VIII
CONTEMPORARIES OF EOZOON
T
THE name Eozoon, or Dawn-animal, raises the question whether we shall ever know any earlier representative of animal life. Here I think it necessary to explain that in suggesting the name Eozoon for the earliest fossil, and Eozoic for the formation in which it is contained, I had no intention to affirm that there may not have been precursors of the Dawn-animal. By the similar term. Eocene, Lyell did not mean to affirm that there may not have been modern types in the preceding geological periods: and so the dawn of animal life may have had its grey or rosy breaking at a time long anterior to that in which Eozoon built its marble reefs. When the fossils of this early auroral time shall be found, it will not be hard to invent appropriate names for them. There are, however, two reasons that give propriety to the name in the present state of our knowledge. One is, that the Laurentian rocks are absolutely the oldest that have yet come under the notice of geologists, and at the present moment it seems extremely improbable that any older sediments exist, at least in a condition to be recognised as such. The other is that Eozoon, as a member of the group Protozoa, of gigantic size and comprehensive type, and oceanic in its habitat, is as likely as any other creature that can be imagined to have been the first representative of animal life on our planet. Vegetable life may have preceded it, nay probably did so by at least one great creative æon, and may have accumulated previous stores of organic matter; but if any older forms of animal life existed, it is certain at least that they cannot have belonged to much simpler or more comprehensive types. It is also to be observed that such forms of life, if they did exist, may have been naked protozoa, which may have left no sign of their existence except a minute trace of carbonaceous matter, and perhaps not even this.
But if we do not know, and perhaps are not likely to know, any animals older than Eozoon, may we not find traces of some of its contemporaries, either in the Eozoon limestones themselves, or other rocks associated with them? Here we must admit that a deep-sea Foraminiferal limestone may give a very imperfect indication of the fauna of its time. A dredger who should have no other information as to the existing population of the world, except what he could gather from the deposits formed under several hundred fathoms of water, would necessarily have very inadequate conceptions of the matter. In like manner a geologist who should have no other information as to the animal life of the Mesozoic ages than that furnished by some of the thick beds of white chalk, might imagine that he had reached a period when the simplest kinds of protozoa predominated over all other forms of life; but this impression would at once be corrected by the examination of other deposits of the same age: so our inferences as to the life of the Laurentian from the contents of its oceanic limestones may be very imperfect, and it may yet yield other and various fossils. Its possibilities are, however, limited by the fact that before we reach this great depth in the earth's crust, we have already left behind in much newer formations all traces of animal life except a few of the lower forms of aquatic invertebrates; so that we are not surprised to find only a limited number of living things, and those of very low type. Do we then know in the Laurentian even a few distinct species, or is our view limited altogether to Eozoon Canadense? In answering this question, we must bear in mind that the Laurentian itself was of vast duration, and that important changes of life may have taken place even between the deposition of the Eozoon limestones and that of those rocks in which we find the comparatively rich fauna of the Primordial age. This subject was discussed by the writer as early as 1865, and I may repeat here what could be said in relation to it at that time:—
"In connection with these remarkable remains, it appeared desirable to ascertain, if possible, what share these or other organic structures may have had in the accumulation of the limestones of the Laurentian series. Specimens were therefore selected by Sir W. E. Logan, and slices were prepared under his direction. On microscopic examination, a number of these were found to exhibit merely a granular aggregation of crystals, occasionally with particles of graphite and other foreign minerals, or a laminated mixture of calcareous and other matters, in the manner of some more modern sedimentary limestones. Others, however, were evidently made up almost entirely of fragments of Eozoon, or of mixtures of these with other calcareous and carbonaceous fragments which afford more or less evidence of organic origin. The contents of these organic limestones may be considered under the following heads:—
1. Remains of Eozoon.
2. Other calcareous bodies, probably organic.
3. Objects imbedded in the serpentine.
4. Carbonaceous matters.
"(1) The more perfect individuals of Eozoon do not constitute the mass of any of the larger specimens in our collections; but considerable portions of some of them are made up of material of similar minute structure, destitute of lamination, and irregularly arranged. Some of this material gives the impression that there may have been organisms similar to Eozoon, but growing in an irregular or acervuline manner without lamination. Of this, however, I cannot be certain; and, on the other hand, there is distinct evidence of the aggregation of fragments of Eozoon in some of these specimens. In some they constitute the greater part of the mass. In others they are imbedded in calcareous matter of a different character, or in serpentine or granular pyroxene. In most of the specimens the cells of the fossils are more or less filled with these minerals; and in some instances it would appear that the calcareous matter of fragments of Eozoon has been in part replaced by serpentine."
