into sea, been confined to one corner of England. During the chalk
period, or "cretaceous epoch," not one of the present great physical
features of the globe was in existence. Our great mountain ranges,
Pyrenees, Alps, Himalayas, Andes, have all been upheaved since the
chalk was deposited, and the cretaceous sea flowed over the sites of
Sinai and Ararat.
All this is certain, because rocks of cretaceous or still later date
have shared in the elevatory movements which gave rise to these
mountain chains; and may be found perched up, in some cases, many
thousand feet high upon their flanks. And evidence of equal cogency
demonstrates that, though in Norfolk the forest-bed rests directly
upon the chalk, yet it does so, not because the period at which the
forest grew immediately followed that at which the chalk was formed,
but because an immense lapse of time, represented elsewhere by
thousands of feet of rock, is not indicated at Cromer.
I must ask you to believe that there is no less conclusive proof that
a still more prolonged succession of similar changes occurred before
the chalk was deposited. Nor have we any reason to think that the
first term in the series of these changes is known. The oldest
sea-beds preserved to us are sands, and mud, and pebbles, the wear and
tear of rocks which were formed in still older oceans.
But, great as is the magnitude of these physical changes of the world,
they have been accompanied by a no less striking series of
modifications in its living inhabitants.
All the great classes of animals, beasts of the field, fowls of the
air, creeping things, and things which dwell in the waters, flourished
upon the globe long ages before the chalk was deposited. Very few,
however, if any, of these ancient forms of animal life were identical
with those which now live. Certainly not one of the higher animals was
of the same species as any of those now in existence. The beasts of
the field, in the days before the chalk, were not our beasts of the
field, nor the fowls of the air such as those which the eye of man has
seen flying, unless his antiquity dates infinitely further back than
we at present surmise. If we could be carried back into those times,
we should be as one suddenly set down in Australia before it was
colonized. We should see mammals, birds, reptiles, fishes, insects,
snails, and the like, clearly recognizable as such, and yet not one of
them would be just the same as those with which we are familiar, and
many would be extremely different.
From that time to the present, the population of the world has
undergone slow and gradual, but incessant, changes. There has been no
grand catastrophe--no destroyer has swept away the forms of life of
one period, and replaced them by a totally new creation; but one
species has vanished and another has taken its place; creatures of one
type of structure have diminished, those of another have increased, as
time has passed on. And thus, while the differences between the living
creatures of the time before the chalk and those of the present day
appear startling, if placed side by side, we are led from one to the
other by the most gradual progress, if we follow the course of Nature
through the whole series of those relics of her operations which she
has left behind.
[Illustration: SKELETON OF THE PTERODACTYL.]
And it is by the population of the chalk sea that the ancient and the
modern inhabitants of the world are most completely connected. The
groups which are dying out flourish, side by side, with the groups
which are now the dominant forms of life.
Thus the chalk contains remains of those flying and swimming
reptiles, the pterodactyl, the ichthyosaurus, and the plesiosaurus,
which are found in no later deposits, but abounded in preceding ages.
The chambered shells called ammonites and belemnites, which are so
characteristic of the period preceding the cretaceous, in like manner
die with it.
[Illustration: THE SKELETON OF THE ICHTHYOSAURUS.]
[Illustration: THE SKELETON OF THE PLESIOSAURUS.]
[Illustration: AMMONITES.]
But, among these fading remainders of a previous state of things, are
some very modern forms of life, looking like Yankee peddlers among a
tribe of red Indians. Crocodiles of modern type appear; bony fishes,
many of them very similar to existing species, almost supplant the
forms of fish which predominate in more ancient seas; and many kinds
of living shell-fish first become known to us in the chalk. The
vegetation acquires a modern aspect. A few living animals are not even
distinguishable as species from those which existed at that remote
epoch. The Globigerina of the present day, for example, is not
different specifically from that of the chalk; and the same may be
said of many other Foraminifera. I think it probable that critical and
unprejudiced examination will show that more than one species of much
higher animals have had a similar longevity; but the only example
which I can at present give confidently is the snake's-head lamp-shell
(_Terebratulina caput serpentis_), which lives in our English seas and
abounded (as _Terebratulina striata_ of authors) in the chalk.
