Land, where some of the species of either country do not exist: Iceland,
Britain, the Mediterranean Sea, North and South America, and the South
Sea Islands, all possess Antarctic _Diatomaceoe_. The silicious coats of
species only known living in the waters of the South Polar Ocean, have,
during past ages, contributed to the formation of rocks; and thus they
outlive several successive creations of organized beings. The phonolite
stones of the Rhine, and the Tripoli stone, contain species identical
with what are now contributing to form a sedimentary deposit (and
perhaps, at some future period, a bed of rock) extending in one
continuous stratum for 400 measured miles. I allude to the shores of the
Victoria Barrier, along whose coast the soundings examined were
invariably charged with diatomaceous remains, constituting a bank which
stretches 200 miles north from the base of Victoria Barrier, while the
average depth of water above it is 300 fathoms, or 1,800 feet. Again,
some of the Antarctic species have been detected floating in the
atmosphere which overhangs the wide ocean between Africa and America. The
knowledge of this marvellous fact we owe to Mr. Darwin, who, when he was
at sea off the Cape de Verd Islands, collected an impalpable powder which
fell on Captain Fitzroy's ship. He transmitted this dust to Ehrenberg,
who ascertained it to consist of the silicious coats, chiefly of American
_Diatomaceoe_, which were being wafted through the upper region of the
air, when some meteorological phenomena checked them in their course and
deposited them on the ship and surface of the ocean.
"The existence of the remains of many species of this order (and amongst
them some Antarctic ones) in the volcanic ashes, pumice, and scoriae of
active and extinct volcanoes (those of the Mediterranean Sea and
Ascension Island, for instance) is a fact bearing immediately upon the
present subject. Mount Erebus, a volcano 12,400 feet high, of the first
class in dimensions and energetic action, rises at once from the ocean in
the seventy-eighth degree of south latitude, and abreast of the
_Diatomaceoe_ bank, which reposes in part on its base. Hence it may not
appear preposterous to conclude that, as Vesuvius receives the waters of
the Mediterranean, with its fish, to eject them by its crater, so the
subterranean and subaqueous forces which maintain Mount Erebus in
activity may occasionally receive organic matter from the bank, and
disgorge it, together with those volcanic products, ashes and pumice.
"Along the shores of Graham's Land and the South Shetland Islands, we
have a parallel combination of igneous and aqueous action, accompanied
with an equally copious supply of _Diatomaceoe_. In the Gulf of Erebus
and Terror, fifteen degrees north of Victoria Land, and placed on the
opposite side of the globe, the soundings were of a similar nature with
those of the Victoria Land and Barrier, and the sea and ice as full of
_Diatomaceoe_. This was not only proved by the deep sea lead, but by the
examination of bergs which, once stranded, had floated off and become
reversed, exposing an accumulation of white friable mud frozen to their
bases, which abounded with these vegetable remains."
The _Challenger_ has explored the Antarctic seas in a region intermediate
between those examined by Sir James Ross's expedition; and the
observations made by Dr. Wyville Thomson and his colleagues in every
respect confirm those of Dr. Hooker:--
"On the 11th of February, lat. 60° 52' S., long. 80° 20' E., and March 3,
lat. 53° 55' S., long. 108° 35' E., the sounding instrument came up
filled with a very fine cream-coloured paste, which scarcely effervesced
with acid, and dried into a very light, impalpable, white powder. This,
when examined under the microscope, was found to consist almost entirely
of the frustules of Diatoms, some of them wonderfully perfect in all the
details of their ornament, and many of them broken up. The species of
Diatoms entering into this deposit have not yet been worked up, but they
appear to be referable chiefly to the genera _Fragillaria, Coscinodiscus,
Choetoceros, Asteromphalus_, and _Dictyocha_, with fragments of the
separated rods of a singular silicious organism, with which we were
unacquainted, and which made up a large proportion of the finer matter of
this deposit. Mixed with the Diatoms there were a few small
_Globigerinoe_, some of the tests and spicules of Radiolarians, and some
sand particles; but these foreign bodies were in too small proportion to
affect the formation as consisting practically of Diatoms alone. On the
4th of February, in lat. 52°, 29' S., long., 71° 36" E., a little to the
north of the Heard Islands, the tow-net, dragging a few fathoms below the
surface, came up nearly filled with a pale yellow gelatinous mass. This
was found to consist entirely of Diatoms of the same species as those
found at the bottom. By far the most abundant was the little bundle of
silicious rods, fastened together loosely at one end, separating from one
another at the other end, and the whole bundle loosely twisted into a
spindle. The rods are hollow, and contain the characteristic endochrome
of the _Diatomaceoe_. Like the _Globigerina_ ooze, then, which it
succeeds to the southward in a band apparently of no great width, the
materials of this silicious deposit are derived entirely from the surface
and intermediate depths. It is somewhat singular that Diatoms did not
appear to be in such large numbers on the surface over the Diatom ooze as
they were a little further north. This may perhaps be accounted for by
our not having struck their belt of depth with the tow-net; or it is
possible that when we found it on the 11th of February the bottom deposit
was really shifted a little to the south by the warm current, the
excessively fine flocculent _débris_ of the Diatoms taking a certain time
to sink. The belt of Diatom ooze is certainly a little further to the
southward in long. 83° E., in the path of the reflux of the Agulhas
current, than in long. 108° E.
