| COUNTRIES. | Square Miles of| Annual Production|
| | Coal Formation.| of Coal in Tons.|
+--------------------------------+----------------+------------------+
|Great Britain and Ireland | 5,400 | 65,887,900 |
|British North America | 7,530 | 1,500,000 |
|United States | 196,650 | 5,000,000 |
|Belgium | 518 | 8,409,330 |
|France | 1,719 | 7,740,317 |
|Prussia and Austria | ---- | 4,200,000 |
|Saxony | 30 | 1,000,000 |
|Russia | 100 | 3,500,000 |
|Japan, China, Borneo, Australia,| | |
| etc. | ---- | 2,000,000 |
+--------------------------------+----------------+------------------+
| Total Produce of the World | ---- | 99,237,547 |
+--------------------------------+----------------+------------------+
The total quantity of coal annually raised over the globe appears
thus to be about 100 millions of tons, of which the produce of Great
Britain is more than two-thirds, and would be sufficient to girdle
the earth at the equator with a belt of 3 feet in thickness and
nearly 5 feet in width. The coal-fields of the United States are
nearly forty times larger than those of Great Britain.
Roscoe gives the following estimated quantities of coal in the
principal countries:--
+-----------------------------------+------------+-------------------+
| | Average | |
| COUNTRIES. | Thickness. | Tons. |
| | No. Feet. | |
+-----------------------------------+------------+-------------------+
|Belgium | 60 | 36,000,000,000 |
|France | 60 | 59,000,000,000 |
|British Islands | 35 | 190,000,000,000 |
|Pennsylvania | 25 | 316,400,000,000 |
|Great Appalachian Coalfield | 25 | 1,387,500,000,000 |
|Indiana, Illinois, Western Kentucky| 25 | 1,277,500,000,000 |
|Missouri, and Arkansas Basin | 10 | 739,000,000,000 |
|North America (assumed thickness | | |
| over an area of 200,000 square | | |
| miles) | 20 | 4,000,000,000,000 |
+-----------------------------------+------------+-------------------+
Unger enumerates 683 plants of the coal-measures, while Brongniart
notices 500. Of the last number there are 6 Thallogens, 346
Acrogens, 135 Gymnosperms, and 13 doubtful plants. This appears
to be a very scanty vegetation, as far as regards the number of
species. It is only equal to about 1/20th of the number of species
now growing on the surface of the soil of Europe. Although,
however, the number of species was small, yet it is probable that
the individuals of a species were numerous. The proportion of
Ferns was very large. There are between 200 and 300 enumerated.
Schimper thinks there are 7 species congeneric with Lycopodium
found in the coal-measures. The following are some of the
Cryptogamous and Phanerogamous genera belonging to the flora of
the Carboniferous period:--Cyclopteris, Neuropteris, Odontopteris,
Sphenopteris, Hymenophyllites, Alethopteris, Pecopteris, Coniopteris,
Cladophlebis, Senftenbergia, Lonchopteris, Glossopteris, Caulopteris,
Lepidodendron (Lepidostrobus, Lepidophyllum, Knorria), Flemingites,
Ulodendron, Halonia, Psaronius, Sigillaria and Stigmaria, Calamites
(Asterophyllites and Sphenophyllum), Noeggerathia, Walchia, Peuce,
Dadoxylon, Pissadendron, Trigonocarpum.
Ferns are the carboniferous fossil group which present the most
obvious and recognisable relationship to plants of the present day.
While cellular plants and those with lax tissues have lost their
characters by the maceration to which they were subjected before
fossilisation took place, ferns are more durable, and retain their
structure. It is rare, however, to find the stalk of the frond
completely preserved down to its base. It is also rare to find
fructification present. In this respect, fossil Ferns resemble
Tree-ferns of the present day, the fronds of which rarely exhibit
fructification. Hooker states that of two or three kinds of New
Zealand Tree-fern, not one specimen in a thousand bears a single
fertile frond, though all abound in barren ones. Only one surface
of the fossil Fern-frond is exposed, and that generally the least
important in a botanical point of view. Fructification is sometimes
evidently seen, as figured by Corda in Senftenbergia. In this case
the fructification is not unlike that of Aneimidictyon of the present
day. Carruthers has recently detected the separate sporangia of Ferns
full of spores in calcareous nodules in coal (Plate I. Fig. 5). These
have the elastic ring characteristic of the Polypodiaceæ, and in
their size, form, and method of attachment, they are allied to the
group Hymenophylleæ. The absence of fructification presents a great
obstacle to the determination of fossil Ferns. Circinate vernation,
so common in modern Ferns, is rarely seen in the fossil species,
and we do not in general meet with rhizomes. Characters taken from
the venation and forms of the fronds are not always to be depended
upon, if we are to judge from the Ferns of the present day. There
is a great similarity between the carboniferous Ferns of Britain
and America; and the same species, or closely allied species of the
same genera as those found in Britain have been met with in South
Africa, South America, and Australia. In the English coal-measures
the species are about 140. The Palæozoic flora of the Arctic regions
also resembles that of the other quarters of the globe. Heer, in
his account of the fossil flora of Bear Island,[7] enumerates the
following plants:--Cardiopteris frondosa, C. polymorpha, Palæopteris
Roemeriana, Sphenopteris Schimperi, Lepidodendron Veltheimianum, L.
