WHAT IS EOZOON?
The shortest answer to this question is, that this ancient fossil
is the skeleton of a creature belonging to that simple and humbly
organized group of animals which are known by the name Protozoa. If
we take as a familiar example of these the gelatinous and microscopic
creature found in stagnant ponds, and known as the _Amœba_[P] (fig.
12), it will form a convenient starting point. Viewed under a low
power, it appears as a little patch of jelly, irregular in form, and
constantly changing its aspect as it moves, by the extension of parts
of its body into finger-like processes or pseudopods which serve as
extempore limbs. When moving on the surface of a slip of glass under
the microscope, it seems, as it were, to flow along rather than creep,
and its body appears to be of a semi-fluid consistency. It may be taken
as an example of the least complex forms of animal life known to us,
and is often spoken of by naturalists as if it were merely a little
particle of living and scarcely organized jelly or protoplasm. When
minutely examined, however, it will not be found so simple as it at
first sight appears. Its outer layer is clear or transparent, and more
dense than the inner mass, which seems granular. It has at one end a
curious vesicle which can be seen gradually to expand and become filled
with a clear drop of liquid, and then suddenly to contract and expel
the contained fluid through a series of pores in the adjacent part of
the outer wall. This is the so-called pulsating vesicle, and is an
organ both of circulation and excretion. In another part of the body
may be seen the nucleus, which is a little cell capable, at certain
times, of producing by its division new individuals. Food when taken
in through the wall of the body forms little pellets, which become
surrounded by a digestive liquid exuded from the enclosing mass into
rounded cavities or extemporised stomachs. Minute granules are seen
to circulate in the gelatinous interior, and may be substitutes for
blood-cells, and the outer layer of the body is capable of protrusion
in any direction into long processes, which are very mobile, and used
for locomotion and prehension. Further, this creature, though destitute
of most of the parts which we are accustomed to regard as proper to
animals, seems to exercise volition, and to show the same appetites
and passions with animals of higher type. I have watched one of these
animalcules endeavouring to swallow a one-celled plant as long as its
own body; evidently hungry and eager to devour the tempting morsel, it
stretched itself to its full extent, trying to envelope the object of
its desire. It failed again and again; but renewed the attempt, until
at length, convinced of its hopelessness, it flung itself away as if in
disappointment, and made off in search of something more manageable.
With the Amœba are found other types of equally simple Protozoa, but
somewhat differently organized. One of these, _Actinophrys_ (fig. 13),
has the body globular and unchanging in form, the outer wall of greater
thickness; the pulsating vesicle like a blister on the surface, and the
pseudopods long and thread-like. Its habits are similar to those of the
Amœba, and I introduce it to show the variations of form and structure
possible even among these simple creatures.
[Footnote P: The alternating animal, alluding to its change of form.]
[Illustration: Fig. 14. _Entosolenia._
A one-celled Foraminifer. Magnified as a transparent object.]
[Illustration: Fig. 15. _Biloculina._
A many-chambered Foraminifer. Magnified as a transparent object.]
[Illustration: Fig. 16. _Polystomella._
A spiral Foraminifer. Magnified as an opaque object.]
The Amœba and Actinophrys are fresh water animals, and are destitute
of any shell or covering. But in the sea there exist swarms of similar
creatures, equally simple in organization, but gifted with the power of
secreting around their soft bodies beautiful little shells or crusts of
carbonate of lime, having one orifice, and often in addition multitudes
of microscopic pores through which the soft gelatinous matter can ooze,
and form outside finger-like or thread-like extensions for collecting
food. In some cases the shell consists of a single cavity only, but in
most, after one cell is completed, others are added, forming a series
of cells or chambers communicating with each other, and often arranged
spirally or otherwise in most beautiful and symmetrical forms. Some of
these creatures, usually named Foraminifera, are locomotive, others
sessile and attached. Most of them are microscopic, but some grow by
multiplication of chambers till they are a quarter of an inch or more
in breadth. (Figs. 14 to 17.)
[Illustration: Fig. 17. _Polymorphina._
A many-chambered Foraminifer. Magnified as an opaque object. Figs. 14
to 17 are from original sketches of Post-pliocene specimens.]
The original skeleton or primary cell-wall of most of these creatures
is seen under the microscope to be perforated with innumerable pores,
and is extremely thin. When, however, owing to the increased size of
the shell, or other wants of the creature, it is necessary to give
strength, this is done by adding new portions of carbonate of lime to
the outside, and to these Dr. Carpenter has given the appropriate name
of "supplemental skeleton;" and this, when covered by new growths,
becomes what he has termed an "intermediate skeleton." The supplemental
skeleton is also traversed by tubes, but these are often of larger size
than the pores of the cell-wall, and of greater length, and branched in
a complicated manner. (Fig. 20.) Thus there are microscopic characters
by which these curious shells can be distinguished from those of
other marine animals; and by applying these characters we learn that
multitudes of creatures of this type have existed in former periods of
the world's history, and that their shells, accumulated in the bottom
of the sea, constitute large portions of many limestones. The manner in
which such accumulation takes place we learn from what is now going on
in the ocean, more especially from the result of the recent deep-sea
dredging expeditions. The Foraminifera are vastly numerous, both near
the surface and at the bottom of the sea, and multiply rapidly; and
as successive generations die, their shells accumulate on the ocean
bed, or are swept by currents into banks, and thus in process of time
constitute thick beds of white chalky material, which may eventually
be hardened into limestone. This process is now depositing a great
thickness of white ooze in the bottom of the ocean; and in times past
it has produced such vast thicknesses of calcareous matter as the chalk
and the nummulitic limestone of Europe and the orbitoidal limestone
of America. The chalk, which alone attains a maximum thickness of 1000
feet, and, according to Lyell, can be traced across Europe for 1100
geographical miles, may be said to be entirely composed of shells
of Foraminifera imbedded in a paste of still more minute calcareous
bodies, the Coccoliths, which are probably products of marine
vegetable life, if not of some animal organism still simpler than the
Foraminifera.
