CONTEMPORARIES AND SUCCESSORS OF EOZOON.
The name Eozoon, or Dawn-animal, raises the question whether we shall
ever know any earlier representative of animal life. Here I think
it necessary to explain that in suggesting the name Eozoon for the
earliest fossil, and Eozoic for the formation in which it is contained,
I had no intention to affirm that there may not have been precursors
of the Dawn-animal. By the similar term, Eocene, Lyell did not mean
to affirm that there may not have been modern types in the preceding
geological periods: and so the dawn of animal life may have had its
gray or rosy breaking at a time long anterior to that in which Eozoon
built its marble reefs. When the fossils of this early auroral time
shall be found, it will not be hard to invent appropriate names for
them. There are, however, two reasons that give propriety to the
name in the present state of our knowledge. One is, that the Lower
Laurentian rocks are absolutely the oldest that have yet come under
the notice of geologists, and at the present moment it seems extremely
improbable that any older sediments exist, at least in a condition to
be recognised as such. The other is that Eozoon, as a member of the
group Protozoa, of gigantic size and comprehensive type, and oceanic in
its habitat, is as likely as any other creature that can be imagined
to have been the first representative of animal life on our planet.
Vegetable life may have preceded it, nay probably did so by at least
one great creative æon, and may have accumulated previous stores of
organic matter; but if any older forms of animal life existed, it is
certain at least that they cannot have belonged to much simpler or more
comprehensive types. It is also to be observed that such forms of life,
if they did exist, may have been naked protozoa, which may have left no
sign of their existence except a minute trace of carbonaceous matter,
and perhaps not even this.
But if we do not know, and perhaps we are not likely to know, any
animals older than Eozoon, may we not find traces of some of its
contemporaries, either in the Eozoon limestones themselves, or other
rocks associated with them? Here we must admit that a deep sea
Foraminiferal limestone may give a very imperfect indication of the
fauna of its time. A dredger who should have no other information as
to the existing population of the world, except what he could gather
from the deposits formed under several hundred fathoms of water, would
necessarily have very inadequate conceptions of the matter. In like
manner a geologist who should have no other information as to the
animal life of the Mesozoic ages than that furnished by some of the
thick beds of white chalk might imagine that he had reached a period
when the simplest kinds of protozoa predominated over all other
forms of life; but this impression would at once be corrected by the
examination of other deposits of the same age: so our inferences as to
the life of the Laurentian from the contents of its oceanic limestones
may be very imperfect, and it may yet yield other and various fossils.
Its possibilities are, however, limited by the fact that before we
reach this great depth in the earth's crust, we have already left
behind in much newer formations all traces of animal life except a
few of the lower forms of aquatic invertebrates; so that we are not
surprised to find only a limited number of living things, and those of
very low type. Do we then know in the Laurentian even a few distinct
species, or is our view limited altogether to Eozoon Canadense? In
answering this question we must bear in mind that the Laurentian itself
was of vast duration, and that important changes of life may have taken
place even between the deposition of the Eozoon limestones and that
of those rocks in which we find the comparatively rich fauna of the
Primordial age. This subject was discussed by the writer as early as
1865, and I may repeat here what could be said in relation to it at
that time:--
"In connection with these remarkable remains, it appeared desirable to
ascertain, if possible, what share these or other organic structures
may have had in the accumulation of the limestones of the Laurentian
series. Specimens were therefore selected by Sir W. E. Logan, and
slices were prepared under his direction. On microscopic examination,
a number of these were found to exhibit merely a granular aggregation
of crystals, occasionally with particles of graphite and other foreign
minerals, or a laminated mixture of calcareous and other matters, in
the manner of some more modern sedimentary limestones. Others, however,
were evidently made up almost entirely of fragments of Eozoon, or of
mixtures of these with other calcareous and carbonaceous fragments
which afford more or less evidence of organic origin. The contents of
these organic limestones may be considered under the following heads:--
1. Remains of Eozoon.
2. Other calcareous bodies, probably organic.
3. Objects imbedded in the serpentine.
4. Carbonaceous matters.
5. Perforations, or worm-burrows.
"1. The more perfect specimens of Eozoon do not constitute the mass
of any of the larger specimens in the collection of the Survey; but
considerable portions of some of them are made up of material of
similar minute structure, destitute of lamination, and irregularly
arranged. Some of this material gives the impression that there may
have been organisms similar to Eozoon, but growing in an irregular
or acervuline manner without lamination. Of this, however, I cannot
be certain; and on the other hand there is distinct evidence of the
aggregation of fragments of Eozoon in some of these specimens. In
some they constitute the greater part of the mass. In others they
are embedded in calcareous matter of a different character, or in
serpentine or granular pyroxene. In most of the specimens the cells of
the fossils are more or less filled with these minerals; and in some
instances it would appear that the calcareous matter of fragments of
Eozoon has been in part replaced by serpentine."
"2. Intermixed with the fragments of Eozoon above referred to, are
other calcareous matters apparently fragmentary. They are of various
angular and rounded forms, and present several kinds of structure. The
most frequent of these is a strong lamination varying in direction
according to the position of the fragments, but corresponding, as
far as can be ascertained, with the diagonal of the rhombohedral
cleavage. This structure, though crystalline, is highly characteristic
of crinoidal remains when preserved in altered limestones. The more
dense parts of Eozoon, destitute of tubuli, also sometimes show this
structure, though less distinctly. Other fragments are compact and
structureless, or show only a fine granular appearance; and these
sometimes include grains, patches, or fibres of graphite. In Silurian
limestones, fragments of corals and shells which have been partially
infiltrated with bituminous matter, show a structure like this. On
comparison with altered organic limestones of the Silurian system,
these appearances would indicate that in addition to the debris of
Eozoon, other calcareous structures, more like those of crinoids,
corals, and shells, have contributed to the formation of the
Laurentian limestones.
