SUBTERRANEAN HEAT--ITS POWERS ILLUSTRATED BY UNDULATIONS
OF THE EARTH’S CRUST.
Gentle Movements of the Earth’s Crust within Historic Times--Roman
Roads and Temples submerged in the Bay of Baiæ--Temple
of Jupiter Serapis--Singular Condition of its Columns--Proof
of Subsidence and subsequent Upheaval--Indications
of a second Subsidence now actually taking place--Gradual
Upheaval of the Coast of Sweden--Summary of the Evidence
adduced to establish this Fact--Subsidence of the Earth’s Crust
on the West Coast of Greenland--Recapitulation, 271
PART II.
THE ANTIQUITY OF THE EARTH CONSIDERED IN
RELATION TO THE HISTORY OF GENESIS.
CHAPTER XVIII.
STATEMENT OF THE QUESTION AND EXPOSITION OF THE AUTHOR’S
VIEW.
The General Principles of Geological Theory accepted by the Author
--These Principles plainly import the extreme Antiquity
of the Earth--Illustration from the Coal, the Chalk, and the
Boulder Clay--This Conclusion not at Variance with the Inspired
History of the Creation--Chronology of the Bible--Genealogies
of Genesis--Date of the Creation not fixed by Moses--Progress
of Opinion on this Point--Cardinal Wiseman, Father
Peronne, Father Pianciani--Doctor Buckland, Doctor Chalmers,
Doctor Pye Smith, Hugh Miller--Author’s View explained--Charge
of Rashness and Irreverence answered--Admonitions
of Saint Augustine and Saint Thomas, 280
CHAPTER XIX.
FIRST HYPOTHESIS;--AN INTERVAL OF INDEFINITE DURATION
BETWEEN THE CREATION OF THE WORLD AND THE FIRST
MOSAIC DAY.
The Heavens and the Earth were created before the First Mosaic
Day--Objection from Exodus, xx. 9-11--Answer--Interpretation
of the Author supported by the best Commentators--Confirmed
by the Hebrew Text--The Early Fathers commonly held
the Existence of created Matter prior to the Work of the Six
Days--Saint Basil, Saint Chrysostom, Saint Ambrose, Venerable
Bede--The most eminent Doctors in the Schools concurred
in this Opinion--Peter Lombard, Hugh of Saint Victor, Saint
Thomas--Also Commentators and Theologians--Perrerius,
Petavius--Distinguished Names on the other side, A Lapide,
Tostatus, Saint Augustine--The Opinion is at least not at
Variance with the Voice of Tradition--This Period of created
Existence may have been of indefinite Length--And the Earth
may have been furnished then as now with countless Tribes of
Plants and Animals--Objections to this Hypothesis proposed
and explained, 300
CHAPTER XX.
SECOND HYPOTHESIS;--THE DAYS OF CREATION LONG PERIODS OF
TIME.
Diversity of Opinion among the Early Fathers regarding the Days
of Creation--Saint Augustine, Philo Judæus, Clement of Alexandria,
Origen, Saint Athanasius, Saint Eucherius, Procopius--Albertus
Magnus, Saint Thomas, Cardinal Cajetan--Inference
from these Testimonies--First Argument in favor of the
popular Interpretation; a Day, in the literal Sense, means a
Period of Twenty-four Hours--Answer--This Word often used
in Scripture for an indefinite Period--Examples from the Old
and New Testament--Second Argument; the Days of Creation
have an Evening and a Morning--Answer--Interpretation of
Saint Augustine, Venerable Bede, and other Fathers of the
Church--Third Argument; the Reason alleged for the Institution
of the Sabbath Day--Answer--The Law of the Sabbath
extended to every Seventh Year as well as to every Seventh Day--The
Seventh Day of God’s Rest a long Period of indefinite
Duration, 318
CHAPTER XXI.
APPLICATION OF THE SECOND HYPOTHESIS TO THE MOSAIC HISTORY
OF CREATION--CONCLUSION.
Summary of the Argument--Striking Coincidence between the
Order of Creation as set forth in the Narrative of Moses and in
the Records of Geology--Comparison illustrated and developed--Scheme
of Adjustment between the Periods of Geology and
the Days of Genesis--Tabular View of this Scheme--Objections
considered--It is not to be regarded as an established Theory,
but as an admissible Hypothesis--Either the first Hypothesis
or the second is sufficient to meet the demands of Geology as
regards the Antiquity of the Earth--Not necessary to suppose
that the Sacred Writer was made acquainted with the long Ages
of Geological Time--He simply records faithfully that which
was committed to his charge--The Mosaic History of Creation
stands alone, without Rivals or Competitors, 343
[Illustration]
LIST OF ILLUSTRATIONS.
PAGE
1. Granitic Rocks off the Shetland Islands, 63
2. Iceberg seen in mid ocean, 1400 miles from land, 75
3. Block of Limestone Rock with Glacial-markings, 78
4, 5, 6, 7, 8. Examples of living Zoophytes:
Campanularia Gelatinosa; Gorgonia Patula, 131
Frustra Pilosa; Madrepora Plantaginea, 132
Corallium Rubrum, 133
9, 10. Fossil Ferns from the Coal Measures, 143
11. Trunk and roots of a forest tree; found erect in a Coal
Mine, near Liverpool, 152
12. Fossil Irish Deer, 163
13. Fossil Wood, showing the rings of annual growth, 171
14, 15. Fossil Fish from Monte Bolea in Italy, 173, 174
16. Group of several Fossil Fish in one block of Limestone, 176
17. Fossil Fish from the Chalk Rock of Sussex, 177
18, 19. Two Skeletons of the Ichthyosaurus, from the Lias of
Dorsetshire, preserved in the Museum of Trinity College,
Dublin, 179
20. Plesiosaurus Cramptonii, from the Lias of Yorkshire,
preserved in the Museum of the Royal Dublin Society, 182
21. The Megatherium, or Great Wild Beast, 185
22. The Mylodon Robustus, 186
23. Section of a Quarry in the Island of Portland, showing the
stumps of an ancient forest standing erect in the solid rock, 189
24. Calamite from the Coal Measures of Newcastle, 191
25. Lepidodendron Sternbergii; a forest tree erect in a Coal Mine, 192
26. Lepidodendron Elegans; Stem and branches, from a Coal Mine,
near Newcastle, 193
27. Section of a Coal Mine near Lyons, showing an ancient forest
enveloped in Sandstone, 194
28. Bird’s-eye View of Santorin during the volcanic eruption
of 1866, 255
LIST OF TABLES.
Table of Stratified Rocks Chronologically arranged, 211
Table of Geological Formations, showing the first appearance on
the Earth of the various forms of Animal Life, 226
Table exhibiting the Genealogies of Genesis according to the
various Readings of the three most ancient Versions, the
Hebrew, the Samaritan, and the Septuagint, 291
Table representing a possible Adjustment of the Mosaic Days with
the Periods of Geology, 251
[Illustration]
GEOLOGY AND REVELATION.
_INTRODUCTORY CHAPTER._
_Scope of the work explained--Geology looked on with suspicion
by Christians--Hailed with triumph by Unbelievers--No
contradiction possible between the works of Nature and the
Word of God--Author not jealous of progress in Geological
Discoveries--Points of contact between Geology and
Revelation--The question stated--The answer--Division of the
work._
Among the various pursuits that engage the human mind, there are few so
attractive as Geology, none so important as Revelation. Each of these
two studies has an interest peculiar to itself. The one is chiefly
concerned about the world in which we are living: the other about the
world to which we are hastening. Geology leads us down into the depths
of the Earth, and there, unfolding to our view a long series of strange
unwritten records impressed on lasting monuments by the hand of Nature,
it proceeds to trace back the history of our Globe through myriads of
ages into the distant past. Revelation, on the other hand, comes to us
from above; and setting forth the far more wonderful records of God’s
dealings with man, holds out the hope of another world “everlasting in
the heavens”[10] which shall still remain when this earth and all the
works that are therein shall have melted away with fervent heat.[11]
But, it may be asked, why should two such incongruous topics be set
down for discussion side by side? To answer this question is to explain
the scope and design of the present work. We are not going to write a
Manual of Geology; nor yet a Treatise on Revelation. Taken separately,
these two subjects have been handled with eminent skill and ability;
the one by the votaries of Science, the other by the friends of
Theology. It is our purpose to consider them not so much in themselves
as in their mutual relations: to compare the conclusions of Geology
with the truths of Revelation; and to inquire if it be possible to
accept the one and yet not to abandon the other.
An uneasy apprehension has long prevailed among devout Christians, and
a declared conviction among a large class of unbelievers, that the
discoveries of Geology are at variance with the facts recorded in the
Book of Genesis. Now, the historical narrative of Genesis lies at the
very foundation of all Revealed Religion. Hence the science of Geology,
has come to be looked on with suspicion by the simple-minded faithful,
and to be hailed with joy, as a new and powerful auxiliary, by that
infidel party which, in these latter days, has assumed a position so
bold and defiant. It is now confidently asserted that we cannot uphold
the teaching of Revelation, unless we shut our eyes to the evidence of
Geology; and that we cannot pursue the study of Geology, if we are not
prepared to renounce our belief in the doctrines of Revelation.
Vet surely this cannot be. Truth cannot be at variance with truth. If
God has recorded the history of our Globe, as Geologists maintain, on
imperishable monuments within the Crust of the Earth, we may be quite
sure He has not contradicted that Record in His Written Word. There
may be for a time, indeed, a conflict between the student of Nature and
the student of Revelation. Each is liable to error when he undertakes
to interpret the record that is placed in his hands. Many a brilliant
Geological theory, received at first with unbounded applause, has been
dissipated by the progress of discovery even within the lifetime of its
author. On the other hand, it cannot be denied that Theologians have
sometimes imputed to the Bible that which the Bible does not teach.
Learned and pious men--Protestants and Catholics alike--once believed
that the Book of Joshua represents the succession of day and night
as produced by the revolution of the Sun around the Earth: whereas
it is now considered quite plain that the Book of Joshua, properly
understood, teaches nothing of the kind; but that the Inspired Writer,
in describing a wonderful phenomenon of Nature, simply employs the
language of men according to the established usage of his time. We need
not wonder, therefore, that a conflict of opinion should sometimes
arise between the Geologist and the Theologian; but a conflict there
cannot be between the story which God has described on His works and
the story He has recorded in His Written Word.
Though we come forward, therefore, among those whose duty and whose
glory it is to uphold Revelation, we are by no means jealous of the
wonderful ardor, and we may add, the wonderful success, with which the
study of Geology has been lately pursued. We have too much confidence
in the truth of our cause to apprehend that it can suffer in any way
from the progress of Natural Science. It is our conviction, rather,
that the more thoroughly the works of Nature are understood, the
more perfectly they will be found to harmonize with the truths of
Revelation. We are not afraid, therefore, to venture into the realms
of Geology and to come face to face with its discoveries. Too long,
perhaps, has this interesting and popular science been neglected by
those who are ranged under the banner of Religion. Let it be ours to
show that the study of God’s works is not incompatible with the belief
in God’s Word; and that it is quite possible to investigate the ancient
history of the world we inhabit without forfeiting our right to a
better.
