Chapter 3

[V]“Coal Flora of Pennsylvania,” vol. iii., Plate 88.

Rill-marks occur in very old rocks,[W]but are perhaps most beautifully preserved in the Carboniferous shales and argillaceous sandstones, and even more elaborately on the modern mud-banks of the Bay of Fundy.[X]Some of these simulate ferns and fronds of Laminariæ, and others resemble roots, fucoids allied toButhotrephis, or the radiating worm-burrows already referred to (Fig. 10).

[W]“Journal of the Geological Society,” vol. xii., p. 251.

[X]“Acadian Geology,” 2d ed., p. 26.

Fig. 10.—Carboniferous rill-mark (Nova Scotia), reduced, to illustrate pretended Algæ.

Shrinkage-cracksare also abundant in some of the Carboniferous beds, and are sometimes accompanied with impressions of rain-drops. When finely reticulated they might be mistaken for the venation of leaves, and, when complicated with little rill-marks tributary to their sides, they precisely resemble theDictyolitesof Hall from the Medina sandstone (Fig. 11).

Fig. 11.—Cast of shrinkage cracks (Carboniferous, Nova Scotia), illustrating pretended Algæ.

An entirely different kind of shrinkage-crack is that which occurs in certain carbonised and flattened plants, and which sometimes communicates to them a marvellous resemblance to the netted under surface of an exogenous leaf. Flattened stems of plants and layers of cortical matter, when carbonised, shrink in such a manner as to produce minute reticulated cracks. These become filled with mineral matter before the coaly substance has been completely consolidated. A further compression occurs, causing the coaly substance to collapse, leaving the little veins of harder mineral matter projecting. These impress their form upon the clay or shale above and below, and thus when the mass is broken open we have a carbonaceous film or thin layer covered with a network of raised lines, and corresponding minute depressed lines on the shale in contact with it. The reticulations are generally irregular, but sometimes they very closely resemble the veins of a reticulately veined leaf. One of the most curious specimens in my possession was collected by Mr. Elder in the Lower Carboniferous of Horton Bluff. The little veins which form the projecting network are in this case white calcite; but at the surface their projecting edges are blackened with a carbonaceous film.

Slickensided bodies, resembling the fossil fruits described by Geinitz asGulielmites, and the objects believedby Fleming and Carruthers[Y]to be casts of cavities filled with fluid, abound in the shales of the Carboniferous and Devonian. They are, no doubt, in most cases the results of the pressure and consolidation of the clay around small solid bodies, whether organic, fragmentary, or concretionary. They are, in short, local slickensides precisely similar to those found so plentifully in the coal under-clays, and which, as I have elsewhere[Z]shown, resulted from the internal giving way and slipping of the mass as the roots of Stigmaria decayed within it. Most collectors of fossil plants in the older formations must, I presume, be familiar with appearances of this kind in connection with small stems, petioles, fragments of wood, and carpolites. I have in my collection petioles of ferns and fruits of the genus Trigonocarpum partially slickensided in this way, and which if wholly covered by this kind of marking could scarcely have been recognised. I have figured bodies of this kind in my report on the Devonian and Upper Silurian plants of Canada, believing them, owing to their carbonaceous covering, to be probably slickensided fruits, though of uncertain nature. In every case I think these bodies must have had a solid nucleus of some sort, as the severe pressure implied in slickensiding is quite incompatible with a mere “fluid-cavity,” even supposing this to have existed.

[Y]“Journal of the Geological Society,” June, 1871.

[Z]Ibid., vol. x., p. 14.

Prof. Marsh has well explained another phase of the influence of hard bodies in producing partial slickensides, in his paper onStylolites, read before the American Association in 1867, and the application of the combined forces of concretionary action and slickensiding to the production of the cone-in-cone concretions, which occur in the coal-formation and as low as the Primordial. I have figured a very perfect and beautiful form of thiskind from the coal-formation of Nova Scotia, which is described in “Acadian Geology”[AA](Fig. 12).

I have referred to these facts here because they are relatively more important in that older period, which may be named the age of Algæ, and because their settlement now will enable us to dispense with discussions of this kind further on. The able memoirs of Nathorst and Williamson should be studied by those who desire further information.

