Chapter VIII: Part I: Historical Development (1)

_Geological Ideas among the Greeks and Romans._--Many geological
phenomena present themselves in so striking a form that they could
hardly fail to impress the imagination of the earliest and rudest
races of mankind. Such incidents as earthquakes and volcanic
eruptions, destructive storms on land and sea, disastrous floods and
landslips suddenly strewing valleys with ruin, must have awakened the
terror of those who witnessed them. Prominent features of landscape,
such as mountain-chains with their snows, clouds and thunderstorms,
dark river-chasms that seem purposely cleft open in order to give
passage to the torrents that rush through them, crags with their
impressive array of pinnacles and recesses must have appealed of old,
as they still do, to the awe and wonder of those who for the first
time behold them. Again, banks of sea-shells in far inland districts
would, in course of time, arrest the attention of the more intelligent
and reflective observers, and raise in their minds some kind of
surmise as to how such shells could ever have come there. These and
other conspicuous geological problems found their earliest solution in
legends and myths, wherein the more striking terrestrial features and
the elemental forces of nature were represented to be the
manifestation of the power of unseen supernatural beings.

The basin of the Mediterranean Sea was especially well adapted, from
its physical conditions, to be the birth-place of such fables. It is a
region frequently shaken by earthquakes, and contains two distinct
centres of volcanic activity, one in the Aegean Sea and one in Italy.
It is bounded on the north by a long succession of lofty snow-capped
mountain-ranges, whence copious rivers, often swollen by heavy rains
or melted snows, carry the drainage into the sea. On the south it
boasts the Nile, once so full of mystery; likewise wide tracts of arid
desert with their dreaded dust storms. The Mediterranean itself,
though an inland sea, is subject to gales, which, on exposed coasts,
raise breakers quite large enough to give a vivid impression of the
power of ocean waves. The countries that surround this great sheet of
water display in many places widely-spread deposits full of sea
shells, like those that still live in the neighbouring bays and gulfs.
Such a region was not only well fitted to supply subjects for
mythology, but also to furnish, on every side, materials which, in
their interest and suggestiveness, would appeal to the reason of
observant men.

It was natural, therefore, that the early philosophers of Greece
should have noted some of these geological features, and should have
sought for other explanations of them than those to be found in the
popular myths. The opinions entertained in antiquity on these subjects
may be conveniently grouped under two heads: (1) Geological processes
now in operation, and (2) geological changes in the past.

Earthquakes and volcanoes.

1. _Contemporary Processes._--The geological processes of the present
time are partly at work underground and partly on the surface of the
earth. The former, from their frequently disastrous character,
received much attention from Greek and Roman authors. Aristotle, in
his _Meteorics_, cites the speculations of several of his predecessors
which he rejects in favour of his own opinion to the effect that
earthquakes are due to the generation of wind within the earth, under
the influence of the warmth of the sun and the internal heat. Wind,
being the lightest and most rapidly moving body, is the cause of
motion in other bodies, and fire, united with wind, becomes flame,
which is endowed with great rapidity of motion. Aristotle looked upon
earthquakes and volcanic eruptions as closely connected with each
other, the discharge of hot materials to the surface being the result
of a severe earthquake, when finally the wind rushes out with
violence, and sometimes buries the surrounding country under sparks
and cinders, as had happened at Lipari. These crude conceptions of
the nature of volcanic action, and the cause of earthquakes, continued
to prevail for many centuries. They are repeated by Lucretius, who,
however, following Anaximenes, includes as one of the causes of
earthquakes the fall of mountainous masses of rock undermined by time,
and the consequent propagation of gigantic tremors far and wide
through the earth. Strabo, having travelled through the volcanic
districts of Italy, was able to recognize that Vesuvius had once been
an active volcano, although no eruption had taken place from it within
human memory. He continued to hold the belief that volcanic energy
arose from the movement of subterranean wind. He believed that the
district around the Strait of Messina, which had formerly suffered
from destructive earthquakes, was seldom visited by them after the
volcanic vents of that region had been opened, so as to provide an
escape for the subterranean fire, wind, water and burning masses. He
cites in his _Geography_ a number of examples of widespread as well as
local sinkings of land, and alludes also to the uprise of the
sea-bottom. He likewise regards some islands as having been thrown up
by volcanic agency, and others as torn from the mainland by such
convulsions as earthquakes.

The most detailed account of earthquake phenomena which has come down
to us from antiquity is that of Seneca in his _Quaestiones Naturales_.
This philosopher had been much interested in the accounts given him by
survivors and witnesses of the earthquake which convulsed the district
of Naples in February A.D. 63. He distinguished several distinct
movements of the ground: 1st, the up and down motion (_succussio_);
2nd, the oscillatory motion (_inclinatio_); and probably a third, that
of trembling or vibration. While admitting that some earthquakes may
arise from the collapse of the walls of subterranean cavities, he
adhered to the old idea, held by the most numerous and important
previous writers, that these commotions are caused mainly by the
movements of wind imprisoned within the earth. As to the origin of
volcanic outbursts he supposed that the subterranean wind in
struggling for an outlet, and whirling through the chasms and
passages, meets with great store of sulphur and other combustible
substances, which by mere friction are set on fire. The elder Pliny
reiterates the commonly accepted opinion as to the efficacy of wind
underground. In discussing the phenomena of earthquakes he remarks
that towns with many culverts and houses with cellars suffer less than
others, and that at Naples those houses are most shaken which stand on
hard ground. It thus appears that with regard to subterranean
geological operations, no advance was made during the time of the
Greeks and Romans as to the theoretical explanation of these
phenomena; but a considerable body of facts was collected, especially
as to the effects of earthquakes and the occurrence of volcanic
eruptions.