The points of contact between Geology and Revelation are chiefly these
two:--First, the Antiquity of the Earth; Secondly, the Antiquity of the
Human Race. In the present Volume we shall confine our attention to the
Antiquity of the Earth. The subject that offers itself for discussion
may be stated in a few words. Geologists maintain that the Crust of the
Earth has been slowly built up by means of a long series of operations
which would require hundreds of thousands, perhaps millions of years
for their accomplishment: whereas the Bible narrative, it is alleged,
allows but the short lapse of six or eight thousand years from the
creation of the world to the present time. The Geological record, then,
seems to contradict the Mosaic; and the question is, how this apparent
contradiction is to be explained.
Some have ventured to solve the problem by rejecting the historical
narrative of the Bible: others by ignoring the plain facts of Geology.
But there is a third class of writers, including many names of the
highest eminence and authority, who contend that we may admit the
extreme Antiquity of our Globe, which Geology so imperatively demands,
without compromising in the smallest degree the truthfulness of the
Mosaic story. They say that the Chronology of the Bible stops short
with Adam, and does not go back to the beginning of the world. By
means of the data which the Bible supplies we may calculate, at least
roughly, the lapse of time from the Creation of Adam to the Birth of
Christ. But from the first beginning of all created things, when God
made the Heavens and the Earth, to the close of the Sixth Day when Adam
was introduced upon the scene, that is an interval which, in the Bible
narrative, is left altogether undefined and uncertain. This is the
view which we hope to develop and to illustrate in the course of the
following pages.
Our task naturally divides itself into two parts. First, it will be
our duty to consider the received theory of Geology, and to examine
in detail some of the interesting and wonderful phenomena on which
it is founded. This course of investigation, while it is plainly
indispensable for the intelligent appreciation of our subject, cannot
fail at the same time to unfold many new and striking views of the
Power, and the Goodness, and the Providence of God. “For the invisible
things of Him from the creation of the world are clearly seen, being
understood by the things that are made; even His eternal Power and
Godhead.”[12]
In the Second Part we shall consider the Antiquity of the Earth in
reference to the History of Genesis. It will be our purpose to show
that, as far as the Bible narrative is concerned, an interval of
countless ages may have elapsed between the first creation of the
Heavens and the Earth and the beginning of the Six Mosaic Days.
Furthermore, we shall contend that, without any prejudice to the Sacred
History, we may suppose these Days themselves to have been, not days
in the ordinary sense of the word, but long and indefinite Periods of
Time. If we succeed in establishing these views, it will be obvious
to infer that, while the Bible enables us to determine, at least by
approximation, the Age of the Human Race, it allows time without limit
for the past history of the Earth.
[Illustration]
PART I.
GEOLOGICAL THEORY AND THE EVIDENCE BY WHICH IT IS SUPPORTED.
_CHAPTER I._
THEORY OF GEOLOGISTS.
_Geology defined--Facts and Theories--Recent progress of
Geology--Stratification of Rocks--Aqueous Rocks; of Mechanical
Origin--of Chemical Origin--of Organic Origin--Igneous Rocks,
Plutonic and Volcanic--Metamorphic Rocks--Summary of the
Rocks that compose the Crust of the Earth--Relative order
of position--Internal condition of the Globe--Movements of
the Earth’s Crust--Subterranean disturbing force--Uplifting
and bending of Strata--Denudation and its Causes--Fossil
Remains--Their Value in Geological Theory._
The object of Geology is to examine and record the appearances
presented by the Crust of the Earth; and by the aid of these
appearances, to trace out the long series of events by which it has
been brought into its present condition. Geology, therefore, like
all other natural sciences, is made up partly of fact, and partly of
theory. It belongs to the Geologist first to investigate the phenomena
which the Crust of the Earth exhibits to the eye. For this purpose he
descends into the mine and the quarry; he visits the lofty cliff by
the sea-shore, the deep ravine on the mountain side, the cutting of a
railway; in a word, every spot where a section of the Earth’s Crust is
exposed to view, either by the action of Nature or by the hand of man.
He then retires into the silence of his closet, with his note-book and
his specimens; and there, having arranged and classified the various
phenomena which he has already examined with his eyes in the outer
world, he proceeds to make his deductions, and to build up his theory.
He seeks to explain how materials, so diverse in their composition,
have come to be piled up together, with such admirable order, and yet
with such endless variety; and how the solid rocks have come to be the
repository of petrified trees and plants and bones and shells, which
seem, as it were, to start up from their graves, and to tell strange
stories of a bygone world.
In the early days of Geology there were comparatively few who devoted
themselves with patient industry to the collection and classification
of facts: while the number was legion of those who, with a very
meagre knowledge of facts, set themselves to build up systems. A
vast multitude of different and conflicting theories were, in this
way, brought into existence, and attracted for a time much public
attention, each one being vehemently defended by its friends and as
vehemently assailed by its enemies. These theories resting on no solid
foundation, could not hold their ground against the advancing tide of
new discoveries. They flourished for a brief space, and then gave way
to others scarcely more substantial, which were destined in their turn
to be likewise rejected and forgotten. Thus it came to pass, from the
manifest instability of its principles, that Geology was long held
in light repute, and practical men set little store by its boasted
discoveries and startling revelations.
But it would be unjust and unphilosophical to condemn the modern theory
of Geologists because of their past errors. We must judge of this
science, not according to what it once was in the feebleness of its
infancy, but according to what it now is in the growing strength of its
mature years. It seems to be in the nature of things that groundless
speculations and wild conjectures go before, and sober Science follows
in their wake. The visionary dreams of the Alchemist led the way to
the science of Chemistry, and the idle fancies of the Astrologist have
given place to the marvellous discoveries of Astronomy. So, too, amidst
the confused mass of conflicting arguments and opinions, by which the
phenomena of Geology were for a long time enveloped and obscured, the
seeds of a new science were slowly germinating. New facts were eagerly
sought after to support or to impugn the favorite theory of the hour;
and though theory after theory passed away, yet the facts remained. In
course of time this accumulation of facts became broad and deep and
solid enough to form a sound basis for inductive reasoning; and thus
almost within our own days Geology may be fairly said to have assumed
the rank and dignity of a science.
During the last quarter of a century it has been studied with a more
ardent enthusiasm than, perhaps, any other science in England, in
France, in Germany, and in America. It has been studied, too, upon
better principles than before: less attention has been paid to the
building up of theories, and far more pains and labor have been
expended on the careful investigation of natural phenomena. There are
still, no doubt, different schools of Geologists which are divided
among themselves as regards many important details of theory; but
there are some general conclusions upon which all Geologists are
substantially agreed, and which, they assure us, are established by
evidence that is absolutely irresistible. It is to these conclusions we
wish to invite the attention of our readers; for they bear very closely
on the question of the Antiquity of the Earth.
Geologists tell us, then, that the materials of which the Earth’s
Crust is composed, are not heaped together in a confused mass, but are
disposed with evident marks of definite and systematic arrangement.
This is an important truth, of which many examples are familiar to us
all, though perhaps we do not all attend to their significance. Thus
in a quarry, we see commonly enough first a bed of limestone, then
above that a bed of gravel, and higher still a bed of clay: and even
the limestone itself is not usually a compact mass, but is arranged in
successive layers, something like the successive courses of masonry in
a building. Now it appears that a very large proportion of the Earth’s
Crust is made up in this way of successive layers, or _strata_, as
they are called by Geologists. These _strata_ are composed of various
substances, such as clay, chalk, sand, lime, and coal; and they present
everywhere the same general appearances. They are known under the
common name of Aqueous Rocks,[13] because it is believed that they
were originally formed under water; and here it is that the professors
of Geology first come into collision with the popular notions that
formerly prevailed.
They hold that these stratified rocks were not arranged as we see them
now, when the Earth first came from the hands of its Creator, but have
been formed, during the lapse of unnumbered ages, by the operation
of natural causes. Nay more, they have divided the rocks into sundry
classes, and they undertake to explain the particular process by which
each several variety has been produced. First in order and importance
are those which derive their existence from the mechanical force of
moving water. The materials of which they are composed first existed in
the form of minute particles, which were transported by the action of
water from one place to another; then they were spread out over a given
surface, just as we now see layers of sand, or mud, or gravel deposited
near the mouths of rivers, or in the estuaries of the sea, or even upon
the land itself during temporary inundations. Lastly, after a long
interval came the slow but certain process of consolidation. The fine
sand was cemented together and became sandstone; the loose gravel by a
similar process was transformed into a solid mass, known by the name of
Conglomerate or Pudding-stone; while the soft mud by simple pressure
was converted into a kind of slaty clay, called Shale. Thus from age to
age Nature was ever building up new strata, and consolidating the old.
Next in order are the Aqueous Rocks, which owe their origin to the
agency of chemical laws. To this class belong many of our limestone
formations. Large quantities of carbonate of lime are held in solution
by water charged with carbonic acid gas: when the carbonic acid, in
course of time, passes off, the carbonate of lime can no longer be held
in solution, and it is accordingly precipitated in a solid form to
the bottom. In this manner was formed that peculiar kind of limestone
called Travertine, which abounds in Italy, and which is well known
to all who have visited Rome, as the stone of which the Coliseum was
built. A still more familiar example, on a small scale, is seen in the
case of Stalactites and Stalagmites. Water saturated with carbonic
acid trickles down the sides, or drops from the roof of a limestone
cavern. In its course it dissolves carbonate of lime, and holds it
in solution; afterward, reaching the floor of the cavern, it slowly
evaporates and leaves behind it a thin sheet of limestone which is
called a Stalagmite; while the icicle-like pendants that are formed by
a similar process, on the roof of the cavern, are called Stalactites.
There is a third class of Aqueous Rocks which are supposed to be
made up almost exclusively of the fragmentary remains of plants and
animals, and are therefore called Organic. The well-known coral reefs,
so dreaded by the sailor in tropical seas, are believed to be nothing
more than a mass of stony skeletons belonging to the minute marine
animalcules known among zoologists as Polyps or Zoophytes. These
little creatures, existing together in countless multitudes, extract
carbonate of lime from the waters of the ocean in which they dwell, and
by the action of their living organs, convert it into a solid frame
or skeleton, which is called coral. From generation to generation the
same process has been going on during the long succession of Geological
ages; and huge masses of coral rock, hundreds of miles in length, have
thus been slowly built up from fathomless depths of the ocean to within
a few feet of its surface. Our vast coal formations, on the other hand,
afford a ready example of rocks which are chiefly composed of vegetable
remains.