[AA]Appendix, p. 676, edition of 1878.

Fig. 12.—Cone-in-cone concretion (Carboniferous, Nova Scotia), illustrating pretended Algæ.

But it may be asked, “Are there no real examples of fossil Algæ?” I believe there are many such, but the difficulty is to distinguish them. Confining ourselves to the older rocks, the following may be noted:

The genusButhotrephisof Hall, which is characterised as having stems, sub-cylindric or compressed, with numerous branches, which are divaricating and sometimes leaf-like, contains some true Algæ. Hall’sB. gracilis, from the Siluro-Cambrian, is one of these. Similar plants, referred to the same species, occur in the Clinton and Niagara formations, and a beautiful species, collected by Col. Grant, of Hamilton, and now in the McGill College collection, represents a broader and more frondose type of distinctly carbonaceous character. It may be described as follows:

Buthotrephis Grantii, S. N. (Fig. 13).—Stems andfronds smooth and slightly striate longitudinally, with curved and interrupted striæ. Stem thick, bifurcating, the divisions terminating in irregularly pinnate fronds, apparently truncate at the extremities. The quantity of carbonaceous matter present would indicate thick, though perhaps flattened, stems and dense fleshy fronds.

Fig. 13.—Buthotrephis Grantii, a genuine Alga from the Silurian, Canada.

The speciesButhotrephis subnodosaandB. flexuosa, from the Utica shale, are also certainly plants, though it is possible, if their structures and fruit were known, some of these might be referred to different genera. All of these plants have either carbonaceous matter or produce organic stains on the matrix.

The organism with diverging wedge-shaped fronds, described by Hall asSphenothallus angustifolius, is also a plant. Fine specimens, in the collection of the Geological Survey of Canada, show distinctevidence of the organic character of the wedge-shaped fronds. It is from the Utica shale, and elsewhere in the Siluro-Cambrian. It is just possible, as suggested by Hall, that this plant may be of higher rank than the Algæ.

The genusPalæophycusof Hall includes a great variety of uncertain objects, of which only a few are probably true Algæ. I have specimens of fragments similar to hisP. virgatus, which show distinct carbonaceous films, and others from the Quebec group, which seem to be cylindrical tubes now flattened, and which have contained spindle-shaped sporangia of large size. Tortuous and curved flattened stems, or fronds, from the Upper Silurian limestone of Gaspé, also show organic matter.

Respecting the forms referred toLicrophycusby Billings, containing stems or semi-cylindrical markings springing from a common base, I have been in great doubt. I have not seen any specimens containing unequivocal organic matter, and am inclined to think that most of them, if not the whole, are casts of worm-burrows, with trails radiating from them.

Though I have confined myself in this notice to plants, or supposed plants, of the Lower Palæozoic, it may be well to mention the remarkable Cauda-Galli fucoids, referred by Hall to the genusSpirophyton, and which are characteristic of the oldest Erian beds. The specimens which I have seen from New York, from Gaspé, and from Brazil, leave no doubt in my mind that these were really marine plants, and that the form of a spiral frond, assigned to them by Hall, is perfectly correct. They must have been very abundant and very graceful plants of the early Erian, immediately after the close of the Silurian period.

We come now to notice certain organisms referred to Algæ, and which are either of animal origin, or are of higher grade than the sea-weeds. We have already discussedthe questions relating toPrototaxites.Drepanophycus, of Goeppert,[AB]I suspect, is only a badly preserved branch or stem of the Erian land-plant known as Arthrostigma. In like manner,Haliserites Dechenianus,[AC]of Goeppert, is evidently the land-plant known asPsilophyton.Sphærococcites dentatusandS. serra—theFucoides dentatusandserraof Brongniart, from Quebec—are graptolites of two species quite common there.[AD]DictyophytonandUphantenia, as described by Hall and the author, are now known to be sponges. They have becomeDictyospongiæ. The curious and very ancient; fossils referred by Forbes to the genusOldhamiaare perhaps still subject to doubt, but are usually regarded as Zoöphytes, though it is quite possible they may be plants. Though I have not seen the specimens, I have no doubt whatever that the plants, or the greater part of them, from the Silurian of Bohemia, described by Stur as Algæ and Characeæ,[AE]are really land-plants, some of them of the genusPsilophyton. I may say in this connection that specimens of flattenedPsilophytonandArthrostigma, in the Upper Silurian and Erian of Gaspé, would probably have been referred to Algæ, but for the fact that in some of them the axis of barred vessels is preserved.

