from specimens obtained from the rich exposures at Gaspé Bay, and which
enabled me to illustrate its parts more fully, perhaps, than those of any
other species of so great antiquity. In the specimens I had obtained I
was able to recognise the forms of the rhizomata, stems, branches, and
rudimentary leaves, and also the internal structure of the stems and
rhizomata, and to illustrate the remarkable resemblance of the forms and
structures to those of the modern _Psilotum_. The fructification was,
however, altogether peculiar, consisting of narrowly ovate sporangia,
borne usually in pairs, on curved and apparently rigid petioles. Under
the microscope these sporangia show indications of cellular structure,
and appear to have been membranous in character. In some specimens
dehiscence appears to have taken place by a slit in one side, and, clay
having entered into the interior, both walls of the spore-case can be
seen. In other instances, being flattened, they might be mistaken for
scales. No spores could be observed in any of the specimens, though in
some the surface was marked by slight, rounded prominences, possibly the
impressions of the spores within. This peculiar and very simple style
of spore-case is also characteristic of other species, and gives to
_Psilophyton_ a very distinct generic character. These naked spore-cases
may be compared to those of such lycopodiaceous plants as _Psilotum_,
in which the scales are rudimentary. They also bear some resemblance,
though on a much larger scale, to the spore-cases of some Erian ferns
(_Archæopteris_), to be mentioned in the sequel. On the whole, however,
they seem most nearly related to the sporocarps of the Rhizocarpeæ.
[Illustration: Fig. 21.--_Lepidodendron_ and _Psilophyton_ (Erian, New
Brunswick). A, _Lepidodendron Gaspianum_. B, C, _Psilophyton elegans_.]
_Arthrostigma_, which is found in the same beds with Psilophyton, was a
plant of more robust growth, with better-developed, narrow, and pointed
leaves, borne in a verticillate or spiral manner, and bearing at the
ends of its branches spikes of naked sporocarps, apparently similar to
those of _Psilophyton_ but more rounded in form. The two genera must
have been nearly related, and the slender branchlets of _Arthrostigma_
are, unless well preserved, scarcely distinguishable from the stems of
_Psilophyton_.[AU]
[AU] Reports of the author on "Devonian Plants," "Geological Survey of
Canada," which see for details as to Erian Flora of northeastern America.
If, now, we compare the vegetation of these and similar ancient plants
with that of modern Rhizocarps, we shall find that the latter still
present, though in a depauperated and diminished form, some of the
characteristics of their predecessors. Some, like _Pilularia_, have
simple linear leaves; others, like _Marsilea_, have leaves in verticils
and cuneate in form; while others, like Azolla and Salvinia, have
frondose leaves, more or less pinnate in their arrangement. The first
type presents little that is characteristic, but there are in the
Erian sandstones and shales great quantities of filamentous and linear
objects which it has been impossible to refer to any genus, and which
might have belonged to plants of the type of _Pilularia_. It is quite
possible, also, that such plants as _Psilophyton glabrum_ and _Cordaites
angustifolia_, of which the fructification is quite unknown, may have
been allied to Rhizocarps. With regard to the verticillate type, we are
at once reminded of _Sphenophyllum_ (Fig. 20), which many palæobotanists
have referred to the _Marsiliacæ_, though, like other Palæozoic Acrogens,
it presents complexities not seen in its modern representatives. _S.
primævum_ of Lesquereux is found in the Hudson River group, and my
_S. antiquum_ in the Middle Erian. Besides these, there are in the
Silurian and Erian beds plants with verticillate leaves which have
been placed with the Annulariæ, but which may have differed from them
in fructification. _Annularia laxa_, of the Erian, and _Protannularia
Harknessii_, of the Siluro-Cambrian, may be given as examples, and must
have been aquatic plants, probably allied to Rhizocarps. It is deserving
of notice, also, that the two best-known species of _Psilophyton_
(_P. princeps_ and _P. robustius_), while allied to Lycopods by the
structure of the stem and such rudimentary foliage as they possess, are
also allied, by the form of their fructification, to the Rhizocarps,
and not to ferns, as some palæobotanists have incorrectly supposed. A
similar remark applies to _Arthrostigma_; and the beautiful pinnately
leaved _Ptilophyton_ may be taken to represent that type of foliage as
seen in modern Rhizocarps, while the allied forms of the Carboniferous
which Lesquereux has named _Trochophyllum_, seem to have had sporocarps
attached to the stem in the manner of _Azolla_.
The whole of this evidence, I think, goes to show that in the Erian
period there were vast quantities of aquatic plants, allied to the modern
Rhizocarps, and that the so-called _Sporangites_ referred to in this
paper were probably the drifted sporocarps and macrospores of some of
these plants, or of plants allied to them in structure and habit, of
which the vegetative organs have perished. I have shown that in the Erian
period there were vast swampy flats covered with _Psilophyton_, and in
similar submerged tracts near to the sea the _Protosalvinia_ may have
filled the waters and have given off the vast multitudes of macrospores
which, drifted by currents, have settled in the mud of the black shales.
We have thus a remarkable example of a group of plants reduced in modern
times to a few insignificant forms, but which played a great role in the
ancient Palæozoic world.
Leaving the Rhizocarps, we may now turn to certain other families of
Erian plants. The first to attract our attention in this age would
naturally be the Lycopods, the club-mosses or ground-pines, which in
Canada and the Eastern States carpet the ground in many parts of our
woods, and are so available for the winter decoration of our houses
and public buildings. If we fancy one of these humble but graceful
plants enlarged to the dimensions of a tree, we shall have an idea of
a _Lepidodendron_, or of any of its allies (Figs. 15, 21). These large
lycopodiaceous trees, which in different specific and generic forms were
probably dominant in the Erian woods, resembled in general those of
modern times in their fruit and foliage, except that their cones were
large, and probably in most cases with two kinds of spores, and their
leaves were also often very long, thus bearing a due proportion to the
trees which they clothed. Their thick stems required, however, more
strength than is necessary in their diminutive successors, and to meet
this want some remarkable structures were introduced similar to those
now found only in the stems of plants of higher rank. The cells and
vessels of all plants consist of thin walls of woody matter, enclosing
the sap and other contents of these sacs and tubes, and when strength is
required it is obtained by lining their interior with successive coats
of the hardest form of woody matter, usually known as lignin. But while
the walls remain thin, they afford free passage to the sap to nourish
every part. If thickened all over, they would become impervious to sap,
and therefore unsuited to one of their most important functions. These
two ends of strength and permeability are secured by partial linings of
lignin, leaving portions of the original wall uncovered. But this may be
done in a great variety of ways.
The most ancient of these contrivances, and one still continued in the
world of plants, is that of the barred or scalariform vessel. This may
be either square or hexagonal, so as to admit of being packed without
leaving vacancies. It is strengthened by a thick bar of ligneous matter
up each angle, and these are connected by cross-bars so as to form a
framework resembling several ladders fastened together. Hence the name
_scalariform_, or ladder-like. Now, in a modern Lycopod there is a
central axis of such barred vessels associated with simpler fibres or
elongated cells. Even in _Sphenophyllum_ and _Psilophyton_, already
referred to as allied to Rhizocarps,[AV] there is such a central axis,
and in the former rigidity is given to this by the vascular and woody
elements being arranged in the form of a three-sided prism or three-rayed
star. But such arrangements would not suffice for a tree, and hence
in the arboreal Lycopods of the Erian age a more complex structure is
introduced. The barred vessels were expanded in the first instance into
a hollow cylinder filled in with pith or cellular tissue, and the outer
rind was strengthened with greatly thickened cells. But even this was not
sufficient, and in the older stems wedge-shaped bundles of barred tissue
were run out from the interior, forming an external woody cylinder, and
inside of the rind were placed bundles of tough bast fibres. Thus, a stem
was constructed having pith, wood, and bark, and capable of additions to
the exterior of the woody wedges by a true exogenous growth. The plan
is, in short, the same with that of the stems of the exogenous trees of
modern times, except that the tissues employed are less complicated.
The structures of these remarkable trees, and the manner in which
they anticipate those of the true exogens of modern times, have been
admirably illustrated by Dr. Williamson, of Manchester. His papers, it
is true, refer to these plants as existing in the Carboniferous age, but
there is every reason to believe that they were of the same character
in the Erian. The plan is the same with that now seen in the stems of
exogenous phænogams, and which has long ceased to be used in those of the
Lycopods. In this way, however, large and graceful lycopodiaceous trees
were constructed in the Erian period, and constituted the staple of its
forests.
[AV] First noticed by the author, "Journal of Geological Society," 1865;
but more completely by Renault, "Comptes Rendus," 1870.
The roots of these trees were equally remarkable with their stems, and
so dissimilar to any now existing that botanists were long disposed to
regard them as independent plants rather than roots. They were similar
in general structure to the stems to which they belonged, but are
remarkable for branching in a very regular manner by bifurcation like
the stems above, and for the fact that their long, cylindrical rootlets
were arranged in a spiral manner and distinctly articulated to the root
after the manner of leaves rather than of rootlets, and fitting them for
growing in homogeneous mud or vegetable muck. They are the so-called
_Stigmaria_ roots, which, though found in the Erian and belonging to
its lycopodiaceous plants, attained to far greater importance in the
Carboniferous period, where we shall meet with them again.
There were different types of lycopodiaceous plants in the Erian. In
addition to humble Lycopods like those of our modern woods and great
Lepidodendra, which were exaggerated Lycopods, there were thick-stemmed
and less graceful species with broad rhombic scars (_Leptophleum_), and
others with the leaf-scars in vertical rows (_Sigillaria_), and others,
again, with rounded leaf-scars, looking like the marks on Stigmaria, and
belonging to the genus _Cyclostigma_. Thus some variety was given to the
arboreal club-mosses of these early forests. (See Fig. 15.)
[Illustration: Fig. 22.--Erian ferns (New Brunswick), A, _Aneimites
obtusa_. C, _Neuropteris polymorpha_. F, _Sphenopteris pilosa_. N,
_Hymenophyllites subfurcatus_.]
Another group of plants which attained to great development in the Erian
age is that of the Ferns or Brackens. The oldest of these yet known
are found in the Middle Erian. The _Eopteris_ of Saporta, from the
Silurian, at one time supposed to carry this type much further back,
has unfortunately been found to be a mere imitative form, consisting of
films of pyrites of leaf-like shapes, and produced by crystallisation.
In the Middle Erian, however, more especially in North America, many
species have been found (Figs. 22 to 24).[AW] I have myself recorded
more than thirty species from the Middle Erian of Canada, and these
belong to several of the genera found in the Carboniferous, though
some are peculiar to the Erian. Of the latter, the best known are
perhaps those of the genus _Archæopteris_ (Fig. 24), so abundant in the
plant-beds of Kiltorcan in Ireland, as well as in North America. In this
genus the fronds are large and luxuriant, with broad obovate pinnules
decurrent, on the leaf-stalk, and with simple sac-like spore-cases
borne on modified pinnæ. Another very beautiful fern found with
_Archæopteris_ is that which I have named _Platyphyllum_, and which grew
on a creeping stem or parasitically on stems of other plants, and had
marginal fructification.[AX] Another very remarkable fern, which some
botanists have supposed may belong to a higher group than the ferns, is
Megalopteris (Fig. 26).
[AW] For descriptions of these ferns, see reports cited above.
[AX] "Reports on Fossil Plants of the Devonian and Upper Silurian of
Canada," 1871, &c.
[Illustration: Fig. 23.--Erian ferns (New Brunswick), B, _Cyclopteris
valida_, and pinnule enlarged, D, _Sphenopteris marginata_, and portion
enlarged. E, _Sphenopteris Harttii_. G, _Hymenophyllites curtilobus_. H,
_Hymenophyllites Gersdorffii_, and portion enlarged. I, _Alethopteris
discrepans_, K, _Pecopteris serrulata_, L, _Pecopteris preciosa_. M,
_Alethopteris Perleyi_.]
[Illustration: Fig. 24.--_Archæopteris Jacksoni_, Dawson (Maine). An
Upper Erian fern, _a_, _b_, Pinnules showing venation.]
[Illustration: Fig. 25.--An Erian tree-fern. _Caulopteris Lockwoodi_,
Dawson, reduced. (From a specimen from Gilboa, New York.)]
Some of the Erian ferns attained to the dimensions of tree-ferns. Large
stems of these, which must have floated out far from land, have been
found by Newberry in the marine limestone of Ohio (_Caulopteris antiqua_
and _C. peregrina_, Newberry),[AY] and Prof. Hall has found in the Upper
Devonian of Gilboa, New York, the remains of a forest of tree-ferns
standing _in situ_ with their great masses of aërial roots attached to
the soil in which they grew (_Caulopteris Lockwoodi_, Dn.).[AZ]
[AY] "Journal of the Geological Society," 1871.