"3. In the serpentine[AE] filling the chambers of a large specimen of
Eozoon from Burgess, there are numerous small pieces of foreign matter;
and the silicate itself is laminated, indicating its sedimentary
nature. Some of the included fragments appear to be carbonaceous,
others calcareous; but no distinct organic structure can be detected
in them. There are, however, in the serpentine, many minute silicious
grains of a bright green colour, resembling green-sand concretions;
and the manner in which these are occasionally arranged in lines and
groups, suggests the supposition that they may possibly be casts of
the interior of minute Foraminiferal shells. They may, however, be
concretionary in their origin.
[Footnote AE: This is the dark green mineral named loganite by Dr.
Hunt.]
"4. In some of the Laurentian limestones submitted to me by Sir W.
E. Logan, and in others which I collected some years ago at Madoc,
Canada West, there are fibres and granules of carbonaceous matter,
which do not conform to the crystalline structure, and present forms
quite similar to those which in more modern limestones result from
the decomposition of algæ. Though retaining mere traces of organic
structure, no doubt would be entertained as to their vegetable origin
if they were found in fossiliferous limestones.
"5. A specimen of impure limestone from Madoc, in the collection of
the Canadian Geological Survey, which seems from its structure to
have been a finely laminated sediment, shows perforations of various
sizes, somewhat scalloped at the sides, and filled with grains of
rounded silicious sand. In my own collection there are specimens
of micaceous slate from the same region, with indications on their
weathered surfaces of similar rounded perforations, having the aspect
of Scolithus, or of worm-burrows.
"Though the abundance and wide distribution of Eozoon, and the
important part it seems to have acted in the accumulation of limestone,
indicate that it was one of the most prevalent forms of animal
existence in the seas of the Laurentian period, the non-existence of
other organic beings is not implied. On the contrary, independently of
the indications afforded by the limestones themselves, it is evident
that in order to the existence and growth of these large Rhizopods, the
waters must have swarmed with more minute animal or vegetable organisms
on which they could subsist. On the other hand, though this is a less
certain inference, the dense calcareous skeleton of Eozoon may indicate
that it also was liable to the attacks of animal enemies. It is also
possible that the growth of Eozoon, or the deposition of the serpentine
and pyroxene in which its remains have been preserved, or both, may
have been connected with certain oceanic depths and conditions, and
that we have as yet revealed to us the life of only certain stations
in the Laurentian seas. Whatever conjectures we may form on these more
problematic points, the observations above detailed appear to establish
the following conclusions:--
"First, that in the Laurentian period, as in subsequent geological
epochs, the Rhizopods were important agents in the accumulation of
beds of limestone; and secondly, that in this early period these low
forms of animal life attained to a development, in point of magnitude
and complexity, unexampled, in so far as yet known, in the succeeding
ages of the earth's history. This early culmination of the Rhizopods is
in accordance with one of the great laws of the succession of living
beings, ascertained from the study of the introduction and progress of
other groups; and, should it prove that these great Protozoans were
really the dominant type of animals in the Laurentian period, this fact
might be regarded as an indication that in these ancient rocks we may
actually have the records of the first appearance of animal life on our
planet."
With reference to the first of the above heads, I have now to state
that it seems quite certain that the upper and younger portions of
the masses of Eozoon often passed into the acervuline form, and the
period in which this change took place seems to have depended on
circumstances. In some specimens there are only a few regular layers,
and then a heap of irregular cells. In other cases a hundred or more
regular layers were formed; but even in this case little groups of
irregular cells occurred at certain points near the surface. This
may be seen in plate III. I have also found some masses clearly not
fragmental which consist altogether of acervuline cells. A specimen
of this kind is represented in fig. 31. It is oval in outline, about
three inches in length, wholly made up of rounded or cylindrical
cells, the walls of which have a beautiful tubular structure, but
there is little or no supplemental skeleton. Whether this is a portion
accidentally broken off from the top of a mass of Eozoon, or a
peculiar varietal form, or a distinct species, it would be difficult
to determine. In the meantime I have described it as a variety,
"_acervulina_," of the species Eozoon Canadense.[AF] Another variety
also, from Petite Nation, shows extremely thin laminæ, closely placed
together and very massive, and with little supplemental skeleton. This
may be allied to the last, and may be named variety "_minor_."
[Footnote AF: _Proceedings of Geological Society_, 1875.]
[Illustration: Fig. 31. _Acervuline Variety of Eozoon, St. Pierre._
(_a._) General form, half natural size. (_b._) Portion of cellular
interior, magnified, showing the course of the tubuli.]
All this, however, has nothing to do with the layers of fragments of
Eozoon which are scattered through the Laurentian limestones. In these
the fossil is sometimes preserved in the ordinary manner, with its
cavities filled with serpentine, and the thicker parts of the skeleton
having their canals filled with this substance. In this case the
chambers may have been occupied with serpentine before it was broken
up. At St. Pierre there are distinct layers of this kind, from half an
inch to several inches in thickness, regularly interstratified with
the ordinary limestone. In other layers no serpentine occurs, but the
interstices of the fragments are filled with crystalline dolomite or
magnesian limestone, which has also penetrated the canals; and there
are indications, though less manifest, that some at least of the layers
of pure limestone are composed of fragmental Eozoon. In the Laurentian
limestone of Wentworth, belonging apparently to the same band with
that of St. Pierre, there are many small rounded pieces of limestone,
evidently the debris of some older rock, broken up and rounded by
attrition. In some of these fragments the structure of Eozoon may be
plainly perceived. This shows that still older limestones composed of
Eozoon were at that time undergoing waste, and carries our view of the
existence of this fossil back to the very beginning of the Laurentian.
