_WHAT MAY BE LEARNED FROM EOZOON._
The microscope has long been a recognised and valued aid of the
geological observer, and is perhaps now in danger of being somewhat
overrated by enthusiastic specialists. To the present writer its use
is no novelty. When, as a very young geologist, collecting fossil
plants in the coal fields of Nova Scotia, I obtained access to the
then recently published work of Witham on the "Internal Structure of
Fossil Vegetables."[61] Fired by the desire to learn something of
the structure of the blocks of fossil wood in my collection, I at
once procured a microscope of what would now be considered a very
imperfect kind, and proceeded to make attempts to slice and examine my
specimens, and was filled with joy when these old blackened stems for
the first time revealed to me their wonderful structures. At the same
time I extended my studies to every minute form of life that could be
obtained from the sea or fresh waters. A few years later (in 1841),
when a student in Edinburgh, I made the acquaintance of Mr. Sanderson
of that city, who had worked for Nicol and Witham in the preparation of
specimens, and learnt the modes which he had employed. Since that time
I have been accustomed to subject every rock, earth or fossil which
came under my notice to microscopic scrutiny, not as a mere specialist
in that mode of observation, or with the parade of methods and details
now customary, but with the view of obtaining valuable facts bearing
on any investigation I might have in hand. It was this habit which
induced my old friend, Sir William Logan, in 1858 and subsequent years
to ask my aid in the study of the forms believed or suspected to be
organic, which had been discovered in the course of his surveys of the
Laurentian rocks. In one respect this was unfortunate. It occupied
much time, interfered to some extent with other researches, led to
unpleasant controversies. But these evils were more than compensated
by the insight which the study gave into the fact of the persistence
of organic structures in highly crystalline rocks, and to the modes
of ascertaining and profiting, by these obscure remains, while it
has guided and stimulated enquiry and thought as to the origin and
history of life. These benefits entitle the researches and discussions
on Eozoon to be regarded as marking a salient point in the history
of geological discovery, and it is to these principally that I would
attract attention in the present chapter.
[61] Edinburgh, 1833.
Perhaps nothing excites more scepticism as to the animal nature of
Eozoon than the prejudice existing among geologists that no organism
can be preserved in rocks so highly crystalline as those of the
Laurentian series. I call this a prejudice, because any one who makes
the microscopic structure of rocks and fossils a special study, soon
learns that fossils and the rocks containing them may undergo the most
remarkable and complete mechanical and chemical changes without losing
their minute structure, and that limestones, if once fossiliferous,
are hardly ever so much altered as to lose all traces of the organisms
which they contained, while it is a most common occurrence to find
highly crystalline rocks of this kind abounding in fossils preserved as
to their minute structure.
Let us, however, look at the precise conditions under which this takes
place.
When calcareous fossils of irregular surface and porous or cellular
texture, such as Eozoon may have been, or corals were and are, become
imbedded in clay, marl, or other soft sediment, they can be washed
out and recovered in a condition similar to that of recent specimens,
except that their pores or cells, if open, may be filled with the
material of the matrix, or if not so open that they can be thus filled,
they may be more or less incrusted with mineral deposits introduced
by water percolating the mass, or may even be completely filled up in
this way. But if such fossils are contained in hard rocks, they usually
fail, when these are broken, to show their external surfaces, and,
breaking across with the containing rock, they exhibit their internal
structure merely,--and this more or less distinctly, according to the
manner in which their cells or cavities have been filled with mineral
matter. Here the microscope becomes of essential service, especially
when the structures are minute. A fragment of fossil wood which to the
naked eye is nothing but a dark stone, or a coral which is merely a
piece of grey or coloured marble, or a specimen of common crystalline
limestone made up originally of coral fragments, presents, when sliced
and magnified, the most perfect and beautiful structure. In such cases
it will be found that ordinarily the original substance of the fossil
remains in a more or less altered state. Wood may be represented by
dark lines of coaly matter, or coral by its white or transparent
calcareous laminæ; while the material which has been introduced, and
which fills the cavities, may so differ in colour, transparency, or
crystallization, as to act differently on light, and so reveal the
original structure. These fillings are very curious. Sometimes they are
mere earthy or muddy matter which has been washed into the cavities.
Sometimes they are transparent and crystalline. Often they are stained
with oxide of iron or coaly materials. They may consist of carbonate
of lime, silica or silicates, sulphate of baryta, oxides of iron,
carbonate of iron, iron pyrite, or sulphides of copper or lead, all of
which are common materials. They are sometimes so complicated that I
have seen even the minute cells of woody structures, each with several
bands of differently coloured materials deposited in succession, like
the coats of an onyx agate.
A further stage of mineralisation occurs when the substance of the
organism is altogether removed and replaced by foreign matter, either
little by little, or by being entirely dissolved or decomposed,
leaving a cavity to be filled by infiltration. In this state are some
silicified woods, and those corals which have been not filled with
but replaced by silica, and can thus sometimes be obtained entire and
perfect by the solution in an acid of the containing limestone, or by
its removal in weathering. In this state are the beautiful silicified
corals obtained from the corniferous limestone of Lake Erie, which are
so perfectly replaced by flinty matter that when weathered out of the
limestone, or treated with acid till the latter is removed, we find
the coral as perfect as when recent. It may be well to present to the
eye these different stages of fossilization. I have attempted to do
this in Fig. 13, taking a tabulate coral of the genus Favosites for an
example, and supposing the material employed to be calcite and silica.