commutatum, L. Carneggiannum, L. Wilkianum, Lepidophyllum Roemeri,
Knorria imbricata, K. acicularis, Calamites radiatus, Cyclostigma
Kiltorkense, Stigmaria ficoides, etc., Cardiocarpum ursinum, C.
punctulatum, besides various sporangia and spores.
[Illustration: Fig. 22, _bis_.]
[Sidenote: Fig. 22, _bis_. Adiantites Lindseæformis.]
The preponderance of Ferns over flowering plants is seen at the
present day in many tropical islands, such as St. Helena and the
Society group, as well as in extra-tropical islands, as New Zealand.
In the latter, Hooker picked 36 kinds in an area of a few acres;
they gave a luxuriant aspect to the vegetation, which presented
scarcely twelve flowering plants and trees besides. An equal area
in the neighbourhood of Sydney (in about the same latitude) would
have yielded upwards of 100 flowering plants, and only two or three
Ferns. This Acrogenous flora, then, seems to favour the idea of
a humid as well as mild and equable climate at the period of the
coal formation--the vegetation being that of islands in the midst
of a vast ocean. Lesquereux, in Silliman's Journal, gives three
sections of Ferns in the Carboniferous strata--viz. Neuropterideæ,
Pecopterideæ, and Sphenopterideæ. In Neuropterideæ fructification has
been seen in Odontopteris. In this genus the spores are in a peculiar
bladdery sporangium. In Neuropterideæ the fructification appears to
have resembled Danæa in some cases, and Osmunda in others. Professor
Geikie has noticed in the lower Carboniferous shales of Slateford,
near Edinburgh, a fern which has been named Adiantites Lindseæformis
by Bunbury (Fig. 22, _bis_). It has pinnules between crescent and
fan shaped. (Mem. Geol. Survey of Edinburgh, 1861, p. 151.)
Among the Ferns found in the clays, ironstones, and sandstones of
the Carboniferous period, we shall give the characters of some
by way of illustration.[8] Pecopteris (Fig. 23) seems to be the
fossil representative, if not congener, of Pteris. Pecopteris
heterophylla (Fig. 24) has a marked resemblance to Pteris
esculenta of New Zealand. The frond of Pecopteris is pinnatifid,
or bi-tri-pinnatifid--the leaflets adhering to the rachis by the
whole length of their base, sometimes confluent; the midrib of the
leaflets runs to the point, and the veins come off from it nearly
perpendicularly, and the fructification when present is at the end of
the veins. Neuropteris (Figs. 25, 26, 27) has a pinnate or bipinnate
frond, with pinnæ somewhat cordate at the base--the midrib of the
pinnæ vanishing towards the apex, and the veins coming off obliquely,
and in an arched manner. Neuropteris gigantea (Fig. 26) has a thick
bare rachis, according to Miller, and seems to resemble much Osmunda
regalis. Odontopteris has leaves like the last, but its leaflets
adhere to the stalk by their whole base, the veins spring from the
base of the leaflets, and pass on towards the point. Sphenopteris
(Fig. 28) has a twice or thrice pinnatifid frond, the leaflets being
narrowed at the base, often wedge-shaped, and the veins generally
arranged as if they radiated from the base. Sphenopteris elegans
resembled Pteris aquilina in having a stout leafless rachis, which
divided at a height of seven or eight inches from its club-like base
into two equal parts, each of which continued to undergo two or three
successive bifurcations. A little below the first forking two divided
pinnæ were sent off. A very complete specimen, with the stipe, was
collected in the coalfield near Edinburgh by Hugh Miller, who has
described it as above. Lonchopteris has its frond multi-pinnatifid,
and the leaflets more or less united together at the base; there is a
distinct midrib, and the veins are reticulated. Cyclopteris (Fig. 29)
has simple orbicular leaflets, undivided or lobed at the margin, the
veins radiating from the base, with no midrib. Schizopteris resembles
the last, but the frond is deeply divided into numerous unequal
segments, which are usually lobed and taper-pointed.
