Chapter 7

Fig. 36.Archæospherinæ from Pargas in Finland.(After Gümbel.)Magnified.

Fig. 36.Archæospherinæ from Pargas in Finland.(After Gümbel.)

Magnified.

Gümbel has further found in beds overlying the older Eozoic series, and probably of the same age with the Canadian Huronian, a different species of Eozoon, with smaller and more contracted chambers, and still finer and more crowded canals. This, which is to be regarded as a distinct species, or at least a well-marked varietal form, he has namedEozoon Bavaricum(fig. 37). Thus this early introduction of life is not peculiar to that old continent which we sometimes call the NewWorld, but applies to Europe as well, and Europe has furnished a successor to Eozoon in the later Eozoic or Huronian period. In rocks of this age in America, after long search and much slicing of limestones, I have hitherto failed to find any decided organic remains other than the Tudor and Madoc specimens of Eozoon. If these are really Huronian and not Laurentian, the Eozoon from this horizon does not sensibly differ from that of the Lower Laurentian. The curious limpet-like objects from Newfoundland, discovered by Murray, and described by Billings,[AH]under the nameAspidella, are believed to be Huronian, but they have no connection with Eozoon, and therefore need not detain us here.

[AH]Canadian Naturalist, 1871.

Fig. 37.Section of Eozoon Bavaricum, with Serpentine, from the Crystalline Limestone of the Hercynian primitive Clay-state Formation at Hohenberg; 25 diameters.(a.) Sparry carbonate of lime. (b.) Cellular carbonate of lime. (c.) System of tubuli. (d.) Serpentine replacing the coarser ordinary variety. (e.) Serpentine and hornblende replacing the finer variety, in the very much contorted portions.

Fig. 37.Section of Eozoon Bavaricum, with Serpentine, from the Crystalline Limestone of the Hercynian primitive Clay-state Formation at Hohenberg; 25 diameters.

(a.) Sparry carbonate of lime. (b.) Cellular carbonate of lime. (c.) System of tubuli. (d.) Serpentine replacing the coarser ordinary variety. (e.) Serpentine and hornblende replacing the finer variety, in the very much contorted portions.

Leaving the Eozoic age, we find ourselves next in the Primordial or Cambrian, and here we discover the seaalready tenanted by many kinds of crustaceans and shell-fishes, which have been collected and described by palæontologists in Bohemia, Scandinavia, Wales, and North America;[AI]curiously enough, however, the rocks of this age are not so rich in Foraminifera as those of some succeeding periods. Had this primitive type played out its part in the Eozoic and exhausted its energies, and did it remain in abeyance in the Primordial age to resume its activity in the succeeding times? It is not necessary to believe this. The geologist is familiar with the fact, that in one formation he may have before him chiefly oceanic and deep-sea deposits, and in another those of the shallower waters, and that alternations of these may, in the same age or immediately succeeding ages, present very different groups of fossils. Now the rocks and fossils of the Laurentian seem to be oceanic in character, while the Huronian and early Primordial rocks evidence great disturbances, and much coarse and muddy sediment, such as that found in shallows or near the land. They abound in coarse conglomerates, sandstones and thick beds of slate or shale, but are not rich in limestones, which do not in the parts of the world yet explored regain their importance till the succeeding Siluro-Cambrian age. No doubt there were, in the Primordial, deep-sea areas swarming with Foraminifera, the successors of Eozoon; but these are as yet unknown or little known, and our known Primordial fauna is chiefly that of the shallows. Enlarged knowledge may thus bridge over much of the apparent gap in the life of these two great periods.

[AI]Barrande, Angelin, Hicks, Hall, Billings, etc.

