Chapter IX: Part I: Historical Development (2)

But many years before the Saxon professor began to teach, clear
evidence had been produced from central France that basalt, one of the
rocks claimed by him as a chemical precipitate and a universal
formation, is a lava which has been poured out in a molten state at
various widely separated periods of time and at many different places.
So far back as 1752 J.E. Guettard (1715-1786) had shown that the
basaltic rocks of Auvergne are true lavas, which have flowed out in
streams from groups of once active cones. Eleven years later the
observation was confirmed and greatly extended by Nicholas Desmarest
(1725-1815), who, during a long course of years, worked out and mapped
the complicated volcanic records of that interesting region, and
demonstrated to all who were willing impartially to examine the
evidence the true volcanic nature of basalt. These views found
acceptance from some observers, but they were vehemently opposed by
the followers of Werner, who, by the force of his genius, made his
theoretical conceptions predominate all over Europe. The controversy
as to the origin of basalt was waged with great vigour during the
later decades of the 18th century. Desmarest took no part in it. He
had accumulated such conclusive proof of the correctness of his
deductions, and had so fully expounded the clearness of the evidence
in their favour furnished by the region of Auvergne, that, when any
one came to consult him on the subject, he contented himself with
giving the advice to "go and see." While the debate was in progress on
the continent, the subject was approached from a new and independent
point of view by Hutton in Scotland. This illustrious philosopher, as
already stated, realized the importance of the internal heat of the
globe in consolidating the sedimentary rocks, and believed that molten
material from the earth's interior has been protruded from below into
the overlying crust. Some of the material thus injected could be
recognized, he thought, in granite and in the various dark massive
rocks which, known in Scotland under the name of "whinstone," were
afterwards called "Trap," and are now grouped under various names,
such as basalt, dolerite and diorite. So important a share did Hutton
thus assign to the internal heat in the geological evolution of the
planet, that he and those who adopted the same opinions were styled
"Plutonists," or, especially where they concerned themselves with the
volcanic origin of basalt, "Vulcanists." The geological world was thus
divided into two hostile camps, that of the Neptunists or Wernerians,
and that of the Plutonists, Vulcanists or Huttonians.

After many years of futile controversy the first serious weakening of
the position of the dominant Neptunist school arose from the defection
of some of the most prominent of Werner's pupils. In particular Jean
Francois D'Aubuisson de Voisins (1769-1819), who had written a
treatise on the aqueous origin of the basalts of Saxony, went
afterwards to Auvergne, where he was speedily a convert to the views
expounded by Desmarest as to the volcanic nature of basalt. Having
thus to relinquish one of the fundamental articles of the Freiberg
faith, he was subsequently led to modify his adherence to others
until, as he himself confessed, his views came almost wholly to agree
with those of Hutton. Not less complete, and even more important, was
the conversion of the great Leopold von Buch (1774-1853). He, too, was
trained by Werner himself, and proved to be the most illustrious pupil
of the Saxon professor. Full of admiration for the Neptunism in which
he had been reared, he, in his earliest separate work, maintained the
aqueous origin of basalt, and contrasted the wide field opened up to
the spirit of observation by his master's teaching with the narrower
outlook offered by "the volcanic theory." But a little further
acquaintance with the facts of nature led Von Buch also to abandon his
earlier prepossessions. It was a personal visit to the volcanic region
of Auvergne that first opened his eyes, and led him to recant what he
had believed and written about basalt. But the abandonment of so
essential a portion of the Wernerian creed prepared the way for
further relinquishments. When a few years later he went to Norway and
found to his astonishment that granite, which he had been taught to
regard as the oldest chemical precipitate from the universal ocean,
could there be seen to have broken through and metamorphosed
fossiliferous limestones, and to have sent veins into them, his faith
in Werner's order of the succession of the rocks in the earth's crust
received a further momentous shock. While one after another of the
Freiberg doctrines crumbled away before him, he was now able to
interrogate nature on a wider field than the narrow limits of Saxony,
and he was thus gradually led to embrace the tenets of the opposite
school. His commanding position, as the most accomplished geologist on
the continent, gave great importance to his recantation of the
Neptunist creed. His defection indeed was the severest blow that this
creed had yet sustained. It may be said to have rung the knell of
Wernerianism, which thereafter rapidly declined in influence, while
Plutonism came steadily to the front, where it has ever since
remained.

