even though the facts for its solution must be sought in a wilderness
known to few except adventurous trappers, hunters, and lumbermen; and
he soon learned that this ancient gneissic formation contained other
rocks beside gneiss, more especially thick and extensive limestones,
and that its beds seemed to have a definite arrangement, and could
be traced over great areas. He addressed himself, therefore, to
the problem of unravelling the tangled "complex," and with a few
hardy assistants, spent years in laboriously tracing its beds along
river courses and over mountains, and in mapping, in a manner never
previously attempted, its several members, designating at the same time
the whole by the term "Laurentian," because it constituted the mass
of the hills lying north of the St. Lawrence, called by old French
geographers the Laurentides, and separating the St. Lawrence Valley and
the region of the great lakes from Hudson's Bay and the Arctic Sea. In
this manner he laid a foundation, which still remains unshaken, for the
geology of the oldest rocks, and prepared the way for the discovery
of the forms afterward named Eozoon Canadense. At the same time Dr.
Sterry Hunt, the chemist of the Survey, was examining chemically the
rocks and minerals collected, and all Sir William's assistants were
instructed to search, more especially in the limestones, for anything
bearing the aspect of fossils. On the other hand. Dr. Carpenter was
independently pursuing his studies of the humbler inhabitants of the
modern ocean, and of the manner in which the pores of their skeletons
became infiltrated with mineral matter, and had kindly contributed
specimens to the collections of the writer in Canada. The discovery
of this most ancient fossil was thus not the chance picking up of a
rare and curious specimen, but the result of several combined lines of
laborious and skilful research.
The following notice of the persons and incidents connected with its
discovery is taken from a previous publication of the writer, with only
a little alteration in terms to suit it to the present date.
The first specimens of Eozoon ever procured, in so far as known, were
collected at Burgess, in Ontario, by a veteran Canadian mineralogist.
Dr. Wilson of Perth, and were sent to Sir William Logan as mineral
specimens. Their chief interest at that time lay in the fact that
certain laminæ of a dark green mineral present in the specimens
were found, on analysis by Dr. Hunt, to be composed of a new hydrous
silicate, allied to serpentine, and which he named loganite, but
which seems to be a mixture of different silicates. The form of this
mineral was not suspected to be of organic origin. Some years after,
in 1858, other specimens, differently mineralized with the minerals
serpentine and pyroxene, were found by Mr. J. McMullen, an explorer in
the service of the Geological Survey, in the limestone of the Grand
Calumet on the river Ottawa. These seem to have at once struck Sir W.
E. Logan as resembling the Silurian fossils known as _Stromatoporæ_,
or layer-corals, and at that time of quite uncertain nature, though
supposed to be allied to some kinds of modern corals. He showed them
to Mr. Billings, the palæontologist of the Survey, and to the writer,
with this suggestion, confirming it with the sagacious consideration
that inasmuch as the Ottawa and Burgess specimens were mineralized
by different substances, yet were alike in form, there was little
probability that they were merely mineral or concretionary. Mr.
Billings was naturally unwilling to risk his reputation in affirming
the organic nature of such specimens; and my own suggestion was that
they should be sliced, and examined microscopically; and that if
fossils, as they presented merely concentric laminæ and no cells, they
would probably prove to be protozoa rather than corals. A few slices
were accordingly made, but no definite structure could be detected.
Nevertheless, Sir William Logan took some of the specimens to the
meeting of the American Association at Springfield, in 1859, and
exhibited them as possibly Laurentian fossils; but the announcement was
evidently received with some incredulity. In 1862 they were exhibited
by Sir William to some geological friends in London, but he remarks
that "few seemed disposed to believe in their organic character, with
the exception of my friend Professor Ramsay." In 1863 the General
Report of the Geological Survey, summing up its work to that time, was
published, under the name of the "Geology of Canada," and in this, at
page 49, will be found two figures of one of the Calumet specimens,
here reproduced, and which, though unaccompanied with any specific
name or technical description, were referred to as probably Laurentian
fossils (Figs. 26 and 27).
[Illustration: Fig. 26.--_Weathered Specimen of Eozoon from the Grand
Calumet._ (Collected by Mr. McMullen.)]