With respect to organic fragments not showing the structure of Eozoon,
I have not as yet been able to refer these to any definite origin. Some
of them may be simply thick portions of the shell of Eozoon with their
pores filled with calcite, so as to present a homogeneous appearance.
Others have much the appearance of fragments of such Primordial forms
as _Archæocyathus_, to be described in the sequel; but after much
careful search, I have thus far been unable to say more than I could
say in 1865.
[Illustration: Fig. 32. _Archæospherinæ from St. Pierre._
(_a._) Specimens dissolved out by acid. The lower one showing interior
septa. (_b._) Specimens seen in section.]
[Illustration: Fig. 33. _Archæospherinæ from Burgess Eozoon._
Magnified.]
[Illustration: Fig. 34. _Archæospherinæ from Wentworth Limestone._
Magnified.]
It is different, however, with the round cells infiltrated with
serpentine and with the silicious grains included in the loganite. I
have already referred to and figured (fig. 18) the remarkable rounded
bodies occurring at Long Lake. I now figure similar bodies found mixed
with fragmental Eozoon and in separate thin layers at St. Pierre (fig.
32), also some of the singular grains found in the loganite occupying
the chambers of Eozoon from Burgess (fig. 33), and a beaded body set
free by acid, with others of irregular forms, from the limestone of
Wentworth (fig. 34). All these I think are essentially of the same
nature, namely, chambers originally invested with a tubulated wall
like Eozoon, and aggregated in groups, sometimes in a linear manner,
sometimes spirally, like those Globigerinæ which constitute the mass
of modern deep-sea dredgings and also of the chalk. These bodies occur
dispersed in the limestone, arranged in thin layers parallel to the
bedding or sometimes in the large chamber-cavities of Eozoon. They
are so variable in size and form that it is not unlikely they may be
of different origins. The most probable of these may be thus stated.
First, they may in some cases be the looser superficial parts of the
surface of Eozoon broken up into little groups of cells. Secondly,
they may be few-celled germs or buds given off from Eozoon. Thirdly,
they may be smaller Foraminifera, structurally allied to Eozoon, but
in habit of growth resembling those little globe-shaped forms which,
as already stated, abound in chalk and in the modern ocean. The latter
view I should regard as highly probable in the case of many of them;
and I have proposed for them, in consequence, and as a convenient name,
_Archæospherinæ_, or ancient spherical animals.
Carbonaceous matter is rare in the true Eozoon limestones, and, as
already stated, I would refer the Laurentian graphite or plumbago
mainly to plants. With regard to the worm-burrows referred to in 1865,
there can be no doubt of their nature, but there is some doubt as to
whether the beds that contain them are really Lower Laurentian. They
may be Upper Laurentian or Huronian. I give here figures of these
burrows as published in 1866[AG] (fig. 35). The rocks which contain
them hold also fragments of Eozoon, and are not known to contain other
fossils.
[Footnote AG: _Journal of Geological Society._]
[Illustration: Fig. 35. _Annelid Burrows, Laurentian or Huronian._
Fig 1. _Transverse section of Worm-burrow_--magnified, as a transparent
object. (_a._) Calcareo-silicious rock. (_b._) Space filled with
calcareous spar. (_c._) Sand agglutinated and stained black. (_d._)
Sand less agglutinated and uncoloured. Fig. 2. _Transverse section of
Worm-burrow on weathered surface_, natural size. Fig. 3. _The same_,
magnified.]
If we now turn to other countries in search of contemporaries of
Eozoon, I may refer first to some specimens found by my friend Dr.
Honeyman at Arisaig, in Nova Scotia, in beds underlying the Silurian
rocks of that locality, but otherwise of uncertain age. I do not vouch
for them as Laurentian, and if of that age they seem to indicate a
species distinct from that of Canada proper. They differ in coarser
tubulation, and in their canals being large and beaded, and less
divergent. I proposed for these specimens, in some notes contributed to
the survey of Canada, the name _Eozoon Acadianum_.
Dr. Gümbel, the Director of the Geological Survey of Bavaria, is
one of the most active and widely informed of European geologists,
combining European knowledge with an extensive acquaintance with the
larger and in some respects more typical areas of the older rocks in
America, and stratigraphical geology with enthusiastic interest in the
microscopic structures of fossils. He at once and in a most able manner
took up the question of the application of the discoveries in Canada
to the rocks of Bavaria. The spirit in which he did so may be inferred
from the following extract:--
"The discovery of organic remains in the crystalline limestones of the
ancient gneiss of Canada, for which we are indebted to the researches
of Sir William Logan and his colleagues, and to the careful microscopic
investigations of Drs. Dawson and Carpenter, must be regarded as
opening a new era in geological science.
"This discovery overturns at once the notions hitherto commonly
entertained with regard to the origin of the stratified primary
limestones, and their accompanying gneissic and quartzose strata,
included under the general name of primitive crystalline schists. It
shows us that these crystalline stratified rocks, of the so-called
primary system, are only a backward prolongation of the chain of
fossiliferous strata; the elements of which were deposited as oceanic
sediment, like the clay-slates, limestones, and sandstones of the
palæozoic formations, and under similar conditions, though at a time
far more remote, and more favourable to the generation of crystalline
mineral compounds.
"In this discovery of organic remains in the primary rocks, we hail
with joy the dawn of a new epoch in the critical history of these
earlier formations. Already in its light, the primeval geological time
is seen to be everywhere animated, and peopled with new animal forms
of whose very existence we had previously no suspicion. Life, which
had hitherto been supposed to have first appeared in the Primordial
division of the Silurian period, is now seen to be immeasurably
lengthened beyond its former limit, and to embrace in its domain the
most ancient known portions of the earth's crust. It would almost
seem as if organic life had been awakened simultaneously with the
solidification of the earth's crust.