[Illustration: BELEMNITES.]
[Illustration: TEREBRATULINA.]
The longest line of human ancestry must hide its diminished head
before the pedigree of this insignificant shell-fish. We Englishmen
are proud to have an ancestor who was present at the Battle of
Hastings. The ancestors of _Terebratulina caput serpentis_ may have
been present at a battle of Ichthyosauria in that part of the sea
which, when the chalk was forming, flowed over the site of Hastings.
While all around has changed, this Terebratulina has peacefully
propagated its species from generation to generation, and stands to
this day as a living testimony to the continuity of the present with
the past history of the globe.
* * * * *
Up to this moment I have stated, so far as I know, nothing but
well-authenticated facts, and the immediate conclusions which they
force upon the mind.
But the mind is so constituted that it does not willingly rest in
facts and immediate causes, but seeks always after a knowledge of the
remoter links in the chain of causation.
Taking the many changes of any given spot of the earth's surface, from
sea to land, and from land to sea, as an established fact, we cannot
refrain from asking ourselves how these changes have occurred. And
when we have explained them--as they must be explained--by the
alternate slow movements of elevation and depression which have
affected the crusts of the earth, we go still further back, and ask,
Why these movements?
I am not certain that any one can give you a satisfactory answer to
that question. Assuredly I cannot. All that can be said for certain
is, that such movements are part of the ordinary course of nature,
inasmuch as they are going on at the present time. Direct proof may be
given, that some parts of the land of the northern hemisphere are at
this moment insensibly rising and others insensibly sinking; and there
is indirect but perfectly satisfactory proof, that an enormous area
now covered by the Pacific has been deepened thousands of feet since
the present inhabitants of that sea came into existence.
Thus there is not a shadow of a reason for believing that the
physical changes of the globe, in past times, have been effected by
other than natural causes.
Is there any more reason for believing that the concomitant
modifications in the forms of the living inhabitants of the globe have
been brought about in any other ways?
Before attempting to answer this question, let us try to form a
distinct mental picture of what has happened in some special case.
The crocodiles are animals which, as a group, have a very vast
antiquity. They abounded ages before the chalk was deposited; they
throng the rivers in warm climates at the present day. There is a
difference in the form of the joints of the backbone, and in some
minor particulars, between the crocodiles of the present epoch and
those which lived before the chalk; but, in the cretaceous epoch, as I
have already mentioned, the crocodiles had assumed the modern type of
structure. Notwithstanding this, the crocodiles of the chalk are not
identically the same as those which lived in the times called "older
tertiary," which succeeded the cretaceous epoch; and the crocodiles of
the older tertiaries are not identical with those of the newer
tertiaries, nor are these identical with existing forms. I leave open
the question whether particular species may have lived on from epoch
to epoch. But each epoch has had its peculiar crocodiles; though all,
since the chalk, have belonged to the modern type, and differ simply
in their proportions and in such structural particulars as are
discernible only to trained eyes.
How is the existence of this long succession of different species of
crocodiles to be accounted for?
Only two suppositions seem to be open to us--either each species of
crocodile has been specially created, or it has arisen out of some
pre-existing form by the operation of natural causes.
Choose your hypothesis; I have chosen mine. I can find no warranty for
believing in the distinct creation of a score of successive species of
crocodiles in the course of countless ages of time. Science gives no
countenance to such a wild fancy; nor can even the perverse ingenuity
of a commentator pretend to discover this sense, in the simple words
in which the writer of Genesis records the proceeding of the fifth and
sixth days of the Creation.
On the other hand, I see no good reason for doubting the necessary
alternative, that all these varied species have been evolved from
pre-existing crocodilian forms by the operation of causes as
completely a part of the common order of nature as those which have
effected the changes of the inorganic world.