Lastly, we find that in the earlier geological ages there existed
much larger Foraminifera than any found in our present seas; and that
these, always sessile on the bottom, grew by the addition of successive
chambers, in the same manner with the smaller species. To some of these
we shall return in the sequel. In the meantime we shall see what claims
Eozoon has to be included among them.
Let us, then, examine the structure of Eozoon, taking a typical
specimen, as we find it in the limestone of Grenville or Petite Nation.
In such specimens the skeleton of the animal is represented by a white
crystalline marble, the cavities of the cells by green serpentine, the
mode of whose introduction we shall have to consider in the sequel.
The lowest layer of serpentine represents the first gelatinous coat
of animal matter which grew upon the bottom, and which, if we could
have seen it before any shell was formed upon its surface, must have
resembled, in appearance at least, the shapeless coat of living slime
found in some portions of the bed of the deep sea, which has received
from Huxley the name _Bathybius_, and which is believed to be a
protozoon of indefinite extension, though it may possibly be merely the
pulpy sarcode of sponges and similar things penetrating the ooze at
their bases. On this primary layer grew a delicate calcareous shell,
perforated by innumerable minute tubuli, and by some larger pores or
septal orifices, while supported at intervals by perpendicular plates
or pillars. Upon this again was built up, in order to strengthen it,
a thickening or supplemental skeleton, more dense, and destitute of
fine tubuli, but traversed by branching canals, through which the
soft gelatinous matter could pass for the nourishment of the skeleton
itself, and the extension of pseudopods beyond it. (Fig. 10.) So was
formed the first layer of Eozoon, which seems in some cases to have
spread by lateral extension over several inches of sea bottom. On this
the process of growth of successive layers of animal sarcode and of
calcareous skeleton was repeated again and again, till in some cases
even a hundred or more layers were formed. (Photograph, Plate III.,
and nature print, Plate V.) As the process went on, however, the
vitality of the organism became exhausted, probably by the deficient
nourishment of the central and lower layers making greater and greater
demands on those above, and so the succeeding layers became thinner,
and less supplemental skeleton was developed. Finally, toward the
top, the regular arrangement in layers was abandoned, and the cells
became a mass of rounded chambers, irregularly piled up in what Dr.
Carpenter has termed an "acervuline" manner, and with very thin walls
unprotected by supplemental skeleton. Then the growth was arrested,
and possibly these upper layers gave off reproductive germs, fitted
to float or swim away and to establish new colonies. We may have
such reproductive germs in certain curious globular bodies, like
loose cells, found in connection with irregular Eozoon in one of
the Laurentian limestones at Long Lake and elsewhere. These curious
organisms I observed some years ago, but no description of them was
published at the time, as I hoped to obtain better examples. I now
figure some of them, and give their description in a note. (Fig. 18).
I have recently obtained numerous additional examples from the beds
holding Eozoon at St. Pierre, on the Ottawa. They occur at this place
on the surface of layers of the limestone in vast numbers, as if they
had been growing separately on the bottom, or had been drifted over
it by currents. These we shall further discuss hereafter. Such was
the general mode of growth of Eozoon, and we may now consider more in
detail some questions as to its gigantic size, its precise mode of
nutrition, the arrangement of its parts, its relations to more modern
forms, and the effects of its growth in the Laurentian seas. In the
meantime a study of our illustration, Plate IV., which is intended as a
magnified restoration of the animal, will enable the reader distinctly
to understand its structure and probable mode of growth, and to avail
himself intelligently of the partial representations of its fossilized
remains in the other plates and woodcuts.
[Illustration: Fig. 18. _Minute Foraminiferal forms from the Laurentian
of Long Lake._
Highly magnified. (_a._) Single cell, showing tubulated wall. (_b, c._)
Portions of same more highly magnified. (_d._) Serpentine cast of a
similar chamber, decalcified, and showing casts of tubuli.]
With respect to its size, we shall find in a subsequent chapter that
this was rivalled by some succeeding animals of the same humble type
in the Silurian age; and that, as a whole, foraminiferal animals have
been diminishing in size in the lapse of geological time. It is indeed
a fact of so frequent occurrence that it may almost be regarded as
a law of the introduction of new forms of life, that they assume in
their early history gigantic dimensions, and are afterwards continued
by less magnificent species. The relations of this to external
conditions, in the case of higher animals, are often complex and
difficult to understand; but in organisms so low as Eozoon and its
allies, they lie more on the surface. Such creatures may be regarded
as the simplest and most ready media for the conversion of vegetable
matter into animal tissues, and their functions are almost entirely
limited to those of nutrition. Hence it is likely that they will be
able to appear in the most gigantic forms under such conditions as
afford them the greatest amount of pabulum for the nourishment of
their soft parts and for their skeletons. There is reason to believe,
for example, that the occurrence, both in the chalk and the deep-sea
mud, of immense quantities of the minute bodies known as Coccoliths
along with Foraminifera, is not accidental. The Coccoliths appear to
be grains of calcareous matter formed in minute plants adapted to a
deep-sea habitat; and these, along with the vegetable and animal debris
constantly being derived from the death of the living things at the
surface, afford the material both of sarcode and shell. Now if the
Laurentian graphite represents an exuberance of vegetable growth in
those old seas proportionate to the great supplies of carbonic acid
in the atmosphere and in the waters, and if the Eozoic ocean was even
better supplied with carbonate of lime than those Silurian seas whose
vast limestones bear testimony to their richness in such material, we
can easily imagine that the conditions may have been more favourable
to a creature like Eozoon than those of any other period of geological
time.
Growing, as Eozoon did, on the floor of the ocean, and covering wide
patches with more or less irregular masses, it must have thrown up from
its whole surface its pseudopods to seize whatever floating particles
of food the waters carried over it. There is also reason to believe,
from the outline of certain specimens, that it often grew upward in
cylindrical or club-shaped forms, and that the broader patches were
penetrated by large pits or oscula, admitting the sea-water deeply into
the substance of the masses. In this way its growth might be rapid and
continuous; but it does not seem to have possessed the power of growing
indefinitely by new and living layers covering those that had died,
in the manner of some corals. Its life seems to have had a definite
termination, and when that was reached an entirely new colony had to
be commenced. In this it had more affinity with the Foraminifera, as
we now know them, than with the corals, though practically it had the
same power with the coral polyps of accumulating limestone in the sea
bottom, a power indeed still possessed by its foraminiferal successors.