[AB]“Fossile Flora,” 1852, p. 92, Table xli.

[AC]Ibid., p. 88, Table ii.

[AD]Brongniart, “Vegeteaux Fossiles,” Plate vi., Figs. 7 to 12.

[AE]“Proceedings of the Vienna Academy,” 1881.Hostinella, of this author, is almost certainlyPsilophyton, and hisBarrandianaseems to includeArthrostigma, and perhaps leafy branches ofBerwynia. These curious plants should be re-examined.

It is not surprising that great difficulties have occurred in the determination of fossil Algæ. Enough, however, remains certain to prove that the old Cambrian and Silurian seas were tenanted with sea-weeds not very dissimilar from those of the present time. It is further probable that some of the graphitic, carbonaceous, and bituminousshales and limestones of the Silurian owe their carbonaceous matters to the decomposition of Algæ, though possibly some of it may have been derived from Graptolites and other corneous Zoöphytes. In any case, such microscopic examinations of these shales as I have made, have not produced any evidence of the existence of plants of higher grade, while those of the Erian and Carboniferous periods, similar to the naked eye, abound in such evidence. It is also to be observed that, on the surfaces of beds of sandstone in the Upper Cambrian, carbonaceousdébris, which seems to be the remains of either aquatic or land plants, is locally not infrequent.

Fig. 14.—Silurian vegetation restored.Protannularia,Berwynia,Nematophyton,Sphenophyllum,Arthrostigma,Psilophyton.

Referring to the land vegetation of the older rocks, it is difficult to picture its nature and appearance. We may imagine the shallow waters filled with aquatic or amphibious Rhizocarpean plants, vast meadows or brakes of the delicatePsilophytonand the starryProtannulariaand some tall trees, perhaps looking like gigantic club-mosses, or possibly with broad, flabby leaves, mostly cellular in texture, and resembling Algæ transferred to the air. Imagination can, however, scarcely realise this strange and grotesque vegetation, which, though possibly copious and luxuriant, must have been simple and monotonous in aspect, and, though it must have produced spores and seeds and even fruits, these were probably all of the types seen in the modern acrogens and gymnosperms.

“In garments green, indistinct in the twilight,They stand like Druids of old, with voices sad and prophetic.”

Prophetic they truly were, as we shall find, of the more varied forests of succeeding times, and they may also help us to realise the aspect of that still older vegetation, which is fossilised in the Laurentian graphite; though it is not impossible that this last may have been of higher and more varied types, and that the Cambrian and Silurian may have been times of depression in the vegetable world, as they certainly were in the submergence of much of the land.

These primeval woods served at least to clothe the nakedness of the new-born land, and they may have sheltered and nourished forms of land-life still unknown to us, as we find as yet only a few insects and scorpions in the Silurian. They possibly also served to abstract from the atmosphere some portion of its superabundant carbonic acid harmful to animal life, and they stored upsupplies of graphite, of petroleum, and of illuminating gas, useful to man at the present day. We may write of them and draw their forms with, the carbon which they themselves supplied.

NOTE TO CHAPTER II.

Examination of Prototaxites(Nematophyton),by Prof. Penhallow, of McGill University.

Prof. Penhallow, having kindly consented to re-examine my specimens, has furnished me with elaborate notes of his facts and conclusions, of which the following is a summary, but which it is hoped will be published in full:

"1.Concentric Layers.—The inner face of each of these is composed of relatively large tubes, having diameters from 13·6 to 34·6 micro-millimetres. The outer face has tubes ranging from 13·8 to 27·6 mm. The average diameter in the lower surface approaches to 34, that in the outer to 13·8. There is, however, no abrupt termination to the surface of the layers, though in some specimens they separate easily, with shining surfaces.