[AZ] _Ibid._
[Illustration: Fig. 26.--_Megalopteris Dawsoni_, Hartt (Erian, New
Brunswick), _a_, Fragment of pinna. _b_, Point of pinnule, _c_, Venation,
(The midrib is not accurately given in this figure.)]
These aërial roots introduce us to a new contrivance for strengthening
the stems of plants by sending out into the soil multitudes of cord-like
cylindrical roots from various heights on the stem, and which form
a series of stays like the cordage of a ship. This method of support
still continues in the modern tree-ferns of the tropics and the southern
hemisphere. In one kind of tree-fern stem from the Erian of New York,
there is also a special arrangement for support, consisting of a
series of peculiarly arranged radiating plates of scalariform vessels,
not exactly like those of an exogenous stem, but doing duty for it
(_Asteropteris_)[BA] Similar plants have been described from the Erian of
Falkenberg, in Germany, and of Saalfeld, in Thuringia, by Goeppert and
Unger, and are referred to ferns by the former, but treated as doubtful
by the latter,[BB] This peculiar type of tree-fern is apparently a
precursor of the more exogenous type of _Heterangium_, recently described
and referred to ferns by Williamson. Here, again, we have a mechanical
contrivance now restricted to higher plants appropriated by these old
cryptogams.
[BA] "Journal of the Geological Society," London, 1881.
[BB] "Sphenopteris Refracta," Goeppert; "Flora des Uebergangsgebirges."
"Cladoxylon Mirabile," Unger; "Palæontologie des Thuringer Waldes."
[Illustration: Fig. 27.--_Calamites radiatus_ (Erian, New Brunswick).]
The history of the ferns in geological time is remarkably different
from that of the Lycopods; for while the latter have long ago descended
from their pristine eminence to a very humble place in nature, the
former still, in the southern hemisphere at least, retain their arboreal
dimensions and ancient dominance.
[Illustration: Fig. 28.--Asterophyllites (Erian, New Brunswick), A,
Asterophyllites latifolia. B, Do., apex of stem (?) fruit, C,
C^1, _A. scutigera_. D, _A. latifolia_, larger whorl of leaves. D^1,
Leaf.]
The family of the _Equisetaceæ_, or mare's-tails, was also represented
by large species of _Calamites_ and by _Asterophyllites_ in the Erian;
but, as its headquarters are in the Carboniferous, we may defer its
consideration till the next chapter. (Figs. 27, 28.)
Passing over these for the present, we find that the flowering plants are
represented in the Erian forests by at least two types of Gymnosperms,
that of _Taxineæ_ or yews, and an extinct family, that of the _Cordaites_
(Figs. 30, 31). The yew-trees are closely allied to the pines and
spruces, and are often included with them in the family of _Coniferæ_.
They differ, however, in the habit of producing berries or drupe-like
fruits instead of cones, and there is some reason to believe that this
was the habit of the Erian trees of this group, though their wood in
some instances resembles rather that of the Araucaria, or Norfolk
Island pine, than that of the modern yews. These trees are chiefly
known to us by their mineralised trunks, which are often found like
drift-wood on modern sand-banks embedded in the Erian sandstones or
limestones. It often shows its structure in the most perfect manner in
specimens penetrated by calcite or silica, or by pyrite, and in which
the original woody matter has been resolved into anthracite or even into
graphite. These trees have true woody tissues presenting that beautiful
arrangement of pores or thin parts enclosed in cup-like discs, which is
characteristic of the coniferous trees, and which is a great improvement
on the barred tissue already referred to, affording a far more strong,
tough, and durable wood, such as we have in our modern pines and yews
(Fig. 29).
[Illustration: Fig. 29.--_Dadoxylon Ouangondianum_, an Erian conifer, A,
Fragment showing Sternberg pith and wood; _a_, medullary sheath; _b_,
pith; _c_, wood; _d_, section of pith, B, Wood-cell; _a_, hexagonal
areole; _b_, pore, _c_, Longitudinal section of wood, showing, _a_,
areolation, and _b_, medullary rays, D, Transverse section, showing,
_a_, wood-cells, and _b_, limit of layer of growth, (B, C, D, highly
magnified.)]
These primitive pines make their appearance in the Middle Erian, in
various parts of America, as well as in Scotland and Germany, and they
are represented by wood indicating the presence of several species. I
have myself indicated and described five species from the Erian of Canada
and the United States. From the fact that these trees are represented
by drifted trunks embedded in sandstones and marine limestones, we may,
perhaps, infer that they grew on the rising grounds of the Erian land,
and that their trunks were carried by river-floods into the sea. No
instance has yet certainly occurred of the discovery of their foliage or
fruit, though there are some fan-shaped leaves usually regarded as ferns
which may have belonged to such trees. These in that case would have
resembled the modern _Gingko_ of China, and some of the fruits referred
to the genus _Cardiocarpum_ may have been produced by them. Various
names have been given to these trees. I have preferred that given by
Unger, _Dadoxylon_, as being more non-committal as to affinities than the
others.[BC] Many of these trees had very long internal pith-cylinders,
with curious transverse tubulæ, and which, when preserved separately,
have been named _Sternbergia_.
[BC] _Araucarites_, Goeppert; _Araucarioxylon_, Kraus.
Allied to these trees, and perhaps intermediate between them and the
_Cycads_, were those known as _Cordaites_ (Fig. 30), which had trunks
resembling those of _Dadoxylon_, but with still larger _Sternbergia_
piths and an internal axis of scalariform vessels, surrounded by a
comparatively thin woody cylinder. Some of them have leaves over a
foot in length, reminding one of the leaves of broad-leaved grasses or
iridaceous plants. Yet their flowers and fruit seem to have been more
nearly allied to the yews than to any other plants (Fig. 31). Their stems
were less woody and their piths larger than in the true pines, and some
of the larger-leaved species must have had thick, stiff branches. They
are regarded as constituting a separate family, intermediate between
pines and cycads, and, beginning in the Middle Devonian, they terminate
in the Permian, where, however, some of the most gigantic species occur.
In so far as the form and structure of the leaves, stems, and fruit are
concerned, there is marvellously little difference between the species
found in the Erian and the Permian. They culminated, however, in the
Carboniferous period, and the coal-fields of southern France have proved
so far the richest in their remains.
[Illustration: Fig. 30.--_Cordaites Robbii_ (Erian, New Brunswick),
_a_, Group of young leaves. _b_, Point of leaf, _c_, Base of leaf, _d_.
Venation, magnified.]
[Illustration: Fig. 31.--Erian fruits, &c., some gymnospermous, and
probably of _Cordaites_ and Taxine trees (St. John, New Brunswick), A,
_Cardiocarpum cornutum_. B, _Cardiocarpum acutum_. C, _Cardiocarpum
Crampii_. D, _Cardiocarpum Baileyi_. E, _Trigonocarpum racemosum_.
E^1, E^2, Fruits enlarged, F, _Antholithes Devonicus_. G, Annularia
acuminata, H, _Asterophyllites acicularis_. H^2, Fruit of the same, K,
_Cardiocarpum_ (? young of _A._), L, _Pinnularia dispalans_ (probably a
root).]
Lastly, a single specimen, collected by Prof. James Hall, of Albany,
at Eighteen-mile Creek, Lake Erie, has the structure of an ordinary
angiospermous exogen, and has been described by me as _Syringoxylon
mirabile_.[BD] This unique example is sufficient to establish the fact
of the existence of such plants at this early date, unless some accident
may have carried a specimen from a later formation to be mixed with
Erian fossils. It is to be observed, however, that the non-occurrence of
any similar wood in all the formations between the Upper Erian and the
Middle Cretaceous suggests very grave doubt as to the authenticity of the
specimen. I record the fact, waiting further discoveries to confirm it.
Of the character of the specimen which I have described I entertain no
doubt.
[BD] "Journal of the Geological Society," vol. xviii.
We shall be better able to realise the significance and relations of this
ancient flora when we have studied that of the succeeding Carboniferous.
We may merely remark here on the fact that, in these forests of the
Devonian and in the marshes on their margins, we find a wonderful
expansion of the now modest groups of Rhizocarps and Lycopods, and that
the flora as a whole belongs to the highest group of Cryptogams and the
lowest of Phænogams, so that it has about it a remarkable aspect of
mediocrity. Further, while there is evidence of some variety of station,
there is also evidence of much equality of climate, and of a condition
of things more resembling that of the insular climates of the temperate
portions of the southern hemisphere than that of North America or Europe
at present.
The only animal inhabitants of these Devonian woods, so far as known,
were a few species of insects, discovered by Hartt in New Brunswick, and
described by Dr. Scudder. Since, however, we now know that scorpions as
well as insects existed in the Silurian, it is probable that these also
occurred in the Erian, though their remains have not yet been discovered.
All the known insects of the Erian woods are allies of the shad-flies and
grasshoppers (_Neuroptera_ and _Orthoptera_), or intermediate between
the two. It is probable that the larvæ of most of them lived in water
and fed upon the abundant vegetable matter there, or on the numerous
minute crustaceans and worms. There were no land vertebrates, so far as
known, but there were fishes (_Dipterus_, etc.), allied to the modern
Barramunda or _Ceratodus_ of Australia, and with teeth suited for
grinding vegetable food. It is also possible that some of the smaller
plate-covered fishes (Placoganoids, like _Pterichthys_) might have fed
on vegetable matter, and, in any case, if they fed on lower animals, the
latter must have subsisted on plants. I mention these facts to show that
the superabundant vegetation of this age, whether aquatic or terrestrial,
was not wholly useless to animals. It is quite likely, also, that we have
yet much to learn of the animal life of the Erian swamps and woods.
NOTES TO CHAPTER III.
I.--Classification of Sporangites.
It is, of course, very unsatisfactory to give names to mere fragments of
plants, yet it seems very desirable to have some means of arranging them.
With respect to the organisms described above, which were originally
called by me _Sporangites_, under the supposition that they were
Sporangia rather than spores, this name has so far been vindicated by the
discovery of the spore-cases belonging to them, so that I think it may
still be retained as a provisional name; but I would designate the whole
as _Protosalviniæ_, meaning thereby plants with rhizocarpean affinities,
though possibly when better understood belonging to different genera. We
may under these names speak of their detached discs as macrospores and of
their cellular envelopes as sporocarps. The following may be recognized
as distinct forms:
1. _Protosalvinia Huronensis_, Dawson, _Syn._, _Sporangites Huronensis_,
"Report on Erian Flora of Canada," 1871.--Macrospores, in the form of
discs or globes, smooth and thick-walled, the walls penetrated by minute
radiating pores. Diameter about one one-hundredth of an inch, or a little
more, When in situ several macrospores are contained in a thin cellular
sporocarp, probably globular in form. From the Upper Erian, and perhaps
Lower Carboniferous shales of Kettle Point, Lake Huron, of various places
in the State of Ohio, and in the shale boulders of the boulder clay of
Chicago and vicinity. First collected at Kettle Point by Sir W. E. Logan,
and in Ohio by Prof. Edward Orton, and at Chicago by Dr. H. A. Johnson
and Mr. B. W. Thomas, also in New York by Prof. J. M. Clarke.
The macrospores collected by Mr. Thomas from the Chicago clays and shales
conform closely to those of Kettle Point, and probably belong to the
same species. Some of them are thicker in the outer wall, and show the
pores much more distinctly. These have been called by Mr. Thomas _S.
Chicagoensis_, and may be regarded as a varietal form. Specimens isolated
from the shale and mounted dry, show what seems to have been the hilum or
scar of attachment better than those in balsam.
Sections of the Kettle Point shale show, in addition to the macrospores,
wider and thinner shreds of vegetable matter, which I am inclined to
suppose to be remains of the sporocarps.
2. _Protosalvinia_ (_Sporangites_) _Braziliensis_, Dawson, "Canadian
Record of Science," 1883.--Macrospores, round, smooth, a little longer
than those of the last species, or about one seventy-fifth of an inch
in diameter, enclosed in round, oval, or slightly reniform sporocarps,
each containing from four to twenty-four macrospores. Longest diameter
of sporocarps three to six millimetres. Structure of wall of sporocarps
hexagonal cellular. Some sporocarps show no macrospores, and may possibly
contain microspores. The specimens are from the Erian of Brazil.
Discovered by Mr. Orville Derby. The formation, according to Mr. Derby,
consists of black shales below, about three hundred feet thick, and
containing the fucoid known as Spirophyton, and probably decomposed
vegetable matter. Above this is chocolate and reddish shale, in which
the well-preserved specimens of Protosalvinia occur. These beds are very
widely distributed, and abound in _Protosalvinia_ and _Spirophyton_.
3. _Protosalvinia_ (_Sporangites_) _bilobata_, Dawson, "Canadian
Record of Science," 1883.--Sporocarps, oval or reniform, three to six
millimetres in diameter, each showing two rounded prominences at the
ends, with a depression in the middle, and sometimes a raised neck or
isthmus at one side connecting the prominences. Structure of sporocarp
cellular. Some of the specimens indicate that each prominence or tubercle
contained several macrospores. At first sight it would be easy to mistake
these bodies for valves of _Beyrichia_.
