A History of Science, Volume 3
by
Henry Smith Williams
Part 2 out of 6
adapted themselves wonderfully to planetary customs,
for all of them revolve in the same direction with the
planets, and in planes not wide of the ecliptic.
Checked in their proud hyperbolic sweep, made captive
in a planetary net, deprived of their trains, these
quondam free-lances of the heavens are now mere
shadows of their former selves. Considered as to mere
bulk, they are very substantial shadows, their extent
being measured in hundreds of thousands of miles; but
their actual mass is so slight that they are quite at the
mercy of the gravitation pulls of their captors. And
worse is in store for them. So persistently do sun and
planets tug at them that they are doomed presently to
be torn into shreds.
Such a fate has already overtaken one of them, under
the very eyes of the astronomers, within the relatively
short period during which these ill-fated comets have.
been observed. In 1832 Biela's comet passed quite
near the earth, as astronomers measure distance, and in
doing so created a panic on our planet. It did no
greater harm than that, of course, and passed on its
way as usual. The very next time it came within telescopic
hail it was seen to have broken into two fragments.
Six years later these fragments were separated
by many millions of miles; and in 1852, when the comet
was due again, astronomers looked for it in vain. It
had been completely shattered.
What had become of the fragments? At that time
no one positively knew. But the question was to be
answered presently. It chanced that just at this period
astronomers were paying much attention to a class of
bodies which they had hitherto somewhat neglected,
the familiar shooting-stars, or meteors. The studies of
Professor Newton, of Yale, and Professor Adams, of
Cambridge, with particular reference to the great
meteor-shower of November, 1866, which Professor Newton
had predicted and shown to be recurrent at intervals
of thirty-three years, showed that meteors are
not mere sporadic swarms of matter flying at random,
but exist in isolated swarms, and sweep about the sun
in regular elliptical orbits.
Presently it was shown by the Italian astronomer
Schiaparelli that one of these meteor swarms moves
in the orbit of a previously observed comet, and other
coincidences of the kind were soon forthcoming. The
conviction grew that meteor swarms are really the
debris of comets; and this conviction became a practical
certainty when, in November, 1872, the earth
crossed the orbit of the ill-starred Biela, and a shower
of meteors came whizzing into our atmosphere in lieu
of the lost comet.
And so at last the full secret was out. The awe-
inspiring comet, instead of being the planetary body
it had all along been regarded, is really nothing more
nor less than a great aggregation of meteoric particles,
which have become clustered together out in space
somewhere, and which by jostling one another or
through electrical action become luminous. So widely
are the individual particles separated that the cometary
body as a whole has been estimated to be thousands of
times less dense than the earth's atmosphere at sea-
level. Hence the ease with which the comet may be
dismembered and its particles strung out into streaming
swarms.
So thickly is the space we traverse strewn with this
cometary dust that the earth sweeps up, according to
Professor Newcomb's estimate, a million tons of it each
day. Each individual particle, perhaps no larger than
a millet seed, becomes a shooting-star, or meteor, as it
burns to vapor in the earth's upper atmosphere. And
if one tiny planet sweeps up such masses of this cosmic
matter, the amount of it in the entire stretch of our system
must be beyond all estimate. What a story it tells
of the myriads of cometary victims that have fallen
prey to the sun since first he stretched his planetary net
across the heavens!
THE FIXED STARS
When Biela's comet gave the inhabitants of the earth
such a fright in 1832, it really did not come within
fifty millions of miles of us. Even the great comet
through whose filmy tail the earth passed in 1861 was
itself fourteen millions of miles away. The ordinary
mind, schooled to measure space by the tiny stretches
of a pygmy planet, cannot grasp the import of such
distances; yet these are mere units of measure compared
with the vast stretches of sidereal space. Were
the comet which hurtles past us at a speed of, say, a
hundred miles a second to continue its mad flight unchecked
straight into the void of space, it must fly on
its frigid way eight thousand years before it could
reach the very nearest of our neighbor stars; and even
then it would have penetrated but a mere arm's-length
into the vistas where lie the dozen or so of sidereal residents
that are next beyond. Even to the trained mind
such distances are only vaguely imaginable. Yet the
astronomer of our century has reached out across this
unthinkable void and brought back many a secret
which our predecessors thought forever beyond human
grasp.
A tentative assault upon this stronghold of the stars
was being made by Herschel at the beginning of the
century. In 1802 that greatest of observing astronomers
announced to the Royal Society his discovery that
certain double stars had changed their relative positions
towards one another since he first carefully charted
them twenty years before. Hitherto it had been supposed
that double stars were mere optical effects. Now
it became clear that some of them, at any rate, are
true "binary systems," linked together presumably by
gravitation and revolving about one another. Halley
had shown, three-quarters of a century before, that the
stars have an actual or "proper" motion in space;
Herschel himself had proved that the sun shares this
motion with the other stars. Here was another shift
of place, hitherto quite unsuspected, to be reckoned
with by the astronomer in fathoming sidereal secrets.
Double Stars
When John Herschel, the only son and the worthy
successor of the great astronomer, began star-gazing in
earnest, after graduating senior wrangler at Cambridge,
and making two or three tentative professional starts in
other directions to which his versatile genius impelled
him, his first extended work was the observation of his
father's double stars. His studies, in which at first he
had the collaboration of Mr. James South, brought to
light scores of hitherto unrecognized pairs, and gave
fresh data for the calculation of the orbits of those
longer known. So also did the independent researches
of F. G. W. Struve, the enthusiastic observer of the
famous Russian observatory at the university of Dorpat,
and subsequently at Pulkowa. Utilizing data
gathered by these observers, M. Savary, of Paris,
showed, in 1827, that the observed elliptical orbits of
the double stars are explicable by the ordinary laws of
gravitation, thus confirming the assumption that Newton's
laws apply to these sidereal bodies. Henceforth
there could be no reason to doubt that the same force
which holds terrestrial objects on our globe pulls at
each and every particle of matter throughout the visible
universe.
The pioneer explorers of the double stars early found
that the systems into which the stars are linked are by
no means confined to single pairs. Often three or four
stars are found thus closely connected into gravitation
systems; indeed, there are all gradations between binary
systems and great clusters containing hundreds or
even thousands of members. It is known, for example,
that the familiar cluster of the Pleiades is not merely
an optical grouping, as was formerly supposed, but an
actual federation of associated stars, some two thousand
five hundred in number, only a few of which are
visible to the unaided eve. And the more carefully
the motions of the stars are studied, the more evident
it becomes that widely separated stars are linked together
into infinitely complex systems, as yet but little
understood. At the same time, all instrumental advances
tend to resolve more and more seemingly single
stars into close pairs and minor clusters. The two
Herschels between them discovered some thousands
of these close multiple systems; Struve and others increased
the list to above ten thousand; and Mr. S. W.
Burnham, of late years the most enthusiastic and successful
of double-star pursuers, added a thousand new
discoveries while he was still an amateur in astronomy,
and by profession the stenographer of a Chicago court.
Clearly the actual number of multiple stars is beyond
all present estimate.
The elder Herschel's early studies of double stars
were undertaken in the hope that these objects might
aid him in ascertaining the actual distance of a star,
through measurement of its annual parallax--that is to
say, of the angle which the diameter of the earth's
orbit would subtend as seen from the star. The expectation
was not fulfilled. The apparent shift of
position of a star as viewed from opposite sides of the
earth's orbit, from which the parallax might be estimated,
is so extremely minute that it proved utterly
inappreciable, even to the almost preternaturally acute
vision of Herschel, with the aid of any instrumental
means then at command. So the problem of star distance
allured and eluded him to the end, and he died
in 1822 without seeing it even in prospect of solution.
His estimate of the minimum distance of the nearest
star, based though it was on the fallacious test of apparent
brilliancy, was a singularly sagacious one, but it
was at best a scientific guess, not a scientific measurement.
The Distance of the Stars
Just about this time, however, a great optician came
to the aid of the astronomers. Joseph Fraunhofer perfected
the refracting telescope, as Herschel had perfected
the reflector, and invented a wonderfully accurate
"heliometer," or sun-measurer. With the aid of
these instruments the old and almost infinitely difficult
problem of star distance was solved. In 1838 Bessel
announced from the Konigsberg observatory that he
had succeeded, after months of effort, in detecting and
measuring the parallax of a star. Similar claims had
been made often enough before, always to prove fallacious
when put to further test; but this time the announcement
carried the authority of one of the greatest
astronomers of the age, and scepticism was silenced.
Nor did Bessel's achievement long await corroboration.
Indeed, as so often happens in fields of discovery,
two other workers had almost simultaneously
solved the same problem--Struve at Pulkowa, where
the great Russian observatory, which so long held the
palm over all others, had now been established; and
Thomas Henderson, then working at the Cape of Good
Hope, but afterwards the Astronomer Royal of Scotland.
Henderson's observations had actual precedence
in point of time, but Bessel's measurements were so
much more numerous and authoritative that he has
been uniformly considered as deserving the chief credit
of the discovery, which priority of publication secured
him.
By an odd chance, the star on which Henderson's observations
were made, and consequently the first star
the parallax of which was ever measured, is our nearest
neighbor in sidereal space, being, indeed, some ten billions
of miles nearer than the one next beyond. Yet
even this nearest star is more than two hundred thousand
times as remote from us as the sun. The sun's
light flashes to the earth in eight minutes, and to Neptune
in about three and a half hours, but it requires
three and a half years to signal Alpha Centauri. And
as for the great majority of the stars, had they been
blotted out of existence before the Christian era, we of
to-day should still receive their light and seem to see
them just as we do. When we look up to the sky, we
study ancient history; we do not see the stars as they
ARE, but as they WERE years, centuries, even millennia
ago.