Although Desmarest had traced in Auvergne a long succession of
volcanic eruptions, of which the oldest went back to a remote period
of time, and although he had shown that this succession, coupled with
the records of contemporaneous denudation, might be used in defining
epochs of geological history, it was not until many years after his
day that volcanic action came to be recognized as a normal part of the
mechanism of our globe, which had been in operation from the remotest
past, and which had left numerous records among the rocks of the
terrestrial crust. During the progress of the controversy between the
two great opposing factions in the later portion of the 18th and the
first three decades of the 19th century, those who espoused the
Vulcanist cause were intent on proving that certain rocks, which are
intercalated among the stratified formations and which were claimed by
the Neptunists as obviously formed by water, are nevertheless of truly
igneous origin. These observers fixed their eyes on the evidence that
the material of such rocks, instead of having been deposited from
aqueous solution, had once been actually molten, and had in that
condition been thrust between the strata, had enveloped portions of
them, and had indurated or otherwise altered them. They spoke of these
masses as "unerupted lavas"; and undoubtedly in innumerable instances
they were right. But their zeal to establish an intrusive origin led
them to overlook the proofs that some intercalated sheets of igneous
material had not been injected into the strata, but had been poured
out at the surface as truly volcanic discharges, and therefore
belonged to the ancient periods represented by the strata between
which they are interposed. It may readily be supposed that any proofs
of the contemporaneous intercalation of such sheets would be eagerly
seized upon by the Neptunists in favour of their aqueous theory. The
influence of the ancient belief that "burning mountains" could only
rise from the combustion of subterranean inflammable materials
extended even into the ranks of the Vulcanists, so far at least as to
lead to a general acquiescence in the assumption that volcanoes
appeared to belong to a late phase in the history of the planet. It
was not until after considerable progress had been made in determining
the palaeontological distinctions and order of succession of the
stratified formations of the earth's crust that it became possible to
trace among these formations a succession of volcanic episodes which
were contemporaneous with them. In no part of the world has an ampler
record of such episodes been preserved than in the British Isles. It
was natural, therefore, that the subject should there receive most
attention. As far back as 1820 Ami Boue (1794-1881) showed that the
Old Red Sandstone of Scotland includes a great series of volcanic
rocks, and that other rocks of volcanic origin are associated with the
Carboniferous formations. H.T. de la Beche (1796-1855) afterwards
traced proofs of contemporaneous eruptions among the Devonian rocks of
the south-west of England. Adam Sedgwick (1785-1873) showed, first in
the Lake District, and afterwards in North Wales, the presence of
abundant volcanic sheets among the oldest divisions of the Palaeozoic
series; while Roderick Impey Murchison (1792-1871) made similar
discoveries among the Lower Silurian rocks. From the time of these
pioneers the volcanic history of the country has been worked out by
many observers until it is now known with a fulness as yet unattained
in any other region.

_Growth of Opinion regarding Earthquakes._--We have seen how crude
were the conceptions of the ancients regarding the causes of volcanic
action, and that they connected volcanoes and earthquakes as results
of the commotion of wind imprisoned within subterranean caverns and
passages. One of the earliest treatises, in which the phenomena of
terrestrial movements were discussed in the spirit of modern science,
was the posthumous collection of papers by Robert Hooke (1635-1703),
entitled _Lectures and Discourses of Earthquakes and Subterranean
Eruptions_, where the probable agency of earthquakes in upheaving and
depressing land is fully considered, but without any definite
pronouncement as to the author's conception of its origin. Hooke still
associated earthquakes with volcanic action, and connected both with
what he called "the general congregation of sulphurous subterraneous
vapours." He conceived that some kind of "fermentation" takes place
within the earth, and that the materials which catch fire and give
rise to eruptions or earthquakes are analogous to those that
constitute gunpowder. The first essay wherein earthquakes are treated
from the modern point of view as the results of a shock that sends
waves through the crust of the earth was written by the Rev. John
Michell, and communicated to the Royal Society in the year 1760. Still
under the old misconception that volcanoes are due to the combustion
of inflammable materials, which he thought might be set on fire by the
spontaneous combustion of pyritous strata, he supposed that, by the
sudden access of large bodies of water to these subterranean fires,
vapour is produced in such quantity and with such force as to give
rise to the shock. From the centre of origin of this shock waves, he
thought, are propagated through the earth, which are largest at the
start and gradually diminish as they travel outwards. By drawing lines
at different places in the direction of the track of these waves, he
believed that the place of common intersection of these lines would be
nearly the centre of the disturbance. In this way he showed that the
great Lisbon earthquake of 1755 had its focus under the Atlantic,
somewhere between the latitudes of Lisbon and Oporto, and he estimated
that the depth at which it originated could not be much less than 1
m., and probably did not exceed 3 m. Michell, however, misconceived
the character of the waves which he described, seeing that he believed
them to be due to the actual propagation of the vapour itself
underneath the surface of the earth. A century had almost passed after
the date of his essay before modern scientific methods of observation
and the use of recording instruments began to be applied to the study
of earthquake phenomena. In 1846 Robert Mallet (1810-1881) published
an important paper "On the Dynamics of Earthquakes" in the
_Transactions of the Royal Irish Academy_. From that time onward he
continued to devote his energies to the investigation, studying the
effects of the Calabrian earthquake of 1857, experimenting on the
transmission of waves of shock through various materials, caused by
exploding charges of gunpowder, and collecting all the information to
be obtained on the subject. His writings, and especially his work in
two volumes on _The First Principles of Observational Seismology_,
must be regarded as having laid the foundations of this branch of
modern geology (see EARTHQUAKE; SEISMOMETER).