Precisely the same illustration would apply to a piece of wood, except
that the cell wall would be carbonaceous matter instead of carbonate
of lime. In this figure the dotted parts represent carbonate of lime,
the diagonally shaded parts silica or a silicate. Thus we have in the
natural state the walls of carbonate of lime and the cavities empty
(_a_). When fossilized the cavities may be merely filled with carbonate
of lime, or they may be filled with silica (_b, c_); or the walls
themselves may be replaced by silica, and the cavities may remain
filled with carbonate of lime (_d_); or both the walls and cavities
may be represented by or filled with silica or silicates (_e_). The
ordinary specimens of Eozoon are supposed to be in the third of these
stages, though some exist in the second, and I have reason to believe
that some have reached to the fifth. I have not met with any in the
fourth stage, though this is not uncommon in Silurian and Devonian
fossils. I have further to remark that the reason why wood and the
cells of corals so readily become silicified is that the organic
matter which they contain, becoming oxidized in decay, produces carbon
dioxide, which, by its affinity for alkalies, can decompose soluble
silicates and thus throw down their silica in an insoluble state. Thus
a fragment of decaying wood imbedded in a deposit holding water and
alkaline silicates almost necessarily becomes silicified. It is also
to be remarked that the ordinary specimens of Eozoon have actually not
attained to the extreme degree of mineralization seen in some much more
recent silicified woods and corals, inasmuch as the portion believed to
have been the original calcareous test has not usually been silicified,
but still remains in the state of calcium carbonate.
[Illustration: Fig. 13.--Diagram showing different States of
Fossilization of a cell of a Tabulate Coral, (_a_) Natural condition
walls calcite, cell empty. (_b_) Walls calcite, cell filled with the
same, (_c_) Walls calcite, cell filled with silica or silicate, (_d_)
Walls silicified, cell filled with calcite. (_e_) Walls silicified,
cell filled with silica or silicate.]
With regard, then, to the calcareous organisms with which we have now
more especially to do, when these are embedded in pure limestone and
filled with the same, so that the whole rock, fossils and cavities,
is one in composition, and when metamorphic action has caused the
whole to become crystalline, and has perhaps removed the remains of
carbonaceous matter, it may be very difficult to detect any traces
of structure. But even in this case careful management of light may
reveal some indications. In many instances, however, even where the
limestones have become perfectly crystalline, and the cleavage planes
cut freely across the fossils, these exhibit their forms and minute
structures in great perfection. This is the case in many of the Lower
Silurian limestones of Canada, as I have elsewhere shown.[62] The grey
crystalline Trenton limestone of Montreal, used as a building stone,
is an excellent illustration. To the naked eye it is a grey marble
composed of cleavable crystals; but when examined in thin slices, it
shows its organic fragments in the greatest beauty, and all their
minute parts are perfectly marked out by delicate carbonaceous lines.
The only exception in this limestone is in the case of the crinoids,
in which the cellular structure is filled with transparent calc-spar,
perfectly identical with the original solid matter, so that they appear
solid and homogeneous, but there are examples in which even the minute
meshes of these become' apparent. The specimen represented in Fig. 14
is a mass of Corals, Polyzoa, and Crinoids, and shows these under a
low power, as represented in the figure. The specimen in Fig. 15 shows
the Laurentian Eozoon in a similar state of preservation. It is from a
sketch by Dr. Carpenter, and exhibits the delicate canals partly filled
with calcite or dolomite, as clear and colourless as that of the shell
itself, and distinguishable only by careful management of the light.
[62] _Canadian Naturalist_, 1859: "Microscopic Structure of Canadian
Limestones."
[Illustration: Fig. 14.--Slice of Crystalline Lower Silurian Limestone;
showing Crinoids, Bryozoa, and Corals in fragments.]
[Illustration: Fig. 15.--Walls of Eozoon penetrated with Canals. The
unshaded portions filled with Calcite. (After Carpenter.)]
In the case of recent and fossil Foraminifers, these very frequently
have their chambers filled solid with calcareous matter, and as Dr.
Carpenter well remarks, even well-preserved Tertiary Nummulites in
this state often fail greatly in showing their structures, though in
the same condition they occasionally show these in great perfection.
Among the finest I have seen are specimens from the Mount of Olives,
and Dr. Carpenter mentions as equally good those of the London clay at
Bracklesham. But in no condition do modern Foraminifera, or those of
the Tertiary and Mesozoic rocks appear in greater perfection than when
filled with the hydrous silicate of iron and potash called glauconite
or green earth, a substance now forming in some parts of the ocean, and
which gives, by the abundance of its little bottle-green concretions
the name of "greensand" to formations of the Cretaceous age both in
Europe and America. In some beds of greensand every grain seems,
to have been moulded into the interior of a microscopic shell, and
has retained its form after the frail envelope has been removed. In
some cases the glauconite has not only filled the chambers but has
penetrated the fine tubulation, and when the shell is removed, either
naturally or by the action of an acid, the silicious fillings of the
interior of the tubes project in minute needles or bundles of threads
of marvellous delicacy from the surface of the cast. It is in the
warmer seas, and especially in the bed of the Egean and of the Gulf
Stream, that such specimens are now most usually found.[63] If we ask
why this mineral glauconite should be associated with foraminiferal
shells, the answer is that they are both products of one kind of
locality. The same sea bottoms in which Foraminifera most abound are
also those in which the chemical conditions for the formation of
glauconite exist. Hence, no doubt, the association of this mineral
with the great foraminiferal formation of the chalk. It is indeed by
no means unlikely that the selection by these creatures of the pure
carbonate of lime from the sea water or its minute plants, may be
the means of setting free the silica, iron, and potash, in a state
suitable for their combination. Similar silicates are found associated
with marine limestones, as far back as the Cambro-Silurian age;
and Dr. Sterry Hunt, than whom no one can be a better authority on
chemical geology, has argued on chemical grounds that the occurrence
of serpentine with the remains of Eozoon is an association of the same
character.
[63] Beautiful specimens of Nummulites preserved in this way, from the
Eocene of Kumpfen in Bavaria, have been communicated to me through the
kindness of Dr. Otto Hahn.
However this may be, the infiltration of the pores of Eozoon with
serpentine and other silicates has evidently been one main means of its
preservation. When so infiltrated no metamorphism short of the complete
fusion of the containing rock could obliterate the minutest points
of structure; and that such fusion has not occurred, the preservation
in the Laurentian rocks of the most delicate lamination of the beds
shows conclusively; while, as already stated, it can be shown that the
alteration which has occurred might have taken place at a temperature
far short of that necessary to fuse limestone. Thus has it happened
that these most ancient fossils have been handed down to our time in a
state of preservation comparable, as Dr. Carpenter states, to that of
the best preserved fossil Foraminifera from the more recent formations
that have come under his observation in the course of all his long
experience.