Action of rivers.

The superficial processes of geology, being much less striking than
those of subterranean energy, naturally attracted less attention in
antiquity. The operations of rivers, however, which so intimately
affect a human population, were watched with more or less care.
Herodotus, struck by the amount of alluvial silt brought down annually
by the Nile and spread over the flat inundated land, inferred that
"Egypt is the gift of the river." Aristotle, in discussing some of the
features of rivers, displays considerable acquaintance with the
various drainage-systems on the north side of the Mediterranean basin.
He refers to the mountains as condensers of the atmospheric moisture,
and shows that the largest rivers rise among the loftiest high
grounds. He shows how sensibly the alluvial deposits carried down to
the sea increase the breadth of the land, and cites some parts of the
shores of the Black Sea, where, in sixty years, the rivers had brought
down such a quantity of material that the vessels then in use required
to be of much smaller draught than previously, the water shallowing so
much that the marshy ground would, in course of time, become dry land.
Strabo supplies further interesting information as to the work of
rivers in making their alluvial plains and in pushing their deltas
seaward. He remarks that these deltas are prevented from advancing
farther outward by the ebb and flow of the tides.

Occurrences of fossils.

2. _Past Processes._--The abundant well-preserved marine shells
exposed among the upraised Tertiary and post-Tertiary deposits in the
countries bordering the Mediterranean are not infrequently alluded to
in Greek and Latin literature. Xenophanes of Colophon (614 B.C.)
noticed the occurrence of shells and other marine productions inland
among the mountains, and inferred from them that the land had risen
out of the sea. A similar conclusion was drawn by Xanthus the Lydian
(464 B.C.) from shells like scallops and cockles, which were found far
from the sea in Armenia and Lower Phrygia. Herodotus, Eratosthenes,
Strato and Strabo noted the vast quantities of fossil shells in
different parts of Egypt, together with beds of salt, as evidence that
the sea had once spread over the country. But by far the most
philosophical opinions on the past mutations of the earth's surface
are those expressed by Aristotle in the treatise already cited.
Reviewing the evidence of these changes, he recognized that the sea
now covers tracts that were once dry land, and that land will one day
reappear where there is now sea. These alternations are to be regarded
as following each other in a certain order and periodicity. But they
are apt to escape our notice because they require successive periods
of time, which, compared with our brief existence, are of enormous
duration, and because they are brought about so imperceptibly that we
fail to detect them in progress. In a celebrated passage in his
_Metamorphoses_, Ovid puts into the mouth of the philosopher
Pythagoras an account of what was probably regarded as the Pythagorean
view of the subject in the Augustan age. It affirms the interchange of
land and sea, the erosion of valleys by descending rivers, the washing
down of mountains into the sea, the disappearance of the rivers and
the submergence of land by earthquake movements, the separation of
some islands from, and the union of others with, the mainland, the
uprise of hills by volcanic action, the rise and extinction of burning
mountains. There was a time before Etna began to glow, and the time is
coming when the mountain will cease to burn.

From this brief sketch it will be seen that while the ancients had
accumulated a good deal of information regarding the occurrence of
geological changes, their interpretations of the phenomena were to a
considerable extent mere fanciful speculation. They had acquired only
a most imperfect conception of the nature and operation of the
geological processes; and though many writers realized that the
surface of the earth has not always been, and will not always remain,
as it is now, they had no glimpse of the vast succession of changes of
that surface which have been revealed by geology. They built
hypotheses on the slenderest basis of fact, and did not realize the
necessity of testing or verifying them.

_Progress of Geological Conceptions in the Middle Ages._--During the
centuries that succeeded the fall of the Western empire little
progress was made in natural science. The schoolmen in the monasteries
and other seminaries were content to take their science from the
literature of Greece and Rome. The Arabs, however, not only collected
and translated that literature, but in some departments made original
observations themselves. To one of the most illustrious of their
number, Avicenna, the translator of Aristotle, a treatise has been
ascribed, in which singularly modern ideas are expressed regarding
mountains, some of which are there stated to have been produced by an
uplifting of the ground, while others have been left prominent, owing
to the wearing away of the softer rocks around them. In either case,
it is confessed that the process would demand long tracts of time for
its completion.

