OPPONENTS AND OBJECTIONS.
The active objectors to the animal nature of Eozoon have been few,
though some of them have returned to the attack with a pertinacity and
determination which would lead one to believe that they think the most
sacred interests of science to be dependent on the annihilation of this
proto-foraminifer. I do not propose here to treat of the objections in
detail. I have presented the case of Eozoon on its own merits, and on
these it must stand. I may merely state that the objectors strive to
account for the existence of Eozoon by purely mineral deposition, and
that the complicated changes which they require to suppose are perhaps
the strongest indirect evidence for the necessity of regarding the
structures as organic. The reader who desires to appreciate this may
consult the notes to this chapter.[AN]
[Footnote AN: Also Rowney and King's papers in _Journal Geological
Society_, August, 1866; and _Proceedings Irish Academy_, 1870 and 1871.]
I confess that I feel disposed to treat very tenderly the position of
objectors. The facts I have stated make large demands on the faith
of the greater part even of naturalists. Very few geologists or
naturalists have much knowledge of the structure of foraminiferal
shells, or would be able under the microscope to recognise them with
certainty. Nor have they any distinct ideas of the appearances of such
structures under different kinds of preservation and mineralisation.
Further, they have long been accustomed to regard the so-called Azoic
rocks as not only destitute of organic remains, but as being in such
a state of metamorphism that these could not have been preserved had
they existed. Few, therefore, are able intelligently to decide for
themselves, and so they are called on to trust to the investigations
of others, and on their testimony to modify in a marked degree their
previous beliefs as to the duration of life on our planet. In these
circumstances it is rather wonderful that the researches made with
reference to Eozoon have met with so general acceptance, and that the
resurrection of this ancient inhabitant of the earth has not aroused
more of the sceptical tendency of our age.
It must not be lost sight of, however, that in such cases there may
exist a large amount of undeveloped and even unconscious scepticism,
which shows itself not in active opposition, but merely in quietly
ignoring this great discovery, or regarding it with doubt, as an
uncertain or unestablished point in science. Such scepticism may best
be met by the plain and simple statements in the foregoing chapters,
and by the illustrations accompanying them. It may nevertheless be
profitable to review some of the points referred to, and to present
some considerations making the existence of Laurentian life less
anomalous than may at first sight be supposed. One of these is the
fact that the discovery of Eozoon brings the rocks of the Laurentian
system into more full harmony with the other geological formations. It
explains the origin of the Laurentian limestones in consistency with
that of similar rocks in the later periods, and in like manner it helps
us to account for the graphite and sulphides and iron ores of these old
rocks. It shows us that no time was lost in the introduction of life
on the earth. Otherwise there would have been a vast lapse of time in
which, while the conditions suitable to life were probably present, no
living thing existed to take advantage of these conditions. Further, it
gives a more simple beginning of life than that afforded by the more
complex fauna of the Primordial age; and this is more in accordance
with what we know of the slow and gradual introduction of new forms of
living things during the vast periods of Palæozoic time. In connection
with this it opens a new and promising field of observation in the
older rocks, and if this should prove fertile, its exploration may
afford a vast harvest of new forms to the geologists of the present and
coming time. This result will be in entire accordance with what has
taken place before in the history of geological discovery. It is not
very long since the old and semi-metamorphic sediments constituting the
great Silurian and Cambrian systems were massed together in geological
classifications as primitive or primary rocks, destitute or nearly
destitute of organic remains. The brilliant discoveries of Sedgwick,
Murchison, Barrande, and a host of others, have peopled these once
barren regions; and they now stretch before our wondering gaze in
the long vistas of early Palæozoic life. So we now look out from the
Cambrian shore upon the vast ocean of the Huronian and Laurentian,
all to us yet tenantless, except for the few organisms, which, like
stray shells cast upon the beach, or a far-off land dimly seen in the
distance, incite to further researches, and to the exploration of the
unknown treasures that still lie undiscovered. It would be a suitable
culmination of the geological work of the last half-century, and one
within reach at least of our immediate successors, to fill up this
great blank, and to trace back the Primordial life to the stage of
Eozoon, and perhaps even beyond this, to predecessors which may have
existed at the beginning of the Lower Laurentian, when the earliest
sediments of that great formation were laid down. Vast unexplored areas
of Laurentian and Huronian rocks exist in the Old World and the New.
The most ample facilities for microscopic examination of rocks may
now be obtained; and I could wish that one result of the publication
of these pages may be to direct the attention of some of the younger
and more active geologists to these fields of investigation. It is to
be observed also that such regions are among the richest in useful
minerals, and there is no reason why search for these fossils should
not be connected with other and more practically useful researches. On
this subject it will not be out of place to quote the remarks which I
made in one of my earlier papers on the Laurentian fossils:--
"This subject opens up several interesting fields of chemical,
physiological, and geological inquiry. One of these relates to the
conclusions stated by Dr. Hunt as to the probable existence of a
large amount of carbonic acid in the Laurentian atmosphere, and of
much carbonate of lime in the seas of that period, and the possible
relation of this to the abundance of certain low forms of plants and
animals. Another is the comparison already instituted by Professor
Huxley and Dr. Carpenter, between the conditions of the Laurentian and
those of the deeper parts of the modern ocean. Another is the possible
occurrence of other forms of animal life than Eozoon and Annelids,
which I have stated in my paper of 1864, after extensive microscopic
study of the Laurentian limestones, to be indicated by the occurrence
of calcareous fragments, differing in structure from Eozoon, but at
present of unknown nature. Another is the effort to bridge over, by
further discoveries similar to that of the _Eozoon Bavaricum_ of
Gümbel, the gap now existing between the life of the Lower Laurentian
and that of the Primordial Silurian or Cambrian period. It is scarcely
too much to say that these inquiries open up a new world of thought and
investigation, and hold out the hope of bringing us into the presence
of the actual origin of organic life on our planet, though this may
perhaps be found to have been Prelaurentian. I would here take the
opportunity of stating that, in proposing the name Eozoon for the
first fossil of the Laurentian, and in suggesting for the period the
name "Eozoic," I have by no means desired to exclude the possibility
of forms of life which may have been precursors of what is now to us
the dawn of organic existence. Should remains of still older organisms
be found in those rocks now known to us only by pebbles in the
Laurentian, these names will at least serve to mark an important stage
in geological investigation."
But what if the result of such investigations should be to produce
more sceptics, or to bring to light mineral structures so resembling
Eozoon as to throw doubt upon the whole of the results detailed in
these chapters? I can fancy that this might be the first consequence,
more especially if the investigations were in the hands of persons
more conversant with minerals than with fossils; but I see no reason
to fear the ultimate results. In any case, no doubt, the value of the
researches hitherto made may be diminished. It is always the fate of
discoverers in Natural Science, either to be followed by opponents who
temporarily or permanently impugn or destroy the value of their new
facts, or by other investigators who push on the knowledge of facts and
principles so far beyond their standpoint that the original discoveries
are cast into the shade. This is a fatality incident to the progress of
scientific work, from which no man can be free; and in so far as such
matters are concerned, we must all be content to share the fate of the
old fossils whose history we investigate, and, having served our day
and generation to give place to others. If any part of our work should
stand the fire of discussion let us be thankful. One thing at least is
certain, that such careful surveys as those in the Laurentian rocks
of Canada which led to the discovery of Eozoon, and such microscopic
examinations as those by which it has been worked up and presented to
the public, cannot fail to yield good results of one kind or another.