[Illustration: Fig. 23-29.]
[Sidenote: Figs. 23 to 29 exhibit the fronds of some of the Ferns
of the Carboniferous epoch. Fig. 23. _Pecopteris (Alethopteris)
aquilina_. Fig. 24. _Pecopteris (Alethopteris) heterophylla_. Fig.
25. _Neuropteris Loshii._ Fig. 26. _Neuropteris gigantea._ Fig. 27.
_Neuropteris acuminata._ Fig. 28. _Sphenopteris affinis._ Fig. 29.
_Cyclopteris dilatata._]
[Illustration: Fig. 30-32.]
[Sidenote: Figs. 30 to 32. Stem of Tree-ferns, called _Caulopteris_.
Fig. 30. _Caulopteris macrodiscus._ Fig. 31. _Caulopteris Balfouri_
(Carr.), Coal-measures. Fig. 32. _Caulopteris Morrisi_ (Carr.),
Coal-measures.]
The rarity of Tree-ferns in the coal-measures has often been
observed, and it is the more remarkable from the durable nature of
their tissues. Several species have, however, been noticed. They
are referred to the genus Caulopteris. One of them, C. macrodiscus
(Fig. 30) has the leaf-scars in linear series. Two other species are
figured, the one a slender form with the scars widely separated,
as in some Alsophilas, C. Balfouri (Fig. 31) from the Somersetshire
coal-field; and the other with larger stems and more closely
aggregated scars, C. Morrisi (Fig. 32), from the coal-measures at
Newcastle. The latter species shows the cavities at the base of the
petiole described by Mohl in many living fern-stems. The fossils
named Psaronius appear to have been fern-stems with a slender axis
and a large mass of adventitious roots, as in some Dicksonias and
in Osmunda regalis. These stems probably belong to some of the
fronds to which other names are given, but as they have not been
found attached, it is impossible to determine the point. Miller has
described a fern as occurring in the coal-measures, which at first
sight presents more the appearance of a Cycadaceous frond than
any other vegetable organism of the carboniferous age except the
Cycadites Caledonicus (Salter), from Cockburnspath Cove. He thus
describes it:--
"From a stipe about a line in thickness there proceed at right
angles, and in alternate order, a series of sessile lanceolate
leaflets, rather more than two inches in length, by about an eighth
part of an inch in breadth, and about three lines apart. Each is
furnished with a slender midrib; and, what seems a singular, though
not entirely unique feature in a Fern, the edges of each are densely
hirsute, and bristle with thick short hair. The venation is not
distinctly preserved."
[Illustration: Fig. 33-34.]
[Illustration: Fig. 36-37.]
[Sidenote: Figs. 33 to 37 exhibit forms of Sigillaria stems found in
the shales of the Carboniferous epoch. Fig. 33. Stem of _Sigillaria
pachyderma_ in an erect position, covered by successive deposits
of sandstone and shale; one of the stems is bifurcated. Fig. 34.
_Sigillaria reniformis_, with its external markings, and roots
which are Stigmarias, as proved by Mr. Binney. Fig. 35. _Sigillaria
pachyderma_, after Lindley and Hutton, from the shale of Killingworth
Colliery, showing the scars or places through which the vessels of
the stem passed to the leaves. Fig. 36. _Sigillaria (Favularia)
tessellata_, from the Denbigh coal-shale, showing the fluted stem
with scars. Fig. 37. _Sigillaria pachyderma_; the stem marked with
scars, and fluted longitudinally.]
[Illustration: Fig. 35.]
Sigillaria (Plate IV. Figs. 1 and 2) is perhaps the most important
plant in the coal formation. The name is derived from sigillum, a
seal, to indicate the seal-like markings in the stem. It is found
in all coal-shales over the world. Schimper mentions 83 species. It
occurs in the form of lofty stems, 40-50 feet high, and 5 feet broad
(Figs. 33 and 34). Many stems of Sigillaria may be seen near Morpeth,
standing erect at right angles to the planes of alternating strata
of shale and sandstone (Fig. 33). They vary from 10 to 20 feet in
height, and from one to three feet in diameter. Sir W. C. Trevelyan
counted 20 portions of these trees within the length of half-a-mile,
of which all but four or five were upright. Brongniart mentions
similar erect stems as being found near St. Etienne. The stem of
Sigillaria is fluted in a longitudinal manner, like a Doric column,
and has a succession of single scars, which indicate the points
of insertion of the leaves (Figs. 35, 36, and 37). When the outer
part of the stem separates like bark, it is found that the markings
presented by the inner surface differ from those seen externally.
