Chapter 6

[Z]Silliman’s Journal[2], xxix., p. 284; xxxii., p. 286.Geology of Canada, p. 577.

[AA]Silliman’s Journal[2], xxxiii., p. 277.Geology of Canada, p. 487.

[AB]Silliman’s Journal[2], xxii., p. 280.

[AC]Report of United States Coast-Survey, 1858, p. 248.

“It appears probable from these observations that glauconite is formed by chemical reactions in the ooze at the bottom of the sea, where dissolved silica comes in contact with iron oxide rendered soluble by organic matter; the resulting silicate deposits itself in the cavities of shells and other vacant spaces. A process analogous to this in its results, has filled the chambers and canals of the LaurentianForaminiferawith other silicates; from the comparative rarity of mechanical impurities in these silicates, however, it would appear that they were deposited in clear water. Alumina and oxide of iron enter into the composition of loganite as well as of glauconite; but in the other replacing minerals, pyroxene and serpentine, we have only silicates of lime and magnesia, which were probably formed by the direct action of alkaline silicates, either dissolved in surface-waters, or in those of submarine springs, upon the calcareous and magnesian salts of the sea-water.”[As stated in the text, the canals of Eozoon are sometimes filled with dolomite, or in part with serpentine and in part with dolomite.]

[As stated in the text, the canals of Eozoon are sometimes filled with dolomite, or in part with serpentine and in part with dolomite.]

(B.)Silurian Limestones holding Fossils infiltrated with Hydrous Silicate.

Since my attention has been directed to this subject, many illustrations have come under my notice of Silurian limestones in which the pores of fossils are infiltrated with hydrous silicates akin to glauconite and serpentine. A limestone of this kind, collected by Mr. Robb, at Pole Hill, in New Brunswick, afforded not only beautiful specimens of portions of Crinoids preserved in this way, but a sufficient quantity of the material was collected for an exact analysis, a note on which was published in the Proceedings of the Royal Irish Academy, 1871.The limestone of Pole Hill is composed almost wholly of organic fragments, cemented by crystalline carbonate of lime, and traversed by slender veins of the same mineral. Among the fragments may be recognised under the microscope portions of Trilobites, and of brachiopod and gastropod shells, and numerous joints and plates of Crinoids. The latter areremarkable for the manner in which their reticulated structure, which is similar to that of modern Crinoids, has been injected with a silicious substance, which is seen distinctly in slices, and still more plainly in decalcified specimens. This filling is precisely similar in appearance to the serpentine filling the canals of Eozoon, the only apparent difference being in the forms of the cells and tubes of the Crinoids, as compared with those of the Laurentian fossil; the same silicious substance also occupies the cavities of some of the small shells, and occurs in mere amorphous pieces, apparently filling interstices. From its mode of occurrence, I have not the slightest doubt that it occupied the cavities of the crinoidal fragments while still recent, and before they had been cemented together by the calcareous paste. This silicious filling is therefore similar on the one hand to that effected by the ancient serpentine of the Laurentian, and on the other to that which results from the depositions of modern glauconite. The analysis of Dr. Hunt, which I give below, fully confirms these analogies.I may add that I have examined under the microscope portions of the substance prepared by Dr. Hunt for analysis, and find it to retain its form, showing that it is the actual filling of the cavities. I have also examined the small amount of insoluble silica remaining after his treatment with acid and alkaline solvents, and find it to consist of angular and rounded grains of quartzose sand.The following are Dr. Hunt’s notes:—"The fossiliferous limestone from Pole Hill, New Brunswick, probably of Upper Silurian age, is light gray and coarsely granular. When treated with dilute hydrochloric acid, it leaves a residue of 5·9 per cent., and the solution gives 1·8 per cent. of alumina and oxide of iron, and magnesia equal to 1·35 of carbonate—the remainder being carbonate of lime. The insoluble matter separated by dilute acid, after washing by decantation from a small amount of fine flocculent matter, consists, apart from an admixture of quartz grains, entirely of casts and moulded forms of a peculiar silicate, which Dr. Dawson has observed in decalcified specimens filling the pores of crinoidal stems; and which when separated by an acid,resembles closely under the microscope the coralloidal forms of arragonite known asflos ferri, the surfaces being somewhat rugose and glistening with crystalline faces. This silicate is sub-translucent, and of a pale green colour, but immediately becomes of a light reddish brown when heated to redness in the air, and gives off water when heated in a tube, without however, changing its form. It is partially decomposed by strong hydrochloric acid, yielding a considerable amount of protosalt of iron. Strong hot sulphuric acid readily and completely decomposes it, showing it to be a silicate of alumina and ferrous oxide, with some magnesia and alkalies, but with no trace of lime. The separated silica, which remains after the action of the acid, is readily dissolved by a dilute solution of soda, leaving behind nothing but angular and partially rounded grains of sand, chiefly of colourless vitreous quartz. An analysis effected in the way just described on 1·187 grammes gave the following results, which give, by calculation, the centesimal composition of the mineral:—

The limestone of Pole Hill is composed almost wholly of organic fragments, cemented by crystalline carbonate of lime, and traversed by slender veins of the same mineral. Among the fragments may be recognised under the microscope portions of Trilobites, and of brachiopod and gastropod shells, and numerous joints and plates of Crinoids. The latter areremarkable for the manner in which their reticulated structure, which is similar to that of modern Crinoids, has been injected with a silicious substance, which is seen distinctly in slices, and still more plainly in decalcified specimens. This filling is precisely similar in appearance to the serpentine filling the canals of Eozoon, the only apparent difference being in the forms of the cells and tubes of the Crinoids, as compared with those of the Laurentian fossil; the same silicious substance also occupies the cavities of some of the small shells, and occurs in mere amorphous pieces, apparently filling interstices. From its mode of occurrence, I have not the slightest doubt that it occupied the cavities of the crinoidal fragments while still recent, and before they had been cemented together by the calcareous paste. This silicious filling is therefore similar on the one hand to that effected by the ancient serpentine of the Laurentian, and on the other to that which results from the depositions of modern glauconite. The analysis of Dr. Hunt, which I give below, fully confirms these analogies.