Already the attention excited by the controversies about Eozoon, by
attracting investigators to the study of various microscopic and
imitative forms in rocks, has promoted the advancement of knowledge,
and must do so still more. For my own part, though I am not content to
base all my reputation on such work as I have done with respect to this
old fossil, I am willing at least to take the responsibility of the
results I have announced, whatever conclusions may be finally reached;
and in the consciousness of an honest effort to extend the knowledge
of nature, to look forward to a better fame than any that could result
from the most successful and permanent vindication of every detail
of our scientific discoveries, even if they could be pushed to a
point which no subsequent investigation in the same difficult line of
research would be able to overpass.
Contenting myself with these general remarks, I shall, for the benefit
of those who relish geological controversy, append to this chapter a
summary of the objections urged by the most active opponents of the
animal nature of Eozoon, with the replies that may be or have been
given; and I now merely add (in fig. 49) a magnified camera tracing of
a portion of a lamina of Eozoon with its canals and tubuli, to show
more fully the nature of the structures in controversy.
[Illustration: Fig. 49. _Portion of a thin Transverse Slice of a Lamina
of Eozoon, magnified, showing its structure, as traced with the camera._
(_a._) Nummuline wall of under side. (_b._) Intermediate skeleton with
canals. (_a´._) Nummuline wall of upper side. The two lower figures
show the lower and upper sides more highly magnified. The specimen is
one in which the canals are unusually well seen.]
It may be well, however, to sum up the evidence as it has been
presented by Sir W. E. Logan, Dr. Carpenter, Dr. Hunt, and the author,
in a short and intelligible form; and I shall do so under a few brief
heads, with some explanatory remarks:--
1. The Lower Laurentian of Canada, a rock formation whose
distribution, age, and structure have been thoroughly worked out by
the Canadian Survey, is found to contain thick and widely distributed
beds of limestone, related to the other beds in the same way in which
limestones occur in the sediments of other geological formations. There
also occur in the same formation, graphite, iron ores, and metallic
sulphides, in such relations as to suggest the idea that the limestones
as well as these other minerals are of organic origin.
2. In the limestones are found laminated bodies of definite form and
structure, composed of calcite alternating with serpentine and other
minerals. The forms of these bodies suggested a resemblance to the
Silurian Stromatoporæ, and the different mineral substances associated
with the calcite in the production of similar forms, showed that these
were not accidental or concretionary.
3. On microscopic examination, it proved that the calcareous laminæ
of these forms were similar in structure to the shells of modern
and fossil Foraminifera, more especially those of the Rotaline and
Nummuline types, and that the finer structures, though usually filled
with serpentine and other hydrous silicates, were sometimes occupied
with calcite, pyroxene, or dolomite, showing that they must when recent
have been empty canals and tubes.
4. The mode of filling thus suggested for the chambers and tubes of
Eozoon, is precisely that which takes place in modern Foraminifera
filled with glauconite, and in Palæozoic crinoids and corals filled
with other hydrous silicates.
5. The type of growth and structure predicated of Eozoon from the
observed appearances, in its great size, its laminated and acervuline
forms, and in its canal system and tubulation, are not only in
conformity with those of other Foraminifera, but such as might be
expected in a very ancient form of that group.
6. Indications exist of other organic bodies in the limestones
containing Eozoon, and also of the Eozoon being preserved not only in
reefs but in drifted fragmental beds as in the case of modern corals.
7. Similar organic structures have been found in the Laurentian
limestones of Massachusetts and New York, and also in those of various
parts of Europe, and Dr. Gümbel has found an additional species in
rocks succeeding the Laurentian in age.
8. The manner in which the structures of Eozoon are affected by the
faulting, development of crystals, mineral veins, and other effects of
disturbance and metamorphism in the containing rocks, is precisely that
which might be expected on the supposition that it is of organic origin.
9. The exertions of several active and able opponents have failed to
show how, otherwise than by organic agency, such structures as those
of Eozoon can be formed, except on the supposition of pseudomorphism
and replacement, which must be regarded as chemically extravagant, and
which would equally impugn the validity of all fossils determined
by microscopic structure. In like manner all comparisons of these
structures with dendritic and other imitative forms have signally
failed, in the opinion of those best qualified to judge.
Another and perhaps simpler way of putting the case is the
following:--Only three general modes of accounting for the existence
of Eozoon have been proposed. The first is that of Professors King and
Rowney, who regard the chambers and canals filled with serpentine as
arising from the erosion or partial dissolving away of serpentine and
its replacement by calcite. The objections to this are conclusive.
It does not explain the nummuline wall, which has to be separately
accounted for by confounding it, contrary to the observed facts,
with the veins of fibrous serpentine which actually pass through
cracks in the fossil. Such replacement is in the highest degree
unlikely on chemical grounds, and there is no evidence of it in the
numerous serpentine grains, nodules, and bands in the Laurentian
limestones. On the other hand, the opposite replacement, that of
limestone by serpentine, seems to have occurred. The mechanical
difficulties in accounting for the delicate canals on this theory are
also insurmountable. Finally, it does not account for the specimens
preserved in pyroxene and other silicates, and in dolomite and calcite.
A second mode of accounting for the facts is that the Eozoon forms are
merely peculiar concretions. But this fails to account for their great
difference from the other serpentine concretions in the same beds, and
for their regularity of plan and the delicacy of their structure, and
also for minerals of different kinds entering into their composition,
and still presenting precisely the same forms and structures. The only
remaining theory is that of the filling of cavities by infiltration
with serpentine. This accords with the fact that such infiltration by
minerals akin to serpentine exists in fossils in later rocks. It also
accords with the known aqueous origin of the serpentine nodules and
bands, the veins of fibrous serpentine, and the other minerals found
filling the cavities of Eozoon. Even the pyroxene has been shown by
Hunt to exist in the Laurentian in veins of aqueous origin. The only
difficulty existing on this view is how a calcite skeleton with such
chambers, canals, and tubuli could be formed; and this is solved by the
discovery that all these facts correspond precisely with those to be
found in the shells of modern oceanic Foraminifera. The existence then
of Eozoon, its structure, and its relations to the containing rocks and
minerals being admitted, no rational explanation of its origin seems at
present possible other than that advocated in the preceding pages.
If the reader will now turn to Plate VIII., page 207, he will find some
interesting illustrations of several very important facts bearing on
the above arguments. Fig. 1 represents a portion of a very thin slice
of a specimen traversed by veins of fibrous serpentine or chrysotile,
and having the calcite of the walls more broken by cleavage planes
than usual. The portion selected shows a part of one of the chambers
filled with serpentine, which presents the usual curdled aspect
almost impossible to represent in a drawing (_s_). It is traversed
by a branching vein of chrysotile (_s_´), which, where cut precisely
parallel to its fibres, shows clear fine cross lines, indicating the
sides of its constituent prisms, and where the plane of section has
passed obliquely to its fibres, has a curiously stippled or frowsy
appearance. On either side of the serpentine band is the nummuline
or proper wall, showing under a low power a milky appearance, which,
with a higher power, becomes resolved into a tissue of the most
beautiful parallel threads, representing the filling of its tubuli.