_History of the Evolution of Stratigraphical Geology._--Men had long
been familiar with the evidence that the present dry land once lay
under the sea, before they began to realize that the rocks, of which
the land consists, contain a record of many alternations of land and
sea, and relics of a long succession of plants and animals from early
and simple types up to the manifold and complex forms of to-day. In
countries where coal-mining had been prosecuted for generations, it
had been recognized that the rocks consist of strata superposed on
each other in a definite order, which was found to extend over the
whole of a district. As far back as 1719 John Strachey drew attention
to this fact in a communication published in the _Philosophical
Transactions_. John Michell (1760), in the paper on earthquakes
already cited, showed that he had acquired a clear understanding of
the order of succession among stratified formations, and perceived
that to disturbances of the terrestrial crust must be ascribed the
fact that the lower or older and more inclined strata form the
mountains, while the younger and more horizontal strata are spread
over the plains.

In Italy G. Arduino (1713-1795) classified the rocks in the north of
the peninsula as Primitive, Secondary, Tertiary and Volcanic. A
similar threefold order was announced for the Harz and Erzgebirge by
J.G. Lehmann in 1756. He recognized in that region an ancient series
of rocks in inclined or vertical strata, which rise to the tops of the
hills and descend to an unknown depth into the interior. These masses,
he thought, were contemporaneous with the making of the world. Next
came the Flotzgebirge, consisting of younger sediments, disposed in
flat or gently inclined sheets which overlie the first and more
disturbed series, and are full of petrified remains of plants and
animals. Lastly he included the mountains which have from time to time
been formed by local accidents. Still more advanced were the
conceptions of G.C. Fuchsel, who in the year 1762 published in Latin
_A History of the Earth and the Sea, based on a History of the
Mountains of Thuringia_; and in 1773, in German, a _Sketch of the most
Ancient History of the Earth and Man_. In these works he described the
stratigraphical relations and general characters of the various
geological formations in his little principality; and taking them as
indicative of a general order of succession, he traced what he
believed to have been a series of revolutions through which the earth
has passed. In interpreting this geological history, he laid great
stress on the evidence of the fossils contained in the rocks. He
recognized that the various formations differ from each other in their
enclosed organic remains, and that from these differences the
existence of former sea-bottoms and land surfaces can be determined.

The labours of these pioneers paved the way for the advent of Werner.
Though the system evolved by this teacher claimed to discard theory
and to be established on a basis of observed facts, it rested on a
succession of hypotheses, for which no better foundation could be
shown than the belief of their author in their validity. Starting from
the extremely limited stratigraphical range displayed in the
geological structure of Saxony, he took it as a type for the rest of
the globe, persuading himself and impressing upon his followers that
the rocks of that small kingdom were to be taken as examples of his
"universal formations." The oldest portion of the series, classed by
him as "Primitive," consisted of rocks which he maintained had been
deposited from chemical solution. Yet they included granite, gneiss,
basalt, porphyry and serpentine, which, even in his own day, were by
many observers correctly regarded as of igneous origin. A later group
of rocks, to which he gave the name of "Transition," comprised, in his
belief, partly chemical, partly mechanical sediments, and contained
the earliest fossil organic remains. A third group, for which he
reserved Lehmann's name "Flotz," was made up chiefly of mechanical
detritus, while youngest of all came the "Alluvial" series of loams,
clays, sands, gravels and peat. It was by the gradual subsidence of
the ocean that, as he believed, the general mass of the dry land
emerged, the first-formed rocks being left standing up, sometimes on
end, to form the mountains, while those of later date, less steeply
inclined, occupied successively lower levels down to the flat alluvial
accumulations of the plains. Neither Werner, nor any of his followers,
ventured to account for what became of the water as the sea-level
subsided, though, in despite of their antipathy to anything like
speculation, they could not help suggesting, as an answer to the
cogent arguments of their opponents, that "one of the celestial bodies
which sometimes approach near to the earth may have been able to
withdraw a portion of our atmosphere and of our ocean." Nor was any
attempt made to explain the extraordinary nature of the supposed
chemical precipitates of the universal ocean. The progress of inquiry
even in Werner's lifetime disproved some of the fundamental portions
of his system. Many of the chemical precipitates were shown to be
masses that had been erupted in a molten state from below. His order
of succession was found not to hold good; and though he tried to
readjust his sequence and to introduce into it modifications to suit
new facts, its inherent artificiality led to its speedy decline after
his death. It must be conceded, however, that the stress which he laid
upon the fact that the rocks of the earth's crust were deposited in a
definite order had an important influence in directing attention to
this subject, and in preparing the way for a more natural system,
based not on mere mineralogical characters, but having regard to the
organic remains, which were now being gathered in ever-increasing
numbers and variety from stratified formations of many different ages
and from all parts of the globe.