After the revival of learning the ancient problem presented by fossil
shells imbedded in the rocks of the interior of many countries
received renewed attention. But the conditions for its solution were
no longer what they had been in the days of the philosophers of
antiquity. Men were not now free to adopt and teach any doctrine they
pleased on the subject. The Christian church had meanwhile arisen to
power all over Europe, and adjudged as heretics all who ventured to
impugn any of her dogmas. She taught that the land and the sea had
been separated on the third day of creation, before the appearance of
any animal life, which was not created until the fifth day. To assert
that the dry land is made up in great part of rocks that were formed
in the sea, and are crowded with the remains of animals, was plainly
to impugn the veracity of the Bible. Again, it had come to be the
orthodox belief that only somewhere about 6000 years had elapsed since
the time of Adam and Eve. If any thoughtful observer, impressed with
the overwhelming force of the evidence that the fossiliferous
formations of the earth's crust must have taken long periods of time
for their accumulation, ventured to give public expression to his
conviction, he ran considerable risk of being proceeded against as a
heretic. It was needful, therefore, to find some explanation of the
facts of nature, which would not run counter to the ecclesiastical
system of the day. Various such interpretations were proposed,
doubtless in an honest endeavour at reconciliation. Three of these
deserve special notice: (1) Many able observers and diligent
collectors of fossils persuaded themselves that these objects never
belonged to organisms of any kind, but should be regarded as mere
"freaks of nature," having no more connexion with any once living
creature than the frost patterns on a window. They were styled
"formed" or "figured" stones, "lapides sui generis," and were asserted
to be due to some inorganic imitative process within the earth or to
the influence of the stars. (2) Observers who could not resist the
evidence of their senses that the fossil shells once belonged to
living animals, and who, at the same time, felt the necessity of
accounting for the presence of marine organisms in the rocks of which
the dry land is largely built up, sought a way out of the difficulty
by invoking the Deluge of Noah. Here was a catastrophe which, they
said, extended over the whole globe, and by which the entire dry land
was submerged even up to the tops of the high hills. True, it only
lasted one hundred and fifty days, but so little were the facts then
appreciated that no difficulty seems to have been generally felt in
crowding the accumulation of the thousands of feet of fossiliferous
formations into that brief space of time. (3) Some more intelligent
men in Italy, recognizing that these interpretations could not be
upheld, fell back upon the idea that the rocks in which fossil shells
are imbedded might have been heaped up by repeated and vigorous
eruptions from volcanic centres. Certain modern eruptions in the
Aegean Sea and in the Bay of Naples had drawn attention to the
rapidity with which hills of considerable size could be piled around
an active crater. It was argued that if Monte Nuovo near Naples could
have been accumulated to a height of nearly 500 ft. in two days, there
seemed to be no reason against believing that, during the time of the
Flood, and in the course of the centuries that have elapsed since
that event, the whole of the fossiliferous rocks might have been
deposited. Unfortunately for this hypothesis it ignored the fact that
these rocks do not consist of volcanic materials.

Leonardo da Vinci; Fracastorio; Falloppio.

So long as the fundamental question remained in dispute as to the true
character and history of the stratified portion of the earth's crust
containing organic remains, geology as a science could not begin its
existence. The diluvialists (those who relied on the hypothesis of the
Flood) held the field during the 16th, 17th and a great part of the
18th century. They were looked on as the champions of orthodoxy; and,
on that account, they doubtless wielded much more influence than would
have been gained by them from the force of their arguments. Yet during
those ages there were not wanting occasional observers who did good
service in combating the prevalent misconceptions, and in preparing
the way for the ultimate triumph of truth. It was more especially in
Italy, where many of the more striking phenomena of geology are
conspicuously displayed, that the early pioneers of the science arose,
and that for several generations the most marked progress was made
towards placing the investigations of the past history of the earth
upon a basis of careful observation and scientific deduction. One of
the first of these leaders was Leonardo da Vinci (1452-1519), who,
besides his achievements in painting, sculpture, architecture and
engineering, contributed some notable observations regarding the great
problem of the origin of fossil shells. He ridiculed the notion that
these objects could have been formed by the influence of the stars,
and maintained that they had once belonged to living organisms, and
therefore that what is now land was formerly covered by the sea.
Girolamo Fracastorio (1483-1553) claimed that the shells could never
have been left by the Flood, which was a mere temporary inundation,
but that they proved the mountains, in which they occur, to have been
successively uplifted out of the sea. On the other hand, even an
accomplished anatomist like Gabriello Falloppio (1523-1562) found it
easier to believe that the bones of elephants, teeth of sharks, shells
and other fossils were mere earthy inorganic concretions, than that
the waters of Noah's Flood could ever nave reached as far as Italy.

Nicolas Steno.

By much the most important member of this early band of Italian
writers was undoubtedly Nicolas Steno (1631-1687), who, though born in
Copenhagen, ultimately settled in Florence. Having made a European
reputation as an anatomist, his attention was drawn to geological
problems by finding that the rocks of the north of Italy contained
what appeared to be sharks' teeth closely resembling those of a
dog-fish, of which he had published the anatomy. Cautiously at first,
for fear of offending orthodox opinions, but afterwards more boldly,
he proclaimed his conviction that those objects had once been part of
living animals, and that they threw light on some of the past history
of the earth. He published in 1669 a small tract, _De solido intra
solidum naturaliter contento_, in which he developed the ideas he had
formed of this history from an attentive study of the rocks. He showed
that the stratified formations of the hills and valleys consist of
such materials as would be laid down in the form of sediment in turbid
water; that where they contain marine productions this water is proved
to have been the sea; that diversities in their composition point to
commingling of currents, carrying different kinds of sediment of which
the heaviest would first sink to the bottom. He made original and
important observations on stratification, and laid down some of the
fundamental axioms in stratigraphy. He reasoned that as the original
position of strata was approximately horizontal, when they are found
to be steeply inclined or vertical, or bent into arches, they have
been disrupted by subterranean exhalations, or by the falling in of
the roofs of underground cavernous spaces. It is to this alteration of
the original position of the strata that the inequalities of the
earth's surface, such as mountains, are to be ascribed, though some
have been formed by the outburst of fire, ashes and stones from inside
the earth. Another effect of the dislocation has been to provide
fissures, which serve as outlets for springs. Steno's anatomical
training peculiarly fitted him for dealing authoritatively with the
question of the nature and origin of the fossils contained in the
rocks. He had no hesitation in affirming that, even if no shells had
ever been found living in the sea, the internal structure of these
fossils would demonstrate that they once formed parts of living
animals. And not only shells, but teeth, bones and skeletons of many
kinds of fishes had been quarried out of the rocks, while some of the
strata had skulls, horns and teeth of land-animals. Illustrating his
general principles by a sketch of what he supposed to have been the
past history of Tuscany, he added a series of diagrams which show how
clearly he had conceived the essential elements of stratigraphy. He
thought he could perceive the records of six successive phases in the
evolution of the framework of that country, and was inclined to
believe that a similar chronological sequence would be found all over
the world. He anticipated the objections that would be brought against
his views on account of the insuperable difficulty in granting the
length of time that would be required for all the geographical
vicissitudes which his interpretation required. He thought that many
of the fossils must be as old as the time of the general deluge, but
he was careful not to indulge in any speculation as to the antiquity
of the earth.