Few will venture to affirm that the reasoning which applies to
crocodiles loses its force among other animals or among plants. If one
series of species has come into existence by the operation of natural
causes, it seems folly to deny that all may have arisen in the same
way.
* * * * *
A small beginning has led us to a great ending. If I were to put the
bit of chalk with which we started into the hot but obscure flame of
burning hydrogen, it would presently shine like the sun. It seems to
me that this physical metamorphosis is no false image of what has been
the result of our subjecting it to a jet of fervent, though nowise
brilliant, thought to-night. It has become luminous, and its clear
rays, penetrating the abyss of the remote past, have brought within
our ken some stages of the evolution of the earth. And in the shifting
"without haste, but without rest" of the land and sea, as in the
endless variation of the forms assumed by living beings, we have
observed nothing but the natural product of the forces originally
possessed by the substance of the universe.
[Illustration]
A BIT OF SPONGE
(Written on Scotland.)
(FROM GLIMPSES OF NATURE.)
BY A. WILSON.
[Illustration]
This morning, despite the promise of rain over-night, has broken with
all the signs and symptoms of a bright July day. The Firth is bathed
in sunlight, and the wavelets at full tide are kissing the strand,
making a soft musical ripple as they retire, and as the pebbles run
down the sandy slope on the retreat of the waves. Beyond the farthest
contact of the tide is a line of seaweed dried and desiccated, mixed
up with which, in confusing array, are masses of shells, and such
_olla podrida_ of the sea.
Tossed up at our very feet is a dried fragment of sponge, which
doubtless the unkind waves tore from its rocky bed. It is not a large
portion of sponge this, but its structure is nevertheless to be fairly
made out, and some reminiscences of its history gleaned, for the sake
of occupying the by no means "bad half-hour" before breakfast. "What
is a sponge?" is a question which you may well ask as a necessary
preliminary to the understanding of its personality.
[Illustration: A SPONGE ATTACHED TO ITS ROCKY BED.]
The questionings of childhood and the questionings of science run in
precisely similar grooves. "What is it?" and "How does it live?" and
"Where does it come from?" are equally the inquiries of childhood, and
of the deepest philosophy which seeks to determine the whole history
of life. This morning, we cannot do better than follow in the
footsteps of the child, and to the question, "What is a sponge?" I
fancy science will be able to return a direct answer. First of all, we
may note that a sponge, as we know it in common life, is the horny
skeleton or framework which was made by, and which supported, the
living parts. These living parts consist of minute masses of that
living jelly to which the name of _protoplasm_ has been applied. This,
in truth, is the universal matter of life. It is the one substance
with which life everywhere is associated, and as we see it simply in
the sponge, so also we behold it (only in more complex guise) in the
man. Now, the living parts of this dried cast-away sponge were found
both in its interior and on its surface. They lined the canals that
everywhere permeate the sponge-substance, and microscopic examination
has told us a great deal about their nature.
[Illustration: FIG. 1. DEVELOPMENT OF A SPONGE (_Olynthus_). 1. The
egg. 2, 3, and 4. The process of egg-division. 5 and 6. The
gastrula-stage. 7. The perfect sponge.]
For, whether found in the canals of the sponge themselves, or embedded
in the sponge-substance, the living sponge-particles are represented
each by a semi-independent mass of protoplasm. So that the first view
I would have you take of the sponge as a living mass, is, that it is a
colony and not a single unit. It is composed, in other words, of
aggregated masses of living particles, which bud out one from the
other, and manufacture the supporting skeleton we know as "the sponge
of commerce" itself. Under the microscope, these living sponge-units
appear in various guises and shapes. Some of them are formless, and,
as to shape, ever-altering masses, resembling that familiar animalcule
of our pools we know as the _Amoeba_. These members of the
sponge-colony form the bulk of the population. They are embedded in
the sponge substance; they wander about through the meshes of the
sponge; they seize food and flourish and grow; and they probably also
give origin to the "eggs" from which new sponges are in due course
produced.
