that, while few objects of interest were brought up within the dredge,
many living creatures came up sticking to the outside of the dredge-bag,
and even to the first few fathoms of the dredge-rope. The mouth of the
dredge doubtless rapidly filled with mud, and thus the things it should
have brought up were shut out. To remedy this inconvenience Captain
Calver devised an arrangement not unlike that employed by the coral-
fishers. He fastened half a dozen swabs, such as are used for drying
decks, to the dredge. A swab is something like what a birch-broom would
be if its twigs were made of long, coarse, hempen yarns. These dragged
along after the dredge over the surface of the mud, and entangled the
creatures living there--multitudes of which, twisted up in the strands of
the swabs, were brought to the surface with the dredge. A further
improvement was made by attaching a long iron bar to the bottom of the
dredge bag, and fastening large bunches of teased-out hemp to the end of
this bar. These "tangles" bring up immense quantities of such animals as
have long arms, or spines, or prominences which readily become caught in
the hemp, but they are very destructive to the fragile organisms which
they imprison; and, now that the trawl can be successfully worked at the
greatest depths, it may be expected to supersede them; at least, wherever
the ground is soft enough to permit of trawling.
It is obvious that between the dredge, the trawl, and the tangles, there
is little chance for any organism, except such as are able to burrow
rapidly, to remain safely at the bottom of any part of the sea which the
_Challenger_ undertakes to explore. And, for the first time in the
history of scientific exploration, we have a fair chance of learning what
the population of the depths of the sea is like in the most widely
different parts of the world.
And now arises the next question. The means of exploration being fairly
adequate, what forms of life may be looked for at these vast depths?
The systematic study of the Distribution of living beings is the most
modern branch of Biological Science, and came into existence long after
Morphology and Physiology had attained a considerable development. This
naturally does not imply that, from the time men began to observe natural
phenomena, they were ignorant of the fact that the animals and plants of
one part of the world are different from those in other regions; or that
those of the hills are different from those of the plains in the same
region; or finally that some marine creatures are found only in the
shallows, while others inhabit the deeps. Nevertheless, it was only after
the discovery of America that the attention of naturalists was powerfully
drawn to the wonderful differences between the animal population of the
central and southern parts of the new world and that of those parts of
the old world which lie under the same parallels of latitude. So far back
as 1667 Abraham Mylius, in his treatise "De Animalium origine et
migratione, populorum," argues that, since there are innumerable species
of animals in America which do not exist elsewhere, they must have been
made and placed there by the Deity: Buffon no less forcibly insists upon
the difference between the Faunae of the old and new world. But the first
attempt to gather facts of this order into a whole, and to coordinate
them into a series of generalizations, or laws of Geographical
Distribution, is not a century old, and is contained in the "Specimen
Zoologiae Geographicae Quadrupedum Domicilia et Migrationes sistens,"
published, in 1777, by the learned Brunswick Professor, Eberhard
Zimmermann, who illustrates his work by what he calls a "Tabula
Zoographica," which is the oldest distributional map known to me.
In regard to matters of fact, Zimmermann's chief aim is to show that
among terrestrial mammals, some occur all over the world, while others
are restricted to particular areas of greater or smaller extent; and that
the abundance of species follows temperature, being greatest in warm and
least in cold climates. But marine animals, he thinks, obey no such law.
The Arctic and Atlantic seas, he says, are as full of fishes and other
animals as those of the tropics. It is, therefore, clear that cold does
not affect the dwellers in the sea as it does land animals, and that this
must be the case follows from the fact that sea water, "propter varias
quas continet bituminis spiritusque particulas," freezes with much more
difficulty than fresh water. On the other hand, the heat of the
Equatorial sun penetrates but a short distance below the surface of the
ocean. Moreover, according to Zimmermann, the incessant disturbance of
the mass of the sea by winds and tides, so mixes up the warm and the cold
that life is evenly diffused and abundant throughout the ocean.
In 1810, Risso, in his work on the Ichthyology of Nice, laid the
foundation of what has since been termed "bathymetrical" distribution, or
distribution in depth, by showing that regions of the sea bottom of
different depths could be distinguished by the fishes which inhabit them.