"The great importance of this discovery cannot be clearly understood,
unless we first consider the various and conflicting opinions
and theories which had hitherto been maintained concerning the
origin of these primary rocks. Thus some, who consider them as the
first-formed crust of a previously molten globe, regard their apparent
stratification as a kind of concentric parallel structure, developed
in the progressive cooling of the mass from without. Others, while
admitting a similar origin of these rocks, suppose their division
into parallel layers to be due, like the lamination of clay-slates,
to lateral pressure. If we admit such views, the igneous origin of
schistose rocks becomes conceivable, and is in fact maintained by many.
"On the other hand, we have the school which, while recognising the
sedimentary origin of these crystalline schists, supposes them to
have been metamorphosed at a later period; either by the internal
heat, acting in the deeply buried strata; by the proximity of eruptive
rocks; or finally, through the agency of permeating waters charged with
certain mineral salts.
"A few geologists only have hitherto inclined to the opinion that
these crystalline schists, while possessing real stratification,
and sedimentary in their origin, were formed at a period when the
conditions were more favourable to the production of crystalline
materials than at present. According to this view, the crystalline
structure of these rocks is an original condition, and not one
superinduced at a later period by metamorphosis. In order, however,
to arrange and classify these ancient crystalline rocks, it becomes
necessary to establish by superposition, or by other evidence,
differences in age, such as are recognised in the more recent
stratified deposits. The discovery of similar organic remains,
occupying a determinate position in the stratification, in different
and remote portions of these primitive rocks, furnishes a powerful
argument in favour of the latter view, as opposed to the notion which
maintains the metamorphic origin of the various minerals and rocks of
these ancient formations; so that we may regard the direct formation of
these mineral elements, at least so far as these fossiliferous primary
limestones are concerned, as an established fact."
His first discovery is thus recorded, in terms which show the very
close resemblance of the Bavarian and Canadian Eozoic.
"My discovery of similar organic remains in the serpentine-limestone
from near Passau was made in 1865, when I had returned from my
geological labours of the summer, and received the recently published
descriptions of Messrs. Logan, Dawson, etc. Small portions of this
rock, gathered in the progress of the Geological Survey in 1854,
and ever since preserved in my collection, having been submitted
to microscopic examination, confirmed in the most brilliant manner
the acute judgment of the Canadian geologists, and furnished
palæontological evidence that, notwithstanding the great distance which
separates Canada from Bavaria, the equivalent primitive rocks of the
two regions are characterized by similar organic remains; showing at
the same time that the law governing the definite succession of organic
life on the earth is maintained even in these most ancient formations.
The fragments of serpentine-limestone, or ophicalcite, in which I first
detected the existence of Eozoon, were like those described in Canada,
in which the lamellar structure is wanting, and offer only what Dr.
Carpenter has called an acervuline structure. For further confirmation
of my observations, I deemed it advisable, through the kindness of
Sir Charles Lyell, to submit specimens of the Bavarian rock to the
examination of that eminent authority, Dr. Carpenter, who, without any
hesitation, declared them to contain Eozoon.
"This fact being established, I procured from the quarries near Passau
as many specimens of the limestone as the advanced season of the year
would permit; and, aided by my diligent and skillful assistants,
Messrs. Reber and Schwager, examined them by the methods indicated by
Messrs. Dawson and Carpenter. In this way I soon convinced myself of
the general similarity of our organic remains with those of Canada.
Our examinations were made on polished sections and in portions etched
with dilute nitric acid, or, better, with warm acetic acid. The most
beautiful results were however obtained by etching moderately thin
sections, so that the specimens may be examined at will either by
reflected or transmitted light.
"The specimens in which I first detected Eozoon came from a quarry
at Steinhag, near Obernzell, on the Danube, not far from Passau. The
crystalline limestone here forms a mass from fifty to seventy feet
thick, divided into several beds, included in the gneiss, whose general
strike in this region is N.W., with a dip of 40°-60° N.E. The limestone
strata of Steinhag have a dip of 45° N.E. The gneiss of this vicinity
is chiefly grey, and very silicious, containing dichroite, and of
the variety known as dichroite-gneiss; and I conceive it to belong,
like the gneiss of Bodenmais and Arber, to that younger division of
the primitive gneiss system which I have designated as the Hercynian
gneiss formation; which, both to the north, between Tischenreuth and
Mahring, and to the south on the north-west of the mountains of Ossa,
is immediately overlaid by the mica-slate formation. Lithologically,
this newer division of the gneiss is characterized by the predominance
of a grey variety, rich in quartz, with black magnesian-mica and
orthoclase, besides which a small quantity of oligoclase is never
wanting. A further characteristic of this Hercynian gneiss is the
frequent intercalation of beds of rocks rich in hornblende, such as
hornblende-schist, amphibolite, diorite, syenite, and syenitic granite,
and also of serpentine and granulite. Beds of granular limestone,
or of calcareous schists are also never altogether wanting; while
iron pyrites and graphite, in lenticular masses, or in local beds
conformable to the great mass of the gneiss strata, are very generally
present.
"In the large quarry of Steinhag, from which I first obtained the
Eozoon, the enclosing rock is a grey hornblendic gneiss, which
sometimes passes into a hornblende-slate. The limestone is in many
places overlaid by a bed of hornblende-schist, sometimes five feet
in thickness, which separates it from the normal gneiss. In many
localities, a bed of serpentine, three or four feet thick, is
interposed between the limestone and the hornblende-schist; and in
some cases a zone, consisting chiefly of scapolite, crystalline and
almost compact, with an admixture however of hornblende and chlorite.