In the case of coral limestones, we know that a large proportion of
these consist not of continuous reefs but of fragments of coral mixed
with other calcareous organisms, spread usually by waves and currents
in continuous beds over the sea bottom. In like manner we find in
the limestones containing Eozoon, layers of fragmental matter which
shows in places the characteristic structures, and which evidently
represents the debris swept from the Eozoic masses and reefs by the
action of the waves. It is with this fragmental matter that the small
rounded organisms already referred to most frequently occur; and while
they may be distinct animals, they may also be the fry of Eozoon, or
small portions of its acervuline upper surface floated off in a living
state, and possibly capable of living independently and of founding new
colonies.
It is only by a somewhat wild poetical licence that Eozoon has been
represented as a "kind of enormous composite animal stretching from the
shores of Labrador to Lake Superior, and thence northward and southward
to an unknown distance, and forming masses 1500 feet in depth." We may
discuss by-and-by the question of the composite nature of masses of
Eozoon, and we see in the corals evidence of the great size to which
composite animals of a higher grade can attain. In the case of Eozoon
we must imagine an ocean floor more uniform and level than that now
existing. On this the organism would establish itself in spots and
patches. These might finally become confluent over large areas, just
as massive corals do. As individual masses attained maturity and died,
their pores would be filled up with limestone or silicious deposits,
and thus could form a solid basis for new generations, and in this way
limestone to an indefinite extent might be produced. Further, wherever
such masses were high enough to be attacked by the breakers, or where
portions of the sea bottom were elevated, the more fragile parts of the
surface would be broken up and scattered widely in beds of fragments
over the bottom of the sea, while here and there beds of mud or sand
or of volcanic debris would be deposited over the living or dead
organic mass, and would form the layers of gneiss and other schistose
rocks interstratified with the Laurentian limestone. In this way, in
short, Eozoon would perform a function combining that which corals and
Foraminifera perform in the modern seas; forming both reef limestones
and extensive chalky beds, and probably living both in the shallow and
the deeper parts of the ocean. If in connection with this we consider
the rapidity with which the soft, simple, and almost structureless
sarcode of these Protozoa can be built up, and the probability that
they were more abundantly supplied with food, both for nourishing their
soft parts and skeletons, than any similar creatures in later times, we
can readily understand the great volume and extent of the Laurentian
limestones which they aided in producing. I say aided in producing,
because I would not desire to commit myself to the doctrine that the
Laurentian limestones are wholly of this origin. There may have been
other animal limestone-builders than Eozoon, and there may have been
limestones formed by plants like the modern Nullipores or by merely
mineral deposition.
[Illustration: Fig. 19. _Section of a Nummulite, from Eocene Limestone
of Syria._
Showing chambers, tubuli, and canals. Compare this and fig. 20 with
figs. 10 and 11.]
[Illustration: Fig. 20. _Portion of shell of Calcarina._
Magnified, after Carpenter. (_a._) Cells. (_b._) Original cell-wall
with tubuli. (_c._) Supplementary skeleton with canals.]
Its relations to modern animals of its type have been very clearly
defined by Dr. Carpenter. In the structure of its proper wall and its
fine parallel perforations, it resembles the _Nummulites_ and their
allies; and the organism may therefore be regarded as an aberrant
member of the Nummuline group, which affords some of the largest and
most widely distributed of the fossil Foraminifera. This resemblance
may be seen in fig. 19. To the Nummulites it also conforms in its
tendency to form a supplemental or intermediate skeleton with canals,
though the canals themselves in their arrangement more nearly resemble
Calcarina, which is represented in fig. 20. In its superposition of
many layers, and in its tendency to a heaped up or acervuline irregular
growth it resembles _Polytrema_ and _Tinoporus_, forms of a different
group in so far as shell-structure is concerned. It may thus be
regarded as a composite type, combining peculiarities now observed in
two groups, or it may be regarded as a representative in the Nummuline
series of Polytrema and Tinoporus in the Rotaline series. At the time
when Dr. Carpenter stated these affinities, it might be objected that
Foraminifera of these families are in the main found in the Modern and
Tertiary periods. Dr. Carpenter has since shown that the curious oval
Foraminifer called _Fusulina_, found in the coal formation, is in like
manner allied to both Nummulites and Rotalines; and still more recently
Mr. Brady has discovered a true Nummulite in the Lower Carboniferous of
Belgium. This group being now fairly brought down to the Palæozoic, we
may hope finally to trace it back to the Primordial, and thus to bring
it still nearer to Eozoon in time.
[Illustration: Fig. 21. _Foraminiferal Rock Builders._
(_a._) Nummulites lævigata--Eocene. (_b._) The same, showing chambered
interior. (_c._) Milioline limestone, magnified--Eocene, Paris. (_d._)
Hard Chalk, section magnified--Cretaceous.]
Though Eozoon was probably not the only animal of the Laurentian seas,
yet it was in all likelihood the most conspicuous and important as
a collector of calcareous matter, filling the same place afterwards
occupied by the reef-building corals. Though probably less efficient
than these as a constructor of solid limestones, from its less
permanent and continuous growth, it formed wide floors and patches
on the sea-bottom, and when these were broken up vast quantities of
limestone were formed from their debris. It must also be borne in mind
that Eozoon was not everywhere infiltrated with serpentine or other
silicious minerals; quantities of its substance were merely filled
with carbonate of lime, resembling the chamber-wall so closely that
it is nearly impossible to make out the difference, and thus is likely
to pass altogether unobserved by collectors, and to baffle even the
microscopist. (Fig. 24.) Although therefore the layers which contain
well characterized Eozoon are few and far between, there is reason to
believe that in the composition of the limestones of the Laurentian
it bore no small part, and as these limestones are some of them
several hundreds of feet in thickness, and extend over vast areas,
Eozoon may be supposed to have been as efficient a world-builder as
the Stromatoporæ of the Silurian and Devonian, the Globigerinæ and
their allies in the chalk, or the Nummulites and Miliolites in the
Eocene. The two latter groups of rock-makers are represented in our
cut, fig. 21; the first will engage our attention in chapter sixth. It
is a remarkable illustration of the constancy of natural causes and of
the persistence of animal types, that these humble Protozoans, which
began to secrete calcareous matter in the Laurentian period, have been
continuing their work in the ocean through all the geological ages,
and are still busy in accumulating those chalky muds with which recent
dredging operations in the deep sea have made us so familiar.
