Discourses
by
Thomas H. Huxley
Part 2 out of 5
the waves, and of whose real nature we are ignorant; or when the coloured
contents of the marine animals who feed on these Algae are examined. To
the south, however, of the belt of ice which encircles the globe, between
the parallels of 50 deg. and 70 deg. S., and in the waters comprised between that
belt and the highest latitude ever attained by man, this vegetation is
very conspicuous, from the contrast between its colour and the white snow
and ice in which it is imbedded. Insomuch, that in the eightieth degree,
all the surface ice carried along by the currents, the sides of every
berg and the base of the great Victoria Barrier itself, within reach of
the swell, were tinged brown, as if the polar waters were charged with
oxide of iron.
"As the majority of these plants consist of very simple vegetable cells,
enclosed in indestructible silex (as other Algae are in carbonate of
lime), it is obvious that the death and decomposition of such multitudes
must form sedimentary deposits, proportionate in their extent to the
length and exposure of the coast against which they are washed, in
thickness to the power of such agents as the winds, currents, and sea,
which sweep them more energetically to certain positions, and in purity,
to the depth of the water and nature of the bottom. Hence we detected
their remains along every icebound shore, in the depths of the adjacent
ocean, between 80 and 400 fathoms. Off Victoria Barrier (a perpendicular
wall of ice between one and two hundred feet above the level of the sea)
the bottom of the ocean was covered with a stratum of pure white or green
mud, composed principally of the silicious shells of the _Diatomaceoe_.
These, on being put into water, rendered it cloudy like milk, and took
many hours to subside. In the very deep water off Victoria and Graham's
Land, this mud was particularly pure and fine; but towards the shallow
shores there existed a greater or less admixture of disintegrated rock
and sand; so that the organic compounds of the bottom frequently bore but
a small proportion to the inorganic." ...
"The universal existence of such an invisible vegetation as that of the
Antarctic Ocean, is a truly wonderful fact, and the more from its not
being accompanied by plants of a high order. During the years we spent
there, I had been accustomed to regard the phenomena of life as differing
totally from what obtains throughout all other latitudes, for everything
living appeared to be of animal origin. The ocean swarmed with
_Mollusca_, and particularly entomostracous _Crustacea_, small whales,
and porpoises; the sea abounded with penguins and seals, and the air with
birds; the animal kingdom was ever present, the larger creatures preying
on the smaller, and these again on smaller still; all seemed carnivorous.
The herbivorous were not recognised, because feeding on a microscopic
herbage, of whose true nature I had formed an erroneous impression. It
is, therefore, with no little satisfaction that I now class the
_Diatomaceoe_ with plants, probably maintaining in the South Polar Ocean
that balance between the vegetable and the animal kingdoms which prevails
over the surface of our globe. Nor is the sustenance and nutrition of the
animal kingdom the only function these minute productions may perform;
they may also be the purifiers of the vitiated atmosphere, and thus
execute in the Antarctic latitudes the office of our trees and grass turf
in the temperate regions, and the broad leaves of the palm, &c., in the
tropics." ...
With respect to the distribution of the _Diatomaceoe_, Dr. Hooker
remarks:--
"There is probably no latitude between that of Spitzbergen and Victoria
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 deg. 52' S., long. 80 deg. 20' E., and March 3,
lat. 53 deg. 55' S., long. 108 deg. 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 deg., 29' S., long., 71 deg. 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 _debris_ 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 deg. E., in the path of the reflux of the Agulhas
current, than in long. 108 deg. 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 _debris_ 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 deg. or
64 deg. 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 deg. S., is being covered by a fine deposit of
silicious mud, more or less mixed, in some parts, with the ice-borne
_debris_ 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 deg. 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 _debris_--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, Mueller, 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.
* * * * *
"In specimens taken with the tow-net the spines are very usually absent;
but that is probably on account of their extreme tenuity; they are broken
off by the slightest touch. In fresh examples from the surface, the dots
indicating the origin of the lost spines may almost always be made out
with a high power. There are never spines on the _Globigerinoe_ from the
bottom, even in the shallowest water."
There can now be no doubt, therefore, that _Globigerinoe_ live at the top
of the sea; but the question may still be raised whether they do not also
live at the bottom. In favour of this view, it has been urged that the
shells of the _Globigerinoe_ of the surface never possess such thick
walls as those which are fouled at the bottom, but I confess that I doubt
the accuracy of this statement. Again, the occurrence of minute
_Globigerinoe_ in all stages of development, at the greatest depths, is
brought forward as evidence that they live _in situ_. But considering the
extent to which the surface organisms are devoured, without
discrimination of young and old, by _Salpoe_ and the like, it is not
wonderful that shells of all ages should be among the rejectamenta. Nor
can the presence of the soft parts of the body in the shells which form
the _Globigerina_ ooze, and the fact, if it be one, that animals living
at the bottom use them as food, be considered as conclusive evidence that
the _Globigerinoe_ live at the bottom. Such as die at the surface, and
even many of those which are swallowed by other animals, may retain much
of their protoplasmic matter when they reach the depths at which the
temperature sinks to 34 deg. or 32 deg. Fahrenheit, where decomposition must
become exceedingly slow.
Another consideration appears to me to be in favour of the view that the
_Globigerinoe_ and their allies are essentially surface animals. This is
the fact brought out by the _Challenger's_ work, that they have a
southern limit of distribution, which can hardly depend upon anything but
the temperature of the surface water. And it is to be remarked that this
southern limit occurs at a lower latitude in the Antarctic seas than it
does in the North Atlantic. According to Dr. Wallich ("The North Atlantic
Sea Bed," p. 157) _Globigerina_ is the prevailing form in the deposits
between the Faroe Islands and Iceland, and between Iceland and East
Greenland--or, in other words, in a region of the sea-bottom which lies
altogether north of the parallel of 60 deg. N.; while in the southern seas,
the _Globigerinoe_ become dwarfed and almost disappear between 50 deg. and
55 deg. S. On the other hand, in the sea of Kamschatka, the _Globigerinoe_
have vanished in 56 deg. N., so that the persistence of the _Globigerina_
ooze in high latitudes, in the North Atlantic, would seem to depend on
the northward curve of the isothermals peculiar to this region; and it is
difficult to understand how the formation of _Globigerina_ ooze can be
affected by this climatal peculiarity unless it be effected by surface
animals.
Whatever may be the mode of life of the _Foraminifera_, to which the
calcareous element of the deep-sea "chalk" owes its existence, the fact
that it is the chief and most widely spread material of the sea-bottom in
the intermediate zone, throughout both the Atlantic and Pacific Oceans,
and the Indian Ocean, at depths from a few hundred to over two thousand
fathoms, is established. But it is not the only extensive deposit which
is now taking place. In 1853, Count Pourtales, an officer of the United
States Coast Survey, which has done so much for scientific hydrography,
observed, that the mud forming the sea-bottom at depths of one hundred
and fifty fathoms, in 31 deg. 32' N., 79 deg. 35' W., off the Coast of Florida,
was "a mixture, in about equal proportions, of _Globigerinoe_ and black
sand, probably greensand, as it makes a green mark when crushed on
paper." Professor Bailey, examining these grains microscopically, found
that they were casts of the interior cavities of _Foraminifera_,
consisting of a mineral known as _Glauconite_, which is a silicate of
iron and alumina. In these casts the minutest cavities and finest tubes
in the Foraminifer were sornetilnes reproduced in solid counterparts of
the glassy mineral, while the calcareous original had been entirely
dissolved away.
Contemporaneously with these observations, the indefatigable Ehrenberg
had discovered that the "greensands" of the geologist were largely made
up of casts of a similar character, and proved the existence of
_Foraminifera_ at a very ancient geological epoch, by discovering such
casts in a greensand of Lower Silurian age, which occurs near St.
Petersburg.
Subsequently, Messrs. Parker and Jones discovered similar casts in
process of formation, the original shell not having disappeared, in
specimens of the sea-bottom of the Australian seas, brought home by the
late Professor Jukes. And the _Challenger_ has observed a deposit of a
similar character in the course of the Agulhas current, near the Cape of
Good Hope, and in some other localities not yet defined.
It would appear that this infiltration of _Foraminifera_ shells with
_Glauconite_ does not take place at great depths, but rather in what may
be termed a sublittoral region, ranging from a hundred to three hundred
fathoms. It cannot be ascribed to any local cause, for it takes place,
not only over large areas in the Gulf of Mexico and the Coast of Florida,
but in the South Atlantic and in the Pacific. But what are the conditions
which determine its occurrence, and whence the silex, the iron, and the
alumina (with perhaps potash and some other ingredients in small
quantity) of which the _Glauconite_ is composed, proceed, is a point on
which no light has yet been thrown. For the present we must be content
with the fact that, in certain areas of the "intermediate zone,"
greensand is replacing and representing the primitively calcareo-
silicious ooze.
The investigation of the deposits which are now being formed in the basin
of the Mediterranean, by the late Professor Edward Forbes, by Professor
Williamson and more recently by Dr. Carpenter, and a comparison of the
results thus obtained with what is known of the surface fauna, have
brought to light the remarkable fact, that while the surface and the
shallows abound with _Foraminifera_ and other calcareous shelled
organisms, the indications of life become scanty at depths beyond 500 or
600 fathoms, while almost all traces of it disappear at greater depths,
and at 1,000 to 2,000 fathoms the bottom is covered with a fine clay.
Dr. Carpenter has discussed the significance of this remarkable fact, and
he is disposed to attribute the absence of life at great depths, partly
to the absence of any circulation of the water of the Mediterranean at
such depths, and partly to the exhaustion of the oxygen of the water by
the organic matter contained in the fine clay, which he conceives to be
formed by the finest particles of the mud brought down by the rivers
which flow into the Mediterranean.
However this may be, the explanation thus offered of the presence of the
fine mud, and of the absence of organisms which ordinarily live at the
bottom, does not account for the absence of the skeletons of the
organisms which undoubtedly abound at the surface of the Mediterranean;
and it would seem to have no application to the remarkable fact
discovered by the _Challenger_, that in the open Atlantic and Pacific
Oceans, in the midst of the great intermediate zone, and thousands of
miles away from the embouchure of any river, the sea-bottom, at depths
approaching to and beyond 3,000 fathoms, no longer consists of
_Globigerina_ ooze, but of an excessively fine red clay.