This has sometimes given rise to the erroneous multiplication of
species and even of genera. Sigillaria elegans, as figured by
Brongniart in Archives du Museum, i. 405, has a stem consisting of a
central cellular axis or medulla, surrounded by a vascular cylinder,
and this is invested by a thick cellular cortical layer, the outer
portion composed of fusiform cells of less diameter than those of
the inner portion. What Brongniart calls medullary rays are mere
cracks or separations in the wedges traversed by vessels. In its
structure it resembles its root Stigmaria, and must be referred to
Lycopodiaceæ, along with Lepidodendron, Halonia, Ulodendron, etc. The
small round sporangia of Sigillaria are borne in a single patch on
the somewhat enlarged bases of some of the leaves. (See Carruthers
on Structure and Affinities of Sigillaria, in Journ. Geol. Soc. Aug.
1869.)
[Illustration: Fig. 38-39.]
[Sidenote: Fig. 38. _Stigmaria ficoides_, root of Sigillaria, giving
off rootlets, which have been compressed.
Fig. 39. _Stigmaria ficoides_ (_S. Anabathra_ of Corda),
which is the root of a Sigillaria. The markings are the points whence
rootlets proceed.]
It has been ascertained by Professor King and Mr. Binney of
Manchester, that the plant called Stigmaria (Fig. 38) is not a
separate genus, but the root of Sigillaria (Plate IV. Figs. 1
and 2). The name is derived from στίγμα, a mark, indicating the
markings on the axis. It is one of the most common productions of the
coal-measures, and consists of long rounded or compressed fragments,
marked externally by shallow circular, oblong, or lanceolate
cavities (Fig. 39) in the centre of slight tubercles, arranged more
or less regularly in a quincuncial manner (Plate III. Fig. 7). The
cavities occasionally present a radiating appearance. The axis of
the fragments is often hollow, and different in texture from the
parts around. This axis consists of a vascular cylinder or woody
system, penetrated by quincuncially arranged meshes or openings,
through which the vascular bundles proceed from the inner surface
of the cylinder to the rootlets (Plate III. Figs. 8 and 9). From
the scars and tubercles arise long ribbon-shaped processes, which
were cylindrical cellular roots, now compressed (Fig. 38). The
vascular cylinder of Stigmaria is composed entirely of scalariform
tissue, pierced by meshes for the passage, from the inner surface
of the cylinder, of the vascular bundles which supply the rootlets.
(Carruthers in Geol. Proc., Aug. 1869.) Stigmaria ficoides (Fig.
38) abounds in the under-clay of a coal-seam, sending out numerous
roots from its tubercles, and pushing up its aerial stem, in the form
of a fluted Sigillaria. On the Bolton and Manchester Railway Mr.
Binney discovered Sigillarias standing erect, and evidently connected
with Stigmarias which extended 20 feet or more.[9] Stigmaria is
regarded by Schimper as roots, not of Sigillaria only, but of
Knorria longifolia (one of the Lepidodendreæ). The base of the stem
of this species of Knorria is Ancestrophyllum, and the upper part
is Didymophyllum Schottini of Goeppert. Professor King and others
suppose that the Fern-like frond called Neuropteris is connected with
Sigillaria, but this is a mere conjecture, set aside by the discovery
of leaves attached to a species allied to Sigillaria elegans, which
establishes that the long linear leaves described under the name
Cyperites are the foliage of this genus. Goldenberg has figured the
fructification, which consists of small sporangia like those of
Flemingites, borne on the basis of but slightly modified leaves.
This establishes the opinion that Sigillaria was an acrogenous plant
belonging to Lycopodiaceæ. Brongniart reckons it as representing an
extinct form of Gymnosperms, and King, having erroneously associated
the Cyclopteris with it, places it between the Ferns and Cycadaceæ.
Mr. Carruthers informs me that he has examined the stem of a true
fluted Sigillaria, with the tissues preserved, and that these agree
with the structure of Lepidodendron, a position in which he had
already placed it from the structure of its fruit.
[Illustration: Fig. 40-41.]
[Sidenote: Figs. 40 to 44 exhibit the stems and fructification of
Lepidodendron. Fig. 40. Bifurcating stem of _Lepidodendron obovatum_
(_elegans_), showing the scale-like scars, and the narrow-pointed
leaves, resembling those of Lycopodium, but much larger. Fig. 41.
Stem of _Lepidodendron crenatum_, with the scars of its leaves.]
[Illustration: Fig. 42-43.]
[Sidenote: Fig. 42. Fructification of Lepidodendron, showing its
cone-like form and spiral arrangement of scales. It is called
_Lepidostrobus Dabadianus_ by Schimper, but it is probably
Triplosporites.
