Sir Charles Lyell, the distinguished geologist, was born at
Kinnordy, Forfarshire, Scotland, Nov. 14, 1797. It was at Oxford
that his scientific interest was first aroused, and after taking an
M.A. degree in 1821 he continued his scientific studies, becoming
an active member of the Geological and Linnæan Societies of London.
In 1826 he was elected a fellow of the Royal Society, and two years
later went with Sir Roderick Murchison on a tour of Europe, and
gathered evidence for the theory of geological uniformity which he
afterwards promulgated. In 1830 he published his great work,
"Principles of Geology: Being an Attempt to Explain the Former
Changes of the Earth's Surface by References to Causes now in
Action," which converted almost the whole geological world to the
doctrine of uniformitarianism, and may be considered the foundation
of modern geology. Lyell died in London on February 22, 1875.
Besides his great work, he also published "The Elements of
Geology," "The Antiquity of Man," "Travels in North America," and
"The Student's Elements of Geology."
_I.--Uniformity in Geological Development_
According to the speculations of some writers, there have been in the
past history of the planet alternate periods of tranquillity and
convulsion, the former enduring for ages, and resembling the state of
things now experienced by man; the other brief, transient, and
paroxysmal, giving rise to new mountains, seas, and valleys,
annihilating one set of organic beings, and ushering in the creation of
another. These theories, however, are not borne out by a fair
interpretation of geological monuments; but, on the contrary, nature
indicates no such cataclysms, but rather progressive uniformity.
Igneous rocks have been supposed to afford evidence of ancient paroxysms
of nature, but we cannot consider igneous rocks proof of any
exceptional paroxysms. Rather, we find ourselves compelled to regard
igneous rocks as an aggregate effect of innumerable eruptions, of
various degrees of violence, at various times, and to consider mountain
chains as the accumulative results of these eruptions. The incumbent
crust of the earth is never allowed to attain that strength and
coherence which would be necessary in order to allow the volcanic force
to accumulate and form an explosive charge capable of producing a grand
paroxysmal eruption. The subterranean power, on the contrary, displays,
even in its most energetic efforts, an intermittent and mitigated
intensity. There are no proofs that the igneous rocks were produced more
abundantly at remote periods.
Nor can we find proof of catastrophic discontinuity when we examine
fossil plants and fossil animals. On the contrary, we find a progressive
development of organic life at successive geological periods.
In Palæozoic strata the entire want of plants of the most complex
organisation is very striking, for not a single dicotyledonous
angiosperm has yet been found, and only one undoubted monocotyledon. In
Secondary, or Mesozoic, times, palms and some other monocotyledons
appeared; but not till the Upper Cretaceous era do we meet with the
principal classes and orders of the vegetable kingdom as now known.
Through the Tertiary ages the forms were perpetually changing, but
always becoming more and more like, generically and specifically, to
those now in being. On the whole, therefore, we find progressive
development of plant life in the course of the ages.
In the case of animal life, progression is equally evident.
Palæontological research leads to the conclusion that the invertebrate
animals flourished before the vertebrate, and that in the latter class
fish, reptiles, birds, and mammalia made their appearance in a
chronological order analogous to that in which they would be arranged
zoologically according to an advancing scale of perfection in their
organisation. In regard to the mammalia themselves, they have been
divided by Professor Owen into four sub-classes by reference to
modifications of their brain. The two lowest are met with in the
Secondary strata. The next in grade is found in Tertiary strata. And the
highest of all, of which man is the sole representative, has not yet
been detected in deposits older than the Post-Tertiary.
It is true that in passing from the older to the newer members of the
Tertiary system we meet with many chasms, but none which separate
entirely, by a broad line of demarcation, one state of the organic world
from another. There are no signs of an abrupt termination of one fauna
and flora, and the starting into life of new and wholly distinct forms.
Although we are far from being able to demonstrate geologically an
insensible transition from the Eocene to the Miocene, or even from the
latter to the recent fauna, yet the more we enlarge and perfect our
general survey the more nearly do we approximate to such a continuous
series, and the more gradually are we conducted from times when many of
the genera and nearly all the species were extinct to those in which
scarcely a single species flourished which we do not know to exist at
present. We must remember, too, that many gaps in animal and floral life
were due to ordinary climatic and geological factors. We could, under no
circumstances, expect to meet with a complete ascending series.