Professor Thomson gives the following account of this capital
discovery:--
"According to our present experience, the deposit of _Globigerina_ ooze
is limited to water of a certain depth, the extreme limit of the pure
characteristic formation being placed at a depth of somewhere about 2,250
fathoms. Crossing from these shallower regions occupied by the ooze into
deeper soundings, we find, universally, that the calcareous formation
gradually passes into, and is finally replaced by, an extremely fine pure
clay, which occupies, speaking generally, all depths below 2,500 fathoms,
and consists almost entirely of a silicate of the red oxide of iron and
alumina. The transition is very slow, and extends over several hundred
fathoms of increasing depth; the shells gradually lose their sharpness of
outline, and assume a kind of 'rotten' look and a brownish colour, and
become more and more mixed with a fine amorphous red-brown powder, which
increases steadily in proportion until the lime has almost entirely
disappeared. This brown matter is in the finest possible state of
subdivision, so fine that when, after sifting it to separate any
organisms it might contain, we put it into jars to settle, it remained
for days in suspension, giving the water very much the appearance and
colour of chocolate.
"In indicating the nature of the bottom on the charts, we came, from
experience and without any theoretical considerations, to use three terms
for soundings in deep water. Two of these, Gl. oz. and r. cl., were very
definite, and indicated strongly-marked formations, with apparently but
few characters in common; but we frequently got soundings which we could
not exactly call '_Globigerina_ ooze' or 'red clay,' and before we were
fully aware of the nature of these, we were in the habit of indicating
them as 'grey ooze' (gr. oz.) We now recognise the 'grey ooze' as an
intermediate stage between the _Globigerina_ ooze and the red clay; we
find that on one side, as it were, of an ideal line, the red clay
contains more and more of the material of the calcareous ooze, while on
the other, the ooze is mixed with an increasing proportion of 'red clay.'
"Although we have met with the same phenomenon so frequently, that we
were at length able to predict the nature of the bottom from the depth of
the soundings with absolute certainty for the Atlantic and the Southern
Sea, we had, perhaps, the best opportunity of observing it in our first
section across the Atlantic, between Teneriffe and St. Thomas. The first
four stations on this section, at depths from 1,525 to 2,220 fathoms,
show _Globigerina_ ooze. From the last of these, which is about 300 miles
from Teneriffe, the depth gradually increases to 2,740 fathoms at 500,
and 2,950 fathoms at 750 miles from Teneriffe. The bottom in these two
soundings might have been called 'grey ooze,' for although its nature has
altered entirely from the _Globigerina_ ooze, the red clay into which it
is rapidly passing still contains a considerable admixture of carbonate
of lime.
"The depth goes on increasing to a distance of 1,150 miles from
Teneriffe, when it reaches 3,150 fathoms; there the clay is pure and
smooth, and contains scarcely a trace of lime. From this great depth the
bottom gradually rises, and, with decreasing depth, the grey colour and
the calcareous composition of the ooze return. Three soundings in 2,050,
1,900, and 1,950 fathoms on the 'Dolphin Rise' gave highly characteristic
examples of the _Globigerina_ formation. Passing from the middle plateau
of the Atlantic into the western trough, with depths a little over 3,000
fathoms, the red clay returned in all its purity; and our last sounding,
in 1,420 fathoms, before reaching Sombrero, restored the _Globigerina_
ooze with its peculiar associated fauna.
"This section shows also the wide extension and the vast geological
importance of the red clay formation. The total distance from Teneriffe
to Sombrero is about 2,700 miles. Proceeding from east to west, we have--
About 80 miles of volcanic mud and sand,
" 350 " _Globigerina_ ooze,
" 1,050 " red clay,
" 330 " _Globigerina_ ooze,
" 850 " red clay,
" 40 " _Globigerina_ ooze;
giving a total of 1,900 miles of red clay to 720 miles of _Globigerina_
ooze.
"The nature and origin of this vast deposit of clay is a question of the
very greatest interest; and although I think there can be no doubt that
it is in the main solved, yet some matters of detail are still involved
in difficulty. My first impression was that it might be the most minutely
divided material, the ultimate sediment produced by the disintegration of
the land, by rivers and by the action of the sea on exposed coasts, and
held in suspension and distributed by ocean currents, and only making
itself manifest in places unoccupied by the _Globigerina_ ooze. Several
circumstances seemed, however, to negative this mode of origin. The
formation seemed too uniform: wherever we met with it, it had the same
character, and it only varied in composition in containing less or more
carbonate of lime.
"Again, the were gradually becoming more and more convinced that all the
important elements of the _Globigerina_ ooze lived on the surface, and it
seemed evident that, so long as the condition on the surface remained the
same, no alteration of contour at the bottom could possibly prevent its
accumulation; and the surface conditions in the Mid-Atlantic were very
uniform, a moderate current of a very equal temperature passing
continuously over elevations and depressions, and everywhere yielding to
the tow-net the ooze-forming _Foraminifera_ in the same proportion. The
Mid-Atlantic swarms with pelagic _Mollusca_, and, in moderate depths, the
shells of these are constantly mixed with the _Globigerina_ ooze,
sometimes in number sufficient to make up a considerable portion of its
bulk. It is clear that these shells must fall in equal numbers upon the
red clay, but scarcely a trace of one of them is ever brought up by the
dredge on the red clay area. It might be possible to explain the absence
of shell-secreting animals living on the bottom, on the supposition that
the nature of the deposit was injurious to them; but then the idea of a
current sufficiently strong to sweep them away is negatived by the
extreme fineness of the sediment which is being laid down; the absence of
surface shells appears to be intelligible only on the supposition that
they are in some way removed.
"We conclude, therefore, that the 'red clay' is not an additional
substance introduced from without, and occupying certain depressed
regions on account of some law regulating its deposition, but that it is
produced by the removal, by some means or other, over these areas, of the
carbonate of lime, which forms probably about 98 per cent. of the
material of the _Globigerina_ ooze. We can trace, indeed, every
successive stage in the removal of the carbonate of lime in descending
the slope of the ridge or plateau where the _Globigerina_ ooze is
forming, to the region of the clay. We find, first, that the shells of
pteropods and other surface _Mollusca_ which are constantly falling on
the bottom, are absent, or, if a few remain, they are brittle and yellow,
and evidently decaying rapidly. These shells of _Mollusca_ decompose more
easily and disappear sooner than the smaller, and apparently more
delicate, shells of rhizopods. The smaller _Foraminifera_ now give way,
and are found in lessening proportion to the larger; the coccoliths first
lose their thin outer border and then disappear; and the clubs of the
rhabdoliths get worn out of shape, and are last seen, under a high power,
as infinitely minute cylinders scattered over the field. The larger
_Foraminifera_ are attacked, and instead of being vividly white and
delicately sculptured, they become brown and worn, and finally they break
up, each according to its fashion; the chamber-walls of _Globigerina_
fall into wedge-shaped pieces, which quickly disappear, and a thick rough
crust breaks away from the surface of _Orbulina_, leaving a thin inner
sphere, at first beautifully transparent, but soon becoming opaque and
crumbling away.
"In the meantime the proportion of the amorphous 'red clay' to the
calcareous elements of all kinds increases, until the latter disappear,
with the exception of a few scattered shells of the larger
_Foraminifera_, which are still found even in the most characteristic
samples of the 'red clay.'
"There seems to be no room left for doubt that the red clay is
essentially the insoluble residue, the _ash_, as it were, of the
calcareous organisms which form the _Globigerina_ ooze, after the
calcareous matter has been by some means removed. An ordinary mixture of
calcareous _Foraminifera_ with the shells of pteropods, forming a fair
sample of _Globigerina_ ooze from near St. Thomas, was carefully washed,
and subjected by Mr. Buchanan to the action of weak acid; and he found
that there remained after the carbonate of lime had been removed, about 1
per cent. of a reddish mud, consisting of silica, alumina, and the red
oxide of iron. This experiment has been frequently repeated with
different samples of _Globigerina_ ooze, and always with the result that
a small proportion of a red sediment remains, which possesses all the
characters of the red clay."
* * * * *
"It seems evident from the observations here recorded, that _clay_, which
we have hitherto looked upon as essentially the product of the
disintegration of older rocks, may be, under certain circumstances, an
organic formation like chalk; that, as a matter of fact, an area on the
surface of the globe, which we have shown to be of vast extent, although
we are still far from having ascertained its limits, is being covered by
such a deposit at the present day.
"It is impossible to avoid associating such a formation with the fine,
smooth, homogeneous clays and schists, poor in fossils, but showing worm-
tubes and tracks, and bunches of doubtful branching things, such as
Oldhamia, silicious sponges, and thin-shelled peculiar shrimps. Such
formations, more or less metamorphosed, are very familiar, especially to
the student of palaeozoic geology, and they often attain a vast thickness.
One is inclined, from the great resemblance between them in composition
and in the general character of the included fauna, to suspect that these
may be organic formations, like the modern red clay of the Atlantic and
Southern Sea, accumulations of the insoluble ashes of shelled creatures.
"The dredging in the red clay on the 13th of March was usually rich. The
bag contained examples, those with calcareous shells rather stunted, of
most of the characteristic deep-water groups of the Southern Sea,
including _Umbellularia, Euplectella, Pterocrinus, Brisinga, Ophioglypha,
Pourtalesia_, and one or two _Mollusca_. This is, however, very rarely
the case. Generally the red clay is barren, or contains only a very small
number of forms."
It must be admitted that it is very difficult, at present, to frame any
satisfactory explanation of the mode of origin of this singular deposit
of red clay.
I cannot say that the theory put forward tentatively, and with much
reservation by Professor Thomson, that the calcareous matter is dissolved
out by the relatively fresh water of the deep currents from the Antarctic
regions, appears satisfactory to me. Nor do I see my way to the
acceptance of the suggestion of Dr. Carpenter, that the red clay is the
result of the decomposition of previously-formed greensand. At present
there is no evidence that greensand casts are ever formed at great
depths; nor has it been proved that _Glauconite_ is decomposable by the
agency of water and carbonic acid.