The information derived from the parallax of a star
by no means halts with the disclosure of the distance of
that body. Distance known, the proper motion of the
star, hitherto only to be reckoned as so many seconds of
arc, may readily be translated into actual speed of progress;
relative brightness becomes absolute lustre, as
compared with the sun; and in the case of the double
stars the absolute mass of the components may be computed
from the laws of gravitation. It is found that
stars differ enormously among themselves in all these
regards. As to speed, some, like our sun, barely creep
through space--compassing ten or twenty miles a second,
it is true, yet even at that rate only passing
through the equivalent of their own diameter in a day.
At the other extreme, among measured stars, is one
that moves two hundred miles a second; yet even this
"flying star," as seen from the earth, seems to change
its place by only about three and a half lunar diameters
in a thousand years. In brightness, some stars yield to
the sun, while others surpass him as the arc-light surpasses
a candle. Arcturus, the brightest measured star,
shines like two hundred suns; and even this giant orb
is dim beside those other stars which are so distant that
their parallax cannot be measured, yet which greet our
eyes at first magnitude. As to actual bulk, of which
apparent lustre furnishes no adequate test, some stars
are smaller than the sun, while others exceed him hundreds
or perhaps thousands of times. Yet one and all,
so distant are they, remain mere disklike points of light
before the utmost powers of the modern telescope.
Revelations of the Spectroscope
All this seems wonderful enough, but even greater
things were in store. In 1859 the spectroscope came
upon the scene, perfected by Kirchhoff and Bunsen,
along lines pointed out by Fraunhofer almost half a
century before. That marvellous instrument, by
revealing the telltale lines sprinkled across a prismatic
spectrum, discloses the chemical nature and physical
condition of any substance whose light is submitted to
it, telling its story equally well, provided the light be
strong enough, whether the luminous substance be near
or far--in the same room or at the confines of space.
Clearly such an instrument must prove a veritable
magic wand in the hands of the astronomer.
Very soon eager astronomers all over the world were
putting the spectroscope to the test. Kirchhoff himself
led the way, and Donati and Father Secchi in Italy,
Huggins and Miller in England, and Rutherfurd in
America, were the chief of his immediate followers.
The results exceeded the dreams of the most visionary.
At the very outset, in 1860, it was shown that such
common terrestrial substances as sodium, iron, calcium,
magnesium, nickel, barium, copper, and zinc exist
in the form of glowing vapors in the sun, and very soon
the stars gave up a corresponding secret. Since then
the work of solar and sidereal analysis has gone on
steadily in the hands of a multitude of workers (prominent
among whom, in this country, are Professor
Young of Princeton, Professor Langley of Washington,
and Professor Pickering of Harvard), and more
than half the known terrestrial elements have been
definitely located in the sun, while fresh discoveries
are in prospect.
It is true the sun also contains some seeming elements
that are unknown on the earth, but this is no
matter for surprise. The modern chemist makes no
claim for his elements except that they have thus far
resisted all human efforts to dissociate them; it would
be nothing strange if some of them, when subjected to
the crucible of the sun, which is seen to vaporize iron,
nickel, silicon, should fail to withstand the test. But
again, chemistry has by no means exhausted the resources
of the earth's supply of raw material, and the
substance which sends its message from a star may
exist undiscovered in the dust we tread or in the air
we breathe. In the year 1895 two new terrestrial elements
were discovered; but one of these had for years
been known to the astronomer as a solar and suspected
as a stellar element, and named helium because of its
abundance in the sun. The spectroscope had reached
out millions of miles into space and brought back this
new element, and it took the chemist a score of years
to discover that he had all along had samples of the
same substance unrecognized in his sublunary laboratory.
There is hardly a more picturesque fact than
that in the entire history of science.
But the identity in substance of earth and sun and
stars was not more clearly shown than the diversity of
their existing physical conditions. It was seen that sun
and stars, far from being the cool, earthlike, habitable
bodies that Herschel thought them (surrounded by
glowing clouds, and protected from undue heat by other
clouds), are in truth seething caldrons of fiery liquid, or
gas made viscid by condensation, with lurid envelopes
of belching flames. It was soon made clear, also,
particularly by the studies of Rutherfurd and of Secchi,
that stars differ among themselves in exact constitution
or condition. There are white or Sirian stars, whose
spectrum revels in the lines of hydrogen; yellow or
solar stars (our sun being the type), showing various
metallic vapors; and sundry red stars, with banded
spectra indicative of carbon compounds; besides the
purely gaseous stars of more recent discovery, which
Professor Pickering had specially studied. Zollner's
famous interpretation of these diversities, as indicative
of varying stages of cooling, has been called in question
as to the exact sequence it postulates, but the general
proposition that stars exist under widely varying conditions
of temperature is hardly in dispute.
The assumption that different star types mark varying
stages of cooling has the further support of modern
physics, which has been unable to demonstrate any way
in which the sun's radiated energy may be restored, or
otherwise made perpetual, since meteoric impact has
been shown to be--under existing conditions, at any
rate--inadequate. In accordance with the theory of
Helmholtz, the chief supply of solar energy is held to
be contraction of the solar mass itself; and plainly this
must have its limits. Therefore, unless some means as
yet unrecognized is restoring the lost energy to the
stellar bodies, each of them must gradually lose its lustre,
and come to a condition of solidification, seeming
sterility, and frigid darkness. In the case of our own
particular star, according to the estimate of Lord
Kelvin, such a culmination appears likely to occur
within a period of five or six million years.
The Astronomy of the Invisible
But by far the strongest support of such a forecast as
this is furnished by those stellar bodies which even now
appear to have cooled to the final stage of star development
and ceased to shine. Of this class examples in
miniature are furnished by the earth and the smaller of
its companion planets. But there are larger bodies of
the same type out in stellar space--veritable "dark
stars"--invisible, of course, yet nowadays clearly recognized.
The opening up of this "astronomy of the invisible"
is another of the great achievements of the nineteenth
century, and again it is Bessel to whom the honor of
discovery is due. While testing his stars for parallax;
that astute observer was led to infer, from certain
unexplained aberrations of motion, that various stars,
Sirius himself among the number, are accompanied by
invisible companions, and in 1840 he definitely predicated
the existence of such "dark stars." The correctness
of the inference was shown twenty years
later, when Alvan Clark, Jr., the American optician,
while testing a new lens, discovered the companion of
Sirius, which proved thus to be faintly luminous.
Since then the existence of other and quite invisible
star companions has been proved incontestably, not
merely by renewed telescopic observations, but by the
curious testimony of the ubiquitous spectroscope.
One of the most surprising accomplishments of that
instrument is the power to record the flight of a luminous
object directly in the line of vision. If the luminous
body approaches swiftly, its Fraunhofer lines are
shifted from their normal position towards the violet
end of the spectrum; if it recedes, the lines shift in the
opposite direction. The actual motion of stars whose
distance is unknown may be measured in this way.
But in certain cases the light lines are seen to oscillate
on the spectrum at regular intervals. Obviously the
star sending such light is alternately approaching and
receding, and the inference that it is revolving about a
companion is unavoidable. From this extraordinary
test the orbital distance, relative mass, and actual
speed of revolution of the absolutely invisible body
may be determined. Thus the spectroscope, which
deals only with light, makes paradoxical excursions
into the realm of the invisible. What secrets may the
stars hope to conceal when questioned by an instrument
of such necromantic power?
But the spectroscope is not alone in this audacious
assault upon the strongholds of nature. It has a worthy
companion and assistant in the photographic film,
whose efficient aid has been invoked by the astronomer
even more recently. Pioneer work in celestial
photography was, indeed, done by Arago in France and
by the elder Draper in America in 1839, but the results
then achieved were only tentative, and it was not till
forty years later that the method assumed really important
proportions. In 1880, Dr. Henry Draper, at
Hastings-on-the-Hudson, made the first successful
photograph of a nebula. Soon after, Dr. David Gill,
at the Cape observatory, made fine photographs of a
comet, and the flecks of starlight on his plates first
suggested the possibilities of this method in charting
the heavens.
Since then star-charting with the film has come virtually
to supersede the old method. A concerted effort
is being made by astronomers in various parts of the
world to make a complete chart of the heavens, and
before the close of our century this work will be accomplished,
some fifty or sixty millions of visible stars being
placed on record with a degree of accuracy hitherto
unapproachable. Moreover, other millions of stars
are brought to light by the negative, which are too distant
or dim to be visible with any telescopic powers
yet attained--a fact which wholly discredits all previous
inferences as to the limits of our sidereal system.
Hence, notwithstanding the wonderful instrumental
advances of the nineteenth century, knowledge of the
exact form and extent of our universe seems more
unattainable than it seemed a century ago.
The Structure of Nebulae
Yet the new instruments, while leaving so much
untold, have revealed some vastly important secrets of
cosmic structure. In particular, they have set at rest
the long-standing doubts as to the real structure and
position of the mysterious nebulae--those lazy masses,
only two or three of them visible to the unaided eye,
which the telescope reveals in almost limitless abundance,
scattered everywhere among the stars, but
grouped in particular about the poles of the stellar
stream or disk which we call the Milky Way.
Herschel's later view, which held that some at least
of the nebulae are composed of a "shining fluid," in
process of condensation to form stars, was generally
accepted for almost half a century. But in 1844, when
Lord Rosse's great six-foot reflector--the largest telescope
ever yet constructed--was turned on the nebulae,
it made this hypothesis seem very doubtful. Just as
Galileo's first lens had resolved the Milky Way into
stars, just as Herschel had resolved nebulae that resisted
all instruments but his own, so Lord Rosse's even
greater reflector resolved others that would not yield to
Herschel's largest mirror. It seemed a fair inference
that with sufficient power, perhaps some day to be attained,
all nebulae would yield, hence that all are in
reality what Herschel had at first thought them--
vastly distant "island universes," composed of aggregations
of stars, comparable to our own galactic system.