"2.Minute Structure.—In longitudinal sections the principal part of the structure consists of longitudinal tubes of indeterminate length, and round in cross-section. They are approximately parallel, but in some cases may be seen to bend sinuously, and are not in direct contact. Finer myceloid tubes, 5·33 mm. in diameter, traverse the structure in all directions, and are believed to branch off from the larger tubes. In a small specimen supposed to be a branch or small stem, and in which the vertical tubes are somewhat distant from one another, this horizontal system is very largely developed; but is less manifest in the older stems. The tubes themselves show no structure. The ray-like openings in the substance of the tissue are evidently original parts of the structure, but not of the nature of medullary rays. They are radiating spaces running outward in an interrupted manner or so tortuously that they appear to be interrupted in their course from the centre towards the surface. They show tubes turning into them, branching into them, and approximately horizontal, but tortuous. On the external surface of some specimens these radial spaces are represented by minute pits irregularlyor spirally arranged. The transverse swellings of the stem show no difference of structure, except that the tubes or cells may be a little more tortuous, and a transverse film of coaly matter extends from the outer coaly envelope inwardly. This may perhaps be caused by some accident of preservation. The outer coaly layer shows tubes similar to those of the stem.[AF]The horizontal or oblique flexures of the large tubes seem to be mainly in the vicinity of the radial openings, and it is in entering these that they have been seen to branch."

[AF]It is possible that these tubes may be merely part of the stem attached to the bark, which seems to me to indicate the same dense cellular structure seen in the bark ofLepidodendra, etc.

The conclusions arrived at by Prof. Penhallow are as follows:

"1. The plant was not truly exogenous, and the appearance of rings is independent of the causes which determine the layers of growth in exogenous plants.

"2. The plant was possessed of no true bark. Whatever cortical layer was present was in all probability a modification of the general structure,[AG]

[AG]On these points I would reserve the considerations: 1. That there must have been some relation between the mode of growth of these great stems and their concentric rings; and, 2. That the evidence of a bark is as strong as in the case of any Palæozoic tree in which the bark is, as usual, carbonised.

"3. An intimate relation exists between the large tubular cells and the myceloid filaments, the latter being a system of small branches from the former; the branching being determined chiefly in certain special openings which simulate medullary rays.

"4. The specimens examined exhibit no evidence of special decay, and the structure throughout is of a normal character.

"5. The primary structure consists of large tubular cells without apparent terminations, and devoid of structural markings, with which is associated a secondary structure of myceloid filaments arising from the former.

"6. The structure ofNematophytonas a whole is unique; at least there is no plant of modern type with which it is comparable. Nevertheless, the loose character of the entire structure; the interminable cells; their interlacing; and, finally, their branching into a secondary series of smaller filaments, point with considerable force to the true relationship of the stem as being with Algæ or other Thallophytes rather than with Grymnosperms. A more recent examinationof a laminated resinous substance found associated with the plant shows that it is wholly amorphous, and, as indicated by distinct lines of flow, that it must have been in a plastic state at a former period. The only evidence of structure was found in certain well-defined mycelia, which may have been derived from associated vegetable matter upon which they were growing, and over which the plastic matrix flowed."

I have only to add to this description that when we consider thatNematophyton Loganiwas a large tree, sometimes attaining a diameter of more than two feet, and a stature of at least twenty before branching; that it had great roots, and gave off large branches; that it was an aërial plant, probably flourishing in the same swampy flats withPsilophyton,Arthrostigma, andLeptophleum; that the peculiar bodies known as Pachytheca were not unlikely its fruit—we have evidence that there were, in the early Palæozoic period, plants scarcely dreamt of by modern botany. Only when the appendages of these plants are more fully known can we hope to understand them. In the mean time, I may state that there were probably different species of these trees, indicated more particularly by the stems I have described asNematoxylonandCelluloxylon[AH]There were, I think, some indications that the plants described by Carruthers asBerwynia, may also be found to have been generically the same. The resinous matter mentioned by Prof. Penhallow is found in great abundance in the beds containingNematophyton, and must, I think, have been an exudation from its bark.

[AH]“Journal Geol. Society of London,” 1863, 1881.

CHAPTER III.

THE ERIAN OF DEVONIAN FORESTS—ORIGIN OF PETROLEUM—THE AGE OF ACROGENS AND GYMNOSPERMS.