I think it probable that we shall have to wait some time for a sufficient
explanation of the origin of the abyssal red clay, no less than for that
of the sublittoral greensand in the intermediate zone. But the importance
of the establishment of the fact that these various deposits are being
formed in the ocean, at the present day, remains the same; whether its
_rationale_ be understood or not.
For, suppose the globe to be evenly covered with sea, to a depth say of a
thousand fathoms--then, whatever might be the mineral matter composing
the sea-bottom, little or no deposit would be formed upon it, the
abrading and denuding action of water, at such a depth, being exceedingly
slight.
Next, imagine sponges, _Radiolaria, Foraminifera_, and diatomaceous
plants, such as those which now exist in the deep-sea, to be introduced:
they would be distributed according to the same laws as at present, the
sponges (and possibly some of the _Foraminifera_), covering the bottom,
while other _Foraminifera_, with the _Radiolaria_ and _Diatomacea_, would
increase and multiply in the surface waters. In accordance with the
existing state of things, the _Radiolaria_ and Diatoms would have a
universal distribution, the latter gathering most thickly in the polar
regions, while the _Foraminifera_ would be largely, if not exclusively,
confined to the intermediate zone; and, as a consequence of this
distribution, a bed of "chalk" would begin to form in the intermediate
zone, while caps of silicious rock would accumulate on the circumpolar
regions.
Suppose, further, that a part of the intermediate area were raised to
within two or three hundred fathoms of the surface--for anything that we
know to the contrary, the change of level might determine the
substitution of greensand for the "chalk"; while, on the other hand, if
part of the same area were depressed to three thousand fathoms, that
change might determine the substitution of a different silicate of
alumina and iron--namely, clay--for the "chalk" that would otherwise be
formed.
If the _Challenger_ hypothesis, that the red clay is the residue left by
dissolved _Foraminiferous_ skeletons, is correct, then all these deposits
alike would be directly, or indirectly, the product of living organisms.
But just as a silicious deposit may be metamorphosed into opal or
quartzite, and chalk into marble, so known metamorphic agencies may
metamorphose clay into schist, clay-slate, slate, gneiss, or even
granite. And thus, by the agency of the lowest and simplest of organisms,
our imaginary globe might be covered with strata, of all the chief kinds
of rock of which the known crust of the earth is composed, of indefinite
thickness and extent.
The bearing of the conclusions which are now either established, or
highly probable, respecting the origin of silicious, calcareous, and
clayey rocks, and their metamorphic derivatives, upon the archaeology of
the earth, the elucidation of which is the ultimate object of the
geologist, is of no small importance.
A hundred years ago the singular insight of Linnaeus enabled him to say
that "fossils are not the children but the parents of rocks,"[9] and the
whole effect of the discoveries made since his time has been to compile a
larger and larger commentary upon this text. It is, at present, a
perfectly tenable hypothesis that all siliceous and calcareous rocks are
either directly, or indirectly, derived from material which has, at one
time or other, formed part of the organized framework of living
organisms. Whether the same generalization may be extended to aluminous
rocks, depends upon the conclusion to be drawn from the facts respecting
the red clay areas brought to light by the _Challenger_. If we accept the
view taken by Wyville Thomson and his colleagues--that the red clay is
the residuum left after the calcareous matter of the _Globigerinoe_ ooze
has been dissolved away--then clay is as much a product of life as
limestone, and all known derivatives of clay may have formed part of
animal bodies.
[Footnote 9: "Petrificata montium calcariorum non filii sed parentes
sunt, cum omnis calx oriatur ab animalibus."--_Systema Naturae_, Ed. xii.,
t. iii., p. 154. It must be recollected that Linnaeus included silex, as
well as limestone, under the name of "calx," and that he would probably
have arranged Diatoms among animals, as part of "chaos." Ehrenberg quotes
another even more pithy passage, which I have not been able to find in
any edition of the _Systema_ accessible to me: "Sic lapides ab
animalibus, nec vice versa. Sic runes saxei non primaevi, sed temporis
filiae."]
So long as the _Globigerinoe_;, actually collected at the surface, have
not been demonstrated to contain the elements of clay, the _Challenger_
hypothesis, as I may term it, must be accepted with reserve and
provisionally, but, at present, I cannot but think that it is more
probable than any other suggestion which has been made.
Accepting it provisionally, we arrive at the remarkable result that all
the chief known constituents of the crust of the earth may have formed
part of living bodies; that they may be the "ash" of protoplasm; that the
"_rupes saxei_" are not only _"temporis,"_ but "_vitae filiae_"; and,
consequently, that the time during which life has been active on the
globe may be indefinitely greater than the period, the commencement of
which is marked by the oldest known rocks, whether fossiliferous or
unfossiliferous.
And thus we are led to see where the solution of a great problem and
apparent paradox of geology may lie. Satisfactory evidence now exists
that some animals in the existing world have been derived by a process of
gradual modification from pre-existing forms. It is undeniable, for
example, that the evidence in favour of the derivation of the horse from
the later tertiary _Hipparion_, and that of the _Hipparion_ from
_Anchitherium_, is as complete and cogent as such evidence can reasonably
be expected to be; and the further investigations into the history of the
tertiary mammalia are pushed, the greater is the accumulation of evidence
having the same tendency. So far from palaeontology lending no support to
the doctrine of evolution--as one sees constantly asserted--that
doctrine, if it had no other support, would have been irresistibly forced
upon us by the palaeontological discoveries of the last twenty years.
If, however, the diverse forms of life which now exist have been produced
by the modification of previously-existing less divergent forms, the
recent and extinct species, taken as a whole, must fall into series which
must converge as we go back in time. Hence, if the period represented by
the rocks is greater than, or co-extensive with, that during which life
has existed, we ought, somewhere among the ancient formations, to arrive
at the point to which all these series converge, or from which, in other
words, they have diverged--the primitive undifferentiated protoplasmic
living things, whence the two great series of plants and animals have
taken their departure.
But, as a matter of fact, the amount of convergence of series, in
relation to the time occupied by the deposition of geological formations,
is extraordinarily small. Of all animals the higher _Vertebrata_ are the
most complex; and among these the carnivores and hoofed animals
(_Ungulata_) are highly differentiated. Nevertheless, although the
different lines of modification of the _Carnivora_ and those of the
_Ungulata_, respectively, approach one another, and, although each group
is represented by less differentiated forms in the older tertiary rocks
than at the present day, the oldest tertiary rocks do not bring us near
the primitive form of either. If, in the same way, the convergence of the
varied forms of reptiles is measured against the time during which their
remains are preserved--which is represented by the whole of the tertiary
and mesozoic formations--the amount of that convergence is far smaller
than that of the lines of mammals between the present time and the
beginning of the tertiary epoch. And it is a broad fact that, the lower
we go in the scale of organization, the fewer signs are there of
convergence towards the primitive form from whence all must have
diverged, if evolution be a fact. Nevertheless, that it is a fact in some
cases, is proved, and I, for one, have not the courage to suppose that
the mode in which some species have taken their origin is different from
that in which the rest have originated.
What, then, has become of all the marine animals which, on the hypothesis
of evolution, must have existed in myriads in those seas, wherein the
many thousand feet of Cambrian and Laurentian rocks now devoid, or almost
devoid, of any trace of life were deposited?
Sir Charles Lyell long ago suggested that the azoic character of these
ancient formations might be due to the fact that they had undergone
extensive metamorphosis; and readers of the "Principles of Geology" will
be familiar with the ingenious manner in which he contrasts the theory of
the Gnome, who is acquainted only with the interior of the earth, with
those of ordinary philosophers, who know only its exterior.
The metamorphism contemplated by the great modern champion of rational
geology is, mainly, that brought about by the exposure of rocks to
subterranean heat; and where no such heat could be shown to have
operated, his opponents assumed that no metamorphosis could have taken
place. But the formation of greensand, and still more that of the "red
clay" (if the _Challenger_ hypothesis be correct) affords an insight into
a new kind of metamorphosis--not igneous, but aqueous--by which the
primitive nature of a deposit may be masked as completely as it can be by
the agency of heat. And, as Wyville Thomson suggests, in the passage I
have quoted above (p. 17), it further enables us to assign a new cause
for the occurrence, so puzzling hitherto, of thousands of feet of
unfossiliferous fine-grained schists and slates, in the midst of
formations deposited in seas which certainly abounded in life. If the
great deposit of "red clay" now forming in the eastern valley of the
Atlantic were metamorphosed into slate and then upheaved, it would
constitute an "azoic" rock of enormous extent. And yet that rock is now
forming in the midst of a sea which swarms with living beings, the great
majority of which are provided with calcareous or silicious shells and
skeletons; and, therefore, are such as, up to this time, we should have
termed eminently preservable.
Thus the discoveries made by the _Challenger_ expedition, like all recent
advances in our knowledge of the phenomena of biology, or of the changes
now being effected in the structure of the surface of the earth, are in
accordance with and lend strong support to, that doctrine of
Uniformitarianism, which, fifty years ago, was held only by a small
minority of English geologists--Lyell, Scrope, and De la Beche--but now,
thanks to the long-continued labours of the first two, and mainly to
those of Sir Charles Lyell, has gradually passed from the position of a
heresy to that of catholic doctrine.
Applied within the limits of the time registered by the known fraction of
the crust of the earth, I believe that uniformitarianism is unassailable.
The evidence that, in the enormous lapse of time between the deposition
of the lowest Laurentian strata and the present day, the forces which
have modified the surface of the crust of the earth were different in
kind, or greater in the intensity of their action, than those which are
now occupied in the same work, has yet to be produced. Such evidence as
we possess all tends in the contrary direction, and is in favour of the
same slow and gradual changes occurring then as now.
But this conclusion in nowise conflicts with the deductions of the
physicist from his no less clear and certain data. It may be certain that
this globe has cooled down from a condition in which life could not have
existed; it may be certain that, in so cooling, its contracting crust
must have undergone sudden convulsions, which were to our earthquakes as
an earthquake is to the vibration caused by the periodical eruption of a
Geyser; but in that case, the earth must, like other respectable parents,
have sowed her wild oats, and got through her turbulent youth, before we,
her children, have any knowledge of her.