Lazzaro Moro.

To the Italian school, as especially typified in Steno, must be
assigned the honour of having thus begun to lay firmly and truly the
first foundation stones of the modern science of geology. The same
school included Antonio Vallisneri (1661-1730), who surpassed his
predecessors in his wider and more exact knowledge of the
fossiliferous rocks that form the backbone of the Italian peninsula,
which he contended were formed during a wide and prolonged submergence
of the region, altogether different from the brief deluge of Noah.
There was likewise Lazzaro Moro (1687-1740), who did good service
against the diluvialists, but the fundamental feature of his system of
nature lay in the preponderant part which, unaware of the great
difference between volcanic materials and ordinary sediment, he
assigned to volcanic action in the production of the sedimentary rocks
of the earth's crust. He supposed that in the beginning the globe was
completely surrounded with water, beneath which the solid earth lay as
a smooth ball. On the third day of creation, however, vast fires were
kindled inside the globe, whereby the smooth surface of stone was
broken up, and portions of it, appearing above the water, formed the
earliest land. From that time onward, volcanic eruptions succeeded
each other, not only on the emerged land, but on the sea-floor, over
which the ejected material spread in an ever augmenting thickness of
sedimentary strata. In this way Moro carried the history of the
stratified rocks beyond the time of the Flood back to the Creation,
which was supposed to have been some 1600 years earlier; and he
brought it down to the present day, when fresh sedimentary deposits
are continually accumulating. He thus incurred no censure from the
ecclesiastical guardians of the faith, and he succeeded in attracting
increased public attention to the problems of geology. The influence
of his teaching, however, was subsequently in great part due to the
Carmelite friar Generelli, who published an eloquent exposition of
Moro's views.

_The Cosmogonists and Theories of the Earth._--While in Italy
substantial progress was made in collecting information regarding the
fossiliferous formations of that country, and in forming conclusions
concerning them based upon more or less accurate observations, the
tendency to mere fanciful speculation, which could not be wholly
repressed in any country, reached a remarkable extravagance in
England. In proportion as materials were yet lacking from which to
construct a history of the evolution of our planet in accordance with
the teaching of the church, imagination supplied the place of
ascertained fact, and there appeared during the last twenty years of
the 18th century a group of English cosmogonists, who, by the
sensational character of their speculations, aroused general attention
both in Britain and on the continent. It may be doubted, however,
whether the effect of their writings was not to hinder the advance of
true science by diverting men from the observation of nature into
barren controversy over unrealities. It is not needful here to do more
than mention the names of Thomas Burnet, whose _Sacred Theory of the
Earth_ appeared in 1681, and William Whiston, whose New Theory of the
Earth was published in 1696. Hardly less fanciful than these writers,
though his practical acquaintance with rocks and fossils was
infinitely greater, was John Woodward, whose _Essay towards a Natural
History of the Earth_ dates from 1695. More important as a
contribution to science was the catalogue of the large collection of
fossils, which he had made from the rocks of England and which he
bequeathed to the university of Cambridge. This catalogue appeared in
1728-1729 with the title of _An attempt towards a Natural History of
the Fossils of England_.

Descartes.

A striking contrast to these cosmogonists is furnished by another
group, which arose in France and Germany, and gave to the world the
first rational ideas concerning the probable primeval evolution of our
globe. The earliest of these pioneers was the illustrious philosopher
Rene Descartes (1596-1650). He propounded a scheme of cosmical
development in which he represented the earth, like the other planets,
to have been originally a mass of glowing material like the sun, and
to have gradually cooled on the outside, while still retaining an
incandescent, self-luminous nucleus. Yet with this noble conception,
which modern science has accepted, Descartes could not shake himself
free from the time-honoured error in regard to the origin of volcanic
action. He thought that certain exhalations within the earth condense
into oil, which, when in violent motion, enters into the subterranean
cavities, where it passes into a kind of smoke. This smoke is from
time to time ignited by a spark of fire and, pressing violently
against its containing walls, gives rise to earthquakes. If the flame
breaks through to the surface at the top of a mountain, it may escape
with enormous energy, hurling forth much earth mingled with sulphur or
bitumen, and thus producing a volcano. The mountain might burn for a
long time until at last its store of fuel in the shape of sulphur or
bitumen would be exhausted. Not only did the philosopher refrain from
availing himself of the high internal temperature of the globe as the
source of volcanic energy, he even did not make use of it as the cause
of the ignition of his supposed internal fuel, but speculated on the
kindling of the subterranean fires by the spirits or gases setting
fire to the exhalations, or by the fall of masses of rock and the
sparks produced by their friction or percussion.