Let us now look more minutely at the nature of the typical specimens
of Eozoon as originally observed and described, and then turn to those
preserved in other ways, or more or less destroyed or defaced. Taking
a polished specimen from Petite Nation, we find the shell represented
by white limestone, and the chambers by light green serpentine. By
acting on the surface with a dilute acid we etch out the calcareous
part, leaving a cast in serpentine of the cavities originally occupied
by the soft animal substance, and when this is done in polished slices,
these may be made to print their own characters on paper, as has
actually been done in the plate prefixed, which is an electrotype from
an etched specimen, and shows both the laminated and acervuline parts
of the fossil. If the process of decalcification has been carefully
executed, we find in the excavated spaces delicate ramifying processes
of opaque serpentine or transparent dolomite, which were originally
imbedded in the calcareous substance, and which are often of extreme
fineness and complexity.[64] (Figs. 18, 19.) These are casts of the
canals which traversed the shell when still inhabited by the animal,
and have subsequently been filled with mineral matter. In evidence
of this we sometimes find in a single canal an outer tubular layer
of serpentine and an inner filling of dolomite, just as vessels of
fossil plants are sometimes filled with successive coats of different
materials. In some well preserved specimens we find the original cell
wall represented by a delicate white film, which under the microscope
shows minute needle-like parallel processes representing its still
finer tubuli. It is evident that to have filled these tubuli, the
serpentine must have been introduced in a state of actual solution,
and must have carried with it no foreign impurities. Consequently
we find that in the chambers themselves the serpentine is pure; and
if we examine it under polarized light, we see that it presents a
singularly curdled or irregularly laminated appearance, as if it had an
imperfectly crystalline structure, and had been deposited in irregular
laminæ, beginning at the sides of the chambers, and filling them toward
the middle, and had afterward been cracked by shrinkage, and the cracks
filled with a second deposit of serpentine.[65] Now, serpentine is a
hydrous silicate of magnesia, and all that we need to suppose is that
in the waters of the Laurentian sea magnesia was present instead of
iron, alumina or potash, and we can understand that the Laurentian
fossil has been petrified by infiltration with serpentine, as more
modern Foraminifera have been with glauconite, which, though it does
not contain magnesia, often has a considerable percentage of alumina.
Further, in specimens of Eozoon from Burgess, the filling mineral is
loganite, a compound of silica, alumina, magnesia and iron with water,
while in other specimens the filling mineral is pyroxene. In like
manner, in certain Silurian limestones from New Brunswick and Wales,
in which the delicate microscopic pores of the skeletons of stalked
starfishes or crinoids have been filled with mineral deposits, so
that when decalcified these are most beautifully represented by their
casts, Dr. Hunt has proved the filling mineral to be[66] intermediate
between serpentine and glauconite. We have, therefore, ample warrant
for adhering to his conclusion that the Laurentian serpentine was
deposited under conditions similar to those of the modern greensand.
Indeed, independently of Eozoon, it is impossible that any geologist
who has studied the manner in which this mineral is associated with
the Laurentian limestones could believe it to have been formed in
any other way. Nor need we be astonished at the fineness of the
infiltration by which these minute tubes, perhaps 1/10000 of an inch
in diameter, are filled with mineral matter. The micro-geologist
well knows how, in more modern deposits, the finest pores of fossils
are filled, and that mineral matter in solution can penetrate the
smallest openings that the microscope can detect. Wherever the fluids
of the living body can penetrate, there also mineral substances can
be carried, and this natural injection, effected under great pressure
and with the advantage of ample time, can surpass any of the feats of
the anatomical manipulator. Fig. 16 represents a microscopic joint of
a Crinoid from the Upper Silurian of New Brunswick, injected with the
hydrous silicate already referred to, and Fig. 17 shows a microscopic
chambered or spiral shell, from a Welsh Silurian limestone, with its
cavities filled with a similar substance.
[64] Very fine specimens can be produced by polishing thin slices, and
then etching them slightly with a very weak acid. (Plate prefixed.)
[65] The same structures may be well seen in thin slices polished, to
be viewed as transparent objects. I may, however, explain that if these
are made roughly, and heated in the process, they may often show only
mineral structures and cleavage planes, whereas, if polished with great
care and slowly, and afterwards cleaned with an acid, they may show the
canals in great perfection.
[66] Silicate of alumina, iron, magnesia, and potash.
[Illustration: Fig. 16.--Joint of a Crinoid, having its Pores injected
with a Hydrous Silicate. Upper Silurian Limestone, Pole Hill, New
Brunswick. Magnified 25 diameters.]
[Illustration: Fig. 17.--Shell from a Silurian Limestone, Wales; its
cavity filled with Hydrous Silicate. Magnified 25 diameters.]
[Illustration: Fig. 18.--Casts of Canals of Eozoon in Serpentine,
decalcified and highly magnified.]
[Illustration: Fig. 19.--Canals of Eozoon. Highly Magnified.]
Taking the specimens preserved by serpentine as typical, we now turn
to certain other and, in some respects, less characteristic specimens,
which are nevertheless very instructive. At the Calumet some of
the masses are partly filled with serpentine and partly with white
pyroxene, an anhydrous silicate of lime and magnesia. The two minerals
can readily be distinguished when viewed with polarized light; and in
some slices I have seen part of a chamber or group of canals filled
with serpentine and part with pyroxene. In this case the pyroxene,
or the materials which now compose it, must have been introduced by
infiltration, as well as the serpentine. This is the more remarkable as
pyroxene is most usually found as an ingredient of igneous rocks; but
Dr. Hunt has shown that in the Laurentian limestones, and also in veins
traversing them, it occurs under conditions which imply its deposition
from water, either cold or warm. Gümbel remarks on this:--"Hunt, in
a very ingenious manner, compares this formation and deposition of
serpentine, pyroxene, and loganite, with that of glauconite, whose
formation has gone on uninterruptedly from the Silurian to the Tertiary
period, and is even now taking place in the depths of the sea; it being
well known that Ehrenberg and others have already shown that many of
the grains of glauconite are casts of the interior of foraminiferal
shells. In the light of this comparison, the notion that the serpentine
and such-like minerals of the primitive limestones have been formed,
in a similar manner, in the chambers of Eozoic Foraminifera, loses any
traces of improbability which it might at first seem to possess."