Nothing can be more distinct than the appearances presented by this
wall and the chrysotile vein, under every variety of magnifying power
and illumination; and all who have had an opportunity of examining my
specimens have expressed astonishment that appearances so dissimilar
should have been confounded with each other. On the lower side two
indentations are seen in the proper wall (_c_). These are connected
with the openings into small subordinate chamberlets, one of which is
in part included in the thickness of the slice. At the upper and lower
parts of the figure are seen portions of the intermediate skeleton
traversed by canals, which in the lower part are very large, though
from the analogy of other specimens it is probable that they have in
their interstices minute canaliculi not visible in this slice. Fig.
2, from the same specimen, shows the termination of one of the canals
against the proper wall, its end expanding into a wide disc of sarcode
on the surface of the wall, as may be seen in similar structures in
modern Foraminifera. In this specimen the canals are beautifully smooth
and cylindrical, but they sometimes present a knotted or jointed
appearance, especially in specimens decalcified by acids, in which
perhaps some erosion has taken place. They are also occasionally
fringed with minute crystals, especially in those specimens in which
the calcite has been partially replaced with other minerals. Fig. 3
shows an example of faulting of the proper wall, an appearance not
infrequently observed; and it also shows a vein chrysotile crossing the
line of fault, and not itself affected by it--a clear evidence of its
posterior origin. Figs. 4 and 5 are examples of specimens having the
canals filled with dolomite, and showing extremely fine canals in the
interstices of the others: an appearance observed only in the thicker
parts of the skeleton, and when these are very well preserved. These
dolomitized portions require some precautions for their observation,
either in slices or decalcified specimens, but when properly managed
they show the structures in very great perfection. The specimen in fig.
5 is from an abnormally thick portion of intermediate skeleton, having
unusually thick canals, and referred to in a previous chapter.
One object which I have in view in thus minutely directing attention
to these illustrations, is to show the nature of the misapprehensions
which may occur in examining specimens of this kind, and at the same
time the certainty which may be attained when proper precautions are
taken. I may add that such structures as those referred to are best
seen in extremely thin slices, and that the observer must not expect
that every specimen will exhibit them equally well. It is only by
preparing and examining many specimens that the best results can be
obtained. It often happens that one specimen is required to show well
one part of the structures, and a different one to show another; and
previous to actual trial, it is not easy to say which portion of
the structures any particular fragment will show most clearly. This
renders it somewhat difficult to supply one's friends with specimens.
Really good slices can be prepared only from the best material and by
skilled manipulators; imperfect slices may only mislead; and rough
specimens may not be properly prepared by persons unaccustomed to the
work, or if so prepared may not turn out satisfactory, or may not be
skilfully examined. These difficulties, however, Eozoon shares with
other specimens in micro-geology, and I have experienced similar
disappointments in the case of fossil wood.
In conclusion of this part of the subject, and referring to the notes
appended to this chapter for further details, I would express the hope
that those who have hitherto opposed the interpretation of Eozoon as
organic, and to whose ability and honesty of purpose I willingly bear
testimony, will find themselves enabled to acknowledge at least the
reasonable probability of that interpretation of these remarkable forms
and structures.
NOTES TO CHAPTER VII.
(A.) Objections of Profs. King and Rowney.
_Trans. Royal Irish Academy, July, 1869._[AO]
[Footnote AO: Reprinted in the _Annals and Magazine of Natural
History_, May, 1874.]
The following summary, given by these authors, may be taken as
including the substance of their objections to the animal nature of
Eozoon. I shall give them in their words and follow them with short
answers to each.
"1st. The serpentine in ophitic rocks has been shown to present
appearances which can only be explained on the view that it undergoes
structural and chemical changes, causing it to pass into variously
subdivided states, and etching out the resulting portions into a
variety of forms--grains and plates, with lobulated or segmented
surfaces--fibres and aciculi--simple and branching configurations.
Crystals of malacolite, often associated with the serpentine,
manifest some of these changes in a remarkable degree.
"2nd. The 'intermediate skeleton' of Eozoon (which we hold to be
the calcareous matrix of the above lobulated grains, etc.) is
completely paralleled in various crystalline rocks--notably marble
containing grains of coccolite (Aker and Tyree), pargasite (Finland),
chondrodite (New Jersey, etc.)
"3rd. The 'chamber casts' in the acervuline variety of Eozoon are
more or less paralleled by the grains of the mineral silicates in the
pre-cited marbles.
"4th. The 'chamber casts' being composed occasionally of loganite and
malacolite, besides serpentine, is a fact which, instead of favouring
their organic origin, as supposed, must be held as a proof of their
having been produced by mineral agencies; inasmuch as these three
silicates have a close pseudomorphic relationship, and may therefore
replace one another in their naturally prescribed order.
"5th. Dr. Gümbel, observing rounded, cylindrical, or tuberculated
grains of coccolite and pargasite in crystalline calcareous marbles,
considered them to be 'chamber casts,' or of organic origin. We have
shown that such grains often present crystalline planes, angles, and
edges; a fact clearly proving that they were originally simple or
compound crystals that have undergone external decretion by chemical
or solvent action.
"6th. We have adduced evidences to show that the 'nummuline layer' in
its typical condition--that is, consisting of cylindrical aciculi,
separated by interspaces filled with calcite--has originated directly
from closely packed fibres; these from chrysotile or asbestiform
serpentine; this from incipiently fibrous serpentine; and the latter
from the same mineral in its amorphous or structureless condition.
"7th. The 'nummuline layer,' in its typical condition, unmistakably
occurs in cracks or fissures, both in Canadian and Connemara ophite.
"8th. The 'nummuline layer' is paralleled by the fibrous coat which
is occasionally present on the surface of grains of chondrodite.
"9th. We have shown that the relative position of two superposed
asbestiform layers (an _upper_ and an _under_ 'proper wall'), and the
admitted fact of their component aciculi often passing continuously
and without interruption from one 'chamber cast' to another, to the
exclusion of the 'intermediate skeleton,' are totally incompatible
with the idea of the 'nummuline layer' having resulted from
pseudopodial tubulation.
"10th. The so-called 'stolons' and 'passages of communication
exactly corresponding with those described in _Cycloclypeus_,'
have been shown to be tabular crystals and variously formed bodies,
belonging to different minerals, wedged crossways or obliquely in the
calcareous interspaces between the grains and plates of serpentine.
"11th. The 'canal system' is composed of serpentine, or malacolite.
Its typical kinds in the first of these minerals may be traced in
all stages of formation out of plates, prisms, and other solids,
undergoing a process of superficial decretion. Those in malacolite
are made up of crystals--single, or aggregated together--that have
had their planes, angles, and edges rounded off; or have become
further reduced by some solvent.
"12th. The 'canal system' in its remarkable branching varieties is
completely paralleled by crystalline configurations in the coccolite
marble of Aker, in Sweden; and in the crevices of a crystal of spinel
imbedded in a calcitic matrix from Amity, New York.
"13th. The _configurations_, presumed to represent the 'canal
systems,' are _totally without any regularity_ of form, of relative
size, or of arrangement; and they occur independently of and apart
from other 'eozoonal features' (Amity, Boden, etc.); facts not only
demonstrating them to be purely mineral products, but which strike at
the root of the idea that they are of organic origin.
"14th. In answer to the argument that as all the foregoing 'eozoonal
features' are occasionally found together in ophite, the combination
must be considered a conclusive evidence of their organic origin,
we have shown, from the composition, physical characters, and
circumstances of occurrence and association of their component
serpentine, that they represent the structural and chemical changes
which are eminently and peculiarly characteristic of this mineral.
It has also been shown that the combination is paralleled to a
remarkable extent in chondrodite and its calcitic matrix.