Leibnitz.

The ideas of Descartes regarding planetary evolution were enlarged and
made more definite by Wilhelm Gottfried Leibnitz (1646-1716), whose
teaching has largely influenced all subsequent speculation on the
subject. In his great tract, the _Protogaea_ (published in 1749,
thirty-three years after his death), he traced the probable passage of
our earth from an original condition of incandescent vapour into that
of a smooth molten globe, which, by continuous cooling, acquired an
external solid crust and rugose surface. He thought that the more
ancient rocks, such as granite and gneiss, might be portions of the
earliest outer crust; and that as the external solidification
advanced, immense subterranean cavities were left which were filled
with air and water. By the collapse of the roofs of these caverns,
valleys might be originated at the surface, while the solid
intervening walls would remain in place and form mountains. By the
disruption of the crust, enormous bodies of water were launched over
the surface of the earth, which swept vast quantities of sediment
together, and thus gave rise to sedimentary deposits. After many
vicissitudes of this kind, the terrestrial forces calmed down, and a
more stable condition of things was established.

An important feature in the cosmogony of Leibnitz is the prominent
place which he assigned to organic remains in the stratified rocks of
the crust. Ridiculing the foolish attempts to account for the presence
of these objects by calling them "sports of nature," he showed that
they are to be regarded as historical monuments; and he adduced a
number of instances wherein successive platforms of strata, containing
organic remains, bear witness to a series of advances and retreats of
the sea. He recognized that some of the fossils appeared to have
nothing like them in the living world of to-day, but some analogous
forms might yet be found, he thought, in still unexplored parts of the
earth; and even if no living representatives should ever be
discovered, many types of animals might have undergone transformation
during the great changes which had affected the surface of the earth.
In spite of his clear realization of the vast store of potential
energy residing within the highly heated interior of the earth,
Leibnitz continued to regard volcanic action as due to the combustion
of inflammable substances enclosed within the terrestrial crust, such
as stone-coal, naphtha and sulphur.

Buffon.

Appealing to a much wider public than Descartes or Leibnitz, and
basing his speculations on a wider acquaintance with the organic and
inorganic realms of nature, G.L.L. de Buffon (1707-1788) was
undoubtedly one of the most influential forces that in Europe guided
the growth of geological ideas during the 18th century. He published
in 1749 a _Theory of the Earth_, in which he adopted views similar to
those of Descartes and Leibnitz as to planetary evolution; but though
he realized the importance of fossils as records of former conditions
of the earth's surface, he accounted for them by supposing that they
had been deposited from a universal ocean, a large part of which had
subsequently been engulfed into caverns in the interior of the globe.
Thirty years later, after having laboured with skill and enthusiasm in
all branches of natural history, he published another work, his famous
_Epoques de la nature_ (1778), which is specially remarkable as the
first attempt to deal with the history of the earth in a chronological
manner, and to compute, on a basis of experiment, the antiquity of the
several stages of this history. His experiments were made with globes
of cast iron, and could not have yielded results of any value for his
purpose; but in so far as his calculations were not mere random
guesses but had some kind of foundation on experiment, they deserve
respectful recognition. He divided the history of our earth into six
periods of unequal duration, the whole comprising a period of some
70,000 or 75,000 years. He supposed that the stage of incandescence,
before the globe had consolidated to the centre, lasted 2936 years,
and that about 35,000 years elapsed before the surface had cooled
sufficiently to be touched, and therefore to be capable of supporting
living things. Terrestrial animal life, however, was not introduced
until 55,000 or 60,000 years after the beginning of the world or about
15,000 years before our time. Looking into the future, he foresaw
that, by continued refrigeration, our globe will eventually become
colder than ice, and this fair face of nature, with its manifold
varieties of plant and animal life, will perish after having existed
for 132,000 years.

Buffon's conception of the operation of the geological agents did not
become broader or more accurate in the interval between the appearance
of his two treatises. He still continued to believe in the lowering of
the ocean by subsidence into vast subterranean cavities, with a
consequent emergence of land. He still looked on volcanoes as due to
the burning of "pyritous and combustible stones," though he now called
in the co-operation of electricity. He calculated that the first
volcanoes could not arise until some 50,000 years after the beginning
of the world, by which time a sufficient extent of dense vegetation
had been buried in the earth to supply them with fuel. He appears to
have had but an imperfect acquaintance with the literature of his own
time. At least there can be little doubt that had he availed himself
of the labours of his own countryman, Jean Etienne Guettard
(1715-1786), of Giovanni Arduino (1714-1795) in Italy, and of Johann
Gottlob Lehmann (d. 1767) and George Christian Fuchsel (1722-1773) in
Germany, he would have been able to give to his "epochs" a more
definite succession of events and a greater correspondence with the
facts of nature.

James Hutton.