So much for the Aqueous or Stratified Rocks. Geology next brings before
us another and a very different group, of which the origin is ascribed
to fire, and which are consequently designated by the title of Igneous
Rocks. In their general appearance they are chiefly distinguished
from the former by the absence of regular stratification; but they
are, nevertheless, intersected by numerous planes of division, or
joints, as they are called, and thus divided into blocks of various
size and form. Geologists believe that these rocks were at one time
reduced to a molten state by the action of intense heat, and afterward
allowed slowly to cool and to crystallize. They are divided into two
classes, the Plutonic and the Volcanic. The Plutonic Rocks are chiefly
granite of some kind or another; and though they now often appear at
the surface, they are supposed to have been produced originally at
a considerable depth within the crust of the Earth, “or sometimes,
perhaps, under a certain weight of incumbent ocean.”[14] The Volcanic
Rocks have been formed at or near the surface of the Earth, and, as the
name implies, they are usually ejected, in a state of fusion, from the
fissures of an active volcano; though not unfrequently they assume the
more imposing form of basaltic columns, as at the Giant’s Causeway in
Ireland, or on the island of Staffa near the coast of Argyleshire in
Scotland.
One group of rocks yet remains to be noticed. They have been called
by various names at different times, but are now generally designated
by the term Metamorphic. In some respects they resemble the Aqueous
Rocks, while, in others, they are more nearly allied to the Igneous.
Like the former, they are stratified in their outward arrangement;
like the latter, they are more or less crystalline in their internal
texture. As to their origin, we are told that they were first deposited
under water, like the Aqueous Rocks, and that afterward their internal
structure was altered by the agency of subterranean heat. Hence the
name Metamorphic, first suggested by Sir Charles Lyell, which conveys
the idea that these rocks have undergone a _change of form_. To this
group belong many varieties of slate, and also the far-famed statuary
marble of Italy.
Our readers will perceive from this brief outline that, if we follow
the theory of Geologists, the rocks which compose the Crust of the
Earth may be conveniently divided, according to their origin, into
three leading groups, the Aqueous, the Igneous, and the Metamorphic.
The Aqueous are formed under water, either by the mechanical force of
the water itself when in motion, or by the agency of chemical laws,
or by the intervention of organic life. Hence they are naturally
subdivided into three classes, the Mechanical, the Chemical, the
Organic. The Igneous Rocks are produced by heat, being first melted
and then allowed to cool. When this process takes place under great
pressure in the depths of the Earth, the result is granite; and the
granite Rocks are called Plutonic: when near the surface, through the
agency of a volcano, the Rocks so formed are called Volcanic. Lastly,
the Metamorphic Rocks are nothing else than Aqueous Rocks, of which the
texture has been altered by the action of intense heat.
As regards the relative order of position amongst these various classes
of rocks, the lowest place seems uniformly to belong to the granitic or
Plutonic group. It is true that the granite will often appear at the
surface of the Earth; but wherever there is a series of rocks piled one
above the other, the granite will always be the lowest. This assertion
is based on two broad facts; first, whenever we get to the bottom
of the other rocks, they are always found to rest on granite; and
secondly, no other rock has ever yet been found beneath it. From this
circumstance granite is conceived to be the solid foundation of the
Earth’s Crust, and so is often called fundamental granite. Above the
granite the Aqueous Rocks have been slowly spread out layer by layer
during the long lapse of ages, now in this part of the world, now in
that, according as each in its turn was exposed to the action of water.
The Volcanic Rocks do not occur in any fixed order of succession. They
are distributed irregularly over almost every country of the globe,
occurring sometimes in the form of cone-shaped mountains, sometimes in
the form of stately pillars, and sometimes in the form of massive solid
walls, called Dykes, forced right through the softer Aqueous Rocks,
which were deposited on the surface of the Earth before the eruption.
As to the Metamorphic Rocks, which are supposed to owe their peculiar
character to the contact of molten mineral matter, wherever they occur,
they are found in the immediate neighborhood of some Igneous Rock.
The condition of the Earth beneath its thin external crust has never
been the subject of direct observation; for Geologists have never yet
been able to penetrate below the granite rocks. Nevertheless, this
subject has been often discussed, and has offered a wide field for
philosophical speculation. Upon one point all are agreed, that within
the Crust of the Earth an intense heat very generally prevails;--a heat
so intense that it would be quite sufficient, acting under ordinary
circumstances, to reduce all known rocks to a state of igneous fusion.
Hence it was a common opinion among the older Geologists that the
condition of our globe is that of a vast central nucleus composed of
molten mineral, and covered over with a comparatively thin external
shell of solid rock. The most eminent Geologists, however, of the
present day, hesitate to accept this opinion. They observe: (1) That
we have not yet learned what the material is of which the interior
of the Earth is composed; therefore we cannot tell for certain what
degree of heat is sufficient to reduce that material to a liquid state.
(2) It is uncertain how far the immense pressure at great depths may
operate to keep matter in a solid state, even when raised to a very
high degree of temperature. (3) There are certain astronomical and
physical difficulties involved in this theory, which have not yet been
fully cleared up. Modern Geologists, therefore, proceeding with more
caution than their predecessors, while they regard the opinion as
probable, refuse to set it down as conclusively demonstrated. But, that
a very high temperature prevails in the interior of our globe, is a
conclusion, they say, which is established by abundant evidence, and
which may be regarded as morally certain.
It may be asked how the various strata of Aqueous Rocks, which
constitute the chief portion of the Earth’s Crust, have been lifted up
above the level of the sea; for, according to our theory, they were all
first deposited under water. This is a question that must inevitably
occur to the mind of every reader, and Geologists are ready with an
answer. They tell us that from the earliest ages the Crust of the Earth
has been subject to disturbance and dislocation. At various times and
in various places it was upheaved, and what had been before the bed of
the ocean became dry land; again it sunk below its former level, and
what had been before dry land became the bed of the ocean. Thus, in the
former case a new stratum which had been deposited at the bottom of the
sea, with all its varied remains of a bygone age, was converted for a
season into the surface of the Earth, and became the theatre of animal
and vegetable life: while in the latter case, the old surface of the
Earth with its countless tribes of animals and plants,--its _fauna_
and _flora_ as they are called,--was submerged beneath the waters,
there to receive in its turn the broken up fragments of a former
world, deposited in the form of mud, or sand, or pebbles, or minute
particles of lime. Nor is this all; it is but a single link in the
chain of Geological chronology. We are asked to believe that, in many
parts of the globe, this upward and downward movement has been going on
alternately for unnumbered ages; so that the very same spot which was
first the bed of the ocean, was afterward dry land, then the bottom of
an estuary or inland lake, then perhaps once more the floor of the sea,
and then dry land again: and furthermore we are assured that, while
it remained in each one of these various conditions, thousands and
thousands of years may have rolled away.
But from what source does that mighty power come which can thus upheave
the solid Earth, and banish the ocean from its bed? We are told in
reply that this giant power dwells in the interior of the Earth
itself, and is no other than the subterranean heat of which we have
already spoken. This vast internal fire acts with unequal force upon
different parts of the shell or Crust of the Earth, uplifting it in
one place, and in another allowing it to subside. Now it is violent
and convulsive, bursting asunder the solid rocks, and shaking the
foundations of the hills: again it is gentle and harmless, upheaving
vast continents with a scarcely perceptible undulation, not unlike the
long, silent swell of the ocean. So it has been from the beginning,
and so it is found to be even now, in this last age of the Geological
Calendar. For even within historic times mountains have been suddenly
upheaved from the level plain; and many parts of the Earth’s Crust have
been subject to a slow, wave-like movement, rising here and subsiding
there, at the rate of perhaps a few feet in a century. Sometimes,
too, the fiery liquid itself has burst its barriers, and poured its
destructive streams of molten rock far down into the peaceful, smiling
valleys.
This theory of an internal disturbing force, which from time to time
produces elevations and depressions of the Earth’s Crust, serves to
explain another phenomenon, that cannot fail to have struck even the
least observant eye. The Aqueous Rocks of mechanical formation are
said to have been composed of minute fragments, which were first held
suspended in water, and afterward fell to the bottom. If this be true,
it follows that these rocks, in the first period of their existence,
must have been arranged in beds parallel to the horizon, or nearly
so. But we now find them, as everybody knows, in a great variety
of positions: sometimes they are parallel to the horizon, sometimes
inclined to it, sometimes at right angles to it; sometimes, too, they
are broken right across, sometimes curved and twisted after a very
fantastic fashion. Now, all these appearances are the natural results
of an upheaving force acting irregularly from below on the solid shell
of the Earth. When the subterranean fire is brought to bear equally at
the same time on a broad extent of surface, then the overlying strata
are bodily lifted up, and preserve their horizontal position. But when
the whole force acts with local intensity on a very contracted area,
then, at that particular spot, the rocks above will be tilted up, and
their position entirely changed. Sometimes they will be only bent and
crushed together, sometimes dislocated and turned over; sometimes,
perhaps, a mountain will be formed, and the rocks before parallel
to the horizon, will afterward remain parallel to the slopes of the
mountain.
There is another process known by the name of Denudation, which we
cannot pass over in silence, for it occupies a very important place in
the Natural History of our globe. Since time first began Denudation
has been ever going on at the surface of the Earth, and it has left
its mark more or less distinctly upon every group of rocks, from the
lowest to the highest. It includes all the various operations by which
the old existing rocks are broken up into fragments, or ground into
powder, or worn away by friction, or dissolved by chemical action,
and then transported from their former site to become the elements
of new strata. Hence the name Denudation; since by these operations
the former surface of the Earth is carried away and a surface before
covered is _laid bare_. The amount of destruction effected by this
process in each successive age is always equal to the bulk of Aqueous
Rocks formed within the same time. This will be at once understood
when we remember that the Aqueous Rocks are produced, for the most
part, by the deposition of sediment; and sediment is nothing else than
the fragments, more or less minute, of pre-existing rocks. What is
deposited on the bed of the ocean has been taken from the surface of
the land; and the new strata are built up from the ruins of the old.
When we see a great building of stone towering aloft to the sky, we
are certain that somewhere else on the Earth a quarry has been opened,
and that the amount of excavation in the quarry is exactly represented
by the bulk of solid masonry in the building. Just in the same way,
the mass of Aqueous Rocks is at once the monument and the measure of
previous Denudation.