Inthe last chapter we were occupied with the comparatively few and obscure remains of plants entombed in the oldest geological formations. We now ascend to a higher plane, that of the Erian or Devonian period, in which, for the first time, we find varied and widely distributed forests.

The growth of knowledge with respect to this flora has been somewhat rapid, and it may be interesting to note its principal stages, as an encouragement to the hope that we may yet learn something more satisfactory respecting the older floras we have just discussed.

In Goeppert’s memoir on the flora of the Silurian, Devonian, and Lower Carboniferous rocks, published in 1860,[AI]he enumerates twenty species as Silurian, but these are all admitted to be Algæ, and several of them are remains which may be fairly claimed by the zoologists as zoophytes, or trails of worms and mollusks. In the Lower Devonian he knows but six species, five of which are Algæ, and the remaining one aSigillaria, but this is of very doubtful nature. In the Middle Devonian he gives but one species, a land-plant of the genusLepidodendron. In the Upper Devonian the number rises to fifty-seven, of which all but seven are terrestrial plants, representing a large number of the genera occurring in the succeeding Carboniferous system.

[AI]Jena, 1860.

Goeppert does not include in his enumeration the plants from the Devonian of Gaspé, described by the author in 1859,[AJ]having seen only an abstract of the paper at the time of writing his memoir, nor does he appear to have any knowledge of the plants of this age described by Lesquereux in Roger’s “Pennsylvania.” These might have added ten or twelve species to his list, some of them probably from the Lower Devonian. It is further to be observed that a few additional species had also been recognised by Peach in the Old Red Sandstone of Scotland.

[AJ]“Journal of the Geological Society of London,” also “Canadian Naturalist.”

But from 1860 to the present time a rich harvest of specimens has been gathered from the Gaspé sandstones, from the shales of southern New Brunswick, from the sandstones of Perry in Maine, and from the wide-spread Erian areas of New York, Pennsylvania, and Ohio. Nearly all these specimens have passed through my hands, and I am now able to catalogue about a hundred species, representing more than thirty genera, and including all the great types of vascular Cryptogams, the Gymnosperms, and even one (still doubtful) Angiosperm. Many new forms have also been described from the Devonian of Scotland and of the Continent of Europe.

Before describing these plants in detail, we may refer to North America for illustration of the physical conditions of the time. In a physical point of view the northern hemisphere presented a great change in the Erian period. There were vast foldings of the crust of the earth, and great emissions of volcanic rock on both sides of the Atlantic. In North America, while at one time the whole interior area of the continent, as far north asthe Great Lakes, was occupied by a vast inland sea, studded with coral islands, the long Appalachian ridge had begun to assume, along with the old Laurentian land, something of the form of our present continent, and on the margins of this Appalachian belt there were wide, swampy flats and shallow-water areas, which, under the mild climate that seems to have characterised this period, were admirably suited to nourish a luxuriant vegetation. Under this mild climate, also, it would seem that new forms of plants were first introduced in the far north, where the long continuance of summer sunlight, along with great warm th, seems to have aided in their introduction and early extension, and thence made their way to the southward, a process which, as Gray and others have shown, has also occurred in later geological times.

The America of this Erian age consisted during the greater part of the period of a more or less extensive belt of land in the north with two long tongues descending from it, one along the Appalachian line in the east, the other in the region west of the Rocky Mountains. On the seaward sides of these there were low lands covered with vegetation, while on the inland side the great interior sea, with its verdant and wooded islands, realised, though probably with shallower water, the conditions of the modern archipelagoes of the Pacific.

Europe presented conditions somewhat similar, having in the earlier and middle portions of the period great sea areas with insular patches of land, and later wide tracts of shallow and in part enclosed water areas, swarming with fishes, and having an abundant vegetation on their shores. These were the conditions of the Eifel and Devonshire limestones, and of the Old Red Sandstone of Scotland, and the Kiltorcan beds of Ireland. In Europe also, as in America, there were in the Erian age great ejections of igneous rock. On both sides of the Atlantic there were somewhat varied and changing conditions ofland and water, and a mild and equable climate, permitting the existence of a rich vegetation in high northern latitudes. Of this latter fact a remarkable example is afforded by the beds holding plants of this age in Spitzbergen and Bear Island, in its vicinity. Here there seem to be two series of plant-bearing strata, one with the vegetation of the Upper Erian, the other with that of the Lower Carboniferous, though both have been united by Heer under his so-called “Ursa Stage” in which he has grouped the characteristic plants of two distinct periods. This has recently been fully established by the researches of Nathorst, though the author had already suggested it as the probable explanation of the strange union of species in the Ursa group of Heer.