But the inference was wrong; for when the spectroscope
was first applied to a nebula in 1864, by Dr. Huggins,
it clearly showed the spectrum not of discrete
stars, but of a great mass of glowing gases, hydrogen
among others. More extended studies showed, it is
true, that some nebulae give the continuous spectrum
of solids or liquids, but the different types intermingle
and grade into one another. Also, the closest affinity
is shown between nebulae and stars. Some nebulae are
found to contain stars, singly or in groups, in their
actual midst; certain condensed "planetary" nebulae
are scarcely to be distinguished from stars of the gaseous
type; and recently the photographic film has
shown the presence of nebulous matter about stars
that to telescopic vision differ in no respect from the
generality of their fellows in the galaxy. The familiar
stars of the Pleiades cluster, for example, appear on the
negative immersed in a hazy blur of light. All in all,
the accumulated impressions of the photographic film
reveal a prodigality of nebulous matter in the stellar
system not hitherto even conjectured.
And so, of course, all question of "island universes"
vanishes, and the nebulae are relegated to their true position
as component parts of the one stellar system--the
one universe--that is open to present human inspection.
And these vast clouds of world-stuff have been found
by Professor Keeler, of the Lick observatory, to be
floating through space at the starlike speed of from
ten to thirty-eight miles per second.
The linking of nebulae with stars, so clearly evidenced
by all these modern observations, is, after all,
only the scientific corroboration of what the elder Herschel's
later theories affirmed. But the nebulae have
other affinities not until recently suspected; for the
spectra of some of them are practically identical with
the spectra of certain comets. The conclusion seems
warranted that comets are in point of fact minor nebulae
that are drawn into our system; or, putting it otherwise,
that the telescopic nebulae are simply gigantic
distant comets.
Lockyer's Meteoric Hypothesis
Following up the surprising clews thus suggested,
Sir Norman Lockyer, of London, has in recent years
elaborated what is perhaps the most comprehensive
cosmogonic guess that has ever been attempted. His
theory, known as the "meteoric hypothesis," probably
bears the same relation to the speculative thought of
our time that the nebular hypothesis of Laplace bore
to that of the eighteenth century. Outlined in a few
words, it is an attempt to explain all the major phenomena
of the universe as due, directly or indirectly, to
the gravitational impact of such meteoric particles, or
specks of cosmic dust, as comets are composed of. Nebulae
are vast cometary clouds, with particles more or
less widely separated, giving off gases through meteoric
collisions, internal or external, and perhaps glowing also
with electrical or phosphorescent light. Gravity eventually
brings the nebular particles into closer aggregations,
and increased collisions finally vaporize the entire
mass, forming planetary nebulae and gaseous stars.
Continued condensation may make the stellar mass
hotter and more luminous for a time, but eventually
leads to its liquefaction, and ultimate consolidation--
the aforetime nebulae becoming in the end a dark or
planetary star.
The exact correlation which Lockyer attempts to
point out between successive stages of meteoric condensation
and the various types of observed stellar bodies
does not meet with unanimous acceptance. Mr.
Ranyard, for example, suggests that the visible nebulae
may not be nascent stars, but emanations from stars,
and that the true pre-stellar nebulae are invisible until
condensed to stellar proportions. But such details
aside, the broad general hypothesis that all the bodies
of the universe are, so to speak, of a single species--
that nebulae (including comets), stars of all types, and
planets, are but varying stages in the life history of a
single race or type of cosmic organisms--is accepted
by the dominant thought of our time as having the
highest warrant of scientific probability.
All this, clearly, is but an amplification of that nebular
hypothesis which, long before the spectroscope gave
us warrant to accurately judge our sidereal neighbors,
had boldly imagined the development of stars out of
nebulae and of planets out of stars. But Lockyer's
hypothesis does not stop with this. Having traced the
developmental process from the nebular to the dark
star, it sees no cause to abandon this dark star to its
fate by assuming, as the original speculation assumed,
that this is a culminating and final stage of cosmic existence.
For the dark star, though its molecular activities
have come to relative stability and impotence,
still retains the enormous potentialities of molar motion;
and clearly, where motion is, stasis is not. Sooner
or later, in its ceaseless flight through space, the dark
star must collide with some other stellar body, as Dr.
Croll imagines of the dark bodies which his "pre-nebular
theory" postulates. Such collision may be long
delayed; the dark star may be drawn in comet-like circuit
about thousands of other stellar masses, and be
hurtled on thousands of diverse parabolic or elliptical
orbits, before it chances to collide--but that matters
not: "billions are the units in the arithmetic of eternity,"
and sooner or later, we can hardly doubt, a collision
must occur. Then without question the mutual
impact must shatter both colliding bodies into vapor,
or vapor combined with meteoric fragments; in short,
into a veritable nebula, the matrix of future worlds.
Thus the dark star, which is the last term of one series
of cosmic changes, becomes the first term of another
series--at once a post-nebular and a pre-nebular condition;
and the nebular hypothesis, thus amplified,
ceases to be a mere linear scale, and is rounded out to
connote an unending series of cosmic cycles, more
nearly satisfying the imagination.
In this extended view, nebulae and luminous stars are
but the infantile and adolescent stages of the life history
of the cosmic individual; the dark star, its adult
stage, or time of true virility. Or we may think of the
shrunken dark star as the germ-cell, the pollen-grain, of
the cosmic organism. Reduced in size, as becomes a
germ-cell, to a mere fraction of the nebular body from
which it sprang, it yet retains within its seemingly non-
vital body all the potentialities of the original organism,
and requires only to blend with a fellow-cell to
bring a new generation into being. Thus may the
cosmic race, whose aggregate census makes up the
stellar universe, be perpetuated--individual solar systems,
such as ours, being born, and growing old, and
dying to live again in their descendants, while the universe
as a whole maintains its unified integrity throughout
all these internal mutations--passing on, it may be,
by infinitesimal stages, to a culmination hopelessly beyond
human comprehension.
III. THE NEW SCIENCE OF PALEONTOLOGY
WILLIAM SMITH AND FOSSIL SHELLS
Ever since Leonardo da Vinci first recognized the
true character of fossils, there had been here and
there a man who realized that the earth's rocky crust
is one gigantic mausoleum. Here and there a dilettante
had filled his cabinets with relics from this monster
crypt; here and there a philosopher had pondered
over them--questioning whether perchance they had
once been alive, or whether they were not mere
abortive souvenirs of that time when the fertile matrix
of the earth was supposed to have
"teemed at a birth
Innumerous living creatures, perfect forms,
Limbed and full grown."
Some few of these philosophers--as Robert Hooke and
Steno in the seventeenth century, and Moro, Leibnitz,
Buffon, Whitehurst, Werner, Hutton, and others in the
eighteenth--had vaguely conceived the importance of
fossils as records of the earth's ancient history, but the
wisest of them no more suspected the full import of the
story written in the rocks than the average stroller in
a modern museum suspects the meaning of the hieroglyphs
on the case of a mummy.
It was not that the rudiments of this story are so
very hard to decipher--though in truth they are hard
enough--but rather that the men who made the attempt
had all along viewed the subject through an atmosphere
of preconception, which gave a distorted
image. Before this image could be corrected it was
necessary that a man should appear who could see
without prejudice, and apply sound common-sense to
what he saw. And such a man did appear towards the
close of the century, in the person of William Smith, the
English surveyor. He was a self-taught man, and perhaps
the more independent for that, and he had the
gift, besides his sharp eyes and receptive mind, of a
most tenacious memory. By exercising these faculties,
rare as they are homely, he led the way to a
science which was destined, in its later developments,
to shake the structure of established thought to its
foundations.
Little enough did William Smith suspect, however,
that any such dire consequences were to come of his act
when he first began noticing the fossil shells that here
and there are to be found in the stratified rocks and
soils of the regions over which his surveyor's duties led
him. Nor, indeed, was there anything of such apparent
revolutionary character in the facts which he
unearthed; yet in their implications these facts were
the most disconcerting of any that had been revealed
since the days of Copernicus and Galileo. In its bald
essence, Smith's discovery was simply this: that the
fossils in the rocks, instead of being scattered haphazard,
are arranged in regular systems, so that any
given stratum of rock is labelled by its fossil population;
and that the order of succession of such groups of
fossils is always the same in any vertical series of strata
in which they occur. That is to say, if fossil A underlies
fossil B in any given region, it never overlies it in
any other series; though a kind of fossils found in one
set of strata may be quite omitted in another. Moreover,
a fossil once having disappeared never reappears
in any later stratum.
From these novel facts Smith drew the commonsense
inference that the earth had had successive populations
of creatures, each of which in its turn had become
extinct. He partially verified this inference by
comparing the fossil shells with existing species of similar
orders, and found that such as occur in older
strata of the rocks had no counterparts among living
species. But, on the whole, being eminently a practical
man, Smith troubled himself but little about the inferences
that might be drawn from his facts. He was
chiefly concerned in using the key he had discovered
as an aid to the construction of the first geological map
of England ever attempted, and he left to others the
untangling of any snarls of thought that might seem
to arise from his discovery of the succession of varying
forms of life on the globe.