The process of Denudation is the work of many and various natural
causes. Heat and cold, rain, hail, and snow, chemical affinities,
the atmosphere itself, all have a share in it; but the largest share
belongs to the mechanical action of moving water. Every little rill
that flows down the mountain side is charged with finely-powdered
sediment which it is ever wearing away from the surface of its own
bed. Every great stream, besides the immense quantities of mud and
sand which in times of flood it carries along in its turbulent course,
has its channel strewn over with pebbles at which it never ceases to
work, rounding off the angles and polishing the surfaces; and these
pebbles, what are they but the fragments of old rocks and the elements
of new,--the rubble-stone of Nature’s edifice on its way from the
quarry to the building? Then there are those mighty rivers, such as the
Amazon, the Orinoco, the Mississippi, the Nile, the Ganges, discharging
into the sea day by day their vast freight of mineral matter, millions
of cubic feet in bulk, and thousands upon thousands of tons in weight.
Often this ponderous volume of mud or sand is carried far out to sea by
the action of currents, but sometimes it is deposited near the shore,
forming what is called a Delta, and exhibiting an admirable example
of stratified rock in the earliest stage of its existence. Lastly, we
have to notice the giant power of the great ocean itself, acting with
untiring energies on the coasts of continents and islands all over the
world, excavating and undermining cliffs, rolling huge rocks hither and
thither, and spreading out the divided fragments in a new order at the
bottom of the sea.
To apprehend fully the magnitude of the effects which may fairly be
ascribed to this last-mentioned power, we must remember that, according
to Geological theory, almost every portion of the Earth’s Crust has
been more than once lifted up above the surface of the ocean, and
afterward depressed below it. It is believed that this alternate
rising and sinking was effected very often, perhaps most commonly,
not by sudden convulsions, but rather by slow or gradual movements.
Now, during this process, as the land was emerging from the waters
or sinking beneath them, new surfaces would be presented in each
succeeding century to the force of the ocean currents and the erosive
action of the breakers; and it is not difficult to conceive that the
accumulated ruins produced, in a long lapse of time, by destructive
agents so powerful, so untiring, so universal, may have readily
furnished the materials for a very large proportion of the Aqueous
Rocks now in existence.
Hitherto we have considered the Crust of the Earth as a great structure
slowly reared up by the hand of Nature; we have spoken of the Rocks
that compose it, of their origin and history, of the order in which
they are disposed, and of the various agencies that have been at
work to mould them into their present form and feature. We have now
to contemplate this marvellous structure under a new aspect; for we
are told by Geologists that it is a vast sepulchre, within which lie
entombed the remains of life that has long since passed away. Each
series of strata is but a new range of tombs; and each tomb has a story
of its own. Here a gigantic monster is disclosed to view, compared
to which the largest beast that now roams through the forest is puny
in form and contemptible in strength: there, within a narrow space,
millions of minute animal frames are found closely compacted together,
each so small that its existence can be detected only by the aid of
a powerful microscope. In one place whole skeletons are found almost
entire, embedded in the bosom of the solid rock; in another, we have a
boundless profusion of bones and shells; and again in another, neither
the skeleton itself appears, nor yet its scattered bones, but simply
the imprint of footsteps once left upon the sandy beach, and still
remaining engraved on the stone into which the fine sand has been
converted chiefly by the agency of pressure. There is no scarcity of
relics in this wonderful charnel-house of Nature. For half a century
the work of plunder has been going on without relaxation or remorse;
the tombs have been yielding up their dead; every city in the civilized
world has filled its museums, and the cabinets of private collectors
are overflowing: but the spoils that have hitherto been carried away
seem to bear a very small proportion to those which yet remain behind.
These remains of animals and plants embedded in the Crust of the
Earth are called Fossils; and Geologists maintain that the Fossils
preserved in each group of strata represent the animals and plants
that flourished on the surface of the Earth, or in the waters of the
ocean, when that group of strata was in process of formation. There
they lived, and there they died, and there they were buried, in the
sand, or the shingle, or the mud that came down from the waters above.
Their descendants, however, still lived on, and new forms of life were
called into being by the voice of the Omnipotent Creator, making, as
it were, a connecting link between the new age of the world that was
coming in and the old one that was passing away. But they, too, died
and found a tomb beneath the waters; for Nature, with unexhausted
energies, was still busy collecting materials from the old rocks, and
building up the new. And so that age passed away like the former, and
another came; and every age was represented by its own group of strata;
and each group of strata was, in its turn, covered over with a new
deposit; and the tombs were all sealed up, with their countless legions
of dead, their massive monuments of stone, their strange hieroglyphic
inscriptions. At length came the last stage of the world’s history, and
man appeared upon the scene; and it is his privilege to descend into
this wonderful sepulchre, and to wander about amidst the monuments, and
to strive to read the inscriptions. In our own days more especially,
eager and enthusiastic students are abroad over the whole face of the
globe, and are gathering together from every country the Fossil Remains
of extinct worlds. By the aid of Natural History they seek to assign to
each its own proper place in the ranks of creation; to trace the rise,
the progress, and the extinction of every species in its turn; and even
to describe the nature and the character of all the various forms of
life that have dwelt upon the Earth from the beginning.
Such is the theory of Geology as expounded at the present day by its
most able and popular advocates. We have passed over a multitude of
minor details that we might not weary our readers, and we have kept
aloof from disputed points that we might not get entangled in a purely
scientific controversy. Our object has simply been to gather together
into a systematic form those more general conclusions which, however
startling they may seem to practical men of the world, and even to many
of those whose minds have been accustomed to the pursuit of science
in other departments, are nevertheless regarded as certain by all
who have devoted their lives to the study of Geology. It now remains
to investigate the facts on which these conclusions are based, and
to consider the line of argument by which so many able and earnest
men have been led to accept them. In this vast field of inquiry we
shall chiefly direct our attention to those points that bear upon the
Antiquity of the Earth; and in attempting to bring home to our readers
the nature and the force of Geological reasoning, we shall confine
ourselves altogether to simple and familiar illustrations.
[Illustration]
[Illustration]
_CHAPTER II._
THEORY OF DENUDATION ILLUSTRATED BY FACTS.
_Principle of reasoning common to all the physical sciences--This
principle applicable to Geology--Carbonic acid an agent
of denudation--Vast quantity of lime dissolved by the
waters of the Rhine and borne away to the German ocean--Disintegration
of rocks by frost--Professor Tyndall on the
Matterhorn--Running water--Its erosive power--An active
and unceasing agent of denudation--Mineral sediment carried
out to sea by the Ganges and other great rivers--Solid
rocks undermined and worn away--Falls of the Clyde at
Lanark--Excavating power of rivers in Auvergne and
Sicily--Falls of Niagara--Transporting power of running
water--Floods in Scotland--Inundation in the valley of
Bagnes in Switzerland._
In the physical sciences it is a common principle of reasoning to
account for the phenomena that come before us in nature, by the
operation of natural causes which we know to exist. Nay, this principle
seems to be almost an instinct of our nature, which guides even the
least philosophical amidst us, in the common affairs of life. When we
stand amongst the ruins of an ancient castle, we feel quite certain
that we have before us, not alone the monument of Time’s destroying
power, but also the monument of human skill and labor in days gone
by. We entertain no doubt that ages ago the sound of the mason’s
hammer was heard upon these walls, now crowned with ivy; that these
moss-grown stones were once hewn fresh in the quarry, and piled up one
upon another by human hands; and that the building itself was designed
by human skill, and intended for the purposes of human habitation and
defence. Or, if we see a footprint in the sand, we conclude that a
living foot has been there; and from the character of the traces it has
left, we judge what was the species of animal to which it belonged,
whether man, or bird, or beast. It is true that God is Omnipotent.
He might, if it had so pleased Him, have built the old castle at the
creation of the world, and allowed it to crumble slowly into ruins: or
he might have built it yesterday, and made a ruin begin to be where no
castle had stood before; and covered the stones with moss, and mantled
the walls in ivy. And as to the footprint in the sand, it were as easy
for Him to make the impress there, as to make the foot that left the
impress. All this is true: but yet if any one were to argue in this
style against us, he would fail to shake our convictions; we should
still unhesitatingly believe that human hands once built the castle,
and that a living foot once trod the shore.
Now, this principle of reasoning is the foundation on which the ablest
modern Geologists claim to build their science. The untiring hand of
Nature is ever busy around us: they ask us to come and look at her
works, and to judge of what she has done in past ages, by that which
she is now doing before our eyes. She is still, they say, building
up her strata all over the globe, of limestone, and sandstone, and
clay; she is still lifting up in one place the bed of the ocean, and
in another submerging the dry land; she is still bursting open the
Crust of the Earth by the action of internal fire, disturbing and
tilting up the horizontal strata; she is still upheaving her mountains
and scooping out her valleys. All these operations are open to our
inspection; we may go forth and study them for ourselves; we may
examine the works that are wrought, and we may discover, too, the
causes by which they are produced. And if it should appear that a very
close analogy exists between these works that are now coming into
existence, and the long series of works that are piled up in the Crust
of the Earth, it is surely not unreasonable to refer the latter class
of phenomena to the action of the same natural causes which we know to
have produced the former.
It cannot be denied that this argument is deserving of a fair and
candid consideration. Let us proceed, then, to examine how far it is
founded on fact, and how far it can be justly applied to the various
heads of Geological theory. We will commence with the origin and
history of Stratified Rocks; for this constitutes, in a manner, the
framework on which the whole system of Geology is supported and held
together. It is alleged that the elements of which Stratified Rocks are
composed are but the broken fragments and minute atoms of pre-existing
rocks, carried off by the agents of Denudation, and spread out over
some distant area in regular beds or layers; which, in progress of
ages, were slowly consolidated into rocks of various quality and
texture. With the view of testing this theory by the light of the
principle just explained, we purpose, in the first place, to exhibit
some examples of the many forms in which the process of Denudation
is going on at the present day all over the world; and afterward, to
show that out of the materials thus obtained Stratified Rocks of every
description--Mechanical, Chemical, Organic--are being regularly built
up in sundry places; and that these correspond in every essential
feature with the Stratified Rocks in the Crust of the Earth.
Among the chemical agents of Denudation, there is none more widely
diffused than Carbonic acid gas. It is everywhere given out by dead
animal and vegetable matter during the process of putrefaction; it is
plentifully evolved from springs in every country; and it is emitted
in enormous quantities from the earth in all volcanic districts, as
well those in which the volcanoes are now extinct as those in which
they are active. Now, it is well known from observation, that carbonic
acid has the property of decomposing many of the hardest rocks,
especially those in which felspar is an ingredient. This phenomenon
is exhibited on a large scale in the ancient volcanic district of
Auvergne, in central France. The carbonic acid, which is abundantly
evolved from the earth, penetrates the crevices and pores of the solid
granite, which being unable to resist its decomposing action, is
rapidly crumbling to pieces. This mysterious decay of hard rock has
been happily called by Dolomieu, “la maladie du granite.”[15]
Again, all the water which flows over the surface of the land is highly
charged with carbonic acid. The rain imbibes it in falling through the
atmosphere; and the rivers receive still further accessions from the
earth as they pursue their course to the sea. In this combination we
discover a powerful agent of Denudation; for limestone rock will be
dissolved by water which is impregnated with carbonic acid. Thus all
the rivers and streams in the world, when they flow through a limestone
channel, are constantly dissolving the solid rock and bearing away the
elements of which it is composed. A single example will be sufficient
to show the magnitude of the results which are thus produced. It has
been calculated by Bischof, a celebrated German chemist, that the
carbonate of lime which is carried each year to the sea by the waters
of the Rhine, is sufficient for the formation of 32,000,000,000 of
oyster shells; or, to view the matter in another light, it would be
sufficient to produce a stratum of limestone one foot thick, and four
square miles in extent.[16] If such be the yearly produce of one
river, how great must be the accumulated effects of all the rivers in
the world since our planet first came from the hand of its Creator!