[Illustration: Fig. 27.--_Cross Section of the Specimen represented in
Fig. 26._
The dark parts are the laminæ of calcareous matter converging to the
outer surface.]
About this time Dr. Hunt happened to mention to me, in connection with
a paper on the mineralization of fossils which he was preparing, that
he proposed to notice the mode of preservation of certain fossil woods
and other things with which I was familiar, and that he would show me
the paper in proof, in order that he might have any suggestions that
occurred to me. On reading it, I observed, among other things, that
he alluded to the supposed Laurentian fossils, under the impression
that the organic part was represented by the serpentine or loganite,
and that the calcareous matter was the filling of the chambers. I took
exception to this, stating that though in the slices before examined
no structure was apparent, still my impression was that the calcareous
matter was the fossil, and the serpentine or loganite the filling. He
said: "In that case, would it not be well to re-examine the specimens,
and to try to discover which view is correct?" He mentioned at the same
time that Sir William had recently shown him some new and beautiful
specimens collected by Mr. Lowe, one of the explorers on the staff
of the Survey, from a third locality, at Grenville, on the Ottawa.
It was supposed that these might throw further light on the subject;
and accordingly Dr. Hunt suggested to Sir William to have additional
slices of these new specimens made by Mr. Weston, of the Survey,
whose skill as a preparer of these and other fossils has often done
good service to science. A few days thereafter, some slices were sent
to me, and were at once put under the microscope. I was delighted to
find in one of the first specimens examined, which happened to be cut
parallel to the laminæ, a beautiful group of tubuli penetrating one of
the calcite layers. Here was evidence, not only that the calcite layers
represented the true skeleton of the fossil, but also of its affinities
with the Foraminifera, whose tubulated supplemental skeleton, as
described and figured by Dr. Carpenter, and represented in specimens
in my collection presented by him, was evidently of the same type with
that preserved in the canals of these ancient fossils. Fig. 28 is an
accurate representation of the first seen group of canals penetrated by
serpentine.
On showing the structures discovered to Sir William Logan, he entered
into the matter with enthusiasm, and had a great number of slices and
afterwards of decalcified specimens prepared, which were placed in my
hands for examination.
[Illustration: Fig. 28.--_Group of Canals in the Supplemental Skeleton
of Eozoon._
Taken from the specimen in which they were first recognised.
(Magnified.)]
[Illustration: Fig. 29.--_Canals of Eozoon, from same specimen,_
(Highly magnified.)]
Feeling that the discovery was most important, but that it would be
met with determined scepticism on the part both of geologists and
biologists, I was not content with examining the typical specimens of
Eozoon, but had slices prepared of
every variety of Laurentian limestone, of altered limestones from the
Cambrian and Silurian, and of serpentine marbles of all the varieties
furnished by our collections. These were examined with ordinary and
polarized light, and with every variety of illumination. Dr. Hunt,
on his part, undertook the chemical investigation of the various
associated minerals. An extensive series of notes and camera tracings
were made of all the appearances observed; and of some of the more
important structures beautiful drawings were executed by the late
Mr. H. S. Smith, the then palæontological draughtsman of the Survey.
The result of the whole investigation was a firm conviction that the
structure was organic and probably foraminiferal, and that it could be
distinguished from any merely mineral or crystalline forms occurring in
these or other limestones.
At this stage of the matter, and after exhibiting to Sir William all
the characteristic appearances in comparison with such concretionary,
dendritic, and crystalline structures as most resembled them, and also
with the structure of recent and fossil Foraminifera, I suggested that
the further prosecution of the matter should be handed over to Mr.
Billings, as palæontologist of the Survey, and as our highest authority
on the fossils of the older rocks.
[Illustration: Fig. 30.--_Casts of Canals of Eozoon, in Serpentine._
Decalcified and highly magnified.]
[Illustration: Fig. 31.--_Group of finest Tubuli._
Highly magnified, from a micro-photograph.]
I was engaged in other researches, and knew that no little labour
must be devoted to the work and to its publication, and that some
controversy might be expected. Mr. Billings, however, with his
characteristic caution and modesty, declined. His hands, he said, were
full of other work, and he had not specially studied the microscopic
appearances of Foraminifera or of mineral substances. It was finally
arranged that I should prepare a description of the fossil, which
Sir William would take to London, along with Dr. Hunt's notes, the
more important specimens, and lists of the structures observed in
each. Sir William was to submit the manuscript and specimens to Dr.