He disseminated his views far and wide, however, in
the course of his journeyings--quite disregarding the
fact that peripatetics went out of fashion when the
printing-press came in--and by the beginning of the
nineteenth century he had begun to have a following
among the geologists of England. It must not for a
moment be supposed, however, that his contention regarding
the succession of strata met with immediate
or general acceptance. On the contrary, it was most
bitterly antagonized. For a long generation after the
discovery was made, the generality of men, prone as
always to strain at gnats and swallow camels, preferred
to believe that the fossils, instead of being deposited in
successive ages, had been swept all at once into their
present positions by the current of a mighty flood--and
that flood, needless to say, the Noachian deluge. Just
how the numberless successive strata could have been
laid down in orderly sequence to the depth of several
miles in one such fell cataclysm was indeed puzzling,
especially after it came to be admitted that the heaviest
fossils were not found always at the bottom; but to
doubt that this had been done in some way was rank
heresy in the early days of the nineteenth century.
CUVIER AND FOSSIL VERTEBRATES
But once discovered, William Smith's unique facts
as to the succession of forms in the rocks would not
down. There was one most vital point, however, regarding
which the inferences that seem to follow from
these facts needed verification--the question, namely,
whether the disappearance of a fauna from the register
in the rocks really implies the extinction of that fauna.
Everything really depended upon the answer to that
question, and none but an accomplished naturalist
could answer it with authority. Fortunately, the most
authoritative naturalist of the time, George Cuvier,
took the question in hand--not, indeed, with the idea
of verifying any suggestion of Smith's, but in the course
of his own original studies--at the very beginning of
the century, when Smith's views were attracting general
attention.
Cuvier and Smith were exact contemporaries, both
men having been born in 1769, that "fertile year"
which gave the world also Chateaubriand, Von Humboldt,
Wellington, and Napoleon. But the French naturalist
was of very different antecedents from the English
surveyor. He was brilliantly educated, had early
gained recognition as a scientist, and while yet a young
man had come to be known as the foremost comparative
anatomist of his time. It was the anatomical
studies that led him into the realm of fossils. Some
bones dug out of the rocks by workmen in a quarry
were brought to his notice, and at once his trained eye
told him that they were different from anything he had
seen before. Hitherto such bones, when not entirely
ignored, had been for the most part ascribed to giants
of former days, or even to fallen angels. Cuvier soon
showed that neither giants nor angels were in question,
but elephants of an unrecognized species. Continuing
his studies, particularly with material gathered from
gypsum beds near Paris, he had accumulated, by the
beginning of the nineteenth century, bones of about
twenty-five species of animals that he believed to be
different from any now living on the globe.
The fame of these studies went abroad, and presently
fossil bones poured in from all sides, and Cuvier's conviction
that extinct forms of animals are represented
among the fossils was sustained by the evidence of
many strange and anomalous forms, some of them of
gigantic size. In 1816 the famous Ossements Fossiles,
describing these novel objects, was published, and vertebrate
paleontology became a science. Among other
things of great popular interest the book contained the
first authoritative description of the hairy elephant,
named by Cuvier the mammoth, the remains of which
bad been found embedded in a mass of ice in Siberia in
1802, so wonderfully preserved that the dogs of the
Tungusian fishermen actually ate its flesh. Bones of
the same species had been found in Siberia several
years before by the naturalist Pallas, who had also
found the carcass of a rhinoceros there, frozen in a
mud-bank; but no one then suspected that these were
members of an extinct population--they were supposed
to be merely transported relics of the flood.
Cuvier, on the other hand, asserted that these and the
other creatures he described had lived and died in the
region where their remains were found, and that most
of them have no living representatives upon the globe.
This, to be sure, was nothing more than William Smith
had tried all along to establish regarding lower forms of
life; but flesh and blood monsters appeal to the imagination
in a way quite beyond the power of mere shells;
so the announcement of Cuvier's discoveries aroused
the interest of the entire world, and the Ossements
Fossiles was accorded a popular reception seldom
given a work of technical science--a reception in
which the enthusiastic approval of progressive geologists
was mingled with the bitter protests of the conservatives.
"Naturalists certainly have neither explored all the
continents," said Cuvier, "nor do they as yet even know
all the quadrupeds of those parts which have been explored.
New species of this class are discovered from
time to time; and those who have not examined with
attention all the circumstances belonging to these discoveries
may allege also that the unknown quadrupeds,
whose fossil bones have been found in the strata
of the earth, have hitherto remained concealed in
some islands not yet discovered by navigators, or in
some of the vast deserts which occupy the middle of
Africa, Asia, the two Americas, and New Holland.
"But if we carefully attend to the kind of quadrupeds
that have been recently discovered, and to the
circumstances of their discovery, we shall easily perceive
that there is very little chance indeed of our ever
finding alive those which have only been seen in a
fossil state.
"Islands of moderate size, and at a considerable distance
from the large continents, have very few quadrupeds.
These must have been carried to them from
other countries. Cook and Bougainville found no
other quadrupeds besides hogs and dogs in the South
Sea Islands; and the largest quadruped of the West
India Islands, when first discovered, was the agouti, a
species of the cavy, an animal apparently between the
rat and the rabbit.
"It is true that the great continents, as Asia, Africa,
the two Americas, and New Holland, have large quadrupeds,
and, generally speaking, contain species common
to each; insomuch, that upon discovering countries
which are isolated from the rest of the world, the
animals they contain of the class of quadruped were
found entirely different from those which existed in
other countries. Thus, when the Spaniards first penetrated
into South America, they did not find it to contain
a single quadruped exactly the same with those of
Europe, Asia, and Africa. The puma, the jaguar, the
tapir, the capybara, the llama, or glama, and vicuna,
and the whole tribe of sapajous, were to them entirely
new animals, of which they had not the smallest
idea....
"If there still remained any great continent to be
discovered, we might perhaps expect to be made acquainted
with new species of large quadrupeds, among
which some might be found more or less similar to those
of which we find the exuviae in the bowels of the earth.
But it is merely sufficient to glance the eye over the
maps of the world and observe the innumerable directions
in which navigators have traversed the ocean,
in order to be satisfied that there does not remain any
large land to be discovered, unless it may be situated
towards the Antarctic Pole, where eternal ice necessarily
forbids the existence of animal life."[1]
Cuvier then points out that the ancients were well
acquainted with practically all the animals on the
continents of Europe, Asia, and Africa now known to
scientists. He finds little grounds, therefore, for belief
in the theory that at one time there were monstrous
animals on the earth which it was necessary to destroy
in order that the present fauna and men might flourish.
After reviewing these theories and beliefs in detail, he
takes up his Inquiry Respecting the Fabulous Animals
of the Ancients. "It is easy," he says, "to reply to
the foregoing objections, by examining the descriptions
that are left us by the ancients of those unknown animals,
and by inquiring into their origins. Now that
the greater number of these animals have an origin,
the descriptions given of them bear the most unequivocal
marks; as in almost all of them we see merely the
different parts of known animals united by an unbridled
imagination, and in contradiction to every established
law of nature."[2]
Having shown how the fabulous monsters of ancient
times and of foreign nations, such as the Chinese, were
simply products of the imagination, having no prototypes
in nature, Cuvier takes up the consideration of the
difficulty of distinguishing the fossil bones of quadrupeds.
We shall have occasion to revert to this part of Cuvier's
paper in another connection. Here it suffices to
pass at once to the final conclusion that the fossil bones
in question are the remains of an extinct fauna, the like
of which has no present-day representation on the
earth. Whatever its implications, this conclusion now
seemed to Cuvier to be fully established.
In England the interest thus aroused was sent to
fever-heat in 1821 by the discovery of abundant beds
of fossil bones in the stalagmite-covered floor of a cave
at Kirkdale, Yorkshire which went to show that England,
too, had once had her share of gigantic beasts.
Dr. Buckland, the incumbent of the chair of geology
at Oxford, and the most authoritative English geologist
of his day, took these finds in hand and showed that
the bones belonged to a number of species, including
such alien forms as elephants, rhinoceroses, hippopotami,
and hyenas. He maintained that all of these
creatures had actually lived in Britain, and that the
caves in which their bones were found had been the
dens of hyenas.
The claim was hotly disputed, as a matter of course.
As late as 1827 books were published denouncing Buckland,
doctor of divinity though he was, as one who had
joined in an "unhallowed cause," and reiterating the old
cry that the fossils were only remains of tropical species
washed thither by the deluge. That they were found
in solid rocks or in caves offered no difficulty, at least
not to the fertile imagination of Granville Penn, the
leader of the conservatives, who clung to the old idea
of Woodward and Cattcut that the deluge had dissolved
the entire crust of the earth to a paste, into
which the relics now called fossils had settled. The
caves, said Mr. Penn, are merely the result of gases
given off by the carcasses during decomposition--
great air-bubbles, so to speak, in the pasty mass, becoming
caverns when the waters receded and the paste
hardened to rocky consistency.
But these and such-like fanciful views were doomed
even in the day of their utterance. Already in 1823
other gigantic creatures, christened ichthyosaurus and
plesiosaurus by Conybeare, had been found in deeper
strata of British rocks; and these, as well as other
monsters whose remains were unearthed in various parts
of the world, bore such strange forms that even the
most sceptical could scarcely hope to find their counterparts
among living creatures. Cuvier's contention that
all the larger vertebrates of the existing age are known
to naturalists was borne out by recent explorations,
and there seemed no refuge from the conclusion that
the fossil records tell of populations actually extinct.
But if this were admitted, then Smith's view that there
have been successive rotations of population could no
longer be denied. Nor could it be in doubt that the
successive faunas, whose individual remains have been
preserved in myriads, representing extinct species by
thousands and tens of thousands, must have required
vast periods of time for the production and growth of
their countless generations.