[I may add here that in the limestone at Côte St. Pierre there are in some of the beds successive laminæ with grains of serpentine and others with crystals of dolomite, and that both contain fragments of Eozoon. It thus seems as if the magnesia associated with the limestone, at some stages of deposition took the form of silicate, and in others that of carbonate. I may also observe here that I have detected fragments of Eozoon in Laurentian limestone from New Brunswick, from Chelmsford in Massachusetts, from Warren County, New York, from Brazil, and from the Alps.]
"(2) Intermixed with the fragments of Eozoon above referred to are other calcareous matters apparently fragmentary. They are of various angular and rounded forms, and present several kinds of structure. The most frequent of these is a strong lamination varying in direction according to the position of the fragments, but corresponding, as far as can be ascertained, with the diagonal of the rhombohedral cleavage. This structure, though crystalline, is highly characteristic of crinoidal remains when preserved in altered limestones. The more dense parts of Eozoon, destitute of tubuli, also sometimes show this structure, though less distinctly. Other fragments are compact and structureless, or show only a fine granular appearance; and these sometimes include grains, patches, or fibres of graphite. In Cambro-Silurian limestones, fragments of corals and shells which have been partially infiltrated with bituminous matter, show a structure like this. On comparison with altered organic limestones of the Cambro-Silurian system, these appearances would indicate that, in addition to the debris of Eozoon, other calcareous structures, more like those of crinoids, corals, and shells, have contributed to the formation of the Laurentian limestones.
"(3) In the hydrous silicate (Loganite) filling the chambers of a large specimen of Eozoon from Burgess, there are numerous small pieces of foreign matter; and the silicate itself is laminated, indicating its sedimentary nature. Some of the included fragments appear to be carbonaceous, others calcareous; but no distinct organic structure can be detected in them. There are, however, in the Loganite, many minute silicious grains of a bright green colour, resembling green-sand concretions; and the manner In which these are occasionally arranged in lines and groups suggests the supposition that they may possibly be casts of the interior of minute Foraminiferal shells. They may, however, be concretionary in their origin ([Fig. 51]).
Fig. 51.—Archæospherinæ from Burgess Eozoon. Grains included in Loganite.
(Magnified.)
"(4) In some of the Laurentian limestones submitted to me by Sir W. E. Logan, and in others from Arnprior on the Ottawa, there are fibres and granules of carbonaceous matter which do not conform to the crystalline structure, and present appearances quite similar to those which in more modern limestones result from the decomposition of the algæ, etc. Though retaining mere traces of organic structure, little doubt would be entertained as to their vegetable origin if they were found in fossiliferous limestones. In limestones of Upper Laurentian age, near St. John, New Brunswick, more distinct fibres occur, and associated with these beds Matthew has found what seem to be spicules of sponges, some simple and others hexactinelled like those of Protospongia of the Cambrian.
Though the abundance and wide distribution of Eozoon, and the important part it seems to have acted in the accumulation of limestone, indicate that it was one of the most prevalent forms of animal existence in the seas of the Laurentian period, the non-existence of other organic beings is not implied. On the contrary, independently of the indications afforded by the limestones themselves, it is evident that in order to the existence and growth of these large Rhizopods, the waters must have swarmed with more minute animal or vegetable organisms on which they could subsist. On the other hand, though this is a less certain inference, the dense calcareous skeleton of Eozoon may indicate that it also was liable to the attacks of animal enemies. It is also possible that the growth of Eozoon or the deposition of the serpentine and pyroxene in which its remains have been preserved, or both, may have been connected with certain oceanic depths and conditions, and that we have as yet revealed to us the life of only certain stations in the Laurentian seas. Whatever conjectures we may form on these more problematic points, the observations above detailed appear to establish the following conclusions:—
First, that in the Laurentian period, as in subsequent geological epochs, the Rhizopods were important agents in the accumulation of beds of limestone; and secondly, that in this early period these low forms of animal life attained to a development, in point of magnitude and complexity, unexampled, in so far as yet known, in the succeeding ages of the earth's history. This early culmination of the Rhizopods is in accordance with one of the great laws of the succession of living beings, ascertained from the study of the introduction and progress of other groups; and, should it prove that these great Protozoans were really the dominant type of animals in the Laurentian period, this fact might be regarded as an indication that in these ancient rocks we may actually have the records of the first appearance of animal life on our planet.