In many parts of the skeleton of Eozoon, and even in the best
infiltrated serpentine specimens, there are portions of the cell wall
and canal system which have been filled with calcareous spar or with
dolomite, so similar to the skeleton that it can be detected only under
the most favourable lights and with great care (Fig. 15, _supra_). It
is further to be remarked that in all the specimens of true Eozoon,
as well as in many other calcareous fossils preserved in ancient
rocks, the calcareous matter, even when its minute structures are not
preserved, or are obscured, presents a minutely granular or curdled
appearance, arising, no doubt, from the original presence of organic
matter, and not recognised in purely inorganic calcite.
Other specimens of fragmental Eozoon from the Petite Nation localities
have their canals filled with dolomite, which probably penetrated them
after they were broken up and imbedded in the rock. I have ascertained,
with respect to these fragments of Eozoon, that they occur abundantly
in certain layers of the Laurentian limestone, beds of some thickness
being in great part made up of them, and coarse and fine fragments
occur in alternate layers, like the broken corals in some Silurian
limestones.
Finally, on this part of the subject, careful observation of many
specimens of Laurentian limestone which present no trace of Eozoon
when viewed by the naked eye, and no evidence of structure when acted
on with acids, are nevertheless organic, and consist of fragments
of Eozoon, and possibly of other organisms, not infiltrated with
silicates, but only with carbonate of lime, and consequently revealing
only obscure indications of their minute structure. I have satisfied
myself of this by long and patient investigations, which scarcely admit
of any adequate representation, either by words or figures.
Every worker in those applications of the microscope to geological
specimens which have been termed micro-geology, is familiar with the
fact that crystalline forces and mechanical movements of material often
play the most fantastic tricks with fossilized organic matter. In
fossil woods, for example, we often have the tissues disorganized, with
radiating crystallizations of calcite and little spherical concretions
of quartz, or disseminated cubes and grains of pyrite, or little
veins filled with sulphate of barium or other minerals. We need not,
therefore, be surprised to find that in the venerable rocks containing
Eozoon, such things occur in the highly crystalline Laurentian
limestones, and even in some still showing the traces of Eozoon. We
find many disseminated crystals of magnetite, pyrite, spinel, mica and
other minerals, curiously curved prisms of vermicular mica, bundles
of aciculi of tremolite and similar substances, veins of calcite
and crysotile or fibrous serpentine, which often traverse the best
specimens. Where these occur abundantly, we usually find no organic
structures remaining, or if they exist, they are in a very defective
state of preservation. Even in specimens presenting the lamination
of Eozoon to the naked eye, these crystalline actions have often
destroyed the minute structure; and I fear that some microscopists
have been victimized, by having under their consideration only
specimens in which the actual characters had been too much defaced to
be discernible. No mistake can be greater than to suppose that any
and every specimen of Laurentian limestone must contain Eozoon. More
especially have I hitherto failed to detect traces of it in those
carbonaceous or graphitic limestones which are so very abundant in the
Laurentian country. Perhaps where vegetable matter was very plentiful
Eozoon did not thrive, or, on the other hand, the growth of Eozoon
may have diminished the quantity of vegetable matter. It is also to
be observed that much compression and distortion have occurred in the
beds of Laurentian limestone and their contained fossils, and also
that the specimens are often broken by faults, some of which are so
small as to appear only on microscopic examination, and to shift the
plates of the fossil just as if they were beds of rock. This, though
it sometimes produces puzzling appearances, is an evidence that the
fossils were hard and brittle when this faulting took place, and is
consequently an additional proof of their extraneous origin. In some
specimens it would seem that the lower and older part of the fossil
had been wholly converted into serpentine or pyroxene, or had so
nearly experienced this change that only small parts of the calcareous
wall can be recognised. These portions correspond with fossil woods
altogether silicified, not only by the filling of the cells, but
also by the conversion of the walls into silica. I have specimens
which manifestly show the transition from the ordinary condition of
filling with serpentine to one in which the cell walls are represented
obscurely by one shade of this mineral and the cavities by another. In
general, however, it will be gathered from the above explanations that
the specimens of Eozoon fall short in thoroughness of mineralization
of some fossils in much more modern rocks. I have specimens of ancient
sponges whose spicular skeletons, originally silicious, have been
replaced by pyrite or bisulphide of iron, and of Tertiary fossil woods
retaining perfectly their most minute structures, yet entirely replaced
by silica, so that not a particle of the original wood remains.
The above considerations as to mode of preservation of Eozoon concur
with those in the previous chapter in showing its oceanic character,
if really a fossil; but the ocean of the Eozoic period may not have
been so deep as at present, and its waters were probably warm and
well stocked with mineral matters derived from the newly formed land,
or from hot springs in its own bottom. On this point the interesting
investigations of Dr. Hunt with reference to the chemical conditions
of the Silurian seas allow us to suppose that the Laurentian ocean may
have been much more richly stored, more especially with salts of lime
and magnesia, than that of subsequent times. Hence the conditions of
warmth, light, and nutriment required by such gigantic Protozoans would
all be present, and hence, also, no doubt, some of the peculiarities of
their mineralization.
I desire by the above statement of facts to show, on the one hand,
that the study of Eozoon, regarded as probably an ancient form of
marine life, aids us in understanding other ancient fossils, and their
manner of preservation; and on the other hand, that those who deny the
organic origin of Eozoon place us in the position of being unable, in
any rational manner, to account for these forms, so characteristic
of the Laurentian limestones, and set at naught the fair conclusions
deducible from the mode of preservation of fossils in the later
formations. The evidence of organic origin is perhaps not conclusive,
and in the present state of knowledge it is certain to be met with much
scepticism, more especially by certain classes of specialists, whose
grasp of knowledge is not sufficiently wide to cover, on the one hand,
fossilization and metamorphism, and on the other, to understand the
lower forms of life. It may, however, be sufficient to qualify us in
turning our thoughts for a few moments to considerations suggested by
the probable origin of animal life in the seas of the Laurentian period.