As these facts came to be generally known, and as it
came to be understood in addition that the very matrix
of the rock in which fossils are imbedded is in
many cases one gigantic fossil, composed of the remains
of microscopic forms of life, common-sense,
which, after all, is the final tribunal, came to the aid of
belabored science. It was conceded that the only
tenable interpretation of the record in the rocks is that
numerous populations of creatures, distinct from one
another and from present forms, have risen and passed
away; and that the geologic ages in which these creatures
lived were of inconceivable length. The rank and
file came thus, with the aid of fossil records, to realize
the import of an idea which James Hutton, and here and
there another thinker, had conceived with the swift intuition
of genius long before the science of paleontology
came into existence. The Huttonian proposition
that time is long had been abundantly established,
and by about the close of the first third of the last
century geologists had begun to speak of "ages" and
"untold aeons of time" with a familiarity which their
predecessors had reserved for days and decades.
CHARLES LYELL COMBATS CATASTROPHISM
And now a new question pressed for solution. If the
earth has been inhabited by successive populations of
beings now extinct, how have all these creatures been
destroyed? That question, however, seemed to present
no difficulties. It was answered out of hand by the
application of an old idea. All down the centuries,
whatever their varying phases of cosmogonic thought,
there had been ever present the idea that past times
were not as recent times; that in remote epochs the
earth had been the scene of awful catastrophes that
have no parallel in "these degenerate days." Naturally
enough, this thought, embalmed in every cosmogonic
speculation of whatever origin, was appealed to in
explanation of the destruction of these hitherto unimagined
hosts, which now, thanks to science, rose from
their abysmal slumber as incontestable, but also as
silent and as thought-provocative, as Sphinx or pyramid.
These ancient hosts, it was said, have been exterminated
at intervals of odd millions of years by the recurrence
of catastrophes of which the Mosaic deluge is
the latest, but perhaps not the last.
This explanation had fullest warrant of scientific authority.
Cuvier had prefaced his classical work with
a speculative disquisition whose very title (Discours
sur les Revolutions du Globe) is ominous of
catastrophism, and whose text fully sustains the augury.
And Buckland, Cuvier's foremost follower across the
Channel, had gone even beyond the master, naming
the work in which he described the Kirkdale fossils,
Reliquiae Diluvianae, or Proofs of a Universal Deluge.
Both these authorities supposed the creatures whose
remains they studied to have perished suddenly in the
mighty flood whose awful current, as they supposed,
gouged out the modern valleys and hurled great blocks
of granite broadcast over the land. And they invoked
similar floods for the extermination of previous populations.
It is true these scientific citations had met with only
qualified approval at the time of their utterance, because
then the conservative majority of mankind did
not concede that there had been a plurality of populations
or revolutions; but now that the belief in past
geologic ages had ceased to be a heresy, the recurring
catastrophes of the great paleontologists were accepted
with acclaim. For the moment science and tradition
were at one, and there was a truce to controversy, except
indeed in those outlying skirmish-lines of thought
whither news from headquarters does not permeate till
it has become ancient history at its source.
The truce, however, was not for long. Hardly had
contemporary thought begun to adjust itself to the
conception of past ages of incomprehensible extent,
each terminated by a catastrophe of the Noachian
type, when a man appeared who made the utterly bewildering
assertion that the geological record, instead
of proving numerous catastrophic revolutions in the
earth's past history, gives no warrant to the pretensions
of any universal catastrophe whatever, near or
remote.
This iconoclast was Charles Lyell, the Scotchman,
who was soon to be famous as the greatest geologist of
his time. As a young man he had become imbued with
the force of the Huttonian proposition, that present
causes are one with those that produced the past
changes of the globe, and he carried that idea to what
he conceived to be its logical conclusion. To his mind
this excluded the thought of catastrophic changes in
either inorganic or organic worlds.
But to deny catastrophism was to suggest a revolution
in current thought. Needless to say, such revolution
could not be effected without a long contest. For
a score of years the matter was argued pro and con.,
often with most unscientific ardor. A mere outline of
the controversy would fill a volume; yet the essential
facts with which Lyell at last established his proposition,
in its bearings on the organic world, may be epitomized
in a few words. The evidence which seems to tell
of past revolutions is the apparently sudden change of
fossils from one stratum to another of the rocks. But
Lyell showed that this change is not always complete.
Some species live on from one alleged epoch
into the next. By no means all the contemporaries
of the mammoth are extinct, and numerous marine
forms vastly more ancient still have living representatives.
Moreover, the blanks between strata in any particular
vertical series are amply filled in with records in the
form of thick strata in some geographically distant
series. For example, in some regions Silurian rocks are
directly overlaid by the coal measures; but elsewhere
this sudden break is filled in with the Devonian rocks
that tell of a great "age of fishes." So commonly are
breaks in the strata in one region filled up in another
that we are forced to conclude that the record shown
by any single vertical series is of but local significance--
telling, perhaps, of a time when that particular sea-bed
oscillated above the water-line, and so ceased to receive
sediment until some future age when it had oscillated
back again. But if this be the real significance of the
seemingly sudden change from stratum to stratum,
then the whole case for catastrophism is hopelessly lost;
for such breaks in the strata furnish the only suggestion
geology can offer of sudden and catastrophic changes
of wide extent.
Let us see how Lyell elaborates these ideas, particularly
with reference to the rotation of species.[2]
"I have deduced as a corollary," he says, "that the
species existing at any particular period must, in the
course of ages, become extinct, one after the other.
'They must die out,' to borrow an emphatic expression
from Buffon, 'because Time fights against them.' If the
views which I have taken are just, there will be no
difficulty in explaining why the habitations of so many
species are now restrained within exceeding narrow
limits. Every local revolution tends to circumscribe
the range of some species, while it enlarges that of
others; and if we are led to infer that new species originate
in one spot only, each must require time to diffuse
itself over a wide area. It will follow, therefore, from
the adoption of our hypothesis that the recent origin
of some species and the high antiquity of others are
equally consistent with the general fact of their limited
distribution, some being local because they have not
existed long enough to admit of their wide dissemination;
others, because circumstances in the animate or
inanimate world have occurred to restrict the range
within which they may once have obtained. . . .
"If the reader should infer, from the facts laid before
him, that the successive extinction of animals and
plants may be part of the constant and regular course
of nature, he will naturally inquire whether there are
any means provided for the repair of these losses? Is
it possible as a part of the economy of our system that
the habitable globe should to a certain extent become
depopulated, both in the ocean and on the land, or
that the variety of species should diminish until some
new era arrives when a new and extraordinary effort
of creative energy is to be displayed? Or is it possible
that new species can be called into being from time to
time, and yet that so astonishing a phenomenon can
escape the naturalist?
"In the first place, it is obviously more easy to prove
that a species once numerously represented in a given
district has ceased to be than that some other which
did not pre-exist had made its appearance--assuming
always, for reasons before stated, that single stocks
only of each animal and plant are originally created,
and that individuals of new species did not suddenly
start up in many different places at once.
"So imperfect has the science of natural history remained
down to our own times that, within the memory
of persons now living, the numbers of known animals
and plants have doubled, or even quadrupled, in
many classes. New and often conspicuous species are
annually discovered in parts of the old continent long
inhabited by the most civilized nations. Conscious,
therefore, of the limited extent of our information, we
always infer, when such discoveries are made, that the
beings in question bad previously eluded our research,
or had at least existed elsewhere, and only migrated at
a recent period into the territories where we now find
them.
"What kind of proofs, therefore, could we reasonably
expect to find of the origin at a particular period of a
new species?
"Perhaps, it may be said in reply, that within the
last two or three centuries some forest tree or new
quadruped might have been observed to appear suddenly
in those parts of England or France which had
been most thoroughly investigated--that naturalists
might have been able to show that no such being inhabited
any other region of the globe, and that there
was no tradition of anything similar having been
observed in the district where it had made its appearance.
"Now, although this objection may seem plausible,
yet its force will be found to depend entirely on the
rate of fluctuation which we suppose to prevail in the
animal world, and on the proportions which such conspicuous
subjects of the animal and vegetable kingdoms
bear to those which are less known and escape
our observation. There are perhaps more than a million
species of plants and animals, exclusive of the
microscopic and infusory animalcules, now inhabiting
the terraqueous globe, so that if only one of these were
to become extinct annually, and one new one were to
be every year called into being, much more than a
million of years might be required to bring about a
complete revolution of organic life.
"I am not hazarding at present any hypothesis as to
the probable rate of change, but none will deny that
when the annual birth and the annual death of one
species on the globe is proposed as a mere speculation,
this, at least, is to imagine no slight degree of instability
in the animate creation. If we divide the surface of
the earth into twenty regions of equal area, one of
these might comprehend a space of land and water
about equal in dimensions to Europe, and might contain
a twentieth part of the million of species which
may be assumed to exist in the animal kingdom. In
this region one species only could, according to the rate
of mortality before assumed, perish in twenty years,
or only five out of fifty thousand in the course of a
century. But as a considerable portion of the whole
world belongs to the aquatic classes, with which we
have a very imperfect acquaintance, we must exclude
them from our consideration, and, if they constitute
half of the entire number, then one species only might
be lost in forty years among the terrestrial tribes.
Now the mammalia, whether terrestrial or aquatic,
bear so small a proportion to other classes of animals,
forming less, perhaps, than a thousandth part of a
whole, that, if the longevity of species in the different
orders were equal, a vast period must elapse before it
would come to the turn of this conspicuous class to
lose one of their number. If one species only of the
whole animal kingdom died out in forty years, no
more than one mammifer might disappear in forty
thousand years, in a region of the dimensions of Europe.
