient and modern writers, are
reviewed; and the merits and defects of the doctrines of Hooke, Ray,
Moro, Buffon, and others, fairly estimated. Great admiration is
expressed for the hypothesis of Hooke, and his explanation of the origin
of the strata is shown to have been more correct than Moro's, while
their theory of the effects of earthquakes was the same. Raspe had not
seen Michell's memoirs, and his views concerning the geological
structure of the earth were perhaps less enlarged; yet he was able to
add many additional arguments in favor of Hook's theory, and to render
it, as he said, a nearer approach to what Hooke would have written had
he lived in later times. As to the periods wherein all the earthquakes
happened, to which we owe the elevation of various parts of our
continents and islands, Raspe says he pretends not to assign their
duration, still less to defend Hooke's suggestion, that the convulsions
almost all took place during the deluge of Noah. He adverts to the
apparent indications of the former tropical heat of the climate of
Europe, and the changes in the species of animals and plants, as among
the most obscure and difficult problems in geology. In regard to the
islands raised from the sea, within the times of history or tradition,
he declares that some of them were composed of strata containing organic
remains, and that they were not, as Buffon had asserted, made of mere
volcanic matter. His work concludes with an eloquent exhortation to
naturalists to examine the isles which rose, in 1707, in the Grecian
Archipelago, and, in 1720, in the Azores, and not to neglect such
splendid opportunities of studying nature "in the act of parturition."
That Hooke's writings should have been neglected for more than half a
century, was matter of astonishment to Raspe; but it is still more
wonderful that his own luminous exposition of that theory should, for
more than another half century, have excited so little interest.

_Fuchsel_, 1762 and 1773.--Fuchsel, a German physician, published, in
1762, a geological description of the country between the Thuringerwald
and the Hartz, and a memoir on the environs of Rudelstadt;[89] and
afterwards, in 1773, a theoretical work on the ancient history of the
earth and of man.[90] He had evidently advanced considerably beyond his
predecessor Lehman, and was aware of the distinctness, both as to
position and fossil contents, of several groups of strata of different
ages, corresponding to the secondary formations now recognized by
geologists in various parts of Germany. He supposed the European
continents to have remained covered by the sea until the formation of
the marine strata, called in Germany "muschelkalk," at the same time
that the terrestrial plants of many European deposits, attested the
existence of dry land which bordered the ancient sea; land which,
therefore, must have occupied the place of the present ocean. The
pre-existing continent had been _gradually_ swallowed up by the sea,
different parts having subsided in succession into subterranean caverns.
All the sedimentary strata were originally horizontal, and their present
state of derangement must be referred to subsequent oscillations of the
ground.

As there were plants and animals in the ancient periods, so also there
must have been men, but they did not all descend from one pair, but were
created at various points on the earth's surface; and the number of
these distinct birth-places was as great as are the original languages
of nations.

In the writings of Fuchsel we see a strong desire manifested to explain
geological phenomena as far as possible by reference to the agency of
known causes; and although some of his speculations were fanciful, his
views coincide much more nearly with those now generally adopted, than
the theories afterwards promulgated by Werner and his followers.

_Brander_, 1766.--Gustavus Brander published, in 1766, his "Fossilia
Hantoniensia," containing excellent figures of fossil shells from the
more modern (or Eocene) marine strata of Hampshire. "Various opinions,"
he says in the preface, "had been entertained concerning the time when
and how these bodies became deposited. Some there are who conceive that
it might have been effected in a wonderful length of time by a gradual
changing and shifting of the sea," &c. But the most common cause
assigned is that of "the deluge." This conjecture, he says, even if the
universality of the flood be not called in question, is purely
hypothetical. In his opinion, fossil animals and testacea were, for the
most part, of unknown species; and of such as were known, the living
analogues now belonged to southern latitudes.

_Soldani_, 1780.--Soldani applied successfully his knowledge of zoology
to illustrate the history of stratified masses. He explained that
microscopic testacea and zoophytes inhabited the depths of the
Mediterranean; and that the fossil species were, in like manner, found
in those deposits wherein the fineness of their particles, and the
absence of pebbles, implied that they were accumulated in a deep sea, or
far from shore. This author first remarked the alternation of marine and
freshwater strata in the Paris basin.[91]

_Fortis--Testa_, 1793.--A lively controversy arose between Fortis and
another Italian naturalist, Testa, concerning the fish of Monte Bolca,
in 1793. Their letters,[92] written with great spirit and elegance, show
that they were aware that a large proportion of the Subapennine shells
were identical with living species, and some of them with species now
living in the torrid zone. Fortis proposed a somewhat fanciful
conjecture, that when the volcanoes of the Vicentin were burning, the
waters of the Adriatic had a higher temperature; and in this manner, he
said, the shells of warmer regions may once have peopled their own seas.
But Testa was disposed to think that these species of testacea were
still common to their own and to equinoctial seas; for many, he said,
once supposed to be confined to hotter regions, had been afterwards
discovered in the Mediterranean.[93]

_Cortesi--Spallanzani--Wallerius--Whitehurst._--While these Italian
naturalists, together with Cortesi and Spallanzani, were busily engaged
in pointing out the analogy between the deposits of modern and ancient
seas, and the habits and arrangement of their organic inhabitants, and
while some progress was making, in the same country, in investigating
the ancient and modern volcanic rocks, some of the most original
observers among the English and German writers, Whitehurst[94] and
Wallerius, were wasting their strength in contending, according to the
old Woodwardian hypothesis, that all the strata were formed by Noah's
deluge. But Whitehurst's description of the rocks of Derbyshire was most
faithful; and he atoned for false theoretical views, by providing data
for their refutation.

_Pallas--Saussure._--Towards the close of the eighteenth century, the
idea of distinguishing the mineral masses on our globe into separate
groups, and studying their relations, began to be generally diffused.
Pallas and Saussure were among the most celebrated whose labors
contributed to this end. After an attentive examination of the two great
mountain chains of Siberia, Pallas announced the result, that the
granitic rocks were in the middle, the schistose at their sides, and the
limestones again on the outside of these; and this he conceived would
prove a general law in the formation of all chains composed chiefly of
primary rocks.[95]

In his "Travels in Russia," in 1793 and 1794, he made many geological
observations on the recent strata near the Wolga and the Caspian, and
adduced proofs of the greater extent of the latter sea at no distant era
in the earth's history. His memoir on the fossil bones of Siberia
attracted attention to some of the most remarkable phenomena in geology.
He stated that he had found a rhinoceros entire in the frozen soil, with
its skin and flesh: an elephant, found afterwards in a mass of ice on
the shore of the North Sea, removed all doubt as to the accuracy of so
wonderful a discovery.[96]

The subjects relating to natural history which engaged the attention of
Pallas, were too multifarious to admit of his devoting a large share of
his labors exclusively to geology. Saussure, on the other hand, employed
the chief portion of his time in studying the structure of the Alps and
Jura, and he provided valuable data for those who followed him. He did
not pretend to deduce any general system from his numerous and
interesting observations; and the few theoretical opinions which escaped
from him, seem, like those of Pallas, to have been chiefly derived from
the cosmological speculations of preceding writers.




CHAPTER IV.

HISTORY OF THE PROGRESS OF GEOLOGY--_continued_.


   Werner's application of geology to the art of
     mining--Excursive character of his lectures--Enthusiasm of his
     pupils--His authority--His theoretical errors--Desmarest's Map
     and Description of Auvergne--Controversy between the
     Vulcanists and Neptunists--Intemperance of the rival
     sects--Hutton's Theory of the earth--His discovery of granite
     veins--Originality of his views--Why opposed--Playfair's
     illustrations--Influence of Voltaire's writings on
     geology--Imputations cast on the Huttonians by Williams,
     Kirwan, and De Luc--Smith's Map of England--Geological Society
     of London--Progress of the science in France--Growing
     importance of the study of organic remains.


_Werner._--The art of mining has long been taught in France, Germany,
and Hungary, in scientific institutions established for that purpose,
where mineralogy has always been a principal branch of instruction.

Werner was named, in 1775, professor of that science in the "School of
Mines," at Freyberg, in Saxony. He directed his attention not merely to
the composition and external characters of minerals, but also to what he
termed "geognosy," or the natural position of minerals in particular
rocks, together with the grouping of those rocks, their geographical
distribution, and various relations. The phenomena observed in the
structure of the globe had hitherto served for little else than to
furnish interesting topics for philosophical discussion; but when Werner
pointed out their application to the practical purposes of mining, they
were instantly regarded by a large class of men as an essential part of
their professional education, and from that time the science was
cultivated in Europe more ardently and systematically. Werner's mind was
at once imaginative and richly stored with miscellaneous knowledge. He
associated every thing with his favorite science, and in his excursive
lectures, he pointed out all the economical uses of minerals, and their
application to medicine; the influence of the mineral composition of
rocks upon the soil, and of the soil upon the resources, wealth, and
civilization of man. The vast sandy plains of Tartary and Africa, he
would say, retained their inhabitants in the shape of wandering
shepherds; the granitic mountains and the low calcareous and alluvial
plains gave rise to different manners, degrees of wealth, and
intelligence. The history even of languages, and the migration of
tribes, had been determined by the direction of particular strata. The
qualities of certain stones used in building would lead him to descant
on the architecture of different ages and nations; and the physical
geography of a country frequently invited him to treat of military
tactics. The charm of his manners and his eloquence kindled enthusiasm
in the minds of his pupils; and many, who had intended at first only to
acquire a slight knowledge of mineralogy, when they had once heard him,
devoted themselves to it as the business of their lives. In a few years,
a small school of mines, before unheard of in Europe, was raised to the
rank of a great university; and men already distinguished in science
studied the German language, and came from the most distant countries to
hear the great oracle of geology.[97]

Werner had a great antipathy to the mechanical labor of writing, and,
with the exception of a valuable treatise on metalliferous veins, he
could never be persuaded to pen more than a few brief memoirs, and those
containing no development of his general views. Although the natural
modesty of his disposition was excessive, approaching even to timidity,
he indulged in the most bold and sweeping generalizations, and he
inspired all his scholars with a most implicit faith in his doctrines.
Their admiration of his genius, and the feelings of gratitude and
friendship which they all felt for him, were not undeserved; but the
supreme authority usurped by him over the opinions of his
contemporaries, was eventually prejudicial to the progress of the
science; so much so, as greatly to counterbalance the advantages which
it derived from his exertions. If it be true that delivery be the first,
second, and third requisite in a popular orator, it is no less certain,
that to travel is of first, second, and third importance to those who
desire to originate just and comprehensive views concerning the
structure of our globe. Now Werner had not travelled to distant
countries; he had merely explored a small portion of Germany, and
conceived, and persuaded others to believe, that the whole surface of
our planet, and all the mountain chains in the world, were made after
the model of his own province. It became a ruling object of ambition in
the minds of his pupils to confirm the generalizations of their great
master, and to discover in the most distant parts of the globe his
"universal formations," which he supposed had been each in succession
simultaneously precipitated over the whole earth from a common
menstruum, or "chaotic fluid." It now appears that the Saxon professor
had misinterpreted many of the most important appearances even in the
immediate neighborhood of Freyberg. Thus, for example, within a day's
journey of his school, the porphyry, called by him primitive, has been
found not only to send forth veins or dikes through strata of the coal
formation, but to overlie them in mass. The granite of the Hartz
mountains, on the other hand, which he supposed to be the nucleus of the
chain, is now well known to traverse the other beds, as near Goslar; and
still nearer Freyberg, in the Erzgebirge, the mica slate does not mantle
round the granite as was supposed, but abuts abruptly against it.
Fragments, also, of the greywacka slate, containing organic remains,
have recently been found entangled in the granite of the Hartz, by M. de
Seckendorf.[98]

The principal merit of Werner's system of instruction consisted in
steadily directing the attention of his scholars to the constant
relations of superposition of certain mineral groups; but he had been
anticipated, as has been shown in the last chapter, in the discovery of
this general law, by several geologists in Italy and elsewhere; and his
leading divisions of the secondary strata were at the same time, and
independently, made the basis of an arrangement of the British strata by
our countryman, William Smith, to whose work I shall refer in the
sequel.

_Controversy between the Vulcanists and Neptunists._--In regard to
basalt and other igneous rocks, Werner's theory was original, but it was
also extremely erroneous. The basalts of Saxony and Hesse, to which his
observations were chiefly confined, consisted of tabular masses capping
the hills, and not connected with the levels of existing valleys, like
many in Auvergne and the Vivarais. These basalts, and all other rocks of
the same family in other countries, were, according to him, chemical
precipitates from water. He denied that they were the products of
submarine volcanoes; and even taught that, in the primeval ages of the
world, there were no volcanoes. His theory was opposed, in a twofold
sense, to the doctrine of the permanent agency of the same causes in
nature; for not only did he introduce, without scruple, many imaginary
causes supposed to have once effected great revolutions in the earth,
and then to have become extinct, but new ones also were feigned to have
come into play in modern times; and, above all, that most violent
instrument of change, the agency of subterranean heat.

So early as 1768, before Werner had commenced his mineralogical studies,
Raspe had truly characterized the basalts of Hesse as of igneous origin.
Arduino, we have seen, had pointed out numerous varieties of trap-rock
in the Vicentin as analogous to volcanic products, and as distinctly
referable to ancient submarine eruptions. Desmarest, as before stated,
had, in company with Fortis, examined the Vicentin in 1766, and
confirmed Arduino's views. In 1772, Banks, Solander, and Troil compared
the columnar basalt of Hecla with that of the Hebrides. Collini, in
1774, recognized the true nature of the igneous rocks on the Rhine,
between Andernach and Bonn. In 1775, Guettard visited the Vivarais, and
established the relation of basaltic currents to lavas. Lastly, in 1779,
Faujas published his description of the volcanoes of the Vivarais and
Velay, and showed how the streams of basalt had poured out from craters
which still remain in a perfect state.[99]

_Desmarest._--When sound opinions had thus for twenty years prevailed in
Europe concerning the true nature of the ancient trap-rocks, Werner by
his simple dictum caused a retrograde movement, and not only overturned
the true theory, but substituted for it one of the most unphilosophical
that can well be imagined. The continued ascendancy of his dogmas on
this subject was the more astonishing, because a variety of new and
striking facts were daily accumulated in favor of the correct opinions
previously entertained. Desmarest, after a careful examination of
Auvergne, pointed out, first, the most recent volcanoes which had their
craters still entire, and their streams of lava conforming to the level
of the present river-courses. He then showed that there were others of
an intermediate epoch, whose craters were nearly effaced, and whose
lavas were less intimately connected with the present valleys; and,
lastly, that there were volcanic rocks, still more ancient, without any
discernible craters or scoriae, and bearing the closest analogy to rocks
in other parts of Europe, the igneous origin of which was denied by the
school of Freyberg.[100]

Desmarest's map of Auvergne was a work of uncommon merit. He first made
a trigonometrical survey of the district, and delineated its physical
geography with minute accuracy and admirable graphic power. He
contrived, at the same time, to express without the aid of colors, many
geological details, including the different ages and sometimes even the
structure, of the volcanic rocks, and distinguishing them from the
fresh-water and the granitic. They alone who have carefully studied
Auvergne, and traced the different lava streams from their craters to
their termination,--the various isolated basaltic cappings,--the
relation of some lavas to the present valleys,---the absence of such
relations in others,--can appreciate the extraordinary fidelity of this
elaborate work. No other district of equal dimensions in Europe
exhibits, perhaps, so beautiful and varied a series of phenomena; and,
fortunately, Desmarest possessed at once the mathematical knowledge
required for the construction of a map, skill in mineralogy, and a power
of original generalization.

_Dolomieu--Montlosier._--Dolomieu, another of Werner's contemporaries,
had found prismatic basalt among the ancient lavas of Etna; and, in
1784, had observed the alternations of submarine lavas and calcareous
strata in the Val di Noto, in Sicily.[101] In 1790, also, he described
similar phenomena in the Vicentin and in the Tyrol.[102] Montlosier
published, in 1788, an essay on the theories of volcanoes of Auvergne,
combining accurate local observations with comprehensive views.
Notwithstanding this mass of evidence the scholars of Werner were
prepared to support his opinions to their utmost extent; maintaining, in
the fulness of their faith, that even obsidian was an aqueous
precipitate. As they were blinded by their veneration for the great
teacher, they were impatient of opposition, and soon imbibed the spirit
of a faction; and their opponents, the Vulcanists, were not long in
becoming contaminated with the same intemperate zeal. Ridicule and irony
were weapons more frequently employed than argument by the rival sects,
till at last the controversy was carried on with a degree of bitterness
almost unprecedented in questions of physical science. Desmarest alone,
who had long before provided ample materials for refuting such a theory,
kept aloof from the strife; and whenever a zealous Neptunist wished to
draw the old man into an argument, he was satisfied with replying, "Go
and see."[103]

_Hutton_, 1788.--It would be contrary to all analogy, in matters of
graver import, that a war should rage with such fury on the Continent,
and that the inhabitants of our island should not mingle in the affray.
Although in England the personal influence of Werner was wanting to
stimulate men to the defence of the weaker side of the question, they
contrived to find good reason for espousing the Wernerian errors with
great enthusiasm. In order to explain the peculiar motives which led
many to enter, even with party feeling, into this contest, it will be
necessary to present the reader with a sketch of the views unfolded by
Hutton, a contemporary of the Saxon geologist. The former naturalist had
been educated as a physician, but declining the practice of medicine, he
resolved, when young, to remain content with the small independence
inherited from his father, and thenceforth to give his undivided
attention to scientific pursuits. He resided at Edinburgh, where he
enjoyed the society of many men of high attainments, who loved him for
the simplicity of his manners, and the sincerity of his character. His
application was unwearied; and he made frequent tours through different
parts of England and Scotland, acquiring considerable skill as a
mineralogist, and consequently arriving at grand and comprehensive views
in geology. He communicated the results of his observations
unreservedly, and with the fearless spirit of one who was conscious that
love of truth was the sole stimulus of his exertions. When at length he
had matured his views, he published, in 1788, his "Theory of the
Earth,"[104] and the same, afterwards more fully developed in a separate
work, in 1795. This treatise was the first in which geology was declared
to be in no way concerned about "questions as to the origin of things;"
the first in which an attempt was made to dispense entirely with all
hypothetical causes, and to explain the former changes of the earth's
crust by reference exclusively to natural agents. Hutton labored to
give fixed principles to geology, as Newton had succeeded in doing to
astronomy; but, in the former science, too little progress had been made
towards furnishing the necessary data, to enable any philosopher,
however great his genius, to realize so noble a project.

_Huttonian theory._--"The ruins of an older world," said Hutton, "are
visible in the present structure of our planet; and the strata which now
compose our continents have been once beneath the sea, and were formed
out of the waste of pre-existing continents. The same forces are still
destroying, by chemical decomposition or mechanical violence, even the
hardest rocks, and transporting the materials to the sea, where they are
spread out, and form strata analogous to those of more ancient date.
Although loosely deposited along the bottom of the ocean, they become
afterwards altered and consolidated by volcanic heat, and then heaved
up, fractured, and contorted."

Although Hutton had never explored any region of active volcanoes, he
had convinced himself that basalt and many other trap-rocks were of
igneous origin, and that many of them had been injected in a melted
state through fissures in the older strata. The compactness of these
rocks, and their different aspect from that of ordinary lava, he
attributed to their having cooled down under the pressure of the sea;
and in order to remove the objections started against this theory, his
friend, Sir James Hall, instituted a most curious and instructive series
of chemical experiments, illustrating the crystalline arrangement and
texture assumed by melted matter cooled under high pressure.

The absence of stratification in granite, and its analogy, in mineral
character, to rocks which he deemed of igneous origin, led Hutton to
conclude that granite also must have been formed from matter in fusion;
and this inference he felt could not be fully confirmed, unless he
discovered at the contact of granite and other strata a repetition of
the phenomena exhibited so constantly by the trap-rocks. Resolved to try
his theory by this test, he went to the Grampians, and surveyed the line
of junction of the granite and superincumbent stratified masses, until
he found in Glen Tilt, in 1785, the most clear and unequivocal proofs in
support of his views. Veins of red granite are there seen branching out
from the principal mass, and traversing the black micaceous schist and
primary limestone. The intersected stratified rocks are so distinct in
color and appearance as to render the example in that locality most
striking, and the alteration of the limestone in contact was very
analogous to that produced by trap veins on calcareous strata. This
verification of his system filled him with delight, and called forth
such marks of joy and exultation, that the guides who accompanied him,
says his biographer, were convinced that he must have discovered a vein
of silver or gold.[105] He was aware that the same theory would not
explain the origin of the primary schists, but these he called primary,
rejecting the term primitive, and was disposed to consider them as
sedimentary rocks altered by heat, and that they originated in some
other form from the waste of previously existing rocks.

By this important discovery of granite veins, to which he had been led
by fair induction from an independent class of facts, Hutton prepared
the way for the greatest innovation of the systems of his predecessors.
Vallisneri had pointed out the general fact that there were certain
fundamental rocks which contained no organic remains, and which he
supposed to have been formed before the creation of living beings. Moro,
Generelli, and other Italian writers, embraced the same doctrine; and
Lehman regarded the mountains called by him primitive, as parts of the
original nucleus of the globe. The same tenet was an article of faith in
the school of Freyberg; and if any one ventured to doubt the possibility
of our being enabled to carry back our researches to the creation of the
present order of things, the granitic rocks were triumphantly appealed
to. On them seemed written, in legible characters, the memorable
inscription--

  "Dinanzi a me non fur cose create
  Se non eterne;"[106]

and no small sensation was excited when Hutton seemed, with unhallowed
hand, desirous to erase characters already regarded by many as sacred.
"In the economy of the world," said the Scotch geologist, "I can find no
traces of a beginning, no prospect of an end;" a declaration the more
startling when coupled with the doctrine, that all past ages on the
globe had been brought about by the slow agency of existing causes. The
imagination was first fatigued and overpowered by endeavoring to
conceive the immensity of time required for the annihilation of whole
continents by so insensible a process; and when the thoughts had
wandered through these interminable periods, no resting-place was
assigned in the remotest distance. The oldest rocks were represented to
be of a derivative nature, the last of an antecedent series, and that,
perhaps, one of many pre-existing worlds. Such views of the immensity of
past time, like those unfolded by the Newtonian philosophy in regard to
space, were too vast to awaken ideas of sublimity unmixed with a painful
sense of our incapacity to conceive a plan of such infinite extent.
Worlds are seen beyond worlds immeasurably distant from each other, and,
beyond them all, innumerable other systems are faintly traced on the
confines of the visible universe.

The characteristic feature of the Huttonian theory was, as before
hinted, the exclusion of all causes not supposed to belong to the
present order of nature. But Hutton had made no step beyond Hooke, Moro,
and Raspe, in pointing out in what manner the laws now governing
subterranean movements might bring about geological changes, if
sufficient time be allowed. On the contrary, he seems to have fallen far
short of some of their views, especially when he refused to attribute
any part of the external configuration of the earth's crust to
subsidence. He imagined that the continents were first gradually
destroyed by aqueous degradation; and when their ruins had furnished
materials for new continents, they were upheaved by violent convulsions.
He therefore required alternate periods of general disturbance and
repose; and such he believed had been, and would forever be, the course
of nature.

Generelli, in his exposition of Moro's system, had made a far nearer
approximation towards reconciling geological appearances with the state
of nature as known to us; for while he agreed with Hutton, that the
decay and reproduction of rocks were always in progress, proceeding with
the utmost uniformity, the learned Carmelite represented the repairs of
mountains by elevation from below to be effected by an equally constant
and synchronous operation. Neither of these theories, considered singly,
satisfies all the conditions of the great problem, which a geologist,
who rejects cosmological causes, is called upon to solve; but they
probably contain together the germs of a perfect system. There can be no
doubt, that periods of disturbance and repose have followed each other
in succession in every region of the globe; but it may be equally true,
that the energy of the subterranean movements has been always uniform as
regards the _whole earth_. The force of earthquakes may for a cycle of
years have been invariably confined, as it is now, to large but
determinate spaces, and may then have gradually shifted its position, so
that another region, which had for ages been at rest, became in its turn
the grand theatre of action.

_Playfair's illustrations of Hutton._--The explanation proposed by
Hutton, and by Playfair, the illustrator of his theory, respecting the
origin of valleys and of alluvial accumulations, was also very
imperfect. They ascribed none of the inequalities of the earth's surface
to movements which accompanied the upheaving of the land, imagining that
valleys in general were formed in the course of ages by the rivers now
flowing in them; while they seem not to have reflected on the excavating
and transporting power which the waves of the ocean might exert on land
during its emergence.

Although Hutton's knowledge of mineralogy and chemistry was
considerable, he possessed but little information concerning organic
remains; they merely served him, as they did Werner, to characterize
certain strata, and to prove their marine origin. The theory of former
revolutions in organic life was not yet fully recognized; and without
this class of proofs in support of the antiquity of the globe, the
indefinite periods demanded by the Huttonian hypothesis appeared
visionary to many; and some, who deemed the doctrine inconsistent with
revealed truths, indulged very uncharitable suspicions of the motives of
its author. They accused him of a deliberate design of reviving the
heathen dogma of an "eternal succession," and of denying that this world
ever had a beginning. Playfair, in the biography of his friend, has the
following comment on this part of their theory:--"In the planetary
motions, where geometry has carried the eye so far, both into the future
and the past, we discover no mark either of the commencement or
termination of the present order. It is unreasonable, indeed, to suppose
that such marks should anywhere exist. The Author of Nature has not
given laws to the universe, which, like the institutions of men, carry
in themselves the elements of their own destruction. He has not
permitted in His works any symptom of infancy or of old age, or any sign
by which we may estimate either their future or their past duration. _He
may put an end, as he no doubt gave a beginning_, to the present system,
at some determinate period of time; but we may rest assured that this
great catastrophe will not be brought about by the laws now existing,
and that it is not indicated, by any thing which we perceive."[107]

The party feeling excited against the Huttonian doctrines, and the open
disregard of candor and temper in the controversy, will hardly be
credited by the reader, unless he recalls to his recollection that the
mind of the English public was at that time in a state of feverish
excitement. A class of writers in France had been laboring industriously
for many years, to diminish the influence of the clergy, by sapping the
foundations of the Christian faith; and their success, and the
consequences of the Revolution, had alarmed the most resolute minds,
while the imagination of the more timid was continually haunted by dread
of innovation, as by the phantom of some fearful dream.

_Voltaire._--Voltaire had used the modern discoveries in physics as one
of the numerous weapons of attack and ridicule directed by him against
the Scriptures. He found that the most popular systems of geology were
accommodated to the sacred writings, and that much ingenuity had been
employed to make every fact coincide exactly with the Mosaic account of
the creation and deluge. It was, therefore, with no friendly feelings
that he contemplated the cultivators of geology in general, regarding
the science as one which had been successfully enlisted by theologians
as an ally in their cause.[108] He knew that the majority of those who
were aware of the abundance of fossil shells in the interior of
continents, were still persuaded that they were proofs of the universal
deluge; and as the readiest way of shaking this article of faith, he
endeavored to inculcate skepticism as to the real nature of such shells,
and to recall from contempt the exploded dogma of the sixteenth century,
that they were sports of nature. He also pretended that vegetable
impressions were not those of real plants.[109] Yet he was perfectly
convinced that the shells had really belonged to living testacea, as may
be seen in his essay "On the formation of Mountains."[110] He would
sometimes, in defiance of all consistency, shift his ground when
addressing the vulgar; and, admitting the true nature of the shells
collected in the Alps and other places, pretend that they were Eastern
species, which had fallen from the hats of pilgrims coming from Syria.
The numerous essays written by him on geological subjects were all
calculated to strengthen prejudices, partly because he was ignorant of
the real state of the science, and partly from his bad faith.[111] On
the other hand, they who knew that his attacks were directed by a desire
to invalidate Scripture, and who were unacquainted with the true merits
of the question, might well deem the old diluvian hypothesis
incontrovertible, if Voltaire could adduce no better argument against it
than to deny the true nature of organic remains.

It is only by careful attention to impediments originating in extrinsic
causes, that we can explain the slow and reluctant adoption of the
simplest truths in geology. First, we find many able naturalists
adducing the fossil remains of marine animals as proofs of an event
related in Scripture. The evidence is deemed conclusive by the multitude
for a century or more; for it favors opinions which they entertained
before, and they are gratified by supposing them confirmed by fresh and
unexpected proofs. Many who see through the fallacy have no wish to
undeceive those who are influenced by it, approving the effect of the
delusion, and conniving at it as a pious fraud; until, finally, an
opposite party, who are hostile to the sacred writings, labor to explode
the erroneous opinion, by substituting for it another dogma, which they
know to be equally unsound.

The heretical Vulcanists were soon after openly assailed in England, by
imputations of the most illiberal kind. We cannot estimate the
malevolence of such a persecution, by the pain which similar
insinuations might now inflict; for although charges of infidelity and
atheism must always be odious, they were injurious in the extreme at
that moment of political excitement; and it was better, perhaps, for a
man's good reception in society, that his moral character should have
been traduced, than that he should become a mark for these poisoned
weapons.

I shall pass over the works of numerous divines, who may be excused for
sensitiveness on points which then excited so much uneasiness in the
public mind; and shall say nothing of the amiable poet Cowper,[112] who
could hardly be expected to have inquired into the merit of doctrines
in physics. But in the foremost ranks of the intolerant are found
several laymen who had high claims to scientific reputation. Among these
appears Williams, a mineral surveyor of Edinburgh, who published a
"Natural History of the Mineral Kingdom," in 1789; a work of great
merit, for that day, and of practical utility, as containing the best
account of the coal strata. In his preface he misrepresents Hutton's
theory altogether, and charges him with considering all rocks to be
lavas of different colors and structure; and also with "warping every
thing to support the eternity of the world."[113] He descants on the
pernicious influence of such skeptical notions, as leading to downright
infidelity and atheism, "and as being nothing less than to depose the
Almighty Creator of the universe from his office."[114]

_Kirwan_--_De Luc._--Kirwan, president of the Royal Academy of Dublin, a
chemist and mineralogist of some merit, but who possessed much greater
authority in the scientific world than he was entitled by his talents to
enjoy, said, in the introduction to his "Geological Essays, 1799," "that
_sound_ geology _graduated_ into religion, and was required to dispel
certain systems of atheism or infidelity, of which they had had recent
experience."[115] He was an uncompromising defender of the aqueous
theory of all rocks, and was scarcely surpassed by Burnet and Whiston,
in his desire to adduce the Mosaic writings in confirmation of his
opinions.

De Luc, in the preliminary discourse to his Treatise on Geology,[116]
says, "The weapons have been changed by which revealed religion is
attacked; it is now assailed by geology, and the knowledge of this
science has become essential to theologians." He imputes the failure of
former geological systems to their having been anti-Mosaical, and
directed against a "sublime tradition." These and similar imputations,
reiterated in the works of De Luc, seem to have been taken for granted
by some modern writers: it is therefore necessary to state, in justice
to the numerous geologists of different nations, whose works have been
considered, that none of them were guilty of endeavoring, by arguments
drawn from physics, to invalidate scriptural tenets. On the contrary,
the majority of those who were fortunate enough "to discover the true
causes of things," rarely deserved another part of the poet's panegyric,
"_Atque metus omnes subjecit pedibus_." The caution and even timid
reserve, of many eminent Italian authors of the earlier period is very
apparent; and there can hardly be a doubt, that they subscribed to
certain dogmas, and particularly to the first diluvian theory, out of
deference to popular prejudices, rather than from conviction. If they
were guilty of dissimulation, we may feel regret, but must not blame
their want of moral courage, reserving rather our condemnation for the
intolerance of the times, and that inquisitorial power which forced
Galileo to abjure, and the two Jesuits to disclaim the theory of
Newton.[117]

Hutton answered Kirwan's attacks with great warmth, and with the
indignation justly excited by unmerited reproach. "He had always
displayed," says Playfair, "the utmost disposition to admire the
beneficent design manifested in the structure of the world; and he
contemplated with delight those parts of his theory which made the
greatest additions to our knowledge of final causes." We may say with
equal truth, that in no scientific works in our language can more
eloquent passages be found, concerning the fitness, harmony, and
grandeur of all parts of the creation, than in those of Playfair. They
are evidently the unaffected expressions of a mind, which contemplated
the study of nature, as best calculated to elevate our conceptions of
the attributes of the First Cause. At any other time the force and
elegance of Playfair's style must have insured popularity to the
Huttonian doctrines; but by a singular coincidence, Neptunianism and
orthodoxy were now associated in the same creed; and the tide of
prejudice ran so strong, that the majority were carried far away into
the chaotic fluid, and other cosmological inventions of Werner. These
fictions the Saxon professor had borrowed with little modification, and
without any improvement, from his predecessors. They had not the
smallest foundation either in Scripture or in common sense, and were
probably approved of by many as being so ideal and unsubstantial, that
they could never come into violent collision with any preconceived
opinions.

According to De Luc, the first essential distinction to be made between
the various phenomena exhibited on the surface of the earth was, to
determine which were the results of causes still in action, and which
had been produced by causes that had ceased to act. The form and
composition of the mass of our continents, he said, and their existence
above the level of the sea, must be ascribed to causes no longer in
action. These continents emerged, at no very remote period, on the
sudden retreat of the ocean, the waters of which made their way into
subterranean caverns. The formation of the rocks which enter into the
crust of the earth began with the precipitation of granite from a
primordial liquid, after which other strata containing the remains of
organized bodies were deposited, till at last the present sea remained
as the residuum of the primordial liquid, and no longer continued to
produce mineral strata.[118]

_William Smith_, 1790.--While the tenets of the rival schools of
Freyberg and Edinburgh were warmly espoused by devoted partisans, the
labors of an individual, unassisted by the advantages of wealth or
station in society, were almost unheeded. Mr. William Smith, an English
surveyor, published his "Tabular View of the British Strata" in 1790,
wherein he proposed a classification of the secondary formations in the
West of England. Although he had not communicated with Werner, it
appeared by this work that he had arrived at the same views respecting
the laws of superposition of stratified rocks; that he was aware that
the order of succession of different groups was never inverted; and that
they might be identified at very distant points by their peculiar
organized fossils.

From the time of the appearance of the "Tabular View," the author
labored to construct a geological map of the whole of England; and with
the greatest disinterestedness of mind, communicated the results of his
investigations to all who desired information, giving such publicity to
his original views, as to enable his contemporaries almost to compete
with him in the race. The execution of his map was completed in 1815,
and remains a lasting monument of original talent and extraordinary
perseverance; for he had explored the whole country on foot, without the
guidance of previous observers, or the aid of fellow-laborers, and had
succeeded in throwing into natural divisions the whole complicated
series of British rocks. D'Aubuisson, a distinguished pupil of Werner,
paid a just tribute of praise to this remarkable performance, observing,
that "what many celebrated mineralogists had only accomplished for a
small part of Germany in the course of half a century, had been effected
by a single individual for the whole of England."[119]

Werner invented a new language to express his divisions of rocks, and
some of his technical terms, such as grauwacke, gneiss, and others,
passed current in every country in Europe. Smith adopted for the most
part English provincial terms, often of barbarous sound, such as gault,
cornbrash, clunch clay; and affixed them to subdivisions of the British
series. Many of these still retain their place in our scientific
classifications, and attest his priority of arrangement.


MODERN PROGRESS OF GEOLOGY.

The contention of the rival factions of the Vulcanists and Neptunists
had been carried to such a height, that these names had become terms of
reproach; and the two parties had been less occupied in searching for
truth, than for such arguments as might strengthen their own cause or
serve to annoy their antagonists. A new school at last arose, who
professed the strictest neutrality, and the utmost indifference to the
systems of Werner and Hutton, and who resolved diligently to devote
their labors to observation. The reaction, provoked by the intemperance
of the conflicting parties, now produced a tendency to extreme caution.
Speculative views were discountenanced, and, through fear of exposing
themselves to the suspicion of a bias towards the dogmas of a party,
some geologists became anxious to entertain no opinion whatever on the
causes of phenomena, and were inclined to skepticism even where the
conclusions deducible from observed facts scarcely admitted of
reasonable doubt.

_Geological Society of London._--But although the reluctance to theorize
was carried somewhat to excess, no measure could be more salutary at
such a moment than a suspension of all attempts to form what were termed
"theories of the earth." A great body of new data were required; and the
Geological Society of London, founded in 1807, conduced greatly to the
attainment of this desirable end. To multiply and record observations,
and patiently to await the result at some future period, was the object
proposed by them; and it was their favorite maxim that the time was not
yet come for a general system of geology, but that all must be content
for many years to be exclusively engaged in furnishing materials for
future generalizations. By acting up to these principles with
consistency, they in a few years disarmed all prejudice, and rescued the
science from the imputation of being a dangerous, or at best but a
visionary pursuit.

A distinguished modern writer has with truth remarked, that the
advancement of three of the main divisions of geological inquiry have
during the last half century been promoted successively by three
different nations of Europe,--the Germans, the English, and the
French.[120] We have seen that the systematic study of what may be
called mineralogical geology had its origin and chief point of activity
in Germany, where Werner first described with precision the mineral
characters of rocks. The classification of the secondary formations,
each marked by their peculiar fossils, belongs, in a great measure, to
England, where the labors before alluded to of Smith, and those of the
most active members of the Geological Society of London, were steadily
directed to these objects. The foundation of the third branch, that
relating to the tertiary formations, was laid in France by the splendid
work of Cuvier and Brongniart, published in 1808, "On the Mineral
Geography and Organic Remains of the Neighborhood of Paris."

We may still trace, in the language of the science and our present
methods of arrangement, the various countries where the growth of these
several departments of geology was at different times promoted. Many
names of simple minerals and rocks remain to this day German; while the
European divisions of the secondary strata are in great part English,
and are, indeed, often founded too exclusively on English types. Lastly,
the subdivisions first established of the succession of strata in the
Paris basin have served as normal groups to which other tertiary
deposits throughout Europe have been compared, even in cases where this
standard was wholly inapplicable.

No period could have been more fortunate for the discovery, in the
immediate neighborhood of Paris, of a rich store of well-preserved
fossils, than the commencement of the present century; for at no former
era had Natural history been cultivated with such enthusiasm in the
French metropolis. The labors of Cuvier in comparative osteology, and of
Lamarck in recent and fossil shells, had raised these departments of
study to a rank of which they had never previously been deemed
susceptible. Their investigations had eventually a powerful effect in
dispelling the illusion which had long prevailed concerning the absence
of analogy between the ancient and modern state of our planet. A close
comparison of the recent and fossil species and the inferences drawn in
regard to their habits, accustomed the geologist to contemplate the
earth as having been at successive periods the dwelling-place of animals
and plants of different races, some terrestrial, and others
aquatic--some fitted to live in seas, others in the waters of lakes and
rivers. By the consideration of these topics, the mind was slowly and
insensibly withdrawn from imaginary pictures of catastrophes and chaotic
confusion, such as haunted the imagination of the early cosmogonists.
Numerous proofs were discovered of the tranquil deposition of
sedimentary matter, and the slow development of organic life. If many
writers, and Cuvier himself in the number, still continued to maintain,
that "the thread of induction was broken,"[121] yet, in reasoning by the
strict rules of induction from recent to fossil species, they in a great
measure disclaimed the dogma which in theory they professed. The
adoption of the same generic, and, in some cases, even of the same
specific, names for the exuviae of fossil animals and their living
analogues, was an important step towards familiarizing the mind with the
idea of the identity and unity of the system in distant eras. It was an
acknowledgment, as it were, that part at least of the ancient memorials
of nature were written in a living language. The growing importance,
then, of the natural history of organic remains may be pointed out as
the characteristic feature of the progress of the science during the
present century. This branch of knowledge has already become an
instrument of great utility in geological classification, and is
continuing daily to unfold new data for grand and enlarged views
respecting the former changes of the earth.

When we compare the result of observations in the last fifty years with
those of the three preceding centuries, we cannot but look forward with
the most sanguine expectations to the degree of excellence to which
geology may be carried, even by the labors of the present generation.
Never, perhaps, did any science, with the exception of astronomy,
unfold, in an equally brief period, so many novel and unexpected truths,
and overturn so many preconceived opinions. The senses had for ages
declared the earth to be at rest, until the astronomer taught that it
was carried through space with inconceivable rapidity. In like manner
was the surface of this planet regarded as having remained unaltered
since its creation, until the geologist proved that it had been the
theatre of reiterated change, and was still the subject of slow but
never-ending fluctuations. The discovery of other systems in the
boundless regions of space was the triumph of astronomy; to trace the
same system through various transformations--to behold it at successive
eras adorned with different hills and valleys, lakes and seas, and
peopled with new inhabitants, was the delightful meed of geological
research. By the geometer were measured the regions of space, and the
relative distances of the heavenly bodies;--by the geologist myriads of
ages were reckoned, not by arithmetical computation, but by a train of
physical events--a succession of phenomena in the animate and inanimate
worlds--signs which convey to our minds more definite ideas than figures
can do of the immensity of time.

Whether our investigation of the earth's history and structure will
eventually be productive of as great practical benefits to mankind as a
knowledge of the distant heavens, must remain for the decision of
posterity. It was not till astronomy had been enriched by the
observations of many centuries, and had made its way against popular
prejudices to the establishment of a sound theory, that its application
to the useful arts was most conspicuous. The cultivation of geology
began at a later period; and in every step which it has hitherto made
towards sound theoretical principles, it had to contend against more
violent prepossessions. The practical advantages already derived from it
have not been inconsiderable; but our generalizations are yet imperfect,
and they who come after us may be expected to reap the most valuable
fruits of our labor. Meanwhile, the charm of first discovery is our own;
and, as we explore this magnificent field of inquiry, the sentiment of a
great historian of our times may continually be present to our minds,
that "he who calls what has vanished back again into being, enjoys a
bliss like that of creating."[122]




CHAPTER V.

PREJUDICES WHICH HAVE RETARDED THE PROGRESS OF GEOLOGY


  Prepossessions in regard to the duration of past time--Prejudices
    arising from our peculiar position as inhabitants of the land--Of
    those occasioned by our not seeing subterranean changes now in
    progress--All these causes combine to make the former course of
    Nature appear different from the present--Objections to the
    doctrine, that causes similar in kind and energy to those now
    acting, have produced the former changes of the earth's surface,
    considered.


If we reflect on the history of the progress of geology, as explained in
the preceding chapters, we perceive that there have been great
fluctuations of opinion respecting the nature of the causes to which
all former changes of the earth's surface are referable. The first
observers conceived the monuments which the geologist endeavors to
decipher to relate to an original state of the earth, or to a period
when there were causes in activity, distinct, in kind and degree, from
those now constituting the economy of nature. These views were gradually
modified, and some of them entirely abandoned, in proportion as
observations were multiplied, and the signs of former mutations more
skilfully interpreted. Many appearances, which had for a long time been
regarded as indicating mysterious and extraordinary agency, were finally
recognized as the necessary result of the laws now governing the
material world; and the discovery of this unlooked-for conformity has at
length induced some philosophers to infer, that, during the ages
contemplated in geology, there has never been any interruption to the
agency of the same uniform laws of change. The same assemblage of
general causes, they conceive, may have been sufficient to produce, by
their various combinations, the endless diversity of effects, of which
the shell of the earth has preserved the memorials; and, consistently
with these principles, the recurrence of analogous changes is expected
by them in time to come.

Whether we coincide or not in this doctrine, we must admit that the
gradual progress of opinion concerning the succession of phenomena in
very remote eras, resembles, in a singular manner, that which has
accompanied the growing intelligence of every people, in regard to the
economy of nature in their own times. In an early state of advancement,
when a great number of natural appearances are unintelligible, an
eclipse, an earthquake, a flood, or the approach of a comet, with many
other occurrences afterwards found to belong to the regular course of
events, are regarded as prodigies. The same delusion prevails as to
moral phenomena, and many of these are ascribed to the intervention of
demons, ghosts, witches, and other immaterial and supernatural agents.
By degrees, many of the enigmas of the moral and physical world are
explained, and, instead of being due to extrinsic and irregular causes,
they are found to depend on fixed and invariable laws. The philosopher
at last becomes convinced of the undeviating uniformity of secondary
causes; and, guided by his faith in this principle, he determines the
probability of accounts transmitted to him of former occurrences, and
often rejects the fabulous tales of former times, on the ground of their
being irreconcilable with the experience of more enlightened ages.

_Prepossessions in regard to the duration of past time._--As a belief in
the want of conformity in the causes by which the earth's crust has been
modified in ancient and modern periods was, for a long time, universally
prevalent, and that, too, amongst men who were convinced that the order
of nature had been uniform for the last several thousand years, every
circumstance which could have influenced their minds and given an undue
bias to their opinions deserves particular attention. Now the reader
may easily satisfy himself, that, however undeviating the course of
nature may have been from the earliest epochs, it was impossible for the
first cultivators of geology to come to such a conclusion, so long as
they were under a delusion as to the age of the world, and the date of
the first creation of animate beings. However fantastical some theories
of the sixteenth century may now appear to us,--however unworthy of men
of great talent and sound judgment,--we may rest assured that, if the
same misconception now prevailed in regard to the memorials of human
transactions, it would give rise to a similar train of absurdities. Let
us imagine, for example, that Champollion, and the French and Tuscan
literati lately engaged in exploring the antiquities of Egypt, had
visited that country with a firm belief that the banks of the Nile were
never peopled by the human race before the beginning of the nineteenth
century, and that their faith in this dogma was as difficult to shake as
the opinion of our ancestors that the earth was never the abode of
living beings until the creation of the present continents, and of the
species now existing,--it is easy to perceive what extravagant systems
they would frame, while under the influence of this delusion, to account
for the monuments discovered in Egypt. The sight of the pyramids,
obelisks, colossal statues, and ruined temples, would fill them with
such astonishment, that for a time they would be as men
spell-bound--wholly incapable of reasoning with sobriety. They might
incline at first to refer the construction of such stupendous works to
some superhuman powers of a primeval world. A system might be invented
resembling that so gravely advanced by Manetho, who relates that a
dynasty of gods originally ruled in Egypt, of whom Vulcan, the first
monarch, reigned nine thousand years; after whom came Hercules and other
demigods, who were at last succeeded by human kings.

When some fanciful speculations of this kind had amused their
imaginations for a time, some vast repository of mummies would be
discovered, and would immediately undeceive those antiquaries who
enjoyed an opportunity of personally examining them; but the prejudices
of others at a distance, who were not eye-witnesses of the whole
phenomena, would not be so easily overcome. The concurrent report of
many travellers would, indeed, render it necessary for them to
accommodate ancient theories to some of the new facts, and much wit and
ingenuity would be required to modify and defend their old positions.
Each new invention would violate a greater number of known analogies;
for if a theory be required to embrace some false principle, it becomes
more visionary in proportion as facts are multiplied, as would be the
case if geometers were now required to form an astronomical system on
the assumption of the immobility of the earth.

Amongst other fanciful conjectures concerning the history of Egypt, we
may suppose some of the following to be started. "As the banks of the
Nile have been so recently colonized for the first time, the curious
substances called mummies could never in reality have belonged to men.
They may have been generated by some _plastic virtue_ residing in the
interior of the earth, or they may be abortions of Nature produced by
her incipient efforts in the work of creation. For if deformed beings
are sometimes born even now, when the scheme of the universe is fully
developed, many more may have been 'sent before their time, scarce half
made up,' when the planet itself was in the embryo state. But if these
notions appear to derogate from the perfection of the Divine attributes,
and if these mummies be in all their parts true representations of the
human form, may we not refer them to the future rather than the
past?--May we not be looking into the womb of Nature, and not her grave?
May not these images be like the shades of the unborn in Virgil's
Elysium--the archetypes of men not yet called into existence?"

These speculations, if advocated by eloquent writers, would not fail to
attract many zealous votaries, for they would relieve men from the
painful necessity of renouncing preconceived opinions. Incredible as
such skepticism may appear, it has been rivalled by many systems of the
sixteenth and seventeenth centuries, and among others by that of the
learned Falloppio, who regarded the tusks of fossil elephants as earthy
concretions, and the pottery or fragments of vases in the Monte
Testaceo, near Rome, as works of nature, and not of art. But when one
generation had passed away, and another, not compromised to the support
of antiquated dogmas, had succeeded, they would review the evidence
afforded by mummies more impartially, and would no longer controvert the
preliminary question, that human beings had lived in Egypt before the
nineteenth century: so that when a hundred years perhaps had been lost,
the industry and talents of the philosopher would be at last directed to
the elucidation of points of real historical importance.

But the above arguments are aimed against one only of many prejudices
with which the earlier geologists had to contend. Even when they
conceded that the earth had been peopled with animate beings at an
earlier period than was at first supposed, they had no conception that
the quantity of time bore so great a proportion to the historical era as
is now generally conceded. How fatal every error as to the quantity of
time must prove to the introduction of rational views concerning the
state of things in former ages, may be conceived by supposing the annals
of the civil and military transactions of a great nation to be perused
under the impression that they occurred in a period of one hundred
instead of two thousand years. Such a portion of history would
immediately assume the air of a romance; the events would seem devoid of
credibility, and inconsistent with the present course of human affairs.
A crowd of incidents would follow each other in thick succession. Armies
and fleets would appear to be assembled only to be destroyed, and cities
built merely to fall in ruins. There would be the most violent
transitions from foreign or intestine war to periods of profound peace,
and the works effected during the years of disorder or tranquillity
would appear alike superhuman in magnitude.

He who should study the monuments of the natural world under the
influence of a similar infatuation, must draw a no less exaggerated
picture of the energy and violence of causes, and must experience the
same insurmountable difficulty in reconciling the former and present
state of nature. If we could behold in one view all the volcanic cones
thrown up in Iceland, Italy, Sicily, and other parts of Europe, during
the last five thousand years, and could see the lavas which have flowed
during the same period; the dislocations, subsidences, and elevations
caused during earthquakes; the lands added to various deltas, or
devoured by the sea, together with the effects of devastation by floods,
and imagine that all these events had happened in one year, we must form
most exalted ideas of the activity of the agents, and the suddenness of
the revolutions. Were an equal amount of change to pass before our eyes
in the next year, could we avoid the conclusion that some great crisis
of nature was at hand? If geologists, therefore, have misinterpreted the
signs of a succession of events, so as to conclude that centuries were
implied where the characters imported thousands of years, and thousands
of years where the language of Nature signified millions, they could
not, if they reasoned logically from such false premises, come to any
other conclusion than that the system of the natural world had undergone
a complete revolution.

We should be warranted in ascribing the erection of the great pyramid to
superhuman power, if we were convinced that it was raised in one day;
and if we imagine, in the same manner, a continent or mountain-chain to
have been elevated during an equally small fraction of the time which
was really occupied in upheaving it, we might then be justified in
inferring, that the subterranean movements were once far more energetic
than in our own times. We know that during one earthquake the coast of
Chili may be raised for a hundred miles to the average height of about
three feet. A repetition of two thousand shocks, of equal violence,
might produce a mountain-chain one hundred miles long, and six thousand
feet high. Now, should one or two only of these convulsions happen in a
century, it would be consistent with the order of events experienced by
the Chilians from the earliest times; but if the whole of them were to
occur in the next hundred years, the entire district must be
depopulated, scarcely any animals or plants could survive, and the
surface would be one confused heap of ruin and desolation.

One consequence of undervaluing greatly the quantity of past time, is
the apparent coincidence which it occasions of events necessarily
disconnected, or which are so unusual, that it would be inconsistent
with all calculation of chances to suppose them to happen at one and the
same time. When the unlooked-for association of such rare phenomena is
witnessed in the present course of nature, it scarcely ever fails to
excite a suspicion of the preternatural in those minds which are not
firmly convinced of the uniform agency of secondary causes;--as if the
death of some individual in whose fate they are interested happens to
be accompanied by the appearance of a luminous meteor, or a comet, or
the shock of an earthquake. It would be only necessary to multiply such
coincidences indefinitely, and the mind of every philosopher would be
disturbed. Now it would be difficult to exaggerate the number of
physical events, many of them most rare and unconnected in their nature,
which were imagined by the Woodwardian hypothesis to have happened in
the course of a few months; and numerous other examples might be found
of popular geological theories, which require us to imagine that a long
succession of events happened in a brief and almost momentary period.

Another liability to error, very nearly allied to the former, arises
from the frequent contact of geological monuments referring to very
distant periods of time. We often behold, at one glance, the effects of
causes which have acted at times incalculably remote, and yet there may
be no striking circumstances to mark the occurrence of a great chasm in
the chronological series of Nature's archives. In the vast interval of
time which may really have elapsed between the results of operations
thus compared, the physical condition of the earth may, by slow and
insensible modifications, have become entirely altered; one or more
races of organic beings may have passed away, and yet have left behind,
in the particular region under contemplation, no trace of their
existence.

To a mind unconscious of these intermediate events, the passage from one
state of things to another must appear so violent, that the idea of
revolutions in the system inevitably suggests itself. The imagination is
as much perplexed by the deception, as it might be if two distant points
in space were suddenly brought into immediate proximity. Let us suppose,
for a moment, that a philosopher should lie down to sleep in some arctic
wilderness, and then be transferred by a power, such as we read of in
tales of enchantment, to a valley in a tropical country, where, on
awaking, he might find himself surrounded by birds of brilliant plumage,
and all the luxuriance of animal and vegetable forms of which Nature is
so prodigal in those regions. The most reasonable supposition, perhaps,
which he could make, if by the necromancer's art he were placed in such
a situation, would be, that he was dreaming; and if a geologist form
theories under a similar delusion, we cannot expect him to preserve more
consistency in his speculations than in the train of ideas in an
ordinary dream.

It may afford, perhaps, a lively illustration of the principle here
insisted upon, if I recall to the reader's recollection the legend of
the Seven Sleepers. The scene of that popular fable was placed in the
two centuries which elapsed between the reign of the emperor Decius and
the death of Theodosius the younger. In that interval of time (between
the years 249 and 450 of our era) the union of the Roman Empire had been
dissolved, and some of its fairest provinces overrun by the barbarians
of the north. The seat of government had passed from Rome to
Constantinople, and the throne from a pagan persecutor to a succession
of Christian and orthodox princes. The genius of the empire had been
humbled in the dust, and the altars of Diana and Hercules were on the
point of being transferred to Catholic saints and martyrs. The legend
relates, "that when Decius was still persecuting the Christians, seven
noble youths of Ephesus concealed themselves in a spacious cavern in the
side of an adjacent mountain, where they were doomed to perish by the
tyrant, who gave orders that the entrance should be firmly secured with
a pile of huge stones. They immediately fell into a deep slumber, which
was miraculously prolonged, without injuring the powers of life, during
a period of 187 years. At the end of that time the slaves of Adolius, to
whom the inheritance of the mountain had descended, removed the stones
to supply materials for some rustic edifice: the light of the sun darted
into the cavern, and the Seven Sleepers were permitted to awake. After a
slumber, as they thought, of a few hours, they were pressed by the calls
of hunger, and resolved that Jamblichus, one of their number, should
secretly return to the city to purchase bread for the use of his
companions. The youth could no longer recognize the once familiar aspect
of his native country, and his surprise was increased by the appearance
of a large cross triumphantly erected over the principal gate of
Ephesus. His singular dress and obsolete language confounded the baker,
to whom he offered an ancient medal of Decius as the current coin of the
empire; and Jamblichus, on the suspicion of a secret treasure, was
dragged before the judge. Their mutual inquiries produced the amazing
discovery, that two centuries were almost elapsed since Jamblichus and
his friends had escaped from the rage of a pagan tyrant."[123]

This legend was received as authentic throughout the Christian world
before the end of the sixth century, and was afterwards introduced by
Mahomet as a divine revelation into the Koran, and from hence was
adopted and adorned by all the nations from Bengal to Africa who
professed the Mahometan faith. Some vestiges even of a similar tradition
have been discovered in Scandinavia. "This easy and universal belief,"
observes the philosophical historian of the Decline and Fall, "so
expressive of the sense of mankind, may be ascribed to the genuine merit
of the fable itself. We imperceptibly advance from youth to age, without
observing the gradual, but incessant, change of human affairs; and even,
in our larger experience of history, the imagination is accustomed, by a
perpetual series of causes and effects, to unite the most distant
revolutions. But if the interval between two memorable eras could be
instantly annihilated; if it were possible, after a momentary slumber of
two hundred years, to display the new world to the eyes of a spectator
who still retained a lively and recent impression of the old, his
surprise and his reflections would furnish the pleasing subject of a
philosophical romance."[124]

_Prejudices arising from our peculiar position as inhabitants of the
land._--The sources of prejudice hitherto considered may be deemed
peculiar for the most part to the infancy of the science, but others
are common to the first cultivators of geology and to ourselves, and are
all singularly calculated to produce the same deception, and to
strengthen our belief that the course of nature in the earlier ages
differed widely from that now established. Although these circumstances
cannot be fully explained without assuming some things as proved, which
it will be the object of another part of this work to demonstrate, it
may be well to allude to them briefly in this place.

The first and greatest difficulty, then, consists in an habitual
unconsciousness that our position as observers is essentially
unfavorable, when we endeavor to estimate the nature and magnitude of
the changes now in progress. In consequence of our inattention to this
subject, we are liable to serious mistakes in contrasting the present
with former states of the globe. As dwellers on the land, we inhabit
about a fourth part of the surface; and that portion is almost
exclusively a theatre of decay, and not of reproduction. We know,
indeed, that new deposits are annually formed in seas and lakes, and
that every year some new igneous rocks are produced in the bowels of the
earth, but we cannot watch the progress of their formation; and as they
are only present to our minds by the aid of reflection, it requires an
effort both of the reason and the imagination to appreciate duly their
importance. It is, therefore, not surprising that we estimate very
imperfectly the result of operations thus invisible to us; and that,
when analogous results of former epochs are presented to our inspection,
we cannot immediately recognize the analogy. He who has observed the
quarrying of stone from a rock, and has seen it shipped for some distant
port, and then endeavors to conceive what kind of edifice will be raised
by the materials, is in the same predicament as a geologist, who, while
he is confined to the land, sees the decomposition of rocks, and the
transportation of matter by rivers to the sea, and then endeavors to
picture to himself the new strata which Nature is building beneath the
waters.

_Prejudices arising from our not seeing subterranean changes._--Nor is
his position less unfavorable when, beholding a volcanic eruption, he
tries to conceive what changes the column of lava has produced, in its
passage upwards, on the intersected strata; or what form the melted
matter may assume at great depths on cooling; or what may be the extent
of the subterranean rivers and reservoirs of liquid matter far beneath
the surface. It should, therefore, be remembered, that the task imposed
on those who study the earth's history requires no ordinary share of
discretion; for we are precluded from collating the corresponding parts
of the system of things as it exists now, and as it existed at former
periods. If we were inhabitants of another element--if the great ocean
were our domain, instead of the narrow limits of the land, our
difficulties would be considerably lessened; while, on the other hand,
there can be little doubt, although the reader may, perhaps, smile at
the bare suggestion of such an idea, that an amphibious being, who
should possess our faculties, would still more easily arrive at sound
theoretical opinions in geology, since he might behold, on the one
hand, the decomposition of rocks in the atmosphere, or the
transportation of matter by running water; and, on the other, examine
the deposition of sediment in the sea, and the imbedding of animal and
vegetable remains in new strata. He might ascertain, by direct
observation, the action of a mountain torrent, as well as of a marine
current; might compare the products of volcanoes poured out upon the
land with those ejected beneath the waters; and might mark, on the one
hand, the growth of the forest, and, on the other, that of the coral
reef. Yet, even with these advantages, he would be liable to fall into
the greatest errors, when endeavoring to reason on rocks of subterranean
origin. He would seek in vain, within the sphere of his observation, for
any direct analogy to the process of their formation, and would
therefore be in danger of attributing them, wherever they are upraised
to view, to some "primeval state of nature."

But if we may be allowed so far to indulge the imagination, as to
suppose a being entirely confined to the nether world--some "dusky
melancholy sprite," like Umbriel, who could "flit on sooty pinions to
the central earth," but who was never permitted to "sully the fair face
of light," and emerge into the regions of water and of air; and if this
being should busy himself in investigating the structure of the globe,
he might frame theories the exact converse of those usually adopted by
human philosophers. He might infer that the stratified rocks, containing
shells and other organic remains, were the oldest of created things,
belonging to some original and nascent state of the planet. "Of these
masses," he might say, "whether they consist of loose incoherent sand,
soft clay, or solid stone, none have been formed in modern times. Every
year some part of them are broken and shattered by earthquakes, or
melted by volcanic fire; and when they cool down slowly from a state of
fusion, they assume a new and more crystalline form, no longer
exhibiting that stratified disposition and those curious impressions and
fantastic markings, by which they were previously characterized. This
process cannot have been carried on for an indefinite time, for in that
case all the stratified rocks would long ere this have been fused and
crystallized. It is therefore probable that the whole planet once
consisted of these mysterious and curiously bedded formations at a time
when the volcanic fire had not yet been brought into activity. Since
that period there seems to have been a gradual development of heat; and
this augmentation we may expect to continue till the whole globe shall
be in a state of fluidity and incandescence."

Such might be the system of the Gnome at the very time that the
followers of Leibnitz, reasoning on what they saw on the outer surface,
might be teaching the opposite doctrine of gradual refrigeration, and
averring that the earth had begun its career as a fiery comet, and might
be destined hereafter to become a frozen mass. The tenets of the schools
of the nether and of the upper world would be directly opposed to each
other, for both would partake of the prejudices inevitably resulting
from the continual contemplation of one class of phenomena to the
exclusion of another. Man observes the annual decomposition of
crystalline and igneous rocks, and may sometimes see their conversion
into stratified deposits; but he cannot witness the reconversion of the
sedimentary into the crystalline by subterranean fire. He is in the
habit of regarding all the sedimentary rocks as more recent than the
unstratified, for the same reason that we may suppose him to fall into
the opposite error if he saw the origin of the igneous class only.

It was not an impossible contingency, that astronomers might have been
placed at some period in a situation much resembling that in which the
geologist seems to stand at present. If the Italians, for example, in
the early part of the twelfth century, had discovered at Amalfi, instead
of the pandects of Justinian, some ancient manuscripts filled with
astronomical observations relating to a period of three thousand years,
and made by some ancient geometers who possessed optical instruments as
perfect as any in modern Europe, they would probably, on consulting
these memorials, have come to a conclusion that there had been a great
revolution in the solar and sidereal systems. "Many primary and
secondary planets," they might say, "are enumerated in these tables,
which exist no longer. Their positions are assigned with such precision
that we may assure ourselves that there is nothing in their place at
present but the blue ether. Where one star is visible to us, these
documents represent several thousands. Some of those which are now
single consisted then of two separate bodies, often distinguished by
different colors, and revolving periodically round a common centre of
gravity. There is nothing analogous to them in the universe at present;
for they were neither fixed stars nor planets, but seem to have stood in
the mutual relation of sun and planet to each other. We must conclude,
therefore, that there has occurred, at no distant period, a tremendous
catastrophe, whereby thousands of worlds have been annihilated at once,
and some heavenly bodies absorbed into the substance of others."

When such doctrines had prevailed for ages, the discovery of some of the
worlds, supposed to have been lost (the satellites of Jupiter, for
example), by aid of the first rude telescope invented after the revival
of science, would not dissipate the delusion, for the whole burden of
proof would now be thrown on those who insisted on the stability of the
system from a remote period, and these philosophers would be required to
demonstrate the existence of _all_ the worlds said to have been
annihilated.

Such popular prejudices would be most unfavorable to the advancement of
astronomy; for, instead of persevering in the attempt to improve their
instruments, and laboriously to make and record observations, the
greater number would despair of verifying the continued existence of the
heavenly bodies not visible to the naked eye. Instead of confessing the
extent of their ignorance, and striving to remove it by bringing to
light new facts, they would indulge in the more easy and indolent
employment of framing imaginary theories concerning catastrophes and
mighty revolutions in the system of the universe.

For more than two centuries the shelly strata of the Subapennine hills
afforded matter of speculation to the early geologists of Italy, and few
of them had any suspicion that similar deposits were then forming in the
neighboring sea. They were as unconscious of the continued action of
causes still producing similar effects, as the astronomers, in the case
above supposed, of the existence of certain heavenly bodies still giving
and reflecting light, and performing their movements as of old. Some
imagined that the strata, so rich in organic remains, instead of being
due to secondary agents, had been so created in the beginning of things
by the fiat of the Almighty. Others, as we have seen, ascribed the
imbedded fossil bodies to some plastic power which resided in the earth
in the early ages of the world. In what manner were these dogmas at
length exploded? The fossil relics were carefully compared with their
living analogues, and all doubts as to their organic origin were
eventually dispelled. So, also, in regard to the nature of the
containing beds of mud, sand, and limestone: those parts of the bottom
of the sea were examined where shells are now becoming annually entombed
in new deposits. Donati explored the bed of the Adriatic, and found the
closest resemblance between the strata there forming, and those which
constituted hills above a thousand feet high in various parts of the
Italian peninsula. He ascertained by dredging that living testacea were
there grouped together in precisely the same manner as were their fossil
analogues in the inland strata; and while some of the recent shells of
the Adriatic were becoming incrusted with calcareous rock, he observed
that others had been newly buried in sand and clay, precisely as fossil
shells occur in the Subapennine hills. This discovery of the identity of
modern and ancient submarine operations was not made without the aid of
artificial instruments, which, like the telescope, brought phenomena
into view not otherwise within the sphere of human observation.

In like manner, the volcanic rocks of the Vicentin had been studied in
the beginning of the last century; but no geologist suspected, before
the time of Arduino, that these were composed of ancient submarine
lavas. During many years of controversy, the popular opinion inclined to
a belief that basalt and rocks of the same class had been precipitated
from a chaotic fluid, or an ocean which rose at successive periods over
the continents, charged with the component elements of the rocks in
question. Few will now dispute that it would have been difficult to
invent a theory more distant from the truth; yet we must cease to wonder
that it gained so many proselytes, when we remember that its claims to
probability arose partly from the very circumstance of its confirming
the assumed want of analogy between geological causes and those now in
action. By what train of investigations were geologists induced at
length to reject these views, and to assent to the igneous origin of the
trappean formations? By an examination of volcanoes now active, and by
comparing their structure and the composition of their lavas with the
ancient trap-rocks.

The establishment, from time to time, of numerous points of
identification, drew at length from geologists a reluctant admission,
that there was more correspondence between the condition of the globe at
remote eras and now, and more uniformity in the laws which have
regulated the changes of its surface, than they at first imagined. If,
in this state of the science, they still despaired of reconciling every
class of geological phenomena to the operations of ordinary causes, even
by straining analogy to the utmost limits of credibility, we might have
expected, at least, that the balance of probability would now have been
presumed to incline towards the close analogy of the ancient and modern
causes. But, after repeated experience of the failure of attempts to
speculate on geological monuments, as belonging to a distinct order of
things, new sects continued to persevere in the principles adopted by
their predecessors. They still began, as each new problem presented
itself, whether relating to the animate or inanimate world, to assume an
original and dissimilar order of nature; and when at length they
approximated, or entirely came round to an opposite opinion, it was
always with the feeling, that they were conceding what they had been
justified _a priori_ in deeming improbable. In a word, the same men who,
as natural philosophers, would have been most incredulous respecting any
extraordinary deviations from the known course of nature, if reported to
have happened _in their own time_, were equally disposed, as geologists,
to expect the proofs of such deviations at every period of the past.

I shall proceed in the following chapters to enumerate some of the
principal difficulties still opposed to the theory of the uniform nature
and energy of the causes which have worked successive changes in the
crust of the earth, and in the condition of its living inhabitants. The
discussion of so important a question on the present occasion may appear
premature, but it is one which naturally arises out of a review of the
former history of the science. It is, of course, impossible to enter
into such speculative topics, without occasionally carrying the novice
beyond his depth, and appealing to facts and conclusions with which he
will be unacquainted, until he has studied some elementary work on
geology, but it may be useful to excite his curiosity, and lead him to
study such works by calling his attention at once to some of the
principal points of controversy.[125]




CHAPTER VI.

DOCTRINE OF THE DISCORDANCE OF THE ANCIENT AND MODERN CAUSES OF CHANGE
CONTROVERTED.


  Climate of the Northern Hemisphere formerly different--Direct proofs
    from the organic remains of the Italian strata--Proofs from analogy
    derived from extinct quadrupeds--Imbedding of animals in
    icebergs--Siberian mammoths--Evidence in regard to temperature, from
    the fossils of tertiary and secondary rocks--From the plants of the
    coal formation--Northern limit of these fossils--Whether such plants
    could endure the long continuance of an arctic night.


_Climate of the Northern hemisphere formerly different._--Proofs of
former revolutions in climate, as deduced from fossil remains, have
afforded one of the most popular objections to the theory which
endeavors to explain all geological changes by reference to those now in
progress on the earth. The probable causes, therefore, of fluctuations
in climate, may first be treated of.

That the climate of the Northern hemisphere has undergone an important
change, and that its mean annual temperature must once have more nearly
resembled that now experienced within the tropics, was the opinion of
some of the first naturalists who investigated the contents of the
ancient strata. Their conjecture became more probable when the shells
and corals of the older tertiary and many secondary rocks were carefully
examined; for the organic remains of these formations were found to be
intimately connected by generic affinity with species now living in
warmer latitudes. At a later period, many reptiles, such as turtles,
tortoises, and large saurian animals, were discovered in European
formations in great abundance; and they supplied new and powerful
arguments, from analogy, in support of the doctrine, that the heat of
the climate had been great when our secondary strata were deposited.
Lastly, when the botanist turned his attention to the specific
determination of fossil plants, the evidence acquired still fuller
confirmation; for the flora of a country is peculiarly influenced by
temperature: and the ancient vegetation of the earth might have been
expected more readily than the forms of animals, to have afforded
conflicting proofs, had the popular theory been without foundation. When
the examination of fossil remains was extended to rocks in the most
northern parts of Europe and North America, and even to the Arctic
regions, indications of the same revolution in climate were discovered.

It cannot be said, that in this, as in many other departments of
geology, we have investigated the phenomena of former eras, and
neglected those of the present state of things. On the contrary, since
the first agitation of this interesting question, the accessions to our
knowledge of living animals and plants have been immense, and have far
surpassed all the data previously obtained for generalizing on the
relation of certain types of organization to particular climates. The
tropical and temperate zones of South America and of Australia have been
explored; and, on close comparison, it has been found that scarcely any
of the species of the animate creation in these extensive continents are
identical with those inhabiting the old world. Yet the zoologist and
botanist, well acquainted with the geographical distribution of organic
beings in other parts of the globe, would have been able, if distinct
groups of species had been presented to them from these regions, to
recognize those which had been collected from latitudes within, and
those which were brought from without the tropics.

Before I attempt to explain the probable causes of great vicissitudes of
temperature on the earth's surface, I shall take a rapid view of some of
the principal data which appear to support the popular opinions now
entertained on the subject. To insist on the soundness of these
inferences, is the more necessary, because some zoologists have
undertaken to vindicate the uniformity of the laws of nature, not by
accounting for former fluctuations in climate, but by denying the value
of the evidence in their favor.[126]

_Proofs from fossil shells in tertiary strata._--In Sicily, Calabria,
and in the neighborhood of Naples, the fossil testacea of the most
modern tertiary formations belong almost entirely to species now
inhabiting the Mediterranean; but as we proceed northwards in the
Italian peninsula we find in the strata called Subapennine an assemblage
of fossil shells departing somewhat more widely from the type of the
neighboring seas. The proportion of species identifiable with those now
living in the Mediterranean is still considerable; but it no longer
predominates, as in the South of Italy and part of Sicily, over the
unknown species. Although occurring in localities which are removed
several degrees farther from the equator (as at Sienna, Parma, Asti,
&c.), the shells yield clear indications of a warmer climate. This
evidence is of great weight, and is not neutralized by any facts of a
conflicting character; such, for instance, as the association, in the
same group, of individuals referable to species now confined to arctic
regions. Whenever any of the fossil shells are identified with living
species foreign to the Mediterranean, it is not in the Northern Ocean,
but nearer the tropics, that they must be sought: on the other hand, the
associated unknown species belong, for the most part, to _genera_ which
are now most largely developed in equinoctial regions, as, for example,
the genera Cancellaria, Cassidaria, Pleurotoma, Conus, and Cypraea.

On comparing the fossils of the tertiary deposits of Paris and London
with those of Bourdeaux, and these again with the more modern strata of
Sicily, we should at first expect that they would each indicate a higher
temperature in proportion as they are situated farther to the south.
But the contrary is true; of the shells belonging to these several
groups, whether freshwater or marine, some are of extinct, others of
living species. Those found in the older, or Eocene, deposits of Paris
and London, although six or seven degrees to the north of the Miocene
strata at Bourdeaux, afford evidence of a warmer climate; while those of
Bourdeaux imply that the sea in which they lived was of a higher
temperature than that of Sicily, where the shelly strata were formed six
or seven degrees nearer to the equator. In these cases the greater
antiquity of the several formations (the Parisian being the oldest and
the Sicilian the newest) has more than counterbalanced the influence
which latitude would otherwise exert, and this phenomenon clearly points
to a gradual and successive refrigeration of climate.

_Siberian Mammoths._--It will naturally be asked, whether some recent
geological discoveries bringing evidence to light of a colder, or as it
has been termed "glacial epoch," towards the close of the tertiary
periods throughout the northern hemisphere, does not conflict with the
theory above alluded to, of a warmer temperature having prevailed in the
eras of the Eocene, Miocene, and Pliocene formations. In answer to this
inquiry, it may certainly be affirmed, that an oscillation of climate
has occurred in times immediately antecedent to the peopling of the
earth by man; but proof of the intercalation of a less genial climate at
an era when nearly all the marine and terrestrial testacea had already
become specifically the same as those now living, by no means rebuts the
conclusion previously drawn, in favor of a warmer condition of the
globe, during the ages which elapsed while the tertiary strata were
deposited. In some of the most superficial patches of sand, gravel, and
loam, scattered very generally over Europe, and containing recent
shells, the remains of extinct species of land quadrupeds have been
found, especially in places where the alluvial matter appears to have
been washed into small lakes, or into depressions in the plains
bordering ancient rivers. Similar deposits have also been lodged in
rents and caverns of rocks, where they may have been swept in by land
floods, or introduced by engulphed rivers during changes in the physical
geography of these countries. The various circumstances under which the
bones of animals have been thus preserved, will be more fully considered
hereafter;[127] I shall only state here, that among the extinct mammalia
thus entombed, we find species of the elephant, rhinoceros,
hippopotamus, bear, hyaena, lion, tiger, monkey (macacus[128]), and many
others; consisting partly of genera now confined to warmer regions.

It is certainly probable that when some of these quadrupeds abounded in
Europe, the climate was milder than that now experienced. The
hippopotamus, for example, is now only met with where the temperature of
the water is warm and nearly uniform throughout the year, and where the
rivers are never frozen over. Yet when the great fossil species
(_Hippopotamus major_, Cuv.) inhabited England, the testacea of our
country were nearly the same as those now existing, and the climate
cannot be supposed to have been very hot. The bones of this animal have
lately been found by Mr. Strickland, together with those of a bear and
other mammalia, at Cropthorn, near Evesham, in Worcestershire, in
alluvial sand, together with twenty-three species of terrestrial and
freshwater shells, all, with two exceptions, of British species. The bed
of sand, containing the shells and bones, reposes on lias, and is
covered with alternating strata of gravel, sand, and loam.[129]

The mammoth also appears to have existed in England when the temperature
of our latitudes could not have been very different from that which now
prevails; for remains of this animal have been found at North Cliff, in
the county of York, in a lacustrine formation, in which all the land and
freshwater shells, thirteen in number, can be identified with species
and varieties now existing in that county. Bones of the bison, also, an
animal now inhabiting a cold or temperate climate, have been found in
the same place. That these quadrupeds, and the indigenous species of
testacea associated with them, were all contemporary inhabitants of
Yorkshire, has been established by unequivocal proof. The Rev. W. V.
Vernon Harcourt caused a pit to be sunk to the depth of twenty-two feet
through undisturbed strata, in which the remains of the mammoth were
found imbedded, together with the shells, in a deposit which had
evidently resulted from tranquil waters.[130]

In the valley of the Thames, as at Ilford and Grays, in Essex, bones of
the elephant and rhinoceros occur in strata abounding in freshwater
shells of the genera Unio, Cyclas, Paludina, Valvata, Ancylus, and
others. These fossil shells belong for the most part to species now
living in the same district, yet some few of them are extinct, as, for
example, a species of Cyrena, a genus no longer inhabiting Europe, and
now entirely restricted to warmer latitudes.

When reasoning on such phenomena, the reader must always bear in mind
that the fossil individuals belonged to _species_ of elephant,
rhinoceros, hippopotamus, bear, tiger, and hyaena, distinct from those
which now dwell within or near the tropics. Dr. Fleming, in a discussion
on this subject, has well remarked that a near resemblance in form and
osteological structure is not always followed, in the existing creation,
by a similarity of geographical distribution; and we must therefore be
on our guard against deciding too confidently, from mere analogy of
anatomical structure, respecting the habits and physiological
peculiarities of _species_ now no more. "The zebra delights to roam over
the tropical plains, while the horse can maintain its existence
throughout an Iceland winter. The buffalo, like the zebra, prefers a
high temperature, and cannot thrive even where the common ox prospers.
The musk-ox, on the other hand, though nearly resembling the buffalo,
prefers the stinted herbage of the arctic regions, and is able, by its
periodical migrations, to outlive a northern winter. The jackal (_Canis
aureus_) inhabits Africa, the warmer parts of Asia, and Greece; while
the isatis (_Canis lagopus_) resides in the arctic regions. The African
hare and the polar hare have their geographical distribution expressed
in their trivial names;"[131] and different species of bears thrive in
tropical, temperate, and arctic latitudes.

Recent investigations have placed beyond all doubt the important fact
that a species of tiger, identical with that of Bengal, is common in the
neighborhood of Lake Aral, near Sussac, in the forty-fifth degree of
north latitude; and from time to time this animal is now seen in
Siberia, in a latitude as far north as the parallel of Berlin and
Hamburgh.[132] Humboldt remarks that the part of Southern Asia now
inhabited by this Indian species of tiger is separated from the Himalaya
by two great chains of mountains, each covered with perpetual snow,--the
chain of Kuenlun, lat. 35 degrees N., and that of Mouztagh, lat. 42
degrees,--so that it is impossible that these animals should merely have
made excursions from India, so as to have penetrated in summer to the
forty-eighth and fifty-third degrees of north latitude. They must remain
all the winter north of the Mouztagh, or Celestial Mountains. The last
tiger killed, in 1828, on the Lena, in lat. 52-1/4 degrees, was in a
climate colder than that of Petersburg and Stockholm.[133]

We learn from Mr. Hodgson's account of the mammalia of Nepal, that the
tiger is sometimes found at the very edge of perpetual snow in the
Himalaya;[134] and Pennant mentions that it is found among the snows of
Mount Ararat in Armenia. The jaguar, also, has been seen in America,
wandering from Mexico, as far north as Kentucky, lat. 37 degrees
N.,[135] and even as far as 42 degrees S. in South America,--a latitude
which corresponds to that of the Pyrenees in the northern
hemisphere.[136] The range of the puma is still wider, for it roams from
the equator to the Straits of Magellan, being often seen at Port Famine,
in lat. 53 degrees 38 minutes S.

A new species of panther (_Felis irbis_), covered with long hair, has
been discovered in Siberia, evidently inhabiting, like the tiger, a
region north of the Celestial Mountains, which are in lat. 42
degrees.[137]

The two-horned African rhinoceros occurs without the tropics at the Cape
of Good Hope, in lat. 34 degrees 29 minutes S., where it is accompanied
by the elephant, hippopotamus, and hyaena. Here the migration of all
these species towards the south is arrested by the ocean; but if the
continent had been prolonged still farther, and the land had been of
moderate elevation, it is very probable that they might have extended
their range to a greater distance from the tropics.

Now, if the Indian tiger can range in our own times to the southern
borders of Siberia, or skirt the snows of the Himalaya, and if the puma
can reach the fifty-third degree of latitude in South America, we may
easily understand how large species of the same _genera_ may once have
inhabited our temperate climates. The mammoth (_E. primigenius_),
already alluded to, as occurring fossil in England, was decidedly
different from the two existing species of elephants, one of which is
limited to Asia, south of the 31 degrees of N. lat., the other to
Africa, where it extends, as before stated, as far south as the Cape of
Good Hope. The bones of the great fossil species are very widely spread
over Europe and North America; but are nowhere in such profusion as in
Siberia, particularly near the shores of the Frozen Ocean. Are we, then,
to conclude that this animal preferred a polar climate? If so, it may
well be asked, by what food was it sustained, and why does it not still
survive near the arctic circle?[138]

Pallas and other writers describe the bones of the mammoth as abounding
throughout all the Lowlands of Siberia, stretching in a direction west
and east, from the borders of Europe to the extreme point nearest
America, and south and north, from the base of the mountains of Central
Asia to the shores of the Arctic Sea. (See map, fig. 1.) Within this
space, scarcely inferior in area to the whole of Europe, fossil ivory
has been collected almost everywhere, on the banks of the Irtish, Obi,
Yenesei, Lena, and other rivers. The elephantine remains do not occur in
the marshes and low plains, but where the banks of the rivers present
lofty precipices of sand and clay, from which circumstance Pallas very
justly inferred that, if sections could be obtained, similar bones might
be found in all the elevated lands intervening between the great rivers.
Strahlenberg, indeed, had stated, before the time of Pallas, that
wherever any of the great rivers overflowed and cut out fresh channels
during floods, more fossil remains of the same kind were invariably
disclosed.

[Illustration: MAP OF SIBERIA.

Fig. 1.

_Map showing the course of the Siberian rivers from south to north, from
temperate to arctic regions, in the country where the fossil bones of
the Mammoth abound._]

As to the position of the bones, Pallas found them in some places
imbedded together with marine remains; in others, simply with fossil
wood, or lignite, such as, he says, might have been derived from
carbonized peat. On the banks of the Yenesei, below the city of
Krasnojarsk, in lat. 56 degrees, he observed grinders, and bones of
elephants, in strata of yellow and red loam, alternating with coarse
sand and gravel, in which was also much petrified wood of the willow and
other trees. Neither here nor in the neighboring country were there any
marine shells, but merely layers of black coal.[139] But grinders of the
mammoth were collected much farther down the same river, near the sea,
in lat. 70 degrees, mixed with _marine_ petrifactions.[140] Many other
places in Siberia are cited by Pallas, where sea shells and fishes'
teeth accompany the bones of the mammoth, rhinoceros, and Siberian
buffalo, or bison (_Bos priscus_). But it is not on the Obi nor the
Yenesei, but on the Lena, farther to the east, where, in the same
parallels of latitude, the cold is far more intense, that fossil remains
have been found in the most wonderful state of preservation. In 1772,
Pallas obtained from Wiljuiskoi, in lat. 64 degrees, from the banks of
the Wiljui, a tributary of the Lena, the carcass of a rhinoceros (_R.
tichorhinus_), taken from the sand in which it must have remained
congealed for ages, the soil of that region being always frozen to
within a slight depth of the surface. This carcass was compared to a
natural mummy, and emitted an odor like putrid flesh, part of the skin
being still covered with black and gray hairs. So great, indeed, was the
quantity of hair on the foot and head conveyed to St. Petersburg, that
Pallas asked whether the rhinoceros of the Lena might not have been an
inhabitant of the temperate regions of middle Asia, its clothing being
so much warmer than that of the African rhinoceros.[141]

Professor Brandt, of St. Petersburg, in a letter to Baron Alex. Von
Humboldt, dated 1846, adds the following particulars respecting this
wonderful fossil relic:--"I have been so fortunate as to extract from
cavities in the molar teeth of the Wiljui rhinoceros a small quantity of
its half-chewed food, among which fragments of pine leaves, one-half of
the seed of a polygonaceous plant, and very minute portions of wood with
porous cells (or small fragments of coniferous wood), were still
recognizable. It was also remarkable, on a close investigation of the
head, that the blood-vessels discovered in the interior of the mass
appeared filled, even to the capillary vessels, with a brown mass
(coagulated blood), which in many places still showed the red color of
blood."[142]

After more than thirty years, the entire carcass of a mammoth (or
extinct species of elephant) was obtained in 1803, by Mr. Adams, much
farther to the north. It fell from a mass of ice, in which it had been
encased, on the banks of the Lena, in lat. 70 degrees; and so perfectly
had the soft parts of the carcass been preserved, that the flesh, as it
lay, was devoured by wolves and bears. This skeleton is still in the
museum of St. Petersburg, the head retaining its integument and many of
the ligaments entire. The skin of the animal was covered, first, with
black bristles, thicker than horse hair, from twelve to sixteen inches
in length; secondly, with hair of a reddish brown color, about four
inches long; and thirdly, with wool of the same color as the hair, about
an inch in length. Of the fur, upwards of thirty pounds' weight were
gathered from the wet sand-bank. The individual was nine feet high and
sixteen feet long, without reckoning the large curved tusks: a size
rarely surpassed by the largest living male elephants.[143]

It is evident, then, that the mammoth, instead of being naked, like the
living Indian and African elephants, was enveloped in a thick shaggy
covering of fur, probably as impenetrable to rain and cold as that of
the musk ox.[144] The species may have been fitted by nature to
withstand the vicissitudes of a northern climate; and it is certain
that, from the moment when the carcasses, both of the rhinoceros and
elephant, above described, were buried in Siberia, in latitudes 64
degrees and 70 degrees N., the soil must have remained frozen, and the
atmosphere nearly as cold as at this day.

The most recent discoveries made in 1843 by Mr. Middendorf, a
distinguished Russian naturalist, and which he communicated to me in
September, 1846, afford more precise information as to the climate of
the Siberian lowlands, at the period when the extinct quadrupeds were
entombed. One elephant was found on the Tas, between the Obi and
Yenesei, near the arctic circle, about lat. 66 degrees 30 minutes N.,
with some parts of the flesh in so perfect a state that the bulb of the
eye is now preserved in the museum at Moscow. Another carcass, together
with a young individual of the same species, was met with in the same
year, 1843, in lat. 75 degrees 15 minutes N., near the river Taimyr,
with the flesh decayed. It was imbedded in strata of clay and sand, with
erratic blocks, at about 15 feet above the level of the sea. In the same
deposit Mr. Middendorf observed the trunk of a larch tree (_Pinus
larix_), the same wood as that now carried down in abundance by the
Taimyr to the Arctic Sea. There were also associated fossil shells of
_living northern_ species, and which are moreover characteristic of the
drift or _glacial_ deposits of Europe. Among these _Nucula pygmaea_,
_Tellina calcarea_, _Mya truncata_, and _Saxicava rugosa_ were
conspicuous.

So fresh is the ivory throughout northern Russia, that, according to
Tilesius, thousands of fossil tusks have been collected and used in
turning; yet others are still procured and sold in great plenty. He
declares his belief that the bones still left in northern Russia must
greatly exceed in number all the elephants now living on the globe.