Found in the same formations with the last species, though, in so far as
the specimens indicate, not precisely in the same beds. Collected by Mr.
Derby.
4. _Protosalvinia Clarkei_, Dawson, _P. bilobata_, Clarke, "American
Journal of Science."--Macrospores two-thirds to one millimetre in
diameter. One, two, or three contained in each sporocarp, which is
cellular. The macrospores have very thick walls with radiating tortuous
tubes. Unless this structure is a result of mineral crystallisation,
these macrospores must have had very thick walls and must have resembled
in structure the thickened cells of stone fruits and of the core of the
pear, or the tests of the Silurian and Erian seeds known as _Pachytheca_,
though on a smaller scale.
It is to be observed that bodies similar to these occur in the Boghead
earthy bitumen, and have been described by Credner.
I have found similar bodies in the so-called "Stellar coal" of the coal
district of Pictou, Nova Scotia, some layers of which are filled with
them. They occur in groups or patches, which seem to be enclosed in a
smooth and thin membrane or sporocarp. It is quite likely that these
bodies are generically distinct from _Protosalvinia_.
5. _Protosalvinia punctata_, Newton, "Geological Magazine," New Series,
December 2d, vol. ii.--Mr. Newton has named the discs found in the
white coal and Tasmanite, _Tasmanites_, the species being _Tasmanites
punctatus_, but as my name _Sporangites_ had priority, I do not think it
necessary to adopt this term, though there can be little doubt that these
organisms are of similar character. The same remark may be made with
reference to the bodies described by Huxley and Newton as occurring in
the Better-bed coal.
In Witham's "Internal Structure of Fossil Vegetables," 1833, Plate XI,
are figures of Lancashire cannel which shows _Sporangites_ of the type of
those in the Erian shales. Quekett, in his "Report on the Torbane Hill
Mineral," 1854, has very well figured similar structures from the Methel
coal and the Lesmahagow cannel coal. These are the earliest publications
on the subject known to me; and Quekett, though not understanding the
nature of the bodies he observed, holds that they are a usual ingredient
in cannel coals.
II.--The Nature and Affinities of Ptilophyton.
(_Lycopodites Vanuxemii_ of "Report on Devonian and Upper Silurian
Plants," Part I., page 35, _L. plumula_ of "Report on Lower Carboniferous
Plants," page 24, Plate I., Figs. 7, 8, 9.) In the reports above referred
to, these remarkable pinnate, frond-like objects were referred to the
genus _Lycopodites_, as had been done by Goeppert in his description
of the European species _Lycopodites pennæformis_, which is very near
to the American Erian form. Since 1871, however, there have been many
new specimens obtained, and very various opinions expressed as to their
affinities. While Hall has named some of them _Plumalina_, and has
regarded them as animal structures, allied to hydroids, Lesquereux
has described some of the Carboniferous forms under the generic name
_Trochophyllum_, which is, however, more appropriate to plants with
verticillate leaves which are included in this genus. Before I had seen
the publications of Hall and Lesquereux on the subject, I had in a paper
on "Scottish Devonian Plants"[BE] separated this group from the genus
_Lycopodites_, and formed for it the genus _Ptilophyton_, in allusion
to the feather-like aspect of the species. My reasons for this, and my
present information as to the nature of these plants, may be stated
as follows: Schimper, in his "Palæontologie Vegetale" (possibly from
inattention to the descriptions or want of access to specimens), doubts
the lycopodiaceous character of species of _Lycopodites_ described in my
published papers on plants of the Devonian of America and in my Report of
1871. Of these, _L. Richardsoni_ and _L. Matthewi_ are undoubtedly very
near to the modern genus _Lycopodium_. _L. Vanuxemii_ is, I admit, more
problematical; but Schimper could scarcely have supposed it to be a fern
or a fucoid allied to _Caulerpa_ had he observed that both in my species
and the allied _L. pennæformis_ of Goeppert, which he does not appear to
notice, the pinnules are articulated upon the stem, and leave scars where
they have fallen off. When in Belfast in 1870, my attention was again
directed to the affinities of these plants by finding in Prof. Thomson's
collection a specimen from Caithness, which shows a plant apparently
of this kind, with the same long narrow pinna? or leaflets, attached,
however, to thicker stems, and rolled up in a circinate manner. It seems
to be a plant in vernation, and the parts are too much crowded and
pressed together to admit of being accurately figured or described; but
I think I can scarcely be deceived as to its true nature. The circinate
arrangement in this case would favour a relationship to ferns; but some
lycopodiaceous plants also roll themselves in this way, and so do the
branches of the plants of the genus _Psilophyton_. (Fig. 17, _supra_.)
[BE] "Canadian Naturalist," 1878.
The specimen consists of a short, erect stem, on which are placed
somewhat stout alternate branches, extending obliquely outward and then
curving inward in a circinate manner. The lower ones appear to produce
on their inner sides short lateral branchlets, and upon these, and also
upon the curved extremities of the branches, are long, narrow, linear
leaves placed in a crowded manner. The specimen is thus not a spike of
fructification, but a young stem or branch in vernation, and which when
unrolled would be of the form of those peculiar pinnate _Lycopodites_
of which _L. Vanuxemii_ of the American Devonian and _L. pennæformis_ of
the European Lower Carboniferous are the types, and it shows, what might
have been anticipated from other specimens, that they were low, tufted
plants, circinate in vernation. The short stem of this plant is simply
furrowed, and bears no resemblance to a detached branch of Lycopodites
Milleri which lies at right angles to it on the same slab. As to the
affinities of the singular type of plants to which this specimen belongs,
I may quote from my "Report on the Lower Carboniferous Plants of Canada,"
in which I have described an allied species, _L. plumula_:
"The botanical relations of these plants must remain subject to doubt,
until either their internal structure or their fructification can be
discovered. In the mean time I follow Goeppert in placing them in what
we must regard as the provisional genus _Lycopodites_. On the one hand,
they are not unlike the slender twigs of _Taxodium_ and similar Conifers,
and the highly carbonaceous character of the stems gives some colour to
the supposition that they may have been woody plants. On the other hand,
they might, so far as form is concerned, be placed with Algæ of the type
of Brongniart's _Chondrites obtusus_, or the modern _Caulerpa plumaria_.
Again, in a plant of this type from the Devonian of Caithness to which
I have referred in a former memoir, the vernation seems to have been
circinate, and Schimper has conjectured that these plants may be ferns,
which seems also to have been the view of Shumard."
On the whole, these plants are allied to Lycopods rather than to ferns;
and as they constitute a small but distinct group, known only, so far
as I am aware, in the Lower Carboniferous and Erian or Devonian, they
deserve a generic name, and I proposed for them in my "Paper on Scottish
Devonian Plants," 1878, that of _Ptilophyton_, a name sufficiently
distinct in sound from Psilophyton, and expressing very well their
peculiar feather-like habit of growth. The genus was defined as follows:
"Branching plants, the branches bearing long, slender leaves in two or
more ranks, giving them a feathered appearance; vernation circinate.
Fruit unknown, but analogy would indicate that it was borne on the bases
of the leaves or on modified branches with shorter leaves."
The Scottish specimen above referred to was named _Pt. Thomsoni_, and was
characterised by its densely tufted form and thick branches. The other
species known are: _Pt. pennæformis_, Goeppert, L. Carboniferous; _Pt.
Vanuxemii_, Dawson, Devonian; _Pt. plumula_, Dawson, L. Carboniferous.
Shumard's _Filicites gracilis_, from the Devonian of Ohio, and Stur's
_Pinites antecedens_, from the Lower Carboniferous of Silesia, may
possibly belong to the same genus. The Scottish specimen referred to is
apparently the first appearance of this form in the Devonian of Europe.
I have at a still later date had opportunities of studying considerable
series of these plants collected by Prof. Williams, of Cornell
University, and prepared a note in reference to them for the American
Association, of which, however, only an abstract has been published.
I have also been favoured by Prof. Lesquereux and Mr. Lacoe, of
Pittston, with the opportunity of studying the specimens referred to
_Trochophyllum_.
Prof. Williams's specimens occur in a dark shale associated with
remains of land-plants of the genera _Psilophyton_. _Rhodea_, &c.,
and also marine shells, of which a small species of _Rhynchonella_ is
often attached to the stems of the _Ptilophyton_. Thus these organisms
have evidently been deposited in marine beds, but in association with
land-plants.
The study of the specimens collected by Prof. Williams develops the
following facts: (1) The plants are not continuous fronds, but slender
stems or petioles, with narrow, linear leaflets attached in a pinnate
manner. (2) The pinnules are so articulated that they break off, leaving
delicate transverse scars, and the lower parts of the stems are often
thus denuded of pinnæ for the length of one or more inches. (3) The
stems curve in such a manner as to indicate a circinate vernation. (4)
In a few instances the fronds were observed to divide dichotomously
toward the top; but this is rare. (5) There are no indications of cells
in the pinnules; but, on the other hand, there is no appearance of
fructification unless the minute granules which roughen some of the
sterns are of this nature. (6) The stems seem to have been lax and
flexuous, and in some instances they seem to have grown on the petioles
of ferns preserved with them in the same beds. (7) The frequency of the
attachment of small brachiopods to the specimens of _Ptilophyton_ would
seem to indicate that the plant stood erect in the water. (8) Some of
the specimens show so much carbonaceous matter as to indicate that the
pinnules were of considerable consistency. All these characters are those
rather of an aquatic plant than of an animal organism or of a land-plant.
The specimens communicated by Prof. Lesquereux and Mr. Lacoe are from the
Lower Carboniferous, and evidently represent a different species with
similar slender pitted stems, often partially denuded of pinnules below;
but the pinnules are much broader and more distant. They are attached
by very narrow bases, and apparently tend to lie on a plane, though they
may possibly have been spirally arranged. On the same slabs are rounded
sporangia or macrospores like those of _Lepidodendron_, but there is no
evidence that these belonged to _Trochophyllum_. On the stems of this
plant, however, there are small, rounded bodies apparently taking the
places of some of the pinnules. These may possibly be spore-cases; but
they may be merely imperfectly developed pinnules. Still the fact that
similar small granules appear on the stems of the Devonian species,
favours the idea that they may be organs of fructification.
The most interesting discovery, however, which results from the study
of Mr. Lacoe's specimens, is that the pinnules were cylindrical and
hollow, and probably served to float the plant. This would account for
many of the peculiarities in the appearance and mode of occurrence of the
Devonian _Ptilophyton_, which are readily explained if it is supposed to
be an aquatic plant, attaching itself to the stems of submerged vegetable
remains and standing erect in the water by virtue of its hollow leaves.
It may well, however, have been a plant of higher organisation than the
Algæ, though no doubt cryptogamous.
The species of _Ptilophyton_ will thus constitute a peculiar group
of aquatic plants, belonging to the Devonian and Lower Carboniferous
periods, and perhaps allied to Lycopods and Pillworts in their
organisation and fruit, but specially distinguished by their linear
leaves serving as floats and arranged pinnately on slender stems. The
only species yet found within the limits of Canada is _Pt. plumula_,
found by Dr. Honeyman in the Lower Carboniferous of Nova Scotia; but as
_Pt. Vanuxemii_ abounds in the Erian of New York, it will no doubt be
found in Canada also.
III.--Tree-Ferns of the Erian Period.
As the fact of the occurrence of true tree-ferns in rocks so old as the
Middle Erian or Devonian has been doubted in some quarters, the following
summary is given from descriptions published in the "Journal of the
Geological Society of London" (1871 and 1881), where figures of the
species will be found:
Of the numerous ferns now known in the Middle and Upper Devonian of
North America, a great number are small and delicate species, which were
probably herbaceous; but there are other species which may have been
tree-ferns. Little definite information, however, has, until recently,
been obtained with regard to their habit of growth.
The only species known to me in the Devonian of Europe is the
_Caulopteris Peachii_ of Salter, figured in the "Quarterly Journal of
the Geological Society" for 1858. The original specimen of this I had an
opportunity of seeing in London, through the kindness of Mr. Etheridge,
and have no doubt that it is the stem of a small arborescent fern, allied
to the genus _Caulopteris_, of the coal formation.
In my paper on the Devonian of Eastern America ("Quarterly Journal
of the Geological Society," 1862), I mentioned a plant found by Mr.
Richardson at Perry, as possibly a species of _Megaphyton_, using that
term to denote those stems of tree-ferns which have the leaf-scars in
two vertical series; but the specimen was obscure, and I have not yet
obtained any other.
More recently, in 1869, Prof. Hall placed in my hands an interesting
collection from Gilboa, New York, and Madison County, New York, including
two trunks surrounded by aërial roots, which I have described as
_Psaronius textilis_ and _P. Erianus_, in my "Revision of the Devonian
Flora," read before the Royal Society.[BF] In the same collection were
two very large petioles, _Rhachiopteris gigantea_ and _R. palmata_, which
I have suggested may have belonged to tree-ferns.