Carpenter, and also to Prof T. Rupert Jones, in the hope that these
eminent authorities would confirm our conclusions, and bring forward
new facts which I might have overlooked or been ignorant of Sir William
saw both gentlemen, who gave their testimony in favour of the organic
and foraminiferal character of the specimens; and Dr. Carpenter in
particular gave much attention to the subject, and worked out the
structure of the delicate tubulation of the surfaces of the laminæ or
cell-walls, which I had not distinguished previously, through a curious
accident as to specimens. Mr. Lowe had been sent back to the Ottawa
to explore, and just before Sir William's departure had sent in some
specimens from a new locality at Petite Nation, similar in general
appearance to those from Grenville, which Sir William took with him
unsliced to England. These showed in a perfect manner the tubuli of
the primary cell-wall, which I had in vain tried to resolve in the
Grenville specimens, and which I did not see until after they had been
detected by Dr. Carpenter in London. Dr. Carpenter thus contributed in
a very important manner to the perfecting of the investigations begun
in Canada, and on him fell the greater part of their illustration and
defence,[23] in so far as Great Britain is concerned.
[Footnote 23: In papers by Dr. Carpenter, subsequently referred to.
Prof. Jones published an able exposition of the facts in the _Popular
Science Monthly_.]
The immediate result was a composite paper in the _Proceedings of the
Geological Society_, by Sir W. E. Logan, Dr. Carpenter, Dr. Hunt, and
myself, in which the geology, palæontology, and mineralogy of _Eozoon
Canadense_ and its containing rocks were first given to the world.[24]
It cannot be wondered at that when geologists and palæontologists
were thus required to believe in the existence of organic remains in
rocks regarded as altogether Azoic and hopelessly barren of fossils,
and to carry back the dawn of life as far before those Cambrian rocks,
which were supposed to contain its first traces, as these are before
the middle period of the earth's life-history, some hesitation should
be felt. Further, the accurate appreciation of the evidence for such a
fossil as Eozoon required an amount of knowledge of minerals, of the
more humble types of animals, and of the conditions of mineralization
of organic remains, possessed by few even of professional geologists.
Thus Eozoon has met with some negative scepticism and positive
opposition--though the latter has been smaller in amount than might
have been anticipated, when we consider the novel and startling
character of the facts adduced. The most annoying element in the
discussion has consisted in the liability of observers, only partially
informed, to confound our specimens with things of very different
character, from which we had taken pains to distinguish them.
[Footnote 24: In _Quarterly Journal of Geological Society_, vol. xxii.;
_Proc. Royal Society_, vol. xv.; _Intellectual Observer_, 1865; _Annals
and Magazine of Natural History_, 1874; and other papers and notices.]
"The united thickness," says Sir William Logan, "of these three great
series, the Lower and Upper Laurentian and Huronian, may possibly far
surpass that of all succeeding rocks, from the base of the Palæozoic to
the present time. We are thus carried back to a period so far remote
that the appearance of the so-called Primordial fauna may be considered
a comparatively modern event."[25] So great a revolution of thought,
and this based on one fossil, of a character little recognisable by
geologists generally, might well tax the faith of a class of men
usually regarded as somewhat faithless and sceptical. Yet this new
extension of life has been very generally received, and has found
its way into text-books and popular treatises. Its opponents have
been under the necessity of inventing the most strange and incredible
pseudomorphoses of mineral substances to account for the facts. As
might have been expected, after the publication of the original paper,
other facts developed themselves. Mr. Vennor found other and scarcely
altered specimens closely allied to the Laurentian forms in the
Hastings series of Tudor, probably of Huronian age. Gümbel recognised
the organism in Laurentian rocks in Bavaria and elsewhere in Europe,
and discovered a new species in the Huronian of Bavaria.[26] Eozoon was
recognised in Laurentian limestones in Massachusetts[27] and New York,
and there has been a rapid growth of new facts increasing our knowledge
of Foraminifera and other humble animals in the succeeding Eozoic and
Palæozoic rocks. Special interest attaches to the discovery by Mr.