Only as yet on the coast of Labrador and neighbouring parts of North America, and in rocks that were formed in seas that washed the old Laurentian rocks, in which Eozoon was already as fully sealed up as it is at this moment, do we find Protozoa which can claim any near kinship to the proto-foraminifer. These are the fossils of the genusArchæocyathus—“ancient cup-sponges, or cup-foraminifers,” which have been described in much detail by Mr. Billings in the reports of the Canadian Survey. Mr. Billings regards them as possibly sponges, or as intermediate between these and Foraminifera, and the silicious spicules found in some of them justify this view, unless indeed, as partly suspected by Mr. Billings, these belong to true sponges which may have grown along with Archæocyathus or attached to it. Certain it is, however, that if allied to sponges, they are allied also to Foraminifera, and that some of them deviate altogether from the sponge type and become calcareous chambered bodies, the animals of which can have differed very little from those of the Laurentian Eozoon. It is to these calcareous Foraminiferal species that I shall at present restrict my attention. I give a few figures, for which I am indebted to Mr. Billings, of three of his species (figs. 38 to 40), with enlarged drawings of the structures of one of them which has the most decidedly foraminiferal characters.

Fig. 38.Archæocyathus Minganensis—a Primordial Protozoon.(After Billings.)(a.) Pores of the inner wall.

Fig. 38.Archæocyathus Minganensis—a Primordial Protozoon.(After Billings.)

(a.) Pores of the inner wall.

Fig. 39.Archæocyathus profundus—showing the base of attachment and radiating chambers.(After Billings.)

Fig. 40.Archæocyathus Atlanticus—showing outer surface and longitudinal and transverse sections.(After Billings.)

Fig. 41.Structures of Archæocyathus Profundus.(a.) Lower acervuline portion. (b.) Upper portion, with three of the radiating laminæ. (c.) Portion of lamina with pores and thickened part with canals. In figs.aandbthe calcareous part is unshaded.

Fig. 41.Structures of Archæocyathus Profundus.

(a.) Lower acervuline portion. (b.) Upper portion, with three of the radiating laminæ. (c.) Portion of lamina with pores and thickened part with canals. In figs.aandbthe calcareous part is unshaded.

To understand Archæocyathus, let us imagine an inverted cone of carbonate of lime from an inch or two to a foot in length, and with its point buried in the mud at the bottom of the sea, while its open cup extends upward into the water. The lower part buried in the soil is composed of an irregular acervuline network of thick calcareous plates, enclosing chambers communicating with one another (figs. 40 and 41A). Above this where the cup expands, its walls are composed of thin outer and inner plates, perforated with innumerable holes, and connected with each other by vertical plates, which are also perforated with round pores, establishing a communication between the radiating chambers into which they divide the thickness of the wall (figs. 38, 39, and 41B). In such a structure the chambers in the wall of the cup and the irregular chambers of the base would be filled with gelatinous animal matter, and the pseudopods would project from the numerous pores in the inner and outer wall. In the older parts of the skeleton, thestructure is further complicated by the formation of thin transverse plates, irregular in distribution, and where greater strength is required a calcareous thickening is added, which in some places shows a canal system like that of Eozoon (fig. 41,B,C).[AJ]As compared with Eozoon, the fossils want its fine perforated wall, but have a more regular plan of growth. There are fragments in the Eozoon limestones which may have belonged to structures like these; and when we know more of the deep sea of the Primordial, we may recover true species of Eozoon from it, or may find forms intermediate between it and Archæocyathus. In the meantime I know no nearer bond of connection between Eozoon and the Primordial age than that furnished by the ancient cup Zoophytes of Labrador, though I have searched very carefully in the fossiliferous conglomerates of Cambrian age on the Lower St. Lawrence, which contain rocks of all the formations from the Laurentian upwards, often with characteristic fossils. I have also made sections of many of the fossiliferous pebbles in these conglomerates without finding any certain remains of such organisms, though the fragments of the crusts of some of the Primordial tribolites, when their tubuli are infiltrated with dark carbonaceous matter, are so like the supplemental skeleton of Eozoon, that but fortheir forms they might readily be mistaken for it; and associated with them are broken pieces of other porous organisms which may belong to Protozoa, though this is not yet certain.

[AJ]On the whole these curious fossils, if regarded as Foraminifera, are most nearly allied to the Orbitolites and Dactyloporæ of the Early Tertiary period, as described by Carpenter.