[BF] Abstract in "Proceedings of the Royal Society," May, 1870; also
"Report on Erian Plants of Canada," 1871.
My determination of the species of _Psaronius_, above mentioned, has
recently been completely confirmed by the discovery on the part of Mr.
Lockwood, of Gilboa, of the upper part of one of these stems, with its
leaf-scars preserved and petioles attached, and also by some remarkable
specimens obtained by Prof. Newberry, of New York, from the Corniferous
limestone of Ohio, which indicate the existence there of three species of
tree-ferns, one of them with aërial roots similar to those of the Gilboa
specimens. The whole of these specimens Dr. Newberry has kindly allowed
me to examine, and has permitted me to describe the Gilboa specimen,
as connected with those which I formerly studied in Prof. Hall's
collections. The specimens from Ohio he has himself named, but allows me
to notice them here by way of comparison with the others. I shall add
some notes on specimens found with the Gilboa ferns.
It may be further observed that the Gilboa specimens are from a bed
containing erect stumps of tree-ferns, in the Chemung group of the Upper
Devonian, while those from Ohio are from a marine limestone, belonging to
the lower part of the Middle Devonian.
1. _Caulopteris Lockwoodi_, Dawson.--Trunk from two to three inches in
diameter, rugose longitudinally. Leaf-scars broad, rounded above, and
radiatingly rugose, with an irregular scar below, arranged spirally in
about five ranks; vascular bundles not distinctly preserved. Petioles
slender, much expanded at the base, dividing at first in a pinnate
manner, and afterwards dichotomously. Ultimate pinnæ with remains of
numerous, apparently narrow pinnules.
This stem is probably the upper part of one or other of the species
of _Psaronius_ found in the same bed (_P. Erianus_, Dawson, and _P.
textilis_, Dawson).[BG] It appears to have been an erect stem embedded
in situ in sandstone, and preserved as a cast. The stem is small, being
only two inches, or a little more, in diameter. It is coarsely wrinkled
longitudinally, and covered with large leaf-scars, each an inch in
diameter, of a horseshoe-shape. The petioles, five of which remain,
separate from these scars with a distinct articulation, except at one
point near the base, where probably a bundle or bundles of vessels passed
into the petiole. They retain their form at the attachment to the stem,
but a little distance from it they are flattened. They are inflated
at the base, and somewhat rapidly diminish in size. The leaf-scars
vary in form, and are not very distinct, but they appear to present
a semicircular row of pits above, largest in the middle. From these
there proceed downward a series of irregular furrows, converging to a
second and more obscure semicircle of pits, within or below which is the
irregular scar or break above referred to. The attitude and form of the
petioles will be seen from Fig. 24, _supra_.
[BG] Memoir on Devonian Flora, "Proceedings of the Royal Society," May,
1870.
The petioles are broken off within a few inches of the stem; but other
fragments found in the same beds appear to show their continuation, and
some remains of their foliage. One specimen shows a series of processes
at the sides, which seem to be the remains of small pinnæ, or possibly
of spines on the margin of the petiole. Other fragments show the
division of the frond, at first in a pinnate manner, and subsequently by
bifurcation; and some fragments show remains of pinnules, possibly of
fertile pinnules. These are very indistinct, but would seem to show that
the plant approached, in the form of its fronds and the arrangement of
its fructification, to the Cyclopterids of the sub-genus _Aneimites_,
one of which (_Aneimites Acadica_), from the Lower Carboniferous of Nova
Scotia, I have elsewhere described as probably a tree-fern,[BH] The
fronds were evidently different from those of _Archæopteris_[BI] a genus
characteristic of the same beds, but of very different habit of growth.
This accords with the fact that there is in Prof. Hall's collection a
mass of fronds of _Cyclopteris_ (_Archæopteris_) Jacksoni, so arranged
as to make it probable that the plant was an herbaceous fern, producing
tufts of fronds on short stems in the ordinary way. The obscurity of
the leaf-scars may render it doubtful whether the plant above described
should be placed in the genus _Caulopteris_ or in _Stemmatopteris_; but
it appears most nearly allied to the former. The genus is at present,
of course, a provisional one; but I have thought it only justice to the
diligent labours of Mr. Lockwood to name this curious and interesting
fossil _Caulopteris Lockwoodi_.
[BH] "Quarterly Journal of the Geological Society," 1860.
[BI] The genus to which the well-known _Cyclopteris_ (_Adiantites_)
_Hibernicus_ of the Devonian of Ireland belongs.
I have elsewhere remarked on the fact that trunks, and petioles, and
pinnules of ferns are curiously dissociated in the Devonian beds--an
effect of water-sorting, characteristic of a period in which the
conditions of deposition were so varied. Another example of this is,
that in the sandstones of Gaspé Bay, which have not as yet afforded
any example of fronds of ferns, there are compressed trunks, which Mr.
Lockwood's specimens allow me at least to conjecture may have belonged
to tree-ferns, although none of them are sufficiently perfect for
description.
Mr. Lockwood's collection includes specimens of _Psaronius textilis_; and
in addition to these there are remains of erect stems somewhat different
in character, yet possibly belonging to the higher parts of the same
species of tree-fern. One of these is a stem crushed in such a manner
that it does not exhibit its form with any distinctness, but surrounded
by smooth, cylindrical roots, radiating from it in bundles, proceeding at
first horizontally, and then curving downward, and sometimes terminating
in rounded ends. They resemble in form and size the aërial roots of
_Psaronius Erianus_; and I believe them to be similar roots from a higher
part of the stem, and some of them young and not prolonged sufficiently
far to reach the ground. This specimen would thus represent the stem
of _P. Erianus_ at a higher level than those previously found. We can
thus in imagination restore the trunk and crown of this once graceful
tree-fern, though we have not the detail of its fronds. Mr. Lockwood's
collections also contain a specimen of the large fern-petiole which I
have named _Rhachiopteris punctata_. My original specimen was obtained by
Prof. Hall from the same horizon in New York. That of Mr. Lockwood is of
larger size, but retains no remains of the frond. It must have belonged
to a species quite distinct from _Caulopteris Lockwoodi_, but which may,
like it, have been a tree-fern.
2. _Caulopteris antiqua_, Newberry.--This is a flattened stem, on a slab
of limestone, containing Brachiopods, Trilobites, &c., of the Corniferous
limestone. It is about eighteen inches in length, and three and a half
inches in average breadth. The exposed side shows about twenty-two large
leaf-scars arranged spirally. Each leaf, where broken off, has left
a rough fracture; and above this is a semicircular impression of the
petiole against the stem, which, as well as the surface of the bases of
the petioles, is longitudinally striated or tuberculated. The structures
are not preserved, but merely the outer epidermis, as a coaly film. The
stem altogether much resembles _Caulopteris Peachii_, but is of larger
size. It differs from _C. Lockwoodi_ in the more elongated leaf-bases,
and in the leaves being more remotely placed; but it is evidently of the
same general character with that species.
3. _Caulopteris_ (_Protopteris_) _peregrina_, Newberry.--This is a much
more interesting species than the last, as belonging to a generic or
subgeneric form not hitherto recognised below the Carboniferous, and
having its minute structure in part preserved.
The specimens are, like the last, on slabs of marine limestone of the
Corniferous formation, and flattened. One represents an upper portion
of the stem with leaf-scars and remains of petioles; another a lower
portion, with aërial roots. The upper part is three inches in diameter,
and about a foot in length, and shows thirty leaf-scars which are about
three-fourths of an inch wide, and rather less in depth. The upper part
presents a distinct rounded and sometimes double marginal line, sometimes
with a slight depression in the middle. The lower part is irregular,
and when most perfect shows seven slender vascular bundles, passing
obliquely downward into the stem. The more perfect leaf-bases have the
structure preserved, and show a delicate, thin-walled, oval parenchyma,
while the vascular bundles show scalariform vessels with short bars in
several rows, in the manner of many modern ferns. Some of the scars show
traces of the hippocrepian mark characteristic of _Protopteris_; and the
arrangement of the vascular bundles at the base of the scars is the same
as in that genus, as are also the general form and arrangement of the
scars. On careful examination, the species is indeed very near to the
typical _P. Sternbergii_, as figured by Corda and Schimper.[BJ]
[BJ] Corda, "Beiträge," Pl. 48, copied by Schimper, Pl. 52.
The genus _Protopteris_ of Sternberg, though the original species (_P.
punctata_) appears as a _Lepidodendron_ in his earlier plate (Plate 4),
and as a _Sigillaria_ (_S. punctata_) in Brongniart's great work, is a
true tree-fern; and the structure of one species (_P. Cottai_) has been
beautifully figured by Corda. The species hitherto described are from the
Carboniferous and Permian.
The second specimen of this species represents a lower part of the stem.
It is thirteen inches long and about four inches in diameter, and is
covered with a mass of flattened aërial roots lying parallel to each
other, in the manner of the _Psaronites_ of the coal-formation and of _P.
Erianus_ of the Upper Erian or Devonian.
4. _Asteropteris noveboracensis_, gen. and sp. n.--The genus
_Asteropteris_ is established for stems of ferns having the axial portion
composed of vertical radiating plates of scalariform tissue embedded in
parenchyma, and having the outer cylinder composed of elongated cells
traversed by leaf-bundles of the type of those of _Zygopteris_.
The only species known to me is represented by a stem 2·5 centimetres in
diameter, slightly wrinkled and pitted externally, perhaps by traces of
aërial roots which have perished. The transverse section shows in the
centre four vertical plates of scalariform or imperfectly reticulated
tissue, placed at right angles to each other, and united in the middle
of the stem. At a short distance from the centre, each of these plates
divides into two or three, so as to form an axis of from ten to twelve
radiating plates, with remains of cellular tissue filling the angular
interspaces. The greatest diameter of this axis is about 1·5 centimetre.
Exterior to the axis the stem consists of elongated cells, with somewhat
thick walls, and more dense toward the circumference. The walls of
these cells present a curious reticulated appearance, apparently caused
by the cracking of the ligneous lining in consequence of contraction
in the process of carbonization. Embedded in this outer cylinder are
about twelve vascular bundles, each with a dumb-bell-shaped group of
scalariform vessels enclosed in a sheath of thick-walled fibres. Each
bundle is opposite to one of the rays of the central axis. The specimen
shows about two inches of the length of the stem, and is somewhat bent,
apparently by pressure, at one end.
This stem is evidently that of a small tree-fern of a type, so far as
known to me, not before described,[BK] and constituting a very complex
and symmetrical form of the group of Palæozoic ferns allied to the
genus _Zygopteris_ of Schimper. The central axis alone has a curious
resemblance to the peculiar stem described by Unger ("Devonian Flora
of Thuringia") under the name of _Cladoxylon mirabile_; and it is just
possible that this latter stem may be the axis of some allied plant. The
large aërial roots of some modern tree-ferns of the genus _Angiopteris_
have, however, an analogous radiating structure.
[BK] Prof. Williamson, to whom I have sent a tracing of the structure,
agrees with me that it is new.
The specimen is from the collection of Berlin H. Wright, Esq., of Penn
Yan, New York, and was found in the Portage group (Upper Erian) of Milo,
New York, where it was associated with large petioles of ferns and trunks
of _Lepidodendra_, probably _L. Chemungense_ and _L. primævum_.
The occurrence of this and other stems of tree-ferns in marine beds
has recently been illustrated by the observation of Prof. A. Agassiz
that considerable quantities of vegetable matter can be dredged from
great depths in the sea on the leeward side of the Caribbean Islands.
The occurrence of these trunks further connects itself with the great
abundance of large petioles (_Rhachiopteris_) in the same beds, while the
rarity of well-preserved fronds is explained by the coarseness of the
beds, and also by the probably long maceration of the plant-remains in
the sea-water.
In connection with this I may refer to the remarkable facts recently
stated by Williamson[BL] respecting the stems known as Heterangium and
_Lyginodendron_. It would seem that these, while having strong exogenous
peculiarities, are really stems of tree-ferns, thus placing this family
in the same position of advancement with the Lycopods and Equisetaceæ of
the Coal period.
[BL] "Proceedings of the Royal Society," January 6, 1887.
IV.--On Erian Trees of the Genus Dadoxylon, Unger. (_Araucarites_ of
Goeppert, _Araucarioxylon_ of Kraus.)
Large woody trunks, carbonised or silicified, and showing wood-cells with
hexagonal areoles having oval pores inscribed in them, occur abundantly
in some beds of the Middle Erian of America, and constitute the most
common kind of fossil wood all the way to the Trias. They have in the
older formations, generally, several rows of pores on each fibre, and
medullary rays composed of two or more series of cells, but become more
simple in these respects in the Permian and Triassic series. The names
_Araucarites_ and _Araucarioxylon_ are perhaps objectionable, inasmuch
as they suppose affinities to _Araucaria_ which may not exist. Unger's
name, which is non-committal, is therefore, I think, to be preferred. In
my "Acadian Geology," and in my "Report on the Geology of Prince Edward
Island," I have given reasons for believing that the foliage of some at
least of these trees was that known as _Walchia_, and that they may have
borne nutlets in the manner of Taxine trees (_Trigonocarpum_, &c). Grand
d'Eury has recently suggested that some of them may have belonged to
_Cordaites_, or to plants included in that somewhat varied and probably
artificial group.