With reference to the first of the above heads, I have now to state that it seems quite certain that the upper and younger portions of the masses of Eozoon often passed into the acervuline form, and the period in which this change took place seems to have depended on circumstances. In some specimens there are only a few regular layers, and then a heap of irregular cells. In other cases a hundred or more regular layers were formed; but even in this case little groups of irregular cells occurred at certain points near the surface. I have also found some masses clearly not fragmental which consist altogether of acervuline cells. A specimen of this kind is represented in [Fig. 52]. It is oval in outline, enclosed in a nodule of serpentine, about three inches in length, wholly made up of rounded or cylindrical cells, the walls of which have a beautiful tubular structure, but there is little or no supplemental skeleton. Whether this is a portion accidentally broken off from the top of a mass of Eozoon, or a peculiar varietal form, or a distinct species, it would be difficult to determine. In the meantime I have described it as a variety, "acervulina" of the species Eozoon Canadense. It admits of comparison with a fragment figured by Dr. Carpenter, which he compares with the chamberlets and tubes of Nummulites lævigata of the Eocene.[39] Another variety also, from Petite Nation, shows extremely thin laminæ, closely placed together and very massive, and with little supplemental skeleton. This may be allied to the last, and may be named variety "minor."[40]
[39] Proceedings of Geological Society, 1875.
[40] Annals and Magazine of Natural History, Sen 4, vol. xiii. p. 457.
All this, however, has nothing to do with the layers of fragments of Eozoon which are scattered through the Laurentian limestones. In these the fossil is sometimes preserved in the ordinary manner, with its cavities filled with serpentine, and the thicker parts of the skeleton having their canals filled with this substance. In this case the chambers may have been occupied with serpentine before it was broken up. At St. Pierre there are distinct layers of this kind, from half an inch to several inches in thickness, regularly interstratified with the ordinary limestone. In other layers no serpentine occurs, but the interstices of the fragments are filled with crystalline dolomite or magnesian limestone, which has also penetrated the canals; and there are indications, though less manifest, that some at least of the layers of pure limestone are composed of fragmental Eozoon.
Fig. 52.—Acervuline Variety of Eozoon, Côte St. Pierre.
(a) General form, half natural size. (b) Portion of cellular interior, magnified, showing the course of the tubuli.
Fig. 53.—Archæospherinæ from Côte St. Pierre.
(a) Specimens dissolved out by acid, the lower one showing interior septa. (b) Specimens seen in section.
In the Laurentian limestone of Wentworth, belonging apparently to the same band with that of St. Pierre, there are many small rounded pieces of limestone, evidently the debris of some older rock, broken up and rounded by attrition. In some of these fragments the structure of Eozoon may be plainly perceived. This shows that still older limestones composed of Eozoon were at that time undergoing waste, and carries our view of the existence of this fossil back to the very beginning of the Grenville series of the Laurentian.
With respect to organic fragments not showing the structure of Eozoon, I have not as yet been able to refer these to any definite origin. Some of them may be simply thick portions of the shell of Eozoon with their pores filled with calcite, so as to present a homogeneous appearance. Others have much the appearance of fragments of such Primordial forms as Archæocyathus, now usually regarded as corals or sponges; but after much careful search, I have thus far been unable to say more than I could say in 1865.
It is different, however, with the round cells infiltrated with serpentine and with the silicious grains included in the loganite. [Fig. 53] shows such bodies found mixed with fragmental Eozoon and in separate thin layers at Côte St. Pierre. In [Fig. 51], I have shown some of the singular grains found in the loganite occupying the chambers of Eozoon from Burgess, and in [Fig. 54] some remarkable forms of this kind found in the limestones of Long Lake and Wentworth. All these, I think, are essentially of the same nature, namely, chambers originally invested with a tubulated wall like Eozoon, and aggregated in groups, sometimes in a linear manner, sometimes spirally, like those Globigerinæ which constitute the mass of modern deep-sea dredgings and also of the chalk.
Fig. 54.—Archæospherinæ from Long Lake Limestone.
(Magnified.)
(a) Single cell, showing tubulated wall. (b, c) Portions of same more highly magnified, (d) Casts decalcified, and showing casts of tubules.