We are as yet ignorant of the entire geographical range of the mammoth;
but its remains have been recently collected from the cliffs of frozen
mud and ice on the east side of Behring's Straits, in Eschscholtz's Bay,
in Russian America, lat. 66 degrees N. As the cliffs waste away by the
thawing of the ice, tusks and bones fall out, and a strong odor of
animal matter is exhaled from the mud.[145]

On considering all the facts above enumerated, it seems reasonable to
imagine that a large region in central Asia, including, perhaps, the
southern half of Siberia, enjoyed, at no very remote period in the
earth's history, a temperate climate, sufficiently mild to afford food
for numerous herds of elephants and rhinoceroses, _of species distinct
from those now living_. It has usually been taken for granted that
herbivorous animals of large size require a very luxuriant vegetation
for their support; but this opinion is, according to Mr. Darwin,
completely erroneous:--"It has been derived," he says, "from our
acquaintance with India and the Indian islands, where the mind has been
accustomed to associate troops of elephants with noble forests and
impenetrable jungles. But the southern parts of Africa, from the tropic
of Capricorn to the Cape of Good Hope, although sterile and desert, are
remarkable for the number and great bulk of the indigenous quadrupeds.
We there meet with an elephant, five species of rhinoceros, a
hippopotamus, a giraffe, the bos caffer, the elan, two zebras, the
quagga, two gnus, and several antelopes. Nor must we suppose, that while
the species are numerous, the individuals of each kind are few. Dr.
Andrew Smith saw, in one day's march, in lat. 24 degrees S., without
wandering to any great distance on either side, about 150 rhinoceroses,
with several herds of giraffes, and his party had killed, on the
previous night, eight hippopotamuses. Yet the country which they
inhabited was thinly covered with grass and bushes about four feet high,
and still more thinly with mimosa-trees, so that the wagons of the
travellers were not prevented from proceeding in a nearly direct
line."[146]

In order to explain how so many animals can find support in this region,
it is suggested that the underwood, of which their food chiefly
consists, may contain much nutriment in a small bulk, and also that the
vegetation has a rapid growth; for no sooner is a part consumed than its
place, says Dr. Smith, is supplied by a fresh stock. Nevertheless, after
making every allowance for this successive production and consumption,
it is clear, from the facts above cited, that the quantity of food
required by the larger herbivora is much less than we have usually
imagined. Mr. Darwin conceives that the amount of vegetation supported
at any one time by Great Britain may exceed, in a ten-fold ratio, the
quantity existing on an equal area in the interior parts of Southern
Africa.[147] It is remarked, moreover, in illustration of the small
connection discoverable between abundance of food and the magnitude of
indigenous mammalia, that while in the desert part of Southern Africa
there are so many huge animals; in Brazil, where the splendor and
exuberance of the vegetation are unrivalled, there is not a single wild
quadruped of large size.[148]

It would doubtless be impossible for herds of mammoths and rhinoceroses
to subsist, at present, throughout the year, even in the southern part
of Siberia, covered as it is with snow during winter; but there is no
difficulty in supposing a vegetation capable of nourishing these great
quadrupeds to have once flourished between the latitudes 40 degrees and
60 degrees N.

Dr. Fleming has hinted, that "the kind of food which the existing
species of elephant prefers, will not enable us to determine, or even to
offer a probable conjecture, concerning that of the extinct species. No
one acquainted with the gramineous character of the food of our
fallow-deer, stag, or roe, would have assigned a lichen to the
reindeer."

Travellers mention that, even now, when the climate of eastern Asia is
so much colder than the same parallels of latitude farther west, there
are woods not only of fir, but of birch, poplar, and alder, on the banks
of the Lena, as far north as latitude 60 degrees.

It has, moreover, been suggested, that as, in our own times, the
northern animals migrate, so the Siberian elephant and rhinoceros may
have wandered towards the north in summer. The musk oxen annually desert
their winter quarters in the south, and cross the sea upon the ice, to
graze for four months, from May to September, on the rich pasturage of
Melville Island, in lat. 75 degrees. The mammoths, without passing so far
beyond the arctic circle, may nevertheless have made excursions, during
the heat of a brief northern summer, from the central or temperate parts
of Asia to the sixtieth parallel of latitude.

Now, in this case, the preservation of their bones, or even occasionally
of their entire carcasses, in ice or frozen soil, may be accounted for,
without resorting to speculations concerning sudden revolutions in the
former state and climate of the earth's surface. We are entitled to
assume, that, in the time of the extinct elephant and rhinoceros, the
Lowland of Siberia was less extensive towards the north than now; for we
have seen (p. 80) that the strata of this Lowland, in which the fossil
bones lie buried, were originally deposited beneath the sea; and we
know, from the facts brought to light in Wrangle's Voyage, in the years
1821, 1822, and 1823, that a slow upheaval of the land along the borders
of the Icy Sea is now constantly taking place, similar to that
experienced in part of Sweden. In the same manner, then, as the shores
of the Gulf of Bothnia are extended, not only by the influx of sediment
brought down by rivers, but also by the elevation and consequent drying
up of the bed of the sea, so a like combination of causes may, in modern
times, have been extending the low tract of land where marine shells
and fossil bones occur in Siberia.[149] Such a change in the physical
geography of that region, implying a constant augmentation in the
quantity of arctic land, would, according to principles to be explained
in the next chapter, tend to increase the severity of the winters. We
may conclude, therefore, that, before the land reached so far to the
north, the temperature of the Siberian winter and summer was more nearly
equalized; and a greater degree of winter's cold may, even more than a
general diminution of the mean annual temperature, have finally
contributed to the extermination of the mammoth and its contemporaries.

On referring to the map (p. 79), the reader will see how all the great
rivers of Siberia flow at present from south to north, from temperate to
arctic regions, and they are all liable, like the Mackenzie, in North
America, to remarkable floods, in consequence of flowing in this
direction. For they are filled with running water in their upper or
southern course when completely frozen over for several hundred miles
near their mouths, where they remain blocked up by ice for six months in
every year. The descending waters, therefore, finding no open channel,
rush over the ice, often changing their direction, and sweeping along
forests and prodigious quantities of soil and gravel mixed with ice. Now
the rivers of Siberia are among the largest in the world, the Yenesei
having a course of 2500, the Lena of 2000 miles; so that we may easily
conceive that the bodies of animals which fall into their waters may be
transported to vast distances towards the Arctic Sea, and, before
arriving there, may be stranded upon and often frozen into thick ice.
Afterwards, when the ice breaks up, they may be floated still farther
towards the ocean, until at length they become buried in fluviatile and
submarine deposits near the mouths of rivers.

Humboldt remarks that near the mouths of the Lena a considerable
thickness of frozen soil may be found at all seasons at the depth of a
few feet; so that if a carcass be once imbedded in mud and ice in such a
region and in such a climate, its putrefaction may be arrested for
indefinite ages.[150] According to Prof. Von Baer of St. Petersburg, the
ground is now frozen permanently to the depth of 400 feet, at the town
of Yakutzt, on the western bank of the Lena, in lat. 62 degrees N., 600
miles distant from the polar sea. Mr. Hedenstrom tells us that,
throughout a wide area in Siberia, the boundary cliffs of the lakes and
rivers consist of alternate layers of earthy materials and ice, in
horizontal stratification;[151] and Mr. Middendorf informed us, in 1846,
that, in his tour there three years before, he had bored in Siberia to
the depth of seventy feet, and, after passing through much frozen soil
mixed with ice, had come down upon a solid mass of pure transparent ice,
the thickness of which, after penetrating two or three yards, they did
not ascertain. We may conceive, therefore, that even at the period of
the mammoth, when the Lowland of Siberia was less extensive towards the
north, and consequently the climate more temperate than now, the cold
may still have been sufficiently intense to cause the rivers flowing in
their present direction to sweep down from south to north the bodies of
drowned animals, and there bury them in drift ice and frozen mud.

If it be true that the carcass of the mammoth was imbedded in pure ice,
there are two ways in which it may have been frozen in. We may suppose
the animal to have been overwhelmed by drift snow. I have been informed
by Dr. Richardson, that, in the northern parts of America, comprising
regions now inhabited by many herbivorous quadrupeds, the drift snow is
often converted into permanent glaciers. It is commonly blown over the
edges of steep cliffs, so as to form an inclined talus hundreds of feet
high; and when a thaw commences, torrents rush from the land, and throw
down from the top of the cliff alluvial soil and gravel. This new soil
soon becomes covered with vegetation, and protects the foundation of
snow from the rays of the sun. Water occasionally penetrates into the
crevices and pores of the snow; but, as it soon freezes again, it serves
the more rapidly to consolidate the mass into a compact iceberg. It may
sometimes happen that cattle grazing in a valley at the base of such
cliffs, on the borders of a sea or river, may be overwhelmed, and at
length inclosed in solid ice, and then transported towards the polar
regions. Or a herd of mammoths returning from their summer pastures in
the north, may have been surprised, while crossing a stream, by the
sudden congelation of the waters. The missionary Huc relates, in his
travels in Thibet in 1846, that, after many of his party had been frozen
to death, they pitched their tents on the banks of the Mouroui-Ousson
(which lower down becomes the famous Blue River), and saw from their
encampment "some black shapeless objects ranged in file across the
stream. As they advanced nearer no change either in form or distinctness
was apparent; nor was it till they were quite close, that they
recognized in them a troop of the wild oxen, called Yak by the
Thibetans.[152] There were more than fifty of them incrusted in the ice.
No doubt they had tried to swim across at the moment of congelation, and
had been unable to disengage themselves. Their beautiful heads,
surmounted by huge horns, were still above the surface, but their bodies
were held fast in the ice, which was so transparent that the position of
the imprudent beasts was easily distinguishable; they looked as if still
swimming, but the eagles and ravens had pecked out their eyes."[153]

The foregoing investigations, therefore, lead us to infer that the
mammoth, and some other extinct quadrupeds fitted to live in high
latitudes, were inhabitants of Northern Asia at a time when the
geographical conditions and climate of that continent were different
from the present. But the age of this fauna was comparatively modern in
the earth's history. It appears that when the oldest or eocene tertiary
deposits were formed, a warm temperature pervaded the European seas and
lands. Shells of the genus Nautilus and other forms characteristic of
tropical latitudes; fossil reptiles, such as the crocodile, turtle, and
tortoise; plants, such as palms, some of them allied to the cocoa-nut,
the screw-pine, the custard-apple, and the acacia, all lead to this
conclusion. This flora and fauna were followed by those of the miocene
formation, in which indications of a southern, but less tropical climate
are detected. Finally, the pliocene deposits, which come next in
succession, exhibit in their organic remains a much nearer approach to
the state of things now prevailing in corresponding latitudes. It was
towards the close of this period that the seas of the northern
hemisphere became more and more filled with floating icebergs often
charged with erratic blocks, so that the waters and the atmosphere were
chilled by the melting ice, and an arctic fauna enabled, for a time, to
invade the temperate latitudes both of N. America and Europe. The
extinction of a considerable number of land quadrupeds and aquatic
mollusca was gradually brought about by the increasing severity of the
cold; but many species survived this revolution in climate, either by
their capacity of living under a variety of conditions, or by migrating
for a time to more southern lands and seas. At length, by modifications
in the physical geography of the northern regions, and the cessation of
floating ice on the eastern side of the Atlantic, the cold was
moderated, and a milder climate ensued, such as we now enjoy in
Europe.[154]

_Proofs from fossils in secondary and still older strata._--A great
interval of time appears to have elapsed between the formation of the
secondary strata, which constitute the principal portion of the elevated
land in Europe, and the origin of the eocene deposits. If we examine the
rocks from the chalk to the new red sandstone inclusive, we find many
distinct assemblages of fossils entombed in them, all of unknown
species, and many of them referable to genera and families now most
abundant between the tropics. Among the most remarkable are reptiles of
gigantic size; some of them herbivorous, others carnivorous, and far
exceeding in size any now known even in the torrid zone. The genera are
for the most part extinct, but some of them, as the crocodile and
monitor, have still representatives in the warmer parts of the earth.
Coral reefs also were evidently numerous in the seas of the same
periods, composed of species often belonging to genera now
characteristic of a tropical climate. The number of large chambered
shells also, including the nautilus, leads us to infer an elevated
temperature; and the associated fossil plants, although imperfectly
known, tend to the same conclusion, the Cycadeae constituting the most
numerous family.

But it is from the more ancient coal-deposits that the most
extraordinary evidence has been supplied in proof of the former
existence of a very different climate--a climate which seems to have
been moist, warm, and extremely uniform, in those very latitudes which
are now the colder, and in regard to temperature, the most variable
regions of the globe. We learn from the researches of Adolphe
Brongniart, Goeppert, and other botanists, that in the flora of the
carboniferous era there was a great predominance of ferns, some of which
were arborescent; as, for example, Caulopteris, Protopteris, and
Psarronius; nor can this be accounted for, as some have supposed, by the
greater power which ferns possess of resisting maceration in water.[155]
This prevalence of ferns indicates a moist, equable, and temperate
climate, and the absence of any severe cold; for such are the conditions
which, at the present day, are found to be most favorable to that tribe
of plants. It is only in the islands of the tropical oceans, and of the
southern temperate zone, such as Norfolk Island, Otaheite, the Sandwich
Islands, Tristan d'Acunha, and New Zealand, that we find any near
approach to that remarkable preponderance of ferns which is
characteristic of the Carboniferous flora. It has been observed that
tree ferns and other forms of vegetation which flourished most
luxuriantly within the tropics, extend to a much greater distance from
the equator in the southern hemisphere than in the northern, being found
even as far as 46 degrees S. latitude in New Zealand. There is little
doubt that this is owing to the more uniform and moist climate
occasioned by the greater proportional area of sea. Next to ferns and
pines, the most abundant vegetable forms in the coal formation are the
Calamites, Lepidodendra, Sigillariae, and Stigmariae. These were
formerly considered to be so closely allied to tropical genera, and to
be so much greater in size than the corresponding tribes now inhabiting
equatorial latitudes, that they were thought to imply an extremely hot,
as well as humid and equable climate. But recent discoveries respecting
the structure and relations of these fossil plants, have shown that they
deviated so widely from all existing types in the vegetable world, that
we have more reason to infer from this evidence a widely different
climate in the Carboniferous era, as compared to that now prevailing,
than a temperature extremely elevated.[156] Palms, if not entirely
wanting when the strata of the carboniferous group were deposited,
appear to have been exceedingly rare.[157] The Coniferae, on the other
hand, so abundantly met with in the coal, resemble Araucariae in
structure, a family of the fir tribe, characteristic at present of the
milder regions of the southern hemisphere, such as Chili, Brazil, New
Holland, and Norfolk Island.

"In regard to the geographical extent of the ancient vegetation, it was
not confined," says M. Brongniart, "to a small space, as to Europe, for
example; for the same forms are met with again at great distances. Thus,
the coal-plants of North America are, for the most part, identical with
those of Europe, and all belong to the same genera. Some specimens,
also, from Greenland, are referable to ferns, analogous to those of our
European coal-mines."[158] The fossil plants brought from Melville
Island, although in a very imperfect state, have been supposed to
warrant similar conclusions;[159] and assuming that they agree with
those of Baffin's Bay, mentioned by M. Brongniart, how shall we explain
the manner in which such a vegetation lived through an arctic night of
several months' duration?[160]

It may seem premature to discuss this question until the true nature of
the fossil flora of the arctic regions has been more accurately
determined; yet, as the question has attracted some attention, let us
assume for a moment that the coal-plants of Melville Island are strictly
analogous to those of the strata of Northumberland--would such a fact
present an inexplicable enigma to the vegetable physiologist?

Plants, it is affirmed, cannot remain in darkness, even for a week,
without serious injury, unless in a torpid state; and if exposed to heat
and moisture they cannot remain torpid, but will grow, and must
therefore perish. If, then, in the latitude of Melville Island, 75
degrees N., a high temperature, and consequent humidity, prevailed at
that period when we know the arctic seas were filled with corals and
large multilocular shells, how could plants of tropical forms have
flourished? Is not the bright light of equatorial regions as
indispensable a condition of their well-being as the sultry heat of the
same countries? and how could they annually endure a night prolonged for
three months?[161]

Now, in reply to this objection, we must bear in mind, in the first
place, that, so far as experiments have been made, there is every reason
to conclude, that the range of intensity of light to which living plants
can accommodate themselves is far wider than that of heat. No palms or
tree ferns can live in our temperate latitudes without protection from
the cold; but when placed in hot-houses they grow luxuriantly, even
under a cloudy sky, and where much light is intercepted by the glass and
frame-work. At St. Petersburg, in lat. 60 degrees N., these plants have
been successfully cultivated in hot-houses, although there they must
exchange the perpetual equinox of their native regions, for days and
nights which are alternately protracted to nineteen hours and shortened
to five. How much farther towards the pole they might continue to live,
provided a due quantity of heat and moisture were supplied, has not yet
been determined; but St. Petersburg is probably not the utmost limit,
and we should expect that in lat. 65 degrees at least, where they would
never remain twenty-four hours without enjoying the sun's light, they
might still exist.

It should also be borne in mind, in regard to tree ferns, that they grow
in the gloomiest and darkest parts of the forests of warm and temperate
regions, even extending to nearly the 46th degree of south latitude in
New Zealand. In equatorial countries, says Humboldt, they abound chiefly
in the temperate, humid, and shady parts of _mountains_. As we know,
therefore, that elevation often compensates for the effect of latitude
in the geographical distribution of plants, we may easily understand
that a class of vegetables, which grows at a certain height in the
torrid zone, would flourish on the plains at greater distances from the
equator, if the temperature, moisture, and other necessary conditions,
were equally uniform throughout the year.

Nor must we forget that in all the examples above alluded to, we have
been speaking of _living_ species; but the coal-plants were of perfectly
distinct species, nay, few of them except the ferns and pines can be
referred to genera or even families of the existing vegetable kingdom.
Having a structure, therefore, and often a form which appears to the
botanist so anomalous, they may also have been endowed with a different
constitution, enabling them to bear a greater variation of circumstances
in regard to light. We find that particular species of plants and tree
ferns require at present different degrees of heat; and that some
species can thrive only in the immediate neighborhood of the equator,
others only a distance from it. In the same manner the _minimum of
light_, sufficient for the now existing species, cannot be taken as the
standard for all analogous tribes that may ever have flourished on the
globe.

But granting that the extreme northern point to which a flora like that
of the Carboniferous era could ever reach, may be somewhere between the
latitudes of 65 degrees and 70 degrees, we should still have to inquire
whether the vegetable remains might not have been drifted from thence,
by rivers and currents, to the parallel of Melville Island, or still
farther. In the northern hemisphere, at present, we see that the
materials for future beds of lignite and coal are becoming amassed in
high latitudes, far from the districts where the forests grew, and on
shores where scarcely a stunted shrub can now exist. The Mackenzie, and
other rivers of North America, carry pines with their roots attached for
many hundred miles towards the north, into the Arctic Sea, where they
are imbedded in deltas, and some of them drifted still farther by
currents towards the pole.

Before we can decide on this question of transportation, we must know
whether the fossil coal-plants occurring in high latitudes bear the
marks of friction and of having decayed previously to fossilization.
Many appearances in our English coal-fields certainly prove that the
plants were not floated from great distances; for the outline of the
stems of succulent species preserve their sharp angles, and others have
their surfaces marked with the most delicate lines and streaks. Long
leaves, also, are attached in many instances to the trunks or
branches;[162] and leaves, we know, in general, are soon destroyed when
steeped in water, although ferns will retain their forms after an
immersion of many months.[163] It seems fair to presume, that most of
the coal-plants grew upon the same land which supplied materials for the
sandstones and conglomerates of the strata in which they are imbedded.
The coarseness of the particles of many of these rocks attests that they
were not borne from very remote localities, and that there was land
therefore in the vicinity wasting away by the action of moving waters.
The progress also of modern discovery has led to the very general
admission of the doctrine that beds of coal have for the most part been
formed of the remains of trees and plants that grew on the spot where
the coal now exists; the land having been successively submerged, so
that a covering of mud and sand was deposited upon accumulations of
vegetable mater. That such has been the origin of some coal-seams is
proved by the upright position of fossil trees, both in Europe and
America, in which the roots terminate downwards in beds of coal.[164]

To return, therefore, from this digression,--the flora of the coal
appears to indicate a uniform and mild temperature in the air, while the
fossils of the contemporaneous mountain-limestone, comprising abundance
of lamelliferous corals, large chambered cephalopods, and crinoidea,
naturally lead us to infer a considerable warmth in the waters of the
northern sea of the Carboniferous period. So also in regard to strata
older than the coal, they contain in high northern latitudes mountain
masses of corals which must have lived and grown on the spot, and large
chambered univalves, such as Orthocerata and Nautilus, all seeming to
indicate, even in regions bordering on the arctic circle, the former
prevalence of a temperature more elevated than that now prevailing.

The warmth and humidity of the air, and the uniformity of climate, both
in the different seasons of the year, and in different latitudes,
appears to have been most remarkable when some of the oldest of the
fossiliferous strata were formed. The approximation to a climate similar
to that now enjoyed in these latitudes does not commence till the era of
the formations termed tertiary; and while the different tertiary rocks
were deposited in succession, from the eocene to the pliocene, the
temperature seems to have been lowered, and to have continued to
diminish even after the appearance upon the earth of a considerable
number of the existing species, the cold reaching its maximum of
intensity in European latitudes during the glacial epoch, or the epoch
immediately antecedent to that in which all the species now contemporary
with man were in being.





CHAPTER VII.

FARTHER EXAMINATION OF THE QUESTION AS TO THE ASSUMED DISCORDANCE OF THE
ANCIENT AND MODERN CAUSES OF CHANGE.


  On the causes of vicissitudes in climate--Remarks on the present
    diffusion of heat over the globe--On the dependence of the mean
    temperature on the relative position of land and sea--Isothermal
    Lines--Currents from equatorial regions--Drifting of
    icebergs--Different temperature of Northern and Southern
    hemispheres--Combination of causes which might produce the extreme
    cold of which the earth's surface is susceptible--Conditions
    necessary for the production of the extreme of heat, and its
    probable effects on organic life.


_Causes of Vicissitudes in Climate._[165]--As the proofs enumerated in
the last chapter indicate that the earth's surface has experienced great
changes of climate since the deposition of the older sedimentary strata,
we have next to inquire how such vicissitudes can be reconciled with the
existing order of nature. The cosmogonist has availed himself of this,
as of every obscure problem in geology, to confirm his views concerning
a period when the planet was in a nascent or half-formed state, or when
the laws of the animate and inanimate world differed essentially from
those now established; and he has in this, as in many other cases,
succeeded so far, as to divert attention from that class of facts which,
if fully understood, might probably lead to an explanation of the
phenomena. At first it was imagined that the earth's axis had been for
ages perpendicular to the plane of the ecliptic, so that there was a
perpetual equinox, and uniformity of seasons throughout the year;--that
the planet enjoyed this "paradisiacal" state until the era of the great
flood; but in that catastrophe, whether by the shock of a comet, or some
other convulsion, it lost its equal poise, and hence the obliquity of
its axis, and with that the varied seasons of the temperate zone, and
the long nights and days of the polar circles.

When the progress of astronomical science had exploded this theory, it
was assumed, that the earth at its creation was in a state of fluidity,
and red-hot, and that ever since that era, it had been cooling down,
contracting its dimensions, and acquiring a solid crust,--an hypothesis
hardly less arbitrary, yet more calculated for lasting popularity;
because, by referring the mind directly to the beginning of things, it
requires no support from observation, nor from any ulterior hypothesis.
But if, instead of forming vague conjectures as to what might have been
the state of the planet at the era of its creation, we fix our thoughts
on the connection at present existing between climate and the
distribution of land and sea; and then consider what influence former
fluctuations in the physical geography of the earth must have had on
superficial temperature, we may perhaps approximate to a true theory. If
doubts and obscurities still remain, they should be ascribed to our
limited acquaintance with the laws of Nature, not to revolutions in her
economy;--they should stimulate us to farther research, not tempt us to
indulge our fancies respecting the imaginary changes of internal
temperature in an embryo world.

_Diffusion of Heat over the Globe._--In considering the laws which
regulate the diffusion of heat over the globe, we must be careful, as
Humboldt well remarks, not to regard the climate of Europe as a type of
the temperature which all countries placed under the same latitude
enjoy. The physical sciences, observes this philosopher, always bear the
impress of the places where they began to be cultivated; and as, in
geology, an attempt was at first made to refer all the volcanic
phenomena to those of the volcanoes in Italy, so in meteorology, a small
part of the old world, the centre of the primitive civilization of
Europe, was for a long time considered a type to which the climate of
all corresponding latitudes might be referred. But this region,
constituting only one-seventh of the whole globe, proved eventually to
be the exception to the general rule. For the same reason, we may warn
the geologist to be on his guard, and not hastily to assume that the
temperature of the earth in the present era is a type of that which most
usually obtains, since he contemplates far mightier alterations in the
position of land and sea, at different epochs, than those which now
cause the climate of Europe to differ from that of other countries in
the same parallels.

It is now well ascertained that zones of equal warmth, both in the
atmosphere and in the waters of the ocean, are neither parallel to the
equator nor to each other.[166] It is also known that the _mean_ annual
temperature may be the same in two places which enjoy very different
climates, for the seasons may be nearly uniform, or violently
contrasted, so that the lines of equal winter temperature do not
coincide with those of equal annual heat or isothermal lines. The
deviations of all these lines from the same parallel of latitude are
determined by a multitude of circumstances, among the principal of which
are the position, direction, and elevation of the continents and
islands, the position and depths of the sea, and the direction of
currents and of winds.

On comparing the two continents of Europe and America, it is found that
places in the same latitudes have sometimes a mean difference of
temperature amounting to 11 degrees, or even in a few cases to 17
degrees Fahr.; and some places on the two continents, which have the
same mean temperature, differ from 7 degrees to 17 degrees in latitude.
Thus, Cumberland House, in North America, having the same latitude (54
degrees N.) as the city of York in England, stands on the isothermal
line of 32 degrees, which in Europe rises to the North Cape, in lat. 71
degrees, but its summer heat exceeds that of Brussels or Paris.[167] The
principal cause of greater intensity of cold in corresponding latitudes
of North America, as contrasted with Europe, is the connection of
America with the polar circle, by a large tract of land, some of which
is from three to five thousand feet in height; and, on the other hand,
the separation of Europe from the arctic circle by an ocean. The ocean
has a tendency to preserve everywhere a mean temperature, which it
communicates to the contiguous land, so that it tempers the climate,
moderating alike an excess of heat or cold. The elevated land, on the
other hand, rising to the colder regions of the atmosphere, becomes a
great reservoir of ice and snow, arrests, condenses, and congeals vapor,
and communicates its cold to the adjoining country. For this reason,
Greenland, forming part of a continent which stretches northward to the
82d degree of latitude, experiences under the 60th parallel a more
rigorous climate than Lapland under the 72d parallel.

But if land be situated between the 40th parallel and the equator, it
produces, unless it be of extreme height, exactly the opposite effect;
for it then warms the tracts of land or sea that intervene between it
and the polar circle. For the surface being in this case exposed to the
vertical, or nearly vertical rays of the sun, absorbs a large quantity
of heat, which it diffuses by radiation into the atmosphere. For this
reason, the western parts of the old continent derive warmth from
Africa, "which, like an immense furnace, distributes its heat to Arabia,
to Turkey in Asia, and to Europe."[168] On the contrary, the
northeastern extremity of Asia experiences in the same latitude extreme
cold; for it has land on the north between the 60th and 70th parallel,
while to the south it is separated from the equator by the Pacific
Ocean.

In consequence of the more equal temperature of the waters of the ocean,
the climate of islands and of coasts differs essentially from that of
the interior of continents, the more maritime climate being
characterized by mild winters, and more temperate summers; for the
sea-breezes moderate the cold of winter, as well as the heat of summer.
When, therefore, we trace round the globe those belts in which the mean
annual temperature is the same, we often find great differences in
climate; for there are _insular_ climates in which the seasons are
nearly equalized, and _excessive_ climates, as they have been termed,
where the temperature of winter and summer is strongly contrasted. The
whole of Europe, compared with the eastern parts of America and Asia,
has an insular climate. The northern part of China, and the Atlantic
region of the United States, exhibit "excessive climates." We find at
New York, says Humboldt, the summer of Rome and the winter of
Copenhagen; at Quebec, the summer of Paris and the winter of Petersburg.
At Pekin, in China, where the mean temperature of the year is that of
the coasts of Brittany, the scorching heats of summer are greater than
at Cairo, and the winters as rigorous as at Upsala.[169]

If lines be drawn round the globe through all those places which have
the same winter temperature, they are found to deviate from the
terrestrial parallels much farther than the lines of equal mean annual
heat. The lines of equal winter in Europe, for example, are often curved
so as to reach parallels of latitude 9 degrees or 10 degrees distant
from each other, whereas the isothermal lines, or those passing through
places having the same mean annual temperature, differ only from 4
degrees to 5 degrees in Europe.

_Influence of currents and drift ice on temperature._--Among other
influential causes, both of remarkable diversity in the mean annual
heat, and of unequal division of heat in the different seasons, are the
direction of currents and the accumulation and drifting of ice in high
latitudes. The temperature of the Lagullas current is 10 degrees or 12
degrees Fahr. above that of the sea at the Cape of Good Hope; for it
derives the greater part of its waters from the Mozambique channel, and
southeast coast of Africa, and from regions in the Indian Ocean much
nearer the line, and much hotter than the Cape.[170] An opposite effect
is produced by the "equatorial" current, which crosses the Atlantic from
Africa to Brazil, having a breadth varying from 160 to 450 nautical
miles. Its waters are cooler by 3 degrees or 4 degrees Fahr. than those
of the ocean under the line, so that it moderates the heat of the
tropics.[171]

But the effects of the Gulf stream on the climate of the North Atlantic
Ocean are far more remarkable. This most powerful of known currents has
its source in the Gulf or Sea of Mexico, which, like the Mediterranean
and other close seas in temperate or low latitudes, is warmer than the
open ocean in the same parallels. The temperature of the Mexican sea in
summer is, according to Rennell, 86 degrees Fahr., or at least 7 degrees
above that of the Atlantic in the same latitude.[172] From this great
reservoir or caldron of warm water, a constant current pours forth
through the straits of Bahama at the rate of 3 or 4 miles an hour; it
crosses the ocean in a northeasterly direction, skirting the great bank
of Newfoundland, where it still retains a temperature of 8 degrees above
that of the surrounding sea. It reaches the Azores in about 78 days,
after flowing nearly 3000 geographical miles, and from thence it
sometimes extends its course a thousand miles farther, so as to reach
the Bay of Biscay, still retaining an excess of 5 degrees above the mean
temperature of that sea. As it has been known to arrive there in the
months of November and January, it may tend greatly to moderate the cold
of winter in countries on the west of Europe. . There is a large tract
in the centre of the North Atlantic, between the parallels of 33 degrees
and 45 degrees N. lat., which Rennell calls the "recipient of the gulf
water." A great part of it is covered by the weed called sargasso
(_Sargassum bacciferum_), which the current floats in abundance from the
Gulf of Mexico. This mass of water is nearly stagnant, is warmer by 7
degrees or 10 degrees than the waters of the Atlantic, and may be
compared to the fresh water of a river overflowing the heavier salt
water of the sea. Rennell estimates the area of the "recipient,"
together with that covered by the main current, as being 2000 miles in
length from E. to W., and 350 in breadth from N. to S., which, he
remarks, is a larger area than that of the Mediterranean. The heat of
this great body of water is kept up by the incessant and quick arrivals
of fresh supplies of warm water from the south; and there can be no
doubt that the general climate of parts of Europe and America is
materially affected by this cause.

It is considered probable by Scoresby that the influence of the Gulf
stream extends even to the sea near Spitzbergen, where its waters may
pass under those of melted ice; for it has been found that in the
neighborhood of Spitzbergen, the water is warmer by 6 degrees or 7
degrees at the depth of one hundred and two hundred fathoms than at the
surface. This might arise from the known law that fresh water passes the
point of greatest density when cooled down below 40 degrees, and between
that and the freezing point expands again. The water of melted ice might
be lighter, both as being fresh (having lost its salt in the decomposing
process of freezing), and because its temperature is nearer the freezing
point than the inferior water of the Gulf stream.

The great glaciers generated in the valleys of Spitzbergen, in the 79
degrees of north latitude, are almost all cut off at the beach, being
melted by the feeble remnant of heat still retained by the Gulf stream.
In Baffin's Bay, on the contrary, on the west coast of Old Greenland,
where the temperature of the sea is not mitigated by the same cause, and
where there is no warmer under-current, the glaciers stretch out from
the shore, and furnish repeated crops of mountainous masses of ice which
float off into the ocean.[173] The number and dimensions of these bergs
is prodigious. Captain Sir John Ross saw several of them together in
Baffin's Bay aground in water fifteen hundred feet deep! Many of them
are driven down into Hudson's Bay, and accumulating there, diffuse
excessive cold over the neighboring continent; so that Captain Franklin
reports, that at the mouth of Hayes' River, which lies in the same
latitude as the north of Prussia or the south of Scotland, ice is found
everywhere in digging wells, in summer, at the depth of four feet! Other
bergs have been occasionally met with, at midsummer, in a state of rapid
thaw, as far south as lat. 40 degrees and longitude about 60 degrees
west, where they cool the water sensibly to the distance of forty or
fifty miles around, the thermometer sinking sometimes 17 degrees, or
even 18 degrees, Fahrenheit, in their neighborhood.[174] It is a
well-known fact that every four or five years a large number of
icebergs, floating from Greenland, double Cape Langaness, and are
stranded on the west coast of Iceland. The inhabitants are then aware
that their crops of hay will fail, in consequence of fogs which are
generated almost incessantly; and the dearth of food is not confined to
the land, for the temperature of the water is so changed that the fish
entirely desert the coast.

_Difference of climate of the Northern and Southern hemispheres._--When
we compare the climate of the northern and southern hemispheres, we
obtain still more instruction in regard to the influence of the
distribution of land and sea on climate. The dry land in the southern
hemisphere is to that of the northern in the ratio only of one to three,
excluding from our consideration that part which lies between the pole
and the 78 degrees of south latitude, which has hitherto proved
inaccessible. And whereas in the northern hemisphere, between the pole
and the thirtieth parallel of north latitude, the land and sea occupy
nearly equal areas, the ocean in the southern hemisphere covers no less
than fifteen parts in sixteen of the entire space included between the
antarctic circle and the thirtieth parallel of south latitude.

This great extent of sea gives a particular character to climates south
of the equator, the winters being mild and the summers cool. Thus, in
Van Dieman's Land, corresponding nearly in latitude to Rome, the winters
are more mild than at Naples, and the summers not warmer than those at
Paris, which is 7 degrees farther from the equator.[175] The effects on
animal and vegetable life are remarkable. Capt. King observed large
shrubs of Fuchsia and Veronica, which in England are treated as tender
plants, thriving and in full flower in Tierra del Fuego with the
temperature at 36 degrees. He states also that humming birds were seen
sipping the sweets of the flowers "after two or three days of constant
rain, snow, and sleet, during which time the thermometer had been at the
freezing point." Mr. Darwin also saw parrots feeding on the seeds of a
tree called the winter's bark, south of lat. 55 degrees, near Cape
Horn.[176]

So the orchideous plants which are parasitical on trees, and are
generally characteristic of the tropics, advance to the 38th and 42d
degree of S. lat., and even beyond the 45th degree in New Zealand, where
they were found by Forster. In South America also arborescent grasses
abound in the dense forests of Chiloe, in lat. 42 degrees S., where
"they entwine the trees into one entangled mass to the height of thirty
or forty feet above the ground. Palm-trees in the same quarter of the
globe grow in lat. 37 degrees, an arborescent grass very like a bamboo
in 40 degrees, and another closely allied kind, of great length, but not
erect, even as far south as 45 degrees."[177]

It has long been supposed that the general temperature of the southern
hemisphere was considerably lower than that of the northern, and that
the difference amounted to at least 10 degrees Fahrenheit. Baron Humboldt,
after collecting and comparing a great number of observations, came to
the conclusion that even a much larger difference existed, but that none
was to be observed within the tropics, and only a small difference as
far as the thirty-fifth and fortieth parallel. Captain Cook was of
opinion that the ice of the antarctic predominated greatly over that of
the arctic region, that encircling the southern pole coming nearer to
the equator by 10 degrees than the ice around the north pole. All the
recent voyages of discovery have tended to confirm this opinion,
although Capt. Weddel penetrated, in 1823, three degrees farther south
than Capt. Cook, reaching lat. 74 degrees 15 minutes South, long. 34
degrees 17 minutes West, and Sir James Ross, in 1842, arrived at lat. 78
degrees 10 minutes S., as high a latitude, within three degrees, as the
farthest point attained by Captain Parry in the arctic circle, or lat.
81 degrees 12 minutes North.

The description given by ancient as well as modern navigators of the sea
and land in high southern latitudes, clearly attests the greater
severity of the climate as compared to arctic regions. In Sandwich Land,
in lat. 59 degrees S., or in nearly the same parallel as the north of
Scotland, Capt. Cook found the whole country, from the summits of the
mountains down to the very brink of the sea-cliffs, "covered many
fathoms thick with everlasting snow," and this on the 1st of February,
the hottest time of the year; and what is still more astonishing, in the
island of S. Georgia, which is in the 54 degrees south latitude, or the
same parallel as Yorkshire, the line of perpetual snow descends to the
level of the ocean.[178] When we consider this fact, and then recollect
that the highest mountains in Scotland, which ascend to an elevation of
nearly 5000 feet, and are four degrees farther to the north, do not
attain the limit of perpetual snow on our side of the equator, we learn
that latitude is one only of many powerful causes, which determine the
climate of particular regions of the globe. Capt. Sir James Ross, in his
exploring expedition in 1841-3, found that the temperature south of the
60th degree of latitude seldom rose above 32 degrees Fahr. During the
two summer months of the year 1841 (January and February) the range of
the thermometer was between 11 degrees and 32 degrees Fahr.; and
scarcely once rose above the freezing point. The permanence of snow in
the southern hemisphere, is in this instance partly due to the floating
ice, which chills the atmosphere and condenses the vapor, so that in
summer the sun cannot pierce through the foggy air. But besides the
abundance of ice which covers the sea to the south of Georgia and
Sandwich Land, we may also, as Humboldt suggests, ascribe the cold of
those countries in part to the absence of land between them and the
tropics.

If Africa and New Holland extended farther to the south, a diminution of
ice would take place in consequence of the radiation of heat from these
continents during summer, which would warm the contiguous sea and rarefy
the air. The heated aerial currents would then ascend and flow more
rapidly towards the south pole, and moderate the winter. In confirmation
of these views, it is stated that the ice, which extends as far as the
68 degrees and 71 degrees of south latitude, advances more towards the
equator whenever it meets an open sea; that is, where the extremities of
the present continents are not opposite to it; and this circumstance
seems explicable only on the principle above alluded to, of the
radiation of heat from the lands so situated.

The cold of the antarctic regions was conjectured by Cook to be due to
the existence of a large tract of land between the seventieth degree of
south latitude and the pole. The justness of these and other
speculations of that great navigator have since been singularly
confirmed by the investigation made by Sir James Ross in 1841. He found
Victoria Land, extending from 71 degrees to 79 degrees S. latitude,
skirted by a great barrier of ice, the height of the land ranging from
4000 to 14,000 feet, the whole entirely covered with snow, except a
narrow ring of black earth surrounding the huge crater of the active
volcano of Mount Erebus, rising 12,400 feet above the level of the sea.
The position of a mountainous territory of such altitude, so near the
pole, and so obvious a source of intense cold, fully explains why
Graham's and Enderby's Land, discovered by Captain Biscoe in 1831-2
(between lat. 64 degrees and 68 degrees S.), presented a most wintry
aspect, covered even in summer with ice and snow, and nearly destitute
of animal life. In corresponding latitudes of the northern hemisphere we
not only meet with herds of wild herbivorous animals, but with land
which man himself inhabits, and where he has even built ports and inland
villages.[179]

The distance to which icebergs float from the polar regions on the
opposite sides of the line is, as might have been anticipated, very
different. Their extreme limit in the northern hemisphere is lat. 40
degrees, as before mentioned, and they are occasionally seen in lat. 42
degrees N., near the termination of the great bank of Newfoundland, and
at the Azores, lat. 42 degrees N., to which they are sometimes drifted
from Baffin's Bay. But in the other hemisphere they have been seen,
within the last few years, at different points off the Cape of Good
Hope, between lat. 36 degrees and 39 degrees.[180] One of these (see
fig. 2) was two miles in circumference, and 150 feet high, appearing
like chalk when the sun was obscured, and having the lustre of refined
sugar when the sun was shining on it. Others rose from 250 to 300 feet
above the level of the sea, and were therefore of great volume below;
since it is ascertained by experiments on the buoyancy of ice floating
in sea-water, that for every cubic foot seen above, there must at least
be eight cubic feet below water.[181] If ice islands from the north
polar regions floated as far, they might reach Cape St. Vincent, and
there, being drawn by the current that always sets in from the Atlantic
through the Straits of Gibraltar, be drifted into the Mediterranean, so
that the serene sky of that delightful region might soon be deformed by
clouds and mists.

[Illustration: Fig. 2.

Iceberg seen off the Cape of Good Hope, April, 1829. Lat. 89 degrees 18
minutes S. Long. 48 degrees 46 minutes E.]

Before the amount of difference between the temperature of the two
hemispheres was ascertained, it was referred by many astronomers to the
precession of the equinoxes, or the acceleration of the earth's motion
in its perihelium; in consequence of which the spring and summer of the
southern hemisphere are now shorter, by nearly eight days, than those
seasons north of the equator. But Sir J. Herschel reminds us that the
excess of eight days in the duration of the sun's presence in the
northern hemisphere is not productive of an excess of annual light and
heat; since, according to the laws of elliptic motion, it is
demonstrable that whatever be the ellipticity of the earth's orbit, the
two hemispheres must receive _equal absolute quantities_ of light and
heat per annum, the proximity of the sun in perigee exactly compensating
the effect of its swifter motion.[182] Humboldt, however, observes, that
there must be a greater loss of heat by radiation in the southern
hemisphere during a winter longer by eight days than that on the other
side of the equator.[183]

Perhaps no very sensible effect may be produced by this source of
disturbance; yet the geologist should bear in mind that to a certain
extent it operates alternately on each of the two hemispheres for a
period of upwards of 10,000 years, dividing unequally the times during
which the annual supply of solar light and heat is received. This cause
may sometimes tend to counterbalance inequalities of temperature
resulting from other far more influential circumstances; but, on the
other hand, it must sometimes tend to increase the extreme of deviation
arising from particular combinations of causes.

But whatever may be at present the inferiority of heat in the temperate
and frigid zones south of the line, it is quite evident that the cold
would be far more intense if there happened, instead of open sea, to be
tracts of elevated land between the 55th and 70th parallel; and, on the
other hand, the cold would be moderated if there were more land between
the line and the forty-fifth degree of south latitude.

_Changes in the position of land and sea may give rise to vicissitudes
in climate._--Having offered these brief remarks on the diffusion of
heat over the globe in the present state of the surface, I shall now
proceed to speculate on the vicissitudes of climate, which must attend
those endless variations in the geographical features of our planet
which are contemplated in geology. That our speculations may be confined
within the strict limits of analogy, I shall assume, 1st, That the
proportion of dry land to sea continues always the same. 2dly, That the
volume of the land rising above the level of the sea is a constant
quantity; and not only that its mean, but that its extreme height, is
liable only to trifling variations. 3dly, That both the mean and extreme
depth of the sea are invariable; and 4thly, It may be consistent with
due caution to assume that the grouping together of the land in
continents is a necessary part of the economy of nature; for it is
possible that the laws which govern the subterranean forces, and which
act simultaneously along certain lines, cannot but produce, at every
epoch, continuous mountain-chains; so that the subdivision of the whole
land into innumerable islands may be precluded.

If it be objected, that the maximum of elevation of land and depth of
sea are probably not constant, nor the gathering together of all the
land in certain parts, nor even perhaps the relative extent of land and
water, I reply, that the arguments about to be adduced will be
strengthened if, in these peculiarities of the surface, there be
considerable deviations from the present type. If, for example, all
other circumstances being the same, the land is at one time more divided
into islands than at another, a greater uniformity of climate might be
produced, the mean temperature remaining unaltered; or if, at another
era, there were mountains higher than the Himalaya, these, when placed
in high latitudes, would cause a greater excess of cold. Or, if we
suppose that at certain periods no chain of hills in the world rose
beyond the height of 10,000 feet, a greater heat might then have
prevailed than is compatible with the existence of mountains thrice that
elevation.

However constant may be the relative proportion of sea and land, we know
that there is annually some small variation in their respective
geographical positions, and that in every century the land is in some
parts raised, and in others depressed in level, and so likewise is the
bed of the sea. By these and other ceaseless changes, the configuration
of the earth's surface has been remodelled again and again, since it was
the habitation of organic beings, and the bed of the ocean has been
lifted up to the height of some of the loftiest mountains. The
imagination is apt to take alarm when called upon to admit the formation
of such irregularities in the crust of the earth, after it had once
become the habitation of living creatures; but, if time be allowed, the
operation need not subvert the ordinary repose of nature; and the result
is in a general view insignificant, if we consider how slightly the
highest mountain-chains cause our globe to differ from a perfect sphere.
Chimborazo, though it rises to more than 21,000 feet above the sea,
would be represented, on a globe of about six feet in diameter, by a
grain of sand less than one-twentieth of an inch in thickness.

The superficial inequalities of the earth, then, may be deemed minute in
quantity, and their distribution at any particular epoch must be
regarded in geology as temporary peculiarities, like the height and
outline of the cone of Vesuvius in the interval between two eruptions.
But although, in reference to the magnitude of the globe, the unevenness
of the surface is so unimportant, it is on the position and direction of
these small inequalities that the state of the atmosphere, and both the
local and general climate, are mainly dependent.

Before considering the effect which a material change in the
distribution of land and sea must occasion, it may be well to remark,
how greatly organic life may be affected by those minor variations,
which need not in the least degree alter the general temperature. Thus,
for example, if we suppose, by a series of convulsions, a certain part
of Greenland to become sea, and, in compensation, a tract of land to
rise and connect Spitzbergen with Lapland,--an accession not greater in
amount than one which the geologist can prove to have occurred in
certain districts bordering the Mediterranean, within a comparatively
modern period,--this altered form of the land might cause an interchange
between the climate of certain parts of North America and of Europe,
which lie in corresponding latitudes. Many European species of plants
and animals would probably perish in consequence, because the mean
temperature would be greatly lowered; and others would fail in America,
because it would there be raised. On the other hand, in places where the
mean annual heat remained unaltered, some species which flourish in
Europe, where the seasons are more uniform, would be unable to resist
the greater heat of the North American summer, or the intenser cold of
the winter; while others, now fitted by their habits for the great
contrast of the American seasons, would not be fitted for the _insular_
climate of Europe. The vine, for example, according to Humboldt, can be
cultivated with advantage 10 degrees farther north in Europe than in North
America. Many plants endure severe frost, but cannot ripen their seeds
without a certain intensity of summer heat and a certain quantity of
light; others cannot endure a similar intensity either of heat or cold.

It is now established that many of the existing species of animals have
survived great changes in the physical geography of the globe. If such
species be termed modern, in comparison to races which preceded them,
their remains, nevertheless, enter into submarine deposits many hundred
miles in length, and which have since been raised from the deep to no
inconsiderable altitude. When, therefore, it is shown that changes in
the temperature of the atmosphere may be the consequence of such
physical revolutions of the surface, we ought no longer to wonder that
we find the distribution of existing species to be _local_, in regard to
_longitude_ as well as latitude. If all species were now, by an exertion
of creative power, to be diffused uniformly throughout those zones where
there is an equal degree of heat, and in all respects a similarity of
climate, they would begin from this moment to depart more and more from
their original distribution. Aquatic and terrestrial species would be
displaced, as Hooke long ago observed, so often as land and water
exchanged places; and there would also, by the formation of new
mountains and other changes, be transpositions of climate, contributing,
in the manner before alluded to, to the local extermination of
species.[184]

If we now proceed to consider the circumstances required for a _general_
change of temperature, it will appear, from the facts and principles
already laid down, that whenever a greater extent of high land is
collected in the polar regions, the cold will augment; and the same
result will be produced when there is more sea between or near the
tropics; while, on the contrary, so often as the above conditions are
reversed, the heat will be greater. (See figs. 5 and 6, p. 111.) If this
be admitted, it will follow, that unless the superficial inequalities of
the earth be fixed and permanent, there must be never-ending
fluctuations in the mean temperature of every zone; and that the climate
of one era can no more be a type of every other; than is one of our four
seasons of all the rest.

It has been well said, that the earth is covered by an ocean, in the
midst of which are two great islands, and many smaller ones; for the
whole of the continents and islands occupy an area scarcely exceeding
one-fourth of the whole superficies of the spheroid. Now, according to
this analogy, we may fairly speculate on the probability that there
would not be usually, at any given epoch of the past, more than about
one-fourth dry land in a particular region; as, for example, near the
poles, or between them and the 75th parallels of N. and S. latitude.
If, therefore, at present there should happen to be, in both these
quarters of the globe, much _more_ than this average proportion of land,
some of it in the arctic region, being above, five thousand feet in
height, and if in antarctic latitudes a mountainous country has been
found varying from 4000 to 14,000 feet in height, this alone affords
ground for concluding that, in the present state of things, the mean
heat of the climate is below that which the earth's surface, in its more
ordinary state, would enjoy. This presumption is heightened when we
reflect on the results of the recent soundings made by Sir James Ross,
in the Southern Ocean, and continued for four successive years, ending
1844, which seem to prove that the mean depth of the Atlantic and
Pacific is as great as Laplace and other eminent astronomers had
imagined;[185] for then we might look not only for more than two-thirds
sea in the frigid zones, but for water of great depth, which could not
readily be reduced to the freezing point. The same opinion is confirmed,
when we compare the quantity of land lying between the poles and the
30th parallels of north and south latitude, with the quantity placed
between those parallels and the equator; for, it is clear, that we have
at present not only more than the usual degree of cold in the polar
regions, but also less than the average quantity of heat within the
tropics.

_Position of land and sea which might produce the extreme of cold of
which the earth's surface is susceptible._--To simplify our view of the
various changes in climate, which different combinations of geographical
circumstances may produce, we shall first consider the conditions
necessary for bringing about the extreme of cold, or what would have
been termed in the language of the old writers the winter of the "great
year," or geological cycle, and afterwards, the conditions requisite to
produce the maximum of heat, or the summer of the same year.

To begin with the northern hemisphere. Let us suppose those hills of the
Italian peninsula and of Sicily, which are of comparatively modern
origin, and contain many fossil shells identical with living species, to
subside again into the sea, from which they have been raised, and that
an extent of land of equal area and height (varying from one to three
thousand feet) should rise up in the Arctic Ocean between Siberia and
the north pole. In speaking of such changes, I shall not allude to the
manner in which I conceive it possible that they may be brought about,
nor of the time required for their accomplishment--reserving for a
future occasion, not only the proofs that revolutions of equal magnitude
have taken place, but that analogous operations are still in gradual
progress. The alteration now supposed in the physical geography of the
northern regions, would cause additional snow and ice to accumulate
where now there is usually an open sea; and the temperature of the
greater part of Europe would be somewhat lowered, so as to resemble more
nearly that of corresponding latitudes of North America: or, in other
words, it might be necessary to travel about 10 degrees farther south in
order to meet with the same climate which we now enjoy. No compensation
would be derived from the disappearance of land in the Mediterranean
countries; but the contrary, since the mean heat of the soil in those
latitudes probably exceeds that which would belong to the sea, by which
we imagine it to be replaced.

But let the configuration of the surface be still farther varied, and
let some large district within or near the tropics, such as Brazil, with
its plains and hills of moderate height, be converted into sea, while
lands of equal elevation and extent rise up in the arctic circle. From
this change there would, in the first place, result a sensible
diminution of temperature near the tropic, for the Brazilian soil would
no longer be heated by the sun; so that the atmosphere would be less
warm, as also the neighboring Atlantic. On the other hand, the whole of
Europe, Northern Asia, and North America, would be chilled by the
enormous quantity of ice and snow, thus generated on the new arctic
continent. If, as we have already seen, there are now some points in the
southern hemisphere where snow is perpetual down to the level of the
sea, in latitudes as low as central England, such might assuredly be the
case throughout a great part of Europe, under the change of
circumstances above supposed: and if at present the extreme range of
drifted icebergs is the Azores, they might easily reach the equator
after the assumed alteration. But to pursue the subject still farther,
let the Himalaya mountains, with the whole of Hindostan, sink down, and
their place be occupied by the Indian Ocean, while an equal extent of
territory and mountains, of the same vast height, rise up between North
Greenland and the Orkney Islands. It seems difficult to exaggerate the
amount to which the climate of the northern hemisphere would then be
cooled.[186]

But the refrigeration brought about at the same time in the southern
hemisphere, would be nearly equal, and the difference of temperature
between the arctic and equatorial latitudes would not be much greater
than at present; for no important disturbance can occur in the climate
of a particular region without its immediately affecting all other
latitudes, however remote. The heat and cold which surround the globe
are in a state of constant and universal flux and reflux. The heated and
rarefied air is always rising and flowing from the equator towards the
poles in the higher regions of the atmosphere; while in the lower, the
colder air is flowing back to restore the equilibrium. That this
circulation is constantly going on in the aerial currents is not
disputed; it is often proved by the opposite course of the clouds at
different heights, and the fact has been farther illustrated in a
striking manner by two recent events. The trade wind continually blows
with great force from the island of Barbadoes to that of St. Vincent;
notwithstanding which, during the eruption of the volcano in the island
of St. Vincent, in 1812, ashes fell in profusion from a great height in
the atmosphere upon Barbadoes.[187] In like manner, during the great
eruption of Sumbawa, in 1815, ashes were carried to the islands of
Amboyna and Banda, which last is about 800 miles east from the site of
the volcano. Yet the southeast monsoon was then at its height.[188] This
apparent transposition of matter against the wind, confirmed the opinion
of the existence of a counter-current in the higher regions, which had
previously rested on theoretical conclusions only.

That a corresponding interchange takes place in the seas, is
demonstrated, according to Humboldt, by the cold which is found to exist
at great depths within the tropics; and, among other proofs, may be
mentioned the mass of warmer water which the Gulf stream is constantly
bearing northwards, while a cooler current flows _from_ the north along
the coast of Greenland and Labrador, and helps to restore the
equilibrium.[189]

Currents of colder and therefore specifically heavier water pass from
the poles towards the equator, which cool the inferior parts of the
ocean; so that the heat of the torrid zone and the cold of the polar
circle balance each other. The refrigeration, therefore, of the polar
regions, resulting from the supposed alteration in the distribution of
land and sea, would be immediately communicated to the tropics, and from
them its influence would extend to the antarctic circle, where the
atmosphere and the ocean would be cooled, so that ice and snow would
augment. Although the mean temperature of higher latitudes in the
southern hemisphere is, as before stated, for the most part, lower than
that of the same parallels in the northern, yet, for a considerable
space on each side of the line, the mean annual heat of the waters is
found to be the same in corresponding parallels. If, therefore, by the
new position of the land, the formation of icebergs had become of common
occurrence in the northern temperate zone, and if these were frequently
drifted as far as the equator, the same degree of cold which they
generated would immediately be communicated as far as the tropic of
Capricorn, and from thence to the lands or ocean to the south.

The freedom, then, of the circulation of heat and cold from pole to pole
being duly considered, it will be evident that the mean temperature
which may prevail at the same point at two distinct periods, may differ
far more widely than that of any two points in the same parallels of
latitude, at one and the same period. For the range of temperature, or
in other words, the curvature of the isothermal lines in a given zone,
and at a given period, must always be circumscribed within narrow
limits, the climate of each place in that zone being controlled by the
combined influence of the geographical peculiarities of all other parts
of the earth. Whereas, if we compare the state of things at two distinct
and somewhat distant epochs, a particular zone may at one time be under
the influence of one class of disturbing causes, and at another time may
be affected by an opposite combination. The lands, for example, to the
north of Greenland cause the present climate of North America to be
colder than that of Europe in the same latitudes; but the excess of cold
is not so great as it would have been if the western hemisphere had been
entirely isolated, or separated from the eastern like a distinct planet.
For not only does the refrigeration produced by Greenland chill to a
certain extent the atmosphere of northern and western Europe, but the
mild climate of Europe reacts also upon North America, and moderates the
chilling influence of the adjoining polar lands.

To return to the state of the earth after the changes above supposed, we
must not omit to dwell on the important effects to which a wide expanse
of perpetual snow would give rise. It is probable that nearly the whole
sea, from the poles to the parallels of 45 degrees, would be frozen
over; for it is well known that the immediate proximity of land is not
essential to the formation and increase of field ice, provided there be
in some part of the same zone a sufficient quantity of glaciers
generated on or near the land, to cool down the sea. Captain Scoresby,
in his account of the arctic regions, observes, that when the sun's rays
"fall upon the snow-clad surface of the ice or land, they are in a great
measure reflected, without producing any material elevation of
temperature; but when they impinge on the black exterior of a ship, the
pitch on one side occasionally becomes fluid while ice is rapidly
generated at the other."[190]

Now field ice is almost always covered with snow;[191] and thus not only
land as extensive as our existing continents, but immense tracts of sea
in the frigid and temperate zones, might present a solid surface covered
with snow, and reflecting the sun's rays for the greater part of the
year. Within the tropics, moreover, where the ocean now predominates,
the sky would no longer be serene and clear, as in the present era; but
masses of floating ice would cause quick condensations of vapor, so that
fogs and clouds would deprive the vertical rays of the sun of half their
power. The whole planet, therefore, would receive annually a smaller
portion of the solar influence, and the external crust would part, by
radiation, with some of the heat which had been accumulated in it,
during a different state of the surface. This heat would be dissipated
in the spaces surrounding our atmosphere, which, according to the
calculations of M. Fourier, have a temperature much inferior to that of
freezing water.

After the geographical revolution above assumed, the climate of
equinoctial lands might be brought at last to resemble that of the
present temperate zone, or perhaps be far more wintry. They who should
then inhabit such small isles and coral reefs as are now seen in the
Indian Ocean and South Pacific, would wonder that zoophytes of large
dimensions had once been so prolific in their seas; or if, perchance,
they found the wood and fruit of the cocoa-nut tree or the palm
silicified by the waters of some ancient mineral spring, or incrusted
with calcareous matter, they would muse on the revolutions which had
annihilated such genera, and replaced them by the oak, the chestnut, and
the pine. With equal admiration would they compare the skeletons of
their small lizards with the bones of fossil alligators and crocodiles
more than twenty feet in length, which, at a former epoch, had
multiplied between the tropics: and when they saw a pine included in an
iceberg, drifted from latitudes which we now call temperate, they would
be astonished at the proof thus afforded, that forests had once grown
where nothing could be seen in their own times but a wilderness of snow.

If the reader hesitate to suppose so extensive an alteration of
temperature as the probable consequence of geographical changes,
confined to one hemisphere, he should remember how great are the local
anomalies in climate now resulting from the peculiar distribution of
land and sea in certain regions. Thus, in the island of South Georgia,
before mentioned (p. 98), Captain Cook found the everlasting snows
descending to the level of the sea, between lat. 54 degrees and 55
degrees S.; no trees or shrubs were to be seen, and in summer a few
rocks only, after a partial melting of the ice and snow, were scantily
covered with moss and tufts of grass. If such a climate can now exist at
the level of the sea in a latitude corresponding to that of Yorkshire in
spite of all those equalizing causes before enumerated, by which the
mixture of the temperatures of distant regions is facilitated throughout
the globe, what rigors might we not anticipate in a winter generated by
the transfer of the mountains of India to our arctic circle!

But we have still to contemplate the additional refrigeration which
might be effected by changes in the relative position of land and sea in
the southern hemisphere. If the remaining continents were transferred
from the equatorial and contiguous latitudes to the south polar regions,
the intensity of cold produced might, perhaps, render the globe
uninhabitable. We are too ignorant of the laws governing the direction
of subterranean forces, to determine whether such a crisis be within the
limits of possibility. At the same time, it may be observed, that no
distribution of land can well be imagined more irregular, or, as it
were, capricious, than that which now prevails; for at present, the
globe may be divided into two equal parts, in such a manner, that one
hemisphere shall be almost entirely covered with water, while the other
shall contain less water than land (see figs. 3 and 4);[192] and, what
is still more extraordinary, on comparing the extratropical lands in the
northern and southern hemispheres, the lands in the northern are found
to be to those in the southern in the proportion of thirteen to
one![193] To imagine all the lands, therefore, in high, and all the sea
in low latitudes, as delineated in fig. 6, p. 111, would scarcely be a
more anomalous state of the surface.

[Illustration: Map showing the present unequal Distribution of LAND and
WATER on the Surface of the GLOBE.

Fig. 3. Here London is taken as a centre, and we behold the greatest
quantity of land existing in one hemisphere.

Fig. 4. Here the centre is the antipodal point to London, and we see the
greatest quantity of water existing in one hemisphere.

The black shading expresses land having land opposite or antipodal to
it.]

[Illustration: Maps showing the position of LAND and SEA which might
produce the Extremes of HEAT and COLD in the Climates of the GLOBE.

Fig. 5.

Extreme of Heat.

Fig. 6.

Extreme of Cold.

OBSERVATIONS.--These maps are intended to show that continents and
islands having the same shape and relative dimensions as those now
existing, might be placed so as to occupy either the equatorial or polar
regions.

In fig. 5, scarcely any of the land extends from the equator towards the
poles beyond the 30th parallel of latitude; and fig. 6, a very small
proportion of it extends from the poles towards the Equator beyond the
40th parallel of latitude.

_Position of land and sea which might give rise to the extreme of
heat._--Let us now turn from the contemplation of the winter of the
"great year," and consider the opposite train of circumstances which
would bring on the spring and summer. To imagine all the lands to be
collected together in equatorial latitudes, and a few promontories only
to project beyond the thirtieth parallel, as represented in the annexed
maps (figs. 5 and 6), would be undoubtedly to suppose an extreme result
of geological change. But if we consider a mere approximation to such a
state of things, it would be sufficient to cause a general elevation of
temperature. Nor can it be regarded as a visionary idea, that amidst the
revolutions of the earth's surface, the quantity of land should, at
certain periods, have been simultaneously lessened in the vicinity of
both the poles, and increased within the tropics. We must recollect that
even now it is necessary to ascend to the height of fifteen thousand
feet in the Andes under the line, and in the Himalaya mountains, which
are without the tropic, to seventeen thousand feet, before we reach the
limit of perpetual snow. On the northern slope, indeed, of the Himalaya
range, where the heat radiated from a great continent moderates the
cold, there are meadows and cultivated land at an elevation equal to the
height of Mont Blanc.[194] If then there were no arctic lands to chill
the atmosphere, and freeze the sea, and if the loftiest chains were near
the line, it seems reasonable to imagine that the highest mountains
might be clothed with a rich vegetation to their summits, and that
nearly all signs of frost would disappear from the earth.

When the absorption of the solar rays was in no region impeded, even in
winter, by a coat of snow, the mean heat of the earth's crust would
augment to considerable depths, and springs, which we know to be in
general an index of the mean temperature of the climate, would be warmer
in all latitudes. The waters of lakes, therefore, and rivers, would be
much hotter in winter, and would be never chilled in summer by melted
snow and ice. A remarkable uniformity of climate would prevail amid the
archipelagoes of the temperate and polar oceans, where the tepid waters
of equatorial currents would freely circulate. The general humidity of
the atmosphere would far exceed that of the present period, for
increased heat would promote evaporation in all parts of the globe. The
winds would be first heated in their passage over the tropical plains,
and would then gather moisture from the surface of the deep, till,
charged with vapor, they arrived at extreme northern and southern
regions, and there encountering a cooler atmosphere, discharged their
burden in warm rain. If, during the long night of a polar winter, the
snows should whiten the summits of some arctic islands, they would be
dissolved as rapidly by the returning sun, as are the snows of Etna by
the blasts of the sirocco.

We learn from those who have studied the geographical distribution of
plants, that in very low latitudes, at present, the vegetation of small
islands remote from continents has a peculiar character; the ferns and
allied families, in particular, bearing a great proportion to the total
number of other plants. Other circumstances being the same, the more
remote the isles are from the continents, the greater does this
proportion become. Thus, in the continent of India, and the tropical
parts of New Holland, the proportion of ferns to the phaenogamous plants
is only as one to twenty-six; whereas, in the South-Sea Islands, it is
as one to four, or even as one to three.[195]

We might expect, therefore, in the summer of the "great year," or cycle
of climate, that there would be a predominance of tree ferns and plants
allied to genera now called tropical, in the islands of the wide ocean,
while many forms now confined to arctic and temperate regions, or only
found near the equator on the summit of the loftiest mountains, would
almost disappear from the earth. Then might those genera of animals
return, of which the memorials are preserved in the ancient rocks of our
continents. The pterodactyle might flit again through the air, the huge
iguanodon reappear in the woods, and the ichthyosaurs swarm once more in
the sea. Coral reefs might be prolonged again beyond the arctic circle,
where the whale and the narwal now abound; and droves of turtles might
begin again to wander through regions now tenanted by the walrus and the
seal.

But not to indulge too far in these speculations, I may observe, in
conclusion, that however great, during the lapse of ages, may be the
vicissitudes of temperature in every zone, it accords with this theory
that the general climate should not experience any sensible change in
the course of a few thousand years; because that period is insufficient
to affect the leading features of the physical geography of the globe.

Notwithstanding the apparent uncertainty of the seasons, it is found
that the mean temperature of particular localities is very constant,
when observations made for a sufficient series of years are compared.

Yet there must be exceptions to this rule; and even the labors of man
have, by the drainage of lakes and marshes, and the felling of extensive
forests, caused such changes in the atmosphere as greatly to raise our
conception of the more important influence of those forces to which, in
certain latitudes, even the existence of land or water, hill or valley,
lake or sea, must be ascribed. If we possessed accurate information of
the amount of _local_ fluctuation in climate in the course of twenty
centuries, it would often, undoubtedly, be considerable. Certain tracts,
for example, on the coast of Holland and of England consisted of
cultivated land in the time of the Romans, which the sea, by gradual
encroachments, has at length occupied. Here, at least, a slight
alteration has been effected; for neither the distribution of heat in
the different seasons, nor the mean annual temperature of the atmosphere
investing the sea, is precisely the same as that which rests upon the
land.

In those countries, also, where earthquakes and volcanoes are in full
activity, a much shorter period may produce a sensible variation. The
climate of the great table-land of Malpais in Mexico, must differ
materially from that which prevailed before the middle of the last
century; for, since that time, six mountains, the highest of them rising
sixteen hundred feet above the plateau, have been thrown up by volcanic
eruptions. It is by the repetition of an indefinite number of such local
revolutions, and by slow movements extending simultaneously over wider
areas, as will be afterwards shown, that a general change of climate may
finally be brought about.




CHAPTER VIII.

ON FORMER CHANGES IN PHYSICAL GEOGRAPHY AND CLIMATE.


  Geographical features of the northern hemisphere, at the period of
    the oldest fossiliferous strata--State of the surface when the
    mountain limestone and coal were deposited--Changes in physical
    geography, between the carboniferous period and the chalk--Abrupt
    transition from the secondary to the tertiary fossils--Accession of
    land, and elevation of mountain chains, after the consolidation of
    the secondary rocks--Explanation of Map, showing the area covered by
    sea, since the commencement of the tertiary period--Astronomical
    theories of the causes of variations in climate--Theory of the
    diminution of the supposed primitive heat of the globe.


In the sixth chapter, I stated the arguments derived from organic
remains for concluding that in the period when the carboniferous strata
were deposited, the temperature of the ocean and the air was more
uniform in the different seasons of the year, and in different
latitudes, than at present, and that there was a remarkable absence of
cold as well as great moisture in the atmosphere. It was also shown that
the climate had been modified more than once since that epoch, and that
it had been reduced, by successive changes, more and more nearly to that
now prevailing in the same latitudes. Farther, I endeavored, in the last
chapter, to prove that vicissitudes in climate of no less importance may
be expected to recur in future, if it be admitted that causes now active
in nature have power, in the lapse of ages, to produce considerable
variations in the relative position of land and sea. It remains to
inquire whether the alterations, which the geologist can prove to have
_actually taken place_ at former periods, in the geographical features
of the northern hemisphere, coincide in their nature, and in the time of
their occurrence, with such revolutions in climate as might naturally
have resulted, according to the meteorological principles already
explained.

_Period of the primary fossiliferous rocks._--The oldest system of
strata which afford by their organic remains any evidence as to climate,
or the former position of land and sea, are those formerly known as the
_transition rocks_, or what have since been termed Lower Silurian or
"primary fossiliferous" formations. These have been found in England,
France, Germany, Sweden, Russia, and other parts of central and northern
Europe, as also in the great Lake district of Canada and the United
States. The multilocular or chambered univalves, including the Nautilus,
and the corals, obtained from the limestones of these ancient groups,
have been compared to forms now most largely developed in tropical seas.
The corals, however, have been shown by M. Milne Edwards to differ
generally from all living zoophytes; so that conclusions as to a warmer
climate drawn from such remote analogies must be received with caution.
Hitherto, few, if any, contemporaneous vegetable remains have been
noticed; but such as are mentioned agree more nearly with the plants of
the carboniferous era than any other, and would therefore imply a warm
and humid atmosphere entirely free from intense cold throughout the
year.

This absence or great scarcity of plants as well as of freshwater shells
and other indications of neighboring land, coupled with the wide extent
of marine strata of this age in Europe and North America, are facts
which imply such a state of physical geography (so far at least as
regards the northern hemisphere) as would, according to the principles
before explained, give rise to such a moist and equable climate. (See p.
109, and fig. 5, p. 111.)

_Carboniferous group._--This group comes next in the order of
succession; and one of its principal members, the mountain limestone,
was evidently a marine formation, as is shown by the shells and corals
which it contains. That the ocean of that period was of considerable
extent in our latitudes, we may infer from the continuity of these
calcareous strata over large areas in Europe, Canada, and the United
States. The same group has also been traced in North America, towards
the borders of the arctic sea.[196]

There are also several regions in Scotland, and in the central and
northern parts of England, as well as in the United States, where marine
carboniferous limestones alternate with strata containing coal, in such
a manner as to imply the drifting down of plants by rivers into the sea,
and the alternate occupation of the same space by fresh and salt water.

Since the time of the earlier writers, no strata have been more
extensively investigated, both in Europe and North America, than those
of the ancient carboniferous group, and the progress of science has led
to a general belief that a large portion of the purest coal has been
formed, not, as was once imagined, by vegetable matter floated from a
distance, but by plants which grew on the spot, and somewhat in the
manner of peat on the spaces now covered by the beds of coal. The former
existence of land in some of these spaces has been proved, as already
stated, by the occurrence of numerous upright fossil trees, with their
roots terminating downwards in seams of coal; and still more generally
by the roots of trees (stigmariae) remaining in their natural position in
the clays which underlie almost every layer of coal.

As some nearly continuous beds of such coal have of late years been
traced in North America, over areas 100 or 200 miles and upwards in
diameter, it may be asked whether the large tracts of ancient land
implied by this fact are not inconsistent with the hypothesis of the
general prevalence of islands at the period under consideration? In
reply, I may observe that the coal-fields must originally have been low
alluvial grounds, resembling in situation the cypress-swamps of the
Mississippi, or the sunderbunds of the Ganges, being liable like them to
be inundated at certain periods by a river or by the sea, if the land
should be depressed a few feet. All the phenomena, organic and
inorganic, imply conditions nowhere to be met with except in the deltas
of large rivers. We have to account for an abundant supply of fluviatile
sediment, carried for ages towards one and the same region, and capable
of forming strata of mud and sand thousands of feet, or even fathoms, in
thickness, many of them consisting of laminated shale, inclosing the
leaves of ferns and other terrestrial plants. We have also to explain
the frequent intercalations of root-beds, and the interposition here and
there of brackish and marine deposits, demonstrating the occasional
presence of the neighboring sea. But these forest-covered deltas could
only have been formed at the termination of large hydrographical basins,
each drained by a great river and its tributaries; and the accumulation
of sediment bears testimony to contemporaneous denudation on a large
scale, and, therefore, to a wide area of land, probably containing
within it one or more mountain chains.

In the case of the great Ohio or Appalachian coal-field, the largest in
the world, it seems clear that the uplands drained by one or more great
rivers were chiefly to the eastward, or they occupied a space now filled
by part of the Atlantic Ocean, for the mechanical deposits of mud and
sand increase greatly in thickness and coarseness of material as we
approach the eastern borders of the coal-field, or the southeast flanks
of the Alleghany mountains, near Philadelphia. In that region numerous
beds of pebbles, often of the size of a hen's egg, are seen to alternate
with beds of pure coal.

But the American coal-fields are all comprised within the 30th and 50th
degrees of north latitude; and there is no reason to presume that the
lands at the borders of which they originated ever penetrated so far or
in such masses into the colder and arctic regions, so as to generate a
cold climate. In the southern hemisphere, where the predominance of sea
over land is now the distinguishing geographical feature, we
nevertheless find a large part of the continent of Australia, as well as
New Zealand, placed between the 30th and 50th degrees of S. latitude.
The two islands of New Zealand taken together, are between 800 and 900
miles in length, with a breadth in some parts of ninety miles, and they
stretch as far south as the 46th degree of latitude. They afford,
therefore, a wide area for the growth of a terrestrial vegetation, and
the botany of this region is characterized by abundance of ferns, one
hundred and forty species of which are already known, some of them
attaining the size of trees. In this respect the southern shores of New
Zealand in the 46th degree of latitude almost vie with tropical islands.
Another point of resemblance between the Flora of New Zealand and that
of the ancient carboniferous period is the prevalence of the fir tribe
or of coniferous wood.

An argument of some weight in corroboration of the theory above
explained respecting the geographical condition of the temperate and
arctic latitudes of the northern hemisphere in the carboniferous period
may also be derived from ah examination of those groups of strata which
immediately preceded the coal. The fossils of the Devonian and Silurian
strata in Europe and North America have led to the conclusion, that they
were formed for the most part in deep seas, far from land. In those
older strata land plants are almost as rare as they are abundant or
universal in the coal measures. Those ancient deposits, therefore, may
be supposed to have belonged to an epoch when dry land had only just
begun to be upraised from the deep; a theory which would imply the
existence during the carboniferous epoch of islands, instead of an
extensive continent, in the area where the coal was formed.

Such a state of things prevailing in the north, from the pole to the
30th parallel of latitude, if not neutralized by circumstances of a
contrary tendency in corresponding regions south of the line, would give
rise to a general warmth and uniformity of climate throughout the globe.

_Changes in physical geography between the formation of the
carboniferous strata and the chalk._--We have evidence in England that
the strata of the ancient carboniferous group, already adverted to,
were, in many instances, fractured and contorted, and often thrown into
a vertical position, before the deposition of some even of the oldest
known secondary rocks, such as the new red sandstone.

Fragments of the older formations are sometimes included in the
conglomerates of the more modern; and some of these fragments still
retain their fossil shells and corals, so as to enable us to determine
the parent rocks from whence they were derived. There are other proofs
of the disturbance at successive epochs of different secondary rocks
before the deposition of others; and satisfactory evidence that, during
these reiterated convulsions, the geographical features of the northern
hemisphere were frequently modified, and that from time to time new
lands emerged from the deep. The vegetation, during some parts of the
period in question (from the lias to the chalk inclusive), when genera
allied to Cycas and Zamia were abundant, appears to have approached to
that of the larger islands of the equatorial zone; such, for example, as
we now find in the West Indian archipelago.[197] These islands appear to
have been drained by rivers of considerable size, which were inhabited
by crocodiles and gigantic oviparous reptiles, both herbivorous and
carnivorous, belonging for the most part to extinct genera. Of the
contemporary inhabitants of the land we have as yet acquired but scanty
information, but we know that there were flying reptiles, insects, and
small mammifers, allied to the marsupial tribes.

A freshwater deposit, called the Wealden, occurs in the upper part of
the secondary series of the south of England, which, by its extent and
fossils, attests the existence in that region of a large river draining
a continent or island of considerable dimensions. We know that this land
was clothed with wood, and inhabited by huge terrestrial reptiles and
birds. Its position so far to the north as the counties of Surrey and
Sussex, at a time when the mean temperature of the climate is supposed
to have been much hotter than at present, may at first sight appear
inconsistent with the theory before explained, that the heat was caused
by the gathering together of all the great masses of land in low
latitudes, while the northern regions were almost entirely sea. But it
must not be taken for granted that the geographical conditions already
described (p. 109, and fig. 5, p. 111) as capable of producing the
extreme of heat were ever combined at any geological period of which we
have yet obtained information. It is more probable, from what has been
stated in the preceding chapters, that a slight approximation to such an
extreme state of things would be sufficient; in other words, if most of
the dry land were tropical, and scarcely any of it arctic or antarctic,
a prodigious elevation of temperature must ensue, even though a part of
some continents should penetrate far into the temperate zones.

_Changes during the tertiary periods._--The secondary and tertiary
formations of Europe, when considered separately, may be contrasted as
having very different characters; the secondary appearing to have been
deposited in open seas, the tertiary in regions where dry land, lakes,
bays, and perhaps inland seas, abounded. The secondary series is almost
exclusively marine; the tertiary, even the oldest part, contains
lacustrine strata, and not unfrequently freshwater and marine beds
alternating. In fact there is evidence of important geographical changes
having occurred between the deposition of the cretaceous system, or
uppermost of the secondary series, and that of the oldest tertiary
group, and still more between the era of the latter and that of the
newer tertiary formations. This change in the physical geography of
Europe and North America was accompanied by an alteration no less
remarkable in organic life, scarcely any _species_ being common both to
the secondary and tertiary rocks, and the fossils of the latter
affording evidence of a different climate.

On the other hand, when we compare the tertiary formations of successive
ages, we trace a gradual approximation in the imbedded fossils, from an
assemblage in which extinct species predominate, to one where the
species agree for the most part with those now existing. In other words,
we find a gradual increase of animals and plants fitted for our present
climates, in proportion as the strata which we examine are more modern.
Now, during all these successive tertiary periods, there are signs of a
great increase of land in European and North American latitudes. By
reference to the map (Pl. 1), and its description, p. 121, the reader
will see that about two-thirds of the present European lands have
emerged since the earliest tertiary group originated. Nor is this the
only revolution which the same region has undergone within the period
alluded to, some tracts which were previously land having gained in
altitude, others, on the contrary, having sunk below their former level.

That the existing lands were not all upheaved at once into their present
position is proved by the most striking evidence. Several Italian
geologists, even before the time of Brocchi, had justly inferred that
the Apennines were elevated several thousand feet above the level of the
Mediterranean before the deposition of the modern Subapennine beds which
flank them on either side. What now constitutes the central calcareous
chain of the Apennines must for a long time have been a narrow ridgy
peninsula, branching off, at its northern extremity, from the Alps near
Savona. This peninsula has since been raised from one to two thousand
feet, by which movement the ancient shores, and, for a certain extent,
the bed of the contiguous sea, have been laid dry, both on the side of
the Mediterranean and the Adriatic.

[Illustration: Fig. 7.]

The nature of these vicissitudes will be explained by the accompanying
diagram, which represents a transverse section across the Italian
peninsula. The inclined strata A are the disturbed formations of the
Apennines, into which the ancient igneous rocks a are supposed to have
intruded themselves. At a lower level on each flank of the chain are the
more recent shelly beds _b b_, which often contain rounded pebbles
derived from the waste of contiguous parts of the older Apennine
limestone. These, it will be seen, are horizontal, and lie in what is
termed "unconformable stratification" on the more ancient series. They
now constitute a line of hills of moderate elevation between the sea and
the Apennines, but never penetrate to the higher and more ancient
valleys of that chain.

The same phenomena are exhibited in the Alps on a much grander scale;
those mountains being composed in some even of their higher regions of
the newer secondary and oldest tertiary formations, while they are
encircled by a great zone of more modern tertiary rocks both on their
southern flank towards the plains of the Po, and on the side of
Switzerland and Austria, and at their eastern termination towards Styria
and Hungary.[198] This newer tertiary zone marks the position of former
seas or gulfs, like the Adriatic, wherein masses of strata accumulated,
some single groups of which are not inferior in thickness to the most
voluminous of our secondary formations in England. Some even of these
newer groups have been raised to the height of three or four thousand
feet, and in proportion to their antiquity, they generally rise to
greater heights, the older of them forming interior zones nearest to the
central ridges of the Alps. We have already ascertained that the Alps
gained accessions to their height and width at several successive
periods, and that the last series of improvements occurred when the
seas were inhabited by many existing species of animals.

We may imagine some future series of convulsions once more to heave up
this stupendous chain, together with the adjoining bed of the sea, so
that the mountains of Europe may rival the Andes in elevation; in which
case the deltas of the Po, Adige, and Brenta, now encroaching upon the
Adriatic, might be uplifted so as to form another exterior belt of
considerable height around the southeastern flank of the Alps.

The Pyrenees, also, have acquired their present altitude, which in Mont
Perdu exceeds eleven thousand feet, since the deposition of the
nummulitic or Eocene division of the tertiary series. Some of the
tertiary strata at the base of the chain are raised to the height of
only a few hundred feet above the sea, and retain a horizontal position,
without partaking in general in the disturbance to which the older
series has been subjected; so that the great barrier between France and
Spain was almost entirely upheaved in the interval between the
deposition of certain groups of tertiary strata.

The remarkable break between the most modern of the known secondary
rocks and the oldest tertiary, may be apparent only, and ascribable to
the present deficiency of our information. Already the marles and green
sand of Heers near Tongres, in Belgium, observed by M. Dumont, and the
"pisolitic limestone" of the neighborhood of Paris, both intermediate in
age between the Maestricht chalk and the lower Eocene strata, begin to
afford us signs of a passage from one state of things to another.
Nevertheless, it is far from impossible that the interval between the
chalk and tertiary formations constituted an era in the earth's history,
when the transition from one class of organic beings to another was,
comparatively speaking, rapid. For if the doctrines above explained in
regard to vicissitudes of temperature are sound, it will follow that
changes of equal magnitude in the geographical features of the globe may
at different periods produce very unequal effects on climate; and, so
far as the existence of certain animals and plants depends on climate,
the duration of species would be shortened or protracted, according to
the rate at which the change of temperature proceeded.

For even if we assume that the intensity of the subterranean disturbing
forces is uniform and capable of producing nearly equal amounts of
alteration on the surface of the planet, during equal periods of time,
still the rate of alteration in climate would be by no means uniform.
Let us imagine the quantity of land between the equator and the tropic
in one hemisphere to be to that in the other as thirteen to one, which,
as before stated, represents the unequal proportion of the
extra-tropical lands in the two hemispheres at present. (See figs. 3 and
4, p. 110.) Then let the first geographical change consist in the
shifting of this preponderance of land from one side of the line to the
other; from the southern hemisphere, for example, to the northern. Now
this need not affect the general temperature of the earth. But if, at
another epoch, we suppose a continuance of the same agency to transfer
an equal volume of land from the torrid zone to the temperate and arctic
regions of the northern and southern hemispheres, or into one of them,
there might be so great a refrigeration of the mean temperature _in all
latitudes_, that scarcely any of the pre-existing races of animals would
survive; and, unless it pleased the Author of Nature that the planet
should be uninhabited, new species, and probably of widely different
forms, would then be substituted in the room of the extinct. We ought
not, therefore, to infer that equal periods of time are always attended
by an equal amount of change in organic life, since a great fluctuation
in the mean temperature of the earth, the most influential cause which
can be conceived in exterminating whole races of animals and plants,
must, in different epochs, require unequal portions of time for its
completion.

[PLATE I. _Map showing the extent of surface in Europe which has at one
period or another been covered by the sea since the commencement of the
deposition of the older or Eocene Tertiary strata._]

This map will enable the reader to perceive at a glance the great extent
of change in the physical geography of Europe, which can be proved to
have taken place since some of the older tertiary strata began to be
deposited. The proofs of submergence, during some part or other of this
period, in all the districts distinguished by ruled lines, are of a most
unequivocal character; for the area thus described is now covered by
deposits containing the fossil remains of animals which could only have
lived in salt water. The most ancient part of the period referred to
cannot be deemed very remote, considered geologically; because the
deposits of the Paris and London basins, and many other districts
belonging to the older tertiary epoch, are newer than the greater part
of the sedimentary rocks (those commonly called secondary and primary
fossiliferous or paleozoic) of which the crust of the globe is composed.
The species, moreover, of marine testacea, of which the remains are
found in these older tertiary formations, are not entirely distinct from
such as now live. Yet, notwithstanding the comparatively recent epoch to
which this retrospect is carried, the variations in the distribution of
land and sea depicted on the map form only a part of those which must
have taken place during the period under consideration. Some
approximation has merely been made to an estimate of the amount of _sea
converted into land_ in parts of Europe best known to geologists; but we
cannot determine how much land has become sea during the same period;
and there may have been repeated interchanges of land and water in the
same places, changes of which no account is taken in the map, and
respecting the amount of which little accurate information can ever be
obtained.

I have extended the sea in some instances beyond the limits of the land
now covered by tertiary formations, and marine drift, because other
geological data have been obtained for inferring the submergence of
these tracts after the deposition of the Eocene strata had begun. Thus,
for example, there are good reasons for concluding that part of the
chalk of England (the North and South Downs, for example, together with
the intervening secondary tracts) continued beneath the sea until the
oldest tertiary beds had begun to accumulate.

A strait of the sea separating England and Wales has also been
introduced, on the evidence afforded by shells of existing species found
in a deposit of gravel, sand, loam, and clay, called the northern drift,
by Sir R. Murchison.[199] And Mr. Trimmer has discovered similar recent
marine shells on the northern coast of North Wales, and on Moel Tryfane,
near the Menai Straits, at the height of 1392 feet above the level of
the sea!

Some raised sea-beaches, and drift containing marine shells, which I
examined in 1843, between Limerick and Dublin, and which have been
traced over other parts of Ireland by different geologists, have
required an extension of the dark lines so as to divide that island into
several. In improving this part of my map I have been especially
indebted to the assistance of Mr. Oldham, who in 1843 announced to the
British Association at Cork the fact that at the period when the drift
or glacial beds were deposited, Ireland must have formed an archipelago
such as is here depicted. A considerable part of Scotland might also
have been represented in a similar manner as under water when the drift
originated.

A portion of Brittany is divided into islands, because it is known to be
covered with patches of marine tertiary strata chiefly miocene. When I
examined these in 1830 and 1843, I convinced myself that the sea must
have covered much larger areas than are now occupied by these small and
detached deposits. The former connection of the White Sea and the Gulf
of Finland is proved by the fact that a multitude of huge erratic blocks
extend over the intervening space, and a large portion of Norway,
Sweden, and Denmark, as well as Germany and Russia, are represented as
sea, on the same evidence, strengthened by the actual occurrence of
fossil sea-shells, of recent species, in the drift of various portions
of those countries. The submergence of considerable areas under large
bodies of fresh water, during the tertiary period, of which there are
many striking geological proofs in Auvergne, and elsewhere, has not been
expressed by ruled lines. They bear testimony to the former existence of
neighboring lands, and a certain elevation of the areas where they occur
above the level of the ocean; they are therefore left blank, together
with all the space that cannot be demonstrated to have been part of the
sea at some time or other, since the commencement of the Eocene epoch.

In compiling this map, which has been entirely recast since the first
edition, I have availed myself of the latest geological maps of the
British isles, and north of Europe; also of those published by the
government surveyors of France, MM. de Beaumont and Dufresnoy; the map
of Germany and part of Europe, by Von Dechen, and that of Italy by M.
Tchihatchoff (Berlin, 1842). Lastly, Sir R. Murchison's important map of
Russia, and the adjoining countries, has enabled me to mark out not only
a considerable area, previously little known, in which tertiary
formations occur; but also a still wider expanse, over which the
northern drift, and erratic blocks with occasional marine shells, are
traceable. The southern limits of these glacial deposits in Russia and
Germany indicate the boundary, so far as we can now determine it, of the
northern ocean, at a period immediately antecedent to that of the human
race.