"15th. The 'regular alternation of lamellæ of calcareous and
silicious minerals' (respectively representing the 'intermediate
skeleton' and 'chamber casts') occasionally seen in ophite, and
considered to be a 'fundamental fact' evidencing an organic
arrangement, is proved to be a _mineralogical_ phenomenon by the
fact that a similar alternation occurs in amphiboline-calcitic
marbles, and gneissose rocks.
"16th. In order to account for certain _untoward_ difficulties
presented by the configurations forming the 'canal system,' and
the aciculi of the 'nummuline layer'--that is, when they occur as
'_solid bundles_'--or are '_closely packed_'--or '_appear to be
glued together_'--Dr. Carpenter has proposed the theory that the
sarcodic extensions which they are presumed to represent have been
'turned into stone' (a 'silicious mineral') 'by Nature's cunning'
('just as the sarcodic layer on the surface of the shell of living
Foraminifers is formed by the spreading out of _coalesced_ bundles
of the pseudopodia that have emerged from the chamber wall')--'by
a process of chemical substitution _before_ their destruction by
ordinary decomposition.' We showed this quasi-alchymical theory to be
altogether unscientific.
"17th. The 'silicious mineral' (serpentine) has been analogued with
those forming the variously-formed casts (in 'glauconite,' etc.)
of recent and fossil Foraminifers. We have shown that the mineral
silicates of Eozoon have no relation whatever to the substances
composing such casts.
"18th. Dr. Hunt, in order to account for the serpentine, loganite,
and malacolite, being the presumed in-filling substances of Eozoon,
has conceived the 'novel doctrine,' that such minerals were
_directly_ deposited in the ocean waters in which this 'fossil'
lived. We have gone over all his evidences and arguments without
finding _one_ to be substantiated.
"19th. Having investigated the alleged cases of 'chambers' and
'tubes' occurring 'filled with calcite,' and presumed to be 'a
conclusive answer to' our 'objections,' we have shown that there are
the strongest grounds for removing them from the category of reliable
evidences on the side of the organic doctrine. The Tudor specimen has
been shown to be equally unavailable.
"20th. The occurrence of the best preserved specimens of Eozoon
Canadense in rocks that are in a '_highly crystalline condition_'
(Dawson) must be accepted as a fact utterly fatal to its organic
origin.
"21st. The occurrence of 'eozoonal features' _solely_ in crystalline
or metamorphosed rocks, belonging to the Laurentian, the Lower
Silurian, and the Liassic systems--never in ordinary unaltered
deposits of these and the intermediate systems--must be assumed as
completely demonstrating their purely mineral origin."
The answers already given to these objections may be summed up
severally as follows:--
1st. This is a mere hypothesis to account for the forms presented by
serpentine grains and by Eozoon. Hunt has shown that it is untenable
chemically, and has completely exploded it in his recent papers on
Chemistry and Geology.[AP] My own observations show that it does not
accord with the mode of occurrence of serpentine in the Laurentian
limestones of Canada.
[Footnote AP: Boston, 1874.]
2nd. Some of the things stated to parallel the intermediate skeleton
of Eozoon, are probably themselves examples of that skeleton. Others
have been shown to have no resemblance to it.
3rd. The words "more or less" indicate the precise value of this
statement, in a question of comparison between mineral and organic
structures. So the prismatic structure of satin-spar may be said
"more or less" to resemble that of a shell, or of the cells of a
Stenopora.
4th. This overlooks the filling of chamber casts with pyroxene,
dolomite, or limestone. Even in the case of loganite this objection
is of no value unless it can be applied equally to the similar
silicates which fill cavities of fossils[AQ] in the Silurian
limestones and in the green-sand.
[Footnote AQ: See for a full discussion of this subject Dr. Hunt's
"Papers" above referred to.]
5th. Dr. Gümbel's observations are those of a highly skilled and
accurate observer. Even if crystalline forms appear in "chamber
casts," this is as likely to be a result of the injury of organic
structures by crystallization, as of the partial effacement of
crystals by other actions. Crystalline faces occur abundantly in many
undoubted fossil woods and corals; and crystals not unfrequently
cross and interfere with the structures in such specimens.
6th. On the contrary, the Canadian specimens prove clearly that the
veins of chrysotile have been filled subsequently to the existence of
Eozoon in its present state, and that there is no connection whatever
between them and the Nummuline wall.
7th. This I have never seen in all my examinations of Eozoon. The
writers must have mistaken veins of fibrous serpentine for the
nummuline wall.
8th. Only if such grains of chondrodite are themselves casts of
foraminiferal chambers. But Messrs. King and Rowney have repeatedly
figured mere groups of crystals as examples of the nummuline wall.
9th. Dr. Carpenter has shown that this objection depends on a
misconception of the structure of modern Foraminifera, which show
similar appearances.
10th. That disseminated crystals occur in the Eozoon limestones is a
familiar fact, and one paralleled in many other more or less altered
organic limestones. Foreign bodies also occur in the chambers filled
with loganite and other minerals; but these need not any more be
confounded with the pillars and walls connecting the laminæ than
the sand filling a dead coral with its lamellæ. Further, it is well
known that foreign bodies are often contained both in the testa and
chambers even of recent Foraminifera.
11th. The canal system is not always filled with serpentine or
malacolite; and when filled with pyroxene, dolomite, or calcite, the
forms are the same. The irregularities spoken of are perhaps more
manifest in the serpentine specimens, because this mineral has in
places encroached on or partially replaced the calcite walls.
12th. If this is true of the Aker marble, then it must contain
Eozoon; and specimens of the Amity limestone which I have examined,
certainly contain large fragments of Eozoon.
13th. The configuration of the canal system is quite definite,
though varying in coarseness and fineness. It is not known to occur
independently of the forms of Eozoon except in fragmental deposits.
14th. The argument is not that they are "occasionally found together
in ophite," but that they are found together in specimens preserved
by different minerals, and in such a way as to show that all these
minerals have filled chambers, canals, and tubuli, previously
existing in a skeleton of limestone.
15th. The lamination of Eozoon is not like that of any rock, but
a strictly limited and definite form, comparable with that of
Stromatopora.
16th. This I pass over, as a mere captious criticism of modes of
expression used by Dr. Carpenter.
17th. Dr. Hunt, whose knowledge of chemical geology should give
the greatest weight to his judgment, maintains the deposition of
serpentine and loganite to have taken place in a manner similar to
that of jollyte and glauconite in undoubted fossils: and this would
seem to be a clear deduction from the facts he has stated, and from
the chemical character of the substances. My own observations of the
mode of occurrence of serpentine in the Eozoon limestones lead me to
the same result.
18th. Dr. Hunt's arguments on the subject, as recently presented
in his _Papers on Chemistry and Geology_, need only be studied by
any candid and competent chemist or mineralogist to lead to a very
different conclusion from that of the objectors.
19th. This is a mere statement of opinion. The fact remains that the
chambers and canals are sometimes filled with calcite.
20th. That the occurrence of Eozoon in crystalline limestones is
"utterly fatal" to its claims to organic origin can be held only by
those who are utterly ignorant of the frequency with which organic
remains are preserved in highly crystalline limestones of all ages.
In addition to other examples mentioned above, I may state that the
curious specimen of Cœnostroma from the Guelph limestone figured
in Chapter VI., has been converted into a perfectly crystalline
dolomite, while its canals and cavities have been filled with
calcite, since weathered out.
21st. This limited occurrence is an assumption contrary to facts.