NOTES TO CHAPTER IV.
(A.) Original Description of Eozoon Canadense.
[As given by the author in the _Journal of the Geological Society_,
February, 1865.]
"At the request of Sir W. E. Logan, I have submitted to microscopic
examination slices of certain peculiar laminated forms, consisting
of alternate layers of carbonate of lime and serpentine, and of
carbonate of lime and white pyroxene, found in the Laurentian
limestone of Canada, and regarded by Sir William as possibly fossils.
I have also examined slices of a large number of limestones from the
Laurentian series, not showing the forms of these supposed fossils.
"The specimens first mentioned are masses, often several inches in
diameter, presenting to the naked eye alternate laminæ of serpentine,
or of pyroxene, and carbonate of lime. Their general aspect, as
remarked by Sir W. E. Logan (_Geology of Canada_, 1863, p. 49),
reminds the observer of that of the Silurian corals of the genus
Stromatopora, except that the laminæ diverge from and approach each
other, and frequently anastomose or are connected by transverse septa.
"Under the microscope the resemblance to Stromatopora is seen to
be in general form merely, and no trace appears of the radiating
pillars characteristic of that genus. The laminæ of serpentine and
pyroxene present no organic structure, and the latter mineral is
highly crystalline. The laminæ of carbonate of lime, on the contrary,
retain distinct traces of structures which cannot be of a crystalline
or concretionary character. They constitute parallel or concentric
partitions of variable thickness, enclosing flattened spaces or
chambers, frequently crossed by transverse plates or septa, in some
places so numerous as to give a vesicular appearance, in others
occurring only at rare intervals. The laminæ themselves are excavated
on their sides into rounded pits, and are in some places traversed by
canals, or contain secondary rounded cells, apparently isolated. In
addition to these general appearances, the substance of the laminæ,
where most perfectly preserved, is seen to present a fine granular
structure, and to be penetrated by numerous minute tubuli, which
are arranged in bundles of great beauty and complexity, diverging
in sheaf-like forms, and in their finer extensions anastomosing so
as to form a network (figs. 10 and 28). In transverse sections, and
under high powers, the tubuli are seen to be circular in outline, and
sharply defined (fig. 29). In longitudinal sections, they sometimes
present a beaded or jointed appearance. Even where the tubular
structure is least perfectly preserved, traces of it can still be
seen in most of the slices, though there are places in which the
laminæ are perfectly compact, and perhaps were so originally.
"With respect to the nature and probable origin of the appearances
above described, I would make the following remarks:--
"1. The serpentine and pyroxene which fill the cavities of the
calcareous matter have no appearance of concretionary structure.
On the contrary, their aspect is that of matter introduced by
infiltration, or as sediment, and filling spaces previously existing.
In other words, the calcareous matter has not been moulded on the
forms of the serpentine and augite, but these have filled spaces
or chambers in a hard calcareous mass. This conclusion is further
confirmed by the fact, to be referred to in the sequel, that the
serpentine includes multitudes of minute foreign bodies, while the
calcareous matter is uniform and homogeneous. It is also to be
observed that small veins of carbonate of lime occasionally traverse
the specimen's, and in their entire absence of structures other than
crystalline, present a striking contrast to the supposed fossils.
"2. Though the calcareous laminæ have in places a crystalline
cleavage, their forms and structures have no relation to this. Their
cells and canals are rounded, and have smooth walls, which are
occasionally lined with films apparently of carbonaceous matter.
Above all, the minute tubuli are different from anything likely to
occur in merely crystalline calc-spar. While in such rocks little
importance might be attached to external forms simulating the
appearances of corals, sponges, or other organisms, these delicate
internal structures have a much higher claim to attention. Nor is
there any improbability in the preservation of such minute parts in
rocks so highly crystalline, since it is a circumstance of frequent
occurrence in the microscopic examination of fossils that the finest
structures are visible in specimens in which the general form and the
arrangement of parts have been obliterated. It is also to be observed
that the structure of the calcareous laminæ is the same, whether the
intervening spaces are filled with serpentine or with pyroxene.
"3. The structures above described are not merely definite and
uniform, but they are of a kind proper to animal organisms, and
more especially to one particular type of animal life, as likely as
any other to occur under such circumstances: I refer to that of the
Rhizopods of the order Foraminifera. The most important point of
difference is in the great size and compact habit of growth of the
specimens in question; but there seems no good reason to maintain
that Foraminifera must necessarily be of small size, more especially
since forms of considerable magnitude referred to this type are known
in the Lower Silurian. Professor Hall has described specimens of
Receptaculites twelve inches in diameter; and the fossils from the
Potsdam formation of Labrador, referred by Mr. Billings to the genus
Archæocyathus, are examples of Protozoa with calcareous skeletons
scarcely inferior in their massive style of growth to the forms now
under consideration.
"These reasons are, I think, sufficient to justify me in regarding
these remarkable structures as truly organic, and in searching for
their nearest allies among the Foraminifera.
"Supposing then that the spaces between the calcareous laminæ, as
well as the canals and tubuli traversing their substance, were once
filled with the sarcode body of a Rhizopod, comparisons with modern
forms at once suggest themselves.
