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Les diagrammes suivants illustrent la m*thode. 1 2 3 2 3 4 5 6 .HyH| \\ '^ V 1 1 [F)'om the Quauteult Journal of the Geological Society /or Awjmt 1807.] NOTES ON FOSSILS KECENTLY OBTAINED FROM THE LAURENTIAN ROCKS OF CANADA, AND OW OBJECTIONS TO THE ORGANIC NATURE OF EOZOON. BY J. W. DAWSON, LL.D., F.ll.S., F.G.S. WITH NOTES BY W. B. CARPENTER, M.IX, F.R.S. [Plates XI. & XII.] Contents. Specimen of Eozoon from Tudor, C. W. 1. General Appearance. 2. Microscopic Clmracters. 3. Concluding Remarks. II. Specimens fnmi Long Lake and Wentworth. III. SpoiiiiuMis from Mudoc. IV. ObjfHitions to tbo Organic na- ture of tlozoott. I. Specimen of Eozoon from Tudou, C. W. This very interesting specimen, submitted to me for examination by Sir W. E. Logan, is, in my opinion, of great importance, as fur- nishing a conclusive answer to all those objections to the organic nature of Eozoon wihch have been founded on comparisons of its structures with the lomis of fibrous, dendritic, or con^rqtionaiy • • •!'•**.'. ;•. :.• '..* . •-• •• • i mmmmmm 258 PR0CEED1NQ8 OF TUB OEOLOOICAL SOCIETY. [May 8, minerals, — objections which, however plausible in the case of highly crystalline rocks, in which organic remains may be simulated by merely mineral appearances readily confoimded with them, are whoUy inapplicable to the present specimen. 1. General Appearance. — The fossil is of a clavate form, six and a half inches in length, and about four inches broad. It is contained in a slab of dark-coloured, coarse, laminated limestone, holding sand, scales of mica, and minute grains and fibres of carbonaceous matter. The surface of the slab shows a weathered section of the fossil (PI. XI.) ; and the thickness remaining in the matrix is scarcely two lines, at least in the part exposed. The septa, or plates of the fossil, are in the state of white carbonate of lime, which shows their form and arrangement very distinctly, in contrast to the dark stone filling the chambers. The specimen lies flat in the plane of strati- fication, and has probably sudBTered some compression. Its septa are convex toward the broad end, and somewhat undulating. In some places they are continuous halfway across the specimen ; in other places they divide and reunite at short distances. A few transverse plates, or connecting columns, are visible ; and there are also a number of small veins or cracks passing nearly at right angles to the septa, and filled with carbonate of lime, similar in general ap- pearance to the septa themselves. On one side, the outline of the fossil is well preserved. The narrow end, which I regard as the basal portion, is rounded. The outline of the side first bends inward, and then outward, forming a graceful double curve, which extends along the greater part of the length. Above this is an abrupt projection, and then a sudden narrowing ; and in the middle of the narrow portion, a part has the chambers obliterated by a white patch of carbonate of lime, below which some of the septa are ben^ downward in the middle. This is probably an efiect of mechanical injury, or of the interference of a calc-spar vein. With the exception of the upper part above referred to, the septa are seen to curve downward rapidly toward the margin, and to coalesce into a lateral wall, which forms the defined edge or limit of the fossil, and in which there are some indications of lateral orifices opening into the chambers. It is worthy of remark that, in this respect, the present specimen corresponds exactly with that which was originally figured by Sir W. Logan in the * Geology of Canada,' p. 49, and which is the only other specimen that exhibited the later{J limit of the form. On the side next the matrix, the septa terminate in blunt edges, and do not coalesce ; as if the organism had been attached by Uiat surface, or had been broken before being imbedded. 2. Mieroscopie Characters. — Under the microscope, with a low power, the margins of the septa appear uneven, as if eroded or tending to an acervuline mode of growth ; but occasionally the septa show a distinct and regular margin. For the most part merely traces of structure are presented, consisting of small parts of canals, filled yfit^'the. d^rk, coloui;^ng-matter of the limestone. In a few ^ «Si 1867.] DAWSON — LAURENTIAN FOSSILS. 