It leaves out of account the Tudor specimens, and also the abundant
occurrence of the Stromatoporoid successors of Eozoon in the
Silurian and Devonian. Further, even if the Eozoon were limited to
the Laurentian, this would not be remarkable; and since all the
Laurentian rocks known to us are more or less altered, it could not
in that case occur in unaltered rocks.
I have gone over these objections seriatim, because, though
individually weak, they have an imposing appearance in the aggregate,
and have been paraded as a conclusive settlement of the questions
at issue. They have even been reprinted in the year just past in an
English journal of some standing, which professes to accept only
original contributions to science, but has deviated from its rule in
their favour. I may be excused for adding a portion of my original
argument in opposition to these objections, as given more at length
in the _Transactions of the Irish Academy_.
1. I object to the authors' mode of stating the question at issue,
whereby they convey to the reader the impression that this is merely
to account for the occurrence of certain peculiar forms in ophite.
With reference to this, it is to be observed that the attention of
Sir William Logan, and of the writer, was first called to Eozoon
by the occurrence in Laurentian rocks of definite forms resembling
the Silurian _Stromatoporæ_, and dissimilar from any concretions or
crystalline structures found in these rocks. With his usual sagacity,
Sir William added to these facts the consideration that the mineral
substances occurring is these forms were so dissimilar as to suggest
that the forms themselves must be due to some extraneous cause rather
than to any crystalline or segregative tendency of their constituent
minerals. These specimens, which were exhibited by Sir William as
probably fossils, at the meeting of the American Association in
1859, and noticed with figures in the Report of the Canadian Survey
for 1863, showed under the microscope no minute structures. The
writer, who had at the time an opportunity of examining them, stated
his belief that if fossils, they would prove to be not Corals but
Protozoa.
In 1864, additional specimens having been obtained by the Survey,
slices were submitted to the writer, in which he at once detected
a well-marked canal-system, and stated, decidedly, his belief that
the forms were organic and foraminiferal. The announcement of this
discovery was first made by Sir W. E. Logan, in _Silliman's Journal_
for 1864. So far, the facts obtained and stated related to definite
forms mineralised by loganite, serpentine, pyroxene, dolomite, and
calcite. But before publishing these facts in detail, extensive
series of sections of all the Laurentian limestones, and of those
of the altered Quebec group of the Green Mountain range, were made,
under the direction of Sir W. E. Logan and Dr. Hunt, and examined
microscopically. Specimens were also decalcified by acids, and
subjected to chemical examination by Dr. Sterry Hunt. The result was
the conviction that the definite laminated forms must be organic,
and further, that there exist in the Laurentian limestones fragments
of such forms retaining their structure, and also other fragments,
probably organic, but distinct from Eozoon. These conclusions were
submitted to the Geological Society of London, in 1864, after the
specimens on which they were based had been shown to Dr. Carpenter
and Professor T. R. Jones, the former of whom detected in some of
the specimens an additional foraminiferal structure--that of the
tubulation of the proper wall, which I had not been able to make out.
Subsequently, in rocks at Tudor, of somewhat later age than those
of the Lower Laurentian at Grenville, similar structures were found
in limestones not more metamorphic than many of those which retain
fossils in the Silurian system. I make this historical statement in
order to place the question in its true light, and to show that it
relates to the organic origin of certain definite mineral masses,
exhibiting, not only the external forms of fossils, but also their
internal structure.
In opposition to these facts, and to the careful deductions drawn
from them, the authors of the paper under consideration maintain that
the structures are mineral and crystalline. I believe that in the
present state of science such an attempt to return to the doctrine
of "plastic-force" as a mode of accounting for fossils would not
be tolerated for a moment, were it not for the great antiquity and
highly crystalline condition of the rocks in which the structures
are found, which naturally create a prejudice against the idea of
their being fossiliferous. That the authors themselves feel this is
apparent from the slight manner in which they state the leading facts
above given, and from their evident anxiety to restrict the question
to the mode of occurrence of serpentine in limestone, and to ignore
the specimens of Eozoon preserved under different mineral conditions.
2. With reference to the general form of Eozoon and its structure
on the large scale, I would call attention to two admissions of
the authors of the paper, which appear to me to be fatal to their
case:--First, they admit, at page 533 [_Proceedings_, vol. x.],
their "inability to explain satisfactorily" the alternating layers
of carbonate of lime and other minerals in the typical specimens of
Canadian Eozoon. They make a feeble attempt to establish an analogy
between this and certain concentric concretionary layers; but the
cases are clearly not parallel, and the laminæ of the Canadian
Eozoon present connecting plates and columns not explicable on any
concretionary hypothesis. If, however, they are unable to explain the
lamellar structure alone, as it appeared to Logan in 1859, is it not
rash to attempt to explain it away now, when certain minute internal
structures, corresponding to what might have been expected on the
hypothesis of its organic origin, are added to it? If I affirm that
a certain mass is the trunk of a fossil tree, and another asserts
that it is a concretion, but professes to be unable to account for
its form and its rings of growth, surely his case becomes very weak
after I have made a slice of it, and have shown that it retains the
structure of wood.
Next, they appear to admit that if specimens occur wholly composed
of carbonate of lime, their theory will fall to the ground. Now such
specimens do exist. They treat the Tudor specimen with scepticism as
probably "strings of segregated calcite." Since the account of that
specimen was published, additional fragments have been collected, so
that new slices have been prepared. I have examined these with care,
and am prepared to affirm that the chambers in these specimens are
filled with a dark-coloured limestone not more crystalline than is
usual in the Silurian rocks, and that the chamber walls are composed
of carbonate of lime, with the canals filled with the same material,
except where the limestone filling the chambers has penetrated into
parts of the larger ones. I should add that the stratigraphical
researches of Mr. Vennor, of the Canadian Survey, have rendered it
probable that the beds containing these fossils, though unconformably
underlying the Lower Silurian, overlie the Lower Laurentian of the
locality, and are, therefore, probably Upper Laurentian, or perhaps
Huronian, so that the Tudor specimens may approach in age to Gümbel's
Eozoon Bavaricum.[AR]
[Footnote AR: I may now refer in addition to the canals filled with
calcite and dolomite, detected by Dr. Carpenter and myself in specimens
from Petite Nation, and mentioned in a previous chapter. See also Plate
VIII.]
Further, the authors of the paper have no right to object to our
regarding the laminated specimen as "typical" Eozoon. If the question
were as to _typical ophite_ the case would be different; but the
question actually is as to certain well-defined forms which we regard
as fossils, and allege to have organic structure on the small scale,
as well as lamination on the large scale. We profess to account for
the acervuline forms by the irregular growth at the surface of the
organisms, and by the breaking of them into fragments confusedly
intermingled in great thicknesses of limestone, just as fragments of
corals occur in Palæozoic limestones; but we are under no obligation
to accept irregular or disintegrated specimens as typical; and when
objectors reason from these fragments, we have a right to point to
the more perfect examples. It would be easy to explain the loose
cells of _Tetradium_ which characterize the bird's-eye limestone
of the Lower Silurian of America, as crystalline structures; but
a comparison with the unbroken masses of the same coral, shows
their true nature. I have for some time made the minute structure
of Palæozoic limestones a special study, and have described some
of them from the Silurian formations of Canada.[AS] I possess now
many additional examples, showing fragments of various kinds of
fossils preserved in these limestones, and recognisable only by the
infiltration of their pores with different silicious minerals. It can
also be shown that in many cases the crystallization of the carbonate
of lime, both of the fossils themselves and of their matrix, has
not interfered with the perfection of the most minute of these
structures.