Looking down from the elevation of our physiological and mental
superiority, it is difficult to realize the exact conditions in which
life exists in creatures so simple as the Protozoa. There may perhaps
be higher intelligences, that find it equally difficult to realize how
life and reason can manifest themselves in such poor houses of clay
as those we inhabit. But placing ourselves near to these creatures,
and entering, as it were, into sympathy with them, we can understand
something of their powers and feelings. In the first place it is plain
that they can vigorously, if roughly, exercise those mechanical,
chemical, and vegetative powers of life which are characteristic of
the animal. They can seize, swallow, digest, and assimilate food; and,
employing its albuminous parts in nourishing their tissues, can burn
away the rest in processes akin to our respiration, or reject it from
their system. Like us, they can subsist only on food which the plant
has previously produced; for in this world, from the beginning of time,
the plant has been the only organism which could use the solar light
and heat as forces to enable it to turn the dead elements of matter
into living, growing tissues, and into organic compounds capable of
nourishing the animal. Like us, the Protozoa expend the food which
they have assimilated in the production of animal force, and in doing
so cause it to be oxidized, or burnt away, and resolved again into
dead matter. It is true that we have much more complicated apparatus
for performing these functions, but it does not follow that these give
us much real superiority, except relatively to the more difficult
conditions of our existence. The gourmand who enjoys his dinner may
have no more pleasure in the act than the Amœba which swallows a
Diatom; and for all that the man knows of the subsequent processes to
which the food is subjected, his interior might be a mass of jelly,
with extemporised vacuoles, like that of his humble fellow-animal. The
clay is after all the same, and there may be as much difficulty in the
making of a simple organism with varied powers, as a more complex frame
for doing higher work.
In order that we may feel, a complicated apparatus of nerves and brain
cells has to be constructed and set to work; but the Protozoon, without
any distinct brain, is all brain, and its sensation is simply direct.
Thus vision in these creatures is probably performed in a rough way by
any part of their transparent bodies, and taste and smell are no doubt
in the same case. Whether they have any perception of sound as distinct
from the mere vibrations ascertained by touch, we do not know. Here,
also, we are not far removed above the Protozoa, especially those of us
to whom touch, seeing and hearing are direct acts, without any thought
or knowledge of the apparatus employed. We might, so far, as well be
Amœbas. As we rise higher we meet with more differences. Yet it is
evident that our gelatinous fellow being can feel pain, dread danger,
desire possessions, enjoy pleasure, and in a direct unconscious way
entertain many of the appetites and passions that affect ourselves.
The wonder is that with so little of organization it can do so much.
Yet, perhaps, life can manifest itself in a broader and more intense
way where there is little organization, and a highly strung and complex
organism is not so much a necessary condition of a higher life as a
mere means of better adapting it to its present surroundings.
A similar lesson is taught by the complexity of their skeletons. We
speak in a crude, unscientific way of these animals accumulating
calcareous matter, and building up reefs of limestone. We must,
however, bear in mind that they are as dependent on their food for the
materials of their skeletons as we are, and that their crusts grow in
the interior of the sarcode just as our bones do within our bodies. The
provision even for nourishing the interior of the skeleton by tubuli
and canals is in principle similar to that involved in the canals,
cells, and canalicules of bone. The Amœba, of course, knows neither
more nor less of this than the average Englishman. It is altogether
a matter of unconscious growth. The process in the Protozoa strikes
some minds, however, as the more wonderful of the two. It is, says
an eminent modern physiologist, a matter of "profound significance"
that this "particle of jelly [the sarcode of a Foraminifer] is capable
of guiding physical forces in such a manner as to give rise to these
exquisite and almost mathematically arranged structures." Respecting
the structures themselves there is no exaggeration in this. No arch
or dome framed by human skill is more perfect in beauty or in the
realization of mechanical ideas than the tests of some Foraminifera,
and none is so complete and wonderful in its internal structure. The
particle of jelly, however, is a figure of speech. The body of the
humblest Foraminifer is much more than this. It is an organism with
divers parts, and it is endowed with the mysterious forces of life
which in it guide the physical forces, just as they do in building up
phosphate of lime in our bones, or indeed, just as the will of the
architect does in building a palace. The profound significance which
this has, reaches beyond the domain of the physical and vital, even
to the spiritual. It clings to all our conceptions of living things:
"quite as much, for example, to the evolution of an animal with all its
parts from a one-celled germ, as to the connection of brain cells with
the manifestations of intelligence." Viewed in this way, we may share
with the author of the sentence I have quoted his feeling of veneration
in the presence of this great wonder of animal life, "burning, and not
consumed," nay, building up, and that in many and beautiful forms. We
may realize it most of all in the presence of the organism which was
perhaps the first to manifest on our planet these marvellous powers.
We must, however, here also, beware of that credulity which makes too
many thinkers limit their conceptions altogether to physical force in
matters of this kind The merely materialistic physiologist is really in
no better position than the savage who quails before the thunderstorm,
or rejoices in the solar warmth, and seeing no force or power beyond,
fancies himself in the immediate presence of his God. In Eozoon we
must discern not only a mass of jelly but a being endowed with that
higher vital force which surpasses vegetable life, and also physical
and chemical forces; and in this animal energy we must see an emanation
from a Will higher than our own, ruling vitality itself; and this not
merely to the end of constructing the skeleton of a Protozoon, but
of elaborating all the wonderful developments of life that were to
follow in succeeding ages, and with reference to which the production
and growth of this creature were initial steps. It is this mystery of
design which really constitutes the "profound significance" of the
foraminiferal skeleton.