Passing from the chemical to the mechanical agents of Denudation, it
is worth while to notice the immense power which is often generated by
the agency of frost, especially in those countries that are subject to
great vicissitudes of heat and cold. During a thaw, water finds its way
into the clefts and joints by which all rocks are traversed, and when
it is afterward converted into ice, it expands with a mechanical force
that is almost irresistible. The hardest rocks are burst asunder, great
blocks are detached from the mountain side, and sent rolling down its
slopes, or tumbling over crags and precipices, until at length they
come to rest in shattered fragments at the bottom of the valley. In
this condition they await but the coming of the winter’s torrent to be
borne still further on their long journey to the sea.
The fearful havoc done in this way by the alternate action of sun and
frost contributes in no small degree to the fantastic and picturesque
forms assumed by the mountain peaks of Switzerland. Huge masses of
rock have been literally hewn away, until nothing has remained behind
but those splintered obelisks and tapering pinnacles so familiar to
the eye amidst the sublime scenery of the Alps. Indeed one of the
greatest perils encountered by the adventurous spirits whose ambition
it is to rival one another in the danger of their exploits, and to
climb whatever was before regarded as inaccessible, arises from the
enormous fragments of rock which are rent almost unceasingly from the
overhanging crags and hurled into the abysses below them. The following
incident related by Professor Tyndall is very much to the point. “We
had gathered up our things, and bent to the work before us, when
suddenly an explosion occurred overhead. Looking aloft, in mid-air was
seen a solid shot from the Matterhorn describing its proper parabola
through the air. It split to pieces as it hit one of the rock-towers
below, and its fragments came down in a kind of spray, which fell wide
of us, but still near enough to compel a sharp look out. Two or three
such explosions occurred afterward, but we crept along the back fin of
the mountain, from which the falling boulders were speedily deflected
right and left.”
This occurred in 1862, on the occasion of an unsuccessful attempt
to reach the highest peak of the Matterhorn. Six years later, when
Professor Tyndall at length actually accomplished the object on which
he seems to have set his heart, he found the work of destruction
still going on. “We were now,” he says in his narrative, “beside a
snow-gully, which was cut by a deep furrow along its centre, and
otherwise scarred by the descent of stones. Here each man arranged his
bundle and himself so as to cross the gully in the minimum of time. The
passage was safely made, a few flying shingle only coming down upon us.
But danger declared itself where it was not expected. Joseph Maquignas
led the way up the rocks. I was next, Pierre Maquignas next, and last
of all the porters. Suddenly a yell issued from the leader: ‘Cachez
vous!’ I crouched instinctively against the rock, which formed a by no
means perfect shelter, when a boulder buzzed past me through the air,
smote the rocks below me, and with a savage hum flew down to the lower
glacier.”[17]
Even in our own country, every one is familiar with the efficacy of
frozen water in producing landslips. The rain which soaks into the
ground in winter, is converted into ice when frost sets in; and upon
steep slopes or precipices, its expansive power bursts open the earth,
and causes large masses of stones and clay to tumble headlong to the
bottom.
But moving water constitutes the most powerful, and, at the same
time, the most universal agent of Denudation. And it is chiefly to the
effects of moving water that we mean to direct attention; because its
action is more striking to the eye, and more easily understood by the
general reader. Every one is aware that the waters of the ocean are
constantly passing off by evaporation into the higher regions of the
atmosphere, and are there condensed into clouds. These clouds in course
of time descend upon all parts of the earth, but especially on the high
and mountainous districts. Then rivulets are formed which flow smoothly
down the gentle slopes of the undulating country, or plunge headlong
over the rocky mountain cliffs; and the rivulets uniting form streams,
and the streams, receiving new tributaries as they advance, become
rivers; and the rivers flow on to the sea, and discharge each day and
each hour their enormous volumes of water back again into the ocean
from which they came. Thus all the water of the world is constantly
in motion, ever hurrying on, as it were, in one unending round of
duty. This is the teaching of daily experience and observation. And
we may add, it is the teaching of Sacred Scripture as well. The Wise
Man said long ago: “All the rivers run into the sea, yet the sea doth
not overflow: unto the place from whence the rivers come, thither they
return to flow again.”[18]
Now, the power of this moving water is a mighty wide-spread agent of
change in the physical condition of the globe. For wherever water is in
motion over the surface of the land, whether it be a rippling stream,
or a mountain torrent, or a majestic river, it is surely wearing away
the channel through which it flows, and carrying along in its course
particles of clay, or sand, or gravel. This subject is illustrated with
great force and great simplicity by Mr. Page. “Every person,” he says,
“must have observed the rivers in his own district, how they become
muddy and turbid during floods of rain, and how their swollen currents
eat away the banks, deepen the channels, and sweep away the sand and
gravel down to some lower level. And if, during this turbid state, he
will have the curiosity to lift a gallon of the water, and allow it
to settle, he will be astonished at the amount of sediment or solid
matter that falls to the bottom. Now, let him multiply this gallon by
the number of gallons daily carried down by the river, and this day
by years and centuries, and he will arrive at some faint idea of the
quantity of matter worn from the land by rivers, and deposited by them
in the ocean. In the same way as one river grinds and cuts for itself a
channel, so does every stream and rill and current of water. The rain
as it falls washes away what the winds and frosts have loosened; the
rill takes it up, and, mingling it with its own burden, gives it to the
stream; the stream takes it up and carries it to the river, and the
river bears it to the ocean.”[19]
When the current is feeble, the greater part of this earthy material is
thrown down upon the way, and forms a stratum of alluvial soil in the
bed of the river, and also in the adjoining lowlands, during the time
of temporary floods. But when several streams unite, then the carrying
power of the current is enormously increased: huge stones are rolled
along, and dashed one against another, and broken into fragments, and
the fragments are rounded by friction, and become pebbles, and the
pebbles become gravel, and the gravel, mud; and the mud is carried on
to the mouth of the river, and there falling to the bottom, it forms a
tongue of land which is called a delta; or else perhaps it chances to
meet with some great ocean current, and then it begins a new journey,
and is borne far away to be deposited in the profound and tranquil
depths of the sea. It is not, however, mineral matter alone that is
transported by the action of rivers. Trees that once were growing on
the banks of the stream, and the bones of animals, and human remains,
and works of art, are seen floating down with the current, and are
found embedded in the sand and mud of the delta at the river’s mouth.
These are some of the actual realities which all may witness, who will
go and study for themselves the history of this wonderful element,
from the time when it first soars aloft as vapor to the sky, until it
returns to the bosom of its parent ocean laden with the spoils of the
land. To some of our readers, perhaps, results of this kind may appear
insignificant, when considered in relation to the enormous bulk of the
stratified rocks. But it should be remembered that the force of which
we speak is unceasing in its operation over the whole surface of the
earth; and even though the work were small which is accomplished in
each successive year, the accumulated effects produced in a lengthened
period of time must be immensely great. Besides, it would be a very
serious error to form our ideas on this subject, as many would seem to
do, from the examples which are to be found within the narrow limits of
our own island. We should rather seek for our illustrations among those
mighty rivers that drain the vast continents of the world, and exhibit
the erosive and transporting power of running water on the grandest
scale.
It happens, fortunately for our purpose, that an attempt has been
made by scientific men to compute the amount of matter discharged
into the sea, by some particular rivers within a given time. For such
a computation it is necessary, in the first place, to calculate the
volume of water that passes down the channel during that time; and
then, by repeated experiments, to ascertain the average proportion of
earthy matter which is held suspended in the water. This has been done
with the greatest care by the Rev. Mr. Everest, in the case of the
river Ganges; and it appears that during the rainy season, which lasts
four months every year, from June to September, about 6,000,000,000
cubic feet of mud are carried along by the stream past the town of
Ghazepoor, near which the observations were made. Now this enormous
bulk of mineral matter would be sufficient to form a stratum of rock
one foot in height, and two hundred and eighteen square miles in
extent. Or, to adopt the computation of Sir Charles Lyell, the amount
which passes by every day is equal to that which might be transported
by 2000 Indiamen, each freighted with a cargo of mud 1400 tons in
weight. And it is important to remember that this estimate represents
but a portion of the sediment which passes into the sea through the
channel of the Ganges; for the observations of Mr. Everest were taken
at a point which is 500 miles from the sea, and at which the river has
not yet received the contributions of its largest tributaries.
We are able, therefore, with some degree of confidence, to estimate
the amount of Denudation which is every year effected by the Ganges.
And, although the same calculations have not yet been applied with
equal care to other great rivers, there is no reason to suppose that
the Ganges is an exception. It is asserted on good grounds that the
Brahmapootra, which unites with the Ganges close to the Bay of Bengal,
carries with it an equal amount of earthy sediment. According to Sir
Charles Lyell, the quantity of solid matter brought down each year by
the Mississippi amounts to 3,702,758,400 cubic feet. And it is said
that 48,000,000 cubic feet of earth are _daily_ discharged into the sea
by the Yellow River in China, called by the natives the Hoang Ho.[20]
Thus year after year the waste of the land is carried away by rivers,
to be spread out over wide areas of the ocean, and perhaps to furnish
the materials of future continents.
The effects of running water in wearing away and transporting masses
of solid rock are not less deserving of our notice. Every one who has
followed the course of a great river when it flows through a rocky
channel, must have observed large blocks projecting from the cliffs
above, which, having been undermined by the action of the water, seem
ready to tumble headlong into the stream; and others lying below, which
had fallen before; and others again which had been already carried a
considerable distance by the winter’s torrent. Even where the rocks
are not displaced, they are gradually being worn away, partly by the
friction of the water, but much more by the grinding action of the
gravel which the water holds in suspension. Not only is the surface of
the rocks thus rounded and polished, but large circular pits, called
_pot-holes_, are formed by the whirling waters of an eddy carrying
round and round a few grains of hard sand.