In studying the vegetation of this remarkable period, we must take merely some of the more important forms as examples, since it would be impossible to notice all the species, and some of them may be better treated in the Carboniferous, where they have their headquarters. (Fig. 15.)

I may first refer to a family which seems to have culminated in the Erian age, and ever since to have occupied a less important place. It is that of the curious aquatic plants known as Rhizocarps,[AK]and referred to in the last chapter.

[AK]Or, as they have recently been named by some botanists, “Heterosporous Filices,” though they are certainly not ferns in any ordinary sense of that term.

My attention was first directed to these organisms by the late Sir W. E. Logan in 1869. He had obtained from the Upper Erian shale of Kettle Point, Lake Huron, specimens filled with minute circular discs, to which he referred, in his report of 1863, as “microscopic orbicular bodies.” Recognising them to be macrospores, or spore-cases, I introduced them into the report on the Erianflora, which I was then preparing, and which was published in 1871, under the nameSporangites Huronensis.

Fig. 15.—Vegetation of the Devonian period, restored.Calamites,Psilophyton,Leptophleum,Lepidodendron,Cordaites,Sigillaria,Dadoxylon,Asterophyllites,Platyphyllum.

In 1871, having occasion to write a communication to the “American Journal of Science” on the question then raised as to the share of spores and spore-cases in the accumulation of coal, a question to be discussed in a subsequentchapter, these curious little bodies were again reviewed, and were described in substance as follows:

“The oldest bed of spore-cases known to me is that at Kettle Point, Lake Huron. It is a bed of brown bituminous shale, burning with much flame, and under a lens is seen to be studded with flattened disc-like bodies, scarcely more than a hundredth of an inch in diameter, which under the microscope are found to be spore-cases (or macrospores) slightly papillate externally (or more properly marked with dark pores), and sometimes showing a point of attachment on one side and a slit more or less elongated and gaping on the other. When slices of the rock are made, its substance is seen to be filled with these bodies, which, viewed as transparent objects, appear yellow like amber, and show little structure, except that the walls can be distinguished from the internal cavity, which may sometimes be seen to enclose patches of granular matter. In the shale containing them are also vast numbers of rounded, translucent granules, which may be escaped spores (microspores).” The bed containing these spores at Kettle Point was stated, in the reports of the “Geological Survey of Canada,” to be twelve or fourteen feet in thickness, and besides these specimens it contained fossil plants referable to the speciesCalamites inornatusandLepidodendron primævum, and I not unnaturally supposed that the Sporangites might be the fruit of the latter plant. I also noticed their resemblance to the spore-cases ofL. corrugatumof the Lower Carboniferous (a Lepidodendron allied toL. primævum), and to those from Brazil described by Carruthers under the nameFlemingites, as well as to those described by Huxley from certain English coals, and to those of the Tasmanite or white coal of Australia. The bed at Kettle Point is shown to be marine by its holding the sea-weed known asSpirophyton, and shells ofLingula.

The subject did not again come under my notice till1882, when Prof. Orton, of Columbus, Ohio, sent me some specimens from the Erian shales of that State, which on comparison seemed undistinguishable fromSporangites Huronensis.[AL]Prof. Orton read an interesting paper on these bodies, at the meeting of the American Association in Montreal, in which were some new and striking facts. One of these was the occurrence of such bodies throughout the black shales of Ohio, extending “from the Huron River, on the shore of Lake Brie, to the mouth of the Scioto, in the Ohio Valley, with an extent varying from ten to twenty miles in breadth,” and estimated to be three hundred and fifty feet in thickness. I have since been informed by my friend Mr. Thomas, of Chicago, that its thickness, in some places at least, must be three times that amount. About the same time. Prof. Williams, of Cornell, and Prof. Clarke, of Northampton, announced similar discoveries in the State of New York, so that it would appear that beds of vast area and of great thickness are replete with these little vegetable discs, usually converted into a highly bituminous, amber-like substance, giving a more or less inflammable character to the containing rock.