There was the _littoral region_ between tide marks with its sand-eels,
pipe fishes, and blennies: the _seaweed region_, extending from low-
water-mark to a depth of 450 feet, with its wrasses, rays, and flat fish;
and the _deep-sea region_, from 450 feet to 1500 feet or more, with
its file-fish, sharks, gurnards, cod, and sword-fish.
More than twenty years later, M.M. Audouin and Milne Edwards carried out
the principle of distinguishing the Faunae of different zones of depth
much more minutely, in their "Recherches pour servir à l'Histoire
Naturelle du Littoral de la France," published in 1832.
They divide the area included between highwater-mark and lowwater-mark of
spring tides (which is very extensive, on account of the great rise and
fall of the tide on the Normandy coast about St. Malo, where their
observations were made) into four zones, each characterized by its
peculiar invertebrate inhabitants. Beyond the fourth region they
distinguish a fifth, which is never uncovered, and is inhabited by
oysters, scallops, and large starfishes and other animals. Beyond this
they seem to think that animal life is absent.[3]
[Footnote 3: "Enfin plus has encore, c'est-à-dire alors loin des côtes,
le fond des eaux ne paraît plus être habité, du moms dans nos mers, par
aucun de ces animaux" (1. c. tom. i. p. 237). The "ces animaux" leaves
the meaning of the authors doubtful.]
Audouin and Milne Edwards were the first to see the importance of the
bearing of a knowledge of the manner in which marine animals are
distributed in depth, on geology. They suggest that, by this means, it
will be possible to judge whether a fossiliferous stratum was formed upon
the shore of an ancient sea, and even to determine whether it was
deposited in shallower or deeper water on that shore; the association of
shells of animals which live in different zones of depth will prove that
the shells have been transported into the position in which they are
found; while, on the other hand, the absence of shells in a deposit will
not justify the conclusion that the waters in which it was formed were
devoid of animal inhabitants, inasmuch as they might have been only too
deep for habitation.
The new line of investigation thus opened by the French naturalists was
followed up by the Norwegian, Sars, in 1835, by Edward Forbes, in our own
country, in 1840,[4] and by Oersted, in Denmark, a few years later. The
genius of Forbes, combined with his extensive knowledge of botany,
invertebrate zoology, and geology, enabled him to do more than any of his
compeers, in bringing the importance of distribution in depth into
notice; and his researches in the Aegean Sea, and still more his
remarkable paper "On the Geological Relations of the existing Fauna and
Flora of the British Isles," published in 1846, in the first volume of
the "Memoirs of the Geological Survey of Great Britain," attracted
universal attention.
[Footnote 4: In the paper in the _Memoirs of the Survey_ cited further
on, Forbes writes:--
"In an essay 'On the Association of Mollusca on the British Coasts,
considered with reference to Pleistocene Geology,' printed in [the
_Edinburgh Academic Annual_ for] 1840, I described the mollusca, as
distributed on our shores and seas, in four great zones or regions,
usually denominated 'The Littoral zone,' 'The region of Laminariae,' 'The
region of Coral-lines,' and 'The region of Corals.' An extensive series
of researches, chiefly conducted by the members of the committee
appointed by the British Association to investigate the marine geology of
Britain by means of the dredge, have not invalidated this classification,
and the researches of Professor Lovén, in the Norwegian and Lapland seas,
have borne out their correctness The first two of the regions above
mentioned had been previously noticed by Lamoureux, in his account of the
distribution (vertically) of sea-weeds, by Audouin and Milne Edwards in
their _Observations on the Natural History of the coast of France_, and
by Sars in the preface to his _Beskrivelser og Jagttayelser_."]
On the coasts of the British Islands, Forbes distinguishes four zones or
regions, the Littoral (between tide marks), the Laminarian (between
lowwater-mark and 15 fathoms), the Coralline (from 15 to 50 fathoms), and
the Deep sea or Coral region (from 50 fathoms to beyond 100 fathoms).