At the falls of the Clyde near Lanark in Scotland, these various
phenomena may be seen to great advantage. Good illustrations are to
be found also in many volcanic regions. Some of the larger streams in
Auvergne have in course of time forced their way through the solid lava
rock, cutting out for themselves channels broad and deep. In Sicily
too, we are told, the river Simeto, whose course was blocked up by a
current of lava about the beginning of the seventeenth century, has
since that time eaten its way through this compact and hardened mass,
and now flows on to the sea through a rocky passage forty feet in depth
and from fifty to several hundred feet in width.[21]
But there is no part of the world yet explored where these effects
are exhibited on the same gigantic scale as at the far-famed Falls
of Niagara. The massive limestone rock from which the waters are
precipitated is slowly but certainly disappearing. An enormous volume
of water, more than a third of a mile in breadth, plunges in a single
bound over a sheer precipice of one hundred and sixty-five feet. The
soft slaty rocks upon which the limestone rests are soon eaten away
by the action of the spray which rises from the pool below; and then
the overhanging cliffs, left without any support, topple over, and
are carried off by the torrent. The position of the Falls, therefore,
is not stationary, but is receding by very sensible degrees in the
direction of Lake Erie, from which the river flows. Speaking of this
phenomenon, Sir Charles Lyell observes with much show of reason: “The
idea 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.”[22]
With a view to enable our readers to understand more fully the
prodigious force which rivers have been known to exert in the
transportation of rocks, it may be useful to draw attention to one or
two principles of physical science. First, we have the well-known law
of Archimedes, that _a solid body immersed in a liquid loses a part
of its weight equal to the weight of the liquid displaced_. Now solid
rock as compared with water, bulk for bulk, is rarely more than three
times, and often not more than twice as heavy. Consequently, according
to this law, almost all rocks will lose a third of their weight, and
many will lose one-half, when immersed in water. Again, it has been
established that _the power of water to move bodies that are in it
increases as the sixth power of the velocity of the current_. Hence,
if the velocity of a current is increased _two-fold_, its moving power
will be increased _sixty-four fold_; if the velocity is increased
_three-fold_, the moving power will be increased _seven hundred and
twenty fold_; and so on.
From these principles it follows, first, that a much smaller power is
required to move a block of stone lying in the bed of a river, than if
it were lying on the surface of the land; and secondly, that a very
slight increase in the velocity of a current effects a very great
increase in its moving power. We need not wonder, then, when we hear of
the enormous masses of rocks and trees and mason-work which are carried
away even by small rivers in times of flood.[23]
Here are a few examples. In August, 1829, a fragment of sandstone,
fourteen feet long, three feet wide, and one foot thick, was carried
by the river Nairn, in Scotland, a distance of two hundred yards. On
the same occasion the river Dee swept away a bridge of five arches,
built of solid granite, which had stood uninjured for twenty years;
the whole mass of masonry sunk into the bed of the stream and was
seen no more. And the river Don, as we are assured on the authority
of Mr. Farquharson, forced a mass of stones four or five hundred
tons in weight up a steep inclined plane, leaving them in a great
rectangular heap on the summit. A small rivulet called the College, in
Northumberland, when swollen by a flood in August, 1827, “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.”[24] But it is needless to multiply examples of
phenomena which are occurring every day around us, and of which many
among our readers have probably been eye-witnesses.
The transporting power of rivers must not always be estimated by the
bulk and velocity of the current; for it is often greatly increased by
some accidental obstruction, which for a time blocks up the channel
through which the river flows. An instructive illustration is afforded
by the river Dranse, which flows through the valley of Bagnes, in
Switzerland, and empties itself into the Rhone above the lake of
Geneva. In the year 1818 the avalanches which fell down from the
mountain side formed a barrier across the valley, and thus effectually
blocked up the course of the stream. The upper part of the valley was,
in consequence, soon converted into a lake which gradually increased in
size as the season advanced. When summer came, and the melting of the
snows began, the ice barrier suddenly gave way with a tremendous crash,
and the lake was emptied in half an hour. The mass of water, thus in
a moment disengaged, burst with destructive violence over the lower
valley, sweeping away rocks, forests, houses, bridges, and cultivated
lands. Thousands of trees were torn up by the roots, fragments of
granite as large as houses were rolled along, and the whole flood
presented the appearance of a moving mass of ruins.
[Illustration]
[Illustration]
_CHAPTER III._
THEORY OF DENUDATION--FURTHER ILLUSTRATIONS.
_The breakers of the ocean--Caverns and fairy bridges
of Kilkee--Italy and Sicily--The Shetland Islands--East
and south coast of Britain--Tracts of land swallowed up
by the sea--Island of Heligoland--Northstrand--Tides and
currents--South Atlantic current--Equatorial current--The Gulf
Stream--Its course described--Examples of its power as an agent
of transport._
While the rain, the rivers, and the streams, are thus wasting away
the mountains and plains of the interior country, the waves of the
sea are exerting a power no less destructive on the coasts of islands
and of continents. The breakers dashing against the foot of a lofty
cliff, dissolve and decompose and wear away the lower strata; and
the overhanging rocks, thus undermined, fall down in course of time
by their own weight. With the next returning wave these rocks are
themselves hurled back against the cliff; and so, as some one has
happily remarked, the land would seem to supply a powerful artillery
for its own destruction. The effects of the breakers are often very
unequal, even on the same line of cliffs. Some parts of the rock are
more yielding than others, or perhaps they are more exposed to the
action of the waves, or perhaps they are divided by larger joints and
more freely admit the destructive element. These parts will be the
first to give way, while the harder and less exposed rock will be left
standing: and in this way forms the most capricious and fantastic are
produced.
No finer examples could be wished for than those which are seen in the
neighborhood of Kilkee, and along the promontory of Loop Head, in the
county of Clare. Sometimes the ground is undermined with caverns, into
which, when the tide is coming in, the waves of the Atlantic rush with
resistless force, making new additions each day to the accumulated
ruins of ages. Sometimes lofty pinnacles of rock are left standing in
the midst of the waters, like giant sentinels stationed there by Nature
to guard the coast. In one or two instances these isolated fragments
are connected with the main land by natural arches of rock, which are
called _fairy bridges_ by the people; but more commonly they appear as
rocky islets, and answer exactly to the poet’s description--
“The roaring tides
The passage broke that land from land divides;
And where the lands retired the rushing ocean rides.”
It is interesting to observe in passing, that, in the original verses
of the Æneid, of which these lines are Dryden’s translation, Virgil
has recorded a belief which prevailed in his time, and which, upon
scientific grounds, is now regarded as highly probable by Geologists,
that the island of Sicily had been once connected by land with Italy,
and was separated from it by the action of the waves:
“Hæc loca, vi quondam et vasta convulsa ruina,
Tantum ævi longinqua valet mutare vetustas!
Dissiluisse ferunt, quum protenus utraque tellus
Una foret; venit medio vi pontus et undis
Hesperium Siculo latus abscidit, arvaque et urbes
Litore deductas angusto interluit æsta.”
Æneid, iii., 414-19.
But whatever may be thought of this opinion thus rendered immortal
by the genius of the poet, we shall not stop to discuss its merits.
For in the present stage of our argument, it is our object to deal,
not with vague and uncertain traditions, nor even with philosophical
speculations, but rather with the facts which are actually going on in
nature, and which any one of our readers may examine for himself. With
this object in view, we shall take a few examples from the Eastern and
Southern coasts of Great Britain, which have been carefully explored by
scientific men for the purpose of observing and recording the amount of
destruction accomplished by the waves within recent times.
[Illustration: Fig. 1.--Granitic rocks to the south of Hillswick Ness,
Shetland. From Lyell’s Principles of Geology.]
The Shetland Islands, exposed to the whole fury of the Atlantic,
present many phenomena not unlike those of Kilkee and Loop Head, but
upon a far grander scale. Whole islands have been swept away by the
resistless power of the waters, and of others nothing remains but
massive pillars of hard rock, which have been well described as rising
up “like the ruins of Palmyra in the desert of the ocean.” Passing
to the mainland, it is recorded that in the year 1795 a village in
Kincardineshire was carried away in a single night, and the sea
advanced a hundred and fifty yards inland, where it has ever since
maintained its ground. In England, almost the whole coast of Yorkshire
is undergoing constant dilapidation. On the south side of Flamborough
Head the cliffs are receding at an average rate of two yards and a
quarter in the year, for a distance of thirty-six miles along the
coast. This would amount to a mile since the Norman Conquest, and
to more than two miles since the occupation of York by the Romans.
It is not surprising, therefore, to learn that many spots marked in
the old maps of the country as the sites of towns or villages, are
now sandbanks in the sea. Even places of historic name have not been
spared. The town of Ravenspur, from which, in 1332, Edward Baliol
sailed for the invasion of Scotland, and at which Henry the Fourth
landed in 1399, to claim the throne of England, has long since been
swallowed up by the devouring element.
On the coast of Norfolk it was calculated, at the beginning of the
present century, that the mean loss of the land was something less
than one yard in the year. The inn at Sherringham was built on
this calculation in 1805, and it was expected to stand for seventy
years. But unfortunately the actual advance of the sea exceeded the
calculation. Sir Charles Lyell, who visited this spot in 1829, relates
that during the five preceding years seventeen yards of the cliff had
been swept away, and nothing but a small garden was then left between
the building and the sea. The same distinguished writer tells us that
in the harbor of this town there was at that time water sufficient to
float a frigate where forty-eight years before had stood a cliff fifty
feet in height with houses built upon it. And remarking upon these
facts, he says, that “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.”
In the neighborhood of Dunwich, once the most considerable seaport on
the coast of Suffolk, the cliffs have been wasting away from an early
period of history. “Two tracts of land which had been taxed in the
time of King Edward the Confessor, are mentioned in the Conqueror’s
survey, made but a few years afterward, as having been devoured by the
sea.” And the memory of other losses in the town itself--including a
monastery, several churches, the town-hall, the jail, and many hundred
houses--together with the dates of their occurrence, is faithfully
preserved in authentic records. In 1740 the sea reached the churchyard
of Saint Nicholas and Saint Francis, so that the graves, the coffins,
and the skeletons, were exposed to view on the face of the cliffs.
Since that time the coffins, and the tombstones, and the churchyard
itself, have disappeared beneath the waves. Nothing now remains of this
once flourishing and populous city but the name alone, which is still
attached to a little village of about twenty houses. The spot on which
the Church of Reculver stands, near the mouth of the Thames, was a
mile inland in the reign of Henry the Eighth; in the year 1834 it was
overhanging the sea; and it would long ago have been demolished, but
for an artificial causeway of stones constructed with a view to break
the force of the waves. It is estimated that the land on the northeast
coast of Kent is receding at the rate of about two feet in the year.
The promontory of Beachy Head in Sussex is also rapidly falling away.
In the year 1813 an enormous mass of chalk, three hundred feet in
length and eighty in breadth, came down with a tremendous crash; and
slips of the same kind have often occurred, both before and since.