"From the polished specimens in the Museum of the Canadian Geological
Survey, it appears certain that these bodies were sessile by a broad
base, and grew by the addition of successive layers of chambers
separated by calcareous laminæ, but communicating with each other by
canals or septal orifices sparsely and irregularly distributed. Small
specimens have thus much the aspect of the modern genera Carpenteria
and Polytrema. Like the first of these genera, there would also seem
to have been a tendency to leave in the midst of the structure a
large central canal, or deep funnel-shaped or cylindrical opening,
for communication with the sea-water. Where the laminæ coalesce, and
the structure becomes more vesicular, it assumes the 'acervuline'
character seen in such modern forms as Nubecularia.
"Still the magnitude of these fossils is enormous when compared with
the species of the genera above named; and from the specimens in the
larger slabs from Grenville, in the museum of the Canadian Survey,
it would seem that these organisms grew in groups, which ultimately
coalesced, and formed large masses penetrated by deep irregular
canals; and that they continued to grow at the surface, while the
lower parts became dead and were filled up with infiltrated matter or
sediment. In short, we have to imagine an organism having the habit
of growth of Carpenteria, but attaining to an enormous size, and by
the aggregation of individuals assuming the aspect of a coral reef.
"The complicated systems of tubuli in the Laurentian fossil indicate,
however, a more complex structure than that of any of the forms
mentioned above. I have carefully compared these with the similar
structures in the 'supplementary skeleton' (or the shell-substance
that carries the vascular system) of Calcarina and other forms, and
can detect no difference except in the somewhat coarser texture of
the tubuli in the Laurentian specimens. It accords well with the
great dimensions of these, that they should thus thicken their walls
with an extensive deposit of tubulated calcareous matter; and from
the frequency of the bundles of tubuli, as well as from the thickness
of the partitions, I have no doubt that all the successive walls, as
they were formed, were thickened in this manner, just as in so many
of the higher genera of more modern Foraminifera.
"It is proper to add that no spicules, or other structures indicating
affinity to the Sponges, have been detected in any of the specimens.
"As it is convenient to have a name to designate these forms, I
would propose that of Eozoon, which will be specially appropriate to
what seems to be the characteristic fossil of a group of rocks which
must now be named Eozoic rather than Azoic. For the species above
described, the specific name of Canadense has been proposed. It may
be distinguished by the following characters:--
"Eozoon Canadense; _gen. et spec. nov._
"_General form._--Massive, in large sessile patches or irregular
cylinders, growing at the surface by the addition of successive
laminæ.
"_Internal structure._--Chambers large, flattened, irregular, with
numerous rounded extensions, and separated by walls of variable
thickness, which are penetrated by septal orifices irregularly
disposed. Thicker parts of the walls with bundles of fine branching
tubuli.
"These characters refer specially to the specimens from Grenville and
the Calumet. There are others from Perth, C. W., which show more
regular laminæ, and in which the tubuli have not yet been observed;
and a specimen from Burgess, C. W., contains some fragments of laminæ
which exhibit, on one side, a series of fine parallel tubuli like
those of Nummulina. These specimens may indicate distinct species;
but on the other hand, their peculiarities may depend on different
states of preservation.
"With respect to this last point, it may be remarked that some of
the specimens from Grenville and the Calumet show the structure of
the laminæ with nearly equal distinctness, whether the chambers are
filled with serpentine or pyroxene, and that even the minute tubuli
are penetrated and filled with these minerals. On the other hand,
there are large specimens in the collection of the Canadian Survey
in which the lower and still parts of the organism are imperfectly
preserved in pyroxene, while the upper parts are more perfectly
mineralized with serpentine."
* * * * *
[The following note was added in a reprint of the paper in the
_Canadian Naturalist_, April, 1865.]
"Since the above was written, thick slices of Eozoon from Grenville
have been prepared, and submitted to the action of hydrochloric acid
until the carbonate of lime was removed. The serpentine then remains
as a cast of the interior of the chambers, showing the form of their
original sarcode-contents. The minute tubuli are found also to have
been filled with a substance insoluble in the acid, so that casts
of these also remain in great perfection, and allow their general
distribution to be much better seen than in the transparent slices
previously prepared. These interesting preparations establish the
following additional structural points:--
"1. That the whole mass of sarcode throughout the organism was
continuous; the apparently detached secondary chambers being, as
I had previously suspected, connected with the larger chambers by
canals filled with sarcode.
"2. That some of the irregular portions without lamination are not
fragmentary, but due to the acervuline growth of the animal; and that
this irregularity has been produced in part by the formation of
projecting patches of supplementary skeleton, penetrated by beautiful
systems of tubuli. These groups of tubuli are in some places very
regular, and have in their axes cylinders of compact calcareous
matter. Some parts of the specimens present arrangements of this kind
as symmetrical as in any modern Foraminiferal shell.
"3. That all except the very thinnest portions of the walls of
the chambers present traces, more or less distinct, of a tubular
structure.
"4. These facts place in more strong contrast the structure of
the regularly laminated species from Burgess, which do not show
tubuli, and that of the Grenville specimens, less regularly
laminated and tubulous throughout. I hesitated however to regard
these two as distinct species, in consequence of the intermediate
characters presented by specimens from the Calumet, which are
regularly laminated like those of Burgess, and tubulous like those
of Grenville. It is possible that in the Burgess specimens, tubuli,
originally present, have been obliterated, and in organisms of this
grade, more or less altered by the processes of fossilisation, large
series of specimens should be compared before attempting to establish
specific distinctions."
(B.) Original Description of the Specimens added by Dr. Carpenter to
the above--in a Letter to Sir W. E. Logan.
[_Journal of Geological Society_, February, 1865.]