I was anxious, even in the title of this map, to guard the reader
against the supposition that it was intended to represent the state of
the physical geography of part of Europe at any _one point of time_. The
difficulty, or rather the impossibility, of restoring the geography of
the globe as it may have existed at any former period, especially a
remote one, consists in this, that we can only point out where part of
the sea has been turned into land, and are almost always unable to
determine what land may have become sea. All maps, therefore, pretending
to represent the geography of remote geological epochs must be ideal.
The map under consideration is not a restoration of a former state of
things, at any particular moment of time, but a synoptical view of a
certain amount of one kind of change (the conversion of sea into land)
known to have been brought about within a given period.

It may be proper to remark that the vertical movements to which the land
is subject in certain regions, occasion alternately the subsidence and
the uprising of the surface; and that, by such oscillations at
successive periods, a great area may have been entirely covered with
marine deposits, although the whole may never have been beneath the
waters at one time; nay, even though the relative proportion of land and
sea may have continued unaltered throughout the whole period. I believe,
however, that since the commencement of the tertiary period, the dry
land in the northern hemisphere has been continually on the increase,
both because it is now greatly in excess beyond the average proportion
which land generally bears to water on the globe, and because a
comparison of the secondary and tertiary strata affords indications, as
I have already shown, of a passage from the condition of an ocean
interspersed with islands to that of a large continent.

But supposing it were possible to represent all the vicissitudes in the
distribution of land and sea that have occurred during the tertiary
period, and to exhibit not only the actual existence of land where there
was once sea, but also the extent of surface now submerged which may
once have been land, the map would still fail to express all the
important revolutions in physical geography which have taken place
within the epoch under consideration. For the oscillations of level, as
was before stated, have not merely been such as to lift up the land from
below the water, but in some cases to occasion a rise of many thousand
feet above the sea. Thus the Alps have acquired an additional altitude
of 4000, and even in some places 10,000 feet; and the Apennines owe a
considerable part of their present height to subterranean convulsions
which have happened within the tertiary epoch.

On the other hand, some mountain chains may have been lowered during the
same series of ages, in an equal degree, and shoals may have been
converted into deep abysses.[200] Since this map was recast in 1847,
geologists have very generally come to the conclusion that the
nummulitic limestone, together with the overlying fucoidal grit and
shale, called "Flysch," in the Alps, belongs to the older tertiary or
Eocene group. As these nummulitic rocks enter into the structure of some
of the most lofty and disturbed parts of the Alps, Apennines,
Carpathians, Pyrenees, and other mountain chains, and form many of the
elevated lands of Africa and Asia, their position almost implies the
ubiquity of the post-Eocene ocean, not, indeed, by the simultaneous, but
by the successive, occupancy of the whole ground by its waters.[201]

_Concluding remarks on changes in physical geography._--The foregoing
observations, it may be said, are confined chiefly to Europe, and
therefore merely establish the increase of dry land in a space which
constitutes but a small portion of the northern hemisphere; but it was
stated in the preceding chapter, that the great Lowland of Siberia,
lying chiefly between the latitudes 55 degrees and 75 degrees N. (an
area nearly equal to all Europe), is covered for the most part by marine
strata, which, from the account given by Pallas, and more recently by
Sir R. Murchison, belongs to a period when all or nearly all the shells
were of a species still living in the north. The emergence, therefore,
of this area from the deep is, comparatively speaking, a very modern
event, and must, as before remarked, have caused a great increase of
cold throughout the globe.

Upon a review, then, of all the facts above enumerated, respecting the
ancient geography of the globe as attested by geological monuments,
there appear good grounds for inferring that changes of climate
coincided with remarkable revolutions in the former position of sea and
land. A wide expanse of ocean, interspersed with islands, seems to have
pervaded the northern hemisphere at the periods when the Silurian and
carboniferous rocks were formed, and a warm and very uniform temperature
then prevailed. Subsequent modifications in climate accompanied the
deposition of the secondary formations, when repeated changes were
effected in the physical geography of our northern latitudes. Lastly,
the refrigeration became most decided, and the climate most nearly
assimilated to that now enjoyed, when the lands in Europe and northern
Asia had attained their full extension, and the mountain chains their
actual height.

Soon after the first publication of this theory of climate, an objection
was made by an anonymous German critic in 1833 that there are no
geological proofs of the prevalence at any former period of a
temperature _lower_ than that now enjoyed; whereas, if the causes above
assigned were the true ones, it might reasonably have been expected that
fossil remains would sometimes indicate colder as well as hotter
climates than those now established.[202] In answer to this objection, I
may suggest, that our present climates are probably far more distant
from the extreme of possible heat than from its opposite extreme of
cold. A glance at the map (fig. 6, p. 111) will show that all the
existing lands might be placed between the 30th parallels of latitude on
each side of the equator, and that even then they would by no means fill
that space. In no other position would they give rise to so high a
temperature. But the present geographical condition of the earth is so
far removed from such a state of things, that the land lying between the
poles and the parallels of 30, is in great excess; so much so that,
instead of being to the sea in the proportion of 1 to 3, which is as
near as possible the average general ratio throughout the globe, it is 9
to 23.[203] Hence it ought not to surprise us if, in our geological
retrospect, embracing perhaps a small part only of a complete cycle of
change in the terrestrial climates, we should happen to discover
everywhere the signs of a higher temperature. The strata hitherto
examined may have originated when the quantity of equatorial land was
always decreasing and the land in regions nearer the poles augmenting in
height and area, until at length it attained its present excess in high
latitudes. There is nothing improbable in supposing that the
geographical revolutions of which we have hitherto obtained proofs had
this general tendency; and in that case the refrigeration must have been
constant, although, for reasons before explained, the rate of cooling
may not have been uniform.

It may, however, be as well to recall the reader's attention to what was
before said of the indication brought to light of late years, of a
considerable oscillation of temperature, in the period immediately
preceding the human era. We have seen that on examining some of the most
northern deposits, those commonly called the northern drift in Scotland,
Ireland, and Canada, in which nearly all, in some cases, perhaps all,
the fossil shells are of recent species, we discover the signs of a
climate colder than that now prevailing in corresponding latitudes on
both sides the Atlantic. It appears that an arctic fauna specifically
resembling that of the present seas, extended farther to the south than
now. This opinion is derived partly from the known habitations of the
corresponding living species, and partly from the abundance of certain
genera of shells and the absence of others.[204] The date of the
refrigeration thus inferred appears to coincide very nearly with the era
of the dispersion of erratic blocks over Europe and North America, a
phenomenon which will be ascribed in the sequel (ch. 16) to the cold
then prevailing in the northern hemisphere. The force, moreover, of the
German critic's objection has been since in a great measure destroyed,
by the larger and more profound knowledge acquired in the last few years
of the ancient carboniferous flora, which has led the ablest botanists
to adopt the opinion, that the climate of the coal period was remarkable
for its warmth, moisture, equability, and freedom from cold, rather than
the intensity of its _tropical heat_. We are therefore no longer
entitled to assume that there has been a constant and gradual decline in
the absolute amount of heat formerly contained in the atmosphere and
waters of the ocean, such as it was conjectured might have emanated from
the incandescent central nucleus of a new and nearly fluid planet,
before the interior had lost, by radiation into surrounding space, a
great part of its original high temperature.

_Astronomical causes of fluctuations in climate._--Sir John Herschel has
lately inquired, whether there are any astronomical causes which may
offer a possible explanation of the difference between the actual
climate of the earth's surface, and those which formerly appear to have
prevailed. He has entered upon this subject, he says, "impressed with
the magnificence of that view of geological revolutions, which regards
them rather as regular and necessary effects of great and general
causes, than as resulting from a series of convulsions and catastrophes,
regulated by no laws, and reducible to no fixed principles." Geometers,
he adds, have demonstrated the absolute invariability of the mean
distance of the earth from the sun; whence it would at first seem to
follow, that the mean annual supply of light and heat derived from that
luminary would be alike invariable: but a closer consideration of the
subject will show, that this would not be a legitimate conclusion; but
that on the contrary, the _mean_ amount of solar radiation is dependent
on the eccentricity of the earth's orbit, and therefore liable to
variation.[205]

Now the eccentricity of the orbit, he continues, is actually
diminishing, and has been so for ages beyond the records of history. In
consequence, the ellipse is in a state of approach to a circle, and the
annual average of solar heat radiated to the earth is actually on the
_decrease_. So far this is in accordance with geological evidence, which
indicates a general refrigeration of climate; but the question remains,
whether the amount of diminution which the eccentricity may have ever
undergone can be supposed sufficient to account for any sensible
refrigeration. The calculations necessary to determine this point,
though practicable, have never yet been made, and would be extremely
laborious; for they must embrace all the perturbations which the most
influential planets, Venus, Mars, Jupiter, and Saturn, would cause in
the earth's orbit, and in each other's movements round the sun.

The problem is also very complicated, inasmuch as it depends not merely
on the ellipticity of the earth's orbit, but on the assumed temperature
of the celestial spaces beyond the earth's atmosphere; a matter still
open to discussion, and on which M. Fourier and Sir J. Herschel have
arrived at very different opinions. But if, says Herschel, we suppose an
extreme case, as if the earth's orbit should ever become as eccentric as
that of the planet Juno or Pallas, a great change of climate might be
conceived to result, the winter and summer temperatures being sometimes
mitigated, and at others exaggerated, in the same latitudes.

It is much to be desired that the calculations alluded to were executed,
as even if they should demonstrate, as M. Arago thinks highly
probable,[206] that the mean amount of solar radiation can never be
materially affected by irregularities in the earth's motion, it would
still be satisfactory to ascertain the point. Such inquiries, however,
can never supersede the necessity of investigating the consequences of
the varying position of continents, shifted as we know them to have been
during successive epochs, from one part of the globe to the other.

Another astronomical hypothesis respecting the possible cause of secular
variations in climate, has been proposed by a distinguished
mathematician and philosopher, M. Poisson. He begins by assuming, 1st,
that the sun and our planetary system are not stationary, but carried
onward by a common movement through space; 2dly, that every point in
space receives heat as well as light from innumerable stars surrounding
it on all sides, so that if a right line of indefinite length be
produced in any direction from such a point, it must encounter a star
either visible or invisible to us. 3dly, He then goes on to assume, that
the different regions of space, which in the course of millions of years
are traversed by our system, must be of very unequal temperature,
inasmuch as some of them must receive a greater, others a less, quantity
of radiant heat from the great stellary inclosure. If the earth, he
continues, or any other large body, pass from a hotter to a colder
region, it would not readily lose in the second all the heat which it
has imbibed in the first region, but retain a temperature increasing
downwards from the surface, as in the actual condition of our
planet.[207]

Now the opinion originally suggested by Sir W. Herschel, that our sun
and its attendant planets were all moving onward through space, in the
direction of the constellation Hercules, is very generally thought by
eminent astronomers to be confirmed. But even if its reality be no
longer matter of doubt, conjectures as to its amount are still vague and
uncertain; and great, indeed, must be the extent of the movement before
this cause alone can work any material alteration in the terrestrial
climates. Mr. Hopkins, when treating of this theory, remarked, that so
far as we were acquainted with the position of the stars not very remote
from the sun, they seem to be so distant from each other, that there are
no points in space among them, where the intensity of radiating heat
would be comparable to that which the earth derives from the sun, except
at points very near to each star. Thus, in order that the earth should
derive a degree of heat from stellar radiation comparable to that now
derived from the sun, she must be in close proximity to some particular
star, leaving the aggregate effect of radiation from the other stars
nearly the same as at present. This approximation, however, to a single
star could not take place consistently with the preservation of the
motion of the earth about the sun, according to its present laws.

Suppose our sun should approach a star within the present distance of
Neptune. That planet could no longer remain a member of the solar
system, and the motions of the other planets would be disturbed in a
degree which no one has ever contemplated as probable since the
existence of the solar system. But such a star, supposing it to be no
larger than the sun, and to emit the same quantity of heat, would not
send to the earth much more than one-thousandth part of the heat which
she derives from the sun, and would therefore produce only a very small
change in terrestrial temperature.[208]

_Variable splendor of stars._--There is still another astronomical
suggestion respecting the possible causes of secular variations in the
terrestrial climates which deserves notice. It has long been known that
certain stars are liable to great and periodical fluctuations in
splendor, and Sir J. Herschel has lately ascertained (Jan. 1840), that a
large and brilliant star, called _alpha_ Orionis, sustained, in the
course of six weeks, a loss of nearly half its light. "This phenomenon,"
he remarks, "cannot fail to awaken attention, and revive those
speculations which were first put forth by my father Sir W. Herschel,
respecting the possibility of a change in the lustre of _our sun
itself_. If there really be a community of nature between the sun and
fixed stars, every proof that we obtain of the extensive prevalence of
such periodical changes in those remote bodies, adds to the probability
of finding something of the kind nearer home." Referring then to the
possible bearing of such facts on ancient revolutions, in terrestrial
climates, he says, that "it is a matter of observed fact, that many
stars _have_ undergone, in past ages, within the records of astronomical
history, very extensive changes in apparent lustre, without a change of
distance adequate to producing such an effect. If our sun were even
_intrinsically_ much brighter than at present, the mean temperature of
the surface of our globe would, of course, be proportionally greater. I
speak now not of periodical, but of secular changes. But the argument
is complicated with the consideration of the possibly imperfect
transparency of the celestial spaces, and with the cause of that
imperfect transparency, which may be due to material non-luminous
particles diffused irregularly in patches analogous to nebulae, but of
greater extent--to _cosmical clouds_, in short--of whose existence we
have, I think, some indication in the singular and apparently capricious
phenomena of temporary stars, and perhaps in the recent extraordinary
sudden increase and hardly less sudden diminution of [Greek: e]
_Argus_."[209]

More recently (1852) Schwabe has observed that the spots on the sun
alternately increase and decrease in the course of every ten years, and
Captain Sabine has pointed out that this variable obscuration coincides
in time both as to its maximum and minimum with changes in all those
terrestrial magnetic variations which are caused by the sun. Hence he
infers that the period of alteration in the spots is a _solar magnetic
period_. Assuming such to be the case, the variable light of some stars
may indicate a similar phenomenon, or they may be stellar magnetic
periods, differing only in the degree of obscuration and its duration.
And as hitherto we have perceived no fluctuation in the heat received by
the earth from the sun coincident with the _solar magnetic period_, so
the fluctuations in the brilliancy of the stars may not perhaps be
attended with any perceptible alteration in their power of radiating
heat. But before we can speculate with advantage in this new and
interesting field of inquiry, we require more facts and observations.

_Supposed gradual diminution of the earth's primitive heat._--The
gradual diminution of the supposed primitive heat of the globe has been
resorted to by many geologists as the principal cause of alterations of
climate. The matter of our planet is imagined, in accordance with the
conjectures of Leibnitz, to have been originally in an intensely heated
state, and to have been parting ever since with portions of its heat,
and at the same time contracting its dimensions. There are, undoubtedly,
good grounds for inferring from recent observation and experiment, that
the temperature of the earth increases as we descend from the surface to
that slight depth to which man can penetrate: but there are no positive
proofs of a secular decrease of internal heat accompanied by
contraction. On the contrary, La Place has shown, by reference to
astronomical observations made in the time of Hipparchus, that in the
last two thousand years at least there has been no sensible contraction
of the globe by cooling; for had this been the case, even to an
extremely small amount, the day would have been shortened, whereas its
length has certainly not diminished during that period by 1/300th of a
second.

Baron Fourier, after making a curious series of experiments on the
cooling of incandescent bodies, considers it to be proved
mathematically, that the actual distribution of heat in the earth's
envelope is precisely that which would have taken place if the globe
had been formed in a medium of a very high temperature, and had
afterwards been constantly cooled.[210] He contends, that although no
contraction can be demonstrated to have taken place within the
historical period (the operation being slow and the time of observation
limited), yet it is no less certain that heat is annually passing out by
radiation from the interior of the globe into the planetary spaces. He
even undertook to demonstrate that the quantity of heat thus transmitted
into space in the course of every century, through every square metre of
the earth's surface, would suffice to melt a column of ice having a
square metre for its base, and being three metres (or 9 feet 10 inches)
high.

It is at the same time denied, that there is any assignable mode in
which the heat thus lost by radiation can be again restored to the
earth, and consequently the interior of our planet must, from the moment
of its creation, have been subject to refrigeration, and is destined
together with the sun and stars forever to grow colder. But I shall
point out in the sequel (chapter 31) many objections to these views, and
to the theory of the intense heat of the earth's central nucleus, and
shall then inquire how far the observed augmentation of temperature, as
we descend below the surface, may be referable to other causes
unconnected with the supposed pristine fluidity of the entire globe.




CHAPTER IX.

THEORY OF THE PROGRESSIVE DEVELOPMENT OF ORGANIC LIFE AT SUCCESSIVE
GEOLOGICAL PERIODS.


  Theory of the progressive development of organic life--Evidence in
    its support inconclusive--Vertebrated animals, and plants of the
    most perfect organization, in strata of very high
    antiquity--Differences between the organic remains of successive
    formations--Comparative modern origin of the human race--The popular
    doctrine of successive development not established by the admission
    that man is of modern origin--Introduction of man, to what extent a
    change in the system.


_Progressive development of organic life._--In the preceding chapters I
have considered whether revolutions in the general climate of the globe
afford any just ground of opposition to the doctrine that the former
changes of the earth which are treated of in geology belong to one
uninterrupted series of physical events governed by ordinary causes.
Against this doctrine some popular arguments have been derived from the
great vicissitudes of the organic creation in times past; I shall
therefore proceed to the discussion of such objections, which have been
thus formally advanced by the late Sir Humphrey Davy. "It is
impossible," he affirms, "to defend the proposition, that the present
order of things is the ancient and constant order of nature, only
modified by existing laws: in those strata which are deepest, and which
must, consequently, be supposed to be the earliest deposited, forms even
of vegetable life are rare; shells and vegetable remains are found in
the next order; the bones of fishes and oviparous reptiles exist in the
following class; the remains of birds, with those of the same genera
mentioned before, in the next order; those of quadrupeds of extinct
species in a still more recent class; and it is only in the loose and
slightly consolidated strata of gravel and sand, and which are usually
called diluvian formations, that the remains of animals such as now
people the globe are found, with others belonging to extinct species.
But, in none of these formations, whether called secondary, tertiary, or
diluvial, have the remains of man, or any of his works, been discovered;
and whoever dwells upon this subject must be convinced, that the present
order of things, and the comparatively recent existence of man as the
master of the globe, is as certain as the destruction of a former and a
different order, and the extinction of a number of living forms which
have no types in being. In the oldest secondary strata there are no
remains of such animals as now belong to the surface; and in the rocks,
which may be regarded as more recently deposited, these remains occur
but rarely, and with abundance of extinct species;--there seems, as it
were, a gradual approach to the present system of things, and a
succession of destructions and creations preparatory to the existence of
man."[211]

In the above passages, the author deduces two important conclusions from
geological data: first, that in the successive groups of strata, from
the oldest to the most recent, there is a progressive development of
organic life, from the simplest to the most complicated
forms;--secondly, that man is of comparatively recent origin, and these
conclusions he regards as inconsistent with the doctrine, "that the
present order of things is the ancient and constant order of nature only
modified by existing laws."

With respect, then, to the first of these propositions, we may ask
whether the theory of the progressive development of animal and
vegetable life, and their successive advancement from a simple to a more
perfect state, has any secure foundation in fact? No geologists who are
in possession of all the data now established respecting fossil remains,
will for a moment contend for the doctrine in all its detail, as laid
down by the distinguished philosopher to whose opinions we have
referred: but naturalists, who are not unacquainted with recent
discoveries, continue to defend it in a modified form. They say that in
the first period of the world (by which they mean the earliest of which
we have yet brought to light any memorials), the vegetation was
characterized by a predominance of cryptogamic plants, while the animals
which coexisted were almost entirely confined to zoophytes, testacea,
and a few fish. Plants of a less simple structure, coniferae and cycadeae,
flourished largely in the next epoch, when oviparous reptiles began also
to abound. Lastly, the terrestrial flora became most diversified and
most perfect when the highest orders of animals, the mammalia and birds,
were called into existence.

Now in the first place, it may be observed, that many naturalists are
guilty of no small inconsistency in endeavoring to connect the phenomena
of the earliest vegetation with a nascent condition of organic life, and
at the same time to deduce from the numerical predominance of certain
forms, the greater heat or uniformity of the ancient climate. The
arguments in favor of the latter conclusion are without any force,
unless we can assume that the rules followed by the Author of Nature in
the creation and distribution of organic beings were the same formerly
as now; and that, as certain families of animals and plants are now most
abundant in, or exclusively confined to regions where there is a certain
temperature, a certain degree of humidity, a certain intensity of light,
and other conditions, so also analogous phenomena were exhibited at
every former era.

If this postulate be denied, and the prevalence of particular families
be declared to depend on a certain order of precedence in the
introduction of different classes into the earth, and if it be
maintained that the standard of organization was raised successively, we
must then ascribe the numerical preponderance, in the earlier ages, of
plants of simpler structure, _not to the heat_, or other climatal
conditions, but to those different laws which regulate organic life in
newly created worlds.

Before we can infer a warm and uniform temperature in high latitudes,
from the presence of 250 species of ferns, some of them arborescent,
accompanied by lycopadiacae of large size, and araucariae, we must be
permitted to assume, that at all times, past, present, and future, a
heated and moist atmosphere pervading the northern hemisphere has a
tendency to produce in the vegetation a predominance of analogous forms.

It should moreover be borne in mind, when we are considering the
question of development from a botanical point of view, that naturalists
are by no means agreed as to the existence of an ascending scale of
organization in the vegetable world corresponding to that which is very
generally recognized in animals. "From the sponge to man," in the
language of De Blainville, there may be a progressive chain of being,
although often broken and imperfect; but if we seek to classify plants
according to a linear arrangement, ascending gradually from the lichen
to the lily or the rose, we encounter incomparably greater difficulties.
Yet the doctrine of a more highly developed organization in the plants
created at successive periods presupposes the admission of such a
graduated scale.

We have as yet obtained but scanty information respecting the state of
the terrestrial flora at periods antecedent to the coal. In the
carboniferous epoch, about 500 species of fossil plants are enumerated
by Adolphe Brongniart, which we may safely regard as a mere fragment of
an ancient flora; since, in Europe alone, there are now no less than
11,000 living species. I have already hinted that the plants which
produced coal were not drifted from a distance, but that nearly all of
them grew on the spots where they became fossil. They appear to have
belonged, as before explained (p. 115), to a peculiar class of
_stations_,--to low level and swampy regions, in the deltas of large
rivers, slightly elevated above the level of the sea. From the study,
therefore, of such a vegetation, we can derive but little insight into
the nature of the contemporaneous upland flora, still less of the plants
of the mountainous or Alpine country; and if so, we are enabled to
account for the apparent monotony of the vegetation, although its
uniform character was doubtless in part owing to a greater uniformity of
climate then prevailing throughout the globe. Some of the commonest
trees of this period, such as the sigillariae, which united the structure
of ferns and of cycadeae, departed very widely from all known living
types. The coniferae and ferns, on the contrary, were very closely allied
to living genera. It is remarkable that none of the exogens of Lindley
(dicotyledonous angiosperms of Brongniart), which comprise four-fifths
of the living flora of the globe, and include all the forest trees of
Europe except the fir-tribe, have yet been discovered in the coal
measures, and a very small number--fifteen species only--of
monocotyledons. If several of these last are true plants, an opinion to
which Messrs. Lindley, Unger, Corda, and other botanists of note
incline, the question whether any of the most highly organized plants
are to be met with in ancient strata is at once answered in the
affirmative. But the determination of these palms being doubtful, we
have as yet in the coal no positive proofs either of the existence of
the most perfect, or of the most simple forms of flowering or flowerless
vegetation. We have no fungi, lichens, hepatici or mosses: yet this
latter class may have been as fully represented then as now.

In the flora of the secondary eras, all botanists agree that palms
existed, although in Europe plants of the family of zamia and cycas
together with coniferae predominated, and must have given a peculiar
aspect to the flora. As only 200 or 300 species of plants are known in
all the rocks ranging from the Trias to the Oolite inclusive, our data
are too scanty as yet to affirm whether the vegetation of this second
epoch was or was not on the whole of a simpler organization than that of
our own times.

In the Lower Cretaceous formation, near Aix-la-Chapelle, the leaves of a
great many dicotyledonous trees have lately been discovered by Dr.
Debey, establishing the important fact of the coexistence of a large
number of angiosperms with cycadeae, and with that rich reptilian fauna
comprising the ichthyosaur, plesiosaur, and pterodactyl, which some had
supposed to indicate a state of the atmosphere unfavorable to a
dicotyledonous vegetation.

The number of plants hitherto obtained from _tertiary_ strata of
different ages is very limited, but is rapidly increasing. They are
referable to a much greater variety of families and classes than an
equal number of fossil species taken from secondary or primary rocks,
the angiosperms bearing the same proportion to the gymnosperms and
acrogens as in the present flora of the globe. This greater variety may,
doubtless, be partly ascribed to the greater diversity of stations in
which the plants grew, as we have in this case an opportunity, rarely
enjoyed in studying the secondary fossils, of investigating inland or
lacustrine deposits accumulated at different heights above the sea, and
containing the memorials of plants washed down from adjoining mountains.

In regard, then, to the strata from the cretaceous to the uppermost
tertiary inclusive, we may affirm that we find in them all the principal
classes of living plants, and during this vast lapse of time four or
five complete changes in the vegetation occurred, yet no step whatever
was made in advance at any of these periods by the addition of more
highly organized species.

If we next turn to the fossils of the animal kingdom, we may inquire
whether, when they are arranged by the geologists in a chronological
series, they imply that beings of more highly developed structure and
greater intelligence entered upon the earth at successive epochs, those
of the simplest organization being the first created, and those more
highly organized being the last.

Our knowledge of the Silurian fauna is at present derived entirely from
rocks of marine origin, no fresh-water strata of such high antiquity
having yet been met with. The fossils, however, of these ancient rocks
at once reduce the theory of progressive development to within very
narrow limits, for already they comprise a very full representation of
the radiata, mollusca, and articulata proper to the sea. Thus, in the
great division of radiata, we find asteriod and helianthoid zoophytes,
besides crinoid and cystidean echinoderms. In the mollusca, between 200
and 300 species of cephalopoda are enumerated. In the articulata we have
the crustaceans represented by more than 200 species of trilobites,
besides other genera of the same class. The remains of fish are as yet
confined to the upper part of the Silurian series; but some of these
belong to placoid fish, which occupy a high grade in the scale of
organization. Some naturalists have assumed that the earliest fauna was
exclusively marine, because we have not yet found a single Silurian
helix, insect, bird, terrestrial reptile or mammifer; but when we carry
back our investigation to a period so remote from the present, we ought
not to be surprised if the only accessible strata should be limited to
deposits formed far from land, because the ocean probably occupied then,
as now, the greater part of the earth's surface. After so many entire
geographical revolutions, the chances are nearly three to one in favor
of our finding that such small portions of the existing continents and
islands as expose Silurian strata to view, should coincide in position
with the ancient ocean rather than the land. We must not, therefore,
too hastily infer, from the absence of fossil bones of mammalia in the
older rocks, that the highest class of vertebrated animals did not exist
in remoter ages. There are regions at present, in the Indian and Pacific
Oceans, coextensive in area with the continents of Europe and North
America, where we might dredge the bottom and draw up thousands of
shells and corals, without obtaining one bone of a land quadruped.
Suppose our mariners were to report, that, on sounding in the Indian
Ocean near some coral reefs, and at some distance from the land, they
drew up on hooks attached to their line portions of a leopard, elephant,
or tapir, should we not be skeptical as to the accuracy of their
statements? and if we had no doubt of their veracity, might we not
suspect them to be unskilful naturalists? or, if the fact were
unquestioned, should we not be disposed to believe that some vessel had
been wrecked on the spot?

The casualties must always be rare by which land quadrupeds are swept by
rivers far out into the open sea, and still rarer the contingency of
such a floating body not being devoured by sharks or other predaceous
fish, such as were those of which we find the teeth preserved in some of
the carboniferous strata. But if the carcass should escape, and should
happen to sink where sediment was in the act of accumulating, and if the
numerous causes of subsequent disintegration should not efface all
traces of the body, included for countless ages in solid rock, is it not
contrary to all calculation of chances that we should hit upon the exact
spot--that mere point in the bed of an ancient ocean, where the precious
relic was entombed? Can we expect for a moment, when we have only
succeeded, amidst several thousand fragments of corals and shells, in
finding a few bones of _aquatic_ or _amphibious_ animals, that we should
meet with a single skeleton of an inhabitant of the land?

Clarence, in his dream, saw, "in the slimy bottom of the deep,"


    ----a thousand fearful wrecks;
  A thousand men, that fishes gnaw'd upon:
  Wedges of gold, great anchors, heaps of pearl.


Had he also beheld, amid "the dead bones that lay scattered by," the
carcasses of lions, deer, and the other wild tenants of the forest and
the plain, the fiction would have been deemed unworthy of the genius of
Shakspeare. So daring a disregard of probability and violation of
analogy would have been condemned as unpardonable, even where the poet
was painting those incongruous images which present themselves to a
disturbed imagination during the visions of the night.

Until lately it was supposed that the old red sandstone, or Devonian
rocks, contained no vertebrate remains except those of fish, but in 1850
the footprints of a chelonian, and in 1851 the skeleton of a reptile,
allied both to the batrachians and lizards, were found in a sandstone of
that age near Elgin in Scotland.[212] Up to the year 1844 it was laid
down as a received dogma in many works of high authority in geology,
that reptiles were not created until after the close of the
carboniferous epoch. In the course of that year, however, Hermann Von
Meyer announced the discovery, in the coal measures of Rhenish Bavaria,
of a reptile, called by him Apateon, related to the salamanders; and in
1847 three species of another genus, called archegosaurus by Goldfuss,
were obtained from the coal of Saarbruck, between Treves and Strasburg.
The footprints of a large quadruped, probably batrachian, had also been
observed by Dr. King in the carboniferous rocks of Pennsylvania in 1844.
The first example of the _bones_ of a reptile in the Coal of North
America was detected so lately as September, 1852, by Mr. G. W. Dawson
and myself in Nova Scotia. These remains, referred by Messrs. Wyman and
Owen to a perennibranchiate batrachian, were met with in the interior of
an erect fossil tree, apparently a sigillaria. They seem clearly to have
been introduced together with sediment into the tree, during its
submergence and after it had decayed and was standing as a hollow
cylinder of bark, this bark being now converted into coal.

When Agassiz, in his great work on fossil fish, described 152 species of
ichthyolites from the Coal, he found them to consist of 94 placoids,
belonging to the families of shark and ray, and 58 ganoids. One family
of the latter he called "sauroid fish," including the megalicthys and
holoptychius, often of great size, and all predaceous. Although true
fish, and not intermediate between that class and reptiles, they seem to
have been more highly organized than any living fish, reminding us of
the skeletons of saurians by the close suture of their cranial bones,
their large conical teeth, striated longitudinally, and the articulation
of the spinous processes with the vertebrae. Among living species they
are most nearly allied to the lepidosteus, or bony pike of the North
American rivers. Before the recent progress of discovery above alluded
to had shown the fallacy of such ideas, it was imagined by some
geologists that this ichthyic type was the more highly developed,
because it took the lead at the head of nature before the class of
reptiles had been created. The confident assumption indulged in till the
year 1844, that reptiles were first introduced into the earth in the
Permian period, shows the danger of taking for granted that the date of
the creation of any family of animals or plants in past time coincides
with the age of the oldest stratified rock in which the geologist has
detected its remains. Nevertheless, after repeated disappointments, we
find some naturalists as much disposed as ever to rely on such negative
evidence, and to feel now as sure that reptiles were not introduced into
the earth till after the Silurian epoch, as they were in 1844, that they
appeared for the first time at an era subsequent to the carboniferous.

Scanty as is the information hitherto obtained in regard to the
articulata of the coal formation, we have at least ascertained that some
insects winged their way through the ancient forests. In the ironstone
of Coalbrook Dale, two species of coleoptera of the Linnaean genus
curculio have been met with: and a neuropterous insect resembling a
corydalis, together with another of the same order related to the
phasmidae. As an example of the insectivorous arachnidae, I may mention
the scorpion of the Bohemian coal, figured by Count Sternberg, in which
even the eyes, skin, and minute hairs were preserved.[213] We need not
despair, therefore, of obtaining eventually fossil representatives of
all the principal orders of hexapods and arachnidae in carboniferous
strata.

Next in chronological order above the Coal comes the allied Magnesian
Limestone, or Permian group, and the secondary formations from the Trias
to the Chalk inclusive. These rocks comprise the monuments of a long
series of ages in which reptiles of every variety of size, form, and
structure peopled the earth; so that the whole period, and especially
that of the Lias and Oolite, has been sometimes called "the age of
reptiles." As there are now mammalia entirely confined to the land;
others which, like the bat and vampire, fly in the air; others, again,
of amphibious habits, frequenting rivers, like the hippopotamus, otter,
and beaver; others exclusively aquatic and marine, like the seal, whale,
and narwal; so in the early ages under consideration, there were
terrestrial, winged, and aquatic reptiles. There were iguanodons walking
on the land, pterodactyls winging their way through the air, monitors
and crocodiles in the rivers, and ichthyosaurs and plesiosaurs in the
ocean. It appears also that some of these ancient saurians approximated
more nearly in their organization to the type of living mammalia than do
any of the reptiles now existing.[214]

In the vast range of strata above alluded to, comprising the Permian,
the Upper New Red Sandstone and Muschelkalk, the Lias, Oolite, Wealden,
Green-sand, and Chalk, scarcely any well-authenticated instances of the
occurrence of fossil birds in Europe are on record, and only two or
three of fossil mammalia.

In regard to the absence of birds, they are usually wanting, for reasons
afterwards to be explained (see chap. 47), in deposits of all ages, even
in the tertiary periods, where we know that birds as well as land
quadrupeds abounded. Some at least of the fossil remains formerly
referred to this class in the Wealden (a great freshwater deposit below
the chalk), have been recently shown by Mr. Owen to belong to
pterodactyls.[215] But in North America still more ancient indications
of the existence of the feathered tribe have been detected, the fossil
foot-marks of a great variety of species, of various sizes, some larger
than the ostrich, others smaller than the plover, having been observed.
These bipeds have left marks of their footsteps on strata of an age
decidedly intermediate between the Lias and the Coal.[216]

[Illustration: Fig. 8.

_Natural Size_.

Thylacotherium Prevostii (_Valenciennes_). Amphitherium (_Owen_). Lower
jaw, from the slate of Stonesfield, near Oxford.[218]]

[Illustration: Fig. 9.

Myrmecobius fasciatus (_Waterhouse_). Recent from Swan River. Lower jaw
of the natural size.[219]]

The examples of mammalia, above alluded to, are confined to the Trias
and the Oolite. In the former, the evidence is as yet limited to two
small molar teeth, described by Professor Plieninger in 1847, under the
generic name of Microlestes. They were found near Stuttgart, and
possess the double fangs so characteristic of mammalia.[217] The other
fossil remains of the same class were derived from one of the inferior
members of the oolitic series in Oxfordshire, and afford more full and
satisfactory evidence, consisting of the lower jaws of three species of
small quadrupeds about the size of a mole. Cuvier, when he saw one of
them (during a visit to Oxford in 1818), referred it to the marsupial
order, stating, however, that it differed from all known carnivora in
having ten molar teeth in a row. Professor Owen afterwards pointed out
that the jaw belonged to an extinct genus, having considerable affinity
to a newly discovered Australian mammifer, the _Myrmecobius_ of
Waterhouse, which has nine molar teeth in the lower jaw. (Fig. 9.) A
more perfect specimen enabled Mr. Owen in 1846 to prove that the
inflection of the angular process of the lower jaw was not sufficiently
marked to entitle the osteologist to infer that this quadruped was
marsupial, as the process is not bent inwards in a greater degree than
in the mole or hedgehog. Hence the genus amphitherium, of which there
are two species from Stonesfield, must be referred to the ordinary or
placental type of insectivorous mammals, although it approximates in
some points of structure to the myrmecobius and allied marsupials of
Australia. The other contemporary genus, called phascolotherium, agrees
much more nearly in osteological character and precisely in the number
of the teeth with the opossums; and is believed to have been truly
marsupial. (Fig. 10.)

[Illustration: Fig. 10.

_Natural size._

Phascolotherium Bucklandi, _Owen_. (_Syn._ Didelphis Bucklandi, _Brod._)
Lower jaw, from Stonesfield.[220]

1. The jaw magnified twice in length. 2. The second molar tooth
magnified six times.]

The occurrence of these most ancient memorials of the mammiferous type,
in so low a member of the oolitic series, while no other representatives
of the same class (if we except the microlestes) have yet been found in
any other of the inferior or superior secondary strata, is a striking
fact, and should serve as a warning to us against hasty generalizations,
founded solely on negative evidence. So important an exception to a
general rule may be perfectly consistent with the conclusion, that a
small number only of mammalia inhabited European latitudes when our
secondary rocks were formed; but it seems fatal to the theory of
progressive development, or to the notion that the order of precedence
in the creation of animals, considered chronologically, has precisely
coincided with the order in which they would be ranked according to
perfection or complexity of structure.

It was for many years suggested that the marsupial order to which the
fossil animals of Stonesfield were supposed exclusively to belong
constitutes the lowest grade in the class Mammalia, and that this order,
of which the brain is of more simple form, evinces an inferior degree of
intelligence. If, therefore, in the oolitic period the marsupial tribes
were the only warm-blooded quadrupeds which had as yet appeared upon our
planet, the fact, it was said, confirmed the theory which teaches that
the creation of the more simple forms in each division of the animal
kingdom preceded that of the more complex. But on how slender a support,
even if the facts had continued to hold true, did such important
conclusions hang! The Australian continent, so far as it has been
hitherto explored, contains no indigenous quadrupeds save those of the
marsupial order, with the exception of a few small rodents, while some
neighboring islands to the north, and even southern Africa, in the same
latitude as Australia, abound in mammalia of every tribe except the
marsupial. We are entirely unable to explain on what physiological or
other laws this singular diversity in the habitations of living mammalia
depends; but nothing is more clear than that the causes which stamp so
peculiar a character on two different provinces of wide extent are
wholly independent of time, or of the age or maturity of the planet.

The strata of the Wealden, although of a later date than the oolite of
Stonesfield, and although filled with the remains of large reptiles,
both terrestrial and aquatic, have not yielded as yet a single marsupial
bone. Were we to assume on such scanty data that no warm-blooded
quadrupeds were then to be found throughout the northern hemisphere,
there would still remain a curious subject of speculation, whether the
entire suppression of one important class of vertebrata, such as the
mammiferous, and the great development of another, such as the
reptilian, implies a departure from fixed and uniform rules governing
the fluctuations of the animal world; such rules, for example, as appear
from one century to another to determine the growth of certain tribes of
plants and animals in arctic, and of other tribes in tropical regions.

In Australia, New Zealand, and many other parts of the southern
hemisphere, where the indigenous land quadrupeds are comparatively few,
and of small dimensions, the reptiles do not predominate in number or
size. The deposits formed at the mouth of an Australian river, within
the tropics, might contain the bones of only a few small marsupial
animals, which, like those of Stonesfield, might hereafter be discovered
with difficulty by geologists; but there would, at the same time, be no
megalosauri and other fossil remains, showing that large saurians were
plentiful on the land and in the waters at a time when mammalia were
scarce. This example, therefore, would afford a very imperfect parallel
to the state of the animal kingdom, supposed to have prevailed during
the secondary periods, when a high temperature pervaded European
latitudes.

It may nevertheless be advantageous to point to some existing anomalies
in the geographical development of distinct classes of vertebrata which
may be comparable to former conditions of the animal creation brought to
light by geology. Thus in the arctic regions, at present, reptiles are
small, and sometimes wholly wanting, where birds, large land quadrupeds,
and cetacea abound. We meet with bears, wolves, foxes, musk oxen, and
deer, walruses, seals, whales, and narwals, in regions of ice and snow,
where the smallest snakes, efts, and frogs are rarely, if ever, seen.

A still more anomalous state of things presents itself in the southern
hemisphere. Even in the temperate zone, between the latitudes 52 degrees
and 56 degrees S., as, for example, in Tierra del Fuego, as well as in
the woody region immediately north of the Straits of Magellan, and in
the Falkland Islands, no reptiles of any kind are met with, not even a
snake, lizard, or frog; but in these same countries we find the guanaco
(a kind of llama), a deer, the puma, a large species of fox, many small
rodentia, besides the seal and otter, together with the porpoise, whale,
and other cetacea.

On what grand laws in the animal physiology these remarkable phenomena
depend, cannot in the present state of science be conjectured; nor could
we predict whether any opposite condition of the atmosphere, in respect
to heat, moisture, and other circumstances, would bring about a state of
animal life which might be called the converse of that above described,
namely, a state in which reptiles of every size and order might abound,
and mammalia disappear.

The nearest approximation to such a fauna is found in the Galapagos
Archipelago. These islands, situated under the equator, and nearly 600
miles west of the coast of Peru, have been called "the land of
reptiles," so great is the number of snakes, large tortoises, and
lizards, which they support. Among the lizards, the first living species
proper to the ocean has been discovered. Yet, although some of these
islands are from 3000 to 4000 feet high, and one of them 75 miles long,
they contain, with the exception of one small mouse, no indigenous
mammifer. Even here, however, it is true that in the neighboring sea
there are seals, and several kinds of cetacea.[221]

It may be unreasonable to look for a nearer analogy between the fauna
now existing in any part of the globe, and that which we can show to
have prevailed when our secondary strata were deposited, because we must
always recollect that a climate like that now experienced at the
equator, coexisting with the unequal days and nights of European
latitudes, was a state of things to which there is now no counterpart on
the globe. Consequently, the type of animal and vegetable existence
required for such a climate might be expected to deviate almost as
widely from that now established, as do the flora and fauna of our
tropical differ from those of our arctic regions.

_In the Tertiary strata._--The tertiary formations were deposited when
the physical geography of the northern hemisphere had been entirely
altered. Large inland lakes had become numerous, as in central France
and other countries. There were gulfs of the sea, into which
considerable rivers emptied themselves, and where strata like those of
the Paris basin were accumulated. There were also formations in
progress, in shallow seas not far from shore, such as are indicated by
portions of the _Faluns_ of the Loire, and the English _Crag_.

The proximity, therefore, of large tracts of dry land to the seas and
lakes then existing, may, in a great measure, explain why the remains of
land animals, so rare in the older strata, are not uncommon in these
more modern deposits. Yet even these have sometimes proved entirely
destitute of mammiferous relics for years after they had become
celebrated for the abundance of their fossil testacea, fish, and
reptiles. Thus the calcaire grossier, a marine limestone of the district
round Paris, had afforded to collectors more than 1100 species of
shells, besides many zoophytes, echinodermata, and the teeth of fish,
before the bones of one or two land quadrupeds were met with in the same
rock. The strata called London and Plastic clay in England have been
studied for more than half a century, and about 400 species of shells,
50 or more of fish, besides several kinds of chelonian and saurian
reptiles, were known before a single mammifer was detected. At length,
in the year 1839, there were found in this formation the remains of a
monkey, an opossum, a bat,[222] and a species of the extinct genus
Hyracotherium, allied to the Peccary or hog tribe.

If we examine the strata above the London clay in England, we first meet
with mammiferous remains in the Isle of Wight, in beds also belonging to
the Eocene epoch, such as the remains of the Palaeotherium,
Anoplotherium, and other extinct quadrupeds, agreeing very closely with
those first found by Cuvier, near Paris, in strata of the same age, and
of similar freshwater origin.

In France we meet with another fauna, both conchological and mammalian
in the Miocene "faluns" of the Loire; above which in the ascending
series in Great Britain we arrive at the coralline crag of Suffolk, a
marine formation which has yielded three or four hundred species of
shells, very different from the Eocene testacea, and of which a large
proportion, although a minority of the whole number, are recent, besides
many corals, echini, foraminifera, and fish, but as yet no relic
decidedly mammalian except the ear-bone of a whale.

In the shelly sand, provincially termed "Red Crag," in Suffolk, which
immediately succeeds the coralline, constituting a newer member of the
same tertiary group, about 250 species of shells have been recognized,
of which a still larger proportion are recent. They are associated with
numerous teeth of fish; but no signs of a warm-blooded quadruped had
been detected until 1839, when the teeth of a leopard, a bear, a hog,
and a species of ruminant, were found at Newbourn, in Suffolk, and since
that time, several other genera of mammalia have been met with in the
same formation, or in the Red Crag.[223]

Of a still newer date is the Norwich Crag, a fluvio-marine deposit of
the Pleiocene epoch, containing a mixture of marine, fluviatile, and
land shells, of which 90 per cent. or more are recent. These beds,
since the time of their first investigation, have yielded a supply of
mammalian bones of the genera mastodon, elephant, rhinoceros, pig,
horse, deer, ox, and others, the bodies of which may have been washed
down into the sea by rivers draining land, of which the contiguity is
indicated by the occasional presence of terrestrial and freshwater
shells.

Our acquaintance with the newer Pleiocene mammalia in Europe, South
America, and Australia, is derived chiefly from cavern deposits, a fact
which we ought never to forget if we desire to appreciate the superior
facilities we enjoy for studying the more modern as compared to the more
ancient terrestrial faunas. We know nothing of the fossil bones which
must have been inclosed in the stalagmite of caverns in the older
Pleiocene, or in the Miocene or Eocene epochs, much less can we derive
any information respecting the inhabitants of the land from a similar
source, when we carry back our inquiries to the Wealden or carboniferous
epochs. We are as well assured that land and rivers then existed, as
that they exist now; but it is evident that even a slight geographical
revolution, accompanied by the submergence and denudation of land, would
reduce to an extreme improbability the chance of our hitting on those
minute points of space where caves may once have occurred in limestone
rocks.

_Fossil quadrumana._--Until within a few years (1836, 1837), not a
single bone of any quadrumanous animal, such as the orang, ape, baboon,
and monkey, had been discovered in a fossil state, although so much
progress had been made in bringing to light the extinct mammalia of
successive tertiary eras, both carnivorous and herbivorous. The total
absence of these anthropomorphous tribes among the records of a former
world, had led some to believe that the type of organization most nearly
resembling the human, came so late in the order of creation, as to be
scarcely, if at all, anterior to that of man. That such generalizations
were premature, I endeavored to point out in the first edition of this
work,[224] in which I stated that the bones of quadrupeds hitherto met
with in tertiary deposits were chiefly those which frequent marshes,
rivers, or the borders of lakes, as the elephant, rhinoceros,
hippopotamus, tapir, hog, deer, and ox, while species which live in
trees are extremely rare in a fossil state. I also hinted, that we had
as yet no data for determining how great a number of the one kind we
ought to find, before we have a right to expect a single individual of
the other. Lastly, I observed that the climate of the more modern (or
Post-Eocene) tertiary periods in England was not tropical, and that in
regard to the London clay, of which the crocodiles, turtles, and fossil
fruits implied a climate hot enough for the quadrumana, we had as yet
made too little progress in ascertaining what were the Eocene
pachydermata of England, to entitle us to expect to have discovered any
quadrumana of the same date.

Since those remarks were first written, in 1829, a great number of
extinct species have been added to our collections of tertiary mammalia
from Great Britain and other parts of the world. At length, between the
years 1836 and 1839, a few remains of quadrumana were found in France
and England, India and Brazil. Those of India, belonging to more than
one extinct species of monkey, were first discovered near the Sutlej, in
lat. 30 degrees N., in tertiary strata, of which the age is not yet
determined; the Brazilian fossil, brought from the basin of the Rio das
Velhas, about lat. 18 degrees S., is referable to a form now peculiar in
America, allied to the genus Callithrix, the species being extinct. The
skull and other bones met with in the South of France belong to a
gibbon, or one of the tailless apes, which stand next in the scale of
organization to the orang. It occurred at Sansan, about forty miles west
of Toulouse, in lat. 43 degrees 40 minutes N., in freshwater strata,
probably of the Miocene or middle tertiary period. Lastly, the English
quadrumane first met with, occurred in a more ancient stratum than the
rest, and at a point more remote from the equator. It belongs to the
genus Macacus, is an extinct species, and was found in Suffolk, in lat.
52 degrees,[225] in the London clay, the fossils of which, such as
crocodiles, turtles, shells of the genus Nautilus, and many curious
fruits, had already led geologists to the conclusion that the climate of
that era (the Eocene) was warm and nearly tropical.

Some years later (in 1846) the jaw of another British species of fossil
monkey, Macacus pliocenus, was announced by Mr. Owen as having been met
with in the newer Pleiocene strata, on the banks of the Thames, at
Grays, in Essex, accompanying the remains of hippopotamus, elephant, and
other quadrupeds, and associated with freshwater and land shells, most
of which are now inhabitants of the British Isles.[226]

When we consider the small area of the earth's surface hitherto
explored geologically, and the new discoveries brought to light daily,
even in the environs of great European capitals, we must feel that it
would be rash to assume that the Lower Eocene deposits mark the era of
the first creation of quadrumana. It would, however, be still more
unphilosophical to infer, as some writers have done, from a single
extinct species of this family obtained in a latitude far from the
tropics, that the Eocene quadrumana did not attain as high a grade of
organization as they do in our own times. What would the naturalist know
of the apes and orangs now contemporary with man, if our investigations
were restricted to such northern latitudes as those where alone the
geologist has hitherto found all the fossil quadrumana of Europe?

_Cetacea._--The absence of Cetacea from rocks older than the Eocene has
been frequently adduced as lending countenance to the theory of the very
late appearance of the highest class of Vertebrata on the earth.
Professor Sedgwick possesses in the Cambridge Museum a mass of
anchylosed cervical vertebrae of a whale, which he found in drift clay
near Ely, and which he has no doubt was washed out of the Kimmeridge
clay, an upper member of the Oolite. According to Professor Owen, it
exhibits well-marked specific characters, distinguishing it from all
other known recent or fossil cetacea. Dr. Leidy, of Philadelphia, has
lately described (1851) two species of cetacea of a new genus, which he
has called Priscodelphinus from the green sand of New Jersey, which
corresponds in age with the English Chalk or the cretaceous strata above
the gault. The specimens consist of dorsal and cervical vertebrae.[227]
Even in the Eocene strata of Europe, the discovery of cetaceans has
never kept pace with that of land quadrupeds. The only instance cited in
Great Britain is a species of Monodon, from the London clay, of doubtful
authenticity as to its geological position. On the other hand, the
gigantic Zeuglodon of North America occurs abundantly in the Middle
Eocene strata of Georgia and Alabama, from which as yet no bones of land
quadrupeds have been obtained.

In the present imperfect state then of our information, we can scarcely
say more than that the cetacea seem to have been scarce in the secondary
and primary periods. It is quite conceivable that when aquatic saurians,
some of them carnivorous, like the Ichthyosaurus, were swarming in the
sea, and when there were large herbivorous reptiles, like the Iguanodon,
on the land, the class of reptiles may, to a certain extent, have
superseded the cetacea, and discharged their functions in the animal
economy.

That mammalia had been created long before the epoch of the Kimmeridge
clay, is shown by the Microlestes of the Trias before alluded to, and by
the Stonesfield quadrupeds from the Inferior Oolite. And we are bound to
remember, whenever we infer the poverty of the flora or fauna of any
given period of the past, from the small number of fossils occurring in
ancient rocks, that it has been evidently no part of the plan of Nature
to hand down to us a complete or systematic record of the former history
of the animate world. We may have failed to discover a single shell,
marine or freshwater, or a single coral or bone in certain sandstones,
such as that of the valley of the Connecticut, where the footprints of
bipeds and quadrupeds abound; but such failure may have arisen, not
because the population of the land or sea was scanty at that era, but
because in general the preservation of any relics of the animals or
plants of former times is the exception to a general rule. Time so
enormous as that contemplated by the geologist may multiply exceptional
cases till they seem to constitute the rule, and so impose on the
imagination as to lead us to infer the non-existence of creatures of
which no monuments happen to remain. Professor Forbes has remarked, that
few geologists are aware how large a proportion of all known species of
fossils are founded on single specimens, while a still greater number
are founded on a few individuals discovered in one spot. This holds true
not only in regard to animals and plants inhabiting the land, the lake,
and the river, but even to a surprising number of the marine mollusca,
articulata, and radiata. Our knowledge, therefore, of the living
creation of any given period of the past may be said to depend in a
great degree on what we commonly call chance, and the casual discovery
of some new localities rich in peculiar fossils may modify or entirely
overthrow all our previous generalizations.

Upon the whole then we derive this result from a general review of the
fossils of the successive tertiary strata, namely, that since the Eocene
period, there have been several great changes in the land quadrupeds
inhabiting Europe, probably not less than five complete revolutions,
during which there has been no step whatever made in advance, no
elevation in the scale of being; so that had man been created at the
commencement of the Eocene era, he would not have constituted a greater
innovation on the state of the animal creation previously established
than now, when we believe him to have begun to exist at the close of the
Pleiocene. The views, therefore, which I proposed in the first edition
of this work, January, 1830, in opposition to the theory of progressive
development, do not seem to me to require material modification,
notwithstanding the large additions since made to our knowledge of
fossil remains.

These views may be thus briefly stated. From the earliest period at
which plants and animals can be proved to have existed, there has been a
continual change going on in the position of land and sea, accompanied
by great fluctuations of climate. To these ever-varying geographical and
climatal conditions the state of the animate world has been unceasingly
adapted. No satisfactory proof has yet been discovered of the gradual
passage of the earth from a chaotic to a more habitable state, nor of
any law of progressive development governing the extinction and
renovation of species, and causing the fauna and flora to pass from an
embryonic to a more perfect condition, from a simple to a more complex
organization.

The principle of adaptation to which I have alluded, appears to have
been analogous to that which now peoples the arctic, temperate, and
tropical regions contemporaneously with distinct assemblages of species
and genera, or which, independently of mere temperature, gives rise to a
predominance of the marsupial or didelphous tribe of quadrupeds in
Australia, of the placental or monodelphous tribe in Asia and Europe, or
which causes a profusion of reptiles without mammalia in the Galapagos
Archipelago, and of mammalia without reptiles in Greenland.

_Recent origin of man._--If, then, the popular theory of the successive
development of the animal and vegetable world, from the simplest to the
most perfect forms, rests on a very insecure foundation; it may be
asked, whether the recent origin of man lends any support to the same
doctrine, or how far the influence of man may be considered as such a
deviation from the analogy of the order of things previously
established, as to weaken our confidence in the uniformity of the course
of nature.

Antecedently to investigation, we might reasonably have anticipated that
the vestiges of man would have been traced back at least as far as those
modern strata in which all the testacea and a certain number of the
mammalia are of existing species, for of all the mammalia the human
species is the most cosmopolite, and perhaps more capable than any other
of surviving considerable vicissitudes in climate, and in the physical
geography of the globe.

No inhabitant of the land exposes himself to so many dangers on the
waters as man, whether in a savage or a civilized state;[228] and there
is no animal, therefore, whose skeleton is so liable to become imbedded
in lacustrine or submarine deposits; nor can it be said that his remains
are more perishable than those of other animals; for in ancient fields
of battle, as Cuvier has observed, the bones of men have suffered as
little decomposition as those of horses which were buried in the same
grave.[229] But even if the more solid parts of our species had
disappeared, the impression of their form would have remained engraven
on the rocks, as have the traces of the tenderest leaves of plants, and
the soft integuments of many animals. Works of art, moreover, composed
of the most indestructible materials, would have outlasted almost all
the organic contents of sedimentary rocks. Edifices, and even entire
cities, have, within the times of history, been buried under volcanic
ejections, submerged beneath the sea, or engulfed by earthquakes; and
had these catastrophes been repeated throughout an indefinite lapse of
ages, the high antiquity of man would have been inscribed in far more
legible characters on the framework of the globe than are the forms of
the ancient vegetation which once covered the islands of the northern
ocean, or of those gigantic reptiles which at still later periods
peopled the seas and rivers of the northern hemisphere.[230]

Dr. Prichard has argued that the human race have not always existed on
the surface of the earth, because "the strata of which our continents
are composed were once a part of the ocean's bed"--"mankind had a
beginning, since we can look back to the period when the surface on
which they lived began to exist."[231] This proof, however, is
insufficient, for many thousands of human beings now dwell in various
quarters of the globe where marine species lived within the times of
history, and, on the other hand, the sea now prevails permanently over
large districts once inhabited by thousands of human beings. Nor can
this interchange of sea and land ever cease while the present causes are
in existence. Terrestrial species, therefore, might be older than the
continents which they inhabit, and aquatic species of higher antiquity
than the lakes and seas which they now people.

But so far as our interpretation of physical movements has yet gone, we
have every reason to infer that the human race is extremely modern, even
when compared to the larger number of species now our contemporaries on
the earth, and we may, therefore, ask whether his creation can be
considered as one step in a supposed progressive system, by which the
organic world has advanced slowly from a more simple to a more complex
and perfect state? If we concede, for a moment, the truth of the
proposition, that the sponge, the cephalopod, the fish, the reptile, the
bird, and the mammifer, have followed each other in regular
chronological order, the creation of each class being separated from the
other by vast intervals of time, should we be able to recognize, in
man's entrance upon the earth, the last term of one and the same series
of progressive developments?

In reply to this question it should first be observed, that the
superiority of man depends not on those faculties and attributes which
he shares in common with the inferior animals, but on his reason, by
which he is distinguished from them. When it is said that the human race
is of far higher dignity than were any pre-existing beings on the earth,
it is the intellectual and moral attributes of our race, rather than the
physical, which are considered; and it is by no means clear that the
organization of man is such as would confer a decided pre-eminence upon
him, if, in place of his reasoning powers, he was merely provided with
such instincts as are possessed by the lower animals.

If this be admitted, it would not follow, even if there were sufficient
geological evidence in favor of the theory of progressive development,
that the creation of man was the last link in the same chain. For the
sudden passage from an irrational to a rational animal, is a phenomenon
of a distinct kind from the passage from the more simple to the more
perfect forms of animal organization and instinct. To pretend that such
a step, or rather leap, can be part of a regular series of changes in
the animal world, is to strain analogy beyond all reasonable bounds.

_Introduction of man, to what extent a change in the system._--But
setting aside the question of progressive development, another and a far
more difficult one may arise out of the admission that man is
comparatively of modern origin. Is not the interference of the human
species, it may be asked, such a deviation from the antecedent course of
physical events, that the knowledge of such a fact tends to destroy all
our confidence in the uniformity of the order of nature, both in regard
to time past and future? If such an innovation could take place after
the earth had been exclusively inhabited for thousands of ages by
inferior animals, why should not other changes as extraordinary and
unprecedented happen from time to time? If one new cause was permitted
to supervene, differing in kind and energy from any before in operation,
why may not others have come into action at different epochs? Or what
security have we that they may not arise hereafter? And if such be the
case, how can the experience of one period, even though we are
acquainted with all the possible effects of the then existing causes, be
a standard to which we can refer all natural phenomena of other periods?

Now these objections would be unanswerable, if adduced against one who
was contending for the absolute uniformity throughout all time of the
succession of sublunary events--if, for example, he was disposed to
indulge in the philosophical reveries of some Egyptian and Greek sects,
who represented all the changes both of the moral and material world as
repeated at distant intervals, so as to follow each other in their
former connection of place and time. For they compared the course of
events on our globe to astronomical cycles; and not only did they
consider all sublunary affairs to be under the influence of the
celestial bodies, but they taught that on the earth, as well as in the
heavens, the same identical phenomena recurred again and again in a
perpetual vicissitude. The same individual men were doomed to be
re-born, and to perform the same actions as before; the same arts were
to be invented, and the same cities built and destroyed. The Argonautic
expedition was destined to sail again with the same heroes, and Achilles
with his Myrmidons to renew, the combat before the walls of Troy.


  Alter erit tum Tiphys, et altera quae vehat Argo
  Dilectos heroas; erunt etiam altera bella,
  Atque iterum ad Trojam magnus mittetur Achilles.[232]


The geologist, however, may condemn these tenets as absurd, without
running into the opposite extreme, and denying that the order of nature
has, from the earliest periods, been uniform in the same sense in which
we believe it to be uniform at present, and expect it to remain so in
future. We have no reason to suppose, that when man first became master
of a small part of the globe, a greater change took place in its
physical condition than is now experienced when districts, never before
inhabited, become successively occupied by new settlers. When a powerful
European colony lands on the shores of Australia, and introduces at once
those arts which it has required many centuries to mature; when it
imports a multitude of plants and large animals from the opposite
extremity of the earth, and begins rapidly to extirpate many of the
indigenous species, a mightier revolution is effected in a brief period
than the first entrance of a savage horde, or their continued occupation
of the country for many centuries, can possibly be imagined to have
produced. If there be no impropriety in assuming that the system is
uniform when disturbances so unprecedented occur in certain localities,
we can with much greater confidence apply the same language to those
primeval ages when the aggregate number and power of the human race, or
the rate of their advancement in civilization, must be supposed to have
been far inferior. In reasoning on the state of the globe immediately
before our species was called into existence, we must be guided by the
same rules of induction as when we speculate on the state of America in
the interval that elapsed between the introduction of man into Asia, the
supposed cradle of our race, and the arrival of the first adventurers on
the shores of the New World. In that interval, we imagine the state of
things to have gone on according to the order now observed in regions
unoccupied by man. Even now, the waters of lakes, seas, and the great
ocean, which teem with life, may be said to have no immediate relation
to the human race--to be portions of the terrestrial system of which man
has never taken, nor ever can take possession; so that the greater part
of the inhabited surface of the planet may still remain as insensible to
our presence as before any isle or continent was appointed to be our
residence.

If the barren soil around Sydney had at once become fertile upon the
landing of our first settlers; if, like the happy isles whereof the
poets have given such glowing descriptions, those sandy tracts had begun
to yield spontaneously an annual supply of grain, we might then, indeed,
have fancied alterations still more remarkable in the economy of nature
to have attended the first coming of our species into the planet. Or if,
when a volcanic island like Ischia was, for the first time, brought
under cultivation by the enterprise and industry of a Greek colony, the
internal fire had become dormant, and the earthquake had remitted its
destructive violence, there would then have been some ground for
speculating on the debilitation of the subterranean forces, when the
earth was first placed under the dominion of man. But after a long
interval of rest, the volcano bursts forth again with renewed energy,
annihilates one half of the inhabitants, and compels the remainder to
emigrate. The course of nature remains evidently unchanged; and, in like
manner, we may suppose the general condition of the globe, immediately
before and after the period when our species first began to exist, to
have been the same, with the exception only of man's presence.

The modifications in the system of which man is the instrument do not,
perhaps, constitute so great a deviation from previous analogy as we
usually imagine; we often, for example, form an exaggerated estimate of
the extent of our power in extirpating some of the inferior animals, and
causing others to multiply; a power which is circumscribed within
certain limits, and which, in all likelihood, is by no means exclusively
exerted by our species.[233] The growth of human population cannot take
place without diminishing the numbers, or causing the entire
destruction, of many animals. The larger beasts of prey, in particular,
give way before us; but other quadrupeds of smaller size, and
innumerable birds, insects, and plants, which are inimical to our
interests, increase in spite of us, some attacking our food, others our
raiment and persons, and others interfering with our agricultural and
horticultural labors. We behold the rich harvest which we have raised by
the sweat of our brow, devoured by myriads of insects, and are often as
incapable of arresting their depredations, as of staying the shock of an
earthquake, or the course of a stream of lava.

A great philosopher has observed, that we can command nature only by
obeying her laws; and this principle is true even in regard to the
astonishing changes which are superinduced in the qualities of certain
animals and plants by domestication and garden culture. I shall point
out in the third book that we can only effect such surprising
alterations by assisting the development of certain instincts, or by
availing ourselves of that mysterious law of their organization, by
which individual peculiarities are transmissible from one generation to
another.[234]

It is probable from these and many other considerations, that as we
enlarge our knowledge of the system, we shall become more and more
convinced, that the alterations caused by the interference of man
deviate far less from the analogy of those effected by other animals
than is usually supposed.[235] We are often misled, when we institute
such comparisons, by our knowledge of the wide distinction between the
instincts of animals and the reasoning power of man; and we are apt
hastily to infer, that the effects of a rational and irrational species,
considered merely as _physical agents_, will differ almost as much as
the faculties by which their actions are directed.

It is not, however, intended that a real departure from the antecedent
course of physical events cannot be traced in the introduction of man.
If that latitude of action which enables the brutes to accommodate
themselves in some measure to accidental circumstances could be imagined
to have been at any former period so great, that the operations of
instinct were as much diversified as are those of human reason, it
might, perhaps, be contended, that the agency of man did not constitute
an anomalous deviation from the previously established order of things.
It might then have been said, that the earth's becoming at a particular
period the residence of human beings, was an era in the moral, not in
the physical world--that our study and contemplation of the earth, and
the laws which govern its animate productions, ought no more to be
considered in the light of a disturbance or deviation from the system,
than the discovery of the satellites of Jupiter should be regarded as a
physical event affecting those heavenly bodies. Their influence in
advancing the progress of science among men, and in aiding navigation
and commerce, was accompanied by no reciprocal action of the human mind
upon the economy of nature in those distant planets; and so the earth
might be conceived to have become, at a certain period, a place of moral
discipline and intellectual improvement to man, without the slightest
derangement of a previously existing order of change in its animate and
inanimate productions.

The distinctness, however, of the human from all other species,
considered merely as an efficient cause in the physical world, is real;
for we stand in a relation to contemporary species of animals and plants
widely different from that which other irrational animals can ever be
supposed to have held to each other. We modify their instincts, relative
numbers, and geographical distribution, in a manner superior in degree,
and in some respects very different in kind from that in which any other
species can affect the rest. Besides, the progressive movement of each
successive generation of men causes the human species to differ more
from itself in power at two distant periods, than any one species of the
higher order of animals differs from another. The establishment,
therefore, by geological evidence, of the first intervention of such a
peculiar and unprecedented agency, long after other parts of the animate
and inanimate world existed, affords ground for concluding that the
experience during thousands of ages of all the events which may happen
on this globe, would not enable a philosopher to speculate with
confidence concerning future contingencies.

If, then, an intelligent being, after observing the order of events for
an indefinite series of ages, had witnessed at last so wonderful an
innovation as this, to what extent would his belief in the regularity of
the system be weakened?--would he cease to assume that there was
permanency in the laws of nature?--would he no longer be guided in his
speculations by the strictest rules of induction? To these questions it
may be answered, that, had he previously presumed to dogmatize
respecting the absolute uniformity of the order of nature, he would
undoubtedly be checked by witnessing this new and unexpected event, and
would form a more just estimate of the limited range of his own
knowledge, and the unbounded extent of the scheme of the universe. But
he would soon perceive that no one of the fixed and constant laws of the
animate or inanimate world was subverted by human agency, and that the
modifications now introduced for the first time were the accompaniments
of new and extraordinary circumstances, and those not of a _physical_
but a _moral_ nature. The deviation permitted would also appear to be as
slight as was consistent with the accomplishment of the new _moral_ ends
proposed, and to be in a great degree temporary in its nature, so that,
whenever the power of the new agent was withheld, even for a brief
period, a relapse would take place to the ancient state of things; the
domesticated animal, for example, recovering in a few generations its
wild instinct, and the garden-flower and fruit-tree reverting to the
likeness of the parent stock.

Now, if it would be reasonable to draw such inferences with respect to
the future, we cannot but apply the same rules of induction to the
past. We have no right to anticipate any modifications in the results of
existing causes in time to come, which are not conformable to analogy,
unless they be produced by the progressive development of human power,
or perhaps by some other new relations which may hereafter spring up
between the moral and material worlds. In the same manner, when we
speculate on the vicissitudes of the animate and inanimate creation in
former ages, we ought not to look for any anomalous results, unless
where man has interfered, or unless clear indications appear of some
other _moral_ source of temporary derangement.




CHAPTER X.

SUPPOSED INTENSITY OF AQUEOUS FORCES AT REMOTE PERIODS.


  Intensity of aqueous causes--Slow accumulation of strata proved by
    fossils--Rate of denudation can only keep pace with
    deposition--Erratics, and effects of ice--Deluges, and the causes to
    which they are referred--Supposed universality of ancient deposits.


_Intensity of aqueous causes._--The great problem considered in the
preceding chapters, namely, whether the former changes of the earth made
known to us by geology, resemble in kind and degree those now in daily
progress, may still be contemplated from several other points of view.
We may inquire, for example, whether there are any grounds for the
belief entertained by many, that the intensity both of aqueous and of
igneous forces, in remote ages, far exceeded that which we witness in
our own times.

First, then, as to aqueous causes: it has been shown, in our history of
the science, that Woodward did not hesitate, in 1695, to teach that the
entire mass of fossiliferous strata contained in the earth's crust had
been deposited in a few months; and, consequently, as their mechanical
and derivative origin was already admitted, the reduction of rocky
masses into mud, sand, and pebbles, the transportation of the same to a
distance, and their accumulation elsewhere in regular strata, were all
assumed to have taken place with a rapidity unparalleled in modern
times. This doctrine was modified by degrees, in proportion as different
classes of organic remains, such as shells, corals, and fossil plants,
had been studied with attention. Analogy led every naturalist to assume,
that each full-grown individual of the animal or vegetable kingdom, had
required a certain number of months or years for the attainment of
maturity, and the perpetuation of its species by generation; and thus
the first approach was made to the conception of a common standard of
time, without which there are no means whatever of measuring the
comparative rate at which any succession of events has taken place at
two distinct periods. This standard consisted of the average duration of
the lives of individuals of the same genera or families in the animal
and vegetable kingdoms; and the multitude of fossils dispersed through
successive strata implied the continuance of the same species for many
generations. At length the idea that species themselves had had a
limited duration, arose out of the observed fact that sets of strata of
different ages contained fossils of distinct species. Finally, the
opinion became general, that in the course of ages, one assemblage of
animals and plants had disappeared after another again and again, and
new tribes had started into life to replace them.

_Denudation._--In addition to the proofs derived from organic remains,
the forms of stratification led also, on a fuller investigation, to the
belief that sedimentary rocks had been slowly deposited; but it was
still supposed that _denudation_, or the power of running water, and the
waves and currents of the ocean, to strip off superior strata, and lay
bare the rocks below, had formerly operated with an energy wholly
unequalled in our times. These opinions were both illogical and
inconsistent, because deposition and denudation are parts of the same
process, and what is true of the one must be true of the other. Their
speed must be always limited by the same causes, and the conveyance of
solid matter to a particular region can only keep pace with its removal
from another, so that the aggregate of sedimentary strata in the earth's
crust can never exceed in volume the amount of solid matter which has
been ground down and washed away by running water. How vast, then, must
be the spaces which this abstraction of matter has left vacant! how far
exceeding in dimensions all the valleys, however numerous, and the
hollows, however vast, which we can prove to have been cleared out by
aqueous erosion! The evidences of the work of denudation are defective,
because it is the nature of every destroying cause to obliterate the
signs of its own agency; but the amount of reproduction in the form of
sedimentary strata must always afford a true measure of the minimum of
denudation which the earth's surface has undergone.

_Erratics._--The next phenomenon to which the advocates of the excessive
power of running water in times past have appealed, is the enormous size
of the blocks called _erratic_, which lie scattered over the northern
parts of Europe and North America. Unquestionably a large proportion of
these blocks have been transported far from their original position, for
between them and the parent rocks we now find, not unfrequently, deep
seas and valleys intervening, or hills more than a thousand feet high.
To explain the present situation of such travelled fragments, a deluge
of mud has been imagined by some to have come from the north, bearing
along with it sand, gravel, and stony fragments, some of them hundreds
of tons in weight. This flood, in its transient passage over the
continents, dispersed the boulders irregularly over hill, valley, and
plain; or forced them along over a surface of hard rock, so as to polish
it and leave it indented with parallel scratches and grooves--such
markings as are still visible in the rocks of Scandinavia, Scotland,
Canada, and many other countries.

There can be no doubt that the myriads of angular and rounded blocks
above alluded to, cannot have been borne along by ordinary rivers or
marine currents, so great is their volume and weight, and so clear are
the signs, in many places, of time having been occupied in their
successive deposition; for they are often distributed at various depths
through heaps of regularly stratified sand and gravel. No waves of the
sea raised by earthquakes, nor the bursting of lakes dammed up for a
time by landslips or by avalanches of snow, can account for the observed
facts; but I shall endeavor to show, in the next book, chap. 15,[236]
that a combination of existing causes may have conveyed erratics into
their present situations.

The causes which will be referred to are, first, the carrying power of
ice, combined with that of running water; and second, the upward
movement of the bed of the sea, converting it gradually into land.
Without entering at present into any details respecting these causes, I
may mention that the transportation of blocks by ice is now
simultaneously in progress in the cold and temperate latitudes, both of
the northern and southern hemisphere, as, for example, on the coasts of
Canada and Gulf of St. Lawrence, and also in Chili, Patagonia, and the
island of South Georgia. In those regions the uneven bed of the ocean is
becoming strewed over with ice-drifted fragments, which have either
stranded on shoals, or been dropped in deep water by melting bergs. The
entanglement of boulders in drift-ice will also be shown to occur
annually in North America, and these stones, when firmly frozen into
ice, wander year after year from Labrador to the St. Lawrence, and reach
points of the western hemisphere farther south than any part of Great
Britain.

The general absence of erratics in the warmer parts of the equatorial
regions of Asia, Africa, and America, confirms the same views. As to the
polishing and grooving of hard rocks, it has lately been ascertained
that glaciers give rise to these effects when pushing forward sand,
pebbles, and rocky fragments, and causing them to grate along the
bottom. Nor can there be any reasonable doubt that icebergs, when they
run aground on the floor of the ocean, must imprint similar marks upon
it.

It is unnecessary, therefore, to refer to deluges, or even to speculate
on the former existence of a climate more severe than that now
prevailing in the western hemisphere, to explain the geographical
distribution of most of the European erratics.

_Deluges._--As deluges have been often alluded to, I shall say something
of the causes which may be supposed to give rise to these grand
movements of water in addition to those already alluded to (p. 9).
Geologists who believe that mountain-chains have been thrown up
suddenly at many successive epochs, imagine that the waters of the
ocean may be raised by these convulsions, and then break in terrific
waves upon the land, sweeping over whole continents, hollowing out
valleys, and transporting sand, gravel, and erratics, to great
distances. The sudden rise of the Alps or Andes, it is said, may have
produced a flood even subsequently to the time when the earth became the
residence of man. But it seems strange that none of the writers who have
indulged their imaginations in conjectures of this kind, should have
ascribed a deluge to the sudden conversion of part of the unfathomable
ocean into a shoal rather than to the rise of mountain-chains. In the
latter case, the mountains themselves could do no more than displace a
certain quantity of atmospheric air, whereas, the instantaneous
formation of the shoal would displace a vast body of water, which being
heaved up to a great height might roll over and permanently submerge a
large portion of a continent.

If we restrict ourselves to combinations of causes at present known, it
would seem that the two principal sources of extraordinary inundations
are, first, the escape of the waters of a large lake raised far above
the sea; and, secondly, the pouring down of a marine current into lands
depressed below the mean level of the ocean.

As an example of the first of these cases, we may take Lake Superior,
which is more than 400 geographical miles in length and about 150 in
breadth, having an average depth of from 500 to 900 feet. The surface of
this vast body of fresh water is no less than 600 feet above the level
of the ocean; the lowest part of the barrier which separates the lake on
its southwest side from those streams which flow into the head waters of
the Mississippi being about 600 feet high. If, therefore, a series of
subsidences should lower any part of this barrier 600 feet, any
subsequent rending or depression, even of a few yards at a time, would
allow the sudden escape of vast floods of water into a hydrographical
basin of enormous extent. If the event happened in the dry season, when
the ordinary channels of the Mississippi and its tributaries are in a
great degree empty, the inundation might not be considerable; but if in
the flood-season, a region capable of supporting a population of many
millions might be suddenly submerged. But even this event would be
insufficient to cause a violent rush of water, and to produce those
effects usually called diluvial; for the difference of level of 600 feet
between Lake Superior and the Gulf of Mexico, when distributed over a
distance of 1800 miles, would give an average fall of only four inches
per mile.

The second case before adverted to is where there are large tracts of
dry land beneath the mean level of the ocean. It seems, after much
controversy, to be at length a settled point, that the Caspian is really
83 feet 6 inches lower than the Black Sea. As the Caspian covers an area
about equal to that of Spain, and as its shores are in general low and
flat, there must be many thousand square miles of country less than 83
feet above the level of that inland sea, and consequently depressed
below the Black Sea and Mediterranean. This area includes the site of
the populous city of Astrakhan and other towns. Into this region the
ocean would pour its waters, if the land now intervening between the Sea
of Azof and the Caspian should subside. Yet even if this event should
occur, it is most probable that the submergence of the whole region
would not be accomplished simultaneously, but by a series of minor
floods, the sinking of the barrier being gradual.[237]

_Supposed universality of ancient deposits._--The next fallacy which has
helped to perpetuate the doctrine that the operations of water were on a
different and grander scale in ancient times, is founded on the
indefinite areas over which homogeneous deposits were supposed to
extend. No modern sedimentary strata, it is said, equally identical in
mineral character and fossil contents, can be traced continuously from
one quarter of the globe to another. But the first propagators of these
opinions were very slightly acquainted with the inconstancy in mineral
composition of the ancient formations, and equally so of the wide spaces
over which the same kind of sediment is now actually distributed by
rivers and currents in the course of centuries. The persistency of
character in the older series was exaggerated, its extreme variability
in the newer was assumed without proof. In the chapter which treats of
river-deltas and the dispersion of sediment by currents, and in the
description of reefs of coral now growing over areas many hundred miles
in length, I shall have opportunities of convincing the reader of the
danger of hasty generalizations on this head.

In regard to the imagined universality of particular rocks of ancient
date, it was almost unavoidable that this notion, when once embraced,
should be perpetuated; for the same kinds of rock have occasionally been
reproduced at successive epochs; and when once the agreement or
disagreement in mineral character alone was relied on as the test of
age, it followed that similar rocks, if found even at the antipodes,
were referred to the same era, until the contrary could be shown.

Now it is usually impossible to combat such an assumption on geological
grounds, so long as we are imperfectly acquainted with the order of
superposition and the organic remains of these same formations. Thus,
for example, a group of red marl and red sandstone, containing salt and
gypsum, being interposed in England between the Lias and the Coal, all
other red marls and sandstones, associated some of them with salt, and
others with gypsum, and occurring not only in different parts of Europe,
but in North America, Peru, India, the salt deserts of Asia, those of
Africa--in a word, in every quarter of the globe, were referred to one
and the same period. The burden of proof was not supposed to rest with
those who insisted on the identity in age of all these groups--their
identity in mineral composition was thought sufficient. It was in vain
to urge as an objection the improbability of the hypothesis which
implies that all the moving waters on the globe were once simultaneously
charged with sediment of a red color.

But the rashness of pretending to identify, in age, all the red
sandstones and marls in question, has at length been sufficiently
exposed, by the discovery that, even in Europe, they belong decidedly to
many different epochs. It is already ascertained, that the red sandstone
and red marl containing the rock-salt of Cardona in Catalonia is newer
than the Oolitic, if not more modern than the Cretaceous period. It is
also known that certain red marls and variegated sandstones in Auvergne
which are undistinguishable in mineral composition from the New Red
Sandstone of English geologists, belong, nevertheless, to the Eocene
period; and, lastly, the gypseous red marl of Aix, in Provence, formerly
supposed to be a marine secondary group, is now acknowledged to be a
tertiary freshwater formation. In Nova Scotia one great deposit of red
marl, sandstone, and gypsum, precisely resembling in mineral character
the "New Red" of England, occurs as a member of the Carboniferous group,
and in the United States near the Falls of Niagara, a similar formation
constitutes a subdivision of the Silurian series.[238]

Nor was the nomenclature commonly adopted in geology without its
influence in perpetuating the erroneous doctrine of universal
formations. Such names, for example, as Chalk, Green Sand, Oolite, Red
Marl, Coal, and others, were given to some of the principal
fossiliferous groups in consequence of mineral peculiarities which
happened to characterize them in the countries where they were first
studied. When geologists had at length shown, by means of fossils and
the order of superposition, that other strata, entirely dissimilar in
color, texture, and composition, were of contemporaneous date, it was
thought convenient still to retain the old names. That these were often
inappropriate was admitted; but the student was taught to understand
them in no other than a chronological sense; so that the Chalk might not
be a white cretaceous rock, but a hard dolomitic limestone, as in the
Alps, or a brown sandstone or green marl, as in New Jersey, U. S. In
like manner, the Green Sand, it was said, might in some places be
represented by red sandstone, red marl, salt, and gypsum, as in the
north of Spain. So the oolitic texture was declared to be rather an
exception than otherwise to the general rule in rocks of the Oolitic
period; and it often became necessary to affirm that no particle of
carbonaceous matter could be detected in districts where the true Coal
series abounded. In spite of every precaution the habitual use of this
language could scarcely fail to instil into the mind of the pupil an
idea that chalk, coal, salt, red marl, or the Oolitic structure were far
more widely characteristic of the rocks of a given age than was really
the case.

There is still another cause of deception, disposing us to ascribe a
more limited range to the newer sedimentary formations as compared to
the older, namely, the very general concealment of the newer strata
beneath the waters of lakes and seas, and the wide exposure above waters
of the more ancient. The Chalk, for example, now seen stretching for
thousands of miles over different parts of Europe, has become visible to
us by the effect, not of one, but of many distinct series of
subterranean movements. Time has been required, and a succession of
geological periods, to raise it above the waves in so many regions; and
if calcareous rocks of the middle and upper tertiary periods have been
formed, as homogeneous in mineral composition throughout equally
extensive regions, it may require convulsions as numerous as all those
which have occurred since the origin of the Chalk to bring them up
within the sphere of human observation. Hence the rocks of more modern
periods may appear partial, as compared to those of remoter eras, not
because of any original inferiority in their extent, but because there
has not been sufficient time since their origin for the development of a
great series of elevatory movements.

In regard, however, to one of the most important characteristics of
sedimentary rocks, their organic remains, many naturalists of high
authority have maintained that the same species of fossils are more
uniformly distributed through formations of high antiquity than in those
of more modern date, and that distinct zoological and botanical
provinces, as they are called, which form so striking a feature in the
living creation, were not established at remote eras. Thus the plants of
the Coal, the shells, the trilobites of the Silurian rocks, and the
ammonites of the Oolite, have been supposed to have a wider geographical
range than any living species of plants, crustaceans, or mollusks. This
opinion seems in certain cases to be well founded, especially in
relation to the plants of the Carboniferous epoch, owing probably to the
more uniform temperature of the globe, at a time when the position of
sea and land was less favorable to variations in climate, according to
principles already explained in the seventh and eighth chapters. But a
recent comparison of the fossils of North American rocks with those of
corresponding ages in the European series, has proved that the
terrestrial vegetation of the Carboniferous epoch is an exception to the
general rule, and that the fauna and flora of the earth at successive
periods, from the oldest Silurian to the newest Tertiary was as
diversified as now. The shells, corals, and other classes of organic
remains demonstrate the fact that the earth might then have been divided
into separate zoological provinces, in a manner analogous to that
observed in the geographical distribution of species now living.




CHAPTER XI.

ON THE SUPPOSED FORMER INTENSITY OF THE IGNEOUS FORCES.


  Volcanic action at successive geological periods--Plutonic rocks of
    different ages--Gradual development of subterranean
    movements--Faults--Doctrine of the sudden upheaval of parallel
    mountain-chains--Objections to the proof of the suddenness of the
    upheaval, and the contemporaneousness of parallel chains--Trains of
    active volcanoes not parallel--As large tracts of land are rising or
    sinking slowly, so narrow zones of land may be pushed up gradually
    to great heights--Bending of strata by lateral pressure--Adequacy of
    the volcanic power to effect this without paroxysmal convulsions.


When reasoning on the intensity of volcanic action at former periods, as
well as on the power of moving water, already treated of, geologists
have been ever prone to represent Nature as having been prodigal of
violence and parsimonious of time. Now, although it is less easy to
determine the relative ages of the volcanic than of the fossiliferous
formations, it is undeniable that igneous rocks have been produced at
all geological periods, or as often as we find distinct deposits marked
by peculiar animal and vegetable remains. It can be shown that rocks
commonly called trappean have been injected into fissures, and ejected
at the surface, both before and during the deposition of the
Carboniferous series, and at the time when the Magnesian Limestone, and
when the Upper New Red Sandstone were formed, or when the Lias, Oolite,
Green Sand, Chalk, and the several tertiary groups newer than the chalk,
originated in succession. Nor is this all: distinct volcanic products
may be referred to the subordinate divisions of each period, such as the
Carboniferous, as in the county of Fife, in Scotland, where certain
masses of contemporaneous trap are associated with the Lower, others
with the Upper Coal measures. And if one of these masses is more
minutely examined, we find it to consist of the products of a great many
successive outbursts, by which scoriae and lava were again and again
emitted, and afterwards consolidated, then fissured, and finally
traversed by melted matter, constituting what are called dikes.[239] As
we enlarge, therefore, our knowledge of the ancient rocks formed by
subterranean heat, we find ourselves compelled to regard them as the
aggregate effects of innumerable eruptions, each of which may have been
comparable in violence to those now experienced in volcanic regions.

It may indeed be said that we have as yet no data for estimating the
relative volume of matter simultaneously in a state of fusion at two
given periods, as if we were to compare the columnar basalt of Staffa
and its environs with the lava poured out in Iceland in 1783; but for
this very reason it would be rash and unphilosophical to assume an
excess of ancient as contrasted with modern outpourings of melted matter
at particular periods of time.[240] It would be still more presumptuous
to take for granted that the more deep-seated effects of subterranean
heat surpassed at remote eras the corresponding effects of internal heat
in our own times. Certain porphyries and granites, and all the rocks
commonly called plutonic, are now generally supposed to have resulted
from the slow cooling of materials fused and solidified under great
pressure; and we cannot doubt that beneath existing volcanoes there are
large spaces filled with melted stone, which must for centuries remain
in an incandescent state, and then cool and become hard and crystalline
when the subterranean heat shall be exhausted. That lakes of lava are
continuous for hundreds of miles beneath the Chilian Andes, seems
established by observations made in the year 1835.[241]

Now, wherever the fluid contents of such reservoirs are poured out
successively from craters in the open air, or at the bottom of the sea,
the matter so ejected may afford evidence by its arrangement of having
originated at different periods; but if the subterranean residue after
the withdrawal of the heat be converted into crystalline or plutonic
rock, the entire mass may seem to have been formed at once, however
countless the ages required for its fusion and subsequent refrigeration.
As the idea that all the granite in the earth's crust was produced
simultaneously, and in a primitive state of the planet, has now been
universally abandoned; so the suggestion above adverted to, may put us
on our guard against too readily adopting another opinion, namely, that
each large mass of granite was generated in a brief period of time.

Modern writers indeed, of authority, seem more and more agreed that in
the case of granitic rocks, the passage from a liquid or pasty to a
solid and crystalline state must have been an extremely gradual process.

The doctrine so much insisted upon formerly, that crystalline rocks,
such as granite, gneiss, mica-schist, quartzite, and others were
produced in the greatest abundance in the earlier ages of the planet,
and that their formation has ceased altogether in our own times, will be
controverted in the next chapter.