Among the writers of the 18th century, who formed philosophical
conceptions of the system of processes by which the life of our earth
as a habitable globe is carried on, a foremost place must be assigned
to James Hutton (1726-1797). Educated for the medical profession, he
studied at Edinburgh and at Paris, and took his doctor's degree at
Leiden. But having inherited a small landed property in Berwickshire,
he took to agriculture, and after putting his land into excellent
order, let his farm and betook himself to Edinburgh, there to gratify
the scientific tastes which he had developed early in life. He had
been more especially led to study minerals and rocks, and to meditate
on the problems which they suggest as to the constitution and history
of the earth. His journeys in Britain and on the continent of Europe
had furnished him with material for reflection; and he had gradually
evolved a system or theory in which all the scattered facts could be
arranged so as to show their mutual dependence and their place in the
orderly mechanism of the world. He used to discuss his views with one
or two of his friends, but refrained from publishing them to the world
until, on the foundation of the Royal Society of Edinburgh, he
communicated an outline of his doctrine to that learned body in 1785.
Some years later he expanded this first essay into a larger work in
two volumes, which were published in 1795 with the title of _Theory of
the Earth, with Proofs and Illustrations_.

John Playfair.

Hutton's teaching has exercised a profound influence on modern
geology. This influence, however, has arisen less from his own
writings than from the account of his doctrines given by his friend
John Playfair in the classic work entitled _Illustrations of the
Huttonian Theory_, published in 1802. Hutton wrote in so prolix and
obscure a style as rather to repel than attract readers. Playfair, on
the other hand, expressed himself in such clear and graceful language
as to command general attention, and to gain wide acceptance for his
master's views. Unlike the older cosmogonists, Hutton refrained from
trying to explain the origin of things, and from speculations as to
what might possibly have been the early history of our globe. He
determined from the outset to interpret the past by what can be seen
to be the present order of nature; and he refused to admit the
operation of causes which cannot be shown to be part of the actual
terrestrial system. Like other observers who had preceded him, he
recognized in the various rocks composing the dry land evidence of
former geographical conditions very different from those which now
prevail. He saw that the vast majority of rocks consist of hardened
sediments and must have been deposited in the sea. He could
distinguish among them an older or Primary series, and a younger or
Secondary series; and did not dispute the existence of a Tertiary
series claimed by Peter Simon Pallas (1741-1811). He believed that
these various aqueous accumulations had been consolidated by
subterranean heat, that the oldest and lowest rocks had suffered most
from this action, that into these more deep-seated masses subsequent
veins and larger bodies of molten matter were injected from below, and
thus that what was originally loose detritus eventually became changed
in such crystalline schists as are now found in mountain-chains. In
the course of these terrestrial revolutions sedimentary strata,
originally more or less nearly horizontal, have been pushed upward,
dislocated, crumpled, placed on end, and even elevated to form ranges
of lofty mountains. Hutton looked upon these disturbances as due to
the expansive power of subterranean heat; but he did not attempt to
sketch the mechanism of the process, and he expressly declined to
offer any conjecture as to how the land so elevated remains in that
position. He thought that the interior of our planet may "be a fluid
mass, melted, but unchanged by the action of heat"; and, far from
connecting volcanoes with the combustion of inflammable substances, as
had been the prevalent belief for so many centuries, he looked upon
them as a beneficent provision of "spiracles to the subterranean
furnace, in order to prevent the unnecessary elevation of land and
fatal effects of earthquakes."

A distinguishing feature of the Huttonian philosophy is to be seen in
the breadth of its conceptions regarding the geological operations
continually in progress on the surface of the globe. Hutton saw that
the land is undergoing a ceaseless process of degradation, through the
influence of the air, frost, rain, rivers and the sea, and that in
course of time, if no countervailing agency should intervene, the
whole of the dry land will be washed away into the sea. But he also
perceived that this universal erosion is not everywhere carried on at
the same rate; that it is specially active along the channels of
torrents and rivers, and that, owing to this difference these channels
are gradually deepened and widened, until the complicated
valley-system of a country is carved out. He recognized that the
detritus worn away from the land must be spread out over the floor of
the sea, so as to form there strata similar to those that compose most
of the dry land. As he could detect in the structure of land
convincing evidence that former sea floors had been elevated to form
the continents and islands of to-day, he could look forward to future
ages, when the same subterranean agency which had raised up the
present land would again be employed to uplift the bed of the existing
ocean, thus to renew the surface of our earth as a habitable globe,
and to start a fresh cycle of erosion and deposition.

Lamarck.

Though Hutton was not unaware that organic remains abound in many of
the stratified rocks, he left them out of consideration in the
elaboration of his theory. It was otherwise with one of his French
contemporaries, the illustrious J.B. Lamarck (1744-1829), who, after
having attained great eminence as a botanist, turned to zoology when
he was nearly fifty years of age, and before long rose to even greater
distinction in that department of science. His share in the
classification and description of the mollusca and in founding
invertebrate palaeontology, his theory of organic evolution and his
philosophical treatment of many biological questions have been tardily
recognized, but his contributions to geology have been less generally
acknowledged. When he accepted the "professorship of zoology; of
insects, of worms and of microscopic animals" at the Museum of Natural
History, Paris, in 1793, he at once entered with characteristic ardour
and capacity into the new field of research then opened to him. In
dealing with the mollusca he considered not merely the living but also
the extinct forms, especially the abundant, varied and well-preserved
genera and species furnished by the Tertiary deposits of the Paris
basin, of which he published descriptions and plates that proved of
essential service in the stratigraphical work of Cuvier and Alexandre
Brongniart (1770-1847). His labours among these relics of ancient seas
and lakes led him to ponder over the past history of the globe, and as
he was seldom dilatory in making known the opinions he had formed, he
communicated some of his conclusions to the National Institute in
1799. These, including a further elaboration of his views, he
published in 1802 in a small volume entitled Hydrogeologie.