250 places (PI. XII. fig. 1), however, these appear as distinct bundles, similar to those in the Grenville specimens, but of fine texture. [Ill fig. 2 is represuntod a portion of the canal-system in a Grenville specimen, in which the canals, which are transparent in one side (being infiltrated with carbonate of lime only) are seen on the other to be partially filled with black matter, probably a carbonaceous residuum of the sarcode which they orip:inally contained. — W.B.C.] In a few rare instances only, can I detect, with a higher power, in the margin of some of the septa, traces of the fine tubulation characteristic of the proper chamber- wall of Eozoon. For the most part this seems to have been obliterated by the infiltration of the tubuli with colourless carbonate of lime, similar to that of the skeleton. In comparing the structure of this specimen with that of those found elsewhere, it would appear that the chambers are more con- tinuous, and wider in proportion to the thickness of the septa, and that the canal-system is more delicate and indistinct than usual. In the two former respects the specimens from the Calumet and from Burgess approach that now under consideration more nearly than do those from Grenville and Petite Nation ; but it would be easy, even in the latter, to find occasional instances of a proportion of parts similar to that in the present example. General form is of little value as a character in such organisms ; and, so far as can be ascertained, this may have been the same in the present specimen and in that originally obtained from the Calumet, while in the spe- cimens from Grenville a massive and aggregative mode of growth seems to have obliterated all distinctness of individual shape. With- out additional specimens, and in the case of creatures so variable as the Foraminifera, it would be rash to decide whether the differ- ences above noticed are of specific value, or depend on age, variability, or state of preservation. For this reason I refer the specimen for the present to Eozoon Canadense, merely distinguishing it as the Tudor variety. From the state of preservation of the fossil, there are no crystalline structures present which can mislead any ordinarily skilful micro- scopist, except the minute veins of calcareous spar traversing the septa, and the cleavage-planes which have been developed in some portions of the latter. I would remark that, as it seemed desirable not to injure any more than was absolutely necessary a unique and verj' valuable specimen, my observations of the microscopic structure have been made on a few slices of small size, — and that, as the microscopic structures are nearly the same in kind with those of specimens figured in former papers, I have not thought it necessary to prepare numerous drawings of them ; while the admirable photograph exe- cuted for Sir \V. E. Logan by Mr. Norman illustrates sufficiently the general form and arrangement of parts (see PI. XI.). 3. Concluding Remarks. — In a letter to Dr. Carpenter, quoted by him in the ' Quarterly Journal of the Geological Society ' for August 1866, p. 228, 1 referred to the occurrence < nee of Eozoon preserved simply •'^ ••. • ; *" "^ • • • •* • ;•. : • '.. > •••••• •••• , ; » . t • 2G0 PROCEEDIKOS OF THE OEOLOOICAL 80CIETT. [Muy 8, \' in carbonate of limo. The specimens which enabled me to make that 8tateh.«nt were obtained at Madoc, near Tudor, this region being one in which the Lauren tian rocks of Canada appear to be less highly metamorphosed than is usual. The specimens from Madoc, however, were mere fragments, imbedded in the limestone, and in- capable of showing the general form. I may explain, in reference to this, that long practice in the examination of these limestones has enabled me to detect the smallest fragments of Eozoon when present, and that in this way I had ascertained the existence of this fossil in one of the limestones of Madoc before the discovery of the fine specimen now under consideration. I am disposed to regard the present specimen as a young indi- vidual, broken from its attachment and imbedded in a sandy calca- reous mud. Its discovery affords the hope that the comparatively unaltered sediments in which it has been preserved, and which also contain the worm-burrows described by mo in the ' Quarterly Journal of the Geological Society' for November*, will hereafter still more largely illustrate the Lauventian fauna. II. Specimens from Long Lake and Wentworth. Specimens from Long Lake, in the collection of the Geological Survey of Canada, exhibit white crystalline limestone with light-green compact or septariiformf serpentine, and much resemble some of the «eri)entine-Ume8tone8 of Grenville. Under the microscope the cal- careous matter presents a delicate areolated appearance, without lamination ; but it is rot an example of acervuline Eozoon, but rather of fragments of such a structure, confusedly aggregated together, and having the interstices and cell-cavities filled with serpentine. I have not found in any of these fragments a canal-system similar to that of Eozoon Canadense, though there are casts of largo stolons, and, under a high power, the calcareous matter shows in many places the peculiar granular or cellular appearance which is one of the characters of the 8uj)plemental skeleton of that species. In a few places a tubulated cell-wall is preserved, with structure similar to that of Eozoon Canadense. Specimens of Laurentian limestone from Wentworth, in