It was in France and in England that the foundations of stratigraphy,
based upon a knowledge of organic remains, were first successfully
laid. Abbe J.L. Giraud-Soulavie (1752-1813), in his _Histoire
naturelle de la France meridionale_, which appeared in seven volumes,
subdivided the limestones of Vivarais into five ages, each marked by a
distinct assemblage of shells. In the lowest strata, representing the
first age, none of the fossils were believed by him to have any living
representatives, and he called these rocks "Primordial." In the next
group a mingling of living with extinct forms was observable. The
third age was marked by the presence of shells of still existing
species. The strata of the fourth series were characterized by
carbonaceous shales or slates, containing remains of primordial
vegetation, and perhaps equivalents of the first three calcareous
series. The fifth age was marked by recent deposits containing remains
of terrestrial vegetation and of land animals. It is remarkable that
these sagacious conclusions should have been formed and published at a
time when the geologists of the Continent were engaged in the
controversy about the origin of basalt, or in disputes about the
character and stratigraphical position of the supposed universal
formations, and when the interest and importance of fossil organic
remains still remained unrecognized by the vast majority of the
combatants.

The rocks of the Paris basin display so clearly an orderly
arrangement, and are so distinguished for the variety and perfect
preservation of their enclosed organic remains, that they could not
fail to attract the early notice of observers. J. E. Guettard, G.F.
Rouelle (1703-1770), N. Desmarest, A.L. Lavoisier (1743-1794) and
others made observations in this interesting district. But it was
reserved for Cuvier (1769-1832) and A. Brongniart (1770-1847) to work
out the detailed succession of the Tertiary formations, and to show
how each of these is characterized by its own peculiar assemblage of
organic remains. The later progress of investigation has slightly
corrected and greatly amplified the tabular arrangement established by
these authors in 1808, but the broad outlines of the Tertiary
stratigraphy of the Paris basin remain still as Cuvier and Brongniart
left them. The most important subsequent change in the classification
of the Tertiary formations was made by Sir Charles Lyell, who,
conceiving in 1828 the idea of a classification of these rocks by
reference to their relative proportions of living and extinct species
of shells, established, in collaboration with G.P. Deshayes, the now
universally accepted divisions Eocene, Miocene and Pliocene.

Long before Cuvier and Brongniart published an account of their
researches, another observer had been at work among the Secondary
formations of the west of England, and had independently discovered
that the component members of these formations were each distinguished
by a peculiar group of organic remains; and that this distinction
could be used to discriminate them over all the region through which
he had traced them. The remarkable man who arrived at this
far-reaching generalization was William Smith (1769-1839), a land
surveyor who, in the prosecution of his professional business, found
opportunities of traversing a great part of England, and of putting
his deductions to the test. As the result of these journeys he
accumulated materials enough to enable him to produce a geological map
of the country, on which the distribution and succession of the rocks
were for the first time delineated. Smith's labours laid the
foundation of stratigraphical geology in England and he was styled
even in his lifetime the "Father of English geology." From his day
onward the significance of fossil organic remains gained rapidly
increasing recognition. Thus in England the outlines traced by him
among the Secondary and Tertiary formations were admirably filled in
by Thomas Webster (1773-1844); while the Cretaceous series was worked
out in still greater detail in the classic memoirs of William Henry
Fitton (1780-1861).