Below the serpentine band, the crystalline limestone appears divided
into distinct beds, and encloses various accidental minerals, among
which are reddish-white mica, chlorite, hornblende, tremolite,
chondrodite, rosellan, garnet, and scapolite, arranged in bands.
In several places the lime is mingled with serpentine, grains or
portions of which, often of the size of peas, are scattered through
the limestone with apparent irregularity, giving rise to a beautiful
variety of ophicalcite or serpentine-marble. These portions, which are
enclosed in the limestone destitute of serpentine, always present a
rounded outline. In one instance there appears, in a high naked wall
of limestone without serpentine, the outline of a mass of ophicalcite,
about sixteen feet long and twenty-five feet high, which, rising from
a broad base, ends in a point, and is separated from the enclosing
limestone by an undulating but clearly defined margin, as already well
described by Wineberger. This mass of ophicalcite recalls vividly a
reef-like structure. Within this and similar masses of ophicalcite in
the crystalline limestone, there are, so far as my observations in 1854
extend, no continuous lines or concentric layers of serpentine to be
observed, this mineral being always distributed in small grains and
patches. The few apparently regular layers which may be observed are
soon interrupted, and the whole aggregation is irregular."
It will be observed that this acervuline Eozoon of Steinhag appears to
exist in large reefs, and that in its want of lamination it differs
from the Canadian examples. In fossils of low organization, like
Foraminifera, such differences are often accidental and compatible with
specific unity, but yet there may be a difference specifically in the
Bavarian Eozoon as compared with the Canadian.
Gümbel also found in the Finnish and Bavarian limestones knotted
chambers, like those of Wentworth above mentioned (fig. 36), which he
regards as belonging to some other organism than Eozoon; and flocculi
having tubes, pores, and reticulations which would seem to point to the
presence of structures akin to sponges or possibly remains of seaweeds.
These observations Gümbel has extended into other localities in Bavaria
and Bohemia, and also in Silesia and Sweden, establishing the existence
of Eozoon fossils in all the Laurentian limestones of the middle and
north of Europe.
[Illustration: Fig. 36. _Archæospherinæ from Pargas in Finland._
(_After Gümbel._)
Magnified.]
Gümbel has further found in beds overlying the older Eozoic series,
and probably of the same age with the Canadian Huronian, a different
species of Eozoon, with smaller and more contracted chambers, and
still finer and more crowded canals. This, which is to be regarded as
a distinct species, or at least a well-marked varietal form, he has
named _Eozoon Bavaricum_ (fig. 37). Thus this early introduction of
life is not peculiar to that old continent which we sometimes call the
New World, but applies to Europe as well, and Europe has furnished a
successor to Eozoon in the later Eozoic or Huronian period. In rocks of
this age in America, after long search and much slicing of limestones,
I have hitherto failed to find any decided organic remains other than
the Tudor and Madoc specimens of Eozoon. If these are really Huronian
and not Laurentian, the Eozoon from this horizon does not sensibly
differ from that of the Lower Laurentian. The curious limpet-like
objects from Newfoundland, discovered by Murray, and described by
Billings,[AH] under the name _Aspidella_, are believed to be Huronian,
but they have no connection with Eozoon, and therefore need not detain
us here.
[Footnote AH: _Canadian Naturalist_, 1871.]
[Illustration: Fig. 37. _Section of Eozoon Bavaricum, with Serpentine,
from the Crystalline Limestone of the Hercynian primitive Clay-state
Formation at Hohenberg; 25 diameters._
(_a._) Sparry carbonate of lime. (_b._) Cellular carbonate of lime.
(_c._) System of tubuli. (_d._) Serpentine replacing the coarser
ordinary variety. (_e._) Serpentine and hornblende replacing the finer
variety, in the very much contorted portions.]
Leaving the Eozoic age, we find ourselves next in the Primordial or
Cambrian, and here we discover the sea already tenanted by many
kinds of crustaceans and shell-fishes, which have been collected and
described by palæontologists in Bohemia, Scandinavia, Wales, and North
America;[AI] curiously enough, however, the rocks of this age are
not so rich in Foraminifera as those of some succeeding periods. Had
this primitive type played out its part in the Eozoic and exhausted
its energies, and did it remain in abeyance in the Primordial age to
resume its activity in the succeeding times? It is not necessary to
believe this. The geologist is familiar with the fact, that in one
formation he may have before him chiefly oceanic and deep-sea deposits,
and in another those of the shallower waters, and that alternations
of these may, in the same age or immediately succeeding ages, present
very different groups of fossils. Now the rocks and fossils of the
Laurentian seem to be oceanic in character, while the Huronian and
early Primordial rocks evidence great disturbances, and much coarse
and muddy sediment, such as that found in shallows or near the land.
They abound in coarse conglomerates, sandstones and thick beds of slate
or shale, but are not rich in limestones, which do not in the parts
of the world yet explored regain their importance till the succeeding
Siluro-Cambrian age. No doubt there were, in the Primordial, deep-sea
areas swarming with Foraminifera, the successors of Eozoon; but these
are as yet unknown or little known, and our known Primordial fauna is
chiefly that of the shallows. Enlarged knowledge may thus bridge over
much of the apparent gap in the life of these two great periods.
[Footnote AI: Barrande, Angelin, Hicks, Hall, Billings, etc.]