"All along the edge of the ice-pack--everywhere, in fact, to the south of
the two stations--on the 11th of February on our southward voyage, and on
the 3rd of March on our return, we brought up fine sand and grayish mud,
with small pebbles of quartz and felspar, and small fragments of mica-
slate, chlorite-slate, clay-slate, gneiss, and granite. This deposit, I
have no doubt, was derived from the surface like the others, but in this
case by the melting of icebergs and the precipitation of foreign matter
contained in the ice.
"We never saw any trace of gravel or sand, or any material necessarily
derived from land, on an iceberg. Several showed vertical or irregular
fissures filled with discoloured ice or snow; but, when looked at
closely, the discoloration proved usually to be very slight, and the
effect at a distance was usually due to the foreign material filling the
fissure reflecting light less perfectly than the general surface of the
berg. I conceive that the upper surface of one of these great tabular
southern icebergs, including by far the greater part of its bulk, and
culminating in the portion exposed above the surface of the sea, was
formed by the piling up of successive layers of snow during the period,
amounting perhaps to several centuries, during which the ice-cap was
slowly forcing itself over the low land and out to sea over a long extent
of gentle slope, until it reached a depth considerably above 200 fathoms,
when the lower specific weight of the ice caused an upward strain which
at length overcame the cohesion of the mass, and portions were rent off
and floated away. If this be the true history of the formation of these
icebergs, the absence of all land _débris_ in the portion exposed above
the surface of the sea is readily understood. If any such exist, it must
be confined to the lower part of the berg, to that part which has at one
time or other moved on the floor of the ice-cap.
"The icebergs, when they are first dispersed, float in from 200 to 250
fathoms. When, therefore, they have been drifted to latitudes of 65° or
64° S., the bottom of the berg just reaches the layer at which the
temperature of the water is distinctly rising, and it is rapidly melted,
and the mud and pebbles with which it is more or less charged are
precipitated. That this precipitation takes place all over the area where
the icebergs are breaking up, constantly, and to a considerable extent,
is evident from the fact of the soundings being entirely composed of such
deposits; for the Diatoms, _Globigerinoe_, and radiolarians are present
on the surface in large numbers; and unless the deposit from the ice were
abundant it would soon be covered and masked by a layer of the exuvia of
surface organisms."
The observations which have been detailed leave no doubt that the
Antarctic sea bottom, from a little to the south of the fiftieth
parallel, as far as 80° S., is being covered by a fine deposit of
silicious mud, more or less mixed, in some parts, with the ice-borne
_débris_ of polar lands and with the ejections of volcanoes. The
silicious particles which constitute this mud, are derived, in part, from
the diatomaceous plants and radiolarian animals which throng the surface,
and, in part, from the spicula of sponges which live at the bottom. The
evidence respecting the corresponding Arctic area is less complete, but
it is sufficient to justify the conclusion that an essentially similar
silicious cap is being formed around the northern pole.