Another phenomenon of animality forced upon our notice by the Protozoa
is that of the conditions of life in animals not individual, as we
are, but aggregative and cumulative in indefinite masses. What, for
instance, the relations to each other of the Polyps, growing together
in a coral mass, or the separate parts of a Sponge, or the separate
lobes of a Foraminifer. In the case of the Polyps we may believe that
there is special sensation in the tentacles and oral opening of each
individual, and that each may experience hunger when in want, or
satisfaction when it is filled with food, and that injuries to one part
of the mass may indirectly affect other parts, but that the nutrition
of the whole mass may be as much unfelt by the individual Polyps as
the processes going on in our own liver are by us. So in the case of a
large Sponge, or Foraminifer, there may be some special sensation in
individual cells, pseudopods, or segments, and the general sensation
may be very limited, while unconscious living powers pervade the
whole. In this matter of aggregation of animals we have thus various
grades. The Foraminifers and Sponges present us with the simplest of
all, and that which most resembles the aggregation of buds in the
plant. The Polyps and complex Bryozoons present a higher and more
specialized type; and though the bilateral symmetry which obtains in
the higher animals is of a different nature, it still at least reminds
us of that multiplication of similar parts which we see in the lower
grades of being. It is worthy of notice here that the lower animals
which show aggregative tendencies present but imperfect indications, or
none at all, of bilateral symmetry. Their bodies, like those of plants,
are for the most part built up around a central axis, or they show
tendencies to spiral modes of growth.
It is this composite sort of life which is connected with the main
geological function of the Foraminifer. While active sensation,
appetite, and enjoyment pervade the pseudopods and external sarcode
of the mass, the hard skeleton common to the whole is growing within;
and in this way the calcareous matter is gradually removed from
the sea water, and built up in solid reefs, or in piles of loose
foraminiferal shells. Thus it is the aggregative or common life,
alike in Foraminifers as in Corals, that tends most powerfully to the
accumulation of calcareous matter; and those creatures whose life is
of this complex character are best suited to be world builders, since
the result of their growth is not merely a cemetery of their osseous
remains, but a huge communistic edifice, to which multitudes of lives
have contributed, and in which successive generations take up their
abode on the remains of their ancestors. This process, so potent in the
progress of the earth's geological history, began, as far as we know,
with Eozoon.
Whether, then, in questioning our proto-foraminifer, we have reference
to the vital functions of its gelatinous sarcode, to the complexity
and beauty of its calcareous test, or to its capacity for effecting
great material results through the union of individuals, we perceive
that we have to do, not with a low condition of those powers which we
designate life, but with their manifestation through the means of a
simple organism; and this in a degree of perfection which we, from our
point of view, would have in the first instance supposed impossible.
If we imagine a world altogether destitute of life, we still might
have geological formations in progress. Not only would volcanoes belch
forth their liquid lavas and their stones and ashes, but the waves and
currents of the ocean and the rains and streams on the land, with the
ceaseless decomposing action of the carbonic acid of the atmosphere,
would be piling up mud, sand, and pebbles in the sea. There might even
be some formation of limestone taking place where springs charged
with bicarbonate of lime were oozing out on the land or the bottom of
the waters. But in such a world all the carbon would be in the state
of carbon dioxide, and all the limestone would either be diffused in
small quantities through various rocks or in limited local beds, or
in solution, perhaps as chloride of calcium, in the sea. Dr. Hunt has
given chemical grounds for supposing that the most ancient seas were
largely supplied with this very soluble salt, instead of the chloride
of sodium, or common salt, which now prevails in the sea water.
Where in such a world would life be introduced? on the land or in the
waters? All scientific probability would say in the latter.[67] The
ocean is now vastly more populous than the land. The waters alone
afford the conditions necessary at once for the most minute and the
grandest organisms, at once for the simplest and for others of the most
complex character. Especially do they afford the best conditions for
those animals which subsist in complex communities, and which aggregate
large quantities of mineral matter in their skeletons. So true is this
that up to the present time all the species of Protozoa and of the
animals most nearly allied to them are aquatic. Even in the waters,
however, plant life, though possibly in very simple forms, must precede
the animal.
[67] A recent writer (Simroth) has, however, undertaken to maintain the
thesis that land life preceded that in the sea. It is unnecessary to
say that he is an evolutionist, influenced by the necessity laid upon
that philosophy to deduce whales, seals, etc., from land animals.
Let humble plants, then, be introduced in the waters, and they would
at once begin to use the solar light for the purpose of decomposing
carbonic acid, and forming carbon compounds which had not before
existed, and which, independently of vegetable life, would never have
existed. At the same time lime and other mineral substances present in
the sea water would be fixed in the tissues of these plants, either
in a minute state of division, as little grains or Coccoliths, or in
more solid masses like those of the Corallines and Nullipores. In this
way a beginning of limestone formation might be made, and quantities
of carbonaceous and bituminous matter, resulting from the decay of
vegetable substances might accumulate on the sea bottom. Now arises
the opportunity for animal life. The plants have collected stores
of organic matter, and their minute germs, along with microscopic
species, are floating everywhere in the sea. The plant has fulfilled
its function as far as the waters are concerned, and now a place is
prepared for the animal. In what form shall it appear? Many of its
higher forms, those which depend upon animal food or on the more
complex plants for subsistence, would obviously be unsuitable. Further,
the sea water is still too much saturated with saline matter to be
fit for the higher animals of the waters. Still further, there may
be a residue of internal heat forbidding coolness, and that solution
of free oxygen which is an essential condition of existence to the
higher forms of life. Something must be found suitable for this saline,
imperfectly oxygenated, tepid sea. Something, too, is wanted that can
aid in introducing conditions more favourable to higher life in the
future. Our experience of the modern world shows us that all these
conditions can be better fulfilled by the Protozoa than by any other
creatures. They can live now equally in those great depths of ocean
where the conditions are most unfavourable to other forms of life,
and in tepid unhealthy pools overstocked with vegetable matter in a
state of putridity. They form a most suitable basis for higher forms
of life. They have remarkable powers of removing mineral matters from
the waters and of fixing them in solid forms. So, in the fitness of
things, a gigantic Foraminifer is just what we need, and after it has
spread itself over the mud and rock of the primeval seas, and built up
extensive reefs therein, other animals may be introduced, capable of
feeding on it, or of sheltering themselves in its stony masses, and
thus we have the appropriate dawn of animal life.
But what are we to say of the cause of this new series of facts, so
wonderfully superimposed upon the merely vegetable and mineral? Must
it remain to us as an act of creation, or was it derived from some
pre-existing matter in which it had been potentially present? Science
fails to inform us, but conjectural "phylogeny" steps in and takes its
place. Haeckel, the prophet of this new philosophy, waves his magic
wand, and simple masses of sarcode spring from inorganic matter, and
form diffused sheets of sea slime, from which are in time separated
distinct amœboid and foraminiferal forms. Experience, however, gives us
no facts whereon to build this supposition, and it remains neither more
nor less scientific or certain than that old fancy of the Egyptians,
which derived animals from the fertile mud of the Nile.