To these examples from Great Britain we may add one or two from the
German Ocean. Seven islands have completely disappeared within a very
narrow area since the time of Pliny; for he counted twenty-three
between Texel and the mouth of the Eider, whereas now there are but
sixteen. The island of Heligoland, at the mouth of the Elbe, has been
for ages subject to great dilapidation. Within the last five hundred
years three-fourths of it have been carried away; and since 1770 the
fragment that remains has been divided into two parts by a channel
which is at present navigable for large ships. A still more remarkable
instance of destruction effected by the waves of the sea occurred in
the island of Northstrand, on the coast of Schleswig. Previous to the
thirteenth century it was attached to the mainland, forming a part
of the continent of Europe, and was a highly cultivated and populous
district about ten miles long, and from six to eight broad. In the year
1240 it was cut off from the coast of Schleswig by an inroad of the
sea, and it gradually wasted away up to the seventeenth century, when
its entire circumference was sixteen geographical miles. Even then the
industrious inhabitants,--about nine thousand in number,--endeavored to
save what remained of their territory by the erection of lofty dykes;
but on the eleventh of October, 1634, the whole island was overwhelmed
by another invasion of the sea, in which 6000 people perished, and
50,000 head of cattle. Three small islets are all that now remain of
this once fertile district.[25]
The breakers of the ocean receive no small aid in their work of
destruction from the action of tides and currents which co-operate with
the winds to keep the waters of the sea in constant motion. And though
the winds may sleep for a time, the tides and currents are always
actively at work, and never for a moment cease to wear away the land.
But they are even more powerful auxiliaries as agents of transport. If
it were not for them, the ruins which fall from the rocks to-day would
to-morrow form a barrier against the waves, and the work of destruction
would cease. But Nature has ordained it otherwise. When the tide
advances, it rolls the broken fragments toward the land, and when it
recedes, it carries them back to the deep; and so by unceasing friction
these fragments are worn away to pebbles, and then, being more easily
transported, they are carried off to sea and deposited in the bed of
the ocean: or else, perhaps, they are cast up on the sloping shore, to
form what is so familiar to us all under the name of a shingle-beach.
This is a subject on which it is needless to enlarge. Every one
knows that the tides have the power of transporting solid matter;
though most of us, perhaps, do not fully appreciate the magnitude of
their accumulated effects, working as they do with untiring energies
upon the coasts of islands and continents all over the world. It is
not, however, so generally known that the ocean is traversed in all
directions by powerful currents, which, from their regularity, their
permanence, and their extent, have been aptly called the rivers of
the ocean. We do not mean here to inquire into the causes of these
currents, upon which the progress of physical science has thrown
considerable light: neither can we hope to describe even the principal
currents that prevail over the vast tracts of water which constitute
about three-fourths of the entire surface of our globe. We shall
content ourselves with tracing the course of one great system, which
may serve to give some idea of their general character and enormous
power.
This system would seem to have its origin with a stream that flows from
the Indian Ocean toward the southwest, and then doubling the Cape of
Good Hope, turns northward along the African coast. It is here called
the South Atlantic Current. When it encounters the shores of Guinea, it
is diverted to the west, and stretches across the Atlantic, traversing
forty degrees of longitude until it reaches the projecting promontory
of Brazil in South America. In this part of its course it is known as
the Equatorial Current, because it follows pretty nearly the line of
the Equator: it varies in breadth from two hundred to five hundred
miles, and it travels at the mean rate of thirty miles a day, though
sometimes its velocity is increased to seventy or eighty. Next, under
the name of the Guyana Current, it pursues a northwesterly direction,
following the line of the coast; and passing close to the island
of Trinidad, becomes diffused, and almost seems to be lost, in the
Caribbean Sea. Nevertheless, it again issues with renewed energy from
the Gulf of Mexico, and rushing through the Straits of Florida at the
rate of four and five miles an hour, it issues once more into the broad
waters of the Atlantic. From this out it is called the Gulf Stream, and
is well known to all who are concerned in Transatlantic navigation;
for it sensibly accelerates the speed of vessels which are bound from
America to Europe, and sensibly retards those sailing from Europe to
America.
The Gulf Stream, however, does not set out on its Transatlantic voyage
directly that it issues from the Straits of Florida. It keeps at
first a northeasterly course, following the outline of the American
continent, passing by New York and Nova Scotia, and brushing the
southern extremity of the great Newfoundland Bank. Then taking leave
of the land, it sweeps right across the Atlantic. After a time it
seems to divide into two branches, one inclining to the south, and
losing itself among the Azores, the other bending toward the north,
washing the shores of Ireland, Scotland, Norway, and reaching even to
the frozen regions of Spitzbergen. The breadth of the Gulf Stream,
when it issues from the Straits of Florida, is about fifty miles, but
it afterward increases to three hundred. Its color is a dark indigo
blue, which, contrasting sharply with the green waters of the Atlantic,
forms a line of junction distinctly visible for some hundreds of miles:
afterward, when this boundary line is no longer sensible to the eye, it
is easily ascertained by the thermometer; for the temperature of the
Gulf Stream is everywhere from eight to ten degrees higher than that of
the surrounding ocean.[26]
We leave our readers to infer from this brief description how immense
must be the power of transport which belongs to such currents as
these. They sweep along the shores of continents, and carry away the
accumulated fragments of rock, which had first been rent from the
cliffs by the waves of the sea, and then borne out to a little distance
by the tides: they pass by the mouths of great rivers, and receiving
the spoils of many a fertile and populous country, and the ruins of
many an inaccessible mountain ridge, they hurry off to deposit this
vast and varied freight in the deep abysses of the ocean. There is one
circumstance, however, which we ought not to pass over in silence; for
it is of especial importance to the Geologist, and might easily escape
the notice of the general reader. It is a well ascertained fact that
plants and fruits and other objects from the West Indian Islands are
annually washed ashore by the Gulf Stream on the northwestern coasts of
Europe. The mast of a man-of-war burnt at Jamaica was after some months
found stranded on one of the Western Islands of Scotland;[27] and
General Sabine tells us that when he was in Norway, in the year 1823,
casks of palm-oil were picked up on the shore near the North Cape,
which belonged to a vessel that had been wrecked the previous year at
Cape Lopez on the African coast.[28] It seems most probable that these
casks of oil must first have crossed the Atlantic from east to west in
the Equatorial Current, then described the circuit of the West Indian
Islands, and finally coming in with the Gulf Stream, recrossed the
Atlantic, performing altogether a journey of more than eight thousand
miles. From these facts it is clear that, by the agency of ocean
currents, the productions of one country may be carried to another
that is far distant. And Geologists do not fail to make use of this
important conclusion when they find the animal and vegetable remains of
different climates associated together in the same strata of the Earth.
[Illustration]
[Illustration]
_CHAPTER IV._
THEORY OF DENUDATION--CONCLUDED.
_Glaciers--Their nature and composition--Their unceasing
motion--Powerful agents of denudation--Icebergs--Their
number and size--Erratic blocks and loose gravel spread out
over mountains, plains, and valleys, at the bottom of the
sea--Characteristic marks of moving ice--Evidence of ancient
glacial action--Illustrations from the Alps--From the mountains
of the Jura--Theory applied to northern Europe--To Scotland,
Wales, and Ireland--The fact of denudation established--Summary
of the evidence--This fact the first step in geological theory._
The next agent of Denudation to which we invite the attention of our
readers, is one of which our own country affords us no example, but
which may be seen in full operation amidst the wild and impressive
scenery of Switzerland. And we know not how we can better introduce the
subject than by the solemn address of a great poet, in whom an ardent
love of nature was blended with a deep sense of religion. As he stood
in the midst of the snow-clad mountains that shut in the valley of
Chamouni, his spirit, “expanded by the genius of the spot,” soared away
from the scenes before him to the Great Invisible Author of all that is
beautiful and sublime in nature, and he poured forth that well-known
hymn of praise and worship in which he thus apostrophizes the massive
glaciers of Mont Blanc:--
“Ye ice-falls! ye that from the mountain’s brow
Adown enormous ravines slope amain--
Torrents, methinks, that heard a mighty voice,
And stopped at once amid their maddest plunge!
Motionless torrents! silent cataracts!
Who made you glorious as the gates of Heaven
Beneath the keen full moon? Who bade the sun
Clothe you with rainbows? Who with living flowers
Of loveliest blue, spread garlands at your feet?
God! let the torrents, like a shout of nations,
Answer! and let the ice-plains echo, God!
God! sing ye meadow-streams with gladsome voice!
Ye pine-groves, with your soft and soul-like sounds!
And they too have a voice, yon piles of snow,
And in their perilous fall shall thunder, God!”[29]
A Glacier is an enormous mass of solid ice filling up a valley, and
stretching from the eternal snows which crown the summits of the
mountains, down to the smiling cornfields and rich pastures of the
plains. It is constantly fed by the accumulated snows of winter,
which, slipping and rolling down the slopes of the mountains, lodge
in the valleys below, and are there converted into ice. For it must
be remembered that the Glacier properly so called does not commonly
extend much higher than 9000 feet above the level of the sea. Beyond
that elevation the compact and massive ice gradually passes into
frozen snow, called by the French Nevé, and by the Germans Firn. The
change which takes place in the condition of the snow as it descends
into the valley is chiefly owing to these two circumstances: first,
it is closely compacted together by the weight of the snowy masses
pressing down upon it from above; and secondly, in the summer months
it is thawed upon the surface during the day by the heat of the
sun, and frozen again at night. On a small scale this process is
practically familiar to every school-boy. When he makes a snow-ball he
is practically converting a mass of snow into ice, and that by a series
of operations very closely resembling those which Nature employs in the
manufacture of a Glacier.
In Switzerland the Glacier is often two or three miles in breadth,
from twenty to thirty miles in length, and five or six hundred feet in
depth. Though so vast in its bulk and so solid in its character, it is
not, as might be supposed, a fixed, immovable mass. On the contrary, it
is moving incessantly, but slowly, down the valley which it occupies,
at the rate of several inches--sometimes one or two feet, and even
more--in the day. In Greenland a Glacier explored by Doctor Hayes, in
his expedition to the North Pole, was found to move for a whole year at
the average rate of a hundred feet a day. It may be thought, perhaps,
that this fact requires further confirmation; but at all events it is
certain that the language of the poet, when he addresses the Glaciers
as “motionless torrents,” though it conveys an accurate and beautiful
idea of the appearance they present to the eye, is not rigorously true
in a scientific sense. Indeed, it is just because the Glaciers are not
motionless that they serve as instruments of Denudation.
Their agency in this respect “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 sloping heap 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 twenty miles long, and its annual progression about five hundred
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 usually remains
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 of snow and ice, often
several yards high. The reason of their projecting above the general
level, is the non-liquefaction of the ice in those parts of the surface
of the Glacier which are protected from the rays of the sun, or the
action of the wind, by the covering of the earth, sand, and stones.