But, in the deeper waters of the Aegean Sea, between the shore and a depth
of 300 fathoms, Forbes was able to make out no fewer than eight zones of
life, in the course of which the number and variety of forms gradually
diminished until, beyond 300 fathoms, life disappeared altogether. Hence
it appeared as if descent in the sea had much the same effect on life, as
ascent on land. Recent investigations appear to show that Forbes was
right enough in his classification of the facts of distribution in depth
as they are to be observed in the Aegean; and though, at the time he
wrote, one or two observations were extant which might have warned him
not to generalize too extensively from his Aegean experience, his own
dredging work was so much more extensive and systematic than that of any
other naturalist, that it is not wonderful he should have felt justified
in building upon it. Nevertheless, so far as the limit of the range of
life in depth goes, Forbes' conclusion has been completely negatived, and
the greatest depths yet attained show not even an approach to a "zero of
life":--
"During the several cruises of H.M. ships _Lightning_ and _Porcupine_ in
the years 1868, 1869, and 1870," says Dr. Wyville Thomson, "fifty-seven
hauls of the dredge were taken in the Atlantic at depths beyond 500
fathoms, and sixteen at depths beyond 1,000 fathoms, and, in all cases,
life was abundant. In 1869, we took two casts in depths greater than
2,000 fathoms. In both of these life was abundant; and with the deepest
cast, 2,435 fathoms, off the month of the Bay of Biscay, we took living,
well-marked and characteristic examples of all the five invertebrate sub-
kingdoms. And thus the question of the existence of abundant animal life
at the bottom of the sea has been finally settled and for all depths, for
there is no reason to suppose that the depth anywhere exceeds between
three and four thousand fathoms; and if there be nothing in the
conditions of a depth of 2,500 fathoms to prevent the full development of
a varied Fauna, it is impossible to suppose that even an additional
thousand fathoms would make any great difference."[5]
[Footnote 5: _The Depths of the Sea_, p. 30. Results of a similar kind,
obtained by previous observers, are stated at length in the sixth
chapter, pp. 267-280. The dredgings carried out by Count Pourtales, under
the authority of Professor Peirce, the Superintendent of the United
States Coast Survey, in the years 1867, 1868, and 1869, are particularly
noteworthy, and it is probably not too much to say, in the words of
Professor Agassiz, "that we owe to the coast survey the first broad and
comprehensive basis for an exploration of the sea bottom on a large
scale, opening a new era in zoological and geological research."]
As Dr. Wyville Thomson's recent letter, cited above, shows, the use of
the trawl, at great depths, has brought to light a still greater
diversity of life. Fishes came up from a depth of 600 to more than 1,000
fathoms, all in a peculiar condition from the expansion of the air
contained in their bodies. On their relief from the extreme pressure,
their eyes, especially, had a singular appearance, protruding like great
globes from their heads. Bivalve and univalve mollusca seem to be rare at
the greatest depths; but starfishes, sea urchins and other echinoderms,
zoophytes, sponges, and protozoa abound.
It is obvious that the _Challenger_ has the privilege of opening a new
chapter in the history of the living world. She cannot send down her
dredges and her trawls into these virgin depths of the great ocean
without bringing up a discovery. Even though the thing itself may be
neither "rich nor rare," the fact that it came from that depth, in that
particular latitude and longitude, will be a new fact in distribution,
and, as such, have a certain importance.
But it may be confidently assumed that the things brought up will very
frequently be zoological novelties; or, better still, zoological
antiquities, which, in the tranquil and little-changed depths of the
ocean, have escaped the causes of destruction at work in the shallows,
and represent the predominant population of a past age.
It has been seen that Audouin and Milne Edwards foresaw the general
influence of the study of distribution in depth upon the interpretation
of geological phenomena. Forbes connected the two orders of inquiry still
more closely; and in the thoughtful essay "On the connection between the
distribution of the existing Fauna and Flora of the British Isles, and
the geological changes which have affected their area, especially during
the epoch of the Northern drift," to which reference has already been
made, he put forth a most pregnant suggestion.
In certain parts of the sea bottom in the immediate vicinity of the
British Islands, as in the Clyde district, among the Hebrides, in the
Moray Firth, and in the German Ocean, there are depressed areas, forming a
kind of submarine valleys, the centres of which are from 80 to 100
fathoms, or more, deep. These depressions are inhabited by assemblages of
marine animals, which differ from those found over the adjacent and
shallower region, and resemble those which are met with much farther
north, on the Norwegian coast. Forbes called these Scandinavian
detachments "Northern outliers."