The great vicissitudes in climate which the earth undoubtedly
experienced, as shown by geological records, have been held to be
themselves proof of sudden violent revolutions in the life-history of
the world. But all the great climatic vicissitudes can be accounted for
by the action of factors still, in operation--subsidences and elevations
of land, alterations in the relative proportions and position of land
and water, variations in the relative position of our planet to the sun
and other heavenly bodies.
Altogether, the conclusion is inevitable that from the remotest period
there has been one uniform and continuous system of change in the
animate and inanimate world, and accordingly every fact collected
respecting the factors at present at work in forming and changing the
world, affords a key to the interpretation of its part. And thus,
although we are mere sojourners on the surface of the planet, chained to
a mere point in space, enduring but for a moment of time, the human mind
is enabled not only to number worlds beyond the unassisted ken of mortal
eye, but to trace the events of indefinite ages before the creation of
our race, and to penetrate into the dark secrets of the ocean and the
heart of the solid globe.
_II.--Changes in the Inorganic World now in Progress_
The great agents of change in the inorganic world may be divided into
two principal classes--the aqueous and the igneous. To the aqueous
belong rain, rivers, springs, currents, and tides, and the action of
frost and snow; to the igneous, volcanoes and earthquakes. Both these
classes are instruments of degradation as well as of reproduction. But
they may also be regarded as antagonist forces, since the aqueous agents
are incessantly labouring to reduce the inequalities of the earth's
surface to a level; while the igneous are equally active in restoring
the unevenness of the external crust, partly by heaping up new matter in
certain localities, and partly by depressing one portion of the earth's
envelope and forcing out another.
We will treat in the first place of the aqueous agents.
RAIN AND RIVERS. When one considers that in some parts of the world as
much as 500 or 600 inches of rain may fall annually, it is easy to
believe that rain _qua_ rain may be a denuding and plastic agent, and in
some parts of the world we find evidence of its action in earth pillars
or pyramids. The best example of earth pillars is seen near Botzen, in
the Tyrol, where there are hundreds of columns of indurated mud, varying
in height from 20 feet to 100 feet. These columns are usually capped by
a single stone, and have been separated by rain from the terrace of
which they once formed a part.
As a rule, however, rain acts through rivers. The power of rivers to
denude and transport is exemplified daily. Even a comparatively small
stream when swollen by rain may move rocks tons in weight, and may
transport thousands of tons of gravel. The greatest damage is done when
rivers are dammed by landslips or by ice. In 1818 the River Dranse was
blocked by ice, and its upper part became a lake. In the hot season the
barrier of ice gave way, and the torrent swept before it rocks, forests,
houses, bridges, and cultivated land. For the greater part of its course
the flood resembled a moving mass of rock and mud rather than of water.
Some fragments of granite rock of enormous size, which might be compared
to houses, were torn out and borne down for a quarter of a mile.
The rivers of unmelted ice called the glaciers act more slowly, but they
also have the power of transporting gravel, sand, and boulders to great
distances, and of polishing and scoring their rocky channels. Icebergs,
too, are potent geological agents. Many of them are loaded with 50,000
to 100,000 tons of rock and earth, which they may carry great distances.
Also in their course they must break, and polish, and scratch the peaks
and points of submarine mountains.
Coast ice, likewise, may transport rocks and earth. Springs also must be
considered as geological agents affecting the face of the globe.
But running water not only denudes it, but also creates land, for
lakes, seas, rivers are seen to form deltas. That Egypt was the gift of
the Nile was the opinion of the Egyptian priests, and there can be no
doubt that the fertility of the alluvial plain above Cairo, and the very
existence of the delta below that city, are due to the action of that
great river, and to its power of transporting mud from the interior of
Africa and depositing it on its inundated plains as well as on that
space which has been reclaimed from the Mediterranean and converted into
land. The delta of the Ganges and Brahmapootra is more than double that
of the Nile. Even larger is the delta of the Mississippi, which has been
calculated to be 12,300 square miles in area.