If we fail to learn anything of the origin of Eozoon, and if its life
processes are just as inscrutable as those of higher creatures, we
can at least enquire as to its history in geological time. In this
respect we find, in the first place, that the Protozoa have not had a
monopoly in their profession of accumulators of calcareous rock.
Originated by Eozoon in the old Laurentian time, this process has
been proceeding throughout the geological ages; and while Protozoa,
equally simple with the great prototype of the race, have been and
are continuing its function, and producing new limestones in every
geological period, and so adding to the volume of the successive
formations, new workers of higher grades have been introduced, capable
of enjoying higher forms of animal activity, and equally of labouring
at the great task of continent building; of existing, too, in seas
less rich in mineral substances than those of the Eozoic time, and for
that very reason better suited to higher and more skilled artists. It
is to be observed in connection with this, that as the work of the
Foraminifers has thus been assumed by others, their size and importance
have diminished, and the larger forms of more recent times have some of
them been fain to build up their hard parts of cemented sand instead of
limestone.
When the marvellous results of recent deep-sea dredgings were first
made known, and it was found that chalky foraminiferal earth is yet
accumulating in the Atlantic, with sponges and sea urchins, resembling
in many respects those whose remains exist in the chalk, the fact was
expressed by the statement that we still live in the chalk period.
Thus stated the conclusion is scarcely correct. We do not live in the
chalk period, but the conditions of the chalk period still exist in the
deeper portions of the sea. We may say more than this. To some extent
the conditions of the Laurentian period still exist in the sea, except
in so far as they have been removed by the action of the Foraminifera
and other limestone builders. To those who can realize the enormous
lapse of time involved in the geological history of the earth, this
conveys an impression almost of eternity in the existence of this
oldest of all the families of the animal kingdom.
We are still more deeply impressed with this when we bring into view
the great physical changes which have occurred since the dawn of life.
When we consider that the skeletons of Eozoon contribute to form the
oldest hills of our continents; that they have been sealed up in solid
marble, and that they are associated with hard crystalline rocks
contorted in the most fantastic manner; that these rocks have almost
from the beginning of geological time been undergoing waste to supply
the material of new formations; that they have witnessed innumerable
subsidences and elevations of the continents; and that the greatest
mountain chains of the earth have been built up from the sea since
Eozoon began to exist,--we acquire a most profound impression of the
persistence of the lower forms of animal life, and know that mountains
may be removed and continents swept away and replaced, before the least
of the humble gelatinous Protozoa can finally perish. Life may be a
fleeting thing in the individual, but as handed down through successive
generations of beings, and as a constant animating power in successive
organisms, it appears, like its Creator, eternal.
This leads to another and very serious question. How long did lineal
descendants of Eozoon exist, and do they still exist? We may for the
present consider this question apart from ideas of derivation and
elevation into higher planes of existence. Eozoon as a species, and
even as a genus, may cease to exist with the Eozoic age, and we have
no evidence whatever that any succeeding creatures are its modified
descendants. As far as their structures inform us, they may as much
claim to be original creations as Eozoon itself. Still descendants of
Eozoon may have continued to exist, though we have not yet met with
them. I should not be surprised to hear of a veritable specimen being
some day dredged alive in the Atlantic or the Pacific. It is also
to be observed that in animals so simple as this many varieties may
appear, widely different from the original. In these the general form
and habit of life are the most likely things to change, the minute
structures much less so. We need not, therefore, be surprised to find
its descendants diminishing in size or altering in general form, while
the characters of the fine tubulation and of the canal system would
remain. We need not wonder if any sessile Foraminifer of the Nummuline
group should prove to be a descendant of Eozoon. It would be less
likely that a Sponge or a Foraminifer of the Rotaline type should
originate from it. If one could only secure a succession of deep-sea
limestones with Foraminifers extending all the way from the Laurentian
to the present time, I can imagine nothing more interesting than to
compare the whole series, with the view of ascertaining the limits of
descent with variation, and the points where new forms are introduced.
We have not yet such a series, but it may be obtained; and as these
creatures are eminently cosmopolitan, occurring over vastly wide areas
of sea bottom, and are very variable, they would afford a better test
of theories of derivation than any that can be obtained from the more
locally distributed and less variable animals of higher grade. I was
much struck with this recently, in examining a series of Foraminifera
from the Cretaceous of Manitoba, and comparing them with the varietal
forms of the same species in the interior of Nebraska, 500 miles to the
south, and with those of the English chalk and of the modern seas. In
all these different times and places we had the same species. In all
they existed under so many varietal forms passing into each other, that
in former times every species had been multiplied by naturalists into
several. Yet, in all, the identical varietal forms were repeated with
the most minute markings the same. Here were at once constancy the most
remarkable, and variations the most extensive. If we dwell on the one
to the exclusion of the other, we reach only one-sided conclusions,
imperfect and unsatisfactory. By taking both into connection we can
alone realize the full significance of the facts. We cannot yet obtain
such series for all geological time; but it may even now be worth while
to enquire, What do we know as to any modification in the case of the
primeval Foraminifers, whether with reference to the derivation from
them of other Protozoa or of higher forms of life?
There is no link in geological fact to connect Eozoon with any of the
Mollusks, Radiates, or Crustaceans of the succeeding Cambrian. What
may be discovered in the future we cannot conjecture; but at present
these stand before us as distinct creations. It would of course be more
probable that Eozoon should be the ancestor of some of the Foraminifera
of the Primordial age, but strangely enough it is very dissimilar
from all these, except Cryptozoum and some forms of Stromatopora; and
here, as already stated, the evidence of minute structure fails to
a great extent. Of actual facts, therefore, we have none; and those
evolutionists who have regarded the dawn animal as an evidence in their
favour have been obliged to have recourse to supposition and assumption.