Fig. 43. Longitudinal section of the fructification,
showing central axis and scales carrying sporangia. The upper
sporangium contains microspores, the lower macrospores; hence it has
the character of Triplosporites.]
[Illustration: Fig. 44.]
[Sidenote: In woodcut 44 are represented the fruits of Selaginella
(one of the Lycopodiums of the present day), Lepidostrobus,
Triplosporites, and Flemingites. Fig. 1. _Selaginella spinulosa_, A.
Braun (_Lycopodium selaginoides_, Linn.) 2. Scale and sporangium from
the upper portion of the cone. 3. Antheridian microspores from the
same. 4. Macrospore. 5. Scale and sporangium from the lower part of
the cone, containing macrospores. 6. _Lepidostrobus ornatus_, Hooker.
7. Three scales and sporangia of ditto. 8. Microspores from the
sporangia of the upper part of the cone of _Triplosporites Brownii_,
Brongn. 9. Macrospore from the sporangia of the lower part (drawn
from Brongniart's description and measurements). 10. Scales and
sporangia of a cone of Flemingites.[10]]
Lepidodendron (Figs. 40 to 44) is another genus of the coal-measures
which differs from those of the present day (Plate IV. Fig. 3).
Lepidodendrons, or fossil Lycopodiaceæ, had spikes of fructification
comparable in size to the cones of firs and cedars, and containing
very large sporangia, even larger than those of Isoetes, to which
they approach in form and structure. Schimper, in 1870, enumerates
56 species of Lepidodendron, all arborescent and carboniferous.
The stem of a Lepidodendron is from 20 to 45 feet high, marked
outside by peculiar scale-like scars (Fig. 41), hence the name of
the plant (λεπίς, a scale, and δένδρον, a tree). Although the scars
on Lepidodendron are usually flattened, yet in some species they
occupy the faces of diamond-shaped projections, elevated one-sixth
of an inch or more above the surface of the stem, and separated from
each other by deep furrows;--the surface bearing the leaf being
perforated by a tubular cavity, through which the bundle of vessels
that diverged from the vascular axis of the stem to the leaf passed
out. The linear or lanceolate leaves are arranged in the same way as
those of Lycopodiums or of Coniferæ, and the branches fork like the
former. The internal structure of the stem is the same as that of
Sigillaria. The fruit of Lepidodendron and allied genera is seen in
Lepidostrobus and Triplosporites (Figs. 42, 43; Plate III, Fig. 10).
Carruthers, in his lecture to the Royal Institution, in describing
the forms of Lepidostrobus, says--"The fruit is a cone composed
of imbricated scales arranged spirally on the axis like the true
leaves, and bearing the sporangia on their horizontal pedicels. Three
different forms of fruit belong to this genus, or it should perhaps
rather be called group of plants. The first of these is the cone
named by Robert Brown Triplosporites (Figs. 42, 43), and described by
him from an exquisitely preserved specimen of an upper portion, in
which the parts are exhibited as clearly in the petrified condition
as if they belonged to a fresh and living plant. The large sporangia
have a double wall, the outer composed of a compact layer of oblong
cells placed endwise, or with the long diameter perpendicular to the
surface; the inner is a delicate cellular membrane. The sporangium
is filled with a great number of very small spores, each composed of
three roundish bodies or sporules. Recently Brongniart and Schimper
have described a complete specimen of this fruit, in which the minute
triple spores are confined to the sporangia of the upper and middle
part of the cone, but the lower portion, which was wanting in Brown's
specimen, bears sporangia filled with simple spherical spores ten or
twelve times larger than the others (woodcut 44, 9).
"The structure of another form of cone (Lepidostrobus) has been
expounded by Dr. Hooker. The arrangement of the different parts
comprising it is precisely similar to what occurs in Triplosporites;
but the sporangia are filled with the minute triple spores throughout
the whole cone (woodcut 44, 6 and 8).
"The third form of cone, described by me under the name Flemingites,
differs from the other two in having a large number of small
sporangia supported on the surface of each scale; and it agrees with
Lepidostrobus in the sporangia containing only small spores (woodcut
44, 10).
"In comparing these fossils with the living club-mosses, one is
struck with the singular agreement in the organisation of plants so
far removed in time, and so different in size, as the recent humble
club-mosses and the palæozoic tree Lepidodendrons. The fruit of
Triplosporites, like that of Selaginella (woodcut 44, 1), contains
large and small spores, the microspores being found in both genera on
the middle and upper scales of the cone, and the macrospores on those
of the lower portion (Fig. 43).