I may add that I have examined under the microscope portions of the substance prepared by Dr. Hunt for analysis, and find it to retain its form, showing that it is the actual filling of the cavities. I have also examined the small amount of insoluble silica remaining after his treatment with acid and alkaline solvents, and find it to consist of angular and rounded grains of quartzose sand.

The following are Dr. Hunt’s notes:—

"The fossiliferous limestone from Pole Hill, New Brunswick, probably of Upper Silurian age, is light gray and coarsely granular. When treated with dilute hydrochloric acid, it leaves a residue of 5·9 per cent., and the solution gives 1·8 per cent. of alumina and oxide of iron, and magnesia equal to 1·35 of carbonate—the remainder being carbonate of lime. The insoluble matter separated by dilute acid, after washing by decantation from a small amount of fine flocculent matter, consists, apart from an admixture of quartz grains, entirely of casts and moulded forms of a peculiar silicate, which Dr. Dawson has observed in decalcified specimens filling the pores of crinoidal stems; and which when separated by an acid,resembles closely under the microscope the coralloidal forms of arragonite known asflos ferri, the surfaces being somewhat rugose and glistening with crystalline faces. This silicate is sub-translucent, and of a pale green colour, but immediately becomes of a light reddish brown when heated to redness in the air, and gives off water when heated in a tube, without however, changing its form. It is partially decomposed by strong hydrochloric acid, yielding a considerable amount of protosalt of iron. Strong hot sulphuric acid readily and completely decomposes it, showing it to be a silicate of alumina and ferrous oxide, with some magnesia and alkalies, but with no trace of lime. The separated silica, which remains after the action of the acid, is readily dissolved by a dilute solution of soda, leaving behind nothing but angular and partially rounded grains of sand, chiefly of colourless vitreous quartz. An analysis effected in the way just described on 1·187 grammes gave the following results, which give, by calculation, the centesimal composition of the mineral:—

"A previous analysis of a portion of the mixture by fusion with carbonate of soda gave, by calculation, 18·80 p. c. of protoxide of iron, and amounts of alumina and combined silica closely agreeing with those just given."The oxygen ratios, as above calculated, are nearly as 3 : 2 : 1 : 1. This mineral approaches in composition to the jollyte of Von Kobell, from which it differs in containing a portion of alkalies, and only one half as much water. In these respects it agrees nearly with the silicate found by Robert Hoffman, at Raspenau, in Bohemia, where it occurs in thin layers alternatingwith picrosmine, and surrounding masses of Eozoon in the Laurentian limestones of that region;[AD]the Eozoon itself being there injected with a hydrous silicate which may be described as intermediate between glauconite and chlorite in composition. The mineral first mentioned is compared by Hoffman to fahlunite, to which jollyte is also related in physical characters as well as in composition. Under the names of fahlunite, gigantolite, pinite, etc., are included a great class of hydrous silicates, which from their imperfectly crystalline condition, have generally been regarded, like serpentine, as results of the alteration of other silicates. It is, however, difficult to admit that the silicate found in the condition described by Hoffman, and still more the present mineral, which injects the pores of palæozoic Crinoids, can be any other than an original deposition, allied in the mode of its formation, to the serpentine, pyroxene, and other minerals which have injected the Laurentian Eozoon, and the serpentine and glauconite, which in a similar manner fill Tertiary and recent shells."

"The oxygen ratios, as above calculated, are nearly as 3 : 2 : 1 : 1. This mineral approaches in composition to the jollyte of Von Kobell, from which it differs in containing a portion of alkalies, and only one half as much water. In these respects it agrees nearly with the silicate found by Robert Hoffman, at Raspenau, in Bohemia, where it occurs in thin layers alternatingwith picrosmine, and surrounding masses of Eozoon in the Laurentian limestones of that region;[AD]the Eozoon itself being there injected with a hydrous silicate which may be described as intermediate between glauconite and chlorite in composition. The mineral first mentioned is compared by Hoffman to fahlunite, to which jollyte is also related in physical characters as well as in composition. Under the names of fahlunite, gigantolite, pinite, etc., are included a great class of hydrous silicates, which from their imperfectly crystalline condition, have generally been regarded, like serpentine, as results of the alteration of other silicates. It is, however, difficult to admit that the silicate found in the condition described by Hoffman, and still more the present mineral, which injects the pores of palæozoic Crinoids, can be any other than an original deposition, allied in the mode of its formation, to the serpentine, pyroxene, and other minerals which have injected the Laurentian Eozoon, and the serpentine and glauconite, which in a similar manner fill Tertiary and recent shells."

[AD]Journ. für Prakt. Chemie, Bd. 106 (Erster Jahrgang, 1869), p. 356.

(C.)Various Minerals filling Cavities of Fossils in the Laurentian.