Of all the fossils of the Silurian rocks those which most resemble Eozoon are theStromatoporæ, or “layer-corals,” whose resemblance to the old Laurentian fossil at once struck Sir William Logan; and these occur in the earliest great oceanic limestones which succeed the Primordial period, those of the Trenton group, in the Siluro-Cambrian. From this they extend upward as far as the Devonian, appearing everywhere in the limestones, and themselves often constituting large masses of calcareous rock. Our figure (fig. 42) shows a small example of one of these fossils; and when sawn asunder or broken across and weathered, they precisely resemble Eozoon in general appearance, especially when, as sometimes happens, their cell-walls have been silicified.

Fig. 42.Stromatopora rugosa, Hall—Lower Silurian, Canada.(After Billings.)The specimen is of smaller size than usual, and is silicified. It is probably inverted in position, and the concentric marks on the outer surface are due to concretions of silica.

Fig. 42.Stromatopora rugosa, Hall—Lower Silurian, Canada.(After Billings.)

The specimen is of smaller size than usual, and is silicified. It is probably inverted in position, and the concentric marks on the outer surface are due to concretions of silica.

There are, however, different types of these fossils. The most common, the Stromatoporæ properly so called, consist of concentric layers of calcareous matter attached to each other by pillar-like processes, which, as well as the layers, are made up of little threads of limestone netted together, or radiating from the tops and bottoms of the pillars, and forming a very porous substance. Though they have been regarded as corals by some, they are more generally believed to be Protozoa; but whether more nearly allied to sponges or to Foraminifera may admit of doubt. Some of the moreporous kinds are not very dissimilar from calcareous sponges, but they generally want true oscula and pores, and seem better adapted to shield the gelatinous body of a Foraminifer projecting pseudopods in search of food, than that of a sponge, living by the introduction of currents of water. Many of the denser kinds, however, have their calcareous floors so solid that they must be regarded as much more nearly akin to Foraminifers, and some of them have the same irregular inosculation of these floors observed in Eozoon.Figs. 43,AtoD, show portions of species of this description, in which the resemblance to Eozoon in structure and arrangement of parts is not remote.

Fig. 43.Structures of Stromatopora.(a.) Portion of an oblique section magnified, showing laminæ and columns. (b.) Portion of wall with pores, and crusted on both sides with quartz crystals. (c.) Thickened portion of wall with canals. (d.) Portion of another specimen, showing irregular laminæ and pillars.

Fig. 43.Structures of Stromatopora.

(a.) Portion of an oblique section magnified, showing laminæ and columns. (b.) Portion of wall with pores, and crusted on both sides with quartz crystals. (c.) Thickened portion of wall with canals. (d.) Portion of another specimen, showing irregular laminæ and pillars.

These fossils, however, show no very distinct canal system or supplemental skeleton, but this also appears in those forms which have been called Caunopora or Cœnostroma. In these the plates are traversed bytubes, or groups of tubes, which in each successive floor give out radiating and branching canals exactly like those of Eozoon, though more regularly arranged; and if we had specimens with the canals infiltrated with glauconite or serpentine, the resemblance would be perfect. When, as in figs. 44 and 45A, these canals are seen on the abraded surface, they appear as little grooves arranged in stars, which resemble the radiating plates of corals, but this resemblance is altogether superficial, and I have no doubt that they are really foraminiferal organisms. This will appear more distinctly from the sections infig. 45B,C, which represents an undescribed species recently found by Mr. Weston, in the Upper Silurian limestone of Ontario.

Fig. 44.Caunopora planulata, Hall—Devonian; showing the radiating canals on a weathered surface.(After Hall.)Fig. 45.Cœnostroma—Guelph Limestone, Upper Silurian, from a specimen collected by Mr. Weston, showing the canals.(a.) Surface with canals, natural size. (b.) Vertical section, natural size. (c.) The same magnified, showing canals and laminæ.

Fig. 44.Caunopora planulata, Hall—Devonian; showing the radiating canals on a weathered surface.(After Hall.)

Fig. 45.Cœnostroma—Guelph Limestone, Upper Silurian, from a specimen collected by Mr. Weston, showing the canals.

(a.) Surface with canals, natural size. (b.) Vertical section, natural size. (c.) The same magnified, showing canals and laminæ.