_Gradual development of subterranean movements._--The extreme violence
of the subterranean forces in remote ages has been often inferred from
the facts that the older rocks are more fractured and dislocated than
the newer. But what other result could we have anticipated if the
quantity of movement had been always equal in equal periods of time?
Time must, in that case, multiply the derangement of strata in the ratio
of their antiquity. Indeed the numerous exceptions to the above rule
which we find in nature, present at first sight the only objection to
the hypothesis of uniformity. For the more ancient formations remain in
many places horizontal, while in others much newer strata are curved and
vertical. This apparent anomaly, however, will be seen in the next
chapter to depend on the irregular manner in which the volcanic and
subterranean agency affect different parts of the earth in succession,
being often renewed again and again in certain areas, while others
remain during the whole time at rest.

That the more impressive effects of subterranean power, such as the
upheaval of mountain-chains, may have been due to multiplied convulsions
of moderate intensity rather than to a few paroxysmal explosions, will
appear the less improbable when the gradual and intermittent development
of volcanic eruptions in times past is once established. It is now very
generally conceded that these eruptions have their source in the same
causes as those which give rise to the permanent elevation and sinking
of land; the admission, therefore, that one of the two volcanic or
subterranean processes has gone on gradually, draws with it the
conclusion that the effects of the other have been elaborated by
successive and gradual efforts.

_Faults._--The same reasoning is applicable to great _faults_, or those
striking instances of the upthrow or downthrow of large masses of rock,
which have been thought by some to imply tremendous catastrophes wholly
foreign to the ordinary course of nature. Thus we have in England
faults, in which the vertical displacement is between 600 and 3000 feet,
and the horizontal extent thirty miles or more, the width of the
fissures since filled up with rubbish varying from ten to fifty feet.
But when we inquire into the proofs of the mass having risen or fallen
suddenly on the one side of these great rents, several hundreds or
thousands of feet above or below the rock with which it was once
continuous on the other side, we find the evidence defective. There are
grooves, it is said, and scratches on the rubbed and polished walls,
which have often one common direction, favoring the theory that the
movement was accomplished by a single stroke, and not by a series of
interrupted movements. But, in fact, the striae are not always parallel
in such cases, but often irregular, and sometimes the stones and earth
which are in the middle of the fault, or fissure, have been polished and
striated by friction in different directions, showing that there have
been slidings subsequent to the first introduction of the fragmentary
matter. Nor should we forget that the last movement must always tend to
obliterate the signs of previous trituration, so that neither its
instantaneousness nor the uniformity of its direction can be inferred
from the parallelism of the striae that have been last produced.

When rocks have been once fractured, and freedom of motion communicated
to detached portions of them, these will naturally continue to yield in
the same direction, if the process of upheaval or of undermining be
repeated again and again. The incumbent mass will always give way along
the lines of least resistance, or where it was formerly rent asunder.
Probably, the effects of reiterated movement, whether upward or
downward, in a fault, may be undistinguishable from those of a single
and instantaneous rise or subsidence; and the same may be said of the
rising or falling of continental masses, such as Sweden or Greenland,
which we know to take place slowly and insensibly.

_Doctrine of the sudden upheaval of parallel mountain-chains._--The
doctrine of the suddenness of many former revolutions in the physical
geography of the globe has been thought by some to derive additional
confirmation from a theory respecting the origin of mountain-chains,
advanced in 1833 by a distinguished geologist, M. Elie de Beaumont. In
several essays on this subject, the last published in 1852, he has
attempted to establish two points; first, that a variety of independent
chains of mountains have been thrown up suddenly at particular periods;
and, secondly, that the contemporaneous chains thus thrown up, preserve
a parallelism the one to the other.

These opinions, and others by which they are accompanied, are so adverse
to the method of interpreting the history of geological changes which I
have recommended in this work, that I am desirous of explaining the
grounds of my dissent, a course which I feel myself the more called upon
to adopt, as the generalizations alluded to are those of a skilful
writer, and an original observer of great talent and experience. I shall
begin, therefore, by giving a brief summary of the principal
propositions laid down in the works above referred to.[242]

1st. M. de Beaumont supposes "that in the history of the earth there
have been long periods of comparative repose, during which the
deposition of sedimentary matter has gone on in regular continuity; and
there have also been short periods of paroxysmal violence, during which
that continuity was broken.

"2dly. At each of these periods of violence or 'revolution,' in the
state of the earth's surface, a great number of mountain-chains have
been formed suddenly.

"3dly. The chains thrown up by a particular revolution have one uniform
direction, being parallel to each other within a few degrees of the
compass, even when situated in remote regions; whilst the chains thrown
up at different periods have, for the most part, different directions.

"4thly. Each 'revolution,' or 'great convulsion,' has fallen in with the
date of another geological phenomenon; namely, 'the passage from one
independent sedimentary formation to another,' characterized by a
considerable difference in 'organic types.'

"5thly. There has been a recurrence of these paroxysmal movements from
the remotest geological periods; and they may still be reproduced, and
the repose in which we live may hereafter be broken by the sudden
upthrow of another system of parallel chains of mountains.

"6thly. The origin of these chains depends not on partial volcanic
action, or a reiteration of ordinary earthquakes, but on the secular
refrigeration of the entire planet. For the whole globe, with the
exception of a thin envelope, much thinner in proportion than the shell
to an egg, is a fused mass, kept fluid by heat, but constantly cooling
and contracting its dimensions. The external crust does not gradually
collapse and accommodate itself century after century to the shrunken
nucleus, subsiding as often as there is a slight failure of support, but
it is sustained throughout whole geological periods, so as to become
partially separated from the nucleus, until at last it gives way
suddenly, cracking and falling in along determinate lines of fracture.
During such a crisis the rocks are subjected to great lateral pressure,
the unyielding ones are crushed, and the pliant strata bent, and are
forced to pack themselves more closely into a smaller space, having no
longer the same room to spread themselves out horizontally. At the same
time, a large portion of the mass is squeezed upwards, because it is in
the upward direction only that the excess in size of the envelope, as
compared to the contracted nucleus, can find relief. This excess
produces one or more of those folds or wrinkles in the earth's crust
which we call mountain-chains.

"Lastly, some chains are comparatively modern; such as the Alps, which
were partly upheaved after the middle tertiary period. The elevation of
the Andes was much more recent, and was accompanied by the simultaneous
outburst for the first time of 270 of the principal volcanoes now
active.[243]

"The agitation of the waters of the ocean caused by this convulsion
probably occasioned that transient and general deluge which is noticed
in the traditions of so many nations."[244]

Several of the topics enumerated in the above summary, such as the cause
of interruptions in the sedimentary series, will be discussed in the
thirteenth chapter, and I shall now confine myself to what I conceive to
be the insufficiency of the proofs adduced in favor of the suddenness of
the upthrow, and the contemporaneousness of the origin of the parallel
chains referred to. At the same time I may remark, that the great body
of facts collected together by M. de Beaumont will always form a most
valuable addition to our knowledge, tending as they do to confirm the
doctrine that different mountain-chains have been formed in succession,
and, as Werner first pointed out, that there are certain determinate
lines of direction or strike in the strata of various countries.

The following may serve as an analysis of the evidence on which the
theory above stated depends. "We observe," says M. de Beaumont, "when we
attentively examine nearly all mountain-chains, that the most recent
rocks extend horizontally up to the foot of such chains, as we should
expect would be the case if they were deposited in seas or lakes, of
which these mountains have partly formed the shores; whilst the other
sedimentary beds, tilted up, and more or less contorted, on the flanks
of the mountains, rise in certain points even to their highest
crests."[245] There are, therefore, in and adjacent to each chain, two
classes of sedimentary rocks, the ancient and inclined beds, and the
newer or horizontal. It is evident that the first appearance of the
chain itself was an event "intermediate between the period when the beds
now upraised were deposited, and the period when the strata were
produced horizontally at its feet."

[Illustration: Fig. 11.]

Thus the chain A assumed its present position after the deposition of
the strata _b_, which have undergone great movements, and before the
deposition of the group _c_, in which the strata have not suffered
derangement.

[Illustration: Fig. 12.]

If we then discover another chain B, in which we find not only the
formation _b_, but the group _c_ also, disturbed and thrown on its
edges, we may infer that the latter chain is of subsequent date to A;
for B must have been elevated _after_ the deposition of _c_, and before
that of the group _d_; whereas A had originated _before_ the strata _c_
were formed.

It is then argued, that in order to ascertain whether other mountain
ranges are of contemporaneous date with A and B, or are referable to
_distinct_ periods, we have only to inquire whether the inclined and
undisturbed sets of strata in each range correspond with or differ from
those in the typical chain A and B.

Now all this reasoning is perfectly correct, so long as the period of
time required for the deposition of the strata _b_ and _c_ is not made
identical in duration with the period of time during which the animals
and plants found fossil in _b_ and _c_ may have flourished; for the
latter, that is to say, the duration of certain groups of species, may
have greatly exceeded, and probably did greatly exceed, the former, or
the time required for the accumulation of certain local deposits, such
as _b_ and _c_ (figs. 11 and 12). In order, moreover, to render the
reasoning correct, due latitude must be given to the term
contemporaneous; for this term must be understood to allude, not to a
moment of time, but to the interval, whether brief or protracted, which
elapsed between two events, namely, between the accumulation of the
inclined and that of the horizontal strata.

But, unfortunately, no attempt has been made in the treatises under
review to avoid this manifest source of confusion, and hence the very
terms of each proposition are equivocal; and the possible length of some
of the intervals is so vast, that to affirm that all the chains raised
in such intervals were _contemporaneous_ is an abuse of language.

In order to illustrate this argument, I shall select the Pyrenees as an
example. Originally M. E. de Beaumont spoke of this range of mountains
as having been uplifted suddenly (_a un seul jet_), but he has since
conceded that in this chain, in spite of the general unity and
simplicity of its structure, six, if not seven, systems of dislocation
of different dates can be recognized.[246] In reference, however, to the
latest, and by far the most important of these convulsions, the chain is
said to have attained its present elevation at a certain epoch in the
earth's history, namely, between the deposition of the chalk, or rocks
of about that age, and that of certain tertiary formations "as old as
the plastic clay;" for the chalk is seen in vertical, curved, and
distorted beds on the flanks of the chain, as the beds _b_, fig. 11,
while the tertiary formations rest upon them in horizontal strata at its
base, as _c_, ibid.

The proof, then, of the extreme suddenness of the convulsion is supposed
to be the shortness of the time which intervened between the formation
of the chalk and the origin of certain tertiary strata.[247] Even if the
interval were deducible within these limits, it might comprise an
indefinite lapse of time. In strictness of reasoning, however, the
author cannot exclude the Cretaceous or Tertiary periods from the
possible duration of the interval during which the elevation may have
taken place. For, in the first place, it cannot be assumed that the
movement of upheaval took place after the close of the Cretaceous
period; we can merely say, that it occurred after the deposition of
certain strata of that period; secondly, although it were true that the
event happened before the formation of all the tertiary strata now at
the base of the Pyrenees, it would by no means follow that it preceded
the whole Tertiary epoch.

The age of the strata, both of the inclined and horizontal series, may
have been accurately determined by M. De Beaumont, and still the
upheaving of the Pyrenees may have been going on before the animals of
the Chalk period, such as are found fossil in England, had ceased to
exist, or when the Maestricht beds were in progress, or during the
indefinite ages which may have elapsed between the extinction of the
Maestricht animals and the introduction of the Eocene tribes, or during
the Eocene epoch, or the rise may have been going on throughout one, or
several, or all of these periods.

It would be a purely gratuitous assumption to say that the inclined
cretaceous strata (_b_, fig. 11) on the flanks of the Pyrenees, were the
very last which were deposited during the Cretaceous period, or that, as
soon as they were upheaved, all or nearly all the species of animals and
plants now found fossil in them were suddenly exterminated; yet, unless
this can be affirmed, we cannot say that the Pyrenees were not upheaved
during the Cretaceous period. Consequently, another range of mountains,
at the base of which cretaceous rocks may lie in horizontal
stratification, may have been elevated, like the chain A, fig. 12,
during some part of the same great period.

There are mountains in Sicily two or three thousand feet high, the tops
of which are composed of limestone, in which a large proportion of the
fossil shells agree specifically with those now inhabiting the
Mediterranean. Here, as in many other countries, the deposits now in
progress in the sea must inclose shells and other fossils specifically
identical with those of the rocks constituting the contiguous land. So
there are islands in the Pacific where a mass of dead coral has emerged
to a considerable altitude, while other portions of the mass remain
beneath the sea, still increasing by the growth of living zoophytes and
shells. The chalk of the Pyrenees, therefore, may at a remote period
have been raised to an elevation of several thousand feet, while the
species found fossil in the same chalk still continued to be represented
in the fauna of the neighboring ocean. In a word, we cannot assume that
the origin of a new range of mountains caused the Cretaceous period to
cease, and served as the prelude to a new order of things in the animate
creation.

To illustrate the grave objections above advanced, against the theory
considered in the present chapter, let us suppose, that in some country
three styles of architecture had prevailed in succession, each for a
period of one thousand years; first the Greek, then the Roman, and then
the Gothic; and that a tremendous earthquake was known to have occurred
in the same district during one of the three periods--a convulsion of
such violence as to have levelled to the ground all the buildings then
standing. If an antiquary, desirous of discovering the date of the
catastrophe, should first arrive at a city where several Greek temples
were lying in ruins and half engulphed in the earth, while many Gothic
edifices were standing uninjured, could he determine on these data the
era of the shock? Could he even exclude any one of the three periods,
and decide that it must have happened during one of the other two?
Certainly not. He could merely affirm that it happened at some period
after the introduction of the Greek style, and before the Gothic had
fallen into disuse. Should he pretend to define the date of the
convulsion with greater precision, and decide that the earthquake must
have occurred after the Greek and before the Gothic period, that is to
say, when the Roman style was in use, the fallacy in his reasoning would
be too palpable to escape detection for a moment.

Yet such is the nature of the erroneous induction which I am now
exposing. For as, in the example above proposed, the erection of a
particular edifice is perfectly distinct from the period of architecture
in which it may have been raised, so is the deposition of chalk, or any
other set of strata, from the geological epochs characterized by certain
fossils to which they may belong.

It is almost superfluous to enter into any farther analysis of the
theory of parallelism, because the whole force of the argument depends
on the accuracy of the data by which the contemporaneous or
non-contemporaneous date of the elevation of two independent chains can
be demonstrated. In every case, this evidence, as stated by M. de
Beaumont, is equivocal, because he has not included in the possible
interval of time between the depositions of the deranged and the
horizontal formations, part of the periods to which each of those
classes of formations are referable. Even if all the geological facts,
therefore, adduced by the author were true and unquestionable, yet the
conclusion that certain chains were or were not simultaneously upraised
is by no means a legitimate consequence.

In the third volume of my first edition of the Principles, which
appeared in April, 1833, I controverted the views of M. de Beaumont,
then just published, in the same terms as I have now restated them. At
that time I took for granted that the chronological date of the newest
rocks entering into the disturbed series of the Pyrenees had been
correctly ascertained. It now appears, however, that some of the most
modern of those disturbed strata belong to the nummulitic formation,
which are regarded by the majority of geologists as Eocene or older
tertiary, an opinion not assented to by M. E. de Beaumont, and which I
cannot discuss here without being led into too long a digression.[248]

Perhaps a more striking illustration of the difficulties we encounter,
when we attempt to apply the theory under consideration even to the best
known European countries, is afforded by what is called "The System of
the Longmynds." This small chain, situated in Shropshire, is the third
of the typical systems to which M. E. de Beaumont compares other
mountain ranges corresponding in _strike_ and structure. The date
assigned to its upheaval is "after the unfossiliferous greywacke, or
Cambrian strata, and before the Silurian." But Sir R. I. Murchison had
shown in 1838, in his "Silurian System," and the British government
surveyors, since that time, in their sections (about 1845), that the
Longmynds and other chains of similar composition in North Wales are
_post-Silurian_. In all of them fossiliferous beds of the lower Silurian
formation, or Llandeilo flags are highly inclined, and often vertical.
In one limited region the Caradoc sandstone, a member of the lower
Silurian, rests unconformably on the denuded edges of the inferior (or
Llandeilo) member of the same group; whilst in some cases both of these
sets of strata are upturned. When, therefore, so grave an error is
detected in regard to the age of a typical chain, we are entitled to
inquire with surprise, by what means nine other _parallel_ chains in
France, Germany, and Sweden, assumed to be "ante-Silurian," have been
made to agree precisely in date with the Longmynds? If they are
correctly represented as having been all deposited before the deposition
of the Silurian strata, they cannot be contemporaneous with the
Longmynds, and they only prove how little reliance can be placed on
parallelism as a test of simultaneousness of upheaval. But in truth it
is impossible, for reasons already given, to demonstrate that each of
those nine chains coincide in date with one another, any more than with
the Longmynds.

The reader will see in the sequel (chap. 31[249]) that Mr. Hopkins has
inferred from astronomical calculations, that the solid crust of the
earth cannot be less than 800 or 1000 miles thick, and may be more. Even
if it be solid to the depth of 100 miles, such a thickness would be
inconsistent with M. E. de Beaumont's hypothesis, which requires a shell
not more than thirty miles thick, or even less. Mr. Hopkins admits that
the exterior of the planet, though solid as a whole, may contain within
it vast lakes or seas of lava. If so, the gradual fusion of rocks, and
the expansive power of heat exerted for ages, as well as the subsequent
contraction of the same during slow refrigeration, may perhaps account
for the origin of mountain-chains, for these, as Dolomieu has remarked,
are "far less important, proportionally speaking, than the inequalities
on the surface of an egg-shell, which to the eye appears smooth." A
"centripetal force" affecting the whole planet as it cools, seems a
mightier cause than is required to produce wrinkles of such
insignificant size.

In pursuing his investigations, M. E. de Beaumont has of late greatly
multiplied the number of successive periods of instantaneous upheaval,
admitting at the same time that occasionally new lines of upthrow have
taken the direction of older ones.[250] These admissions render his
views much more in harmony with the principles advocated in this work,
but they impair the practical utility of parallelism considered as a
chronological test; for no rule is laid down for limiting the interval,
whether in time or space, which may separate two parallel lines of
upheaval of different dates.[251]

Among the various propositions above laid down (p. 164), it will be
seen that the sudden rise of the Andes is spoken of as a modern event,
but Mr. Darwin has brought together ample data in proof of the local
persistency of volcanic action throughout a long succession of
geological periods, beginning with times antecedent to the deposition of
the oolitic and cretaceous formations of Chili, and continuing to the
historical epoch. It appears that some of the parallel ridges which
compose the Cordilleras, instead of being contemporaneous, were
successively and slowly upheaved at widely different epochs. The whole
range, after twice subsiding some thousands of feet, was brought up
again by a slow movement in mass, during the era of the Eocene tertiary
formations, after which the whole sank down once more several hundred
feet, to be again uplifted to its present level by a slow and often
interrupted movement.[252] In a portion of this latter period the
"Pampean mud" was formed, in which the Megatherium mylodon and other
extinct quadrupeds are buried. This mud contains in it recent species of
shells, some of them proper to brackish water, and is believed by Mr.
Darwin to be an estuary or delta deposit. M. A. d'Orbigny, however, has
advanced an hypothesis referred to by M. E. de Beaumont, that the
agitation and displacement of the waters of the ocean, caused by the
elevation of the Andes, gave rise to a deluge, of which this Pampean
mud, which rises sometimes to the height of 12,000 feet, is the result
and monument.[253]

In studying many chains of mountains, we find that the strike or line of
outcrop of continuous sets of strata, and the general direction of the
chain, may be far from rectilinear. Curves forming angles of 20 degrees
or 30 degrees may be found in the same range as in the Alleghanies; just
as trains of active volcanoes and the zones throughout which modern
earthquakes occur are often linear, without running in straight lines.
Nor are all of these, though contemporaneous or belonging to our own
epoch, by any means parallel, but some at right angles, the one to the
other.

_Slow upheaval and subsidence._--Recent observations have disclosed to
us the wonderful fact, that not only the west coast of South America,
but also other large areas, some of them several thousand miles in
circumference, such as Scandinavia, and certain archipelagoes in the
Pacific, are slowly and insensibly rising; while other regions, such as
Greenland, and parts of the Pacific and Indian Oceans, in which atolls
or circular coral islands abound, are as gradually sinking. That all the
existing continents and submarine abysses may have originated in
movements of this kind, continued throughout incalculable periods of
time, is undeniable, and the denudation which the dry land appears
everywhere to have suffered, favors the idea that it was raised from the
deep by a succession of upward movements, prolonged throughout
indefinite periods. For the action of waves and currents on land slowly
emerging from the deep, affords the only power by which we can conceive
so many deep valleys and wide spaces to have been denuded as those which
are unquestionably the effects of running water.

But perhaps it may be said that there is no analogy between the slow
upheaval of broad plains or table-lands, and the manner in which we must
presume all mountain-chains, with their inclined strata, to have
originated. It seems, however, that the Andes have been rising century
after century, at the rate of several feet, while the Pampas on the east
have been raised only a few inches in the same time. Crossing from the
Atlantic to the Pacific, in a line passing through Mendoza, Mr. Darwin
traversed a plain 800 miles broad, the eastern part of which has emerged
from beneath the sea at a very modern period. The slope from the
Atlantic is at first very gentle, then greater, until the traveller
finds, on reaching Mendoza, that he has gained, almost insensibly, a
height of 4000 feet. The mountainous district then begins suddenly, and
its breadth from Mendoza to the shores of the Pacific is 120 miles, the
average height of the principal chain being from 15,000 to 16,000 feet,
without including some prominent peaks, which ascend much higher. Now
all we require, to explain the origin of the principal inequalities of
level here described, is to imagine, first, a zone of more violent
movement to the west of Mendoza, and, secondly, to the east of that
place, an upheaving force, which died away gradually as it approached
the Atlantic. In short, we are only called upon to conceive, that the
region of the Andes was pushed up four feet in the same period in which
the Pampas near Mendoza rose one foot, and the plains near the shores of
the Atlantic one inch. In Europe we have learnt that the land at the
North Cape ascends about five feet in a century, while farther to the
south the movements diminish in quantity first to a foot, and then, at
Stockholm, to three inches in a century, while at certain points still
farther south there is no movement.

But in what manner, it is asked, can we account for the great lateral
pressure which has been exerted not only in the Andes, Alps, and other
chains, but also on the strata of many low and nearly level countries?
Do not the folding and fracture of the beds, the anticlinal and
synclinal ridges and troughs, as they are called, and the vertical, and
even sometimes the inverted position of the beds, imply an abruptness
and intensity in the disturbing force wholly different in kind and
energy to that which now rends the rocks during ordinary earthquakes? I
shall treat more fully in the sequel (end of chap. 32) of the probable
subterranean sources, whether of upward or downward movement, and of
great lateral pressure; but it may be well briefly to state in this
place that in our own times, as, for example, in Chili, in 1822, the
volcanic force has overcome the resistance, and permanently uplifted a
country of such vast extent that the weight and volume of the Andes must
be insignificant in comparison, even if we indulge the most moderate
conjectures as to the thickness of the earth's crust above the volcanic
foci.

To assume that any set of strata with which we are acquainted are made
up of such cohesive and unyielding materials, as to be able to resist a
power of such stupendous energy, if its direction, instead of being
vertical, happened to be oblique or horizontal, would be extremely rash.
But if they could yield to a sideway thrust, even in a slight degree,
they would become squeezed and folded to any amount if subjected for a
sufficient number of times to the repeated action of the same force. We
can scarcely doubt that a mass of rock several miles thick was uplifted
in Chili in 1822 and 1835, and that a much greater volume of solid
matter is upheaved wherever the rise of the land is very gradual, as in
Scandinavia, the development of heat being probably, in that region, at
a greater distance from the surface. If continents, rocked, shaken, and
fissured, like the western region of South America, or very gently
elevated, like Norway and Sweden, do not acquire in a few days or hours
an additional height of several thousand feet, this can arise from no
lack of mechanical force in the subterranean moving cause, but simply
because the antagonist power, or the strength, toughness, and density of
the earth's crust is insufficient to resist, so long, as to allow the
volcanic energy an indefinite time to accumulate. Instead of the
explosive charge augmenting in quantity for countless ages, it finds
relief continuously, or by a succession of shocks of moderate violence,
so as never to burst or blow up the covering of incumbent rock in one
grand paroxysmal convulsion. Even in its most energetic efforts it
displays an intermittent and mitigated intensity, being never permitted
to lay a whole continent in ruins. Hence the numerous eruptions of lava
from the same vent, or chain of vents, and the recurrence of similar
earthquakes for thousands of years along certain areas or zones of
country. Hence the numerous monuments of the successive ejection and
injection of melted matter in ancient geological epochs, and the
fissures formed in distinct ages, and often widened and filled at
different eras.

Among the causes of lateral pressure, the expansion by heat of large
masses of solid stone intervening between others which have a different
degree of expansibility, or which happen not to have their temperature
raised at the same time, may play an important part. But as we know that
rocks have so often sunk down thousands of feet below their original
level, we can hardly doubt that much of the bending of pliant strata,
and the packing of the same into smaller spaces, has frequently been
occasioned by subsidence. Whether the failure of support be produced by
the melting of porous rocks, which, when fluid, and subjected to great
pressure, may occupy less room than before, or which, by passing from a
pasty to a crystalline condition, may, as in the case of granite,
according to the experiments of Deville, suffer a contraction of 10 per
cent., or whether the sinking be due to the subtraction of lava driven
elsewhere to some volcanic orifice, and there forced outwards, or
whether it be brought on by the shrinking of solid and stony masses
during refrigeration, or by the condensation of gases, or any other
imaginable cause, we have no reason to incline to the idea that the
consequent geological changes are brought about so suddenly, as that
large parts of continents are swallowed up at once in unfathomable
subterranean abysses. If cavities be formed, they will be enlarged
gradually, and as gradually filled. We read, indeed, accounts of
engulphed cities and areas of limited extent which have sunk down many
yards at once; but we have as yet no authentic records of the sudden
disappearance of mountains, or the submergence or emergence of great
islands. On the other hand, the creeps in coal mines[254] demonstrate
that gravitation begins to act as soon as a moderate quantity of matter
is removed even at a great depth. The roof sinks in, or the floor of the
mine rises, and the bent strata often assume as regularly a curved and
crumpled arrangement as that observed on a grander scale in
mountain-chains. The absence, indeed, of chaotic disorder, and the
regularity of the plications in geological formations of high antiquity,
although not unfrequently adduced to prove the unity and
instantaneousness of the disturbing force, might with far greater
propriety be brought forward as an argument in favor of the successive
application of some irresistible but moderated force, such as that which
can elevate or depress a continent.

In conclusion, I may observe that one of the soundest objections to the
theory of the sudden upthrow or downthrow of mountain-chains is this,
that it provides us with too much force of one kind, namely, that of
subterranean movement, while it deprives us of another kind of
mechanical force, namely, that exerted by the waves and currents of the
ocean, which the geologist requires for the denudation of land during
its slow upheaval or depression. It may be safely affirmed that the
quantity of igneous and aqueous action,--of volcanic eruption and
denudation,--of subterranean movement and sedimentary deposition,--not
only of past ages, but of one geological epoch, or even the fraction of
an epoch, has exceeded immeasurably all the fluctuations of the
inorganic world which have been witnessed by man. But we have still to
inquire whether the time to which each chapter or page or paragraph of
the earth's autobiography relates, was not equally immense when
contrasted with a brief era of 3000 or 5000 years. The real point on
which the whole controversy turns, is the relative amount of work done
by mechanical force in given quantities of time, past and present.
Before we can determine the relative intensity of the force employed, we
must have some fixed standard by which to measure the time expended in
its development at two distinct periods. It is not the magnitude of the
effects, however gigantic their proportions, which can inform us in the
slightest degree whether the operation was sudden or gradual, insensible
or paroxysmal. It must be shown that a slow process could never in any
series of ages give rise to the same results.

The advocate of paroxysmal energy might assume a uniform and fixed rate
of variation in times past and present for the animate world, that is to
say, for the dying-out and coming-in of species, and then endeavor to
prove that the changes of the inanimate world have not gone on in a
corresponding ratio. But the adoption of such a standard of comparison
would lead, I suspect, to a theory by no means favorable to the pristine
intensity of natural causes. That the present state of the organic world
is not stationary, can be fairly inferred from the fact, that some
species are known to have become extinct in the course even of the last
three centuries, and that the exterminating causes always in activity,
both on the land and in the waters, are very numerous; also, because man
himself is an extremely modern creation; and we may therefore reasonably
suppose that some of the mammalia now contemporary with man, as well as
a variety of species of inferior classes, may have been recently
introduced into the earth, to supply the places of plants and animals
which have from time to time disappeared. But granting that some such
secular variation in the zoological and botanical worlds is going on,
and is by no means wholly inappreciable to the naturalist, still it is
certainly far less manifest than the revolution always in progress in
the inorganic world. Every year some volcanic eruptions take place, and
a rude estimate might be made of the number of cubic feet of lava and
scoriae poured or cast out of various craters. The amount of mud and sand
deposited in deltas, and the advance of new land upon the sea, or the
annual retreat of wasting sea-cliffs, are changes the minimum amount of
which might be roughly estimated. The quantity of land raised above or
depressed below the level of the sea might also be computed, and the
change arising from such movements in a century might be conjectured.
Suppose the average rise of the land in some parts of Scandinavia to be
as much as five feet in a hundred years, the present sea-coast might be
uplifted 700 feet in fourteen thousand years; but we should have no
reason to anticipate, from any zoological data hitherto acquired, that
the molluscous fauna of the northern seas would in that lapse of years
undergo any sensible amount of variation. We discover sea-beaches in
Norway 700 feet high, in which the shells are identical with those now
inhabiting the German Ocean; for the rise of land in Scandinavia,
however insensible to the inhabitants, has evidently been rapid when
compared to the rate of contemporaneous change in the testaceous fauna
of the German Ocean. Were we to wait therefore until the mollusca shall
have undergone as much fluctuation as they underwent between the period
of the Lias and the Upper Oolite formations; or between the Oolite and
Chalk, nay, even between any two of eight subdivisions of the Eocene
series, what stupendous revolutions in physical geography ought we not
to expect, and how many mountain-chains might not be produced by the
repetition of shocks of moderate violence, or by movements not even
perceptible by man!

Or, if we turn from the mollusca to the vegetable kingdom, and ask the
botanist how many earthquakes and volcanic eruptions might be expected,
and how much the relative level of land and sea might be altered, or how
far the principal deltas will encroach upon the ocean, or the sea-cliffs
recede from the present shores, before the species of European
forest-trees will die out, he would reply that such alterations in the
inanimate world might be multiplied indefinitely before he should have
reason to anticipate, by reference to any known data, that the existing
species of trees in our forests would disappear and give place to
others. In a word, the movement of the inorganic world is obvious and
palpable, and might be likened to the minute-hand of a clock, the
progress of which can be seen and heard, whereas the fluctuations of the
living creation are nearly invisible, and resemble the motion of the
hour-hand of a timepiece. It is only by watching it attentively for some
time, and comparing its relative position after an interval, that we can
prove the reality of its motion.[255]




CHAPTER XII.

DIFFERENCE IN TEXTURE OF THE OLDER AND NEWER ROCKS.


  Consolidation of fossiliferous strata--Some deposits originally
    solid--Transition and slaty texture--Crystalline character of
    Plutonic and Metamorphic rocks--Theory of their origin--Essentially
    subterranean--No proofs that they were produced more abundantly at
    remote periods.


Another argument in favor of the dissimilarity of the causes operating
at remote and recent eras has been derived by many geologists from the
more compact, stony, and crystalline texture of the older as compared
with the newer rocks.

_Consolidation of strata._--This subject may be considered, first in
reference to the fossiliferous strata; and, secondly, in reference to
those crystalline and stratified rocks which contain no organic remains,
such as gneiss and mica-schist. There can be no doubt that the former of
these classes, or the fossiliferous, are generally more compact and
stony in proportion as they are more ancient. It is also certain that a
great part of them were originally in a soft and incoherent state, and
that they have been since consolidated. Thus we find occasionally that
shingle and sand have been agglutinated firmly together by a ferruginous
or siliceous cement, or that lime in solution has been introduced, so as
to bind together materials previously incoherent. Organic remains have
sometimes suffered a singular transformation, as for example,] where
shells, corals, and wood are silicified, their calcareous or ligneous
matter having been replaced by nearly pure silica. The constituents of
some beds have probably set and become hard for the first time when they
emerged from beneath the water.

But, on the other hand, we observe in certain formations now in
progress, particularly in coral reefs, and in deposits from the waters
of mineral springs, both calcareous and siliceous, that the texture of
rocks may sometimes be stony from the first. This circumstance may
account for exceptions to the general rule, not unfrequently met with,
where solid strata are superimposed on others of a plastic and
incoherent nature, as in the neighborhood of Paris, where the tertiary
formations, consisting often of compact limestone and siliceous grit,
are more stony than the subjacent chalk.

It will readily be understood, that the various solidifying causes,
including those above enumerated, together with the pressure of
incumbent rocks and the influence of subterranean heat, must all of them
require time in order to exert their full power. If in the course of
ages they modify the aspect and internal structure of stratified
deposits, they will give rise to a general distinctness of character in
the older as contrasted with the newer formations. But this distinctness
will not be the consequence of any original diversity; they will be
unlike, just as the wood in the older trees of a forest usually differs
in texture and hardness from that of younger individuals of the same
species.

_Transition texture_.--In the original classification, of Werner, the
highly crystalline rocks, such as granite and gneiss, which contain no
organic remains, were called primary, and the fossiliferous strata
secondary, while to another class of an age intermediate between the
primary and secondary he gave the name of transition. They were termed
transition because they partook in some degree in their mineral
composition of the nature of the most crystalline rocks, such as gneiss
and mica-schist, while they resembled the fossiliferous series in
containing occasionally organic remains, and exhibiting evident signs of
a mechanical origin. It was at first imagined, that the rocks having
this intermediate texture had been all deposited subsequently to the
series called primary, and before all the more earthy and fossiliferous
formations. But when the relative position and organic remains of these
transition rocks were better understood, it was perceived that they did
not all belong to one period. On the contrary, the same mineral
characters were found in strata of very different ages, and some
formations occurring in the Alps, which several of the ablest scholars
of Werner had determined to be transition, were ultimately ascertained,
by means of their fossil contents and position, to be members of the
Cretaceous, and even of the nummulitic or Eocene period. These strata
had, in fact, acquired the _transition_ texture from the influence of
causes which, since their deposition had modified their internal
arrangement.

_Texture and origin of Plutonic and metamorphic rocks_.--Among the most
singular of the changes superinduced on rocks, we have occasionally to
include the slaty texture, the divisional planes of which sometimes
intersect the true planes of stratification, and even pass directly
through imbedded fossils. If, then, the crystalline, the slaty, and
other modes of arrangement, once deemed characteristic of certain
periods in the history of the earth, have in reality been assumed by
fossiliferous rocks of different ages and at different times, we are
prepared to inquire whether the same may not be true of the most highly
crystalline state, such as that of gneiss, mica-schist, and statuary
marble. That the peculiar characteristics of such rocks are really due
to a variety of modifying causes has long been suspected by many
geologists, and the doctrine has gained ground of late, although a
considerable difference of opinion still prevails. According to the
original Neptunian theory, all the crystalline formations were
precipitated from a universal menstruum or chaotic fluid antecedently to
the creation of animals and plants, the unstratified granite having been
first thrown down so as to serve as a floor or foundation on which
gneiss and other stratified rocks might repose. Afterwards, when the
igneous origin of granite was no longer disputed, many conceived that a
thermal ocean enveloped the globe, at a time when the first-formed crust
of granite was cooling, but when it still retained much of its heat. The
hot waters of this ocean held in solution the ingredients of gneiss,
mica-schist, hornblende-schist, clay-slate, and marble, rocks which were
precipitated, one after the other, in a crystalline form. No fossils
could be inclosed in them, the high temperature of the fluid and the
quantity of mineral matter which it held in solution, rendering it unfit
for the support of organic beings.

It would be inconsistent with the plan of this work to enter here into a
detailed account of what I have elsewhere termed the _metamorphic
theory_;[256] but I may state that it is now demonstrable in some
countries that fossiliferous formations, some of them of the age of the
Silurian strata, as near Christiana in Norway, others belonging to the
Oolitic period, as around Carrara in Italy, have been converted
partially into gneiss, mica-schist, and statuary marble. The
transmutation has been effected apparently by the influence of
subterranean heat, acting under great pressure, or by chemical and
electrical causes operating in a manner not yet understood, and which
have been termed _Plutonic_ action, as expressing, in one word, all the
modifying causes which may be brought into play at great depths, and
under conditions never exemplified at the surface. To this Plutonic
action the fusion of granite itself in the bowels of the earth, as well
as the superinducement of the metamorphic texture into sedimentary
strata, must be attributed; and in accordance with these views the age
of each metamorphic formation may be said to be twofold, for we have
first to consider the period when it originated, as an aqueous deposit,
in the form of mud, sand, marl, or limestone; secondly, the date at
which it acquired a crystalline texture. The same strata, therefore,
may, according to this view, be very ancient in reference to the time of
their deposition, and very modern in regard to the period of their
assuming the metamorphic character.

_No proofs that these crystalline rocks were produced more abundantly at
remote periods_.--Several modern writers, without denying the truth of
the Plutonic or metamorphic theory, still contend that the crystalline
and non-fossiliferous formations, whether stratified or unstratified,
such as gneiss and granite, are essentially ancient as a class of rocks.
They were generated, say they, most abundantly in the primeval state of
the globe, since which time the quantity produced has been always on the
decrease, until it became very inconsiderable in the Oolitic and
Cretaceous periods, and quite evanescent before the commencement of the
tertiary epoch.

Now the justness of these views depends almost entirely on the question
whether granite, gneiss, and other rocks of the same order ever
originated at the surface, or whether, according to the opinions above
adopted, they are essentially subterranean in their origin, and
therefore entitled to the appellation of _hypogene_. If they were formed
superficially in their present state, and as copiously in the modern as
in the more ancient periods, we ought to see a greater abundance of
tertiary and secondary than of primary granite and gneiss; but if we
adopt the hypogene theory before explained, their rapid diminution in
volume among the visible rocks in the earth's crust in proportion as we
investigate the formations of newer date, is quite intelligible. If a
melted mass of matter be now cooling very slowly at the depth of several
miles beneath the crater of an active volcano, it must remain invisible
until great revolutions in the earth's crust have been brought about. So
also if stratified rocks have been subjected to Plutonic action, and
after having been baked or reduced to semi-fusion, are now cooling and
crystallizing far under ground, it will probably require the lapse of
many periods before they will be forced up to the surface and exposed to
view, even at a single point. To effect this purpose there may be need
of as great a development of subterranean movement as that which in the
Alps, Andes, and Himalaya has raised marine strata containing ammonites
to the height of 8000, 14,000, and 16,000 feet. By parity of reasoning
we can hardly expect that any hypogene rocks of the tertiary periods
will have been brought within the reach of human observation, seeing
that the emergence of such rocks must always be so long posterior to the
date of their origin, and still less can formations of this class become
generally visible until so much time has elapsed as to confer on them a
high relative antiquity. Extensive denudation must also combine with
upheaval before they can be displayed at the surface throughout wide
areas.

All geologists who reflect on subterranean movements now going on, and
the eruptions of active volcanoes, are convinced that great changes are
now continually in progress in the interior of the earth's crust far
out of sight. They must be conscious, therefore, that the
inaccessibility of the regions in which these alterations are taking
place, compels them to remain in ignorance of a great part of the
working of existing causes, so that they can only form vague conjectures
in regard to the nature of the products which volcanic heat may
elaborate under great pressure.

But when they find in mountain-chains of high antiquity, that what was
once the interior of the earth's crust has since been forced outwards
and exposed to view, they will naturally expect in the examination of
those mountainous regions, to have an opportunity of gratifying their
curiosity by obtaining a sight not only of the superficial strata of
remote eras, but also of the contemporaneous nether-formed rocks. Having
recognized, therefore, in such mountain-chains some ancient rocks of
aqueous and volcanic origin, corresponding in character to superficial
formations of modern date, they will regard any other class of ancient
rocks, such as granite and gneiss, as the _residual phenomena_ of which
they are in search. These latter rocks will not answer the expectations
previously formed of their probable nature and texture, unless they wear
a foreign and mysterious aspect, and have in some places been fused or
altered by subterranean heat; in a word, unless they differ wholly from
the fossiliferous strata deposited at the surface, or from the lava and
scoriae thrown out by volcanoes in the open air. It is the total
distinctness, therefore, of crystalline formations, such as granite,
hornblende-schist, and the rest, from every substance of which the
origin is familiar to us, that constitutes their claim to be regarded as
the effects of causes now in action in the subterranean regions. They
belong not to an order of things which has passed away; they are not the
monuments of a primeval period, bearing inscribed upon them in obsolete
characters the words and phrases of a dead language; but they teach us
that part of the living language of nature, which we cannot learn by our
daily intercourse with what passes on the habitable surface.




CHAPTER XIII.

UNIFORMITY IN THE SERIES OF PAST CHANGES IN THE ANIMATE AND INANIMATE
WORLD.


  Supposed alternate periods of repose and disorder--Observed facts in
    which this doctrine has originated--These may be explained by
    supposing a uniform and uninterrupted series of changes--Threefold
    consideration of this subject; first, in reference to the living
    creation, extinction of species, and origin of new animals and
    plants; secondly, in reference to the changes produced in the
    earth's crust by the continuance of subterranean movements in
    certain areas, and their transference after long periods to new
    areas; thirdly, in reference to the laws which govern the formation
    of fossiliferous strata, and the shifting of the areas of
    sedimentary deposition--On the combined influence of all these modes
    and causes of change in producing breaks and chasms in the chain of
    records--Concluding remarks on the identity of the ancient and
    present system of terrestrial changes.


_Origin of the doctrine of alternate periods of repose and
disorder._--It has been truly observed, that when we arrange the
fossiliferous formations in chronological order, they constitute a
broken and defective series of monuments: we pass without any
intermediate gradations, from systems of strata which are horizontal to
other systems which are highly inclined, from rocks of peculiar mineral
composition to others which have a character wholly distinct,--from one
assemblage of organic remains to another, in which frequently all the
species, and most of the genera, are different. These violations of
continuity are so common, as to constitute the rule rather than the
exception, and they have been considered by many geologists as
conclusive in favor of sudden revolutions in the inanimate and animate
world. According to the speculations of some writers, there have been in
the past history of the planet alternate periods of tranquillity and
convulsion, the former enduring for ages, and resembling that state of
things now experienced by man: the other brief, transient, and
paroxysmal, giving rise to new mountains, seas, and valleys,
annihilating one set of organic beings, and ushering in the creation of
another.

It will be the object of the present chapter to demonstrate, that these
theoretical views are not borne out by a fair interpretation of
geological monuments. It is true that in the solid framework of the
globe, we have a chronological chain of natural records, and that many
links in this chain are wanting; but a careful consideration of all the
phenomena will lead to the opinion that the series was originally
defective,--that it has been rendered still more so by time--that a
great part of what remains is inaccessible to man, and even of that
fraction which is accessible, nine-tenths are to this day unexplored.

_How the facts may be explained by assuming a uniform series of
changes._--The readiest way, perhaps, of persuading the reader that we
may dispense with great and sudden revolutions in the geological order
of events, is by showing him how a regular and uninterrupted series of
changes in the animate and inanimate world may give rise to such breaks
in the sequence, and such unconformability of stratified rocks, as are
usually thought to imply convulsions and catastrophes. It is scarcely
necessary to state, that the order of events thus assumed to occur, for
the sake of illustration, must be in harmony with all the conclusions
legitimately drawn by geologists from the structure of the earth, and
must be equally in accordance with the changes observed by man to be now
going on in the living as well as in the inorganic creation. It may be
necessary in the present state of science to supply some part of the
assumed course of nature hypothetically; but if so, this must be done
without any violation of probability, and always consistently with the
analogy of what is known both of the past and present economy of our
system. Although the discussion of so comprehensive a subject must carry
the beginner far beyond his depth, it will also, it is hoped, stimulate
his curiosity, and prepare him to read some elementary treatises on
geology with advantage, and teach him the bearing on that science of the
changes now in progress on the earth. At the same time it may enable him
the better to understand the intimate connection between the second and
third books of this work, the former of which is occupied with the
changes in the inorganic, the latter with those of the organic creation.

In pursuance, then, of the plan above proposed, I shall consider in this
chapter, first, what may be the course of fluctuation in the animate
world; secondly, the mode in which contemporaneous subterranean
movements affect the earth's crust; and, thirdly, the laws which
regulate the deposition of sediment.


UNIFORMITY OF CHANGE CONSIDERED FIRST IN REFERENCE TO THE LIVING
CREATION.

First, in regard to the vicissitudes of the living creation, all are
agreed that the sedimentary strata found in the earth's crust are
divisible into a variety of groups, more or less dissimilar in their
organic remains and mineral composition. The conclusion universally
drawn from the study and comparison of these fossiliferous groups is
this, that at successive periods distinct tribes of animals and plants
have inhabited the land and waters, and that the organic types of the
newer formations are more analogous to species now existing, than those
of more ancient rocks. If we then turn to the present state of the
animate creation, and inquire whether it has now become fixed and
stationary, we discover that, on the contrary, it is in a state of
continual flux--that there are many causes in action which tend to the
extinction of species, and which are conclusive against the doctrine of
their unlimited durability. But natural history has been successfully
cultivated for so short a period, that a few examples only of local, and
perhaps but one or two of absolute, extirpation can as yet be proved,
and these only where the interference of man has been conspicuous. It
will nevertheless appear evident, from the facts and arguments detailed
in the third book (from the thirty-seventh to the forty-second chapters,
inclusive) that man is not the only exterminating agent; and that,
independently of his intervention, the annihilation of species is
promoted by the multiplication and gradual diffusion of every animal or
plant. It will also appear, that every alteration in the physical
geography and climate of the globe cannot fail to have the same
tendency. If we proceed still farther, and inquire whether new species
are substituted from time to time for those which die out, and whether
there are certain laws appointed by the Author of Nature to regulate
such new creations, we find that the period of human observation is as
yet too short to afford data for determining so weighty a question. All
that can be done is to show that the successive introduction of new
species may be a constant part of the economy of the terrestrial system,
without our having any right to expect that we should be in possession
of direct proof of the fact. The appearance again and again of new
species may easily have escaped detection, since the numbers of known
animals and plants have augmented so rapidly within the memory of
persons now living, as to have doubled in some classes, and quadrupled
in others. It will also be remarked in the sequel (book iii. chap. 43),
that it must always be more easy if species proceeded originally from
single stocks, to prove that one which formerly abounded in a given
district has ceased to be, than that another has been called into being
for the first time. If, therefore, there be as yet only one or two
unequivocal instances of extinction, namely, those of the dodo and
solitaire (see ch. 41), it is scarcely reasonable as yet to hope that we
should be cognizant of a single instance of the first appearance of a
new species.

_Recent origin of man, and gradual approach in the tertiary fossils of
successive periods from an extinct to the recent fauna._--The geologist,
however, if required to advance some fact which may lend countenance to
the opinion that in the most modern times, that is to say, after the
greater part of the existing fauna and flora were established on the
earth, there has still been a new species superadded, may point to man
himself as furnishing the required illustration--for man must be
regarded by the geologist as a creature of yesterday, not merely in
reference to the past history of the organic world, but also in relation
to that particular state of the animate creation of which he forms a
part. The comparatively modern introduction of the human race is proved
by the absence of the remains of man and his works, not only from all
strata containing a certain proportion of fossil shells of extinct
species, but even from a large part of the newest strata, in which all
the fossil individuals are referable to species still living.

To enable the reader to appreciate the full force of this evidence, I
shall give a slight sketch of the information obtained from the newer
strata, respecting fluctuations in the animate world, in times
immediately antecedent to the appearance of man.

In tracing the series of fossiliferous formations from the more ancient
to the more modern, the first deposits in which we meet with assemblages
of organic remains, having a near analogy to the fauna of certain parts
of the globe in our own time, are those commonly called tertiary. Even
in the Eocene, or oldest subdivision of these tertiary formations, some
few of the testacea belong to existing species, although almost all of
them, and apparently all the associated vertebrata, are now extinct.
These Eocene strata are succeeded by a great number of more modern
deposits, which depart gradually in the character of their fossils from
the Eocene type, and approach more and more to that of the living
creation. In the present state of science, it is chiefly by the aid of
shells that we are enabled to arrive at these results, for of all
classes the testacea are the most generally diffused in a fossil state,
and may be called the medals principally employed by nature, in
recording the chronology of past events. In the Miocene deposits, which
are next in succession to the Eocene, we begin to find a considerable
number, although still a minority, of recent species, intermixed with
some fossils common to the preceding epoch. We then arrive at the
Pliocene strata, in which species now contemporary with man begin to
preponderate, and in the newest of which nine-tenths of the fossils
agree with species still inhabiting the neighboring sea.

In this passing from the older to the newer members of the tertiary
system we meet with many chasms, but none which separate entirely, by a
broad line of demarcation, one state of the organic world from another.
There are no signs of an abrupt termination of one fauna and flora, and
the starting into life of new and wholly distinct forms. Although we are
far from being able to demonstrate geologically an insensible transition
from the Eocene to the Miocene, or even from the latter to the recent
fauna, yet the more we enlarge and perfect our general survey, the more
nearly do we approximate to such a continuous series, and the more
gradually are we conducted from times when many of the genera and nearly
all the species were extinct, to those in which scarcely a single
species flourished which we do not know to exist at present. Dr. A.
Philippi, indeed, after an elaborate comparison of the fossil tertiary
shells of Sicily with those now living in the Mediterranean, announces
as the result of his examination that there are strata in that island,
which attest a very gradual passage from a period, when only thirteen in
a hundred of the shells were like the species now living in the sea, to
an era when the recent species had attained a proportion of ninety-five
in a hundred. There is therefore evidence, he says, in Sicily of this
revolution in the animate world having been effected "without the
intervention of any convulsion or abrupt changes, certain species having
from time to time died out, and others having been introduced, until at
length the existing fauna was elaborated."

It had often been objected that the evidence of fossil species occurring
in two consecutive formations, was confined to the testacea or
zoophytes, the characters of which are less marked and decisive than
those afforded by the vertebrate animals. But Mr. Owen has lately
insisted on the important fact, that not a few of the quadrupeds which
now inhabit our island, and among others the horse, the ass, the hog,
the smaller wild ox, the goat, the red deer, the roe, the beaver, and
many of the diminutive rodents, are the same as those which once
coexisted with the mammoth, the great northern hippopotamus, two kinds
of rhinoceros, and other mammalia long since extinct. "A part," he
observes, "and not the whole of the modern tertiary fauna has perished,
and hence we may conclude that the cause of their destruction has not
been a violent and universal catastrophe from which none could
escape."[257]

Had we discovered evidence that man had come into the earth at a period
as early as that when a large number of the fossil quadrupeds now
living, and almost all the recent species of land, freshwater, and
marine shells were in existence, we should have been compelled to
ascribe a much higher antiquity to our species, than even the boldest
speculations of the ethnologist require, for no small part of the great
physical revolution depicted on the map of Europe (Pl. 3), before
described, took place very gradually after the recent testacea abounded
almost to the exclusion of the extinct. Thus, for example, in the
deposits called the "northern drift," or the glacial formation of Europe
and North America, the fossil marine shells can easily be identified
with species either now inhabiting the neighboring sea, or living in the
seas of higher latitudes. Yet they exhibit no memorials of the human
race, or of articles fabricated by the hand of man. Some of the newest
of these strata passing by the name of "raised beaches," occur at
moderate elevations on the coast of England, Scotland, and Ireland.
Other examples are met with on a more extended scale in Scandinavia, as
at the height of 200 feet at Uddevalla in Sweden, and at twice that
elevation, near Christiana, in Norway, also at an altitude of 600 or 700
feet in places farther north. They consist of beds of sand and clay,
filling hollows in a district of granite and gneiss, and they must
closely resemble the accumulations of shelly matter now in progress at
the bottom of the Norwegian fiords. The rate at which the land is now
rising in Scandinavia, is far too irregular in different places to
afford a safe standard for estimating the minimum of time required for
the upheaval of the fundamental granite, and its marine shelly
covering, to the height of so many hundred feet; but according to the
greatest average, of five or six feet in a century, the period required
would be very considerable, and nearly the whole of it, as well as the
antecedent epoch of submergence, seems to have preceded the introduction
of man into these parts of the earth.

There are other post-tertiary formations of fluviatile origin, in the
centre of Europe, in which the absence of human remains is perhaps still
more striking, because, when formed, they must have been surrounded by
dry land. I allude to the silt or _loess_ of the basin of the Rhine,
which must have gradually filled up the great valley of that river since
the time when its waters, and the contiguous lands, were inhabited by
the existing species of freshwater and terrestrial mollusks. Showers of
ashes, thrown out by some of the last eruptions of the Eifel volcanoes,
fell during the deposition of this fluviatile silt, and were
interstratified with it. But these volcanoes became exhausted, the
valley was re-excavated through the silt, and again reduced to its
present form before the period of human history. The study, therefore,
of this shelly silt reveals to us the history of a long series of
events, which occurred after the testacea now living inhabited the land
and rivers of Europe, and the whole terminated without any signs of the
coming of man into that part of the globe.

To cite a still more remarkable example, we observe in Sicily a lofty
table-land and hills, sometimes rising to the height of 3000 feet,
capped with a limestone, in which from 70 to 85 per cent. of the fossil
testacea are specifically identical with those now inhabiting the
Mediterranean. These calcareous and other argillaceous strata of the
same age are intersected by deep valleys which have been gradually
formed by denudation, but have not varied materially in width or depth
since Sicily was first colonized by the Greeks. The limestone, moreover,
which is of so late a date in geological chronology, was quarried for
building those ancient temples of Girgenti and Syracuse, of which the
ruins carry us back to a remote era in human history. If we are lost in
conjectures when speculating on the ages required to lift up these
formations to the height of several thousand feet above the sea, how
much more remote must be the era when the same rocks were gradually
formed beneath the waters!

To conclude, it appears that, in going back from the recent to the
Eocene period, we are carried by many successive steps from the fauna
now contemporary with man to an assemblage of fossil species wholly
different from those now living. In this retrospect we have not yet
succeeded in tracing back a perfect transition from the recent to an
extinct fauna; but there are usually so many species in common to the
groups which stand next in succession as to show that there is no great
chasm, no signs of a crisis when one class of organic beings was
annihilated to give place suddenly to another. This analogy, therefore,
derived from a period of the earth's history which can best be compared
with the present state of things, and more thoroughly investigated than
any other, leads to the conclusion that the extinction and creation of
species, has been and is the result of a slow and gradual change in the
organic world.


UNIFORMITY OF CHANGE CONSIDERED, SECONDLY, IN REFERENCE TO SUBTERRANEAN
MOVEMENTS.

To pass on to another of the three topics before proposed for
discussion, the reader will find, in the account given in the second
book of the earthquakes recorded in history, that certain countries
have, from time immemorial, been rudely shaken again and again, while
others, comprising by far the largest part of the globe, have remained
to all appearance motionless. In the regions of convulsion rocks have
been rent asunder, the surface has been forced up into ridges, chasms
have opened, or the ground throughout large spaces has been permanently
lifted up above or let down below its former level. In the regions of
tranquillity some areas have remained at rest, but others have been
ascertained by a comparison of measurements, made at different periods,
to have risen by an insensible motion, as in Sweden, or to have subsided
very slowly, as in Greenland. That these same movements, whether
ascending or descending, have continued for ages in the same direction
has been established by geological evidence. Thus, we find both on the
east and west coast of Sweden, that ground which formerly constituted
the bottom of the Baltic and of the ocean has been lifted up to an
elevation of several hundred feet above high-water mark. The rise within
the historical period has not amounted to many yards, but the greater
extent of antecedent upheaval is proved by the occurrence in inland
spots, several hundred feet high, of deposits filled with fossil shells
of species now living either in the ocean or the Baltic.

To detect proofs of slow and gradual subsidence must in general be more
difficult; but the theory which accounts for the form of circular coral
reefs and lagoon islands, and which will be explained in the last
chapter of the third book, will satisfy the reader that there are spaces
on the globe, several thousand miles in circumference, throughout which
the downward movement has predominated for ages, and yet the land has
never, in a single instance, gone down suddenly for several hundred feet
at once. Yet geology demonstrates that the persistency of subterranean
movements in one direction has not been perpetual throughout all past
time. There have been great oscillations of level by which a surface of
dry land has been submerged to a depth of several thousand feet, and
then at a period long subsequent raised again and made to emerge. Nor
have the regions now motionless been always at rest; and some of those
which are at present the theatres of reiterated earthquakes have
formerly enjoyed a long continuance of tranquillity. But although
disturbances have ceased after having long prevailed, or have
recommenced after a suspension for ages, there has been no universal
disruption of the earth's crust or desolation of the surface since
times the most remote. The non-occurrence of such a general convulsion
is proved by the perfect horizontally now retained by some of the most
ancient fossiliferous strata throughout wide areas.

_Inferences derived from unconformable strata._--That the subterranean
forces have visited different parts of the globe at successive periods,
is inferred chiefly from the unconformability of strata belonging to
groups of different ages. Thus, for example, on the borders of Wales and
Shropshire we find the slaty beds of the ancient Silurian system curved
and vertical, while the beds of the overlying carboniferous shale and
sandstone are horizontal. All are agreed, that in such a case the older
set of strata had suffered great dislocation before the deposition of
the newer or carboniferous beds, and that these last have never since
been convulsed by any movements of excessive violence. But the strata of
the inferior group suffered only a local derangement, and rocks of the
same age are by no means found everywhere in a curved or vertical
position. In various parts of Europe, and particularly near Lake Wener
in the south of Sweden, and in many parts of Russia, beds of the same
Silurian system maintain the most perfect horizontality; and a similar
observation may be made respecting limestones and shales of the like
antiquity in the great lake district of Canada and the United States.
They are still as flat and horizontal as when first formed; yet since
their origin not only have most of the actual mountain-chains been
uplifted, but the very rocks of which those mountains are composed
have been formed.

It would be easy to multiply instances of similar unconformability in
formations of other ages; but a few more will suffice. The coal measures
before alluded to as horizontal on the borders of Wales are vertical in
the Mendip Hills in Somersetshire, where the overlying beds of the New
Red Sandstone are horizontal. Again, in the Wolds of Yorkshire the last
mentioned sandstone supports on its curved and inclined beds the
horizontal Chalk. The Chalk again is vertical on the flanks of the
Pyrenees, and the tertiary strata repose unconformably upon it.

_Consistency of local disturbances with general uniformity._--As almost
every country supplies illustrations of the same phenomena, they who
advocate the doctrine of alternate periods of disorder and repose may
appeal to the facts above described, as proving that every district has
been by turns convulsed by earthquakes and then respited for ages from
convulsions. But so it might with equal truth be affirmed that every
part of Europe has been visited alternately by winter and summer,
although it has always been winter and always summer in some part of the
planet, and neither of these seasons has ever reigned simultaneously
over the entire globe. They have been always shifting about from place
to place; but the vicissitudes which recur thus annually in a single
spot are never allowed to interfere with the invariable uniformity of
seasons throughout the whole planet.

So, in regard to subterranean movements, the theory of the perpetual
uniformity of the force which they exert on the earth's crust is quite
consistent with the admission of their alternate development and
suspension for indefinite periods within limited geographical areas.


UNIFORMITY OF CHANGE CONSIDERED, THIRDLY, IN REFERENCE TO SEDIMENTARY
DEPOSITION.

It now remains to speak of the laws governing the deposition of new
strata. If we survey the surface of the globe we immediately perceive
that it is divisible into areas of deposition and non-deposition, or, in
other words, at any given time there are spaces which are the
recipients, others which are not the recipients of sedimentary matter.
No new strata, for example, are thrown down on dry land, which remains
the same from year to year; whereas, in many parts of the bottom of seas
and lakes, mud, sand, and pebbles are annually spread out by rivers and
currents. There are also great masses of limestone growing in some seas,
or in mid-ocean, chiefly composed of corals and shells.

_No sediment deposited on dry land._--As to the dry land, so far from
being the receptacle of fresh accessions of matter, it is exposed almost
everywhere to waste away. Forests may be as dense and lofty as those of
Brazil, and may swarm with quadrupeds, birds, and insects, yet at the
end of ten thousand years one layer of black mould, a few inches thick,
may be the sole representative of those myriads of trees, leaves,
flowers, and fruits, those innumerable bones and skeletons of birds,
quadrupeds, and reptiles, which tenanted the fertile region. Should this
land be at length submerged, the waves of the sea may wash away in a few
hours the scanty covering of mould, and it may merely impart a darker
shade of color to the next stratum of marl, sand, or other matter newly
thrown down. So also at the bottom of the ocean where no sediment is
accumulating, sea-weed, zoophytes, fish, and even shells, may multiply
for ages and decompose, leaving no vestige of their form or substance
behind. Their decay, in water, although more slow, is as certain and
eventually as complete as in the open air. Nor can they be perpetuated
for indefinite periods in a fossil state, unless imbedded in some matrix
which is impervious to water, or which at least does not allow a free
percolation of that fluid, impregnated as it usually is, with a slight
quantity of carbonic or other acid. Such a free percolation may be
prevented either by the mineral nature of the matrix itself, or by the
superposition of an impermeable stratum: but if unimpeded, the fossil
shell or bone will be dissolved and removed, particle after particle,
and thus entirely effaced, unless petrifaction or the substitution of
mineral for organic matter happen to take place.

That there has been land as well as sea at all former geological
periods, we know from the fact, that fossil trees and terrestrial plants
are imbedded in rocks of every age. Occasionally lacustrine and
fluviatile shells, insects, or the bones of amphibious or land reptiles,
point to the same conclusion. The existence of dry land at all periods
of the past implies, as before mentioned, the partial deposition of
sediment, or its limitation to certain areas; and the next point to
which I shall call the reader's attention, is the shifting of these
areas from one region to another.

First, then, variations in the site of sedimentary deposition are
brought about independently of subterranean movements. There is always a
slight change from year to year, or from century to century. The
sediment of the Rhone, for example, thrown into the Lake of Geneva, is
now conveyed to a spot a mile and a half distant from that where it
accumulated in the tenth century, and six miles from the point where the
delta began originally to form. We may look forward to the period when
this lake will be filled up, and then the distribution of the
transported matter will be suddenly altered, for the mud and sand
brought down from the Alps will thenceforth, instead of being deposited
near Geneva, be carried nearly 200 miles southwards, where the Rhone
enters the Mediterranean.

In the deltas of large rivers, such as those of the Ganges and Indus,
the mud is first carried down for many centuries through one arm, and on
this being stopped up it is discharged by another, and may then enter
the sea at a point 50 or 100 miles distant from its first receptacle.
The direction of marine currents is also liable to be changed by various
accidents, as by the heaping up of new sand-banks, or the wearing away
of cliffs and promontories.

But, secondly, all these causes of fluctuation in the sedimentary areas
are entirely subordinate to those great upward or downward movements of
land which have been already described as prevailing over large tracts
of the globe. By such elevation or subsidence certain spaces are
gradually submerged, or made gradually to emerge:--in the one case
sedimentary deposition may be suddenly renewed after having been
suspended for ages, in the other as suddenly made to cease after having
continued for an indefinite period.

_Causes of variation in mineral character of successive sedimentary
groups._--If deposition be renewed after a long interval, the new strata
will usually differ greatly from the sedimentary rocks previously formed
in the same place, and especially if the older rocks have suffered
derangement, which implies a change in the physical geography of the
district since the previous conveyance of sediment to the same spot. It
may happen, however, that, even when the inferior group is horizontal
and conformable to the upper strata, these last may still differ
entirely in mineral character, because since the origin of the older
formation the geography of some distant country has been altered. In
that country rocks before concealed may have become exposed by
denudation; volcanoes may have burst out and covered the surface with
scoriae and lava, or new lakes may have been formed by subsidence; and
other fluctuations may have occurred, by which the materials brought
down from thence by rivers to the sea have acquired a distinct mineral
character.

It is well known that the stream of the Mississippi is charged with
sediment of a different color from that of the Arkansas and Red Rivers,
which are tinged with red mud, derived from rocks of porphyry in "the
far west." The waters of the Uruguay, says Darwin, draining a granitic
country, are clear and black, those of the Parana, red.[258] The mud
with which the Indus is loaded, says Burnes, is of a clayey hue, that of
the Chenab, on the other hand, is reddish, that of the Sutlej is more
pale.[259] The same causes which make these several rivers, sometimes
situated at no great distance the one from the other, to differ greatly
in the character of their sediment, will make the waters draining the
same country at different epochs, especially before and after great
revolutions in physical geography, to be entirely dissimilar. It is
scarcely necessary to add, that marine currents will be affected in an
analogous manner in consequence of the formation of new shoals, the
emergence of new islands, the subsidence of others, the gradual waste of
neighboring coasts, the growth of new deltas, the increase of coral
reefs, and other changes.

_Why successive sedimentary groups contain distinct fossils._--If, in
the next place, we assume, for reasons before stated, a continual
extinction of species and introduction of others into the globe, it will
then follow that the fossils of strata formed at two distant periods on
the same spot, will differ even more certainly than the mineral
composition of the same. For rocks of the same kind have sometimes been
reproduced in the same district after a long interval of time, whereas
there are no facts leading to the opinion that species which have once
died out have ever been reproduced. The submergence then of land must be
often attended by the commencement of a new class of sedimentary
deposits, characterized by a new set of fossil animals and plants, while
the reconversion of the bed of the sea into land may arrest at once and
for an indefinite time the formation of geological monuments. Should the
land again sink, strata will again be formed; but one or many entire
revolutions in animal or vegetable life may have been completed in the
interval.

_Conditions requisite for the original completeness of a fossiliferous
series._--If we infer, for reasons before explained, that fluctuations
in the animate world are brought about by the slow and successive
removal and creation of species, we shall be convinced that a rare
combination of circumstances alone can give rise to such a series of
strata as will bear testimony to a gradual passage from one state of
organic life to another. To produce such strata nothing less will be
requisite than the fortunate coincidence of the following conditions:
first, a never-failing supply of sediment in the same region throughout
a period of vast duration; secondly, the fitness of the deposit in every
part for the permanent preservation of imbedded fossils; and, thirdly, a
gradual subsidence to prevent the sea or lake from being filled up and
converted into land.

It will appear in the chapter on coral reefs,[260] that, in certain
parts of the Pacific and Indian Oceans, most of these conditions, if not
all, are complied with, and the constant growth of coral, keeping pace
with the sinking of the bottom of the sea, seems to have gone on so
slowly, for such indefinite periods, that the signs of a gradual change
in organic life might probably be detected in that quarter of the globe,
if we could explore its submarine geology. Instead of the growth of
coralline limestone, let us suppose, in some other place, the continuous
deposition of fluviatile mud and sand, such as the Ganges and
Brahmapootra have poured for thousands of years into the Bay of Bengal.
Part of this bay, although of considerable depth, might at length be
filled up before an appreciable amount of change was effected in the
fish, mollusca, and other inhabitants of the sea and neighboring land.
But, if the bottom be lowered by sinking at the same rate that it is
raised by fluviatile mud, the bay can never be turned into dry land. In
that case one new layer of matter may be superimposed upon another for a
thickness of many thousand feet, and the fossils of the inferior beds
may differ greatly from those entombed in the uppermost, yet every
intermediate gradation may be indicated in the passage from an older to
a newer assemblage of species. Granting, however, that such an unbroken
sequence of monuments may thus be elaborated in certain parts of the
sea, and that the strata happen to be all of them well adapted to
preserve the included fossils from decomposition, how many accidents
must still concur before these submarine formations will be laid open to
our investigation! The whole deposit must first be raised several
thousand feet, in order to bring into view the very foundation; and
during the process of exposure the superior beds must not be entirely
swept away by denudation.

In the first place, the chances are as three to one against the mere
emergence of the mass above the waters, because three-fourths of the
globe are covered by the ocean. But if it be upheaved and made to
constitute part of the dry land, it must also, before it can be
available for our instruction, become part of that area already surveyed
by geologists; and this area comprehends perhaps less than a tenth of
the whole earth. In this small fraction of land already explored, and
still very imperfectly known, we are required to find a set of strata,
originally of limited extent, and probably much lessened by subsequent
denudation.

Yet it is precisely because we do not encounter at every step the
evidence of such gradations from one state of the organic world to
another, that so many geologists embrace the doctrine of great and
sudden revolutions in the history of the animate world. Not content with
simply availing themselves, for the convenience of classification, of
those gaps and chasms which here and there interrupt the continuity of
the chronological series, as at present known, they deduce, from the
frequency of these breaks in the chain of records, an irregular mode of
succession in the events themselves both in the organic and inorganic
world. But, besides that some links of the chain which once existed are
now clearly lost and others concealed from view, we have good reason to
suspect that it was never complete originally. It may undoubtedly be
said, that strata have been always forming somewhere, and therefore at
every moment of past time nature has added a page to her archives; but,
in reference to this subject, it should be remembered that we can never
hope to compile a consecutive history by gathering together monuments
which were originally detached and scattered over the globe. For as the
species of organic beings contemporaneously inhabiting remote regions
are distinct, the fossils of the first of several periods which may be
preserved in any one country, as in America, for example, will have no
connection with those of a second period found in India, and will
therefore no more enable us to trace the signs of a gradual change in
the living creation, than a fragment of Chinese history will fill up a
blank in the political annals of Europe.

The absence of any deposits of importance containing recent shells in
Chili, or anywhere on the western coast of South America, naturally led
Mr. Darwin to the conclusion that "where the bed of the sea is either
stationary or rising, circumstances are far less favorable than where
the level is sinking to the accumulation of conchiferous strata of
sufficient thickness and extension to resist the average vast amount of
denudation."[261] An examination of the superficial clay, sand, and
gravel of the most modern date in Norway and Sweden, where the land is
also rising, would incline us to admit a similar proposition. Yet in
these cases there has been a supply of sediment from the waste of the
coast and the interior, especially in Patagonia and Chili. Nevertheless
wherever the bottom of the sea has been continually elevated, the total
thickness of sedimentary matter accumulating at depths suited to the
habitation of most of the species of shells can never be great, nor can
the deposits be thickly covered by superincumbent matter, so as to be
consolidated by pressure. When they are upheaved, therefore, the waves
on the beach will bear down and disperse the loose materials; whereas if
the bed of the sea subsides slowly, a mass of strata containing
abundance of such species as live at moderate depths may increase in
thickness to any amount, and may extend over a broad area, as the water
gradually encroaches on the land. If, then, at particular periods, as in
the Miocene epoch, for example, both in Europe and North America,
contemporaneous shelly deposits have originated, and have been preserved
at very distant points, it may arise from the prevalence at that period
of simultaneous subsidence throughout very wide areas. The absence in
the same quarters of the globe of strata marking the ages which
immediately succeeded, may be accounted for by supposing that the level
of the bed of the sea and the adjoining land was stationary or was
undergoing slow upheaval.

How far some of the great violations of continuity which now exist in
the chronological table of fossiliferous rocks, will hereafter be
removed or lessened, must at present be mere matter of conjecture. The
hiatus which exists in Great Britain between the fossils of the Lias and
those of the Magnesian Limestone, is supplied in Germany by the rich
fauna and flora of the Muschelkalk, Keuper, and Bunter Sandstein, which
we know to be of a date precisely intermediate; those three formations
being interposed in Germany between others which agree perfectly in
their organic remains with our Lias and Magnesian Limestone. Until
lately the fossils of the Coal-measures were separated from those of the
antecedent Silurian group by a very abrupt and decided line of
demarcation; but recent discoveries have brought to light in Devonshire,
Belgium, the Eifel, and Westphalia, the remains of a fauna of an
intervening period. This connecting link is furnished by the fossil
shells, fish, and corals of the Devonian or Old Red Sandstone group, and
some species of this newly intercalated fauna are found to be common to
it and the subjacent Silurian rocks, while other species belong to it in
common with the Coal-measures. We have also in like manner had some
success of late years in diminishing the hiatus which still separates
the Cretaceous and Eocene periods in Europe. Still we must expect, for
reasons before stated, that some such chasms will forever continue to
occur in some parts of our sedimentary series.

_Consistency of the theory of gradual change with the existence of great
breaks in the series._--To return to the general argument pursued in
this chapter, it is assumed, for reasons above explained, that a slow
change of species is in simultaneous operation everywhere throughout the
habitable surface of sea and land; whereas the fossilization of plants
and animals is confined to those areas where new strata are produced.
These areas, as we have seen, are always shifting their position; so
that the fossilizing process, by means of which the commemoration of the
particular state of the organic world, at any given time, is affected,
may be said to move about, visiting and revisiting different tracts in
succession.

To make still more clear the supposed working of this machinery, I shall
compare it to a somewhat analogous case that might be imagined to occur
in the history of human affairs. Let the mortality of the population of
a large country represent the successive extinction of species, and the
births of new individuals the introduction of new species. While these
fluctuations are gradually taking place everywhere, suppose
commissioners to be appointed to visit each province of the country in
succession, taking an exact account of the number, names, and individual
peculiarities of all the inhabitants, and leaving in each district a
register containing a record of this information. If, after the
completion of one census, another is immediately made on the same plan,
and then another, there will, at last, be a series of statistical
documents in each province. When those belonging to any one province
are arranged in chronological order, the contents of such as stand next
to each other will differ according to the length of the intervals of
time between the taking of each census. If, for example, there are sixty
provinces, and all the registers are made in a single year, and renewed
annually, the number of births and deaths will be so small, in
proportion to the whole of the inhabitants, during the interval between
the compiling of the two consecutive documents, that the individuals
described in such documents will be nearly identical; whereas, if the
survey of each of the sixty provinces occupies all the commissioners for
a whole year, so that they are unable to revisit the same place until
the expiration of sixty years, there will then be an almost entire
discordance between the persons enumerated in two consecutive registers
in the same province. There are, undoubtedly, other causes besides the
mere quantity of time, which may augment or diminish the amount of
discrepancy. Thus, at some periods a pestilential disease may have
lessened the average duration of human life, or a variety of
circumstances may have caused the births to be unusually numerous, and
the population to multiply; or, a province may be suddenly colonized by
persons migrating from surrounding districts.

These exceptions may be compared to the accelerated rate of fluctuation
in the fauna and flora of a particular region, in which the climate and
physical geography may be undergoing an extraordinary degree of
alteration.

But I must remind the reader, that the case above proposed has no
pretensions to be regarded as an exact parallel to the geological
phenomena which I desire to illustrate; for the commissioners are
supposed to visit the different provinces in rotation; whereas the
commemorating processes by which organic remains become fossilized,
although they are always shifting from one area to the other, are yet
very irregular in their movements. They may abandon and revisit many
spaces again and again before they once approach another district; and,
besides this source of irregularity, it may often happen that, while the
depositing process is suspended, denudation may take place, which may be
compared to the occasional destruction by fire or other causes of some
of the statistical documents before mentioned. It is evident that, where
such accidents occur, the want of continuity in the series may become
indefinitely great, and that the monuments which follow next in
succession will by no means be equidistant from each other in point of
time.

If this train of reasoning be admitted, the occasional distinctness of
the fossil remains, in formations immediately in contact, would be a
necessary consequence of the existing laws of sedimentary deposition and
subterranean movement, accompanied by a constant mortality and
renovation of species.

As all the conclusions above insisted on are directly opposed to
opinions still popular, I shall add another comparison, in the hope of
preventing any possible misapprehension of the argument. Suppose we had
discovered two buried cities at the foot of Vesuvius, immediately
superimposed upon each other, with a great mass of tuff and lava
intervening, just as Portici and Resina, if now covered with ashes,
would overlie Herculaneum. An antiquary might possibly be entitled to
infer, from the inscriptions on public edifices, that the inhabitants of
the inferior and older city were Greeks, and those of the modern towns
Italians. But he would reason very hastily if he also concluded from
these data that there had been a sudden change from the Greek to the
Italian language in Campania. But if he afterwards found _three_ buried
cities, one above the other, the intermediate one being Roman, while, as
in the former example, the lowest was Greek and the uppermost Italian,
he would then perceive the fallacy of his former opinion, and would
begin to suspect that the catastrophes by which the cities were inhumed
might have no relation whatever to the fluctuations in the language of
the inhabitants; and that, as the Roman tongue had evidently intervened
between the Greek and Italian, so many other dialects may have been
spoken in succession, and the passage from the Greek to the Italian may
have been very gradual; some terms growing obsolete, while others were
introduced from time to time.

If this antiquary could have shown that the volcanic paroxysms of
Vesuvius were so governed as that cities should be buried one above the
other, just as often as any variation occurred in the language of the
inhabitants, then, indeed, the abrupt passage from a Greek to a Roman,
and from a Roman to an Italian city, would afford proof of fluctuations
no less sudden in the language of the people.

So, in Geology, if we could assume that it is part of the plan of Nature
to preserve, in every region of the globe, an unbroken series of
monuments to commemorate the vicissitudes of the organic creation, we
might infer the sudden extirpation of species, and the simultaneous
introduction of others, as often as two formations in contact are found
to include dissimilar organic fossils. But we must shut our eyes to the
whole economy of the existing causes, aqueous, igneous, and organic, if
we fail to perceive _that such in not the plan of Nature_.

_Concluding remarks on the identity of the ancient and present system of
terrestrial changes._--I shall now conclude the discussion of a question
with which we have been occupied since the beginning of the fifth
chapter; namely, whether there has been any interruption, from the
remotest periods, of one uniform system of change in the animate and
inanimate world. We were induced to enter into that inquiry by
reflecting how much the progress of opinion in Geology had been
influenced by the assumption that the analogy was slight in kind, and
still more slight in degree, between the causes which produced the
former revolutions of the globe, and those now in every-day operation.
It appeared clear that the earlier geologists had not only a scanty
acquaintance with existing changes, but were singularly unconscious of
the amount of their ignorance. With the presumption naturally inspired
by this unconsciousness, they had no hesitation in deciding at once that
time could never enable the existing powers of nature to work out
changes of great magnitude, still less such important revolutions as
those which are brought to light by Geology. They, therefore, felt
themselves at liberty to indulge their imaginations in guessing at what
_might be_, rather than inquiring _what is_; in other words, they
employed themselves in conjecturing what might have been the course of
nature at a remote period, rather than in the investigation of what was
the course of nature in their own times.

It appeared to them more philosophical to speculate on the possibilities
of the past, than patiently to explore the realities of the present; and
having invented theories under the influence of such maxims, they were
consistently unwilling to test their validity by the criterion of their
accordance with the ordinary operations of nature. On the contrary, the
claims of each new hypothesis to credibility appeared enhanced by the
great contrast, in kind or intensity, of the causes referred to, and
those now in operation.

Never was there a dogma more calculated to foster indolence, and to
blunt the keen edge of curiosity, than this assumption of the
discordance between the ancient and existing causes of change. It
produced a state of mind unfavorable in the highest degree to the candid
reception of the evidence of those minute but incessant alterations
which every part of the earth's surface is undergoing, and by which the
condition of its living inhabitants is continually made to vary. The
student, instead of being encouraged with the hope of interpreting the
enigmas presented to him in the earth's structure,--instead of being
prompted to undertake laborious inquiries into the natural history of
the organic world, and the complicated effects of the igneous and
aqueous causes now in operation, was taught to despond from the first.
Geology, it was affirmed, could never rise to the rank of an exact
science,--the greater number of phenomena must forever remain
inexplicable, or only be partially elucidated by ingenious conjectures.
Even the mystery which invested the subject was said to constitute one
of its principal charms, affording, as it did, full scope to the fancy
to indulge in a boundless field of speculation.

The course directly opposed to this method of philosophizing consists in
an earnest and patient inquiry, how far geological appearances are
reconcilable with the effect of changes now in progress, or which may be
in progress in regions inaccessible to us, and of which the reality is
attested by volcanoes and subterranean movements. It also endeavors to
estimate the aggregate result of ordinary operations multiplied by time,
and cherishes a sanguine hope that the resources to be derived from
observation and experiment, or from the study of nature such as she now
is, are very far from-being exhausted. For this reason all theories are
rejected which involve the assumption of sudden and violent catastrophes
and revolutions of the whole earth, and its inhabitants,--theories which
are restrained by no reference to existing analogies, and in which a
desire is manifested to cut, rather than patiently to untie, the Gordian
knot.

We have now, at least, the advantage of knowing, from experience, that
an opposite method has always put geologists on the road that leads to
truth,--suggesting views which, although imperfect at first, have been
found capable of improvement, until at last adopted by universal
consent; while the method of speculating on a former distinct state of
things and causes, has led invariably to a multitude of contradictory
systems, which have been overthrown one after the other,--have been
found incapable of modification,--and which have often required to be
precisely reversed.

The remainder of this work will be devoted to an investigation of the
changes now going on in the crust of the earth and its inhabitants. The
importance which the student will attach to such researches will mainly
depend in the degree of confidence which he feels in the principles
above expounded. If he firmly believes in the resemblance or identity of
the ancient and present system of terrestrial changes, he will regard
every fact collected respecting the causes in diurnal action as
affording him a key to the interpretation of some mystery in the past.
Events which have occurred at the most distant periods in the animate
and inanimate world, will be acknowledged to throw light on each other,
and the deficiency of our information respecting some of the most
obscure parts of the present creation will be removed. For as, by
studying the external configuration of the existing land and its
inhabitants, we may restore in imagination the appearance of the ancient
continents which have passed away, so may we obtain from the deposits of
ancient seas and lakes an insight into the nature of the subaqueous
processes now in operation, and of many forms of organic life, which,
though now existing, are veiled from sight. Rocks, also, produced by
subterranean fire in former ages, at great depths in the bowels of the
earth, present us, when upraised by gradual movements, and exposed to
the light of heaven, with an image of those changes which the
deep-seated volcano may now occasion in the nether regions. Thus,
although we are mere sojourners on the surface of the planet, chained to
a mere point in space, enduring but for a moment of time, the human mind
is not only enabled to number worlds beyond the unassisted ken of mortal
eye, but to trace the events of indefinite ages before the creation of
our race, and is not even withheld from penetrating into the dark
secrets of the ocean, or the interior of the solid globe; free, like the
spirit which the poet described as animating the universe,


                  ----ire per omnes
  Terrasque, tractusque maris, coelumque profundum.





BOOK II.

CHANGES IN THE INORGANIC WORLD.

AQUEOUS CAUSES.




CHAPTER XIV.


  Division of the subject into changes of the organic and inorganic
    world--Inorganic causes of change divided into aqueous and
    igneous--Aqueous causes first considered--Fall of rain--Recent
    rain-prints in mud--Destroying and transporting power of running
    water--Newly formed valleys in Georgia--Sinuosities of rivers--Two
    streams when united do not occupy a bed of double
    surface--Inundations in Scotland--Floods caused by landslips in the
    White Mountains--Bursting of a lake in Switzerland--Devastations
    caused by the Anio at Tivoli--Excavations in the lavas of Etna by
    Sicilian rivers--Gorge of the Simeto--Gradual recession of the
    cataract of Niagara.


_Division of the subject._--Geology was defined to be the science which
investigates the former changes that have taken place in the organic as
well as in the inorganic kingdoms of nature. As vicissitudes in the
inorganic world are most apparent, and as on them all fluctuations in
the animate creation must in a great measure depend, they may claim our
first consideration. The great agents of change in the inorganic world
may be divided into two principal classes, the aqueous and the igneous.
To the aqueous belong Rain, Rivers, Torrents, Springs, Currents, and
Tides; to the igneous, Volcanoes, and Earthquakes. Both these classes
are instruments of decay as well as of reproduction; but they may also
be regarded as antagonist forces. For the aqueous agents are incessantly
laboring to reduce the inequalities of the earth's surface to a level;
while the igneous are equally active in restoring the unevenness of the
external crust, partly by heaping up new matter in certain localities,
and partly by depressing one portion, and forcing out another, of the
earth's envelope.

It is difficult, in a scientific arrangement, to give an accurate view
of the combined effects of so many forces in simultaneous operation;
because, when we consider them separately, we cannot easily estimate
either the extent of their efficacy, or the kind of results which they
produce. We are in danger, therefore, when we attempt to examine the
influence exerted singly by each, of overlooking the modifications which
they produce on one another; and these are so complicated, that
sometimes the igneous and aqueous forces co-operate to produce a joint
effect, to which neither of them unaided by the other could give
rise,--as when repeated earthquakes unite with running water to widen a
valley; or when a thermal spring rises up from a great depth, and
conveys the mineral ingredients with which it is impregnated from the
interior of the earth to the surface. Sometimes the organic combine with
the inorganic causes; as when a reef, composed of shells and corals,
protects one line of coast from the destroying power of tides or
currents, and turns them against some other point; or when drift timber,
floated into a lake, fills a hollow to which the stream would not have
had sufficient velocity to convey earthy sediment.

It is necessary, however, to divide our observations on these various
causes, and to classify them systematically, endeavoring as much as
possible to keep in view that the effects in nature are mixed and not
simple, as they may appear in an artificial arrangement.

In treating, in the first place, of the aqueous causes, we may consider
them under two divisions; first, those which are connected with the
circulation of water from the land to the sea, under which are included
all the phenomena of rain, rivers, glaciers, and springs; secondly,
those which arise from the movements of water in lakes, seas, and the
ocean, wherein are comprised the phenomena of waves, tides, and
currents. In turning our attention to the former division, we find that
the effects of rivers may be subdivided into, first, those of a
destroying and transporting, and, secondly, those of a renovating
nature; in the former are included the erosion of rocks and the
transportation of matter to lower levels; in the renovating class, the
formation of deltas by the influx of sediment, and the shallowing of
seas; but these processes are so intimately related to each other, that
it will not always be possible to consider them under their separate
heads.

_Fall of Rain._--It is well known that the capacity of the atmosphere to
absorb aqueous vapor, and hold it in suspension, increases with every
increment of temperature. This capacity is also found to augment in a
higher ratio than the augmentation of the heat. Hence, as was first
suggested by the geologist, Dr. Hutton, when two volumes of air, of
different temperatures, both saturated with moisture, mingle together,
clouds and rain are produced, for a mean degree of heat having resulted
from the union of the two moist airs, the excess of vapor previously
held in suspension by the warmer of the two is given out, and if it be
in sufficient abundance is precipitated in the form of rain.

As the temperature of the atmosphere diminishes gradually from the
equator towards the pole, the evaporation of water and the quantity of
rain diminish also. According to Humboldt's computation, the average
annual depth of rain at the equator is 96 inches, while in lat. 45
degrees it is only 29 inches, and in lat. 60 degrees not more than 17
inches. But there are so many disturbing causes, that the actual
discharge, in any given locality, may deviate very widely from this
rule. In England, for example, where the average fall at London is
24-1/2 inches, as ascertained at the Greenwich Observatory, there is
such irregularity in some districts, that while at Whitehaven, in
Cumberland, there fell in 1849, 32 inches, the quantity of rain in
Borrowdale, near Keswick (only 15 miles to the westward), was no less
than 142 inches![262] In like manner, in India, Colonel Sykes found by
observations made in 1847 and 1848, that at places situated between 17
degrees and 18 degrees north lat., on a line drawn across the Western
Ghauts in the Deccan, the fall of rain varied from 21 to 219
inches.[263] The annual average in Bengal is probably below 80 inches,
yet Dr. G. Hooker witnessed at Churrapoonjee, in the year 1850, a fall
of 30 inches in 24 hours, and in the same place during a residence of
six months (from June to November) 530 inches! This occurred on the
south face of the Khasia (or Garrow) mountains in Eastern Bengal (see
map, Chap. XVIII.), where the depth during the whole of the same year
probably exceeded 600 inches. So extraordinary a discharge of water,
which, as we shall presently see, is very local, may be thus accounted
for. Warm, southerly winds, blowing over the Bay of Bengal, and becoming
laden with vapor during their passage, reach the low level delta of the
Ganges and Brahmapootra, where the ordinary heat exceeds that of the
sea, and where evaporation is constantly going on from countless marshes
and the arms of the great rivers. A mingling of two masses of damp air
of different temperatures probably causes the fall of 70 or 80 inches of
rain, which takes place on the plains. The monsoon having crossed the
delta, impinges on the Khasia mountains, which rise abruptly from the
plain to a mean elevation of between 4000 and 5000 feet. Here the wind
not only encounters the cold air of the mountains, but, what is far more
effective as a refrigerating cause, the aerial current is made to flow
upwards, and to ascend to a height of several thousand feet above the
sea. Both the air and the vapor contained in it, being thus relieved of
much atmospheric pressure, expand suddenly, and are cooled by
rarefaction. The vapor is condensed, and about 500 inches of rain are
thrown down annually, nearly twenty times as much as falls in Great
Britain in a year, and almost all of it poured down in six months. The
channel of every torrent and river is swollen at this season, and much
sandstone horizontally stratified, and other rocks are reduced to sand
and gravel by the flooded streams. So great is the superficial waste (or
_denudation_), that what would otherwise be a rich and luxuriantly
wooded region, is converted into a wild and barren moorland.