the collec- tion of the Geological Survey, exhibit many rounded siliceous bodies, some of which are apparently grains ot sand, or small pebbles ; but others, especially when freed from the calcareous matter by a dilute acid, appear as roimdcd bodies, with rough surfaces, either separate or aggregated in lines or groups, and having minute vermicular pro- cesses projecting from their surfaces (PI. XII. fig. 3). At first sight these suggest the idea of spicules ; but I think it on the whole more likely that they are casts of cavities and tubes belonging to some cal- careous Foraminiferal organism which has disappeared. Similar bodies, found in the limestone of Bavaria, have been described by * Vol. ntii. p. 608. t I use the term " septariiform " to denote the curved appearance so often preeented bv the Laurentian serpentine. ■ r • ■ • I • • • • ■ • • • , • It • • • » t • 1 I 1807.] DAWSON LAUKENTIAN FOSSILS. 261 often Oiimbol, who intorprota them in tho same way*. Thoy may Jilso 1)0 comi)aroJ with tho silioeoua bodies mentioned in a former paper US uccuiTing in tho Loguuite filling tho chambers of specimens uf Eozoon from Burgoss. III. Specimens from Madoc. T have already referred to fragments of Eozoon occurring in the limestone at Madoc, one of which, found several years ago, I did not then venture to describe as a fossil. It projected from the sur- face of tho limestone, being composed of a yellowish dolomite, and looking like a fragment of a thick shell. When sliced, it presents interiorly a crj'stallino dolomite, limited and separated from the enclosing rock by a thin wall having a granular or porous structure and excavated into rounded recesses in the manner of Eozoon. It lies obliquely to the bedding, and evidently represents a hollow flattened calcareous wall filled by infiltration. The limestone which afforded this form was near the beds holding the apparently worm- burrows described in the Society's Journal for November, 1866. [A thin section of this body, carefully examined microscopically, presents numerous and very characteristic examples of the canal- system of Eozoon, exhibiting both the large widely branching systems of canals and the smaller and more penicillate tufts (PI. XII. figs. 4, 5) shown in the most perfect of the serpentinous si)ecimens — but with this difffercnce, that the canals, being filled with a material either identical with or very similar to that of tho substance in which they are excavated, are so transparent as only to bo brought into view by careful management of the light. — W.B.C.] IV. Objections to the Organic Natitre of Eozoon. The discovery of the specimen from Tudor, above described, may appear to render unnecessary any reference to the elaborate attempt made by Profs. King and Rowney to explain the structures of Eozoon by a comparison with the- forms of fibrous and dendritic minerals t, more especially as Dr. Carpenter has already shown their inaccuracy in many important points. I think, however, that it may serve a useful purpose shortly to point out the more essential respects in which this comparison fails with regard to the Canadian specimens — with the view of relieving tho discussion from matters irrelevant to it, and of fixing more exactly the limits of crystalline and organic forms in the serpentine-limestones and similar rocks. The fundamental error of Messrs. King and Ilo\\'Tiey arises from defective observation — in failing to distinguish, in the Canadian limestones themselves, between organic and crystalline forms. This is naturally followed by the identification of tdl these forms, whether mineral or organic, with a variety of purely crjstallino arrangements occurring in other rocks, leading to their attaching the term * Proceedings of Royal Academy of Munich, 18(56 ; Q. J. G. S. vol. mi. pt. i. p. 185 et seq. t Quart. Joum. Geol. See. vol. xxii. pt. ii. p. 23. I- 262 PROCEEDINGS OF THE OEOLOOICAL SOCIETY. [^>^y 8, "Eozoonal" to any rock which shows any of the characters, whether mineral or organic, thus arbitrarily attached to the Canadian Eozoon. This is obnously a process by which the structure of any fossil might bo proved to be a mere Ituua natura. A notjible illustration of this is afforded by their regarding the veins of fibrous serpentine, or chrysotile, which occur in the Cana- dian specimens, as identical with the tubulated cell-wall of Eozoon — although they admit that these veins traverse all the structures indifferently and do not conform to the walls of the chambers. But any microscopist who possesses specimens of Eozoon containing these chiysotile veins may readily satisfy himself that, under a high power, they resolve themselves \nUi prismatic cn/atals in imme- diate contact with each other • whereas, under a similar power, the true cell-wall is seen to consist of dender, undulating, roundeil threads of serpentine, penetrating a ma trix of carbonate of lim^. Under