"The careful examination which I have made, in accordance with
the request you were good enough to convey to me from Dr. Dawson
and to second on your own part, with the structure of the very
extraordinary fossil which you have brought from the Laurentian
rocks of Canada,[Q] enables me most unhesitatingly to confirm the
sagacious determination of Dr. Dawson as to its Rhizopod characters
and Foraminiferal affinities, and at the same time furnishes new
evidence of no small value in support of that determination. In
this examination I have had the advantage of a series of sections
of the fossil much superior to those submitted to Dr. Dawson; and
also of a large series of decalcified specimens, of which Dr. Dawson
had only the opportunity of seeing a few examples after his memoir
had been written. These last are peculiarly instructive; since
in consequence of the complete infiltration of the chambers and
canals, originally occupied by the sarcode-body of the animal, by
mineral matter insoluble in dilute nitric acid, the removal of the
calcareous shell brings into view, not only the internal casts of
the chambers, but also casts of the interior of the 'canal system'
of the 'intermediate' or 'supplemental skeleton,' and even casts of
the interior of the very fine parallel tubuli which traverse the
proper walls of the chambers. And, as I have remarked elsewhere,[R]
'such casts place before us far more exact representations of the
configuration of the animal body, and of the connections of its
different parts, than we could obtain even from living specimens by
dissolving away their shells with acid; its several portions being
disposed to heap themselves together in a mass when they lose the
support of the calcareous skeleton.'
[Footnote Q: The specimens submitted to Dr. Carpenter were taken from a
block of Eozoon rock, obtained in the Petite Nation seigniory, too late
to afford Dr. Dawson an opportunity of examination. They are from the
same horizon as the Grenville specimens.--W. E. L.]
[Footnote R: _Introduction to the Study of the Foraminifera_, p. 10.]
"The additional opportunities I have thus enjoyed will be found,
I believe, to account satisfactorily for the differences to be
observed between Dr. Dawson's account of the Eozoon and my own. Had
I been obliged to form my conclusions respecting its structure only
from the specimens submitted to Dr. Dawson, I should very probably
have seen no reason for any but the most complete accordance with
his description: while if Dr. Dawson had enjoyed the advantage of
examining the entire series of preparations which have come under my
own observation, I feel confident that he would have anticipated the
corrections and additions which I now offer.
"Although the general plan of growth described by Dr. Dawson, and
exhibited in his photographs of vertical sections of the fossil,
is undoubtedly that which is typical of Eozoon, yet I find that
the acervuline mode of growth, also mentioned by Dr. Dawson, very
frequently takes its place in the more superficial parts, where
the chambers, which are arranged in regular tiers in the laminated
portions, are heaped one upon another without any regularity, as is
particularly well shown in some decalcified specimens which I have
myself prepared from the slices last put into my hands. I see no
indication that this departure from the normal type of structure
has resulted from an injury; the transition from the regular to the
irregular mode of increase not being abrupt but gradual. Nor shall I
be disposed to regard it as a monstrosity; since there are many other
Foraminifera in which an originally definite plan of growth gives
place, in a later stage, to a like acervuline piling-up of chambers.
"In regard to the form and relations of the chambers, I have little
to add to Dr. Dawson's description. The evidence afforded by their
internal casts concurs with that of sections, in showing that the
segments of the sarcode-body, by whose aggregation each layer was
constituted, were but very incompletely divided by shelly partitions;
this incomplete separation (as Dr. Dawson has pointed out) having
its parallel in that of the secondary chambers in Carpenteria. But I
have occasionally met with instances in which the separation of the
chambers has been as complete as it is in Foraminifera generally; and
the communication between them is then established by several narrow
passages exactly corresponding with those which I have described and
figured in Cycloclypeus.[S]
[Footnote S: _Op. cit._, p. 294.]
"The mode in which each successive layer originates from the one
which had preceded it, is a question to which my attention has been
a good deal directed; but I do not as yet feel confident that I
have been able to elucidate it completely. There is certainly no
regular system of apertures for the passage of stolons giving origin
to new segments, such as are found in all ordinary Polythalamous
Foraminifera, whether their type of growth be rectilinear, spiral,
or cyclical; and I am disposed to believe that where one layer is
separated from another by nothing else than the proper walls of
the chambers,--which, as I shall presently show, are traversed by
multitudes of minute tubuli giving passage to pseudopodia,--the
coalescence of these pseudopodia on the external surface would
suffice to lay the foundation of a new layer of sarcodic segments.
But where an intermediate or supplemental skeleton, consisting of a
thick layer of solid calcareous shell, has been deposited between
two successive layers, it is obvious that the animal body contained
in the lower layer of chambers must be completely cut off from
that which occupies the upper, unless some special provision exist
for their mutual communication. Such a provision I believe to have
been made by the extension of bands of sarcode, through canals left
in the intermediate skeleton, from the lower to the upper tier of
chambers. For in such sections as happen to have traversed thick
deposits of the intermediate skeleton, there are generally found
passages distinguished from those of the ordinary canal-system by
their broad flat form, their great transverse diameter, and their
non-ramification. One of these passages I have distinctly traced
to a chamber, with the cavity of which it communicated through two
or three apertures in its proper wall; and I think it likely that
I should have been able to trace it at its other extremity into a
chamber of the superjacent tier, had not the plane of the section
passed out of its course. Riband-like casts of these passages are
often to be seen in decalcified specimens, traversing the void spaces
left by the removal of the thickest layers of the intermediate
skeleton.
"But the organization of a new layer seems to have not unfrequently
taken place in a much more considerable extension of the sarcode-body
of the pre-formed layer; which either folded back its margin
over the surface already consolidated, in a manner somewhat like
that in which the mantle of a Cyprœa doubles back to deposit
the final surface-layer of its shell, or sent upwards wall-like
lamellæ, sometimes of very limited extent, but not unfrequently of
considerable length, which, after traversing the substance of the
shell, like trap-dykes in a bed of sandstone, spread themselves out
over its surface. Such, at least, are the only interpretations I can
put upon the appearances presented by decalcified specimens. For
on the one hand, it is frequently to be observed that two bands of
serpentine (or other infiltrated mineral), which represent two layers
of the original sarcode-body of the animal, approximate to each other
in some part of their course, and come into complete continuity;
so that the upper layer would seem at that part to have had its
origin in the lower. Again, even where these bands are most widely
separated, we find that they are commonly held together by vertical
lamellæ of the same material, sometimes forming mere tongues, but
often running to a considerable length. That these lamellæ have not
been formed by mineral infiltration into accidental fissures in the
shell, but represent corresponding extensions of the sarcode-body,
seems to me to be indicated not merely by the characters of their
surface, but also by the fact that portions of the canal-system may
be occasionally traced into connection with them.