TIDES AND CURRENTS. The transporting and destroying and constructive
power of tides and currents is, in many respects, analogous to that of
rivers, but extends to wider areas, and is, therefore, of more
geological importance. The chief influence of the ocean is exerted at
moderate depths below the surface on all areas which are slowly rising,
or attempting, as it were, to rise above the sea; but its influence is
also seen round the coast of every continent and island.
* * * * *
We shall now consider the igneous agents that act on the earth's
surface. These agents are chiefly volcanoes and earthquakes, and we find
that both usually occur in particular parts of the world. At various
times and at various places within historical times volcanic eruptions
and earthquakes have both proved their potency to alter the face of the
earth.
The principal geological facts and theories with regard to volcanoes and
earthquakes are as follows.
The primary causes of the volcano and the earthquake are to a great
extent the same, and connected with the development of heat and chemical
action at various depths in the interior of the globe.
Volcanic heat has been supposed to be the result of the original high
temperature of the molten planet, and the planet has been supposed to
lose heat by radiation. Recent inquiries, however, suggest that the
apparent loss of heat may arise from the excessive local development of
volcanic action.
Whatever the original shape of our planet, it must in time have become
spheroidal by the gradual operation of centrifugal force acting on
yielding materials brought successively within its action by aqueous and
igneous causes.
The heat in mines and artesian wells increases as we descend, but not in
uniform ratio in different regions. Increase at a uniform ratio would
imply such heat in the central nucleus as must instantly fuse the crust.
Assuming that there are good astronomical grounds for inferring the
original fluidity of the planet, yet such pristine fluidity need not
affect the question of volcanic heat, for the volcanic action of
successive periods belongs to a much more modern state of the globe, and
implies the melting of different parts of the solid crust one after the
other.
The supposed great energy of the volcanic forces in the remoter periods
is by no means borne out by geological observations on the quantity of
lava produced by single eruptions in those several periods.
The old notion that the crystalline rocks, whether stratified or
unstratified, such as granite and gneiss, were produced in the lower
parts of the earth's crust at the expense of a central nucleus slowly
cooling from a state of fusion by heat has now had to be given up, now
that granite is found to be of all ages, and now that we know the
metamorphic rocks to be altered sedimentary strata, implying the
denudation of a previously solidified crust.
The powerful agency of steam or aqueous vapour in volcanic eruptions
leads us to compare its power of propelling lava to the surface with
that which it exerts in driving water up the pipe of an Icelandic
geyser. Various gases also, rendered liquid by pressure at great depths,
may aid in causing volcanic outbursts, and in fissuring and convulsing
the rocks during earthquakes.
The chemical character of the products of recent eruptions suggests that
large bodies of salt water gain access to the volcanic foci. Although
this may not be the primary cause of volcanic eruptions, which are
probably due to the aqueous vapour intimately mixed with molten rock,
yet once the crust is shattered through, the force and frequency of
eruptions may depend in some measure on the proximity of large bodies of
water.
The permanent elevation and subsidence of land now observed, and which
may have been going on through past ages, may be connected with the
expansion and contraction of parts of the solid crust, some of which
have been cooling from time to time, while others have been gaining
heat.
In the preservation of the average proportion of land and sea, the
igneous agents exert a conservative power, restoring the unevenness of
the surface which the levelling power of water in motion would tend to
destroy. If the diameter of the planet remains always the same, the
downward movements of the crust must be somewhat in excess, to
counterbalance the effects of volcanoes and mineral springs, which are
always ejecting material so as to raise the level of the surface of the
earth. Subterranean movements, therefore, however destructive they may
be during great earthquakes, are essential to the well-being of the
habitable surface, and even to the very existence of terrestrial and
aquatic species.
_III.--Changes of the Organic World now in Progress_
In 1809 Lamarck introduced the idea of transmutation of species,
suggesting that by changes in habitat, climate, and manner of living one
species may, in the course of generations, be transformed into a new
and distinct species.
In England, however, the idea remained dormant till in 1844 a work
entitled the "Vestiges of Creation" reinforced it with many new facts.
In this work the unity of plan exhibited by the whole organic creation,
fossil and recent, and the mutual affinities of all the different
classes of the animal and vegetable kingdoms, were declared to be in
harmony with the idea of new forms having proceeded from older ones by
the gradually modifying influence of environment. In 1858 the theory was
put on a new and sound basis by Wallace and Darwin, who added the
conception of natural selection, suggesting that variations in species
are naturally produced, and that the variety fittest to survive in the
severe struggle for existence must survive, and transmit the
advantageous variation, implying the gradual evolution of new species.