These bodies occur dispersed in the limestone, arranged in thin layers parallel to the bedding or sometimes in the large chamber-cavities of Eozoon. They are so variable in size and form that it is not unlikely they may be of different origins. The most probable of these may be thus stated. First, they may in some cases be the looser superficial parts of the surface of Eozoon broken up into little groups of cells. Secondly, they may be few-celled germs or buds given off from Eozoon. This would correspond with what Carpenter, and more recently Brady and Lester, have observed in the case of some of the larger of the modern Foraminifera. Thirdly, they may be smaller Foraminifera, structurally allied to Eozoon, but in habit of growth resembling those little globe-shaped forms which, as already stated, abound in chalk and in the modern ocean. The latter view I should regard as highly probable in the case of many of them; and I have proposed for them, in consequence, and as a convenient name, Archæospherinæ or ancient spherical animals. Carbonaceous matter is rare in the true Eozoon limestones, and, as already stated, I would refer the Laurentian graphite or plumbago mainly to plants.
Dr. Gümbel, the Director of the Geological Survey of Bavaria, is one of the most active and widely informed of European geologists, combining European knowledge with an extensive acquaintance with the larger and in some respects more typical areas of the older rocks in America, and stratigraphical geology with enthusiastic interest in the microscopic structures of fossils. He at once, and in a most able manner, took up the question of the application of the discoveries in Canada to the rocks of Bavaria. The spirit in which he did so may be inferred from the following extract:—
"The discovery of organic remains in the crystalline limestones of the ancient gneiss of Canada, for which we are indebted to the researches of Sir William Logan and his colleagues, and to the careful microscopic investigations of Drs. Dawson and Carpenter, must be regarded as opening a new era in geological science.
"This discovery overturns at once the notions hitherto commonly entertained with regard to the origin of the stratified primary limestones, and their accompanying gneissic and quartzose strata, included under the general name of primitive crystalline schists. It shows us that these crystalline stratified rocks, of the so-called primary system, are only a backward prolongation of the chain of fossiliferous strata; the elements of which were deposited as oceanic sediment, like the clay-slates, limestones, and sandstones of the Palæozoic formations, and under similar conditions, though at a time far more remote, and more favourable to the generation of crystalline mineral compounds.
"In this discovery of organic remains in the primary rocks, we hail with joy the dawn of a new epoch in the critical history of these earlier formations. Already in its light, the primeval geological time is seen to be everywhere animated, and peopled with new animal forms of whose very existence we had previously no suspicion. Life, which had hitherto been supposed to have first appeared in the Primordial division of the Silurian period, is now seen to be immeasurably lengthened beyond its former limit, and to embrace in its domain the most ancient known portions of the earth's crust. It would almost seem as if organic life had been awakened simultaneously with the solidification of the earth's crust."
Gümbel has described from limestones of Laurentian age in various parts of Europe forms referable to Eozoon or to Archæospherinæ, and I have found fragmental Eozoon in specimens collected by Favre in the supposed Archæan nucleus of the Alps.
Gümbel also found in the Finnish and Bavarian limestones knotted chambers, like those of Wentworth above mentioned ([Fig. 55]), which he regards as belonging to some other organism than Eozoon; and flocculi having tubes, pores, and reticulations which would seem to point to the presence of structures akin to sponges or possibly remains of seaweeds. These observations Gümbel has extended into other localities in Bavaria and Bohemia, and also in Silesia and Sweden, establishing the existence of Eozoon fossils in all the Laurentian limestones of the middle and north of Europe.
Fig. 55.—Archæospherinæ from Pargas in Finland. (After Gümbel.)
(Magnified.)
Gümbel has further found in beds overlying the older Eozoic series, and probably of the same age with the Canadian Huronian, a different species of Eozoon, with smaller and more contracted chambers, and still finer and more crowded canals. This, which is to be regarded as a distinct species, or at least a well-marked varietal form, he has named Eozoon Bavaricum ([Fig. 56]). Thus this early introduction of life is not peculiar to that old continent which we sometimes call the New World, but applies to Europe as well, and Europe has furnished a successor to Eozoon in the later Eozoic or Huronian period.
Fig. 56.—Section of Eozoon Bavaricum, with Serpentine, from the Crystalline Limestone of the Hercynian primitive Clay-slate Formation at Hohenberg; 25 diameters (probably Huronian).