The earliest discovery of trees of this kind in the Erian of America was
that of Matthew and Hartt, who found large trunks, which I afterwards
described as _Dadoxylon Ouangondianum_, in the Erian sandstone of St.
John, New Brunswick, hence named by those geologists the "Dadoxylon
sandstone." A little later, similar wood was found by Prof. Hall and
Prof. Newberry in the Hamilton group of New York and Ohio, and the allied
wood of the genus _Ormoxylon_ was obtained by Prof. Hall in the Portage
group of the former State. These woods proved to be specifically distinct
from that of St. John, and were named by me _D. Halli_, _D. Newberryi_,
and _Ormoxylon Erianum_. The three species of _Dadoxylon_ agreed in
having composite medullary rays, and would thus belong to the group
_Palæoxylon_ of Brongniart. In the case of _Ormoxylon_ this character
could not be very distinctly ascertained, but the medullary rays appeared
to be simple.
I am indebted to Prof. J. M. Clarke, of Amherst College, Massachusetts,
for some well-preserved specimens of another species from the Genesee
shale of Canandaigua, New York. They show small steins or branches, with
a cellular pith surrounded with wood of coniferous type, showing two
to three rows of slit-formed, bordered pores in hexagonal borders. The
medullary sheath consists of pseudo-scalariform and reticulated fibres;
but the most remarkable feature of this wood is the structure of the
medullary rays, which are very frequent, but short and simple, sometimes
having as few as four cells superimposed. This is a character not before
observed in coniferous trees of so great age, and allies this Middle
Erian form with some Carboniferous woods which have been supposed to
belong to _Cordaites_ or _Sigillaria_. In any case this structure is new,
and I have named the species _Dadoxylon Clarkii_, after its discoverer.
The specimens occur, according to Prof. Clarke, in a calcareous layer
which is filled with the minute shells of _Styliola fissurella_ of Hall,
believed to be a Pteropod; and containing also shells of _Goniatites_ and
_Gyroceras_. The stems found are only a few inches in diameter, but may
be branches of larger trees.
It thus appears that we already know five species of Coniferous trees
of the genus _Dadoxylon_ in the Middle Erian of America, an interesting
confirmation of the facts otherwise known as to the great richness and
variety of this ancient flora. The late Prof. Goeppert informed me that
he had recognised similar wood in the Devonian of Germany, and there
can be no doubt that the fossil wood discovered by Hugh Miller in the
Old Red Sandstone of Scotland, and described by Salter and McNab, is of
similar character, and probably belongs to the genus _Dadoxylon_. Thus
this type of Coniferous tree seems to have been as well established and
differentiated into species in the Middle Devonian as in the succeeding
Carboniferous.
I may here refer to the fact that the lower limit of the trees of
this group coincides, in America, with the upper limit of those
problematical trees which in the previous chapter I have named Protogens
(_Nematophyton_, _Celluloxlyon_,[BM] _Nematoxylon_[BN]), though
_Aporoxylon_ of Unger extends, in Thuringia, up to the Upper Devonian
(Cypridina schists).
[BM] "Journal of the Geological Society," May, 1881.
[BN] _Ibid._, vol. xix, 1863.
V.--Scottish Devonian Plants of Hugh Miller and others. (Edinburgh
Geological Society, 1877.)
Previously to the appearance of my descriptions of Devonian plants
from North America, Hugh Miller had described forms from the Devonian
of Scotland, similar to those for which I proposed the generic name
_Psilophyton_; and I referred to these in this connection in my earliest
description of that genus.[BO] He had also recognised what seemed to be
plants allied to Lycopods and Conifers. Mr. Peach and Mr. Duncan had made
additional discoveries of this kind, and Sir J. Hooker and Mr. Salter had
described some of these remains. More recently Messrs. Peach, Carruthers,
and McNab have worked in this field, and still later[BP] Messrs. Jack and
Etheridge have summed up the facts and have added some that are new.
[BO] "Journal of the Geological Society," London, 1859.
[BP] _Ibid._, 1877.
The first point to which I shall refer, and which will lead to the
other matters to be discussed, is the relation of the characteristic
_Lepidodendron_ of the Devonian of eastern America, _L. Gaspianum_, to
_L. nothum_ of Unger and of Salter. At the time when I described this
species I had not access to Scottish specimens of _Lepidodendron_ from
the Devonian, but these had been well figured and described by Salter,
and had been identified with _L. nothum_ of Unger, a species evidently
distinct from mine, as was also that figured and described by Salter,
whether identical or not with Unger's species. In 1870 I had for the
first time an opportunity to study Scottish specimens in the collection
of Mr. Peach; and on the evidence thus afforded I stated confidently
that these specimens represented a species distinct from _L. Gaspianum_,
perhaps even generically so.[BQ] It differs from _L. Gaspianum_ in
its habit of growth by developing small lateral branches instead of
bifurcating, and in its foliage by the absence or obsolete character of
the leaf-bases and the closely placed and somewhat appressed leaves. If
an appearance of swelling at the end of a lateral branch in one specimen
indicates a strobile of fructification, then its fruit was not dissimilar
from that of the Canadian species in its position and general form,
though it may have differed in details. On these grounds I declined to
identify the Scottish species with _L. Gaspianum_. The Lepidodendron
from the Devonian of Belgium described and figured by Crepin,[BR] has
a better claim to such identification, and would seem to prove that
this species existed in Europe as well as in America. I also saw in Mr.
Peach's collection in 1870 some fragments which seemed to me distinct
from Salter's species, and possibly belonging to _L. Gaspianum_.[BS]
[BQ] "Report on Devonian Plants of Canada," 1871.
[BR] "Observations sur quelques Plantes Fossiles des dépôts Devoniens."
[BS] "Proceedings of the Geological Society of London," March, 1871.
In the earliest description of _Psilophyton_ I recognised its probable
generic affinity with Miller's "dichotomous plants," with Salter's
"rootlets," and with Goeppert's _Haliserites Dechenianus_, and stated
that I had "little doubt that materials exist in the Old Red Sandstone of
Scotland for the reconstruction of at least one species of this genus."
Since, however, Miller's plants had been referred to coniferous roots,
and to fucoids, and Goeppert's _Haliserites_ was a name applicable only
to fucoids, and since the structure and fruit of my plants placed them
near to Lycopods, I was under the necessity of giving them a special
generic name, nor could I with certainty affirm their specific identity
with any European species. The comparison of the Scottish specimens with
woody rootlets, though incorrect, is in one respect creditable to the
acumen of Salter, as in almost any state of preservation an experienced
eye can readily perceive that branchlets of _Psilophyton_ must have been
woody rather than herbaceous, and their appearance is quite different
from that of any true Algæ.
The type of _Psilophyton_ is my _P. princeps_, of which the whole of the
parts and structures are well known, the entire plant being furnished in
abundance and in situ in the rich plant-beds of Gaspé. A second species,
_P. robustius_, has also afforded well-characterised fructification. _P.
elegans_, whose fruit appears as "oval scales," no doubt bore sac-like
spore-cases resembling those of the other species, but in a different
position, and perfectly flattened in the specimens procured. The only
other Canadian species, _P. glabrum_, being somewhat different in
appearance from the others, and not having afforded any fructification,
must be regarded as uncertain.
The generic characters of the first three species may be stated as
follows:
Stems dichotomous, with rudimentary subulate leaves, sometimes obsolete
in terminal branchlets and fertile branches; and in decorticated
specimens represented only by punctiform scars. Young branches circinate.
Rhizomata cylindrical, with circular root-areoles. Internal structure of
stem, an axis of scalariform vessels enclosed in a sheath of imperfect
woody tissue and covered with a cellular bark more dense externally.
Fruit, naked sac-like spore-cases, in pairs or clusters, terminal or
lateral.
The Scottish specimens conform to these characters in so far as they are
known, but not having as yet afforded fruit or internal structure, they
cannot be specifically determined with certainty. More complete specimens
should be carefully searched for, and will no doubt be found.
In Belgium, M. Crepin has described a new species from the Upper Devonian
of Condroz under the name _P. Condrusianum_ (1875). It wants, however,
some of the more important characters of the genus, and differs in having
a pinnate ramification, giving it the aspect of a fern. In a later paper
(1876) the author considers this species distinct from _Psilophyton_, and
proposes for it a new generic name _Rhacophyton_.
The characters given by Mr. Carruthers, in his paper of 1873, for the
species _P. Dechenianum_, are very few and general: "Lower branches short
and frequently branching, giving the plant an oblong circumscription."
Yet even these characters do not apply, so far as known, to Miller's
fucoids or Salter's rootlets or Goeppert's _Haliserites_. They merely
express the peculiar mode of branching already referred to in Salter's
_Lepidodendron nothum_. The identification of the former plants with
the _Lepidodendron_ and _Lycopodites_, indeed, rests only on mere
juxtaposition of fragments, and on the slight resemblance of the
decorticated ends of the branches of the latter plants to _Psilophyton_.
It is contradicted by the obtuse ends of the branches of the
_Lepidodendron_ and _Lycopodites_, and by the apparently strobilaceous
termination of some of them.
Salter's description of his _Lepidodendron nothum_ is quite definite, and
accords with specimens placed in my hands by Mr. Peach: "Stems half an
inch broad, tapering little, branches short; set on at an acute angle,
blunt at their terminations. Leaves in seven to ten rows, very short,
not a line long, and rather spreading than closely imbricate." These
characters, however, in so far as they go, are rather those of the genus
_Lycopodites_ than of _Lepidodendron_, from which this plant differs
in wanting any distinct leaf-bases, and in its short, crowded leaves.
It is to be observed that they apply also to Salter's _Lycopodites
Milleri_, and that the difference of the foliage of that species may be
a result merely of different state of preservation. For these reasons I
am disposed to place these two supposed species together, and to retain
for the species the name _Lycopodites Milleri_. It may be characterised
by the description above given, with merely the modification that the
leaves are sometimes nearly one-third of an inch long and secund (Fig.
17, _supra_, lower figure).
Decorticated branches of the above species may no doubt be mistaken
for _Psilophyton_, but are nevertheless quite distinct from it, and
the slender branching dichotomous stems, with terminations which, as
Miller graphically states, are "like the tendrils of a pea," are too
characteristic to be easily mistaken, even when neither fruit nor leaves
appear. With reference to fructification, the form of _L. Milleri_
renders it certain that it must have borne strobiles at the ends of its
branchlets, or some substitute for these, and not naked spore-cases like
those of _Psilophyton_.
The remarkable fragment communicated by Sir Philip Egerton to Mr.
Carruthers,[BT] belongs to a third group, and has, I think, been quite
misunderstood. I am enabled to make this statement with some confidence,
from the fact that the reverse or counterpart of Sir Philip's specimen
was in the collection of Sir Wyville Thomson, and was placed by him in
my hands in 1870. It was noticed in my paper on "New Devonian Plants,"
in the "Journal of the Geological Society of London," and referred to my
genus _Ptilophyton_, as stated above under Section II., page 86 _et seq._
[BT] "Journal of Botany," 1873.
Mr. Salter described, in 1857,[BU] fragments of fossil wood from the
Scottish Devonian, having the structure of Dadoxylon, though very
imperfectly preserved; and Prof. McNab has proposed[BV] the generic name
_Palæopitys_ for another specimen of coniferous wood collected by Hugh
Miller, and referred to by him in the "Testimony of the Rocks." From
Prof. McNab's description, I should infer that this wood may, after all,
be generically identical with the woods usually referred to Dadoxylon
of Unger (_Araucarioxylon_ of Kraus). The description, however, does
not mention the number and disposition of the rows of pores, nor the
structure of the medullary rays, and I have not been able to obtain
access to the specimens themselves. I have described five species of
Dadoxylon from the Middle and Upper Erian of America, all quite distinct
from the Lower Carboniferous species. There is also one species of an
allied genus, Ormoxylon. All these have been carefully figured, and it is
much to be desired that the Scottish specimens should be re-examined and
compared with them.
[BU] "Journal of the London Geological Society."
[BV] "Transactions of the Edinburgh Botanical Society," 1870.
Messrs. Jack and Etheridge have given an excellent summary of our present
knowledge of the Devonian flora of Scotland, in the Journal of the
London Geological Society (1877). From this it would appear that species
referable to the genera _Calamities_, _Lepidodendron_, _Lycopodites_,
_Psilophyton_, _Arthrostigma_, _Archæopteris_, _Caulopteris_,
_Palæopitys_, _Araucarioxylon_, and _Stigmaria_ have been recognised.