Vennor, and by Walcott and Matthew, to be mentioned in the sequel,
and tending to bridge over the interval between the Laurentian fossil
and those of the Lower Cambrian. Another fact, whose significance is
not to be over-estimated, is the recognition both by Dr. Carpenter
and myself of specimens in which the canals are occupied by dolomite
or by calcite like that of the organism itself I have made several
visits to the locality at Petite Nation originally discovered by
Mr. Lowe, in company with Dr. Carpenter, Dr. Bonney,[28] and other
skilled observers, and have very carefully studied all the facts with
reference to the mode of occurrence of the forms in the beds, and their
association with layers of fragmental Eozoon, and have found that these
are strictly in accordance with the theory that these old Laurentian
limestones are truly marine deposits, holding the remains of the sea
animals of their time.
[Footnote 25: _Journal Geological Society_, February, 1865.]
[Footnote 26: _Ueber das Vorkommen von Eozoon_, 1866.]
[Footnote 27: By Mr. Bicknell at Newbury, and Mr. Burbank at
Chelmsford. The latter gentleman has since maintained that the
limestones at the latter place are not true beds; but his own
descriptions and figures lead to the belief that this is an error
of observation on his part. The Eozoon in the Chelmsford specimens
and in those of Warren, New York, is in small and rare fragments in
serpentinous limestone.]
[Footnote 28: See an excellent account of one of these visits by Dr.
Bonney, _Geological Magazine_, 1895.]
Eozoon is not, however, the only witness to the great fact of
Laurentian life, of which it is the most conspicuous exponent. In many
of the Laurentian limestones, mixed with innumerable fragments of
Eozoon, there are other fragments with traces of organic structure of
a different character. There are also casts in silicious matter which
seem to indicate smaller species of Foraminifera; and large laminated
forms, apparently organic, yet distinct from Eozoon. Some of these must
be noticed in the following pages.
Other discoveries also are foreshadowed here. The microscope may
yet detect the true nature and affinities of some of the fragments
associated with Eozoon. Less altered portions of the Laurentian rocks
may be found, where even the vegetable matter may retain its organic
forms, and where fossils may be recognised by their external outlines
as well as by their internal structure. Thus the time may come when
the rocks now called Primordial shall not be held to be so in any
strict sense, and when swarming dynasties of Protozoa and other low
forms of life may be known as inhabitants of oceans vastly ancient as
compared with even the old Primordial seas. Who knows whether even the
land of the Laurentian time may not have been clothed with plants,
perhaps as much more strange and weird than those of the Devonian and
Carboniferous, as those of the latter are when compared with modern
forests?
_THE DAWN OF LIFE_
VII
_THE DAWN OF LIFE_
In the Grenvillian system, as represented in the vicinity of the
Ottawa River, perfect specimens of Eozoon are found in one only of
the principal limestones there exposed, and in certain layers of that
limestone, and they are associated with concretions and grains of the
greenish mineral serpentine, which, as we shall see, has much to do
with their preservation. As exposed on broken surfaces, the specimens
consist of concentric layers of greenish serpentine and white calcite,
not, however, even or uniform, as in ordinary concretions having
concentric structure, but often approaching and uniting with each
other, so as to constitute wide flat chambers, and forming patches from
an inch to nearly a foot in diameter, while some of the larger patches
seem to coalesce or to become confluent. On weathered surfaces the
serpentine laminæ often become brown, owing to the rusting of the iron
contained in them, and project above the general surface, in this case
resembling very much the appearance of the layer-corals so plentiful in
some limestones of later date.
The external forms of Eozoon are at first sight not very obvious,
as they adhere very closely to the containing rock; but the smaller
specimens, when entirely weathered out or disengaged by the solution of
the limestone in an acid, usually present the form of a broad inverted
cone, like some modern sponges or the broader turbinate fossil corals
(Fig. 32). The limestone having, like the other beds of the formation,
been much compressed and folded, the specimens of Eozoon are sometimes
crumpled in these folds or broken across by small cracks or faults,
which shift the laminæ slightly out of their places. The cracks thus
formed are also sometimes filled with a fibrous variety of serpentine,
known to mineralogists as chrysotile and popularly as "rock cotton"
or "asbestus." It is finely fibrous, and of a silky lustre, and must
have been deposited by water in the cracks and fissures formed by the
fracturing of the rock and the contained fossils, by movements taking
place after the whole was hardened. Accordingly these veins often cross
not only the rock, but also the serpentine and calcite layers of the
contained masses of Eozoon, without regard to the direction of their
laminæ, though sometimes they run parallel to the structure, the rock
having broken more easily in that direction.