polarized light more especially, the difference is conspicuously apparent. It is true that, in many specimens and parts of specimens, the cell- wall of Eozoon is badly preserved and fails to show its structure ; but in no instance does it present the appearance of chrj'sotile, or of any other fibrous mineral, when examined with care under suffi- ciently high powers. In my original examination of Sir William Logan's specimens from Qrenville and the Calumet, I did not detect the finely tubulated ceU-wall, which is very imperfectly preacrved in those specimens ; but the veins of fibrous serpentine weie well known to me ; and when Dr. Caqjenter discovered the tubulation of tlie cell-wall in the specimens from Petite Nation, I compared this structure with that of these veins, and satisfied myself of its dis- tinctness before acceding to his conclusions on this point. It would also appear that the radiating and sheaf-like bundles of crystals of tremolite, or similar prismatic minerals, which occur in ihc Canadian serpentines, and also abound in those of Connemara, have been confounded with the tubulation of Eozoon ; but these crystals have no definite relation to the forms of that fossil, and often occur where these are entirely absent ; and in any case they are distinguishable by their straight prismatic shape and their angular divergence from each other. Much use has also been made of the amorphous masses of opaque serpentinous matter which appear in some parts of the structure of Eozoon. These I regard as, in most cases, simply results of alteration or defective preservation, though they might also arise from the presence of foreign matters in the chambers, or from an incrustation of mineral matter before tlie final filling up of the cells. Generally their forms are purely inorganic ; but in some cases they retain indications of the structures of Eozoon. With reference to the canal-system of Eozoon, no value can be attached to loose comparisons of a structure so definite with the forms of dendritic silver and the filaments of moss-agates ; still less can any resemblance be established between the canal-system and vermicular crystals of mica. These occur abundantly in some ser- pentines from the Calumet, and might readily be mistaken for 1807.] DAWHON — LACRKNTIAN F088IL8. 203 organic forms ; but their rhombic or hexagonal outline when seen in cross section, their transvorse cleavage-planes, and their want of any definite arrangement or relation to any general organic form are sufficient to undeceive any practised observer. I hove not seen specimens of the mctaxite from lieicheustein referred to by Messrs. King and Rowney ; but it is evident, from the description and figure given of it, that, whether organic or otherwise, it is not similar to the canals of Eozoon C'anadense. But all these and similar compa- risons are evidently worthless when it is considered that they have to account for definite, ramifying, cylindrical forms, penetrating a skeleton or matrix of limestone, which has itself a definite arrange- ment and structure, and, further, when we find that these forms are represented by substances so diverse as serpentine, pyroxene, lime- stone, and carbonaceous matter. This is intelligible on the suppo- sition of tubes filled with foreign matters, but not on that of dendri- tic crystallization. If all specimens of Eozoon were of the acervuline character, the comparisons of the chamber-casts with concretionary granules might have some plausibility. But it is to be observed that the laminated arrangement is the tjrpical one ; and the study of the larger speci- mens, cut under the direction of Sir W. E. Logan, shows that these laminated forms must have grown on certain strata-planes before the deposition of the overlying beds, and that the beds are, in part, com- posed of the broken fragments of similar laminated structures. Further, much of the apparently acervuline Eozoon rock is composed of such broken fragments, the interstices between which should not be confounded with the chambers ; while the fact that the serpen- tine fills such interstices as well as the chambers shows that its arrangement is not concretionary*. Again, these chambers are ' filled in different specimens with serpentine, pyroxene, loganite, cal- careous spar, chondrodite, or even with arenaceous limestone. It is also to be observed that the examination of a number of limestones, other than Canadian, by Messrs. King and llowney, has obliged them to admit that the laminated forms in combination with the canal-system are " essentially Canadian," and that the only instances of structures clearly resembling the Canadian specimens are afforded by limestones Laurentian in age and in some of which (as, for in- stance, in those of Bavaria and Scandinavia) Carpenter and Giimbel have actually found the structure of Eozoon. The other serpentine- limestones examined (for example, that of Skye) are admitted to fail in essential points of structure ; and the only serpentine believed to be of eruptive origin examined by them is confessedly destitute of all semblance of Eozoon. Similar results have been attained by the more careful researches of Prof. Giimbel, whose paper is well de- serving of study by all who have any dDuhts on this subject. In the above remarks I have not referred to the disputed case of the Connemara limestones ; but I may state that I have not been able » I do not include here the " aeptariiform " structure referred to above, which is common in the Canadian serpentine and has no connexion with the forma of the chambers. 