There are probably many species of these curious fossils, but their discrimination is difficult, and their nomenclature confused, so that it would not be profitable to engage the attention of the reader with it except in a note. Their state of preservation, however, is so highly illustrative of that of Eozoon that a word as to this will not be out of place. They aresometimes preserved merely by infiltration with calcite or dolomite, and in this case it is most difficult to make out their minute structures. Often they appear merely as concentrically laminated masses which, but for their mode of occurrence, might be regarded as mere concretions. In other cases the cell-walls and pillars are perfectly silicified, and then they form beautiful microscopic objects, especially when decalcified with an acid. In still other cases, they are preserved like Eozoon, the walls being calcareous and the chambers filled with silica. In this state when weathered or decalcified they are remarkably like Eozoon, but I have not met with any having their minute pores and tubes so well preserved as in some of the Laurentian fossils. In many of them, however, the growth and overlapping of the successive amœba-like coats of sarcode can be beautifully seen, exactly as on the surface of a decalcified piece of Eozoon. Those in my collection which most nearly resemble the Laurentian specimensare from the older part of the Lower Silurian series; but unfortunately their minute structures are not well preserved.

In the Silurian and Devonian ages, these Stromatoporæ evidently carried out the same function as the Eozoon in the Laurentian. Winchell tells us that in Michigan and Ohio single specimens can be found several feet in diameter, and that they constitute the mass of considerable beds of limestone. I have myself seen in Canada specimens a foot in diameter, with a great number of laminæ. Lindberg[AK]has given a most vivid account of their occurrence in the Isle of Gothland. He says that they form beds of large irregular discs and balls, attaining a thickness of five Swedish feet, and traceable for miles along the coast, and the individual balls are sometimes a yard in diameter. In some of them the structure is beautifully preserved. In others, or in parts of them, it is reduced to a mass of crystalline limestone. This species is of the Cœnostroma type, and is regarded by Lindberg as a coral, though he admits its low type and resemblance to Protozoa. Its continuous calcareous skeleton he rightly regards as fatal to its claim to be a true sponge. Such a fossil, differing as it does in minute points of structure from Eozoon, is nevertheless probably allied to it in no very distant way, and a successor to its limestone-making function. Those which most nearly approach to Foraminifera are those with thick and solid calcareous laminæ, and with a radiating canalsystem; and one of the most Eozoon-like I have seen, is a specimen of the undescribed species already mentioned from the Guelph (Upper Silurian) limestone of Ontario, collected by Mr. Weston, and now in the Museum of the Geological Survey. I have attempted to represent its structures infig. 44.

[AK]Transactions of Swedish Academy, 1870.

In the rocks extending from the Lower Silurian and perhaps from the Upper Cambrian to the Devonian inclusive, the type and function of Eozoon are continued by the Stromatoporæ, and in the earlier part of this time these are accompanied by the Archæocyathids, and by another curious form, more nearly allied to the latter than to Eozoon, theReceptaculites. These curious and beautiful fossils, which sometimes are a foot in diameter, consist, like Archæocyathus, of an outer and inner coat enclosing a cavity; but these coats are composed of square plates withpores at the corners, and they are connected by hollow pillars passing in a regular manner from the outer to the inner coat. They have been regarded by Salter as Foraminifers, while Billings considers their nearest analogues to be the seed-like germs of some modern silicious sponges. On the whole, if not Foraminifera, they must have been organisms intermediate between these and sponges, and they certainly constitute one of the most beautiful and complex types of the ancient Protozoa, showing the wonderful perfection to which these creatures attained at a very early period. (Figs. 46, 47, 48.)

Fig. 46.Receptaculites, restored.(After Billings.)(a.) Aperture. (b.) Inner wall. (c.) Outer wall. (n.) Nucleus, or primary chamber. (v.) Internal cavity.Fig. 47.Diagram of Wall and Tubes of Receptaculites.(After Billings.)(b.) Inner wall. (c.) Outer wall. (d.) Section of plates. (e.) Pore of inner wall. (f.) Canal of inner wall. (g.) Radial stolon. (h.) Cyclical stolon. (k.) Suture of plates of outer wall.Fig. 48.Receptaculites, Inner Surface of Outer Wall with the Stolons remaining on its Surface.(After Billings.)

Fig. 46.Receptaculites, restored.(After Billings.)