So far as the evidence afforded by the superficial crust of the earth
goes, the modern geologist can, _ex animo_, repeat the saying of Hutton,
"We find no vestige of a beginning--no prospect of an end." However, he
will add, with Hutton, "But in thus tracing back the natural operations
which have succeeded each other, and mark to us the course of time past,
we come to a period in which we cannot see any further." And if he seek
to peer into the darkness of this period, he will welcome the light
proffered by physics and mathematics.
IV
YEAST
[1871]
It has been known, from time immemorial, that the sweet liquids which may
be obtained by expressing the juices of the fruits and stems of various
plants, or by steeping malted barley in hot water, or by mixing honey
with water--are liable to undergo a series of very singular changes, if
freely exposed to the air and left to themselves, in warm weather.
However clear and pellucid the liquid may have been when first prepared,
however carefully it may have been freed, by straining and filtration,
from even the finest visible impurities, it will not remain clear. After
a time it will become cloudy and turbid; little bubbles will be seen
rising to the surface, and their abundance will increase until the liquid
hisses as if it were simmering on the fire. By degrees, some of the solid
particles which produce the turbidity of the liquid collect at its
surface into a scum, which is blown up by the emerging air-bubbles into a
thick, foamy froth. Another moiety sinks to the bottom, and accumulates
as a muddy sediment, or "lees."
When this action has continued, with more or less violence, for a certain
time, it gradually moderates. The evolution of bubbles slackens, and
finally comes to an end; scum and lees alike settle at the bottom, and
the fluid is once more clear and transparent. But it has acquired
properties of which no trace existed in the original liquid. Instead of
being a mere sweet fluid, mainly composed of sugar and water, the sugar
has more or less completely disappeared; and it has acquired that
peculiar smell and taste which we call "spirituous." Instead of being
devoid of any obvious effect upon the animal economy, it has become
possessed of a very wonderful influence on the nervous system; so that in
small doses it exhilarates, while in larger it stupefies, and may even
destroy life.
Moreover, if the original fluid is put into a still, and heated
moderately, the first and last product of its distillation is simple
water; while, when the altered fluid is subjected to the same process,
the matter which is first condensed in the receiver is found to be a
clear, volatile substance, which is lighter than water, has a pungent
taste and smell, possesses the intoxicating powers of the fluid in an
eminent degree, and takes fire the moment it is brought in contact with a
flame. The Alchemists called this volatile liquid, which they obtained
from wine, "spirits of wine," just as they called hydrochloric acid
"spirits of salt," and as we, to this day, call refined turpentine
"spirits of turpentine." As the "spiritus," or breath, of a man was
thought to be the most refined and subtle part of him, the intelligent
essence of man was also conceived as a sort of breath, or spirit; and, by
analogy, the most refined essence of anything was called its "spirit."
And thus it has come about that we use the same word for the soul of man
and for a glass of gin.
At the present day, however, we even more commonly use another name for
this peculiar liquid--namely, "alcohol," and its origin is not less
singular. The Dutch physician, Van Helmont, lived in the latter part of
the sixteenth and the beginning of the seventeenth century--in the
transition period between alchemy and chemistry--and was rather more
alchemist than chemist. Appended to his "Opera Omnia," published in 1707,
there is a very needful "Clavis ad obscuriorum sensum referendum," in
which the following passage occurs.--
"ALCOHOL.--Chymicis est liquor aut pulvis summe subtilisatus, vocabulo
Orientalibus quoque, cum primis Habessinis, familiari, quibus _cohol_
speciatim pulverem impalpabilem ex antimonio pro oculis tingendis denotat
... Hodie autem, ob analogiam, quivis pulvis tenerior ut pulvis oculorum
cancri summe subtilisatus _alcohol_ audit, haud aliter ac spiritus
rectificatissimi _alcolisati_ dicuntur."
Similarly, Robert Boyle speaks of a fine powder as "alcohol"; and, so
late as the middle of the last century, the English lexicographer, Nathan
Bailey, defines "alcohol" as "the pure substance of anything separated
from the more gross, a very fine and impalpable powder, or a very pure,
well-rectified spirit." But, by the time of the publication of
Lavoisier's "Traite Elementaire de Chimie," in 1789, the term "alcohol,"
"alkohol," or "alkool" (for it is spelt in all three ways), which Van
Helmont had applied primarily to a fine powder, and only secondarily to
spirits of wine, had lost its primary meaning altogether; and, from the
end of the last century until now, it has, I believe, been used
exclusively as the denotation of spirits of wine, and bodies chemically
allied to that substance.
The process which gives rise to alcohol in a saccharine fluid is known
tones as "fermentation"; a term based upon the apparent boiling up or
"effervescence" of the fermenting liquid, and of Latin origin.
Our Teutonic cousins call the same process "gaehren," "gaesen," "goeschen,"
and "gischen"; but, oddly enough, we do not seem to have retained their
verb or their substantive denoting the action itself, though we do use
names identical with, or plainly derived from, theirs for the scum and
lees. These are called, in Low German, "gaescht" and "gischt"; in Anglo-
Saxon, "gest," "gist," and "yst," whence our "yeast." Again, in Low
German and in Anglo-Saxon there is another name for yeast, having the
form "barm," or "beorm"; and, in the Midland Counties, "barm" is the name
by which yeast is still best known. In High German, there is a third name
for yeast, "hefe," which is not represented in English, so far as I know.
All these words are said by philologers to be derived from roots
expressive of the intestine motion of a fermenting substance. Thus "hefe"
is derived from "heben," to raise; "barm" from "beren" or "baeren," to
bear up; "yeast," "yst," and "gist," have all to do with seething and
foam, with "yeasty" waves, and "gusty" breezes.
The same reference to the swelling up of the fermenting substance is seen
in the Gallo-Latin terms "levure" and "leaven."
It is highly creditable to the ingenuity of our ancestors that the
peculiar property of fermented liquids, in virtue of which they "make
glad the heart of man," seems to have been known in the remotest periods
of which we have any record. All savages take to alcoholic fluids as if
they were to the manner born. Our Vedic forefathers intoxicated
themselves with the juice of the "soma"; Noah, by a not unnatural
reaction against a superfluity of water, appears to have taken the
earliest practicable opportunity of qualifying that which he was obliged
to drink; and the ghosts of the ancient Egyptians were solaced by
pictures of banquets in which the wine-cup passes round, graven on the
walls of their tombs. A knowledge of the process of fermentation,
therefore, was in all probability possessed by the prehistoric
populations of the globe; and it must have become a matter of great
interest even to primaeval wine-bibbers to study the methods by which
fermented liquids could be surely manufactured. No doubt it was soon
discovered that the most certain, as well as the most expeditious, way of
making a sweet juice ferment was to add to it a little of the scum, or
lees, of another fermenting juice. And it can hardly be questioned that
this singular excitation of fermentation in one fluid, by a sort of
infection, or inoculation, of a little ferment taken from some other
fluid, together with the strange swelling, foaming, and hissing of the
fermented substance, must have always attracted attention from the more
thoughtful. Nevertheless, the commencement of the scientific analysis of
the phenomena dates from a period not earlier than the first half of the
seventeenth century.
At this time, Van Helmont made a first step, by pointing out that the
peculiar hissing and bubbling of a fermented liquid is due, not to the
evolution of common air (which he, as the inventor of the term "gas,"
calls "gas ventosum"), but to that of a peculiar kind of air such as is
occasionally met with in caves, mines, and wells, and which he calls "gas
sylvestre."
But a century elapsed before the nature of this "gas sylvestre," or, as
it was afterwards called, "fixed air," was clearly determined, and it was
found to be identical with that deadly "choke-damp" by which the lives of
those who descend into old wells, or mines, or brewers' vats, are
sometimes suddenly ended; and with the poisonous aeriform fluid which is
produced by the combustion of charcoal, and now goes by the name of
carbonic acid gas.
During the same time it gradually became evident that the presence of
sugar was essential to the production of alcohol and the evolution of
carbonic acid gas, which are the two great and conspicuous products of
fermentation. And finally, in 1787, the Italian chemist, Fabroni, made
the capital discovery that the yeast ferment, the presence of which is
necessary to fermentation, is what he termed a "vegeto-animal" substance;
that is, a body which gives of ammoniacal salts when it is burned, and
is, in other ways, similar to the gluten of plants and the albumen and
casein of animals.
These discoveries prepared the way for the illustrious Frenchman,
Lavoisier, who first approached the problem of fermentation with a
complete conception of the nature of the work to be done. The words in
which he expresses this conception, in the treatise on elementary
chemistry to which reference has already been made, mark the year 1789 as
the commencement of a revolution of not less moment in the world of
science than that which simultaneously burst over the political world,
and soon engulfed Lavoisier himself in one of its mad eddies.
"We may lay it down as an incontestable axiom that, in all the operations
of art and nature, nothing is created; an equal quantity of matter exists
both before, and after the experiment: the quality and quantity of the
elements remain precisely the same, and nothing takes place beyond
changes and modifications in the combinations of these elements. Upon
this principle the whole art of performing chemical experiments depends;
we must always suppose an exact equality between the elements of the body
examined and those of the products of its analysis.
"Hence, since from must of grapes we procure alcohol and carbonic acid, I
have an undoubted right to suppose that must consists of carbonic acid
and alcohol. From these premisses we have two modes of ascertaining what
passes during vinous fermentation: either by determining the nature of,
and the elements which compose, the fermentable substances; or by
accurately examining the products resulting from fermentation; and it is
evident that the knowledge of either of these must lead to accurate
conclusions concerning the nature and composition of the other. From
these considerations it became necessary accurately to determine the
constituent elements of the fermentable substances; and for this purpose
I did not make use of the compound juices of fruits, the rigorous
analysis of which is perhaps impossible, but made choice of sugar, which
is easily analysed, and the nature of which I have already explained.
This substance is a true vegetable oxyd, with two bases, composed of
hydrogen and carbon, brought to the state of an oxyd by means of a
certain proportion of oxygen; and these three elements are combined in
such a way that a very slight force is sufficient to destroy the
equilibrium of their connection."