[AL]These shales have been described, as to their chemical and geological relations, by Dr. T. Sterry Hunt, “American Journal of Science,” 1863, and by Dr. Newberry, in the “Reports of the Geological Survey of Ohio,” vol. i., 1863, and vol. iii., 1878.

Another fact insisted on by Prof. Orton was the absence of Lepidodendroid cones, and the occurrence of filamentous vegetable matter, to which the Sporangites seemed to be in some cases attached in groups. Prof. Orton also noticed the absence of the trigonal form, which belongs to the spores of many Lepidodendra, though this is not a constant character. In the discussion on Prof. Orton’s paper, I admitted that the facts detailed by him shook my previous belief of the lycopodiaceous characterof these bodies, and induced me to suspect, with Prof. Orton, that they might have belonged to some group of aquatic plants lower than the Lycopods.

Since the publication of my paper on Rhizocarps in the Palæozoic period above referred to, I have received two papers from Mr. Edward Wethered, F. G. S., in one of which he describes spores of plants found in the lower limestone shales of the Forest of Dean, and in the other discusses more generally the structure and origin of Carboniferous coal-beds.[AM]In both papers he refers to the occurrence in these coals and shales of organisms essentially similar to the Erian spores.

[AM]“Cotteswold Naturalists' Field Club,” 1884; “Journal of the Royal Microscopical Society,” 1885.

In the “Bulletin of the Chicago Academy of Science,” January, 1884, Dr. Johnson and Mr. Thomas, in their paper on the “Microscopic Organisms of the Boulder Clay of Chicago and Vicinity,” noticeSporangites Huronensisas among these organisms, and have discovered them also in large numbers in the precipitate from Chicago city water-supply. They refer them to the decomposition of the Erian shales, of which boulders filled with these organisms are of frequent occurrence in the Chicago clays. The Sporangites and their accompaniments in the boulder clay are noticed in a paper by Dr. G. M. Dawson, in the “Bulletin of the Chicago Academy,” June, 1885.

Prof. Clarke has also described, in the “American Journal of Science” for April, 1885, the forms already alluded to, and which he finds to consist of macrospores enclosed in sporocarps. He compares these with mySporangites HuronensisandProtosalvinia bilobata, but I think it is likely that one of them at least is a distinct species.

I may add that in the “Geological Magazine” for 1875, Mr. Newton, F. G. S., of the Geological Survey ofEngland, published a description of the Tasmanite and Australian white coal, in which he shows that the organisms in these deposits are similar to mySporangites Huronensis, and to the macrospores previously described by Prof. Huxley, from the Better-bed coal. Mr. Newton does not seem to have been aware of my previous description ofSporangites, and proposes the nameTasmanites punctatusfor the Australian form.

Here we have the remarkable fact that the waste macrospores, or larger spores of a species of Cryptogamous plant, occur dispersed in countless millions of tons through the shales of the Erian in Canada and the United States.

No certain clue seemed to be afforded by all these observations as to the precise affinities of these widely distributed bodies; but this was furnished shortly after from an unexpected quarter. In March, 1883, Mr. Orville Derby, of the Geological Survey of Brazil, sent me specimens found in the Erian of that country, which seemed to throw a new light on the whole subject. These I described and pointed out their connection withSporangitesat the meeting of the American Association at Minneapolis, in 1883, and subsequently published my notes respecting them in its proceedings, and in the “Canadian Record of Science.”

Mr. Derby’s specimens contained the curious spiral sea-weed known asSpirophyton, and also minute rounded Sporangites like those obtained in the Erian of Ohio, and of which specimens had been sent to me some years before by the late Prof. Hartt. But they differed in showing the remarkable fact that these rounded bodies are enclosed in considerable numbers in spherical and oval sacs, the walls of which are composed of a tissue of hexagonal cells, and which resemble in every respect the involucres or spore-sacs of the little group of modern acrogens known as Rhizocarps, and living in shallowwater. More especially they resemble the sporocarps of the genusSalvinia. This fact opened up an entirely new field of investigation, and I at once proceeded to compare the specimens with the fructification of modern Rhizocarps, and found that substantially these multitudinous spores embedded in the Erie shales may be regarded as perfectly analogous to the larger spores of the modernSalvinia natansof Europe, as may be seen by the representation of them inFig. 16.