More characteristic however, are certain units of this living
sponge-colony which live in the lining membrane of the canals. In
point of fact, a sponge is a kind of Venice, a certain proportion of
whose inhabitants, like those of the famous Queen of the Adriatic
herself, live on the banks of the waterways. Just as in Venice we find
the provisions for the denizens of the city brought to the inhabitants
by the canals, so from the water, which, as we shall see, is
perpetually circulating through a sponge, the members of the
sponge-colony receive their food.
Look, again, at the sponge-fragment which lies before us. You perceive
half a dozen large holes or so, each opening on a little eminence, as
it were. These apertures, bear in mind, we call _oscula_. They are the
exits of the sponge-domain. But a close inspection of a sponge shows
that it is riddled with finer and smaller apertures. These latter are
the _pores_, and they form the entrances to the sponge-domain.
On the banks of the canal you may see growing plentifully in summer
time a green sponge, which is the common fresh-water species. Now, if
you drop a living specimen of this species into a bowl of water, and
put some powdered indigo into the water, you may note how the currents
are perpetually being swept in by the pores and out by the oscula. In
every living sponge this perpetual and unceasing circulation of water
proceeds. This is the sole evidence the unassisted sight receives of
the vitality of the sponge-colony, and the importance of this
circulation in aiding life in these depths, to be fairly carried out
cannot readily be over-estimated.
[Illustration: WHERE SPONGES GROW.]
Let us now see how this circulation is maintained. Microscopically
regarded, we see here and there, in the sides of the sponge-passages,
little chambers and recesses which remind one of the passing-places in
a narrow canal. Lining these chambers, we see living sponge-units of a
type different from the shapeless specks we noted to occur in the
meshes of the sponge substance itself. The units of the recesses each
consist of a living particle, whose free extremity is raised into a
kind of collar, from which projects a lash-like filament known as a
flagellum.
This lash is in constant movement. It waves to and fro in the water,
and the collection of lashes we see in any one chamber acts as a
veritable brush, which by its movement not only sweeps water in by the
pores, but sends it onwards through the sponge, and in due time sends
it out by the bigger holes, or oscula. This constant circulation in
the sponge discharges more than one important function. For, as
already noted, it serves the purpose of nutrition, in that the
particles on which sponge-life is supported are swept into the colony.
Again, the fresh currents of water carry with them the oxygen gas
which is a necessity of sponge existence, as of human life; while,
thirdly, waste matters, inevitably alike in sponge and in man as the
result of living, are swept out of the colony, and discharged into the
sea beyond. Our bit of sponge has thus grown from a mere dry fragment
into a living reality. It is a community in which already, low as it
is, the work of life has come to be discharged by distinct and fairly
specialized beings.
The era of new sponge-life is inaugurated by means of egg-development,
although there exists another fashion (that of gemmules or buds)
whereby out of the parental substance young sponges are produced. A
sponge-egg develops, as do all eggs, in a definite cycle. It undergoes
division (Fig. 1); its one cell becomes many; and its many cells
arrange themselves first of all into a cup-like form (5, 6 and 7),
which may remain in this shape if the sponge is a simple one, or
become developed into the more complex shape of the sponges we know.
In every museum you may see specimens of a beautiful vase-like
structure seemingly made of spun-glass. This is a flinty sponge, the
"Venus flower-basket," whose presence in the sponge family redeems it
from the charge that it contains no things of beauty whatever. So,
too, the rocks are full of fossil-sponges, many of quaint form. Our
piece of sponge, as we may understand, has yet other bits of history
attached to it.... Meanwhile, think over the sponge and its ways, and
learn from it that out of the dry things of life, science weaves many
a fairy tale.
[Illustration]
THE GREATEST SEA-WAVE EVER KNOWN
(FROM LIGHT SCIENCE IN LEISURE HOURS.)
BY R.A. PROCTOR.