The plants described by these gentlemen from the Old Red Sandstone of
Callender, I should suppose, from their figures and descriptions, to
belong to the genus _Arthrostigma_, rather than to Psilophyton. I do
not attach any importance to the suggestions referred to by them, that
the apparent leaves may be leaf-bases. Long leaf-bases, like those
characteristic of _Lepidofloyos_, do not occur in these humbler plants
of the Devonian. The stems with delicate "horizontal processes" to which
they refer may belong to _Ptilophyton_ or to _Pinnularia_.
In conclusion, I need scarcely say that I do not share in the doubts
expressed by some British palæontologists as to the distinctness of
the Devonian and Carboniferous floras. In eastern America, where these
formations are mutually unconformable, there is, of course, less room
for doubt than in Ireland and in western America, where they are
stratigraphically continuous. Still, in passing from the one to the
other, the species are for the most part different, and new generic forms
are met with, and, as I have elsewhere shown, the physical conditions of
the two periods were essentially different.[BW]
[BW] "Reports on Devonian Plants and Lower Carboniferous Plants of
Canada."
It is, however, to be observed that since--as Stur and others have
shown--_Calamities radiatus_, and other forms distinctively Devonian in
America, occur in Europe in the Lower Carboniferous, it is not unlikely
that the Devonian flora, like that of the Tertiary, appeared earlier in
America. It is also probable, as I have shown in the "Reports" already
referred to, that it appeared earlier in the Arctic than in the temperate
zone. Hence an Arctic or American flora, really Devonian, may readily be
mistaken for Lower Carboniferous by a botanist basing his calculations on
the fossils of temperate Europe. Even in America itself, it would appear,
from recent discoveries in Virginia and Ohio, that certain Devonian forms
lingered longer in those regions than farther to the northeast;[BX] and
it would not be surprising if similar plants occurred in later beds in
Devonshire or in the south of Europe than in Scotland. Still, these
facts, properly understood, do not invalidate the evidence of fossil
plants as to geological age, though errors arising from the neglect of
them are still current.
[BX] Andrews, "Palæontology of Ohio," vol. ii.; Meek, "Fossil Plants from
Western Virginia," Philosophical Society, Washington, 1875.
VI.--Geological Relations of some Plant-bearing Beds of Eastern Canada.
("Report on Erian Plants," 1871.)
The Gaspé sandstones have been fully described by Sir W. E. Logan,
in his "Report on the Geology of Canada," 1863. He there assigns to
them a thickness of seven thousand and thirty-six feet, and shows that
they rest conformably on the Upper Silurian limestones of the Lower
Helderberg group (Ludlow), and are in their turn overlaid unconformably
by the conglomerates which form the base of the Carboniferous rocks of
New Brunswick. I shall add here merely a few remarks on points in their
physical character connected with the occurrence of plants in them.
_Prototaxites_ (_Nematophyton_) _Logani_ and other characteristic Lower
Erian plants occur in the base of the sandstones at Little Gaspé. This
fact, along with the occurrence, as stated in my paper of 1863, of
rhizomes of _Psilophyton_ preserving their scalariform structure, in
the upper part of the marine Upper Silurian limestones,[BY] proves the
flora of the Devonian rocks to have had its beginning at least in the
previous geological period, and to characterise the lower as well as the
upper beds of the Devonian series. In this connection I may state that,
from their marine fossils, as well as their stratigraphical arrangement,
Sir W. E. Logan and Mr. Billings regard the lower portions of the Gaspé
sandstones as the equivalents of the Oriskany sandstone of New York.
On the other hand, the great thickness of this formation, the absence
of Lower Devonian fossils from its upper part, and the resemblance of
the upper beds to those of the newer members of the Devonian elsewhere,
render it probable that the Gaspé sandstones, though deficient in the
calcareous members of the system, seen farther to the westward, represent
the whole of the Devonian period.
[BY] The marine fossils of these beds have been determined by Mr.
Billings. They are Upper Silurian, with an intermixture of Lower Devonian
in the upper part. Fragments of _Nematophyton_ occur in beds of the same
age in the Bay des Chaleurs, at Cape Bon Ami.
The Gaspé sandstones, as their name imports, are predominantly
arenaceous, and often coarsely so, the sandstones being frequently
composed of large grains and studded with quartz-pebbles. Grey and buff
are prevalent colours, but red beds also occur, more especially in the
upper portion. There are also interstratified shaly beds, sometimes
occurring in groups of considerable thickness, and associated with
fine-grained and laminated argillaceous sandstone, the whole having
in many places the lithological aspect of the coal-measures. At one
place, near the middle of the series, there is a bed of coal from one
inch to three inches in thickness, associated with highly bituminous
shales abounding in remains of plants, and also containing fragments
of crustaceans and fishes (_Pterygotus_, _Ctenacanthus ?_ &c). The
beds connected with this coal are grey sandstones and grey and dark
shales, much resembling those of the ordinary coal formation. The
coal is shining and laminated, and both its roof and floor consist of
laminated bituminous shale with fragments of _Psilophyton_. It has no
true under-clay, and has been, I believe, a peaty mass of rhizomes of
_Psilophyton_. It occurs near Tar Point, on the south side of Gaspé Bay,
a place so named from the occurrence of a thick dyke of trap holding
petroleum in its cavities. The coal is of considerable horizontal extent,
as in its line of strike a similar bed has been discovered on the Douglas
River, about four miles distant. It has not been recognised on the north
side of the bay, though we find there beds, probably on very nearly the
same horizon, holding _Psilophyton_ in situ.
As an illustration of one of the groups of shaly beds, and of the
occurrence of roots of _Psilophyton_, I may give the following sectional
list of beds seen near "Watering Brook," on the north shore of the bay.
The order is descending:
FT. IN.
1. Grey sandstones and reddish pebbly sandstone of great
thickness
2. Bright-red shale 8 0
3. Grey shales with stems of _Psilophyton_, very abundant
but badly preserved 0 5
4. Grey incoherent clay, slickensided, and with many
rhizomes and roots of _Psilophyton_ 0 3
5. Hard grey clay or shale, with fragments and roots of
_Psilophyton_ 4 0
6. Red shale 8 0
7. Grey and reddish crumbling sandstone
Groups of beds similar to the above, but frequently much more rich in
fossils, occur in many parts of the section, and evidently include fossil
soils of the nature of under-clays, on which little else appears to have
grown than a dense herbage of _Psilophyton_, along with plants of the
genus _Arthrostigma_.
In addition to these shaly groups, there are numerous examples of beds of
shale of small thickness included in coarse sandstones, and these beds
often occur in detached fragments, as if the remnants of more continuous
layers partially removed by currents of water. It is deserving of notice
that nearly all these patches of shale are interlaced with roots or
stems of _Psilophyton_, which sometimes project beyond their limits into
the sandstone, as if the vegetable fibres had preserved the clay from
removal. In short, these lines of patches of shale seem to be remnants
of soils on which _Psilophyton_ has flourished abundantly, and which
have been partially swept away by the currents which deposited the sand.
Some of the smaller patches may even be fragments of tough swamp soils
interwoven with roots, drifted by the agency of the waves or possibly by
ice; such masses are often moved in this way on the borders of modern
swamps on the sea-coast.
The only remaining point connected with local geology to which I shall
allude is the admirable facilities afforded by the Gaspé coast both for
ascertaining the true geological relations of the beds, and for studying
the Devonian plants, as distinctly exposed on large surfaces of rock.
On the coast of the river St. Lawrence, at Cape Rozier and its vicinity,
the Lower Silurian rocks of the Quebec group are well exposed, and are
overlaid unconformably by the massive Upper Silurian limestones of Cape
Gaspé, which rise into cliffs six hundred feet in height, and can be
seen filled with their characteristic fossils on both sides of the cape.
Resting upon these, and dipping at high angles toward Gaspé Bay, are the
Devonian sandstones, which are exposed in rugged cliffs slightly oblique
to their line of strike, along a coast-line of ten miles in length, to
the head of the bay. On the opposite side of the bay they reappear; and,
thrown into slight undulations by three anticlinal curves, occupy a
line of coast fifteen miles in length. The perfect manner in which the
plant-bearing beds are exposed in these fine natural sections may serve
to account for the completeness with which the forms and habits of growth
of the more abundant species can be described.
In the Bay des Chaleurs, similar rocks exist with some local variations.
In the vicinity of Campbellton are calcareous and magnesian breccia
or agglomerate, hard shales, conglomerates and sandstones of Lower
Devonian age. The agglomerate and lower shales contain abundant remains
of fishes of the genera _Cephalaspis_, _Coccosteus_, _Ctenacanthus_,
and _Homacanthus_, and also fragments of _Pterygotus_. The shales
and sandstones abound in remains of _Psilophyton_, with which are
_Nematophyton_, _Arthrostigma_, and _Leptophleum_ of the same species
found in the Lower Devonian of Gaspé Bay. These beds near Campbellton dip
to the northward, and the Restigouche River here occupies a synclinal,
for on the opposite side, at Bordeaux Quarry, there are thick beds of
grey sandstone dipping to the southward, and containing large silicified
trunks of Prototaxites, in addition to _Psilophyton_. These beds are
all undoubtedly Lower Erian, but farther to the eastward, on the north
side of the river, there are newer and overlying strata. These are best
seen at Scaumenac Bay, opposite Dalhousie, between Cape Florissant
and Maguacha Point, where they consist of laminated and fine-grained
sandstone, with shales of grey colours, but holding some reddish beds
at top, and overlaid unconformably by a great thickness of Lower
Carboniferous red conglomerate and sandstone. In these beds numerous
fossil fishes have been found, among which Mr. Whiteaves recognises
species of _Pterichthys_, _Glyptolepis_, _Cheirolepis_, &c. With these
are found somewhat plentifully four species of fossil ferns, all of Upper
Erian types, of which one is peculiar to this locality; but the others
are found in the Upper Erian of Perry, in Maine, or in the Cat skill
group of New York.
In order that distinct notions may be conveyed as to the geological
horizons of the species, I may state that the typical Devonian or Erian
series of Canada and New York may be divided in descending order into--1.
The Chemung group, including the Chemung and Portage sandstones and
shales. 2. The Hamilton group, including the Genesee, Hamilton, and
Marcellus shales. 3. The Corniferous limestone and its associated beds.
4 The Oriskany sandstone. As the Corniferous limestone, which is the
equivalent of the Lower Carboniferous limestone in the Carboniferous
period, is marine, and affords scarcely any plants, we may, as is usually
done for like purposes in the Carboniferous, group it with the Oriskany
under the name Lower Erian. The Hamilton rocks will then be Middle Erian,
and the Chemung group Upper Erian. In the present state of our knowledge,
the series may be co-ordinated with the rocks of Gaspé, New Brunswick,
and Maine, as in the following table:
| New York | Gaspé | Southern | Coast
Subdivisions. | and | and Bay des | New | of
| Western Canada.| Chaleurs. | Brunswick. | Maine.
--------------+----------------+--------------+--------------+-----------
Upper | Chemung | Upper |Mispec Group. | Perry
Devonian or | Group. | Sandstones. | Shale, |Sandstones.
Erian. | |Long Cove, &c.| Sandstone, |
| | Scauminac | and |
| | Beds. |Conglomerate. |
| | | |
Middle | Hamilton | Middle | Little R. |
Devonian or | Group. | Sandstones. | Group |
Erian. | | Bois Brulé, | (including |
| | Cape Oiseau, | Cordaite |
| | &c. | Shales and |
| | | Dadoxylon |
| | | Sandstone).|
| | | |
Lower | Corniferous | Lower | Lower |
Devonian or | and | Sandstones. |Conglomerates,|
Erian. | Oriskany | Gaspé Basin, | &c. |
| groups. | Little Gaspé,| |
| | &c. | |
| | Campbellton | |
| | Beds. | |
--------------+----------------+--------------+--------------+-----------
It may be proper, before closing this note, to state the reasons which
have induced me to suggest in the following pages the use of the term
"Erian," as equivalent to "Devonian," for the great system of formations
intervening between the Upper Silurian and the Lower Carboniferous in
America. I have been induced to adopt this course by the following
considerations: 1. The great area of undisturbed and unaltered rocks
of this age, including a thickness in some places of eighteen thousand
feet, and extending from east to west through the Northern States of the
Union and western Canada for nearly seven hundred miles, while it spreads
from north to south from the northern part of Michigan far into the
Middle States, is undoubtedly the most important Devonian area now known
to geologists. 2. This area has been taken by all American geologists
as their typical Devonian region. It is rich in fossils, and these have
been thoroughly studied and admirably illustrated by the New York and
Canadian Surveys. 3. The rocks of this area surround the basin of Lake
Erie, and were named, in the original reports of the New York Survey,
the "_Erie Division_" 4. Great difficulties have been experienced in
the classification of the European Devonian, and the uncertainties thus
arising have tended to throw doubt on the results obtained in America in
circumstances in which such difficulties do not occur.