"It is easy, therefore, to see that in a small portion
of such an area, in countries, for example, of the
size of England and France, periods of much greater
duration must elapse before it would be possible to
authenticate the first appearance of one of the larger
plants or animals, assuming the annual birth and death
of one species to be the rate of vicissitude in the animal
creation throughout the world."[3]
In a word, then, said Lyell, it becomes clear that the
numberless species that have been exterminated in the
past have died out one by one, just as individuals of a
species die, not in vast shoals; if whole populations
have passed away, it has been not by instantaneous
extermination, but by the elimination of a species now
here, now there, much as one generation succeeds another
in the life history of any single species. The
causes which have brought about such gradual exterminations,
and in the long lapse of ages have resulted
in rotations of population, are the same natural
causes that are still in operation. Species have died
out in the past as they are dying out in the present,
under influence of changed surroundings, such as altered
climate, or the migration into their territory of
more masterful species. Past and present causes are
one--natural law is changeless and eternal.
Such was the essence of the Huttonian doctrine,
which Lyell adopted and extended, and with which his
name will always be associated. Largely through his
efforts, though of course not without the aid of many
other workers after a time, this idea--the doctrine of
uniformitarianism, it came to be called--became the
accepted dogma of the geologic world not long after the
middle of the nineteenth century. The catastrophists,
after clinging madly to their phantom for a generation,
at last capitulated without terms: the old heresy became
the new orthodoxy, and the way was paved for a
fresh controversy.
THE ORIGIN OF SPECIES
The fresh controversy followed quite as a matter of
course. For the idea of catastrophism had not concerned
the destruction of species merely, but their
introduction as well. If whole faunas had been extirpated
suddenly, new faunas had presumably been introduced
with equal suddenness by special creation;
but if species die out gradually, the introduction of new
species may be presumed to be correspondingly gradual.
Then may not the new species of a later geological
epoch be the modified lineal descendants of the
extinct population of an earlier epoch?
The idea that such might be the case was not new.
It had been suggested when fossils first began to attract
conspicuous attention; and such sagacious thinkers as
Buffon and Kant and Goethe and Erasmus Darwin had
been disposed to accept it in the closing days of the
eighteenth century. Then, in 1809, it had been contended
for by one of the early workers in systematic
paleontology--Jean Baptiste Lamarck, who had studied
the fossil shells about Paris while Cuvier studied the
vertebrates, and who had been led by these studies to
conclude that there had been not merely a rotation but
a progression of life on the globe. He found the fossil
shells--the fossils of invertebrates, as he himself had
christened them--in deeper strata than Cuvier's vertebrates;
and he believed that there had been long ages
when no higher forms than these were in existence, and
that in successive ages fishes, and then reptiles, had
been the highest of animate creatures, before mammals,
including man, appeared. Looking beyond the pale of
his bare facts, as genius sometimes will, he had insisted
that these progressive populations had developed one
from another, under influence of changed surroundings,
in unbroken series.
Of course such a thought as this was hopelessly misplaced
in a generation that doubted the existence of extinct
species, and hardly less so in the generation that
accepted catastrophism; but it had been kept alive by
here and there an advocate like Geoffrey Saint-Hilaire,
and now the banishment of catastrophism opened the
way for its more respectful consideration. Respectful
consideration was given it by Lyell in each recurring
edition of his Principles, but such consideration led to
its unqualified rejection. In its place Lyell put forward
a modified hypothesis of special creation. He assumed
that from time to time, as the extirpation of a species
had left room, so to speak, for a new species, such new
species had been created de novo; and he supposed that
such intermittent, spasmodic impulses of creation manifest
themselves nowadays quite as frequently as at any
time in the past. He did not say in so many words
that no one need be surprised to-day were he to see a
new species of deer, for example, come up out of the
ground before him, "pawing to get free," like Milton's
lion, but his theory implied as much. And that theory,
let it be noted, was not the theory of Lyell alone, but
of nearly all his associates in the geologic world. There
is perhaps no other fact that will bring home to one so
vividly the advance in thought of our own generation
as the recollection that so crude, so almost unthinkable
a conception could have been the current doctrine of
science less than half a century ago.
This theory of special creation, moreover, excluded
the current doctrine of uniformitarianism as night excludes
day, though most thinkers of the time did not
seem to be aware of the incompatibility of the two
ideas. It may be doubted whether even Lyell himself
fully realized it. If he did, he saw no escape from the
dilemma, for it seemed to him that the record in the
rocks clearly disproved the alternative Lamarckian hypothesis.
And almost with one accord the paleontologists
of the time sustained the verdict. Owen, Agassiz,
Falconer, Barrande, Pictet, Forbes, repudiated the idea
as unqualifiedly as their great predecessor Cuvier had
done in the earlier generation. Some of them did, indeed,
come to believe that there is evidence of a progressive
development of life in the successive ages, but
no such graded series of fossils had been discovered as
would give countenance to the idea that one species had
ever been transformed into another. And to nearly
every one this objection seemed insuperable.
But in 1859 appeared a book which, though not
dealing primarily with paleontology, yet contained a
chapter that revealed the geological record in an
altogether new light. The book was Charles Darwin's
Origin of Species, the chapter that wonderful citation of
the "Imperfections of the Geological Record." In this
epoch-making chapter Darwin shows what conditions
must prevail in any given place in order that fossils
shall be formed, how unusual such conditions are, and
how probable it is that fossils once imbedded in sediment
of a sea-bed will be destroyed by metamorphosis
of the rocks, or by denudation when the strata are
raised above the water-level. Add to this the fact that
only small territories of the earth have been explored
geologically, he says, and it becomes clear that the
paleontological record as we now possess it shows but a
mere fragment of the past history of organisms on the
earth. It is a history "imperfectly kept and written in
a changing dialect. Of this history we possess the last
volume alone, relating only to two or three countries.
Of this volume only here and there a short chapter has
been preserved, and of each page only here and there a
few lines." For a paleontologist to dogmatize from
such a record would be as rash, he thinks, as "for a
naturalist to land for five minutes on a barren point of
Australia and then discuss the number and range of its
productions."
This citation of observations, which when once pointed
out seemed almost self-evident, came as a revelation
to the geological world. In the clarified view now
possible old facts took on a new meaning. It was recalled
that Cuvier had been obliged to establish a new
order for some of the first fossil creatures he examined,
and that Buckland had noted that the nondescript
forms were intermediate in structure between allied existing
orders. More recently such intermediate forms
had been discovered over and over; so that, to name
but one example, Owen had been able, with the aid of
extinct species, to "dissolve by gradations the apparently
wide interval between the pig and the camel."
Owen, moreover, had been led to speak repeatedly of
the "generalized forms" of extinct animals, and Agassiz
had called them "synthetic or prophetic types," these
terms clearly implying "that such forms are in fact
intermediate or connecting links." Darwin himself had
shown some years before that the fossil animals of any
continent are closely related to the existing animals
of that continent--edentates predominating, for example,
in South America, and marsupials in Australia.
Many observers had noted that recent strata everywhere
show a fossil fauna more nearly like the existing
one than do more ancient strata; and that fossils from
any two consecutive strata are far more closely related
to each other than are the fossils of two remote formations,
the fauna of each geological formation being,
indeed, in a wide view, intermediate between preceding
and succeeding faunas.
So suggestive were all these observations that Lyell,
the admitted leader of the geological world, after reading
Darwin's citations, felt able to drop his own crass
explanation of the introduction of species and adopt
the transmutation hypothesis, thus rounding out the
doctrine of uniformitarianism to the full proportions in
which Lamarck had conceived it half a century before.
Not all paleontologists could follow him at once, of
course; the proof was not yet sufficiently demonstrative
for that; but all were shaken in the seeming security
of their former position, which is always a necessary
stage in the progress of thought. And popular interest
in the matter was raised to white heat in a twinkling.
So, for the third time in this first century of its existence,
paleontology was called upon to play a leading
role in a controversy whose interest extended far beyond
the bounds of staid truth-seeking science. And
the controversy waged over the age of the earth had
not been more bitter, that over catastrophism not more
acrimonious, than that which now raged over the question
of the transmutation of species. The question had
implications far beyond the bounds of paleontology, of
course. The main evidence yet presented had been
drawn from quite other fields, but by common consent
the record in the rocks might furnish a crucial test of
the truth or falsity of the hypothesis. "He who rejects
this view of the imperfections of the geological
record," said Darwin, "will rightly reject the whole
theory."
With something more than mere scientific zeal, therefore,
paleontologists turned anew to the records in the
rocks, to inquire what evidence in proof or refutation
might be found in unread pages of the "great stone
book." And, as might have been expected, many
minds being thus prepared to receive new evidence,
such evidence was not long withheld.
FOSSIL MAN
Indeed, at the moment of Darwin's writing a new
and very instructive chapter of the geologic record was
being presented to the public--a chapter which for the
first time brought man into the story. In 1859 Dr.
Falconer, the distinguished British paleontologist,
made a visit to Abbeville, in the valley of the Somme,
incited by reports that for a decade before bad been
sent out from there by M. Boucher de Perthes. These
reports had to do with the alleged finding of flint implements,
clearly the work of man, in undisturbed gravel-
beds, in the midst of fossil remains of the mammoth
and other extinct animals. What Falconer saw there
and what came of his visit may best be told in his own
words:
"In September of 1856 I made the acquaintance
of my distinguished friend M. Boucher de Perthes,"
wrote Dr. Falconer, "on the introduction of M. Desnoyers
at Paris, when he presented to me the earlier
volume of his Antiquites celtiques, etc., with which I thus
became acquainted for the first time. I was then fresh
from the examination of the Indian fossil remains of
the valley of the Jumna; and the antiquity of the human
race being a subject of interest to both, we conversed
freely about it, each from a different point of
view. M. de Perthes invited me to visit Abbeville, in
order to examine his antediluvian collection, fossil
and geological, gleaned from the valley of the Somme.