[Footnote AS: In the _Canadian Naturalist_.]
The fact that the chambers are usually filled with silicates is
strangely regarded by the authors as an argument against the organic
nature of Eozoon. One would think that the extreme frequency of
silicious fillings of the cavities of fossils, and even of silicious
replacement of their tissues, should have prevented the use of such
an argument, without taking into account the opposite conclusions to
be drawn from the various kinds of silicates found in the specimens,
and from the modern filling of Foraminifera by hydrous silicates, as
shown by Ehrenberg, Mantell, Carpenter, Bailey, and Pourtales.[AT]
Further, I have elsewhere shown that the loganite is proved by its
texture to have been a fragmental substance, or at least filled
with loose _debris_; that the Tudor specimens have the cavities
filled with a sedimentary limestone, and that several fragmental
specimens from Madoc are actually wholly calcareous. It is to be
observed, however, that the wholly calcareous specimens present
great difficulties to an observer; and I have no doubt that they are
usually overlooked by collectors in consequence of their not being
developed by weathering, or showing any obvious structure in fresh
fractures.
[Footnote AT: _Quarterly Journal Geol. Society_, 1864.]
3. With regard to the canal system, the authors persist in
confusing the casts of it which occur in serpentine with "metaxite"
concretions, and in likening them to dendritic crystallizations of
silver, etc., and coralloidal forms of carbonate of lime. In answer
to this, I think it quite sufficient to say that I fail to perceive
the resemblance as other than very imperfectly imitative. I may add,
that the case is one of the occurrence of a canal structure in forms
which on other grounds appear to be organic, while the concretionary
forms referred to are produced under diverse conditions, none of
them similar to those of which evidence appears in the specimens of
Eozoon. With the singular theory of pseudomorphism, by means of which
the authors now supplement their previous objections, I leave Dr.
Hunt to deal.
4. With respect to the proper wall and its minute tubulation, the
essential error of the authors consists in confounding it with
fibrous and acicular crystals, and in maintaining that because the
tubuli are sometimes apparently confused and confluent they must
be inorganic. With regard to the first of these positions, I may
repeat what I have stated in former papers--that the true cell-wall
presents minute cylindrical processes traversing carbonate of lime,
and usually nearly parallel to each other, and often slightly
bulbose at the extremity. Fibrous serpentine, on the other hand,
appears as angular crystals, closely packed together, while the
numerous spicular crystals of silicious minerals which often appear
in metamorphic limestones, and may be developed by decalcification,
appear as sharp angular needles usually radiating from centres or
irregularly disposed. Their own plate (Ophite from Skye, King and
Rowney's Paper, _Proc. R. I. A._, vol. x.), is an eminent example
of this; and whatever the nature of the crystals represented, they
have no appearance of being true tubuli of Eozoon. I have very often
shown microscopists and geologists the cell-wall along with veins of
chrysotile and coatings of acicular crystals occurring in the same or
similar limestones, and they have never failed at once to recognise
the difference, especially under high powers.
I do not deny that the tubulation is often imperfectly preserved,
and that in such cases the casts of the tubuli may appear to be
glued together by concretions of mineral matter, or to be broken
or imperfect. But this occurs in all fossils, and is familiar to
any microscopist examining them. How difficult is it in many cases
to detect the minute structure of Nummulites and other fossil
Foraminifera? How often does a specimen of fossil wood present in one
part distorted and confused fibres or mere crystals, with the remains
of the wood forming phragmata between them, when in other parts it
may show the most minute structures in perfect preservation? But
who would use the disintegrated portions to invalidate the evidence
of the parts better preserved? Yet this is precisely the argument
of Professors King and Rowney, and which they have not hesitated
in using in the case of a fossil so old as Eozoon, and so often
compressed, crushed, and partly destroyed by mineralization.
I have in the above remarks confined myself to what I regard as
absolutely essential by way of explanation and defence of the
organic nature of Eozoon. It would be unprofitable to enter into the
multitude of subordinate points raised by the authors, and their
theory of mineral pseudomorphism is discussed by my friend Dr. Hunt;
but I must say here that this theory ought, in my opinion, to afford
to any chemist a strong presumption against the validity of their
objections, especially since it confessedly does not account for all
the facts, while requiring a most complicated series of unproved and
improbable suppositions.
The only other new features in the communication to which this note
refers are contained in the "supplementary note." The first of
these relates to the grains of coccolite in the limestone of Aker,
in Sweden. Whether or not these are organic, they are apparently
different from _Eozoon Canadense_. They, no doubt, resemble the
grains referred to by Gümbel as possibly organic, and also similar
granular objects with projections which, in a previous paper, I have
described from Laurentian limestones in Canada. These objects are of
doubtful nature; but if organic, they are distinct from Eozoon. The
second relates to the supposed crystals of malacolite from the same
place. Admitting the interpretation given of these to be correct,
they are no more related to Eozoon than are the curious vermicular
crystals of a micaceous mineral which I have noticed in the Canadian
limestones.
The third and still more remarkable case is that of a spinel from
Amity, New York, containing calcite in its crevices, including a
perfect canal system preserved in malacolite. With reference to
this, as spinels of large size occur in veins in the Laurentian
rocks, I am not prepared to say that it is absolutely impossible that
fragments of limestone containing Eozoon may not be occasionally
associated with them in their matrix. I confess, however, that
until I can examine such specimens, which I have not yet met with,
I cannot, after my experience of the tendencies of Messrs. Rowney
and King to confound other forms with those of Eozoon, accept their
determinations in a matter so critical and in a case so unlikely.[AU]
[Footnote AU: I have since ascertained that Laurentian limestone found
at Amity, New York, and containing spinels, does hold fragments of the
intermediate skeleton of Eozoon. The limestone may have been originally
a mass of fragments of this kind with the aluminous and magnesian
material of the spinel in their interstices.]
If all specimens of Eozoon were of the acervuline character, the
comparison of the chamber-casts with concretionary granules might
have some plausibility. But it is to be observed that the laminated
arrangement is the typical one; and the study of the larger
specimens, cut under the direction of Sir W. E. Logan, shows that
these laminated forms must have grown on certain strata-planes before
the deposition of the overlying beds, and that the beds are, in part,
composed of the broken fragments of similar laminated structures.
Further, much of the apparently acervuline Eozoon rock is composed
of such broken fragments, the interstices between which should not
be confounded with the chambers: while the fact that the serpentine
fills such interstices as well as the chambers shows that its
arrangement is not concretionary. Again, these chambers are filled in
different specimens with serpentine, pyroxene, loganite, calcareous
spar, chondrodite, or even with arenaceous limestone. It is also to
be observed that the examination of a number of limestones, other
than Canadian, by Messrs. King and Rowney, has obliged them to admit
that the laminated forms in combination with the canal-system are
"essentially Canadian," and that the only instances of structures
clearly resembling the Canadian specimens are afforded by limestones
Laurentian in age, and in some of which (as, for instance, in those
of Bavaria and Scandinavia) Carpenter and Gümbel have actually found
the structure of Eozoon. The other serpentine-limestones examined
(for example, that of Skye) are admitted to fail in essential points
of structure; and the only serpentine believed to be of eruptive
origin examined by them is confessedly destitute of all semblance
of Eozoon. Similar results have been attained by the more careful
researches of Prof. Gümbel, whose paper is well deserving of study by
all who have any doubts on this subject.