Only as yet on the coast of Labrador and neighbouring parts of North
America, and in rocks that were formed in seas that washed the old
Laurentian rocks, in which Eozoon was already as fully sealed up as
it is at this moment, do we find Protozoa which can claim any near
kinship to the proto-foraminifer. These are the fossils of the genus
_Archæocyathus_--"ancient cup-sponges, or cup-foraminifers," which
have been described in much detail by Mr. Billings in the reports of
the Canadian Survey. Mr. Billings regards them as possibly sponges,
or as intermediate between these and Foraminifera, and the silicious
spicules found in some of them justify this view, unless indeed, as
partly suspected by Mr. Billings, these belong to true sponges which
may have grown along with Archæocyathus or attached to it. Certain
it is, however, that if allied to sponges, they are allied also to
Foraminifera, and that some of them deviate altogether from the sponge
type and become calcareous chambered bodies, the animals of which can
have differed very little from those of the Laurentian Eozoon. It is
to these calcareous Foraminiferal species that I shall at present
restrict my attention. I give a few figures, for which I am indebted to
Mr. Billings, of three of his species (figs. 38 to 40), with enlarged
drawings of the structures of one of them which has the most decidedly
foraminiferal characters.
[Illustration: Fig. 38. _Archæocyathus Minganensis--a Primordial
Protozoon._ (_After Billings._)
(_a._) Pores of the inner wall.]
[Illustration: Fig. 39. _Archæocyathus profundus--showing the base of
attachment and radiating chambers._ (_After Billings._)]
[Illustration: Fig. 40. _Archæocyathus Atlanticus--showing outer
surface and longitudinal and transverse sections._ (_After Billings._)]
[Illustration: Fig. 41. _Structures of Archæocyathus Profundus._
(_a._) Lower acervuline portion. (_b._) Upper portion, with three of
the radiating laminæ. (_c._) Portion of lamina with pores and thickened
part with canals. In figs. _a_ and _b_ the calcareous part is unshaded.]
To understand Archæocyathus, let us imagine an inverted cone of
carbonate of lime from an inch or two to a foot in length, and with
its point buried in the mud at the bottom of the sea, while its open
cup extends upward into the water. The lower part buried in the soil
is composed of an irregular acervuline network of thick calcareous
plates, enclosing chambers communicating with one another (figs. 40
and 41 A). Above this where the cup expands, its walls are composed
of thin outer and inner plates, perforated with innumerable holes,
and connected with each other by vertical plates, which are also
perforated with round pores, establishing a communication between the
radiating chambers into which they divide the thickness of the wall
(figs. 38, 39, and 41 B). In such a structure the chambers in the wall
of the cup and the irregular chambers of the base would be filled with
gelatinous animal matter, and the pseudopods would project from the
numerous pores in the inner and outer wall. In the older parts of the
skeleton, the structure is further complicated by the formation of
thin transverse plates, irregular in distribution, and where greater
strength is required a calcareous thickening is added, which in some
places shows a canal system like that of Eozoon (fig. 41, B, C).[AJ]
As compared with Eozoon, the fossils want its fine perforated wall,
but have a more regular plan of growth. There are fragments in the
Eozoon limestones which may have belonged to structures like these;
and when we know more of the deep sea of the Primordial, we may
recover true species of Eozoon from it, or may find forms intermediate
between it and Archæocyathus. In the meantime I know no nearer bond of
connection between Eozoon and the Primordial age than that furnished
by the ancient cup Zoophytes of Labrador, though I have searched very
carefully in the fossiliferous conglomerates of Cambrian age on the
Lower St. Lawrence, which contain rocks of all the formations from the
Laurentian upwards, often with characteristic fossils. I have also made
sections of many of the fossiliferous pebbles in these conglomerates
without finding any certain remains of such organisms, though the
fragments of the crusts of some of the Primordial tribolites, when
their tubuli are infiltrated with dark carbonaceous matter, are so like
the supplemental skeleton of Eozoon, that but for their forms they
might readily be mistaken for it; and associated with them are broken
pieces of other porous organisms which may belong to Protozoa, though
this is not yet certain.
[Footnote AJ: On the whole these curious fossils, if regarded as
Foraminifera, are most nearly allied to the Orbitolites and Dactyloporæ
of the Early Tertiary period, as described by Carpenter.]
Of all the fossils of the Silurian rocks those which most resemble
Eozoon are the _Stromatoporæ_, or "layer-corals," whose resemblance
to the old Laurentian fossil at once struck Sir William Logan; and
these occur in the earliest great oceanic limestones which succeed the
Primordial period, those of the Trenton group, in the Siluro-Cambrian.
From this they extend upward as far as the Devonian, appearing
everywhere in the limestones, and themselves often constituting large
masses of calcareous rock. Our figure (fig. 42) shows a small example
of one of these fossils; and when sawn asunder or broken across and
weathered, they precisely resemble Eozoon in general appearance,
especially when, as sometimes happens, their cell-walls have been
silicified.
[Illustration: Fig. 42. _Stromatopora rugosa, Hall--Lower Silurian,
Canada._ (_After Billings._)
The specimen is of smaller size than usual, and is silicified. It is
probably inverted in position, and the concentric marks on the outer
surface are due to concretions of silica.]
There are, however, different types of these fossils. The most common,
the Stromatoporæ properly so called, consist of concentric layers of
calcareous matter attached to each other by pillar-like processes,
which, as well as the layers, are made up of little threads of
limestone netted together, or radiating from the tops and bottoms of
the pillars, and forming a very porous substance. Though they have
been regarded as corals by some, they are more generally believed
to be Protozoa; but whether more nearly allied to sponges or to
Foraminifera may admit of doubt. Some of the more porous kinds are
not very dissimilar from calcareous sponges, but they generally want
true oscula and pores, and seem better adapted to shield the gelatinous
body of a Foraminifer projecting pseudopods in search of food, than
that of a sponge, living by the introduction of currents of water. Many
of the denser kinds, however, have their calcareous floors so solid
that they must be regarded as much more nearly akin to Foraminifers,
and some of them have the same irregular inosculation of these floors
observed in Eozoon. Figs. 43, A to D, show portions of species of
this description, in which the resemblance to Eozoon in structure and
arrangement of parts is not remote.