There was one stratigraphical domain, however, into which William
Smith did not enter. He traced his sequence of rocks down into the
Coal Measures, but contented himself with only a vague reference to
what lay underneath that formation. Though some of these underlying
rocks had in various countries yielded abundant fossils, they had
generally suffered so much from terrestrial disturbances, and their
order of succession was consequently often so much obscured throughout
western Europe, that they remained but little known for many years
after the stratigraphy of the Secondary and Tertiary series had been
established. At last in 1831 Murchison began to attack this _terra
incognita_ on the borders of South Wales, working into it from the Old
Red Sandstone, the stratigraphical position of which was well known.
In a few years he succeeded in demonstrating the existence of a
succession of formations, each distinguished by its own peculiar
assemblage of organic remains which were distinct from those in any of
the overlying strata. To these formations he gave the name of Silurian
(q.v.). From the key which his researches supplied, it was possible to
recognize in other countries the same order of formations and the same
sequence of fossils, so that, in the course of a few years,
representatives of the Silurian system were found far and wide over
the globe. While Murchison was thus engaged, Sedgwick devoted himself
to the more difficult task of unravelling the complicated structure of
North Wales. He eventually made out the order of the several
formations there, with their vast intercalations of volcanic material.
He named them the Cambrian system (q.v.), and found them to contain
fossils, which, however, lay for some time unexamined by him. He at
first believed, as Murchison also did, that his rocks were all older
than any part of the Silurian series. It was eventually discovered
that a portion of them was equivalent to the lower part of that
series. The oldest of Sedgwick's groups, containing distinctive
fossils, retain the name Cambrian, and are of high interest, as they
enclose the remains of the earliest faunas which are yet well known.
Sedgwick and Murchison rendered yet another signal service to
stratigraphical geology by establishing, in 1839, on a basis of
palaeontological evidence supplied by W. Lonsdale, the independence of
the Devonian system (q.v.).

For many years the rocks below the oldest fossiliferous deposits
received comparatively little attention. They were vaguely described
as the "crystalline schists" and were often referred to as parts of
the primeval crust in which no chronology was to be looked for. W.E.
Logan (1798-1875) led the way, in Canada, by establishing there
several vast series of rocks, partly of crystalline schists and
gneisses (Laurentian) and partly of slates and conglomerates
(Huronian). Later observers, both in Canada and the United States,
have greatly increased our knowledge of these rocks, and have shown
their structure to be much more complex than was at first supposed
(see ARCHEAN SYSTEM).

During the latter half of the 19th century the most important
development of stratigraphical geology was the detailed working out
and application of the principle of zonal classification to the
fossiliferous formations--that is, the determination of the sequence
and distribution of organic remains in these formations, and the
arrangement of the strata into zones, each of which is distinguished
by a peculiar assemblage of fossil species (see under Part VI.). The
zones are usually named after one especially characteristic species.
This system of classification was begun in Germany with reference to
the members of the Jurassic system (q.v.) by A. Oppel (1856-1858) and
F.A. von Quenstedt (1858), and it has since been extended through the
other Mesozoic formations. It has even been found to be applicable to
the Palaeozoic rocks, which are now subdivided into palaeontological
zones. In the Silurian system, for example, the graptolites have been
shown by C. Lapworth to furnish a useful basis for zonal subdivisions.
The lowest fossiliferous horizon in the Cambrian rocks of Europe and
North America is known as the _Olenellus_ zone, from the prominence in
it of that genus of trilobite.

Another conspicuous feature in the progress of stratigraphy during the
second half of the 19th century was displayed by the rise and rapid
development of what is known as Glacial geology. The various deposits
of "drift" spread over northern Europe, and the boulders scattered
across the surface of the plains had long attracted notice, and had
even found a place in popular legend and superstition. When men began
to examine them with a view to ascertain their origin, they were
naturally regarded as evidences of the Noachian deluge. The first
observer who drew attention to the smoothed and striated surfaces of
rock that underlie the Drifts was Hutton's friend, Sir James Hall, who
studied them in the lowlands of Scotland and referred them to the
action of great debacles of water, which, in the course of some
ancient terrestrial convulsion, had been launched across the face of
the country. Playfair, however, pointed out that the most potent
geological agents for the transportation of large blocks of stone are
the glaciers. But no one was then bold enough to connect the travelled
boulders with glaciers on the plains of Germany and of Britain. Yet
the transporting agency of ice was invoked in explanation of their
diffusion. It came to be the prevalent belief among the geologists of
the first half of the 19th century, that the fall of temperature,
indicated by the gradual increase in the number of northern species of
shells in the English Crag deposits, reached its climax during the
time of the Drift, and that much of the north and centre of Europe was
then submerged beneath a sea, across which floating icebergs and floes
transported the materials of the Drift and dropped the scattered
boulders. As the phenomena are well developed around the Alps, it was
necessary to suppose that the submergence involved the lowlands of the
Continent up to the foot of that mountain chain--a geographical change
so stupendous as to demand much more evidence than was adduced in its
support. At last Louis Agassiz (1807-1873), who had varied his
palaeontological studies at Neuchatel by excursions into the Alps, was
so much struck by the proofs of the former far greater extension of
the Swiss glaciers, that he pursued the investigation and satisfied
himself that the ice had formerly extended from the Alpine valleys
right across the great plain of Switzerland, and had transported huge
boulders from the central mountains to the flanks of the Jura. In the
year 1840 he visited Britain and soon found evidence of similar
conditions there. He showed that it was not by submergence in a sea
cumbered with floating ice, but by the former presence of vast
glaciers or sheets of ice that the Drift and erratic blocks had been
distributed. The idea thus propounded by him did not at once command
complete approval, though traces of ancient glaciers in Scotland and
Wales were soon detected by native geologists, particularly by W.
Buckland, Lyell, J.D. Forbes and Charles Maclaren. Robert Chambers
(1802-1871) did good service in gathering additional evidence from
Scotland and Norway in favour of Agassiz's views, which steadily
gained adherents until, after some quarter of a century, they were
adopted by the great majority of geologists in Britain, and
subsequently in other countries. Since that time the literature of
geology has been swollen by a vast number of contributions in which
the history of the Glacial period, and its records both in the Old and
New World, have been fully discussed.