This treatise, though it did not reach a second edition and has never
been reprinted, deserves an honourable place in geological literature.
Its object, the author states, was to present some important and novel
considerations, which he thought should form the basis of a true
theory of the earth. He entirely agreed with the doctrine of the
subaerial degradation of the land and the erosion of valleys by
running water. Not even Playfair could have stated this doctrine more
emphatically, and it is worthy of notice that Playfair's
_Illustrations of the Huttonian Theory_ appeared in the same year with
Lamarck's book. The French naturalist, however, carried his
conclusions so far as to take no account of any great movements of the
terrestrial crust, which might have produced or modified the main
physical features of the surface of the globe. He thought that all
mountains, except such as were thrown up by volcanic agency or local
accidents, have been cut out of plains, the original surfaces of which
are indicated by the crests and summits of these elevations.

Lamarck, in reflecting upon the wide diffusion of fossil shells and
the great height above the sea at which they are found, conceived the
extraordinary idea that the ocean basin has been scoured out by the
sea, and that, by an impulse communicated to the waters through the
influence chiefly of the moon, the sea is slowly eating away the
eastern margins of the continents, and throwing up detritus on their
western coasts, and is thus gradually shifting its basin round the
globe. He would not admit the operation of cataclysms; but insisted as
strongly as Hutton on the continuity of natural processes, and on the
necessity of explaining former changes of the earth's surface by
causes which can still be seen to be in operation. As might be
anticipated from his previous studies, he brought living things and
their remains into the forefront of his theory of the earth. He looked
upon fossils as one of the chief means of comprehending the
revolutions which the surface of the earth has undergone; and in his
little volume he again and again dwells on the vast antiquity to which
these revolutions bear witness. He acutely argues, from the condition
of fossil shells, that they must have lived and died where their
remains are now found.

In the last part of his treatise Lamarck advances some peculiar
opinions in physics and chemistry, which he had broached eighteen
years before, but which had met with no acceptance among the
scientific men of his time. He believed that the tendency of all
compound substances is to decay, and thereby to be resolved into their
component constituents. Yet he saw that the visible crust of the earth
consists almost wholly of compound bodies. He therefore set himself to
solve the problem thus presented. Perceiving that the biological
action of living organisms is constantly forming combinations of
matter, which would never have otherwise come into existence, he
proceeded to draw the extraordinary conclusion that the action of
plant and animal life (the _Pouvoir de la vie_) upon the inorganic
world is so universal and so potent, that the rocks and minerals which
form the outer part of the earth's crust are all, without exception,
the result of the operations of once living bodies. Though this
sweeping deduction must be allowed to detract from the value of
Lamarck's work, there can be no doubt that he realized, more fully
than any one had done before him, the efficacy of plants and animals
as agents of geological change.

Cuvier.

The last notable contributor to the cosmological literature of geology
was another illustrious Frenchman, the comparative anatomist Cuvier
(1769-1832). He was contemporary with Lamarck, but of a very different
type of mind. The brilliance of his speculations, and the charm with
which he expounded them, early gained for him a prominent place in the
society of Paris. He too was drawn by his zoological studies to
investigate fossil organic remains, and to consider the former
conditions of the earth's surface, of which they are memorials. It was
among the vertebrate organisms of the Paris basin that he found his
chief material, and from them that he prepared the memoirs which led
to him being regarded as the founder of vertebrate palaeontology. But
beyond their biological interest, they awakened in him a keen desire
to ascertain the character and sequence of the geographical
revolutions to which they bear witness. He approached the subject from
an opposite and less philosophical point of view than that of Lamarck,
coming to it with certain preconceived notions, which affected all
his subsequent writings. While Lamarck was by instinct an
evolutionist, who sought to trace in the history of the past the
operation of the same natural processes as are still at work, Cuvier,
on the other hand, was a catastrophist, who invoked a succession of
vast cataclysms to account for the interruptions in the continuity of
the geological record.

In a preliminary _Discourse_ prefixed to his _Recherches sur les
ossemens fossiles_ (1821) Cuvier gave an outline of what he conceived
to have been the past history of our globe, so far as he had been able
to comprehend it from his investigations of the Tertiary formations of
France. He believed that in that history evidence can be recognized of
the occurrence of many sudden and disastrous revolutions, which, to
judge from their effects on the animal life of the time, must have
exceeded in violence anything we can conceive at the present day, and
must have been brought about by other agencies than those which are
now in operation. Yet, in spite of these catastrophes, he saw that
there has been an upward progress in the animal forms inhabiting the
globe, until the series ended in the advent of man. He could not,
however, find any evidence that one species has been developed from
another, for in that case there should have been traces of
intermediate forms among the stratified formations, where he affirmed
that they had never been found. A prominent position in the
_Discourse_ is given to a strenuous argument to disprove the alleged
antiquity of some nations, and to show that the last great catastrophe
occurred not more than some 5000 or 6000 years ago. Cuvier thus linked
himself with those who in previous generations had contended for the
efficacy of the Deluge. But his researches among fossil animals had
given him a far wider outlook into the geological past, and had opened
up to him a succession of deeply interesting problems in the history
of life upon the earth, which, though he had not himself material for
their solution, he could foresee would be cleared up in the future.