(a.) Aperture. (b.) Inner wall. (c.) Outer wall. (n.) Nucleus, or primary chamber. (v.) Internal cavity.

Fig. 47.Diagram of Wall and Tubes of Receptaculites.(After Billings.)

(b.) Inner wall. (c.) Outer wall. (d.) Section of plates. (e.) Pore of inner wall. (f.) Canal of inner wall. (g.) Radial stolon. (h.) Cyclical stolon. (k.) Suture of plates of outer wall.

Fig. 48.Receptaculites, Inner Surface of Outer Wall with the Stolons remaining on its Surface.(After Billings.)

I might trace these ancient forms of foraminiferal life further up in the geological series, and show how in the Carboniferous there are nummulitic shells conforming to the general type of Eozoon, and in some cases making up the mass of great limestones.[AL]Further, in the great chalk series and its allied beds, and in the Lower Tertiary, there are not only vast foraminiferal limestones, but gigantic species reminding us of Stromatopora and Eozoon.[AM]Lastly, more diminutive species are doing similar work on a great scale in the modern ocean. Thus we may gather up the broken links of the chain of foraminiferal life, and affirm that Eozoon has never wanted some representative to uphold its family and function throughout all the vast lapse of geological time.

[AL]Fusulina, as recently described by Carpenter,Archæodiscusof Brady, and the Nummulite recently found in the Carboniferous of Belgium.

[AM]ParkeriaandLoftusiaof Carpenter.

NOTES TO CHAPTER VI.

(A.)Stromatoporidæ, Etc.

For the best description of Archæocyathus, I may refer toThe Palæozoic Fossils of Canada, by Mr. Billings, vol. i. There also, and in Mr. Salter’s memoir inThe Decades of the Canadian Survey, will be found all that is known of the structure of Receptaculites. For the American Stromatoporæ I may refer to Winchell’s paper in theProceedings of the American Association, 1866; to Professor Hall’s Descriptions of New Species of Fossils from Iowa,Report of the State Cabinet, Albany, 1872; and to the Descriptions of Canadian Species by Dr. Nicholson, in hisReport on the Palæontology of Ontario, 1874.The genus Stromatopora of Goldfuss was defined by him as consisting of laminæ of a solid and porous character, alternating and contiguous, and constituting a hemispherical or sub-globose mass. In this definition, the porous strata are really those of the fossil, the alternating solid strata being the stony filling of the chambers; and the descriptions of subsequent authors have varied according as, from the state of preservation of the specimens or other circumstances, the original laminæ or the filling of the spaces attracted their attention. In the former case the fossil could be described as consisting of laminæ made up of interlaced fibrils of calcite, radiating from vertical pillars which connect the laminæ. In the latter case, the laminæ, appear as solid plates, separated by very narrow spaces, and perforated with round vertical holes representing the connecting pillars. These Stromatoporæ range from the Lower Silurian to the Devonian, inclusive, and many species have been described; but their limits are not very definite, though there are undoubtedly remarkable differences in the distances of the laminæ and in their texture, and in the smooth or mammillated character of the masses. Hall’s genus Stromatocerium belongs to these forms, and D’Orbigny’s genus Sparsispongia refers to mammillated species, sometimes with apparent oscula.

The genus Stromatopora of Goldfuss was defined by him as consisting of laminæ of a solid and porous character, alternating and contiguous, and constituting a hemispherical or sub-globose mass. In this definition, the porous strata are really those of the fossil, the alternating solid strata being the stony filling of the chambers; and the descriptions of subsequent authors have varied according as, from the state of preservation of the specimens or other circumstances, the original laminæ or the filling of the spaces attracted their attention. In the former case the fossil could be described as consisting of laminæ made up of interlaced fibrils of calcite, radiating from vertical pillars which connect the laminæ. In the latter case, the laminæ, appear as solid plates, separated by very narrow spaces, and perforated with round vertical holes representing the connecting pillars. These Stromatoporæ range from the Lower Silurian to the Devonian, inclusive, and many species have been described; but their limits are not very definite, though there are undoubtedly remarkable differences in the distances of the laminæ and in their texture, and in the smooth or mammillated character of the masses. Hall’s genus Stromatocerium belongs to these forms, and D’Orbigny’s genus Sparsispongia refers to mammillated species, sometimes with apparent oscula.