(a) Sparry carbonate of lime, (b) Cellular carbonate of lime, (c) System of tubuli. (d) Serpentine replacing the coarser ordinary variety, (e) Serpentine and hornblende replacing the finer variety, in the very much contorted portions.
In rocks of this age in America, after long search and much slicing of limestones, I have hitherto failed to find any decided foraminiferal remains other than the Tudor and Madoc specimens, which may be of this age. They are laminated forms resembling Eozoon, but I have reason to believe that their minute structure more closely resembles that of Cryptozoon, though it is somewhat obscure. If these are really Huronian and not Laurentian, the Eozoon from this horizon does not sensibly differ from that of the Lower Laurentian.
We are indebted to Mr. Matthew, of St. John, New Brunswick, who has so greatly distinguished himself by his discoveries in the Cambrian of that region, for some remarkable additions to the contemporaries of Eozoon. One of these is a laminated body, like Eozoon in its general appearance, but growing in crowded masses which by mutual pressure become columnar ([Fig. 57]). In the best preserved specimens each layer seems to consist of a thin lamina separated from its neighbours by a finely granular mass, traversed by innumerable irregular tubes. This recalls the structure of Cryptozoon of Hall, which, as we have seen, is found in pre-Cambrian rocks in Colorado, and abounds in the Upper Cambrian in New York, in Minnesota, and in different parts of Canada, but Archæozoon differs in its form and habit of growth. If the Stromatoporæ of the Ordovician and Silurian are hydroids, this may also be the case with Cryptozoon; but so far as its own structure is concerned, it approaches most nearly to the fossils known as Loftusia in the Carboniferous and later formations, and these are generally regarded as Foraminiferal. We may thus have another giant Foraminiferal organism which contributed to the building up of rocks in the Laurentian seas.
Fig. 57.—Archæozoon Acadiense, Matthew. Diagrammatic transverse and longitudinal sections of a small specimen.
Specimen in Peter Redpath Museum.
Pre-Palæozoic Rocks of Southern New Brunswick,
as tabulated by Matthew:—"
ARCHÆAN
| EOZOIC | Thickness Feet. | |
Coastal series (or system), 1872.— | 10,000 | |
Coldbrook Series (or System), 1865.— | 15,000 | |
Upper series (or system) of Laurentian, 1872. Upper division.—Argillites, limestones, graphitic shales. Fossils. In upper part of the upper limestones of the South basin, fragmental Eozoon, observed by Sir J. W. Dawson in specimens sent him. In middle of upper limestones in Middle basin, spicules of sponges. In graphitic shale of South basin, spicules of Halichondrites graphitiferus. In lowest limestone of the Middle basin, the reef of columnar fossils described as Archæozoon | 750 | |
Middle division.—Quartzites, silicious schists, Fossils Cyathospongia (?) eozoica near the top of this division | 450 | |
Lower division.—Limestones and gneisses. No Fossils known | 260[41] | |
Lower series of Laurentian.— | ? |
[41] The above thicknesses are on the authority of Dr. L. W. Bailey. Report Progress Geological Survey Canada, 1879, pp. 10, D. D., and 21, D. D. Dr. R. W. Ells in the same Report, p. 6, D., describes these rocks, sixty miles east of St. John, as one system, with a thickness of 14,000 feet.
Fig. 57A.—Archæozoon Acadiense, Matthew.
Horizontal and vertical sections of a group of specimens, reduced.
(From Photographs.)
This discovery is also of importance as connecting Eozoon through Cryptozoon with large organisms, probably Protozoa, extending upward to the top of the Cambrian, and thus forming a link of connection between the life of the Eozoic and that of the Palæozoic period. Matthew has also described forms which he regards as spicules of sponges from the Laurentian of New Brunswick.[42] One of these seems to present cruciform needles forming square areas, like the Protospongia of Salter, from the Cambrian. The other has simple elongate needle-like spicules arranged in bundles. Matthew summarizes the rocks containing these fossils as in the table on p, 216, in descending order, the highest bed being below the Etcheminian.[43] The first and second groups, it will be observed, are equivalent to the Huronian; the third corresponds to the Grenvillian, and the fourth to the Lower Laurentian.
[42] Fuller descriptions of these rocks may be found in Rep. Prog. Geol. Surv. of Canada, 1872, pp. 30, 34, etc.
[43] Bulletin Nat. Hist. Society of New Brunswick, 1890 where further details are given as to the fossils.
DIFFICULTIES AND OBJECTIONS