There is no doubt that the constituent particles of this mud may
agglomerate into a dense rock, such as that formed at Oran on the shores
of the Mediterranean, which is made up of similar materials. Moreover, in
the case of freshwater deposits of this kind it is certain that the
action of percolating water may convert the originally soft and friable,
fine-grained sandstone into a dense, semi-transparent opaline stone, the
silicious organized skeletons being dissolved, and the silex re-deposited
in an amorphous state. Whether such a metamorphosis as this occurs in
submarine deposits, as well as in those formed in fresh water, does not
appear; but there seems no reason to doubt that it may. And hence it may
not be hazardous to conclude that very ordinary metamorphic agencies may
convert these polar caps into a form of quartzite.
In the great intermediate zone, occupying some 110° of latitude, which
separates the circumpolar Arctic and Antarctic areas of silicious
deposit, the Diatoms and _Radiolaria_ of the surface water and the
sponges of the bottom do not die out, and, so far as some forms are
concerned, do not even appear to diminish in total number; though, on a
rough estimate, it would appear that the proportion of _Radiolaria_ to
Diatoms is much greater than in the colder seas. Nevertheless the
composition of the deep-sea mud of this intermediate zone is entirely
different from that of the circumpolar regions.
The first exact information respecting the nature of this mud at depths
greater than 1,000 fathoms was given by Ehrenberg, in the account which
he published in the "Monatsberichte" of the Berlin Academy for the year
1853, of the soundings obtained by Lieut. Berryman, of the United States
Navy, in the North Atlantic, between Newfoundland and the Azores.
Observations which confirm those of Ehrenberg in all essential respects
have been made by Professor Bailey, myself, Dr. Wallich, Dr. Carpenter,
and Professor Wyville Thomson, in their earlier cruises; and the
continuation of the _Globigerina_ ooze over the South Pacific has been
proved by the recent work of the _Challenger_, by which it is also shown,
for the first time, that, in passing from the equator to high southern
latitudes, the number and variety of the _Foraminifera_ diminishes, and
even the _Globigerinoe_ become dwarfed. And this result, it will be
observed, is in entire accordance with the fact already mentioned that,
in the sea of Kamschatka, the deep-sea mud was found by Bailey to contain
no calcareous organisms.
Thus, in the whole of the "intermediate zone," the silicious deposit
which is being formed there, as elsewhere, by the accumulation of sponge-
spicula, _Radiolaria_, and Diatoms, is obscured and overpowered by the
immensely greater amount of calcareous sediment, which arises from the
aggregation of the skeletons of dead _Foraminifera_. The similarity of
the deposit, thus composed of a large percentage of carbonate of lime,
and a small percentage of silex, to chalk, regarded merely as a kind of
rock, which was first pointed out by Ehrenberg,[5] is now admitted on all
hands; nor can it be reasonably doubted, that ordinary metamorphic
agencies are competent to convert the "modern chalk" into hard limestone
or even into crystalline marble.
[Footnote 5: The following passages in Ehrenberg's memoir on _The
Organisms in the Chalk which are still living_ (1839), are conclusive:--
"7. The dawning period of the existing living organic creation, if such a
period is distinguishable (which is doubtful), can only be supposed to
have existed on the other side of, and below, the chalk formation; and
thus, either the chalk, with its widespread and thick beds, must enter
into the series of newer formations; or some of the accepted four great
geological periods, the quaternary, tertiary, and secondary formations,
contain organisms which still live. It is more probable, in the
proportion of 3 to 1, that the transition or primary period is not
different, but that it is only more difficult to examine and understand,
by reason of the gradual and prolonged chemical decomposition and
metamorphosis of many of its organic constituents."
"10. By the mass-forming _Infasoria_ and _Polythalamia_, secondary are
not distinguishable from tertiary formations; and, from what has been
said, it is possible that, at this very day, rock masses are forming in
the sea, and being raised by volcanic agencies, the constitution of
which, on the whole, is altogether similar to that of the chalk. The
chalk remains distinguishable by its organic remains as a formation, but
not as a kind of rock."]