(B.) Reply by Dr. Hunt to Chemical Objections--(_Ibid._).
"In the _Proceedings of the Royal Irish Academy_, for July 12,
1869, Messrs. King and Rowney have given us at length their latest
corrected views on various questions connected with Eozoon Canadense.
Leaving to my friend, Dr. Dawson, the discussion of the zoological
aspects of the question, I cannot forbear making a few criticisms
on the chemical and mineralogical views of the authors. The problem
which they had before them was to explain the occurrence of certain
forms which, to skilled observers, like Carpenter, Dawson, and
Rupert Jones, appear to possess all the structural character of the
calcareous skeleton of a foraminiferal organism, and moreover to
show how it happens that these forms of crystalline carbonate of
lime are associated with serpentine in such a way as to lead these
observers to conclude that this hydrous silicate of magnesia filled
and enveloped the calcareous skeleton, replacing the perishable
sarcode. The hypothesis now put forward by Messrs. King and Rowney
to explain the appearances in question, is, that all this curiously
arranged serpentine, which appears to be a cast of the interior of a
complex foraminiferal organism, has been shaped or sculptured out of
plates, prisms, and other solids of serpentine, by "the erosion and
incomplete waste of the latter, _the definite shapes_ being residual
portions of the solid that have not completely disappeared." The
calcite which limits these definite shapes, or, in other words, what
is regarded as the calcareous skeleton of Eozoon, is a 'replacement
pseudomorph' of calcite taking the place of the wasted and eroded
serpentine. It was not a calcareous fossil, filled and surrounded
by the serpentine, but was formed in the midst of the serpentine
itself, by a mysterious agency which dissolved away this mineral to
form a mould, in which the calcite was cast. This marvellous process
can only be paralleled by the operations of that plastic force in
virtue of which sea-shells were supposed by some old naturalists
to be generated in the midst of rocky strata. Such equivocally
formed fossils, whether oysters or Foraminifers, may well be termed
_pseudomorphs_, but we are at a loss to see with what propriety the
authors of this singular hypothesis invoke the doctrines of mineral
pseudomorphism, as taught by Rose, Blum, Bischof, and Dana. In
replacement pseudomorphs, as understood by these authors, a mineral
species disappears and is replaced by another which retains the
external form of the first. Could it be shown that the calcite of the
cell-wall of Eozoon was once serpentine, this portion of carbonate
of lime would be a replacement pseudomorph after serpentine; but why
the portions of this mineral, which on the hypothesis of Messrs. King
and Rowney have been thus replaced, should assume the forms of a
foraminiferal skeleton, is precisely what our authors fail to show,
and, as all must see, is the gist of the whole matter.
"Messrs. King and Rowney, it will be observed, assume the existence
of calcite as a replacement pseudomorph after serpentine, but give
no evidence of the possibility of such pseudomorphs. Both Rose and
Bischof regard serpentine itself as in all cases, of pseudomorphous
origin, and as the last result of the changes of a number of mineral
species, but give us no example of the pseudomorphous alteration of
serpentine itself. It is, according to Bischof, the very insolubility
and unalterability of serpentine which cause it to appear as the
final result of the change of so many mineral species. Delesse,
moreover, in his carefully prepared table of pseudomorphous minerals,
in which he has resumed the results of his own and all preceding
observers, does not admit the pseudomorphic replacement of serpentine
by calcite, nor indeed by any other species.[AV] If, then, such
pseudomorphs exist, it appears to be a fact hitherto unobserved,
and our authors should at least have given us some evidence of this
remarkable case of pseudomorphism by which they seek to support their
singular hypothesis.
[Footnote AV: _Annales des Mines_, 5, xvi., 317.]
"I hasten to say, however, that I reject with Scheerer, Delesse
and Naumann, a great part of the supposed cases of mineral
pseudomorphism, and do not even admit the pseudomorphous origin of
serpentine itself, but believe that this, with many other related
silicates, has been formed by direct chemical precipitation. This
view, which our authors do me the honour to criticise, was set
forth by me in 1860 and 1861,[AW] and will be found noticed more
in detail in the _Geological Report of Canada_, for 1866, p. 229.
I have there and elsewhere maintained that 'steatite, serpentine,
pyroxene, hornblende, and in many cases garnet, epidote, and other
silicated minerals, are formed by a crystallization and molecular
re-arrangement of silicates, generated by chemical processes in
waters at the earth's surface.'[AX]
[Footnote AW: _Amer. Journ. Science_ (2), xxix., 284; xxxii., 286.]
[Footnote AX: _Ibid._, xxxvii., 266; xxxviii., 183.]
"This view, which at once explains the origin of all these bedded
rocks, and the fact that their constituent mineral species, like
silica and carbonate of lime, replace the perishable matter of
organic forms, is designated by Messrs. King and Rowney 'as so
completely destitute of the characters of a scientific hypothesis
as to be wholly unworthy of consideration,' and they speak of my
attempt to maintain this hypothesis as 'a total collapse.' How far
this statement is from the truth my readers shall judge. My views
as to the origin of serpentine and other silicated minerals were
set forth by me as above in 1860-1864, before anything was known
of the mineralogy of Eozoon, and were forced upon me by my studies
of the older crystalline schists of North America. Naumann had
already pointed out the necessity of some such hypothesis when he
protested against the extravagances of the pseudomorphist school,
and maintained that the beds of various silicates found in the
crystalline schists are original deposits, and not formed by an
epigenic process (_Geognosie_, ii., 65, 154, and _Bull. Soc. Geol.
de France_, 2, xviii., 678). This conclusion of Naumann's I have
attempted to explain and support by numerous facts and observations,
which have led me to the hypothesis in question. Gümbel, who accepts
Naumann's view, sustains my hypothesis of the origin of these rocks
in a most emphatic manner,[AY] and Credner, in discussing the genesis
of the Eozoic rocks, has most ably defended it.[AZ] So much for my
theoretical views so contemptuously denounced by Messrs. King and
Rowney, which are nevertheless unhesitatingly adopted by the two
geologists of the time who have made the most special studies of the
rocks in question,--Gümbel in Germany, and Credner in North America.
[Footnote AY: _Proc. Royal Bavarian Acad._ for 1866, translated in
_Can. Naturalist_, iii., 81.]
[Footnote AZ: _Die Gliederung der Eozoischen Formations gruppe
Nord.-Amerikas,--a Thesis defended before the University of Leipzig,
March 15, 1869_, by Dr. Hermann Credner. Halle, 1869, p. 53.]