After giving the details of his analysis of sugar and of the products of
fermentation, Lavoisier continues:--
"The effect of the vinous fermentation upon sugar is thus reduced to the
mere separation of its elements into two portions; one part is oxygenated
at the expense of the other, so as to form carbonic acid; while the other
part, being disoxygenated in favour of the latter, is converted into the
combustible substance called alkohol; therefore, if it were possible to
re-unite alkohol and carbonic acid together, we ought to form sugar."[1]
[Footnote 1: _Elements of Chemistry_. By M. Lavoisier. Translated by
Robert Kerr. Second Edition, 1793 (pp. 186-196).]
Thus Lavoisier thought he had demonstrated that the carbonic acid and the
alcohol which are produced by the process of fermentation, are equal in
weight to the sugar which disappears; but the application of the more
refined methods of modern chemistry to the investigation of the products
of fermentation by Pasteur, in 1860, proved that this is not exactly
true, and that there is a deficit of from 5 to 7 per cent of the sugar
which is not covered by the alcohol and carbonic acid evolved. The
greater part of this deficit is accounted for by the discovery of two
substances, glycerine and succinic acid, of the existence of which
Lavoisier was unaware, in the fermented liquid. But about 1-1/2 per cent.
still remains to be made good. According to Pasteur, it has been
appropriated by the yeast, but the fact that such appropriation takes
place cannot be said to be actually proved.
However this may be, there can be no doubt that the constituent elements
of fully 98 per cent. of the sugar which has vanished during fermentation
have simply undergone rearrangement; like the soldiers of a brigade, who
at the word of command divide themselves into the independent regiments
to which they belong. The brigade is sugar, the regiments are carbonic
acid, succinic acid, alcohol, and glycerine.
From the time of Fabroni, onwards, it has been admitted that the agent by
which this surprising rearrangement of the particles of the sugar is
effected is the yeast. But the first thoroughly conclusive evidence of
the necessity of yeast for the fermentation of sugar was furnished by
Appert, whose method of preserving perishable articles of food excited so
much attention in France at the beginning of this century. Gay-Lussac, in
his "Memoire sur la Fermentation,"[2] alludes to Appert's method of
preserving beer-wort unfermented for an indefinite time, by simply
boiling the wort and closing the vessel in which the boiling fluid is
contained, in such a way as thoroughly to exclude air; and he shows that,
if a little yeast be introduced into such wort, after it has cooled, the
wort at once begins to ferment, even though every precaution be taken to
exclude air. And this statement has since received full confirmation from
Pasteur.
[Footnote 2: _Annales de Chimie_, 1810.]
On the other hand, Schwann, Schroeder and Dutch, and Pasteur, have amply
proved that air may be allowed to have free access to beer-wort, without
exciting fermentation, if only efficient precautions are taken to prevent
the entry of particles of yeast along with the air.
Thus, the truth that the fermentation of a simple solution of sugar in
water depends upon the presence of yeast, rests upon an unassailable
foundation; and the inquiry into the exact nature of the substance which
possesses such a wonderful chemical influence becomes profoundly
interesting.
The first step towards the solution of this problem was made two
centuries ago by the patient and painstaking Dutch naturalist,
Leeuwenhoek, who in the year 1680 wrote thus:--
"Saepissime examinavi fermnentum cerevisiae, semperque hoc ex globulis per
materiam pellucidam fluitantibus, quarm cerevisiam esse censui, constare
observavi: vidi etiam evidentissime, unumquemque hujus fermenti globulum
denuo ex sex distinctis globulis constare, accurate eidem quantitate et
formae, cui globulis sanguinis nostri, respondentibus.
"Verum talis mihi de horum origine et formatione conceptus formabam;
globulis nempe ex quibus farina Tritici, Hordei, Avenae, Fagotritici, se
constat aquae calore dissolvi et aquae commisceri; hac, vero aqua, quam
cerevisiam vocare licet, refrigescente, multos ex minimis particulis in
cerevisia coadunari, et hoc pacto efficere particulam sive globulum, quae
sexta pars est globuli faecis, et iterum sex ex hisce globulis
conjungi."[3]
[Footnote 3: Leeuwenhoek, _Arcana Naturae Detecta._ Ed. Nov., 1721.]
Thus Leeuwenhoek discovered that yeast consists of globules floating in a
fluid; but he thought that they were merely the starchy particles of the
grain from which the wort was made, rearranged. He discovered the fact
that yeast had a definite structure, but not the meaning of the fact. A
century and a half elapsed, and the investigation of yeast was
recommenced almost simultaneously by Cagniard de la Tour in France, and
by Schwann and Kuetzing in Germany. The French observer was the first to
publish his results; and the subject received at his hands and at those
of his colleague, the botanist Turpin, full and satisfactory
investigation.
The main conclusions at which they arrived are these. The globular, or
oval, corpuscles which float so thickly in the yeast as to make it muddy,
though the largest are not more than one two-thousandth of an inch in
diameter, and the smallest may measure less than one seven-thousandth of
an inch, are living organisms. They multiply with great rapidity by
giving off minute buds, which soon attain the size of their parent, and
then either become detached or remain united, forming the compound
globules of which Leeuwenhoek speaks, though the constancy of their
arrangement in sixes existed only in the worthy Dutchman's imagination.
It was very soon made out that these yeast organisms, to which Turpin
gave the name of _Torula cerevisioe_, were more nearly allied to the
lower Fungi than to anything else. Indeed Turpin, and subsequently
Berkeley and Hoffmann, believed that they had traced the development of
the _Torula_ into the well-known and very common mould--the _Penicillium
glaucum_. Other observers have not succeeded in verifying these
statements; and my own observations lead me to believe, that while the
connection between _Torula_ and the moulds is a very close one, it is of
a different nature from that which has been supposed. I have never been
able to trace the development of _Torula_ into a true mould; but it is
quite easy to prove that species of true mould, such as _Penicillium_,
when sown in an appropriate nidus, such as a solution of tartrate of
ammonia and yeast-ash, in water, with or without sugar, give rise to
_Toruloe_, similar in all respects to _T. cerevisioe_, except that they
are, on the average, smaller. Moreover, Bail has observed the development
of a _Torula_ larger than _T. cerevisioe_, from a _Mucor_, a mould allied
to _Penicillium_.
It follows, therefore, that the _Toruloe_, or organisms of yeast, are
veritable plants; and conclusive experiments have proved that the power
which causes the rearrangement of the molecules of the sugar is
intimately connected with the life and growth of the plant. In fact,
whatever arrests the vital activity of the plant also prevents it from
exciting fermentation.
Such being the facts with regard to the nature of yeast, and the changes
which it effects in sugar, how are they to be accounted for? Before
modern chemistry had come into existence, Stahl, stumbling, with the
stride of genius, upon the conception which lies at the bottom of all
modern views of the process, put forward the notion that the ferment,
being in a state of internal motion, communicated that motion to the
sugar, and thus caused its resolution into new substances. And Lavoisier,
as we have seen, adopts substantially the same view. But Fabroni, full of
the then novel conception of acids and bases and double decompositions,
propounded the hypothesis that sugar is an oxide with two bases, and the
ferment a carbonate with two bases; that the carbon of the ferment unites
with the oxygen of the sugar, and gives rise to carbonic acid; while the
sugar, uniting with the nitrogen of the ferment, produces a new substance
analogous to opium. This is decomposed by distillation, and gives rise to
alcohol. Next, in 1803, Thenard propounded a hypothesis which partakes
somewhat of the nature of both Stahl's and Fabroni's views. "I do not
believe with Lavoisier," he says, "that all the carbonic acid formed
proceeds from the sugar. How, in that case, could we conceive the action
of the ferment on it? I think that the first portions of the acid are due
to a combination of the carbon of the ferment with the oxygen of the
sugar, and that it is by carrying off a portion of oxygen from the last
that the ferment causes the fermentation to commence--the equilibrium
between the principles of the sugar being disturbed, they combine afresh
to form carbonic acid and alcohol."
The three views here before us may be familiarly exemplified by supposing
the sugar to be a card-house. According to Stahl, the ferment is somebody
who knocks the table, and shakes the card-house down; according to
Fabroni, the ferment takes out some cards, but puts others in their
places; according to Thenard, the ferment simply takes a card out of the
bottom story, the result of which is that all the others fall.
As chemistry advanced, facts came to light which put a new face upon
Stahl's hypothesis, and gave it a safer foundation than it previously
possessed. The general nature of these phenomena may be thus stated:--A
body, A, without giving to, or taking from, another body B, any material
particles, causes B to decompose into other substances, C, D, E, the sum
of the weights of which is equal to the weight of B, which decomposes.
Thus, bitter almonds contain two substances, amygdalin and synaptase,
which can be extracted, in a separate state, from the bitter almonds. The
amygdalin thus obtained, if dissolved in water, undergoes no change; but
if a little synaptase be added to the solution, the amygdalin splits up
into bitter almond oil, prussic acid, and a kind of sugar.
A short time after Cagniard de la Tour discovered the yeast plant,
Liebig, struck with the similarity between this and other such processes
and the fermentation of sugar, put forward the hypothesis that yeast
contains a substance which acts upon sugar, as synaptase acts upon
amygdalin. And as the synaptase is certainly neither organized nor alive,
but a mere chemical substance, Liebig treated Cagniard de la Tour's
discovery with no small contempt, and, from that time to the present, has
steadily repudiated the notion that the decomposition of the sugar is, in
any sense, the result of the vital activity of the _Torula_. But, though
the notion that the _Torula_ is a creature which eats sugar and excretes
carbonic acid and alcohol, which is not unjustly ridiculed in the most
surprising paper that ever made its appearance in a grave scientific
journal,[4] may be untenable, the fact that the _Toruloe_ are alive, and
that yeast does not excite fermentation unless it contains living
_Toruloe_, stands fast. Moreover, of late years, the essential
participation of living organisms in fermentation other than the
alcoholic, has been clearly made out by Pasteur and other chemists.