After the current of warm air has been thus drained of a large portion
of its moisture, it still continues its northerly course to the opposite
flank of the Khasia range, only 20 miles farther north, and here the
fall of rain is reduced to 70 inches in the year. The same wind then
blows northwards across the valley of the Brahmapootra, and at length
arrives so dry and exhausted at the Bhootan Himalaya (lat. 28 degrees
N.), that those mountains, up to the height of 5000 feet, are naked and
sterile, and all their outer valleys arid and dusty. The aerial current
still continuing its northerly course and ascending to a higher region,
becomes further cooled, condensation again ensues, and Bhootan, above
5000 feet, is densely clothed with vegetation.[264]

In another part of India, immediately to the westward, similar phenomena
are repeated. The same warm and humid winds, copiously charged with
aqueous vapor from the Bay of Bengal, hold their course due north for
300 miles across the flat and hot plains of the Ganges, till they
encounter the lofty Sikkim mountains. (See map, Chap. XVIII.) On the
southern flank of these they discharge such a deluge of rain that the
rivers in the rainy season rise twelve feet in as many hours. Numerous
landslips, some of them extending three or four thousand feet along the
face of the mountains, composed of granite, gneiss, and slate, descend
into the beds of streams, and dam them up for a time, causing temporary
lakes, which soon burst their barriers. "Day and night," says Dr.
Hooker, "we heard the crashing of falling trees, and the sound of
boulders thrown violently against each other in the beds of torrents. By
such wear and tear rocky fragments swept down from the hills are in part
converted into sand and fine mud; and the turbid Ganges, during its
annual inundation, derives more of its sediment from this source than
from the waste of the fine clay of the alluvial plains below.[265]

On the verge of the tropics a greater quantity of rain falls annually
than at the equator. Yet parts even of the tropical latitudes are
entirely destitute of rain: Peru, for example, which owes its vegetation
solely to rivers and nightly dews. In that country easterly winds
prevail, blowing from the Pacific, and these being intercepted by the
Andes, and cooled as they rise, are made to part with all their moisture
before reaching the low region to the leeward. The desert zone of North
Africa, between lat. 15 degrees and 30 degrees N., is another instance
of a rainless region. Five or six consecutive years may pass in Upper
Egypt, Nubia, and Dongola, or in the Desert of Sahara, without rain.

From the facts above mentioned, the reader will infer that in the course
of successive geological periods there will be great variations in the
quantity of rain falling in one and the same region. At one time there
may be none whatever during the whole year; at another a fall of 100 or
500 inches; and these two last averages may occur on the two opposite
flanks of a mountain-chain, not more than 20 miles wide. While,
therefore, the valleys in one district are widened and deepened
annually, they may remain stationary in another, the superficial soil
being protected from waste by a dense covering of vegetation. This
diversity depends on many geographical circumstances, but principally on
the height of the land above the sea, the direction of the prevailing
winds, and the relative position, at the time being, of the plains,
hills, and the ocean, conditions all of which are liable in the course
of ages to undergo a complete revolution.

_Recent rain-prints._--When examining, in 1842, the extensive mud-flats
of Nova Scotia, which are exposed at low tide on the borders of the Bay
of Fundy, I observed not only the foot-prints of birds which had
recently passed over the mud, but also very distinct impressions of
rain-drops. A peculiar combination of circumstances renders these
mud-flats admirably fitted to receive and retain any markings which may
happen to be made on their surface. The sediment with which the waters
are charged is extremely fine, being derived from the destruction of
cliffs of red sandstone and shale, and as the tides rise fifty feet and
upwards, large areas are laid dry for nearly a fortnight between the
spring and neap tides. In this interval the mud is baked in summer by a
hot sun, so that it solidifies and becomes traversed by cracks, caused
by shrinkage. Portions of the hardened mud between these cracks may then
be taken up and removed without injury. On examining the edges of each
slab, we observe numerous layers, formed by successive tides, each layer
being usually very thin, sometimes only one-tenth of an inch thick. When
a shower of rain falls, the highest portion of the mud-covered flat is
usually too hard to receive any impressions; while that recently
uncovered by the tide near the water's edge is too soft. Between these
areas a zone occurs, almost as smooth and even as a looking-glass, on
which every drop forms a cavity of circular or oval form, and, if the
shower be transient, these pits retain their shape permanently, being
dried by the sun, and being then too firm to be effaced by the action of
the succeeding tide, which deposits upon them a new layer of mud. Hence
we often find, in splitting open a slab an inch or more thick, on the
upper surface of which the marks of recent rain occur, that an inferior
layer, deposited during some previous rise of the tide, exhibits on its
under side perfect casts of rain-prints, which stand out in relief, the
moulds of the same being seen on the layer below. But in some cases,
especially in the more sandy layers, the markings have been somewhat
blunted by the tide, and by several rain-prints having been joined into
one by a repetition of drops falling on the same spot; in which case the
casts present a very irregular and blistered appearance.

The finest examples which I have seen of these rain-prints were sent to
me by Dr. Webster, from Kentville, on the borders of the Bay of Mines,
in Nova Scotia. They were made by a heavy shower which fell on the 21st
of July, 1849, when the rise and fall of the tides were at their
maximum. The impressions (see fig. 13) consist of cup-shaped or
hemispherical cavities, the average size of which is from one-eighth to
one-tenth of an inch across, but the largest are fully half an inch in
diameter, and one-tenth of an inch deep. The depth is chiefly below the
general surface or plane of stratification, but the walls of the cavity
consist partly of a prominent rim of sandy mud, formed of the matter
which has been forcibly expelled from the pit. All the cavities having
an oval form are deeper at one end, where they have also a higher rim,
and all the deep ends have the same direction, showing towards which
quarter the wind was blowing. Two or more drops are sometimes seen to
have interfered with each other; in which case it is usually possible to
determine which drop fell last, its rim being unbroken.

[Illustration: Fig. 13.

Recent rain-prints, formed July 21, 1849, at Kentville, Bay of Fundy,
Nova Scotia. The arrow represents the direction of the shower.]

On some of the specimens the winding tubular tracks of worms are seen,
which have been bored just beneath the surface (see fig. 13, _left
side_). They occasionally pass under the middle of a rain-mark, having
been formed subsequently. Sometimes the worms have dived beneath the
surface, and then reappeared. All these appearances, both of rain-prints
and worm-tracks, are of great geological interest, as their exact
counterparts are seen in rocks of various ages, even in formations of
very high antiquity.[266] Small cavities, often corresponding in size to
those produced by rain, are also caused by air-bubbles rising up through
sand or mud; but these differ in character from rain-prints, being
usually deeper than they are wide, and having their sides steeper.
These, indeed, are occasionally vertical, or overarching, the opening at
the top being narrower than the pit below. In their mode, also, of
mutual interference they are unlike rain-prints.[267]

In consequence of the effects of mountains in cooling currents of moist
air, and causing the condensation of aqueous vapor in the manner above
described, it follows that in every country, as a general rule, the more
elevated regions become perpetual reservoirs of water, which descends
and irrigates the lower valleys and plains. The largest quantity of
water is first carried to the highest region, and then made to descend
by steep declivities towards the sea; so that it acquires superior
velocity, and removes more soil, than it would do if the rain had been
distributed over the plains and mountains equally in proportion to their
relative areas. The water is also made by these means to pass over the
greatest distances before it can regain the sea.

It has already been observed that in higher latitudes, where the
atmosphere being colder is capable of holding less water in suspension,
a diminished fall of rain takes place. Thus at St. Petersburg, the
amount is only 16 inches, and at Uleaborg in the Gulf of Bothnia (N.
lat. 65 degrees), only 13-1/2 inches, or less than half the average of
England, and even this small quantity descends more slowly in the
temperate zone, and is spread more equally over the year than in
tropical climates. But in reference to geological changes, frost in the
colder latitude acts as a compensating power in the disintegration of
rocks, and the transportation of stones to lower levels.

Water when converted into ice augments in bulk more than one-twentieth
of its volume, and owing to this property it widens the minute crevices
(or _joints_) of rocks into which it penetrates. Ice also in various
ways, as will be shown in the next chapter, gives buoyancy to mud and
sand, even to huge blocks of stone, enabling rivers of moderate size and
velocity to carry them to a great distance.

The mechanical force exerted by running water in undermining cliffs, and
rounding off the angles of hard rock, is mainly due to the intermixture
of foreign ingredients. Sand and pebbles, when hurried along by the
violence of the stream, are thrown against every obstacle lying in their
way, and thus a power of attrition is acquired, capable of wearing
through the hardest siliceous stones, on which water alone could make no
impression.

_Newly formed valleys._--When travelling in Georgia and Alabama, in
1846, I saw in both those States the commencement of hundreds of valleys
in places where the native forest had recently been removed. One of
these newly formed gulleys or ravines is represented in the annexed
woodcut (fig. 14), from a drawing which I made on the spot. It occurs
three miles and a half due west of Milledgeville, the capital of
Georgia, and is situated on the farm of Pomona, on the direct road to
Macon.[268]

Twenty years ago, before the land was cleared, it had no existence; but
when the trees of the forest were cut down, cracks three feet deep were
caused by the sun's heat in the clay; and, during the rains, a sudden
rush of water through the principal crack deepened it at its lower
extremity, from whence the excavating power worked backwards, till, in
the course of twenty years, a chasm, measuring no less than 55 feet in
depth, 300 yards in length, and varying in width from 20 to 180 feet,
was the result. The high road has been several times turned to avoid
this cavity, the enlargement of which is still proceeding, and the old
line of road may be seen to have held its course directly over what is
now the wildest part of the ravine. In the perpendicular walls of this
great chasm appear beds of clay and sand, red, white, yellow, and
green, produced by the decomposition in situ of hornblendic gneiss,
with layers and veins of quartz, which remain entire, to prove that the
whole mass was once solid and crystalline.

[Illustration: Fig. 14.

Ravine on the farm of Pomona, near Milledgeville, Georgia, as it
appeared January, 1846.

Excavated in twenty years, 55 feet deep, and 180 feet broad.]

I infer, from the rapidity of the denudation which only began here after
the removal of the native wood, that this spot, elevated about 600 feet
above the sea, has been always covered with a dense forest, from the
remote time when it first emerged from the sea. The termination of the
cavity on the right hand in the foreground is the head or upper end of
the ravine, and in almost every case, such gulleys are lengthened by the
streams cutting their way backwards. The depth at the upper end is
often, as in this case, considerable, and there is usually at this
point, during floods, a small cascade.

_Sinuosities of rivers._--In proportion as such valleys are widened,
sinuosities are caused by the deflection of the stream first to one
side and then to the other. The unequal hardness of the materials
through which the channel is eroded tends partly to give new directions
to the lateral force of excavation. When by these, or by accidental
shiftings of the alluvial matter in the channel, the current is made to
cross its general line of descent, it eats out a curve in the opposite
bank, or in the side of the hills bounding the valley, from which curve
it is turned back again at an equal angle, so that it recrosses the line
of descent, and gradually hollows out another curve lower down in the
opposite bank, till the whole sides of the valley, or river bed, present
a succession of salient and retiring angles. Among the causes of
deviation from a straight course, by which torrents and rivers tend in
mountainous regions to widen the valleys through which they flow, may be
mentioned the confluence of lateral torrents, swollen irregularly at
different seasons by partial storms, and discharging at different times
unequal quantities of sand, mud, and pebbles, into the main channel.

[Illustration: Fig. 15.]

When the tortuous flexures of a river are extremely great, as often
happens in alluvial plains, the aberration from the direct line of
descent may be restored by the river cutting through the isthmus which
separates two neighboring curves. Thus in the annexed diagram, the
extreme sinuosity of the river has caused it to return for a brief space
in a contrary direction to its main course, so that a peninsula is
formed, and the isthmus (at _a_) is consumed on both sides by currents
flowing in opposite directions. In this case an island is soon
formed,--on either side of which a portion of the stream usually
remains.

_Transporting power of water._--In regard to the transporting power of
water, we may often be surprised at the facility with which streams of a
small size, and descending a slight declivity, bear along coarse sand
and gravel; for we usually estimate the weight of rocks in air, and do
not reflect on their comparative buoyancy when submerged in a denser
fluid. The specific gravity of many rocks is not more than twice that of
water, and very rarely more than thrice, so that almost all the
fragments propelled by a stream have lost a third, and many of them a
half, of what we usually term their weight.

It has been proved by experiment, in contradiction to the theories of
the earlier writers on hydrostatics, to be a universal law, regulating
the motion of running water, that the velocity at the bottom of the
stream is everywhere less than in any part above it, and is greatest at
the surface. Also that the superficial particles in the middle of the
stream move swifter than those at the sides. This retardation of the
lowest and lateral currents is produced by friction; and when the
velocity is sufficiently great, the soil composing the sides and bottom
gives way. A velocity of three inches per second at the bottom is
ascertained to be sufficient to tear up fine clay,--six inches per
second, fine sand,--twelve inches per second, fine gravel,--and three
feet per second, stones of the size of an egg.[269]

When this mechanical power of running water is considered, we are
prepared for the transportation before alluded to of large quantities of
gravel, sand, and mud, by torrents which descend from mountainous
regions. But a question naturally arises, How the more tranquil rivers
of the valleys and plains, flowing on comparatively level ground, can
remove the prodigious burden which is discharged into them by their
numerous tributaries, and by what means they are enabled to convey the
whole mass to the sea? If they had not this removing power, their
channels would be annually choked up, and the valleys of the lower
country, and plains at the base of mountain-chains, would be continually
strewed over with fragments of rock and sterile sand. But this evil is
prevented by a general law regulating the conduct of running
water,--that two equal streams do not, when united, occupy a bed of
double surface. Nay, the width of the principal river, after the
junction of a tributary, sometimes remains the same as before, or is
even lessened. The cause of this apparent paradox was long ago explained
by the Italian writers, who had studied the confluence of the Po and its
feeders in the plains of Lombardy.

The addition of a smaller river augments the velocity of the main
stream, often in the same proportion as it does the quantity of water.
Thus the Venetian branch of the Po swallowed up the Ferranese branch and
that of Panaro without any enlargement of its own dimensions. The cause
of the greater velocity is, first, that after the union of two rivers
the water, in place of the friction of four shores, has only that of two
to surmount; 2dly, because the main body of the stream being farther
distant from the banks, flows on with less interruption; and lastly,
because a greater quantity of water moving more swiftly, digs deeper
into the river's bed. By this beautiful adjustment, the water which
drains the interior country is made continually to occupy less room as
it approaches the sea; and thus the most valuable part of our
continents, the rich deltas and great alluvial plains, are prevented
from being constantly under water.

_River floods in Scotland_, 1829.--Many remarkable illustrations of the
power of running water in moving stones and heavy materials were
afforded by the storm and floods which occurred on the 3d and 4th of
August, 1829, in Aberdeenshire and other counties in Scotland. The
elements during this storm assumed all the characters which mark the
tropical hurricanes; the wind blowing in sudden gusts and whirlwinds,
the lightning and thunder being such as is rarely witnessed in our
climate, and heavy rain falling without intermission. The floods
extended almost simultaneously, and with equal violence over that part
of the northeast of Scotland which would be cut off by two lines drawn
from the head of Lochrannoch, one towards Inverness and the other to
Stonehaven. The united line of the different rivers which were flooded,
could not be less than from five to six hundred miles in length; and the
whole of their courses were marked by the destruction of bridges, roads,
crops, and buildings. Sir T. D. Lauder has recorded the destruction of
thirty-eight bridges, and the entire obliteration of a great number of
farms and hamlets. On the Nairn, a fragment of sandstone, fourteen feet
long by three feet wide and one foot thick, was carried above 200 yards
down the river. Some new ravines were formed on the sides of mountains
where no streams had previously flowed, and ancient river-channels,
which had never been filled from time immemorial, gave passage to a
copious flood.[270]

The bridge over the Dee at Ballater consisted of five arches, having
upon the whole a water-way of 260 feet. The bed of the river, on which
the piers rested, was composed of rolled pieces of granite and gneiss.
The bridge was built of granite, and had stood uninjured for twenty
years; but the different parts were swept away in succession by the
flood, and the whole mass of masonry disappeared in the bed of the
river. "The river Don," observes Mr. Farquharson, in his account of the
inundations, "has upon my own premises forced a mass of four or five
hundred tons of stones, many of them two or three hundred pounds'
weight, up an inclined plane, rising six feet in eight or ten yards, and
left them in a rectangular heap, about three feet deep on a flat
ground:--the heap ends abruptly at its lower extremity."[271]

The power even of a small rivulet, when swollen by rain, in removing
heavy bodies, was exemplified in August, 1827, in the College, a small
stream which flows at a slight declivity from the eastern watershed of
the Cheviot Hills. Several thousand tons' weight of gravel and sand were
transported to the plain of the Till, and a bridge, then in progress of
building, was carried away, some of the arch-stones of which, weighing
from half to three quarters of a ton each, were propelled two miles down
the rivulet. On the same occasion, the current tore away from the
abutment of a mill-dam a large block of greenstone-porphyry, weighing
nearly two tons, and transported it to the distance of a quarter of a
mile. Instances are related as occurring repeatedly, in which from one
to three thousand tons of gravel are, in like manner, removed by this
streamlet to still greater distances in one day.[272]

_Floods caused by landslips_, 1826.--The power which running water may
exert in the lapse of ages, in widening and deepening a valley, does not
so much depend on the volume and velocity of the stream usually flowing
in it, as on the number and magnitude of the obstructions which have, at
different periods, opposed its free passage. If a torrent, however
small, be effectually dammed up, the size of the valley above the
barrier, and its declivity below, and not the dimensions of the torrent,
will determine the violence of the dabacle. The most universal source of
local deluges, are landslips, slides, or avalanches, as they are
sometimes called, when great masses of rock and soil, or sometimes ice
and snow, are precipitated into the bed of a river, the boundary cliffs
of which have been thrown down by the shock of an earthquake, or
undermined by springs or other causes. Volumes might be filled with the
enumeration of instances on record of these terrific catastrophes; I
shall therefore select a few examples of recent occurrence, the facts of
which are well authenticated.

Two dry seasons in the White Mountains, in New Hampshire (United
States), were followed by heavy rains on the 28th August, 1826, when
from the steep and lofty declivities which rise abruptly on both sides
of the river Saco, innumerable rocks and stones, many of sufficient size
to fill a common apartment, were detached, and in their descent swept
down before them, in one promiscuous and frightful ruin, forests,
shrubs, and the earth which sustained them. Although there are numerous
indications on the steep sides of these hills of former slides of the
same kind, yet no tradition had been handed down of any similar
catastrophe within the memory of man, and the growth of the forest on
the very spots now devastated, clearly showed that for a long interval
nothing similar had occurred. One of these moving masses was afterwards
found to have slid three miles, with an average breadth of a quarter of
a mile. The natural excavations commenced generally in a trench a few
yards in depth and a few rods in width, and descended the mountains,
widening and deepening till they became vast chasms. At the base of
these hollow ravines was seen a confused mass of ruins, consisting of
transported earth, gravel, rocks, and trees. Forests of spruce-fir and
hemlock, a kind of fir somewhat resembling our yew in foliage, were
prostrated with as much ease as if they had been fields of grain; for,
where they disputed the ground, the torrent of mud and rock accumulated
behind, till it gathered sufficient force to burst the temporary
barrier.

The valleys of the Amonoosuck and Saco presented, for many miles, an
uninterrupted scene of desolation; all the bridges being carried away,
as well as those over their tributary streams. In some places, the road
was excavated to the depth of from fifteen to twenty feet; in others, it
was covered with earth, rocks, and trees, to as great a height. The
water flowed for many weeks after the flood, as densely charged with
earth as it could be without being changed into mud, and marks were seen
in various localities of its having risen on either side of the valley
to more than twenty-five feet above its ordinary level. Many sheep and
cattle were swept away, and the Willey family, nine in number, who in
alarm had deserted their house, were destroyed on the banks of the Saco;
seven of their mangled bodies were afterwards found near the river,
buried beneath drift-wood and mountain ruins.[273] Eleven years after
the event, the deep channels worn by the avalanches of mud and stone,
and the immense heaps of boulders and blocks of granite in the river
channel, still formed, says Professor Hubbard, a picturesque feature in
the scenery.[274]

When I visited the country in 1845, eight years after Professor Hubbard,
I found the signs of devastation still very striking; I also
particularly remarked that although the surface of the bare granitic
rocks had been smoothed by the passage over them of so much mud and
stone, there were no continuous parallel and rectilinear furrows, nor
any of the fine scratches or striae which characterize _glacial_ action.
The absence of these is nowhere more clearly exemplified than in the
bare rocks over which passed the great "Willey slide" of 1826.[275]

But the catastrophes in the White Mountains are insignificant, when
compared to those which are occasioned by earthquakes, when the boundary
hills, for miles in length, are thrown down into the hollow of a valley.
I shall have opportunities of alluding to inundations of this kind, when
treating expressly of earthquakes, and shall content myself at present
with selecting an example of a flood due to a different cause.

_Flood in the valley of Bagnes_, 1818.--The valley of Bagnes is one of
the largest of the lateral embranchments of the main valley of the
Rhone, above the Lake of Geneva. Its upper portion was, in 1818,
converted into a lake by the damming up of a narrow pass, by avalanches
of snow and ice, precipitated from an elevated glacier into the bed of
the river Dranse. In the winter season, during continued frost, scarcely
any water flows in the bed of this river to preserve an open channel, so
that the ice barrier remained entire until the melting of the snows in
spring, when a lake was formed above, about half a league in length,
which finally attained in some parts a depth of about two hundred feet,
and a width of about seven hundred feet. To prevent or lessen the
mischief apprehended from the sudden bursting of the barrier, an
artificial gallery, seven hundred feet in length, was cut through the
ice, before the waters had risen to a great height. When at length they
accumulated and flowed through this tunnel, they dissolved the ice, and
thus deepened their channel, until nearly half of the whole contents of
the lake were slowly drained off. But at length, on the approach of the
hot season, the central portion of the remaining mass of ice gave way
with a tremendous crash, and the residue of the lake was emptied in half
an hour. In the course of its descent, the waters encountered several
narrow gorges, and at each of these they rose to a great height, and
then burst with new violence into the next basin, sweeping along rocks,
forests, houses, bridges, and cultivated land. For the greater part of
its course the flood resembled a moving mass of rock and mud, rather
than of water. Some fragments of granitic rocks, of enormous magnitude,
and which from their dimensions, might be compared without exaggeration
to houses, were torn out of a more ancient alluvion, and borne down for
a quarter of a mile. One of the fragments moved was sixty paces in
circumference.[276] The velocity of the water, in the first part of its
course, was thirty-three feet per second, which diminished to six feet
before it reached the Lake of Geneva, where it arrived in six hours and
a half, the distance being forty-five miles.[277]

This flood left behind it, on the plains of Martigny, thousands of trees
torn up by the roots, together with the ruins of buildings. Some of the
houses in that town were filled with mud up to the second story. After
expanding in the plain of Martigny, it entered the Rhone, and did no
farther damage; but some bodies of men, who had been drowned above
Martigny, were afterwards found, at the distance of about thirty miles,
floating on the farther side of the Lake of Geneva, near Vevay.

The waters, on escaping from the temporary lake, intermixed with mud and
rock, swept along, for the first four miles, at the rate of above twenty
miles an hour; and M. Escher, the engineer, calculated that the flood
furnished 300,000 cubic feet of water every second--an efflux which is
five times greater than that of the Rhine below Basle. Now, if part of
the lake had not been gradually drained off, the flood would have been
nearly double, approaching in volume to some of the largest rivers in
Europe. It is evident, therefore, that when we are speculating on the
excavating force which a river may have exerted in any particular
valley, the most important question is, not the volume of the existing
stream, nor the present levels of its channel, nor even the nature of
the rocks, but the probability of a succession of floods at some period
since the time when the valley may have been first elevated above the
sea.

For several months after the dabacle of 1818, the Dranse, having no
settled channel, shifted its position continually from one side to the
other of the valley, carrying away newly-erected bridges, undermining
houses, and continuing to be charged with as large a quantity of earthy
matter as the fluid could hold in suspension. I visited this valley four
months after the flood, and was witness to the sweeping away of a
bridge, and the undermining of part of a house. The greater part of the
ice-barrier was then standing, presenting vertical cliffs 150 feet high,
like ravines in the lava-currents of Etna or Auvergne, where they are
intersected by rivers.

Inundations, precisely similar, are recorded to have occurred at former
periods in this district, and from the same cause. In 1595, for example,
a lake burst, and the waters, descending with irresistible fury,
destroyed the town of Martigny, where from sixty to eighty persons
perished. In a similar flood, fifty years before, 140 persons were
drowned.

_Flood at Tivoli_, 1826.--I shall conclude with one more example derived
from a land of classic recollections, the ancient Tibur, and which,
like all the other inundations above alluded to, occurred within the
present century. The younger Pliny, it will be remembered, describes a
flood on the Anio, which destroyed woods, rocks, and houses, with the
most sumptuous villas and works of arts.[278] For four or five centuries
consecutively, this "headlong stream," as Horace truly called it, has
often remained within its bounds, and then, after so long an interval of
rest, has at different periods inundated its banks again, and widened
its channel. The last of these catastrophes happened 15th Nov. 1826,
after heavy rains, such as produced the floods before alluded to in
Scotland. The waters appear also to have been impeded by an artificial
dike, by which they were separated into two parts, a short distance
above Tivoli. They broke through this dike; and leaving the left trench
dry, precipitated themselves, with their whole weight, on the right
side. Here they undermined, in the course of a few hours, a high cliff,
and widened the river's channel about fifteen paces. On this height
stood the church of St. Lucia, and about thirty-six houses of the town
of Tivoli, which were all carried away, presenting as they sank into the
roaring flood, a terrific scene of destruction to the spectators on the
opposite bank. As the foundations were gradually removed, each building,
some of them edifices of considerable height, was first traversed with
numerous rents, which soon widened into large fissures, until at length
the roofs fell in with a crash, and then the walls sunk into the river,
and were hurled down the cataract below.[279]

The destroying agency of the flood came within two hundred yards of the
precipice on which the beautiful temple of Vesta stands; but fortunately
this precious relic of antiquity was spared, while the wreck of modern
structures was hurled down the abyss. Vesta, it will be remembered, in
the heathen mythology, personified the stability of the earth; and when
the Samian astronomer, Aristarchus, first taught that the earth revolved
on its axis, and round the sun, he was publicly accused of impiety, "for
removing the everlasting Vesta from her place." Playfair observed, that
when Hutton ascribed instability to the earth's surface, and represented
the continents which we inhabit as the theatre of incessant change and
movement, his antagonists, who regarded them as unalterable, assailed
him in a similar manner with accusations founded on religious
prejudices.[280] We might appeal to the excavating power of the Anio as
corroborative of one of the most controverted parts of the Huttonian
theory; and if the days of omens had not gone by, the geologists who now
worship Vesta might regard the late catastrophe as portentous. We may,
at least, recommend the modern votaries of the goddess to lose no time
in making a pilgrimage to her shrine, for the next flood may not respect
the temple.

_Excavation of rocks by running water._--The rapidity with which even
the smallest streams hollow out deep channels in soft and destructible
soils is remarkably exemplified in volcanic countries, where the sand
and half-consolidated tuffs opposed but a slight resistance to the
torrents which descend the mountain-side. After the heavy rains which
followed the eruption of Vesuvius in 1824, the water flowing from the
Atrio del Cavallo cut, in three days, a new chasm through strata of tuff
and ejected volcanic matter, to the depth of twenty-five feet. I found
the old mule-road, in 1828, intersected by this new ravine.

The gradual erosion of deep chasms through some of the hardest rocks, by
the constant passage of running water, charged with foreign matter, is
another phenomenon of which striking examples may be adduced.
Illustrations of this excavating power are presented by many valleys in
central France where the channels of rivers have been barred up by solid
currents of lava, through which the streams have re-excavated a passage,
to the depth of from twenty to seventy feet and upwards, and often of
great width. In these cases there are decisive proofs that neither the
sea, nor any denuding wave or extraordinary body of water, has passed
over the spot since the melted lava was consolidated. Every hypothesis
of the intervention of sudden and violent agency is entirely excluded,
because the cones of _loose_ scoriae, out of which the lavas flowed, are
oftentimes at no great elevation above the rivers, and have remained
undisturbed during the whole period which has been sufficient for the
hollowing out of such enormous ravines.

_Recent excavation by the Simeto._--But I shall at present confine
myself to examples derived from events which have happened since the
time of history.

[Illustration: Fig. 16.

Recent excavation of lava at the foot of Etna by the river Simeto.]

At the western base of Etna, a current of lava (A A, fig. 16),
descending from near the summit of the great volcano, has flowed to the
distance of five or six miles, and then reached the alluvial plain of
the Simeto, the largest of the Sicilian rivers, which skirts the base of
Etna, and falls into the sea a few miles south of Catania. The lava
entered the river about three miles above the town of Aderno, and not
only occupied its channel for some distance, but, crossing to the
opposite side of the valley, accumulated there in a rocky mass.
Gemmellaro gives the year 1603 as the date of the eruption.[281] The
appearance of the current clearly proves, that it is one of the most
modern of those of Etna; for it has not been covered or crossed by
subsequent streams or ejections, and the olives which had been planted
on its surface were all of small size, when I examined the spot in 1828,
yet they were older than the natural wood on the same lava. In the
course, therefore, of about two centuries, the Simeto has eroded a
passage from fifty to several hundred feet wide, and in some parts from
forty to fifty feet deep.

The portion of lava cut through is in no part porous or scoriaceous, but
consists of a compact homogeneous mass of hard blue rock, somewhat
inferior in weight to ordinary basalt, and containing crystals of
olivine and glassy felspar. The general declivity of this part of the
bed of the Simeto is not considerable; but, in consequence of the
unequal waste of the lava, two water-falls occur at Passo Manzanelli,
each about six feet in height. Here the chasm (B, fig. 16) is about
forty feet deep, and only fifty broad.

The sand and pebbles in the river-bed consist chiefly of a brown
quartzose sandstone, derived from the upper country; but the materials
of the volcanic rock itself must have greatly assisted the attrition.
This river, like the Caltabiano on the eastern side of Etna, has not yet
cut down to the ancient bed of which it was dispossessed, and of which
the probable position is indicated in the annexed diagram (C, fig. 16).

On entering the narrow ravine where the water foams down the two
cataracts, we are entirely shut out from all view of the surrounding
country; and a geologist who is accustomed to associate the
characteristic features of the landscape with the relative age of
certain rocks, can scarcely dissuade himself from the belief that he is
contemplating a scene in some rocky gorge of a primary district. The
external forms of the hard blue lava are as massive as any of the most
ancient trap-rocks of Scotland. The solid surface is in some parts
smoothed and almost polished by attrition, and covered in others with a
white lichen, which imparts to it an air of extreme antiquity, so as
greatly to heighten the delusion. But the moment we reascend the cliff
the spell is broken; for we scarcely recede a few paces, before the
ravine and river disappear, and we stand on the black and rugged surface
of a vast current of lava, which seems unbroken, and which we can trace
up nearly to the distant summit of that majestic cone which Pindar
called "the pillar of heaven," and which still continues to send forth a
fleecy wreath of vapor, reminding us that its fires are not extinct, and
that it may again give out a rocky stream, wherein other scenes like
that now described may present themselves to future observers.

[Illustration: Fig. 17. Lake Erie. The Falls.

Limestone Shale.

Lewiston. Niagara River. Queenstown.]

_Falls of Niagara._--The falls of Niagara afford a magnificent example
of the progressive excavation of a deep valley in solid rock. That river
flows over a flat table-land, in a depression of which Lake Erie is
situated. Where it issues from the lake, it is nearly a mile in width,
and 330 feet above Lake Ontario, which is about 30 miles distant. For
the first fifteen miles below Lake Erie the surrounding country,
comprising Upper Canada on the west, and the state of New York on the
east, is almost on a level with its banks, and nowhere more than thirty
or forty feet above them.[282] (See fig. 17.) The river being
occasionally interspersed with low wooded islands, and having sometimes
a width of three miles, glides along at first with a clear, smooth, and
tranquil current, falling only fifteen feet in as many miles, and in
this part of its course resembling an arm of Lake Erie. But its
character is afterwards entirely changed, on approaching the Rapids,
where it begins to rush and foam over a rocky and uneven limestone
bottom, for the space of nearly a mile, till at length it is thrown down
perpendicularly 165 feet at the Falls. Here the river is divided into
two sheets of water by an island, the largest cataract being more than a
third of a mile broad, the smaller one having a breadth of six hundred
feet. When the water has precipitated itself into an unfathomable pool,
it rushes with great velocity down the sloping bottom of a narrow chasm,
for a distance of seven miles. This ravine varies from 200 to 400 yards
in width from cliff to cliff; contrasting, therefore, strongly in its
breadth with that of the river above. Its depth is from 200 to 300 feet,
and it intersects for about seven miles the table-land before described,
which terminates suddenly at Queenstown in an escarpment or long line of
inland cliff facing northwards, towards Lake Ontario. The Niagara, on
reaching the escarpment and issuing from the gorge, enters the flat
country, which is so nearly on a level with Lake Ontario, that there is
only a fall of about four feet in the seven additional miles which
intervene between Queenstown and the shores of that lake.

It has long been the popular belief that the Niagara once flowed in a
shallow valley across the whole platform, from the present site of the
Falls to the escarpment (called the Queenstown heights), where it is
supposed that the cataract was first situated, and that the river has
been slowly eating its way backwards through the rocks for the distance
of seven miles. This hypothesis naturally suggests itself to every
observer, who sees the narrowness of the gorge at its termination, and
throughout its whole course, as far up as the Falls, above which point
the river expands as before stated. The boundary cliffs of the ravine
are usually perpendicular, and in many places undermined on one side by
the impetuous stream. The uppermost rock of the table-land at the Falls
consists of hard limestone (a member of the Silurian series), about
ninety feet thick, beneath which lie soft shales of equal thickness,
continually undermined by the action of the spray, which rises from the
pool into which so large a body of water is projected, and is driven
violently by gusts of wind against the base of the precipice. In
consequence of this action, and that of frost, the shale disintegrates
and crumbles away, and portions of the incumbent rock overhang 40 feet,
and often when unsupported tumble down, so that the Falls do not remain
absolutely stationary at the same spot, even for half a century.
Accounts have come down to us, from the earliest period of observation,
of the frequent destruction of these rocks, and the sudden descent of
huge fragments in 1818 and 1828, are said to have shaken the adjacent
country like an earthquake. The earliest travellers, Hennepin and Kalm,
who in 1678 and 1751 visited the Falls, and published views of them,
attest the fact, that the rocks have been suffering from dilapidation
for more than a century and a half, and that some slight changes, even
in the scenery of the cataract have been brought about within that time.
The idea, therefore, of perpetual and progressive waste is constantly
present to the mind of every beholder; and as that part of the chasm,
which has been the work of the last hundred and fifty years resembles
precisely, in depth, width, and character, the rest of the gorge which
extends seven miles below, it is most natural to infer, that the entire
ravine has been hollowed out in the same manner, by the recession of the
cataract.

It must at least be conceded, that the river supplies an adequate cause
for executing the whole task thus assigned to it, provided we grant
sufficient time for its completion. As this part of the country was a
wilderness till near the end of the last century, we can obtain no
accurate data for estimating the exact rate at which the cataract has
been receding. Mr. Bakewell, son of the eminent geologist of that name,
who visited the Niagara in 1829, made the first attempt to calculate
from the observations of one who had lived forty years at the Falls, and
who had been the first settler there, that the cataract had during that
period gone back about a yard annually. But after the most careful
inquiries which I was able to make, during my visit to the spot in
1841-2, I came to the conclusion that the average of one foot a year
would be a much more probable conjecture. In that case, it would have
required thirty-five thousand years for the retreat of the Falls, from
the escarpment of Queenstown to their present site. It seems by no means
improbable that such a result would be no exaggeration of the truth,
although we cannot assume that the retrograde movement has been uniform.
An examination of the geological structure of the district, as laid open
in the ravine, shows that at every step in the process of excavation,
the height of the precipice, the hardness of the materials at its base,
and the quantity of fallen matter to be removed, must have varied. At
some points it may have receded much faster than at present, but in
general its progress was probably slower, because the cataract, when it
began to recede, must have had nearly twice its present height.

From observations made by me in 1841, when I had the advantage of being
accompanied by Mr. Hall, state geologist of New York, and in 1842, when
I re-examined the Niagara district, I obtained geological evidence of
the former existence of an old river-bed, which, I have no doubt,
indicates the original channel through which the waters once flowed from
the Falls to Queenstown, at the height of nearly three hundred feet
above the bottom of the present gorge. The geological monuments alluded
to, consist of patches of sand and gravel, forty feet thick, containing
fluviatile shells of the genera Unio, Cyclas, Melania, &c., such as now
inhabit the waters of the Niagara above the Falls. The identity of the
fossil species with the recent is unquestionable, and these freshwater
deposits occur at the edge of the cliffs bounding the ravine, so that
they prove the former extension of an elevated shallow valley, four
miles below the falls, a distinct prolongation of that now occupied by
the Niagara, in the elevated region intervening between Lake Erie and
the Falls. Whatever theory be framed for the hollowing out of the ravine
further down, or for the three miles which intervene between the
whirlpool and Queenstown, it will always be necessary to suppose the
former existence of a barrier of _rock_, not of loose and destructible
materials, such as those composing the drift in this district, somewhere
immediately below the whirlpool. By that barrier the waters were held
back for ages, when the fluviatile deposit, 40 feet in thickness, and
250 feet above the present channel of the river, originated. If we are
led by this evidence to admit that the cataract has cut back its way for
four miles, we can have little hesitation in referring the excavation of
the remaining three miles below to a like agency, the shape of the chasm
being precisely similar.

There have been many speculations respecting the future recession of the
Falls, and the deluge that might be occasioned by the sudden escape of
the waters of Lake Erie, if the ravine should ever be prolonged 16 miles
backwards. But a more accurate knowledge of the geological succession of
the rocks, brought to light by the State Survey, has satisfied every
geologist that the Falls would diminish gradually in height before they
travelled back two miles, and in consequence of a gentle dip of the
strata to the south, the massive limestone now at the top would then be
at their base, and would retard, and perhaps put an effectual stop to,
the excavating process.




CHAPTER XV.

TRANSPORTATION OF SOLID MATTER BY ICE.


  Carrying power of river-ice--Rocks annually conveyed into the St.
    Lawrence by its tributaries--Ground-ice; its origin and transporting
    power--Glaciers--Theory of their downward movement--Smoothed and
    grooved rocks--The moraine unstratified--Icebergs covered with mud
    and stones--Limits of glaciers and icebergs--Their effects on the
    bottom when they run aground--Packing of coast-ice--Boulders drifted
    by ice on coast of Labrador--Blocks moved by ice in the Baltic.


The power of running water to carry sand, gravel, and fragments of rock
to considerable distances is greatly augmented in those regions where,
during some part of the year, the frost is of sufficient intensity to
convert the water, either at the surface or bottom of rivers, into ice.

This subject may be considered under three different heads:--first, the
effect of surface-ice and ground-ice in enabling streams to remove
gravel and stones to a distance; secondly, the action of glaciers in the
transport of boulders, and in the polishing and scratching of rocks;
thirdly, the floating off of glaciers charged with solid matter into the
sea, and the drifting of icebergs and coast-ice.

_River-ice._--Pebbles and small pieces of rock may be seen entangled in
ice, and floating annually down the Tay in Scotland, as far as the mouth
of that river. Similar observations might doubtless be made respecting
almost all the larger rivers of England and Scotland; but there seems
reason to suspect that the principal transfer from place to place of
pebbles and stones adhering to ice goes on unseen by us under water. For
although the specific gravity of the compound mass may cause it to sink,
it may still be very buoyant, and easily borne along by a feeble
current. The ice, moreover, melts very slowly at the bottom of running
streams in winter, as the water there is often nearly at the freezing
point, as will be seen from what will be said in the sequel of
ground-ice.

As we traverse Europe in the latitudes of Great Britain, we find the
winters more severe, and the rivers more regularly frozen over. M.
Lariviere relates that, being at Memel on the Baltic in 1821, when the
ice of the river Niemen broke up, he saw a mass of ice thirty feet long
which had descended the stream, and had been thrown ashore. In the
middle of it was a triangular piece of granite, about a yard in
diameter, resembling in composition the red granite of Finland.[283]

When rivers in the northern hemisphere flow from south to north, the ice
first breaks up in the higher part of their course, and the flooded
waters, bearing along large icy fragments, often arrive at parts of the
stream which are still firmly frozen over. Great inundations are thus
frequently occasioned by the obstructions thrown in the way of the
descending waters, as in the case of the Mackenzie in North America, and
the Irtish, Obi, Yenesei, Lena, and other rivers of Siberia. (See map,
fig. 1, p. 79.) A partial stoppage of this kind lately occurred (Jan.
31, 1840) in the Vistula, about a mile and a half above the city of
Dantzic, where the river, choked up by packed ice, was made to take a
new course over its right bank, so that it hollowed out in a few days a
deep and broad channel, many leagues in length, through a tract of
sand-hills which were from 40 to 60 feet high.

In Canada, where the winter's cold is intense, in a latitude
corresponding to that of central France, several tributaries of the St.
Lawrence begin to thaw in their upper course, while they remain frozen
over lower down, and thus large slabs of ice are set free and thrown
upon the unbroken sheet of ice below. Then begins what is called the
packing of the drifted fragments; that is to say, one slab is made to
slide over another, until a vast pile is built up, and the whole being
frozen together, is urged onwards by the force of the dammed up waters
and drift-ice. Thus propelled, it not only forces along boulders, but
breaks off from cliffs, which border the rivers, huge pieces of
projecting rock. By this means several buttresses of solid masonry,
which, up to the year 1836, supported a wooden bridge on the St.
Maurice, which falls into the St. Lawrence, near the town of Trois
Rivieres, lat. 46 degrees 20 minutes, were thrown down, and conveyed by
the ice into the main river; and instances have occurred at Montreal of
wharfs and stone-buildings, from 30 to 50 feet square, having been
removed in a similar manner. We learn from Captain Bayfield that anchors
laid down within high-water mark, to secure vessels hauled on shore for
the winter, must be cut out of the ice on the approach of spring, or
they would be carried away. In 1834, the Gulnare's bower-anchor,
weighing half a ton, was transported some yards by the ice, and so
firmly was it fixed, that the force of the moving ice broke a
chain-cable suited for a 10-gun brig, and which had rode the Gulnare
during the heaviest gales in the gulf. Had not this anchor been cut out
of the ice, it would have been earned into deep water and lost.[284]

[Illustration: PLATE II.

BOULDERS DRIFTED BY ICE ON SHORES OF THE ST. LAWRENCE

View taken by Lieut. Bowen, from the N. E., in the Spring of 1835, at
Richelieu Rapid, lat. 46 degrees N.]

The scene represented in the annexed plate (pl. 2), from a drawing by
Lieutenant Bowen, R. N., will enable the reader to comprehend the
incessant changes which the transport of boulders produces annually on
the low islands, shores, and bed of the St. Lawrence above Quebec. The
fundamental rocks at Richelieu Rapid, situated in lat. 46 degrees N., are
limestone and slate, which are seen at low-water to be covered with
boulders of granite. These boulders owe their spheroidal form chiefly to
weathering, or action of frost, which causes the surface to exfoliate
in concentric plates, so that all the more prominent angles are removed.
At the point _a_ is a cavity in the mud or sand of the beach, now filled
with water, which was occupied during the preceding winter (1835) by the
huge erratic _b_, a mass of granite, 70 tons' weight, found in the
spring following (1836) at a distance of several feet from its former
position. Many small islands are seen on the river, such as _c d_, which
afford still more striking proofs of the carrying and propelling power
of ice. These islets are never under water, yet every winter ice is
thrown upon them in such abundance, that it _packs_ to the height of 20,
and even 30 feet, bringing with it a continual supply of large stones or
boulders, and carrying away others; the greatest number being deposited,
according to Lieutenant Bowen, on the edge of deep water. On the island
_d_, on the left of the accompanying view, a lighthouse is represented,
consisting of a square wooden building, which having no other foundation
than the boulders, requires to be taken down every winter, and rebuilt
on the reopening of the river.

These effects of frost, which are so striking on the St. Lawrence above
Quebec, are by no means displayed on a smaller scale below that city,
where the gulf rises and falls with the tide. On the contrary; it is in
the estuary, between the latitudes 47 degrees and 49 degrees, that the
greatest quantity of gravel and boulders of large dimensions are carried
down annually towards the sea. Here the frost is so intense, that a
dense sheet of ice is formed at low water, which, on the rise of the
tide, is lifted up, broken, and thrown in heaps on the extensive shoals
which border the estuary. When the tide recedes, this packed ice is
exposed to a temperature sometimes 30 degrees below zero, which freezes
together all the loose pieces of ice, as well as the granitic and other
boulders. The whole of these are often swept away by a high tide, or
when the river is swollen by the melting of the snow in Spring. One huge
block of granite, 15 feet long by 10 feet both in width and height, and
estimated to contain 1500 cubic feet, was conveyed in this manner to
some distance in the year 1837, its previous position being well known,
as up to that time it had been used by Captain Bayfield as a mark for
the surveying station.

_Ground-ice._--When a current of cold air passes over the surface of a
lake or stream it abstracts from it a quantity of heat, and the specific
gravity of the water being thereby increased, the cooled portion sinks.
This circulation may continue until the whole body of fluid has been
cooled down to the temperature of 40 degrees F., after which, if the cold
increase, the vertical movement ceases, the water which is uppermost
expands and floats over the heavier fluid below, and when it has
attained a temperature of 32 degrees Fahr. it sets into a sheet of ice. It
should seem therefore impossible, according to this law of congelation,
that ice should ever form at the bottom of a river; and yet such is the
fact, and many speculations have been hazarded to account for so
singular a phenomenon. M. Arago is of opinion that the mechanical action
of a running stream produces a circulation by which the entire body of
water is mixed up together, and cooled alike, and the whole being thus
reduced to the freezing point, ice begins to form at the bottom for two
reasons, first, because there is less motion there, and secondly,
because the water is in contact with solid rock or pebbles which have a
cold surface.[285] Whatever explanation we adopt, there is no doubt of
the fact, that in countries where the intensity and duration of the cold
is great, rivers and torrents acquire an increase of carrying power by
the formation of what is called ground-ice. Even in the Thames we learn
from Dr. Plott that pieces of this kind of ice, having gravel frozen on
to their under side, rise up from the bottom in winter, and float on the
surface. In the Siberian rivers, Weitz describes large stones as having
been brought up from the river's bed in the same manner, and made to
float.[286]

_Glaciers._--In the temperate zone, the snow lies for months in winter
on the summit of every high mountain, while in the arctic regions, a
long summer's day of half a year's duration is insufficient to melt the
snow, even on land just raised above the level of the sea. It is
therefore not surprising, since the atmosphere becomes colder in
proportion as we ascend in it, that there should be heights, even in
tropical countries, where the snow never melts. The lowest limit to
which the perpetual snow extends downwards, from the tops of mountains
at the equator, is an elevation of not less than 16,000 feet above the
sea; while in the Swiss Alps, in lat. 46 degrees N. it reaches as low as
8,500 feet above the same level, the loftier peaks of the Alpine chain
being from 12,000 to 15,000 feet high. The frozen mass augmenting from
year to year would add indefinitely to the altitude of alpine summits,
were it not relieved by its descent through the larger and deeper
valleys to regions far below the general snow-line. To these it slowly
finds its way in the form of rivers of ice, called glaciers, the
consolidation of which is produced by pressure, and by the congelation
of water infiltered into the porous mass, which is always undergoing
partial liquefaction, and receiving in summer occasional showers of rain
on its surface. In a day of hot sunshine, or mild rain, innumerable
rills of pure and sparkling water run in icy channels along the surface
of the glaciers, which in the night shrink, and come to nothing. They
are often precipitated in bold cascades into deep fissures in the ice,
and contribute together with springs to form torrents, which flow in
tunnels at the bottom of the glaciers for many a league, and at length
issue at their extremities, from beneath beautiful caverns or arches.
The waters of these streams are always densely charged with the finest
mud, produced by the grinding of rock and sand under the weight of the
moving mass. (See fig. 18.)

[Illustration: Fig 18.

Glacier with medial and lateral moraines and with terminal cave.]

The length of the Swiss glaciers is sometimes twenty miles, their width
in the middle portion, where they are broadest, occasionally two or
three miles; their depth or thickness sometimes more than 600 feet. When
they descend steep slopes, and precipices, or are forced through narrow
gorges, the ice is broken up, and assumes the most fantastic and
picturesque forms, with lofty peaks and pinnacles, projecting above the
general level. These snow-white masses are often relieved by a dark
background of pines, as in the valley of Chamouni; and are not only
surrounded with abundance of the wild rhododendron in full flower, but
encroach still lower into the region of cultivation, and trespass on
fields where the tobacco-plant is flourishing by the side of the
peasant's hut.

The cause of glacier motion has of late been a subject of careful
investigation and much keen controversy. Although a question of physics,
rather than of geology, it is too interesting to allow me to pass it by
without some brief mention. De Saussure, whose travels in the Alps are
full of original observations, as well as sound and comprehensive
general views, conceived that the weight of the ice might be sufficient
to urge it down the slope of the valley, if the sliding motion were
aided by the water flowing at the bottom. For this "gravitation theory"
Charpentier, followed by Agassiz, substituted the hypothesis of
dilatation. The most solid ice is always permeable to water, and
penetrated by innumerable fissures and capillary tubes, often extremely
minute. These tubes imbibe the aqueous fluid during the day, which
freezes, it is said, in the cold of the night, and expands while in the
act of congelation. The distension of the whole mass exerts an immense
force, tending to propel the glacier in the direction of least
resistance--"in other words, down the valley." This theory was opposed
by Mr. Hopkins on mathematical and mechanical grounds, in several able
papers. Among other objections, he pointed out that the friction of so
enormous a body as a glacier on its bed is so great, that the vertical
direction would always be that of least resistance, and if a
considerable distension of the mass should take place, by the action of
freezing, it would tend to increase its thickness, rather than
accelerate its downward progress. He also contended (and his arguments
were illustrated by many ingenious experiments), that a glacier can move
along an extremely slight slope, solely by the influence of gravitation,
owing to the constant dissolution of ice in contact with the rocky
bottom, and the number of separate fragments into which the glacier is
divided by fissures, so that freedom of motion is imparted to its
several parts somewhat resembling that of an imperfect fluid. To this
view Professor James Forbes objected, that gravitation would not supply
an adequate cause for the sliding of solid ice down slopes having an
inclination of no more than four or five degrees, still less would it
explain how the glacier advances where the channel expands and
contracts. The Mer de Glace in Chamouni, for example, after being 2000
yards wide, passes through a strait only 900 yards in width. Such a
gorge, it is contended, would be choked up by the advance of any solid
mass, even if it be broken up into numerous fragments. The same acute
observer remarked, that water in the fissures and pores of glaciers
cannot, and does not part with its latent heat, so as to freeze every
night to a great depth, or far in the interior of the mass. Had the
dilatation theory been true, the chief motion of the glacier would have
occurred about sunset, when the freezing of the water must be greatest,
and it had, in fact, been at first assumed by those who favored that
hypothesis, that the mass moved faster at the sides, where the melting
of ice was promoted by the sun's heat, reflected from boundary
precipices.

Agassiz appears to have been the first to commence, in 1841, aided by a
skilful engineer, M. Escher de la Linth, a series of exact measurements
to ascertain the laws of glacier motion, and he soon discovered,
contrary to his preconceived notions, that the stream of ice moved more
slowly at the sides than at the centre, and faster in the middle region
of the glacier than at its extremity.[287] Professor James Forbes, who
had joined Mr. Agassiz during his earlier investigations in the Alps,
undertook himself an independent series of experiments, which he
followed up with great perseverance, to determine the laws of glacier
motion. These he found to agree very closely with the laws governing the
course of rivers, their progress being greater in the centre than at the
sides, and more rapid at the surface than at the bottom. This fact was
verified by carefully fixing a great number of marks in the ice,
arranged in a straight line, which gradually assumed a beautiful curve,
the middle part pointing down the glacier, and showing a velocity there,
double or treble that of the lateral parts.[288] He ascertained that the
rate of advance by night was nearly the same as by day, and that even
the hourly march of the icy stream could be detected, although the
progress might not amount to more than six or seven inches in twelve
hours. By the incessant though invisible advance of the marks placed on
the ice, "time," says Mr. Forbes, "was marked out as by a shadow on a
dial, and the unequivocal evidence which I obtained, that even while
walking on a glacier we are, day by day, and hour by hour, imperceptibly
carried on by the resistless flow of the icy stream, filled me with
admiration." (Travels in the Alps, p. 133.) In order to explain this
remarkable regularity of motion, and its obedience to laws so strictly
analogous to those of fluids, the same writer proposed the theory that
the ice, instead of being solid and compact, is a viscous or plastic
body, capable of yielding to great pressure, and the more so in
proportion as its temperature is higher, and as it approaches more
nearly to the melting point. He endeavors to show that this hypothesis
will account for many complicated phenomena, especially for a ribboned
or veined structure which is everywhere observable in the ice, and might
be produced by lines of discontinuity, arising from the different rates
at which the various portions of the semi-rigid glacier advance and pass
each other. Many examples are adduced to prove that a glacier can model
itself to the form of the ground over which it is forced, exactly as
would happen if it possessed a certain ductility, and this power of
yielding under intense pressure, is shown not to be irreconcilable with
the idea of the ice being sufficiently compact to break into fragments,
when the strain upon its parts is excessive; as where the glacier turns
a sharp angle, or descends upon a rapid or convex slope. The increased
velocity in summer is attributed partly to the greater plasticity of the
ice, when not exposed to intense cold, and partly to the hydrostatic
pressure of the water in the capillary tubes, which imbibe more of this
liquid in the hot season.

On the assumption of the ice being a rigid mass, Mr. Hopkins attributed
the more rapid motions in the centre to the unequal rate at which the
broad stripes of ice, intervening between longitudinal fissures,
advance; but besides that there are parts of the glacier where no such
fissures exist, such a mode of progression, says Mr. Forbes, would cause
the borders of large transverse rents or "crevasses," to be jagged like
a saw, instead of being perfectly even and straight-edged.[289] An
experiment recently made by Mr. Christie, secretary to the Royal
Society, appears to demonstrate that ice, under great pressure,
possesses a sufficient degree of moulding and self-adapting power to
allow it to be acted upon, as if it were a pasty substance. A hollow
shell of iron an inch and a half thick, the interior being ten inches in
diameter, was filled with water, in the course of a severe winter, and
exposed to the frost, with the fuze-hole uppermost. A portion of the
water expanded in freezing, so as to protrude a cylinder of ice from the
fuze-hole; and this cylinder continued to grow inch by inch in
proportion as the central nucleus of water froze. As we cannot doubt
that an outer shell of ice is first formed, and then another within, the
continued rise of the column through the fuze-hole must proceed from the
squeezing of successive shells of ice concentrically formed, through the
narrow orifice; and yet the protruded cylinder consisted of entire, and
not fragmentary ice.[290]

The agency of glaciers in producing permanent geological changes
consists partly in their power of transporting gravel, sand, and huge
stones to great distances, and partly in the smoothing, polishing, and
scoring of their rocky channels, and the boundary walls of the valleys
through which they pass. At the foot of every steep cliff or precipice
in high Alpine regions, a talus is seen of rocky fragments detached by
the alternate action of frost and thaw. If these loose masses, instead
of accumulating on a stationary base, happen to fall upon a glacier,
they will move along with it, and, in place of a single heap, they will
form in the course of years a long stream of blocks. If a glacier be 20
miles long, and its annual progression about 500 feet, it will require
about two centuries for a block thus lodged upon its surface to travel
down from the higher to the lower regions, or to the extremity of the
icy mass. This terminal point remains usually unchanged from year to
year, although every part of the ice is in motion, because the
liquefaction by heat is just sufficient to balance the onward movement
of the glacier, which may be compared to an endless file of soldiers,
pouring into a breach, and shot down as fast as they advance.

The stones carried along on the ice are called in Switzerland the
"moraines" of the glacier. There is always one line of blocks on each
side or edge of the icy stream, and often several in the middle, where
they are arranged in long ridges or mounds, often several yards high.
(See fig. 18, p. 223.) The cause of these "medial moraines" was first
explained by Agassiz, who referred them to the confluence of tributary
glaciers.[291] Upon the union of two streams of ice, the right lateral
moraine of one of the streams comes in contact with the left lateral
moraine of the other, and they afterwards move on together, in the
centre, if the confluent glaciers are equal in size, or nearer to one
side if unequal.

All sand and fragments of soft stone which fall through fissures and
reach the bottom of the glaciers, or which are interposed between the
glacier and the steep sides of the valley, are pushed along, and ground
down into mud, while the larger and harder fragments have their angles
worn off. At the same time the fundamental and boundary rocks are
smoothed and polished, and often scored with parallel furrows, or with
lines and scratches produced by hard minerals, such as crystals of
quartz, which act like the diamond upon glass.[292] This effect is
perfectly different from that caused by the action of water, or a muddy
torrent forcing along heavy fragments; for when stones are fixed firmly
in the ice, and pushed along by it under great pressure, in straight
lines, they scoop out long rectilinear furrows or grooves parallel to
each other.[293] The discovery of such markings at various heights far
above the surface of the existing glaciers and for miles beyond their
present terminations, affords geological evidence of the former
extension of the ice beyond its present limits in Switzerland and other
countries.

The moraine of the glacier, observes Charpentier, is entirely devoid of
stratification, for there has been no sorting of the materials, as in
the case of sand, mud, and pebbles, when deposited by running water. The
ice transports indifferently, and to the same spots, the heaviest blocks
and the finest particles, mingling all together, and leaving them in one
confused and promiscuous heap wherever it melts.[294]

_Icebergs._--In countries situated in high northern latitudes, like
Spitzbergen, between 70 degrees and 80 degrees N., glaciers, loaded with
mud and rock, descend to the sea, and there huge fragments of them float
off and become icebergs. Scoresby counted 500 of these bergs drifting
along in latitudes 69 degrees and 70 degrees N., which rose above the
surface from the height of 100 to 200 feet, and measured from a few
yards to a mile in circumference.[295] Many of them were loaded with
beds of earth and rock of such thickness, that the weight was
conjectured to be from 50,000 to 100,000 tons. Specimens of the rocks
were obtained, and among them were granite, gneiss, mica-schist,
clay-slate, granular felspar, and greenstone. Such bergs must be of
great magnitude; because the mass of ice below the level of the water is
about eight times greater than that above. Wherever they are dissolved,
it is evident that the "moraine" will fall to the bottom of the sea. In
this manner may submarine valleys, mountains, and platforms become
strewed over with gravel, sand, mud, and scattered blocks of foreign
rock, of a nature perfectly dissimilar from all in the vicinity, and
which may have been transported across unfathomable abysses. If the
bergs happen to melt in still water, so that the earthy and stony
materials may fall tranquilly to the bottom, the deposit will probably
be unstratified, like the terminal moraine of a glacier; but whenever
the materials are under the influence of a current of water as they
fall, they will be sorted and arranged according to their relative
weight and size, and therefore more or less perfectly stratified.

In a former chapter it was stated that some ice islands have been known
to drift from Baffin's Bay to the Azores, and from the South Pole to the
immediate neighborhood of the Cape of Good Hope, so that the area over
which the effects of moving ice may be experienced, comprehends a large
portion of the globe.

We learn from Von Buch that the most southern point on the continent of
Europe at which a glacier comes down to the sea is in Norway, in lat.
67 degrees N.[296] But Mr. Darwin has shown, that they extend to the
sea, in South America, in latitudes more than 20 degrees nearer the
equator than in Europe; as, for example, in Chili, where, in the Gulf of
Penas, lat. 46 degrees 40 minutes S., or the latitude of central France;
and in Sir George Eyre's Sound, in the latitude of Paris, they give
origin to icebergs, which were seen in 1834 carrying angular pieces of
granite, and stranding them in fiords, where the shores were composed of
clay-slate.[297] A large proportion, however, of the ice-islands seen
floating both in the northern and southern hemispheres, are probably not
generated by glaciers, but rather by the accumulation of coast ice. When
the sea freezes at the base of a lofty precipice, the sheet of ice is
prevented from adhering to the land by the rise and fall of the tide.
Nevertheless, it often continues on the shore at the foot of the cliff,
and receives accessions of drift snow blown from the land. Under the
weight of this snow the ice sinks slowly if the water be deep, and the
snow is gradually converted into ice by partial liquefaction and
re-congelation. In this manner, islands of ice of great thickness and
many leagues in length, originate, and are eventually blown out to sea
by off-shore winds. In their interior are inclosed many fragments of
stone which had fallen upon them from overhanging cliffs during their
formation. Such floating icebergs are commonly flat-topped, but their
lower portions are liable to melt in latitudes where the ocean at a
moderate depth is usually warmer than the surface water and the air.
Hence their centre of gravity changes continually, and they turn over
and assume very irregular shapes.

In a voyage of discovery made in the antarctic regions in 1839, a
dark-colored angular mass of rock was seen imbedded in an iceberg,
drifting along in mid-ocean in lat. 61 degrees S. That part of the rock
which was visible was about 12 feet in height, and from 5 to 6 in width,
but the dark color of the surrounding ice indicated that much more of
the stone was concealed. A sketch made by Mr. Macnab, when the vessel
was within a quarter of a mile of it, is now published.[298] This
iceberg, one of many observed at sea on the same day, was between 250
and 300 feet high, and was no less than 1400 miles from any certainly
known land. It is exceedingly improbable, says Mr. Darwin, in his notice
of this phenomenon, that any land will hereafter be discovered within
100 miles of the spot, and it must be remembered that the erratic was
still firmly fixed in the ice, and may have sailed for many a league
farther before it dropped to the bottom.[299]

Captain Sir James Ross, in his antarctic voyage in 1841, 42, and 43, saw
multitudes of icebergs transporting stones and rocks of various sizes,
with frozen mud, in high southern latitudes. His companion, Dr. J.
Hooker, informs me that he came to the conclusion that most of the
southern icebergs have stones in them, although they are usually
concealed from view by the quantity of snow which falls upon them.

In the account given by Messrs. Dease and Simpson, of their recent
arctic discoveries, we learn that in lat. 71 degrees N., long. 156
degrees W., they found "a long low spit, named Point Barrow, composed of
gravel and coarse sand, in some parts more than a quarter of a mile
broad, which the pressure of the ice had forced up into numerous mounds,
that, viewed from a distance, assumed the appearance of huge boulder
rocks."[300]

This fact is important, as showing how masses of drift ice, when
stranding on submarine banks, may exert a lateral pressure capable of
bending and dislocating any yielding strata of gravel, sand, or mud. The
banks on which icebergs occasionally run aground between Baffin's Bay
and Newfoundland, are many hundred feet under water, and the force with
which they are struck will depend not so much on the velocity as the
momentum of the floating ice-islands. The same berg is often carried
away by a change of wind, and then driven back again upon the same bank,
or it is made to rise and fall by the waves of the ocean, so that it may
alternately strike the bottom with its whole weight, and then be lifted
up again until it has deranged the superficial beds over a wide area. In
this manner the geologist may account, perhaps, for the circumstance
that in Scandinavia, Scotland, and other countries where erratics are
met with, the beds of sand, loam, and gravel are often vertical, bent,
and contorted into the most complicated folds, while the underlying
strata, although composed of equally pliant materials, are horizontal.
But some of these curvatures of loose strata may also have been due to
repeated alternations of layers of gravel and sand, ice and snow, the
melting of the latter having caused the intercalated beds of
indestructible matter to assume their present anomalous position.

There can be little doubt that icebergs must often break off the peaks
and projecting points of submarine mountains, and must grate upon and
polish their surface, furrowing or scratching them in precisely the same
way as we have seen that glaciers act on the solid rocks over which they
are propelled.[301]

To conclude: it appears that large stones, mud, and gravel are carried
down by the ice of rivers, estuaries, and glaciers, into the sea, where
the tides and currents of the ocean, aided by the wind, cause them to
drift for hundreds of miles from the place of their origin. Although it
will belong more properly to the seventh and eighth chapters to treat of
the transportation of solid matter by the movements of the ocean, I
shall add here what I have farther to say on this subject in connection
with ice.

The saline matter which sea-water holds in solution, prevents its
congelation, except where the most intense cold prevails. But the
drifting of the snow from the land often renders the surface-water
brackish near the coast, so that a sheet of ice is readily formed there,
and by this means a large quantity of gravel is frequently conveyed from
place to place, and heavy boulders also, when the coast-ice is packed
into dense masses. Both the large and small stones thus conveyed usually
travel in one direction like shingle-beaches, and this was observed to
take place on the coast of Labrador and Gulf of St. Lawrence, between
the latitudes 50 degrees and 60 degrees N., by Capt. Bayfield, during
his late survey. The line of coast alluded to is strewed over for a
distance of 700 miles with ice-borne boulders, often 6 feet in diameter,
which are for the most part on their way from north to south, or in the
direction of the prevailing current. Some points on this coast have been
observed to be occasionally deserted, and then again at another season
thickly bestrewed with erratics.

[Illustration: Fig. 19.

Boulders, chiefly of granite, stranded by ice on the coast of Labrador,
between lat. 50 degrees and 60 degrees N. (Lieut. Bowen, R. N.)]

The accompanying drawing (fig. 19), for which I am indebted to Lieut.
Bowen, R. N., represents the ordinary appearance of the Labrador coast,
between the latitudes of 50 degrees and 60 degrees N. Countless blocks,
chiefly granitic, and of various sizes, are seen lying between high and
low-water mark. Capt. Bayfield saw similar masses carried by ice through
the Straits of Belle Isle, between Newfoundland and the American
continent, which he conceives may have travelled in the course of years
from Baffin's Bay, a distance which may be compared in our hemisphere to
the drifting of erratics from Lapland and Iceland as far south as
Germany, France, and England.

It may be asked in what manner have these blocks been originally
detached? We may answer that some have fallen from precipitous cliffs,
others have been lifted up from the bottom of the sea, adhering by their
tops to the ice, while others have been brought down by rivers and
glaciers.

The erratics of North America are sometimes angular, but most of them
have been rounded either by friction or decomposition. The granite of
Canada, as before remarked (p. 221 ), has a tendency to concentric
exfoliation, and scales off in spheroidal coats when exposed to the
spray of the sea during severe frosts. The range of the thermometer in
that country usually exceeds, in the course of the year, 100 degrees, and
sometimes 120 degrees F.; and, to prevent the granite used in the
buildings of Quebec from peeling off in winter, it is necessary to oil
and paint the squared stones.

In parts of the Baltic, such as the Gulf of Bothnia, where the quantity
of salt in the water amounts in general to one fourth only of that in
the ocean, the entire surface freezes over in winter to the depth of 5
or 6 feet. Stones are thus frozen in, and afterwards lifted up about 3
feet perpendicularly on the melting of the snow in summer, and then
carried by floating ice-islands to great distances. Professor Von Baer
states, in a communication on this subject to the Academy of St.
Petersburg, that a block of granite, weighing a million of pounds, was
carried by ice during the winter of 1837-8 from Finland to the island of
Hockland, and two other huge blocks were transported about the years
1806 and 1814 by packed ice on the south coast of Finland, according to
the testimony of the pilots and inhabitants, one block having travelled
about a quarter of a mile, and lying about 18 feet above the level of
the sea.[302]

More recently Dr. Forchhammer has shown that in the Sound, the Great
Belt, and other places near the entrance of the Baltic, ground-ice forms
plentifully at the bottom and then rises to the surface, charged with
sand and gravel, stones and sea-weed. Sheets of ice, also, with included
boulders, are driven up on the coast during storms, and "packed" to a
height of 50 feet. To the motion of such masses, but still more to that
of the ground-ice, the Danish professor attributes the striation of
rocky surfaces, forming the shores and bed of the sea, and he relates a
striking fact to prove that large quantities of rocky fragments are
annually carried by ice out of the Baltic. "In the year 1807," he says,
"at the time of the bombardment of the Danish fleet, an English
sloop-of-war, riding at anchor in the roads at Copenhagen, blew up. In
1844, or thirty-seven years afterwards, one of our divers, known to be
a trustworthy man, went down to save whatever might yet remain in the
shipwrecked vessel. He found the space between decks entire, but covered
with blocks from 6 to 8 cubic feet in size, and some of them heaped one
upon the other. He also affirmed, that all the sunk ships which he had
visited in the Sound, were in like manner strewed over with blocks."

Dr. Forchhammer also informs us, that during an intense frost in
February, 1844, the Sound was suddenly frozen over, and sheets of ice,
driven by a storm, were heaped up at the bottom of the Bay of Taarbeijk,
threatening to destroy a fishing-village on the shore. The whole was
soon frozen together into one mass, and forced up on the beach, forming
a mound more than 16 feet high, which threw down the walls of several
buildings. "When I visited the spot next day, I saw ridges of ice, sand,
and pebbles, not only on the shore, but extending far out into the
bottom of the sea, showing how greatly its bed had been changed, and how
easily, where it is composed of rock, it may be furrowed and streaked by
stones firmly fixed in the moving ice."[303]




CHAPTER XVI.

PHENOMENA OF SPRINGS.


 Origin of Springs--Artesian wells--Borings at Paris--Distinct causes
    by which mineral and thermal waters may be raised to the
    surface--Their connection with volcanic agency--Calcareous
    springs--Travertin of the Elsa--Baths of San Vignone and of San
    Filippo, near Radicofani--Spheroidal structure in travertin--Lake of
    the Solfatara, near Rome--Travertin at Cascade of Tivoli--Gypseous,
    siliceous, and ferruginous springs--Brine springs--Carbonated
    springs--Disintegration of granite in Auvergne--Petroleum
    springs--Pitch lake of Trinidad.


_Origin of springs._--The action of running water on the surface of the
land having been considered, we may next turn our attention to what may
be termed "the subterranean drainage," or the phenomena of springs.
Every one is familiar with the fact, that certain porous soils, such as
loose sand and gravel, absorb water with rapidity, and that the ground
composed of them soon dries up after heavy showers. If a well be sunk in
such soils, we often penetrate to considerable depths before we meet
with water; but this is usually found on our approaching the lower parts
of the formation, where it rests on some impervious bed; for here the
water, unable to make its way downwards in a direct line, accumulates as
in a reservoir, and is ready to ooze out into any opening which may be
made, in the same manner as we see the salt water flow into, and fill,
any hollow which we dig in the sands of the shore at low tide.

The facility with which water can percolate loose and gravelly soils is
clearly illustrated by the effect of the tides in the Thames between
Richmond and London. The river, in this part of its course, flows
through a bed of gravel overlying clay, and the porous superstratum is
alternately saturated by the water of the Thames as the tide rises, and
then drained again to the distance of several hundred feet from the
banks when the tide falls, so that the wells in this tract regularly ebb
and flow.

If the transmission of water through a porous medium be so rapid, we
cannot be surprised that springs should be thrown out on the side of a
hill, where the upper set of strata consist of chalk, sand, or other
permeable substances, while the subjacent are composed of clay or other
retentive soils. The only difficulty, indeed, is to explain why the
water does not ooze out everywhere along the line of junction of the two
formations, so as to form one continuous land-soak, instead of a few
springs only, and these far distant from each other. The principal cause
of this concentration of the waters at a few points is, first, the
frequency of rents and fissures, which act as natural drains; secondly,
the existence of inequalities in the upper surface of the impermeable
stratum, which lead the water, as valleys do on the external surface of
a country, into certain low levels and channels.

That the generality of springs owe their supply to the atmosphere is
evident from this, that they become languid, or entirely cease to flow,
after long droughts, and are again replenished after a continuance of
rain. Many of them are probably indebted for the constancy and
uniformity of their volume to the great extent of the subterranean
reservoirs with which they communicate, and the time required for these
to empty themselves by percolation. Such a gradual and regulated
discharge is exhibited, though in a less perfect degree, in every great
lake which is not sensibly affected in its level by sudden showers, but
only slightly raised; so that its channel of efflux, instead of being
swollen suddenly like the bed of a torrent, is enabled to carry off the
surplus water gradually.

Much light has been thrown, of late years, on the theory of springs, by
the boring of what are called by the French "Artesian wells," because
the method has long been known and practised in Artois; and it is now
demonstrated that there are sheets, and in some places currents of fresh
water, at various depths in the earth. The instrument employed in
excavating these wells is a large augur, and the cavity bored is usually
from three to four inches in diameter. If a hard rock is met with, it is
first triturated by an iron rod, and the materials being thus reduced to
small fragments or powder, are readily extracted. To hinder the sides of
the well from falling in, as also to prevent the spreading of the
ascending water in the surrounding soil, a jointed pipe is introduced,
formed of wood in Artois, but in other countries more commonly of metal.
It frequently happens that, after passing through hundreds of feet of
retentive soils, a water-bearing stratum is at length pierced, when the
fluid immediately ascends to the surface, and flows over. The first rush
of the water up the tube is often violent, so that for a time the water
plays like a fountain, and then, sinking, continues to flow over
tranquilly, or sometimes remains stationary at a certain depth below the
orifice of the well. This spouting of the water in the first instance is
probably owing to the disengagement of air and carbonic acid gas, for
both of these have been seen to bubble up with the water.[304]

At Sheerness, at the mouth of the Thames, a well was bored on a low
tongue of land near the sea, through 300 feet of the blue clay of
London, below which a bed of sand and pebbles was entered, belonging,
doubtless, to the plastic clay formation; when this stratum was pierced,
the water burst up with impetuosity, and filled the well. By another
perforation at the same place, the water was found at the depth of 328
feet below the surface clay; it first rose rapidly to the height of 189
feet, and then, in the course of a few hours, ascended to an elevation
of eight feet above the level of the ground. In 1824 a well was dug at
Fulham, near the Thames, at the Bishop of London's, to the depth of 317
feet, which, after traversing the tertiary strata, was continued through
67 feet of chalk. The water immediately rose to the surface, and the
discharge was about 50 gallons per minute. In the garden of the
Horticultural Society at Chiswick, the borings passed through 19 feet of
gravel, 242-1/2 feet of clay and loam, and 67-1/2 feet of chalk, and the
water then rose to the surface from a depth of 329 feet.[305] At the
Duke of Northumberland's, above Chiswick, the borings were carried to
the extraordinary depth of 620 feet, so as to enter the chalk, when a
considerable volume of water was obtained, which rose four feet above
the surface of the ground. In a well of Mr. Brooks, at Hammersmith, the
rush of water from a depth of 360 feet was so great, as to inundate
several buildings and do considerable damage; and at Tooting, a
sufficient stream was obtained to turn a wheel, and raise the water to
the upper stories of the houses.[306] In 1838, the total supply obtained
from the chalk near London was estimated at six million gallons a day,
and, in 1851, at nearly double that amount, the increase being
accompanied by an average fall of no less than two feet a year in the
level to which the water rose. The water stood commonly, in 1822, at
high-water mark, and had sunk in 1851 to 45, and in some wells to 65
feet below high-water mark.[307] This fact shows the limited capacity of
the subterranean reservoir. In the last of three wells bored through the
chalk at Tours, to the depth of several hundred feet, the water rose 32
feet above the level of the soil, and the discharge amounted to 300
cubic yards of water every twenty-four hours.[308]

By way of experiment, the sinking of a well was commenced at Paris in
1834, which had reached, in November, 1839, a depth of more than 1600
English feet, and yet no water ascended to the surface. The government
were persuaded by M. Arago to persevere, if necessary, to the depth of
more than 2000 feet; but when they had descended above 1800 English feet
below the surface, the water rose through the tube (which was about ten
inches in diameter), so as to discharge half a million of gallons of
limpid water every twenty-four hours. The temperature of the water
increased at the rate of 1.8 degrees F. for every 101 English feet, as
they went down, the result agreeing very closely with the anticipations
of the scientific advisers of this most spirited undertaking.

Mr. Briggs, the British consul in Egypt, obtained water between Cairo
and Suez, in a calcareous sand, at the depth of thirty feet; but it did
not rise in the well.[309] But other borings in the same desert, of
variable depth, between 50 and 300 feet, and which passed through
alternations of sand, clay, and siliceous rock, yielded water at the
surface.[310]

The rise and overflow of the water in Artesian wells is generally
referred, and apparently with reason, to the same principle as the play
of an artificial fountain. Let the porous stratum or set of strata, _a_
_a_, rest on the impermeable rock _d_, and be covered by another mass of
an impermeable nature. The whole mass _a_ _a_ may easily, in such a
position, become saturated with water, which may descend from its higher
and exposed parts--a hilly region to which clouds are attracted, and
where rain falls in abundance. Suppose that at some point, as at _b_, an
opening be made, which gives a free passage upwards to the waters
confined in _a_ _a_, at so low a level that they are subjected to the
pressure of a considerable column of water collected in the more
elevated portion of the same stratum. The water will then rush out, just
as the liquid from a large barrel which is tapped, and it will rise to a
height corresponding to the level of its point of departure, or, rather,
to a height which balances the pressure previously exerted by the
confined waters against the roof and sides of the stratum or reservoir
_a_ _a_. In like manner, if there happen to be a natural fissure _c_, a
spring will be produced at the surface on precisely the same principle.

[Illustration: Fig. 20.]

Among the causes of the failure of Artesian wells, we may mention those
numerous rents and faults which abound in some rocks, and the deep
ravines and valleys by which many countries are traversed; for, when
these natural lines of drainage exist, there remains a small quantity
only of water to escape by artificial issues. We are also liable to be
baffled by the great thickness either of porous or impervious strata, or
by the dip of the beds, which may carry off the waters from the
adjoining high lands to some trough in an opposite direction, as when
the borings are made at the foot of an escarpment where the strata
incline inwards, or in a direction opposite to the face of the cliffs.

The mere distance of hills or mountains need not discourage us from
making trials; for the waters which fall on these higher lands readily
penetrate to great depths through highly inclined or vertical strata, or
through the fissures of shattered rocks, and after flowing for a great
distance, must often reascend and be brought up again by other fissures,
so as to approach the surface in the lower country. Here they may be
concealed beneath the covering of undisturbed horizontal beds, which it
may be necessary to pierce in order to reach them. It should be
remembered, that the course of waters flowing under ground bears but a
remote resemblance to that of rivers on the surface, there being, in the
one case, a constant descent from a higher to a lower level from the
source of the stream to the sea; whereas, in the other, the water may at
one time sink far below the level of the ocean, and afterwards rise
again high above it.

Among other curious facts ascertained by aid of the borer, it is proved
that in strata of different ages and compositions, there are often open
passages by which the subterranean waters circulate. Thus, at St. Ouen,
in France, five distinct sheets of water were intersected in a well, and
from each of these a supply obtained. In the third waterbearing stratum,
at the depth of 150 feet, a cavity was found in which the borer fell
suddenly about a foot, and thence the water ascended in great
volume.[311] The same falling of the instrument, as in a hollow space,
has been remarked in England and other countries. At Tours, in 1830, a
well was perforated quite through the chalk, when the water suddenly
brought up, from a depth of 364 feet, a great quantity of fine sand,
with much vegetable matter and shells. Branches of a thorn several
inches long, much blackened by their stay in the water, were recognized,
as also the stems of marsh plants, and some of their roots, which were
still white, together with the seeds of the same in a state of
preservation, which showed that they had not remained more than three or
four months in the water. Among the seeds were those of the marsh plant
_Galium uliginosum_; and among the shells, a freshwater species
(_Planorbis marginatus_), and some land species, as _Helix rotundata_,
and _H. striata_. M. Dujardin, who, with others, observed this
phenomenon, supposes that the waters had flowed from some valleys of
Auvergne or the Vivarais since the preceding autumn.[312]

An analogous phenomenon is recorded at Reimke, near Bochum in
Westphalia, where the water of an Artesian well brought up, from a
depth of 156 feet, several small fish, three or four inches long, the
nearest streams in the country being at a distance of some leagues.[313]

In both cases it is evident that water had penetrated to great depths,
not simply by filtering through a porous mass, for then it would have
left behind the shells, fish, and fragments of plants, but by flowing
through some open channels in the earth. Such examples may suggest the
idea that the leaky beds of rivers are often the feeders of springs.


MINERAL AND THERMAL SPRINGS.

Almost all springs, even those which we consider the purest, are
impregnated with some foreign ingredients, which, being in a state of
chemical solution, are so intimately blended with the water as not to
affect its clearness, while they render it, in general, more agreeable
to our taste, and more nutritious than simple rain-water. But the
springs called mineral contain an unusual abundance of earthy matter in
solution, and the substances with which they are impregnated correspond
remarkably with those evolved in a gaseous form by volcanoes. Many of
these springs are thermal, _i. e._, their temperature is above the mean
temperature of the place, and they rise up through all kinds of rock;
as, for example, through granite, gneiss, limestone, or lava, but are
most frequent in volcanic regions, or where violent earthquakes have
occurred at eras comparatively modern.

The water given out by hot springs is generally more voluminous and less
variable in quantity at different seasons than that proceeding from any
others. In many volcanic regions, jets of steam, called by the Italians
"stufas," issue from fissures, at a temperature high above the boiling
point, as in the neighborhood of Naples, and in the Lipari Isles, and
are disengaged unceasingly for ages. Now, if such columns of steam,
which are often mixed with other gases, should be condensed before
reaching the surface by coming in contact with strata filled with cold
water, they may give rise to thermal and mineral springs of every degree
of temperature. It is, indeed, by this means only, and not by
hydrostatic pressure, that we can account for the rise of such bodies of
water from great depths; nor can we hesitate to admit the adequacy of
the cause, if we suppose the expansion of the same elastic fluids to be
sufficient to raise columns of lava to the lofty summits of volcanic
mountains. Several gases, the carbonic acid in particular, are
disengaged in a free state from the soil in many districts, especially
in the regions of active or extinct volcanoes; and the same are found
more or less intimately combined with the waters of all mineral springs,
both cold and thermal. Dr. Daubeny and other writers have remarked, not
only that these springs are most abundant in volcanic regions, but that
when remote from them, their site usually coincides with the position of
some great derangement in the strata; a fault, for example, or great
fissure, indicating that a channel of communication has been opened with
the interior of the earth at some former period of local convulsion. It
is also ascertained that at great heights in the Pyrenees and Himalaya
mountains hot springs burst out from granitic rocks, and they are
abundant in the Alps also, these chains having all been disturbed and
dislocated at times comparatively modern, as can be shown by independent
geological evidence.

The small area of volcanic regions may appear, at first view, to present
an objection to these views, but not so when we include earthquakes
among the effects of igneous agency. A large proportion of the land
hitherto explored by geologists can be shown to have been rent or shaken
by subterranean movements since the oldest tertiary strata were formed.
It will also be seen, in the sequel, that new springs have burst out,
and others have had the volume of their waters augmented, and their
temperature suddenly raised after earthquakes, so that the description
of these springs might almost with equal propriety have been given under
the head of "igneous causes," as they are agents of a mixed nature,
being at once igneous and aqueous.

But how, it will be asked, can the regions of volcanic heat send forth
such inexhaustible supplies of water? The difficulty of solving this
problem would, in truth, be insurmountable, if we believed that all the
atmospheric waters found their way into the basin of the ocean; but in
boring near the shore we often meet with streams of fresh water at the
depth of several hundred feet below the sea level; and these probably
descend, in many cases, far beneath the bottom of the sea, when not
artificially intercepted in their course. Yet, how much greater may be
the quantity of salt water which sinks beneath the floor of the ocean,
through the porous strata of which it is often composed, or through
fissures rent in it by earthquakes. After penetrating to a considerable
depth, this water may encounter a heat of sufficient intensity to
convert it into vapor, even under the high pressure to which it would
then be subjected. This heat would probably be nearest the surface in
volcanic countries, and farthest from it in those districts which have
been longest free from eruptions or earthquakes.

It would follow from the views above explained, that there must be a
twofold circulation of terrestrial waters; one caused by solar heat, and
the other by heat generated in the interior of our planet. We know that
the land would be unfit for vegetation, if deprived of the waters raised
into the atmosphere by the sun; but it is also true that mineral springs
are powerful instruments in rendering the surface subservient to the
support of animal and vegetable life. Their heat is said to promote the
development of the aquatic tribes in many parts of the ocean, and the
substances which they carry up from the bowels of the earth to the
habitable surface, are of a nature and in a form which adapts them
peculiarly for the nutrition of animals and plants.

As these springs derive their chief importance to the geologist from
the quantity and quality of the earthy materials which, like volcanoes,
they convey from below upwards, they may properly be considered in
reference to the ingredients which they hold in solution. These consist
of a great variety of substances; but chiefly salts with bases of lime,
magnesia, alumine, and iron, combined with carbonic, sulphuric, and
muriatic acids. Muriate of soda, silica, and free carbonic acid are
frequently present; also springs of petroleum, or liquid bitumen, and of
naphtha.

_Calcareous springs._--Our first attention is naturally directed to
springs which are highly charged with calcareous matter, for these
produce a variety of phenomena of much interest in geology. It is known
that rain-water collecting carbonic acid from the atmosphere has the
property of dissolving the calcareous rocks over which it flows, and
thus, in the smallest ponds and rivulets, matter is often supplied for
the earthy secretions of testacea, and for the growth of certain plants
on which they feed. But many springs hold so much carbonic acid in
solution, that they are enabled to dissolve a much larger quantity of
calcareous matter than rain-water; and when the acid is dissipated in
the atmosphere, the mineral ingredients are thrown down, in the form of
porous tufa or of more compact travertin.[314]

_Auvergne._--Calcareous springs, although most abundant in limestone
districts, are by no means confined to them, but flow out
indiscriminately from all rock formations. In central France, a district
where the primary rocks are unusually destitute of limestone, springs
copiously charged with carbonate of lime rise up through the granite and
gneiss. Some of these are thermal, and probably derive their origin from
the deep source of volcanic heat, once so active in that region. One of
these springs, at the northern base of the hill upon which Claremont is
built, issues from volcanic peperino, which rests on granite. It has
formed, by its incrustations, an elevated mound of travertin, or white
concretionary limestone, 240 feet in length, and, at its termination,
sixteen feet high and twelve wide. Another encrusting spring in the same
department, situated at Chaluzet, near Pont Gibaud, rises in a gneiss
country, at the foot of a regular volcanic cone, at least twenty miles
from any calcareous rock. Some masses of tufaceous deposit, produced by
this spring, have an oolitic texture.