[Illustration]
August 13th, 1868, one of the most terrible calamities which has ever
visited a people befell the unfortunate inhabitants of Peru. In that
land earthquakes are nearly as common as rain storms are with us; and
shocks by which whole cities are changed into a heap of ruins are by
no means infrequent. Yet even in Peru, "the land of earthquakes," as
Humboldt has termed it, no such catastrophe as that of August, 1868,
had occurred within the memory of man. It was not one city which was
laid in ruins, but a whole empire. Those who perished were counted by
tens of thousands, while the property destroyed by the earthquake was
valued at millions of pounds sterling.
Although so many months have passed since this terrible calamity took
place, scientific men have been busily engaged, until quite recently,
in endeavoring to ascertain the real significance of the various
events which were observed during and after the occurrence of the
earthquake. The geographers of Germany have taken a special interest
in interpreting the evidence afforded by this great manifestation of
Nature's powers. Two papers have been written recently on the great
earthquake of August 13th, 1868--one by Professor von Hochsteter, the
other by Herr von Tschudi, which present an interesting account of the
various effects, by land and by sea, which resulted from the
tremendous upheaving force to which the western flanks of the Peruvian
Andes were subjected on that day. The effects on land, although
surprising and terrible, only differ in degree from those which have
been observed in other earthquakes. But the progress of the great
sea-wave which was generated by the upheaval of the Peruvian shores
and propagated over the whole of the Pacific Ocean differs altogether
from any earthquake phenomena before observed. Other earthquakes have
indeed been followed by oceanic disturbances; but these have been
accompanied by terrestrial motions, so as to suggest the idea that
they had been caused by the motion of the sea-bottom or of the
neighboring land. In no instance has it ever before been known that a
well-marked wave of enormous proportions should have been propagated
over the largest ocean tract on our globe by an earth-shock whose
direct action was limited to a relatively small region, and that
region not situated in the centre, but on one side of the wide area
traversed by the wave.
We propose to give a brief sketch of the history of this enormous
sea-wave. In the first place, however, it may be well to remind the
reader of a few of the more prominent features of the great shock to
which this wave owed its origin.
It was at Arequipa, at the foot of the lofty volcanic mountain Misti,
that the most terrible effects of the great earthquake were
experienced. Within historic times Misti has poured forth no lava
streams, but that the volcano is not extinct is clearly evidenced by
the fact that in 1542 an enormous mass of dust and ashes was vomited
forth from its crater. On August 13th. 1868, Misti showed no signs of
being disturbed. So far as the volcanic neighbor was concerned, the
forty-four thousand inhabitants of Arequipa had no reason to
anticipate the catastrophe which presently befell them. At five
minutes past five an earthquake shock was experienced, which, though
severe, seems to have worked little mischief. Half a minute later,
however, a terrible noise was heard beneath the earth; a second shock
more violent than the first was felt, and then began a swaying motion,
gradually increasing in intensity. In the-course of the first minute
this motion had become so violent that the inhabitants ran in terror
out of their houses into the streets and squares. In the next two
minutes the swaying movement had so increased that the more lightly
built houses were cast to the ground, and the flying people could
scarcely keep their feet. "And now," says Von Tschudi, "there followed
during two or three minutes a terrible scene. The swaying motion which
had hitherto prevailed changed into fierce vertical upheaval. The
subterranean roaring increased in the most terrifying manner; then
were heard the heart-piercing shrieks of the wretched people, the
bursting of walls, the crashing fall of houses and churches, while
over all rolled thick clouds of a yellowish-black dust, which, had
they been poured forth many minutes longer, would have suffocated
thousands." Although the shocks had lasted but a few minutes, the whole
town was destroyed. Not one building remained uninjured, and there
were few which did not lie in shapeless heaps of ruins.
At Tacna and Arica the earth-shock was less severe, but strange and
terrible phenomena followed it. At the former place a circumstance
occurred the cause and nature of which yet remain a mystery. About
three hours after the earthquake--in other words, at about eight
o'clock in the evening--an intensely brilliant light made its
appearance above the neighboring mountains. It lasted for fully half
an hour, and has been ascribed to the eruption of some as yet unknown
volcano.