[Footnote 4: "Das entraethselte Geheimniss der geistigen Gaehrung
(Vorlaenfige briefliche Mittheilung)" is the title of an anonymous
contribution to Woehler and Liebig's _Annalen der Pharmacie_ for 1839, in
which a somewhat Rabelaisian imaginary description of the organisation of
the "yeast animals" and of the manner in which their functions are
performed, is given with a circumstantiality worthy of the author of
_Gulliver's Travels_. As a specimen of the writer's humour, his account
of what happens when fermentation comes to an end may suffice. "Sobald
naemlich die Thiere keinen Zucker mehr vorfinden, so fressen sie sich
gegenseitig selbst auf, was durch eine eigene Manipulation geschieht;
alles wird verdant bis auf die Eier, welche unveraendert durch den
Darmkanal hineingehen; man hat zuletzt wieder gaehrungsfaehige Hefe,
naemlich den Saamen der Thiere, der uebrig bleibt."] However, it may be
asked, is there any necessary opposition between the so-called "vital"
and the strictly physico-chemical views of fermentation? It is quite
possible that the living _Torula_ may excite fermentation in sugar,
because it constantly produces, as an essential part of its vital
manifestations, some substance which acts upon the sugar, just as the
synaptase acts upon the amygdalin. Or it may be, that, without the
formation of any such special substance, the physical condition of the
living tissue of the yeast plant is sufficient to effect that small
disturbance of the equilibrium of the particles of the sugar, which
Lavoisier thought sufficient to effect its decomposition.
Platinum in a very fine state of division--known as platinum black, or
_noir de platine_--has the very singular property of causing alcohol to
change into acetic acid with great rapidity. The vinegar plant, which is
closely allied to the yeast plant, has a similar effect upon dilute
alcohol, causing it to absorb the oxygen of the air, and become converted
into vinegar; and Liebig's eminent opponent, Pasteur, who has done so
much for the theory and the practice of vinegar-making, himself suggests
that in this case--
"La cause du phenomene physique qui accompagne la vie de la plante reside
dans un etat physique propre, analogue a celui du noir de platine. Mais
il est essentiel de remarquer que cet etat physique de la plante est
etroitement lie avec la vie de cette plante."[5]
[Footnote 5: _Etudes sur les Mycodermes_, Comptes-Rendus, liv., 1862.]
Now, if the vinegar plant gives rise to the oxidation of alcohol, on
account of its merely physical constitution, it is at any rate possible
that the physical constitution of the yeast plant may exert a decomposing
influence on sugar.
But, without presuming to discuss a question which leads us into the very
arcana of chemistry, the present state of speculation upon the _modus
operandi_ of the yeast plant in producing fermentation is represented, on
the one hand, by the Stahlian doctrine, supported by Liebig, according to
which the atoms of the sugar are shaken into new combinations either
directly by the _Toruloe_, or indirectly, by some substance formed by
them; and, on the other hand, by the Thenardian doctrine, supported by
Pasteur, according to which the yeast plant assimilates part of the
sugar, and, in so doing, disturbs the rest, and determines its resolution
into the products of fermentation. Perhaps the two views are not so much
opposed as they seem at first sight to be.
But the interest which attaches to the influence of the yeast plants upon
the medium in which they live and grow does not arise solely from its
bearing upon the theory of fermentation. So long ago as 1838, Turpin
compared the _Toruloe_ to the ultimate elements of the tissues of animals
and plants--"Les organes elementaires de leurs tissus, comparables aux
petits vegetaux des levures ordinaires, sont aussi les decompositeurs des
substances qui les environnent."
Almost at the same time, and, probably, equally guided by his study of
yeast, Schwann was engaged in those remarkable investigations into the
form and development of the ultimate structural elements of the tissues
of animals, which led him to recognise their fundamental identity with
the ultimate structural elements of vegetable organisms.
The yeast plant is a mere sac, or "cell," containing a semi-fluid matter,
and Schwann's microscopic analysis resolved all living organisms, in the
long run, into an aggregation of such sacs or cells, variously modified;
and tended to show, that all, whatever their ultimate complication, begin
their existence in the condition of such simple cells.
In his famous "Mikroskopische Untersuchungen" Schwann speaks of _Torula_
as a "cell"; and, in a remarkable note to the passage in which he refers
to the yeast plant, Schwann says:--
"I have been unable to avoid mentioning fermentation, because it is the
most fully and exactly known operation of cells, and represents, in the
simplest fashion, the process which is repeated by every cell of the
living body."
In other words, Schwann conceives that every cell of the living body
exerts an influence on the matter which surrounds and permeates it,
analogous to that which a _Torula_ exerts on the saccharine solution by
which it is bathed. A wonderfully suggestive thought, opening up views of
the nature of the chemical processes of the living body, which have
hardly yet received all the development of which they are capable.
Kant defined the special peculiarity of the living body to be that the
parts exist for the sake of the whole and the whole for the sake of the
parts. But when Turpin and Schwann resolved the living body into an
aggregation of quasi-independent cells, each, like a _Torula_, leading
its own life and having its own laws of growth and development, the
aggregation being dominated and kept working towards a definite end only
by a certain harmony among these units, or by the superaddition of a
controlling apparatus, such as a nervous system, this conception ceased
to be tenable. The cell lives for its own sake, as well as for the sake
of the whole organism; and the cells which float in the blood, live at
its expense, and profoundly modify it, are almost as much independent
organisms as the _Toruloe_ which float in beer-wort.
Schwann burdened his enunciation of the "cell theory" with two false
suppositions; the one, that the structures he called "nucleus"[6] and
"cell-wall" are essential to a cell; the other, that cells are usually
formed independently of other cells; but, in 1839, it was a vast and
clear gain to arrive at the conception, that the vital functions of all
the higher animals and plants are the resultant of the forces inherent in
the innumerable minute cells of which they are composed, and that each of
them is, itself, an equivalent of one of the lowest and simplest of
independent living beings--the _Torula_.
[Footnote 6: Later investigations have thrown an entirely new light upon
the structure and the functional importance of the nucleus; and have
proved that Schwann did not over-estimate its importance. 1894.]
From purely morphological investigations, Turpin and Schwann, as we have
seen, arrived at the notion of the fundamental unity of structure of
living beings. And, before long, the researches of chemists gradually led
up to the conception of the fundamental unity of their composition.
So far back as 1803, Thenard pointed out, in most distinct terms, the
important fact that yeast contains a nitrogenous "animal" substance; and
that such a substance is contained in all ferments. Before him, Fabroni
and Fourcroy speak of the "vegeto-animal" matter of yeast. In 1844 Mulder
endeavoured to demonstrate that a peculiar substance, which he called
"protein," was essentially characteristic of living matter.
In 1846, Payen writes:--
"Enfin, une loi sans exception me semble apparaitre dans les faits
nombreux que j'ai observes et conduire a envisager sous un nouveau jour
la vie vegetale; si je ne m'abuse, tout ce que dans les tissus vegetaux
la vue directe ou amplifiee nous permet de discerner sous la forme de
cellules et de vaisseaux, ne represente autre chose que les enveloppes
protectrices, les reservoirs et les conduits, a l'aide desquels les corps
animes qui les secretent et les faconnent, se logent, puisent et
charrient leurs aliments, deposent et isolent les matieres excretees."
And again:--
"Afin de completer aujourd'hui l'enonce du fait general, je rappellerai
que les corps, doue des fonctions accomplies dans les tissus des plantes,
sont formes des elements qui constituent, en proportion peu variable, les
organismes animaux; qu'ainsi l'on est conduit a reconnaitre une immense
unite de composition elementaire dans tous les corps vivants de la
nature."[7]
[Footnote 7: Mem. sur les Developpements des Vegetaux, &c.--_Mem.
Presentees_. ix. 1846.]
In the year (1846) in which these remarkable passages were published, the
eminent German botanist, Von Mohl invented the word "protoplasm," as a
name for one portion of those nitrogenous contents of the cells of living
plants, the close chemical resemblance of which to the essential
constituents of living animals is so strongly indicated by Payen. And
through the twenty-five years that have passed, since the matter of life
was first called protoplasm, a host of investigators, among whom Cohn,
Max Schulze, and Kuehne must be named as leaders, have accumulated
evidence, morphological, physiological, and chemical, in favour of that
"immense unite de composition elementaire dans tous les corps vivants de
la nature," into which Payen had, so early, a clear insight.
As far back as 1850, Cohn wrote, apparently without any knowledge of what
Payen had said before him:--
"The protoplasm of the botanist, and the contractile substance and
sarcode of the zoologist, must be, if not identical, yet in a high degree
analogous substances. Hence, from this point of view, the difference
between animals and plants consists in this; that, in the latter, the
contractile substance, as a primordial utricle, is enclosed within an
inert cellulose membrane, which permits it only to exhibit an internal
motion, expressed by the phenomena of rotation and circulation, while, in
the former, it is not so enclosed. The protoplasm in the form of the
primordial utricle is, as it were, the animal element in the plant, but
which is imprisoned, and only becomes free in the animal; or, to strip
off the metaphor which obscures simple thought, the energy of organic
vitality which is manifested in movement is especially exhibited by a
nitrogenous contractile substance, which in plants is limited and
fettered by an inert membrane, in animals not so."[8]
[Footnote 8: Cohn, "Ueber Protococcus pluvialis," in the _Nova Acta_ for
1850.]
In 1868, thinking that an untechnical statement of the views current
among the leaders of biological science might be interesting to the
general public, I gave a lecture embodying them in Edinburgh. Those who
have not made the mistake of attempting to approach biology, either by
the high _a priori_ road of mere philosophical speculation, or by the
mere low _a posteriori_ lane offered by the tube of a microscope, but
have taken the trouble to become acquainted with well-ascertained facts
and with their history, will not need to be told that in what I had to
say "as regards protoplasm" in my lecture "On the Physical Basis of Life"
(Vol. I. of these Essays, p. 130), there was nothing new; and, as I hope,
nothing that the present state of knowledge does not justify us in
believing to be true. Under these circumstances, my surprise may be
imagined, when I found, that the mere statement of facts and of views,
long familiar to me as part of the common scientific property of
Continental workers, raised a sort of storm in this country, not only by
exciting the wrath of unscientific persons whose pet prejudices they
seemed to touch, but by giving rise to quite superfluous explosions on
the part of some who should have been better informed.
Dr. Stirling, for example, made my essay the subject of a special
critical lecture,[9] which I have read with much interest, though, I
confess, the meaning of much of it remains as dark to me as does the
"Secret of Hegel" after Dr. Stirling's elaborate revelation of it. Dr.