_Valley of the Elsa._--If we pass from the volcanic district of France
to that which skirts the Apennines in the Italian peninsula, we meet
with innumerable springs which have precipitated so much calcareous
matter, that the whole ground in some parts of Tuscany is coated over
with tufa and travertin, and sounds hollow beneath the foot.

In other places in the same country, compact rocks are seen descending
the slanting sides of hills, very much in the manner of lava currents,
except that they are of a white color and terminate abruptly when they
reach the course of a river. These consist of a calcareous precipitate
from springs, some of which are still flowing, while others have
disappeared or changed their position. Such masses are frequent on the
slope of the hills which bound the valley of the Elsa, one of the
tributaries of the Arno, which flows near Colle, through a valley
several hundred feet deep, shaped out of a lacustrine formation,
containing fossil shells of existing species. I observed here that the
travertin was unconformable to the lacustrine beds, its inclination
according with the slope of the sides of the valley. One of the finest
examples which I saw was at the Molino delle Caldane, near Colle. The
Sena, and several other small rivulets which feed the Elsa, have the
property of encrusting wood and herbs with calcareous stone. In the bed
of the Elsa itself, aquatic plants, such as Charae, which absorb large
quantities of carbonate of lime, are very abundant.

[Illustration: Fig. 21.

Section of travertin, San Vignone.]

_Baths of San Vignone._--Those persons who have merely seen the action
of petrifying waters in England, will not easily form an adequate
conception of the scale on which the same process is exhibited in those
regions which lie nearer to the active centres of volcanic disturbance.
One of the most striking examples of the rapid precipitation of
carbonate of lime from thermal waters, occurs in the hill of San Vignone
in Tuscany, at a short distance from Radicofani, and only a few hundred
yards from the high road between Sienna and Rome. The spring issues from
near the summit of a rocky hill, about 100 feet in height. The top of
the hill stretches in a gently inclined platform to the foot of Mount
Amiata, a lofty eminence, which consists in great part of volcanic
products. The fundamental rock, from which the spring issues, is a black
slate, with serpentine (_b_ _b_, fig. 21), belonging to the older
Apennine formation. The water is hot, has a strong taste, and, when not
in very small quantity, is of a bright green color. So rapid is the
deposition near the source, that in the bottom of a conduit-pipe for
carrying off the water to the baths, and which is inclined at an angle
of 30 degrees, half a foot of solid travertin is formed every year. A more
compact rock is produced where the water flows slowly; and the
precipitation in winter, when there is least evaporation, is said to be
more solid, but less in quantity by one-fourth, than in summer. The rock
is generally white; some parts of it are compact, and ring to the
hammer; others are cellular, and with such cavities as are seen in the
carious part of bone or the siliceous millstone of the Paris basin. A
portion of it also below the village of San Vignone consists of
incrustations of long vegetable tubes, and may be called tufa. Sometimes
the travertin assumes precisely the botryoidal and mammillary forms,
common to similar deposits in Auvergne, of a much older date; and, like
them, it often scales off in thin, slightly undulating layers.

A large mass of travertin (_c_, fig. 21) descends the hill from the
point where the spring issues, and reaches to the distance of about half
a mile east of San Vignone. The beds take the slope of the hill at about
an angle of 6 degrees, and the planes of stratification are perfectly
parallel. One stratum, composed of many layers, is of a compact nature,
and fifteen feet thick; it serves as an excellent building stone, and a
mass of fifteen feet in length was, in 1828, cut out for the new bridge
over the Orcia. Another branch of it (_a_, fig. 21) descends to the
west, for 250 feet in length, of varying thickness, but sometimes 200
feet deep; it is then cut off by the small river Orcia, as some glaciers
in Switzerland descend into a valley till their progress is suddenly
arrested by a transverse stream of water.

The abrupt termination of the mass of rock at the river, where its
thickness is undiminished, clearly shows that it would proceed much
farther if not arrested by the stream, over which it impends slightly.
But it cannot encroach upon the channel of the Orcia, being constantly
undermined, so that its solid fragments are seen strewed amongst the
alluvial gravel. However enormous, therefore, the mass of solid rock may
appear which has been given out by this single spring, we may feel
assured that it is insignificant in volume when compared to that which
has been carried to the sea since the time when it began to flow. What
may have been the length of that period of time we have no data for
conjecturing. In quarrying the travertin, Roman tiles have been
sometimes found at the depth of five or six feet.

_Baths of San Filippo._--On another hill, not many miles from that last
mentioned, and also connected with Mount Amiata, the summit of which is
about three miles distant, are the celebrated baths of San Filippo. The
subjacent rocks consist of alternations of black slate, limestone, and
serpentine. There are three warm springs containing carbonate and
sulphate of lime, and sulphate of magnesia. The water which supplies the
baths falls into a pond, where it has been known to deposit a solid mass
_thirty feet thick_ in about _twenty years_.[315] A manufactory of
medallions in basso-relievo is carried on at these baths. The water is
conducted by canals into several pits, in which it deposits travertin
and crystals of sulphate of lime. After being thus freed from its
grosser parts, it is conveyed by a tube to the summit of a small
chamber, and made to fall through a space of ten or twelve feet. The
current is broken in its descent by numerous crossed sticks, by which
the spray is dispersed around upon certain moulds, which are rubbed
lightly over with a solution of soap, and a deposition of solid matter
like marble is the result, yielding a beautiful cast of the figures
formed in the mould. The geologist may derive from these experiments
considerable light, in regard to the high slope of the strata at which
some semi-crystalline precipitations can be formed; for some of the
moulds are disposed almost perpendicularly, yet the deposition is nearly
equal in all parts.

A hard stratum of stone, about a foot in thickness, is obtained from the
waters of San Filippo in four months; and, as the springs are powerful,
and almost uniform in the quantity given out, we are at no loss to
comprehend the magnitude of the mass which descends the hill, which is a
mile and a quarter in length and the third of a mile in breadth, in some
places attaining a thickness of 250 feet at least. To what length it
might have reached it is impossible to conjecture, as it is cut off,
like the travertin of San Vignone, by a small stream, where it
terminates abruptly. The remainder of the matter held in solution is
carried on probably to the sea.

_Spheroidal structure in travertin._--But what renders this recent
limestone of peculiar interest to the geologist, is the spheroidal form
which it assumes, analogous to that of the cascade of Tivoli, afterwards
to be described. (See fig. 22, p. 244.) The lamination of some of the
concentric masses is so minute that sixty may be counted in the
thickness of an inch, yet, notwithstanding these marks of gradual and
successive deposition, sections are sometimes exhibited of what might
seem to be perfect spheres. This tendency to a mammillary and globular
structure arises from the facility with which the calcareous matter is
precipitated in nearly equal quantities on all sides of any fragment of
shell or wood or any inequality of the surface over which the mineral
water flows, the form of the nucleus being readily transmitted through
any number of successive envelopes. But these masses can never be
perfect spheres, although they often appear such when a transverse
section is made in any line not in the direction of the point of
attachment. There are, indeed, occasionally seen small oolitic and
pisolitic grains, of which the form is globular; for the nucleus, having
been for a time in motion in the water, has received fresh accessions of
matter on all sides.

In the same manner I have seen, on the vertical walls of large
steam-boilers, the heads of nails or rivets covered by a series of
enveloping crusts of calcareous matter, usually sulphate of lime; so
that a concretionary nodule is formed, preserving a nearly globular
shape, when increased to a mass several inches in diameter. In these, as
in many travertins, there is often a combination of the concentric and
radiated structure.

_Campagna di Roma._--The country around Rome, like many parts of the
Tuscan States already referred to, has been at some former period the
site of numerous volcanic eruptions; and the springs are still copiously
impregnated with lime, carbonic acid, and sulphuretted hydrogen. A hot
spring was discovered about 1827, near Civita Vecchia, by Signor
Riccioli, which deposits alternate beds of a yellowish travertin, and a
white granular rock, not distinguishable, in hand specimens, either in
grain, color, or composition, from statuary marble. There is a passage
between this and ordinary travertin. The mass accumulated near the
spring is in some places about six feet thick.

_Lake of the Solfatara._--In the Campagna, between Rome and Tivoli, is
the Lake of the Solfatara, called also Lago di Zolfo (lacus albula),
into which flows continually a stream of tepid water from a smaller
lake, situated a few yards above it. The water is a saturated solution
of carbonic acid gas, which escapes from it in such quantities in some
parts of its surface, that it has the appearance of being actually in
ebullition. "I have found by experiment," says Sir Humphry Davy, "that
the water taken from the most tranquil part of the lake, even after
being agitated and exposed to the air, contained in solution more than
its own volume of carbonic acid gas, with a very small quantity of
sulphuretted hydrogen. Its high temperature, which is pretty constant at
80 degrees of Fahr., and the quantity of carbonic acid that it contains,
render it peculiarly fitted to afford nourishment to vegetable life. The
banks of travertin are everywhere covered with reeds, lichen, confervae,
and various kinds of aquatic vegetables; and at the same time that the
process of vegetable life is going on, the crystallizations of the
calcareous matter, which is everywhere deposited, in consequence of the
escape of carbonic acid, likewise proceed. There is, I believe, no place
in the world where there is a more striking example of the opposition or
contrast of the laws of animate and inanimate nature, of the forces of
inorganic chemical affinity, and those of the powers of life."[316]

The same observer informs us that he fixed a stick in a mass of
travertin covered by the water in the month of May, and in April
following he had some difficulty in breaking, with a sharp-pointed
hammer, the mass which adhered to the stick, and which was several
inches in thickness. The upper part was a mixture of light tufa and the
leaves of confervae; below this was a darker and more solid travertin,
containing black and decomposed masses of confervae; in the inferior part
the travertin was more solid, and of a gray color, but with cavities
probably produced by the decomposition of vegetable matter.[317]

The stream which flows out of this lake fills a canal about nine feet
broad and four deep, and is conspicuous in the landscape by a line of
vapor which rises from it. It deposits calcareous tufa in this channel,
and the Tiber probably receives from it, as well as from numerous other
streams, much carbonate of lime in solution, which may contribute to the
rapid growth of its delta. A large proportion of the most splendid
edifices of ancient and modern Rome are built of travertin, derived from
the quarries of Ponte Lucano, where there has evidently been a lake at a
remote period, on the same plain as that already described.

[Illustration: Fig. 22.

Section of spheroidal concretionary Travertin under the Cascade of
Tivoli.]

_Travertin of Tivoli._--In the same neighborhood the calcareous waters
of the Anio incrust the reeds which grow on its banks, and the foam of
the cataract of Tivoli forms beautiful pendant stalactites. On the sides
of the deep chasm into which the cascade throws itself, there is seen an
extraordinary accumulation of horizontal beds of tufa and travertin,
from four to five hundred feet in thickness. The section immediately
under the temples of Vesta and the Sibyl, displays, in a precipice about
four hundred feet high, some spheroids which are from _six to eight feet
in diameter_, each concentric layer being about the eighth of an inch in
thickness. The preceding diagram exhibits about fourteen feet of this
immense mass, as seen in the path cut out of the rock in descending from
the temple of Vesta to the Grotto di Nettuno. I have not attempted to
express in this drawing the innumerable thin layers of which these
magnificent spheroids are composed, but the lines given mark some of the
natural divisions into which they are separated by minute variations in
the size or color of the laminae. The undulations also are much smaller
in proportion to the whole circumference than in the drawing. The beds
(_a_ _a_) are of hard travertin and soft tufa; below them is a pisolite
(_b_), the globules being of different sizes: underneath this appears a
mass of concretionary travertin (_c_ _c_), some of the spheroids being
of the above-mentioned extraordinary size. In some places (as at _d_)
there is a mass of amorphous limestone, or tufa, surrounded by
concentric layers. At the bottom is another bed of pisolite (_b_), in
which the small nodules are about the size and shape of beans, and some
of them of filberts, intermixed with some smaller oolitic grains. In the
tufaceous strata, wood is seen converted into a light tufa.

There can be little doubt that the whole of this deposit was formed in
an extensive lake which existed when the external configuration of this
country varied greatly from that now observed. The Anio throws itself
into a ravine excavated in the ancient travertin, and its waters give
rise to masses of calcareous stone, scarcely if at all distinguishable
from the older rock. I was shown, in 1828, in the upper part of the
travertin, the hollow left by a cart-wheel, in which the outer circle
and the spokes had been decomposed, and the spaces which they filled
left void. It seemed to me at the time impossible to explain the
position of this mould without supposing that the wheel was imbedded
before the lake was drained; but Sir R. Murchison suggests that it may
have been washed down by a flood into the gorge in modern times, and
then incrusted with calcareous tufa in the same manner as the wooden
beam of the church of St. Lucia was swept down in 1826, and stuck fast
in the Grotto of the Syren, where it still remains, and will eventually
be quite imbedded in travertin.

I have already endeavored to explain (p. 241), when speaking of the
travertin of San Filippo, how the spheroidal masses represented in
figure 22 may have been formed.

_Sulphureous and gypseus springs._--The quantity of other mineral
ingredients wherewith springs in general are impregnated, is
insignificant in comparison to lime, and this earth is most frequently
combined with carbonic acid. But as sulphuric acid, and sulphuretted
hydrogen are very frequently supplied by springs, gypsum may, perhaps,
be deposited largely in certain seas and lakes. Among other gypseous
precipitates at present known on the land, I may mention those of Baden,
near Vienna, which feed the public bath. Some of these supply singly
from 600 to 1000 cubic feet of water per hour, and deposit a fine
powder, composed of a mixture of sulphate of lime with sulphur and
muriate of lime.[318] The thermal waters of Aix, in Savoy, in passing
through strata of Jurassic limestone, turn them into gypsum or sulphate
of lime. In the Andes, at the Puenta del Inca, Lieutenant Brand found a
thermal spring at the temperature of 91 degrees Fahr., containing a large
proportion of gypsum with carbonate of lime and other ingredients.[319]
Many of the mineral springs of Iceland, says Mr. R. Bunsen, deposit
gypsum.[320] and sulphureous acid gas escapes plentifully from them as
from the volcanoes of the same island. It may, indeed, be laid down as a
general rule, that the mineral substances dissolved in hot springs agree
very closely with those which are disengaged in a gaseous form from the
craters of active volcanoes.

_Siliceous springs.--Azores._--In order that water should hold a very
large quantity of silica in solution, it seems necessary that it should
be raised to a high temperature.[321] The hot springs of the Valle das
Fernas, in the island of St. Michael, rising through volcanic rocks,
precipitate vast quantities of siliceous sinter. Around the circular
basin of the largest spring, which is between twenty and thirty feet in
diameter, alternate layers are seen of a coarser variety of sinter mixed
with clay, including grass, ferns, and reeds, in different states of
petrifaction. In some instances, alumina, which is likewise deposited
from the hot waters, is the mineralizing material. Branches of the same
ferns which now flourish in the island are found completely petrified,
preserving the same appearance as when vegetating, except that they
acquire an ash-gray color. Fragments of wood, and one entire bed from
three to five feet in depth, composed of reeds now common in the island,
have become completely mineralized.

The most abundant variety of siliceous sinter occurs in layers, from a
quarter to half an inch in thickness, accumulated on each other often to
the height of a foot and upwards, and constituting parallel, and for the
most part horizontal, strata many yards in extent. This sinter has often
a beautiful semi-opalescent lustre. A recent breccia is also in the act
of forming, composed of obsidian, pumice, and scoriae, cemented by
siliceous sinter.[322]

_Geysers of Iceland._--But the hot springs in various parts of Iceland,
particularly the celebrated geysers, afford the most remarkable example
of the deposition of silex.[323] The circular reservoirs into which the
geysers fall, are lined in the interior with a variety of opal, and
round the edges with sinter. The plants incrusted with the latter
substance have much the same appearance as those incrusted with
calcareous tufa in our own country. They consist of various grasses, the
horse-tail (_Equisetum_), and leaves of the birch-tree, which are the
most common of all, though no trees of this species now exist in the
surrounding country. The petrified stems also of the birch occur in a
state much resembling agatized wood.[324]

By analysis of the water, Mr. Faraday has ascertained that the solution
of the silex is promoted by the presence of the alkali, soda. He
suggests that the deposition of silica in an insoluble state takes place
partly because the water when cooled by exposure to the air is unable
to retain as much silica as when it issues from the earth at a
temperature of 180 degrees or 190 degrees Fahr.; and partly because the
evaporation of the water decomposes the compound of silica and soda
which previously existed. This last change is probably hastened by the
carbonic acid of the atmosphere uniting with the soda. The alkali, when
disunited from the silica, would readily be dissolved in and removed by
running water.[325]

Mineral waters, even when charged with a small proportion of silica, as
those of Ischia, may supply certain species of corals, sponges, and
infusoria, with matter for their siliceous secretions; but there is
little doubt that rivers obtain silex in solution from another and far
more general source, namely, the decomposition of felspar. When this
mineral, which is so abundant an ingredient in the hypogene and trappean
rocks, has disintegrated, it is found that the residue, called porcelain
clay, contains a small proportion only of the silica which existed in
the original felspar, the other part having been dissolved and removed
by water.[326]

_Ferruginous springs._--The waters of almost all springs contain some
iron in solution; and it is a fact familiar to all, that many of them
are so copiously impregnated with this metal, as to stain the rocks or
herbage through which they pass, and to bind together sand and gravel
into solid masses. We may naturally, then, conclude that this iron,
which is constantly conveyed from the interior of the earth into lakes
and seas, and which does not escape again from them into the atmosphere
by evaporation, must act as a coloring and cementing principle in the
subaqueous deposits now in progress. Geologists are aware that many
ancient sandstones and conglomerates are bound together or colored by
iron.

_Brine springs._--So great is the quantity of muriate of soda in some
springs, that they yield one-fourth of their weight in salt. They are
rarely, however, so saturated, and generally contain, intermixed with
salt, carbonate and sulphate of lime, magnesia, and other mineral
ingredients. The brine springs of Cheshire are the richest in our
country; those of Northwich being almost saturated. Those of Barton
also, in Lancashire, and Droitwich in Worcestershire, are extremely
rich.[327] They are known to have flowed for more than 1000 years, and
the quantity of salt which they have carried into the Severn and Mersey
must be enormous. These brine springs rise up through strata of
sandstone and red marl, which contain large beds of rock salt. The
origin of the brine, therefore, may be derived in this and many other
instances from beds of fossil salt; but as muriate of soda is one of the
products of volcanic emanations and of springs in volcanic regions, the
original source of salt may be as deep seated as that of lava.

Many springs in Sicily contain muriate of soda, and the "fiume salso,"
in particular, is impregnated with so large a quantity, that cattle
refuse to drink of it. A hot spring, rising through granite, at Saint
Nectaire, in Auvergne, may be mentioned as one of many, containing a
large proportion of muriate of soda, together with magnesia and other
ingredients.[328]

_Carbonated springs.--Auvergne._--Carbonic acid gas is very plentifully
disengaged from springs in almost all countries, but particularly near
active or extinct volcanoes. This elastic fluid has the property of
decomposing many of the hardest rocks with which it comes in contact,
particularly that numerous class in whose composition felspar is an
ingredient. It renders the oxide of iron soluble in water, and
contributes, as was before stated, to the solution of calcareous matter.
In volcanic districts these gaseous emanations are not confined to
springs, but rise up in the state of pure gas from the soil in various
places. The Grotto del Cane, near Naples, affords an example, and
prodigious quantities are now annually disengaged from every part of the
Limagne d'Auvergne, where it appears to have been developed in equal
quantity from time immemorial. As the acid is invisible, it is not
observed, except an excavation be made, wherein it immediately
accumulates, so that it will extinguish a candle. There are some springs
in this district, where the water is seen bubbling and boiling up with
much noise, in consequence of the abundant disengagement of this gas. In
the environs of Pont-Gibaud, not far from Clermont, a rock belonging to
the gneiss formation, in which lead-mines are worked, has been found to
be quite saturated with carbonic acid gas, which is constantly
disengaged. The carbonates of iron, lime, and manganese are so
dissolved, that the rock is rendered soft, and the quartz alone remains
unattacked.[329] Not far off is the small volcanic cone of Chaluzet,
which once broke up through the gneiss, and sent forth a lava stream.

_Supposed atmosphere of carbonic acid._--Prof. Bischoff in his history
of volcanoes,[330] has shown what enormous quantities of carbonic acid
gas are exhaled in the vicinity of the extinct craters of the Rhine (in
the neighborhood of the Laacher-see, for example, and the Eifel), and
also in the mineral springs of Nassau and other countries, where there
are no immediate traces of volcanic action. It would be easy to
calculate in how short a period the solid carbon, thus emitted from the
interior of the earth in an invisible form, would amount to a quantity
as great as could be obtained from the trees of a large forest, and how
many thousand years would be required to supply the materials of a dense
seam of pure coal from the same source. Geologists who favor the
doctrine of the former existence of an atmosphere highly charged with
carbonic acid, at the period of the ancient coal-plants, have not
sufficiently reflected on the continual disengagement of carbon, which
is taking place in a gaseous form from springs, as also in a free state
from the ground and from volcanic craters into the air. We know that
all plants are now engaged in secreting carbon, and many thousands of
large trees are annually floated down by great rivers, and buried in
their alluvial deposits; but before we can assume that the quantity of
carbon which becomes permanently locked up in the earth by such agency
will bring about an essential change in the chemical composition of the
atmosphere, we must be sure that the trees annually buried contain more
carbon than is given out from the interior of the earth in the same
lapse of time. Every large area covered by a dense mass of peat, bears
ample testimony to the fact, that several million tons of carbon have
been taken from the air, by the powers of vegetable life, and stored up
in the earth's crust, a large quantity of oxygen having been at the same
time set free; but we cannot infer from these circumstances, that the
constitution of the atmosphere has been materially deranged, until we
have data for estimating the rate at which dead animal and vegetable
substances are daily putrefying,--organic remains and various calcareous
rocks decomposing, and volcanic regions emitting fresh volumes of
carbonic acid gas. That the ancient carboniferous period was one of vast
duration all geologists are agreed; instead, therefore, of supposing an
excess of carbonic acid in the air at that epoch, for the support of a
peculiar flora, we may imagine Time to have multiplied the quantity of
carbon given out annually by mineral springs, volcanic craters, and
other sources, until the component elements of any given number of
coal-seams had been evolved from below, without any variation taking
place in the constitution of the atmosphere. It has been too common, in
reasoning on this question, to compute the loss of carbon by the volume
of coal stored up in the ancient strata, and to take no account of the
annual gain, by the restoration of carbonic acid to the atmosphere,
through the machinery above alluded to.[331]

_Disintegrating effects of carbonic acid._--The disintegration of
granite is a striking feature of large districts in Auvergne, especially
in the neighborhood of Clermont. This decay was called by Dolomieu, "la
maladie du granite;" and the rock may with propriety be said to have
_the rot_, for it crumbles to pieces in the hand. The phenomenon may,
without doubt, be ascribed to the continual disengagement of carbonic
acid gas from numerous fissures.

In the plains of the Po, between Verona and Parma, especially at Villa
Franca, south of Mantua, I observed great beds of alluvium, consisting
chiefly of primary pebbles, percolated by spring-water, charged with
carbonate of lime and carbonic acid in great abundance. They are for the
most part incrusted with calc-sinter; and the rounded blocks of gneiss,
which have all the outward appearance of solidity, have been so
disintegrated by the carbonic acid as readily to fall to pieces.

The subtraction of many of the elements of rocks by the solvent power of
carbonic acid, ascending both in a gaseous state and mixed with
spring-water in the crevices of rocks, must be one of the most powerful
sources of those internal changes and rearrangements of particles so
often observed in strata of every age. The calcareous matter, for
example, of shells, is often entirely removed and replaced by carbonate
of iron, pyrites, silex, or some other ingredient, such as mineral
waters usually contain in solution. It rarely happens, except in
limestone rocks, that the carbonic acid can dissolve all the constituent
parts of the mass; and for this reason, probably, calcareous rocks are
almost the only ones in which great caverns and long winding passages
are found.

_Petroleum springs._--Springs of which the waters contain a mixture of
petroleum and the various minerals allied to it, as bitumen, naphtha,
asphaltum, and pitch, are very numerous, and are, in many cases,
undoubtedly connected with subterranean fires, which raise or sublime
the more subtle parts of the bituminous matters contained in rocks. Many
springs in the territory of Modena and Parma, in Italy, produce
petroleum in abundance; but the most powerful, perhaps, yet known, are
those on the Irawadi, in the Burman empire. In one locality there are
said to be 520 wells, which yield annually 400,000 hogsheads of
petroleum.[332]

_Pitch lake of Trinidad._--Fluid bitumen is seen to ooze from the bottom
of the sea, on both sides of the island of Trinidad, and to rise up to
the surface of the water. Near Cape La Braye there is a vortex which, in
stormy weather, according to Captain Mallet, gushes out, raising the
water five or six feet, and covers the surface for a considerable space
with petroleum, or tar; and the same author quotes Gumilla, as stating,
in his "Description of the Orinoco," that about seventy years ago, a
spot of land on the western coast of Trinidad, near half-way between the
capital and an Indian village, sank suddenly, and was immediately
replaced by a small lake of pitch, to the great terror of the
inhabitants.[333]

It is probable that the great pitch lake of Trinidad owes its origin to
a similar cause; and Dr. Nugent has justly remarked, that in that
district all the circumstances are now combined from which deposits of
pitch may have originated. The Orinoco has for ages been rolling down
great quantities of woody and vegetable bodies into the surrounding sea,
where, by the influence of currents and eddies, they may be arrested and
accumulated in particular places. The frequent occurrence of earthquakes
and other indications of volcanic action in those parts lend countenance
to the opinion, that these vegetable substances may have undergone, by
the agency of subterranean fire, those transformations and chemical
changes which produce petroleum; and this may, by the same causes, be
forced up to the surface, where, by exposure to the air, it becomes
inspissated, and forms the different varieties of pure and earthy pitch,
or asphaltum, so abundant in the island.[334]

It may be stated generally, that a large portion of the finer particles
and the more crystalline substances, found in sedimentary rocks of
different ages, are composed of the same elements as are now held in
solution by springs, while the coarser materials bear an equally strong
resemblance to the pebbles and sedimentary matter carried down by
torrents and rivers. It should also be remembered, that it is not only
during inundations, when the muddy sediment is apparent, that rivers are
busy in conveying solid matter to the sea, but that even when their
waters are perfectly transparent, they are annually bearing along vast
masses of carbon, lime, and silica to the ocean.




CHAPTER XVII.

REPRODUCTIVE EFFECTS OF RIVERS.


  Lake deltas--Growth of the delta of the Upper Rhine in the Lake of
    Geneva--Computation of the age of deltas--Recent deposits in Lake
    Superior--Deltas of inland seas--Course of the Po--Artificial
    embankments of the Po and Adige--Delta of the Po, and other rivers
    entering the Adriatic--Rapid conversion of that gulf into
    land--Mineral characters of the new deposits--Marine delta of the
    Rhone--Various proofs of its increase--Stony nature of its
    deposits--Coast of Asia Minor--Delta of the Nile.


DELTAS IN LAKES.

I have already spoken in the 14th chapter of the action of running
water, and of the denuding power of rivers, but we can only form a just
conception of the excavating and removing force exerted by such bodies
of water, when we have the advantage of examining the reproductive
effects of the same agents: in other words, of beholding in a palpable
form the aggregate amount of matter, which they have thrown down at
certain points in their alluvial plains, or in the basins of lakes and
seas. Yet it will appear, when we consider the action of currents, that
the growth of deltas affords a very inadequate standard by which to
measure the entire carrying power of running water, since a considerable
portion of fluviatile sediment is swept far out to sea.

Deltas may be divided into, first, those which are formed in lakes;
secondly, those in island seas, where the tides are almost
imperceptible; and, thirdly, those on the borders of the ocean. The most
characteristic distinction between the lacustrine and marine deltas
consists in the nature of the organic remains which become imbedded in
their deposits; for, in the case of a lake, it is obvious that these
must consist exclusively of such genera of animals as inhabit the land
or the waters of a river or a lake; whereas, in the other case, there
will be an admixture, and most frequently a predominance, of animals
which inhabit salt water. In regard, however, to the distribution of
inorganic matter, the deposits of lakes and seas are formed under very
analogous circumstances.

_Lake of Geneva._--Lakes exemplify the first reproductive operations in
which rivers are engaged when they convey the detritus of rocks and the
ingredients of mineral springs from mountainous regions. The accession
of new land at the mouth of the Rhone, at the upper end of the Lake of
Geneva, or the Leman Lake, presents us with an example of a considerable
thickness of strata which have accumulated since the historical era.
This sheet of water is about thirty-seven miles long, and its breadth is
from two to eight miles. The shape of the bottom is very irregular, the
depth having been found by late measurements to vary from 20 to 160
fathoms.[335] The Rhone, where it enters at the upper end, is turbid and
discolored; but its waters, where it issues at the town of Geneva, are
beautifully clear and transparent. An ancient town, called Port Vallais
(Portus Valesiae of the Romans), once situated at the water's edge, at
the upper end, is now more than a mile and a half inland--this
intervening alluvial tract having been acquired in about eight
centuries. The remainder of the delta consists of a flat alluvial plain,
about five or six miles in length, composed of sand and mud, a little
raised above the level of the river, and full of marshes.

Sir Henry De la Beche found, after numerous soundings in all parts of
the lake, that there was a pretty uniform depth of from 120 to 160
fathoms throughout the central region, and on approaching the delta, the
shallowing of the bottom began to be very sensible at a distance of
about a mile and three quarters from the mouth of the Rhone; for a line
drawn from St. Gingoulph to Vevey gives a mean depth of somewhat less
than 600 feet, and from that part of the Rhone, the fluviatile mud is
always found along the bottom.[336] We may state, therefore, that the
new strata annually produced are thrown down upon a slope about two
miles in length; so that, notwithstanding the great depth of the lake,
the new deposits are inclined at so slight an angle, that the dip of the
beds would be termed, in ordinary geological language, horizontal.

The strata probably consist of alternations of finer and coarser
particles; for, during the hotter months from April to August, when the
snows melt, the volume and velocity of the river are greatest, and large
quantities of sand, mud, vegetable matter, and drift-wood are
introduced; but during the rest of the year, the influx is comparatively
feeble, so much so, that the whole lake, according to Saussure, stands
six feet lower. If, then, we could obtain a section of the accumulation
formed in the last eight centuries, we should see a great series of
strata, probably from 600 to 900 feet thick (the supposed original depth
of the head of the lake), and nearly two miles in length, inclined at a
very slight angle. In the mean time, a great number of smaller deltas
are growing around the borders of the lake, at the mouths of rapid
torrents, which pour in large masses of sand and pebbles. The body of
water in these torrents is too small to enable them to spread out the
transported matter over so extensive an area as the Rhone does. Thus,
for example, there is a depth of eighty fathoms within half a mile of
the shore, immediately opposite the great torrent which enters east of
Ripaille, so that the dip of the strata in that minor delta must be
about four times as great as those deposited by the main river at the
upper extremity of the lake.[337]

_Chronological computations of the age of deltas._--The capacity of this
basin being now ascertained, it would be an interesting subject of
inquiry, to determine in what number of years the Leman Lake will be
converted into dry land. It would not be very difficult to obtain the
elements for such a calculation, so as to approximate at least to the
quantity of time required for the accomplishment of the result. The
number of cubic feet of water annually discharged by the river into the
lake being estimated, experiments might be made in the winter and summer
months, to determine the proportion of matter held in suspension or in
chemical solution by the Rhone. It would be also necessary to allow for
the heavier matter drifted along at the bottom, which might be estimated
on hydrostatical principles, when the average size of the gravel and the
volume and velocity of the stream at different seasons were known.
Supposing all these observations to have been made, it would be more
easy to calculate the future than the former progress of the delta,
because it would be a laborious task to ascertain, with any degree of
precision, the original depth and extent of that part of the lake which
is already filled up. Even if this information were actually obtained by
borings, it would only enable us to approximate within a certain number
of centuries to the time when the Rhone began to form its present delta;
but this would not give us the date of the origin of the Leman Lake in
its present form, because the river may have flowed into it for
thousands of years, without importing any sediment whatever. Such would
have been the case, if the waters had first passed through a chain of
upper lakes; and that this was actually the fact, seems indicated by the
course of the Rhone between Martigny and the Lake of Geneva, and, still
more decidedly, by the channels of many of its principal feeders.

If we ascend, for example, the valley through which the Dranse flows, we
find that it consists of a succession of basins, one above the other, in
each of which there is a wide expanse of flat alluvial lands, separated
from the next basin by a rocky gorge, once perhaps the barrier of a
lake. The river seems to have filled these lakes, one after the other,
and to have partially cut through the barriers, some of which it is
still gradually eroding to a greater depth. Before, therefore, we can
pretend even to hazard a conjecture as to the era at which the principal
delta of Lake Leman or any other delta commenced, we must be thoroughly
acquainted with the geographical features and geological history of the
whole system of higher valleys which communicate with the main stream,
and all the changes which they have undergone since the last series of
convulsions which agitated and altered the face of the country.

_Lake Superior._--Lake Superior is the largest body of freshwater in the
world, being above 1700 geographical miles in circumference when we
follow the sinuosities of its coasts, and its length, on a curved line
drawn through its centre, being more than 400, and its extreme breadth
above 150 geographical miles. Its surface is nearly as large as the
whole of England. Its average depth varies from 80 to 150 fathoms; but,
according to Captain Bayfield, there is reason to think that its
greatest depth would not be overrated at 200 fathoms, so that its bottom
is, in some parts, nearly 600 feet below the level of the Atlantic, its
surface being about as much above it. There are appearances in different
parts of this, as of the other Canadian lakes, leading us to infer that
its waters formerly occupied a higher level than they reach at present;
for at a considerable distance from the present shores, parallel lines
of rolled stones and shells are seen rising one above the other, like
the seats of an amphitheatre. These ancient lines of shingle are exactly
similar to the present beaches in most bays, and they often attain an
elevation of 40 or 50 feet above the present level. As the heaviest
gales of wind do not raise the waters more than three or four feet, the
elevated beaches have by some been referred to the subsidence of the
lake at former periods, in consequence of the wearing down of its
barrier; by others to the upraising of the shores by earthquakes, like
those which have produced similar phenomena on the coast of Chili.

The streams which discharge their waters into Lake Superior are several
hundred in number, without reckoning those of smaller size; and the
quantity of water supplied by them is many times greater than that
discharged at the Falls of St. Mary, the only outlet. The evaporation,
therefore, is very great, and such as might be expected from so vast an
extent of surface. On the northern side, which is encircled by primary
mountains, the rivers sweep in many large boulders with smaller gravel
and sand, chiefly composed of granitic and trap rocks. There are also
currents in the lake in various directions, caused by the continued
prevalence of strong winds, and to their influence we may attribute the
diffusion of finer mud far and wide over great areas; for by numerous
soundings made during Captain Bayfield's survey, it was ascertained that
the bottom consists generally of a very adhesive clay, containing shells
of the species at present existing in the lake. When exposed to the air,
this clay immediately becomes indurated in so great a degree, as to
require a smart blow to break it. It effervesces slightly with diluted
nitric acid, and is of different colors in different parts of the lake;
in one district blue, in another red, and in a third white, hardening
into a substance resembling pipeclay.[338] From these statements, the
geologist will not fail to remark how closely these recent lacustrine
formations in America resemble the tertiary argillaceous and calcareous
marls of lacustrine origin in Central France. In both cases many of the
genera of shells most abundant, as Limnea and Planorbis, are the same;
and in regard to other classes of organic remains there must be the
closest analogy, as I shall endeavor more fully to explain when speaking
of the imbedding of plants and animals in recent deposits.


DELTAS OF INLAND SEAS.

Having thus briefly considered some of the lacustrine deltas now in
progress, we may next turn our attention to those of inland seas.

_Course of the Po._--The Po affords an instructive example of the manner
in which a great river bears down to the sea the matter poured into it
by a multitude of tributaries descending from lofty chains of mountains.
The changes gradually effected in the great plain of Northern Italy,
since the time of the Roman republic, are considerable. Extensive lakes
and marshes have been gradually filled up, as those near Placentia,
Parma, and Cremona, and many have been drained naturally by the
deepening of the beds of rivers. Deserted river-courses are not
unfrequent, as that of the Serio Morto, which formerly fell into the
Adda, in Lombardy. The Po also itself has often deviated from its
course, having after the year 1390 deserted part of the territory of
Cremona, and invaded that of Parma; its old channel being still
recognizable, and bearing the name of Po Morto. There is also an old
channel of the Po in the territory of Parma, called Po Vecchio, which
was abandoned in the twelfth century, when a great number of towns were
destroyed.

_Artificial embankments of Italian rivers._--To check these and similar
aberrations, a general system of embankment has been adopted; and the
Po, Adige, and almost all their tributaries, are now confined between
high artificial banks. The increased velocity acquired by streams thus
closed in, enables them to convey a much larger portion of foreign
matter to the sea; and, consequently, the deltas of the Po and Adige
have gained far more rapidly on the Adriatic since the practice of
embankment became almost universal. But, although more sediment is borne
to the sea, part of the sand and mud, which in the natural state of
things would be spread out by annual inundations over the plain, now
subsides in the bottom of the river-channels; and their capacity being
thereby diminished, it is necessary, in order to prevent inundations in
the following spring, to extract matter from the bed, and to add it to
the banks of the river. Hence it happens that these streams now traverse
the plain on the top of high mounds, like the waters of aqueducts, and
at Ferrara the surface of the Po has become more elevated than the roofs
of the houses.[339] The magnitude of these barriers is a subject of
increasing expense and anxiety, it having been sometimes found necessary
to give an additional height of nearly one foot to the banks of the
Adige and Po in a single season.

The practice of embankment was adopted on some of the Italian rivers as
early as the thirteenth century; and Dante, writing in the beginning of
the fourteenth, describes, in the seventh circle of hell, a rivulet of
tears separated from a burning sandy desert by embankments "like those
which, between Ghent and Bruges, were raised against the ocean, or those
which the Paduans had erected along the Brenta to defend their villas on
the melting of the Alpine snows."


  Quale i Fiamminghi tra Guzzante e Bruggia,
  Temendo il fiotto che in ver lor s'avventa,
  Fanno lo schermo, perche il mar si fuggia,
  E quale i Padovan lungo la Brenta,
  Per difender lor ville e lor castelli,
  Anzi che Chiarentana il caldo senta.--

  _Inferno_, Canto xv.


In the Adriatic, from the northern part of the Gulf of Trieste, where
the Isonzo enters, down to the south of Ravenna, there is an
uninterrupted series of recent accessions of land, more than 100 miles
in length, which, within the last 2000 years, have increased from _two
to twenty miles in breadth_. A line of sand-bars of great length has
been formed nearly all along the western coast of this gulf, inside of
which are lagunes, such as those of Venice, and the large lagune of
Comacchio, 20 miles in diameter. Newly deposited mud brought down by the
streams is continually lessening the depth of the lagunes, and
converting part of them into meadows.[340] The Isonzo, Tagliamento,
Piave, Brenta, Adige, and Po, besides many other inferior rivers,
contribute to this advance of the coast-line and to the shallowing of
the lagunes and the gulf.

_Delta of the Po._--The Po and the Adige may now be considered as
entering by one common delta, for two branches of the Adige are
connected with arms of the Po, and thus the principal delta has been
pushed out beyond those bars which separate the lagunes from the sea.
The rate of the advance of this new land has been accelerated, as before
stated, since the system of embanking the rivers became general,
especially at that point where the Po and Adige enter. The waters are no
longer permitted to spread themselves far and wide over the plains, and
to leave behind them the larger portion of their sediment. Mountain
torrents also have become more turbid since the clearing away of
forests, which once clothed the southern flanks of the Alps. It is
calculated that the mean rate of advance of the delta of the Po on the
Adriatic between the years 1200 and 1600 was 25 yards or metres a year,
whereas the mean annual gain from 1600 to 1804 was 70 metres.[341]

Adria was a seaport in the time of Augustus, and had, in ancient times,
given its name to the gulf; it is now about twenty Italian miles inland.
Ravenna was also a seaport, and is now about four miles from the main
sea. Yet even before the practice of embankment was introduced, the
alluvium of the Po advanced with rapidity on the Adriatic; for Spina, a
very ancient city, originally built in the district of Ravenna, at the
mouth of a great arm of the Po, was, so early as the commencement of our
era, eleven miles distant from the sea.[342]

But although so many rivers are rapidly converting the Adriatic into
land, it appears, by the observations of M. Morlot, that since the time
of the Romans, there has been a general subsidence of the coast and bed
of this sea in the same region to the amount of five feet, so that the
advance of the new-made land has not been so fast as it would have been
had the level of the coast remained unaltered. The signs of a much
greater depression anterior to the historical period have also been
brought to light by an Artesian well, bored in 1847, to the depth of
more than 400 feet, which still failed to penetrate through the modern
fluviatile deposit. The auger passed chiefly through beds of sand and
clay, but at four several depths, one of them very near the bottom of
the excavation, it pierced beds of turf, or accumulations of vegetable
matter, precisely similar to those now formed superficially on the
extreme borders of the Adriatic. Hence we learn that a considerable area
of what was once land has sunk down 400 feet in the course of ages.[343]

The greatest depth of the Adriatic, between Dalmatia and the mouths of
the Po, is twenty-two fathoms; but a large part of the Gulf of Trieste
and the Adriatic, opposite Venice, is less than twelve fathoms deep.
Farther to the south, where it is less affected by the influx of great
rivers, the gulf deepens considerably. Donati, after dredging the
bottom, discovered the new deposits to consist partly of mud and partly
of rock, the rock being formed of calcareous matter, incrusting shells.
He also ascertained, that particular species of testacea were grouped
together in certain places, and were becoming slowly incorporated with
the mud or calcareous precipitates.[344] Olivi, also, found some
deposits of sand, and others of mud, extending half way across the gulf;
and he states that their distribution along the bottom was evidently
determined by the prevailing current.[345] It is probable, therefore,
that the finer sediment of all the rivers at the head of the Adriatic
may be intermingled by the influence of the current; and all the central
parts of the gulf may be considered as slowly filling up with horizontal
deposits, similar to those of the Subapennine hills, and containing many
of the same species of shells. The Po merely introduces at present fine
sand and mud, for it carries no pebbles farther than the spot where it
joins the Trebia, west of Piacenza. Near the northern borders of the
basin, the Isonzo, Tagliamento, and many other streams, are forming
immense beds of sand and some conglomerate; for here some high mountains
of Alpine limestone approach within a few miles of the sea.

In the time of the Romans, the hot-baths of Monfalcone were on one of
several islands of Alpine limestone, between which and the mainland, on
the north, was a channel of the sea, about a mile broad. This channel is
now converted into a grassy plain, which surrounds the islands on all
sides. Among the numerous changes on this coast, we find that the
present channel of the Isonzo is several miles to the west of its
ancient bed, in part of which, at Ronchi, the old Roman bridge which
crossed the Via Appia was lately found buried in fluviatile silt.

_Marine delta of the Rhone._--The lacustrine delta of the Rhone in
Switzerland has already been considered (p. 251), its contemporaneous
marine delta may now be described. Scarcely has the river passed out of
the Lake of Geneva before its pure waters are again filled with sand and
sediment by the impetuous Arve, descending from the highest Alps, and
bearing along in its current the granitic detritus annually brought down
by the glaciers of Mont Blanc. The Rhone afterwards receives vast
contributions of transported matter from the Alps of Dauphiny, and the
primary and volcanic mountains of Central France; and when at length it
enters the Mediterranean, it discolors the blue waters of that sea with
a whitish sediment, for the distance of between six and seven miles,
throughout which space the current of fresh water is perceptible.

Strabo's description of the delta is so inapplicable to its present
configuration, as to attest a complete alteration in the physical
features of the country since the Augustan age. It appears, however,
that the head of the delta, or the point at which it begins to ramify,
has remained unaltered since the time of Pliny, for he states that the
Rhone divided itself at Arles into two arms. This is the case at
present; one of the branches, the western, being now called Le Petit
Rhone, which is again subdivided before entering the Mediterranean. The
advance of the base of the delta, in the last eighteen centuries, is
demonstrated by many curious antiquarian monuments. The most striking of
these is the great and unnatural datour of the old Roman road from
Ugernum to Beziers (_Boeterrae_) which went round by Nismes
(_Nemausus_). It is clear that, when this was first constructed, it was
impossible to pass in a direct line, as now, across the delta, and that
either the sea or marshes intervened in a tract now consisting of terra
firma.[346] Astruc also remarks, that all the places on low lands, lying
to the north of the old Roman road between Nismes and Beziers, have
names of Celtic origin, evidently given to them by the first inhabitants
of the country; whereas, the places lying south of that road, towards
the sea, have names of Latin derivation, and were clearly founded after
the Roman language had been introduced.

Another proof, also, of the great extent of land which has come into
existence since the Romans conquered and colonized Gaul, is derived from
the fact, that the Roman writers never mention the thermal waters of
Balaruc in the delta, although they were well acquainted with those of
Aix, and others still more distant, and attached great importance to
them, as they invariably did to all hot springs. The waters of Balaruc,
therefore, must have formerly issued under the sea--a common phenomenon
on the borders of the Mediterranean; and on the advance of the delta
they continued to flow out through the new deposits.

Among the more direct proofs of the increase of land, we find that Mese,
described under the appellation of Mesua Collis by Pomponius Mela,[347]
and stated by him to be nearly an island, is now far inland. Notre Dame
des Ports, also, was a harbor in 898, but is now a league from the
shore. Psalmodi was an island in 815, and is now two leagues from the
sea. Several old lines of towers and sea-marks occur at different
distances from the present coast, all indicating the successive retreat
of the sea, for each line has in its turn become useless to mariners;
which may well be conceived, when we state that the Tower of Tignaux,
erected on the shore so late as the year 1737, is already a mile remote
from it.[348]

By the confluence of the Rhone and the currents of the Mediterranean,
driven by winds from the south, sand-bars are often formed across the
mouths of the river; by these means considerable spaces become divided
off from the sea, and subsequently from the river also, when it shifts
its channels of efflux. As some of these lagoons are subject to the
occasional ingress of the river when flooded, and of the sea during
storms, they are alternately salt and fresh. Others, after being filled
with salt water, are often lowered by evaporation till they become more
salt than the sea; and it has happened, occasionally, that a
considerable precipitate of muriate of soda has taken place in these
natural salterns. During the latter part of Napoleon's career, when the
excise laws were enforced with extreme rigor, the police was employed to
prevent such salt from being used. The fluviatile and marine shells
inclosed in these small lakes often live together in brackish water; but
the uncongenial nature of the fluid usually produces a dwarfish size,
and sometimes gives rise to strange varieties in form and color.

Captain Smyth in his survey of the coast of the Mediterranean, found the
sea opposite the mouth of the Rhone, to deepen gradually from four to
forty fathoms, within a distance of six or seven miles, over which the
discolored fresh water extends; so that the inclination of the new
deposits must be too slight to be appreciable in such an extent of
section as a geologist usually obtains in examining ancient formations.
When the wind blew from the southwest, the ships employed in the survey
were obliged to quit their moorings; and when they returned, the new
sand-banks in the delta were found covered over with a great abundance
of marine shells. By this means, we learn how occasional beds of drifted
marine shells may become interstratified with freshwater strata at a
river's mouth.

_Stony nature of its deposits._--That a great proportion, at least, of
the new deposit in the delta of the Rhone consists of _rock_, and not of
loose incoherent matter, is perfectly ascertained. In the Museum at
Montpelier is a cannon taken up from the sea near the mouth of the
river, imbedded in a crystalline calcareous rock. Large masses, also,
are continually taken up of an arenaceous rock, cemented by calcareous
matter, including multitudes of broken shells of recent species. The
observations lately made on this subject corroborate the former
statement of Marsilli, that the earthy deposits of the coast of
Languedoc form a stony substance, for which reason he ascribes a certain
bituminous, saline, and glutinous nature to the substances brought down
with sand by the Rhone.[349] If the number of mineral springs charged
with carbonate of lime which fall into the Rhone and its feeders in
different parts of France be considered, we shall feel no surprise at
the lapidification of the newly deposited sediment in this delta. It
should be remembered, that the fresh water introduced by rivers being
lighter than the water of the sea, floats over the latter, and remains
upon the surface for a considerable distance. Consequently it is exposed
to as much evaporation as the waters of a lake; and the area over which
the river-water is spread, at the junction of great rivers and the sea,
may well be compared, in point of extent, to that of considerable lakes.

Now, it is well known, that so great is the quantity of water carried
off by evaporation in some lakes, that it is nearly equal to the water
flowing in; and in some inland seas, as the Caspian, it is quite equal.
We may, therefore, well suppose that, in cases where a strong current
does not interfere, the greater portion not only of the matter held
mechanically in suspension, but of that also which is in chemical
solution, may be precipitated at no great distance from the shore. When
these finer ingredients are extremely small in quantity, they may only
suffice to supply crustaceous animals, corals, and marine plants, with
the earthy particles necessary for their secretions; but whenever it is
in excess (as generally happens if the basin of a river lie partly in a
district of active or extinct volcanoes), then will solid deposits be
formed, and the shells will at once be included in a rocky mass.

_Coast of Asia Minor._--Examples of the advance of the land upon the sea
are afforded by the southern coast of Asia Minor. Admiral Sir F.
Beaufort has pointed out in his survey the great alterations effected
since the time of Strabo, where havens are filled up, islands joined to
the mainland, and where the whole continent has increased many miles in
extent. Strabo himself, on comparing the outline of the coast in his
time with its ancient state, was convinced, like our countryman, that
it had gained very considerably upon the sea. The new-formed strata of
Asia Minor consist _of stone_, not of loose incoherent materials. Almost
all the streamlets and rivers, like many of those in Tuscany and the
south of Italy, hold abundance of carbonate of lime in solution, and
precipitate travertin, or sometimes bind together the sand and gravel
into solid sandstones and conglomerates; every delta and sand-bar thus
acquires solidity, which often prevents streams from forcing their way
through them, so that their mouths are constantly changing their
position.[350]

_Delta of the Nile._--That Egypt was "the gift of the Nile," was the
opinion of her priests before the time of Herodotus; and Rennell
observes, that the "configuration and composition of the low lands leave
no room for doubt that the sea once washed the base of the rocks on
which the pyramids of Memphis stand, the _present_ base of which is
washed by the inundation of the Nile, at an elevation of 70 or 80 feet
above the Mediterranean. But when we attempt to carry back our ideas to
the remote period when the foundation of the delta was first laid, we
are lost in the contemplation of so vast an interval of time."[351]
Herodotus observes, "that the country round Memphis seemed formerly to
have been an arm of the sea gradually filled by the Nile, in the same
manner as the Meander, Achelous, and other streams, had formed deltas.
Egypt, therefore, he says, like the Red Sea, was once a long narrow bay,
and both gulfs were separated by a small neck of land. If the Nile, he
adds, should by any means have an issue into the Arabian Gulf, it might
choke it up with earth in 20,000 or even, perhaps, in 10,000 years; and
why may not the Nile have filled a still greater gulf with mud in the
space of time which has passed before our age?"[352]

The distance between Memphis and the most prominent part of the delta in
a straight line north and south, is about 100 geographical miles; the
length of the base of the delta is more than 200 miles if we follow the
coast between the ancient extreme eastern and western arms; but as these
are now blocked up, that part only of Lower Egypt which intervenes
between the Rosetta and Damietta branches, is usually called the delta,
the coast line of which is about 90 miles in length. The bed of the
river itself, says Sir J. G. Wilkinson, undergoes a gradual increase of
elevation varying in different places, and always lessening in
proportion as the river approaches the sea. "This increase of elevation
in perpendicular height is much smaller in Lower than in Upper Egypt,
and in the delta it diminishes still more; so that, according to an
approximate calculation, the land about Elephantine, or the first
cataract, lat. 24 degrees 5 minutes, has been raised nine feet in 1700
years; at Thebes, lat. 25 degrees 43 minutes, about seven feet; and at
Heliopolis and Cairo, lat. 30 degrees, about five feet ten inches. At
Rosetta and the mouths of the Nile, lat. 31 degrees 30 minutes, the
diminution in the perpendicular thickness of the deposit is lessened in
a much greater decreasing ratio than in the straitened valley of Central
and Upper Egypt, owing to the great extent, east and west, over which
the inundation spreads."[353]

For this reason the alluvial deposit does not cause the delta to
protrude rapidly into the sea, although some ancient cities are now a
mile or more inland, and the mouths of the Nile, mentioned by the
earlier geographers, have been many of them silted up, and the outline
of the coast entirely changed.

The bed of the Nile always keeps pace with the general elevation of the
soil, and the banks of this river, like those of the Mississippi and its
tributaries (see p. 265), are much higher than the flat land at a
distance, so that they are seldom covered during the highest
inundations. In consequence of the gradual rise of the river's bed, the
annual flood is constantly spreading over a wider area, and the alluvial
soil encroaches on the desert, covering, to the depth of six or seven
feet, the base of statues and temples which the waters never reached
3000 years ago. Although the sands of the Libyan deserts have in some
places been drifted into the valley of the Nile, yet these aggressions,
says Wilkinson, are far more than counterbalanced by the fertilizing
effect of the water which now reaches farther inland towards the desert,
so that the number of square miles of arable soil is greater at present
than at any previous period.

_Mud of the Nile._--On comparing the different analyses which have been
published of this mud, it will be found that it contains a large
quantity of argillaceous matter, with much peroxide of iron, some
carbonate of lime, and a small proportion of carbonate of magnesia. The
latest and most careful analysis by M. Lassaigne shows a singularly
close resemblance in the proportions of the ingredients of silica,
alumina, iron, carbon, lime, and magnesia, and those observed in
ordinary mica;[354] but a much larger quantity of calcareous matter is
sometimes present.

In many places, as at Cairo, where artificial excavations have been
made, or where the river has undermined its banks, the mud is seen to be
thinly stratified, the upper part of each annual layer consisting of
earth of a lighter color than the lower, and the whole separating easily
from the deposit of the succeeding year. These annual layers are
variable in thickness; but, according to the calculations of Girard and
Wilkinson, the mean annual thickness of a layer at Cairo cannot exceed
that of a sheet of thin pasteboard, and a stratum of two or three feet
must represent the accumulation of a thousand years.

The depth of the Mediterranean is about twelve fathoms at a small
distance from the shore of the delta; it afterwards increases gradually
to 50, and then suddenly descends to 380 fathoms, which is, perhaps, the
original depth of the sea where it has not been rendered shallower by
fluviatile matter. We learn from Lieut. Newbold that nothing but the
finest and lightest ingredients reach the Mediterranean, where he has
observed the sea discolored by them to the distance of 40 miles from the
shore.[355] The small progress of the delta in the last 2000 years
affords, perhaps, no measure for estimating its rate of growth when it
was an inland bay, and had not yet protruded itself beyond the
coast-line of the Mediterranean. A powerful current now sweeps along the
shores of Africa, from the Straits of Gibraltar to the prominent
convexity of Egypt, the western side of which is continually the prey of
the waves; so that not only are fresh accessions of land checked, but
ancient parts of the delta are carried away. By this cause, Canopus and
some other towns have been overwhelmed; but to this subject I shall
again refer when speaking of tides and currents.




CHAPTER XVIII.

REPRODUCTIVE EFFECTS OF RIVERS--_continued_.


  Deltas formed under the influence of tides--Basin and delta of the
    Mississippi--Alluvial plain--River-banks and bluffs--Curves of the
    river--Natural rafts and snags--New lakes, and effects of
    earthquakes--Antiquity of the delta--Delta of the Ganges and
    Brahmapootra--Head of the delta and Sunderbunds--Islands formed and
    destroyed--Crocodiles--Amount of fluviatile sediment in the
    water--Artesian boring at Calcutta--Proofs of subsidence--Age of the
    delta--Convergence of deltas--Origin of existing deltas not
    contemporaneous--Grouping of strata and stratification in
    deltas--Conglomerates--Constant interchange of land and sea.


In the last chapter several examples were given of the deltas of inland
seas, where the influence of the tides is almost imperceptible. We may
next consider those marine or oceanic deltas, where the tides play an
important part in the dispersion of fluviatile sediment, as in the Gulf
of Mexico, where they exert a moderate degree of force, and then in the
Bay of Bengal, where they are extremely powerful. In regard to
estuaries, which Rennel termed "negative deltas," they will be treated
of more properly when our attention is specially turned to the
operations of tides and currents (chapters 20, 21, and 22). In this
case, instead of the land gaining on the sea at the river's mouth, the
tides penetrate far inland beyond the general coast-line.


BASIN AND DELTA OF THE MISSISSIPPI.

_Alluvial plain._--The hydrographical basin of the Mississippi displays,
on the grandest scale, the action of running water on the surface of a
vast continent. This magnificent river rises nearly in the forty-ninth
parallel of north latitude, and flows to the Gulf of Mexico in the
twenty-ninth--a course, including its meanders, of more than three
thousand miles. It passes from a cold climate, where the hunter obtains
his furs and peltries, traverses the temperate latitudes, and discharges
its waters into the sea in the region of rice, the cotton plant, and the
sugar-cane. From near its mouth at the Balize a steamboat may ascend for
2000 miles with scarcely any perceptible difference in the width of the
river. Several of its tributaries, the Red River, the Arkansas, the
Missouri, the Ohio, and others, would be regarded elsewhere as of the
first importance, and, taken together, are navigable for a distance many
times exceeding that of the main stream. No river affords a more
striking illustration of the law before mentioned, that an augmentation
of volume does not occasion a proportional increase of surface, nay, is
even sometimes attended with a narrowing of the channel. The Mississippi
is half a mile wide at its junction with the Missouri, the latter being
also of equal width; yet the united waters have only, from their
confluence to the mouth of the Ohio, a medial width of about half a
mile. The junction of the Ohio seems also to produce no increase, but
rather a decrease, of surface.[356] The St. Francis, White, Arkansas,
and Red rivers are also absorbed by the main stream with scarcely any
apparent increase of its width, although here and there it expands to a
breadth of 1-1/2, or even to 2 miles. On arriving at New Orleans, it is
somewhat less than half a mile wide. Its depth there is very variable,
the greatest at high water being 168 feet. The mean rate at which the
whole body of water flows is variously estimated; according to Mr.
Forshey the mean velocity of the current at the surface, somewhat
exceeds 2-1/4 miles an hour when the water is at a mean height. For 300
miles above New Orleans the distance measured by the winding river is
about twice as great as the distance in a right line. For the first 100
miles from the mouth the rate of fall is 1.80 inch per mile, for the
second hundred 2 inches, for the third 2.30, for the fourth 2.57.

The alluvial plain of the Mississippi begins to be of great width below
Cape Girardeau, 50 miles above the junction of the Ohio. At this
junction it is about 50 miles broad, south of which it contracts to
about 30 miles at Memphis, expands again to 80 miles at the mouth of the
White River, and then, after various contractions and expansions,
protrudes beyond the general coast-line, in a large delta, about 90
miles in width, from N. E. to S. W. Mr. Forshey estimates the area of
the great plain as above defined at 31,200 square miles, with a
circumference of about 3000 miles, exceeding the area of Ireland. If
that part of this plain which lies below, or to the south of the
branching off of the highest arm, called the Atchafalaya, be termed the
delta, it constitutes less than half of the whole, being 14,000 square
British miles in area. The delta may be said to be bounded on the east,
west, and south by the sea; on the north chiefly by the broad
valley-plain which entirely resembles it in character as in origin. The
east and west boundaries of the alluvial region above the head of the
delta consists of cliffs or bluffs, which on the east side of the
Mississippi are very abrupt, and are undermined by the river at many
points. They consist, from Baton Rouge in Louisiana, where they
commence, as far north as the borders of Kentucky, of geological
formations newer than the cretaceous, the lowest being Eocene, and the
uppermost consisting of loam, resembling the loess of the Rhine, and
containing freshwater and land shells almost all of existing species.
(See fig. 23.) These recent shells are associated with the bones of the
mastodon, elephant, tapir, mylodon, horse, ox, and other quadrupeds,
most of them of extinct species.

I have endeavored to show in my Second Visit to the United States, that
this extensive formation of loam is either an ancient alluvial plain or
a delta of the great river, formed originally at a lower level, and
since upheaved, and partially denuded.

[Illustration: Fig. 23.

VALLEY OF THE MISSISSIPPI.]

The Mississippi in that part of its course which is below the mouth of
the Ohio, frequently washes the eastern bluffs, but never once comes in
contact with the western. These are composed of similar formations; but
I learn from Mr. Forshey that they rise up more gently from the alluvial
plain (as at _a_, fig. 23). It is supposed that the waters are thrown to
the eastern side, because all the large tributary rivers entering from
the west have filled that side of the great valley with their deltas, or
with a sloping mass of clay and sand; so that the opposite bluffs are
undermined, and the Mississippi is slowly but incessantly advancing
eastward.[357]

_Curves of the Mississippi._--The river traverses the plain in a
meandering course, describing immense curves. After sweeping round the
half of a circle, it is carried in a rapid current diagonally across the
ordinary direction of its channel, to another curve of similar shape.
Opposite to each of these, there is always a sand-bar, answering, in the
convexity of its form, to the concavity of "the bend," as it is
called.[358] The river, by continually wearing these curves deep,
returns, like many other streams before described, on its own track, so
that a vessel in some places, after sailing for twenty-five or thirty
miles, is brought round again to within a mile of the place whence it
started. When the waters approach so near to each other, it often
happens at high floods that they burst through the small tongue of
land, and insulate a portion, rushing through what is called the
"cut-off," so that vessels may pass from one point to another in half a
mile to a distance which it previously required a voyage of twenty miles
to reach. As soon as the river has excavated the new passage, bars of
sand and mud are formed at the two points of junction with the old bend,
which is soon entirely separated from the main river by a continuous
mud-bank covered with wood. The old bend then becomes a semicircular
lake of clear water, inhabited by large gar-fish, alligators, and wild
fowl, which the steam-boats have nearly driven away from the main
river. A multitude of such crescent-shaped lakes, scattered far and wide
over the alluvial plain, the greater number of them to the west, but
some of them also eastward of the Mississippi, bear testimony of the
extensive wanderings of the great stream in former ages. For the last
two hundred miles above its mouth the course of the river is much less
winding than above, there being only in the whole of that distance one
great curve, that called the "English Turn." This great straightness of
the stream is ascribed by Mr. Forshey to the superior tenacity of the
banks, which are more clayey in this region.

[Illustration: Fig. 24.

Section of channel, bank, levees (_a_ and _b_), and swamps of
Mississippi river.]

The Mississippi has been incorrectly described by some of the earlier
geographers, as a river running along the top of a long hill, or mound
in a plain. In reality it runs in a valley, from 100 to 200 or more feet
in depth, as _a_, _c_, _b_, fig. 24, its banks forming long strips of
land parallel to the course of the main stream, and to the swamps _g_,
_f_, and _d_, _e_, lying on each side. These extensive morasses, which
are commonly well-wooded, though often submerged for months
continuously, are rarely more than fifteen feet below the summit level
of the banks. The banks themselves are occasionally overflowed, but are
usually above water for a breadth of about two miles. They follow all
the curves of the great river, and near New Orleans are raised
artificially by embankments (or levees), _a b_, fig. 24, through which
the river when swollen sometimes cuts a deep channel (or crevasse),
inundating the adjoining low lands and swamps, and not sparing the lower
streets of the great city.

The cause of the uniform upward slope of the river-bank above the
adjoining alluvial plain is this: when the waters charged with sediment
pass over the banks in the flood season, their velocity is checked among
the herbage and reeds, and they throw down at once the coarser and more
sandy matter with which they are charged. But the fine particles of mud
are carried farther on, so that at the distance of about two miles, a
thin film of fine clay only subsides, forming a stiff unctuous black
soil, which gradually envelops the base of trees growing on the borders
of the swamps.

_Waste of the banks._--It has been said of a mountain torrent, that "it
lays down what it will remove, and removes what it has laid down;" and
in like manner the Mississippi, by the continual shifting of its course,
sweeps away, during a great portion of the year, considerable tracts of
alluvium, which were gradually accumulated by the overflow of former
years, and the matter now left during the spring-floods will be at some
future time removed. After the flood season, when the river subsides
within its channel, it acts with destructive force upon the alluvial
banks, softened and diluted by the recent overflow. Several acres at a
time, thickly covered with wood, are precipitated into the stream; and
large portions of the islands are frequently swept away.

"Some years ago," observes Captain Hall, "when the Mississippi was
regularly surveyed, all its islands were numbered, from the confluence
of the Missouri to the sea; but every season makes such revolutions, not
only in the number, but in the magnitude and situation of these islands,
that this enumeration is now almost obsolete. Sometimes large islands
are entirely melted away; at other places they have attached themselves
to the main shore, or, which is the more correct statement, the interval
has been filled up by myriads of logs cemented together by mud and
rubbish."[359]

_Rafts._--One of the most interesting features in the great rivers of
this part of America is the frequent accumulation of what are termed
"rafts," or masses of floating trees, which have been arrested in their
progress by snags, islands, shoals, or other obstructions, and made to
accumulate, so as to form natural bridges, reaching entirely across the
stream. One of the largest of these was called the raft of the
Atchafalaya, an arm of the Mississippi, which was certainly at some
former time the channel of the Red River, when the latter found its way
to the Gulf of Mexico by a separate course. The Atchafalaya being in a
direct line with the general direction of the Mississippi, catches a
large portion of the timber annually brought down from the north; and
the drift-trees collected in about thirty-eight years previous to 1816
formed a continuous raft, no less than ten miles in length, 220 yards
wide, and eight feet deep. The whole rose and fell with the water, yet
was covered with green bushes and trees, and its surface enlivened in
the autumn by a variety of beautiful flowers. It went on increasing till
about 1835, when some of the trees upon it had grown to the height of
about sixty feet. Steps were then taken by the State of Louisiana to
clear away the whole raft, and open the navigation, which was effected,
not without great labor, in the space of four years.

The rafts on Red River are equally remarkable: in some parts of its
course, cedar-trees are heaped up by themselves, and in other places,
pines. On the rise of the waters in summer hundreds of these are seen,
some with their green leaves still upon them, just as they have fallen
from a neighboring bank, others leafless, broken and worn in their
passage from a far distant tributary: wherever they accumulate on the
edge of a sand-bar they arrest the current, and soon become covered with
sediment. On this mud the young willows and the poplars called
cotton-wood spring up, their boughs still farther retarding the stream,
and as the inundation rises, accelerating the deposition of new soil.
The bank continuing to enlarge, the channel at length becomes so narrow
that a single long tree may reach from side to side, and the remaining
space is then soon choked up by a quantity of other timber.

"Unfortunately for the navigation of the Mississippi," observes Captain
Hall, "some of the largest trunks, after being cast down from the
position on which they grew, get their roots entangled with the bottom
of the river, where they remain anchored, as it were, in the mud. The
force of the current naturally gives their tops a tendency downwards,
and, by its flowing past, soon strips them of their leaves and branches.
These fixtures, called snags, or planters, are extremely dangerous to
the steam-vessels proceeding up the stream, in which they lie like a
lance in rest, concealed beneath the water, with their sharp ends
pointed directly against the bows of the vessels coming up. For the most
part these formidable snags remain so still that they can be detected
only by a slight ripple above them, not perceptible to inexperienced
eyes. Sometimes, however, they vibrate up and down, alternately showing
their heads above the surface and bathing them beneath it."[360] So
imminent, until lately, was the danger caused by these obstructions,
that almost all the boats on the Mississippi were constructed on a
particular plan, to guard against fatal accidents; but in the last ten
years, by the aid of the power of steam and the machinery of a
snag-boat, as it is called, the greater number of these trunks of trees
have been drawn out of the mud.[361]

The prodigious quantity of wood annually drifted down by the Mississippi
and its tributaries, is a subject of geological interest, not merely as
illustrating the manner in which abundance of vegetable matter becomes,
in the ordinary course of nature, imbedded in submarine and estuary
deposits, but as attesting the constant destruction of soil and
transportation of matter to lower levels by the tendency of rivers to
shift their courses. Each of these trees must have required many years,
some of them centuries, to attain their full size; the soil, therefore,
whereon they grew, after remaining undisturbed for long periods, is
ultimately torn up and swept away.

It is also found in excavating at New Orleans, even at the depth of
several yards below the level of the sea, that the soil of the delta
contains innumerable trunks of trees, layer above layer, some prostrate,
as if drifted, others broken off near the bottom, but remaining still
erect, and with their roots spreading on all sides, as if in their
natural position. In such situations they appeared to me to indicate a
sinking of the ground, as the trees must formerly have grown in marshes
above the sea-level. In the higher parts of the alluvial plain, for many
hundred miles above the head of the delta, similar stools and roots of
trees are also seen buried in stiff clay at different levels, one above
the other, and exposed to view in the banks at low water. They point
clearly to the successive growth of forests in the extensive swamps of
the plain, where the ground was slowly raised, year after year, by the
mud thrown down during inundations. These roots and stools belong
chiefly to the deciduous cypress (_Taxodium distichum_), and other
swamp-trees, and they bear testimony to the constant shifting of the
course of the great river, which is always excavating land originally
formed at some distance from its banks.

_Formation of lakes in Louisiana._.--Another striking feature in the
basin of the Mississippi, illustrative of the changes now in progress,
is the formation by natural causes of great lakes, and the drainage of
others. These are especially frequent in the basin of the Red River in
Louisiana, where the largest of them, called Bistineau, is more than
_thirty miles_ long, and has a medium depth of from _fifteen_ to
_twenty_ feet. In the deepest parts are seen numerous cypress-trees, of
all sizes, now dead, and most of them with their tops broken by the
wind, yet standing erect under water. This tree resists the action of
air and water longer than any other, and, if not submerged throughout
the whole year, will retain life for an extraordinary period. Lake
Bistineau, as well as Black Lake, Cado Lake, Spanish Lake, Natchitoches
Lake, and many others, have been formed, according to Darby, by the
gradual elevation of the bed of Red River, in which the alluvial
accumulations have been so great as to raise its channel, and cause its
waters, during the flood season, to flow up the mouths of many
tributaries, and to convert parts of their courses into lakes. In the
autumn, when the level of Red River is again depressed, the waters rush
back, and some lakes become grassy meadows, with streams meandering
through them.[362] Thus, there is a periodical flux and reflux between
Red River and some of these basins, which are merely reservoirs,
alternately emptied and filled, like our tide estuaries--with this
difference, that in the one case the land is submerged for several
months continuously, and in the other twice in every twenty-four hours.
It has happened, in several cases, that a raft of timber or a bar has
been thrown by Red River across some of the openings of these channels,
and then the lakes become, like Bistineau, constant repositories of
water. But, even in these cases, their level is liable to annual
elevation and depression, because the flood of the main river, when at
its height, passes over the bar; just as, where sand-hills close the
entrance of an estuary on the Norfolk or Suffolk coast, the sea, during
some high tide or storm, has often breached the barrier and inundated
again the interior.

I am informed by Mr. Featherstonhaugh that the plains of the Red River
and the Arkansas are so low and flat, that whenever the Mississippi
rises thirty feet above its ordinary level, those great tributaries are
made to flow back, and inundate a region of vast extent. Both the
streams alluded to contain red sediment, derived from the decomposition
of red porphyry; and since 1833, when there was a great inundation in
the Arkansas, an immense swamp has been formed near the Mammelle
mountain, comprising 30,000 acres, with here and there large lagoons,
where the old bed of the river was situated; in which innumerable trees,
for the most part dead, are seen standing, of cypress, cotton-wood, or
poplar, the triple-thorned acacia, and others, which are of great size.
Their trunks appear as if painted red for about fifteen feet from the
ground; at which height a perfectly level line extends through the whole
forest, marking the rise of the waters during the last flood.[363]

But most probably the causes above assigned for the recent origin of
these lakes are not the only ones. Subterranean movements have altered,
so lately as the years 1811-12, the relative levels of various parts of
the basin of the Mississippi, situated 300 miles northeast of Lake
Bistineau. In those years the great valley, from the mouth of the Ohio
to that of the St. Francis, including a tract 300 miles in length, and
exceeding in area the whole basin of the Thames, was convulsed to such a
degree, as to create new islands in the river, and lakes in the alluvial
plain. Some of these were on the left or east bank of the Mississippi,
and were twenty miles in extent; as, for example, those named Reelfoot
and Obion in Tennessee, formed in the channels or valleys of small
streams bearing the same names.[364]

But the largest area affected by the great convulsion lies eight or ten
miles to the westward of the Mississippi, and inland from the town of
New Madrid, in Missouri. It is called "the sunk country," and is said
to extend along the course of the White Water and its tributaries, for
a distance of between seventy and eighty miles north and south, and
thirty miles or more east and west. Throughout this area, innumerable
submerged trees, some standing leafless, others prostrate, are seen; and
so great is the extent of lake and marsh, that an active trade in the
skins of muskrats, mink, otters, and other wild animals, is now carried
on there. In March, 1846, I skirted the borders of the "sunk country"
nearest to New Madrid, passing along the Bayou St. John and Little
Prairie, where dead trees of various kinds, some erect in the water,
others fallen, and strewed in dense masses over the bottom, in the
shallows, and near the shore, were conspicuous. I also beheld countless
rents in the adjoining dry alluvial plains, caused by the movements of
the soil in 1811-12, and still open, though the rains, frost, and river
inundations, have greatly diminished their original depth. I observed,
moreover, numerous circular cavities, called "sunk holes," from ten to
thirty yards wide, and twenty feet or more in depth, which interrupt the
general level of the plain. These were formed by the spouting out of
large quantities of sand and mud during the earthquakes.[365]

That the prevailing changes of level in the delta and alluvial plain of
the Mississippi have been caused by the subsidence, rather than the
upheaval of land, appears to me established by the fact, that there are
no protuberances of upraised alluvial soil, projecting above the level
surface of the great plain. It is true that the gradual elevation of
that plain, by new accessions of matter, would tend to efface every
inequality derived from this source, but we might certainly have
expected to find more broken ground between the opposite bluffs, had
local upthrows of alluvial strata been of repeated occurrence.

_Antiquity of the delta._--The vast size of the alluvial plain both
above and below the head of the delta, or the branching off of the
uppermost arm of the Atchafalaya, has been already alluded to. Its
superficial dimensions, according to Mr. Forshey, exceed 30,000 square
miles, nearly half of which belong to the true delta. The deposits
consist partly of sand originally formed upon or near the banks of the
river, and its tributaries, partly of gravel, swept down the main
channel, of which the position has continually shifted, and partly of
fine mud slowly accumulated in the swamps. The farther we descend the
river towards its mouth, the finer becomes the texture of the sediment.
The whole alluvial formation, from the base of the delta upwards, slopes
with a very gentle inclination, rising about three inches in a mile from
the level of the sea at the Balize, to the height of about 200 feet in a
distance of about 800 miles.

That a large portion of this fluviatile deposit, together with the
fluvio-marine strata now in progress near the Balize, consists of mud
and sand with much vegetable matter intermixed, may be inferred from
what has been said of the abundance of drift trees floated down every
summer. These are seen matted together into a net-work around the
extensive mud banks at the extreme mouths of the river. Every one
acquainted with the geography of Louisiana is aware that the most
southern part of the delta forms a long narrow tongue of land protruding
for 50 miles into the Gulf of Mexico, at the end of which are numerous
channels of discharge. This singular promontory consists simply of the
river and its two low, flat banks, covered with reeds, young willows,
and poplars. Its appearance answers precisely to that of the banks far
in the interior, when nothing appears above water during inundations but
the higher part of the sloping glacis or bank. In the one case we have
the swamps or an expanse of freshwater with the tops of trees appearing
above, in the other the bluish green surface of the Gulf of Mexico. An
opinion has very commonly prevailed that this narrow promontory, the
newest product of the river, has gained very rapidly upon the sea, since
the foundation of New Orleans; but after visiting the Balize in 1846, in
company with Dr. Carpenter, and making many inquiries of the pilots, and
comparing the present outline of the coast with the excellent Spanish
chart, published by Charlevoix 120 years before, we came to a different
conclusion. The rate of permanent advance of the new land has been very
slow, not exceeding perhaps one mile in a century. The gain may have
been somewhat more rapid in former years, when the new strip of soil
projected less far into the gulf, since it is now much more exposed to
the action of a strong marine current. The tides also, when the waters
of the river are low, enter into each opening, and scour them out,
destroying the banks of mud and the sand-bars newly formed during the
flood season.

An observation of Darby, in regard to the strata composing part of this
delta, deserves attention. In the steep banks of the Atchafalaya, before
alluded to, the following section, he says, is observable at low
water:--first an upper stratum, consisting invariably of bluish clay,
common to the banks of the Mississippi; below this a stratum of red
ochreous earth, peculiar to Red River, under which the blue clay of the
Mississippi again appears; and this arrangement is constant, proving, as
that geographer remarks, that the waters of the Mississippi and the Red
River occupied alternately, at some former periods, considerable tracts
below their present point of union.[366] Such alternations are probably
common in submarine spaces situated between two converging deltas; for,
before the two rivers unite, there must almost always be a certain
period when an intermediate tract will by turns be occupied and
abandoned by the waters of each stream; since it can rarely happen that
the season of highest flood will precisely correspond in each. In the
case of the Red River and Mississippi, which carry off the waters from
countries placed under widely distant latitudes, an exact coincidence in
the time of greatest inundation is very improbable.

The antiquity of the delta, or length of the period which has been
occupied in the deposition of so vast a mass of alluvial matter, is a
question which may well excite the curiosity of every geologist.
Sufficient data have not yet been obtained to afford a full and
satisfactory answer to the inquiry, but some approximation may already
be made to the minimum of time required.

When I visited New Orleans, in February, 1846, I found that Dr. Riddell
had made numerous experiments to ascertain the proportion of sediment
contained in the waters of the Mississippi; and he concluded that the
mean annual amount of solid matter was to the water as 1/1245 in weight,
or about 1/3000 in volume.[367] From the observations of the same
gentleman, and those of Dr. Carpenter and Mr. Forshey, an eminent
engineer, to whom I have before alluded, the average width, depth, and
velocity of the Mississippi, and thence the mean annual discharge of
water were deduced. I assumed 528 feet, or the tenth of a mile, as the
probable thickness of the deposit of mud and sand in the delta; founding
my conjecture chiefly on the depth of the Gulf of Mexico, between the
southern point of Florida and the Balize, which equals on an average 100
fathoms, and partly on some borings 600 feet deep in the delta, near
Lake Pontchartrain, north of New Orleans, in which the bottom of the
alluvial matter is said not to have been reached. The area of the delta
being about 13,600 square statute miles, and the quantity of solid
matter annually brought down by the river 3,702,758,400 cubic feet, it
must have taken 67,000 years for the formation of the whole; and if the
alluvial matter of the plain above be 264 feet deep, or half that of the
delta,[368] it must have required 33,500 more years for its
accumulation, even if its area be estimated as only equal to that of the
delta, whereas it is in fact larger. If some deduction be made from the
time here stated, in consequence of the effect of the drift-wood, which
must have aided in filling up more rapidly the space above alluded to, a
far more important allowance must be made on the other hand, for the
loss of matter, owing to the finer particles of mud not settling at the
mouths of the river, but being swept out far to sea during the
predominant action of the tides, and the waves in the winter months,
when the current of fresh water is feeble. Yet however vast the time
during which the Mississippi has been transporting its earthy burden to
the ocean, the whole period, though far exceeding, perhaps, 100,000
years, must be insignificant in a geological point of view, since the
bluffs or cliffs, bounding the great valley, and therefore older in
date, and which are from 50 to 250 feet in perpendicular height, consist
in great part of loam containing land, fluviatile, and lacustrine shells
of species still inhabiting the same country. (See fig. 23, p. 265.)

Before we take leave of the great delta, we may derive an instructive
lesson from the reflection that the new deposits already formed, or now
accumulating, whether marine or freshwater, must greatly resemble in
composition, and the general character of their organic remains, many
ancient strata, which enter largely into the earth's structure. Yet
there is no sudden revolution in progress, whether on the land or in the
waters, whether in the animate or the inanimate world. Notwithstanding
the excessive destruction of soil and uprooting of trees, the region
which yields a never-failing supply of drift-wood is densely clothed
with noble forests, and is almost unrivalled in its power of supporting
animal and vegetable life. In spite of the undermining of many a lofty
bluff, and the encroachments of the delta on the sea--in spite of the
earthquake, which rends and fissures the soil, or causes areas more than
sixty miles in length to sink down several yards in a few months, the
general features of the district remain unaltered, or are merely
undergoing a slow and insensible change. Herds of wild deer graze on the
pastures, or browse upon the trees; and if they diminish in number, it
is only where they give way to man and the domestic animals which follow
in his train. The bear, the wolf, the fox, the panther, and the
wild-cat, still maintain themselves in the fastnesses of the forests of
cypress and gum-tree. The racoon and the opossum are everywhere
abundant, while the musk-rat, otter, and mink still frequent the rivers
and lakes, and a few beavers and buffaloes have not yet been driven from
their ancient haunts. The waters teem with alligators, tortoises, and
fish, and their surface is covered with millions of migratory waterfowl,
which perform their annual voyage between the Canadian lakes and the
shores of the Mexican Gulf. The power of man begins to be sensibly felt,
and many parts of the wilderness to be replaced by towns, orchards, and
gardens. The gilded steamboats, like moving palaces, stem the force of
the current, or shoot rapidly down the descending stream, through the
solitudes of the forests and prairies. Already does the flourishing
population of the great valley far exceed that of the thirteen United
States when first they declared their independence. Such is the state of
a continent where trees and stones are hurried annually by a thousand
torrents, from the mountains to the plains, and where sand and finer
matter are swept down by a vast current to the sea, together with the
wreck of countless forests and the bones of animals which perish in the
inundations. When these materials reach the gulf, they do not render the
waters unfit for aquatic animals; but on the contrary, the ocean here
swarms with life, as it generally does where the influx of a great river
furnishes a copious supply of organic and mineral matter. Yet many
geologists, when they behold the spoils of the land heaped in successive
strata, and blended confusedly with the remains of fishes, or
interspersed with broken shells and corals; when they see portions of
erect trunks of trees with their roots still retaining their natural
position, and one tier of these preserved in a fossil state above
another, imagine that they are viewing the signs of a turbulent instead
of a tranquil and settled state of the planet. They read in such
phenomena the proof of chaotic disorder and reiterated catastrophes,
instead of indications of a surface as habitable as the most delicious
and fertile districts now tenanted by man.


DELTA OF THE GANGES AND BRAHMAPOOTRA.

[Illustration: Fig. 25.

MAP OF THE DELTA OF THE GANGES AND BRAHMAPOOTRA.]

As an example of a still larger delta advancing upon the sea in
opposition to more powerful tides, I shall next describe that of the
Ganges and Brahmapootra (or Burrampooter). These, the two principal
rivers of India, descend from the highest mountains in the world, and
partially mingle their waters in the low plains of Hindostan, before
reaching the head of the Bay of Bengal. The Brahmapootra, somewhat the
larger of the two, formerly passed to the east of Dacca, even so lately
as the beginning of the present century, pouring most of its waters into
one of the numerous channels in the delta called "the Megna." By that
name the main stream was always spoken of by Rennell and others in their
memoirs on this region. But the main trunk now unites with an arm of the
Ganges considerably higher up, at a point about 100 miles distant from
the sea; and it is constantly, according to Dr. Hooker, working its way
westward, having formerly, as may be seen by ancient maps, moved
eastward for a long period.

The area of the delta of the combined rivers, for it is impossible now
to distinguish what belongs to each, is considerably more than double
that of the Nile, even if we exclude from the delta a large extent of
low, flat, alluvial plain, doubtless of fluviatile origin, which
stretches more than 100 miles to the hills west of Calcutta (see map,
fig. 25), and much farther in a northerly direction beyond the head of
the great delta. The head of a delta is that point where the first arm
is given off. Above that point a river receives the waters of
tributaries flowing from higher levels; below it, on the contrary, it
gives out portions of its waters to lower levels, through channels which
flow into adjoining swamps, or which run directly to the sea. The
Mississippi, as before described, has a single head, which originated at
an unknown period when the Red River joined it. In the great delta of
Bengal there may be said to be two heads nearly equidistant from the
sea, that of the Ganges (G, map, fig. 25), about 30 miles below
Rajmahal, or 216 statute miles in a direct line from the sea, and that
of the Brahmapootra (B), below Chirapoonjee, where the river issues from
the Khasia mountains, a distance of 224 miles from the Bay of Bengal.

It will appear, by reference to the map, that the great body of fresh
water derived from the two rivers enters the bay on its eastern side;
and that a large part of the delta bordering on the sea is composed of a
labyrinth of rivers and creeks, all filled with salt water, except those
immediately communicating with the Hoogly, or principal arm of the
Ganges. This tract alone, known by the name of the Woods, or Sunderbunds
(more properly Soonderbuns), a wilderness infested by tigers and
crocodiles, is, according to Rennell, equal in extent to the whole
principality of Wales.[369]

On the sea-coast there are eight great openings, each of which has
evidently, at some ancient period, served in its turn as the principal
channel of discharge. Although the flux and reflux of the tide extend
even to the heads of the delta when the rivers are low, yet, when they
are periodically swollen by tropical rains, their volume and velocity
counteract the tidal current, so that, except very near the sea, the ebb
and flow become insensible. During the flood season, therefore, the
Ganges and Brahmapootra almost assume in their delta, the character of
rivers entering an inland sea; the movements of the ocean being then
subordinate to the force of the rivers, and only slightly disturbing
their operations. The great gain of the delta in height and area takes
place during the inundations; and, during other seasons of the year, the
ocean makes reprisals, scouring out the channels, and sometimes
devouring rich alluvial plains.

_Islands formed and destroyed._--Major R. H. Colebrooke, in his account
of the course of the Ganges, relates examples of the rapid filling up of
some of its branches, and the excavation of new channels, where the
number of square miles of soil removed in a short time (the column of
earth being 114 feet high) was truly astonishing. Forty square miles, or
25,600 acres, are mentioned as having been carried away, in one place,
in the course of a few years.[370] The immense transportation of earthy
matter by the Ganges and Brahmapootra is proved by the great magnitude
of the islands formed in their channels during a period far short of
that of a man's life. Some of these, many miles in extent, have
originated in large sand-banks thrown up round the points at the angular
turning of the rivers, and afterwards insulated by breaches of the
streams. Others, formed in the main channel, are caused by some
obstruction at the bottom. A large tree, or a sunken boat, is sometimes
sufficient to check the current, and cause a deposit of sand, which
accumulates till it usurps a considerable portion of the channel. The
river then undermines its banks on each side, to supply the deficiency
in its bed, and the island is afterwards raised by fresh deposits during
every flood. In the great gulf below Luckipour, formed by the united
waters of the Ganges and Megna, some of the islands, says Rennell, rival
in size and fertility the Isle of Wight. While the river is forming new
islands in one part, it is sweeping away old ones in others. Those newly
formed are soon overrun with reeds, long grass, the Tamarix Indica, and
other shrubs, forming impenetrable thickets, where the tiger, the
rhinoceros, the buffalo, deer, and other wild animals, take shelter. It
is easy, therefore, to perceive, that both animal and vegetable remains
may occasionally be precipitated into the flood, and become imbedded in
the sediment which subsides in the delta.