Ehrenberg appears to have taken it for granted that the _Globigerinoe_
and other _Foraminifera_ which are found in the deep-sea mud, live at the
great depths in which their remains are found; and he supports this
opinion by producing evidence that the soft parts of these organisms are
preserved, and may be demonstrated by removing the calcareous matter with
dilute acids. In 1857, the evidence for and against this conclusion
appeared to me to be insufficient to warrant a positive conclusion one
way or the other, and I expressed myself in my report to the Admiralty on
Captain Dayman's soundings in the following terms:--
"When we consider the immense area over which this deposit is spread, the
depth at which its formation is going on, and its similarity to chalk,
and still more to such rocks as the marls of Caltanisetta, the question,
whence are all these organisms derived? becomes one of high scientific
interest.
"Three answers have suggested themselves:--
"In accordance with the prevalent view of the limitation of life to
comparatively small depths, it is imagined either: 1, that these
organisms have drifted into their present position from shallower waters;
or 2, that they habitually live at the surface of the ocean, and only
fall down into their present position.
"1. I conceive that the first supposition is negatived by the extremely
marked zoological peculiarity of the deep-sea fauna.
"Had the _Globigerinoe_ been drifted into their present position from
shallow water, we should find a very large proportion of the
characteristic inhabitants of shallow waters mixed with them, and this
would the more certainly be the case, as the large _Globigerinoe_, so
abundant in the deep-sea soundings, are, in proportion to their size,
more solid and massive than almost any other _Foraminifera_. But the fact
is that the proportion of other _Foraminifera_ is exceedingly small, nor
have I found as yet, in the deep-sea deposits, any such matters as
fragments of molluscous shells, of _Echini_, &c., which abound in shallow
waters, and are quite as likely to be drifted as the heavy
_Globigerinoe_. Again, the relative proportions of young and fully formed
_Globigerinoe_ seem inconsistent with the notion that they have travelled
far. And it seems difficult to imagine why, had the deposit been
accumulated in this way, _Coscinodisci_ should so almost entirely
represent the _Diatomaceoe_.
"2. The second hypothesis is far more feasible, and is strongly supported
by the fact that many _Polycistineoe [Radiolaria]_ and _Coscinodisci_ are
well known to live at the surface of the ocean. Mr. Macdonald, Assistant-
Surgeon of H.M.S. _Herald_, now in the South-Western Pacific, has lately
sent home some very valuable observations on living forms of this kind,
met with in the stomachs of oceanic mollusks, and therefore certainly
inhabitants of the superficial layer of the ocean. But it is a singular
circumstance that only one of the forms figured by Mr. Macdonald is at
all like a _Globigerina_, and there are some peculiarities about even
this which make me greatly doubt its affinity with that genus. The form,
indeed, is not unlike that of a _Globigerina_, but it is provided with
long radiating processes, of which I have never seen any trace in
_Globigerina_. Did they exist, they might explain what otherwise is a
great objection to this view, viz., how is it conceivable that the heavy
_Globigerina_ should maintain itself at the surface of the water?
"If the organic bodies in the deep-sea soundings have neither been
drifted, nor have fallen from above, there remains but one alternative--
they must have lived and died where they are.
"Important objections, however, at once suggest themselves to this view.
How can animal life be conceived to exist under such conditions of light,
temperature, pressure, and aeration as must obtain at these vast depths?
"To this one can only reply that we know for a certainty that even very
highly-organized animals do continue to live at a depth of 300 and 400
fathoms, inasmuch as they have been dredged up thence; and that the
difference in the amount of light and heat at 400 and at 2,000 fathoms is
probably, so to speak, very far less than the difference in complexity of
organisation between these animals and the humbler _Protozoa_ and
_Protophyta_ of the deep-sea soundings.
"I confess, though as yet far from regarding it proved that the
_Globigerinoe_ live at these depths, the balance of probabilities seems
to me to incline in that direction. And there is one circumstance which
weighs strongly in my mind. It may be taken as a law that any genus of
animals which is found far back in time is capable of living under a
great variety of circumstances as regards light, temperature, and
pressure. Now, the genus _Globigerina_ is abundantly represented in the
cretaceous epoch, and perhaps earlier.
"I abstain, however, at present from drawing any positive conclusions,
preferring rather to await the result of more extended observations."[6]
[Footnote 6: Appendix to Report on Deep-sea Soundings in the Atlantic
Ocean, by Lieut.-Commander Joseph Dayman. 1857.]