Stirling's method of dealing with the subject is peculiar. "Protoplasm"
is a question of history, so far as it is a name; of fact, so far as it
is a thing. Dr. Stirling, has not taken the trouble to refer to the
original authorities for his history, which is consequently a travesty;
and still less has he concerned himself with looking at the facts, but
contents himself with taking them also at second-hand. A most amusing
example of this fashion of dealing with scientific statements is
furnished by Dr. Stirling's remarks upon my account of the protoplasm of
the nettle hair. That account was drawn up from careful and often-
repeated observation of the facts. Dr. Stirling thinks he is offering a
valid criticism, when he says that my valued friend Professor Stricker
gives a somewhat different statement about protoplasm. But why in the
world did not this distinguished Hegelian look at a nettle hair for
himself, before venturing to speak about the matter at all? Why trouble
himself about what either Stricker or I say, when any tyro can see the
facts for himself, if he is provided with those not rare articles, a
nettle and a microscope? But I suppose this would have been
"_Aufklaerung_"--a recurrence to the base common-sense philosophy of the
eighteenth century, which liked to see before it believed, and to
understand before it criticised Dr. Stirling winds up his paper with the
following paragraph:--
[Footnote 9: Subsequently published under the title of "As regards
Protoplasm."]
"In short, the whole position of Mr. Huxley, (1) that all organisms
consist alike of the same life-matter, (2) which life-matter is, for its
part, due only to chemistry, must be pronounced untenable--nor less
untenable (3) the materialism he would found on it."
The paragraph contains three distinct assertions concerning my views, and
just the same number of utter misrepresentations of them. That which I
have numbered (1) turns on the ambiguity of the word "same," for a
discussion of which I would refer Dr. Stirling to a great hero of
"_Aufklaerung_" Archbishop Whately; statement number (2) is, in my
judgment, absurd, and certainly I have never said anything resembling it;
while, as to number (3), one great object of my essay was to show that
what is called "materialism" has no sound philosophical basis!
As we have seen, the study of yeast has led investigators face to face
with problems of immense interest in pure chemistry, and in animal and
vegetable morphology. Its physiology is not less rich in subjects for
inquiry. Take, for example, the singular fact that yeast will increase
indefinitely when grown in the dark, in water containing only tartrate of
ammonia a small percentage of mineral salts and sugar. Out of these
materials the _Toruloe_ will manufacture nitrogenous protoplasm,
cellulose, and fatty matters, in any quantity, although they are wholly
deprived of those rays of the sun, the influence of which is essential to
the growth of ordinary plants. There has been a great deal of speculation
lately, as to how the living organisms buried beneath two or three
thousand fathoms of water, and therefore in all probability almost
deprived of light, live. If any of them possess the same powers as yeast
(and the same capacity for living without light is exhibited by some
other fungi) there would seem to be no difficulty about the matter.
Of the pathological bearings of the study of yeast, and other such
organisms, I have spoken elsewhere. It is certain that, in some animals,
devastating epidemics are caused by fungi of low order--similar to those
of which _Torula_ is a sort of offshoot. It is certain that such diseases
are propagated by contagion and infection, in just the same way as
ordinary contagious and infectious diseases are propagated. Of course, it
does not follow from this, that all contagious and infectious diseases
are caused by organisms of as definite and independent a character as the
_Torula_; but, I think, it does follow that it is prudent and wise to
satisfy one's self in each particular case, that the "germ theory" cannot
and will not explain the facts, before having recourse to hypotheses
which have no equal support from analogy.
V
ON THE FORMATION OF COAL
[1870]
The lumps of coal in a coal-scuttle very often have a roughly cubical
form. If one of them be picked out and examined with a little care, it
will be found that its six sides are not exactly alike. Two opposite
sides are comparatively smooth and shining, while the other four are much
rougher, and are marked by lines which run parallel with the smooth
sides. The coal readily splits along these lines, and the split surfaces
thus formed are parallel with the smooth faces. In other words, there is
a sort of rough and incomplete stratification in the lump of coal, as if
it were a book, the leaves of which had stuck together very closely.
Sometimes the faces along which the coal splits are not smooth, but
exhibit a thin layer of dull, charred-looking substance, which is known
as "mineral charcoal."
Occasionally one of the faces of a lump of coal will present impressions,
which are obviously those of the stem, or leaves, of a plant; but though
hard mineral masses of pyrites, and even fine mud, may occur here and
there, neither sand nor pebbles are met with.
When the coal burns, the chief ultimate products of its combustion are
carbonic acid, water, and ammoniacal products, which escape up the
chimney; and a greater or less amount of residual earthy salts, which
take the form of ash. These products are, to a great extent, such as
would result from the burning of so much wood.
These properties of coal may be made out without any very refined
appliances, but the microscope reveals something more. Black and opaque
as ordinary coal is, slices of it become transparent if they are cemented
in Canada balsam, and rubbed down very thin, in the ordinary way of
making thin sections of non-transparent bodies. But as the thin slices,
made in this way, are very apt to crack and break into fragments, it is
better to employ marine glue as the cementing material. By the use of
this substance, slices of considerable size and of extreme thinness and
transparency may be obtained.[1]
[Footnote 1: My assistant in the Museum of Practical Geology, Mr. Newton,
invented this excellent method of obtaining thin slices of coal.]
Now let us suppose two such slices to be prepared from our lump of coal--
one parallel with the bedding, the other perpendicular to it; and let us
call the one the horizontal, and the other the vertical, section. The
horizontal section will present more or less rounded yellow patches and
streaks, scattered irregularly through the dark brown, or blackish,
ground substance; while the vertical section will exhibit mere elongated
bars and granules of the same yellow materials, disposed in lines which
correspond, roughly, with the general direction of the bedding of the
coal.
This is the microscopic structure of an ordinary piece of coal. But if a
great series of coals, from different localities and seams, or even from
different parts of the same seam, be examined, this structure will be
found to vary in two directions. In the anthracitic, or stone-coals,
which burn like coke, the yellow matter diminishes, and the ground
substance becomes more predominant, blacker, and more opaque, until it
becomes impossible to grind a section thin enough to be translucent;
while, on the other hand, in such as the "Better-Bed" coal of the
neighbourhood of Bradford, which burns with much flame, the coal is of a
far lighter, colour and transparent sections are very easily obtained. In
the browner parts of this coal, sharp eyes will readily detect multitudes
of curious little coin-shaped bodies, of a yellowish brown colour,
embedded in the dark brown ground substance. On the average, these little
brown bodies may have a diameter of about one-twentieth of an inch. They
lie with their flat surfaces nearly parallel with the two smooth faces of
the block in which they are contained; and, on one side of each, there
may be discerned a figure, consisting of three straight linear marks,
which radiate from the centre of the disk, but do not quite reach its
circumference. In the horizontal section these disks are often converted
into more or less complete rings; while in the vertical sections they
appear like thick hoops, the sides of which have been pressed together.
The disks are, therefore, flattened bags; and favourable sections show
that the three-rayed marking is the expression of three clefts, which
penetrate one wall of the bag.
The sides of the bags are sometimes closely approximated; but, when the
bags are less flattened, their cavities are, usually, filled with
numerous, irregularly rounded, hollow bodies, having the same kind of
wall as the large ones, but not more than one seven-hundredth of an inch
in diameter.
In favourable specimens, again, almost the whole ground substance appears
to be made up of similar bodies--more or less carbonized or blackened--
and, in these, there can be no doubt that, with the exception of patches
of mineral charcoal, here and there, the whole mass of the coal is made
up of an accumulation of the larger and of the smaller sacs.
But, in one and the same slice, every transition can be observed from
this structure to that which has been described as characteristic of
ordinary coal. The latter appears to rise out of the former, by the
breaking-up and increasing carbonization of the larger and the smaller
sacs. And, in the anthracitic coals, this process appears to have gone to
such a length, as to destroy the original structure altogether, and to
replace it by a completely carbonized substance.
Thus coal may be said, speaking broadly, to be composed of two
constituents: firstly, mineral charcoal; and, secondly, coal proper. The
nature of the mineral charcoal has long since been determined. Its
structure shows it to consist of the remains of the stems and leaves of
plants, reduced a little more than their carbon. Again, some of the coal
is made up of the crushed and flattened bark, or outer coat, of the stems
of plants, the inner wood of which has completely decayed away. But what
I may term the "saccular matter" of the coal, which, either in its
primary or in its degraded form constitutes by far the greater part of
all the bituminous coals I have examined, is certainly not mineral
charcoal; nor is its structure that of any stem or leaf. Hence its real
nature is at first by no means apparent, and has been the subject of much
discussion.
The first person who threw any light upon the problem, as far as I have
been able to discover, was the well-known geologist, Professor Morris. It
is now thirty-four years since he carefully described and figured the
coin-shaped bodies, or larger sacs, as I have called them, in a note
appended to the famous paper "On the Coalbrookdale Coal-Field," published
at that time, by the present President of the Geological Society, Mr.
Prestwich. With much sagacity, Professor Morris divined the real nature
of these bodies, and boldly affirmed them to be the spore-cases of a
plant allied to the living club-mosses.
But discovery sometimes makes a long halt; and it is only a few years
since Mr. Carruthers determined the plant (or rather one of the plants)
which produces these spore-cases, by finding the discoidal sacs still
adherent to the leaves of the fossilized cone which produced them. He
gave the name of _Flemingites gracilis_ to the plant of which the cones
form a part. The branches and stem of this plant are not yet certainly
known, but there is no sort of doubt that it was closely allied to the
_Lepidodendron_, the remains of which abound in the coal formation. The
_Lepidodendra_ were shrubs and trees which put one more in mind of an
_Araucaria_ than of any other familiar plant; and the ends of the
fruiting branches were terminated by cones, or catkins, somewhat like the
bodies so named in a fir, or a willow. These conical fruits, however, did
not produce seeds; but the leaves of which they were composed bore upon
their surfaces sacs full of spores or sporangia, such as those one sees
on the under surface of a bracken leaf. Now, it is these sporangia of the
Lepidodendroid plant _Flemingites_ which were identified by Mr.
Carruthers with the free sporangia described by Professor Morris, which
are the same as the large sacs of which I have spoken. And, more than
this, there is no doubt that the small sacs are the spores, which were
originally contained in the sporangia.