[Illustration: Fig. 32.--_Entire specimen of Eozoon, disengaged from
the matrix and showing its turbinate form, enclosed in the outline of a
larger specimen of similar form._
Both natural size, Côte St. Pierre. (Specimens in Peter Redpath
Museum.)]
Bearing in mind these general points of material form and appearance,
we may now proceed to inquire as to the following points: (1) _The
structures visible in the specimens_; (2) _The manner in which they are
represented by different mineral substances, and how these are to be
accounted for_; (3) _The explanation of the whole on the supposition
that we are dealing with an animal fossil_.
(1) In regard to the first of these questions, I may quote here, with
some slight alteration, from a recent memoir of my own[29]:--
[Footnote 29: _London Geological Magazine_, 1895.]
In recent years I have been disposed to attach more importance than
formerly to the general form of Eozoon. The earlier examples studied
were, for the most part, imbedded in the limestone in such a manner
as to give little definite information as to external form; and at a
later date, when Sir William Logan employed one of his assistants, Mr.
Lowe, to quarry large specimens at Grenville and Côte St. Pierre, the
attempt was made to secure the most massive blocks possible, in order
to provide large slabs for showy museum specimens.
[Illustration: Fig. 33.--_Weathered surface of Eozoon._ Showing
sections of two funnels or tubes with limiting walls, Côte St. Pierre.]
More recently, when collections have been made from the eroded and
crumbling surfaces of the limestone in its wider exposures, it was
found that specimens of moderate size had been weathered out, and
could, either naturally or by treatment with acid, be entirely
separated from the matrix. Such specimens sometimes showed, either on
the surfaces or on the sides of "funnels" and tubes penetrating the
mass (Figs. 33, 34), a confluence of the laminæ, constituting a porous
cortex or limiting structure. Specimens of this kind were figured in
1888, and I was enabled to add to the characters of the species that
the original and proper form was "broadly turbinate with a depression
or cavity above, and occasionally with oscula or pits penetrating the
mass." The great flattened masses thus seemed to represent confluent or
overgrown individuals, often contorted by the folding of the enclosing
beds.
[Illustration: Fig. 34.--_Section of the Base of a specimen of Eozoon._]
This specimen shows an oscuilform, cylindrical funnel, cut in such
a manner as to show its _reticulated wall_ and the descent of the
laminæ toward it. Two-thirds of natural size. From a photograph. Col.
Carpenter, also in Redpath Museum.
[This illustration (from Prof. Prestwich's "Geology," vol. ii. p. 21)
has been courteously lent by the Clarendon Press, Oxford.]
There are also in well-preserved specimens certain constant properties
of the calcite and serpentine layers. The former are continuous,
and connected at intervals, so that if the silicious filling of
the chambers could be removed, the calcareous portion would form a
continuous skeleton, while the serpentine filling the chambers, when
the calcareous plates are dissolved out by an acid, forms a continuous
cast of the animal matter filling the chambers (Fig. 36). This cast
of the sarcodous material, when thus separated, is very uniformly
and beautifully mammillated on the surfaces of the laminæ, and this
tuberculation gradually passes upward into smaller chambers having
amœboid outlines, and finally into rounded chamberlets. It is also
a very constant point of structure that the lower laminæ of calcite
are thicker than those above, and have the canal-systems larger and
coarser. There is thus in the more perfect specimens a definite plan of
macroscopical structure (Fig. 35).
[Illustration: Fig. 35.--_Structure of small specimen of Eozoon,
calcareous matter removed._]
1. Natural size. 2. Acervuline cells of upper part. 3. Group of the
same coalescing into a lamina with tuberculated surface. 4. Laminæ with
tuberculated surfaces in section. (See also Fig. 36.)
[Illustration: Fig. 36.--_Decalcified Eozoon, in section, slightly
enlarged._ Showing the character of the sarcodous laminæ now replaced
by Serpentine.]