Dr. Wallich, Professor Wyville Thomson, and Dr. Carpenter concluded that
the _Globigerinoe_ live at the bottom. Dr. Wallich writes in 1862--"By
sinking very fine gauze nets to considerable depths, I have repeatedly
satisfied myself that _Globigerina_ does not occur in the superficial
strata of the ocean."[7] Moreover, having obtained certain living star-
fish from a depth of 1,260 fathoms, and found their stomachs full of
"fresh-looking _Globigerinoe_" and their _débris_--he adduces this fact
in support of his belief that the _Globigerinoe_ live at the bottom.
[Footnote 7: The _North Atlantic Sea-bed_, p. 137.]
On the other hand, Müller, Haeckel, Major Owen, Mr. Gwyn Jeffries, and
other observers, found that _Globigerinoe_, with the allied genera
_Orbulina_ and _Pulvinulina_, sometimes occur abundantly at the surface
of the sea, the shells of these pelagic forms being not unfrequently
provided with the long spines noticed by Macdonald; and in 1865 and 1866,
Major Owen more especially insisted on the importance of this fact. The
recent work of the _Challenger_ fully confirms Major Owen's statement. In
the paper recently published in the proceedings of the Royal Society,[8]
from which a quotation has already been made, Professor Wyville Thomson
says:--
"I had formed and expressed a very strong opinion on the matter. It
seemed to me that the evidence was conclusive that the _Foraminifera_
which formed the _Globigerina_ ooze lived on the bottom, and that the
occurrence of individuals on the surface was accidental and exceptional;
but after going into the thing carefully, and considering the mass of
evidence which has been accumulated by Mr. Murray, I now admit that I was
in error; and I agree with him that it may be taken as proved that all
the materials of such deposits, with the exception, of course, of the
remains of animals which we now know to live at the bottom at all depths,
which occur in the deposit as foreign bodies, are derived from the
surface.
[Footnote 8: "Preliminary Notes on the Nature of the Sea-bottom procured
by the soundings of H.M.S. _Challenger_ during her cruise in the Southern
Seas, in the early part of the year 1874."--_Proceedings of the Royal
Society_, Nov. 26, 1874.]
"Mr. Murray has combined with a careful examination of the soundings a
constant use of the tow-net, usually at the surface, but also at depths
of from ten to one hundred fathoms; and he finds the closest relation to
exist between the surface fauna of any particular locality and the
deposit which is taking place at the bottom. In all seas, from the
equator to the polar ice, the tow-net contains _Globigerinoe_. They are
more abundant and of a larger size in warmer seas; several varieties,
attaining a large size and presenting marked varietal characters, are
found in the intertropical area of the Atlantic. In the latitude of
Kerguelen they are less numerous and smaller, while further south they
are still more dwarfed, and only one variety, the typical _Globigerina
bulloides_, is represented. The living _Globigerinoe_ from the tow-net
are singularly different in appearance from the dead shells we find at
the bottom. The shell is clear and transparent, and each of the pores
which penetrate it is surrounded by a raised crest, the crest round
adjacent pores coalescing into a roughly hexagonal network, so that the
pores appear to lie at the bottom of a hexagonal pit. At each angle of
this hexagon the crest gives off a delicate flexible calcareous spine,
which is sometimes four or five times the diameter of the shell in
length. The spines radiate symmetrically from the direction of the centre
of each chamber of the shell, and the sheaves of long transparent needles
crossing one another in different directions have a very beautiful
effect. The smaller inner chambers of the shell are entirely filled with
an orange-yellow granular sarcode; and the large terminal chamber usually
contains only a small irregular mass, or two or three small masses run
together, of the same yellow sarcode stuck against one side, the
remainder of the chamber being empty. No definite arrangement and no
approach to structure was observed in the sarcode, and no
differentiation, with the exception of round bright-yellow oil-globules,
very much like those found in some of the radiolarians, which are
scattered, apparently irregularly, in the sarcode. We never have been
able to detect, in any of the large number of _Globigerinoe_ which we
have examined, the least trace of pseudopodia, or any extension, in any
form, of the sarcode beyond the shell.
* * * * *