These reasons are, I think, sufficient to warrant me in holding the great
_Erie Division_ of the New York geologists as the typical representative
of the rocks deposited between the close of the Upper Silurian and the
beginning of the Carboniferous period, and to use the term Erian as the
designation of this great series of deposits as developed in America,
in so far at least as their flora is concerned. In doing so, I do not
wish to introduce a new name merely for the sake of novelty; but I hope
to keep before the minds of geologists the caution that they should
not measure the Erian formations of America, or the fossils which they
contain, by the comparatively depauperated representatives of this
portion of the geological scale in the Devonian of western Europe.
VII.--On the Relations of the so-called "Ursa Stage" of Bear Island with
the Palæozoic Flora of North America.
The following note is a verbatim copy of that published by me in
1873, and the accuracy of which has now been vindicated by the recent
observations of Nathorst:
The plants catalogued by Dr. Heer, and characterising what he calls
the "Ursa Stage," are in part representatives of those of the American
flora which I have described as the "Lower Carboniferous Coal-Measures"
(Subcarboniferous of Dana), and whose characteristic species, as
developed in Nova Scotia, I noticed in the "Journal of the Geological
Society" in 1858 (vol. xv.). Dr. Heer's list, however, includes some
Upper Devonian forms; and I would suggest that either the plants of two
distinct beds, one Lower Carboniferous and the other Upper Devonian, have
been near to or in contact with each other and have been intermixed, or
else that in this high northern latitude, in which (for reasons stated
in my "Report on the Devonian Flora"[BZ]) I believe the Devonian plants
to have originated, there was an actual intermixture of the two floras.
In America, at the base of the Carboniferous of Ohio, a transition of
this kind seems to occur; but elsewhere in northeastern America the Lower
Carboniferous plants are usually unmixed with the Devonian.
[BZ] "Geological Survey of Canada," 1871.
Dr. Heer, however, proceeds to identify these plants with those of the
American Chemung, and even with those of the Middle Devonian of New
Brunswick, as described by me--a conclusion from which I must altogether
dissent, inasmuch as the latter belong to beds which were disturbed and
partially metamorphosed before the deposition of the lowest Carboniferous
or "Subcarboniferous" beds.
Dr. Heer's error seems to have arisen from want of acquaintance with the
rich flora of the Middle Devonian, which, while differing in species, has
much resemblance in its general facies, and especially in its richness in
ferns, to that of the coal-formation.
To geologists acquainted with the stratigraphy and the accompanying
animal fossils, Dr. Heer's conclusions will of course appear untenable;
but they may regard them as invalidating the evidence of fossil plants;
and for this reason it is, I think, desirable to give publicity to the
above statements.
I consider the British equivalent of the lower coal-measures of eastern
America to be the lower limestone shales, the _Tweedian group_ of Mr.
Tate (1858), but which have sometimes been called the "Calciferous
Sandstone" (a name preoccupied for a Cambrian group in America). This
group does not constitute "beds of passage" to the Devonian, more
especially in eastern America, where the lower coal-formation rests
unconformably on the Devonian, and is broadly distinguished by its
fossils.
The above notes would not have been extended to so great length, but
for the importance of the Erian flora as the precursor of that of the
Carboniferous, and the small amount of attention hitherto given to it by
geologists and botanists.
CHAPTER IV.
THE CARBONIFEROUS FLORA--CULMINATION OF THE
ACROGENS--FORMATION OF COAL.
Ascending from the Erian to the Carboniferous system, so called because
it contains the greatest deposits of anthracite and bituminous coal, we
are still within the limits of the Palæozoic period. We are still within
the reign of the gigantic club-mosses, cordaites, and taxine pines. At
the close of the Erian there had been over the whole northern hemisphere
great changes of level, accompanied by active volcanic phenomena, and
under these influences the land flora seems to have much diminished. At
length all the old Erian species had become extinct, and their place was
supplied by a meagre group of lycopods, ferns, and pines of different
species from those of the preceding Erian. This is the flora of the Lower
Carboniferous series, the Tweedian of England, the Horton series of Nova
Scotia, the lower coal-measures of Virginia, the culm of Germany. But
the land again subsided, and the period of the marine limestone of the
Lower Carboniferous was introduced. In this the older flora disappeared,
and when the land emerged we find it covered with the rich flora of the
coal-formation proper, in which the great tribes of the lycopods and
cordaites attained their maxima, and the ferns were continued as before,
though under new generic and specific forms.
[Illustration: Fig. 32.--Foliage from the coal-formation, _a_,
_Alethopteris lonchitica_, fern (Moose River). _b_, _Sphenophyllum
Schlotheimii_ (Pietou). _c_, _Lepidodendron binerve_ (Sydney), _d_,
_Asterophyllites foliosa_ (_?_) (Sydney). _e_, _Cordaites_ (Joggins).
_f_, _Neuropteris rarinervis_, fern (Sydney). _g_, _Odontopteris
subcuneata_, fern (Sydney).]
There is something very striking in this succession of a new plant
world without any material advance. It is like passing in the modern
world from one district to another, in which we see the same forms of
life, only represented by distinct though allied species. Thus, when
the voyager crosses the Atlantic from Europe to America, he meets with
pines, oaks, birches, poplars, and beeches of the same genera with those
he had left behind; but the species are distinct. It is something like
this that meets us in our ascent into the Carboniferous world of plants.
Yet we know that this is a succession in time, that all our old Erian
friends are dead and buried long ago, and that these are new forms lately
introduced (Fig. 32).
Conveying ourselves, then, in imagination forward to the time when our
greatest accumulations of coal were formed, and fancying that we are
introduced to the American or European continent of that period, we find
ourselves in a new and strange world. In the Devonian age, and even in
the succeeding Lower Carboniferous, there was in the interior of America
a wide inland sea, with forest belts clinging to its sides or clothing
its islands. But in the coal period this inland sea had given place
to vast swampy flats, and which, instead of the oil-bearing shales
of the Erian, were destined to produce those immense and wide-spread
accumulations of vegetable matter which constitute our present beds of
bituminous and anthracite coal. The atmosphere of these great swamps
is moist and warm. Their vegetation is most exuberant, but of forms
unfamiliar to modern eyes, and they swarm with insects, millipedes, and
scorpions, and with batrachian reptiles large and small, among which we
look in vain for representatives of the birds and beasts of the present
day.
[Illustration: Fig. 33.--_Sigillariæ_, restored. A, _Sigillaria Brownii_.
B, _Sigillaria elegans_.]
[Illustration: Fig. 34.--_Sigillaria Lorwayana_, Dawson. _a_, Zones of
fruit-scars. _b_, Leaf-scar enlarged, _c_, Fruit-scar enlarged. See
appended note.]
[Illustration: Fig. 35.--Stem of _Sigillaria Brownii_. reduced. Natural
size.]
[Illustration: Fig. 36.--Two ribs of _Sigillaria Brownii_.]
[Illustration: Fig. 37.--Portion of lower part of stem of _S. Brownii_.
Natural size.]
Prominent among the more gigantic trees of these swampy forests are
those known to us as _Sigillariæ_ (Fig. 33). They have tall, pillar-like
trunks, often several feet in diameter, ribbed like fluted columns, but
in the reverse way, and spreading at the top into a few thick branches,
which are clothed with long, grass-like leaves. They resemble in some
respects the Lepidodendra of the Erian age, but are more massive, with
ribbed instead of scaly trunks, and longer leaves. If we approach one
of them more closely, we are struck with the regular ribs of its trunk,
dotted with rows of scars of fallen leaves, from which it receives its
name _Sigillaria_, or seal-tree (Figs. 34-37). If we cut into its stem,
we find that, instead of the thin bark and firm wood with which we are
familiar in our modern trees, it has a hard external rind, then a great
thickness of cellular matter with rope-like bands of fibres, constituting
an inner bark, while in the centre is a firm, woody axis of comparatively
small diameter, and somewhat intermediate in its structures between that
of the Lepidodendra and those of the cycads and the taxine conifers.
Thus a great stem, five feet in diameter, may consist principally of
cellular and bast fibres with very little true woody matter. The roots
of this tree are perhaps its most singular feature. They usually start
from the stem in four main branches, then regularly bifurcate several
times, and then run out into great cylindrical cables, running for a
long distance, and evidently intended to anchor the plant firmly in a
soft and oozy soil. They were furnished with long, cylindrical rootlets
placed regularly in a spiral manner, and so articulated that when they
dropped off they left regular rounded scars. They are, in short, the
_Stigmariæ_, which we have already met with in the Erian (Figs. 38, 39).
In Fig. 33 I have endeavoured to restore these strange trees. It is not
wonderful that such plants have caused much botanical controversy. It was
long before botanists could be convinced that their roots are properly
roots at all, and not stems of some aquatic plant. Then the structure of
their stems is most puzzling, and their fruit is an enigma, for while
some have found connected with them cones supposed to resemble those of
lycopods, others attribute to them fruits like those of yew-trees. For
years I have been myself gathering materials from the rich coal-formation
deposits of Nova Scotia in aid of the solution of these questions, and
in the mean time Dr. Williamson, of Manchester, and Renault and other
botanists in France, have been amassing and studying stores of specimens,
and it is still uncertain who may finally be the fortunate discoverer
to set all controversies at rest. My present belief is, that the true
solution consists in the fact that there are many kinds of _Sigillariæ_.
While in the modern forests of America and Europe the species of any of
our ordinary trees, as oaks, birches, or maples, may almost be counted
on one's fingers, Schimper in his vegetable palæontology enumerates
about eighty species of Carboniferous _Sigillariæ_; and while on the one
hand many of these are so imperfectly known that they may be regarded
as uncertain, on the other hand many species must yet remain to be
discovered.[CA] Now, in so vast a number of species there must be a
great range of organisation, and, indeed, it has already been attempted
to subdivide them into several generic groups. The present state of the
question appears to me to be this, that in these _Sigillariæ_ we have
a group divisible into several forms, some of which will eventually be
classed with the Lepidodendra as lycopods, while others will be found
to be naked-seeded phænogams, allied to the pines and cycads, and to a
remarkable group of trees known as _Cordaites_, which we must shortly
notice.
[CA] In a recent memoir (Berlin, 1887) Stur has raised the number of
species in one subdivision of the _Sigillariæ_ (the _Favulariæ_) to
forty-seven!
[Illustration: Fig. 38.--_Stigmaria_ root, seen from above, showing its
regular divisions. From "Acadian Geology".]
[Illustration: Fig. 39.--Portion of bark of _Stigmaria_, showing scars of
attachment of rootlets.]
Before considering other forms of Carboniferous vegetation, let us
glance at the accumulation of coal, and the agency of the forests of
_Sigillariæ_ therein. Let us imagine, in the first instance, such trees
as those represented in the figures, growing thickly together over vast
swampy flats, with quantities of undergrowth of ferns and other plants
beneath their shade, and accumulating from age to age in a moist soil
and climate a vast thickness of vegetable mould and trunks of trees, and
spores and spore-cases, and we have the conditions necessary for the
growth of coal. Many years ago it was observed by Sir William Logan that
in the coal-field of South Wales it was the rule with rare exceptions
that, under every bed of coal, there is a bed of clay filled with roots
of the _Stigmaria_, already referred to as the root of _Sigillaria_. This
discovery has since been extended to all the coal-fields of Europe and
America, and it is a perfectly conclusive fact as regards the origin of
coal. Each of these "under-clays," as they are called, must, in fact,
have been a soil on which grew, in the first instance, Sigillariæ and
other trees having stigmaria-roots. Thus, the growth of a forest of
_Sigillariæ_ was the first step toward the accumulation of a bed of
coal. More than this, in some of the coarser and more impure coals,
where there has been sufficient earthy matter to separate and preserve
impressions of vegetable forms, we can see that the mass of the coal is
made up of flattened _Sigillariæ_, mixed with vegetable _débris_ of all
kinds, including sometimes vast quantities of lepidodendroid spores,
and the microscopic study of the coal gives similar results (Fig. 40).
Further, on the surfaces of many coals, and penetrating the shales or
sandstones which form their roofs, we find erect stumps of sigillaria
and other trees, showing that the accumulation of the coal terminated as
it had begun, by a forest-growth. I introduce here a section of a few of
the numerous beds of coal exposed in the cliffs of the South Joggins, in
Nova Scotia, in illustration of these facts. We can thus see how in the
slowly subsiding areas of the coal-swamps successive beds of coal were
accumulated, alternating with beds of sandstone and shale (Figs. 41, 42).
For other details of this kind I must refer to papers mentioned in the
sequel.
[Illustration: Fig. 40.--Vegetable tissues from coal. _a_, _Sigillaria_
and _Cordaites_. _Calamodendron_.]