"Although Dr. Dawson has noticed that some parts of the sections
which he examined present the fine tubulation characteristic of
the shells of the Nummuline Foraminifera, he does not seem to have
recognised the fact, which the sections placed in my hands have
enabled me most satisfactorily to determine,--that the proper
walls of the chambers everywhere present the fine tubulation of
the Nummuline shell; a point of the highest importance in the
determination of the affinities of Eozoon. This tubulation, although
not seen with the clearness with which it is to be discerned in
recent examples of the Nummuline type, is here far better displayed
than it is in the majority of fossil Nummulites, in which the
tubuli have been filled up by the infiltration of calcareous
matter, rendering the shell-substance nearly homogeneous. In Eozoon
these tubuli have been filled up by the infiltration of a mineral
different from that of which the shell is composed, and therefore
not coalescing with it; and the tubular structure is consequently
much more satisfactorily distinguishable. In decalcified specimens,
the free margins of the casts of the chambers are often seen to be
bordered with a delicate white glistening fringe; and when this
fringe is examined with a sufficient magnifying power, it is seen to
be made up of a multitude of extremely delicate aciculi, standing
side by side like the fibres of asbestos. These, it is obvious, are
the internal casts of the fine tubuli which perforated the proper
wall of the chambers, passing directly from its inner to its outer
surface; and their presence in this situation affords the most
satisfactory confirmation of the evidence of that tubulation afforded
by thin sections of the shell-wall.
"The successive layers, each having its own proper wall, are
often superposed one upon another without the intervention of any
supplemental or intermediate skeleton such as presents itself in
all the more massive forms of the Nummuline series; but a deposit
of this form of shell-substance, readily distinguishable by its
homogeneousness from the finely tubular shell immediately investing
the segments of the sarcode-body, is the source of the great
thickening which the calcareous zones often present in vertical
sections of Eozoon. The presence of this intermediate skeleton has
been correctly indicated by Dr. Dawson; but he does not seem to have
clearly differentiated it from the proper wall of the chambers.
All the tubuli which he has described belong to that canal system
which, as I have shown,[T] is limited in its distribution to the
intermediate skeleton, and is expressly designed to supply a channel
for its nutrition and augmentation. Of this canal system, which
presents most remarkable varieties in dimensions and distribution, we
learn more from the casts presented by decalcified specimens, than
from sections, which only exhibit such parts of it as their plane may
happen to traverse. Illustrations from both sources, giving a more
complete representation of it than Dr. Dawson's figures afford, have
been prepared from the additional specimens placed in my hands.
[Footnote T: _Op. cit._, pp. 50, 51.]
"It does not appear to me that the canal system takes its origin
directly from the cavity of the chambers. On the contrary, I believe
that, as in Calcarina (which Dr. Dawson has correctly referred to as
presenting the nearest parallel to it among recent Foraminifera),
they originate in lacunar spaces on the outside of the proper
walls of the chambers, into which the tubuli of those walls open
externally; and that the extensions of the sarcode-body which
occupied them were formed by the coalescence of the pseudopodia
issuing from those tubuli.[U]
[Footnote U: _Op. cit._, p. 221.]
"It seems to me worthy of special notice, that the canal system,
wherever displayed in transparent sections, is distinguished by a
yellowish brown coloration, so exactly resembling that which I have
observed in the canal system of recent Foraminifera (as Polystomella
and Calcarina) in which there were remains of the sarcode-body, that
I cannot but believe the infiltrating mineral to have been dyed by
the remains of sarcode still existing in the canals of Eozoon at the
time of its consolidation. If this be the case, the preservation
of this colour seems to indicate that no considerable metamorphic
action has been exerted upon the rock in which this fossil occurs.
And I should draw the same inference from the fact that the organic
structure of the shell is in many instances even more completely
preserved than it usually is in the Nummulites and other Foraminifera
of the Nummulitic limestone of the early Tertiaries.
"To sum up,--That the _Eozoon_ finds its proper place in the
Foraminiferal series, I conceive to be conclusively proved by its
accordance with the great types of that series, in all the essential
characters of organization;--namely, the structure of the shell
forming the proper wall of the chambers, in which it agrees precisely
with Nummulina and its allies; the presence of an intermediate
skeleton and an elaborate canal system, the disposition of which
reminds us most of Calcarina; a mode of communication of the chambers
when they are most completely separated, which has its exact parallel
in Cycloclypeus; and an ordinary want of completeness of separation
between the chambers, corresponding with that which is characteristic
of Carpenteria.
"There is no other group of the animal kingdom to which Eozoon
presents the slightest structural resemblance; and to the suggestion
that it may have been of kin to Nullipore, I can offer the most
distinct negative reply, having many years ago carefully studied the
structure of that stony Alga, with which that of Eozoon has nothing
whatever in common.
"The objections which not unnaturally occur to those familiar with
only the ordinary forms of Foraminifera, as to the admission of
Eozoon into the series, do not appear to me of any force. These have
reference in the first place to the great _size_ of the organism; and
in the second, to its exceptional mode of growth.
"1. It must be borne in mind that all the Foraminifera normally
increase by the continuous gemmation of new segments from those
previously formed; and that we have, in the existing types, the
greatest diversities in the extent to which this gemmation may
proceed. Thus in the Globigerinæ, whose shells cover to an unknown
thickness the sea bottom of all that portion of the Atlantic Ocean
which is traversed by the Gulf Stream, only eight or ten segments
are ordinarily produced by continuous gemmation; and if new segments
are developed from the last of these, they detach themselves so
as to lay the foundation of independent Globigerinæ. On the other
hand in Cycloclypeus, which is a discoidal structure attaining two
and a quarter inches in diameter, the number of segments formed by
continuous gemmation must be many thousand. Again, the Receptaculites
of the Canadian Silurian rocks, shown by Mr. Salter's drawings[V]
to be a gigantic Orbitolite, attains a diameter of twelve inches;
and if this were to increase by vertical as well as by horizontal
gemmation (after the manner of Tinoporus or Orbitoides) so that one
discoidal layer would be piled on another, it would form a mass
equalling Eozoon in its ordinary dimensions. To say, therefore, that
Eozoon cannot belong to the Foraminifera on account of its gigantic
size, is much as if a botanist who had only studied plants and
shrubs were to refuse to admit a tree into the same category. The
very same continuous gemmation which has produced an Eozoon would
produce an equal mass of independent Globigerinæ, if after eight
or ten repetitions of the process, the new segments were to detach
themselves.