_Rise and Progress of Palaeontological Geology._--As this branch of
the science deals with the evidence furnished by fossil organic
remains as to former geographical conditions, it early attracted
observers who, in the superficial beds of marine shells found at some
distance from the coast, saw proofs of the former submergence of the
land under the sea. But the occurrence of fossils embedded in the
heart of the solid rocks of the mountains offered much greater
difficulties of explanation, and further progress was consequently
slow. Especially baneful was the belief that these objects were mere
sports of nature, and had no connexion with any once living organisms.
So long as the true organic origin of the fossil plants and animals
contained in the rocks was in dispute, it was hardly possible that
much advance could be made in their systematic study, or in the
geological deductions to be drawn from them. One good result of the
controversy, however, was to be seen in the large collections of these
"formed stones" that were gathered together in the cabinets and
museums of the 17th and 18th centuries. The accumulation and
comparison of these objects naturally led to the production of
treatises in which they were described and not unfrequently
illustrated by good engravings. Switzerland was more particularly
noted for the number and merit of its works of this kind, such as
that of K.N. Lang (_Historia lapidum figuratorum Helvetiae_, 1708) and
those of Johann Jacob Scheuchzer (1672-1733). In England, also,
illustrated treatises were published both by men who looked on fossils
as mere freaks of nature, and by those who regarded them as proofs of
Noah's flood. Of the former type were the works of Martin Lister
(1638-1712) and Robert Plot (_Natural History of Oxfordshire_, 1677).
The Celtic scholar Edward Llwyd (1660-1709) wrote a Latin treatise
containing good plates of a thousand fossils in the Ashmolean Museum,
Oxford, and J. Woodward, in 1728-1729, published his _Natural History
of the Fossils of England_, already mentioned, wherein he described
his own extensive collection, which he bequeathed to the University of
Cambridge, where it is still carefully preserved. The most voluminous
and important of all these works, however, appeared at a later date at
Nuremberg. It was begun by G.W. Knorr (1705-1761), who himself
engraved for it a series of plates, which for beauty and accuracy have
seldom been surpassed. After his death the work was continued by
J.E.I. Walch (1725-1778), and ultimately consisted of four massive
folio volumes and nearly 300 plates under the title of _Lapides
diluvii universalis testes_. Although the authors supposed their
fossils to be relics of Noah's flood, their work must be acknowledged
to mark a distinct onward stage in the palaeontological department of
geology.