This I was unable to accomplish then, but I reserved
it for a future occasion.
"In October, 1856, having determined to proceed to
Sicily, I arranged by correspondence with M. Boucher
de Perthes to visit Abbeville on my journey through
France. I was at the time in constant communication
with Mr. Prestwich about the proofs of the antiquity
of the human race yielded by the Broxham
Cave, in which he took a lively interest; and I engaged
to communicate to him the opinions at which I should
arrive, after my examination of the Abbeville collection.
M. de Perthes gave me the freest access to his
materials, with unreserved explanations of all the facts
of the case that had come under his observation; and
having considered his Menchecourt Section, taken with
such scrupulous care, and identified the molars of elephas
primigenius, which he had exhumed with his own
hands deep in that section, along with flint weapons,
presenting the same character as some of those found
in the Broxham Cave, I arrived at the conviction that
they were of contemporaneous age, although I was not
prepared to go along with M. de Perthes in all his inferences
regarding the hieroglyphics and in an industrial
interpretation of the various other objects which
he had met with."[4]
That Dr. Falconer was much impressed by the collection
of M. de Perthes is shown in a communication
which he sent at once to his friend Prestwich:
"I have been richly rewarded," he exclaims. "His
collection of wrought flint implements, and of the objects
of every description associated with them, far
exceeds everything I expected to have seen, especially
from a single locality. He has made great additions,
since the publication of his first volume, in the second,
which I now have by me. He showed me flint hatchets
which HE HAD DUG UP with his own hands, mixed INDISCRIMINATELY
with molars of elephas primigenius. I examined
and identified plates of the molars and the
flint objects which were got along with them. Abbeville
is an out-of-the-way place, very little visited; and
the French savants who meet him in Paris laugh at
Monsieur de Perthes and his researches. But after devoting
the greater part of a day to his vast collection,
I am perfectly satisfied that there is a great deal of fair
presumptive evidence in favor of many of his speculations
regarding the remote antiquity of these industrial
objects and their association with animals now extinct.
M. Boucher's hotel is, from the ground floor to garret, a
continued museum, filled with pictures, mediaeval art,
and Gaulish antiquities, including antediluvian flint-knives,
fossil-bones, etc. If, during next summer,
you should happen to be paying a visit to France, let
me strongly recommend you to come to Abbeville. I
am sure you would be richly rewarded."[5]
This letter aroused the interest of the English geologists,
and in the spring of 1859 Prestwich and Mr.
(afterwards Sir John) Evans made a visit to Abbeville
to see the specimens and examine at first hand the
evidences as pointed out by Dr. Falconer. "The evidence
yielded by the valley of the Somme," continues
Falconer, in speaking of this visit, "was gone into with
the scrupulous care and severe and exhaustive analysis
which are characteristic of Mr. Prestwich's researches.
The conclusions to which he was conducted were communicated
to the Royal Society on May 12, 1859, in his
celebrated memoir, read on May 26th and published
in the Philosophical Transactions of 1860, which, in addition
to researches made in the valley of the Somme,
contained an account of similar phenomena presented
by the valley of the Waveney, near Hoxne, in Suffolk.
Mr. Evans communicated to the Society of Antiquaries
a memoir on the character and geological position of
the 'Flint Implements in the Drift,' which appeared in
the Archaeologia for 1860. The results arrived at by
Mr. Prestwich were expressed as follows:
"First. That the flint implements are the result of
design and the work of man.
"Second. That they are found in beds of gravel, sand,
and clay, which have never been artificially disturbed.
"Third. That they occur associated with the remains
of land, fresh-water, and marine testacea, of
species now living, and most of them still common in
the same neighborhood, and also with the remains of
various mammalia--a few species now living, but more
of extinct forms.
"Fourth. That the period at which their entombment
took place was subsequent to the bowlder-clay
period, and to that extent post-glacial; and also that
it was among the latest in geological time--one apparently
anterior to the surface assuming its present
form, so far as it regards some of the minor features."[6]
These reports brought the subject of the very significant
human fossils at Abbeville prominently before
the public; whereas the publications of the original discoverer,
Boucher de Perthes, bearing date of 1847, had
been altogether ignored. A new aspect was thus given
to the current controversy.
As Dr. Falconer remarked, geology was now passing
through the same ordeal that astronomy passed in the
age of Galileo. But the times were changed since the
day when the author of the Dialogues was humbled before
the Congregation of the Index, and now no Index
Librorum Prohibitorum could avail to hide from eager
human eyes such pages of the geologic story as Nature
herself had spared. Eager searchers were turning the
leaves with renewed zeal everywhere, and with no small
measure of success. In particular, interest attached
just at this time to a human skull which Dr. Fuhlrott
had discovered in a cave at Neanderthal two or three
years before--a cranium which has ever since been
famous as the Neanderthal skull, the type specimen of
what modern zoologists are disposed to regard as a
distinct species of man, Homo neanderthalensis. Like
others of the same type since discovered at Spy, it is
singularly simian in character--low-arched, with receding
forehead and enormous, protuberant eyebrows.
When it was first exhibited to the scientists at Berlin
by Dr. Fuhlrott, in 1857, its human character was
doubted by some of the witnesses; of that, however,
there is no present question.
This interesting find served to recall with fresh significance
some observations that had been made in
France and Belgium a long generation earlier, but
whose bearings had hitherto been ignored. In 1826
MM. Tournal and Christol had made independent discoveries
of what they believed to be human fossils
in the caves of the south of France; and in 1827
Dr. Schmerling had found in the cave of Engis, in
Westphalia, fossil bones of even greater significance.
Schmerling's explorations had been made with the
utmost care, and patience. At Engis he had found
human bones, including skulls, intermingled with those
of extinct mammals of the mammoth period in a way
that left no doubt in his mind that all dated from
the same geological epoch. He bad published a full
account of his discoveries in an elaborate monograph
issued in 1833.
But at that time, as it chanced, human fossils were
under a ban as effectual as any ever pronounced by
canonical index, though of far different origin. The
oracular voice of Cuvier had declared against the
authenticity of all human fossils. Some of the bones
brought him for examination the great anatomist had
pettishly pitched out of the window, declaring them
fit only for a cemetery, and that had settled the matter
for a generation: the evidence gathered by lesser workers
could avail nothing against the decision rendered
at the Delphi of Science. But no ban, scientific or
canonical, can longer resist the germinative power of a
fact, and so now, after three decades of suppression,
the truth which Cuvier had buried beneath the weight
of his ridicule burst its bonds, and fossil man stood revealed,
if not as a flesh-and-blood, at least as a skeletal
entity.
The reception now accorded our prehistoric ancestor
by the progressive portion of the scientific world
amounted to an ovation; but the unscientific masses,
on the other hand, notwithstanding their usual fondness
for tracing remote genealogies, still gave the men
of Engis and Neanderthal the cold shoulder. Nor
were all of the geologists quite agreed that the
contemporaneity of these human fossils with the animals
whose remains had been mingled with them had been
fully established. The bare possibility that the bones
of man and of animals that long preceded him had been
swept together into the eaves in successive ages, and in
some mysterious way intermingled there, was clung to
by the conservatives as a last refuge. But even this
small measure of security was soon to be denied them,
for in 1865 two associated workers, M. Edouard Lartet
and Mr. Henry Christy, in exploring the caves of Dordogne,
unearthed a bit of evidence against which no
such objection could be urged. This momentous exhibit
was a bit of ivory, a fragment of the tusk of a
mammoth, on which was scratched a rude but unmistakable
outline portrait of the mammoth itself. If all
the evidence as to man's antiquity before presented
was suggestive merely, here at last was demonstration;
for the cave-dwelling man could not well have drawn
the picture of the mammoth unless he had seen that
animal, and to admit that man and the mammoth had
been contemporaries was to concede the entire case.
So soon, therefore, as the full import of this most instructive
work of art came to be realized, scepticism as
to man's antiquity was silenced for all time to come.
In the generation that has elapsed since the first
drawing of the cave-dweller artist was discovered, evidences
of the wide-spread existence of man in an early
epoch have multiplied indefinitely, and to-day the
paleontologist traces the history of our race back beyond
the iron and bronze ages, through a neolithic or
polished-stone age, to a paleolithic or rough-stone age,
with confidence born of unequivocal knowledge. And
he looks confidently to the future explorer of the earth's
fossil records to extend the history back into vastly
more remote epochs, for it is little doubted that paleolithic
man, the most ancient of our recognized progenitors,
is a modern compared to those generations that
represented the real childhood of our race.
THE FOSSIL-BEDS OF AMERICA
Coincidently with the discovery of these highly suggestive
pages of the geologic story, other still more instructive
chapters were being brought to light in America.
It was found that in the Rocky Mountain region,
in strata found in ancient lake beds, records of the
tertiary period, or age of mammals, had been made and
preserved with fulness not approached in any other region
hitherto geologically explored. These records were
made known mainly by Professors Joseph Leidy, O. C.
Marsh, and E. D. Cope, working independently, and
more recently by numerous younger paleontologists.
The profusion of vertebrate remains thus brought to
light quite beggars all previous exhibits in point of mere
numbers. Professor Marsh, for example, who was first
in the field, found three hundred new tertiary species
between the years 1870 and 1876. Meanwhile, in
cretaceous strata, he unearthed remains of about two
hundred birds with teeth, six hundred pterodactyls,
or flying dragons, some with a spread of wings of twenty-
five feet, and one thousand five hundred mosasaurs
of the sea-serpent type, some of them sixty feet or more
in length. In a single bed of Jurassic rock, not larger
than a good-sized lecture-room, he found the remains
of one hundred and sixty individuals of mammals, representing
twenty species and nine genera; while beds
of the same age have yielded three hundred reptiles,
varying from the size of a rabbit to sixty or eighty feet
in length.