How did these isolated patches of a northern population get into these
deep places? To explain the mystery, Forbes called to mind the fact that,
in the epoch which immediately preceded the present, the climate was much
colder (whence the name of "glacial epoch" applied to it); and that the
shells which are found fossil, or sub-fossil, in deposits of that age are
precisely such as are now to be met with only in the Scandinavian, or
still more Arctic, regions. Undoubtedly, during the glacial epoch, the
general population of our seas had, universally, the northern aspect
which is now presented only by the "northern outliers"; just as the
vegetation of the land, down to the sea-level, had the northern character
which is, at present, exhibited only by the plants which live on the tops
of our mountains. But, as the glacial epoch passed away, and the present
climatal conditions were developed, the northern plants were able to
maintain themselves only on the bleak heights, on which southern forms
could not compete with them. And, in like manner, Forbes suggested that,
after the glacial epoch, the northern animals then inhabiting the sea
became restricted to the deeps in which they could hold their own against
invaders from the south, better fitted than they to flourish in the
warmer waters of the shallows. Thus depth in the sea corresponded in its
effect upon distribution to height on the land.
The same idea is applied to the explanation of a similar anomaly in the
Fauna of the Aegean:--
"In the deepest of the regions of depth of the Aegean, the representation
of a Northern Fauna is maintained, partly by identical and partly by
representative forms.... The presence of the latter is essentially due to
the law (of representation of parallels of latitude by zones of depth),
whilst that of the former species depended on their transmission from
their parent seas during a former epoch, and subsequent isolation. That
epoch was doubtless the newer Pliocene or Glacial Era, when the _Mya
truncata_ and other northern forms now extinct in the Mediterranean, and
found fossil in the Sicilian tertiaries, ranged into that sea. The
changes which there destroyed the _shallow water_ glacial forms, did not
affect those living in the depths, and which still survive."[6]
[Footnote 6: _Memoirs of the Geological Survey of Great Britain_, Vol. i.
p. 390.]
The conception that the inhabitants of local depressions of the sea
bottom might be a remnant of the ancient population of the area, which
had held their own in these deep fastnesses against an invading Fauna, as
Britons and Gaels have held out in Wales and in Scotland against
encroaching Teutons, thus broached by Forbes, received a wider
application than Forbes had dreamed of when the sounding machine first
brought up specimens of the mud of the deep sea. As I have pointed out
elsewhere,[7] it at once became obvious that the calcareous sticky mud of
the Atlantic was made up, in the main, of shells of _Globigerina_ and
other _Foraminifera_, identical with those of which the true chalk is
composed, and the identity extended even to the presence of those
singular bodies, the Coccoliths and Coccospheres, the true nature of
which is not yet made out. Here then were organisms, as old as the
cretaceous epoch, still alive, and doing their work of rock-making at the
bottom of existing seas. What if _Globigerina_ and the Coccoliths should
not be the only survivors of a world passed away, which are hidden
beneath three miles of salt water? The letter which Dr. Wyville Thomson
wrote to Dr. Carpenter in May, 1868, out of which all these expeditions
have grown, shows that this query had become a practical problem in Dr.
Thomson's mind at that time; and the desirableness of solving the problem
is put in the foreground of his reasons for urging the Government to
undertake the work of exploration:--
[Footnote 7: See above, "On a Piece of Chalk," p. 13.]
"Two years ago, M. Sars, Swedish Government Inspector of Fisheries, had
an opportunity, in his official capacity, of dredging off the Loffoten
Islands at a depth of 300 fathoms. I visited Norway shortly after his
return, and had an opportunity of studying with his father, Professor
Sars, some of his results. Animal forms were _abundant_; many of them
were new to science; and among them was one of surpassing interest, the
small crinoid, of which you have a specimen, and which we at once
recognised as a degraded type of the _Apiocrinidoe_, an order hitherto
regarded as extinct, which attained its maximum in the Pear Encrinites of
the Jurassic period, and whose latest representative hitherto known was
the _Bourguettocrinus_ of the chalk. Some years previously, Mr.
Absjornsen, dredging in 200 fathoms in the Hardangerfjord, procured
several examples of a Starfish (_Brisinga_), which seems to find its
nearest ally in the fossil genus _Protaster_. These observations place it
beyond a doubt that animal life is abundant in the ocean at depths
varying from 200 to 300 fathoms, that the forms at these great depths
differ greatly from those met with in ordinary dredgings, and that, at
all events in some cases, these animals are closely allied to, and would
seem to be directly descended from, the Fauna of the early tertiaries.