The following on this subject is from a memoir by Dr. Hunt in theTwenty-first Report of the Regents of the University of New York, 1874:—"Recent investigations have shown that in some cases the dissemination of certain of these minerals through the crystalline limestones is connected with organic forms. The observations of Dr. Dawson and myself on the Eozoon Canadense showed that certain silicates, namely serpentine, pyroxene, and loganite, had been deposited in the cells and chambers left vacant by the disappearance of the animal matter from the calcareous skeleton of the foraminiferous organism; so that when this calcareous portion is removed by an acid there remains a coherent mass, which is a cast of the soft parts ofthe animal, in which, not only the chambers and connecting canals, but the minute tubuli and pores are represented by solid mineral silicates. It was shown that this process must have taken place immediately after the death of the animal, and must have depended on the deposition of these silicates from the waters of the ocean."The train of investigation thus opened up, has been pursued by Dr. Gümbel, Director of the Geological Survey of Bavaria, who, in a recent remarkable memoir presented to the Royal Society of that country, has detailed his results."Having first detected a fossil identical with the Canadian Eozoon (together with several other curious microscopic organic forms not yet observed in Canada), replaced by serpentine in a crystalline limestone from the primitive group of Bavaria, which he identified with the Laurentian system of this country, he next discovered a related organism, to which he has given the name of Eozoon Bavaricum. This occurs in a crystalline limestone belonging to a series of rocks more recent than the Laurentian, but older than the Primordial zone of the Lower Silurian, and designated by him the Hercynian clay slate series, which he conceives may represent the Cambrian system of Great Britain, and perhaps correspond to the Huronian series of Canada and the United States. The cast of the soft parts of this new fossil is, according to Gümbel, in part of serpentine, and in part of hornblende."His attention was next directed to the green hornblende (pargasite) which occurs in the crystalline limestone of Pargas in Finland, and remains when the carbonate of lime is dissolved as a coherent mass closely resembling that left by the irregular and acervuline forms of Eozoon. The calcite walls also sometimes show casts of tubuli…. A white mineral, probably scapolite was found to constitute some tubercles associated with the pargasite, and the two mineral species were in some cases united in the same rounded grain."Similar observations were made by him upon specimens of coccolite or green pyroxene, occurring in rounded and wrinkled grains in a Laurentian limestone from New York. These,according to Gümbel, present the same connecting cylinders and branching stems as the pargasite, and are by him supposed to have been moulded in the same manner…. Very beautiful evidences of the same organic structure consisting of the casts of tubuli and their ramifications, were also observed by Gümbel in a purely crystalline limestone, enclosing granules of chondrodite, hornblende, and garnet, from Boden in Saxony. Other specimens of limestone, both with and without serpentine and chondrodite, were examined without exhibiting any traces of these peculiar forms; and these negative results are justly deemed by Gümbel as going to prove that the structure of the others is really, like that of Eozoon, the result of the intervention of organic forms. Besides the minerals observed in the replacing substance of Eozoon in Canada, viz., serpentine, pyroxene, and loganite, Gümbel adds chondrodite, hornblende, scapolite, and probably also pyrallolite, quartz, iolite, and dichroite."

The following on this subject is from a memoir by Dr. Hunt in theTwenty-first Report of the Regents of the University of New York, 1874:—

"Recent investigations have shown that in some cases the dissemination of certain of these minerals through the crystalline limestones is connected with organic forms. The observations of Dr. Dawson and myself on the Eozoon Canadense showed that certain silicates, namely serpentine, pyroxene, and loganite, had been deposited in the cells and chambers left vacant by the disappearance of the animal matter from the calcareous skeleton of the foraminiferous organism; so that when this calcareous portion is removed by an acid there remains a coherent mass, which is a cast of the soft parts ofthe animal, in which, not only the chambers and connecting canals, but the minute tubuli and pores are represented by solid mineral silicates. It was shown that this process must have taken place immediately after the death of the animal, and must have depended on the deposition of these silicates from the waters of the ocean.

"The train of investigation thus opened up, has been pursued by Dr. Gümbel, Director of the Geological Survey of Bavaria, who, in a recent remarkable memoir presented to the Royal Society of that country, has detailed his results.

"Having first detected a fossil identical with the Canadian Eozoon (together with several other curious microscopic organic forms not yet observed in Canada), replaced by serpentine in a crystalline limestone from the primitive group of Bavaria, which he identified with the Laurentian system of this country, he next discovered a related organism, to which he has given the name of Eozoon Bavaricum. This occurs in a crystalline limestone belonging to a series of rocks more recent than the Laurentian, but older than the Primordial zone of the Lower Silurian, and designated by him the Hercynian clay slate series, which he conceives may represent the Cambrian system of Great Britain, and perhaps correspond to the Huronian series of Canada and the United States. The cast of the soft parts of this new fossil is, according to Gümbel, in part of serpentine, and in part of hornblende.

"His attention was next directed to the green hornblende (pargasite) which occurs in the crystalline limestone of Pargas in Finland, and remains when the carbonate of lime is dissolved as a coherent mass closely resembling that left by the irregular and acervuline forms of Eozoon. The calcite walls also sometimes show casts of tubuli…. A white mineral, probably scapolite was found to constitute some tubercles associated with the pargasite, and the two mineral species were in some cases united in the same rounded grain.

"Similar observations were made by him upon specimens of coccolite or green pyroxene, occurring in rounded and wrinkled grains in a Laurentian limestone from New York. These,according to Gümbel, present the same connecting cylinders and branching stems as the pargasite, and are by him supposed to have been moulded in the same manner…. Very beautiful evidences of the same organic structure consisting of the casts of tubuli and their ramifications, were also observed by Gümbel in a purely crystalline limestone, enclosing granules of chondrodite, hornblende, and garnet, from Boden in Saxony. Other specimens of limestone, both with and without serpentine and chondrodite, were examined without exhibiting any traces of these peculiar forms; and these negative results are justly deemed by Gümbel as going to prove that the structure of the others is really, like that of Eozoon, the result of the intervention of organic forms. Besides the minerals observed in the replacing substance of Eozoon in Canada, viz., serpentine, pyroxene, and loganite, Gümbel adds chondrodite, hornblende, scapolite, and probably also pyrallolite, quartz, iolite, and dichroite."