Three or four species of crocodile, of two distinct sub-genera, abound
in the Ganges, and its tributary and contiguous waters; and Mr. H. T.
Colebrooke informed me, that he had seen both forms in places far
inland, many hundred miles from the sea. The Gangetic crocodile, or
Gavial (in correct orthography, Garial), is confined to the fresh water,
living exclusively on fish, but the commoner kinds, called Koomiah and
Muggar, frequent both fresh and salt, being much larger and fiercer in
salt and brackish water.[371] These animals swarm in the brackish water
along the line of sand-banks, where the advance of the delta is most
rapid. Hundreds of them are seen together in the creeks of the delta,
or basking in the sun on the shoals without. They will attack men and
cattle, destroying the natives when bathing, and tame and wild animals
which come to drink. "I have not unfrequently," says Mr. Colebrooke,
"been witness to the horrid spectacle of a floating corpse seized by a
crocodile with such avidity, that he half emerged above the water with
his prey in his mouth." The geologist will not fail to observe how
peculiarly the habits and distribution of these saurians expose them to
become imbedded in the horizontal strata of fine mud, which are annually
deposited over many hundred square miles in the Bay of Bengal. The
inhabitants of the land, which happen to be drowned or thrown into the
water, are usually devoured by these voracious reptiles; but we may
suppose the remains of the saurians themselves to be continually
entombed in the new formations. The number, also, of bodies of the
poorer class of Hindoos thrown annually into the Ganges is so great,
that some of their bones or skeletons can hardly fail to be occasionally
enveloped in fluviatile mud.

It sometimes happens, at the season when the periodical flood is at its
height, that a strong gale of wind, conspiring with a high spring-tide,
checks the descending current of the river, and gives rise to most
destructive inundations. From this cause, in 1763, the waters at
Luckipour rose six feet above their ordinary level, and the inhabitants
of a considerable district, with their houses and cattle, were totally
swept away.

The population of all oceanic deltas are particularly exposed to suffer
by such catastrophes, recurring at considerable intervals of time; and
we may safely assume that such tragical events have happened again and
again since the Gangetic delta was inhabited by man. If human experience
and forethought cannot always guard against these calamities, still less
can the inferior animals avoid them; and the monuments of such
disastrous inundations must be looked for in great abundance in strata
of all ages, if the surface of our planet has always been governed by
the same laws. When we reflect on the general order and tranquillity
that reigns in the rich and populous delta of Bengal, notwithstanding
the havoc occasionally committed by the depredations of the ocean, we
perceive how unnecessary it is to attribute the imbedding of successive
races of animals in older strata to extraordinary energy in the causes
of decay and reproduction in the infancy of our planet, or to those
general catastrophes and sudden revolutions so often resorted to.

_Deposits in the delta._--The quantity of mud held in suspension by the
waters of the Ganges and Brahmapootra is found, as might be expected, to
exceed that of any of the rivers alluded to in this or the preceding
chapters; for, in the first place, their feeders flow from mountains of
unrivalled altitude, and do not clear themselves in any lakes, as does
the Rhine in the Lake of Constance, or the Rhone in that of Geneva. And,
secondly, their whole course is nearer the equator than that of the
Mississippi, or any great river, respecting which careful experiments
have been made, to determine the quantity of its water and earthy
contents. The fall of rain, moreover, as we have before seen, is
excessive on the southern flanks of the first range of mountains which
rise from the plains of Hindostan, and still more remarkable is the
quantity sometimes poured down in one day. (See above, p. 200.) The sea,
where the Ganges and Brahmapootra discharge their main stream at the
flood season, only recovers its transparency at the distance of from 60
to 100 miles from the delta; and we may take for granted that the
current continues to transport the finer particles much farther south
than where the surface water first becomes clear. The general slope,
therefore, of the new strata must be extremely gentle. According to the
best charts, there is a gradual deepening from four to about sixty
fathoms, as we proceed from the base of the delta to the distance of
about one hundred miles into the Bay of Bengal. At some few points
seventy, or even one hundred, fathoms are obtained at that distance.

One remarkable exception, however, occurs to the regularity of the shape
of the bottom. Opposite the middle of the delta, at the distance of
thirty or forty miles from the coast, a deep submarine valley occurs,
called the "swatch of no ground," about fifteen miles in diameter, where
soundings of 180, and even 300, fathoms fail to reach the bottom. (See
map, p. 275.) This phenomenon is the more extraordinary, since the
depression runs north to within five miles of the line of shoals; and
not only do the waters charged with sediment pass over it continually,
but, during the monsoons, the sea, loaded with mud and sand, is beaten
back in that direction towards the delta. As the mud is known to extend
for eighty miles farther into the gulf, an enormous thickness of matter
must have been deposited in "the swatch." We may conclude, therefore,
either that the original depth of this part of the Bay of Bengal was
excessive, or that subsidences have occurred in modern times. The latter
conjecture is the less improbable, as the whole area of the delta has
been convulsed in the historical era by earthquakes, and actual
subsidences have taken place in the neighboring coast of Chittagong,
while "the swatch" lies not far from the volcanic band which connects
Sumatra, Barren Island, and Ramree.[372]

Opposite the mouth of the Hoogly river, and immediately south of Saugor
Island, four miles from the nearest land of the delta, a new islet was
formed about twenty years ago, called Edmonstone Island, on the centre
of which a beacon was erected as a landmark in 1817. In 1818 the island
had become two miles long and half a mile broad, and was covered with
vegetation and shrubs. Some houses were then built upon it, and in 1820
it was used as a pilot station. The severe gale of 1823 divided it into
two parts, and so reduced its size as to leave the beacon standing out
in the sea, where, after remaining seven years, it was washed away. The
islet in 1836 had been converted by successive storms into a sand-bank,
half a mile long, on which a sea-mark was placed.

Although there is evidence of gain at some points, the general progress
of the coast is very slow; for the tides, when the river water is low,
are actively employed in removing alluvial matter. In the Sunderbunds
the usual rise and fall of the tides is no more than eight feet, but, on
the east side of the delta, Dr. Hooker observed, in the winter of 1851,
a rise of from sixty to eighty feet, producing among the islands at the
mouths of the Megna and Fenny rivers, a lofty wave or "bore" as they
ascend, and causing the river water to be ponded back, and then to sweep
down with great violence when the tide ebbs. The bay for forty miles
south of Chittagong is so fresh that neither algae nor mangroves will
grow in it. We may, therefore, conceive how effective may be the current
formed by so great a volume of water in dispersing fine mud over a wide
area. Its power is sometimes augmented by the agitation of the bay
during hurricanes in the month of May. The new superficial strata
consists entirely of fine sand and mud; such, at least, are the only
materials which are exposed to view in regular beds on the banks of the
numerous creeks. Neither here or higher up the Ganges, could Dr. Hooker
discover any land or freshwater shells in sections of the banks, which
in the plains higher up sometimes form cliffs eighty feet in height at
low water. In like manner I have stated[373] that I was unable to find
any buried shells in the delta or modern river cliffs of the
Mississippi.

No substance so coarse as gravel occurs in any part of the delta of the
Ganges and Brahmapootra, nor nearer the sea than 400 miles. Yet it is
remarkable that the boring of an Artesian well at Fort William, near
Calcutta, in the years 1835-1840, displayed, at the depth of 120 feet,
clay and sand with pebbles. This boring was carried to a depth of 481
feet below the level of Calcutta, and the geological section obtained in
the operation has been recorded with great care. Under the surface soil,
at a depth of about ten feet, they came to a stiff blue clay about forty
feet in thickness; below which was sandy clay, containing in its lower
portion abundance of decayed vegetable matter, which at the bottom
assumed the character of a stratum of black peat two feet thick. This
peaty mass was considered as a clear indication (like the "dirt-bed" of
Portland) of an ancient terrestrial surface, with a forest or Sunderbund
vegetation. Logs and branches of a red-colored wood occur both above and
immediately below the peat, so little altered that Dr. Wallich was able
to identify them with the Soondri tree, _Heritiera littoralis_, one of
the most prevalent forms, at the base of the delta. Dr. Falconer tells
me that similar peat has been met with at other points round Calcutta at
the depth of nine feet and twenty-five feet. It appears, therefore, that
there has been a sinking down of what was originally land in this
region, to the amount of seventy feet or more perpendicular; for
Calcutta is only a few feet above the level of the sea, and the
successive peat-beds seem to imply that the subsidence of the ground was
gradual or interrupted by several pauses. Below the vegetable mass they
entered upon a stratum of yellowish clay about ten feet thick,
containing horizontal layers of kunkar (or kankar), a nodular,
concretionary, argillaceous limestone, met with abundantly at greater or
less depths in all parts of the valley of the Ganges, over many
thousand square miles, and always presenting the same characters, even
at a distance of one thousand miles north of Calcutta. Some of this
kunkar is said to be of very recent origin in deposits formed by river
inundations near Saharanpoor. After penetrating 120 feet, they found
loam containing water-worn fragments of mica-slate and other kinds of
rock, which the current of the Ganges can no longer transport to this
region. In the various beds pierced through below, consisting of clay,
marl, and friable sandstone, with kunkar here and there intermixed, no
organic remains of decidedly marine origin were met with. Too positive a
conclusion ought not, it is true, to be drawn from such a fact, when we
consider the narrow bore of the auger and its effect in crushing shells
and bones. Nevertheless, it is worthy of remark, that the only fossils
obtained in a recognizable state were of a fluviatile or terrestrial
character. Thus, at the depth of 350 feet, the bony shell of a tortoise,
or trionyx, a freshwater genus, was found in sand, resembling the living
species of Bengal. From the same stratum, also, they drew up the lower
half of the humerus of a ruminant, at first referred to a hyaena. It was
the size and shape, says Dr. Falconer, of the shoulder-bone of the
_Cervus porcinus_, or common hog-deer, of India. At the depth of 380
feet, clay with fragments of lacustrine shells was incumbent on what
appears clearly to have been another "dirt-bed," or stratum of decayed
wood, implying a period of repose of some duration, and a forest-covered
land, which must have subsided 300 feet, to admit of the subsequent
superposition of the overlying deposits. It has been conjectured that,
at the time when this area supported trees, the land extended much
farther out into the Bay of Bengal than now, and that in later times the
Ganges, while enlarging its delta, has been only recovering lost ground
from the sea.

At the depth of about 400 feet below the surface, an abrupt change was
observed in the character of the strata, which were composed in great
part of sand, shingle, and boulders, the only fossils observed being the
vertebrae of a crocodile, shell of a trionyx, and fragments of wood very
little altered, and similar to that buried in beds far above. These
gravelly beds constituted the bottom of the section at the depth of 481
feet, when the operations were discontinued, in consequence of an
accident which happened to the auger.

The occurrence of pebbles at the depths of 120 and 400 feet implies an
important change in the geographical condition of the region around or
near Calcutta. The fall of the river, or the general slope of the
alluvial plain may have been formerly greater; or, before a general and
perhaps unequal subsidence, hills once nearer the present base of the
delta may have risen several hundred feet, forming islands in the bay,
which may have sunk gradually, and become buried under fluviatile
sediment.

_Antiquity of the delta._--It would be a matter of no small scientific
interest, if experiments were made to enable us to determine, with some
degree of accuracy, the mean quantity of earthy matter discharged
annually into the sea by the united waters of the Ganges and
Brahmapootra. The Rev. Mr. Everest instituted, in 1831-2, a series of
observations on the earthy matter brought down by the Ganges, at
Ghazepoor, 500 miles from the sea. He found that, in 1831, the number of
cubic feet of water discharged by the river per second at that place
was, during the


  Rains (4 months)        494,208
  Winter (5 months)        71,200
  Hot weather (3 months)   36,330


so that we may state in round numbers that 500,000 cubic feet per second
flow down during the four months of the flood season, from June to
September, and less than 60,000 per second during the remaining eight
months.

The average quantity of solid matter suspended in the water during the
rains was, by weight, 1/428th part; but as the water is about one-half
the specific gravity of the dried mud, the solid matter discharged is
1/856th part in bulk, or 577 cubic feet per second. This gives a total
of 6,082,041,600 cubic feet for the discharge in the 122 days of the
rain. The proportion of sediment in the waters at other seasons was
comparatively insignificant, the total amount during the five winter
months being only 247,881,600 cubic feet, and during the three months of
hot weather 38,154,240 cubic feet. The total annual discharge, then,
would be 6,368,077,440 cubic feet.

This quantity of mud would in one year raise a surface of 228-1/2 square
miles, or a square space, each side of which should measure 15 miles, a
height of one foot. To give some idea of the magnitude of this result,
we will assume that the specific gravity of the dried mud is only
one-half that of granite (it would, however, be more); in that case, the
earthy matter discharged in a year would equal 3,184,038,720 cubic feet
of granite. Now about 12-1/2 cubic feet of granite weigh one ton; and it
is computed that the great Pyramid of Egypt, if it were a solid mass of
granite, would weigh about 600,000,000 tons. The mass of matter,
therefore, carried down annually would, according to this estimate, more
than equal in weight and bulk forty-two of the great pyramids of Egypt,
and that borne down in the four months of the rains would equal forty
pyramids. But if, without any conjecture as to what may have been the
specific gravity of the mud, we attend merely to the weight of solid
matter actually proved by Mr. Everest to have been contained in the
water, we find that the number of tons weight which passed down in the
122 days of the rainy season was 339,413,760, which would give the
weight of fifty-six pyramids and a half; and in the whole year
355,361,464 tons, or nearly the weight of sixty pyramids.

The base of the great Pyramid of Egypt covers eleven acres, and its
perpendicular height is about five hundred feet. It is scarcely possible
to present any picture to the mind which will convey an adequate
conception of the mighty scale of this operation, so tranquilly and
almost insensibly carried on by the Ganges, as it glides through its
alluvial plain, even at a distance of 500 miles from the sea. It may,
however, be stated, that if a fleet of more than eighty Indiamen, each
freighted with about 1400 tons' weight of mud, were to sail down the
river every hour of every day and night for four months continuously,
they would only transport from the higher country to the sea a mass of
solid matter equal to that borne down by the Ganges, even in this part
of its course, in the four months of the flood season. Or the exertions
of a fleet of about 2000 such ships going down daily with the same
burden, and discharging it into the gulf, would be no more than
equivalent to the operations of the great river.

The most voluminous current of lava which has flowed from Etna within
historical times was that of 1669. Ferrara, after correcting Borelli's
estimate, calculated the quantity of cubic yards of lava in this current
at 140,000,000. Now, this would not equal in bulk one-fifth of the
sedimentary matter which is carried down in a single year by the Ganges,
past Ghazepoor, according to the estimate above explained; so that it
would require five grand eruptions of Etna to transfer a mass of lava
from the subterranean regions to the surface, equal in volume to the mud
carried down in one year to that place.

Captain R. Strachey, of the Bengal Engineers, has remarked to me, not
only that Ghazepoor, where Mr. Everest's observations were made, is 500
miles from the sea, but that the Ganges has not been joined there by its
most important feeders. These drain upon the whole 750 miles of the
Himalaya, and no more than 150 miles of that mountain-chain have sent
their contributions to the main trunk at Ghazepoor. Below that place,
the Ganges is joined by the Gogra, Gunduk, Khosee, and Teesta from the
north, to say nothing of the Sone flowing from the south, one of the
largest of the rivers which rise in the table-land of central India.
(See map, fig. 25, p. 275.) Moreover the remaining 600 miles of the
Himalaya comprise that eastern portion of the basin where the rains are
heaviest. (See above, p. 200.) The quantity of water therefore carried
down to the sea may probably be four or five times as much as that which
passes Ghazepoor.

The Brahmapootra, according to Major Wilcox,[374] in the month of
January, when it is near its minimum, discharges 150,000 cubic feet of
water per second at Gwalpara, not many miles above the head of its
delta. Taking the proportions observed at Ghazepoor at the different
seasons as a guide, the probable average discharge of the Brahmapootra
for the whole year may be estimated at about the same as that of the
Ganges. Assuming this; and secondly, in order to avoid the risk of
exaggeration, that the proportion of sediment in their waters is about a
third less than Mr. Everest's estimate, the mud borne down to the Bay of
Bengal in one year would equal 40,000 millions of cubic feet, or between
six and seven times as much as that brought down to Ghazepoor, according
to Mr. Everest's calculations in 1831, and ten times as much as that
conveyed annually by the Mississippi to the Gulf of Mexico.

Captain Strachey estimates the annually inundated portion of the delta
at 250 miles in length by 80 in breadth, making an area of 20,000 square
miles. The space south of this in the bay, where sediment is thrown
down, may be 300 miles from E. to W. by 150 N. and S., or 45,000 square
miles, which, added to the former, gives a surface of 65,000 square
miles, over which the sediment is spread out by the two rivers. Suppose
then the solid matter to amount to 40,000 millions of cubic feet per
annum, the deposit, he observes, must be continued for forty-five years
and three-tenths to raise the whole area a height of one foot, or 13,600
years to raise it 300 feet; and this, as we have seen, is much less than
the thickness of the fluviatile strata actually penetrated, (and the
bottom not reached) by the auger at Calcutta.

Nevertheless we can by no means deduce from these data alone, what will
be the future rate of advance of the delta, nor even predict whether the
land will gain on the sea, or remain stationary. At the end of 13,000
years the bay may be less shallow than now, provided a moderate
depression, corresponding to that experienced in part of Greenland for
many centuries shall take place (see chap. 30). A subsidence quite
insensible to the inhabitants of Bengal, not exceeding two feet three
inches in a century, would be more than sufficient to counterbalance all
the efforts of the two mighty rivers to extend the limits of their
delta. We have seen that the Artesian borings at Calcutta attest, what
the vast depth of the "swatch" may also in all likelihood indicate, that
the antagonist force of subsidence has predominated for ages over the
influx of fluviatile mud, preventing it from raising the plains of
Bengal, or from filling up a larger portion of the bay.


CONCLUDING REMARKS ON DELTAS.

_Convergence of deltas._--If we possessed an accurate series of maps of
the Adriatic for many thousand years, our retrospect would, without
doubt, carry us gradually back to the time when the number of rivers
descending from the mountains into that gulf by independent deltas was
far greater in number. The deltas of the Po and the Adige, for instance,
would separate themselves within the _recent_ era, as, in all
probability, would those of the Isonzo and the Torre. If, on the other
hand, we speculate on future changes, we may anticipate the period when
the number of deltas will greatly diminish; for the Po cannot continue
to encroach at the rate of a mile in a hundred years, and other rivers
to gain as much in six or seven centuries upon the shallow gulf, without
new junctions occurring from time to time; so that Eridanus, "the king
of rivers," will continually boast a greater number of tributaries. The
Ganges and the Brahmapootra have perhaps become partially confluent in
the same delta within the historical, or at least within the human era;
and the date of the junction of the Red River and the Mississippi would,
in all likelihood, have been known, if America had not been so recently
discovered. The union of the Tigris and the Euphrates must undoubtedly
have been one of the modern geographical changes of our Earth, for Col.
Rawlinson informs me that the delta of those rivers has advanced two
miles in the last sixty years, and is supposed to have encroached about
forty miles upon the Gulf of Persia in the course of the last
twenty-five centuries.

When the deltas of rivers, having many mouths, converge, a partial union
at first takes place by the confluence of some one or more of their
arms; but it is not until the main trunks are connected above the head
of the common delta, that a complete intermixture of their joint waters
and sediment takes place. The union, therefore, of the Po and Adige, and
of the Ganges and Brahmapootra, is still incomplete. If we reflect on
the geographical extent of surface drained by rivers such as now enter
the Bay of Bengal, and then consider how complete the blending together
of the greater part of their transported matter has already become, and
throughout how vast a delta it is spread by numerous arms, we no longer
feel so much surprise at the area occupied by some ancient formations of
homogeneous mineral composition. But our surprise will be still farther
lessened, when we afterwards inquire (ch. 21) into the action of tides
and currents in disseminating sediment.

_Age of existing deltas._--If we could take for granted, that the
relative level of land and sea had remained stationary ever since all
the existing deltas began to be formed--could we assume that their
growth commenced at one and the same instant when the present continents
acquired their actual shape--we might understand the language of
geologists who speak of "the epoch of existing continents." They
endeavor to calculate the age of deltas from this imaginary fixed
period; and they calculate the gain of new land upon the sea, at the
mouths of rivers, as having begun everywhere simultaneously. But the
more we study the history of deltas, the more we become convinced that
upward and downward movements of the land and contiguous bed of the sea
have exerted, and continue to exert, an influence on the physical
geography of many hydrographical basins, on a scale comparable in
magnitude or importance to the amount of fluviatile deposition effected
in an equal lapse of time. In the basin of the Mississippi, for example,
proofs both of descending and ascending movements to a vertical amount
of several hundred feet can be shown to have taken place since the
existing species of land and freshwater shells lived in that
region.[375]

The deltas also of the Po and Ganges have each, as we have seen (p.
257), when probed by the Artesian auger, borne testimony to a gradual
subsidence of land to the extent of several hundred feet--old
terrestrial surfaces, turf, peat, forest-land, and "dirt-beds," having
been pierced at various depths. The changes of level at the mouth of the
Indus in Cutch (see below, chap. 27), and those of New Madrid in the
valley of the Mississippi (see p. 270, and chap. 27), are equally
instructive, as demonstrating unceasing fluctuations in the levels of
those areas into which running water is transporting sediment. If,
therefore, the exact age of all modern deltas could be known, it is
scarcely probable that we should find any two of them in the world to
have coincided in date, or in the time when their earliest deposits
originated.

_Grouping of strata in deltas._--The changes which have taken place in
deltas, even within the times of history, may suggest many important
considerations in regard to the manner in which subaqueous sediment is
distributed. With the exception of some cases hereafter to be noticed,
there are some general laws of arrangement which must evidently hold
good in almost all the lakes and seas now filling up. If a lake, for
example, be encircled on two sides by lofty mountains, receiving from
them many rivers and torrents of different sizes, and if it be bounded
on the other sides, where the surplus waters issue, by a comparatively
low country, it is not difficult to define some of the leading
geological features which must characterize the lacustrine formation,
when this basin shall have been gradually converted into dry land by the
influx of sediment. The strata would be divisible into two principal
groups: the _older_ comprising those deposits which originated on the
side adjoining the mountains, where numerous deltas first began to form;
and the _newer_ group consisting of beds deposited in the more central
parts of the basin, and towards the side farthest from the mountains.
The following characters would form the principal marks of distinction
between the strata in each series:--The more ancient system would be
composed, for the most part, of coarser materials, containing many beds
of pebbles and sand, often of great thickness, and sometimes dipping at
a considerable angle. These, with associated beds of finer ingredients,
would, if traced round the borders of the basin, be seen to vary greatly
in color and mineral composition, and would also be very irregular in
thickness. The beds, on the contrary, in the newer group, would consist
of finer particles, and would be horizontal, or very slightly inclined.
Their color and mineral composition would be very homogeneous throughout
large areas, and would differ from almost all the separate beds in the
older series.

The following causes would produce the diversity here alluded to between
the two great members of such lacustrine formations:--When the rivers
and torrents first reach the edge of the lake, the detritus washed down
by them from the adjoining heights sinks at once into deep water, all
the heavier pebbles and sand subsiding near the shore. The finer mud is
carried somewhat farther out, but not to the distance of many miles, for
the greater part may be seen, as, for example, where the Rhone enters
the Lake of Geneva, to fall down in clouds to the bottom, not far from
the river's mouth. Thus alluvial tracts are soon formed at the mouths of
every torrent and river, and many of these in the course of ages become
of considerable extent. Pebbles and sand are then transported farther
from the mountains; but in their passage they decrease in size by
attrition, and are in part converted into mud and sand. At length some
of the numerous deltas, which are all directed towards a common centre,
approach near to each other; those of adjoining torrents become united,
and each is merged, in its turn, in the delta of the largest river,
which advances most rapidly into the lake, and renders all the minor
streams, one after the other, its tributaries. The various mineral
ingredients of all are thus blended together into one homogeneous
mixture, and the sediment is poured out from a common channel into the
lake.

As the average size of the transported particles decreases, while the
force and volume of the main river augments, the newer deposits are
diffused continually over a wider area, and are consequently more
horizontal than the older. When at first there were many independent
deltas near the borders of the basin, their separate deposits differed
entirely from each other; one may have been charged, like the Arve where
it joins the Rhone, with white sand and sediment derived from
granite--another may have been black, like many streams in the Tyrol,
flowing from the waste of decomposing rocks of dark slate--a third may
have been colored by ochreous sediment, like the Red River in
Louisiana--a fourth, like the Elsa in Tuscany, may have held much
carbonate of lime in solution. At first they would each form distinct
deposits of sand, gravel, limestone, marl, or other materials; but,
after their junction, new chemical combinations and a distinct color
would be the result, and the particles, having been conveyed ten,
twenty, or a greater number of miles over alluvial plains, would become
finer.

In those deltas where the tides and strong marine currents interfere,
the above description would only be applicable, with certain
modifications. If a series of earthquakes accompany the growth of a
delta, and change the levels of the land from time to time, as in the
region where the Indus now enters the sea, the phenomena will depart
still more widely from the ordinary type. If, after a protracted period
of rest, a delta sinks down, pebbles may be borne along in shallow water
near the foot of the boundary hills, so as to form conglomerates
overlying the fine mud previously thrown into deeper water in the same
area.

_Causes of stratification in deltas._--The stratified arrangement, which
is observed to prevail so generally in aqueous deposits, is most
frequently due to variations in the velocity of running water, which
cannot sweep along particles of more than a certain size and weight when
moving at a given rate. Hence, as the force of the stream augments or
decreases, the materials thrown down in successive layers at particular
places are rudely sorted, according to their dimensions, form, and
specific gravity. Where this cause has not operated, as where sand, mud,
and fragments of rock are conveyed by a glacier, a confused heap of
rubbish devoid of all stratification is produced.

Natural divisions are also occasioned in deltas, by the interval of time
which separates annually the deposition of matter during the periodical
rains, or melting of snow upon the mountains. The deposit of each year
may acquire some degree of consistency before that of the succeeding
year is superimposed. A variety of circumstances also give rise
annually, or sometimes from day to day, to slight variations in color,
fineness of the particles, and other characters, by which alternations
of strata distinct in texture and mineral ingredients must be produced.
Thus, for example, at one period of the year, drift-wood may be carried
down, and, at another, mud, as was before stated to be the case in the
delta of the Mississippi; or at one time, when the volume and velocity
of the stream are greatest, pebbles and sand may be spread over a
certain area, over which, when the waters are low, fine matter or
chemical precipitates are formed. During inundations, the turbid current
of fresh water often repels the sea for many miles; but when the river
is low, salt water again occupies the same space. When two deltas are
converging, the intermediate space is often, for reasons before
explained, alternately the receptacle of different sediments derived
from the converging streams (see p. 272). The one is, perhaps, charged
with calcareous, the other with argillaceous matter; or one sweeps down
sand and pebbles, the other impalpable mud. These differences may be
repeated with considerable regularity, until a thickness of hundreds of
feet of alternating beds is accumulated. The multiplication, also, of
shells and corals in particular spots, and for limited periods, gives
rise occasionally to lines of separation, and divides a mass which might
otherwise be homogeneous into distinct strata.

An examination of the shell marl now forming in the Scotch lakes, or the
sediment termed "warp," which subsides from the muddy water of the
Humber and other rivers, shows that recent deposits are often composed
of a great number of extremely thin layers, either even or slightly
undulating, and preserving a general parallelism to the planes of
stratification. Sometimes, however, the laminae in modern strata are
disposed diagonally at a considerable angle, which appears to take place
where there are conflicting movements in the waters. In January, 1829, I
visited, in company with Professor L. A. Necker, of Geneva, the
confluence of the Rhone and Arve, when those rivers were very low, and
were cutting channels through the vast heaps of dabris thrown down from
the waters of the Arve in the preceding spring. One of the sandbanks
which had formed, in the spring of 1828, where the opposing currents of
the two rivers neutralized each other, and caused a retardation in the
motion, had been undermined; and the following is an exact
representation of the arrangement of laminae exposed in a vertical
section. The length of the portion here seen is about twelve feet, and
the height five. The strata A A consist of irregular alternations of
pebbles and sand in undulating beds: below these are seams of very fine
sand B B, some as thin as paper, others about a quarter of an inch
thick. The strata C C are composed of layers of fine greenish-gray sand
as thin as paper. Some of the inclined beds will be seen to be thicker
at their upper, others at their lower extremity, the inclination of some
being very considerable. These layers must have accumulated one on the
other by lateral apposition, probably when one of the rivers was very
gradually increasing or diminishing in velocity, so that the point of
greatest retardation caused by their conflicting currents shifted
slowly, allowing the sediment to be thrown down in successive layers on
a sloping bank. The same phenomenon is exhibited in older strata of all
ages.[376]

[Illustration: Fig. 26.

Section of a sand-bank in the bed of the Arve at its confluence with the
Rhone, showing the stratification of deposits where currents meet.]

If the bed of a lake or of the sea be sinking, whether at a uniform or
an unequal rate, or oscillating in level during the deposition of
sediment, these movements will give rise to a different class of
phenomena, as, for example, to repeated alternations of shallow-water
and deep-water deposits, each with peculiar organic remains, or to
frequent repetitions of similar beds, formed at a uniform depth, and
inclosing the same organic remains, and to other results too complicated
and varied to admit of enumeration here.

_Formation of conglomerates._--Along the base of the Maritime Alps,
between Toulon and Genoa, the rivers, with few exceptions, are now
forming strata of conglomerate and sand. Their channels are often
several miles in breadth, some of them being dry, and the rest easily
forded for nearly eight months in the year, whereas during the melting
of the snow they are swollen, and a great transportation of mud and
pebbles takes place. In order to keep open the main road from France to
Italy, now carried along the sea-coast, it is necessary to remove
annually great masses of shingle brought down during the flood season. A
portion of the pebbles are seen in some localities, as near Nice, to
form beds of shingle along the shore, but the greater part are swept
into a deep sea. The small progress made by the deltas of minor rivers
on this coast need not surprise us, when we recollect that there is
sometimes a depth of two thousand feet at a few hundred yards from the
beach, as near Nice. Similar observations might be made respecting a
large proportion of the rivers in Sicily, and among others, respecting
that which, immediately north of the port of Messina, hurries annually
vast masses of granitic pebbles into the sea.

_Constant interchange of land and sea._--I may here conclude my remarks
on deltas, observing that, imperfect as is our information of the
changes which they have undergone within the last three thousand years,
they are sufficient to show how constant an interchange of sea and land
is taking place on the face of our globe. In the Mediterranean alone,
many flourishing inland towns, and a still greater number of ports, now
stand where the sea rolled its waves since the era of the early
civilization of Europe. If we could compare with equal accuracy the
ancient and actual state of all the islands and continents, we should
probably discover that millions of our race are now supported by lands
situated where deep seas prevailed in earlier ages. In many districts
not yet occupied by man, land animals and forests now abound where ships
once sailed; and, on the other hand, we shall find, on inquiry, that
inroads of the ocean have been no less considerable. When to these
revolutions, produced by aqueous causes, we add analogous changes
wrought by igneous agency, we shall, perhaps, acknowledge the justice of
the conclusion of Aristotle, who declared that the whole land and sea on
our globe periodically changed places.[377]




CHAPTER XIX.

DESTROYING AND TRANSPORTING EFFECTS OF TIDES AND CURRENTS.


  Difference in the rise of tides--Lagullas and Gulf
    currents--Velocity of currents--Causes of currents--Action of the
    sea on the British coast--Shetland Islands--Large blocks
    removed--Isles reduced to clusters of rocks--Orkney isles--Waste of
    East coast of Scotland--and East coast of England--Waste of the
    cliffs of Holderness, Norfolk, and Suffolk--Sand-dunes, how far
    chronometers--Silting up of estuaries--Yarmouth estuary--Suffolk
    coast--Dunwich--Essex coast--Estuary of the Thames--Goodwin
    Sands--Coast of Kent--Formation of the Straits of Dover--South coast
    of England--Sussex--Hants--Dorset--Portland--Origin of the Chesil
    Bank--Cornwall--Coast of Brittany.


Although the movements of great bodies of water, termed tides and
currents, are in general due to very distinct causes, their effects
cannot be studied separately; for they produce, by their joint action,
aided by that of the waves, those changes which are objects of
geological interest. These forces may be viewed in the same manner as we
before considered rivers, first, as employed in destroying portions of
the solid crust of the earth and removing them to other places;
secondly, as reproductive of new strata.

_Tides._--It would be superfluous at the present day to offer any
remarks on the cause of the tides. They are not perceptible in lakes or
in most inland seas; in the Mediterranean even, deep and extensive as is
that sea, they are scarcely sensible to ordinary observation, their
effects being quite subordinate to those of the winds and currents. In
some places, however, as in the Straits of Messina, there is an ebb and
flow to the amount of two feet and upwards; at Naples and at the
Euripus, of twelve or thirteen inches; and at Venice, according to
Rennell, of five feet.[378] In the Syrtes, also, of the ancients, two
wide shallow gulfs, which penetrate very far within the northern coast
of Africa, between Carthage and Cyrene, the rise is said to exceed five
feet.[379]

In islands remote from any continent, the ebb and flow of the ocean is
very slight, as at St. Helena, for example, where it is rarely above
three feet.[380] In any given line of coast, the tides are greatest in
narrow channels, bays, and estuaries, and least in the intervening
tracts where the land is prominent. Thus, at the entrance of the estuary
of the Thames and Medway, the rise of the spring tides is eighteen feet;
but when we follow our eastern coast from thence northward, towards
Lowestoff and Yarmouth, we find a gradual diminution, until at the
places last mentioned, the highest rise is only seven or eight feet.
From this point there begins again to be an increase, so that at Comer,
where the coast again retires towards the west, the rise is sixteen
feet; and towards the extremity of the gulf called "the Wash," as at
Lynn and in Boston Deeps, it is from twenty-two to twenty-four feet, and
in some extraordinary cases twenty-six feet. From thence again there is
a decrease towards, the north, the elevation at the Spurn Point being
from nineteen to twenty feet, and at Flamborough Head and the Yorkshire
coast from fourteen to sixteen feet.[381]

At Milford Haven in Pembrokeshire, at the mouth of the Bristol Channel,
the tides rise thirty-six feet; and at King-Road near Bristol, forty-two
feet. At Chepstow on the Wye, a small river which opens into the estuary
of the Severn, they reach fifty feet, and sometimes sixty-nine, and even
seventy-two feet. A current which sets in on the French coast, to the
west of Cape La Hague, becomes pent up by Guernsey, Jersey, and other
islands, till the rise of the tide is from twenty to forty-five feet,
which last height it attains at Jersey, and at St. Malo, a seaport of
Brittany. The tides in the Basin of Mines, at the head of the Bay of
Fundy in Nova Scotia, rise to the height of seventy feet.

There are, however, some coasts where the tides seem to offer an
exception to the rule above mentioned; for while there is scarcely any
rise in the estuary of the Plata in S. America, there is an extremely
high tide on the open coast of Patagonia, farther to the south. Yet even
in this region the tides reach their greatest elevation (about fifty
feet) in the Straits of Magellan, and so far at least they conform to
the general rule.[382]

_Currents._--The most extensive and best determined system of currents,
is that which has its source in the Indian Ocean under the influence of
the trade winds; and which, after doubling the Cape of Good Hope,
inclines to the northward, along the western coast of Africa, then
across the Atlantic, near the equator, where it is called the equatorial
current, and is lost in the Caribbean Sea, yet seems to be again revived
in the current which issues from the Gulf of Mexico. From thence it
flows rapidly through the Straits of Bahama, taking the name of the Gulf
Stream, and passing in a northeasterly direction, by the Banks of
Newfoundland, towards the Azores.

We learn from the posthumous work of Rennell on this subject, that the
Lagullas current, so called from the cape and bank of that name, is
formed by the junction of two streams, flowing from the Indian Ocean;
the one from the channel of Mozambique, down the southeast coast of
Africa; the other from the ocean at large. The collective stream is from
ninety to one hundred miles in breadth, and runs at the rate of from two
and a half to more than four miles per hour. It is at length turned
westward by the Lagullas bank, which rises from a sea of great depth to
within one hundred fathoms of the surface. It must therefore be
inferred, says Rennell, that the current here is more than one hundred
fathoms deep, otherwise the main body of it would pass across the bank,
instead of being deflected westward, so as to flow round the Cape of
Good Hope. From this cape it flows northward, as before stated, along
the western coast of Africa, taking the name of the South Atlantic
current. It then enters the Bight, or Bay of Benin, and is turned
westward, partly by the form of the coast there, and partly, perhaps, by
the Guinea current, which runs from the north into the same great bay.
From the centre of this bay proceeds the equatorial current already
mentioned, holding a westerly direction across the Atlantic, which it
traverses, from the coast of Guinea to that of Brazil, flowing
afterwards by the shores of Guiana to the West Indies. The breadth of
this current varies from 160 to 450 geographical miles, and its velocity
is from twenty-five to seventy-nine miles per day, the mean rate being
about thirty miles. The length of its whole course is about 4000 miles.
As it skirts the coast of Guiana, it is increased by the influx of the
waters of the Amazon and Orinoco, and by their junction acquires
accelerated velocity. After passing the island of Trinidad it expands,
and is almost lost in the Caribbean Sea; but there appears to be a
general movement of that sea towards the Mexican Gulf, which discharges
the most powerful of all currents through the Straits of Florida, where
the waters run in the northern part with a velocity of four or five
miles an hour, having a breadth of from thirty-five to fifty miles.[383]

The temperature of the Gulf of Mexico is 86 degrees F. in summer, or 6
degrees higher than that of the ocean, in the same parallel (25 degrees
N. lat.), and a large proportion of this warmth is retained, even where
the stream reaches the 43 degrees N. lat. After issuing from the Straits
of Florida, the current runs in a northerly direction to Cape Hatteras,
in North Carolina, about 35 degrees N. lat., where it is more than
seventy miles broad, and still moves at the rate of seventy-five miles
per day. In about the 40 degrees N. lat., it is turned more towards the
Atlantic by the extensive banks of Nantucket and St. George, which are
from 200 to 300 feet beneath the surface of the sea; a clear proof that
the current exceeds that depth. On arriving near the Azores, the stream
widens, and overflows, as it were, forming a large expanse of warm water
in the centre of the North Atlantic, over a space of 200 or 300 miles
from north to south, and having a temperature of from 8 degrees to 10
degrees Fahr. above the surrounding ocean. The whole area, covered by
the Gulf water, is estimated by Rennell at 2000 miles in length, and, at
a mean, 350 miles in breadth; an area more extensive than that of the
Mediterranean. The warm water has been sometimes known to reach the Bay
of Biscay, still retaining five degrees of temperature above that of the
adjoining ocean; and a branch of the Gulf current occasionally drifts
fruits, plants, and wood, the produce of America and the West Indies, to
the shores of Ireland and the Hebrides.

From the above statements we may understand why Rennell has
characterized some of the principal currents as oceanic rivers, which he
describes as being from 50 to 250 miles in breadth, and having a
rapidity exceeding that of the largest navigable rivers of the
continents, and so deep as to be sometimes obstructed, and occasionally
turned aside, by banks, the tops of which do not rise within forty,
fifty, or even one hundred fathoms of the surface of the sea.[384]

_Greatest velocity of currents._--The ordinary velocity of the principal
currents of the ocean is from one to three miles per hour; but when the
boundary lands converge, large bodies of water are driven gradually into
a narrow space, and then wanting lateral room, are compelled to raise
their level. Whenever this occurs their velocity is much increased. The
current which runs through the Race of Alderney, between the island of
that name and the main land, has a velocity of about eight English miles
an hour. Captain Hewett found that in the Pentland Firth, the stream, in
ordinary spring tides, runs ten miles and a half an hour, and about
thirteen miles during violent storms. The greatest velocity of the tidal
current through the "Shoots" or New Passage, in the Bristol Channel, is
fourteen English miles an hour; and Captain King observed, in his survey
of the Straits of Magellan, that the tide ran at the same rate through
the "First Narrows," and about eight geographical miles an hour, in
other parts of those straits.

_Causes of currents._--That movements of no inconsiderable magnitude
should be impressed on an expansive ocean, by winds blowing for many
months in one direction, may easily be conceived, when we observe the
effects produced in our own seas by the temporary action of the same
cause. It is well known that a strong southwest or northwest wind
invariably raises the tides to an unusual height along the west coast of
England and in the Channel; and that a northwest wind of any
continuance causes the Baltic to rise two feet and upwards above its
ordinary level. Smeaton ascertained by experiment, that in a canal four
miles in length, the water was kept up four inches higher at one end
than at the other, merely by the action of the wind along the canal; and
Rennell informs us that a large piece of water, ten miles broad, and
generally only three feet deep, has, by a strong wind, had its waters
driven to one side, and sustained so as to become six feet deep, while
the windward side was laid dry.[385]

As water, therefore, he observes, when pent up so that it cannot escape,
acquires a higher level, so, in a place _where it can escape_, the same
operation produces a current; and this current will extend to a greater
or less distance, according to the force by which it is produced. By the
side of the principal oceanic currents, such as the Lagullas and the
Gulf Stream, are parallel "counter-currents" running steadily in an
opposite direction.

Currents flowing alternately in opposite directions are occasioned by
the rise and fall of the tides. The effect of this cause is, as before
observed, most striking in estuaries and channels between islands.

A third cause of oceanic currents is evaporation by solar heat, of which
the great current setting through the Straits of Gibraltar into the
Mediterranean is a remarkable example, and will be fully considered in
the next chapter. A stream of colder water also flows from the Black Sea
into the Mediterranean. It must happen in many other parts of the world
that large quantities of water raised from one tract of the ocean by
solar heat, are carried to some other where the vapor is condensed and
falls in the shape of rain, and this, in flowing back again to restore
equilibrium, will cause sensible currents.

These considerations naturally lead to the inquiry whether the level of
those seas out of which currents flow, is higher than that of seas into
which they flow. If not, the effect must be immediately equalized by
under-currents or counter-currents. Arago is of opinion that, so far as
observations have gone, there are no exact proofs of any such difference
of level. It was inferred from the measurements of M. Lepare, that the
level of the Mediterranean, near Alexandria, was lower by 26 feet 6
inches, than the Red Sea near Suez at low water, and about 30 feet lower
than the Red Sea at the same place at high water,[386] but Mr. Robert
Stevenson affirms, as the result of a more recent survey, that there is
no difference of level between the two seas.[387]

It was formerly imagined that there was an equal, if not greater,
diversity in the relative levels of the Atlantic and Pacific, on the
opposite sides of the Isthmus of Panama. But the levellings carried
across that isthmus by Capt. Lloyd, in 1828, to ascertain the relative
height of the Pacific Ocean at Panama, and of the Atlantic at the mouth
of the river Chagres, have shown, that the difference of mean level
between those oceans is not considerable, and, contrary to expectation,
the difference which does exist is in favor of the greater height of the
Pacific. According to this survey, the mean height of the Pacific is
three feet and a half, or 3.52 above the Atlantic, if we assume the mean
level of a sea to coincide with the mean between the extremes of the
elevation and depression of the tides; for between the extreme levels of
the greatest tides in the Pacific, at Panama, there is a difference of
27.44 feet; and at the usual spring tides 21.22 feet; whereas at Chagres
this difference is only 1.16 feet, and is the same at all seasons of the
year.

The tides, in short, in the Caribbean Sea are scarcely perceptible, not
equalling those in some parts of the Mediterranean, whereas the rise is
very high in the Bay of Panama; so that the Pacific is at high tide
lifted up several feet above the surface of the Gulf of Mexico, and then
at low water let down as far below it.[388] But astronomers are agreed
that, on mathematical principles, the rise of the tidal wave above the
mean level of a particular sea must be greater than the fall below it;
and although the difference has been hitherto supposed insufficient to
cause an appreciable error, it is, nevertheless, worthy of observation,
that the error, such as it may be, would tend to reduce the small
difference, now inferred, from the observations of Mr. Lloyd, to exist
between the levels of the two oceans.

There is still another way in which heat and cold must occasion great
movements in the ocean, a cause to which, perhaps, currents are
principally due. Whenever the temperature of the surface of the sea is
lowered, condensation takes place, and the superficial water, having its
specific gravity increased, falls to the bottom, upon which lighter
water rises immediately and occupies its place. When this circulation of
ascending and descending currents has gone on for a certain time in high
latitudes, the inferior parts of the sea are made to consist of colder
or heavier fluid than the corresponding depths of the ocean between the
tropics. If there be a free communication, if no chain of submarine
mountains divide the polar from the equatorial basins, a horizontal
movement will arise by the flowing of colder water from the poles to the
equator, and there will then be a reflux of warmer superficial water
from the equator to the poles. A well-known experiment has been adduced
to elucidate this mode of action in explanation of the "trade
winds."[389] If a long trough, divided in the middle by a sluice or
partition, have one end filled with water and the other with
quicksilver, both fluids will remain quiet so long as they are divided;
but when the sluice is drawn up, the heavier fluid will rush along the
bottom of the trough, while the lighter, being displaced, will rise,
and, flowing in an opposite direction, spread itself at the top. In like
manner the expansion and contraction of sea-water by heat and cold, have
a tendency to set under-currents in motion from the poles to the
equator, and to cause counter-currents at the surface, which are
impelled in a direction contrary to that of the prevailing trade winds.
The geographical and other circumstances being very complicated, we
cannot expect to trace separately the movements due to each cause, but
must be prepared for many anomalies, especially as the configuration of
the bed of the ocean must often modify and interfere with the course of
the inferior currents, as much as the position and form of continents
and islands alter the direction of those on the surface. Thus on
sounding at great depths in the Mediterranean, Captains Berard and
D'Urville have found that the cold does not increase in a high ratio as
in the tropical regions of the ocean, the thermometer remaining fixed at
about 55 degrees F. between the depths of 1000 and 6000 feet. This might
have been anticipated, as Captain Smyth in his survey had shown that the
deepest part of the Straits of Gibraltar is only 1320 feet, so that a
submarine barrier exists there which must prevent the influx of any
under-current of the ocean cooled by polar ice.

Each of the four causes above mentioned, the wind, the tides,
evaporation, and the expansion and contraction of water by heat and
cold, may be conceived to operate independently of the others, and
although the influence of all the rest were annihilated. But there is
another cause, the rotation of the earth on its axis, which can only
come into play when the waters have already been set in motion by some
one or all of the forces above described, and when the direction of the
current so raised happens to be from south to north, or from north to
south.

The principle on which this cause operates is probably familiar to the
reader, as it has long been recognized in the case of the trade winds.
Without enlarging, therefore, on the theory, it will be sufficient to
offer an example of the mode of action alluded to. When a current flows
from the Cape of Good Hope towards the Gulf of Guinea, it consists of a
mass of water, which, on doubling the Cape, in lat. 35 degrees, has a
rotatory velocity of about 800 miles an hour; but when it reaches the
line, where it turns westward, it has arrived at a parallel where the
surface of the earth is whirled round at the rate of 1000 miles an hour,
or about 200 miles faster. If this great mass of water was transferred
suddenly from the higher to the lower latitude, the deficiency of its
rotatory motion, relatively to the land and water with which it would
come into juxtaposition, would be such as to cause an apparent motion of
the most rapid kind (of no less than 200 miles an hour) from east to
west.

In the case of such a sudden transfer, the eastern coast of America,
being carried round in an opposite direction, might strike against a
large body of water with tremendous violence, and a considerable part of
the continent might be submerged. This disturbance does not occur,
because the water of the stream, as it advances gradually into new zones
of the sea which are moving more rapidly, acquires by friction an
accelerated velocity. Yet as this motion is not imparted
instantaneously, the fluid is unable to keep up with the full speed of
the new surface over which it is successively brought. Hence, to borrow
the language of Herschel, when he speaks of the trade winds, "it lags or
hangs back, in a direction opposite to the earth's rotation, that is,
from east to west,"[390] and thus a current, which would have run simply
towards the north but for the rotation, may acquire a relative direction
towards the west.

We may next consider a case where the circumstances are the converse of
the above. The Gulf Stream flowing from about lat. 20 degrees is at first
impressed with a velocity of rotation of about 940 miles an hour, and
runs to the lat. 40 degrees, where the earth revolves only at the rate
of 766 miles, or 174 miles slower. In this case a relative motion of an
opposite kind may result; and the current may retain an excess of
rotatory velocity, tending continually to deflect it eastward. Polar
currents, therefore, or those flowing from high to low latitudes, are
driven towards the eastern shores of continents, while tropical currents
flowing towards the poles are directed against their western shores.

Thus it will be seen that currents depend, like the tides, on no
temporary or accidental circumstances, but on the laws which preside
over the motions of the heavenly bodies. But although the sum of their
influence in altering the surface of the earth may be very constant
throughout successive epochs, yet the points where these operations are
displayed in fullest energy shift perpetually. The height to which the
tides rise, and the violence and velocity of currents, depend in a great
measure on the actual configuration of the land, the contour of a long
line of continental or insular coast, the depth and breadth of channels,
the peculiar form of the bottom of seas--in a word, on a combination of
circumstances which are made to vary continually by many igneous and
aqueous causes, and, amongst the rest, by the tides and currents
themselves. Although these agents, therefore, of decay and reproduction
are local in reference to periods of short duration, such as those which
history embraces, they are nevertheless universal, if we extend our
views to a sufficient lapse of ages.

_Destroying and transporting power of currents._--After these
preliminary remarks on the nature and causes of currents, their velocity
and direction, we may next consider their action on the solid materials
of the earth. We shall find that their efforts are, in many respects,
strictly analogous to those of rivers. I have already treated in the
third chapter, of the manner in which currents sometimes combine with
ice, in carrying mud, pebbles, and large fragments of rock to great
distances. Their operations are more concealed from our view than those
of rivers, but extend over wider areas, and are therefore of more
geological importance.

_Waste of the British coasts._--_Shetland Islands_.--If we follow the
eastern and southern shores of the British islands, from our Ultima
Thule in Shetland to the Land's End in Cornwall, we shall find evidence
of a series of changes since the historical era, very illustrative of
the kind and degree of force exerted by tides and currents co-operating
with the waves of the sea. In this survey we shall have an opportunity
of tracing their joint power on islands, promontories, bays, and
estuaries; on bold, lofty cliffs, as well as on low shores; and on every
description of rock and soil, from granite to blown sand.

The northernmost group of the British islands, the Shetland, are
composed of a great variety of rocks, including granite, gneiss,
mica-slate, serpentine, greenstone, and many others, with some secondary
rocks, chiefly sandstone and conglomerate. These islands are exposed
continually to the uncontrolled violence of the Atlantic, for no land
intervenes between their western shores and America. The prevalence,
therefore, of strong westerly gales, causes the waves to be sometimes
driven with irresistible force upon the coast, while there is also a
current setting from the north. The spray of the sea aids the
decomposition of the rocks, and prepares them to be breached by the
mechanical force of the waves. Steep cliffs are hollowed out into deep
caves and lofty arches; and almost every promontory ends in a cluster of
rocks, imitating the forms of columns, pinnacles, and obelisks.

_Drifting of large masses of rock._--Modern observations show that the
reduction of continuous tracts to such insular masses is a process in
which nature is still actively engaged. "The isle of Stenness," says Dr.
Hibbert, "presents a scene of unequalled desolation. In stormy winters,
huge blocks of stones are overturned, or are removed from their native
beds, and hurried up a slight acclivity to a distance almost incredible.
In the winter of 1802, a tabular-shaped mass, eight feet two inches by
seven feet, and five feet one inch thick, was dislodged from its bed,
and removed to a distance of from eighty to ninety feet. I measured the
recent bed from which a block had been carried away the preceding winter
(A. D. 1818), and found it to be seventeen feet and a half by seven
feet, and the depth two feet eight inches. The removed mass had been
borne to a distance of thirty feet, when it was shivered into thirteen
or more lesser fragments, some of which, were carried still farther,
from 30 to 120 feet. A block, nine feet two inches by six feet and a
half, and four feet thick, was hurried up the acclivity to a distance of
150 feet."[391]

At Northmavine, also, angular blocks of stone have been removed in a
similar manner to considerable distances by the waves of the sea, some
of which are represented in the annexed figure.

_Effects of lightning._--In addition to numerous examples of masses
detached and driven by the waves, tides, and currents from their place,
some remarkable effects of lightning are recorded in these isles. At
Funzie, in Fetlar, about the middle of the last century, a rock of
mica-schist, 105 feet long, ten feet broad, and in some places four feet
thick, was in an instant torn by a flash of lightning from its bed, and
broken into three large and several smaller fragments. One of these,
twenty-six feet long, ten feet broad, and four feet thick, was simply
turned over. The second, which was twenty-eight feet long, seventeen
broad, and five feet in thickness, was hurled across a high point to the
distance of fifty yards. Another broken mass, about forty feet long, was
thrown still farther, but in the same direction, quite into the sea.
There were also many smaller fragments scattered up and down.[392]

[Illustration: Fig. 27.

Stony fragments drifted by the sea. Northmavine, Shetland.]

When we thus see electricity co-operating with the violent movements of
the ocean in heaping up piles of shattered rocks on dry land and beneath
the waters, we cannot but admit that a region which shall be the
theatre, for myriads of ages, of the action of such disturbing causes,
might present, at some future period, if upraised far above the bosom of
the deep, a scene of havoc and ruin that may compare with any now found
by the geologist on the surface of our continents.

In some of the Shetland Isles, as on the west of Meikle Roe, dikes, or
veins of soft granite, have mouldered away; while the matrix in which
they were inclosed, being of the same substance, but of a firmer
texture, has remained unaltered. Thus, long narrow ravines, sometimes
twenty feet wide, are laid open, and often give access to the waves.
After describing some huge cavernous apertures into which the sea flows
for 250 feet in Roeness, Dr. Hibbert, writing in 1822, enumerates other
ravages of the ocean. "A mass of rock, the average dimensions of which
may perhaps be rated at twelve or thirteen feet square, and four and a
half or five in thickness, was first moved from its bed, about fifty
years ago, to a distance of thirty feet, and has since been twice turned
over."

_Passage forced by the sea through porphyritic rocks._--"But the most
sublime scene is where a mural pile of porphyry, escaping the process
of disintegration that is devastating the coast, appears to have been
left as a sort of rampart against the inroads of the ocean;--the
Atlantic, when provoked by wintry gales, batters against it with all the
force of real artillery--the waves having, in their repeated assaults,
forced themselves an entrance. This breach, named the Grind of the Navir
(fig. 28), is widened every winter by the overwhelming surge that,
finding a passage through it, separates large stones from its sides, and
forces them to a distance of no less than 180 feet. In two or three
spots, the fragments which have been detached are brought together in
immense heaps, that appear as an accumulation of cubical masses, the
product of some quarry."[393]

[Illustration: Fig. 28.

Grind of the Navir--passage forced by the sea through rocks of hard
porphyry.]

It is evident from this example, that although the greater
indestructibility of some rocks may enable them to withstand, for a
longer time, the action of the elements, yet they cannot permanently
resist. There are localities in Shetland, in which rocks of almost every
variety of mineral composition are suffering disintegration; thus the
sea makes great inroads on the clay slate of Fitfel Head, on the
serpentine of the Vord Hill in Fetlar, and on the mica-schist of the Bay
of Triesta, on the east coast of the same island, which decomposes into
angular blocks. The quartz rock on the east of Walls, and the gneiss and
mica-schist of Garthness, suffer the same fate.

_Destruction of islands._--Such devastation cannot be incessantly
committed for thousands of years without dividing islands, until they
become at last mere clusters of rocks, the last shreds of masses once
continuous. To this state many appear to have been reduced, and
innumerable fantastic forms are assumed by rocks adjoining these islands
to which the name of Drongs is applied, as it is to those of similar
shape in Feroe.

[Illustration: Fig. 29.

Granitic rocks named the Drongs, between Papa Stour and Hillswick Ness.]

[Illustration: Fig. 30.

Granitic rocks to the south of Hillswick Ness, Shetland.]

The granite rocks (fig. 29), between Papa Stour and Hillswick Ness
afford an example. A still more singular cluster of rocks is seen to the
south of Hillswick Ness (fig. 30), which presents a variety of forms as
viewed from different points, and has often been likened to a small
fleet of vessels with spread sails.[394] We may imagine that in the
course of time Hillswick Ness itself may present a similar wreck, from
the unequal decomposition of the rocks whereof it is composed,
consisting of gneiss and mica-schist traversed in all directions by
veins of felspar-porphyry.

Midway between the groups of Shetland and Orkney is Fair Island, said to
be composed of sandstone with high perpendicular cliffs. The current
runs with such velocity, that during a calm, and when there is no swell,
the rocks on its shores are white with the foam of the sea driven
against them. The Orkneys, if carefully examined, would probably
illustrate our present topic as much as the Shetland group. The
northeast promontory of Sanda, one of these islands, has been cut off in
modern times by the sea, so that it became what is now called Start
Island, where a lighthouse was erected in 1807, since which time the new
strait has grown broader.

_East coast of Scotland._--To pass over to the main land of Scotland, we
find that in Inverness-shire there have been inroads of the sea at Fort
George, and others in Morayshire, which have swept away the old town of
Findhorn. On the coast of Kincardineshire, an illustration was afforded
at the close of the last century, of the effect of promontories in
protecting a line of low shore. The village of Mathers, two miles south
of Johnshaven, was built on an ancient shingle beach, protected by a
projecting ledge of limestone rock. This was quarried for lime to such
an extent that the sea broke through, and in 1795 carried away the whole
village in one night, and penetrated 150 yards inland, where it has
maintained its ground ever since, the new village having been built
farther inland on the new shore. In the bay of Montrose, we find the
North Esk and the South Esk rivers pouring annually into the sea large
quantities of sand and pebbles; yet they have formed no deltas, for the
waves, aided by the current, setting across their mouths, sweep away all
the materials. Considerable beds of shingle, brought down by the North
Esk, are seen along the beach.

Proceeding southwards, we learn that at Arbroath, in Forfarshire, which
stands on a rock of red sandstone, gardens and houses have been carried
away since the commencement of the present century by encroachments of
the sea. It had become necessary before 1828, to remove the lighthouses
at the mouth of the estuary of the Tay, in the same county, at Button
Ness, which were built on a tract of blown sand, the sea having
encroached for three-quarters of a mile.

_Force of waves and currents in estuaries._--The combined power which
waves and currents can exert in _estuaries_ (a term which I confine to
bays entered both by rivers and the tides of the sea), was remarkably
exhibited during the building of the Bell Rock Lighthouse, off the mouth
of the Tay. The Bell Rock is a sunken reef, consisting of red sandstone,
being from twelve to sixteen feet under the surface at high water, and
about twelve miles from the mainland. At the distance of 100 yards,
there is a depth, in all directions of two or three fathoms at low
water. In 1807, during the erection of the lighthouse, six large blocks
of granite, which had been landed on the reef, were removed by the force
of the sea, and thrown over a rising ledge to the distance of twelve or
fifteen paces; and an anchor, weighing about 22 cwt., was thrown up upon
the rock.[395] Mr. Stevenson informs us moreover, that drift stones,
measuring upwards of thirty cubic feet, or more than two tons' weight,
have, during storms, been often thrown upon the rock from the deep
water.[396]

_Submarine forests._--Among the proofs that the sea has encroached on
the land bordering the estuary of the Tay, Dr. Fleming has mentioned a
submarine forest which has been traced for several miles along the
northern shore of the county of Fife.[397] But subsequent surveys seem
to have shown that the bed of peat containing tree-roots, leaves, and
branches, now occurring at a lower level than the Tay, must have come
into its present position by a general sinking of the ground on which
the forest grew. The peat-bed alluded to is not confined, says Mr.
Buist, to the present channel of the Tay, but extends far beyond it, and
is covered by stratified clay from fifteen to twenty-five feet in
thickness, in the midst of which, in some places, is a bed full of
sea-shells.[398] Recent discoveries having established the fact that
upward and downward movements have affected our island since the general
coast-line had nearly acquired its present shape, we must hesitate
before we attribute any given change to a single cause, such as the
local encroachment of the sea upon low land.

On the coast of Fife, at St. Andrew's, a tract of land, said to have
intervened between the castle of Cardinal Beaton and the sea, has been
entirely swept away, as were the last remains of the Priory of Crail, in
the same county, in 1803. On both sides of the Frith of Forth, land has
been consumed; at North Berwick in particular, and at Newhaven, where an
arsenal and dock, built in the reign of James IV., in the fifteenth
century, has been overflowed.

_East coast of England._--If we now proceed to the English coast, we
find records of numerous lands having been destroyed in Northumberland,
as those near Bamborough and Holy Island, and at Tynemouth Castle, which
now overhangs the sea, although formerly separated from it by a strip of
land. At Hartlepool, and several other parts of the coast of Durham
composed of magnesian limestone, the sea has made considerable inroads.

_Coast of Yorkshire._--Almost the whole coast of Yorkshire, from the
mouth of the Tees to that of the Humber, is in a state of gradual
dilapidation. That part of the cliffs which consist of lias, the oolite
series, and chalk, decays slowly. They present abrupt and naked
precipices, often 300 feet in height; and it is only at a few points
that the grassy covering of the sloping talus marks a temporary
relaxation of the erosive action of the sea. The chalk cliffs are worn
into caves and needles in the projecting headland of Flamborough, where
they are decomposed by the salt spray, and slowly crumble away. But the
waste is most rapid between that promontory and Spurn Point, or the
coast of Holderness, as it is called, a tract consisting of beds of
clay, gravel, sand, and chalk rubble. The irregular intermixture of the
argillaceous beds causes many springs to be thrown out, and this
facilitates the undermining process, the waves beating against them, and
a strong current setting chiefly from the north. The wasteful action is
very conspicuous at Dimlington Height, the loftiest point in Holderness,
where the beacon stands on a cliff 146 feet above high water, the whole
being composed of clay, with pebbles scattered through it.[399] "For
many years," says Professor Phillips, "the rate at which the cliffs
recede from Bridlington to Spurn, a distance of thirty-six miles, has
been found by measurement to equal on an average two and a quarter yards
annually, which, upon thirty-six miles of coast, would amount to about
thirty acres a year. At this rate, the coast, the mean height of which
above the sea is about forty feet, has lost one mile in breadth since
the Norman Conquest, and more than two miles since the occupation of
York (Eboracum) by the Romans."[400] The extent of this denudation, as
estimated by the number of cubic feet of matter removed annually, will
be again spoken of in chapter 22.

In the old maps of Yorkshire, we find spots, now sand-banks in the sea,
marked as the ancient sites of the towns and villages of Auburn,
Hartburn, and Hyde. "Of Hyde," says Pennant, "only the tradition is
left; and near the village of Hornsea, a street called Hornsea Beck has
long since been swallowed."[401] Owthorne and its church have also been
in great part destroyed, and the village of Kilnsea; but these places
are now removed farther inland. The annual rate of encroachment at
Owthorne for several years preceding 1830, is stated to have averaged
about four yards. Not unreasonable fears are entertained that at some
future time the Spurn Point will become an island, and that the ocean,
entering into the estuary of the Humber, will cause great
devastation.[402] Pennant, after speaking of the silting up of some
ancient ports in that estuary, observes, "But, in return, the sea has
made most ample reprisals; the site, and even the very names of several
places, once towns of note upon the Humber, are now only recorded in
history; and Ravensper was at one time a rival to Hull (Madox, Ant.
Exch. i. 422), and a port so very considerable in 1332, that Edward
Baliol and the confederated English barons sailed from hence to invade
Scotland; and Henry IV., in 1399, made choice of this port to land at,
to effect the deposal of Richard II.; yet the whole of this has long
since been devoured by the merciless ocean; extensive sands, dry at low
water, are to be seen in their stead."[403]

Pennant describes Spurn Head as a promontory in the form of a sickle,
and says the land, for some miles to the north, was "perpetually preyed
on by the fury of the German Sea, which devours whole acres at a time,
and exposes on the shores considerable quantities of beautiful amber."

_Lincolnshire._--The maritime district of Lincolnshire consists chiefly
of lands that lie below the level of the sea, being protected by
embankments. Some of the fens were embanked and drained by the Romans;
but after their departure the sea returned, and large tracts were
covered with beds of silt, containing marine shells, now again converted
into productive lands. Many dreadful catastrophes are recorded by
incursions of the sea, whereby several parishes have been at different
times overwhelmed.

_Norfolk._--The decay of the cliffs of Norfolk and Suffolk is incessant.
At Hunstanton, on the north, the undermining of the lower arenaceous
beds at the foot of the cliff, causes masses of red and white chalk to
be precipitated from above. Between Hunstanton and Weybourne, low hills,
or dunes, of blown sand, are formed along the shore, from fifty to sixty
feet high. They are composed of dry sand, bound in a compact mass by the
long creeping roots of the plant called Marram (_Arundo arenaria_). Such
is the present set of the tides, that the harbors of Clay, Wells, and
other places are securely defended by these barriers; affording a clear
proof that it is not the strength of the material at particular points
that determines whether the sea shall be progressive or stationary, but
the general contour of the coast.

The waves constantly undermine the low chalk cliffs, covered with sand
and clay, between Weybourne and Sherringham, a certain portion of them
being annually removed. At the latter town I ascertained, in 1829, some
facts which throw light on the rate at which the sea gains upon the
land. It was computed, when the present inn was built, in 1805, that it
would require seventy years for the sea to reach the spot: the mean loss
of land being calculated, from previous observations, to be somewhat
less than one yard, annually. The distance between the house and the sea
was fifty yards; but no allowance was made for the slope of the ground
being _from_ the sea, in consequence of which the waste was naturally
accelerated every year, as the cliff grew lower, there being at each
succeeding period less matter to remove when portions of equal area fell
down. Between the years 1824 and 1829, no less than seventeen yards were
swept away, and only a small garden was then left between the building
and the sea. There was, in 1829, a depth of twenty feet (sufficient to
float a frigate) at one point in the harbor of that port, where, only
forty-eight years before, there stood a cliff fifty feet high, with
houses upon it! If once in half a century an equal amount of change were
produced suddenly by the momentary shock of an earthquake, history would
be filled with records of such wonderful revolutions of the earth's
surface; but, if the conversion of high land into deep sea be gradual,
it excites only local attention. The flagstaff of the Preventive Service
station, on the south side of this harbor, was thrice removed inland
between the years 1814 and 1829, in consequence of the advance of the
sea.

Farther to the south we find cliffs, composed, like those of Holderness
before mentioned, of alternating strata of blue clay, gravel, loam, and
fine sand. Although they sometimes exceed 300 feet in height, the havoc
made on the coast is most formidable. The whole site of ancient Cromer
now forms part of the German Ocean, the inhabitants having gradually
retreated inland to their present situation, from whence the sea still
threatens to dislodge them. In the winter of 1825, a fallen mass was
precipitated from near the lighthouse, which covered twelve acres,
extending far into the sea, the cliffs being 250 feet in height.[404]
The undermining by springs has sometimes caused large portions of the
upper part of the cliffs, with houses still standing upon them, to give
way, so that it is impossible, by erecting breakwaters at the base of
the cliffs, permanently to ward off the danger.

[Illustration: Fig. 31.

Tower of the buried Church of Eccles, Norfolk, A. D. 1839.

The inland slope of the hills of blown sand is shown in this view, with
the lighthouse of Hasborough in the distance.]

On the same coast, says Mr. R. C. Taylor, the ancient villages of
Shipden, Wimpwell, and Eccles have disappeared; several manors and large
portions of neighboring parishes having, piece after piece, been
swallowed up; nor has there been any intermission, from time immemorial,
in the ravages of the sea along a line of coast twenty miles in length,
in which these places stood.[405] Of Eccles, however, a monument still
remains in the rained tower of the old church, which is half buried in
the dunes of sand within a few paces (60?) of the sea-beach (fig. 31).
So early as 1605 the inhabitants petitioned James I. for a reduction of
taxes, as 300 acres of land, and all their houses, save fourteen, had
then been destroyed by the sea. Not one half that number of acres now
remains in the parish, and hills of blown sand now occupy the site of
the houses which were still extant in 1605. When I visited the spot in
1839, the sea was fast encroaching on the sand-hills, and had laid open
on the beach the foundations of a house fourteen yards square, the upper
part of which had evidently been pulled down before it had been buried
under sand. The body of the church has also been long buried, but the
tower still remains visible.

M. E. de Beaumont has suggested that sand-dunes in Holland and other
countries may serve as natural chronometers, by which the date of the
existing continents may be ascertained. The sands, he says, are
continually blown inland by the force of the winds, and by observing the
rate of their march we may calculate the period when the movement
commenced.[406] But the example just given will satisfy every geologist
that we cannot ascertain the starting-point of dunes, all coasts being
liable to waste, and the shores of the Low Countries in particular,
being not only exposed to inroads of the sea, but, as M. de Beaumont
himself has well shown, having even in historical times undergone a
change of level. The dunes may indeed, in some cases, be made use of as
chronometers, to enable us to assign a minimum of antiquity to existing
coast-lines; but this test must be applied with great caution, so
variable is the rate at which the sands may advance into the interior.

Hills of blown sand, between Eccles and Winterton, have barred up and
excluded the tide for many hundred years from the mouths of several
small estuaries; but there are records of nine breaches, from 20 to 120
yards wide, having been made through these, by which immense damage was
done to the low grounds in the interior. A few miles south of
Happisburgh, also, are hills of blown sand, which extend to Yarmouth.
These _dunes_ afford a temporary protection to the coast, and an inland
cliff, about a mile long, at Winterton, shows clearly that at that point
the sea must have penetrated formerly farther than at present.

_Silting up of estuaries_--At Yarmouth, the sea has not advanced upon
the sands in the slightest degree since the reign of Elizabeth. In the
time of the Saxons, a great estuary extended as far as Norwich, which
city, is represented; even in the thirteenth and fourteenth centuries,
as "situated on the banks of an arm of the sea." The sands whereon
Yarmouth is built, first became firm and habitable ground about the year
1008, from which time a line of dunes has gradually increased in height
and breadth, stretching across the whole entrance of the ancient
estuary, and obstructing the ingress of the tides so completely, that
they are only admitted by the narrow passage which the river keeps open,
and which has gradually shifted several miles to the south. The ordinary
tides at the river's mouth rise, at present, only to the height, of
three or four feet, the spring tides to about eight or nine.

By the exclusion of the sea, thousands of acres in the interior have
become cultivated lands; and, exclusive of smaller pools, upwards of
sixty freshwater lakes have been formed, varying in depth from fifteen
to thirty feet, and in extent from one acre to twelve hundred.[407] The
Yare, and other rivers, frequently communicate with these sheets of
water; and thus they are liable to be filled up gradually with
lacustrine and fluviatile deposits, and to be converted into land
covered with forests. Yet it must not be imagined, that the acquisition
of new land fit for cultivation in Norfolk and Suffolk indicates any
permanent growth of the eastern limits of our island to compensate its
reiterated losses. No _delta_ can form on such a shore.

Immediately off Yarmouth, and parallel to the shore, is a great range of
sand-banks, the shape of which varies slowly from year to year, and
often suddenly after great storms. Captain Hewitt, R. N., found in these
banks, in 1836, a broad channel sixty-five feet deep, where there was
only a depth of four feet during a prior survey in 1822. The sea had
excavated to the depth of sixty feet in the course of fourteen years, or
perhaps a shorter period. The new channel thus formed serves at present
(1838), for the entrance of ships into Yarmouth Roads; and the magnitude
of this change shows how easily a new set of the waves and currents
might endanger the submergence of the land gained within the ancient
estuary of the Yare.

That great banks should be thrown across the mouths of estuaries on our
eastern coast, where there is not a large body of river-water to
maintain an open channel, is perfectly intelligible, when we bear in
mind that the marine current, sweeping along the coast, is charged with
the materials of wasting cliffs, and ready to form a bar anywhere the
instant its course is interrupted or checked by any opposing stream. The
mouth of the Yare has been, within the last five centuries, diverted
about four miles to the south. In like manner it is evident that, at
some remote period, the river Alde entered the sea at Aldborough, until
its ancient outlet was barred up and at length transferred to a point no
less than ten miles distant to the southwest. In this case, ridges of
sand and shingle, like those of Lowestoff Ness, which will be described
by and by, have been thrown up between the river and the sea; and an
ancient sea-cliff is to be seen now inland.

It may be asked why the rivers on our east coast are always deflected
southwards, although the tidal current flows alternately from the south
and north? The cause is to be found in the superior force of what is
commonly called "the flood tide from the north," a tidal wave derived
from the Atlantic, a small part of which passes eastward up the English
Channel, and through the Straits of Dover and then northwards, while the
principal body of water, moving much more rapidly in a more open sea, on
the western side of Britain, first passes the Orkneys, and then turning,
flows down between Norway and Scotland, and sweeps with great velocity
along our eastern coast. It is well known that the highest tides on this
coast are occasioned by a powerful northwest wind, which raises the
eastern part of the Atlantic, and causes it to pour a greater volume of
water into the German Ocean. This circumstance of a violent _off-shore_
wind being attended with a rise of the waters, instead of a general
retreat of the sea, naturally excites the wonder of the inhabitants of
our coast. In many districts they look with confidence for a rich
harvest of that valuable manure, the sea-weed, when the north-westerly
gales prevail, and are rarely disappointed.

[Illustration: Fig. 32.

Map of Lowestoff Ness, Suffolk.[408]

_a_, _a_. The dotted lines express a series of sand and shingle, forming
the extremity of the triangular space called the Ness.

_b_, _b_, _b_. The dark line represents the inland cliff on which the
town of Lowestoff stands, between which and the sea is the Ness.]

_Coast of Suffolk._--The cliffs of Suffolk, to which we next proceed,
are somewhat less elevated than those of Norfolk, but composed of
similar alternations of clay, sand, and gravel. From Gorleston in
Suffolk, to within a few miles north of Lowestoff, the cliffs are slowly
undermined. Near the last-mentioned town, there is an inland cliff about
sixty feet high, the sloping talus of which is covered with turf and
heath. Between the cliff and the sea is a low flat tract of sand called
the Ness, nearly three miles long, and for the most part out of reach of
the highest tides. The point of the Ness projects from the base of the
original cliff to the distance of 660 yards. This accession of land,
says Mr. Taylor, has been effected at distinct and distant intervals, by
the influence of currents running between the land and a shoal about a
mile off Lowestoff, called the Holm Sand. The lines of growth in the
Ness are indicated by a series of concentric ridges or embankments
inclosing limited areas, and several of these ridges have been formed
within the observation of persons now living. A rampart of heavy
materials is first thrown up to an unusual altitude by some
extraordinary tide, attended with a violent gale. Subsequent tides
extend the base of this high bank of shingle, and the interstices are
then filled with sand blown from the beach. The Arundo and other marine
plants by degrees obtain a footing; and creeping along the ridge, give
solidity to the mass, and form in some cases a matted covering of turf.
Meanwhile another mound is forming externally, which by the like process
rises and gives protection to the first. If the sea forces its way
through one of the external and incomplete mounds, the breach is soon
repaired. After a while the marine plants within the areas inclosed by
these embankments are succeeded by a better species of herbage affording
good pasturage, and the sands become sufficiently firm to support
buildings.

_Destruction of Dunwich by the sea._--Of the gradual destruction of
Dunwich, once the most considerable seaport on this coast, we have many
authentic records. Gardner, in his history of that borough, published
in 1754, shows, by reference to documents, beginning with Doomsday Book,
that the cliffs at Dunwich, Southwold, Eastern, and Pakefield, have been
always subject to wear away. At Dunwich, in particular, two tracts of
land which had been taxed in the eleventh century, in the time of King
Edward the Confessor, are mentioned in the Conqueror's survey, made but
a few years afterwards, as having been devoured by the sea. The losses,
at a subsequent period, of a monastery,--at another of several
churches,--afterwards of the old port,--then of four hundred houses at
once,--of the church of St. Leonard, the high-road, town-hall, jail, and
many other buildings, are mentioned, with the dates when they perished.
It is stated that, in the sixteenth century, not one-quarter of the town
was left standing; yet the inhabitants retreating inland, the name was
preserved, as has been the case with many other ports when their ancient
site has been blotted out. There is, however, a church of considerable
antiquity still standing, the last of twelve mentioned in some records.
In 1740, the laying open of the churchyard of St. Nicholas and St.
Francis, in the sea-cliffs, is well described by Gardner, with the
coffins and skeletons exposed to view--some lying on the beach, and
rocked


  "In cradle of the rude imperious surge."


Of these cemeteries no remains can now be seen. Ray also says, "that
ancient writings make mention of a wood a mile and a half to the east of
Dunwich, the site of which must at present be so far within the
sea."[409] This city, once so flourishing and populous, is now a small
village, with about twenty houses, and one hundred inhabitants.

There is an old tradition, "that the tailors sat in their shops at
Dunwich, and saw the ships in Yarmouth Bay;" but when we consider how
far the coast at Lowestoff Ness projects between these places, we cannot
give credit to the tale, which, nevertheless, proves how much the
inroads of the sea in times of old had prompted men of lively
imagination to indulge their taste for the marvellous.

Gardner's description of the cemeteries laid open by the waves reminds
us of the scene which has been so well depicted by Bewick,[410] and of
which numerous points on the same coast might have suggested the idea.
On the verge of a cliff, which the sea has undermined, are represented
the unshaken tower and western end of an abbey. The eastern aisle is
gone, and the pillars of the cloister are soon to follow. The waves have
almost isolated the promontory, and invaded the cemetery, where they
have made sport with the mortal relics, and thrown up a skull upon the
beach. In the foreground is seen a broken tombstone, erected, as its
legend tells, "to _perpetuate_ the memory"--of one whose name is
obliterated, as is that of the county for which he was "Custos
Rotulorum." A cormorant is perched on the monument, defiling it, as if
to remind some moralizer like Hamlet, of "the base uses" to which things
sacred may be turned. Had this excellent artist desired to satirize
certain popular theories of geology, he might have inscribed the stone
to the memory of some philosopher who taught "the permanency of existing
continents"--"the era of repose"--"the impotence of modern causes."

The incursions of the sea at Aldborough, were formerly very destructive,
and this borough is known to have been once situated a quarter of a mile
east of the present shore. The inhabitants continued to build farther
inland, till they arrived at the extremity of their property, and then
the town decayed greatly; but two sand-banks, thrown up at a short
distance, now afford a temporary safeguard to the coast. Between these
banks and the present shore, where the current now flows, the sea is
twenty-four feet deep on the spot where the town formerly stood.

_Essex._--Harwich is said to have owed its rise to the destruction of
Orwell, a town which stood on the spot now called "the west rocks," and
was overwhelmed by an inroad of the sea since the Conquest.
Apprehensions have been entertained that the isthmus on which Harwich
stands may at no remote period become an island, for the sea may be
expected to make a breach near Lower Dover Court, where Beacon Cliff is
composed of horizontal beds of London clay containing septaria. It had
wasted away considerably between the years 1829 and 1838, at both which
periods I examined this coast. In that short interval several gardens
and many houses had been swept into the sea, and in April, 1838, a whole
street was threatened with destruction. The advance of the sea is much
accelerated by the traffic carried on in septaria, which are shipped off
for cement as fast as they fall down upon the beach. These stones, if
allowed to remain in heaps on the shore, would break the force of the
waves and retard the conversion of the peninsula into an island, an
event which might be followed by the destruction of the town of Harwich.
Captain Washington, R. N., ascertained in 1847, that Beacon Cliff, above
mentioned, which is about fifty feet high, had given way at the rate of
forty feet in forty-seven years, between 1709 and 1756; eighty feet
between 1756 and 1804; and three hundred and fifty feet between the
latter period and 1841; showing a rapidly accelerated rate of
destruction.[411]

Among other losses it is recorded that, since the year 1807, a field
called the Vicar's Field, which belonged to the living of Harwich, has
been overwhelmed;[412] and in the year 1820 there was a considerable
space between the battery at Harwich, built in the beginning of the
present century, and the sea; part of the fortification had been swept
away in 1829, and the rest then overhung the water.

At Walton Naze, in the same county, the cliffs, composed of London clay,
capped by the shelly sands of the crag, reach the height of about 100
feet, and are annually undermined by the waves. The old churchyard of
Walton has been washed away, and the cliffs to the south are constantly
disappearing.

_Kent.--Isle of Sheppey._--On the coast bounding the estuary of the
Thames, there are numerous examples both of the gain and loss of land.
The Isle of Sheppey, which is now about six miles long by four in
breadth, is composed of London clay. The cliffs on the north, which are
from sixty to eighty feet high, decay rapidly, fifty acres having been
lost in twenty years, between 1810 and 1830. The church at Minster, now
near the coast, is said to have been in the middle of the island in
1780; and if the present rate of destruction should continue, we might
calculate the period, and that not a very remote one, when the whole
island will be annihilated. On the coast of the mainland, to the east of
Sheppey, is Herne Bay: a place still retaining the name of a bay,
although it is no longer appropriate, as the waves and currents have
swept away the ancient headlands. There was formerly a small promontory
in the line of the shoals where the present pier is built, by which the
larger bay was divided into two, called the Upper and Lower.[413]

[Illustration: Fig. 33.

View of Reculver Church, taken in the year 1781.

1. Isle of Sheppey. 2. Ancient chapel now destroyed. The cottage between
this chapel and the cliff was demolished by the sea, in 1782.]

Still farther east stands the church of Reculver, upon a cliff composed
of clay and sand, about twenty-five feet high. Reculver (Regulvium) was
an important military station in the time of the Romans, and appears,
from Leland's account, to have been, so late as Henry VIII.'s reign,
nearly one mile distant from the sea. In the "Gentleman's Magazine,"
there is a view of it, taken in 1781, which still represents a
considerable space as intervening between the north wall of the
churchyard and the cliff.[414] Sometime before the year 1780, the waves
had reached the site of the ancient Roman camp or fortification, the
walls of which had continued for several years after they were
undermined to overhang the sea, being firmly cemented into one mass.
They were eighty yards nearer the sea than the church, and they are
spoken of in the "Topographica Britannica," in the year 1780, as having
recently fallen down. In 1804, part of the churchyard with some
adjoining houses was washed away, and the ancient church, with its two
spires, was dismantled and abandoned as a place of worship, but kept in
repair as a landmark well known to mariners. I visited the spot in June,
1851, and saw human bones and part of a wooden coffin projecting from
the cliff, near the top. The whole building would probably have been
swept away long ere this, had not the force of the waves been checked by
an artificial causeway of stones and large wooden piles driven into the
sands on the beach to break the force of the waves.

[Illustration: Fig. 34.

Reculver Church, in 1834.]

_Isle of Thanet._--The isle of Thanet was, in the time of the Romans,
separated from the rest of Kent by a navigable channel, through which
the Roman fleets sailed on their way to and from London. Bede describes
this small estuary as being, in the beginning of the eighth century,
three furlongs in breadth; and it is supposed that it began to grow
shallow about the period of the Norman conquest. It was so far silted up
in the year 1485, that an act was then obtained to build a bridge across
it; and it has since become marsh land with small streams running
through it. On the coast, Bedlam Farm, belonging to the hospital of that
name, lost eight acres in the twenty years preceding 1830, the land
being composed of chalk from forty to fifty feet above the level of the
sea. It has been computed that the average waste of the cliff between
the North Foreland and the Reculvers, a distance of about eleven miles,
is not less than two feet per annum. The chalk cliffs on the south of
Thanet, between Ramsgate and Pegwell Bay, have on an average lost three
feet per annum for the last ten years (preceding 1830).

_Goodwin Sands._--The Goodwin Sands lie opposite this part of the
Kentish coast. They are about ten miles in length, and are in some parts
three, and in others seven, miles distant from the shore; and, for a
certain space, are laid bare at low water. That they are a remnant of
land, and not "a mere accumulation of sea sand," as Rennell
imagined,[415] may be presumed from the fact that, when the erection of
a lighthouse on this shoal was in contemplation by the Trinity Board in
the year 1817, it was found, by borings, that the bank consisted of
fifteen feet of sand, resting on blue clay; and, by subsequent borings,
the subjacent chalk has been reached. An obscure tradition has come down
to us, that the estates of Earl Goodwin, the father of Harold, who died
in the year 1053, were situated here, and some have conjectured that
they were overwhelmed by the flood mentioned in the Saxon chronicle,
_sub anno 1099_. The last remains of an island, consisting, like
Sheppey, of clay, may perhaps have been carried away about that time.

[Illustration: Fig. 35.

Shakspeare's Cliff in 1836, seen from the northeast.]

There are other records of waste in the county of Kent, as at Deal; and
at Dover, where Shakspeare's Cliff, composed entirely of chalk, has
suffered greatly, and continually diminishes in height, the slope of the
hill being towards the land. (See fig. 35.) There was an immense
landslip from this cliff in 1810, by which Dover was shaken as if by an
earthquake, and a still greater one in 1772.[416] We may suppose,
therefore, that the view from the top of the precipice in the year 1600,
when the tragedy of King Lear was written, was more "fearful and dizzy"
than it is now. The best antiquarian authorities are agreed, that Dover
Harbor was formerly an estuary, the sea flowing up a valley between the
chalk hills. The remains found in different excavations confirm the
description of the spot given by Caesar and Antoninus, and there is clear
historical evidence to prove that at an early period there was no
shingle at all at Dover.[417]

_Straits of Dover._--In proceeding from the northern parts of the German
Ocean towards the Straits of Dover, the water becomes gradually more
shallow, so that, in the distance of about two hundred leagues, we pass
from a depth of 120 to that of 58, 38, 18, and even less than 2 fathoms.
The shallowest part follows a line drawn between Romney Marsh and
Boulogne. From this point the English Channel again deepens
progressively as we proceed westward, so that the Straits of Dover may
be said to part two seas.[418]

Whether England was formerly united with France has often been a
favorite subject of speculation. So early as 1605 our countryman
Verstegan, in his "Antiquities of the English Nation," observed that
many preceding writers had maintained this opinion, but without
supporting it by any weighty reasons. He accordingly endeavors himself
to confirm it by various arguments, the principal of which are, first,
the proximity and identity of the composition of the opposite cliffs and
shores of Albion and Gallia, which, whether flat and sandy, or steep and
chalky, correspond exactly with each other; secondly the occurrence of a
submarine ridge, called "our Lady's Sand," extending from shore to shore
at no great depth, and which, from its composition, appears to be the
original basis of the isthmus; thirdly, the identity of the noxious
animals in France and England, which could neither have swum across, nor
have been introduced by man. Thus no one, he says, would have imported
wolves, therefore "these wicked beasts did of themselves pass over." He
supposes the ancient isthmus to have been about six English miles in
breadth, composed entirely of chalk and flint, and in some places of no
great height above the sea-level. The operation of the waves and tides,
he says, would have been more powerful when the straits were narrower,
and even now they are destroying cliffs composed of similar materials.
He suggests the possible co-operation of earthquakes; and when we
consider how many submarine forests skirt the southern and eastern
shores of England, and that there are raised beaches at many points
above the sea-level, containing fossil shells of recent species, it
seems reasonable to suppose that such upward and downward movements,
taking place perhaps as slowly as those now in progress in Sweden and
Greenland, may have greatly assisted the denuding force of "the ocean
stream," [Greek: Potamoio mega sthenos Ocheanoto].

_Folkstone._--At Folkstone, the sea undermines the chalk and subjacent
strata. About the year 1716 there was a remarkable sinking of a tract of
land near the sea, so that houses became visible from certain points at
sea, and from particular spots on the sea cliffs, from whence they could
not be seen previously. In the description of this subsidence in the
Phil. Trans. 1716, it is said, "that the land consisted of a solid stony
mass (chalk), resting on wet clay (gault), so that it slid forwards
towards the sea, just as a ship is launched on tallowed planks." It is
also stated that, within the memory of persons then living, the cliff
there had been washed away to the extent of ten rods.

Encroachments of the sea at Hythe are also on record; but between this
point and Rye there has been a gain of land within the times of history;
the rich level tract called Romney Marsh, or Dungeness, about ten miles
in width and five in breadth, and formed of silt, having received great
accession. It has been necessary, however, to protect it from the sea,
from the earliest periods, by embankments, the towns of Lydd and Romney
being the only parts of the marsh above the level of the highest
tides.[419] Mr. Redman has cited numerous old charts and trustworthy
authorities to prove that the average annual increase of the promontory
of shingle called Dungeness amounted for two centuries, previous to
1844, to nearly six yards. Its progress, however, has fluctuated during
that period; for between 1689 and 1794, a term of 105 years, the rate
was as much as 8-1/4 yards per annum.[420] It is ascertained that the
shingle is derived from the westward. Whether the pebbles are stopped by
the meeting of the tide from the north flowing through the Straits of
Dover, with that which comes up the Channel from the west, as was
formerly held, or by the check given to the tidal current by the waters
of the Rother, as some maintain, is still a disputed question.