[Illustration: Fig. 43. _Structures of Stromatopora._
(_a._) Portion of an oblique section magnified, showing laminæ and
columns. (_b._) Portion of wall with pores, and crusted on both sides
with quartz crystals. (_c._) Thickened portion of wall with canals.
(_d._) Portion of another specimen, showing irregular laminæ and
pillars.]
These fossils, however, show no very distinct canal system or
supplemental skeleton, but this also appears in those forms which have
been called Caunopora or Cœnostroma. In these the plates are traversed
by tubes, or groups of tubes, which in each successive floor give out
radiating and branching canals exactly like those of Eozoon, though
more regularly arranged; and if we had specimens with the canals
infiltrated with glauconite or serpentine, the resemblance would be
perfect. When, as in figs. 44 and 45 A, these canals are seen on the
abraded surface, they appear as little grooves arranged in stars,
which resemble the radiating plates of corals, but this resemblance
is altogether superficial, and I have no doubt that they are really
foraminiferal organisms. This will appear more distinctly from the
sections in fig. 45 B, C, which represents an undescribed species
recently found by Mr. Weston, in the Upper Silurian limestone of
Ontario.
[Illustration: Fig. 44. _Caunopora planulata, Hall--Devonian; showing
the radiating canals on a weathered surface._ (_After Hall._)]
[Illustration: Fig. 45. _Cœnostroma--Guelph Limestone, Upper Silurian,
from a specimen collected by Mr. Weston, showing the canals._
(_a._) Surface with canals, natural size. (_b._) Vertical section,
natural size. (_c._) The same magnified, showing canals and laminæ.]
There are probably many species of these curious fossils, but their
discrimination is difficult, and their nomenclature confused, so that
it would not be profitable to engage the attention of the reader
with it except in a note. Their state of preservation, however, is
so highly illustrative of that of Eozoon that a word as to this
will not be out of place. They are sometimes preserved merely by
infiltration with calcite or dolomite, and in this case it is most
difficult to make out their minute structures. Often they appear
merely as concentrically laminated masses which, but for their mode
of occurrence, might be regarded as mere concretions. In other cases
the cell-walls and pillars are perfectly silicified, and then they
form beautiful microscopic objects, especially when decalcified with
an acid. In still other cases, they are preserved like Eozoon, the
walls being calcareous and the chambers filled with silica. In this
state when weathered or decalcified they are remarkably like Eozoon,
but I have not met with any having their minute pores and tubes so
well preserved as in some of the Laurentian fossils. In many of them,
however, the growth and overlapping of the successive amœba-like coats
of sarcode can be beautifully seen, exactly as on the surface of a
decalcified piece of Eozoon. Those in my collection which most nearly
resemble the Laurentian specimens are from the older part of the Lower
Silurian series; but unfortunately their minute structures are not well
preserved.
In the Silurian and Devonian ages, these Stromatoporæ evidently carried
out the same function as the Eozoon in the Laurentian. Winchell tells
us that in Michigan and Ohio single specimens can be found several feet
in diameter, and that they constitute the mass of considerable beds of
limestone. I have myself seen in Canada specimens a foot in diameter,
with a great number of laminæ. Lindberg[AK] has given a most vivid
account of their occurrence in the Isle of Gothland. He says that they
form beds of large irregular discs and balls, attaining a thickness of
five Swedish feet, and traceable for miles along the coast, and the
individual balls are sometimes a yard in diameter. In some of them the
structure is beautifully preserved. In others, or in parts of them,
it is reduced to a mass of crystalline limestone. This species is of
the Cœnostroma type, and is regarded by Lindberg as a coral, though
he admits its low type and resemblance to Protozoa. Its continuous
calcareous skeleton he rightly regards as fatal to its claim to be a
true sponge. Such a fossil, differing as it does in minute points of
structure from Eozoon, is nevertheless probably allied to it in no very
distant way, and a successor to its limestone-making function. Those
which most nearly approach to Foraminifera are those with thick and
solid calcareous laminæ, and with a radiating canal system; and one
of the most Eozoon-like I have seen, is a specimen of the undescribed
species already mentioned from the Guelph (Upper Silurian) limestone
of Ontario, collected by Mr. Weston, and now in the Museum of the
Geological Survey. I have attempted to represent its structures in fig.
44.
[Footnote AK: _Transactions of Swedish Academy_, 1870.]
[Illustration: Fig. 46. _Receptaculites, restored._ (_After Billings._)
(_a._) Aperture. (_b._) Inner wall. (_c._) Outer wall. (_n._) Nucleus,
or primary chamber. (_v._) Internal cavity.]
[Illustration: Fig. 47. _Diagram of Wall and Tubes of Receptaculites._
(_After Billings._)
(_b._) Inner wall. (_c._) Outer wall. (_d._) Section of plates. (_e._)
Pore of inner wall. (_f._) Canal of inner wall. (_g._) Radial stolon.
(_h._) Cyclical stolon. (_k._) Suture of plates of outer wall.]
[Illustration: Fig. 48. _Receptaculites, Inner Surface of Outer Wall
with the Stolons remaining on its Surface._ (_After Billings._)]
In the rocks extending from the Lower Silurian and perhaps from the
Upper Cambrian to the Devonian inclusive, the type and function of
Eozoon are continued by the Stromatoporæ, and in the earlier part of
this time these are accompanied by the Archæocyathids, and by another
curious form, more nearly allied to the latter than to Eozoon, the
_Receptaculites_. These curious and beautiful fossils, which sometimes
are a foot in diameter, consist, like Archæocyathus, of an outer and
inner coat enclosing a cavity; but these coats are composed of square
plates with pores at the corners, and they are connected by hollow
pillars passing in a regular manner from the outer to the inner coat.