It was in France that palaeontological geology began to be cultivated
in a scientific spirit. The potter Bernard Palissy, as far back as
1580, had dwelt on the importance of fossil shells as monuments of
revolutions of the earth's surface; but the observer who first
undertook the detailed study of the subject was Jean Etienne Guettard,
who began in 1751 to publish his descriptions of fossils in the form
of memoirs presented to the Academy of Sciences of Paris. To him they
were not only of deep interest as monuments of former types of
existence, but they had an especial value as records of the changes
which the country had undergone from sea to land and from land to sea.
More especially noteworthy was a monograph by him which appeared in
1765 bearing the title "On the accidents that have befallen Fossil
Shells compared with those which are found to happen to shells now
living in the Sea." In this treatise he showed that the fossils have
been encrusted with barnacles and serpulae, have been bored into by
other organisms, and have often been rounded or broken before final
entombment; and he inferred that these fossils must have lived and
died on the sea-floor under similar conditions to those which obtain
on the sea-floor to-day. His argument was the most triumphant that had
ever been brought against the doctrine of _lusus naturae_, and that of
the efficacy of Noah's flood--doctrines which still held their ground
in Guettard's day. When Soulavie, Cuvier and Brongniart in France, and
William Smith in England, showed that the rock formations of the
earth's crust could be arranged in chronological order, and could be
recognized far and wide by means of their enclosed organic remains,
the vast significance of these remains in geological research was
speedily realized, and palaeontological geology at once entered on a
new and enlarged phase of development. But apart from their value as
chronological monuments, and as witnesses of former conditions of
geography, fossils presented in themselves a wide field of
investigation as types of life that had formerly existed, but had now
passed away. It was in France that this subject first took definite
shape as an important branch of science. The mollusca of the Tertiary
deposits of the Paris basin became, in the hands of Lamarck, the basis
on which invertebrate palaeontology was founded. The same series of
strata furnished to Cuvier the remains of extinct land animals, of
which, by critical study of their fragmentary bones and skeletons, he
worked out restorations that may be looked on as the starting-point of
vertebrate palaeontology. These brilliant researches, rousing
widespread interest in such studies, showed how great a flood of light
could be thrown on the past history of the earth and its inhabitants.
But the full significance of these extinct types of life could not be
understood so long as the doctrine of the immutability of species, so
strenuously upheld by Cuvier, maintained its sway among naturalists.
Lamarck, as far back as the year 1800, had begun to propound his
theory of evolution and the transformation of species; but his views,
strongly opposed by Cuvier and the great body of naturalists of the
day, fell into neglect. Not until after the publication in 1859 of the
_Origin of Species_ by Charles Darwin were the barriers of old
prejudice in this matter finally broken down. The possibility of
tracing the ancestry of living forms back into the remotest ages was
then perceived; the time-honoured fiction that the stratified
formations record a series of catastrophes and re-creations was
finally dissipated; and the earth's crust was seen to contain a noble,
though imperfect, record of the grand evolution of organic types of
which our planet has been the theatre.

_Development of Petrographical Geology._--Theophrastus, the favourite
pupil of Aristotle, wrote a treatise _On Stones_, which has come down
to our own day, and may be regarded as the earliest work on
petrography. At a subsequent period Pliny, in his _Natural History_,
collected all that was known in his day regarding the occurrence and
uses of minerals and rocks. But neither of these works is of great
scientific importance, though containing much interesting information.
Minerals from their beauty and value attracted notice before much
attention was paid to rocks, and their study gave rise to the science
of mineralogy long before geology came into existence. When rocks
began to be more particularly scrutinized, it was chiefly from the
side of their usefulness for building and other economic purposes. The
occurrence of marine shells in many of them had early attracted
attention to them. But their varieties of composition and origin did
not become the subject of serious study until after Linnaeus and J.G.
Wallerius in the 18th century had made a beginning. The first
important contribution to this department of the science was that of
Werner, who in 1786 published a classification and description of
rocks in which he arranged them in two divisions, simple and compound,
and further distinguished them by various external characters and by
their relative age. The publication of this scheme may be said to mark
the beginning of scientific petrography. Werner's system, however, had
the serious defect that the chronological order in which he grouped
the rocks, and the hypothesis by which he accounted for them as
chemical precipitates from the original ocean, were both alike
contrary to nature. It was hardly possible indeed that much progress
could be made in this branch of geology until chemistry and mineralogy
had made greater advances; and especially until it was possible to
ascertain the intimate chemical and mineralogical composition, and the
minute structure of rocks. The study, however, continued to be pursued
in Germany, where the influence of Werner's enthusiasm still led men
to enter the petrographical rather than the palaeontological domain.
The resources of modern chemistry were pressed into the service, and
analyses were made and multiplied to such a degree that it seemed as
if the ultimate chemical constitution of every type of rock had now
been thoroughly revealed. The condition of the science in the middle
of the 19th century was well shown by J.L.A. Roth, who in 1861
collected about 1000 trustworthy analyses which up to that time had
been made. But though the chemical elements of the rocks had been
fairly well determined, the manner in which they were combined in the
compound rocks could for the most part be only more or less plausibly
conjectured. As far back as 1831 an account was published of a process
devised by William Nicol of Edinburgh, whereby sections of fossil wood
could be cut, mounted on glass, and reduced to such a degree of
transparency as to be easily examined under a microscope. Henry Sorby,
of Sheffield, having seen Nicol's preparations, perceived how
admirably adapted the process was for the study of the minute
structure and composition of rocks. In 1858 he published in the
_Quarterly Journal of the Geological Society_ a paper "On the
Microscopical Structure of Crystals." This essay led to a complete
revolution of petrographical methods and gave a vast impetus to the
study of rocks. Petrology entered upon a new and wider field of
investigation. Not only were the mineralogical constituents of the
rocks detected, but minute structures were revealed which shed new
light on the origin and history of these mineral masses, and opened up
new paths in theoretical geology. In the hands of H. Vogelsang, F.
Zirkel, H. Rosenbusch, and a host of other workers in all civilized
countries, the literature of this department of the science has grown
to a remarkable extent. Armed with the powerful aid of modern optical
instruments, geologists are now able with far more prospect of success
to resume the experiments begun a century before by de Saussure and
Hall. G.A. Daubree, C. Friedel, E. Sarasin, F. Fouque and A. Michel
Levy in France, C. Doelter y Cisterich and E. Hussak of Gratz, J.
Morozewicz of Warsaw and others, have greatly advanced our knowledge
by their synthetical analyses, and there is every reason to hope that
further advances will be made in this field of research.