Rye, situated to the south of Romney Marsh, was once destroyed by the
sea, but it is now two miles distant from it. The neighboring town of
Winchelsea was destroyed in the reign of Edward I., the mouth of the
Rother stopped up, and the river diverted into another channel. In its
old bed, an ancient vessel, apparently a Dutch merchantman, was found
about the year 1824. It was built entirely of oak, and much
blackened.[421] Large quantities of hazel-nuts, peat, and wood are found
in digging in Romney Marsh.

_South coast of England._--Westward of Hastings, or of St. Leonard's,
the shore line has been giving way as far as Pevensey Bay, where
formerly there existed a haven now entirely blocked up by shingle. The
degradation has equalled for a series of years seven feet per annum in
some places, and several martello towers had in consequence, before
1851, been removed by the Ordnance.[422] At the promontory of Beachy
Head a mass of chalk, three hundred feet in length, and from seventy to
eighty in breadth, fell in the year 1813 with a tremendous crash; and
similar slips have since been frequent.[423]

About a mile to the west of the town of Newhaven, the remains of an
ancient intrenchment are seen on the brow of Castle Hill. This
earth-work, supposed to be Roman, was evidently once of considerable
extent and of an oval form, but the greater part has been cut away by
the sea. The cliffs, which are undermined here, are high; more than one
hundred feet of chalk being covered by tertiary clay and sand, from
sixty to seventy feet in thickness. In a few centuries the last vestiges
of the plastic clay formation on the southern borders of the chalk of
the South Downs on this coast will probably be annihilated, and future
geologists will learn, from historical documents, the ancient
geographical boundaries of this group of strata in that direction. On
the opposite side of the estuary of the Ouse, on the east of Newhaven
harbor, a bed of shingle, composed of chalk flints derived from the
waste of the adjoining cliffs, had accumulated at Seaford for several
centuries. In the great storm of November, 1824, this bank was entirely
swept away, and the town of Seaford inundated. Another great beach of
shingle is now forming from fresh materials.

The whole coast of Sussex has been incessantly encroached upon by the
sea from time immemorial; and, although sudden inundations only, which
overwhelmed fertile or inhabited tracts, are noticed in history, the
records attest an extraordinary amount of loss. During a period of no
more than eighty years, there are notices of about _twenty_ inroads, in
which tracts of land of from twenty to _four hundred acres_ in extent
were overwhelmed at once, the value of the tithes being mentioned in the
Taxatio Ecclesiastica.[424] In the reign of Elizabeth, the town of
Brighton was situated on that tract where the chain pier now extends
into the sea. In the year 1665, twenty-two tenements had been destroyed
under the cliff. At that period there still remained under the cliff 113
tenements, the whole of which were overwhelmed in 1703 and 1705. No
traces of the ancient town are now perceptible, yet there is evidence
that the sea has merely resumed its ancient position at the base of the
cliffs, the site of the whole town having been merely a beach abandoned
by the ocean for ages.

_Hampshire.--Isle of Wight._--It would be endless to allude to all the
localities on the Sussex and Hampshire coasts where the land has given
way; but I may point out the relation which the geological structure of
the Isle of Wight bears to its present shape, as attesting that the
coast owes its outline to the continued action of the sea. Through the
middle of the island runs a high ridge of chalk strata, in a vertical
position, and in a direction east and west. This chalk forms the
projecting promontory of Culver Cliff on the east, and of the Needles on
the west; while Sandown Bay on the one side, and Compton Bay on the
other, have been hollowed out of the softer sands and argillaceous
strata, which are inferior, in geological position, to the chalk.

The same phenomena are repeated in the Isle of Purbeck, where the line
of vertical chalk forms the projecting promontory of Handfast Point; and
Swanage Bay marks the deep excavation made by the waves in the softer
strata, corresponding to those of Sandown Bay.

_Hurst Castle bank--progressive motion of sea beaches._--Although the
loose pebbles and grains of sand composing any given line of sea-beach
are carried sometimes one way, sometimes another, they have,
nevertheless, an ultimate motion in one particular direction.[425] Their
progress, for example, on the south coast of England, is from west to
east, which is owing partly to the action of the waves driven eastwards
by the prevailing wind, and partly to the current, or the motion of the
general body of water caused by the tides and winds. The force of the
waves gives motion to pebbles which the velocity of the currents alone
would be unable to carry forwards; but as the pebbles are finally
reduced to sand or mud, by continual attrition, they are brought within
the influence of a current; and this cause must determine the course
which the main body of matter derived from wasting cliffs will
eventually take.

It appears, from the observations of Mr. Palmer and others, that if a
pier or groin be erected anywhere on our southern or southeastern coast
to stop the progress of the beach, a heap of shingle soon collects on
the western side of such artificial barriers. The pebbles continue to
accumulate till they rise as high as the pier or groin, after which they
pour over in great numbers during heavy gales.[426]

The western entrance of the Channel, called the Solent, is crossed for
more than two-thirds of its width by the shingle-bank of Hurst Castle,
which is about two miles long, seventy yards broad, and twelve feet
high, presenting an inclined plane to the west. This singular bar
consists of a bed of rounded chalk flints, resting on a submarine
argillaceous base. The flints and a few other pebbles, intermixed, are
derived from the waste of Hordwell, and other cliffs to the westward,
where tertiary strata, capped with a covering of broken chalk flints,
from five to fifty feet thick, are rapidly undermined. In the great
storm of November, 1824, this bank of shingle was moved bodily forwards
for forty yards towards the northeast; and certain piles, which served
to mark the boundaries of two manors, were found after the storm on the
opposite side of the bar. At the same time many acres of pasture land
were covered by shingle, on the farm of Westover, near Lymington. But
the bar was soon restored in its old position by pebbles drifted from
the west; and it appears from ancient maps that it has preserved the
same general outline and position for centuries.[427]

Mr. Austen remarks that, as a general rule, it is only when high tides
concur with a gale of wind, that the sea reaches the base of cliffs so
as to undermine them and throw down earth and stone. But the waves are
perpetually employed in abrading and fashioning the materials already
strewed over the beach. Much of the gravel and shingle is always
travelling up and down, between high-water mark and a slight depth below
the level of the lowest tides, and occasionally the materials are swept
away and carried into deeper water. Owing to these movements every
portion of our southern coast may be seen at one time or other in the
condition of bare rock. Yet other beds of sand and shingle soon collect,
and, although composed of new materials, invariably exhibit on the same
spots precisely similar characters.[428]

The cliffs between Hurst Shingle Bar and Christchurch are undermined
continually, the sea having often encroached for a series of years at
the rate of a yard annually. Within the memory of persons now living, it
has been necessary thrice to remove the coast-road farther inland. The
tradition, therefore, is probably true, that the church of Hordwell was
once in the middle of that parish, although now (1830) very near the
sea. The promontory of Christchurch Head gives way slowly. It is the
only point between Lymington and Poole Harbor, in Dorsetshire, where any
hard stony masses occur in the cliffs. Five layers of large ferruginous
concretions, somewhat like the septaria of the London clay, have
occasioned a resistance at this point, to which we may ascribe this
headland. In the mean time, the waves have cut deeply into the soft
sands and loam of Poole Bay; and, after severe frosts, great landslips
take place, which by degrees become enlarged into narrow ravines, or
chines, as they are called, with vertical sides. One of these chines,
near Boscomb, has been deepened twenty feet within a few years. At the
head of each there is a spring, the waters of which have been chiefly
instrumental in producing these narrow excavations, which are sometimes
from 100 to 150 feet deep.

_Isle of Portland._--The peninsulas of Purbeck and Portland are
continually wasting away. In the latter, the soft argillaceous
substratum (Kimmeridge clay) hastens the dilapidation of the
superincumbent mass of limestone.

In 1655 the cliffs adjoining the principal quarries in Portland gave way
to the extent of one hundred yards, and fell into the sea; and in
December, 1734, a slide to the extent of 150 yards occurred on the east
side of the isle, by which several skeletons buried between slabs of
stone, were discovered. But a much more memorable occurrence of this
nature, in 1792, occasioned probably by the undermining of the cliffs,
is thus described in Hutchin's History of Dorsetshire:--"Early in the
morning the road was observed to crack: this continued increasing, and
before two o'clock the ground had sunk several feet, and was in one
continued motion, but attended with no other noise than what was
occasioned by the separation of the roots and brambles, and now and then
a falling rock. At night it seemed to stop a little, but soon moved
again; and, before morning, the ground from the top of the cliff to the
water-side had sunk in some places fifty feet perpendicular. The extent
of ground that moved was about _a mile and a quarter_ from north to
south, and 600 yards from east to west."

_Formation of the Chesil Bank._--Portland is connected with the mainland
by the Chesil Bank, a ridge of shingle about seventeen miles in length,
and, in most places, nearly a quarter of a mile in breadth. The pebbles
forming this immense barrier are chiefly siliceous, all loosely thrown
together, and rising to the height of from twenty to thirty feet above
the ordinary high-water mark; and at the southeastern end, which is
nearest the Isle of Portland, where the pebbles are largest, forty feet.
The fundamental rocks whereon the shingle rests are found at the depth
of a few yards only below the level of the sea. The formation of that
part of the bar which attaches Portland to the mainland may have been
due to an original shoal or reef, or to the set of the tides in the
narrow channel, by which the course of the pebbles, which are always
coming from the west, has been arrested. It is a singular fact that,
throughout the Chesil Bank, the pebbles increase gradually in size as we
proceed southeastward, or as we go farther from the quarter which
supplied them. Had the case been reversed, we should naturally have
attributed the circumstance to the constant wearing down of the pebbles
by friction, as they are rolled along a beach seventeen miles in length.
But the true explanation of the phenomenon is doubtless this: the tidal
current runs strongest from west to east, and its power is greater in
the more open channel or farther from the land. In other words its force
increases southwards, and as the direction of the bank is from northwest
to southeast, the size of the masses coming from the westward and thrown
ashore must always be largest where the motion of the water is most
violent. Colonel Reid states that all calcareous stones rolled along
from the west are soon ground into sand, and in this form they pass
round Portland Island.[429]

The storm of 1824 burst over the Chesil Bank with great fury, and the
village of Chesilton, built upon its southern extremity, was
overwhelmed, with many of the inhabitants. The same storm carried away
part of the Breakwater at Plymouth, and huge masses of rock, from two to
five tons in weight, were lifted from the bottom of the weather side,
and rolled fairly to the top of the pile. One block of limestone,
weighing seven tons, was washed round the western extremity of the
Breakwater, and carried 150 feet.[430] The propelling power is derived
in these cases from the breaking of the waves, which run fastest in
shallow water, and for a short space far exceed the most rapid currents
in swiftness. It was in the same month, and also during a spring-tide,
that a great flood is mentioned on the coasts of England, in the year
1099. Florence of Worcester says, "On the third day of the nones of Nov.
1099, the sea came out upon the shore and buried towns and men very
many, and oxen and sheep innumerable." We also read in the Saxon
Chronicle, for the year 1099, "This year eke on St. Martin's mass day,
the 11th of Novembre, sprung up so much of the sea flood, and so myckle
harm did, as no man minded that it ever afore did, and there was the ylk
day a new moon."

South of the Bill, or southern point of Portland, is a remarkable shoal
in the channel at the depth of seven fathoms, called "the Shambles,"
consisting entirely of rolled and broken shells of Purpura lapillus,
Mytilus edulis, and other species now living. This mass of light
materials is always in motion, varying in height from day to day, and
yet the shoal remains constant.

_Dorsetshire.--Devonshire._--At Lyme Regis, in Dorsetshire, the "Church
Cliffs," as they are called, consisting of lias about one hundred feet
in height, gradually fell away at the rate of one yard a year, from 1800
to 1829.[431]

[Illustration: Fig. 36.

Landslip, near Axmouth, Dec. 1839. (Rev. W. D. Conybeare.)


  A. Tract of Downs still remaining at their original level.
  B. New ravine.
  C, D. Sunk and fractured strip united to A, before the convulsion.
  D, E. Bendon undercliff as before, but more fissured, and thrust
          forward about fifty feet, towards the sea.
  F. Pyramidal crag, sunk from seventy to twenty feet in height.
  G. New reef upheaved from the sea.


]

An extraordinary landslip occurred on the 24th of December, 1839, on the
coast between Lyme Regis and Axmouth, which has been described by the
Rev. W. D. Conybeare, to whose kindness I am indebted for the
accompanying section, fig. 36. The tract of downs ranging there along
the coast is capped by chalk (_h_), which rests on sandstone,
alternating with chert (_i_), beneath which is more than 100 feet of
loose sand (_k_), with concretions at the bottom, and belonging like _i_
to the green-sand formation; the whole of the above masses, _h_, _i_,
_k_, reposing on retentive beds of clay (_l_), belonging to the lias,
which shelves towards the sea. Numerous springs issuing from the loose
sand (_k_), have gradually removed portions of it, and thus undermined
the superstratum, so as to have caused subsidences at former times, and
to have produced a line of undercliff between D and E. In 1839 an
excessively wet season had saturated all the rocks with moisture, so as
to increase the weight of the incumbent mass, from which the support had
already been withdrawn by the action of springs. Thus the superstrata
were precipitated into hollows prepared for them, and the adjacent
masses of partially undermined rock, to which the movement was
communicated, were made to slide down on a slippery basis of watery sand
towards the sea. These causes gave rise to a convulsion, which began on
the morning of the 24th of December, with a crashing noise; and, on the
evening of the same day, fissures were seen opening in the ground, and
the walls of tenements rending and sinking, until a deep chasm or
ravine, B, was formed, extending nearly three-quarters of a mile in
length, with a depth of from 100 to 150 feet, and a breadth exceeding
240 feet. At the bottom of this deep gulf lie fragments of the original
surface thrown together in the wildest confusion. In consequence of
lateral movements, the tract intervening between the new fissure and the
sea, including the ancient undercliff, was fractured, and the whole line
of sea-cliff carried bodily forwards for many yards. "A remarkable
pyramidal crag, F, off Culverhole Point, which lately formed a
distinguishing landmark, has sunk from a height of about seventy to
twenty feet, and the main cliff, E, before more than fifty feet distant
from this insulated crag, is now brought almost close to it. This motion
of the sea-cliff has produced a farther effect, which may rank among the
most striking phenomena of this catastrophe. The lateral pressure of the
descending rocks has urged the neighboring strata, extending beneath the
shingle of the shore, by their state of unnatural condensation, to burst
upwards in a line parallel to the coast--thus an elevated ridge, G, more
than a mile in length, and rising more than forty feet, covered by a
confused assemblage of broken strata, and immense blocks of rock,
invested with sea-weed and corallines, and scattered over with shells
and star-fish, and other productions of the deep, forms an extended reef
in front of the present range of cliffs."[432]

A full account of this remarkable landslip, with a plan, sections, and
many fine illustrative drawings, was published by Messrs. Conybeare and
Buckland,[433] from one of which the annexed cut has been reduced, fig.
37.

[Illustration: Fig. 37.

View of the Axmouth landslip from Great Bindon, looking westward to the
Sidmouth hills, and estuary of the Exe. From an original drawing by Mrs.
Buckland.]

_Cornwall._--Near Penzance, in Cornwall, there is a projecting tongue of
land, called the "Green," formed of granitic sand, from which more than
thirty acres of pasture land have been gradually swept away, in the
course of the last two or three centuries.[434] It is also said that St.
Michael's Mount, now an insular rock, was formerly situated in a wood,
several miles from the sea; and its old Cornish name (Caraclowse in
Cowse) signifies, according to Carew, the Hoar Rock in the wood.[435]
Between the Mount and Newlyn there is seen under the sand, black
vegetable mould, full of hazel-nuts, and the branches, leaves, roots,
and trunks of forest-trees, all of indigenous species. This stratum has
been traced seaward as far as the ebb permits, and many proofs of a
submerged vegetable accumulation, with stumps of trees in the position
in which they grew, have been traced, says Sir Henry De la Beche, round
the shores of Devon, Cornwall, and Western Somerset. The facts not only
indicate a change in the relative level of the sea and land, since the
species of animals and plants were the same as those now living in this
district; but, what is very remarkable, there seems evidence of the
submergence having been effected, in part at least, since the country
was inhabited by man.[436]

A submarine forest occurring at the mouth of the Parret in
Somersetshire, on the south side of the Bristol Channel, was described
by Mr. L. Horner, in 1815, and its position attributed to subsidence. A
bed of peat is there seen below the level of the sea, and the trunks of
large trees, such as the oak and yew, having their roots still
diverging as they grew, and fixed in blue clay.[437]

_Tradition of loss of land in Cornwall._--The oldest historians mention
a tradition in Cornwall, of the submersion of the Lionnesse, a country
said to have stretched from the Land's End to the Scilly Islands. The
tract, if it existed, must have been thirty miles in length, and perhaps
ten in breadth. The land now remaining on either side is from two
hundred to three hundred feet high; the intervening sea about three
hundred feet deep. Although there is no authentic evidence for this
romantic tale, it probably originated in some former inroads of the
Atlantic, accompanying, perhaps, a subsidence of land on this
coast.[438]

_West coast of England._--Having now brought together an ample body of
proofs of the destructive operations of the waves, tides, and currents,
on our eastern and southern shores, it will be unnecessary to enter into
details of changes on the western coast, for they present merely a
repetition of the same phenomena, and in general on an inferior scale.
On the borders of the estuary of the Severn the flats of Somersetshire
and Gloucestershire have received enormous accessions, while, on the
other hand, the coast of Cheshire, between the rivers Mersey and Dee,
has lost, since the year 1764, many hundred yards, and some affirm more
than half a mile, by the advance of the sea upon the abrupt cliffs of
red clay and marls. Within the period above mentioned several
lighthouses have been successively abandoned.[439] There are traditions
in Pembrokeshire[440] and Cardiganshire[441] of far greater losses of
territory than that which the Lionnesse tale of Cornwall pretends to
commemorate. They are all important, as demonstrating that the earliest
inhabitants were familiar with the phenomenon of incursions of the sea.

_Loss of land on the coast of France._--The French coast, particularly
that part of Brittany, where the tides rise to an extraordinary height,
is the constant prey of the waves. In the ninth century many villages
and woods are reported to have been carried away, the coast undergoing
great change, whereby the hill of St. Michael was detached from the
mainland. The parish of Bourgneuf, and several others in that
neighborhood, were overflowed in the year 1500. In 1735, during a great
storm, the ruins of Palnel were seen uncovered in the sea.[442]




CHAPTER XX.

ACTION OF TIDES AND CURRENTS--_continued_.


  Inroads of the sea at the mouths of the Rhine in Holland--Changes in
    the arms of the Rhine--Proofs of subsidence of land--Estuary of the
    Bies Bosoh, formed in 1421--Zuyder Zee, in the 13th century--Islands
    destroyed--Delta of the Ems converted into a bay--Estuary of the
    Dollart formed--Encroachment of the sea on the coast of Sleswick--On
    shores of North America--Tidal wave, called the Bore--Influence of
    tides and currents on the mean level of seas--Action of currents in
    inland lakes and seas--Baltic--Cimbrian deluge--Straits of
    Gibraltar--No under-current there--Whether salt is precipitated in
    the Mediterranean--Waste of shores of Mediterranean.


_Inroads of the sea at the mouths of the Rhine._--The line of British
coast considered in the preceding chapter offered no example of the
conflict of two great antagonist forces; the influx, on the one hand, of
a river draining a large continent, and, on the other, the action of the
waves, tides, and currents of the ocean. But when we pass over by the
Straits of Dover to the Continent, and proceed northeastwards, we find
an admirable illustration of such a contest, where the ocean and the
Rhine are opposed to each other, each disputing the ground now occupied
by Holland; the one striving to shape out an estuary, the other to form
a delta. There was evidently a period when the river obtained the
ascendancy, when the shape and perhaps the relative level of the coast
and set of the tides were very different; but for the last two thousand
years, during which man has witnessed and actively participated in the
struggle, the result has been in favor of the ocean; the area of the
whole territory having become more and more circumscribed; natural and
artificial barriers having given away, one after another; and many
hundred thousand human beings having perished in the waves.

_Changes in the arms of the Rhine._--The Rhine, after flowing from the
Grison Alps, copiously charged with sediment, first purifies itself in
the Lake of Constance, where a large delta is formed; then swelled by
the Aar and numerous other tributaries, it flows for more than six
hundred miles towards the north; when, entering a low tract, it divides
into two arms, about ten miles northeast of Cleves,--a point which must
therefore be considered the head of its delta. (See[A], map, fig. 8.)
In speaking of the delta, I do not mean to assume that all that part of
Holland which is comprised within the several arms of the Rhine can be
called a delta in the strictest sense of the term; because some portion
of the country thus circumscribed, as, for example, a part of Gelderland
and Utrecht, consists of strata which may have been deposited in the sea
before the Rhine existed. These older tracts may either have been raised
like the Ullah Bund in Cutch, during the period when the sediment of
the Rhine was converting a part of the sea into land, or they may have
constituted islands previously.

[Illustration: Fig. 38.

The dark tint between Antwerp and Nieuport, represents part of the
Netherlands which was land in the time of the Romans, then overflowed by
the sea before and during the 5th century, and afterwards reconverted
into land.]

When the river divides north of Cleves, the left arm takes the name of
the Waal; and the right, retaining that of the Rhine, is connected, a
little farther to the north, by an artificial canal with the river
Yssel. The Rhine then flowing westward divides again southeast of
Utrecht, and from this point it takes the name of the Leck, a name which
was given to distinguish it from the northern arm called the old Rhine,
which was sanded up until the year 1825, when a channel was cut for it,
by which it now enters the sea at Catwyck. It is common, in all great
deltas, that the principal channels of discharge should shift from time
to time, but in Holland so many magnificent canals have been
constructed, and have so diverted, from time to time, the course of the
waters, that the geographical changes in this delta are endless, and
their history, since the Roman era, forms a complicated topic of
antiquarian research. The present head of the delta is about forty
geographical miles from the nearest part of the gulf called the Zuyder
Zee, and more than twice that distance from the general coast-line. The
present head of the delta of the Nile is about 80 or 90 geographical
miles from the sea; that of the Ganges, as before stated, 220; and that
of the Mississippi about 180, reckoning from the point where the
Atchafalaya branches off to the extremity of the new tongue of land in
the Gulf of Mexico. But the comparative distance between the heads of
deltas and the sea affords no positive data for estimating the relative
magnitude of the alluvial tracts formed by their respective rivers, for
the ramifications depend on many varying and temporary circumstances,
and the area over which they extend does not hold any constant
proportion to the volume of water in the river.

The Rhine therefore has at present three mouths. About two-thirds of its
waters flow to the sea by the Waal, and the remainder is carried partly
to the Zuyder Zee by the Yssel, and partly to the ocean by the Leck. As
the whole coast to the south as far as Ostend, and on the north to the
entrance of the Baltic, has, with few exceptions, from time immemorial,
yielded to the force of the waves, it is evident that the common delta
of the Rhine, Meuse, and Scheldt, for these three rivers may all be
considered as discharging their waters into the same part of the sea,
would, if its advance had not been checked, have become extremely
prominent; and even if it had remained stationary, would long ere this
have projected far beyond the rounded outline of the coast, like that
strip of land already described at the mouth of the Mississippi. But we
find, on the contrary, that the islands which skirt the coast have not
only lessened in size, but in number also, while great bays have been
formed in the interior by incursions of the sea.

In order to explain the incessant advance of the ocean on the shores and
inland country of Holland, M. E. de Beaumont has suggested that there
has in all probability been a general depression or sinking of the land
below its former level over a wide area. Such a change of level would
enable the sea to break through the ancient line of sand-banks and
islands which protected the coast,--would lead to the enlargement of
bays, the formation of new estuaries, and ultimately to the entire
submergence of land. These views appear to be supported by the fact that
several peat-mosses of fresh-water origin now occur under the level of
the sea, especially on the site of the Zuyder Zee and Lake Flevo,
presently to be mentioned. Several excavations also made for wells at
Utrecht, Amsterdam, and Rotterdam have proved, that below the level of
the ocean, the soil near the coast consists of alternations of sand with
marine shells, and beds of peat and clay, which have been traced to the
depth of fifty feet and upwards.[443]

I have said that the coast to the south as far as Ostend has given way.
This statement may at first seem opposed to the fact, that the tract
between Antwerp and Nieuport, shaded black in the annexed map (fig. 38),
although now dry land, and supporting a large population, has, within
the historical period, been covered with the sea. This region, however,
consisted, in the time of the Romans, of woods, marshes, and
peat-mosses, protected from the ocean by a chain of sandy dunes, which
were afterwards broken through during storms, especially in the fifth
century. The waters of the sea during these irruptions threw down upon
the barren peat a horizontal bed of fertile clay, which is in some
places three yards thick, full of recent shells and works of art. The
inhabitants, by the aid of embankments and the sand dunes of the coast,
have succeeded, although not without frequent disasters, in defending
the soil thus raised by the marine deposit.[444]

_Inroads of the Sea in Holland._--If we pass to the northward of the
territory just alluded to, and cross the Scheldt, we find that between
the fourteenth and eighteenth centuries parts of the islands Walcheren
and Beveland were swept away, and several populous districts of Kadzand,
losses which far more than counterbalance the gain of land caused by the
sanding up of some pre-existing creeks. In 1658 the Island Orisant was
annihilated. One of the most memorable inroads of the sea occurred in
1421, when the tide, pouring into the mouth of the united Meuse and
Waal, burst through a dam in the district between Dort and
Gertrudenberg, and overflowed seventy-two villages, forming a large
sheet of water called the Bies Bosch. (See map, fig. 38.) Thirty-five of
the villages were irretrievably lost, and no vestige, even of their
ruins, was afterwards seen. The rest were redeemed, and the site of the
others, though still very generally represented on maps as an estuary,
has in fact been gradually filled up by alluvial deposits, and had
become in 1835, as I was informed by Professor Moll, an immense plain,
yielding abundant crops of hay, though still uninhabited. To the north
of the Meuse is a long line of shore covered with sand dunes, where
great encroachments have taken place from time to time, in consequence
chiefly of the prevalence of southeasterly winds, which blow down the
sands towards the sea. The church of Scheveningen, not far from the
Hague, was once in the middle of the village, and now stands on the
shore, half the place having been overwhelmed by the waves in 1570.
Catwyck, once far from the sea, is now upon the shore; two of its
streets having been overflowed, and land torn away to the extent of 200
yards, in 1719. It is only by the aid of embankments that Petten, and
several other places farther north, have been defended against the sea.

_Formation of the Zuyder Zee and Straits of Staveren._--Still more
important are the changes which have taken place on the coast opposite
the right arm of the Rhine, or the Yssel, where the ocean has burst
through a large isthmus, and entered the inland lake Flevo, which, in
ancient times, was, according to Pomponius Mela, formed by the
overflowing of the Rhine over certain lowlands. It appears that, in the
time of Tacitus, there were several lakes on the present site of the
Zuyder Zee, between Friesland and Holland. The successive inroads by
which these and a great part of the adjoining territory, were
transformed into a great gulf, began about the commencement, and were
completed towards the close, of the thirteenth century. Alting gives the
following relation of the occurrence, drawn from manuscript documents of
contemporary inhabitants of the neighboring provinces. In the year
1205, the island now called Wieringen, to the south of the Texel, was
still a part of the mainland, but during several high floods, of which
the dates are given, ending in December, 1251, it was separated from the
continent. By subsequent incursions the sea consumed great parts of the
rich and populous isthmus, a low tract which stretched on the north of
Lake Flevo, between Staveren in Friesland and Medemblick in Holland,
till at length a breach was completed about the year 1282, and
afterwards widened. Great destruction of land took place when the sea
first broke in, and many towns were swept away; but there was afterwards
a reaction to a certain extent, large tracts, at first submerged, having
been gradually redeemed. The new straits south of Staveren are more than
half the width of those of Dover, but are very shallow, the greatest
depth not exceeding two or three fathoms. The new bay is of a somewhat
circular form, and between _thirty_ and _forty_ miles in diameter. How
much of this space may formerly have been occupied by Lake Flevo is
unknown. (See map, fig. 38.)

_Destruction of islands._--A series of islands stretching from the Texel
to the mouths of the Weser and Elbe are probably the last relics of a
tract once continuous. They have greatly diminished in size, and have
lost about a third of their number, since the time of Pliny; for that
naturalist counted twenty-three islands between the Texel and Eider,
whereas there are now only sixteen, including Heligoland and
Neuwerk.[445] The island of Heligoland, at the mouth of the Elbe,
consists of a rock of red marl of the Keuper formation (of the Germans),
and is bounded by perpendicular red cliffs, above 200 feet high.
Although, according to some accounts, it has been greatly reduced in
size since the year 800, M. Wiebel assures us, that the ancient map by
Meyer cannot be depended upon, and that the island, according to the
description still extant by Adam of Bremen, was not much larger than
now, in the time of Charlemagne. On comparing the map made in the year
1793 by the Danish engineer Wessel, the average encroachment of the sea
on the cliffs, between that period and the year 1848 (or about half a
century), did not amount to more than three feet.[446] On the other
hand, some few islands have extended their bounds in one direction, or
become connected with others, by the sanding-up of channels; but even
these, like Juist, have generally given way as much on the north towards
the sea as they have gained on the south, or land side.

_The Dollart formed._--While the delta of the Rhine has suffered so
materially from the movements of the ocean, it can hardly be supposed
that minor rivers on the same coast should have been permitted to extend
their deltas. It appears that in the time of the Romans there was an
alluvial plain of great fertility, where the Ems entered the sea by
three arms. This low country stretched between Groningen and Friesland,
and sent out a peninsula to the northeast towards Emden. A flood in 1277
first destroyed part of the peninsula. Other inundations followed at
different periods throughout the fifteenth century. In 1507, a part only
of Torum, a considerable town, remained standing; and in spite of the
erection of dams, the remainder of that place, together with
market-towns, villages, and monasteries, to the number of fifty, were
finally overwhelmed. The new gulf, which was called the Dollart,
although small in comparison to the Zuyder Zee, occupied no less than
six square miles at first; but part of this space was, in the course of
the two following centuries, again redeemed from the sea. The small bay
of Leybucht, farther north, was formed in a similar manner in the
thirteenth century; and the bay of Harlbucht in the middle of the
sixteenth. Both of these have since been partially reconverted into dry
land. Another new estuary, called the Gulf of Jahde, near the mouth of
the Weser, scarcely inferior in size to the Dollart, has been gradually
hollowed out since the year 1016, between which era and 1651 a space of
about four square miles has been added to the sea. The rivulet which now
enters this inlet is very small; but Arens conjectures that an arm of
the Weser had once an outlet in that direction.

_Coast of Sleswick._--Farther north we find so many records of waste on
the western coast of Sleswick, as to lead us to anticipate that, at no
distant period in the history of the physical geography of Europe,
Jutland may become an island, and the ocean may obtain a more direct
entrance into the Baltic. Indeed, the temporary insulation of the
northern extremity of Jutland has been affected no less than four times
within the records of history, the ocean having as often made a breach
through the bar of sand, which usually excludes it from the Lym Fiord.
This long frith is 120 miles in length including its windings, and
communicates at its eastern end with the Baltic. The last irruption of
salt water happened in 1824, and the fiord was still open in 1837, when
some vessels of thirty tons' burden passed through.

The Marsh islands between the rivers Elbe and Eider are mere banks, like
the lands formed of the "warp" in the Humber, protected by dikes. Some
of them, after having been inhabited with security for more than ten
centuries, have been suddenly overwhelmed. In this manner, in 1216, no
less than ten thousand of the inhabitants of Eiderstede and Ditmarsch
perished; and on the 11th of October, 1634, the islands and the whole
coast, as far as Jutland, suffered by a dreadful deluge.

_Destruction of Northstrand by the sea._--Northstrand, up to the year
1240, was, with the islands Sylt and Fohr, so nearly connected with the
mainland as to appear a peninsula, and was called North Friesland, a
highly cultivated and populous district. It measured from nine to eleven
geographical miles from north to south, and six to eight from east to
west. In the above-mentioned year it was torn asunder from the
continent, and in part overwhelmed. The Isle of Northstrand, thus
formed, was, towards the end of the sixteenth century, only four
geographical miles in circumference, and was still celebrated for its
cultivation and numerous population. After many losses, it still
contained nine thousand inhabitants. At last, in the year 1634, on the
evening of the 11th of October, a flood passed over the whole island,
whereby 1300 houses, with many churches, were lost; fifty thousand head
of cattle perished, and above six thousand men. Three small islets, one
of them still called Northstrand, alone remained, which are now
continually wasting.

The redundancy of river water in the Baltic, especially during the
melting of ice and snow in spring, causes in general an outward current
through the channel called the Cattegat. But after a continuance of
northwesterly gales, especially during the height of the spring-tides,
the Atlantic rises, and pouring a flood of water into the Baltic,
commits dreadful devastations on the isles of the Danish Archipelago.
This current even acts, though with diminished force, as far eastward as
the vicinity of Dantzic.[447] Accounts written during the last ten
centuries attest the wearing down of promontories on the Danish coast,
the deepening of gulfs, the severing of peninsulas from the mainland,
and the waste of islands, while in several cases marsh land, defended
for centuries by dikes, has at last been overflowed, and thousands of
the inhabitants whelmed in the waves. Thus the island Barsoe, on the
coast of Sleswick, has lost, year after year, an acre at a time, and the
island Alsen suffers in like manner.

_Cimbrian deluge._--As we have already seen that during the flood before
mentioned, 6000 men and 50,000 head of cattle perished on Northstrand on
the western coast of Jutland, we are all well prepared to find that this
peninsula, the Cimbrica Chersonesus of the ancients, has from a remote
period been the theatre of like catastrophes. Accordingly, Strabo
records a story, although he treats it as an incredible fiction, that,
during a high tide, the ocean rose upon this coast so rapidly, that men
on horseback were scarcely able to escape.[448] Florus, alluding to the
same tradition, says, "Cimbri, Teutoni, atque Tigurini, ab extremis
Galliae profugi, cum terras eorum inundasset Oceanus, novas sedes toto
orbe quaerebant."[449] This event, commonly called the "Cimbrian Deluge,"
is supposed to have happened about three centuries before the Christian
era; but it is not improbable that the principal catastrophe was
preceded and followed by many devastations like those experienced in
modern times on the islands and shores of Jutland, and such calamities
may well be conceived to have forced on the migration of some maritime
tribes.

_Inroads of the sea on the eastern shores of North America._--After so
many authentic details respecting the destruction of the coast in parts
of Europe best known, it will be unnecessary to multiply examples of
analogous changes in more distant regions of the world. It must not,
however, be imagined that our own seas form any exception to the general
rule. Thus, for example, if we pass over to the eastern coast of North
America, where the tides rise, in the Bay of Fundy, to a great
elevation, we find many facts attesting the incessant demolition of
land. Cliffs, often several hundred feet high, composed of sandstone,
red marl, and other rocks, which border that bay and its numerous
estuaries, are perpetually undermined. The ruins of these cliffs are
gradually carried, in the form of mud, sand, and large boulders, into
the Atlantic by powerful currents, aided at certain seasons by drift
ice, which forms along the coast, and freezes round large stones.

At Cape May, on the north side of Delaware Bay, in the United States,
the encroachment of the sea was shown by observations made consecutively
for sixteen years, from 1804 to 1820, to average about nine feet a
year;[450] and at Sullivan's Island, which lies on the north side of the
entrance of the harbor of Charleston, in South Carolina, the sea carried
away a quarter of a mile of land in three years, ending in 1786.[451]

_Tidal wave called "the Bore."_--Before concluding my remarks on the
action of the tides, I must not omit to mention the wave called "the
Bore," which is sometimes produced in a river where a large body of
water is made to rise suddenly, in consequence of the contraction of the
channel. This wave terminates abruptly on the inland side; because the
quantity of water contained in it is so great, and its motion so rapid,
that time is not allowed for the surface of the river to be immediately
raised by means of transmitted pressure. A tide wave thus rendered
abrupt has a close analogy, observes Mr. Whewell, to the waves which
curl over and break on a shelving shore.[452]

The Bore which enters the Severn, where the phenomenon is of almost
daily occurrence, is sometimes nine feet high, and at spring-tides
rushes up the estuary with extraordinary rapidity. The finest example
which I have seen of this wave was at Nova Scotia,[453] where the tide
is said to rise in some places seventy feet perpendicular, and to be the
highest in the world. In the large estuary of the Shubenacadie, which
connects with another estuary called the Basin of Mines, itself an
embranchment of the Bay of Fundy, a vast body of water comes rushing up,
with a roaring noise, into a long narrow channel, and while it is
ascending, has all the appearance of pouring down a slope as steep as
that of the celebrated rapids of the St. Lawrence. In picturesque
effect, however, it bears no comparison, for instead of the transparent
green water and snow-white foam of the St. Lawrence, the whole current
of the Shubenacadie is turbid and densely charged with red mud. The same
phenomenon is frequently witnessed in the principal branches of the
Ganges and in the Megna as before mentioned (p. 279). "In the Hoogly,"
says Rennell, "the Bore commences at Hoogly Point, the place where the
river first contracts itself, and is perceptible above Hoogly Town; and
so quick is its motion, that it hardly employs four hours in travelling
from one to the other, though the distance is nearly seventy miles. At
Calcutta it sometimes occasions an instantaneous rise of five feet; and
both here, and in every other part of its track, the boats, on its
approach, immediately quit the shore, and make for safety to the middle
of the river. In the channels, between the islands in the mouth of the
Megna, the height of the Bore is said to exceed twelve feet; and is so
terrific in its appearance, and dangerous in its consequences, that no
boat will venture to pass at spring-tide."[454] These waves may
sometimes cause inundations, undermine cliffs, and still more frequently
sweep away trees and land animals from low shores, so that they may be
carried down, and ultimately imbedded in fluviatile or submarine
deposits.


CURRENTS IN INLAND LAKES AND SEAS.

In such large bodies of water as the North American lakes, the
continuance of a strong wind in one direction often causes the elevation
of the water, and its accumulation on the leeward side; and while the
equilibrium is restoring itself, powerful currents are occasioned. In
October, 1833, a strong current in Lake Erie, caused partly by the set
of the waters towards the outlet of the lake, and partly by the
prevailing wind, burst a passage through the extensive peninsula called
Long Point, and soon excavated a channel more than nine feet deep and
nine hundred feet wide. Its width and depth have since increased, and a
new and costly pier has been erected; for it is hoped that this event
will permanently improve the navigation of Lake Erie for
steamboats.[455] On the opposite, or southern coast of this lake, in
front of the town of Cleveland, the degradation of the cliffs had been
so rapid for several years preceding a survey made in 1837, as to
threaten many towns with demolition.[456] In the Black Sea, also,
although free from tides, we learn from Pallas that there is a
sufficiently strong current to undermine the cliffs in many parts, and
particularly in the Crimea.

_Straits of Gibraltar._--It is well known that a powerful current sets
constantly from the Atlantic into the Mediterranean, and its influence
extends along the whole southern borders of that sea, and even to the
shores of Asia Minor. Captain Smyth found, during his survey, that the
central current ran constantly at the rate of from three to six miles an
hour eastward into the Mediterranean, the body of water being three
miles and a half wide. But there are also two lateral currents--one on
the European, and one on the African side; each of them about two miles
and a half broad, and flowing at about the same rate as the central
stream. These lateral currents ebb and flow with the tide, setting
alternately into the Mediterranean and into the Atlantic. The excess of
water constantly flowing in is very great, and there is only one cause
to which this can be attributed, the loss of water in the Mediterranean
by evaporation. That the level of this sea should be considerably
depressed by this cause is quite conceivable, since we know that the
winds blowing from the shores of Africa are hot and dry; and
hygrometrical experiments recently made in Malta and other places, show
that the mean quantity of moisture in the air investing the
Mediterranean is equal only to one half of that in the atmosphere of
England. The temperature also of the great inland sea is upon an average
higher, by 3-1/2 degrees of Fahrenheit, than the eastern part of the
Atlantic Ocean in the same latitude, which must greatly promote its
evaporation. The Black Sea being situated in a higher latitude, and
being the receptacle of rivers flowing from the north, is much colder,
and its expenditure far less; accordingly it does not draw any supply
from the Mediterranean, but, on the contrary, contributes to it by a
current flowing outwards, for the most part of the year, through the
Dardanelles. The discharge, however, at the Bosphorus is so small, when
compared to the volume of water carried in by rivers, as to imply a
great amount of evaporation in the Black Sea.

_Whether salt be precipitated in the Mediterranean._--It is, however,
objected, that evaporation carries away only fresh water, and that the
current from the Atlantic is continually bringing in salt water: why,
then, do not the component parts of the waters of the Mediterranean
vary? or how can they remain so nearly the same as those of the ocean?
Some have imagined that the excess of salt might be carried away by an
under-current running in a contrary direction to the superior; and this
hypothesis appeared to receive confirmation from a late discovery, that
the water taken up about fifty miles within the Straits, from a depth of
670 fathoms, contained a quantity of salt _four times greater_ than the
water of the surface. Dr. Wollaston,[457] who analyzed this water
obtained by Captain Smyth, truly inferred that an under-current of such
denser water flowing outward, if of equal breadth and depth with the
current near the surface, would carry out as much salt below as is
brought in above, although it moved with less than one-fourth part of
the velocity, and would thus prevent a perpetual increase of saltness in
the Mediterranean beyond that existing in the Atlantic. It was also
remarked by others, that the result would be the same, if the swiftness
being equal, the inferior current had only one-fourth of the volume of
the superior. At the same time there appeared reason to conclude that
this great specific gravity was only acquired by water at immense
depths; for two specimens of the water, taken within the Mediterranean,
at the distance of some hundred miles from the Straits, and at depths of
400 and even 450 fathoms, were found by Dr. Wollaston not to exceed in
density that of many ordinary samples of sea-water. Such being the case,
we can now prove that the vast amount of salt brought into the
Mediterranean _does not_ pass out again by the Straits; for it appears
by Captain Smyth's soundings, which Dr. Wallaston had not seen, that
between the capes of Trafalgar and Spartel, which are twenty-two miles
apart, and where the Straits are shallowest, the deepest part, which is
on the side of Cape Spartel, is only 220 fathoms. It is therefore
evident, that if water sinks in certain parts of the Mediterranean, in
consequence of the increase of its specific gravity, to greater depths
than 220 fathoms, it can never flow out again into the Atlantic, since
it must be stopped by the submarine barrier which crosses the shallowest
part of the Straits of Gibraltar.

The idea of the existence of a counter-current, at a certain depth,
first originated in the following circumstances:--M. De l'Aigle,
commander of a privateer called the Phoenix of Marseilles, gave chase
to a Dutch merchant-ship, near Ceuta Point, and coming up with her in
the middle of the gut, between Tariffa and Tangier, gave her one
broadside, which directly sunk her. A few days after, the sunken ship,
with her cargo of brandy and oil, was cast ashore near Tangier, which is
at least four leagues to the westward of the place where she went down,
and to which she must have floated in a direction contrary to the course
of the _central_ current.[458] This fact, however, affords no evidence
of an under-current, because the ship, when it approached the coast,
would necessarily be within the influence of a lateral current, which
running westward twice every twenty-four hours, might have brought back
the vessel to Tangier.

What, then, becomes of the excess of salt?--for this is an inquiry of
the highest geological interest. The Rhone, the Po, the Nile, and many
hundred minor streams and springs, pour annually into the Mediterranean
large quantities of carbonate of lime, together with iron, magnesia,
silica, alumina, sulphur, and other mineral ingredients in a state of
chemical solution. To explain why the influx of this matter does not
alter the composition of this sea has never been regarded as a
difficulty; for it is known that calcareous rocks are forming in the
delta of the Rhone, in the Adriatic, on the coast of Asia Minor, and in
other localities. Precipitation is acknowledged to be the means whereby
the surplus mineral matter is disposed of, after the consumption of a
certain portion in the secretions of testacea, zoophytes, and other
marine animals. But before muriate of soda can, in like manner, be
precipitated, the whole Mediterranean ought, according to the received
principles of chemistry, to become as much saturated with salt as Lake
Aral, the Dead Sea, or the brine-springs of Cheshire.

It is undoubtedly true, in regard to small bodies of water, that every
particle must be fully saturated with muriate of soda before a single
crystal of salt can be formed; such is probably the case in all natural
salterns: such, for example, as those described by travellers as
occurring on the western borders of the Black Sea, where extensive
marshes are said to be covered by thin films of salt after a rapid
evaporation of sea-water. The salt _atangs_ of the Rhone, where salt has
sometimes been precipitated in considerable abundance, have been already
mentioned. In regard to the depth of the Mediterranean, it appears that
between Gibraltar and Ceuta, Captain Smyth sounded to the enormous depth
of 950 fathoms, and found there a gravelly bottom, with fragments of
broken shells. Saussure sounded to the depth of two thousand feet,
within a few yards of the shore, at Nice; and M. Barard has lately
fathomed to the depth of more than six thousand feet in several places
without reaching the bottom.[459]

The central abysses, therefore, of this sea are, in all likelihood, at
least as deep as the Alps are high; and, as at the depth of seven
hundred fathoms only, water has been found to contain a proportion of
salt four times greater than at the surface, we may presume that the
excess of salt may be much greater at the depth of two or three miles.
After evaporation, the surface water becomes impregnated with a slight
excess of salt, and its specific gravity being thus increased, it
instantly falls to the bottom, while lighter water rises to the top, or
flows in laterally, being always supplied by rivers and the current from
the Atlantic. The heavier fluid, when it arrives at the bottom, cannot
stop if it can gain access to any lower part of the bed of the sea, not
previously occupied by water of the same density.

How far this accumulation of brine can extend before the inferior strata
of water will part with any of their salt, and what difference in such a
chemical process the immense pressure of the incumbent ocean, or the
escape of heated vapors, thermal springs, or submarine volcanic
eruptions, might occasion, are questions which cannot be answered in the
present state of science.

The Straits of Gibraltar are said to become gradually wider by the
wearing down of the cliffs on each side at many points; and the current
sets along the coast of Africa, so as to cause considerable inroads in
various parts, particularly near Carthage. Near the Canopic mouth of the
Nile, at Aboukir, the coast was greatly devastated in the year 1784,
when a small island was nearly consumed. By a series of similar
operations, the old site of the cities of Nicropolis, Taposiris, Parva
and Canopus, have become a sand-bank.[460]




CHAPTER XXI.

REPRODUCTIVE EFFECTS OF TIDES AND CURRENTS.


  Estuaries, how formed--Silting up of estuaries does not compensate
    the loss of land on the borders of the ocean--Bed of the German
    Ocean--Composition and extent of its sand-banks--Strata deposited by
    currents in the English channel--On the shores of the
    Mediterranean--At the mouths of the Amazon, Orinoco, and
    Mississippi--Wide area over which strata may be formed by this
    cause.


From the facts enumerated in the last chapter, it appears that on the
borders of the ocean, currents and tides co-operating with the waves of
the sea are most powerful instruments in the destruction and
transportation of rocks; and as numerous tributaries discharge their
alluvial burden into the channel of one great river, so we find that
many rivers deliver their earthy contents to one marine current, to be
borne by it to a distance, and deposited in some deep receptacle of the
ocean. The current, besides receiving this tribute of sedimentary matter
from streams draining the land, acts also itself on the coast, as does a
river on the cliffs which bound a valley. Yet the waste of cliffs by
marine currents constitutes on the whole a very insignificant portion of
the denudation annually effected by aqueous causes, as I shall point out
in the sequel of this chapter (p. 339).

In inland seas, where the tides are insensible, or on those parts of the
borders of the ocean where they are feeble, it is scarcely possible to
prevent a harbor at a river's mouth from silting up; for a bar of sand
or mud is formed at points where the velocity of the turbid river is
checked by the sea, or where the river and a marine current neutralize
each other's force. For the current, as we have seen, may, like the
river, hold in suspension a large quantity of sediment, or, co-operating
with the waves, may cause the progressive motion of a shingle beach in
one direction. I have already alluded to the erection of piers and
groins at certain places on our southern coast, to arrest the course of
the shingle and sand (see p. 318). The immediate effect of these
temporary obstacles is to cause a great accumulation of pebbles on one
side of the barrier, after which the beach still moves on round the end
of the pier at a greater distance from the land. This system, however,
is often attended with a serious evil, for during storms the waves throw
suddenly into the harbor the vast heap of pebbles which have collected
for years behind the groin or pier, as happened during a great gale
(Jan. 1839) at Dover.

The formation and keeping open of large estuaries are due to the
_combined influence_ of tidal currents and rivers; for when the tide
rises, a large body of water suddenly enters the mouth of the river,
where, becoming confined within narrower bounds, while its momentum is
not destroyed, it is urged on, and, having to pass through a contracted
channel, rises and runs with increased velocity, just as a stream when
it reaches the arch of a bridge scarcely large enough to give passage to
its waters, rushes with a steep fall through the arch. During the ascent
of the tide, a body of fresh water, flowing down in an opposite
direction from the higher country, is arrested in its course for several
hours; and thus a large lake of fresh and brackish water is accumulated,
which, when the sea ebbs, is let loose, as on the removal of an
artificial sluice or dam. By the force of this retiring water, the
alluvial sediment both of the river and of the sea is swept away, and
transported to such a distance from the mouth of the estuary, that a
small part only can return with the next tide.

It sometimes happens, that during a violent storm a large bar of sand is
suddenly made to shift its position, so as to prevent the free influx of
the tides, or efflux of river water. Thus about the year 1500 the sands
at Bayonne were suddenly thrown across the mouth of the Adour. That
river, flowing back upon itself, soon forced a passage to the northward
along the sandy plain of Capbreton, till at last it reached the sea at
Boucau, at the distance of _seven leagues_ from the point where it had
formerly entered. It was not till the year 1579 that the celebrated
architect Louis de Foix undertook, at the desire of Henry III., to
reopen the ancient channel, which he at last effected with great
difficulty.[461]

In the estuary of the Thames at London, and in the Gironde, the tide
rises only for five hours and ebbs seven, and in all estuaries the water
requires a longer time to run down than up; so that the preponderating
force is always in the direction which tends to keep open a deep and
broad passage. But for reasons already explained, there is naturally a
tendency in all estuaries to silt up partially, since eddies, and
backwaters, and points where opposing streams meet, are very numerous,
and constantly change their position.

Many writers have declared that the gain on our eastern coast, since the
earliest periods of history, has more than counterbalanced the loss; but
they have been at no pains to calculate the amount of loss, and have
often forgotten that, while the new acquisitions are manifest, there are
rarely any natural monuments to attest the former existence of the land
that has been carried away. They have also taken into their account
those tracts artificially recovered, which are often of great
agricultural importance, and may remain secure, perhaps, for thousands
of years, but which are only a few feet above the mean level of the sea,
and are therefore exposed to be overflowed again by a small proportion
of the force required to move cliffs of considerable height on our
shores. If it were true that the area of land annually abandoned by the
sea in estuaries were equal to that invaded by it, there would still be
no compensation _in kind_.

The tidal current which flows out from the northwest, and bears against
the eastern coast of England, transports, as we have seen, materials of
various kinds. Aided by the waves, it undermines and sweeps away the
granite, gneiss, trap-rocks, and sandstone of Shetland, and removes the
gravel and loam of the cliffs of Holderness, Norfolk, and Suffolk, which
are between twenty and three hundred feet in height, and which waste at
various rates of from one foot to six yards annually. It also bears
away, in co-operation with the Thames and the tides, the strata of
London clay on the coast of Essex and Sheppey. The sea at the same time
consumes the chalk with its flints for many miles continuously on the
shores of Kent and Sussex--commits annual ravages on the freshwater
beds, capped by a thick covering of chalk-flint gravel, in Hampshire,
and continually saps the foundations of the Portland limestone. It
receives, besides, during the rainy months, large supplies of pebbles,
sand, and mud, which numerous streams from the Grampians, Cheviots, and
other chains, send down to the sea. To what regions, then, is all this
matter consigned? It is not retained in mechanical suspension by the
waters of the ocean, nor does it mix with them in a state of chemical
solution--it is deposited _somewhere_, yet certainly not in the
immediate neighborhood of our shores; for, in that case, there would
soon be a cessation of the encroachment of the sea, and large tracts of
low land, like Romney Marsh, would almost everywhere encircle our
island.

As there is now a depth of water exceeding thirty feet, in some spots
where towns like Dunwich flourished but a few centuries ago, it is clear
that the current not only carries far away the materials of the wasted
cliffs, but is capable also of excavating the bed of the sea to a
certain moderate depth.

So great is the quantity of matter held in suspension by the tidal
current on our shores, that the waters are in some places artificially
introduced into certain lands below the level of the sea; and by
repeating this operation, which is called "warping," for two or three
years, considerable tracts have been raised, in the estuary of the
Humber, to the height of about six feet. If a current, charged with such
materials, meets with deep depressions in the bed of the ocean, it must
often fill them up; just as a river, when it meets with a lake in its
course, fills it gradually with sediment.

I have said (p. 337) that the action of the waves and currents on
sea-cliffs, or their power to remove matter from above to below the
sea-level, is insignificant in comparison with the power of rivers to
perform the same task. As an illustration we may take the coast of
Holderness described in the last chapter (p. 304). It is composed, as we
have seen, of very destructible materials, is thirty-six miles long, and
its average height may be taken at forty feet. As it has wasted away at
the rate of two and a quarter yards annually, for a long period, it will
be found on calculation that the quantity of matter thrown down into the
sea every year, and removed by the current, amounts to 51,321,600 cubic
feet. It has been shown that the united Ganges and Brahmapootra carry
down to the Bay of Bengal 40,000,000,000 of cubic feet of solid matter
every year, so that their transporting power is no less than 780 times
greater than that of the sea on the coast above-mentioned; and in order
to produce a result equal to that of the two Indian rivers, we must have
a line of wasting coast, like that of Holderness, nearly 28,000 miles in
length, or longer than the entire circumference of the globe by above
3000 miles. The reason of so great a difference in the results may be
understood when we reflect that the operations of the ocean are limited
to a single line of cliff surrounding a large area, whereas great rivers
with their tributaries, and the mountain torrents which flow into them,
act simultaneously on a length of bank almost indefinite.

Nevertheless we are by no means entitled to infer, that the denuding
force of the great ocean is a geological cause of small efficacy, or
inferior to that of rivers. Its chief influence is exerted at moderate
depths below the surface, on all those areas which are slowly rising, or
are attempting, as it were, to rise above the sea. From data hitherto
obtained respecting subterranean movements, we can scarcely speculate on
an average rate of upheaval of more than two or three feet in a century.
An elevation to this amount is taking place in Scandinavia, and probably
in many submarine areas as vast as those which we know to be sinking
from the proofs derived from circular lagoon islands or coral atolls.
(See chap. 50.) Suppose strata as destructible as those of the Wealden,
or the lower and upper cretaceous formation, or the tertiary deposits of
the British Isles to be thus slowly upheaved, how readily might they all
be swept away by waves and currents in an open sea! How entirely might
each stratum disappear as it was brought up successively and exposed to
the breakers! Shoals of wide extent might be produced, but it is
difficult to conceive how any continent could ever be formed under such
circumstances. Were it not indeed for the hardness and toughness of the
crystalline and volcanic rocks, which are often capable of resisting the
action of the waves, few lands might ever emerge from the midst of an
open sea.

_Supposed filling up of the German Ocean._--The German Ocean is deepest
on the Norwegian side, where the soundings give 190 fathoms; but the
mean depth of the whole basin may be stated at no more than thirty-one
fathoms.[462] The bed of this sea is traversed by several enormous
banks, the greatest of which is the Dogger Bank, extending for upwards
of 354 miles from north to south. The whole superficies of these shoals
is equal to about one-third of the whole extent of England and Scotland.
The average height of the banks measures, according to Mr. Stevenson,
about seventy-eight feet; the upper portion of them consisting of fine
and coarse siliceous sand, mixed with comminuted corals and shells.[463]
It had been supposed that these vast submarine hills were made up bodily
of loose materials supplied from the waste of the English, Dutch, and
other coasts; but the survey of the North Sea, conducted by Captain
Hewett, affords ground for suspecting this opinion to be erroneous. If
such immense mounds of sand and mud had been accumulated under the
influence of currents, the same causes ought nearly to have reduced to
one level the entire bottom of the German Ocean; instead of which some
long narrow ravines are found to intersect the banks. One of these
varies from seventeen to forty-four fathoms in depth, and has very
precipitous sides; in one part, called the "Inner Silver Pits," it is
fifty-five fathoms deep. The shallowest parts of the Dogger Bank were
found to be forty-two feet under water, except in one place, where the
wreck of a ship had caused a shoal. Such uniformity in the minimum depth
of water seems to imply that the currents, which vary in their velocity
from a mile to two miles and a half per hour, have power to prevent the
accumulation of drift matter in places of less depth.

_Strata deposited by currents._--It appears extraordinary, that in some
tracts of the sea, adjoining the coast of England, where we know that
currents are not only sweeping along rocky masses, thrown down, from
time to time, from the high cliffs, but also occasionally scooping out
channels in the regular strata, there should exist fragile shells and
tender zoophytes in abundance, which live uninjured by these violent
movements. The ocean, however, is in this respect a counterpart of the
land; and as, on the continents, rivers may undermine their banks,
uproot trees, and roll along sand and gravel, while their waters are
inhabited by testacea and fish, and their alluvial plains are adorned
with rich vegetation and forests, so the sea may be traversed by rapid
currents, and its bed may here and there suffer great local derangement,
without any interruption of the general order and tranquillity. It has
been ascertained by soundings in all parts of the world, that where new
deposits are taking place in the sea, coarse sand and small pebbles
commonly occur near the shore, while farther from land, and in deeper
water, finer sand and broken shells are spread out over the bottom.
Still farther out, the finest mud and ooze are alone met with. Mr.
Austen observes that this rule holds good in every part of the English
Channel examined by him. He also informs us, that where the tidal
current runs rapidly in what are called "races," where surface
undulations are perceived in the calmest weather, over deep banks, the
discoloration of the water does not arise from the power of such a
current to disturb the bottom at a depth of 40 or 80 fathoms, as some
have supposed. In these cases, a column of water sometimes 500 feet in
height, is moving onwards with the tide clear and transparent above,
while the lower portion holds fine sediment in suspension (a fact
ascertained by soundings), when suddenly it impinges upon a bank, and
its height is reduced to 300 feet. It is thus made to boil up and flow
off at the surface, a process which forces up the lower strata of water
charged with fine particles of mud, which in their passage from the
coast had gradually sunk to a depth of 300 feet or more.[464]

One important character in the formations produced by currents is, the
immense extent over which they may be the means of diffusing homogeneous
mixtures, for these are often coextensive with a great line of coast;
and, by comparison with their deposits, the deltas of rivers must shrink
into significance. In the Mediterranean, the same current which is
rapidly destroying many parts of the African coast, between the Straits
of Gibraltar and the Nile, checks also the growth of the delta of the
Nile, and drifts the sediment of that great river to the eastward. To
this source may be attributed the rapid accretions of land on parts of
the Syrian shores where rivers do not enter.

Among the greatest deposits now in progress, and of which the
distribution is chiefly determined by currents, we may class those
between the mouths of the Amazon and the southern coast of North
America. Captain Sabine found that the equatorial current before
mentioned (p. 292) was running with the rapidity of four miles an hour
where it crosses the stream of the Amazon, which river preserves part of
its original impulse, and has its waters not wholly mingled with those
of the ocean at the distance of 300 miles from its mouth.[465] The
sediment of the Amazon is thus constantly carried to the northwest as
far as to the mouths of the Orinoco, and an immense tract of swamp is
formed along the coast of Guiana, with a long range of muddy shoals
bordering the marshes, and becoming converted into land.[466] The
sediment of the Orinoco is partly detained, and settles near its mouth,
causing the shores of Trinidad to extend rapidly, and is partly swept
away into the Carribean Sea by the Guinea current. According to
Humboldt, much sediment is carried again out of the Carribean Sea into
the Gulf of Mexico.

It should not be overlooked that marine currents, even on coasts where
there are no large rivers, may still be the agents of spreading not only
sand and pebbles, but the finest mud, far and wide over the bottom of
the ocean. _For several thousand miles_ along the western coast of South
America, comprising the larger parts of Peru and Chili, there is a
perpetual rolling of shingle along the shore, part of which, as Mr.
Darwin has shown, are incessantly reduced to the finest mud by the
waves, and swept into the depths of the Pacific by the tides and
currents. The same author however has remarked that, notwithstanding the
great force of the waves on that shore, all rocks 60 feet under water
are covered by sea-weed, showing that the bed of the sea is not denuded
at that depth, the effects of the winds being comparatively superficial.

In regard to the distribution of sediment by currents it may be
observed, that the rate of subsidence of the finer mud carried down by
every great river into the ocean, or of that caused by the rolling of
the waves upon a shore, must be extremely slow; for the more minute the
separate particles of mud, the slower will they sink to the bottom, and
the sooner will they acquire what is called their terminal velocity. It
is well known that a solid body, descending through a resisting medium,
falls by the force of gravity, which is constant, but its motion is
resisted by the medium more and more as its velocity increases, until
the resistance becomes sufficient to counteract the farther increase of
velocity. For example, a leaden ball, one inch diameter, falling through
air of density as at the earth's surface, will never acquire greater
velocity than 260 feet per second, and, in water, its greatest velocity
will be 8 feet 6 inches per second. If the diameter of the ball were
1/100 of an inch, the terminal velocities in air would be 26 feet, and
in water .86 of a foot per second.

Now, every chemist is familiar with the fact, that minute particles
descend with extreme slowness through water, the extent of their surface
being very great in proportion to their weight, and the resistance of
the fluid depending on the amount of surface. A precipitate of sulphate
of baryta, for example, will sometimes require more than five or six
hours to subside one inch;[467] while oxalate and phosphate of lime
require nearly an hour to subside about an inch and a half and two
inches respectively,[468] so exceedingly small are the particles of
which these substances consist.

When we recollect that the depth of the ocean is supposed frequently to
exceed three miles, and that currents run through different parts of
that ocean at the rate of four miles an hour, and when at the same time
we consider that some fine mud carried away from the mouths of rivers
and from sea-beaches, where there is a heavy surf, as well as the
impalpable powder showered down by volcanoes, may subside at the rate of
only an inch per hour, we shall be prepared to find examples of the
transportation of sediment over areas of indefinite extent.

It is not uncommon for the emery powder used in polishing glass to take
more than an hour to sink one foot. Suppose mud composed of coarser
particles to fall at the rate of two feet per hour, and these to be
discharged into that part of the Gulf Stream which preserves a mean
velocity of three miles an hour for a distance of two thousand miles; in
twenty-eight days these particles will be carried 2016 miles, and will
have fallen only to a depth of 224 fathoms.

In this example, however, it is assumed that the current retains its
superficial velocity at the depth of 224 fathoms, for which we have as
yet no data, although we have seen that the motion of a current may
continue at the depth of 100 fathoms. (See above, p. 28.) Experiments
should be made to ascertain the rate of currents at considerable
distances from the surface, and the time taken by the finest sediment to
settle in sea-water of a given depth, and then the geologist may
determine the area over which homogeneous mixtures may be simultaneously
distributed in certain seas.




CHAPTER XXII.

IGNEOUS CAUSES.


  Changes of the inorganic world, _continued_--Igneous
    causes--Division of the subject--Distinct volcanic regions--Region
    of the Andes--System of volcanoes extending from the Aleutian isles
    to the Molucca and Sunda islands--Polynesian archipelago--Volcanic
    region extending from Central Asia to the Azores--Tradition of
    deluges on the shores of the Bosphorus, Hellespont, and Grecian
    isles--Periodical alternation of earthquakes in Syria and Southern
    Italy--Western limits of the European region--Earthquakes rarer and
    more feeble as we recede from the centres of volcanic action.
    Extinct volcanoes not to be included in lines of active vents.


We have hitherto considered the changes wrought, since the times of
history and tradition, by the continued action of aqueous causes on the
earth's surface; and we have next to examine those resulting from
igneous agency. As the rivers and springs on the land, and the tides and
currents in the sea, have, with some slight modifications, been fixed
and constant to certain localities from the earliest periods of which we
have any records, so the volcano and the earthquake have, with few
exceptions, continued, during the same lapse of time, to disturb the
same regions. But as there are signs, on almost every part of our
continent, of great power having been exerted by running water on the
surface of the land, and by waves, tides, and currents on cliffs
bordering the sea, where, in modern times, no rivers have excavated, and
no waves or tidal currents undermined--so we find signs of volcanic
vents and violent subterranean movements in places where the action of
fire or internal heat has long been dormant. We can explain why the
intensity of the force of aqueous causes should be developed in
succession in different districts. Currents, for example, tides, and the
waves of the sea, cannot destroy coasts, shape out or silt up estuaries,
break through isthmuses, and annihilate islands, form shoals in one
place, and remove them from another, without the direction and position
of their destroying and transporting power becoming transferred to new
localities. Neither can the relative levels of the earth's crust, above
and beneath the waters, vary from time to time, as they are admitted to
have varied at former periods, and as it will be demonstrated that they
still do, without the continents being, in the course of ages, modified,
and even entirely altered, in their external configuration. Such events
must clearly be accompanied by a complete change in the volume,
velocity, and direction of the streams and land floods to which certain
regions give passage. That we should find, therefore, cliffs where the
sea once committed ravages, and from which it has now retired--estuaries
where high tides once rose, but which are now dried up--valleys hollowed
out by water, where no streams now flow, is no more than we should
expect; these and similar phenomena are the necessary consequences of
physical causes now in operation; and if there be no instability in the
laws of nature, similar fluctuations must recur again and again in time
to come.

But, however natural it may be that the force of running water in
numerous valleys, and of tides and currents in many tracts of the sea,
should now be _spent_, it is by no means so easy to explain why the
violence of the earthquake and the fire of the volcano should also have
become locally extinct at successive periods. We can look back to the
time when the marine strata, whereon the great mass of Etna rests, had
no existence; and that time is extremely modern in the earth's history.
This alone affords ground for anticipating that the eruptions of Etna
will one day cease.


  Nec quae sulfureis ardet fornacibus, AEtna
  Ignea semper erit, _neque enim fuit ignea semper_,

  (Ovid, _Metam._ lib. 15-340,)


are the memorable words which are put into the mouth of Pythagoras by
the Roman poet, and they are followed by speculations as to the cause of
volcanic vents shifting their positions. Whatever doubts the philosopher
expresses as to the nature of these causes, it is assumed, as
incontrovertible, that the points of eruption will hereafter vary,
_because they have formerly done so_; a principle of reasoning which, as
I have endeavored to show in former chapters, has been too much set at
naught by some of the earlier schools of geology, which refused to
conclude that great revolutions in the earth's surface are now in
progress, or that they will take place hereafter, _because_ they have
often been repeated in former ages.

_Division of the subject._--Volcanic action may be defined to be "the
influence exerted by the heated interior of the earth on its external
covering." If we adopt this definition, without connecting it, as
Humboldt has done, with the theory of secular refrigeration, or the
cooling down of an original heated and fluid nucleus, we may then class
under a general head all the subterranean phenomena, whether of
volcanoes, or earthquakes, and those insensible movements of the land,
by which, as will afterwards appear, large districts may be depressed or
elevated, without convulsions. According to this view, I shall consider
first, the volcano; secondly, the earthquake; thirdly, the rising or
sinking of land in countries where there are no volcanoes or
earthquakes; fourthly, the probable _causes_ of the changes which result
from subterranean agency.

It is a very general opinion that earthquakes and volcanoes have a
common origin; for both are confined to certain regions, although the
subterranean movements are least violent in the immediate proximity of
volcanic vents, especially where the discharge of aeriform fluids and
melted rock is made constantly from the same crater. But as there are
particular regions, to which both the points of eruption and the
movements of great earthquakes are confined, I shall begin by tracing
out the geographical boundaries of some of these, that the reader may
be aware of the magnificent scale on which the agency of subterranean
fire is now simultaneously developed. Over the whole of the vast tracts
alluded to, active volcanic vents are distributed at intervals, and most
commonly arranged in a linear direction. Throughout the intermediate
spaces there is often abundant evidence that the subterranean fire is at
work continuously, for the ground is convulsed from time to time by
earthquakes; gaseous vapors, especially carbonic acid gas, are
disengaged plentifully from the soil; springs often issue at a very high
temperature, and their waters are usually impregnated with the same
mineral matters as are discharged by volcanoes during eruptions.


VOLCANIC REGIONS.

_Region of the Andes._--Of these great regions, that of the Andes of
South America is one of the best defined, extending from the southward
of Chili to the northward of Quito, from about lat. 43 degrees S. to
about 2 degrees N. of the equator. In this range, however, comprehending
forty-five degrees of latitude, there is an alternation on a grand scale
of districts of active with those of extinct volcanoes, or which, if not
spent, have at least been dormant for the last three centuries. How long
an interval of rest may entitle us to consider a volcano as entirely
extinct is not easily determined; but we know that in Ischia there
intervened between two consecutive eruptions a pause of seventeen
centuries; and the discovery of America is an event of far too recent a
date to allow us even to conjecture whether different portions of the
Andes, nearly the whole of which are subject to earthquakes, may not
experience alternately a cessation and renewal of eruptions.

The first line of active vents which have been seen in eruption in the
Andes extends from lat. 43 degrees 28 minutes S.; or, from Yantales,
opposite the isle of Chiloe, to Coquimbo, in lat. 30 degrees S.; to
these thirteen degrees of latitude succeed more than eight degrees in
which no recent volcanic eruptions have been observed. We then come to
the volcanoes of Bolivia and Peru, reaching six degrees from S. to N.,
or from lat. 21 degrees S. to lat. 15 degrees S. Between the Peruvian
volcanoes and those of Quito, another space intervenes of no less than
fourteen degrees of latitude, said to be free from volcanic action so
far as yet known. The volcanoes of Quito then succeed, beginning about
100 geographical miles south of the equator, and continuing for about
130 miles north of the line, when there occurs another undisturbed
interval of more than six degrees of latitude, after which we arrive at
the volcanoes of Guatemala or Central America, north of the Isthmus of
Panama.[469]

Having thus traced out the line from south to north, I may first state,
in regard to the numerous vents of Chili, that the volcanoes of Yantales
and Osorno were in eruption during the great earthquake of 1835, at the
same moment that the land was shaken in Chiloe, and in some parts of the
Chilian coast permanently upheaved; whilst at Juan Fernandez, at the
distance of no less than 720 geographical miles from Yantales, an
eruption took place beneath the sea. Some of the volcanoes of Chili are
of great height, as that of Antuco, in lat. 37 degrees 40 minutes S.,
the summit of which is at least 16,000 feet above the sea. From the
flanks of this volcano, at a great height, immense currents of lava have
issued, one of which flowed in the year 1828. This event is said to be
an exception in the general rule; few volcanoes in the Andes, and none
of those in Quito, having been seen in modern times to pour out lava,
but having merely ejected vapor or scoriae.

Both the basaltic (or augitic) lavas, and those of the felspathic class,
occur in Chili and other parts of the Andes; but the volcanic rocks of
the felspathic family are said by Von Buch to be generally not trachyte,
but a rock which has been called andesite, or a mixture of augite and
albite. The last-mentioned mineral contains soda instead of the potash
found in common felspar.

The volcano of Rancagua, lat. 34 degrees 15 minutes S., is said to be
always throwing out ashes and vapors like Stromboli, a proof of the
permanently heated state of certain parts of the interior of the earth
below. A year rarely passes in Chili without some slight shocks of
earthquakes, and in certain districts not a month. Those shocks which
come from the side of the ocean are the most violent, and the same is
said to be the case in Peru. The town of Copiapo was laid waste by this
terrible scourge in the years 1773, 1796, and 1819, or in both cases
after regular intervals of twenty-three years. There have, however, been
other shocks in that country in the periods intervening between the
dates above mentioned, although probably all less severe, at least on
the exact site of Copiapo. The evidence against a regular recurrence of
volcanic convulsions at stated periods is so strong as a general fact,
that we must be on our guard against attaching too much importance to a
few striking but probably accidental coincidences. Among these last
might be adduced the case of Lima, violently shaken by an earthquake on
the 17th of June, 1578, and again on the very same day, 1678; or the
eruptions of Coseguina in the year 1709 and 1809, which are the only two
recorded of that volcano previous to that of 1835.[470]

Of the permanent upheaval of land after earthquakes in Chili, I shall
have occasion to speak in the next chapter, when it will also be seen
that great shocks often coincide with eruptions, either submarine or
from the cones of the Andes, showing the identity of the force which
elevates continents with that which causes volcanic outbursts.[471]

The space between Chili and Peru, in which no volcanic action has been
observed, is 160 nautical leagues from south to north. It is, however,
as Von Buch observes, that part of the Andes which is least known,
being thinly peopled, and in some parts entirely desert. The volcanoes
of Peru rise from a lofty platform to vast heights above the level of
the sea, from 17,000 to 20,000 feet. The lava which has issued from
Viejo, lat. 16 degrees 55 minutes S., accompanied by pumice, is composed
of a mixture of crystals of albitic felspar, hornblende, and mica, a
rock which has been considered as one of the varieties of andesite. Some
tremendous earthquakes which have visited Peru in modern times will be
mentioned in a subsequent chapter.

The volcanoes of Quito, occurring between the second degree of south and
the third degree of north latitude, rise to vast elevations above the
sea, many of them being between 14,000 and 18,000 feet high. The Indians
of Lican have a tradition that the mountain called L'Altar, or Capac
Urcu, which means "the chief," was once the highest of those near the
equator, being higher than Chimborazo; but in the reign of Ouainia
Abomatha, before the discovery of America, a prodigious eruption took
place, which lasted eight years, and broke it down. The fragments of
trachyte, says M. Boussingault, which once formed the conical summit of
this celebrated mountain, are at this day spread over the plain.[472]
Cotopaxi is the most lofty of all the South American volcanoes which
have been in a state of activity in modern times, its height being
18,858 feet; and its eruptions have been more frequent and destructive
than those of any other mountain. It is a perfect cone, usually covered
with an enormous bed of snow, which has, however, been sometimes melted
suddenly during an eruption; as in January, 1803, for example, when the
snows were dissolved in one night.

Deluges are often caused in the Andes by the liquefaction of great
masses of snow, and sometimes by the rending open, during earthquakes,
of subterranean cavities filled with water. In these inundations fine
volcanic sand, loose stones, and other materials which the water meets
with in its descent, are swept away, and a vast quantity of mud, called
"moya," is thus formed and carried down into the lower regions. Mud
derived from this source descended, in 1797, from the sides of
Tunguragua in Quito, and filled valleys a thousand feet wide to the
depth of six hundred feet, damming up rivers and causing lakes. In these
currents and lakes of moya, thousands of small fish are sometimes
enveloped, which, according to Humboldt, have lived and multiplied in
subterranean cavities. So great a quantity of these fish were ejected
from the volcano of Imbaburu in 1691, that fevers, which prevailed at
the period, were attributed to the effluvia arising from the putrid
animal matter.

In Quito, many important revolutions in the physical features of the
country are said to have resulted, within the memory of man, from the
earthquakes by which it has been convulsed. M. Boussingault declares his
belief, that if a full register had been kept of all the convulsions
experienced here and in other populous districts of the Andes, it would
be found that the trembling of the earth had been incessant. The
frequency of the movement, he thinks, is not due to volcanic explosions,
but to the continual falling in of masses of rock which have been
fractured and upheaved in a solid form at a comparatively recent epoch;
but a longer series of observations would be requisite to confirm this
opinion. According to the same author, the height of several mountains
of the Andes has diminished in modern times.[473]

The great crest or cordillera of the Andes is depressed at the Isthmus
of Panama to a height of about 1000 feet, and at the lowest point of
separation between the two seas near the Gulf of San Miguel, to 150
feet. What some geographers regard as a continuation of that chain in
Central America lies to the east of a series of volcanoes, many of which
are active in the provinces of Pasto, Popayan, and Guatemala. Coseguina,
on the south side of the Gulf of Fonseca, was in eruption in January,
1835, and some of its ashes fell at Truxillo, on the shores of the Gulf
of Mexico. What is still more remarkable, on the same day, at Kingston,
in Jamaica, the same shower of ashes fell, having been carried by an
upper counter-current against the regular east wind which was then
blowing. Kingston is about 700 miles distant from Coseguina, and these
ashes must have been more than four days in the air, having travelled
170 miles a day. Eight leagues to the southward of the crater, the ashes
covered the ground to the depth of three yards and a half, destroying
the woods and dwellings. Thousands of cattle perished, their bodies
being in many instances one mass of scorched flesh. Deer and other wild
animals sought the towns for protection; many birds and quadrupeds were
found suffocated in the ashes, and the neighboring streams were strewed
with dead fish.[474] Such facts throw light on geological monuments, for
in the ashes thrown out at remote periods from the volcanoes of
Auvergne, now extinct, we find the bones and skeletons of lost species
of quadrupeds.

_Mexico._--The great volcanic chain, after having thus pursued its
course for several thousand miles from south to north, sends off a
branch in a new direction in Mexico, in the parallel of the city of that
name, and is prolonged in a great platform between the eighteenth and
twenty-second degrees of north latitude. Five active volcanoes traverse
Mexico from west to east--Tu[\x]tla, Orizaba, Popocatepetl, Jorullo, and
Colima. Jorullo, which is in the centre of the great platform, is no
less than 120 miles from the nearest ocean--an important circumstance,
as showing that the proximity of the sea is not a necessary condition,
although certainly a very general characteristic of the position of
active volcanoes. The extraordinary eruption of this mountain, in 1759,
will be described in the sequel. If the line which connects these five
vents be prolonged in a westerly direction, it cuts the volcanic group
of islands called the Isles of Revillagigedo.

To the north of Mexico there are said to be three, or according to
some, five volcanoes in the peninsula of California; and a volcano is
reported to have been in eruption in the N. W. coast of America, near
the Colombia river, lat. 45 degrees 37 minutes N.

_West Indies._--To return to the Andes of Quito: Von Buch inclines to
the belief that if we were better acquainted with the region to the east
of the Madalena, and with New Granada and the Caraccas, we might find
the volcanic chain of the Andes to be connected with that of the West
Indian or Carribee Islands. The truth of this conjecture has almost been
set at rest by the eruption, in 1848, of the volcano of Zamba, in New
Grenada, at the mouth of the river Madalena.[475]

Of the West Indian islands there are two parallel series: the one to the
west, which are all volcanic, and which rise to the height of several
thousand feet; the others to the east, for the most part composed of
calcareous rocks, and very low. In the former or volcanic series, are
Granada, St. Vincent, St. Lucia, Martinique, Dominica, Guadaloupe,
Montserrat, Nevis, and St. Eustace. In the calcareous chain are Tobago,
Barbadoes, Mariegallante, Grandeterre, Desirade, Antigua, Barbuda, St.
Bartholomew, and St. Martin. The most considerable eruptions in modern
times have been those of St. Vincent. Great earthquakes have agitated
St. Domingo, as will be seen in the twenty-ninth chapter.

I have before mentioned (p. 270) the violent earthquake which in 1812
convulsed the valley of the Mississippi at New Madrid, for the space of
300 miles in length, of which more will be said in the twenty-seventh
chapter. This happened exactly at the same time as the great earthquake
of Caraccas, so that it is possible that these two points are parts of
one subterranean volcanic region. The island of Jamaica, with a tract of
the contiguous sea, has often experienced tremendous shocks; and these
are frequent along a line extending from Jamaica to St. Domingo and
Porto Rico.

Thus it will be seen that, without taking account of the West Indian and
Mexican branches, a linear train of volcanoes and tracts shaken by
earthquakes may be traced from the island of Chiloe and opposite coast
to Mexico, or even perhaps to the mouth of the Colombia river--a
distance upon the whole as great as from the pole to the equator. In
regard to the western limits of the region, they lie deep beneath the
waves of the Pacific, and must continue unknown to us. On the east they
are not prolonged, except where they include the West Indian Islands, to
a great distance; for there seem to be no indications of volcanic
disturbances in Buenos Ayres, Brazil, and the United States of North
America.

[Illustration: Fig. 89.

MAP OF ACTIVE VOLCANOES AND ATOLLS of THE INDIAN ARCHIPELAGO, and Part
of the adjoining PACIFIC OCEAN.]

_Volcanic region from the Aleutian Isles to the Moluccas and Isles of
Sunda._--On a scale which equals or surpasses that of the Andes, is
another line of volcanic action, which commences, on the north, with the
Aleutian Isles in Russian America, and extends, first in a westerly
direction for nearly 200 geographical miles, and then southwards, with
few interruptions, throughout a space of between sixty and seventy
degrees of latitude to the Moluccas, where it sends off a branch to the
southeast while the principal train continues westerly through Sumbawa
and Java to Sumatra, and then in a northwesterly direction to the Bay of
Bengal.[476] This volcanic line, observes Von Buch, may be said to
follow throughout its course the external border of the continent of
Asia; while the branch which has been alluded to as striking southeast
from the Moluccas, passes from New Guinea to New Zealand, conforming,
though somewhat rudely, to the outline of Australia.[477]

The connection, however, of the New Guinea volcanoes with the line in
Java (as laid down in Von Buch's map) is not clearly made out. By
consulting Darwin's map of coral reefs and active volcanoes,[478] the
reader will see that we might almost with equal propriety include the
Mariana and Bonin volcanoes in a band with New Guinea. Or if we allow so
much latitude in framing zones of volcanic action, we must also suppose
the New Hebrides, Solomon Isles, and New Ireland to constitute one line
(see map, fig. 39, p. 351).

The northern extremity of the volcanic region of Asia, as described by
Von Buch, is on the borders of Cook's Inlet, northeast of the Peninsula
of Alaska, where one volcano, in about the sixtieth degree of latitude,
is said to be 14,000 feet high. In Alaska itself are cones of vast
height, which have been seen in eruption, and which are covered for
two-thirds of their height downwards with perpetual snow. The summit of
the loftiest peak is truncated, and is said to have fallen in during an
eruption in 1786. From Alaska the line is continued through the Aleutian
or Fox Islands to Kamtschatka. In the Aleutian Archipelago eruptions are
frequent, and about thirty miles to the north of Unalaska, near the Isle
of Umnack, a new island was formed in 1796. It was first observed after
a storm, at a point in the sea from which a column of smoke had been
seen to rise. Flames then issued from the new islet which illuminated
the country for ten miles round; a frightful earthquake shook the
new-formed cone, and showers of stones were thrown as far as Umnack. The
eruption continued for several months, and eight years afterwards, in
1804, when it was explored by some hunters, the soil was so hot in some
places that they could not walk on it. According to Langsdorf and
others, this new island, which is now several thousand feet high, and
two or three miles in circumference, has been continually found to have
increased in size when successively visited by different travellers; but
we have no accurate means of determining how much of its growth, if any,
has been due to upheaval, or how far it has been exclusively formed by
the ejection of ashes and streams of lava. It seems, however, to be well
attested that earthquakes of the most terrific description agitate and
alter the bed of the sea and surface of the land throughout this tract.

The line is continued in the southern extremity of the Peninsula of
Kamtschatka, where there are many active volcanoes, which, in some
eruptions, have scattered ashes to immense distances. The largest and
most active of these is Klutschew, lat. 56 degrees 3 minutes N., which
rises at once from the sea to the prodigious height of 15,000 feet.
Within 700 feet of the summit, Erman saw, in 1829, a current of lava,
emitting a vivid light, flow down the northwest side to the foot of the
cone. A flow of lava from the summit of Mont Blanc to its base in the
valley of Chamouni would afford but an inadequate idea of the declivity
down which this current descended. Large quantities of ice and snow
opposed for a time a barrier to the lava, until at length the fiery
torrent overcame, by its heat and pressure, this obstacle, and poured
down the mountain side with a frightful noise, which was heard for a
distance of more than fifty miles.[479]

The Kurile chain of islands constitutes the prolongation of the
Kamtschatka range, where a train of volcanic mountains, nine of which
are known to have been in eruption, trends in a southerly direction. The
line is then continued to the southwest in the great island of Jesso,
and again in Nipon, the principal of the Japanese group. It then extends
by Loo Choo and Formosa to the Philippine Islands, and thence by Sangir
and the northeastern extremity of Celebes to the Moluccas (see map, fig.
39). Afterwards it passes westward through Sumbawa to Java.

There are said to be thirty-eight considerable volcanoes in Java, some
of which are more than 10,000 feet high. They are remarkable for the
quantity of sulphur and sulphureous vapors which they discharge. They
rarely emit lava, but rivers of mud issue from them, like the moya of
the Andes of Quito. The memorable eruption of Galongoon, in 1822, will
be described in the twenty-fifth chapter. The crater of Taschem, at the
eastern extremity of Java, contains a lake strongly impregnated with
sulphuric acid, a quarter of a mile long, from which a river of acid
water issues, which supports no living creature, nor can fish live in
the sea near its confluence. There is an extinct crater near Batur,
called Guevo Upas, or the Valley of Poison, about half a mile in
circumference, which is justly an object of terror to the inhabitants of
the country. Every living being which penetrates into this valley falls
down dead, and the soil is covered with the carcasses of tigers, deer,
birds, and even the bones of men; all killed by the abundant emanations
of carbonic acid gas, by which the bottom of the valley is filled.

In another crater in this land of wonders, near the volcano of Talaga
Bodas, we learn from M. Reinwardt, that the sulphureous exhalations have
killed tigers, birds, and innumerable insects; and the soft parts of
these animals, such as the fibres, muscles, nails, hair, and skin,
are very well preserved, while the bones are corroded, and entirely
destroyed.

We learn from observations made in 1844, by Mr. Jukes, that a recent
tertiary formation composed of limestone and resembling the coral rock
of a fringing reef, clings to the flanks of all the volcanic islands
from the east end of Timor to the west end of Java. These modern
calcareous strata are often white and chalk-like, sometimes 1000 feet
and upwards above the sea, regularly stratified in thick horizontal
beds, and they show that there has been a general elevation of these
islands at a comparatively modern period.[480]

The same linear arrangement which is observed in Java holds good in the
volcanoes of Sumatra, some of which are of great height, as Berapi,
which is more than 12,000 feet above the sea, and is continually
smoking. Hot springs are abundant at its base. The volcanic line then
inclines slightly to the northwest, and points to Barren Island, lat.
12 degrees 15 minutes N., in the Bay of Bengal. This volcano was in
eruption in 1792, and will be described in the twenty-sixth chapter. The
volcanic train then extends, according to Dr. Macclelland, to the island
of Narcondam, lat. 13 degrees. 22 minutes N., which is a cone seven or
eight hundred feet high, rising from deep water, and said to present
signs of lava currents descending from the crater to the base.
Afterwards the train stretches in the same direction to the volcanic
island of Ramree, about lat. 19 degrees. N., and the adjoining island of
Cheduba, which is represented in old charts as a burning mountain. Thus
we arrive at the Chittagong coast, which in 1762 was convulsed by a
tremendous earthquake (see chap. 29).[481]

To enumerate all the volcanic regions of the Indian and Pacific oceans
would lead me far beyond the proper limits of this treatise; but it will
appear in the last chapter of this volume, when coral reefs are treated
of, that the islands of the Pacific consist alternately of linear groups
of two classes, the one lofty, and containing active volcanoes, and
marine strata above the sea-level, and which have been undergoing
upheava