"I think the latter result might almost have been anticipated; and,
probably, further investigation will largely add to this class of data,
and will give us an opportunity of testing our determinations of the
zoological position of some fossil types by an examination of the soft
parts of their recent representatives. The main cause of the destruction,
the migration, and the extreme modification of animal types, appear to be
change of climate, chiefly depending upon oscillations of the earth's
crust. These oscillations do not appear to have ranged, in the Northern
portion of the Northern Hemisphere, much beyond 1,000 feet since the
commencement of the Tertiary Epoch. The temperature of deep waters seems
to be constant for all latitudes at 39°; so that an immense area of the
North Atlantic must have had its conditions unaffected by tertiary or
post-tertiary oscillations."[8]
[Footnote 8: The Depths of the Sea, pp. 51-52.]
As we shall see, the assumption that the temperature of the deep sea is
everywhere 39° F. (4° Cent.) is an error, which Dr. Wyville Thomson
adopted from eminent physical writers; but the general justice of the
reasoning is not affected by this circumstance, and Dr. Thomson's
expectation has been, to some extent, already verified.
Thus besides _Globigerina_, there are eighteen species of deep-sea
_Foraminifera_ identical with species found in the chalk. Imbedded in the
chalky mud of the deep sea, in many localities, are innumerable cup-
shaped sponges, provided with six-rayed silicious spicula, so disposed
that the wall of the cup is formed of a lacework of flinty thread. Not
less abundant, in some parts of the chalk formation, are the fossils
known as _Ventriculites_, well described by Dr. Thomson as "elegant vases
or cups, with branching root-like bases, or groups of regularly or
irregularly spreading tubes delicately fretted on the surface with an
impressed network like the finest lace"; and he adds, "When we compare
such recent forms as _Aphrocallistes, Iphiteon, Holtenia_, and
_Askonema_, with certain series of the chalk _Ventriculites_, there
cannot be the slightest doubt that they belong to the same family--in
some cases to very nearly allied genera."[9]
[Footnote 9: _The Depths of the Sea_, p. 484.]
Professor Duncan finds "several corals from the coast of Portugal more
nearly allied to chalk forms than to any others."
The Stalked Crinoids or Feather Stars, so abundant in ancient times, are
now exclusively confined to the deep sea, and the late explorations have
yielded forms of old affinity, the existence of which has hitherto been
unsuspected. The general character of the group of star fishes imbedded
in the white chalk is almost the same as in the modern Fauna of the deep
Atlantic. The sea urchins of the deep sea, while none of them are
specifically identical with any chalk form, belong to the same general
groups, and some closely approach extinct cretaceous genera.
Taking these facts in conjunction with the positive evidence of the
existence, during the Cretaceous epoch, of a deep ocean where now lies
the dry land of central and southern Europe, northern Africa, and western
and southern Asia; and of the gradual diminution of this ocean during the
older tertiary epoch, until it is represented at the present day by such
teacupfuls as the Caspian, the Black Sea, and the Mediterranean; the
supposition of Dr. Thomson and Dr. Carpenter that what is now the deep
Atlantic, was the deep Atlantic (though merged in a vast easterly
extension) in the Cretaceous epoch, and that the _Globigerina_ mud has
been accumulating there from that time to this, seems to me to have a
great degree of probability. And I agree with Dr. Wyville Thomson against
Sir Charles Lyell (it takes two of us to have any chance against his
authority) in demurring to the assertion that "to talk of chalk having
been uninterruptedly formed in the Atlantic is as inadmissible in a
geographical as in a geological sense."
If the word "chalk" is to be used as a stratigraphical term and
restricted to _Globigerina_ mud deposited during the Cretaceous epoch, of
course it is improper to call the precisely similar mud of more recent
date, chalk. If, on the other hand, it is to be used as a mineralogical
term, I do not see how the modern and the ancient chalks are to be
separated--and, looking at the matter geographically, I see no reason to
doubt that a boring rod driven from the surface of the mud which forms
the floor of the mid-Atlantic would pass through one continuous mass of
_Globigerina_ mud, first of modern, then of tertiary, and then of
mesozoic date; the "chalks" of different depths and ages being
distinguished merely by the different forms of other organisms associated
with the _Globigerinoe_.