Phillip’s genus Caunopora was formed to receive specimens with concentric cellular layers traversed by “long vermiform cylindrical canals;” while Winchell’s genus Cœnostroma includes species with these vermiform canals arranged in a radiate manner, diverging from little eminences in the concentric laminæ. The distinction between these last genera does not seem to be very clear, and may depend on the state of preservation of the specimens. A more important distinction appears to exist between those that have a single vertical canal from which the subordinate canals diverge, and those that have groups of such canals.Some species of the Cœnostroma group have very dense calcareous laminæ traversed by the canals; but it does not seem that any distinction has yet been made between the proper wall and the intermediate skeleton; and most observers have been prevented from attending to such structures by the prevailing idea that these fossils are either corals or sponges, while the state of preservation of the more delicate tissues is often very imperfect.

Some species of the Cœnostroma group have very dense calcareous laminæ traversed by the canals; but it does not seem that any distinction has yet been made between the proper wall and the intermediate skeleton; and most observers have been prevented from attending to such structures by the prevailing idea that these fossils are either corals or sponges, while the state of preservation of the more delicate tissues is often very imperfect.

(B.)Localities of Eozoon, or of Limestones supposed to contain it.

In Canada the principal localities of Eozoon Canadense are at Grenville, Petite Nation, the Calumets Rapids, Burgess, Tudor, and Madoc. At the two last places the fossil occurs in beds which may be on a somewhat higher horizon than the others. Mr. Vennor has recently found specimens which have the general form of Eozoon, though the minute structure is not preserved, at Dalhousie, in Lanark Co., Ontario. One specimen from this place is remarkable from having been mineralized in part by a talcose mineral associated with serpentine.I have examined specimens from Chelmsford, in Massachusetts, and from Amity and Warren County, New York, the latter from the collection of Professor D. S. Martin, which show the canals of Eozoon in a fair state of preservation, though the specimens are fragmental, and do not show the laminated structure.

I have examined specimens from Chelmsford, in Massachusetts, and from Amity and Warren County, New York, the latter from the collection of Professor D. S. Martin, which show the canals of Eozoon in a fair state of preservation, though the specimens are fragmental, and do not show the laminated structure.

In European specimens of limestones of Laurentian age, from Tunaberg and Fahlun in Sweden, and from the Western Islands of Scotland, I have hitherto failed to recognise the characteristic structure of the fossil. Connemara specimens have also failed to afford me any satisfactory results, and specimens of a serpentine limestone from the Alps, collected by M. Favre, and communicated to me by Dr. Hunt, though in general texture they much resemble acervuline Eozoon, do not show its minute structures.

Plate VII.Untouched nature-print of part of a large specimen of Eozoon, from Petite Nation.The lighter portions are less perfect than in the original, owing to the finer laminæ of serpentine giving way. The dark band at one side is one of the deep lacunæ or oscula.

Plate VII.

Untouched nature-print of part of a large specimen of Eozoon, from Petite Nation.

The lighter portions are less perfect than in the original, owing to the finer laminæ of serpentine giving way. The dark band at one side is one of the deep lacunæ or oscula.

CHAPTER VII.OPPONENTS AND OBJECTIONS.

Theactive 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]

[AN]Also Rowney and King’s papers inJournal Geological Society, August, 1866; andProceedings 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 naturalistshave 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 ofLaurentian 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. Thebrilliant 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 remarkswhich 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 theEozoon Bavaricumof 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 nameEozoon 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 andgeneration 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 beor have been given; and I now merely add (infig. 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.

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.

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 formationwhose 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 impugnthe 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 serpentineconcretions 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 toPlate. VIII., page 207, he will find some interesting illustrations of several very important facts bearing on the above arguments.Fig. 1represents a portion of a very thin slice of a specimen traversed by veins of fibrous serpentine or chrysotile, and having the calcite ofthe 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 minutecanaliculi 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. 3shows 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 5are 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 infig. 5is 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 minutelydirecting 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 Eozoonas 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]

Back to Index Next