We may imagine Eozoon itself, however, to state its experience as
follows:--"I, Eozoon Canadense, being a creature of low organization
and intelligence, and of practical turn, am no theorist, but have a
lively appreciation of such facts as I am able to perceive. I found
myself growing upon the sea bottom, and know not whence I came. I grew
and flourished for ages, and found no let or hindrance to my expansion,
and abundance of food was always floated to me without my having to go
in search of it. At length a change came. Certain creatures with hard
snouts and jaws began to prey on me. Whence they came I know not; I
cannot think that they came from the germs which I had dispersed so
abundantly throughout the ocean. Unfortunately, just at the same time
lime became a little less abundant in the waters, perhaps because of
the great demands I myself had made, and thus it was not so easy as
before to produce a thick supplemental skeleton for defence. So I had
to give way. I have done my best to avoid extinction; but it is clear
that I must at length be overcome, and must either disappear or subside
into a humbler condition, and that other creatures better provided for
the new conditions of the world must take my place." In such terms we
may suppose that this patriarch of the seas might tell his history, and
mourn his destiny, though he might also congratulate himself on having
in an honest way done his duty and fulfilled his function in the world,
leaving it to other and perhaps wiser creatures to dispute as to his
origin and fate, while perhaps much less perfectly fulfilling the ends
of their own existence.
Thus our dawn animal has positively no story to tell as to its own
introduction or its transmutation into other forms of existence.
It leaves the mystery of creation where it was, but in connection
with the subsequent history of life we can learn from it a little
as to the laws which have governed the succession of animals in
geological time. First, we may learn that the plan of creation has
been progressive, that there has been an advance from the few low and
generalized types of the primæval ocean to the more numerous, higher,
and more specialized types of more recent times. Secondly, we learn
that the lower types, when first introduced, and before they were
subordinated to higher forms of life, existed in some of their grandest
modifications as to form and complexity, and that in succeeding ages,
when higher types were replacing them, they were subjected to decay and
degeneracy. Thirdly, we learn that while the species has a limited term
of existence in geological time, any large type of animal existence,
like that of the Foraminifera or Sponges, for example, once introduced,
continues and finds throughout all the vicissitudes of the earth some
appropriate residence. Fourthly, as to the mode of introduction of new
types, or whether such creatures as Eozoon had any direct connection
with the subsequent introduction of Mollusks, Worms, or Crustaceans, it
is altogether silent, nor can it predict anything as to the order or
manner of their introduction.
Had we been permitted to visit the Laurentian seas, and to study Eozoon
and its contemporary Protozoa when alive, it is plain that we could not
have foreseen or predicted from the consideration of such organisms
the future development of life. No amount of study of the prototypal
Foraminifer could have led us distinctly to the conception of even a
Sponge or a Polyp, much less of any of the higher animals. Why is this?
The answer is that the improvement into such higher types does not
take place by any change of the elementary sarcode, either in those
chemical, mechanical, or vital properties which we can study, but in
the adding to it of new structures. In the Sponge, which is perhaps
the nearest type of all, we have the movable pulsating cilium and true
animal cellular tissue, and along with this the spicular or fibrous
skeleton, these structures leading to an entire change in the mode of
life and subsistence. In the higher types of animals it is the same.
Even in the highest we have white blood corpuscles and germinal matter,
which, in so far as we know, carry on no higher forms of life than
those of an Amœba; but they are now made subordinate to other kinds
of tissues, of great variety and complexity, which never have been
observed to arise out of the growth of any Protozoon. There would be
only a few conceivable inferences which the highest finite intelligence
could deduce as to the development of future and higher animals. He
might infer that the Foraminiferal sarcode, once introduced, might be
the substratum or foundation of other but unknown tissues in the higher
animals, and that the Protozoon type might continue to subsist side
by side with higher forms of living things, as they were successively
introduced. He might also infer that the elevation of the animal
kingdom would take place with reference to those new properties of
sensation and voluntary motion in which the humblest animals diverge
from the life of the plant.
It is important that these points should be clearly before our minds,
because there has been current of late among naturalists a loose way
of writing with reference to them, which seems to have imposed on many
who are not naturalists. It has been said, for example, that such an
organism as Eozoon may include potentially all the structures and
functions of the higher animals, and that it is possible that we might
be able to infer or calculate all these with as much certainty as we
can calculate an eclipse or any other physical phenomenon. Now, there
is not only no foundation in fact for these assertions, but it is, from
our present standpoint, not conceivable that they can ever be realized.
The laws of inorganic matter give no data whence any _à priori_
deductions or calculations could be made as to the structure and
vital forces of the plant. The plant gives no data from which we can
calculate the functions of the animal. The Protozoon gives no data from
which we can calculate the specialties of the Mollusk, the Articulate,
or the Vertebrate. Nor, unhappily, do the present conditions of life of
themselves give us any sure grounds for predicting the new creations
that may be in store for our old planet. Those who think to build a
philosophy and even a religion on such data are mere dreamers, and have
no scientific basis for their dogmas. They are as blind guides as our
primæval Protozoon himself would be in matters whose real solution lies
in the harmony of our own higher and immaterial nature with the Being
who is the Author of all life--the Father "from whom every family in
heaven and earth is named."
References:--"Life's Dawn on Earth." London, 1885. Specimens of
Eozoon in the Peter Redpath Museum, Montreal, 1888.
_THE APPARITION AND SUCCESSION OF ANIMAL FORMS._
DEDICATED TO THE MEMORY OF
THE EMINENT SWISS AND AMERICAN ZOOLOGIST
LOUIS AGASSIZ,
The Founder of the Modern School of American Biology,
and of
SIR RICHARD OWEN,
A Great and Philosophical Naturalist,
to whose Teaching I and very many Others owe our earliest
introduction to the Principle of Homology
in the Animal Kingdom.
Modern Ideas of Derivation--Development of Animal Forms in
Time--Various Theories of Derivation--History of Organic Types--History
of Organs--Testimony of the Geological Record--Laws of the Succession
Development and Evolution--Evolutionist Theologians
[Illustration: Old Forms of Trilobites, from the Lower Cambrian
(p. 173 _et seq._)
_Olenellus Thompsoni_, Emmons.
_Agnostus vir_, Matthew.
_Paradoxides regina_, Matthew.]