The living club-mosses are, for the most part, insignificant and creeping
herbs, which, superficially, very closely resemble true mosses, and none
of them reach more than two or three feet in height. But, in their
essential structure, they very closely resemble the earliest
Lepidodendroid trees of the coal: their stems and leaves are similar; so
are their cones; and no less like are the sporangia and spores; while
even in their size, the spores of the _Lepidodendron_ and those of the
existing _Lycopodium_, or club-moss, very closely approach one another.
Thus, the singular conclusion is forced upon us, that the greater and the
smaller sacs of the "Better-Bed" and other coals, in which the primitive
structure is well preserved, are simply the sporangia and spores of
certain plants, many of which were closely allied to the existing club-
mosses. And if, as I believe, it can be demonstrated that ordinary coal
is nothing but "saccular" coal which has undergone a certain amount of
that alteration which, if continued, would convert it into anthracite;
then, the conclusion is obvious, that the great mass of the coal we burn
is the result of the accumulation of the spores and spore-cases of
plants, other parts of which have furnished the carbonized stems and the
mineral charcoal, or have left their impressions on the surfaces of the
layer.
Of the multitudinous speculations which, at various times, have been
entertained respecting the origin and mode of formation of coal, several
appear to be negatived, and put out of court, by the structural facts the
significance of which I have endeavoured to explain. These facts, for
example, do not permit us to suppose that coal is an accumulation of
peaty matter, as some have held.
Again, the late Professor Quekett was one of the first observers who gave
a correct description of what I have termed the "saccular" structure of
coal; and, rightly perceiving that this structure was something quite
different from that of any known plant, he imagined that it proceeded
from some extinct vegetable organism which was peculiarly abundant
amongst the coal-forming plants. But this explanation is at once shown to
be untenable when the smaller and the larger sacs are proved to be spores
or sporangia.
Some, once more, have imagined that coal was of submarine origin; and
though the notion is amply and easily refuted by other considerations, it
may be worth while to remark, that it is impossible to comprehend how a
mass of light and resinous spores should have reached the bottom of the
sea, or should have stopped in that position if they had got there.
At the same time, it is proper to remark that I do not presume to suggest
that all coal must needs have the same structure; or that there may not
be coals in which the proportions of wood and spores, or spore-cases, are
very different from those which I have examined. All I repeat is, that
none of the coals which have come under my notice have enabled me to
observe such a difference. But, according to Principal Dawson, who has so
sedulously examined the fossil remains of plants in North America, it is
otherwise with the vast accumulations of coal in that country.
"The true coal," says Dr. Dawson, "consists principally of the flattened
bark of Sigillarioid and other trees, intermixed with leaves of Ferns and
_Cordaites_, and other herbaceous _debris_, and with fragments of decayed
wood, constituting 'mineral charcoal,' all these materials having
manifestly alike grown and accumulated where we find them."[2]
[Footnote 2: _Acadian Geology_, 2nd edition, p. 135.]
When I had the pleasure of seeing Principal Dawson in London last summer,
I showed him my sections of coal, and begged him to re-examine some of
the American coals on his return to Canada, with an eye to the presence
of spores and sporangia, such as I was able to show him in our English
and Scotch coals. He has been good enough to do so; and in a letter dated
September 26th, 1870, he informs me that--
"Indications of spore-cases are rare, except in certain coarse shaly
coals and portions of coals, and in the roofs of the seams. The most
marked case I have yet met with is the shaly coal referred to as
containing _Sporangites_ in my paper on the conditions of accumulation of
coal ("Journal of the Geological Society," vol. xxii. pp. 115, 139, and
165). The purer coals certainly consist principally of cubical tissues
with some true woody matter, and the spore-cases, &c., are chiefly in the
coarse and shaly layers. This is my old doctrine in my two papers in the
"Journal of the Geological Society," and I see nothing to modify it. Your
observations, however, make it probable that the frequent _clear spots_
in the cannels are spore-cases."
Dr. Dawson's results are the more remarkable, as the numerous specimens
of British coal, from various localities, which I have examined, tell one
tale as to the predominance of the spore and sporangium element in their
composition; and as it is exactly in the finest and purest coals, such as
the "Better-Bed" coal of Lowmoor, that the spores and sporangia obviously
constitute almost the entire mass of the deposit.
Coal, such as that which has been described, is always found in sheets,
or "seams," varying from a fraction of an inch to many feet in thickness,
enclosed in the substance of the earth at very various depths, between
beds of rock of different kinds. As a rule, every seam of coal rests upon
a thicker, or thinner, bed of clay, which is known as "under-clay." These
alternations of beds of coal, clay, and rock may be repeated many times,
and are known as the "coal-measures"; and in some regions, as in South
Wales and in Nova Scotia, the coal-measures attain a thickness of twelve
or fourteen thousand feet, and enclose eighty or a hundred seams of coal,
each with its under-clay, and separated from those above and below by
beds of sandstone and shale.
The position of the beds which constitute the coal-measures is infinitely
diverse. Sometimes they are tilted up vertically, sometimes they are
horizontal, sometimes curved into great basins; sometimes they come to
the surface, sometimes they are covered up by thousands of feet of rock.
But, whatever their present position, there is abundant and conclusive
evidence that every under-clay was once a surface soil. Not only do
carbonized root-fibres frequently abound in these under-clays; but the
stools of trees, the trunks of which are broken off and confounded with
the bed of coal, have been repeatedly found passing into radiating roots,
still embedded in the under-clay. On many parts of the coast of England,
what are commonly known as "submarine forests" are to be seen at low
water. They consist, for the most part, of short stools of oak, beech,
and fir-trees, still fixed by their long roots in the bed of blue clay in
which they originally grew. If one of these submarine forest beds should
be gradually depressed and covered up by new deposits, it would present
just the same characters as an under-clay of the coal, if the
_Sigillaria_ and _Lepidodendron_ of the ancient world were substituted
for the oak, or the beech, of our own times.
In a tropical forest, at the present day, the trunks of fallen trees, and
the stools of such trees as may have been broken by the violence of
storms, remain entire for but a short time. Contrary to what might be
expected, the dense wood of the tree decays, and suffers from the ravages
of insects, more swiftly than the bark. And the traveller, setting his
foot on a prostrate trunk, finds that it is a mere shell, which breaks
under his weight, and lands his foot amidst the insects, or the reptiles,
which have sought food or refuge within.
The trees of the coal forests present parallel conditions. When the
fallen trunks which have entered into the composition of the bed of coal
are identifiable, they are mere double shells of bark, flattened together
in consequence of the destruction of the woody core; and Sir Charles
Lyell and Principal Dawson discovered, in the hollow stools of coal trees
of Nova Scotia, the remains of snails, millipedes, and salamander-like
creatures, embedded in a deposit of a different character from that which
surrounded the exterior of the trees. Thus, in endeavouring to comprehend
the formation of a seam of coal, we must try to picture to ourselves a
thick forest, formed for the most part of trees like gigantic club-
mosses, mares'-tails, and tree-ferns, with here and there some that had
more resemblance to our existing yews and fir-trees. We must suppose
that, as the seasons rolled by, the plants grew and developed their
spores and seeds; that they shed these in enormous quantities, which
accumulated on the ground beneath; and that, every now and then, they
added a dead frond or leaf; or, at longer intervals, a rotten branch, or
a dead trunk, to the mass.
A certain proportion of the spores and seeds no doubt fulfilled their
obvious function, and, carried by the wind to unoccupied regions,
extended the limits of the forest; many might be washed away by rain into
streams, and be lost; but a large portion must have remained, to
accumulate like beech-mast, or acorns, beneath the trees of a modern
forest.
But, in this case it may be asked, why does not our English coal consist
of stems and leaves to a much greater extent than it does? What is the
reason of the predominance of the spores and spore-cases in it?
A ready answer to this question is afforded by the study of a living
full-grown club-moss. Shake it upon a piece of paper, and it emits a
cloud of fine dust, which falls over the paper, and is the well-known
Lycopodium powder. Now this powder used to be, and I believe still is,
employed for two objects which seem, at first sight, to have no
particular connection with one another. It is, or was, employed in making
lightning, and in making pills. The coats of the spores contain so much
resinous matter, that a pinch of Lycopodium powder, thrown through the
flame of a candle, burns with an instantaneous flash, which has long done
duty for lightning on the stage. And the same character makes it a
capital coating for pills; for the resinous powder prevents the drug from
being wetted by the saliva, and thus bars the nauseous flavour from the
sensitive papilla; of the tongue.
But this resinous matter, which lies in the walls of the spores and
sporangia, is a substance not easily altered by air and water, and hence
tends to preserve these bodies, just as the bituminized cerecloth
preserves an Egyptian mummy; while, on the other hand, the merely woody
stem and leaves tend to rot, as fast as the wood of the mummy's coffin
has rotted. Thus the mixed heap of spores, leaves, and stems in the coal-
forest would be persistently searched by the long-continued action of air
and rain; the leaves and stems would gradually be reduced to little but
their carbon, or, in other words, to the condition of mineral charcoal in
which we find them; while the spores and sporangia remained as a
comparatively unaltered and compact residuum.
There is, indeed, tolerably clear evidence that the coal must, under some
circumstances, have been converted into a substance hard enough to be
rolled into pebbles, while it yet lay at the surface of the earth; for in
some seams of coal, the courses of rivulets, which must have been living
water, while the stratum in which their remains are found was still at
the surface, have been observed to contain rolled pebbles of the very
coal through which the stream has cut its way.
The structural facts are such as to leave no alternative but to adopt the
view of the origin of such coal as I have described, which has just been
stated; but, happily, the process is not without analogy at the present
day. I possess a specimen of what is called "white coal" from Australia.
It is an inflammable material, burning with a bright flame and having
much the consistence and appearance of oat-cake, which, I am informed
covers a considerable area. It consists, almost entirely, of a compacted
mass of spores and spore-cases. But the fine particles of blown sand
which are scattered through it, show that it must have accumulated,
subaerially, upon the surface of a soil covered by a forest of
cryptogamous plants, probably tree-ferns.
As regards this important point of the subaerial region of coal, I am
glad to find myself in entire accordance with Principal Dawson, who bases
his conclusions upon other, but no less forcible, considerations. In a
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