_Rise of Physiographical Geology._--Until stratigraphical geology had
advanced so far as to show of what a vast succession of rocks the
crust of the earth is built up, by what a long and complicated series
of revolutions these rocks have come to assume their present
positions, and how enormous has been the lapse of time which all these
changes represent, it was not possible to make a scientific study of
the surface features of our globe. From ancient times it had been
known that many parts of the land had once been under the sea; but
down even to the beginning of the 19th century the vaguest conceptions
continued to prevail as to the operations concerned in the submergence
and elevation of land, and as to the processes whereby the present
outlines of terrestrial topography were determined. We have seen, for
instance, that according to the teaching of Werner the oldest rocks
were first precipitated from solution in the universal ocean to form
the mountains, that the vertical position of their strata was
original, that as the waters subsided successive formations were
deposited and laid bare, and that finally the superfluous portion of
the ocean was whisked away into space by some unexplained co-operation
of another planetary body. Desmarest, in his investigation of the
volcanic history of Auvergne, was the first observer to perceive by
what a long process of sculpture the present configuration of the land
has been brought about. He showed conclusively that the valleys have
been carved out by the streams that flow in them, and that while they
have sunk deeper and deeper into the framework of the land, the spaces
of ground between them have been left as intervening ridges and hills.
De Saussure learnt a similar lesson from his studies of the Alps, and
Hutton and Playfair made it a cardinal feature in their theory of the
earth. Nevertheless the idea encountered so much opposition that it
made but little way until after the middle of the 19th century.
Geologists preferred to believe in convulsions of nature, whereby
valleys were opened and mountains were upheaved. That the main
features of the land, such as the great mountain-chains, had been
produced by gigantic plication of the terrestrial crust was now
generally admitted, and also that minor fractures and folds had
probably initiated many of the valleys. But those who realized most
vividly the momentous results achieved by ages of subaerial denudation
perceived that, as Hutton showed, even without the aid of underground
agency, the mere flow of water in streams across a mass of land must
in course of time carve out just such a system of valleys as may
anywhere be seen. It was J.B. Jukes who, in 1862, first revived the
Huttonian doctrine, and showed how completely it explained the
drainage-lines in the south of Ireland. Other writers followed in
quick succession until, in a few years, the doctrine came to be widely
recognized as one of the established principles of modern geology.
Much help was derived from the admirable illustrations of
land-sculpture and river-erosion supplied from the Western Territories
and States of the American Union.

Another branch of physiographical geology which could only come into
existence after most of the other departments of the science had made
large progress, deals with the evolution of the framework of each
country and of the several continents and oceans of the globe. It is
now possible, with more or less confidence, to trace backward the
history of every terrestrial area, to see how sea and land have there
succeeded each other, how rivers and lakes have come and gone, how the
crust of the earth has been ridged up at widely separated intervals,
each movement determining some line of mountains or plains, how the
boundaries of the oceans have shifted again and again in the past, and
thus how, after so prolonged a series of revolutions, the present
topography of each country, and of the globe as a whole, has been
produced. In the prosecution of this subject maps have been
constructed to show what is conjectured to have been the distribution
of sea and land during the various geological periods in different
parts of the world, and thus to indicate the successive stages through
which the architecture of the land has been gradually evolved. The
most noteworthy contribution to this department of the science is the
_Antlitz der Erde_ of Professor Suess of Vienna. This important and
suggestive work has been translated into French and English.