(D.)Glauconites.

The following is from a paper by Dr. Hunt in theReport of the Survey of Canadafor 1866:—"In connection with the Eozoon it is interesting to examine more carefully into the nature of the matters which have been called glauconite or green-sand. These names have been given to substances of unlike composition, which, however, occur under similar conditions, and appear to be chemical deposits from water, filling cavities in minute fossils, or forming grains in sedimentary rocks of various ages. Although greenish in colour, and soft and earthy in texture, it will be seen that the various glauconites differ widely in composition. The variety best known, and commonly regarded as the type of the glauconites, is that found in the green-sand of Cretaceous age in New Jersey, and in the Tertiary of Alabama; the glauconite from the Lower Silurian rocks of the Upper Mississippi is identical with it in composition. Analysis shows these glauconites to be essentially hydrous silicates of protoxyd of iron, with more or less alumina, and small butvariable quantities of magnesia, besides a notable amount of potash. This alkali is, however, sometimes wanting, as appears from the analysis of a green-sand from Kent in England, by that careful chemist, the late Dr. Edward Turner, and in another examined by Berthier, from thecalcaire grossier, near Paris, which is essentially a serpentine in composition, being a hydrous silicate of magnesia and protoxyd of iron. A comparison of these last two will show that the loganite, which fills the ancient Foraminifer of Burgess, is a silicate nearly related in composition.I. Green-sand from thecalcaire grossier, near Paris. Berthier (cited by Beudant,Mineralogie, ii., 178).II. Green-sand from Kent, England. Dr. Edward Turner (cited by Rogers, Final Report, Geol. N. Jersey, page 206).III. Loganite from the Eozoon of Burgess.IV. Green-sand, Lower Silurian; Red Bird, Minnesota.V. Green-sand, Cretaceous, New Jersey.VI. Green-sand, Lower Silurian, Orleans Island.The last four analyses are by myself.

The following is from a paper by Dr. Hunt in theReport of the Survey of Canadafor 1866:—

"In connection with the Eozoon it is interesting to examine more carefully into the nature of the matters which have been called glauconite or green-sand. These names have been given to substances of unlike composition, which, however, occur under similar conditions, and appear to be chemical deposits from water, filling cavities in minute fossils, or forming grains in sedimentary rocks of various ages. Although greenish in colour, and soft and earthy in texture, it will be seen that the various glauconites differ widely in composition. The variety best known, and commonly regarded as the type of the glauconites, is that found in the green-sand of Cretaceous age in New Jersey, and in the Tertiary of Alabama; the glauconite from the Lower Silurian rocks of the Upper Mississippi is identical with it in composition. Analysis shows these glauconites to be essentially hydrous silicates of protoxyd of iron, with more or less alumina, and small butvariable quantities of magnesia, besides a notable amount of potash. This alkali is, however, sometimes wanting, as appears from the analysis of a green-sand from Kent in England, by that careful chemist, the late Dr. Edward Turner, and in another examined by Berthier, from thecalcaire grossier, near Paris, which is essentially a serpentine in composition, being a hydrous silicate of magnesia and protoxyd of iron. A comparison of these last two will show that the loganite, which fills the ancient Foraminifer of Burgess, is a silicate nearly related in composition.

I. Green-sand from thecalcaire grossier, near Paris. Berthier (cited by Beudant,Mineralogie, ii., 178).

II. Green-sand from Kent, England. Dr. Edward Turner (cited by Rogers, Final Report, Geol. N. Jersey, page 206).

III. Loganite from the Eozoon of Burgess.

IV. Green-sand, Lower Silurian; Red Bird, Minnesota.

V. Green-sand, Cretaceous, New Jersey.

VI. Green-sand, Lower Silurian, Orleans Island.

The last four analyses are by myself.

Plate VI.From a Photo. by Weston.Vincent Brooks, Day & Son Lith.CANAL SYSTEM OF EOZOON.SLICES OF THE FOSSIL (MAGNIFIED.)To face Chap. 6.

Plate VI.

From a Photo. by Weston.

Vincent Brooks, Day & Son Lith.

CANAL SYSTEM OF EOZOON.

SLICES OF THE FOSSIL (MAGNIFIED.)

To face Chap. 6.

CHAPTER VI.CONTEMPORARIES AND SUCCESSORS OF EOZOON.

Thename Eozoon, or Dawn-animal, raises the question whether we shall ever know any earlier representative of animal life. Here I think it necessary to explain that in suggesting the name Eozoon for the earliest fossil, and Eozoic for the formation in which it is contained, I had no intention to affirm that there may not have been precursors of the Dawn-animal. By the similar term, Eocene, Lyell did not mean to affirm that there may not have been modern types in the preceding geological periods: and so the dawn of animal life may have had its gray or rosy breaking at a time long anterior to that in which Eozoon built its marble reefs. When the fossils of this early auroral time shall be found, it will not be hard to invent appropriate names for them. There are, however, two reasons that give propriety to the name in the present state of our knowledge. One is, that the Lower Laurentian rocks are absolutely the oldest that have yet come under the notice of geologists, and at the present moment it seems extremely improbable that any older sediments exist, at least in a condition to be recognised as such. The other is that Eozoon, as a member ofthe group Protozoa, of gigantic size and comprehensive type, and oceanic in its habitat, is as likely as any other creature that can be imagined to have been the first representative of animal life on our planet. Vegetable life may have preceded it, nay probably did so by at least one great creative æon, and may have accumulated previous stores of organic matter; but if any older forms of animal life existed, it is certain at least that they cannot have belonged to much simpler or more comprehensive types. It is also to be observed that such forms of life, if they did exist, may have been naked protozoa, which may have left no sign of their existence except a minute trace of carbonaceous matter, and perhaps not even this.