Returning to the more special subject of this work, I may remark that the
lepidodendroid trees and the ferns, both the arborescent and herbaceous
kinds, are even more richly represented in the Carboniferous than in the
preceding Erian, I must, however, content myself with merely introducing
a few representatives of some of the more common kinds, in an appended
note, and here give a figure of a well-known Lower Carboniferous
lepidodendron, with its various forms of leaf-bases, and its foliage and
fruit (Fig. 43), and a similar illustration of an allied generic form,
that known as _Lepidophloios_[CB] (Fig. 44).
[CB] For full descriptions of these, see "Acadian Geology."
[Illustration: Fig. 41.--Beds associated with the main coal (S. Joggins,
Nova Scotia). 1, Shale and sandstone--plants with _Spirorbis_ attached;
rain-marks (?). (2, Sandstone and shale, eight feet--erect _Calamites_;
3, Gray sandstone, seven feet; 4, Gray shale, four feet--an erect
coniferous (?) tree, rooted on the shale, passes up through fifteen feet
of the sandstones and shale.) 5, Gray sandstone, four feet. 6, Gray
shale, six inches--prostrate and erect trees, with rootlets, leaves,
_Naiadites_, and _Spirorbis_ on the plants. 7, Main coal-seam, five feet
of coal in two seams. 8, Underclay, with rootlets.]
Another group which claims our attention is that of the _Calamites_.
These are tall, cylindrical, branchless stems, with whorls of branchlets,
bearing needle-like leaves and spreading in stools from the base, so
as to form dense thickets, like Southern cane-brakes (Fig. 46). They
bear, in habit of growth and fructification, a close relation to our
modern equisetums, or mare's-tails, but, as in other cases we have met
with, are of gigantic size and comparatively complex structure. Their
stems, in cross-section, show radiating bundles of fibres, like those
of exogenous woods, yet the whole plan of structure presents some
curious resemblances to the stems of their humble successors, the modern
mare's-tails. It would seem, from the manner in which dense brakes of
these _Calamites_ have been preserved in the coal-formation of Nova
Scotia, that they spread over low and occasionally inundated flats, and
formed fringes on the seaward sides of the great Sigillaria forests.
In this way they no doubt contributed to prevent the invasion of the
areas of coal accumulation by the muddy waters of inundations, and thus,
though they may not have furnished much of the material of coal, they
no doubt contributed to its purity. Many beautiful plants of the genera
Asterophyllites and _Annularia_ are supposed to have been allied to the
_Calamites_, or to have connected them with the _Rhizocarps_. The stems
and fruit of these plants have strong points of resemblance to those of
_Sphenophyllum_, and the leaves are broad, and not narrow and angular
like those of the true _Calamites_ (Fig. 45).
[Illustration: Fig. 42.--Erect _Sigillaria_, standing on a coal-seam (S.
Joggins, Nova Scotia).]
[Illustration: Fig. 43.--_Lepidodendron corrugatum_, Dawson, a tree
characteristic of the Lower Carboniferous, A, Restoration. B, Leaf,
natural size, C, Cone and branch, D, Branch and leaves, E. Various forms
of leaf-areoles. F, _Sporangium_, I, L, M, Bark, with leaf-scars, N,
Bark, with leaf-scars of old stem, O, Decorticated stem (_Knorria_).]
[Illustration: Fig. 44.--_Lepidophloios Acadianus_, Dawson, a
lepidodendroid tree of the coal-formation, A, Restoration. B, Portion
of bark (two thirds natural size), C, Ligneous surface of the same, F,
Cone (two thirds natural size). G, Leaf (natural, size), K, Portion of
woody cylinder, showing outer and inner series of vessels magnified, L,
Scalariform vessels (highly magnified), M, Various forms of leaf-scars
and leaf-bases (natural size).]
[Illustration: Fig. 45.--_Asterophyllites_, _Sphenophyllum_, and
_Annularia_. A, _Asterophyllites trinerne_. A^1, Leaf enlarged, B,
_Annularia sphenophylloides_. B^1, Leaf enlarged, C, _Sphenophyllum
erosum_. C^1, Leaflet enlarged. C^2, Scalariform vessel of
_Sphenophyllum_. D, _Pinnularia ramosissima_, probably a root.]
No one has done more than my friend Dr. Williamson, of Manchester, to
illustrate the structure of Calamites, and he has shown that these
plants, like other cryptogams of the Carboniferous, had mostly stems
with regular fibrous wedges, like those of exogens. The structure of
the stem is, indeed, so complex, and differs so much in different
stages of growth, and different states of preservation, that we are
in danger of falling into the greatest confusion in classifying these
plants. Sometimes what we call a Calamite is a mere cast of its pith
showing longitudinal striæ and constrictions at the nodes. Sometimes
we have the form of the outer surface of the woody cylinder, showing
longitudinal ribs, nodes, and marks of the emission of the branchlets.
Sometimes we have the outer surface of the plant covered with a smooth
bark showing flat ribs, or almost smooth, and having at the nodes regular
articulations with the bases of the verticillate branchlets, or on the
lower part of the stem the marks of the attachment of the roots. The
Calamites grew in dense clumps, budding off from one another, sometimes
at different levels, as the mud or sand accumulated about their stems,
and in some species there were creeping rhizomata or root-stocks (Figs.
46 to 49).
[Illustration: Fig. 46.--_Calamites_. A, _C. Suckovii_. B, _C. Cistii_.
(From "Acadian Geology.")]
[Illustration: Fig. 47.--Erect _Calamites_, with roots attached (Nova
Scotia).]
[Illustration: Fig. 48.--Node of _C. Cistii_, with long leaves (Nova
Scotia).]
But all Calamites were not alike in structure. In a recent paper[CC]
Dr. Williamson describes three distinct structural types. What he
regards as typical Calamites has in its woody zone wedges of barred
vessels, with thick bands of cellular tissue separating them. A second
type, which he refers to _Calamopitus_, has woody bundles composed of
reticulated or multiporous fibres, with their porous sides parallel to
the medullary rays, which are better developed than in the previous form.
The intervening cellular masses are composed of elongated cells. This is
a decided advance in structure, and is of the type of those forms having
the most woody and largest stems, which Brongniart named _Calamodendron_
(Fig. 50). A third form, to which Dr. Williamson seems to prefer to
assign this last name, has the tissue of the woody wedges barred, as
in the first, but the medullary rays are better developed than in the
second. In this third form the intermediate tissue, or primary medullary
rays, is truly fibrous, and with secondary medullary rays traversing
it. My own observations lead me to infer that there was a fourth type
of calamitean stem, less endowed with woody matter, and having a
larger fistulous or cellular cavity than any of those described by Dr.
Williamson.
[CC] "Memoirs of the Philosophical Society," Manchester, 1886-'87.
[Illustration: Fig. 49.--Erect _Calamites_ (_C. Suckovii_), showing the
mode of growth of new stems (_b_), and different forms of the ribs (_a_,
_c_). (Pictou, Nova Scotia.) Half natural size.]
There is every reason to believe that all these various and complicated
stems belonged to higher and nobler types of mare's-tails than those of
the modern world, and that their fructification was equisetaceous and of
the form known as _Calamostachys_.
We have already seen that noble tree-ferns existed in the Erian period,
and these were continued, and their number and variety greatly extended,
in the Carboniferous. In regard to the structure of their stems, and the
method of supporting these by aërial roots, the tree-ferns of all ages
have been nearly alike, and the form and structure of the leaves, except
in some comparatively rare and exceptional types, has also been much the
same. Any ordinary observer examining a collection of coal-formation
ferns recognises at once their kinship to the familiar brackens of our
own time. Their fructification is, unfortunately, rarely preserved, so
that we are not able, in the case of many species, to speak confidently
of their affinities with modern forms; but the knowledge of this subject
has been constantly extending, and a sufficient amount of information
has been obtained to enable us to say something as to their probable
relationships. (Figs. 51 to 55.)
[Illustration: Fig. 50.--Stems of _Calamodendron_ and tissues magnified
(Nova Scotia), _a_, _b_, Casts of axis in sandstone, with woody envelope
(reduced). _c_, _d_, Woody tissue (highly magnified).]
The families into which modern ferns are divided are, it must be
confessed, somewhat artificial, and in the case of fossil ferns, in
which the fructification is for the most part wanting, it is still more
so, depending in great part on the form and venation of the divisions
of the fronds. Of about eight families into which modern ferns are
divided, seven are found in a fossil state, and of these, four at least,
the _Cyathaceæ_, the _Ophioglosseæ_, the _Hymenophyllaceæ_, and the
_Marattiaceæ_, go back to the coal-formation.[CD]
[CD] Mr. R. Kidston has recently described very interesting forms of fern
fructification from the coal-formation of Great Britain, and much has
been done by European palæobotanists, and also by Lesquereux and Fontaine
in America.
[Illustration: Fig. 51.--Group of coal-formation ferns, A, _Odontopteris
subcuneata_ (Bunbury), B, _Neuropteris cordata_ (Brongniart). C,
_Alethopteris lonchitica_ (Brongniart). D, _Dictyopteris obliqua_
(Bunbury). E, _Phyllopteris antiqua_ (Dawson), magnified; E^1, Natural
size, F, _Neuropteris cyclopteroides_ (Dawson).]
[Illustration: Fig. 52.--_Alethopteris grandis_ (Dawson). Middle
coal-formation of Nova Scotia.]
[Illustration: Fig. 53.--_Cyclopteris_ (_Aneimites_) _Acadica_ (Dawson),
a tree-fern of the Lower Carboniferous. _a_, Pinnules. _b_, Fragment of
petiole. _c_, Remains of fertile pinnules.]
[Illustration: Fig. 54.--_Sphenopteris latior_, Dawson. Coal-formation,
_a_, Pinnule magnified, with traces of fructification.]
[Illustration: Fig. 55.--Fructification of Palæozoic ferns, _a_, Thecæ of
_Archæopteris_ (Erian). _b_, Theca of _Senftenbergia_ (Carboniferous).
_c_, Thecæ of _Asterotheca_ (Carboniferous).]
[Illustration: Fig. 56.--Tree-ferns of the Carboniferous. A, _Megaphyton
magnificum_, Dawson, restored. B, Leaf-scar of the same, two thirds
natural size. B^1, Row of leaf-scars, reduced. C, _Palæopteris Harttii_,
scars half natural size. D, _Acadica_, scars half natural size.]
Some of these ferns have the more complex kind of spore-case, with a
jointed, elastic ring. It is to be observed, however, that those forms
which have a simple spore-case, either netted or membranous, and without
annulus, are most common in the Devonian and lowest Carboniferous.
Some of the forms in these old rocks are somewhat difficult to place
in the system. Of these, the species of _Archæopteris_, of the Upper
and Middle Erian, are eminent as examples. This type, however, scarcely
extends as high as the coal-formation.[CE] Some of the tree-ferns of the
Carboniferous present very remarkable features. One of these, of the
genus _Megaphyton_, seems to have two rows of great leaves, one at each
side of the stem, which was probably sustained by large bundles of aërial
roots (Fig. 56).
[CE] The pretty little ferns of the genus _Botrychium_ (moonwort), so
common in American and European woods, seem to be their nearest modern
allies.
In the Carboniferous, as in the Erian, there are leaves which have been
referred to ferns, but are subject to doubt, as possibly belonging to
broad-leaved taxine trees allied to the gingko-tree of China. One of
these, represented in Fig. 57, has been found in the coal-formation of
Nova Scotia, and referred to the doubtful genus _Noeggerathia_. Fontaine
has proposed for similar leaves found in Virginia the new generic name
_Saportea_.
[Illustration: Fig. 57.--_Noeggerathia disbar_ (half natural size).]
Ferns, as might be inferred from their great age, are at the present time
dispersed over the whole world; but their headquarters, and the regions
to which tree-ferns are confined, are the more moist climates of the
tropics and of the southern hemisphere. The coal-swamps of the northern
hemisphere seem to have excelled even these favoured regions of the
present world as a paradise for ferns.
I have already stated that the Carboniferous constitutes the headquarters
of the _Cordaites_ (Fig. 58), of which a large number of species have
been described, both in Europe and America. We sometimes, though
rarely, find their stems showing structure. In this case we have a
large cellular pith, often divided by horizontal partitions into flat
chambers, and constituting the objects which, when detached, are called
_Sternbergiæ_ (Fig. 62). These Sternbergia piths, however, occur in true
conifers as well, as they do in the modern world in some trees, like our
common butternut, of higher type; and I showed many years ago that the
Sternbergia type may be detected in the young twigs of the balsam-fir
(_Abies balsamifera_). The pith was surrounded by a ring of scalariform
or barred tissue, often of considerable thickness, and in young stems so
important as to have suggested lycopodiaceous affinities. But as the stem
grew in size, a regular ring of woody wedges, with tissue having rounded
or hexagonal pores or discs, like those of pines, was developed. Outside
this was a bark, often apparently of some thickness. This structure in
many important points resembles that of cycads, and also approaches to
the structure of Sigillaria, while in its more highly developed forms it
approximates to that of the conifers.
[Illustration: Fig. 58.--_Cordaites_ (_Dorycordaites_), Grand d'Eury,
reduced.]