264 PBOCEXDIVOS OF THE OEOLOOICAL 80CIBTT. [May 8, i I to satisfy myself of the occurroiico of the structures of Eozoon in such specimens as I have had the opportunity to examine *. It is perhaps necessary to add that there exists in Canada abundance of Laurontian limestone which shows no indication of the structures of Eozoon. In some cases it is evident that such structures have not been present. In other cases they may have been obliterated by processes of crystallization. As in the cose of other fossils, it is only in certain beds, and in certain parts of those beds, that well-charac- terized specimens can bo found. I may also repeat here that in the original examination of Eozoon, in the spring of 1864, 1 was fur- nished by Sir W. E. Logan with specimens of all these limestones, and also with serpentine-limestones of Silurian age, and that, while all possible care was taken to compare these with the specimens of Eozoon, it was not thought necessary to publish notices of the crys- talline and concretionary forms observed, many of which were very curious and might afford materials for other papers of the nature of that criticised in the above remarks. [The examination of a large number of sections of a specimen of Eozoon recently placed in my hands by Sir William Logan, in which the canal-system is extraordinarily well preserved, enables me to supply a most unexpected confirmation of Dr. Dawson's state- ments in regard to the occurrence of dendritic and other forms of this system, which cannot be accounted for by the intrusion of any foreign mineral; for many parts of the calcareous lamella) in these sections, which, when viewed by ordinary transmitted light, appear quite homogeneous and structureless, are found, when the light is reduced by Collins's " graduating diaphragm," to exhibit a most beautiful development of various forms of canal-system (often resembling those of Dr. Dawson's Madoc specimen represented in PI. XII. figs. 4, 5), which cross the cleavage-planes of the shell-sub- stance in every direction. Now these parts, when subjected to decal- cification, show no trace of canal-system ; so that it is obvious, both from their optical and from their chemical reactions, that the sub- stance fiUing the canals must have been carbonate of lime, which has thus completely solidified the shell layer, having been de- posited in the canals previously excavated in its interior, just as crystalline carbonate of lime fills up the reticular spaces of the skeleton of Echinodermata fossilized in a calcareous matrix. This fact affords conclusive evidence of organic structure, since no con- ceivable process of crystallization could give origin to dendritic extensions of carbonate of lime disposed on exactly the same crys- talline system with the calcite which includes it, the two substances bei]ng mineralogically homogeneous, and only structurally distin- guishable by the effect of their junction -surfaces on the course of faint rays of light transmitted through them. — ^W. B. C.J * Such Irish specimens of serpentine limestone as I hnvc seen, appear much more highly crystalline than the beds in Canada which contain Eozoon. P*:l in 1807.] DAWSON — IAUHKNTIAN F088ILR. 205 EXPLANATION OP PLATES XL and XI J. Plats XI. Spocimen of Eosoon Canadente, imbedded in a dark-mloiirod honiofi|ipneon8 linte- stono ocourring in tlin T^owpr Laurcntian loriea, at Tudor, Canada Wett ; two-thirda the natural size. Pl-ATK XIL Pig. I Sootion of one of Ihe calcareous InyorH of the Tudor Npflciinon i Plat« XI.), ■howing oanal-gyatem ii)ip«>rfoctly infiltrated with black (carbona- ceous?) matter; magniflod 120 diameters. 2. Section of the slielly layer of a gpeciinen of Fjnzonv from Orenville, gliowing a minute form of cnnnl-Hystem partly ii)jeott>d with black matter, and partly witii w^rpontine; magnified i2U dianietora. 3. BiliceotiB bodira (internal caHts?) from a 8iN>cimon of Fjtzinm from Wentwortli ; magni(ii>d .^t) diaincterH. 4. 5. Sections of a fragment of Koi'otm from the Madoc limestone, nhowing various forms of csnal-Hystem filled with carboiuile of lime ; inag- fied 120 diainuten. l! t t u, ! i I -Ijil Guar', :n-;rr nPcl.Soc Vol XXHl^ PI XU je vviiae jtii M ScV Kajohart :ann EOZOON CAWAUEN5E.