But if we do not know, and perhaps we are not likely to know, any animals older than Eozoon, may we not find traces of some of its contemporaries, either in the Eozoon limestones themselves, or other rocks associated with them? Here we must admit that a deep sea Foraminiferal limestone may give a very imperfect indication of the fauna of its time. A dredger who should have no other information as to the existing population of the world, except what he could gather from the deposits formed under several hundred fathoms of water, would necessarily have very inadequate conceptions of the matter. In like manner a geologist who should have no other information as to the animal life of the Mesozoic ages than that furnished by some of the thick beds of white chalk might imagine that he had reached a period when thesimplest kinds of protozoa predominated over all other forms of life; but this impression would at once be corrected by the examination of other deposits of the same age: so our inferences as to the life of the Laurentian from the contents of its oceanic limestones may be very imperfect, and it may yet yield other and various fossils. Its possibilities are, however, limited by the fact that before we reach this great depth in the earth’s crust, we have already left behind in much newer formations all traces of animal life except a few of the lower forms of aquatic invertebrates; so that we are not surprised to find only a limited number of living things, and those of very low type. Do we then know in the Laurentian even a few distinct species, or is our view limited altogether to Eozoon Canadense? In answering this question we must bear in mind that the Laurentian itself was of vast duration, and that important changes of life may have taken place even between the deposition of the Eozoon limestones and that of those rocks in which we find the comparatively rich fauna of the Primordial age. This subject was discussed by the writer as early as 1865, and I may repeat here what could be said in relation to it at that time:—

"In connection with these remarkable remains, it appeared desirable to ascertain, if possible, what share these or other organic structures may have had in the accumulation of the limestones of the Laurentian series. Specimens were therefore selected by Sir W. E. Logan, and slices were prepared under his direction.On microscopic examination, a number of these were found to exhibit merely a granular aggregation of crystals, occasionally with particles of graphite and other foreign minerals, or a laminated mixture of calcareous and other matters, in the manner of some more modern sedimentary limestones. Others, however, were evidently made up almost entirely of fragments of Eozoon, or of mixtures of these with other calcareous and carbonaceous fragments which afford more or less evidence of organic origin. The contents of these organic limestones may be considered under the following heads:—

1. Remains of Eozoon.

2. Other calcareous bodies, probably organic.

3. Objects imbedded in the serpentine.

4. Carbonaceous matters.

5. Perforations, or worm-burrows.

"1. The more perfect specimens of Eozoon do not constitute the mass of any of the larger specimens in the collection of the Survey; but considerable portions of some of them are made up of material of similar minute structure, destitute of lamination, and irregularly arranged. Some of this material gives the impression that there may have been organisms similar to Eozoon, but growing in an irregular or acervuline manner without lamination. Of this, however, I cannot be certain; and on the other hand there is distinct evidence of the aggregation of fragments of Eozoon in some of these specimens. In some theyconstitute the greater part of the mass. In others they are embedded in calcareous matter of a different character, or in serpentine or granular pyroxene. In most of the specimens the cells of the fossils are more or less filled with these minerals; and in some instances it would appear that the calcareous matter of fragments of Eozoon has been in part replaced by serpentine."

"2. Intermixed with the fragments of Eozoon above referred to, are other calcareous matters apparently fragmentary. They are of various angular and rounded forms, and present several kinds of structure. The most frequent of these is a strong lamination varying in direction according to the position of the fragments, but corresponding, as far as can be ascertained, with the diagonal of the rhombohedral cleavage. This structure, though crystalline, is highly characteristic of crinoidal remains when preserved in altered limestones. The more dense parts of Eozoon, destitute of tubuli, also sometimes show this structure, though less distinctly. Other fragments are compact and structureless, or show only a fine granular appearance; and these sometimes include grains, patches, or fibres of graphite. In Silurian limestones, fragments of corals and shells which have been partially infiltrated with bituminous matter, show a structure like this. On comparison with altered organic limestones of the Silurian system, these appearances would indicate that in addition to the debris of Eozoon, other calcareous structures, more like those of crinoids, corals, andshells, have contributed to the formation of the Laurentian limestones.

"3. In the serpentine[AE]filling the chambers of a large specimen of Eozoon from Burgess, there are numerous small pieces of foreign matter; and the silicate itself is laminated, indicating its sedimentary nature. Some of the included fragments appear to be carbonaceous, others calcareous; but no distinct organic structure can be detected in them. There are, however, in the serpentine, many minute silicious grains of a bright green colour, resembling green-sand concretions; and the manner in which these are occasionally arranged in lines and groups, suggests the supposition that they may possibly be casts of the interior of minute Foraminiferal shells. They may, however, be concretionary in their origin.

[AE]This is the dark green mineral named loganite by Dr. Hunt.

"4. In some of the Laurentian limestones submitted to me by Sir W. E. Logan, and in others which I collected some years ago at Madoc, Canada West, there are fibres and granules of carbonaceous matter, which do not conform to the crystalline structure, and present forms quite similar to those which in more modern limestones result from the decomposition of algæ. Though retaining mere traces of organic structure, no doubt would be entertained as to their vegetable origin if they were found in fossiliferous limestones.