"It would be a thankless task to follow Messrs. King and Rowney
through their long paper, which abounds in statements as unsound as
those I have just exposed, but I cannot conclude without calling
attention to one misconception of theirs as to my view of the origin
of limestones. They quote Professor Hull's remark to the effect that
the researches of the Canadian geologists and others have shown that
the oldest known limestones of the world owe their origin to Eozoon,
and remark that the existence of great limestone beds in the Eozoic
rocks seems to have influenced Lyell, Ramsay, and others in admitting
the received view of Eozoon. Were there no other conceivable source
of limestones than Eozoon or similar calcareous skeletons, one might
suppose that the presence of such rocks in the Laurentian system
could have thus influenced these distinguished geologists, but
there are found beneath the Eozoon horizon two great formations of
limestone in which this fossil has never been detected. When found,
indeed, it owes its conservation in a readily recognisable form to
the fact, that it was preserved by the introduction of serpentine
at the time of its growth. Above the unbroken Eozoon reefs are
limestones made up apparently of the debris of Eozoon thus preserved
by serpentine, and there is no doubt that this calcareous rhizopod,
growing in water where serpentine was not in process of formation,
might, and probably did, build up pure limestone beds like those
formed in later times from the ruins of corals and crinoids. Nor
is there anything inconsistent in this with the assertion which
Messrs. King and Rowney quote from me, viz., that the popular notion
that _all limestone formations_ owe their origin to organic life is
based upon a fallacy. The idea that marine organisms originate the
carbonate of lime of their skeletons, in a manner somewhat similar to
that in which plants generate the organic matter of theirs, appears
to be commonly held among certain geologists. It cannot, however,
be too often repeated that animals only appropriate the carbonate
of lime which is furnished them by chemical reaction. Were there
no animals present to make use of it, the carbonate of lime would
accumulate in natural waters till these became saturated, and would
then be deposited in an insoluble form; and although thousands of
feet of limestone have been formed from the calcareous skeletons
of marine animals, it is not less true that great beds of ancient
marble, like many modern travertines and tufas, have been deposited
without the intervention of life, and even in waters from which
living organisms were probably absent. To illustrate this with the
parallel case of silicious deposits, there are great beds made
up of silicious shields of diatoms. These during their lifetime
extracted from the waters the dissolved silica, which, but for their
intervention, might have accumulated till it was at length deposited
in the form of schist or of crystalline quartz. In either case the
function of the coral, the rhizopod, or the diatom is limited to
assimilating the carbonate of lime or the silica from its solution,
and the organised form thus given to these substances is purely
accidental. It is characteristic of our authors, that, rather than
admit the limestone beds of the Eozoon rocks to have been formed like
beds of coralline limestone, or deposited as chemical precipitates
like travertine, they prefer, as they assure us, to regard them as
the results of that hitherto unheard-of process, the pseudomorphism
of serpentine; as if the deposition of the carbonate of lime in
the place of dissolved serpentine were a simpler process than its
direct deposition in one or the other of the ways which all the world
understands!"
(C.) Dr. Carpenter on the Foraminiferal Relations of Eozoon.
In the _Annals of Natural History_, for June, 1874, Dr. Carpenter
has given a crushing reply to some objections raised in that journal
by Mr. Carter. He first shows, contrary to the statement of Mr.
Carter, that the fine nummuline tubulation corresponds precisely in
its direction with reference to the chambers, with that observed in
Nummulites and Orbitoides. In the second place, he shows by clear
descriptions and figures, that the relation of the canal system to
the fine tubulation is precisely that which he had demonstrated in
more recent nummuline and rotaline Foraminifera. In the third place
he adduces additional facts to show that in some specimens of Eozoon
the calcareous skeleton has been filled with calcite before the
introduction of any foreign mineral matter. He concludes the argument
in the following words:--
"I have thus shown:--(1) that the 'utter incompatibility' asserted
by my opponents to exist between the arrangement of the supposed
'nummuline tubulation' of Eozoon and true Nummuline structure, so far
from having any real existence, really furnishes an additional point
of conformity; and (2) that three most striking and complete points
of conformity exist between the structure of the best-preserved
specimens of Eozoon, and that of the Nummulites whose tubulation I
described in 1849, and of the Calcarina whose tubulation and canal
system I described in 1860.
"That I have not troubled myself to reply to the reiterated arguments
in favour of the doctrine [of mineral origin] advanced by Professors
King and Rowney on the strength of the occurrence of undoubted
results of mineralization in the Canadian Ophite, and of still more
marked evidences of the same action in other Ophites, has been
simply because these arguments appeared to me, as I thought they
must also appear to others, entirely destitute of logical force.
Every scientific palæontologist I have ever been acquainted with has
taken the _best_ preserved specimens, not the _worst_, as the basis
of his reconstructions; and if he should meet with distinct evidence
of characteristic organic structure in even a very small fragment
of a doubtful form, he would consider the organic origin of that
form to be thereby substantiated, whatever might be the evidence of
purely mineral arrangement which the greater part of his specimen
may present,--since he would regard that arrangement as a probable
result of _subsequent_ mineralization, by which the original organic
structure has been more or less obscured. If this is _not_ to be our
rule of interpretation, a large part of the palæontological work
of our time must be thrown aside as worthless. If, for example,
Professors King and Rowney were to begin their study of Nummulites
by the examination of their most mineralized forms, they would deem
themselves justified (according to their canons of interpretation)
in denying the existence of the tubulation and canalization which I
described (in 1849) in the N. lævigata preserved almost unaltered in
the London Clay of Bracklesham Bay.
"My own notions of Eozoic structure have been formed on the
examination of the Canadian specimens selected by the experienced
discrimination of Sir William Logan, as those in which there was
_least_ appearance of metamorphism; and having found in these what I
regarded as unmistakable evidence of an organic structure conformable
to the foraminiferal type, I cannot regard it as any disproof of
that conformity, either to show that the true Eozoic structure has
been frequently altered by mineral metamorphism, or to adduce the
occurrence of Ophites more or less resembling the Eozoon of the
Canadian Laurentians at various subsequent geological epochs. The
existence of any number or variety of _purely mineral_ Ophites would
not disprove the organic origin of the Canadian Eozoon--unless
it could be shown that some wonderful process of mineralization
is competent to construct not only its multiplied alternating
lamellæ of calcite and serpentine, the dendritic extensions of the
latter into the former, and the 'acicular layer' of decalcified
specimens, but (1) the _pre-existing canalization_ of the calcareous
lamellæ, (2) the _unfilled nummuline tubulation_ of the proper
wall of the chambers, and (3) the peculiar _calcarine_ relation of
the canalization and tubulation, here described and figured from
specimens in the highest state of preservation, showing the _least_
evidence of any mineral change.
"On the other hand, Professors King and Rowney began their studies of
Eozoic structure upon the Galway Ophite--a rock which Sir Roderick
Murchison described to me at the time as having been so much 'tumbled
about,' that he was not at all sure of its geological position, and
which exhibits such obvious evidences of mineralization, with such
an entire absence of any vestige of organic structure, that I should
never for a moment have thought of crediting it with an organic
origin, but for the general resemblance of its serpentine-grains
to those of the 'acervuline' portion of the Canadian Eozoon. They
pronounced with the most positive certainty upon the mineral origin
of the Canadian Eozoon, before they had subjected transparent
sections of it to any of that careful comparison with similar
sections of recent Foraminifera, which had been the basis of
Dr. Dawson's original determination, and of my own subsequent
confirmation, of its organic structure.
[Illustration:
Plate VIII.
_Eozoon and Chrysotile Veins, etc._
Fig. 1.--Portion of two laminæ and intervening serpentine,
with chrysotile vein. (_a._) Proper wall tubulated. (_b._)
Intermediate skeleton, with large canals. (_c._) Openings of
small chamberlets filled with serpentine. (_s._) Serpentine
filling chamber. (_s^1._) Vein of chrysotile, showing its
difference from the proper wall.
Fig. 2.--Junction of a canal and the proper wall. Lettering as in
Fig. 1.
Fig. 3.--Proper wall shifted by a fault, and more recent chrysotile
vein not faulted. Lettering as in Fig. 1.
Fig. 4.--Large and small canals filled with dolomite.
Fig. 5.--Abnormally thick portion of intermediate skeleton, with
large tubes and small canals filled with dolomite.]