They have been regarded by Salter as Foraminifers, while Billings
considers their nearest analogues to be the seed-like germs of some
modern silicious sponges. On the whole, if not Foraminifera, they must
have been organisms intermediate between these and sponges, and they
certainly constitute one of the most beautiful and complex types of
the ancient Protozoa, showing the wonderful perfection to which these
creatures attained at a very early period. (Figs. 46, 47, 48.)
I might trace these ancient forms of foraminiferal life further up in
the geological series, and show how in the Carboniferous there are
nummulitic shells conforming to the general type of Eozoon, and in some
cases making up the mass of great limestones.[AL] Further, in the great
chalk series and its allied beds, and in the Lower Tertiary, there are
not only vast foraminiferal limestones, but gigantic species reminding
us of Stromatopora and Eozoon.[AM] Lastly, more diminutive species are
doing similar work on a great scale in the modern ocean. Thus we may
gather up the broken links of the chain of foraminiferal life, and
affirm that Eozoon has never wanted some representative to uphold its
family and function throughout all the vast lapse of geological time.
[Footnote AL: _Fusulina_, as recently described by Carpenter,
_Archæodiscus_ of Brady, and the Nummulite recently found in the
Carboniferous of Belgium.]
[Footnote AM: _Parkeria_ and _Loftusia_ of Carpenter.]
NOTES TO CHAPTER VI.
(A.) Stromatoporidæ, Etc.
For the best description of Archæocyathus, I may refer to _The
Palæozoic Fossils of Canada_, by Mr. Billings, vol. i. There also,
and in Mr. Salter's memoir in _The Decades of the Canadian Survey_,
will be found all that is known of the structure of Receptaculites.
For the American Stromatoporæ I may refer to Winchell's paper in the
_Proceedings of the American Association_, 1866; to Professor Hall's
Descriptions of New Species of Fossils from Iowa, _Report of the
State Cabinet, Albany_, 1872; and to the Descriptions of Canadian
Species by Dr. Nicholson, in his _Report on the Palæontology of
Ontario_, 1874.
The genus Stromatopora of Goldfuss was defined by him as consisting
of laminæ of a solid and porous character, alternating and
contiguous, and constituting a hemispherical or sub-globose mass.
In this definition, the porous strata are really those of the
fossil, the alternating solid strata being the stony filling of the
chambers; and the descriptions of subsequent authors have varied
according as, from the state of preservation of the specimens or
other circumstances, the original laminæ or the filling of the spaces
attracted their attention. In the former case the fossil could be
described as consisting of laminæ made up of interlaced fibrils of
calcite, radiating from vertical pillars which connect the laminæ.
In the latter case, the laminæ, appear as solid plates, separated
by very narrow spaces, and perforated with round vertical holes
representing the connecting pillars. These Stromatoporæ range from
the Lower Silurian to the Devonian, inclusive, and many species have
been described; but their limits are not very definite, though there
are undoubtedly remarkable differences in the distances of the laminæ
and in their texture, and in the smooth or mammillated character
of the masses. Hall's genus Stromatocerium belongs to these forms,
and D'Orbigny's genus Sparsispongia refers to mammillated species,
sometimes with apparent oscula.
Phillip's genus Caunopora was formed to receive specimens with
concentric cellular layers traversed by "long vermiform cylindrical
canals;" while Winchell's genus Cœnostroma includes species with
these vermiform canals arranged in a radiate manner, diverging from
little eminences in the concentric laminæ. The distinction between
these last genera does not seem to be very clear, and may depend
on the state of preservation of the specimens. A more important
distinction appears to exist between those that have a single
vertical canal from which the subordinate canals diverge, and those
that have groups of such canals.
Some species of the Cœnostroma group have very dense calcareous
laminæ traversed by the canals; but it does not seem that any
distinction has yet been made between the proper wall and the
intermediate skeleton; and most observers have been prevented from
attending to such structures by the prevailing idea that these
fossils are either corals or sponges, while the state of preservation
of the more delicate tissues is often very imperfect.
(B.) Localities of Eozoon, or of Limestones supposed to contain it.
In Canada the principal localities of Eozoon Canadense are at
Grenville, Petite Nation, the Calumets Rapids, Burgess, Tudor, and
Madoc. At the two last places the fossil occurs in beds which may be
on a somewhat higher horizon than the others. Mr. Vennor has recently
found specimens which have the general form of Eozoon, though the
minute structure is not preserved, at Dalhousie, in Lanark Co.,
Ontario. One specimen from this place is remarkable from having been
mineralized in part by a talcose mineral associated with serpentine.
I have examined specimens from Chelmsford, in Massachusetts, and from
Amity and Warren County, New York, the latter from the collection of
Professor D. S. Martin, which show the canals of Eozoon in a fair
state of preservation, though the specimens are fragmental, and do
not show the laminated structure.
In European specimens of limestones of Laurentian age, from Tunaberg
and Fahlun in Sweden, and from the Western Islands of Scotland, I
have hitherto failed to recognise the characteristic structure of
the fossil. Connemara specimens have also failed to afford me any
satisfactory results, and specimens of a serpentine limestone from
the Alps, collected by M. Favre, and communicated to me by Dr. Hunt,
though in general texture they much resemble acervuline Eozoon, do
not show its minute structures.
[Illustration:
Plate VII.
_Untouched nature-print of part of a large specimen of Eozoon, from
Petite Nation._
The lighter portions are less perfect than in the original, owing to
the finer laminæ of serpentine giving way. The dark band at one side is
one of the deep lacunæ or oscula.]