_Gradual Shaping of Geology into a Distinct Branch of Science._--It
will be seen from the foregoing historical sketch that it was only
after the lapse of long centuries, and from the labours of many
successive generations of observers and writers, that what we now know
as the science of geology came to be recognized as a distinct
department of natural knowledge, founded upon careful and extended
study of the structure of the earth, and upon observation of the
natural processes, which are now at work in changing the earth's
surface. The term "geology,"[1] descriptive of this branch of the
investigation of nature, was not proposed until the last quarter of
the 18th century by Jean Andre De Luc (1727-1817) and Horace Benedict
De Saussure (1740-1749). But the science was then in a markedly
half-formed condition, theoretical speculation still in large part
supplying the place of deductions from a detailed examination of
actual fact. In 1807 a few enterprising spirits founded the Geological
Society of London for the special purpose of counteracting the
prevalent tendency and confining their intention "to investigate the
mineral structure of the earth." The cosmogonists and framers of
Theories of the Earth were succeeded by other schools of thought. The
Catastrophists saw in the composition of the crust of the earth
distinct evidence that the forces of nature were once much more
stupendous in their operation than they now are, and that they had
from time to time devastated the earth's surface; extirpating the
races of plants and animals, and preparing the ground for new
creations of organized life. Then came the Uniformitarians, who,
pushing the doctrines of Hutton to an extreme which he did not
propose, saw no evidence that the activity of the various geological
causes has ever seriously differed from what it is at present. They
were inclined to disbelieve that the stratified formations of the
earth's crust furnish conclusive evidence of a gradual progression,
from simple types of life in the oldest strata to the most highly
developed forms in the youngest; and saw no reason why remains of the
higher vertebrates should not be met with among the Palaeozoic
formations. Sir Charles Lyell (1797-1875) was the great leader of this
school. His admirably clear and philosophical presentations of
geological facts which, with unwearied industry, he collected from the
writings of observers in all parts of the world, impressed his views
upon the whole English-speaking world, and gave to geological science
a coherence and interest which largely accelerated its progress. In
his later years, however, he frankly accepted the views of Darwin in
regard to the progressive character of the geological record.

The youngest of the schools of geological thought is that of the
Evolutionists. Pointing to the whole body of evidence from inorganic
and organic nature, they maintain that the history of our planet has
been one of continual and unbroken development from the earliest
cosmical beginnings down to the present time, and that the crust of
the earth contains an abundant, though incomplete, record of the
successive stages through which the plant and animal kingdoms have
reached their existing organization. The publication of Darwin's
_Origin of Species_ in 1859, in which evolution was made the key to
the history of the animal and vegetable kingdoms, produced an
extraordinary revolution in geological opinion. The older schools of
thought rapidly died out, and evolution became the recognized creed of
geologists all over the world.

Werner.

_Development of Opinion regarding Igneous Rocks._--So long as the idea
prevailed that volcanoes are caused by the combustion of inflammable
substances underground, there could be no rational conception of
volcanic action and its products. Even so late as the middle of the
18th century, as above remarked, such a good observer as Lazzaro Moro
drew so little distinction between volcanic and other rocks that he
could believe the fossiliferous formations to have been mainly formed
of materials ejected from eruptive vents. After his time the notion
continued to prevail that all the rocks which form the dry land were
laid down under water. Even streams of lava, which were seen to flow
from an active crater, were regarded only as portions of sedimentary
or other rocks, which had been melted by the fervent heat of the
burning inflammable materials that had been kindled underground. In
spite of the speculations of Descartes and Leibnitz, it was not yet
generally comprehended that there exists beneath the terrestrial crust
a molten magma, which, from time to time, has been injected into that
crust, and has pierced through it, so as to escape at the surface with
all the energy of an active volcano. What we now recognize to be
memorials of these former injections and propulsions were all
confounded with the rocks of unquestionably aqueous origin. The last
great teacher by whom these antiquated doctrines were formulated into
a system and promulgated to the world was Abraham Gottlob Werner
(1749-1815), the most illustrious German mineralogist and geognost of
the second half of the 18th century. While still under twenty-six
years of age, he was appointed teacher of mining and mineralogy at the
Mining Academy of Freiberg in Saxony--a post which he continued to
fill up to the end of his life. Possessed of great enthusiasm for his
subject, clear, methodical and eloquent in his exposition of it, he
soon drew around him men from all parts of the world, who repaired to
study under the great oracle of what he called geognosy (Gr. [Greek:
ge], the earth, [Greek: gnosis], knowledge) or earth-knowledge.
Reviving doctrines that had been current long before his time, he
taught that the globe was once completely surrounded with an ocean,
from which the rocks of the earth's crust were deposited as chemical
precipitates, in a certain definite order over the whole planet. Among
these "universal formations" of aqueous origin were included many
rocks, which have long been recognized to have been once molten, and
to have risen from below into the upper parts of the terrestrial
crust. Werner, following the old tradition, looked upon volcanoes as
modern features in the history of the planet, which could not have
come into existence until a sufficient amount of vegetation had been
buried to furnish fuel for their maintenance. Hence he attached but
little importance to them, and did not include in his system of rocks
any division of volcanic or igneous materials. From the predominant
part assigned by him to the sea in the accumulation of the materials
of the visible part of the earth, Werner and his school were known as
"Neptunists."

Origin of basalt.