The cause of _medial moraines_ was first explained by Agassiz, who
referred them to the confluence of tributary Glaciers. 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
afterward move on together, in the centre, if the confluent Glaciers
are equal in size, or nearer to one side if unequal.
“Fragments of stone and sand which fall through crevasses in the ice,
and get interposed between the moving Glacier and the fundamental rock,
are pushed along so as to have their angles more or less worn off, and
many of them are entirely ground down into mud. Some blocks are pushed
along between the ice and the steep boundary rocks of the valley,
and these, like the rocky channel at the bottom of the valley, often
become smoothed and polished, and 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. The effect is perfectly
different from that caused by the action of water, or a muddy torrent
forcing along heavy stones; for these not being held like fragments of
rock in ice, and not being pushed along under great pressure, cannot
scoop out long rectilinear furrows or grooves parallel to each other.
The discovery of such markings at various heights far above the surface
of 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.”[30]
[Illustration: Fig. 2.--Iceberg seen in mid-ocean 1400 miles from any
known land.]
Sometimes, however, it happens, especially in extreme northern and
southern latitudes, that the glacier valley leads down to the sea.
In such cases, huge masses of ice are floated off, and, with their
ponderous burden of gravel, mud, and rocks, are carried away by
currents toward the equator. Immense numbers of these floating islands
of ice, or Icebergs, as they are called, are seen by mariners drifting
along in the Northern and Southern oceans. In 1822 Scoresby counted
five hundred between the latitudes 69° and 70° N., many of which
measured a mile in circumference, and rose two hundred feet above the
surface of the sea.[31] The annexed drawing, copied by kind permission
of the author from Sir Charles Lyell’s Principles of Geology, affords a
good idea of the appearance that such Icebergs present to the eye. The
one represented in the fore-ground was supposed to reach a height of
nearly three hundred feet, and was observed with many others floating
about in the Southern Ocean at a distance of 1400 miles from any known
land. An angular mass of rock was visible on the surface. The part
exposed was twelve feet high and from five to six broad: but it was
conjectured, from the color of the surrounding ice, that the greater
part of the stone was concealed from view.
How enormous must be the magnitude of those ponderous masses may be
learned from the fact that the bulk of ice below the level of the water
is about eight times as great as that above: and in point of fact,
Captain Sir John Ross saw several of them aground in Baffin’s Bay,
where the water was 1500 feet deep. It has been calculated that the
beds of earth and stones which they carry along cannot be less than
from 50,000 to 100,000 tons in weight. Sir Charles Lyell, writing in
1865 from the results of the latest investigations on this subject,
says: “Many had supposed that the magnitude commonly attributed to
icebergs by unscientific navigators was exaggerated; but now it appears
that the popular estimate of their dimensions has rather fallen within
than beyond the truth. Many of them, carefully measured by the
officers of the French exploring expedition of the Astrolabe, were
between 100 and 225 feet high above water, and from two to five miles
in length. Captain d’Urville ascertained one of them, which he saw
floating, to be _thirteen miles long_, and a hundred feet high, with
walls perfectly vertical.”[32]
They have been known to drift from Baffin’s Bay to the Azores, and
from the South Pole to the Cape of Good Hope.[33] As they approach the
milder climate of the temperate zones, the ice gradually melts away,
and thus the moraines of arctic and antarctic glaciers are deposited
at the bottom of the deep sea. In this way, submarine mountains
and valleys and table-lands are strewn over with scattered blocks
of foreign rocks, and gravel, and mud, which have been transported
hundreds of miles across the unfathomable abysses of the ocean.
* * * * *
Though we are chiefly concerned with Glaciers and Icebergs as agents
of Denudation, yet we cannot pass away from the subject without
referring to the Geological theory of an ancient Glacial Period. This
little digression from the main purport of our present argument will
not be unacceptable, we hope, to our readers. The theory is in itself
interesting and ingenious; and it offers an admirable illustration
of the kind of reasoning by which Geologists are guided in their
speculations.
It is well known that the action of moving ice leaves a very peculiar
and characteristic impress on the surface of the rocks, and even on the
general aspect of the country over which it passes. This is no mystery
of science, but a plain fact which any one that chooses may observe
for himself. Every Glacier carries along in its course a vast quantity
of loose gravel, hard sand, and large angular stones. A considerable
proportion of these materials in course of time fall through crevasses
in the ice, and become firmly embedded in the under surface of the
Glacier. Then, as the moving mass slowly descends the valley, they
are shoved along under enormous pressure, and the surface of the
rocks beneath is furrowed, scratched, and polished, in a remarkable
and unmistakable manner. The furrows and scratches are rectilinear
and parallel to an extent never seen in the marks produced by any
other natural agency: and they always coincide more or less in their
direction with the general course of the valley. A reciprocal action
often takes place: the large blocks of stone, frozen into the under
surface of the Glacier, are themselves scored and polished by friction
against the floor and sides of the valley.
[Illustration: Fig. 3.--Block of Limestone furrowed, scratched, and
polished, from the Glacier of Rosenlaui, Switzerland. (Lyell.)
_aa_, White streaks or scratches. _bb_, Furrows.]
Similar effects are produced by Icebergs; not of course when drifting
about in the deep sea, but when they come into contact with a
gently-shelving coast and grate along the bottom. These mountains of
ice, laden with the débris of the land, are often carried along with
the velocity of from two to three miles an hour; and before their
enormous momentum can be entirely destroyed, an extensive surface of
rock must have been rounded, grooved, and scarred, pretty much in the
same way as by the action of a Glacier. There can be no failure of
the grinding materials. During the process of melting, the Iceberg is
constantly turning over according as the centre of gravity shifts its
position; and thus a new part of its surface, with fresh angular blocks
of stone, together with fresh masses of sand and gravel, is constantly
brought into contact with the floor of the ocean. And this is not mere
theory. All these phenomena may be witnessed any day on the shores of
Baffin’s Bay and Hudson’s Bay, and along the coast of Labrador.
Again, the evidence of glacial action may be discovered in the
materials themselves which have been transported by ice. Many of the
large erratic blocks, after having travelled immense distances, exhibit
the same sharp angular appearance as if they had only just fallen
down from the cliff on the mountain side. By this circumstance they
are at once distinguished from blocks of stone transported by running
water; for in these the angles are sure to be rounded off by friction.
Sometimes, too, they are deposited not only far away from the same
rock, but in regions where no rock of the same kind exists. In the
case of Icebergs, they are not unfrequently carried many hundreds of
miles before being dropped into the depths of the ocean, and, in the
course of their long journey, borne over the lofty ridges of submarine
mountain chains.
Furthermore, it often happens that a Glacier shrinks backward up the
valley, and sometimes even disappears altogether. When the melting of
the ice at the lower extremity exactly balances its onward progress,
then the Glacier seems stationary to the eye, and occupies from year to
year the same position. But, when a number of hot seasons follow one
another in immediate succession, the ice is melted more rapidly than
the Glacier advances, and in consequence it gradually becomes shorter,
and seems to the eye to recede toward the upper parts of the valley. In
this case the long lines of moraines, which before had rested on the
ice, are left spread out on the plains or deposited on the slopes of
the mountain. Immense blocks of stone are by this means frequently set
down on the summits of lofty crags, and in such like positions to which
they could not be brought by any other natural agency. These Perched
Blocks, as they are called, and also those long regular mounds of earth
and stones abound in several of the Swiss valleys, and constitute a
very striking feature of Alpine scenery.
Now, it appears that all these various characteristic marks of glacial
operations can be distinctly traced in many countries where the action
of moving ice has been unknown within the period of history. And on
this fact is founded the Geological theory of an ancient Glacial
Period. We are confidently assured that a great part of Northern
Europe, including even our own islands, not to speak of America and
other countries as well in the northern as in the southern hemisphere,
were, in some far distant age, the scene of those same phenomena
which are witnessed at the present day amid the solemn grandeur of
the Alps, and in the frozen wastes of the Arctic regions. In that age
enormous Glaciers moved slowly downward from the snow-clad heights over
innumerable valleys now rich with the fruits of the earth; ponderous
Icebergs floated over wide areas of the ocean, where now the dry land
appears; and vast piles of promiscuous rubbish, with great angular
blocks of stone, were deposited on the slopes and crests of submarine
mountains that now tower hundreds of feet above the level of the sea.
To illustrate this theory, we would begin with a country where the
vestiges of glacial operations in past times may be studied side by
side with the glacial phenomena of the present day. In Switzerland
it needs but little skill to discern many marks and tokens of moving
ice where moving ice is no longer found. In descending, for example,
the valley of the Hasli or the valley of the Rhone, the intelligent
traveller can hardly fail to observe how the rocks all around are
scarred and furrowed, precisely after the same fashion as the rocks in
the higher parts of the same valleys are now being scarred and furrowed
by the Glacier of the Aar and the Glacier of the Rhone. At intervals,
too, may be seen long mounds of unstratified gravel and mud, with large
fragments of rock, in every way resembling the terminal moraines now
daily accumulating at the extremities of existing Glaciers. When these
facts are once distinctly brought home to the mind, it is impossible to
resist the conclusion that several of the Alpine Glaciers once extended
far beyond their present limits down the valleys of Switzerland.
If we proceed a little distance to the mountains of the Jura, now
wholly devoid of Glaciers, we shall find that the same glacial
phenomena with which we have become so familiar in the Alps, are still
everywhere presented to the eye. And we feel instinctively impelled to
pursue the same line of inductive reasoning. Moving ice, we know from
abundant observation, is capable of producing these effects: nor have
we ever seen effects of this kind produced by any other cause: nay,
there is no other natural agent known that is capable of producing such
effects: it is therefore reasonable to infer that moving ice was the
cause of these effects; and that, in some bygone age, great masses of
ice moved slowly over the valleys of the Jura as they now move slowly
over the valleys of the Alps.
Another circumstance may here be noticed which is well worthy of
consideration. The Alps are composed of granite, gneiss, and such like
crystalline rocks: the Jura, of limestone and various other formations,
altogether different from those of the Alps. Now, scattered loosely
over the valleys of the Jura, and perched upon its lofty crests, we
find immense angular blocks--some of them as large as cottages--of
the Alpine rocks. The question naturally arises, how have they been
transported to their present site. Certainly not by the action of
water; for in that case the projecting angles would have been rounded
off, and the sharp edges worn away. But the work might have been easily
accomplished by the power of moving ice, and could not have been
accomplished by any other natural agency with which we are acquainted.
Thus we are led to conclude that the Glaciers of the Alps must, by some
means or another, have once made their way northward across the great
valley of Switzerland, fifty miles wide, and deposited their ponderous
burdens of gravel, sand, and erratic blocks on the mountains of the
Jura.