Further, Darwin showed that other varieties may be perpetuated by sexual
selection.
On investigating the geographical distribution of animals and plants we
find that the extent to which the species of mammalia, birds, insects,
landshells, and plants (whether flowering or cryptogamous) agree with
continental species; or the degree in which those of different islands
of the same group agree with each other has an unmistakable relation to
the known facilities enjoyed by each class of crossing the ocean. Such a
relationship accords well with the theory of variation and natural
selection, but with no other hypothesis yet suggested for explaining the
origin of species.
From what has been said of the changes which are always going on in the
habitable surface of the world, and the manner in which some species are
constantly extending their range at the expense of others, it is evident
that the species existing at any particular period may, in the course of
ages, become extinct one after the other.
If such, then, be the law of the organic world, if every species is
continually losing some of its varieties, and every genus some of its
species, it follows that the transitional links which once, according to
the doctrine of transmutation, must have existed, will, in the great
majority of cases, be missing. We learn from geological investigations
that throughout an indefinite lapse of ages the whole animate creation
has been decimated again and again. Sometimes a single representative
alone remains of a type once dominant, or of which the fossil species
may be reckoned by hundreds. We rarely find that whole orders have
disappeared, yet this is notably the case in the class of reptiles,
which has lost some orders characterised by a higher organisation than
any now surviving in that class. Certain genera of plants and animals
which seem to have been wholly wanting, and others which were feebly
represented in the Tertiary period, are now rich in species, and appear
to be in such perfect harmony with the present conditions of existence
that they present us with countless varieties, confounding the zoologist
or botanist who undertakes to describe or classify them.
We have only to reflect on the causes of extinction, and we at once
foresee the time when even in these genera so many gaps will occur, so
many transitional forms will be lost, that there will no longer be any
difficulty in assigning definite limits to each surviving species. The
blending, therefore, of one generic or specific form into another must
be an exception to the general rule, whether in our own time or in any
period of the past, because the forms surviving at any given moment will
have been exposed for a long succession of antecedent periods to those
powerful causes of extinction which are slowly but incessantly at work
in the organic and inorganic worlds.
They who imagine that, if the theory of transmutation be true, we ought
to discover in a fossil state all the intermediate links by which the
most dissimilar types have been formerly connected together, expect a
permanence and completeness of records such as is never found. We do not
find even that all recently extinct plants have left memorials of their
existence in the crust of the earth; and ancient archives are certainly
extremely defective. To one who is aware of the extreme imperfection of
the geological record, the discovery of one or two missing links is a
fact of small significance; but each new form rescued from oblivion is
an earnest of the former existence of hundreds of species, the greater
part of which are irrevocably lost.
A somewhat serious cause of disquiet and alarm arises out of the
supposed bearing of this doctrine of the origin of species by
transmutation on the origin of man, and his place in nature. It is
clearly seen that there is such a close affinity, such an identity in
all essential points, in our corporeal structure, and in many of our
instincts and passions with those of the lower animals--that man is so
completely subjected to the same general laws of reproduction, increase,
growth, disease, and death--that if progressive development, spontaneous
variation, and natural selection have for millions of years directed the
changes of the rest of the organic world, we cannot expect to find that
the human race has been exempted from the same continuous process of
evolution.
Such a near bond of connection between man and the rest of the animate
creation is regarded by many as derogatory to our dignity. But we have
already had to exchange the pleasing conceptions indulged in by poets
and theologians as to the high position in the scale of being held by
our early progenitors for humble and more lowly beginnings, the joint
labours of the geologist and archæologist having left us in no doubt of
the ignorance and barbarism of Palæolithic man.
It is well, too, to remember that the high place we have reached in the
scale of being has been gained step by step, by a conscientious study
of natural phenomena, and by fearlessly teaching the doctrines to which
they point. It is by faithfully weighing evidence without regard to
preconceived notions, by earnestly and patiently searching for what is
true, not what we wish to be true, that we have attained to that
dignity, which we may in vain hope to claim through the rank of an ideal
parentage.