[Footnote V: _First Decade of Canadian Fossils_, pl. x.]
"It is to be remembered, moreover, that the largest masses of sponges
are formed by continuous gemmation from an original Rhizopod segment;
and that there is no _à priori_ reason why a Foraminiferal organism
should not attain the same dimensions as a Poriferal one,--the
intimate relationship of the two groups, notwithstanding the
difference between their skeletons, being unquestionable.
"2. The difficulty arising from the zoophytic plan of growth of
Eozoon is at once disposed of by the fact that we have in the recent
Polytrema (as I have shown, _op. cit._, p. 235) an organism nearly
allied in all essential points of structure to Rotalia, yet no
less aberrant in its plan of growth, having been ranked by Lamarck
among the Millepores. And it appears to me that Eozoon takes its
place quite as naturally in the Nummuline series as Polytrema in
the Rotaline. As we are led from the typical Rotalia, through the
less regular Planorbulina, to Tinoporus, in which the chambers are
piled up vertically, as well as multiplied horizontally, and thence
pass by an easy gradation to Polytrema, in which all regularity of
external form is lost; so may we pass from the typical Operculina or
Nummulina, through Heterostegina and Cycloclypeus to Orbitoides, in
which, as in Tinoporus, the chambers multiply both by horizontal and
by vertical gemmation; and from Orbitoides to Eozoon the transition
is scarcely more abrupt than from Tinoporus to Polytrema.
"The general acceptance, by the most competent judges, of my views
respecting the primary value of the characters furnished by the
intimate structure of the shell, and the very subordinate value
of plan of growth, in the determination of the affinities of
Foraminifera, renders it unnecessary that I should dwell further on
my reasons for unhesitatingly affirming the Nummuline affinities of
Eozoon from the microscopic appearances presented by the proper wall
of its chambers, notwithstanding its very aberrant peculiarities;
and I cannot but feel it to be a feature of peculiar interest in
geological inquiry, that the true relations of by far the earliest
fossil yet known should be determinable by the comparison of a
portion which the smallest pin's head would cover, with organisms at
present existing."
(C.) Note on Specimens From Long Lake and Wentworth.
[_Journal of Geological Society_, August, 1867.]
"Specimens from Long Lake, in the collection of the Geological
Survey of Canada, exhibit white crystalline limestone with light
green compact or septariiform[W] serpentine, and much resemble some
of the serpentine limestones of Grenville. Under the microscope the
calcareous matter presents a delicate areolated appearance, without
lamination; but it is not an example of acervuline Eozoon, but rather
of fragments of such a structure, confusedly aggregated together, and
having the interstices and cell-cavities filled with serpentine. I
have not found in any of these fragments a canal system similar to
that of Eozoon Canadense, though there are casts of large stolons,
and, under a high power, the calcareous matter shows in many places
the peculiar granular or cellular appearance which is one of the
characters of the supplemental skeleton of that species. In a few
places a tubulated cell-wall is preserved, with structure similar to
that of Eozoon Canadense.
[Footnote W: I use the term "septariiform" to denote the _curdled_
appearance so often presented by the Laurentian serpentine.]
"Specimens of Laurentian limestone from Wentworth, in the collection
of the Geological Survey, exhibit many rounded silicious bodies, some
of which are apparently grains of sand, or small pebbles; but others,
especially when freed from the calcareous matter by a dilute acid,
appear as rounded bodies, with rough surfaces, either separate or
aggregated in lines or groups, and having minute vermicular processes
projecting from their surfaces. At first sight these suggest the
idea of spicules; but I think it on the whole more likely that
they are casts of cavities and tubes belonging to some calcareous
Foraminiferal organism which has disappeared. Similar bodies, found
in the limestone of Bavaria, have been described by Gümbel, who
interprets them in the same way. They may also be compared with the
silicious bodies mentioned in a former paper as occurring in the
loganite filling the chambers of specimens of _Eozoon_ from Burgess."
These specimens will be more fully referred to under Chapter VI.
(D.) Additional Structural Facts.
I may mention here a peculiar and interesting structure which has
been detected in one of my specimens while these sheets were passing
through the press. It is an abnormal thickening of the calcareous
wall, extending across several layers, and perforated with large
parallel cylindrical canals, filled with dolomite, and running in
the direction of the laminæ; the intervening calcite being traversed
by a very fine and delicate canal system. It makes a nearer approach
to some of the Stromatoporæ mentioned in Chapter VI. than any other
Laurentian structure hitherto observed, and may be either an abnormal
growth of Eozoon, consequent on some injury, or a parasitic mass of
some Stromatoporoid organism overgrown by the laminæ of the fossil.
The structure of the dolomite in this specimen indicates that it
first lined the canals, and afterward filled them; an appearance
which I have also observed recently in the larger canals filled
with serpentine (Plate VIII., fig. 5). The cut below is an attempt,
only partially successful, to show the Amœba-like appearance, when
magnified, of the casts of the chambers of Eozoon, as seen on the
decalcified surface of a specimen broken parallel to the laminæ.
[Illustration: Fig. 21_a_.]
[Illustration:
Plate V.
_Nature-print of Eozoon, showing laminated, acervuline, and fragmental
portions._
This is printed from an electrotype taken from an etched slab of
Eozoon, and not touched with a graver except to remedy some accidental
flaws in the plate. The diagonal white line marks the course of a
calcite vein.]