"5. A specimen of impure limestone from Madoc, in the collection of the Canadian Geological Survey, which seems from its structure to have been a finelylaminated sediment, shows perforations of various sizes, somewhat scalloped at the sides, and filled with grains of rounded silicious sand. In my own collection there are specimens of micaceous slate from the same region, with indications on their weathered surfaces of similar rounded perforations, having the aspect of Scolithus, or of worm-burrows.

"Though the abundance and wide distribution of Eozoon, and the important part it seems to have acted in the accumulation of limestone, indicate that it was one of the most prevalent forms of animal existence in the seas of the Laurentian period, the non-existence of other organic beings is not implied. On the contrary, independently of the indications afforded by the limestones themselves, it is evident that in order to the existence and growth of these large Rhizopods, the waters must have swarmed with more minute animal or vegetable organisms on which they could subsist. On the other hand, though this is a less certain inference, the dense calcareous skeleton of Eozoon may indicate that it also was liable to the attacks of animal enemies. It is also possible that the growth of Eozoon, or the deposition of the serpentine and pyroxene in which its remains have been preserved, or both, may have been connected with certain oceanic depths and conditions, and that we have as yet revealed to us the life of only certain stations in the Laurentian seas. Whatever conjectures we may form on these more problematic points, the observations above detailed appear to establish the following conclusions:—

“First, that in the Laurentian period, as in subsequent geological epochs, the Rhizopods were important agents in the accumulation of beds of limestone; and secondly, that in this early period these low forms of animal life attained to a development, in point of magnitude and complexity, unexampled, in so far as yet known, in the succeeding ages of the earth’s history. This early culmination of the Rhizopods is in accordance with one of the great laws of the succession of living beings, ascertained from the study of the introduction and progress of other groups; and, should it prove that these great Protozoans were really the dominant type of animals in the Laurentian period, this fact might be regarded as an indication that in these ancient rocks we may actually have the records of the first appearance of animal life on our planet.”

With reference to the first of the above heads, I have now to state that it seems quite certain that the upper and younger portions of the masses of Eozoon often passed into the acervuline form, and the period in which this change took place seems to have depended on circumstances. In some specimens there are only a few regular layers, and then a heap of irregular cells. In other cases a hundred or more regular layers were formed; but even in this case little groups of irregular cells occurred at certain points near the surface. This may be seen in plate III. I have also found some masses clearly not fragmental which consist altogether of acervuline cells. A specimen of this kind is represented infig. 31. It isoval in outline, about three inches in length, wholly made up of rounded or cylindrical cells, the walls of which have a beautiful tubular structure, but there is little or no supplemental skeleton. Whether this is a portion accidentally broken off from the top of a mass of Eozoon, or a peculiar varietal form, or a distinct species, it would be difficult to determine. In the meantime I have described it as a variety, “acervulina,” of the species Eozoon Canadense.[AF]Another variety also, from Petite Nation, shows extremely thin laminæ, closely placed together and very massive, and with little supplemental skeleton. This may be allied to the last, and may be named variety “minor.”

[AF]Proceedings of Geological Society, 1875.

Fig. 31.Acervuline Variety of Eozoon, St. Pierre.(a.) General form, half natural size. (b.) Portion of cellular interior, magnified, showing the course of the tubuli.

Fig. 31.Acervuline Variety of Eozoon, St. Pierre.

(a.) General form, half natural size. (b.) Portion of cellular interior, magnified, showing the course of the tubuli.

All this, however, has nothing to do with the layersof fragments of Eozoon which are scattered through the Laurentian limestones. In these the fossil is sometimes preserved in the ordinary manner, with its cavities filled with serpentine, and the thicker parts of the skeleton having their canals filled with this substance. In this case the chambers may have been occupied with serpentine before it was broken up. At St. Pierre there are distinct layers of this kind, from half an inch to several inches in thickness, regularly interstratified with the ordinary limestone. In other layers no serpentine occurs, but the interstices of the fragments are filled with crystalline dolomite or magnesian limestone, which has also penetrated the canals; and there are indications, though less manifest, that some at least of the layers of pure limestone are composed of fragmental Eozoon. In the Laurentian limestone of Wentworth, belonging apparently to the same band with that of St. Pierre, there are many small rounded pieces of limestone, evidently the debris of some older rock, broken up and rounded by attrition. In some of these fragments the structure of Eozoon may be plainly perceived. This shows that still older limestones composed of Eozoon were at that time undergoing waste, and carries our view of the existence of this fossil back to the very beginning of the Laurentian.

With respect to organic fragments not showing the structure of Eozoon, I have not as yet been able to refer these to any definite origin. Some of them may be simply thick portions of the shell of Eozoon withtheir pores filled with calcite, so as to present a homogeneous appearance. Others have much the appearance of fragments of such Primordial forms asArchæocyathus, to be described in the sequel; but after much careful search, I have thus far been unable to say more than I could say in 1865.

Fig. 32.Archæospherinæ from St. Pierre.(a.) Specimens dissolved out by acid. The lower one showing interior septa. (b.) Specimens seen in section.

Fig. 32.Archæospherinæ from St. Pierre.

(a.) Specimens dissolved out by acid. The lower one showing interior septa. (b.) Specimens seen in section.

Fig. 33.Archæospherinæ from Burgess Eozoon.Magnified.

Fig. 33.Archæospherinæ from Burgess Eozoon.

Magnified.

Fig. 34.Archæospherinæ from Wentworth Limestone.Magnified.

Fig. 34.Archæospherinæ from Wentworth Limestone.

Magnified.