But the chief interest of these fossils from the West is
not their number but their nature; for among them are
numerous illustrations of just such intermediate types
of organisms as must have existed in the past if the
succession of life on the globe has been an unbroken
lineal succession. Here are reptiles with bat-like wings,
and others with bird-like pelves and legs adapted for
bipedal locomotion. Here are birds with teeth, and
other reptilian characters. In short, what with reptilian
birds and birdlike reptiles, the gap between
modern reptiles and birds is quite bridged over. In a
similar way, various diverse mammalian forms, as the
tapir, the rhinoceros, and the horse, are linked together
by fossil progenitors. And, most important of all,
Professor Marsh has discovered a series of mammalian
remains, occurring in successive geological epochs,
which are held to represent beyond cavil the actual line
of descent of the modern horse; tracing the lineage of
our one-toed species back through two and three toed
forms, to an ancestor in the eocene or early tertiary
that had four functional toes and the rudiment of a
fifth. This discovery is too interesting and too important
not to be detailed at length in the words of the
discoverer.
Marsh Describes the Fossil Horse
"It is a well-known fact," says Professor Marsh,
"that the Spanish discoverers of America discovered
no horses on this continent, and that the modern horse
(Equus caballus, Linn.) was subsequently introduced
from the Old World. It is, however, not so generally
known that these animals had formerly been abundant
here, and that long before, in tertiary time, near
relatives of the horse, and probably his ancestors, existed
in the far West in countless numbers and in a
marvellous variety of forms. The remains of equine
mammals, now known from the tertiary and quaternary
deposits of this country, already represent more than
double the number of genera and species hitherto found
in the strata of the eastern hemisphere, and hence afford
most important aid in tracing out the genealogy
of the horses still existing.
"The animals of this group which lived in America
during the three diversions of the tertiary period were
especially numerous in the Rocky Mountain regions,
and their remains are well preserved in the old lake
basins which then covered so much of that country.
The most ancient of these lakes--which extended over
a considerable part of the present territories of Wyoming
and Utah--remained so long in eocene times that
the mud and sand, slowly deposited in it, accumulated
to more than a mile in vertical thickness. In these
deposits vast numbers of tropical animals were
entombed, and here the oldest equine remains occur,
four species of which have been described. These
belong to the genus Orohippus (Marsh), and are all of a
diminutive size, hardly bigger than a fox. The skeletons
of these animals resemble that of the horse in
many respects, much more indeed than any other
existing species, but, instead of the single toe on each
foot, so characteristic of all modern equines, the various
species of Orohippus had four toes before and three
behind, all of which reached the ground. The skull,
too, was proportionately shorter, and the orbit was not
enclosed behind by a bridge of bone. There were fifty
four teeth in all, and the premolars were larger than
the molars. The crowns of these teeth were very short.
The canine teeth were developed in both sexes, and the
incisors did not have the "mark" which indicates the
age of the modern horse. The radius and ulna were
separate, and the latter was entire through the whole
length. The tibia and fibula were distinct. In the
forefoot all the digits except the pollex, or first, were
well developed. The third digit is the largest, and its
close resemblance to that of the horse is clearly marked.
The terminal phalanx, or coffin-bone, has a shallow
median bone in front, as in many species of this group
in the later tertiary. The fourth digit exceeds the
second in size, and the second is much the shortest of
all. Its metacarpal bone is considerably curved outward.
In the hind-foot of this genus there are but
three digits. The fourth metatarsal is much larger
than the second.
"The larger number of equine mammals now known
from the tertiary deposits of this country, and their
regular distributions through the subdivisions of this
formation, afford a good opportunity to ascertain the
probable descent of the modern horse. The American
representative of the latter is the extinct Equus
fraternus (Leidy), a species almost, if not wholly,
identical with the Old World Equus caballus (Linnaeus),
to which our recent horse belongs. Huxley
has traced successfully the later genealogy of the horse
through European extinct forms, but the line in America
was probably a more direct one, and the record is
more complete. Taking, then, as the extreme of a
series, Orohippus agilis (Marsh), from the eocene, and
Equus fraternus (Leidy), from the quaternary, intermediate
forms may be intercalated with considerable certainty
from thirty or more well-marked species that
lived in the intervening periods. The natural line of
descent would seem to be through the following genera:
Orohippus, of the eocene; Miohippus and Anchitherium,
of the miocene; Anchippus, Hipparion, Protohippus,
Phohippus, of the pliocene; and Equus, quaternary
and recent.
The most marked changes undergone by the successive
equine genera are as follows: First, increase in
size; second, increase in speed, through concentration
of limb bones; third, elongation of head and neck, and
modifications of skull. The eocene Orohippus was the
size of a fox. Miohippus and Anchitherium, from the
miocene, were about as large as a sheep. Hipparion
and Pliohippus, of the pliocene, equalled the ass in
height; while the size of the quaternary Equus was
fully up to that of a modern horse.
"The increase of speed was equally well marked, and
was a direct result of the gradual formation of the
limbs. The latter were slowly concentrated by the
reduction of their lateral elements and enlargement
of the axial bone, until the force exerted by each
limb came to act directly through its axis in the
line of motion. This concentration is well seen--e.g.,
in the fore-limb. There was, first, a change in the
scapula and humerus, especially in the latter, which
facilitated motion in one line only; second, an expansion
of the radius and reduction of the ulna, until the
former alone remained entire and effective; third, a
shortening of all the carpal bones and enlargement of
the median ones, insuring a firmer wrist; fourth, an increase
of size of the third digit, at the expense of those
of each side, until the former alone supported the
limb.
"Such is, in brief, a general outline of the more
marked changes that seemed to have produced in
America the highly specialized modern Equus from his
diminutive four-toed predecessor, the eocene Orohippus.
The line of descent appears to have been direct,
and the remains now known supply every important
intermediate form. It is, of course, impossible to say
with certainty through which of the three-toed genera
of the pliocene that lived together the succession came.
It is not impossible that the latter species, which appear
generically identical, are the descendants of more
distinct pliocene types, as the persistent tendency in
all the earlier forms was in the same direction.
Considering the remarkable development of the group
through the tertiary period, and its existence even
later, it seems very strange that none of the species
should have survived, and that we are indebted for our
present horse to the Old World."[7]
PALEONTOLOGY OF EVOLUTION
These and such-like revelations have come to light in
our own time--are, indeed, still being disclosed. Needless
to say, no index of any sort now attempts to conceal
them; yet something has been accomplished towards
the same end by the publication of the discoveries
in Smithsonian bulletins and in technical memoirs of
government surveys. Fortunately, however, the results
have been rescued from that partial oblivion by
such interpreters as Professors Huxley and Cope, so
the unscientific public has been allowed to gain at
least an inkling of the wonderful progress of paleontology
in our generation.
The writings of Huxley in particular epitomize the
record. In 1862 he admitted candidly that the paleontological
record as then known, so far as it bears on the
doctrine of progressive development, negatives that
doctrine. In 1870 he was able to "soften somewhat
the Brutus-like severity" of his former verdict, and to
assert that the results of recent researches seem "to
leave a clear balance in favor of the doctrine of the
evolution of living forms one from another." Six
years later, when reviewing the work of Marsh in
America and of Gaudry in Pikermi, he declared that,
"on the evidence of paleontology, the evolution of
many existing forms of animal life from their predecessors
is no longer an hypothesis, but an historical
fact." In 1881 he asserted that the evidence gathered
in the previous decade had been so unequivocal that,
had the transmutation hypothesis not existed, "the
paleontologist would have had to invent it."
Since then the delvers after fossils have piled proof
on proof in bewildering profusion. The fossil-beds in
the "bad lands" of western America seem inexhaustible.
And in the Connecticut River Valley near relatives
of the great reptiles which Professor Marsh and
others have found in such profusion in the West left
their tracks on the mud-flats--since turned to sandstone;
and a few skeletons also have been found. The
bodies of a race of great reptiles that were the lords of
creation of their day have been dissipated to their elements,
while the chance indentations of their feet as
they raced along the shores, mere footprints on the
sands, have been preserved among the most imperishable
of the memory-tablets of the world.
Of the other vertebrate fossils that have been found
in the eastern portions of America, among the most
abundant and interesting are the skeletons of mastodons.
Of these one of the largest and most complete is
that which was unearthed in the bed of a drained lake
near Newburg, New York, in 1845. This specimen was
larger than the existing elephants, and had tusks eleven
feet in length. It was mounted and described by Dr.
John C. Warren, of Boston, and has been famous for
half a century as the "Warren mastodon."
But to the student of racial development as recorded
by the fossils all these sporadic finds have but incidental
interest as compared with the rich Western fossil-
beds to which we have already referred. From records
here unearthed, the racial evolution of many mammals
has in the past few years been made out in greater or
less detail. Professor Cope has traced the ancestry of
the camels (which, like the rhinoceroses, hippopotami,
and sundry other forms now spoken of as "Old World,"
seem to have had their origin here) with much completeness.
A lemuroid form of mammal, believed to be of the
type from which man has descended, has also been
found in these beds. It is thought that the descendants
of this creature, and of the other "Old-World"
forms above referred to, found their way to Asia, probably,
as suggested by Professor Marsh, across a bridge
at Bering Strait, to continue their evolution on the
other hemisphere, becoming extinct in the land of their
nativity. The ape-man fossil found in the tertiary
strata of the island of Java in 1891 by the Dutch
surgeon Dr. Eugene Dubois, and named Pithecanthropus
erectus, may have been a direct descendant of the
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