Fig. 16.—Sporangites(Protosalvinia). A,Sporangites Braziliensis, natural size, AX, Same, magnified, B,Sp. biloba, natural size, C, Detached macrospores. D, Spore-cases of Salvinia natans. DX, Same, magnified. E, Shale with sporangites, vertical section, highly magnified.

The typical macrospores from the Erian shales are perfectly circular in outline, and in the flattened state appear as discs with rounded edges, their ordinary diameter being from one seventy-fifth to one one-hundredth of an inch, though they vary considerably in size. This, however, I do not regard as an essential character. The edges, as seen in profile, are smooth, but the flat surface often presents minute dark spots, which at first I mistookfor papillæ, but now agree with Mr. Thomas in recognising them as minute pores traversing the wall of the disc, and similar to those which Mr. Newton has described in Tasmanite, and which Mr. Wethered has also recognised in the similar spores of the Forest of Dean shales. The walls also sometimes show faint indications of concentric lamination, as if they had been thickened by successive deposits.

As seen by transmitted light, and either in front or in profile, the discs are of a rich amber colour, translucent and structureless, except the pores above referred to. The walls are somewhat thick, or from one-tenth to one-twentieth the diameter of the disc in thickness. They never exhibit the triradiate marking seen in spores of Lycopods, nor any definite point of attachment, though they sometimes show a minute elongated spot which may be of this nature, and they are occasionally seen to have opened by slits on the edge or front, where there would seem to have been a natural line of dehiscence. The interior is usually quite vacant or structureless, but in some cases there are curved internal markings which may indicate a shrunken lining membrane, or the remains of a prothallus or embryo. Occasionally a fine granular substance appears in the interior, possibly remains of microspores.

The discs are usually detached and destitute of any envelope, but fragments of flocculent cellular matter are associated with them, and in one specimen from the corniferous limestone of Ohio, in Mr. Thomas’s collection, I have found a group of eight or more discs partly enclosed in a cellular sac-like membrane of similar character to that enclosing the Brazilian specimens already referred to.

The characters of all the specimens are essentially similar, and there is a remarkable absence of other organisms in the shale. In one instance only, I have observed a somewhat smaller round body with a dark centre ornucleus, and a wide translucent margin, marked by a slight granulation. Even this, however, may indicate nothing more than a different state of preservation.

It is proper to observe here that the wall or enclosing sac of these macrospores must have been of very dense consistency, and now appears as a highly bituminous substance, in this agreeing with that of the spores of Lycopods, and, like them, having been when recent of a highly carbonaceous and hydrogenous quality, very combustible and readily admitting of change into bituminous matter. In the paper already referred to, on spore-cases in coals, I have noticed that the relative composition of lycopodium and cellulose is as follows:

Thus, such spores are admirably suited for the production of highly carbonaceous or bituminous coals, etc.

Nothing is more remarkable in connection with these bodies than their uniformity of structure and form over so great areas and throughout so great thickness of rock, and the absence of any other kind of spore-case. This is more especially noteworthy in contrast with the coarse coals and bituminous shales of the Carboniferous, which usually contain a great variety of spores and sporangia, indicating the presence of many species of acrogenous plants, while the Erian shales, on the contrary, indicate the almost exclusive predominance of one form. This contrast is well seen in the Bedford shales overlying these beds, and I believe Lower Carboniferous.[AN]Specimens of these have been kindly communicated to me by Prof. Orton, and have been prepared by Mr. Thomas. In these we see the familiar Carboniferous spores with triradiate markings calledTriletesby Reinsch, and which are similar to those of Lycopodiaceous plants. Still more abundantare those spinous and hooked spores or sporangia, to which the namesSporocarpon,Zygosporites, andTraquariahave been given, and some of which Williamson has shown to be spores of Lycopodiaceous plants.[AO]

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