It is different, however, with the round cells infiltrated with serpentine and with the silicious grains included in the loganite. I have already referred to and figured (fig. 18) the remarkable rounded bodies occurring at Long Lake. I now figure similar bodies found mixed with fragmental Eozoon and in separate thin layers at St. Pierre (fig. 32), also some of the singular grains found in the loganite occupying the chambers of Eozoon from Burgess (fig. 33), and a beaded body set free by acid, with others of irregular forms, from the limestone of Wentworth (fig. 34). All these I think are essentially of the same nature, namely, chambers originally invested with a tubulated wall like Eozoon, and aggregated in groups,sometimes in a linear manner, sometimes spirally, like those Globigerinæ which constitute the mass of modern deep-sea dredgings and also of the chalk. These bodies occur dispersed in the limestone, arranged in thin layers parallel to the bedding or sometimes in the large chamber-cavities of Eozoon. They are so variable in size and form that it is not unlikely they may be of different origins. The most probable of these may be thus stated. First, they may in some cases be the looser superficial parts of the surface of Eozoon broken up into little groups of cells. Secondly, they may be few-celled germs or buds given off from Eozoon. Thirdly, they may be smaller Foraminifera, structurally allied to Eozoon, but in habit of growth resembling those little globe-shaped forms which, as already stated, abound in chalk and in the modern ocean. The latter view I should regard as highly probable in the case of many of them; and I have proposed for them, in consequence, and as a convenient name,Archæospherinæ, or ancient spherical animals.

Carbonaceous matter is rare in the true Eozoon limestones, and, as already stated, I would refer the Laurentian graphite or plumbago mainly to plants. With regard to the worm-burrows referred to in 1865, there can be no doubt of their nature, but there is some doubt as to whether the beds that contain them are really Lower Laurentian. They may be Upper Laurentian or Huronian. I give here figures of these burrows as published in 1866[AG](fig. 35). The rocks which contain them hold also fragments of Eozoon, and are not known to contain other fossils.

[AG]Journal of Geological Society.

Fig. 35.Annelid Burrows, Laurentian or Huronian.Fig 1.Transverse section of Worm-burrow—magnified, as a transparent object. (a.) Calcareo-silicious rock. (b.) Space filled with calcareous spar. (c.) Sand agglutinated and stained black. (d.) Sand less agglutinated and uncoloured. Fig. 2.Transverse section of Worm-burrow on weathered surface, natural size.Fig. 3.The same, magnified.

Fig. 35.Annelid Burrows, Laurentian or Huronian.

Fig 1.Transverse section of Worm-burrow—magnified, as a transparent object. (a.) Calcareo-silicious rock. (b.) Space filled with calcareous spar. (c.) Sand agglutinated and stained black. (d.) Sand less agglutinated and uncoloured. Fig. 2.Transverse section of Worm-burrow on weathered surface, natural size.Fig. 3.The same, magnified.

If we now turn to other countries in search of contemporaries of Eozoon, I may refer first to some specimens found by my friend Dr. Honeyman at Arisaig, in Nova Scotia, in beds underlying the Silurian rocks of that locality, but otherwise of uncertain age. I do not vouch for them as Laurentian, and if of that age they seem to indicate a species distinct from that of Canada proper. They differ in coarser tubulation, and in their canals being large and beaded, and less divergent. I proposed for these specimens, in some notes contributed to the survey of Canada, the nameEozoon Acadianum.

Dr. Gümbel, the Director of the Geological Surveyof 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 favourableto the generation of crystalline mineral compounds.

"In this discovery of organic remains in the primary rocks, we hail with joy the dawn of a new epoch in the critical history of these earlier formations. Already in its light, the primeval geological time is seen to be everywhere animated, and peopled with new animal forms of whose very existence we had previously no suspicion. Life, which had hitherto been supposed to have first appeared in the Primordial division of the Silurian period, is now seen to be immeasurably lengthened beyond its former limit, and to embrace in its domain the most ancient known portions of the earth’s crust. It would almost seem as if organic life had been awakened simultaneously with the solidification of the earth’s crust.

"The great importance of this discovery cannot be clearly understood, unless we first consider the various and conflicting opinions and theories which had hitherto been maintained concerning the origin of these primary rocks. Thus some, who consider them as the first-formed crust of a previously molten globe, regard their apparent stratification as a kind of concentric parallel structure, developed in the progressive cooling of the mass from without. Others, while admitting a similar origin of these rocks, suppose their division into parallel layers to be due, like the lamination of clay-slates, to lateral pressure. If we admit such views, the igneous origin of schistose rocks becomes conceivable, and is in fact maintained by many.

"On the other hand, we have the school which, while recognising the sedimentary origin of these crystalline schists, supposes them to have been metamorphosed at a later period; either by the internal heat, acting in the deeply buried strata; by the proximity of eruptive rocks; or finally, through the agency of permeating waters charged with certain mineral salts.

“A few geologists only have hitherto inclined to the opinion that these crystalline schists, while possessing real stratification, and sedimentary in their origin, were formed at a period when the conditions were more favourable to the production of crystalline materials than at present. According to this view, the crystalline structure of these rocks is an original condition, and not one superinduced at a later period by metamorphosis. In order, however, to arrange and classify these ancient crystalline rocks, it becomes necessary to establish by superposition, or by other evidence, differences in age, such as are recognised in the more recent stratified deposits. The discovery of similar organic remains, occupying a determinate position in the stratification, in different and remote portions of these primitive rocks, furnishes a powerful argument in favour of the latter view, as opposed to the notion which maintains the metamorphic origin of the various minerals and rocks of these ancient formations; so that we may regard the direct formation of these mineral elements, at least so far as these fossiliferous primary limestones are concerned, as an established fact.”

His first discovery is thus recorded, in terms which show the very close resemblance of the Bavarian and Canadian Eozoic.

"My discovery of similar organic remains in the serpentine-limestone from near Passau was made in 1865, when I had returned from my geological labours of the summer, and received the recently published descriptions of Messrs. Logan, Dawson, etc. Small portions of this rock, gathered in the progress of the Geological Survey in 1854, and ever since preserved in my collection, having been submitted to microscopic examination, confirmed in the most brilliant manner the acute judgment of the Canadian geologists, and furnished palæontological evidence that, notwithstanding the great distance which separates Canada from Bavaria, the equivalent primitive rocks of the two regions are characterized by similar organic remains; showing at the same time that the law governing the definite succession of organic life on the earth is maintained even in these most ancient formations. The fragments of serpentine-limestone, or ophicalcite, in which I first detected the existence of Eozoon, were like those described in Canada, in which the lamellar structure is wanting, and offer only what Dr. Carpenter has called an acervuline structure. For further confirmation of my observations, I deemed it advisable, through the kindness of Sir Charles Lyell, to submit specimens of the Bavarian rock to the examination of that eminent authority, Dr. Carpenter, who, without any hesitation, declared them to contain Eozoon.

"This fact being established, I procured from the quarries near Passau as many specimens of the limestone as the advanced season of the year would permit; and, aided by my diligent and skillful assistants, Messrs. Reber and Schwager, examined them by the methods indicated by Messrs. Dawson and Carpenter. In this way I soon convinced myself of the general similarity of our organic remains with those of Canada. Our examinations were made on polished sections and in portions etched with dilute nitric acid, or, better, with warm acetic acid. The most beautiful results were however obtained by etching moderately thin sections, so that the specimens may be examined at will either by reflected or transmitted light.

"The specimens in which I first detected Eozoon came from a quarry at Steinhag, near Obernzell, on the Danube, not far from Passau. The crystalline limestone here forms a mass from fifty to seventy feet thick, divided into several beds, included in the gneiss, whose general strike in this region is N.W., with a dip of 40°-60° N.E. The limestone strata of Steinhag have a dip of 45° N.E. The gneiss of this vicinity is chiefly grey, and very silicious, containing dichroite, and of the variety known as dichroite-gneiss; and I conceive it to belong, like the gneiss of Bodenmais and Arber, to that younger division of the primitive gneiss system which I have designated as the Hercynian gneiss formation; which, both to the north, between Tischenreuth and Mahring, and to the south on the north-west of the mountains of Ossa,is immediately overlaid by the mica-slate formation. Lithologically, this newer division of the gneiss is characterized by the predominance of a grey variety, rich in quartz, with black magnesian-mica and orthoclase, besides which a small quantity of oligoclase is never wanting. A further characteristic of this Hercynian gneiss is the frequent intercalation of beds of rocks rich in hornblende, such as hornblende-schist, amphibolite, diorite, syenite, and syenitic granite, and also of serpentine and granulite. Beds of granular limestone, or of calcareous schists are also never altogether wanting; while iron pyrites and graphite, in lenticular masses, or in local beds conformable to the great mass of the gneiss strata, are very generally present.

"In the large quarry of Steinhag, from which I first obtained the Eozoon, the enclosing rock is a grey hornblendic gneiss, which sometimes passes into a hornblende-slate. The limestone is in many places overlaid by a bed of hornblende-schist, sometimes five feet in thickness, which separates it from the normal gneiss. In many localities, a bed of serpentine, three or four feet thick, is interposed between the limestone and the hornblende-schist; and in some cases a zone, consisting chiefly of scapolite, crystalline and almost compact, with an admixture however of hornblende and chlorite. Below the serpentine band, the crystalline limestone appears divided into distinct beds, and encloses various accidental minerals, among which are reddish-white mica, chlorite, hornblende, tremolite,chondrodite, rosellan, garnet, and scapolite, arranged in bands. In several places the lime is mingled with serpentine, grains or portions of which, often of the size of peas, are scattered through the limestone with apparent irregularity, giving rise to a beautiful variety of ophicalcite or serpentine-marble. These portions, which are enclosed in the limestone destitute of serpentine, always present a rounded outline. In one instance there appears, in a high naked wall of limestone without serpentine, the outline of a mass of ophicalcite, about sixteen feet long and twenty-five feet high, which, rising from a broad base, ends in a point, and is separated from the enclosing limestone by an undulating but clearly defined margin, as already well described by Wineberger. This mass of ophicalcite recalls vividly a reef-like structure. Within this and similar masses of ophicalcite in the crystalline limestone, there are, so far as my observations in 1854 extend, no continuous lines or concentric layers of serpentine to be observed, this mineral being always distributed in small grains and patches. The few apparently regular layers which may be observed are soon interrupted, and the whole aggregation is irregular."

It will be observed that this acervuline Eozoon of Steinhag appears to exist in large reefs, and that in its want of lamination it differs from the Canadian examples. In fossils of low organization, like Foraminifera, such differences are often accidental and compatible with specific unity, but yet there may be adifference specifically in the Bavarian Eozoon as compared with the Canadian.

Gümbel also found in the Finnish and Bavarian limestones knotted chambers, like those of Wentworth above mentioned (fig. 36), which he regards as belonging to some other organism than Eozoon; and flocculi having tubes, pores, and reticulations which would seem to point to the presence of structures akin to sponges or possibly remains of seaweeds. These observations Gümbel has extended into other localities in Bavaria and Bohemia, and also in Silesia and Sweden, establishing the existence of Eozoon fossils in all the Laurentian limestones of the middle and north of Europe.

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